1985ApJS ... 59. .447H © 1985.TheAmericanAstronomicalSociety.Allrightsreserved.PrintedinU.S.A. The AstrophysicalJournalSupplementSeries,59:447-498,1985December band imagingstudiesdescribedinthesepapersdemonstrated number ofrichX-rayluminousclusters(Heckman1981; gas systemsarepresentinandaroundthecentralgalaxies ofa Cowie etal1983,hereafterCHJY).Thedifferentialnarrow- operated bytheAssociationofUniversities forResearchinAstronomy, Inc., undercontractwiththeNational ScienceFoundation. 2 1 It isnowknownthatspatiallyextended,opticallyemitting Alfred P.SloanFoundationFellow. VisitingAstronomeratKittPeak NationalObservatory,whichis 1 2 91/2 17-2_ l l 3l/1 1 LONG-SLIT SPECTROSCOPYOFGASINTHECORESX-RAYLUMINOUSCLUSTERS between 70and180hkms"kpc"and,ifinterpretedasrotation,isconsistentwithM/L^20inthe X6584). ThepresenceoftheopticalemissionisshowntodependonwhethercentraldensityhotX-ray brightness fi=23magarcsec". in thegalaxypotential,whichshownopreferentialalignmentwithmajororminoraxisofgalaxy.In will beastrongfunctionofthezclustersobservedandepochclusterformation,sothatfuture ing toacoolingtimeof7X10A"years.Thisresultisnaturallyunderstoodintermsthe“radiative brightness ofbetween2x10“ergscmsarcsecand6xl0inHa+[Nn] within theslitsandwhichprovideanunbiasedsurveyofclustercoreregionstoalimitingvisualsurface central 3h~kpcofthesegalaxies.Wenotethattheopticalemissionsystemsareverysimilarinmorphological context ofthecooling-flowmodel,upperboundsonclustercorespecificangularmomentumperunitmass galaxy. Studyofthemorphologyandkinematicsthesesystemsshowsthickshearingdisks,probablyrotating of theemissioninclustersisconfinedwithin10h~kpcorlessnucleusdominantcentral observations ofclustersatredshiftsz>0.2willbegreatinterest. of thecoolingtimeisaweakadditionalargumentforlowvalueHandpointoutthatcriticaldensity regulation” model,wherethehotgascoolsandaccretestoformopticalsystems.Wesuggestthatlength gas ofO,N,andSarenear-solar.ExceptforA1795,whichpossessesaveryextendedfaintfilamentsystem,most emitting gasexceedsacriticalvalueofroughly8X10"hcm"[h=H/(100kms"Mpc")],correspond- Subject headings:galaxies:clustering—intergalactic medium—galaxies:nuclei gas arediscussed.Redshiftsandpositionsgivenforthe59objects(52galaxiessevenstars)whichfell spectra orinthecolorgradientsofcentralgalaxycontinuum.Upperlimitsondustcontentcluster and kinematicalappearancetothoseinisolatedellipticalgalaxies. these clustershaveopticalemissionintheircores,andsevendonot(downtoourlimitingdetectablesurface v v 0 0 <1000 /z"kms"kpcareobtained.Themagnitudeoftheprojectedshearinopticallyemittingdiskslies 1 An additionalresultisthattherenoevidenceofanystarformationinthecentralgalaxies,either We arguethattheemissionisshock-excitedbyshocksinrange70-90kms"andabundances We reporttheresultsoflong-slitspectroscopyobtainedforcoreregions14clustersgalaxies.Seven Finally wediscusscurrentandfutureobservationsinthe UV andIR. © American Astronomical Society • Provided by theNASA Astrophysics Data System Center forTheoreticalPhysics,SpaceResearch,andPhysicsDepartment,MassachusettsInstituteofTechnology; Laboratory forHighEnergyAstrophysics,NASA/GoddardSpaceFlightCenter;DepartmentofPhysicsandAstronomy, Space TelescopeScienceInstitute;andPhysicsAstronomyDepartment,JohnsHopkinsUniversity I. INTRODUCTION redshifts —spectrophotometry Astronomy Department,BostonUniversity;andSpaceTelescopeScienceInstitute University ofMaryland;andSpaceTelescopeScienceInstitute Received 1984December10;accepted1985June4 1,2 Lennox L.Cowie 1 1 Esther M.Hu Zhong Wang ABSTRACT AND X-ray luminousclusterscools inaHubbletimeandaccretes central galaxy.Thesalientsoft X-raypropertieswhichchar- (1977). Inthesemodels,gasinthecenterofsomemost acterize suchgasinflowand accretion are(1)stronglypeaked forward byCowieandBinney(1977)FabianNulsen “radiative regulation”modelsoftheX-rayemittinggas put to thecentralregionsof cluster,settlingfinallyontothe systems wasmotivatedbythetheoreticalpredictionsof the the existenceofnuclearcomponentsand,morerarely, ex- the brighterlines(Ha,[Nii],and[Sn]).Thesearchforsuch tended filamentsofemission,andgaveluminositiesinafew of 1985ApJS ... 59. .447H 2-1 7 which wedonotfindevidenceforinourownmeasurements. 0.5 within50kpcofthenucleuscentralgalaxy]for have colorswhicharemarginallydistinguishablefromthoseof low-mass objects(Jura1977;CowieandBinney interaction, theionizationmechanism,andultimatefateof X-ray data(Mushotzky1984;JonesandFormanFabian potentials ofthecentralgalaxiesand,inmoreextendedcases whether materialisaccretingandtomeasurethegravitational lead toimportantconstraintsonstarformationifverified,but rates of-100h~Myrhavebeeninferredfromthe models, thereremainfascinatingquestions:largemassinfall galaxy itself.Evenwithinthecontextofcooling-flow cally emittinggaswhichisseenindeedthebaseofsuchan et al1981a),andmanyofthesecoolingclustersareobserved accretion flowratherthanbeingproducedbythecentral galaxy inthePerseusCluster(e.g.,Rubinetal.1977;Kent mation isobtainedonthechemicalabundancesofemit- respect tothecentralgalaxiescanbeuseddetermine of greatinterest. radio sourcesassociatedwiththem.Thequestionofwhether Finally, manyofthesecentralgalaxieshavepowerful O’Connell (1983)indicatethatsuchastellarpopulationmight mation undersuchconditionscalculatedbySarazinand several ofthesecooling-flowcandidates,aresultwhichwould there arelargesystematicradialcolorgradients[A(2?-F)> the parentgalaxy.Valentijn(1983)hasrecentlyclaimedthat Cañizares 1981).“Accretionpopulation”modelsofstarfor- formation atthebaseofsuchhigh-pressureflowsmayfavor to havecDgalaxiesattheircores.Thenatureofthegas-galaxy the gasseeninthesecaseshaveyettobedetermined.Star ity atthesoftspectralend(Mushotzkyetal.1981;Cañizares was detectedinX-rayspectrometricexperimentswithsensitiv- presence ofalow-temperaturecomponent(~10K),which systems discussedbyHeckmanandCHJY. such informationhasbeenavailableforthemajorityof the and Sargent1979),forM87(FordButcher no studies havebeenmadeforNGC1275,whichisthecentral such asA1795,theclusterpotentialitself.Inaddition,infor- the coldaccretingmaterialispoweringthesesourcesclearly gas, whichmaybetentativelyidentifiedwiththeHeckman detectable asfilamentarycondensationsofopticallyemitting in X-rayimagingdata(JonesandForman1984),(2)the ting gasanditsionizationmechanism.Whilesuchdetailed these questions.Thekinematicsoftheemission-linegaswith and CHJYsystems. gas aboutthenucleusofcentralgalaxy,aswasindeedseen information onallknownandsuspectedemission-linesystems suggested thatsuchcoolingmaterialwouldeventuallybe surface brightnessreflectingthehighlocaldensityofcooling present. indication ofwhetheroptical emissionwasobservedtobe long-slit observationsusing the cryogeniccameraatKitt listed inHeckmanandCHJY(andalsotoconfirmthedetec- Peak 4mtelescope.Parameters ofthe14clustersincludedin 1981; Mushotzky1984).Cowie,Fabian,andNulsen(1980) tions quotedtodate),wehaveundertakenaprogram of this programaresummarized inTable1,alongwithan 0 448 Detailed spectroscopyofthesesystemscananswermany It remainstobeconvincinglydemonstratedthattheopti- In anattempttoprovideacoherentbodyofspectroscopic © American Astronomical Society • Provided by theNASA Astrophysics Data System HU, COWIE,ANDWANG 112 -1 -3 49 -1 91/2l -3l/2 l vidual clustersaregiveninthelastsubsection(§III/). identical fromclustertocluster,andlineratioswerecomputed near thewavelengthofredshiftedHaforcentral be measured(§IIIa).Emission-lineprofilesandthecorre- central galaxycolors(§Hie).Annotateddescriptionsofindi- objects inourslitexposureswhichweresufficientlybrightto with adiscussionoftheestimatedmeasurementaccuracies processing andcalibrationofthedataaregivenin§II,along each slittostudythepossibleeffectsofstarformationon emission systemsaregivenin§\l\d.Finally,B—Vand from residualspectraformedbysubtractingascaledcon- features, thespectrumofcentralgalaxyappearsnearly galaxy (§Illb).Apartfromthepresenceofnarrowemission structed byforming100Abandpassregionscenteredonand detailed descriptionofourdata.Redshiftsaretabulatedforall is interestedonlyinthefinalinterpretation.)In§IVaweshow Contour plotsshowingthekinematicsofgasinextended sponding continuumcontributionsalongeachslitwerecon- and comparisonwithpreviouswork.In§IIIwepresenta § IV.(Thereadermayskipdirectlytothissectionifheorshe tinuum templateoftheunderlyingcentralgalaxy(§IIIc). with radioproperties.Weargue thatthepresenceofcentral in turnthatthepressurerisesbylessthanafactorof20 the we estimatethatthemassofgasinopticalfilament places anupperboundof3XlO(AVsinz)Monthe central galaxyorcluster,demonstratingthattheopticalsys- of thehotgasinclusterandnottomorphology interesting questionofwhy theabundancesaresonearto ratios mightprovideaveryinterestingconstraint.In§TVd we mass ofthecDplusclusterwithinthisradius,whereiis within 3Akpc.Inonecase(A1795)filamentationextends potential ofthecDs,wefindtypicalM/Lratios~20/z radio sourcesintheclusters withopticalemissionmustbe dances inclusters(e.g.,Mushotzky 1984)andemphasizesthe cooling flow.Thisriseisconsistentwithcooling-flowmodels density inthefilamentsislessthan1000cm,whichimplies systems islessthan10Af,orafactorofatleast less minor axes.Usingtheshearofdisktomeasure length ofthistimescaleweaklyfavorslowvaluesH.In km sMpc)],whichcorrespondstoacoolingtimeof that thepresenceofopticalemissionistiedtoproperties cosmic. ThisagreeswellwithX-raymeasurementsofabun- discuss excitationmechanismsandconcludethatthefilaments for standardclusterpotentials,butmoreaccurate[Sn] line angle betweentheshearvectorandlineofsight.In§IVc shearing orrotatingdiskswhichdonotalignwithmajor § IVbwediscussthekinematicsofgasflows,pointingout 7X10 [T/(1XlOK)]h~yrs.Wearguethatthe found toberoughly8X10hcm""[h=Hq/(100 occur whenthegasdensityexceedsacriticalcentralvalue tems areindeedformedbycoolingofhotgas.Coolingflows solar. In§IVewediscussthe correlationofopticalemission are likelytobeshock-heated.Weconsidertheabundances in than themassofhotgas.Wealsoshowthat gas to 40h~kpcfromthecDcenter.Theshearinthisfilament that thegaswithincDgalaxiesappearstoformthick the gas(N,0,S),whichweshowtobegenerallyclose to V —Rcolordistributionsalongtheslitwereconstructed g v 0 0 gas A discussionoftheconsequencestheseresultsisgivenin Details oftheinstrumentation,observingconfiguration,and 1985ApJS ... 59. .447H © American Astronomical Society • W Ë H £ < ^ U on w £ S & Q :¡i ,Uh on PJ Pi 00 5 § s O 73 tí o £T oq I rN, v sw -r W Ö O »o \o ÖÖÖÖÖÖÖÖÖÖÖÖÖÖ oooooooooooooo OOcNCN^HCXJTfco^oOrttNCNOi-H r-( O m ■'sf '•O ÖÖÖÖÖÖÖÖÖÖÖÖÖÖ oooooooooooooo UO^rHr-COr-'NONOOONONOr'COON «yor-'NOTt(NONriTtcoONcor-'rti—( ^ OONNOT—Ii Or^cOi—irHOOOi—(
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4500 5000 5500 6000 6500 7000 7500 8000 WAVELENGTH Fig. lb Fig. 1.—(a) Sample 60 integration on the IIDS standard star EG 11. Signal from successive slits stepped across the star has been co-added, and the light distribution along each slit summed, to form this net calibration exposure. Stellar absorption features at Ha and Hß can be readily seen. Also evident are the atmospheric absorption bands (B: 6867-6944 A, b: 7168-7394 A, and A : 7594-7684 A) at long wavelengths, as well as the residual emission from the strong [O i] À5577 night-sky line, (b) Ratio of four individual spectra on EG 11 to the average value of the four spectra obtained. The upper three spectra were formed by co-adding exposures in which the slit was stepped across the star in one-slit-wide steps. The bottom plot shows a properly sampled case where the stepping interval was | slit wide.
