We present the correlations between stellar mass, star formation rate (SFR) and [NII]/Ha flux ratio as indicator of gas-phase metallicity for a sample of 222 galaxies at 0.8 < z < 2.6 and log(M*/Msun)=9.0-11.5 from the LUCI, SINS/zC-SINF and KMOS3D surveys. This sample provides a unique analysis of the mass-metallicity relation (MZR) over an extended redshift range using consistent data analysis techniques and strong-line metallicity indicator. We find a constant slope at the low-mass end of the relation and can fully describe its redshift evolution through the evolution of the characteristic turnover mass where the relation begins to flatten at the asymptotic metallicity. At fixed mass and redshift, our data do not show a correlation between the [NII]/Ha ratio and SFR, which disagrees with the 0.2-0.3dex offset in [NII]/Ha predicted by the fundamental relation between stellar mass, SFR and metallicity discussed in recent literature. However, the overall evolution towards lower [NII]/Ha at earlier times does broadly agree with these predictions.
We analyze the resolved stellar populations of 473 massive star-forming galaxies at 0.7 < z < 1.5, with multi-wavelength broad-band imaging from CANDELS and Halpha surface brightness profiles at the same kiloparsec resolution from 3D-HST. Together, this unique data set sheds light on how the assembled stellar mass is distributed within galaxies, and where new stars are being formed. We find the Halpha morphologies to resemble more closely those observed in the ACS I band than in the WFC3 H band, especially for the larger systems. We next derive a novel prescription for Halpha dust corrections, which accounts for extra extinction towards HII regions. The prescription leads to consistent SFR estimates and reproduces the observed relation between the Halpha/UV luminosity ratio and visual extinction, both on a pixel-by-pixel and on a galaxy-integrated level. We find the surface density of star formation to correlate with the surface density of assembled stellar mass for spatially resolved regions within galaxies, akin to the so-called main sequence of star formation established on a galaxy-integrated level. Deviations from this relation towards lower equivalent widths are found in the inner regions of galaxies. Clumps and spiral features, on the other hand, are associated with enhanced Halpha equivalent widths, bluer colors, and higher specific star formation rates compared to the underlying disk. Their Halpha/UV luminosity ratio is lower than that of the underlying disk, suggesting the ACS clump selection preferentially picks up those regions of elevated star formation activity that are the least obscured by dust. Our analysis emphasizes that monochromatic studies of galaxy structure can be severely limited by mass-to-light ratio variations due to dust and spatially inhomogeneous star formation histories.
We perform a detailed analysis of the resolved colors and stellar populations of a complete sample of 323 star-forming galaxies at 0.5 < z < 1.5, and 326 star-forming galaxies at 1.5 < z < 2.5 in the ERS and CANDELS-Deep region of GOODS-South. Galaxies were selected to be more massive than 10^10 Msun and have specific star formation rates above 1/t_H. We model the 7-band optical ACS + near-IR WFC3 spectral energy distributions of individual bins of pixels, accounting simultaneously for the galaxy-integrated photometric constraints available over a longer wavelength range. We analyze variations in rest-frame color, stellar surface mass density, age, and extinction as a function of galactocentric radius and local surface brightness/density, and measure structural parameters on luminosity and stellar mass maps. We find evidence for redder colors, older stellar ages, and increased dust extinction in the nuclei of galaxies. Big star-forming clumps seen in star formation tracers are less prominent or even invisible on the inferred stellar mass distributions. Off-center clumps contribute up to ~20% to the integrated SFR, but only 7% or less to the integrated mass of all massive star-forming galaxies at z ~ 1 and z ~ 2, with the fractional contributions being a decreasing function of wavelength used to select the clumps. The stellar mass profiles tend to have smaller sizes and M20 coefficients, and higher concentration and Gini coefficients than the light distribution. Our results are consistent with an inside-out disk growth scenario with brief (100 - 200 Myr) episodic local enhancements in star formation superposed on the underlying disk. Alternatively, the young ages of off-center clumps may signal inward clump migration, provided this happens efficiently on the order of an orbital timescale.
