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THE OH MEGAMASER LUMINOSITY FUNCTION ABSTRACT We Present View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by CERN Document Server THE OH MEGAMASER LUMINOSITY FUNCTION Jeremy Darling & Riccardo Giovanelli Department of Astronomy and National Astronomy and Ionosphere Center, Cornell University, Ithaca, NY 14853; [email protected]; [email protected] Submitted to the Astrophysical Journal, 22 January 2002; accepted 21 February 2002. ABSTRACT We present the 1667 MHz OH megamaser luminosity function derived from a single flux-limited sur- vey. The Arecibo Observatory OH megamaser (OHM) survey has doubled the number of known OH megamasers, and we list the complete catalog of OHMs detected by the survey here, including three rede- tections of known OHMs. OHMs are produced in major galaxy mergers which are (ultra)luminous in the 0:64 far-infrared. The OH luminosity function follows a power law in integrated line luminosity, Φ LOH− 3 1 2:2 3:8 ∝ Mpc− dex− , and is well-sampled for 10 L <LOH < 10 L . The OH luminosity function is incor- porated into predictions of the detectability and areal density of OHMs in high redshift OH surveys for a variety of current and planned telescopes and merging evolution scenarios parameterized by (1 + z)m in the merger rate ranging from m = 0 (no evolution) to m = 8 (extreme evolution). Up to dozens of OHMs may be detected per square degree per 50 MHz by a survey reaching an rms noise of 100 µJy per 0.1 MHz channel. An adequately sensitive “OH Deep Field” would significantly constrain the evo- lution exponent m even if no detections are made. In addition to serving as luminous tracers of massive mergers, OHMs may also trace highly obscured nuclear starburst activity and the formation of binary supermassive black holes. Subject headings: masers — galaxies: interactions — galaxies: evolution — galaxies: luminosity function — galaxies: starburst — radio lines: galaxies 1. introduction roughly 102:5 L , and a steep falloff out to 104 L .We are now in a position to recompute the OH LF from a OH megamasers are luminous masing lines at 1667 and single complete survey with well-defined selection criteria 1665 MHz which are at least a million times more lumi- extracted from the PSCz, a flux-limited catalog which also nous than typical OH masers associated with compact HII has well-defined selection criteria (Saunders et al. 2000). regions. OH megamasers (OHMs) are produced in (ul- An OH LF will be a useful guide for deep surveys for OHMs tra)luminous infrared galaxies ([U]LIRGs), major galaxy mergers undergoing extreme bursts of circumnuclear star which can be related to the merging history of galaxies, the dust-obscured star formation history of the Universe, formation. OH megamasers are especially promising as and the production of some portions of the low frequency tracers of dust obscured star formation and merging galax- ies because they can potentially be observed at high red- gravitational wave background. This paper presents an overview of the Arecibo OH shifts with modern radio telescopes in reasonable integra- megamaser survey, focusing on the issues pertinent to con- tion times, they favor regions of high dust opacity where ultraviolet, optical, and even near-IR emission can be ex- structing an OH luminosity function (OH LF) from the survey results. Selection methods and the complete cata- tremely difficult to detect, and their detection automat- log of detected OHMs are presented in 2. Section 3 dis- ically provides an accurate redshift measurement. The § Arecibo Observatory1 OH megamaser survey is a flux- cusses the methods used to compute the OH luminosity function, presents the OH LF, and compares it to previ- limited survey designed to quantify the relationships be- tween merging galaxies and the OH megamasers (OHMs) ous results for OHMs and ULIRGs. The OH LF is then they produce with the goal of using OHMs as luminous applied to the problem of detecting OHMs at high redshift in 4 and some discussion is made of the utility of OHMs tracers of mergers at high redshifts (Darling & Giovanelli § 2000, 2001, 2002; hereafter Papers I, II, III). Central to as tracers of galaxy evolution, including merging, dust- the application of OHMs as tracers of merging galaxies at obscured nuclear starbursts, and the formation of binary supermassive black holes. various redshifts is a measurement of the low redshift OH Note that Papers I–III assume a cosmology with H = luminosity function. 