arXiv:2101.05818v1 [astro-ph.GA] 14 Jan 2021 egr,adterdhf nomto htcmsautomatic comes that dens information of redshift gala with the regions OHMs and and of mergers, correlation 1997), strong associ- The al. 2007). et (Darling are Skinner gas 1991; they ac formation al. and star et nuclear (Henkel intense 2014), mergers, infra galaxy al. the es- with et ultra-luminous ated Zhang are for or ([U]LIRG; OHMs luminous signpost in 1999): galaxies a found well Baan is always (e.g. are wassentially which mechanism (OHMs) It luminosity pumping megamasers megamasers. maser FIR OH name with Galac- that the than correlated on them luminous early earning more recognized times masers, million OH ob a rare tic are relatively still majority are The e masers (Baan OH ago decades extragalactic four 1982), nearly discovery first their Despite Introduction 1. .M a e Hulst der van M. J. aur 8 2021 18, January Astronomy ⋆ elyM Hess M. Kelley [email protected] rgts Hmgmsr(H)kon emauealwrlimit lower a measure We known. (OHM) megamaser OH brightest epeettesrniiosdtcino h w anO mas OH main two the of detection serendipitous the present We z H aelt iei h aesuc.Wt oa Hluminos OH total a With source. same the in line satellite MHz aesaemre.Bsdo ulse nrrdadfrultr pu far maser log( and OH with infrared of (ULIRG) to published models on line detailed Based satellite merger. compare OH late-stage to MHz which 1612 by the constraint for measured ratio limiting nec fteidvda anadstlieO 8c lines. cm 18 words. OH Key satellite AWES, and in main found individual be may the that of masers each OH in of number predicted conditi the physical on the with consistent are properties galaxy aais interactions Galaxies: .Mulder H. 12 11 10 ⊙ 9 8 6 7 5 4 3 2 1 = ikuiesti rnne etrfrIfrainTechn Information for Center Groningen Rijksuniversiteit no anke nttt,Uiest fAsedm Postb Amsterdam, of University Institute, Pannekoek Anton et fEetia niern,Camr nvriyo Te of University Chalmers Engineering, Electrical of Dept. ynyIsiuefrAtooy colo hsc,Univers Physics, of School Astronomy, for Institute Sydney SR srnm n pc cec,AsrlaTlsoeNat Telescope Australia Science, Space and Astronomy CSIRO sr pc etro eee hsclIsiue Profsoyu Institute, Physical Lebedev of Center Space Astro eateto hsc,Vrii oyehi nttt and Institute Polytechnic Virginia Physics, of Department et fAtooy nv fCp on rvt a 3 Ronde X3, Bag Private Town, Cape of Univ. Astronomy, A of Astronomy, Dept. and Physics Germany of Bochum, Faculty Bochum, University Ruhr USA 80309, of CO Department Boulder, Astronomy, UCB, Space and Astrophysics for Center aty srnmclIsiue nvriyo Groningen, of University Institute, Astronomical Kapteyn SRN h ehrad nttt o ai srnm,Pos Astronomy, Radio for Institute Netherlands the ASTRON, .Kutkin A. 0 . 91 nteutree pri ieae xrglci Su Extragalactic Wide-area Apertif untargeted the in 19612 & pri iwo h HMgmsrIA 10597+5926: IRAS Megamaser OH the of view Apertif Astrophysics 1 aes–Glxe:idvda:IA 10597 IRAS individual: Galaxies: – Masers .J Norden J. M. , H1 mstlielnsi ieae H wide-area in lines satellite cm 18 OH 1 2 1 , .H .M Coolen M. W. H. A. , 2 , L 6 ⋆ IR T .M Lucero M. D. , .Roberts H. , / L aucitn.ms_ohmaser_accepted no. manuscript ⊙ ) = 12 1 .C Oostrum C. L. , . 4 negigasa us iha siae trformation star estimated an with burst star a undergoing 24, 3 .Dénes H. , 7 Ra , 1 .J Wijnholds J. S. ff .Damstra S. , el Morganti aella 1 .Adebahr B. , 1 , 11 n epnil o eybih H msin ial,w pr we Finally, emission. OHM bright very for responsible ons .Ruiter M. , + voe ue,w n htteglx sa lr uiosinf luminous ultra an is galaxy the that find we fluxes, aviolet tivity jects. 