On the Stellar Populations in Faint Red Galaxies in the Hubble Ultra Deep Field

TL;DR

This study investigates faint red galaxies at redshifts 2-3 in the Hubble Ultra Deep Field, revealing diverse properties, limited evolved stellar population candidates, and implications for galaxy assembly history.

Contribution

It provides new insights into the properties and evolution of low-luminosity, red-selected galaxies at high redshift using deep Hubble and Spitzer data.

Findings

Diverse galaxy properties over 1 < z < 3.5

Limited evolved stellar population candidates at high z

At least two-thirds of present-day early-type galaxies form after z=2.5

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]