1 1 ◦ The Arecibo OH megamaser survey is the first sur- 75 km s− Mpc− , q =0,andΩΛ = 0 for ease of com- parison with previous◦ (U)LIRG surveys such as Kim & vey with adequate statistics to construct an OH lumi- nosity function (LF) from a flux-limited sample. Baan Sanders (1998). This analysis, however, assumes a more (1991) computed a OH luminosity function from the 48 likely cosmology which is flat but accelerating: ΩM =0:3 and Ω =07. All of the OHM data presented here have OHMs which were known at the time under the assump- Λ : tion that they constituted a flux-limited sample and that been converted to this cosmology. the fraction of LIRGs showing detectable OHMs is con- 2. the arecibo oh megamaser survey stant. Baan’s OH LF has a Schecter-type profile which 0 2 is slowly falling from LOH =10–10 L ,hasakneeat Papers I–III present a survey for OHMs conducted at 1 The Arecibo Observatory is part of the National Astronomy and the Arecibo Observatory covering one quarter of the sky Ionosphere Center, which is operated by Cornell University under a to a depth of roughly one gigaparsec. The survey doubles cooperative agreement with the National Science Foundation. the number of known OH megamasers and quantifies the 1 2 Darling & Giovanelli relationship between luminous infrared galaxies and OH megamasers. The survey builds the foundation required to employ OH megamasers as tracers of major galaxy merg- ers, dust-obscured star formation, and the formation of binary supermassive black holes spanning the epoch of galaxy evolution to the present. Here we present details of the survey relevant to constructing an OH LF: the candi- date selection criteria and the complete catalog of detected OHMs with properties converted to a flat ΩΛ =0:7cos- mology. 2.1. Candidate Selection For the Arecibo OH megamaser survey, candidates were selected from the Point Source Catalog redshift sur- vey (PSCz; Saunders et al. 2000), supplemented by the NASA/IPAC Extragalactic Database.2 The PSCz catalog is a flux-limited (IRAS f60µm > 0:6 Jy) redshift survey of 15,000 IRAS galaxies over 84% of the sky (see Saunders et al. 2000). We select IRAS sources which are in the Arecibo sky (0◦ <δ<37◦), were detected at 60 µm, and have 0:1 z 0:45. The lower redshift bound is set to avoid local≤ radio≤ frequency interference (RFI), while the upper bound is set by the bandpass of the wide L-band receiver at Arecibo, although an effective upper bound is imposed around z =0:23 by the radio frequency in- terference (RFI) environment, as discussed in 3.3. No constraints are placed on FIR colors or luminosity.§ The redshift requirement limits the number of candidates in the Arecibo sky to 311. The condition that candidates have z>0:1 automatically selects (U)LIRGs if they are included in the PSCz. The strong influence of LFIR on OHM fraction in LIRGs (see Paper III) is the primary reason for our high detection rate compared to previous surveys (e.g. Staveley-Smith et al. 1992; Baan, Haschick, & Henkel 1992). 2 The NASA/IPAC Extragalactic Database (NED) is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Adminis- tration. OH Megamaser Luminosity Function 3 Table 1 Arecibo Survey OH Megamasers: Optical Redshifts and FIR Properties IRAS Name αδzRef cz czCMB DL f60µm f100µm log LF 1 2 FSC B1950 B1950 z km/s km/s h75− Mpc Jy Jy h75− L (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) 01562+2528 01 56 12.0 +25 27 59 0.1658 1 49707(505) 49441(506) 739(8) 0.809( 57) 1.62(24) 11.9 02524+2046 02 52 26.8 +20 46 54 0.1815 1 54421(125) 54213(129) 788(2) 0.958( 77) < 4.79 11.81–1 03521+0028 03 52 08.5 +00 28 21 0.1522 2 45622(138) 45501(142) 674(2) 2.638(237) 3.83(34) 12.2 03566+1647 03 56 37.8 +16 47 57 0.1335 1 40033( 54) 39911( 65) 585(1) 0.730( 66) < 2.37 11.40–1 04121+0223 04 12 10.5 +02 23 12 0.1216 3 36454(250) 36362(253) 529(4) 0.889( 62) < 2.15 11.40–1 06487+2208 06 48 45.1 +22 08 06 0.1437 4 43080(300) 43206(302) 637(5) 2.070(166) 2.36(26) 12.1 07163+0817 07 16 23.7 +08 17 34 0.1107 1 33183(110) 33367(115) 482(2) 0.891( 89) 1.37(11) 11.5 07572+0533 07 57 17.9 +05 33 16 0.1894 1 56783(122) 57022(126) 865(2) 0.955( 76) 1.30(20) 12.0 08201+2801 08 20 10.1 +28 01 19 0.1680 5 50365( 70) 50583( 77) 757(1) 1.171( 70) 1.43(16) 12.0 08279+0956 08 27 56.1 +09 56 41 0.2085 1 62521(107) 62788(110) 963(2) 0.586( 64) < 1.26 11.75–1 08449+2332 08 44 55.6 +23 32 12 0.1510 1 45277(102) 45530(106) 675(2) 0.867( 69) 1.20(17) 11.7 08474+1813 08 47 28.3 +18 13 14 0.1450 5 43470( 70) 43739( 75) 646(1) 1.279(115) 1.54(18) 11.9 09039+0503 09 03 56.4 +05 03 28 0.1250 5 37474( 70) 37781( 73) 551(1) 1.484( 89) 2.06(21) 11.8 09531+1430 09 53 08.3 +14 30 22 0.2151 1 64494(148) 64818(149) 998(2) 0.777( 62) 1.04(14) 12.0 09539+0857 09 53 54.9 +08 57 23 0.1290 5 38673( 70) 39008( 72) 570(1) 1.438(101) 1.04(18) 11.7 10035+2740 10 03 36.7 +27 40 19 0.1662 1 49826(300) 50116(301) 750(5) 1.144(126) 1.63(161) 12.0 10339+1548 10 33 58.1 +15 48 11 0.1965 1 58906(122) 59242(123) 903(2) 0.977( 59) 1.35(16) 12.0 10378+1108a 10 37 49.1 +11 09 08 0.1362 2
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