The rest-frame optical properties of high-redshift galaxies

Abstract

We present the first results from the F̲aint I̲nfra-R̲ed E̲xtragalactic S̲urvey (FIRES) of the Rubble Deep Field (HDF) South. Using a combination of very deep ground-based near infrared (NIR) data with the WFPC2 Hubble Space Telescope data, we constructed a K(s)-band selected sample to K(s,AB) ≤ 26.0. To interpret this data, we developed a new photometric redshift technique and tested it using spectroscopic redshifts in the HDF-N and HDF-S. Our accuracy was Δz/(1 + z) ≈ 0.07 for z < 6. We derived realistic error estimates in z(phot) by accounting both for template mismatch and for the dependence of the redshift uncertainty on the photometric errors. We estimated the rest-frame optical luminosities from an initial NIR data set and found 90 times more galaxies at 2 < z < 3.5 and Lʳᵉˢᵗ(B) > 5 x 10¹⁰ h⁻² L(⊙,B) than are expected from local luminosity functions. This discrepancy can be explained if L*, B increases by a factor of 2.4-3.2 with respect to locally determined values. Using all available NIR data in the HDF-S, we then derived the rest-frame colors (U - B)(rest), (B - V)(rest), and (U - V)(rest) of all galaxies with K(s,AB) < 25. Eight of the 12 rest-frame optically reddest galaxies at 2 < z(phot) < 3.2 would have been missed by the U-dropout selection criteria. Three of the galaxies at z > 2 have strong rest-frame optical breaks with colors corresponding to those of present day Sbc's. Using theoretical relations between the color and stellar mass-to-light ratio M/L , we estimated the M/L and stellar mass M . Using these estimates, we found that the most massive galaxies at any redshift are those with the reddest rest-frame colors and those that would be missed by the U-dropout technique. We also found that the stellar mass budget at z < 3.2 has significant contributions from galaxies redder than local Scd's. There are, however, large uncertainties in the M/L analysis and we have a relatively small field. Confirmation of these results will require additional modeling, observations over a larger area, and extensive spectroscopic follow up. We found an intrinsically bright (Lʳᵉˢᵗ(V) =5.10x10¹⁰ h⁻² L(⊙,V)) U-dropout galaxy in the HDF-S with z(spec) = 2.793. This galaxy has an extended ring-like morphology, and a co-moving diameter of ≳ 9.4 h⁻¹ Kpc for a Ω(M) = 0.3, Ω(Λ) = 0.7 cosmology. The light profile appears more centrally concentrated and symmetric at longer wavelengths and this object may have an older population superimposed on a star-forming disk.