Abstract
How and when did galaxies form and assemble their stars and stellar mass? The answer to these questions, so crucial to astrophysics and cosmology, requires the full reconstruction of the ...so-called cosmic star formation rate density (SFRD), i.e., the evolution of the average star formation rate per unit volume of the universe. While the SFRD has been reliably traced back to 10–11 billion years ago, its evolution is still poorly constrained at earlier cosmic epochs, and its estimate is mainly based on galaxies luminous in the ultraviolet and with low obscuration by dust. This limited knowledge is largely due to the lack of an unbiased census of all types of star-forming galaxies in the early universe. We present a new approach to finding dust-obscured star-forming galaxies based on their emission at radio wavelengths coupled with the lack of optical counterparts. Here, we present a sample of 197 galaxies selected with this method. These systems were missed by previous surveys at optical and near-infrared wavelengths, and 22 of them are at very high redshift (i.e.,
z
> 4.5). The contribution of these elusive systems to the SFRD is substantial and can be as high as 40% of the previously known SFRD based on UV-luminous galaxies. The mere existence of such heavily obscured galaxies in the first two billion years after the Big Bang opens new avenues to investigate the early phases of galaxy formation and evolution, and to understand the links between these systems and the massive galaxies that ceased their star formation at later cosmic times.
Abstract
The star formation rate density (SFRD) history of the universe is well constrained up to redshift
z
∼ 2. At earlier cosmic epochs, the picture has been largely inferred from UV-selected ...galaxies (e.g., Lyman-break galaxies; LBGs). However, the inferred star formation rates of LBGs strongly depend on the assumed dust extinction correction, which is not well constrained at high
z
, while observations in the radio domain are not affected by this issue. In this work we measure the SFRD from a 1.4 GHz selected sample of ∼600 galaxies in the GOODS-N field up to redshift ∼3.5. We take into account the contribution of active galactic nuclei from the infrared-radio correlation. We measure the radio luminosity function, fitted with a modified Schechter function, and derive the SFRD. The cosmic SFRD shows an increase up to
z
∼ 2 and then an almost flat plateau up to
z
∼ 3.5. Our SFRD is in agreement with those from other far-IR/radio surveys and a factor 2 higher than those from LBG samples. We also estimate that galaxies lacking a counterpart in the HST/WFC3
H
-band (
H-
dark) make up ∼25% of the
ϕ
-integrated SFRD relative to the full sample at
z
∼ 3.2, and up to 58% relative to LBG samples.
Abstract
About 12 billion years ago, the Universe was first experiencing light again after the dark ages, and galaxies filled the environment with stars, metals, and dust. How efficient was this ...process? How fast did these primordial galaxies form stars and dust? We can answer these questions by tracing the star formation rate density (SFRD) back to its widely unknown high-redshift tail, traditionally observed in the near-infrared (NIR), optical, and UV bands. Thus, objects with a large amount of dust were missing. We aim to fill this knowledge gap by studying radio-selected NIR-dark (RS-NIRdark) sources, i.e., sources not having a counterpart at UV-to-NIR wavelengths. We widen the sample of Talia et al. from 197 to 272 objects in the Cosmic Evolution Survey (COSMOS) field, including also photometrically contaminated sources, which were previously excluded. Another important step forward consists in the visual inspection of each source in the bands from
u
* to MIPS 24
μ
m. According to their “environment” in the different bands, we are able to highlight different cases of study and calibrate an appropriate photometric procedure for the objects affected by confusion issues. We estimate that the contribution of RS-NIRdark sources to the cosmic SFRD at 3 <
z
< 5 is ∼10%–25% of that based on UV-selected galaxies.
The mid-infrared-to-ultraviolet (0.1–10 μm) spectral energy distribution (SED) shapes of 407 X-ray-selected radio-quiet type 1 active galactic nuclei (AGN) in the wide-field ‘Cosmic Evolution Survey’ ...(COSMOS) have been studied for signs of evolution. For a sub-sample of 200 radio-quiet quasars with black hole mass estimates and host galaxy corrections, we studied their mean SEDs as a function of a broad range of redshift, bolometric luminosity, black hole mass and Eddington ratio, and compared them with the Elvis et al. (E94) type 1 AGN mean SED. We found that the mean SEDs in each bin are closely similar to each other, showing no statistical significant evidence of dependence on any of the analysed parameters. We also measured the SED dispersion as a function of these four parameters, and found no significant dependences. The dispersion of the XMM-COSMOS SEDs is generally larger than E94 SED dispersion in the ultraviolet, which might be due to the broader ‘window function’ for COSMOS quasars, and their X-ray-based selection.