© American Astronomical Society • Provided by the NASA Astrophysics Data System SPECTROSCOPY OF GAS IN CLUSTER CORES 453
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WAVELENGTH (ANGSTROMS) Fig. 2.—Ratio of light obtained in individual shts to the normalized sum of light obtained in all shts for EG 11 is plotted as a function of wavelength as a measure of the effects of differential refraction. A position angle of 95° was used.
interest to form effective apertures, and relative line strengths constructed using the sky exposure and locally flattened for were obtained. The length of observations on the objects pixel variations using the normalized quartz exposure. The means the sequence must be carried out over several nights, array was then rectified to remove barrel distortion by map- and variations in seeing and transparency together with de- ping the shape of the night-sky lines and distorting the array gradation in the slit positioning imply larger errors than in the to force them to run parallel to the slit direction. Finally, calibration stars. Comparison of two sequences covering the wavelength calibration was made by fitting a sixth-order poly- same region at different position angles in A1795 (cf. Table 7) nomial to the local He-Ne-Ar calibration spectra. suggests an estimate of about 20% for the relative intensity A similar reduction procedure was followed for the second- error between 5000 and 7000 Â. run data but using procedures written by the authors at Space Two direct tests were made of the accuracy of the calibra- Telescope Science Institute. The major difference lies in the tion. In Figure 3 we show a comparison of our intensity- use of the night-sky lines as the primary wavelength calibrator. calibrated spectrum of A1795 with scanner data tabulated in This has the advantage of tracking the effects of flexure during Wilkinson, Hine, and Sargent (1981). This comparison tests the exposure and of allowing the programs to be highly the relative calibration, which appears accurate to better than automated, but suffers from a relative scarcity of fines at the 0.1 mag over the wavelength range. As a second test, g and r short-wavelength end, which slightly degrades the accuracy of surface brightness and g - r colors were compared with the the blue wavelength calibration. Since the kinematics is most results of Hoessel (1980) as shown in Table 3. (More details easily studied in the strong red fines of Ha, [N n], and [S n], on the calculation of the equivalent colors may be found in we considered this defect acceptable for the present work. § III.) These results suggest that g — r has a maximum error In both cases, flatness of the sky background was tested of 0.18 mag and is generally good to 0.1 mag. The absolute using those long exposures where the object was relatively calibration is generally accurate to 0.2 mag, with extreme confined. Typically, away from strong night-sky fines, individ- errors of 0.45 mag. As expected, the present data underesti- ual columns are flat at the l%-2% level. The wavelength mate the surface brightness (with the largest errors occurring calibration was tested by intercomparing He-Ne-Ar and night- in the first run, where the photometric quality was relatively sky fines and appears to be generally accurate at the 1 A level, poor) and obtains too red a g - r color, since we are guiding with extreme variations of up to 2 A. near the red bandpass. On the basis of these considerations At this point the data were intensity-calibrated, using a and tests, we shall assume a conservative error limit of 0.2 profile constructed from the average of all the calibration stars mag in relative fluxing and 0.5 mag in absolute calibration. obtained for the particular run. We deliberately did not use the additional information on variability which was available, b) Reduction since it was unclear how accurately the time variations in Preliminary reduction of the first-run data was made using transparencies in the first run could be removed. Nor were any the standard IPPS procedures at Kitt Peak. The array was (small) air-mass corrections applied. The net efficiency of the normalized in the slit direction to a broad-band slit profile system from above the atmosphere through to detection ranges
© American Astronomical Society • Provided by the NASA Astrophysics Data System LüO U) O cr < h) a a (/) if) o < CD 00 00Lü X O (X ÛÜ O ü_< (Z ZD 00 WAVELENGTH (ANGSTROMS) Fig. 3.—Comparison of nuclear spectrum of A1795 with Wilkinson, Hine, and Sargent (1981). Squares represent aperture (10'.'5 diameter) photometry of A1795 reduced on the Oke (1974) system of AB magnitudes. Sampling bandpasses are 160 A below 5800 A and 360 A above 5800 A. An absolute offset has been applied to the aperture points to make them coincident with the nuclear surface brightnesses.
TABLE 3 Comparison with Hoessel Colors Cryocam Hoessel and Coworkers 5 Cluster g-r /•(central) /•(averaged) g~r A85 (1)... 20.72 20.16 0.56 19.99 20.06 0.54 A85 (2)... 20.59 20.08 0.51 19.99 20.06 0.54 A133 20.07 19.50 0.57 A262 19.46 18.78 0.69 A401 20.83 20.10 0.72 19.03 19.54 0.69 A496 19.69 18.94 0.75 18.31 18.58 0.57 A644 20.73 20.05 0.68 A754 19.90 19.46 0.44 0.62c A978 19.73 19.18 0.55 17.84 18.60 0.56 All26 (1). 20.18 19.60 0.58 19.14 19.52 0.74 All26 (2). 20.30 19.67 0.63 19.14 19.57 0.74 A1775Ad . 19.54 19.04 0.50 17.97 19.01 0.60 A1775Bd . 20.42 19.94 0.48 17.97 19.01 0.60 A1795 (1). 20.11 19.69 0.43 18.94 19.29 0.51 A1795 (2). 20.03 19.63 0.40 18.94 19.29 0.51 A2029 ... 20.01 19.56 0.50 19.09 19.35 0.61 A2052 ... 19.78 19.24 0.54 18.90 19.17 0.57 A2142 ... 20.80 20.31 0.49 19.62 20.08 0.61
Note.—Entries refer to observations from slits positioned across the nucleus of each central galaxy. Where the nucleus has been observed at more than one position angle (A85, A1126, and A1795), observations are given in the order listed in Table 2. aAverage surface brightness over ±2" along slit. (Slit width is 177 for A1795 and A2142, and 372 for remaining galaxies.) Colors g and r are calculated from Oke AB magnitudes as g = AB(5000)—0.02 and r = AB(6500) + 0.17. bHoessel value approximately averaged over aperture. We have used the core radius (ß) and peak central intensities (7 ) obtained by Hoessel 1980 for spherically symmetric modified C 2 Hubble law fits, /(r) = /c/[l + (r/ß) ], to calculate averages over a rectangular aperture. c Value taken from Melnick and Quintana 1984 photometry done on g, r color system used by Hoessel. d Hoessel quotes a single value for this binary system; separate cryocam colors for components A and B are given here.
American Astronomical Society • Provided by the NASA Astrophysics Data System V"X SPECTROSCOPY OF GAS IN CLUSTER CORES 455 O'! LO ft LO co00
WAVELENGTH (ANGSTROMS) Fig. 4.—The instrumental throughput of the cryogenic camera in our described configuration calculated from exposures of the calstar EG 11 using the Oke (1974) fluxes for this star, a mirror area of 7t(200 cm)2, and a system gain of 3.5 electrons per ADU count (de Veny 1985). This shows a net optical throughput from above the atmosphere to readout of better than 10% near 6000 A, with a steep dechne at the blue end.
from a maximum of about 12% at 6500 Á down to about 2% in. DESCRIPTION at 4500 Â (Fig. 4). For some of our purposes, such as construction of pseu- a) Redshifts docolor profiles, the data were used directly in this form. As a first step in using the data, redshifts were obtained for However, for the spectral and kinematic work an extremely each object along the slits which was sufficiently bright to be accurate removal of the night-sky fines is desirable. Removal measured. These redshifts are given in Table 4 and the objects of the night-sky background was made in two stages. First, a shown in the finding charts of Figure 6 (Plate 23). Stars quadratic fit was made to the sky along individual columns (indicated by zero-redshift entries in the table) are not shown. excluding all objects which could be seen on a broad-band slit Galaxies for which emission fines were seen are designated by image formed by summing along the wavelength direction. an e following the measured redshift. For each cluster in The sky background generated in this way was subtracted Table 4 we give the velocity correction from heliocentric to from the image to form a preliminary cleaned array. A new galactic standard of rest and then a fist of the measured broad-band image of the slit was generated and multiplied by objects as marked on the finding charts of Figure 6. For each the spectrum of the brightest object to form a new array which object we show the slit exposures on which it appears (Table was subtracted from the image. Cosmic rays were then re- 2), its position along the slit in the coordinates of Figure 7, its moved by intercomparing this array with a (3x3) median position relative to the center (peak surface brightness) of the filtered array. All objects still visible on the array (emission cD in arcseconds (positive is east and north in X and 7), its fines and objects differing in spectral type from the primary measured heliocentric redshift, previously measured redshifts object) were excluded and a sixth-order polynomial fitted to where available, and finally detailed comments. the columns of the residual array. The remaining night sky Generally, measured objects had to have a typical surface was now subtracted to form the final image. The procedure brightness in excess of 2x10“18 ergs cm-2 s-1 arcsec-2 A-1 provides accurate removal of even the strong night-sky fines, in the slit or, expressed in equivalent visual magnitudes, a such as [O i] \5577, without damaging the low fight level surface brightness above 23 mag arcsec-2. However, for some wings of the galaxy profile. For most of our purposes the data objects, particularly those with emission fines, accurate red- were used in this form. shifts can be obtained at fainter levels. The redshifts were Finally, the instrumental profile in wavelength space was measured using a cross-correlation method, where the data mapped across the array using the night-sky fines on un- were belled, normalized to a smoothed version of themselves, cleaned frames. Where desired, the instrumental profile could and then offset to zero. The cross-correlation of this with then be deconvolved in subregions of the array using the Lucy either a template cD spectrum or with an emission-fine spec- algorithm (Lucy 1974). This procedure can give an enhance- trum from a spiral galaxy was then formed. To accommodate ment of the resolution by a factor of 2 at the expense of an objects with very different spectral character, the cross-corre- increase in the noise levels (cf. Fig. 5). For some purposes, lation can be done over restricted wavelength intervals includ- such as kinematic mapping or obtaining [S n] fine ratios, the ing only selected absorption or emission features from either improved resolution is extremely useful. template. Internal self-consistency and slit-to-sfit variations
© American Astronomical Society • Provided by the NASA Astrophysics Data System 1985ApJS ... 59. .447H ». \ * •5 Table 4. redshift determinationsfollowingthenumberingschemeofTable4. North isup,andeasttotheleft.Forclusterswithmoresporadicredshiftcoveragein the literature,othergalaxieswith known redshiftswithinthefinding-chartregionareindicated.These aredesignatedaccordingtothereferencesgivenin Hu, CoWIE,ANDWang{seepage 455) '•2— Â496* A85 Fig. 6.—FindingchartsoftheclusterregionsmadefromPalomar Eprintsareshown.Eachfieldshowsa6'Xregion,withlabelsforobjects # - © American Astronomical Society •Provided bythe NASAAstrophysics Data System y4 2 HSM.0527 -3 -1 */ '• r*•• i— A2Q52 *" ••*./*•• A1775 A644 A133 /2 * ■•.**/"- • »'-5 1 * ^•%« *R.075 2 \ f *• ♦ •-R.058* 3- ., 5 .• >4 R.055 . .09613 ♦A262 A2142 A1795 A754 » ■] * 1.'• • .08536 # .g-—***•# 7 HS103 • m .% pi/ ' 4 *HS111 \ ,•.0957/ # X * HS102 2 • A978 ». .V• M01*‘ ■ .iri • 3,*# PLATE 23 -i ♦ V"x 456 HU, COWIE, AND WANG Vol. 59 O'! LO ft LO co00
DEREDSHIFTED WAVELENGTH (ANGSTROMS) DEREDSHIFTED WAVELENGTH (ANGSTROMS)
DEREDSHIFTED WAVELENGTH (ANGSTROMS) DEREDSHIFTED WAVELENGTH (ANGSTROMS) Fig. 5a Fig. 5.—(a, b) The spectrum in a 7" X7" aperture was formed for two peaks in the A1795 filament by averaging slits 2-5 and then averaging ±4 pixels about the central pixel of each of the bright regions. A red spectrum (around Ha) and a blue spectrum (around Hß) is shown for each region (left-hand figures). The night skylines were used to measure the broadening of the spectral lines locally in wavelength space and the instrument profile deconvolved to enhance the locad resolution. The results of performing such a deconvolution using the Lucy (1974) algorithm are shown in the right-hand graphs. Typically we have been able to reduce the FWHM by about a factor of 2 at the cost of some enhancement in the noise. The improvement in resolution separates the important [S ii] doublet and the Ha, [N n] complex.
for the same object suggest that the redshifts are accurate to quoted errors. Some problematic cases arise in comparing with better than 0.0003 (equivalent velocity errors of -100 km results quoted in Hoessel, Gunn, and Thuan (1980, hereafter s-1) for the brighter objects, with errors perhaps twice as large HGT), as might be expected, since the HGT redshifts are not at our low surface brightness limit. Comparison with previous homogeneous in origin and do not have error estimates. redshift measurements are given in Table 4 and are generally Typical examples are A1775, where the result quoted by HGT consistent with this error estimate. The measurements of appears to be the mean of the two bright central galaxies (cf. Hintzen and his collaborators provide a set of data with large Table 1), or A2052, where we differ by 0.0010 from HGT’s overlap and are generally consistent with our data within the value of 0.0351 (we obtain z = 0.0340 heliocentric, or 0.0341
© American Astronomical Society • Provided by the NASA Astrophysics Data System V"X No. 4,1985 SPECTROSCOPY OF GAS IN CLUSTER CORES 457
DEREDSHIFTED WAVELENGTH (ANGSTROMS)
DEREDSHIFTED WAVELENGTH (ANGSTROMS) Fig. 5b
