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We combine Hubble Space Telescope (HST) G102 and G141 near-IR (NIR) grism spectroscopy with HST/WFC3-UVIS, HST/WFC3-IR, and Spitzer/IRAC [3.6 μm] photometry to assemble a sample of massive (log (Mstar/M☼) ∼ 11.0) and quenched (specific star formation rate <0.01 Gyr–1) galaxies at z ∼ 1.5. Our sample of 41 galaxies is the largest with G102+G141 NIR spectroscopy for quenched sources at these redshifts. In contrast to the local universe, z ∼ 1.5 quenched galaxies in the high-mass range have a wide range of stellar population properties. We find that their spectral energy distributions (SEDs) are well fitted with exponentially decreasing star formation histories and short star formation timescales (τ ⩽ 100 Myr). Quenched galaxies also show a wide distribution in ages, between 1 and 4 Gyr. In the (u – r)0-versus-mass space quenched galaxies have a large spread in rest-frame color at a given mass. Most quenched galaxies populate the z ∼ 1.5 red sequence (RS), but an important fraction of them (32%) have substantially bluer colors. Although with a large spread, we find that the quenched galaxies on the RS have older median ages (3.1 Gyr) than the quenched galaxies off the RS (1.5 Gyr). We also show that a rejuvenated SED cannot reproduce the observed stacked spectra of (the bluer) quenched galaxies off the RS. We derive the upper limit on the fraction of massive galaxies on the RS at z ∼ 1.5 to be <43%. We speculate that the young quenched galaxies off the RS are in a transition phase between vigorous star formation at z > 2 and the z ∼ 1.5 RS. According to their estimated ages, the time required for quenched galaxies off the RS to join their counterparts on the z ∼ 1.5 RS is of the order of ∼1 Gyr. [ABSTRACT FROM AUTHOR]

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 multiband 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. [ABSTRACT FROM AUTHOR]