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The Infrared Diameter { Velocity Dispersion Relation for Elliptical Galaxies

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The Infrared Diameter { Velocity Dispersion Relation for Elliptical Galaxies View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by CERN Document Server The Infrared Diameter { Velo city Disp ersion Relation for Elliptical Galaxies Michael D. Gregg Institute for Geophysics and Planetary Physics Lawrence Livermore National Laboratory L-413, 7000 East Avenue Livermore, CA 94550 [email protected] lnl.gov ABSTRACT Using single channel infrared photometry from the literature, a provisional K-band diameter{velo city disp ersion relation for elliptical galaxies in the Coma and Virgo clus- ters is derived. The Coma cluster relation has 1.5 times lower scatter at K than in B or V. Excluding 4 outliers, the RMS scatter at K for 24 galaxies in Coma is only 4.8% in distance, close to the limit implied by the observational errors. Distance estimates based on the IR D relation will be more accurate than those derived from optical data. The improvement in the infrared is attributed to a decrease in sensitivity to stellar p opulation parameters (age, metallicity, and slop e of the IMF) as well as lower internal extinction from dust compared to the optical. That the D relation has a larger scatter in the optical indicates that there are detectable, but small, stellar p opu- lation or dust content di erences among the Coma ellipticals. Since the D relations are based on the fundamental plane, this result promises that the fundamental plane is thinner in the infrared than it is in the optical. Infrared photometric data available for Virgo are limited to just 13 ob jects; the spread in distance due to the depth of the cluster precludes any signi cant improvement over B and V. A relative Coma-Virgo distance of 5.56 is derived from the K band data, in agreement with estimates in other colors and using other techniques, indicating that there is no signi cant age di erence between Virgo and Coma ellipticals. Subject headings: galaxies: distances | galaxies: elliptical 1 Guzman & Lucey 1993). By analogy with the 1. Intro duction TF relation, it is natural to susp ect that replac- There are two p opular metho ds for determin- ing B-band with infrared photometry might lead ing redshift-indep endent distances to galaxies. to an improvement in the accuracy of distances Both rely on a tight correlation between a sp ec- estimated by D and FP plane techniques n troscopically determined distance-indep endent mea- (Guzman & Lucey 1993; Gregg 1995). This pa- sure of the gravitational p otential and a photo- p er presents evidence that the D metho d, and metrically determined distance-dep endent mea- by inference the FP, has signi cantly less scatter sure of apparent size. The Tully-Fisher (TF) re- in the IR than in the optical for ellipticals in the lation for spirals (Tully & Fisher 1977) is based Coma cluster. on the correlation between luminosity and rota- tional velo city. The D technique for ellip- n 2. Derivation of Infrared Diameters ticals (Dressler et al. 1987; D87) dep ends on the Using IR data from Bower, Lucey, & Ellis correlation between a surface brightness dep en- (1992a; BLE), it has b een shown elsewhere that dent diameter and the central velo city disp ersion the K-band (2:2) magnitude-velo city disp ersion ( ). relation for 25 early typ e galaxies in the Coma When rst intro duced, the TF metho d em- cluster has a scatter smaller by a factor of 1.9 ployed B band photometry, necessitating rela- than the B band D relation (Gregg 1995). tively large and uncertain corrections for inter- Because the IR magnitudes are from single chan- nal extinction which vary with galaxy morphol- nel photometry in a 17" ap erture, the derived ogy and star formation rate (Aaronson, Huchra, IR relation is between velo city disp ersion and a & Mould 1979 AHM). Di ering current SFR's metric size. For a useful distance indicator, it probably also contribute to the spread in B mag- is necessary to de ne a size based on structural nitudes. The accuracy of the TF metho d was parameters of the galaxies individually; the FP improved markedly when AHM intro duced the or D relations accomplish this using the half use of H band (1:6) photometry where extinc- light-radius R or D . D87 de ne D as the diam- e n n tion corrections are reduced to negligible levels eter of a circular ap erture within which the