Article

# A Substantial Population of Red Galaxies at z > 2: Modeling of the Spectral Energy Distributions of an Extended Sample

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University of California, Santa Cruz, Santa Cruz, California, United States
(Impact Factor: 6.28). 12/2008; 616(1):40. DOI: 10.1086/424838
Source: arXiv

ABSTRACT We investigate the nature of the substantial population of high-redshift galaxies with Js - Ks ≥ 2.3 colors recently discovered as part of our Faint Infrared Extragalactic Survey (FIRES). This color cut efficiently isolates galaxies at z > 2 with red rest-frame optical colors ("distant red galaxies" [DRGs]). We select Js - Ks ≥ 2.3 objects in both FIRES fields, the ≈25 × 25 Hubble Deep Field-South (HDF-S) and the ≈5' × 5' field around the MS 1054-03 cluster at z = 0.83; the surface densities at Ks,Vega < 21 mag are 1.6 ± 0.6 and 1.0 ± 0.2 arcmin-2, respectively. We here discuss a subsample of 34 DRGs at 2 ≤ z ≤ 3.5: 11 at Ks,Vega < 22.5 mag in HDF-S and 23 at Ks,Vega < 21.7 mag in the MS 1054-03 field. This sample enables for the first time a robust assessment of the population properties of DRGs. We analyze the λ = 0.3-2.2 μm spectral energy distributions (SEDs) constructed from our very deep near-infrared (NIR) and optical imaging collected at the ESO Very Large Telescope and from the Hubble Space Telescope. We develop diagnostics involving the I814 - Js, Js - H, and H - Ks colors to argue that the red NIR colors of our DRG sample cannot be attributed solely to interstellar dust extinction and require for many the presence of an evolved stellar population with a prominent Balmer/4000 Å break. In the rest frame, the optical colors of DRGs fall within the envelope of normal nearby galaxies and the ultraviolet colors suggest a wide range in star formation activity and/or extinction. This is in stark contrast with the much bluer and more uniform SEDs of Lyman break galaxies (LBGs). From evolutionary synthesis modeling assuming constant star formation (CSF), we derive for the DRGs old ages, large extinctions, and high stellar masses, mass-to-light ratios, and star formation rates (SFRs). For solar metallicity, a Salpeter initial mass function (IMF) between 0.1 and 100 M☉, and the Calzetti et al. extinction law, the median values for the HDF-S (MS 1054-03 field) sample are 1.7 (2.0) Gyr, AV = 2.7 (2.4) mag, M* = 0.8 (1.6) × 1011 M☉, M*/LV,* = 1.2 (2.3) M☉ L, and SFR = 120 (170) M☉ yr-1. Models assuming exponentially declining SFRs with e-folding timescales in the range from 10 Myr to 1 Gyr generally imply younger ages, lower extinction, and lower SFRs, but similar stellar masses within a factor of 2. Compared to LBGs at similar redshifts and rest-frame V-band luminosities, DRGs are older, more massive, and more obscured for any given star formation history. For the entire sample of Ks-band selected galaxies in the FIRES fields at 2 ≤ z ≤ 3.5 and to the above magnitude limits, we find that the derived ages, extinctions, and stellar masses increase with redder Js - Ks colors. Although the rest-frame optical colors of the DRGs are similar to those of local normal galaxies, the derived properties are quite different; detailed studies of this new z > 2 population may significantly enhance our understanding of how massive galaxies assembled their stellar mass.

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##### Article: The Progenitors of Local Ultra-massive Galaxies Across Cosmic Time: from Dusty Star-bursting to Quiescent Stellar Populations
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ABSTRACT: Using the UltraVISTA catalogs, we investigate the evolution in the 11.4 Gyr since z=3 of the progenitors of local ultra-massive galaxies ($\log{(M_{\rm star}/M_{\odot})}\approx11.8$; UMGs), providing a complete and consistent picture of how the most massive galaxies at z=0 have assembled. By selecting the progenitors with a semi-empirical approach using abundance matching, we infer a growth in stellar mass of 0.56 dex, 0.45 dex, and 0.27 dex from z=3, z=2, and z=1, respectively, to z=0. At z<1, the progenitors of UMGs constitute a homogeneous population of only quiescent galaxies with old stellar populations. At z>1, the contribution from star-forming galaxies progressively increases, with the progenitors at 2<z<3 being dominated by massive ($M_{\rm star} \approx 2 \times 10^{11}$M$_{\odot}$), dusty ($A_{\rm V}\sim$1-2.2 mag), star-forming (SFR$\sim$100-400 M$_{\odot}$ yr$^{-1}$) galaxies with a large range in stellar ages. At z=2.75, ~15% of the progenitors are quiescent, with properties typical of post-starburst galaxies with little dust extinction and strong Balmer break, and showing a large scatter in color. Our findings indicate that local UMGs have been mostly assembled between z=3 and z=1.5. Most of the quenching of the star-forming progenitors happened between z=2.75 and z=1.25, in good agreement with the typical formation redshift and scatter in age of z=0 UMGs as derived from their fossil records. We show that the progenitors of local UMGs, including the star-forming ones, have never lived on the blue cloud since z=3, challenging previously proposed pictures for the formation of local massive spheroids, and we propose an alternative path for the formation of local UMGs consistent with our findings.
The Astrophysical Journal 01/2014; 794(1). DOI:10.1088/0004-637X/794/1/65 · 6.28 Impact Factor
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##### Article: On the Stellar Populations in Faint Red Galaxies in the Hubble Ultra Deep Field
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ABSTRACT: We study the nature of faint, red-selected galaxies at z ~ 2-3 using the Hubble Ultra Deep Field (HUDF) and Spitzer IRAC photometry. We detect candidate galaxies to H < 26 mag, probing lower-luminosity (lower mass) galaxies at these redshifts. We identify 32 galaxies satisfying the (J - H) > 1.0 mag color selection, 16 of which have unblended [3.6um] and [4.5um] IRAC photometry. We derive photometric redshifts, masses, and stellar population parameters for these objects. We find that the selected objects span a diverse range of properties over a large range of redshifts, 1 < z < 3.5. A substantial fraction (11/32) appear to be lower-redshift (z < 2.5), heavily obscured dusty galaxies or edge-on spiral galaxies, while others (12/32) appear to be galaxies at 2 < z < 3.5 whose light at rest-frame optical wavelengths is dominated by evolved stellar populations. Interestingly, by including Spitzer data many candidates for galaxies dominated by evolved stellar populations are rejected, and for only a subset of the sample (6/16) do the data favor this interpretation. We place an upper limit on the space and stellar mass density of candidate massive evolved galaxies. The z > 2.5 objects that are dominated by evolved stellar populations have a space density at most one-third that of z ~ 0 red, early-type galaxies. Therefore, at least two-thirds of present-day early-type galaxies assemble or evolve into their current configuration at redshifts below 2.5. We find a dearth of candidates for low-mass galaxies at 1.5 < z < 3 that are dominated by passively evolving stellar populations even though the data should be sensitive to them; thus, at these redshifts, galaxies whose light is dominated by evolved stellar populations are restricted to only those galaxies that have assembled high stellar mass.[Abridged] Comment: 18 pages, 10 figures, and 4 tables. Accepted for publication in ApJ
The Astrophysical Journal 01/2008; 677(2). DOI:10.1086/529114 · 6.28 Impact Factor
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The Astrophysical Journal 12/2008; 682(2):896. DOI:10.1086/589677 · 6.28 Impact Factor