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Register a new userGalaxy Stellar Mass Functions from z~10 to z~6 using the Deepest Spitzer/IRAC Data: No Significant Evolution in the Stellar-to-Halo Mass Ratio of Galaxies in the First Gyr of Cosmic Time
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We present new stellar mass functions at $zsim6$, $zsim7$, $zsim8$, $zsim9$ and, for the first time, $zsim10$, constructed from $sim800$ Lyman-Break galaxies previously identified over the XDF/UDF, parallels and the five CANDELS fields. Our study is distinctive due to (1) the much deeper ($sim200$ hour) wide-area Spitzer/IRAC imaging at $3.6mu$m and $4.5mu$m from the GOODS Re-ionization Era wide Area Treasury from Spitzer (GREATS) program and (2) consideration of $zsim6-10$ sources over a $3times$ larger area than previous HST+Spitzer studies. The Spitzer/IRAC data enable $ge2sigma$ rest-frame optical detections for an unprecedented $50%$ of galaxies down to a stellar mass limit of $sim10^{8}mathcal{M}_odot$ across all redshifts. Schechter fits to our volume densities suggest a combined evolution in characteristic mass $mathcal{M}^*$ and normalization factor $phi^*$ between $zsim6$ and $zsim8$. The stellar mass density (SMD) increases by $sim1000times$ in the $sim500$ Myr between $zsim10$ and $zsim6$, with indications of a steeper evolution between $zsim10$ and $zsim8$, similar to the previously-reported trend of the star-formation rate density. Strikingly, abundance matching to the Bolshoi-Planck simulation indicates halo mass densities evolving at approximately the same rate as the SMD between $zsim10$ and $zsim4$. Our results show that the stellar-to-halo mass ratios, a proxy for the star-formation efficiency, do not change significantly over the huge stellar mass build-up occurred from $zsim10$ to $zsim6$, indicating that the assembly of stellar mass closely mirrors the build-up in halo mass in the first $sim1$ Gyr of cosmic history. JWST is poised to extend these results into the first galaxy epoch at $zgtrsim10$.
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We investigate the cosmic evolution of the ratio between black hole mass (MBH) and host galaxy total stellar mass (Mstellar) out to z~2.5 for a sample of 100 X-ray-selected moderate-luminosity, broad-line active galactic nuclei (AGNs) in the Chandra-COSMOS Legacy Survey. By taking advantage of the deep multi-wavelength photometry and spectroscopy in the COSMOS field, we measure in a uniform way the galaxy total stellar mass using a SED decomposition technique and the black hole mass based on broad emission line measurements and single-epoch virial estimates. Our sample of AGN host galaxies has total stellar masses of 10^10-12Msun, and black hole masses of 10^7.0-9.5Msun. Combining our sample with the relatively bright AGN samples from the literature, we find no significant evolution of the MBH-Mstellar relation with black hole-to-host total stellar mass ratio of MBH/Mstellar~0.3% at all redshifts probed. We conclude that the average black hole-to-host stellar mass ratio appears to be consistent with the local value within the uncertainties, suggesting a lack of evolution of the MBH-Mstellar relation up to z~2.5.
We measure the evolution of the rest-frame UV luminosity function (LF) and the stellar mass function (SMF) of Lyman-alpha (Lya) emitters (LAEs) from z~2 to z~6 by exploring ~4000 LAEs from the SC4K sample. We find a correlation between Lya luminosity (LLya) and rest-frame UV (M_UV), with best-fit M_UV=-1.6+-0.2 log10(LLya/erg/s)+47+-12 and a shallower relation between LLya and stellar mass (Mstar), with best-fit log10( Mstar/Msun)=0.9+-0.1 log10(LLya/erg/s)-28+-4.0. An increasing LLya cut predominantly lowers the number density of faint M_UV and low Mstar LAEs. We estimate a proxy for the full UV LFs and SMFs of LAEs with simple assumptions of the faint end slope. For the UV LF, we find a brightening of the characteristic UV luminosity (M_UV*) with increasing redshift and a decrease of the characteristic number density (Phi*). For the SMF, we measure a characteristic stellar mass (Mstar*/Msun) increase with increasing redshift, and a Phi* decline. However, if we apply a uniform luminosity cut of log10 (LLya/erg/s) >= 43.0, we find much milder to no evolution in the UV and SMF of LAEs. The UV luminosity density (rho_UV) of the full sample of LAEs shows moderate evolution and the stellar mass density (rho_M) decreases, with both being always lower than the total rho_UV and rho_M of more typical galaxies but slowly approaching them with increasing redshift. Overall, our results indicate that both rho_UV and rho_M of LAEs slowly approach the measurements of continuum-selected galaxies at z>6, which suggests a key role of LAEs in the epoch of reionisation.
