Search

We report on a Hubble Space Telescope search for rest-frame ultraviolet emission from the host galaxies of five far-infrared-luminous z ≃ 6 quasars and the z = 5.85 hot-dust-free quasar SDSS J0005–0006. We perform 2D surface brightness modeling for each quasar using a Markov Chain Monte Carlo estimator, to simultaneously fit and subtract the quasar point source in order to constrain the underlying host galaxy emission. We measure upper limits for the quasar host galaxies of mJ > 22.7 mag and mH > 22.4 mag, corresponding to stellar masses of M* < 2 × 1011M⊙. These stellar mass limits are consistent with the local MBH − M* relation. Our flux limits are consistent with those predicted for the UV stellar populations of z ≃ 6 host galaxies, but likely in the presence of significant dust (mag). We also detect a total of up to nine potential z ≃ 6 quasar companion galaxies surrounding five of the six quasars, separated from the quasars by 1.″4–3.″2, or 8.4–19.4 kpc, which may be interacting with the quasar hosts. These nearby companion galaxies have UV absolute magnitudes of −22.1 to −19.9 mag and UV spectral slopes β of −2.0 to −0.2, consistent with luminous star-forming galaxies at z ≃ 6. These results suggest that the quasars are in dense environments typical of luminous z ≃ 6 galaxies. However, we cannot rule out the possibility that some of these companions are foreground interlopers. Infrared observations with the James Webb Space Telescope will be needed to detect the z ≃ 6 quasar host galaxies and better constrain their stellar mass and dust content. [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]

We present the size evolution of passively evolving galaxies at z ~ 2 identified in Wide-Field Camera 3 imaging from the Early Release Science program. Our sample was constructed using an analog to the passive BzK galaxy selection criterion, which isolates galaxies with little or no ongoing star formation at z ≿ 1.5. We identify 30 galaxies in ~40 arcmin² to H < 25 mag. By fitting the 10-band Hubble Space Telescope photometry from 0.22 µm ≾ λobs ≾ 1.6 µm with stellar population synthesis models, we simultaneously determine photometric redshift, stellar mass, and a bevy of other population parameters. Based on the six galaxies with published spectroscopic redshifts, we estimate a typical redshift uncertainty of ~0.033(1+z). We determine effective radii from Sérsic profile fits to the H-band image using an empirical point-spread function. By supplementing our data with published samples, we propose a mass-dependent size evolution model for passively evolving galaxies, where the most massive galaxies (M* ~ 1011 M⊙) undergo the strongest evolution from z ~ 2 to the present. Parameterizing the size evolution as (1 + z)-α, we find a tentative scaling of α ≈ (-0.6 ± 0.7) + (0.9 ± 0.4) log(M*/109 M⊙), where the relatively large uncertainties reflect the poor sampling in stellar mass due to the low numbers of highredshift systems. We discuss the implications of this result for the redshift evolution of the M*-Re relation for red galaxies. [ABSTRACT FROM AUTHOR]

We present a sample of 17 newly discovered ultracool dwarf candidates later than ~M8, drawn from 231.90 arcmin² of Hubble Space Telescope Wide Field Camera 3 infrared imaging. By comparing the observed number counts for 17.5 ≤ J125 ≤ 25.5 AB mag to an exponential disk model, we estimate a vertical scale height of zscl = 290 ± 25 (random) ± 31 (systematic) pc for a binarity fraction of fb = 0. While our estimate is roughly consistent with published results, we suggest that the differences can be attributed to sample properties, with the present sample containing far more substellar objects than previous work. We predict the object counts should peak at J125 ~ 24 AB mag due to the exponentially declining number density at the edge of the disk. We conclude by arguing that trend in scale height with spectral type may breakdown for brown dwarfs since they do not settle onto the main sequence. [ABSTRACT FROM AUTHOR]