mean and the ux is mainly from the oldest p opula- B band surface brightness is 20.75 mag/sq arc- tion of stars which is p erhaps more uniform from sec and show that log(D )iswell correlated with n galaxy to galaxy (AHM). log ( ), reducing the scatter by a factor of two There is increasing evidence from sp ectro- from the Fab er-Jackson (B vs. log ( )) relation T scopic studies suggesting that the stellar p opu- (Fab er & Jackson 1976). Typical ellipticals have lation of ordinary elliptical galaxies can b e a mix B-K 4.0, so a K band diameter (D ) which ap- K of ages (e.g., O'Connell 1980; Rose 1985; Pickles proximates D would enclose a mean K surface n 1985, Bower et al. 1990, Gonzales 1993). Ex- brightness of 16.75 mag/sq arcsec. treme cases such as merger remnants have exp e- The Virgo and Coma D are based on CCD n rienced strong bursts of star formation (Carter photometry (D87; Burstein et al. 1988, B88). et al. 1988; Schweizer et al. 1990). Dust has The ideal IR version of a D relation would use also b een shown to exist in a large fraction of 1 K band imaging ;however, with some simple as- ellipticals. There is good evidence that the dis- tances derived from D and the closely related n 1 Jorgensen, Franx, & Kjaergaard (1993) have demon- fundamental plane (FP) technique (Djorgovski & strated that the FP is an intrinsically more accurate dis- Davis 1987) for some ellipticals are in uenced by tance indicator than D . Using the ts detailed here, one or more of these factors (Gregg 1992, 1995; it is p ossible to deriveanIRversion of the FP. Because 2 sumptions a provisional D relation can be smaller than the error estimates for log(D ) Burstein K n derived for the Coma and Virgo clusters from the et al. (1987) and comparable to those in log(D ) V data of Persson, Frogel, & Aaronson (PFA 1979) (LGCT). The derived log(D ) are listed in Table K and BLE; b oth present high quality single chan- 1 along with their A , D from B88, and the V e n nel IR photometry for early typ e galaxies in the band equivalent, D (ap erture diameter enclos- V Coma and Virgo clusters. The BLE photometry ing 19.80 mag/sq arcsec) from BLE. Note that has b een calibrated to b e on the same system as although V band A from LGCT have b een used e that of PFA (see BLE for discussion) and their in deriving D , strict photometric indep endence K much larger body of photometry sup ersedes the between the V and K band results is maintained earlier PFA work. As BLE present no new IR by adopting D from BLE. V photometry for Virgo, the data of PFA are used PFA present JHK photometry of 13 Virgo here. ellipticals through 2 ap ertures (29" and 56"), 1=4 Table 5 of BLE lists K magnitudes through an which allows D to b e derived from an R law K e ective ap erture of 17" for 25 E or E/S0 and 3 t without recourse to any optical data. For S0 galaxies in the Coma cluster which also have comparison, D values were also derived for the K log ( ) > 2:0 in Davies et al. (1988) or Dressler Virgo ellipticals using the same metho d as the (1987). Corrections for background light, red- Coma ellipticals, i.e., by adopting an optical A e shift, and Galactic reddening were applied as de- and tting to a single ap erture. It is testimony tailed in BLE and PFA. D can b e derived from to the high quality of the data from PFA, BLE, K 1=4 these single ap erture data by assuming an R and B88 that the two metho ds give identical re- law pro le and adopting an e ective diameter sults within a few p ercent and that these are in A from the V band photometry of Lucey et al. turn extremely well correlated with the diame- e (1991a LGCT) for the ellipticals and the Third ters in B and V. This test serves as a con dence Reference Catalog (de Vaucouleurs et al. 1991) check on the derived IR diameters for the Coma for the S0's. In the absence of color gradients, A galaxies. Table 1 includes the 13 Virgo ellipti- e is indep endentofwavelength and in most ellipti- cals from PFA and their calculated D , along K cals, color gradients are negligible (PFA; Peletier, with D (B88) and D (BLE). One of the ob- n V Valentjin, & Jameson 1990). jects, NGC 4387, with log ( ) < 2:0, is excluded 1=4 from the analysis to follow. The R ts are uniquely determined by the ap erture photometry and e ective diameter. Er- 2.1. Velo city Disp ersions rors have b een estimated by deriving D after K varying b oth quantities by their estimated stan- Velo city disp ersions from Davies et al.
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