corrected for galactic rotation and expressed in the same units measurements significantly increased the number of redshifts as HGT’s value). In this case, HGT may be quoting either available in the cluster, we have also recomputed the mean Cohen and Osterbrock (1981) or Schmidt (1965), who also cluster redshift (zclus new) which is given in Table 1 in local give this value. Melnick and Sargent (1977), however, obtain a galactic standard of rest. A word of caution may be in order: value of 0.0339, which is in good agreement with our result, our sample consists primarily of faint galaxies in the cluster while a more recent measurement by Hoessel, Borne, and core, whereas most cluster redshift samples cover a more Schneider (1985) also disagrees with the quoted HGT value by extended sample of bright galaxies. a similar amount. For some of the objects Hoessel and Schneider (1985) have measured positions relative to the peak cD intensity, and we show these in brackets. The present b) Line Emission Profiles positions have only about 3" accuracy, owing to the slit width As the second step in the reduction procedure, narrow-band and the extended nature of the objects. (100 Á) images were formed for each slit given in Table 2 by The heliocentric redshifts (zmeas) ^ galaxies are also summing over wavelength at the position of redshifted Ha listed in Table 1. For many of the cases, where the present (using the presently determined redshift of the cD galaxy) and
© American Astronomical Society • Provided by the NASA Astrophysics Data System -1 -1 _1 -1 _1 1985ApJS ... 59. .447H 1 1 -1 1 _1 _1 l A2029; AK=+21kms: A1795; bV=+36kms: A1775; bV=+30kms: A1126; hV=—108kms: A754; AK=-234kms: A978; AK=-215kms": A644; AK=-221kms“: A496; AL=-118kms: A401; AL=+63kms": A262; AL=-f186kms: A133; AK=T16kms: A85; AK=+84kms\ 4. SI 4. SI. 4. S6+S8 4. SI 4. S2+S1 2. SI. 6. S8 2. SI 2. S2+S1 2. SI 2. SI 2. S2+S1 4. S3 5. Sl- 3. SI. 7. S9 3. SI 2. SI. 3. SI 1. Nucleus 2. SI 2. SI 2. S2 6. S5 1. Nucleus 8. S9+S8 5. S7 3. S2+S9 1. Nucleus 5. SI 1. Nucleus 1. Nucleus 1. Nucleus 5. SI 3. SI 1. Nucleus 5. S3 3. S2+S1 1. Nucleus 3. SI 3. SI 1. Nucleus 7. S7+S6 5. S5 3. S2 2. S2+S1 1. Nucleus 1. Nucleus 1. Nucleus Cluster/Object Identification S2 . © American Astronomical Society Position (arcsec) + 128 + 117 -102 + 121 Slit + 39 + 10 -17 -21 + 10 + 58 + 82 + 16 -44 -96 + 59 + 38 + 14 + 30 + 38 -39 -77 + 44 + 61 + 23 -33 + 18 + 50 -62 -31 -61 + 60 -50 + 80 + 98 + 9 -5 -3 0 0 0 0 0 0 0 0 0 0 0 (arcsec) + 101 -52 + 20 + 40 + 50 + 10 -24 -16 -17 -18 -21 -10 -14 -32 -60 -80 -98 + 15 + 29 -31 -13 + 14 -47 -88 -14 + 23 + 2 -4 -9 + 5 -3 + 9 + 5 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 (arcsec) -124 + 120 + 19 + 36 + 71 -57 + 38 + 14 + 30 + 37 + 13 + 25 -80 -16 + 94 + 57 + 21 -33 -77 -12 -38 + 47 + 31 + 10 -35 + 57 + 43 + 40 -13 AT -8 + 1 -2 + 5 + 4 + 1 + 7 + 6 Redshifts TABLE 4 0 0 0 0 0 0 0 0 0 0 0 Provided bythe NASA Astrophysics Data System 0.0779 0.0772 0.0584 0.0554 0.0603 0.0629 0.0623 0.0632 0.0756 0.0545 0.0551 0.0718 0.0642 0.0765 0.0753 0.0757: 0.0694 0.0838 0.0884 0.0838 0.0553 0.0706 0.0691 0.0704 0.0332 0.0326 0.0329 0.0328 0.0742 0.0761 0.0152 c 0.0154 0.0162 0.0572 0.0564 0.0469c 0.0675 0.0741 0.0567 0.304 0.0478 c 0.0558 0 0 0 0 0 0 0 0.0769 0.0776 0.0634 Hintzen;0.0630HGT 0.0752 secondnucleusH;0.0749KOS 0.0837 HSM;0.0832HGT 0.053 Dressler’szbasedonmeanof 0.0330 MS;HGT 0.057 Reichert;0.0570SR 0.0713 0.0693 H;0.0687KOS;radiotailgalaxy; 0.0553 MQ;0.0550FD;Pet;0.0545Hilletal. 0.0745 HST;0.0750HGT 0.0151 FD;0.0152MS;0.0155MD;NGC705 0.0161 FD;0.0165MS;0.0168MD;NGC708 0.0553 HGTmeasurednucleus ^ref 0.0717 HGTappearstobeaverageoftwonuclei Dressier No.36 Dressier No.33 (-578,-778) Dressier No.1(ref. sky featureoverMg(+279,-578) confused withprimaryandnight- second nucleus(+472,-275) 1981); 0.0776HGT at leasttwounidentifiedgalaxies;0.0534HGT HSM measuredzofoneotherclustergalaxy second nucleus Ca H+K,Gband,Hß,Mgi,NaD too faintforPalomarSkySurvey Hß, [Oin],I],Ha,[Nil],[Sii] Comments 1985ApJS ... 59. .447H -152 -1 -21 -16 -21 17 -162 -2 peak valueof3X10ergscmsarcsecforHa + km swithrespecttothecentralgalaxy,whichisseen asa galaxies. (ThesecasesareindicatedinTable1.)Thepeak negative dipsinceitappearsinthecontinuumbandpass. We ergs cmsarcsec.A978isapeculiarcasewhere there [N ii],downtoA133,whichhasapeakvalueof2X10 surface brightness(Table5)rangesfromA1795,whichhasa Table 6basedonthe1.5%subtractionerror. not detectedatquitelowlimits,whicharesummarized in do notbelievethatthissystemisrealandwilltreat this present dataandshouldbeconsidered withdrawn. without correspondingnuclear gasisnotconfirmedbythe nucleus ofthecDgalaxy.In mostoftheothersystems emission asanupperbound.Theremainingsixsystems are are someverymarginalindicationsofHaand[Nn]at— 2500 A\6548,6584 alongtheslit.Thelineandcontinuumsurface cD galaxyitself.Inparticular, thetentativesuggestionof emission, whileextended,is seen onlynearthenucleusof brightnesses alongeachslitareshowninFigure7.Awayfrom cm sarcsec.Nearthepeaks,errorscausedby the Ha4-[Nii]surfacebrightnessexceedsabout2X10"ergs and offslitsgivesthesurfacebrightnessofHa+[Nii] at thesurroundingcontinuum.Thedifferencebetweenon CHJY thatA2029andA2142 mighthaveextendedemission filamentary systemsextendingfartherthan10"from the emission intheseregionsarelessthan10ergscms generally lessthan1.5%ofcontinuumsurfacebrightness,as continuum subtractiondominate.Theerrorsare arcsec inHa+[Nn]. can beseenfromFigure7.Typicalupperlimitsongaseous the peaksincontinuum,gasmaygenerallybedetectedif Half oftheobservedsystemshavegasincorescD Only threeoftheclusters(A262,A1795,A2052)have -1 -1 Tarenghi 1977;HSM:Hintzen,Scott,andMcKee1980;MQ:MelnickQuintana1984;Pet:Peterson1970;HilletaL:al. under the“Comments”column. of comparison. Dressier: Dressier1980forA978,1981A2029;H:Hintzen1979;KOS:Kirshner,Oemler,andSchechter1978;Hintzen: Hintzen 1980; Schmidt:Schmidt1965;CO:CohenandOsterbrock1981;HS:HintzenScott1979. Slee andReynolds1984;FD:FaberDressier1977;MS:MelnickSargentMD:MossDickensHST:Hintzen,Scott, A2142; AK=+137kms: A2052; AV=+31kms: 4. S4 2. SI 3. S4 1. Nucleus 2. SI 9. S5 6. SI+S2 8. S5 1. Nucleus 7. S1+S2S3S4 Objects withpositionsmeasuredrelativetothepeakcDintensityasgiveninHoesselandSchneider1985have(AA\AT)tabulated HGT entrieshavebeenconvertedtoheliocentricvalues(bythesubtractionofAK=300sin/cosbastabulatedforeachcluster)purposes Note.—Sources of(heliocentric)redshifts:HGT:Hoessel,Gunn,andThuan1980;Reichert:G.Reichert1984,privatecommunication;SR: Cluster/Object Identification © American Astronomical Society • Provided by theNASA Astrophysics Data System Position (arcsec) + 165 Slit + 27 + 52 -53 + 96 + 56 + 6 -8 0 0 SPECTROSCOPY OFGASINCLUSTERCORES (arcsec) AX -62 -17 + 15 + 54 -22 -21 + 4 + 5 0 TABLE 4—Continued (arcsec) + 149 + 21 -51 + 46 -81 -52 AY + 5 + 6 0 line casesistheappearance of previouslyundetectableweak in Figures9and10areextremely cleanofabsorptionfeatures presence ofnuclearemissionordust.Inthesecases the This maybedueeithertodifferentialrefractionor the weak emissionlinesinthenucleus(cf.Heckman1980), we ing continuumabsorptionlineswhichcanseverelydistort lines suchasHßand[Om]À5007 ingalaxiessuchasAll26. normalized andsubtractedfromeachofthe14galaxies.In the for allsystemswithemission linesandaresummarizedin from thecDgalaxy.Particularly noteworthyfortheemission- obtain thenormalization.Theresidualspectrawhichareshown case ofthetwonearestcentralgalaxies(inA262andinA496) shown inFigure8.Thetemplatespectrumwasthensuitably adopted thefollowingprocedure.Allgalaxieswithoutemis- with opticalemissionandthosewithout. template wasmultipliedbyasecond-orderpolynomial to the continuumslopediffersappreciablyfromtemplate. spectrum ofanaveragecDnucleus.Thistemplate is sion lineswereaddedtogethertoformatemplateof the xies arevirtuallyidentical.Schneider,Gunn,andHoessel distinguishable differencebetweenthestellarspectraofcDs (1983) findaverysimilarresultforthecDg-rcolorswhich was thende-redshiftedusingthepresentlydeterminedred- are highlyinvariant.Withthepresentdatathereisnoreadily servations theunderlyingcontinuumspectraofcDgala- from thesedataisthatattheresolutionofpresentob- slit passingthroughthenucleus.Ineachcase,spectrum summing ±2"aboutthepeakcontinuumintensityforeach shifts forthecDgalaxygiveninTable1.Thefirstpointnoted In ordertostressthesepointsandalsoremoveunderly- We nextformedspectraofthenucleuseachgalaxyby Line ratiosweremeasuredfor template-subtractedspectra 0.0960 0.0917 0.0813 0.0913 0.0338 0.0340 0.0820 0.0855 0.0723 0.0221c 0.0912 HS;0.0906HGT 0.0338 MS;0.0349Schmidt;0.0351CO; 0.0219c DressierNo.19;quotedzisnear c) LineStrengths , ( +471,+4.'8) ( +476,5'.'2) 0.0350 HGT(seetext) nucleus ofspiraldisk(slit3) Comments 459 o
ARCSEC
St ä «N a
ARCSEC
Fig. 7.—Profiles of Ha -I- [N n] surface brightness along each slit (solid line). The labeling of the slits in parentheses follows Table 2. A 100 À bandpass slit image is formed, centered on Ha redshifted to the z of the central brightest galaxy (as determined in the present work), together with a continuum image corresponding to the sum of two 50 A bands on either side of the main band. For multiple nuclei and binary systems (such as A1775), where component redshifts span a wide redshift range, profiles were constructed for each redshift system. The solid line shows the difference between line and continuum bands. The diamonds show 10% of the continuum surface brightness (with the zero point for these curves offset by 10~16 ergs cm-2 s-.1 arcsec-2). Line features can generally be distinguished at about 2%-3% of continuum. 460
© American Astronomical Society • Provided by the NASA Astrophysics Data System ERGS/0U2 SEC SQ ARCSEC ERGS/042 SEC SQ ARCSEC ERGS/CM2 SEC SQ ARCSEC © American Astronomical Society • Provided by theNASA Astrophysics Data System ARCSEC Fig. 7—Continued 461 8 % a PM S? 3 tx E-16 E-16 - E— 15 E-ia E-16 E-16 E-16 E-16 1.5 -5 -2 5 2 2 a -150 -100 6 1 T NUCLEUS OFA496(SLIT1) NUCLEUS OFA401(SLIT1) JK. ARCSEC ARCSEC II <*•> O t O 100 150 100 150 ft
ERGS/CM2 SEC SQ ARCSEC ERGS/042 SEC SQ ARCSEC ERGS/042 SEC SQ ARCSEC E— 1ft- E- 15 E—16 E-16 1.5 -5 5 2 -150 -IOC © American Astronomical Society • Provided by theNASA Astrophysics Data System 1 1 SLITWOFNUCLEUSA496(SLIT2) -50 O50 ARCSEC lOO 150 Fig. 7—Continued 462 a CM ä » NUCLEUS OFAT126(SUTT) LO V" in X ft
ERGS/CM2 SEC SQ ARCSEC ERGS/CU2 SEC SQ ARCSEC ERGS/CU2 SEC SQ ARCSEC © American Astronomical Society • Provided by theNASA Astrophysics Data System Fig. 7—Continued 463 a 04 ti 91 a 04 » ä 1 SLITEOFNUCLEUSA1795(SUT2) ERGS/CM2 SEC SQ ARCSEC ERGS/CM2 SEC SQ ARCSEC ERGS/0yl2 SEC SQ ARCSEC © American Astronomical Society • Provided by theNASA Astrophysics Data System 9 SLITSEOFNUCLEUSA1795(SLIT7) Fig. 7—Continued 464 a » 9 CM a CM ä 3 E-1C E-15 E—15 E-15 E— 16- 2.4 3.2 1.5 -8 8 -150 1 SLITWOFNUCLEUSA1795(SLIT9) -100 -50 NUCLEUS OFA2029(SLIT1) NUCLEUS OFA1795(SLIT8) ARCSEC O 50 lOO ft
ERGS/CM2 SEC SQ ARCSEC ERGS/CM2 SEC SQ ARCSEC ERGS/CM2 SEC SQ ARCSEC -150 -100 © American Astronomical Society • Provided by theNASA Astrophysics Data System 5 SLITSEOFNUCLEUSA2Q29(SLIT4) 2 SLITSEOFNUCLEUSA2029(SLIT2) 4 SLITSEOFNUCLEUSA2Q29(SLIT3) 100 150 Fig. 7—Continued 465 04 ä I 8 a £ 04 8 04 æ » 13 SLITSEOFNUCLEUSA2029(SLIT5) NUCLEUS OFA2142(SLIT1) ft
ERGS/CM2 SEC SO ARCSEC ERGS/OI2 SEC SQ ARCSEC ERGS/CM2 SEC SQ ARCSEC © American Astronomical Society • A2142 (SLIT3) Fig. 7—Continued Provided bythe NASA Astrophysics Data System CM 8 ft a a CM S æ a CM 8 a E—17 E-16 - E—17 1.5 -5 5 -150 A2142 (SLIT7) A2142 (SLIT5) A2142 (SLIT6) 1985ApJS ... 59. .447H -1f a a e d c g 1f Al 795nucleus 60 kmsshock A133 A85 A1126 A262 . A496. A2052 stellar absorption,theratioswithH/?arelistedasuncertain(colon). LV filamentsofNGC1275. 90 kms'shock b within ouruncertaintiesisconsistent withastandardBalmer weaker, however.)Ha/H/lgenerally liesintherange3-4and Tables 5and7.Thespectraaredominatedbylowerionization very characteristicofthespectra ofgasinnormalgalactic [N n]/Haratiosfromspectrum tospectrum.However,thisis decrement. Oneanomalyisthe strengthandvariabilityofthe obtained byKentandSargent(1979)onthelow-velocity stages, and[Oin]isweak.Theyareverysimilartothose filament systemaroundNGC1275inPerseus.(The[S n] is d b g e c a f Filament towardtail. Filament nearnucleus. “Blob” toNE Basedonsumoftwoneighboringslitsonly. Values fromvBHMgivenonsecondlineinparentheses. ValuesfromKentandSargent1979. ValuesfromStauffer1981givenonsecondlineinparentheses.Since theseratiosarebasedonmeasuredemission-hnefluxesuncorrectedforunderlying ValuesfromCohenandOsterbrock1981givenonsecondlineina parentheses. Average oftwoslitspassingthroughnucleus. ShockedlineratiosfromthemodelsofShullandMcKee1979. Cluster © American Astronomical Society • Provided by theNASA Astrophysics Data System ,a,b -21 Peak SurfaceBrightness (ergs cmsarcsec) 15 -15 -15 15 -15 ARCSEC 2.2X10“ 3.2X10 Ha +[NII] 1.6 X10 1.8X10“ 1.5X10 16 16 16 16 -17 2xl0" 4X10" 9X10" 2X10" 9xl0 SPECTROSCOPY OFGASINCLUSTERCORES Summary ofPeakSurfaceBrightnessandLineRatios -4.6 -4.1 -2.1 ~ 4.6 (8.3) (2.5) (3.3) (6.3:) Hiß Ha 4.8 4.0 3.2 2.1 3.1 3.7 3.3 3.2 Fig. 7—Continued [O m]À5007 TABLE 5 ( <0.5) ~ 0.6 Hiß (2.9:) (4.2) (0.6) 0.6 0.8 0.4 0.6 0.01 0.8 0.4 0.6 0.8 1.9 1.5 8 basis ofinterstellarhydrogen inthesedirections(E_<0.07, nuclei (e.g.,Keel1983).[Sii]isrelativelyweakcompared with hot 10Kgasisalsoexpected theoreticallytobesmall,with Table 1).Clusterreddening caused bydustintheextended Ha. these clusters.Thisisconsistent withvaluespredictedonthe trast toPerseus,thereislittleforegroundreddeningany of typical valuesofE_<0.1 (e.g.,CowieandBinney1977). ßv Bv The valuesoftheBalmerdecrementsuggestthat,incon- [N h]X6583[Su]ÀÀ6716,6731[O] ~1.2 (2.9) (2.7) (0.6) (0.8) 0.9 0.5 0.7 0.85 0.9 0.9 Ha 0.1 2.0 2.0 1.3 1.7 - 2 Line Ratios -0.6 (0.4) (2.4) (1.47) (0.8) 0.8 0.6 0.8 0.9 0.9 0.5 0.6 0.9 2.2 1.6 1.3 Ha - 2 -0.1 weak (0.2) (0.30) (0.3) Ha 0.4 0.1 0.2 0.4 0.6 0.2 0.3 0.3 0.3 0.2 X6300 [Su]X6716 [S il]X6731 (1.1) high 2.0 2.0 1.8 1.1 -1 1.6 1.7 1.5 -1 1.4 467 468 HU, COWIE, AND WANG Vol. 59 O'! LO ft LO co00
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o LÜ 00 _J < cn o
4500 5000 5500 6000 6500 7000 DEREDSHIFTED WAVELENGTH (ANGSTROM) Fig. 8.—Template spectrum of cD galaxy nucleus (aribtrary normalization) formed by adding the spectra within ±2" of the nucleus in the slits crossing the nuclei of A401, A644, A754, the two central galaxies of A1775, A2029, and A2142. Also shown is the result of dividing the average spectrum into the average spectrum of the four galaxies observed in the first run, which shows the universal character of the cDs and the lack of systematic effects between first and second runs.
