The ages, masses and star-formation rates of spectroscopically confirmed z~6 galaxies in CANDELS

Abstract

We report the results of a study exploring the stellar populations of 13 luminous (L>L*), spectroscopically confirmed, galaxies in the redshift interval 5.5<z<6.5, all with WFC3/IR and IRAC imaging from the HST/CANDELS and Spitzer/SEDS surveys. Based on fitting the observed photometry with SED templates covering a wide range of different star-formation histories, and a self consistent treatment of Lyman-alpha emission, we find that the derived stellar masses lie within the range 10^9 Msun < M*< 10^10 Msun and are robust to within a factor of two. In contrast, we confirm previous reports that the ages of the stellar populations are poorly constrained. Although the best-fitting models for three objects have ages >= 300 Myr, the degeneracies introduced by dust extinction mean that only two of these objects actually require a >300 Myr old stellar population to reproduce the observed photometry. Moreover, when considering only smoothly-varying star-formation histories, we observe a clear tension between the data and models such that a galaxy SED template with an old age is often chosen in order to try and fit objects with blue UV-slopes but red UV-to-optical colours. To break this tension we explore SED fitting with two-component models (burst plus on-going star-formation) and allow for nebular emission. On average, the inclusion of nebular emission leads to lower stellar-mass estimates (median offset 0.18 dex), moderately higher specific star-formation rates, and allows for a wider range of plausible stellar ages. However, based on our SED modelling, we find no strong evidence for extremely young ages in our sample (<50 Myr). Finally, considering all of the different star-formation histories explored, we find that the median best-fitting ages are of the order 200-300 Myr and that the objects with the tightest constraints indicate ages in the range 50-200 Myr (Abridged).

23 pages, 12 figures, for submission to MNRAS

References in corpus (7)

• On the X-ray, optical emission line and black hole mass properties of local Seyfert galaxies
• The Subaru/XMM-Newton Deep Survey (SXDS) - II. Optical Imaging and Photometric Catalogs
• The luminosity function, halo masses and stellar masses of luminous Lyman-break galaxies at redshifts 5<z<6
• The flux ratio of the [OIII] 5007,4959 lines in AGN: Comparison with theoretical calculations
• The Stellar Mass Density at z~6 from Spitzer Imaging of i-drop Galaxies
• Constructing Merger Trees that Mimic N-Body Simulations
• Mapping the Dark Matter From UV Light at High Redshift: An Empirical Approach to Understand Galaxy Statistics

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