We estimate the galaxy stellar mass function and stellar mass density for star-forming and quiescent galaxies with 0.2 < z < 4. We construct a large, deep (Ks < 24) sample of 220 000 galaxies ...selected using the new UltraVISTA DR1 data release. Our analysis is based on precise 30-band photometricredshifts. By comparing these photometric redshifts with 10,800 spectroscopic redshifts from the zCOSMOS bright and faint surveys, we find a precision of σΔz/(1 + z) = 0.008 at i+ < 22.5 and σΔz/(1 + z) = 0.03 at 1.5 < z < 4. We derive the stellar mass function and correct for the Eddington bias. We find a mass-dependent evolution of the global and star-forming populations, with the low-mass end of the mass functions evolving more rapidly than the high-mass end. This mass-dependent evolution is a direct consequence of the star formation being “quenched” in galaxies more massive than ℳ ≳ 1010.7 − 10.9ℳ⊙. For the mass function of the quiescent galaxies, we do not find any significant evolution of the high-mass end at z < 1; however we observe a clear flattening of the faint-end slope. From z ~ 3 to z ~ 1, the density of quiescent galaxies increases over the entire mass range. Their comoving stellar mass density increases by 1.6 dex between z ~ 3 and z ~ 1 and by less than 0.2 dex at z < 1. We infer the star formation history from the mass density evolution. This inferred star formation history is in excellent agreement with instantaneous star formation rate measurements at z < 1.5, while we find differences of 0.2 dex at z > 1.5 consistent with the expected uncertainties. We also develop a new method to infer the specific star formation rate from the mass function of star-forming galaxies. We find that the specific star formation rate of 1010 − 10.5ℳ⊙ galaxies increases continuously in the redshift range 1 < z < 4. Finally, we compare our results with a semi-analytical model and find that these models overestimate the density of low mass quiescent galaxies by an order of magnitude, while the density of low-mass star-forming galaxies is successfully reproduced.
STRUCTURAL PARAMETERS OF GALAXIES IN CANDELS van der Wel, A; Bell, E F; Haussler, B ...
The Astrophysical journal. Supplement series,
12/2012, Letnik:
203, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We present global structural parameter measurements of 109,533 unique, H sub(F160W)-selected objects from the CANDELS multi-cycle treasury program. Sersic model fits for these objects are produced ...with GALFIT in all available near-infrared filters (H sub(F160W), J sub(F125W) and, for a subset, Y sub(F105W)). The parameters of the best-fitting Sersic models (total magnitude, half-light radius, Sersic index, axis ratio, and position angle) are made public, along with newly constructed point-spread functions for each field and filter. Random uncertainties in the measured parameters are estimated for each individual object based on a comparison between multiple, independent measurements of the same set of objects. To quantify systematic uncertainties, we create a mosaic with simulated galaxy images with a realistic distribution of input parameters and then process and analyze the mosaic in an identical manner as the real data. We find that accurate and precise measurements-to 10% or better-of all structural parameters can typically be obtained for galaxies with H sub(F160W) < 23, with comparable fidelity for basic size and shape measurements for galaxies to H sub(F160W) ~ 24.5.
Context.
How galaxies form, assemble, and cease their star formation is a central question within the modern landscape of galaxy evolution studies. These processes are indelibly imprinted on the ...galaxy stellar mass function (SMF), and its measurement and understanding is key to uncovering a unified theory of galaxy evolution.
Aims.
We present constraints on the shape and evolution of the galaxy SMF, the quiescent galaxy fraction, and the cosmic stellar mass density across 90% of the history of the Universe from
z
= 7.5 → 0.2 as a means to study the physical processes that underpin galaxy evolution.
Methods.
The COSMOS survey is an ideal laboratory for studying representative galaxy samples. Now equipped with deeper and more homogeneous near-infrared coverage exploited by the COSMOS2020 catalog, we leverage the large 1.27 deg
2
effective area to improve sample statistics and understand spatial variations (cosmic variance) – particularly for rare, massive galaxies – and push to higher redshifts with greater confidence and mass completeness than previous studies. We divide the total stellar mass function into star-forming and quiescent subsamples through
NUVrJ
color-color selection. The measurements are then fit with single- and double-component Schechter functions to infer the intrinsic galaxy stellar mass function, the evolution of its key parameters, and the cosmic stellar mass density out to
z
= 7.5. Finally, we compare our measurements to predictions from state-of-the-art cosmological simulations and theoretical dark matter halo mass functions.
Results.
We find a smooth, monotonic evolution in the galaxy stellar mass function since
z
= 7.5, in general agreement with previous studies. The number density of star-forming systems have undergone remarkably consistent growth spanning four decades in stellar mass from
z
= 7.5 → 2 whereupon high-mass systems become predominantly quiescent (“downsizing”). Meanwhile, the assembly and growth of low-mass quiescent systems only occurred recently, and rapidly. An excess of massive systems at
z
≈ 2.5 − 5.5 with strikingly red colors, with some being newly identified, increase the observed number densities to the point where the SMF cannot be reconciled with a Schechter function.
Conclusions.
Systematics including cosmic variance and/or active galactic nuclei contamination are unlikely to fully explain this excess, and so we speculate that they may be dust-obscured populations similar to those found in far infrared surveys. Furthermore, we find a sustained agreement from
z
≈ 3 − 6 between the stellar and dark matter halo mass functions for the most massive systems, suggesting that star formation in massive halos may be more efficient at early times.