The small variation in g - r colors for cD galaxies seen by means that the pressure increase between core and nucleus is Schneider, Gunn, and Hoessel (1983) provides additional ob- less than a factor of 20 and probably significantly smaller. servational confirmation of this, suggesting ^ < 0.1 in the Again, Kent and Sargent (1979) obtain a similar result for that clusters if the variation in color caused by difierences in low-velocity filament system in NGC 1275, as do van Breugel, reddening from cluster to cluster is not to be too large Heckman, and Miley (1984) for the case of A1795. compared with the observations. Finally, in A1795, Norgaard-Nielsen, Jorgensen, and Hansen (1984) have de- tected Lya emission using the International Ultraviolet Ex- d) Kinematics plorer (IUE) satellite with a luminosity of 9X1041 h~2 ergs For each slit containing emission lines, contour plots of the s-1, or L(Lya)/L(H.ß) = 23. Such a high ratio would suggest Ha + [N ii] complex were formed, with one axis in velocity EB_ v < 0.2 for either the photoionization or the shock models space centered at Ha in the presently measured galaxy red- we discuss in § IY of the paper. shift given in Table 1 and the second axis in position along the The [S il] A6716/A6731 ratio provides a direct density slit centered at the position of the peak continuum intensity. diagnostic. Within the typical error of about 0.4 in the ratio, These plots are shown in Figure 11. The velocity at each ratios for all emission spectra lie at the low-density value of position (based on an average of Ha and [N il] À6584) was -3 1.4. Adopting ne ^ 1000 cm on this basis (e.g., Osterbrock then measured at each distinct position along the slit. These -1 1974) implies in turn that the dimensionless pressures (neT) velocities are generally accurate to about 50 km s , though for these systems must be substantially less than 107 cm-3 K. for the faintest emission the errors may be larger. The kine- Since the dimensionless pressures in the hot X-ray gas in the matic structure is complex, but in all the cases where there is cluster are typically around 5x105 cm-3 K, this in turn enough information to judge, the gas within the galaxy ap-
© American Astronomical Society • Provided by the NASA Astrophysics Data System r"x No. 4,1985 SPECTROSCOPY OF GAS IN CLUSTER CORES 469 O'! LO a LO CO00
o cr I— U1 o < CJ LÜ m o cx < o IS) u LÜ S) CN O S) o ex LU
DEREDSHIFTED WAVELENGTH (ANGSTROM) Fig. 9. — Shown are the spectra within ±2" of the nucleus of slits passing through the nuclei of several of the central galaxies. Below these are shown the spectra after subtraction of the normalized template spectrum. In A1126 and A1795, where we have two slits cutting the nuclei, only the spectrum of the first is shown, but both residuals are plotted with the second offset by 10“17ergs cm-2 s-1 arcsec-2 A-1. For A262 the middle plot shows the gradient which remains in the spectrum after template subtraction possibly an effect of dust extinction. This spectrum has divided by a second-order polynomial fit to form the residual spectrum at the bottom, for ease of comparing fine features.
pears to be in the form of a thick disk, not aligned with the nucleus and is about +3.5 h~l kpc in extent, the gradient is continuum major or minor axes, and to show shearing along roughly 50 h km s-1 kpc-1 with maximum velocities of about the disk with typical projected velocities ranging over + 200 km s-1, and the mean velocity is about —150 km s-1 + 200-350 km s-1. The situation appears to be very similar to in extent. The very bright blob 4" (4 h~l kpc) to the north of that in the extended optical systems in normal ellipticals the nucleus lies at —350 km s-1. As CHJY point out, the which have been recently studied by Demoulin-Ulrich, elongation of this material and the long filament (Io west of Butcher, and Boksenberg (1984). north) reflect the north-south elongation of this cluster while The most complete information available is for A1795, and the galaxy itself is nearly circular. this is summarized in Figure 12. As can be seen clearly in the In A496 the shear in the gas is nearly perpendicular to our contour plots, there is only a very small velocity gradient slit directions, which were aligned along the major axis of the along the extended filament seen by CHJY in this system galaxy and which appear to be crossing the emission disk at a which runs from about —180 km s_1 near the galaxy to near sharp angle. The position angle of the rotation and elongation 0 km s-1 at the tip, some 40 h~l kpc away. The line-of-sight is very approximately 90° east of north, or approximately at velocity shear here is less than 4.5 h km s-1 kpc-1. The gas right angles to the CHJY position angle for the galaxy major near the nucleus of the galaxy itself lies near the galaxy axis. In this case the cluster is nearly circularly symmetric as redshift. There is a systematic velocity gradient present in the summarized in CHJY. Maximum velocities observed are about gas within the galaxy which may be seen most clearly in slits 8 + 200 km s1. and 9, which are oriented along the elongation of this material For A1126 the elongation and shear appear to run nearly (13° east of north). In slit 9 the structure is centered on the along slit 2, which is at a position angle of 82.5° east of north.
© American Astronomical Society • Provided by the NASA Astrophysics Data System 470 HU, COWIE, AND WANG Vol. 59 1.5 E-16 a
o a: (— ui o z < o UJ Ul o q: < o œ CJ LU Ul C\l O on o z LxJ
DEREDSHIFTED WAVELENGTH (ANGSTROM) Fig. 9—Continued
This is significantly angled with respect to the first slit, which e) Color Gradients was aligned along the secondary nucleus and the nearby The color gradients in the cooling-flow cDs are of consider- companion galaxy. Extremal velocities are —300 and +200 able interest, since star formation might result in significant km s_1. In this case the gas extends over about 9 h~l kpc, and color changes, and Valentijn (1983) has recently suggested the shear is about 60 h km s-1 kpc-1. that there could be large B — V gradients (up to 0.7 mag) In A262, where only a single slit is available, the gas in the across some cooling-flow cDs such as A496 and A85. As a nucleus is at +240 km s-1 with respect to the galaxy, while final general reduction, pseudocolor surface brightness profiles the long filament is at a constant velocity of + 20 km s-1. in equivalent R, F, 2?, g, and r bands were computed for In A2052 we see little sign of shear in our single slit, and the each slit. The R, F, and B profiles were calculated by forming bulk of the gas is near zero velocity. However, this object was the average intensity over 200 A bandpasses centered on 7000 also observed by Demoulin-Ulrich, Butcher, and Boksenberg À (Ä), 5500 À (F), and 4500 À {B) and converting to -1 9 (1984), who measured a velocity gradient of 70 h km s magnitudes using the convention mR = 0 1.74 X10 ergs -1 -2 -1 -2 -1 -9 -2 -1 kpc , which is very similar to our values in the other cases cm s arcsec A , mK = 0-> 3.64XlO ergs cm s where the slits were better aligned along the gas. arcsec-2 A-1, and = 0-> 6.61 XlO-9 ergs cm-2 s-1 In A85 shearing and elongation can be seen most easily in arcsec-2 A-1. In order to avoid spurious effects from the slit 6, where the gradient is very approximately 100 km s-1 night-sky cleaning procedure, only the raw (uncleaned) data arcsec-1 or 125 h km s-1 kpc-1. The position angle of 5° east were used with a linear background subtraction. For data of north is inclined at about 55° to the position of the major obtained in theo first run, the low-wavelength cutoff for the axis of the galaxy as given in CHJY. spectra at 4500 A forced us to use a blue bandpass centered at Finally, in A133 the gas appears to have velocities of about 4700 À. The g- and r-magnitudes were computed from mono- 140 km s-1 down to about - 60 km s-1, but in this very weak chromatic Oke AB fluxes according to g = AB(5000)—0.02 system there is relatively little more that can be said. and r = AB(6500)+0.17. These relationships were derived by
© American Astronomical Society • Provided by the NASA Astrophysics Data System No. 4,1985 SPECTROSCOPY OF GAS IN CLUSTER CORES 471
DEREDSHIFTED WAVELENGTH (ANGSTROM) Fig. 9—Continued
comparing scanner spectrophotometry results reported by Oke /) Notes on Properties of Individual Clusters and Gunn (1983) for four F subdwarfs with their g and r colors given in Thuan and Gunn (1976). i) A85 B, V, and R profiles for slits in four representative clusters Extended optical line emission from A85 was first reported are shown in Figure 13. The profiles are truncated at B = 26 by Heckman (1981). More detailed pictures in several band- mag arcsec-2, below which we consider that our background passes are given by CHJY. These show an elongated system corrections are probably suspect. For each slit V — R, B — V, with a scale of about 10"-15". This structure is confirmed by and B — R colors were calculated. These were then averaged the present slit exposures. The emission system is thick but over the two sides of the profile to remove any systematic elongated along a NNE-SSW direction. The shape appears offsets caused by spatial shifts in the profile as a function of very similar to the total Ha picture in CHJY’s Plate 4. wavelength (e.g. S-distortion). The color profiles are also There are no signs whatsoever of more extended emission in shown in Figure 13. As can be seen from this figure, variations our covered area at a 2xl0-17 ergs cm-2 s“1 arcsec-2 level above the 0.1 mag level could be easily and reliably dis- except in two of the galaxies which do have emission-line tinguished either along individual slits or in slit-to-sht varia- systems (cf. Table 4). This is also consistent with the CHJY tions. We see no such gradients in any of the galaxies. In photographs. The lack of extended emission from this system particular, we can easily rule out the variation m B-V from allows us to estimate the luminosity of the system by summing 1.44 at the nucleus to 0.66 at 60" which Valentijn claimed to our slits. This gives F(Ha -l-[N n]) = 6X10-15 ergs cm-2 s-1, have seen in A496. Valentijn’s (1983) result in which he or, using a mean cluster redshift of 0.0513 (Table 1), a obtains large radial color gradients for a number of cD luminosity of 2X1040 h~2 ergs s-1 in Ha + [N n]. The peak galaxies may have arisen from slight nonlinearity in his surface brightness of 2xl0-16 ergs cm-2 s-1 arcsec-2 in Ha calibration procedure. agrees extremely well with CHJY (2.3X10-16 ergs cm-2 s-1
© American Astronomical Society • Provided by the NASA Astrophysics Data System 472 HU, COWIE, AND WANG Vol. 59 1 .s a
o cr I— in o z < o Ld U1 O cr < o u Ld 00 o QL DEREDSHIFTED WAVELENGTH (ANGSTROM) Fig. 9—Continued arcsec-2). However, because the size of the object is smaller faint for spectroscopic or kinematic work, and only the Ha + than the value assumed by CHJY, our luminosity is smaller by [N ii] complex is clearly seen in the spectra (Fig. 9), with [N n] a factor of 4. Heckman also overestimated the luminosity by slightly stronger than Ha. Previous HEAO 1 A-2 observations about a factor of 10. Both of these overestimates are probably reported by Reichert et al (1981) noted that a low tempera- caused by continuum subtraction problems which are severe ture (T < 2 X107 K) was required, based on constraints from in the imaging work for nuclear emission. The present results spectral fits to the source. This cluster has been seen as a could underestimate the luminosity if there were strong fila- strong soft X-ray source by EXOSAT (R. F. Mushotzky 1984, ments outside the slit positions, but the CHJY photographs do private communication), and the central galaxy of the cluster not appear consistent with this. overlies the radio source MSH 01-201 (Ghigo and Owen Although high-resolution radio maps have failed to confirm 1973; Véron 1977; Slee and Reynolds 1984). A second nucleus a radio source coincident with the central cD, Slee and 475 to the north is burned out on the Palomar image, but Reynolds (1984) report the presence of a steep-spectrum source shows up as the bright starlike feature on the second slit (Fig. — 6(5 to the northeast from their VLA measurements at 80 4). The velocity separation between the two nuclei is only 150 MHz and 1.465 GHz. km s-1 (Table 4). ii) A133 iii) A262 A133 is the weakest system definitely detected in the pres- The bright central galaxy of this cluster, NGC 708, was ent study and the only system not previously known to have observed by Peterson (1970) and found to show emission lines. optical emission. The emission appears confined within a few The extended nature of the emission-line system, covering arcseconds of the nucleus on the basis of the two slits ob- more than 20" along our slit, has not been previously reported tained. A very crude estimate of the (Ha + [N n]) flux is in the literature, but unpublished aperture photometry taken 2 X10“15 ergs cm-2 s-1, which for our redshift of 0.0572 gives with the Lick scanner by Stauffer (private communication in L(Ha + [N n]) = 7Xl039 h~2 ergs s-1. The system is too advance of the present observations) had already shown the © American Astronomical Society • Provided by the NASA Astrophysics Data System 1985ApJS ... 