We analyze the dependence of galaxy structure (size and Sersic index) and mode of star formation (Sigma_SFR and SFR_IR/SFR_UV) on the position of galaxies in the SFR versus Mass diagram. Our sample comprises roughly 640000 galaxies at z~0.1, 130000 galaxies at z~1, and 36000 galaxies at z~2. Structural measurements for all but the z~0.1 galaxies were based on HST imaging, and SFRs are derived using a Herschel-calibrated ladder of SFR indicators. We find that a correlation between the structure and stellar population of galaxies (i.e., a Hubble sequence) is already in place since at least z~2.5. At all epochs, typical star-forming galaxies on the main sequence are well approximated by exponential disks, while the profiles of quiescent galaxies are better described by de Vaucouleurs profiles. In the upper envelope of the main sequence, the relation between the SFR and Sersic index reverses, suggesting a rapid build-up of the central mass concentration in these starbursting outliers. We observe quiescent, moderately and highly star-forming systems to co-exist over an order of magnitude or more in stellar mass. At each mass and redshift, galaxies on the main sequence have the largest size. The rate of size growth correlates with specific SFR, and so does Sigma_SFR at each redshift. A simple model using an empirically determined SF law and metallicity scaling, in combination with an assumed geometry for dust and stars is able to relate the observed Sigma_SFR and SFR_IR/SFR_UV, provided a more patchy dust geometry is assumed for high-redshift galaxies.
We compare multi-wavelength SFR indicators out to z~3 in GOODS-South. Our analysis uniquely combines U-to-8um photometry from FIREWORKS, MIPS 24um and PACS 70, 100, and 160um photometry from the PEP survey, and Ha spectroscopy from the SINS survey. We describe a set of
We investigate the star formation history of the universe using FIREWORKS, a multiwavelength survey of the CDFS. We study the evolution of the specific star formation rate (sSFR) with redshift in different mass bins from z = 0 to z ~ 3. We find that the sSFR increases with redshift for all masses. The logarithmic increase of the sSFR with redshift is nearly independent of mass, but this cannot yet be verified at the lowest-mass bins at z > 0.8, due to incompleteness. We convert the sSFRs to a dimensionless growth rate to facilitate a comparison with a semi-analytic galaxy formation model that was implemented on the Millennium Simulation. The model predicts that the growth rates and sSFRs increase similarly with redshift for all masses, consistent with the observations. However, we find that for all masses, the inferred observed growth rates increase more rapidly with redshift than the model predictions. We discuss several possible causes for this discrepancy, ranging from field-to-field variance,
We present a Ks-selected catalog, dubbed FIREWORKS, for the Chandra Deep Field South (CDFS) containing photometry in U_38, B_435, B, V, V_606, R, i_775, I, z_850, J, H, Ks, [3.6 um], [4.5 um], [5.8 um], [8.0 um], and the MIPS [24 um] band. The imaging has a typical Ks limit of 24.3 mag (5 sigma, AB) and coverage over 113 arcmin^2 in all bands and 138 arcmin^2 in all bands but H. We cross-correlate our catalog with the 1 Ms X-ray catalog by Giacconi et al. (2002) and with all available spectroscopic redshifts to date. We find and explain systematic differences in a comparison with the z_850 + Ks-selected GOODS-MUSIC catalog that covers ~90% of the field. We exploit the U38-to-24 micron photometry to determine which Ks-selected galaxies at 1.5<z<2.5 have the brightest total IR luminosities and which galaxies contribute most to the integrated total IR emission. The answer to both questions is that red galaxies are dominating in the IR. This is true no matter whether color is defined in the rest-frame UV, optical, or optical-to-NIR. We do find however that among the reddest galaxies in the rest-frame optical, there is a population of sources with only little mid-IR emission, suggesting a quiescent nature.