96—Glxe:IM—Rdolns aais—Glxe:star Galaxies: — galaxies lines: Radio — ISM Galaxies: — 5926 ABSTRACT 1 al. t ally lg,PO o 14,90 AGoign h Netherlands the Groningen, CA 9700 11044, Box P.O. ology, red .Ivashina M. , tt nvriy 0Ws apsDie lcsug A2406 VA Blacksburg, Drive, Campus West 50 University, State ..Bx80 70A rnne,TeNetherlands The Groningen, AV 9700 800, Box P.O. xy hooy ohnug Sweden Gothenburg, chnology, ny t.84 Str. znaya t fSde,Sde,NwSuhWls20,Australia 2006, Wales South New Sydney, Sydney, of ity 1 s929 00G mtra,TeNetherlands The Amsterdam, GE 1090 94249, us e rlnsa 67ad16 H soitdwt RS10597 IRAS with associated MHz 1665 and 1667 at lines er ae Hstlieln esrmnspoieapotentially a provide measurements line satellite OH date. 1 n .Ziemke J. and , , t flog( of ity bs2 90A,Diglo h Netherlands The Dwingeloo, AA, 7990 2, tbus srpyia n lntr cecs nvriyo Color of University Sciences, Planetary and Astrophysical pn ehnss pia mgn hw h aayi likel is galaxy the shows imaging Optical mechanisms. mping 2 4 oa aiiy OBx7,Epn S 70 Australia 1710, NSW Epping 76, Box PO Facility, ional vy(WS,adtesbeun esrmn fteO 1612 OH the of measurement subsequent the and (AWES), rvey .A Moss A. V. , n ore therein). may regions sources emission compact and the in of found 30% is to emission Up nucleus. di the withi of be confined region is pc emission resoluti 100 maser arcsecond the a than that show greater have at that Those mega- studied OH Gree been dozen a have 2010; order masers of al. target- Only et 2012). Observatory, Fernandez Willett telescopes Telescope, by 2002, Parkes Bank Obse Giovanelli radio Arecibo 1992a; line & 1989; Darling al. dish al. et tory, et MHz Norris Baan single 1992; al. FT, 1667 et with Staveley-Smith 300 the sources NRAO IRAS (e.g. of bright detection ing the through e 2009). galaxy Roy hierarchical & McKean of 2005; test Lo a (e.g. hi thus models merger and lution the Universe, of the tracer valuable of a tory them make detection, a from n siaetettlnme fO aesta ilb detect be will that masers OH of number total the estimate and .Darling J. , oc 71 ot Africa South 7701, bosch tooia nttt ARB,Uiesttsrse150, Universitätsstrasse (AIRUB), Institute stronomical 1 o h 1667 the for or a Leeuwen van Joeri , h aoiyo xrglci Hmsr aebe found been have masers OH extragalactic of majority The ff s ihnte10p ein hl h aoiyo the of majority the while region, pc 100 the within use / L 2 197Mso,Russia Moscow, 117997 32, 10 / L .Mre Loose Marcel G. , ⊙ ) 3 / 8 .A .Adams K. A. E. , 1 62rtoof ratio 1612 = , , 9 12 , 3 1 . 90 .A Oosterloo A. T. , ± 0 aeo 179 of rate . 1 3 RS10597 IRAS 03, , 11 R i 1612 .J Vermaas J. N. , surveys 1 oehMaan Yogesh , 1 > , 2 ± 45 .J .d Blok de G. J. W. , 1 40 . , hc stehighest the is which 9 ∼ 2 ril ubr ae1o 9 of 1 page number, Article .Schulz R. , + M 0p nsz L 2005, (Lo size in pc 10 96i h fourth the is 5926 ⊙ yr vd nupdate an ovide 1 − .Vohl D. , 1 ae galaxy rared hs host These . 1 , 11 + d,389 ado, © valuable ,USA 1, us — burst 96at 5926 1 .Mika Á. , 44780 , S 2021 ESO 1 a y , ed 1 5 , , 2 , rva- vo- on. 1 s- n n , A&A proofs: manuscript no. ms_ohmaser_accepted