59. .447H No. 4,1985 displaced toshowtheemission-hnestructure.Forcaseswheremorethanonenuclearspectrumhasbeenobserved,spectraaregiven intheorder residuals fromthetime-variableatmosphericabsorptionbandscanbeseenatlong-wavelengthend. specified inTable2.Residualsfromthesubtractionofstrongnight-skyfines(e.g.,[Oi]A5577)canbeseen;andforhighestredshift cluster,A1126, Fig. 10.—Residualspectraofthegaswithin±2"centershtspassingthroughnuclei.Zeropointsfortheseplotshavebeen arbitrarily 17 16 16 16 17 17 17 8 A2029 9X10" A1775 1.8X10" A978 1.5X10" A754 1.0X10" A644 7X10" A401 6X10" brightness basedon1.5%ofpeak continuum A2142 5X10" surface brightnessina100Abandpass. Upper LimitsonPeakSurfaceBrightness © American Astronomical Society • Provided by theNASA Astrophysics Data System a 21- Upper limitsonHa+[Nn]peaksurface Cluster (ergscm“sarcsec) TABLE 6 Peak SurfaceBrightness Ha +[NII] SPECTROSCOPY OFGASINCLUSTERCORES DEREDSHIFTED WAVELENGTH(ANGSTROM) 162 21 15 392-1 brightness of6x10“ergscm"s"arcsec"within this emission systemtobeextendedonscalesofafewarcseconds. ergs cm"s"arcsec". aperture agreeswellwithourpresentpeakvalueof1.6X10" Ha +[Nii]ina4"roundaperture.Hisaveragesurface Stauffer’s datagivealuminosityof8xl0h~ergssfor A262 hasahigh(~75%)percentageofspirals(e.g.,Moss and brightness ratherthanasingleoutstandinglybrightcD. The radio andopticalemission.Kotanyi andEkers(1979)reported central galaxyisaweakextended radiosource(cf.Collaetal. core regioncontainsninegalaxiesofroughlycomparable give clustermorphologyastypeC9,indicatingthatthecentral (1970) classifythisasBMtypeIII;StrubleandRood(1982) Dickens 1977;Kalloglyan1969,1971).BautzandMorgan classic cDclustersofBautz-Morgan(BM)typeIor II, data, wecansayverylittleabout therelativemorphologyof that theradiostructurewas orientedatapositionangleof 1975; Fantiétal1982),although, withthepresentlimited Unlike themajorityofclustersstudiedhere,whichare 473 1985ApJS ... 59. .447H l 17-2 nucleus alsoshowsnoopticallyemittinggasdowntoour none ofthegalaxyspectra(includingthatcD)contain (1977) forclustervelocitydispersionstudies.Theystatethat coverage hasbeenmadebyHintzen,Scott,andTarenghi causes someproblemswiththeimaging.Extensiveredshift in Table5). extent of4h~kpcisverysimilartothatM87,asarethe sensitivity limitof2x10“ergscmsarcsec. strong emissionlines.Oursingle-shtobservationacrossthe or CHJYowingtothepresenceofanearbybrightstarwhich (both inStauffer’sdataandthepresentresultssummarized more analogoustotheM87filaments(cf.FordandButcher 1970), hasnotbeenpreviouslydiscussedbyeitherHeckman stronger in[Sii]thanisthecaseremainingsystems and Forman1984).Thespectrumofthesystemmaybe 1979) thantotheflowsinricherclusters.Thespatial not findevidenceforthefilamentsystem.Thepresentwork nuclear emissioninA496,whileFabianetal.(1981¿>)claimed have beenfoundwithin7'ofthisgalaxy(Slingo1974;Bums ter (BMtypeIII),andthelowerX-rayluminosity(cf.Jones typical surfacebrightnesses,thestructureofpresentclus- north. Thistendencytooffset fromthecontinuumpeak(in cally distributedatthenucleus andstretchingslightlyless confirms theCHJYresults.Strongemissionisseensymmetri- central cD,tworadiotailsources(4C13.17Aand4C13.17B) 474 roughly 35°totheminoraxis ofthegalaxy. this casetheminoraxis)becomes mostpronouncedinthe than ±10".Fortheshtsto westtheemissionoffsetsto the nuclearemissionandshowedthatitwasextended,but did to haveseenextendedfilamentsinthissystem.CHJYfound and Ulmer1980). outermost sht,andsuggests an elongatedshapetiltedatvery - 80°withrespecttoaweakdustlane.Thissystemmaybe This cluster,oneoftheclassiccDs(BautzandMorgan Heckman (1981)madeapossible(marginal)detection of Although noradiosourcehasbeenidentifiedwiththe © American Astronomical Society • Provided by theNASA Astrophysics Data System Ni A5199.... covers sameregionatdifferentpositionangle,secondvaluesareshowninbrackets. [N il]À6548.. [O i]X6364... [O i]A6300... He I\5876... [O in]A.5007 [O in]Á.4959.. Hß À4861.... [S il]A6731... [S il]A6717... [Nu] A6583.. H« A6563.... iv) A401 v) A496 Note.—Ratios formedbysummingsetofslitscoveringregion.Wheresecond Line ~10 Nucleus 100 40 20 29 27 29 90 54 7 7 5 (-8) (~6) (~H) (20) (7) (34) (30) (63) (84) (100) (35) (26) HU, COWIE,ANDWANG Emission-Line RatiosinA1795 Bright “Blob”toNE TABLE 7 100 (100) 25 (13) 35 (25) 37 (36) 32 (30) 78 (48) 91 (84) 30 (25) ...(7) ...(6) ...(11) 40 402_1 14-2 2-1 16 17-2 17 412- -21 -1 7(4) zen, Scott,andMcKee1980),whichwasforagalaxywell imaging workbecauseonlyoneredshiftwasavailable(Hint- presence ofextendedfilamentarystructureawayfromthe present results. within 10"ofthenucleus,whichagainisconsistentwith limits. CHJYstatethattheemissionseemsprimarilyconfined with thevaluesquotedbyCHJYofbetween4.5X10and luminosity exceeds6X10h~ergss,whichisconsistent 6X10“ ergscms.ThecorrespondingHa-t-[Nn] cm~ sarcsec,oraflux(Ha+[Nn])inexcessof region wherethesurfacebrightnessexceeds5xl0~ergs of itshighX-rayluminosityandcentraldensity(Abramopoulos relative velocityofthesecondgalaxywithinenvelope of only othernoteworthypointaboutthepresentdatais the and Ku1983),butwasexcludedfromtheCHJYnarrow-band combined Haand[Nn]lines. nucleus atabout2X10“ergscmsarcsecinthe (1981h) claimedwerepresenttothesouthofgalaxy.In limit foropticalemissioninthe nucleusdownto2X10“ergs with theshtpassingthrough thenucleus,pushesupper optical emissionwasdetected. Thepresentobservation,made study withnarrow-bandimagingwouldbeofinterest. The accurate redshiftisavailableforthecentralgalaxy,further sign ofanyemissionfromthecentralgalaxy,butnowthat an separated fromtheclustercenter.Thepresentdatashow no the areacoveredbyshts,presentworkrulesout 1.3 XlOh~ergss,butislargerthanHeckman’supper minutes ofarcfromtheoptical clustercenter. cm sarcsec.Abramopoulos andKu(1983)notedthat the primary. the cD,whichismovingatonly300kmswithrespect to the X-raycentroidof IPC imageisoffsetbyseveral This clusterwasaninterestingcandidateforstudybecause The presentdatacrudelysuggestan8"Xsizeforthe A754 isoneoftheclustersstudiedbyCHJYforwhichno Our shtsshouldhavecutthefilamentsthatFabianetal. Near GalaxyTail Filament Regions 100 ~ 3 40 24 32 28 35 85 12 vii) A754 vi) A644 100 25 28 31 17 70 16 10 4 4 or 00 or LO LO V" X ft KINEMATICS OF A85 (SLIT 2) KINEMATICS OF A85 (SLIT 6) © American Astronomical Society • Provided by theNASA Astrophysics Data System (OBSOav) NOIllSOd 1 1 o •^3 CX 1 ^ 3 'o •ag “rS < & Æ cd 1 • Sg -a Æ 'O ■K CO 12 'o 3 la -e^ ^ s li .5 ^ i2 > sl £ ^ S öO cd -a 1/3 O cä cC S -c 0 Í3 LO ^ t: i3 S 5 ^ o 3 8 ¿3 a> <3 la c ^ ■- QJ C ^ w o > c ï ?.a *> S Ö cd c C/3 'O ^ 3 3 X o3 oo y ^t c ö (U ^ o ^ CA S 2^ o3 TJ c ^ c/3 (D 1/3 ^ C/3 o oo c * ÔÛ-C 1) o w .3 s f 1 I CA^ SJá a X) a -O Fig. 11 — Continued (33S0dV) NOLUSOd All © American Astronomical Society • Provided by the NASA Astrophysics Data System 1985ApJS ... 59. .447H © American Astronomical Society • Provided by theNASA Astrophysics Data System (D3S0dV) NOIllSOd (OBSOdV) NOIllSOd 478 (J > LÜ o CO —I Fig. 11 — Continued KINEMATICS OF AI 795 (SLIT 1) 40 KINEMATICS OF A1795 (SLIT 2) © American Astronomical Society • Provided by theNASA Astrophysics Data System (03S0av) NOlilSOd 479 V" X KINEMATICS OF AI 795 (SLIT 3) ^ KINEMATICS OF A1795 (SLIT 4) © American Astronomical Society • Provided by theNASA Astrophysics Data System (DBSOdV) NOIllSOd w 480 or 00 or LO LO V" X ft KINEMATICS OF AI 795 (SLIT 6) KINEMATICS OF A1795 (SLIT 8) © American Astronomical Society • Provided by theNASA Astrophysics Data System (OBSOdV) NOIllSOd (oasoav) Nomsod 481 o CN o o o T o O O O O O CN o o O I LÜ o o > _l 0 o' 1 1985ApJS ... 59. .447H © American Astronomical Society • Provided by theNASA Astrophysics Data System (03S0av) NOlilSOd (03S0HV) NOlilSOd o ÜJ o o È co > _J Fig. 11 — Continued 1985ApJS ... 59. .447H 12 16 2 16-2 based onanaveragezoftwo ormoreunidentifiedcluster images. been causedbyseeingvariations betweenonandoffband have detectedsphericallysymmetricextendedemission results withameasuredredshiftof0.0542showthatifthere is sistent withthepresentresults.TheHeckmanresultmayhave s“ arcsec”within10"radius,whichdoesnotappear con- found anaveragesurfacebrightnessof2.9x10”ergscm“ gas nearthenucleusofthissystem,itliesatlevelsless than centered onthenucleusofthisgalaxy.However,present and 10)isconfinedwithin3"ofthenucleus.Heckman 1X10" ergscms“arcsecforHa+[Nn](cf.Figs. 7 underlying galaxy.Aplussignindicatesthepositionofnucleusinshtcoverage. shown, withmeasuredvelocitiesfortheHasystemdesignatedalongeachslit.Thezero-pointvelocityisreferencedtoabsorption-line redshiftofthe superposed onacontourplotoftheemission-hnegas(fromCHJY,Fig.3h).Onright,plottedtosamescale,slitcoverageemission systemis The clusterredshiftofz=0.053 givenbyDressier(1980)is Based onaredshiftof0.0527,Heckman(1981)claimed to Fig. 12.—MeasuredvelocitiesoftheHa+[Nn]gaseousemissioninA1795.Shownonleftarepeak features © American Astronomical Society • Provided by theNASA Astrophysics Data System viii) A978 SPECTROSCOPY OFGASINCLUSTERCORES is associatedwiththebrightest continuumcomponent.Along 47° withrespecttothisaxis.Theemissionisslightlyextended peared confinedprimarilytothenucleus.Weobtained two FWHM of275.Thereisno emission seenineithershtaway slightly separatedpeaksandaFWHMof4".Alltheemission galaxy presentinAll26,andtheotherorientedatanangle of from thenucleus. the secondsht,emission showsnostructureandhasa along theaxisofsymmetryfirstsht—having two slits: oneorientedalongthetwonucleiandcompanion pared withourownmeasurementof0.0545. galaxies. HGTgiveavalueofz=0.0534(heliocentric), com- Heckman (1981)detectedemissionfromA1126whichap- ix) A1126 483 Fig. 13.—Equivalent R {triangles), V {solid line), and B {crosses) surface brightness along sample slits for the clusters A85, A496, and A1795, which have cool gas emission, and A2142, which does not. For each slit V — R {triangles), B — V {crosses), and B - R {solid line) were calculated, and averaged over the two sides of the profile to remove any systematic gradients caused by spatial offsets in the peak brightness as a function of color (e.g., S-distortion). The resulting colors were then plotted as a function of the displacement from the peak. Fixed reference lines are shown for each cluster so that possible color gradients and variations from slit to slit may be visually assessed. 484 © American Astronomical Society • Provided by the NASA Astrophysics Data System 00 LO ft MAGS/SO ARCSEC MAGS/SQ ARCSEC MAGS/SO ARCSEC © American Astronomical Society • Provided by theNASA Astrophysics Data System ARCSEC ARCSEC Fig. 13—Continued 485 00 LO ft MAGS/SO ARCSEC MAGS/SQ ARCSEC MAGS/SO ARCSEC © American Astronomical Society • Provided by theNASA Astrophysics Data System Fig. 13—Continued 486 co 00 O'! LO LO V" X ft I MAGS/SO ARCSEC MAGS/SO ARCSEC © American Astronomical Society • Provided by theNASA Astrophysics Data System Fig. 13—Continued 487 NUCLEUS OFA2142(SLIT8) 1985ApJS ... 59. .447H l -1 412- 15-2_ 2-1 -2_140 -21 -17 402-1 1 -15 in velocity(Table4),whilethenearbycompaniongalaxyand we alsofindthattheenvelopeseemstobeprimarilyat z =0.0694forthebrighter,southeastcomponentand while bothseemtoliewithinacommonenvelope,thered- in verygoodagreementwiththepresentroughestimate. within thegalaxywasextendedoverabout4-8h~ kpc. with Jenner’ssuggestion. be distinguishedonthesecondary,whichseemsconsistent brighter galaxy’sredshiftandthatbothsystemscan km s),suggestingthatthetwogalaxies,whilespatially 0.0753 forthefainter,northwestcomponent,orAy«1800 check whethertherewasfainteremissionineitherofthe (1981) givesatotalvalueof1.2X10h~ergss,whichis extent ofthegas,weobtainaflux9x10“ergscms region adjacenttothe“void”;however,becausetheirmagni- overlapping, arephysicallyquitedistinct.Inthepresentdata to thenorthwestofbrightergalaxy,whichisalsoaradio h~ ergss,aboutafactorof2lessthanHeckman’supper for Ha+[Nu],whichtheredshiftof0.0852giveninTable present paper,althoughthe intensity calibrationinvBHMis paper andtwowiththeKitt Peakhigh-gainvideospectrome- found bySargent(1973)inhisredshiftsurveyofthe 4C from Hintzen(1979). {m ~15),thebestestimateofmeanclusterredshiftisstill Kirshner, Oemler,andSchechter(1978)redshiftstudiesofthe shifts ofthetwogalaxiesarequitedistinct(wemeasure tail galaxy(MileyandHarris1977).Jenner(1974)foundthat, limit. ergs cms,oranupperlimittotheluminosityof4X10 ergs cmsarcsecinHaT[Nn],whichwithin central galaxiesofthissystem.Theupperlimitis4X10 sion inthecenterofA1775.Thepresentslitwasobtainedto the gaseousemissionareatvelocityofprimary. 