Andrew Bunker

Abstract:

We investigate the evolution of the galaxy stellar mass function at high redshift (z ≥ 5) using a pair of large cosmological hydrodynamical simulations: MassiveBlack and Massive Black-II. By combining these simulations, we can study the properties of galaxies with stellar masses greater than 108M⊙ h-1 and (comoving) number densities of log10(φ [Mpc-3 dex-1 h3]) > -8. Observational determinations of the galaxy stellar mass function at very high redshift typically assume a relation between the observed ultraviolet (UV) luminosity and stellar massto- light ratio which is applied to high-redshift samples in order to estimate stellar masses. This relation can also be measured from the simulations. We do this, finding two significant differences with the usual observational assumption: it evolves strongly with redshift and has a different shape. Using this relation to make a consistent comparison between galaxy stellar mass functions, we find that at z=6 and above the simulation predictions are in good agreement with observed data over the whole mass range. Without using the correct UV luminosity and stellar mass-to-light ratio, the discrepancy would be up to two orders of magnitude for large galaxies (>1010M⊙ h-1). At z = 5, however, the stellar mass function for low-mass galaxies (<109M⊙ h-1) is overpredicted by factors of a few, consistent with the behaviour of the UV luminosity function, and perhaps a sign that feedback in the simulation is not efficient enough for these galaxies. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

The recent Hubble Space Telescope near-infrared imaging with the Wide-Field Camera #3 (WFC 3) of the Great Observatories Origins Deep Survey South (GOODS-S) field in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) programme covering nearly 100 arcmin2, along with already existing Advanced Camera for Surveys optical data, makes possible the search for bright galaxy candidates at redshift z≈7-9 using the Lyman break technique. We present the first analysis of z'-drop z≈7 candidate galaxies in this area, finding 19 objects. We also analyse Y-drops at z≈8, trebling the number of bright (HAB < 27 mag) Y-drops from our previous work, and compare our results with those of other groups based on the same data. The bright high-redshift galaxy candidates we find serve to better constrain the bright end of the luminosity function at those redshift, and may also be more amenable to spectroscopic confirmation than the fainter ones presented in various previous work on the smaller fields (the Hubble Ultra Deep Field and the WFC 3 Early Release Science observations).We also look at the agreement with previous luminosity functions derived from WFC3 drop-out counts, finding a generally good agreement, except for the luminosity function of Yan et al. at z≈8, which is strongly ruled out. ©2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

Spectroscopic observations of Hα and Hβ emission lines of 128 star-forming galaxies in the redshift range 0.75 ≤ z ≤ 1.5 are presented. These data were taken with slitless spectroscopy using the G102 and G141 grisms of the Wide-Field-Camera 3 (WFC3) on board the Hubble Space Telescope as part of the WFC3 Infrared Spectroscopic Parallel survey. Interstellar dust extinction is measured from stacked spectra that cover the Balmer decrement (Hα/Hβ). We present dust extinction as a function of Hα luminosity (down to 3 × 1041 erg s-1), galaxy stellar mass (reaching 4 × 108 M, and rest-frame Hα equivalent width. The faintest galaxies are two times fainter in Hα luminosity than galaxies previously studied at z ∼ 1.5. An evolution is observed where galaxies of the same Hα luminosity have lower extinction at higher redshifts, whereas no evolution is found within our error bars with stellar mass. The lower Hα luminosity galaxies in our sample are found to be consistent with no dust extinction. We find an anti-correlation of the [O III] λ5007/Hα flux ratio as a function of luminosity where galaxies with L Hα < 5 × 1041 erg s-1 are brighter in [O III] λ5007 than Hα. This trend is evident even after extinction correction, suggesting that the increased [O III] λ5007/Hα ratio in low-luminosity galaxies is likely due to lower metallicity and/or higher ionization parameters. © 2013. The American Astronomical Society. All rights reserved..