In fact, at radio frequencies, OH has two main lines at 1665 width of new and upgraded instruments undertaking these sur- and 1667 MHz and two satellite lines at 1612 and 1720 MHz veys will allow the simultaneous measurement of main and (Radford 1964). Extragalactic OHMs exhibit a broad range of satellite lines, while also detecting or putting limits on the H i 1667/1665 hyperfine ratios (from RH < 1 to RH > 10) with an emission and absorption strength (Gupta et al. 2020). Apertif average close to RH ∼ 5 (McBride et al. 2013). The variation is one of these upgraded survey machines: a new phased ar- observed in this property has been successfully modeled as a ray feed (PAF) instrument on the Westerbork Synthesis Radio combination of a clumpy maser medium of overlapping clouds Telescope undertaking commensurate spectral line, continuum, (Parra et al. 2005), and far-infrared line overlap with pumping and polarization surveys in the frequency range 1130-1430 MHz primarily occurring through the 53 µm line (Lockett & Elitzur (Adams & van Leeuwen 2019; van Capellen et al., in prep; Hess 2008). The former explains how compact masers (with typically et al., in prep). In addition to directly detecting H i in galaxies high RH values) appear embeddedin a diffuse emission (with low out to z ∼ 0.07 (and through H i stacking or absorption out to the RH) in high resolution very long baseline interferometry (VLBI) bandwidth limit, z ∼ 0.2), the observations are capable of detect- observations (Lonsdale 2002). Together these models account ing extragalactic OH masers where the 1667 MHz line has been for how warmer dust is correlated with higher infrared luminosi- redshifted to 0.166 < z < 0.476. ties (Willett et al. 2011; Lockett & Elitzur 2008). In this paper, we present the untargeted, serendipitous detec- However, very little is known about the ratio between main tion of IRAS 10597+5926in both the 1667 and 1665 main lines, and satellite lines in OHMs. In local thermodynamic equilib- and a measurement of the 1612 MHz satellite line with a inte- rium (LTE), the emission line ratios between are expected to grated signal-to-noise ratio of 2.2σ which we treat as an upper be 1 : 5 : 9 : 1 for 1612 : 1665 : 1667 : 1720 MHz. Mea- limit. We use published infrared (IR) and far ultraviolet (FUV) suring the ratio of satellite to main lines provides a test for fluxes available in the NASA/IPAC Extragalactic Database1 to complex maser pumping models which predict the 1667/1612 calculate the host galaxy properties including star formation rate (R1612) and 1667/1720 (R1720) ratios based on variation in the and stellar mass, and confirm that IRAS 10597+5926 is an ul- optical depth of the 1667 MHz line and the assumption that all tra luminous infared galaxy (ULIRG). The 1612 MHz emission lines have the same excitation temperature (Lockett & Elitzur measurement, is the highest 1667/1612 ratio lower limit mea- 2008; McBride et al. 2013, see also Willett et al. 2011). There sured to date, and the most stringent constraint on existing maser are only four extragalactic detections of 1612 MHz in emis- pumping models. This measurement demonstrates the power of sion which is a requirement to measure the 1667/1612 line ratio: upcoming untargeted, large-volume H i surveys, where the broad Arp 220 (Baan & Haschick 1987), Arp 299/IC694 and Mrk 231 bandwidth is valuable for simultaneously observing multiple OH (Baan et al. 1992a), and IRAS F15107+0724 (McBride et al. lines either directly or through the potential of OH stacking. The 2013). (A tentative detection of II Zw 96/IRAS 20550+1655 by detection of IRAS 10597+5926 also showcases the automated Baan et al. 1989 was refuted by McBride et al. 2013). Their cor- source finding/inspection tools under development which make responding measurements of the 1667/1612 ratio span R1612 ∼ discoveries within these surveys, and the harvesting of data from 7 − 29 over a relatively narrow range in 1667 MHz optical spectral line sources possible. depth (Baan et al. 1992a; McBride et al. 2013). In addition,M82 Throughout this paper we assume a ΛCDM cosmology with −1 −1 is detected with a complex mix of 1612 MHz emission and H0 = 70km s Mpc , ΩM = 0.27, ΩΛ = 0.73. absorption (Seaquist et al. 1997) and three extragalactic OH masing sources have been detected in 1612 MHz absorption: NGC 253 (Frayer et al. 1998); PKS 1413+135 (Darling 2004); 2. Apertif data PMN J0134-0931(Kanekar et al. 2005). In all of the cases when 2.1. Data reduction, imaging, and source finding 1612 MHz is detected in absorption, the 1720 MHz line is found in conjugate emission. In contrast, while Arp 220 is detected The area of sky containing IRAS 10597+5926 was observed in in 1612 MHz emission, the 1720 MHz line is seen in absorp- October 2019 (ObsId 191003042) as part of the ongoing Aper- tion (Baan & Haschick 1987). These complex cases have not yet tif wide-area extragalactic imaging survey, AWES. The Apertif been captured in the discussion of the maser pumping models. spectral line, continuum, and polarization surveys will be de- In addition to probing the state of the masing gas, satel- scribed in detail in Hess et al (in prep). In short, Apertif is a lite lines of OH are used to measure the universality of fun- phased array feed instrument upgrade to the Westerbork Synthe- sis Radio Telescope, which increases the field-of-view to 6.4- damental constants at high redshift (Varshalovich & Potekhin 2 1995; Darling 2003; Chengalur & Kanekar 2003). The four OH 8 deg and the spectral bandwidth to 300 MHz from 1130- lines have different dependencies on the fine structure constant, 1430 MHz. Every AWES survey pointing is observed for 11.5 2 hours. The data are reduced through an automated data reduc- α = e /~c, the electron-proton mass ratio, µ = me/mp, and tion pipeline called Apercal (Schulz et al. 2020, Adebahr et al, the proton gyromagnetic ratio, gp (Kanekar et al. 2005). Early quasar studies claimed a possible changing α (e.g. Webb et al. in prep) which produces cleaned multi-frequency continuum 2001). While no evidence for changing fundamental constants (Stokes I) images; polarization (Stokes V) images and (Stokes has been found to date from cm lines, only two OH sources are Q- and U-) cubes; and continuum-subtracted spectral line dirty known which have been used for such studies (PKS 1413+135, image cubes with 12.2–36.6 kHz resolution. The raw, calibrated, z = 0.24671; PMN J0134-0931, z = 0.765; Darling 2004; and imaged data from the first 12 months of observing (1 July 2019 - 30 June 2020) are publicly available as part of the first Kanekar et al. 2012, 2018), and a small number of sources us- 2 ing other lines (e.g. ammonia, Flambaum & Kozlov 2007; or Apertif data release (Apertif DR1; Adams et al, in prep). methanol, Jansen et al. 2011). As part of ongoing Apertif work towards developing a cata- i Large volume radio spectral line surveys at 1.4 GHz, typ- log of H spectral line sources, the data was run through a spec- ically aimed at targeting the 21 cm line of neutral hydrogen, 1 http://ned.ipac.caltech.edu; The NASA/IPAC Extragalactic Database H i, provide an unprecedented opportunity to discover and study (NED) is funded by the National Aeronautics and Space Administration the rare, but cosmologically important extragalactic OH mega- and operated by the California Institute of Technology. masers (e.g. Briggs 1998; Suess et al. 2016). The large band- 2 PID: http://hdl.handle.net/21.12136/B014022C-978B-40F6-96C6-1A3B1F4A3DB0
Article number, page 2 of 9 K. M. Hess et al.: Apertif view of an OH megamaser