A Search for Lyman Break Galaxies in the CDF-S Using Swift UVOT

Abstract

While the Swift satellite is primarily designed to study gamma-ray bursts, its ultraviolet and optical imaging and spectroscopy capabilities are also being used for a variety of scientific programs. In this study, we use the UV/Optical Telescope (UVOT) instrument aboard Swift to discover 0.5 < z < 2 Lyman break galaxies (LBGs). UVOT has covered ∼ 266 arcmin 2 at >60ks exposure time, achieving a limiting magnitude of u < 24.5, in the Chandra Deep Field South (CDF-S). Applying UVOT near-ultraviolet color selection, we select 50 UV-dropouts from this UVOT CDF-S data. We match the selected sources with available multiwavelength data from GOODS-South, MUSYC, and COMBO-17 to characterize the spectral energy distributions for these galaxies and determine stellar masses, star formation rates (SFRs), and dust attenuations. We compare these properties for LBGs selected in this paper versus z ∼ 3 LBGs and other CDF-S galaxies in the same redshift range (0.5 < z < 2), identified using photometric redshift techniques. The z ∼ 1 LBGs have stellar masses of Log M * /M ⊙ = 9.4 ± 0.6, which is slightly lower than z ∼ 3 LBGs ( Log M * /M ⊙ = 10.2 ± 0.4) and slightly higher compared to the z ∼ 1 CDF-S galaxies ( Log M * /M ⊙ = 8.7 ± 0.7). Similarly, our sample of z ∼ 1 LBGs has SFRs (derived using both ultraviolet and infrared data, where available) of Log SFR/(M ⊙ yr −1 ) = 0.7 ± 0.6, which is nearly an order of magnitude lower than z ∼ 3 LBGs ( Log SFR/M ⊙ yr −1 = 1.5 ± 0.4), but slightly higher than the comparison z ∼ 1 sample of CDF-S galaxies ( Log SFR/M ⊙ yr −1 = 0.2 ± 0.7). We find that our z ∼ 1 UV-dropouts have A FUV = 2.0 ± 1.0, which is higher than z ∼ 3 LBGs ( A FUV = 1.0 ± 0.5), but is similar to the distribution of dust attenuations in the other CDF-S galaxies ( A FUV ∼ 2.8 ± 1.5). Using the GOODS-South multiwavelength catalog of galaxies, we simulate a larger and fainter sample of LBGs to compare their properties with those of the UVOT-selected LBG sample. We conclude that UVOT can be useful for finding and studying the bright end of 0.5< z <2.0 LBGs.