1 givesL(Ha+[NIi])=7xl0h~ergss.Heckman very rough.Inparticular,we agreewithvBHMthatCHJY cryogenic camerainamodesimilartothoseofthepresent obtained threespectraoftheA1795gas—oneusing the rather clearlyseeninFigure7. fainter thanthecentralregions,andthisresultcanalso be show thatthefilamentsystemisaboutanorderofmagnitude stretching toabout40/Tkpcfromthecentralgalaxy.CHJY Finally, CHJYshowedthepresenceofafilamentsystem survey ofA1795.Heckman(1981)showedthattheemission sources. ItwasalsonotedbyHintzen(1980)inhisredshift Heckman’s outerradiusof7'.'5wouldgiveaflux8xl0 tude limitforgalaxyredshiftdeterminationsisratherbright acter ofthespectraasseenby vBHMissimilartothatofthe ter atahigherresolutionof 2.2A.Thelow-ionizationchar- 488 R -1 The slightlyfaintergalaxyinthebinarypairliesabout20" The twonucleiwithinAll26areseparatedby1150kms This clusterisnearthecenterofregionNP5from Van Breugel,Heckman,andMiley(1984,hereafter,vBHM) Heckman (1981)obtainedonlyupperlimitsforlineemis- If weadopttheFWHMof4"asgivingmaximum Optical emissionfromthecentralgalaxyofA1795was © American Astronomical Society • Provided by theNASA Astrophysics Data System xi) A1795 x) A1775 HU, COWIE,ANDWANG 1 l l 2 172 present (cf.Fig.12andthediscussionof§IIId). of thegas.Wewouldnowarguethatsuchrotationmaybe X6731/(Ha H-[Nil]X6584)==17%inthenucleusandabout proximately —75kms“with respecttotheprimary,andhas nuclei). Thesecondarynucleushasavelocityshiftof ap- with thepresentmeasurements. vBHM’s Table6gives^([Sn]XX6716,6731)/(Ha+[Nn])= underestimated theirlimitson[Sn]([SX6716/(Ha+ cD. Allfourgalaxiescommontobothsamplesarewithin our his clustervelocitydispersionstudies,andincludesdetermina- well coveredwiththeslitspectroscopyofDressier(1981)in velocity-position contourmapinFigure11showsgoodbasic A1795 isalsogivenbyvBHM.Theirslitconfiguration a weakextensionrunningabout 5"(2.5h~kpc)awayfrom a peaksurfacebrightnesswhich isafactorof2.6fainter. from themainnucleus(see,e.g.,Matthews,Morgan, and of z=0.0010isjustwithintheerrorsquotedbybothstudies. ( =A2029No.4inthepresentnotation),whereourdifference quoted errors,withtheworstcasebeingDressler’sNo. 33 ments withexternalsources,sincethenuclearregionhasbeen 23% inthenucleusand12%filament,goodagreement 26% inthenucleusand14%filament.Interpreting [N ii])<10%).Thepresentdata(Table5)give[Su] Schmidt 1964,Fig.11,foraphotographshowingthe two ting thesecondnucleusinthissystemat776(3.7h~ kpc) tions foranumberoffaintgalaxiesaswellthebright closest toourslit8,andcomparisonoftheirFigure8withthe 8% inthefilament,and[Sn]X6716/(Ha+[Nil]X6584)= Schmidt (1965)isstronglyconcentrated tothenucleusbuthas did notdetecttheblueshiftedgasinA1795whichisseen agreement. WiththeirmorelimitedvelocitycoveragevBHM imaging. Whilenonuclearemissionwasseenaroundthe reader totheirpaperfordiscussionoftheradiosourceproper- central galaxyandtheopticalemission,werefer slit 9ofFigure11,andconsequentlyarguedagainstrotation central galaxy,thesingleHa-t-[Nu]frameshowedtwobright (slit 5,80";slits3and4,-25"->-30").Weconfirm confirmation withfurtherobservations.Ourextensivelong-slit regions, extendingover4or5pixels,whichmighthavebeen ties. the relativemorphologyofradiosource4C26.42in confirming evidenceofthesestructuresintherelevantslits features asemission-linegasstructures,sincethereisno coverage ofA2029withthecryocamhasruledoutthese associated withemissionstructures.CHJYcautionedthat arcsec“. these identificationsshouldberegardedastentative,pending tivity ofthecryogeniccamera,or2x10“ergscm“s“ the absenceofnuclearopticalemissionatincreasedsensi- The opticalemissionwhich wasoriginallydetectedby The singleexposurewasalignedalongthemajoraxiscut- A2029 providesthebestcheckofourredshiftmeasure- A briefdiscussionofthekinematicsemissionin Also presentedbyvBHMisaverycompletediscussionof This clusterwasonestudiedbyCHJYwithnarrow-band xiii) A2052 xii) A2029 Vol. 59 1985ApJS. S thesecondarynucleus.Theemission-linestrengthsaregivenin -1 -1 -1 -1 16-2l -172 -21 -1 particular, whydoonlysomeclustershavecentralemission, non orwhetheritisassociatedwiththeindividualgalaxies. In optically emittinggaswhichweobserveisaclusterphenome- pears highlyprobablethatthisisasubclusteredsystemofthe Morgan typeIorI-II. Inallcasesthecentralgalaxy and whatdistinguishesthese cases? unusual (QuintanaandLawrie1982)mayalsosuggest km sdifferentfromtheprimary.HintzenandScottdo inside thelargegalaxyhasaredshiftof0.0917,only100 cluster redshift.Therelativevelocitydifferencesare560and compare thevelocitiesoftwogalaxieswithmean distribution whichisnotconsistentwithaGaussian.Itap- quote ahighradialvelocitydispersionof1241kms,but were concerned,however,thatthisfeaturemighthavebeenan that wearedealingwithamultiplesystem. 1990 kms,respectively.Suchlargedeviationsarehighly Huchra, andGeller(1983).Asecondtestofthispointisto redshift galaxyhasaof0.0813,or-3000kmsin central binaryheat0.0913(Table1andHintzenScott coverage ofA2142showsnoemissioninthissystemabovea in therange(1-2)X10“ergscms~arcsec.CHJY type discussedbyBeers,Geller,andHuchra(1982) their datawhentakenwithouradditionalmaterialshowa quite strange.Thetwolargegalaxieswhichcomposethe surface brightnessofabout3xl0ergscmsarcsec. does indeedappeartohavebeenspurious.Ourextensiveslit dure onourowndatashowedthatitcouldeasilyreduceHß our valuesbeingabout40%higherthanCohenand Table 7.CohenandOsterbrock(1981)havepreviouslygiven the oppositesense.However,smallsecondarynucleus 1979) and0.0961(HintzenScott1979),aseparationof and cautionedthatconfirmationwasrequired.Thisfeature artifact causedbymultiplecosmic-rayhitsontheCCDchip, cm sarcsecforthesurfacebrightnessofHa+[Nn]at measurements ofA2052atsimilarresolution.Theirlineratios Osterbrock’s. Thisalmostcertainlyrelatestothetemplate appear toheprimarilyinthestrengthofBalmerlines,with are comparedwithoursinTable5.Theirrelativevaluesmatch 1400 kms.Thelargegalaxylyingclosetothe0.0913 filament tothenortheastwithHa+[Nn]surfacebrightness strengths byafactorof2. sured onanunsubtractedspectrum.Ourtestsofthisproce- subtraction process.CohenandOsterbrockappliedasimilar the presentmeasurementsonlytoabout40%.Thedifferences the nucleusofthisgalaxy,suggestedtheremightexista template subtractionbutthenaveragedresultswithdatamea- No. 4,1985 16 The majorityofthesampleare richAbellclustersofBautz- The centralquestionwhichwemustaddressiswhetherthe The redshiftstructureofthecentralregionsA2142seems CHJY, whileobservingonlyanupperlimitof1X10~ergs i) OpticalPropertiesoftheClusters andCentralGalaxies © American Astronomical Society • Provided by theNASA Astrophysics Data System a) TheOriginoftheOpticalEmission IV. DISCUSSION xiv) A2142 SPECTROSCOPY OFGASINCLUSTERCORES 2-3+1/ -2l/13 (r/a)]^, andthose of JonesandForman,whoinde- (1983), whoforcedtheirKing modelfitstoanisothermal resolution datawouldliewelloffourdensityplots(Fig.14). surface brightnessfunction isoftheform£(/*)=^[l+ form [dimensionlesstemperature parameterß=1,wherethe few toseveralXlOhcmobtainedwiththesehigh- corresponding hranges.Thecentralbindensityvalues of a (Fabian etal.1981a)andA496(Nulsen1982)with the deprojection ofhigh-resolutionimager(HRI)imagesA426 can beobtainedbycomparingcentraldensitiesfromradial have valuesabovetherangeof«.Anextrememeasure this tween thedensityvaluesobtained byAbramopoulosandKu reflect boththespatialresolutionofIPCdetector,and the estimates theactualpeakcentralvaluesbyamountswhich value forthecentermostbin,though,astheynote,itunder- The valuetheyquoteforthecentraldensitynissolution lines. seen fromTable8forcaseswithdetectedemission,n can angular binningintervalsadoptedfortheanalysis.Ascan be deprojection techniquetofollowthevariationofdensityand central galaxyfailtodistinguishcaseswhereopticallyemitting temperature insuccessiveannulithroughtheregionofexcess. subset oftheJonesandFormandatasample,usedradial from theirfit.)Thesevaluesshouldbedistinguished (Abramopoulos andKu1983;JonesForman1984).(Jones model fitstotheX-raysurfacebrightnessofcluster globally derivedparametersobtainedfromextrapolatedKing most oftheclustersinoursample.Centralgasdensity, gas occurs. cluster galaxiesarenotdistinguishableinthepresentdata densed.) large coreradiiandwhicharerelativelylesscentrallycon- in thelowestsurfacebrightnessgalaxies.(Themorerelevant morphological criterionfordistinguishingcaseswithemission. A262 toD5(A85,A496)(cf.Fig.6),andthereseemsbeno and Formanspecificallyexcludetheregionofcentralexcess apart fromthepresenceorabsenceofnarrowemission emission detectionsarisingfromthoseclusterswhichhave quantity heremaybethegalaxycoreradius—withweakest high end.Again,thereseemtobenogroundsforselectingout those obtainedbyStewartetal(19846),who,foraselected summarized inTable8.Thecentralgasdensitiesnare temperature, andX-rayluminosityinthe2-10keVbandare marginal resultthattheweakestemissiondetectionsareseen cases withemission,thoughwenoteinpassingtherather A2142 atthelowendtoA262,A978,A1775andA496 galaxy rangesthroughD2casessuchasA2029,A401,and possesses theextendedenvelopestructurecharacteristicofD galaxies alsospanarelativelynarrowrangefromA85and as containing“cDgalaxies.”Theellipticityofthecentral clusters designatedbyMatthews,Morgan,andSchmidt(1964) or cDgalaxies,andoursampleincludesfiveoftheoriginal10 0 0 c c 0 We furtherdistinguish,forpurposesofcomparison,be- As notedin§III,theunderlyingspectraofallcentral In summary,opticalpropertiesofboththeclusterand Measured valuesofX-rayparametersarenowavailablefor Continuum centralsurfacebrightnessesforallthe ii) X-RayProperties 489 1985ApJS ... 59. .447H 2 21 14 pendently determinedthisindexforeachclusterusingx within eachsample. overlap betweenthetwosamples,makedirectcomparison of differences inanalysismethods,combinedwiththesmall minimization, withtypicalß-valuesaround\.Theseandother should examinetrendsindensityandcoolingtimeseparately these twodatasetsdifficult,andwestressthatthereader included pointsestimatedfromthefilterimagingdata of brightness ofCHJY(their Fig. [PI.1]).ForA2199we not availableinthepresent survey.ForA426(Perseus)we able) ortheAbramopoulosandKudensities,temperature, calculated asurfacebrightness assuming,asstatedinCHJY, ergs cm"s"arcsec"from theplotofHa+[Nn]surface CHJY andHeckman(1981)forwhichspectroscopicdata are 15, and16.Forthepurposesofthesecomparisonswehave and the2-10keVX-rayluminosityaregiveninFigures 14, assume asurfacebrightness ofpeakemission1.8x10" Stewart etal.(19846)centraldensities(wheretheseareavail- 490 Plots ofpeakopticalemissionsurfacebrightnessagainstthe © American Astronomical Society • Provided by theNASA Astrophysics Data System e e Temperatures arefromHEAO1A-2HEDdeterminationsofMushotzky1984unlessotherwisenoted. redshift determinations(whereapplicable).NotethatMcKeeetal.assumea7keVclustertempera- A1775 isoutsidethe90%errorboxforX-raysource. (range ofacceptablevalues)andAbramopoulosKu1983(singlevalues).Centralbinvaluesnare mated approximatelyatthe20%level. communication) givesatemperatureof2.2keV. A2063.. A426... Luminosities (2-10keV)aretakenfromPiccinottietal.1982orMcKee1980usingourimproved from theStewartetal.(19846)radialdeconvolutiontechnique.Seetextformoredetaileddiscussion. McKee etal.1980.All26isa3odetection,butbelowtheadoptedfluxcutoffforstatisticalsample. A2319.. A2199.. A1367.. A576... A2142 A2052 A2029 A1795 A978 ture. Forlow-temperaturecasessuchasA133andA262thequotedluminositiesmaybeunderesti- A1775 A1126 ... A754 A401 A644 A496 A262 A133 A85 c g e d f c b a Cluster IPC measurementfromJonesandForman1984. Not observedwithEinstein. Note.—Sources forextrapolatedcentraldensitydeterminations«areJonesandForman1984 From Nulsenetal.1982. Entries forA978,A1126,andA1775arecalculatedfromTable3(upperlimitsofnondetection)in Mushotzky andSmith1980;arecentEXOSATobservationofA262byMushotzky(private Reichert eial.1981. R.F. Mushotzky1984,privatecommunication. 0 3l/2 (10 hcm) 11.6-13.3 4.1- 4.7 4.5- 6.9 4.8- 6.9 5.5- 6.2 1.0- 1.7 52-1.6 9.8- 39 5.8- 10.6 4.8-7.8 6.8-8.8 7.0 2.6 4.7 8.3 7.7 9.6 7.7 Summary ofClusterX-RayProperties HU, COWIE,ANDWANG TABLE 8 16.3 11.5 11.6 12.0 5.7 8.1 3.4 8.2 , 3l/2 with detectedopticalemissionhavecentralgasdensitieshigher proximate. Themoststrikingpointtonoteisthatallclusters pixels (2.'8X2'.'8).Thesevaluesshouldberegardedasap- luminosity (2-10keV).Clusters selectedhereweregenerally HEA 01A-2HEDmeasurements.Whilethemediantempera- perature ismoreambiguous(Fig.15).Temperaturesgiven in below thisvalue. without opticalemission,withtheexceptionofA2029, lie no-detection cases,bothgroupsshowabroaddistribution in Table 8arealsoglobalquantitiesderived,inmostcases,from evident thattherearecases which arequiteX-rayluminous observed temperatures. for clusters(cf.Hintzen,Scott, andMcKee1980).Hereitis from thehigh-luminosityend oftheX-rayluminosityfunction ture forclusterswithdetectedemissionislessthanthat the than about8x10“hcm"(Fig.14),andthatallclusters that thedetectedemissionisconcentratedincentral4 In Figure16weplotoptical emissionagainstX-ray The relationshipbetweenopticalemissionandX-raytem- a C d C 4.75 ±0.75 a 6.55 +1.0 Z 3.6 ±0.6 2.8± 1.0 6.4 ±0.4 6.2 +1.5 8.4 ±1.6 5.75Í} 3 8.2 ±0.8 2.4±0.8 5.7±0.8 s b °--0.75 r o+0.70 r c+0.5 o xr+3.0 > 5.5 < 1.7 (keV) kT gas 1.0 42-1 (10 h~ergss) L.