Ultraviolet to Mid‐Infrared Observations of Star‐forming Galaxies atz ∼ 2: Stellar Masses and Stellar Populations

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Abstract
We present the broad-band UV through mid-infrared spectral energy distributions (SEDs) of a sample of 72 spectroscopically-confirmed star-forming galaxies at z=2.30+/-0.3. Located in a 72 arcmin-squared field centered on the bright background QSO, HS1700+643, these galaxies were pre-selected to lie at z~2 based solely on their rest-frame UV colors and luminosities, and should be representative of UV-selected samples at high redshift. In addition to deep ground-based photometry spanning from 0.35-2.15 microns, we make use of Spitzer/IRAC data, which probes the rest-frame near-IR at z~2. The range of stellar populations present in the sample is investigated with simple, single-component stellar population synthesis models. Emphasizing stellar mass estimates, which are less subject to systematic uncertainties than other parameters, we find =10.32+/-0.51 for the sample. Allowing for the possibility of episodic star formation, we find that typical galaxies in our sample could contain up to three times more stellar mass in an old underlying burst than what was inferred from single-component modeling. In contrast, mass estimates for the most massive galaxies in the sample (M*>10^11 Msun) are fairly insensitive to the method used to model the stellar population. Galaxies in this massive tail, which are also the oldest objects in the sample, could plausibly evolve into the passive galaxies discovered at z~1.7 with near-IR selection techniques. In the general framework of hierarchical galaxy formation and mergers, which implies episodic star-formation histories, galaxies at high redshift may pass in and out of UV-selected and near-IR color-selected samples as they evolve from phases of active star formation to quiescence and back again (Abridged).Comment: 30 pages including 12 figures. Accepted for publication in ApJ. Complete version with full resolution figures available at http://astron.berkeley.edu/~aes/shapley_fullres.ps.g