UV-CONTINUUM SLOPES ATz∼ 4-7 FROM THE HUDF09+ERS+CANDELS OBSERVATIONS: DISCOVERY OF A WELL-DEFINED UV COLOR-MAGNITUDE RELATIONSHIP FORz⩾ 4 STAR-FORMING GALAXIES

Abstract

Ultra-deep Advanced Camera for Surveys (ACS) and WFC3/IR HUDF+HUDF09 data, along with the wide-area GOODS+ERS+CANDELS data over the CDF-S GOODS field, are used to measure UV colors, expressed as the UV-continuum slope β, of star-forming galaxies over a wide range of luminosity (0.1L * z=3 to 2L * z=3 ) at high redshift (z ∼ 7 to z ∼ 4). β is measured using all ACS and WFC3/IR passbands uncontaminated by Lyα and spectral breaks. Extensive tests show that our β measurements are only subject to minimal biases. Using a different selection procedure, Dunlop et al. recently found large biases in their β measurements. To reconcile these different results, we simulated both approaches and found that β measurements for faint sources are subject to large biases if the same passbands are used both to select the sources and to measure β. High-redshift galaxies show a well-defined restframe UV color-magnitude (CM) relationship that becomes systematically bluer toward fainter UV luminosities. No evolution is seen in the slope of the UV CM relationship in the first 1.5 Gyr, though there is a small evolution in the zero point to redder colors from z ∼ 7 to z ∼ 4. This suggests that galaxies are evolving along a well-defined sequence in the L UV -color (β) plane (a "star-forming sequence"?). Dust appears to be the principal factor driving changes in the UV color β with luminosity. These new larger β samples lead to improved dust extinction estimates at z ∼ 4-7 and confirm that the extinction is essentially zero at low luminosities and high redshifts. Inclusion of the new dust extinction results leads to (1) excellent agreement between the star formation rate (SFR) density at z ∼ 4-8 and that inferred from the stellar mass density; and (2) to higher specific star formation rates (SSFRs) at z 4, suggesting that the SSFR may evolve modestly (by factors of ∼2) from z ∼ 4-7 to z ∼ 2.

The circumgalactic medium of high-redshift galaxies

“…Our simulation reproduces the observed cosmic star formation rate (Bouwens et al 2012) and stellar mass densities (González et al 2011) for 4 z < ∼ 10. We define a galactic environment as a connected patch of enriched gas with metallicity exceeding a chosen threshold, i.e.…”

Galaxy formation in the Planck cosmology – I. Matching the observed evolution of star formation rates, colours and stellar masses

“…As in previous figures we show results for the new model of this paper as a solid red line, results for the model of as a dashed red line, and results for the model as a dotted red line. The observations are taken from COSMOS (Karim et al 2011), the Bouwens et al (2012) sample of Lyman-break galaxies, combined Herschel and HST H band-selected catalogues (Schreiber et al 2015) and the Behroozi et al (013a) compilation. The observed rate has a broad peak at relatively low redshift (z ∼ 2 to 3) and declines significantly by z = 0 but also to higher redshift.…”

Galactic outflow and diffuse gas properties at z ≥ 1 using different baryonic feedback models

“…The SFRD (in M⊙ yr −1 Mpc −3 ) is computed by summing over all the SF occurring in each simulation box at a time, and dividing it by the time-step interval and the box volume. Observational data ranges are shown as the grey shaded region, taken mainly from Cucciati et al (2012), and the compilations therein originally from Perez-Gonzalez et al Bouwens et al (2012). SN feedback clearly has a significant impact on the SFRD; compared to E35nw, SF is reduced by a factor of several in the other runs at z < 8.…”