(2-10 keV) a f > 0.07: f f 0.8 0.35 0.12 0.21 0.5 3.1 3.1 7.0 5.0 2.6 2.4 0.6 4.6 0.09 0.7 1.0 3.0 2.1 1.6 1985ApJS ... 59. .447H 1721 densities. Wehaveincludeddetectionsandestimatedupperlimitsfrompreviousnarrow-bandfilterimagingbyCHJYHeckman(1981). Aconservative data set,althoughbothgroupshavebeenplottedhereforconvenience.Itcanbeseenthatdetectedemissionisweightedtowardclusters of highcentralgas derived fromX-rayIPCimagingdata.AsterisksindicatedensityvaluesdeterminedbyStewartetal.(1984/?);trianglesestimated centraldensities upper limitof5x10ergscms using theglobalprofilefitsofAbramopoulosandKu(1983).Asdiscussedintext,comparisonsshouldbemadeonlybetweenpoints withinthesame measured inthispaper;squaresdenote estimateddetectionsandupperlimitsfrompreviousfilterimaging byCHJYandHeckman(1981). Fig. 14.—Peaknuclear(within±2")surfacebrightnessinHa+[Nn]emission(cf.7)isplottedagainstcentralclustergasdensity (cf. Table1)as Fig. 15.—Peaknuclearsurfacebrightness inHa+[Nn]emissionisplottedagainstX-raytemperature. Asterisksindicatepeaksurfacebrightnesses © American Astronomical Society • Provided by theNASA Astrophysics Data System 21 arcsec Àhasbeenadoptedfornondetectionofemissionintheslitspectra. E-15 E-14 E- E-16 -17 1 1 1 136 A1367-,,. A401 ^ nLnLn!/n|/ J754 - A^ A576 A1 775Kar\ I A v -A------A-A- A2319 312 * DENSITY (X10/i^CM A2142 X-RAY TEMPERATURE(keV) A 13,3 A644 7 A2063 A262 A2052 * A A496 A A2029 A1795 * A85 A2199 * 1985ApJS ... 59. .447H 91/2l/1 3l/1- 7 4 3l/1- Hubble timeforq=0.(This valuescalesinverselywith cluster atmosphereis6.7X10 h~yr,or60h%ofthe central densityequaltoa of8X10~hcmanda of theHubbletime.Thetotal timeforgaswithaninitial brightness ofthegasreflectitsinteractionwithcentral sion systemsisaclusterphenomenonwhoseoccurrence temperature of6X10Kto coolto10Katthebaseofa galaxy, anditisthisinteractionwhichdeterminestheproper- cooled, thematerialgravitationallyaccretestocentral or X-raypropertiesoftheclusterasawhole.However,once related toanyopticalpropertiesofthegalaxyor radiative regulationmodels:theinflowofmaterialto the an equivalentcentralcoolingtimefortheclusteroforder dependent onlyonthecentraldensityandtemperaturemea- cluster coreisaresultofcoolinginthecentralgas,and is galaxy andthelocalpotentialofcentralgalaxy. central gasdensity,themorphology,kinematics,andsurface density, asinferredfromX-raymeasurements.However,while ties oftheopticalemission. sured intheX-raywavelengthsratherthanbeingafeature correlated withahigh(>8xl0~hcm)centralgas which donothaveopticalemission.(Thereis,however,some convert fromdetectorcountstoactualfluxes.). dependence onthetemperatureofinputspectrumto the existenceofsuchgassystemsissimplyaquestion Q 492 The criticalvalueofcentralgasdensitymustcorrespond to This behaviorisfairlysimplyunderstoodintermsofthe We concludethatthepresenceofthesecentralopticalemis- Fig. 16.—PeaknuclearsurfacebrightnessinHa+[Nn]emissionisplottedagainstX-rayluminosity(2-10keV).Plotsymbolsaredefined asinFig.15. © American Astronomical Society • Provided by theNASA Astrophysics Data System iii) Conclusion E-16 - E-14 r E-13 E-17 -15 1 1 i 42 X-RAY LUMINOSITY(X10hERGS/CMSEC) HU, COWIE,ANDWANG A978 4 ^ i" A262 A1367 4 □ -1 l/1 9l/1 -1 -1 10l/9 7 require 7/<160kmsMpc.Finally,wenotethatthe h yr.Wenotethatifthehotgasatmospheresincluster with emissionrangefromabout3.5X10hyrupto brightness versuscoolingtime.BasedontheJones-Forman initial densitybuthasacomplicateddependenceon critical densityisastrongfunctionofz,dependingbothon (which arelocatedatanaveragezof0.05)isonly45%the Mpc. Iftheclustergaswasfullyformedatz=4,wewould Hubble timeforq=0,andwemusthave/7<55kms formed atz=1,thenthetimescaleavailabletoclusters interest, bothindeterminingtheepochwhengaseousatmo- the formationepochandmoreweaklyon7/;thusmeasure- and Abramopoulos-Kudensitiesthecoolingtimesinclusters temperature.) InFigure17weshowthecentralopticalsurface on theHubbleconstant. ments onnasafunctionofzwouldbeconsiderable 10 hyr,withmostoftheclusterslyingaround7X10 A2029, theoneclusterwhere thecentralX-raydensitywould which therearestronglimits onsuchanexcess,doesnot. X-ray excess.Thefiveofthese sevenclusterswhichhave were observedwiththeEinsteinObservatorybyJones and natures ofthecooling-flowsystems,suchascentralexcess spheres weresetupandinprovidingveryroughconstraints emission intheX-rayorcentralcoolergas(T~10K)seen in central excessesallhave opticalemission.A1775,for cooling flows,wemayaskhowitcorrelateswithother sig- Forman (1984),whogaveaquantitative measureofthecentral seven (A85,A262,A426,A1775,A1795,A2029,andA2199) the softX-raybands.Of14clustersplottedinFigure 14, o Q0 0 crit A2063 Finally, giventhattheopticalemissionisproducedby 4 □ A2052Q A496 A133 * A2199 A1 126 )K A644 ^ 4- W’€41 A177: A1795 ¥ A2319 A426 □ J A401 A20: A2029 A214S Vol. 59 1985ApJS ... 59. .447H -1 l 10 base ofthecoolingflowand thattheyaresupportedbytheir would bethattheyaretransient rotatingdisksformedatthe which hadunambiguousdetectionsofintermediate-tempera- have opticalemission,alsohasonlyanupperlimitforthe have suggestedcoolingtobeprobablebutwhichdoesnot projection Heinthe50-100 h kmskpcrange. optical elongationsofthegalaxies. Valuesoftheshearsseenin limits onthepresenceofsuchgas. Demoulin-Ulrich, Butcher,andBoksenberg(1984).Theposi- elongation. AsimilarconclusionwasreachedforA2052 by centrated inthecentralregions(<5h~kpcradial sep- (SSS) aboardEinstein(Mushotzky1984).Ofthese,thefour central X-rayexcess,althoughthislimitisquiteweak.Eightof elongated diskshapeswhichappeartoshearalongthe disk emission. A2029isaweakambiguouscase.Theremaining ture gas(A426,A496,A1795,andA2199)allhaveoptical and A2199)wereobservedwiththesolidstatespectrometer tion anglesofthedisksdonotseemtocorrelatewith the aration fromthegalaxypeak)ofgalaxiesandformsthick, the 14clusters(A85,A401,A426,A496,A1795,A2029,A2142, three clusters(A85,A401,andA2142)onlyhaveweakupper No. 4,1985 of 10years. Additional pointsestimatedfrompreviousimagingworkbyHeckman(1981)andCHJYarealsoplotted.AdashedreferenceUnemarks off acoolingtime using therangeofextrapolatedcentraldensitiesfromJonesandForman(1984){diamonds)AbramopoulosKu(1983){triangles) withthe temperatures UstedinTable8.ForA133thecoohng-timeUmitscorrespondtoupperUmitandbest-estimateofReichert etal.(1981). 4 The mostreasonableinterpretation forthesestructures As wediscussedin§Hid,mostoftheemissioniscon- Fig. 17.—PeaknuclearsurfacebrightnessinHa+[Nii]emissionisplottedagainstcoolingtimeforgastoreach10K.Coolingtimeswere computed b) GasKinematicsandtheGravitationalPotentialsof © American Astronomical Society • Provided by theNASA Astrophysics Data System Galaxies andClusters i) GalaxyPotentials SPECTROSCOPY OFGASINCLUSTERCORES 2 2-1 l _1l 9210 11 L, fromwhichwewouldestimatequitetypicalM/Linthe cooling woulddroprapidly. etal. 1984¿>),then/0.16h.Asimplepredictionwould be higher resolutionobservations,thiscrudecalculationraises a 0v that thefractionalnumber ofclusterswhichhavebegun discussed intheprevioussubsection, sincewewouldexpect sistent withexpectationsbased onthecooling-timearguments fewer suchsystemsshouldbeseenatz>0.2.Thisis con- Hubble timeandareputtingmassintothecentralcores of central regions.Iftheflowshaveexistedforafraction/of the the criticaldensitytoriserapidly asafunctionofzandhence that coolingsystemsarearecentphenomenonand far average ofthecoolingflowsinA85andA1795fromStewart these galaxiesatacurrentrateof65h~Myr (the serious problemwiththeamountofmassprocessedinto the proximate radiusmayberoughlyestimatedfromtherband and theM/Lvaluesshouldbebettermeasuredbyfurther range 10-30h. results ofHoessel(1980)andtheg-rcolorsHoessel, cally symmetric.TheintegratedvisualHghtwithinthisap- h~ Mwithinthisradiusifthemassdistributionisspheri- galaxy. DeprojectedmaximumvelocitieswouldthenHeat Gunn, andThuan(1980)wheretheseareavailable,give around ±300kmsatdistancesofroughlyAh~kpcfrom angular momentumagainstthegravitationalpotentialof typical valuesintherangefrom3XlOh-Lto10h~ the nuclei.Thisinturnwouldimplyatypicalmassof-10 Q q e While theuncertaintiesofcalculationarefairlylarge, 493 1985ApJS ... 59. .447H 6 -3 l 16-2_ -1 -17 l 1/2-1 25 -3 1 -253 by ashockwhichmovesintotheclumpatvelocity(McKee possibility asfollows.Ifmaterialcoolsoutinfairlylarge-scale and Cowie1975) stant densitythereafter.Thecooledregionsarerepressurized regions ofsized(oftheorderkiloparsecs),wemayfollow ever, theopticalresultsmaybeusedtoargueagainstthis being seeninopticalemission(C.L.Sarazin1984,private where a~\(dependingonthepressureriseinconfining temperature dropstoabout3X10Kandwouldbeatcon- showed thatcoolingoccursatconstantpressureuntilthe M decreasingasonemovesinwardfortheseclusters.How- 494 moving intoamediumofdensity-0.2cm,givinganHa medium) andcistheisothermalsoundspeedatinitial the argumentsofCowie,Fabian,andNulsen(1980),who surface brightnessofM87andPerseusshowthis—with Stewart etal(1984a)arguethatvariationsintheX-ray communication). Fabian,Nulsen,andCañizares(1984) much ofthematerialhassettledoutatlargerradiiwithout moment thatmatterisuniformlydistributedinthecluster data. Amorepreciseformulationofthisargumentmaybe each shocksurface.Thiswouldeasilybeseeninthepresent fraction ofthecoolingmaterialreachedcoresandthat formation ofthefilamentinA1795,anabsolutelowerbound cluster, p,obeystherelationship center, thisinturnimpliesthatthecentralmassdensity shearing inthepotentialwellofcluster.Assumingfor of 4.5h~kpc.Almostirrespectivethemechanism found inCowie,Fabian,andNulsen(1980). surface brightnessof—10“ergscmsarcsecbehind the ingoingshockhasavelocityofabout250kmsandis temperature, orabout1000kmsforT=7X10K.Thus to thevelocityshearinthisobjectwouldseembetidal and, ascanbeseeninFigure12,hasasmallbutdistinctshear where wehavewrittenthevelocityshearasdv/dr.Setting interest asacheckoncluster potentialestimates. pirical Kingmodel)of150+ 50h~kpc(JonesandForman The principalconclusionisthattherenounusuallydeep dv/dr <4.5X2hkms,wherewehavemadeallowance ples offaintextendedfilaments ofthistypewouldbegreat may simplyimplythatthevelocity shearofthefilamenttiesat for projectioneffects,weobtainp<1.6x10“hgcm . etal (1972)methodwithaline-of-sightvelocitydispersion of central gravitationalpotentialwellinthiscluster.Thisvalue is an anglegreaterthan60°to thelineofsight.Furtherexam- 780 kms“(Hintzen1980)andaclustercoreradius (em- traditional virialtheoremarguments.Thus,applyingtheRood also lowerthanthevaluewhichwouldbeobtainedfrom 1984) wouldgivep==3Xl0 hgcm“.However,this 0 c 0 c c l An alternativeexplanationwouldbethatonlyasmall The filamentseeninA1795extendstoabout40h~kpc © American Astronomical Society • Provided by theNASA Astrophysics Data System ii) ClusterandGalaxyPotentialinA1795 T 4 /L ^ Pcould 1/2 = ac. 0 ? HU, COWIE,ANDWANG (1) l1 l1 1/2 l/1 l/6-1 112 17 5/e 26l/23 29 l/2 3 1652 1 3412 73 kpc, whichwouldimplyanangularrotationvelocitylessthan N thenumberofgalaxiescontributinggastocore,seemsa per unitmassofapproximately1000h~kms“kpc.Assum- core itselfmustbelessthanthevalueof1000h~kms“ uncertain point,thespecificangularmomentumofcluster each galaxy’sorbit,andavaluesmallerby(^rbit/^Hubble) o/N, whereaisthevelocitydispersionofgalaxiesand rather thanfallingtonearthegalaxycenter.Inretrospect h~ kms.Thisissmaller(byaboutanorderofmagni- kpc. Itwouldthenhavehadaninitialsystematicvelocityof20 ing that10h~Morsoofmaterialhasbeenaccretedfrom we obtainatypicalvalueofthespecificangularmomentum 1.3 X10“radianss“ifthegasoriginatedat50kpc. significant overestimate,sincethemasslossisaveragedover (1980), whopredictedthatgaswouldstagnateat50kpcorso currently accretingmaterialoriginatedataradiusof50h~ near thecriticalvalueof1.6X10“hgcm“,then imply thatthedensityincoolgasliesroughlybetween150 place limitsontheclusterpotential.)Theseconsiderations with thisresult.(However,moreaccuratemeasurementsofthe low-density regimeandrequiredimensionlesscentralpres- suggested valueinCowie,Fabian,andNulsen,whichissimply tude) thanthevaluesuggestedbyCowie,Fabian,andNulsen mately intherange150-10,000hM.Thisislessthan10“ limits onthepressureratioandcould,atleastinprinciple, h~ timesthecentralpressureinhotgas.Cooling-flow the coreandthattypicalgasdensitiesinclustercoresare material. Theopticalphaseisthereforeaverytransitory one core andcorrespondstoabout100years’worthofaccreted of thetypicalmasshotX-rayemittinggasincluster cm“. Themassofemittingcoolgasisthenveryapproxi- ergs s“werequireavolumeemissionmeasureof~10h doublet ratiowouldbeofconsiderableinterestinrefiningthe models inKingmodelclusterpotentialsimplyatypicalpres- ionization bytheEUVfrom thecoolinggaswouldproducea km s"rangeandphotoionizationbyanuclearsourcehaving for thecoolinggas. and 1000cm“.ForatypicalHaluminosityofabout10h sure riseofabout3betweenthecoreradiusandcenter sures (nT)oflessthan10Kcm“,afactor17 the flow(CowieandBinney1977),whichisquiteconsistent (Table 5)areshockmodelswithvelocitiesinthe50-100 Heckman (1980),theonlytwomodelswhichseemtoaccount of theA1795filament.Thus, the regionoffilamentlyingat and similarargumentsmaybe appliedtothebrighterregions spectrum similartoahigher velocityradiativeshock.)CHJY satisfactorily forthetypeofspectrumseeninthesesystems that photoionizationmodels werenotenergeticallyfeasible, and Huetai(1983)demonstrated forNGC1275inPerseus a power-lawspectrumwithspectralindexaround—1.