Stellar Populations of Lyman Break Galaxies at z ~= 1-3 in the HST/WFC3 Early Release Science Observations

We analyze the spectral energy distributions (SEDs) of Lyman break galaxies (LBGs) at z ~= 1-3 selected using the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) UVIS channel filters. These HST/WFC3 observations cover about 50 arcmin² in the GOODS-South field as a part of the WFC3 Early Release Science program. These LBGs at z ~= 1-3 are selected using dropout selection criteria similar to high-redshift LBGs. The deep multi-band photometry in this field is used to identify best-fit SED models, from which we infer the following results: (1) the photometric redshift estimate of these dropout-selected LBGs is accurate to within few percent; (2) the UV spectral slope β is redder than at high redshift (z > 3), where LBGs are less dusty; (3) on average, LBGs at z ~= 1-3 are massive, dustier, and more highly star forming, compared to LBGs at higher redshifts with similar luminosities (0.1L* <~ L <~ 2.5L*), though their median values are similar within 1σ uncertainties. This could imply that identical dropout selection technique, at all redshifts, finds physically similar galaxies; and (4) the stellar masses of these LBGs are directly proportional to their UV luminosities with a logarithmic slope of ~0.46, and star formation rates are proportional to their stellar masses with a logarithmic slope of ~0.90. These relations hold true—within luminosities probed in this study—for LBGs from z ~= 1.5 to 5. The star-forming galaxies selected using other color-based techniques show similar correlations at z ~= 2, but to avoid any selection biases, and for direct comparison with LBGs at z > 3, a true Lyman break selection at z ~= 2 is essential. The future HST UV surveys, both wider and deeper, covering a large luminosity range are important to better understand LBG properties and their evolution.