We derive stellar masses from SED fitting to rest-frame optical and UV fluxes for 401 star-forming galaxies at z 4, 5, and 6 from Hubble-WFC3/IR observations of the ERS combined with the deep GOODS-S Spitzer/IRAC data (and include a previously-published z 7 sample). A mass-luminosity relation with strongly luminosity-dependent M/Luv ratios is found for the largest sample (299 galaxies) at z 4. The relation M propto L_{UV,1500}^(1.7+/-0.2) has a well-determined intrinsic sample variance of 0.5 dex. This relation is also consistent with the more limited samples at z 5-7. This z 4 mass-luminosity relation, and the well-established faint UV luminosity functions at z 4-7, are used to derive galaxy mass functions (MF) to masses M~10^8 at z 4-7. A bootstap approach is used to derive the MFs to account for the large scatter in the M--Luv relation and the luminosity function uncertainties, along with an analytical crosscheck. The MFs are also corrected for the effects of incompleteness. The incompleteness-corrected MFs are steeper than previously found, with slopes alpha_M-1.4 to -1.6 at low masses. These slopes are, however, still substantially flatter than the MFs obtained from recent hydrodynamical simulations. We use these MFs to estimate the stellar mass density (SMD) of the universe to a fixed M_{UV,AB}<-18 as a function of redshift and find a SMD growth propto(1+z)^{-3.4 +/-0.8} from z 7 to z 4. We also derive the SMD from the completeness-corrected MFs to a mass limit M~10^{8} Msun. Such completeness-corrected MFs and the derived SMDs will be particularly important for model comparisons as future MFs reach to lower masses.
We reliably extend the stellar mass-size relation over $0.2leq z leq2$ to low stellar mass galaxies by combining the depth of Hubble Frontier Fields (HFF) with the large volume covered by CANDELS. Galaxies are simultaneously modelled in multiple bands using the tools developed by the MegaMorph project, allowing robust size (i.e., half-light radius) estimates even for small, faint, and high redshift galaxies. We show that above 10$^7$M$_odot$, star-forming galaxies are well represented by a single power law on the mass-size plane over our entire redshift range. Conversely, the stellar mass-size relation is steep for quiescent galaxies with stellar masses $geq 10^{10.3}$M$_odot$ and flattens at lower masses, regardless of whether quiescence is selected based on star-formation activity, rest-frame colours, or structural characteristics. This flattening occurs at sizes of $sim1$kpc at $zleq1$. As a result, a double power law is preferred for the stellar mass-size relation of quiescent galaxies, at least above 10$^7$M$_odot$. We find no strong redshift dependence in the slope of the relation of star-forming galaxies as well as of high mass quiescent galaxies. We also show that star-forming galaxies with stellar masses $geq$10$^{9.5}$M$_odot$ and quiescent galaxies with stellar masses $geq10^{10.3}$M$_odot$ have undergone significant size growth since $zsim2$, as expected; however, low mass galaxies have not. Finally, we supplement our data with predominantly quiescent dwarf galaxies from the core of the Fornax cluster, showing that the stellar mass-size relation is continuous below 10$^7$M$_odot$, but a more complicated functional form is necessary to describe the relation.
We study the evolution in the number density of the highest mass galaxies over $0.4<z<1.5$ (covering 9 Gyr). We use the Spitzer/HETDEX Exploratory Large-Area (SHELA) Survey, which covers 17.5 $mathrm{deg}^2$ with eight photometric bands spanning 0.3-4.5 $mu$m within the SDSS Stripe 82 field. This size produces the lowest counting uncertainties and cosmic variance yet for massive galaxies at $zsim1.0$. We study the stellar mass function (SMF) for galaxies with $log(M_ast/M_odot)>10.3$ using a forward-modeling method that fully accounts for statistical and systematic uncertainties on stellar mass. From $z$=0.4 to 1.5 the massive end of the SMF shows minimal evolution in its shape: the characteristic mass ($M^ast$) evolves by less than 0.1 dex ($pm$0.05 dex); the number density of galaxies with $log (M_ast/M_odot) >11$ stays roughly constant at $log (n/mathrm{Mpc}^{-3})$ $simeq$ $-$3.4 ($pm$0.05), then declines to $log (n/mathrm{Mpc}^{-3})$=$-$3.7 ($pm$0.05) at $z$=1.5. We discuss the uncertainties in the SMF, which are dominated by assumptions in the star formation history and details of stellar population synthesis models for stellar mass estimations. For quiescent galaxies, the data are consistent with no (or slight) evolution ($lesssim0.1$ dex) in the characteristic mass nor number density from $zsim 1.5$ to the present. This implies that any mass growth (presumably through dry mergers) of the quiescent massive galaxy population must balance the rate of mass losses from late-stage stellar evolution and the formation of quenching galaxies from the star-forming population. We provide a limit on this mass growth from $z=1.0$ to 0.4 of $Delta M_ast/M_astleq$ 45% (i.e., $simeq0.16$ dex) for quiescent galaxies more massive than $10^{11}$ $M_odot$.
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