(Self- 0 0 - 0.1wouldseemmoreappropriate.Irrespectiveofthisvery e The [Sn]lineratiossummarizedinTable5hetowardthe If thedisksaresupportedbyrotationasseemslikely,then Following thediscussionsofKentandSargent(1979) d) IonizationMechanismsandChemicalAbundances c) MassofCoolGas iii) AngularMomentum Vol. 59 1985ApJS ... 59. .447H -1 4-5 16-2 -3 -3 -3 _1 -1 -1 39_1- 432-1 -1 2 392_1 by Dopita(1977).Withoutthe[On]X3727/H/?ratiothereis XX6717,6731/Hß and[Nn]X6584/H/?ratiostoestimate km s,wherewehaveusedtheresultsofShullandMcKee dances. Weshalldrawprimarilyonthediagnosticdiagramsof 6.8XlO“, Z(N)=1.2X10andZ(S)1.6xl0~.] and McKee,weareassumingcosmicabundancesofZ(O) = cosmic abundance(towithinfactorsof2).[FollowingShull brightness of10“ergscmsarcsecinHa(cf.Shull preshock densityofabout10cmtoproduceasurface McKee (1979). conditions andthenattempttoobtaintheelementabun- driven intothecoolinggasbysurroundingthermalpres- literature (e.g.,Matthews,Morgan,andSchmidt1964). Re- suggest thatoxygen,nitrogen,andsulfurareinapproximately an ambiguityintheresults.However,availablelineratios 20 cm. used toinferapreshockdensityoflessthan250cm.Ifthe result usingthe[Om]X5007/Hßratio,whichrunsfrom0.4 Dopita (1977)andonthemodelscomputedbyShull 1980), wemayusethelineratiosasdiagnosticsofshock also theoreticallyplausible(e.g.Cowie,Fabian,andNulsen sure, asseemslikelyontheobservationalgroundsandis brightness. Herewewishtoaddress twoquestions:(1)isthere have cooling-flowsystemson thebasisofX-raysurface the abundancesinA1795accordingtomethodsoutlined and McKee1979),whileforv=60kmswewouldrequire shock densitiesdirectly.Forü=80kmswerequirea surface, wemayusethesurfacebrightnesstoestimatepre- filaments arehomogeneousandcorrespondtoasingleshock oxygen abundancesarenear-cosmic,wecanconfirmthis galaxies oftheclustersfound tohavenuclearopticalemission, radio sourcesfrequentlyoccur incentralgalaxiesthoughtto existence ofabrightradiosourcehasbeenwellknownin the summarized inTable5.The[Sn]lineratios5maybe the range70-90kms.Ifweassumeformomentthat a significantexcessofradioobjects coincidentwiththecentral cently JonesandForman(1984) haveshownthatcompact to 2andcorrespondsshockvelocitiesrangingfrom7090 the range0.5-2,which,fromDopita,givesashockvelocityin luminosity at1500Aofonly6X10ergss.second Norgaard-Nielsen, Jorgensen,andHansenÇL984)givea photons isconvertedintoHß,wewouldrequireanionizing kpc. Thus,itcoverslessthan0.5%ofa40kpcspherical flux wouldchangebymorethananorderofmagnitude. nuclear luminosityinexcessof2x10h~ergss,while edge-on, itisunlikelythesurfaceareaofthisregionexceeds a distanceofabout40/zkpcfromthenucleusA1795has argument againstphotoionizationistherelativeuniformityof surface. Sinceapproximately1%oftheenergyinionizing correction. Evenassumingthatthefilamentisadiskseen the lineratiosalongA1795filament,whereionizing 100 kpc,sincetheobservedtransversesizeislessthanafew an Haluminosityof10h~ergsswithoutreddening sh sh No. 4,1985 Where [Oin]X5007/[0i]X6300ismeasurable,itliesin Thus, assumingthatthematerialisshock-excitedbyshocks Given thetypicalshockconditions,wemayuse[Sn] The relationshipbetweennuclearopticalemissionandthe © American Astronomical Society • Provided by theNASA Astrophysics Data System e) CorrelationwithRadioProperties SPECTROSCOPY OFGASINCLUSTERCORES -1 -1 with theclusterandwere well separatedfromthecluster X-ray emissioniscentered. center. Nosourceswereseen coincidentwiththecentralcD. is aradiotailsource.) Wielebinski (1980)andSleeSiegman(1983)havecovered A1775 thereisaradiosourcecoincidentwithonenucleusof and Siegman1983)radiosource. High-resolutionVLAmaps coincident witheithernucleus.(Anearbygalaxy(~1'5away) A401, 4Cradiotailsources(4C13.74Aand13.74B)have source detectionsinthisfield wereunlikelytobeassociated survey ofextragalacticX-ray sources.Theyconcludedthat Radio observationsbyAndernach,Waldthausen, and center ofemissioncoincidentwiththesoutheastcomponent. centroid quotedbyAbramopoulosandKu(1983)place the investigations whichfailedtodisclosethepresenceofaradio km s.Thisangularseparationmaymarginallycorrespond this regionatavarietyoffrequencies,anddisclosenosource separation betweenthetwoprominentcentralgalaxies(At; — been foundnearthecentralregions(Slingo1974;Bumsand northwest componentwithavelocityseparationof-1800 1350 kms).HRIimagesandthepositionofX-ray away). Ulmer 1980)butquitedistinctfromthecentralgalaxy(-7' the binarysystem,whichmaybenucleusupon with thecentralgalaxy,A1775isperhapsmostprominent source coincidentwiththecentralgalaxy.Again,incaseof and Skellem1978)wereboththesubjectofintensiveradio to theabsolutepositionalaccuracyofHRI.Thusfor southeast (radio)component,whichlies~20"awayfromthe tions placethecenterofX-rayemissioncoincidentwith source (cf.forexample,MileyandHarris1977).HRIobserva- system identifiedwith4C26.41andfoundtobearadiotail as aradiosource,withthesoutheastcomponentofthisbinary 00—011 (Véron1977).However,thepositionofthree of thecentralgalaxy.Tabulatedfittedsourcepositionsare cluster field).Finally,forAll26SleeandSiegman(1983)lista map at1465GHzsuperposeduponaCCDimageofthe radio componentsseeninthisclusterhesome6'5northeastof properties fortheseobjects? and Slee,inpreparation). MHz data.ForAll26thefindingsurveycitedbySleeand given onlywheresuchquantitiescanbederivedfrom160 emission, twoare4Cradiosources(A1795=42.26[cf. Siegman (1983)isanunpublished2700MHzsurvey(Wilson source whosecrudepositionisconsistentwiththecoordinates [Colla etal1975;Fantiétal1982]).Amongtheremaining Hill designation(A133=MSH01-201;cf.Véron1977;A496 1981]). TwomorearesouthernradiosourceswithMills-Slee- [Matthews, Morgan,andSchmidt1964;CohenOsterbrock the cD(seeSleeandReynolds1984forahigh-resolutionVLA two clusters,A85isassociatedwiththesouthernsourceMSH Sargent 1973;vBHM1984];A2052=3C317=4C07.40 and (2)aretherecharacteristicspectralormorphological = MSH04—112).A262isaBolognasource(B2.30149+35 A2029 iscoincidentwithasteep spectrum(a=—1.36;Slee A644 wasobservedbySleeandQuinn(1979)inan80MHz A2142 isanotherbinaryclusterwithalargekinematic A401 (BumsandUlmer1980)A754(Mills,Hunstead, Among theclusterswhichlackopticalemissioncoincident Of thecentralgalaxiesinsevenclustersfoundtohave 495 1985ApJS ... 59. .447H 4 6 678 4 5 presently beingstudiedintheoptical.Thecoolingtimeat \5303 presentsaveryexcitingpossibilityfordetectinggasat present data,wemaytakeAfromKurtz,VandenBout, material studiedtodateintheX-raysand10Kgas region ofsky. of theliterature.Itsdeclination(—6°)makesitasouthern radio source(4C06.53)associatedwiththisclusteriswell (R. A.White1983,privatecommunication)disclosenuclear coronal linesshouldbephysicallyassociatedwithandhave We concludethattheincidenceofradioemissionishigher less thantheresolutionofsurveys(~2'-3';cf.Sleeand given inSleeandSiegman(1983). separated fromthenuclearregion.Asample160MHzcon- cooling elementsnear10K(O,Ne,andFe)toFe is cooling-flow energetics.Usingtheformula 10 Ktemperaturesintermediatebetweenthe-10 radio characteristicsintheabovedata. on thefewto10arcsecondlevel.Whilespectralindicesofa compact sourcesamongthecentralbrightestgalaxieslacking does not,ascomparedwithoneoutofsevencaseshaving coincident compactnuclearradiosources,whileone(A85) seven caseswithnuclearopticalemissionappeartohave sample’s centralbrightestgalaxies,wenotethatfiveofthe source, butitdoesnotappeartobeincludedinsurveys(e.g., tour plotofthisregionwith-2'half-powerbeamwidthis structure atscalesoftensarcseconds,whilethestrong4C and Angel(1972)adoptAfromRaymond,Cox, and given inCowie(1981),istheluminosityofline, M is the sameopticalmorphologyas10Kgas. these temperaturesissufficientlyshort(—10yr)thatthe sources seeninclusters,therearenospecialdistinguishing apart fromthisandthegeneralcompactnatureofradio among theemission-linecentralbrightestgalaxies,butthat Reynolds 1984];A1795[vBHM])typicalstructurescalesare emission, withoneambiguouscase.Inallinstanceswhere Smith (1976)toperformthe integration, giving approximately cosmic,asseemslikelyonthebasisof the few ofthesesourcesshowsteepslopes(e.g.,forA133,a= Siegman 1983,Table2,forasummary.)Wherehigh-resolu- such radiosourcesareseen,theirextentshavetypicallybeen the BolognaB2survey)whichmightreasonablycoverthis the emissivityofline,andAisnetcoolingfunction. the massflowrate,misaverageperparticle,A is tion surveyshavebeenundertaken(e.g.,A133[Sleeand üne 496 — 1.63[SleeandSiegman1983]),mosthaveslopesof1. tot tot l ine No referencestoA978werefoundinapreliminarysearch The luminosityofthelinesismosteasilyestimatedfrom Study ofcoronallinessuchas[Fex]X6374andxiv] Summarizing theincidenceofradiogalaxiesamongour Assuming thattheratioofabundancesdominant L([Fex] X6374)=1.5X10 © American Astronomical Society • Provided by theNASA Astrophysics Data System ^~2mJ A(r) 0tot /) CoronalLineEmission 5kM r°° 39 1 100 Mqyr“ M dT, ergs s HU, COWIE,ANDWANG (4a) (3) 3 182 172 182 21 4 152 1 172 2 2 21 4 2 172 2 will beeasilydetectableinmany ofthestrongerUVabsorp- less than0.15(A1795)and0.8(Perseus)ifweassumestandard mÁ absorptionfeaturecould bedetectedatthe3alevelin resolution modeaboardthe HubbleSpaceTelescope),a25 other UVlinesmustlieatvalueslessthanoraround5% of exposure ofA1795(Hu,Cowie,andBlades1985)showsthat however; thus[Cn]X1335shouldbe10“weakerthanLya, be atapproximately4X10“ergscm"s“arcsec". where theopticalemittinggascoversapproximately200 brightness of1.5X10“ergscm"s"arcsec“.ForA1795, parameters ofthehigh-resolution spectrographinmoderate- Nielsen, Jorgensen,andHansen1984;Hu,Cowie,Blades reddening curves. Lya. Thereddeningintheseclustersmustconservatively be of veryroughly10and0.1,respectively.Adeep14hourIUE (1984) andFabian,Nulsen,Arnaudhavedetected work couldandshouldresultinapositivedetection. lems dominatetheerror,and(5-10)X10"ergscm"s" been unabletofindconclusiveevidenceforthislineinanyof background islowerat5300A,wehaveconcentratedour approximately 4hours.Atthis levelthegasinfilaments Lya inA1795andPerseus,respectively,withLya/Haratios and [Cni]X977shouldbeweakerthanLyabyafactorofless optical spectra,wewouldmakeasimplepredictionthatinthe rate of100h~Myr“(Stewartetal.19846)astypical efforts onsearchingfor[Fexiv]X5303.Adoptingasize and 2xl0, andnetthroughput efficiencyof1%(roughlythe at about2x10"ergscm"s"arcsec“A"(Norgaard- detectable intheUVwhichcanbeusedtodetectforeground McKee 1979).OtherUVlinesshouldbeextremelyweak, absence ofreddeningF(Lya)/F(Ha)=16-27(Shulland shock velocitiesof70-90kms“,asissuggestedbythe clearly wellwithinrangeandfurther,slightlymoresensitive seen alongtheA1795filamentatlevelsof10"ergscm“s" arcsec“ awayfromthenucleus.Inparticularnoemissionis arcsec“ nearthenuclei,wherecontinuumsubtractionprob- arcsec andA/=100h~Myr“,*S([Fexiv]X5303)would 1985) andwitha2.4mtelescope,spectrographofresolution spectrographs. InA1795theUVcontinuumnear1500A lies absorption linesintheclustergivensufficientlysensitive UV than 5xl0".Norgaard-Nielsen,Jorgensen,andHansen arcsec". However,despitethefailureofthissearch,weare the clusters.Typicallimitsare(3-6)X10"ergscm“s" the opticallydetectedclusters,wewouldpredictasurface Since [Fex]\6374isblendedwith[Oi]X6364,andthesky the opticalregionsof50arcsecatz=0.05andamassflow 0 0 391 Assuming thatthegasisshock-excitedwithcharacteristic Despite detectionlimitscomparabletothisvalue,wehave Both A1795andPerseushavenuclearcontinuumsources L([Fexiv] \5303)=2X10(f-)ergss". g) ObservationsatOtherWavelengths i) UltravioletEmissionandAbsorption \ 100Myr/ q Vol. 59 (4b) 1985ApJS ... 59. .447H 3 32 11 1 where 0isacharacteristictimescale,andthattheentering No. 4,1985 Then into theclustergasis ing bythehotgasisveryshort(BurkeandSilk1974;Barlow medium (0.002bymass),reflectingitslowerabundances. mass ingrainshasavalueofhalfthattheinterstellar in thecentralregionswheren_ishighgrainswillbe vetskii (1969),whoclaimedt=0.4orE_^0.1forstan- evidence foranyextinctioninclustersasawholeisthe properties, itseemsworthwhiletoreconsiderthiscalculation, history ofgalaxygaslossinto thecluster.Integratingover The principaluncertaintyhere is0,whichdependsonthe neously distributedthroughtheclustergas. concentrated aroundthegalaxiesratherthanbeinghomoge- dard grainproperties. emission. might havebeenand/orshouldbecapableofdetectingthis more particularlybecauseIRASand/orfutureIRmissions assume thattheamountofmaterialcurrentlybeinginjected galaxies, and,second,aspointedoutbySilkandBurke(1974), where n_isthehot-gasdensityinunitsof10“cm“.There temperatures of and Salpetergiveasputteringdestructiontimeingasofthese 1978; DraineandSalpeter1979).Fora0.1/¿mgrain, somewhat uncertainobservationsofKarachentsevandLipo- first thatfromthediscussionincurrentpaperwehave dances, andX-raymassestemperaturesintheclustergas cluster atmosphereswhichremainsubstantiallycorrect.How- E_