19 September, 2013 13:59

Low Masses and High Redshifts: The Evolution of the Mass-Metallicity Relation

Alaina Henry, Claudia Scarlata, Alberto Dominguez, Matthew Malkan, Crystal L. Martin, Brian Siana, Hakim Atek, Alejandro G. Bedregal, James W. Colbert, Marc Rafelski, Nathaniel Ross,Harry Teplitz, Andrew J. Bunker, Alan Dressler, Nimish Hathi, Daniel Masters, Patrick McCarthy, Amber Straughn
(Submitted on 17 Sep 2013)

We present the first robust measurement of the high redshift mass-metallicity (MZ) relation at 10^{8}< M/M_{\sun} < 10^{10}, obtained by stacking spectra of 83 emission-line galaxies with secure redshifts between 1.3 < z < 2.3. For these redshifts, infrared grism spectroscopy with the Hubble Space Telescope Wide Field Camera 3 is sensitive to the R23 metallicity diagnostic: ([OII]3726,3729 + [OIII] 4959,5007)/H\beta. Using spectra stacked in four mass quartiles, we find a MZ relation that declines significantly with decreasing mass, extending from 12+log(O/H) = 8.8 at M=10^{9.8} M_{\sun} to 12+log(O/H)= 8.2 at M=10^{8.2} M_{\sun}. After correcting for systematic offsets between metallicity indicators, we compare our MZ relation to measurements from the stacked spectra of galaxies with M>10^{9.5} M_{\sun} and z~2.3. Within the statistical uncertainties, our MZ relation agrees with the z~2.3 result, particularly since our somewhat higher metallicities (by around 0.1 dex) are qualitatively consistent with the lower mean redshift z=1.76 of our sample. For the masses probed by our data, the MZ relation shows a steep slope which is suggestive of feedback from energy-driven winds, and a cosmological downsizing evolution where high mass galaxies reach the local MZ relation at earlier times. In addition, we show that our sample falls on an extrapolation of the star-forming main sequence (the SFR-M_{*} relation) at this redshift. This result indicates that grism emission-line selected samples do not have preferentially high SFRs. Finally, we report no evidence for evolution of the mass-metallicity-SFR plane; our stack-averaged measurements show excellent agreement with the local relation.

Comments: Accepted for publication in ApJ Letters
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)
Cite as: arXiv:1309.4458 [astro-ph.CO]
(or arXiv:1309.4458v1 [astro-ph.CO] for this version)

The role of galaxy interaction in the SFR-M relation: characterizing morphological properties of Herschel-selected galaxies at 0.2<z<1.5

Chao-Ling Hung (1), David B. Sanders (1), Caitlin M. Casey (1), Nicholas Lee (1), Joshua E. Barnes (1), Peter Capak (2), Jeyhan S. Kartaltepe (3), Michael Koss (1), Kirsten L. Larson (1),Emeric Le Floc’h (4), Kelly Lockhart (1), Allison W. S. Man (5,1), Andrew W. Mann (1), Laurie Riguccini (6,7), Nicholas Scoville (8), Myrto Symeonidis (9,10) ((1) IfA Hawaii, (2) SSC Caltech, (3) NOAO, (4) CEA-Saclay, (5) DARK Denmark, (6) NASA Ames, (7) BAER, (8) Caltech, (9) Sussex, (10) UCL)
(Submitted on 17 Sep 2013)

Galaxy interactions/mergers have been shown to dominate the population of IR luminous galaxies (log(LIR)>11.6Lsun) in the local Universe (z<0.25). Recent studies based on the relation between galaxies’ star formation rates and stellar mass (the SFR-M relation or the galaxy main sequence (MS)) have suggested that galaxy interaction/mergers may only become significant when galaxies fall well above the galaxy MS. Since the typical SFR at given M increases with redshift, the existence of galaxy MS implies that massive, IR-luminous galaxies at high-z may not necessarily be driven by galaxy interactions. We examine the role of galaxy interactions in the SFR-M relation by carrying out a morphological analysis of 2084 Herschel-selected galaxies at 0.2 < z < 1.5 in the COSMOS field. Herschel-PACS and -SPIRE observations covering the full 2-deg^2 COSMOS field provide one of the largest far-IR selected samples of high-redshift galaxies with well-determined redshifts to date, with sufficient sensitivity at z ~ 1, to sample objects lying on and above the galaxy MS. Using a detailed visual classification scheme, we show that the fraction of "disk galaxies" decreases and the fraction of "irregular" galaxies increases systematically with increasing LIR out to z ~ 1.5 and z ~ 1.0, respectively. At log(LIR) > 11.5 Lsun, >50% of the objects show evident features of strongly interacting/merger systems, where this percentage is similar to the studies of local IR-luminous galaxies. The fraction of interacting/merger systems also systematically increases with the deviation from the SFR-M relation, supporting the view that galaxies fall above the MS are more dominated by mergers than the MS galaxies. Meanwhile, we find that ~18% of massive IR-luminous MS galaxies are classified as interacting systems, where this population may not evolve through the evolutionary track predicted by a simple gas exhaustion model.

Comments: 14 pages, 11 figures, ApJ accepted
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1309.4459 [astro-ph.CO]
(or arXiv:1309.4459v1 [astro-ph.CO] for this version)
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