On the Stellar Populations in Faint Red Galaxies in the Hubble Ultra Deep Field1 Academic Article uri icon


  • We study the nature of faint red-selected galaxies at z ∼ 2-3 using the Hubble Ultra Deep Field (HUDF) and Spitzer Infrared Array Camera (IRAC) photometry. Given the magnitude limit of the HST data, we detect candidate galaxies to HAB < 26 mag, probing lower luminosity (lower mass) galaxies at these redshifts. We identify 32 galaxies satisfying the (J 110 - H160)AB > 1.0 mag color selection, 16 of which have unblended [3.6 μm] and [4.5 μm] photometry from Spitzer. Using this multiwavelength data set, 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) of the (J110 - H160)AB > 1-0 mag population 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. We argue that longer wavelength data (≲1 μm, rest frame) are essential for interpreting the properties of the stellar populations in red-selected galaxies at these redshifts. 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. These objects have a surface density of ∼1 arcmin -2, We place an upper limit on the space density of candidate massive evolved galaxies with 2.5 < z < 3.5 and HAB160 ≤ 26 mag of n = 6.6-3.0+2.0 × 10-4 Mpc-3, with a corresponding upper limit on the stellar mass density of p* = 5.6-2.8+4.48 × 107 M⊙ Mpc -3. 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 (≲ 2 × 10 10 M⊙) 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.

author list (cited authors)

  • Stutz, A. M., Papovich, C., & Eisenstein, D. J.

citation count

  • 13

publication date

  • April 2008