We present the first results from a near-IR spectroscopic survey of the COSMOS field, using the Fiber Multi-Object Spectrograph on the Subaru telescope, designed to characterize the star-forming ...galaxy population at 1.4 < z < 1.7. The high-resolution mode is implemented to detect Hα in emission between 1.6-1.8 μm with f {sub Hα} ∼> 4 × 10{sup –17} erg cm{sup –2} s{sup –1}. Here, we specifically focus on 271 sBzK-selected galaxies that yield a Hα detection thus providing a redshift and emission line luminosity to establish the relation between star formation rate and stellar mass. With further J-band spectroscopy for 89 of these, the level of dust extinction is assessed by measuring the Balmer decrement using co-added spectra. We find that the extinction (0.6 ∼< A {sub Hα} ∼< 2.5) rises with stellar mass and is elevated at high masses compared to low-redshift galaxies. Using this subset of the spectroscopic sample, we further find that the differential extinction between stellar and nebular emission E {sub star}(B – V)/E {sub neb}(B – V) is 0.7-0.8, dissimilar to that typically seen at low redshift. After correcting for extinction, we derive an Hα-based main sequence with a slope (0.81 ± 0.04) and normalization similar to previous studies at these redshifts.
We investigate the relationships between stellar mass, gas-phase oxygen abundance (metallicity), star formation rate (SFR), and dust content of star-forming galaxies at z ~ 1.6 using Subaru/FMOS ...spectroscopy in the COSMOS field. The mass-metallicity (MZ) relation at z ~ 1.6 is steeper than the relation observed in the local universe. The steeper MZ relation at z ~ 1.6 is mainly due to evolution in die stellar mass where the MZ relation begins to turnover and flatten. This turnover mass is 1.2 dex larger at z ~ 1.6. The most massive galaxies at z ~ 1.6(~10 super(11) M sub(middot in circle)) are enriched to the level observed in massive galaxies in the local universe. The MZ relation we measure at z ~ 1.6 supports the suggestion of an empirical upper metallicity limit that does not significantly evolve with redshift. We find an anti-correlation between metallicity and SFR for galaxies at a fixed stellar mass at z ~ 1.6, which is similar to trends observed in the local universe. We do not find a relation between stellar mass, metallicity, and SFR that is independent of redshift; rather, our data suggest that there is redshift evolution in this relation. We examine the relation between stellar mass, metallicity, and dust extinction, and find that at a fixed stellar mass, dustier galaxies tend to be more metal rich. From examination of the stellar masses, metallicities, SFRs, and dust extinctions, we conclude that stellar mass is most closely related to dust extinction.
This paper presents a new search for
z
≥ 7.5 galaxies using the COSMOS2020 photometric catalogues. Finding galaxies at the reionisation epoch through deep imaging surveys remains observationally ...challenging. The larger area covered by ground-based surveys such as COSMOS enables the discovery of the brightest galaxies at these high redshifts. Covering 1.4 deg
2
, our COSMOS catalogues were constructed from the latest UltraVISTA data release (DR4) combined with the final
Spitzer
/IRAC COSMOS images and the Hyper-Suprime-Cam Subaru Strategic Program DR2 release. We identified 17 new 7.5 <
z
< 10 candidate sources, and confirm 15 previously published candidates. Using deblended photometry extracted by fitting surface brightness models on multi-band images, we selected four candidates which would be rejected using fixed aperture photometry. We tested the robustness of all our candidates by comparing six different photometric redshift estimates. Finally, we computed the galaxy UV luminosity function in three redshift bins centred at
z
= 8, 9, 10. We find no clear evolution of the number density of the brightest galaxies
M
UV
< −21.5, in agreement with previous works. Rapid changes in the quenching efficiency or attenuation by dust could explain such a lack of evolution between
z
∼ 8 and
z
∼ 9. A spectroscopic confirmation of the redshifts, already planned with JWST and the Keck telescopes, will be essential to confirm our results.
ABSTRACT Local starbursts have a higher efficiency of converting gas into stars, as compared to typical star-forming galaxies at a given stellar mass, possibly indicative of different modes of star ...formation. With the peak epoch of galaxy formation occurring at z > 1, it remains to be established whether such an efficient mode of star formation is occurring at high redshift. To address this issue, we measure the molecular gas content of seven high-redshift (z ∼ 1.6) starburst galaxies with the Atacama Large Millimeter/submillimeter Array and IRAM/Plateau de Bure Interferometer. Our targets are selected from the sample of Herschel far-infrared-detected galaxies having star formation rates (∼300-800 M yr−1) elevated ( 4×) above the star-forming main sequence (MS) and included in the FMOS-COSMOS near-infrared spectroscopic survey of star-forming galaxies at z ∼ 1.6 with Subaru. We detect CO emission in all cases at high levels of significance, indicative of high gas fractions (∼30%-50%). Even more compelling, we firmly establish with a clean and systematic selection that starbursts, identified as MS outliers, at high redshift generally have a lower ratio of CO to total infrared luminosity as compared to typical MS star-forming galaxies, although with a smaller offset than expected based on past studies of local starbursts. We put forward a hypothesis that there exists a continuous increase in star formation efficiency with elevation from the MS with galaxy mergers as a possible physical driver. Along with a heightened star formation efficiency, our high-redshift sample is similar in other respects to local starbursts, such as being metal rich and having a higher ionization state of the interstellar medium.
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