We report a sizable class of type 1 active galactic nuclei (AGNs) with unusually weak near-infrared (1-3 Delta *mm) emission in the XMM-COSMOS type 1 AGN sample. The fraction of these 'hot-dust-poor' ...AGNs increases with redshift from 6% at low redshift (z < 2) to 20% at moderate high redshift (2 < z < 3.5). There is no clear trend of the fraction with other parameters: bolometric luminosity, Eddington ratio, black hole mass, and X-ray luminosity. The 3 Delta *mm emission relative to the 1 Delta *mm emission is a factor of 2-4 smaller than the typical Elvis et al. AGN spectral energy distribution (SED), which indicates a 'torus' covering factor of 2%-29%, a factor of 3-40 smaller than required by unified models. The weak hot dust emission seems to expose an extension of the accretion disk continuum in some of the source SEDs. We estimate the outer edge of their accretion disks to lie at (0.3-2.0) X 104 Schwarzschild radii, ~10-23 times the gravitational stability radii. Formation scenarios for these sources are discussed.
We present the physical extent of C ii 158 m line-emitting gas from 46 star-forming galaxies at z = 4-6 from the ALMA Large Program to INvestigate C ii at Early Times (ALPINE). Using exponential ...profile fits, we measure the effective radius of the C ii line ( ) for individual galaxies and compare them with the rest-frame ultraviolet (UV) continuum ( ) from Hubble Space Telescope images. The effective radius exceeds by factors of ∼2-3, and the ratio of increases as a function of Mstar. We do not find strong evidence that the C ii line, rest-frame UV, and far-infrared (FIR) continuum are always displaced over 1 kpc scale from each other. We identify 30% of isolated ALPINE sources as having an extended C ii component over 10 kpc scales detected at 4.1 -10.9 beyond the size of rest-frame UV and FIR continuum. One object has tentative rotating features up to ∼10 kpc, where the 3D model fit shows the rotating C ii-gas disk spread over 4 times larger than the rest-frame UV-emitting region. Galaxies with the extended C ii line structure have high star formation rate, high stellar mass (Mstar), low Ly equivalent width, and more blueshifted (redshifted) rest-frame UV metal absorption (Ly line), as compared to galaxies without such extended C ii structures. Although we cannot rule out the possibility that a selection bias toward luminous objects may be responsible for such trends, the star-formation-driven outflow also explains all these trends. Deeper observations are essential to test whether the extended C ii line structures are ubiquitous to high-z star-forming galaxies.
We present the first C II 158
μ
m luminosity function (LF) at
z
∼ 5 from a sample of serendipitous lines detected in the ALMA Large Program to INvestigate C II at Early times (ALPINE). A study of ...the 118 ALPINE pointings revealed several serendipitous lines. Based on their fidelity, we selected 14 lines for the final catalog. According to the redshift of their counterparts, we identified eight out of 14 detections as C II lines at
z
∼ 5, along with two as CO transitions at lower redshifts. The remaining four lines have an elusive identification in the available catalogs and we considered them as C II candidates. We used the eight confirmed C II and the four C II candidates to build one of the first C II LFs at
z
∼ 5. We found that 11 out of these 12 sources have a redshift very similar to that of the ALPINE target in the same pointing, suggesting the presence of overdensities around the targets. Therefore, we split the sample in two (a “clustered” and “field” subsample) according to their redshift separation and built two separate LFs. Our estimates suggest that there could be an evolution of the C II LF between
z
∼ 5 and
z
∼ 0. By converting the C II luminosity to the star-formation rate, we evaluated the cosmic star-formation rate density (SFRD) at
z
∼ 5. The clustered sample results in a SFRD ∼10 times higher than previous measurements from UV–selected galaxies. On the other hand, from the field sample (likely representing the average galaxy population), we derived a SFRD ∼1.6 higher compared to current estimates from UV surveys but compatible within the errors. Because of the large uncertainties, observations of larger samples will be necessary to better constrain the SFRD at
z
∼ 5. This study represents one of the first efforts aimed at characterizing the demography of C II emitters at
z
∼ 5 using a mm selection of galaxies.
Using moderate-resolution optical spectra from 58 background Lyman-break galaxies and quasars at z~ 2.3-3 within a 11'.5 x 13'.5 area of the COSMOS field (~ 1200 deg super(-2) projected area density ...or ~2.4h super(-1) Mpc mean transverse separation), we reconstruct a 3D tomographic map of the foreground Ly alpha forest absorption at 2.2 < z< 2.5 with an effective smoothing scale of epsilon sub(3D)approximate 2.5 h super(-1) Mpc comoving. Comparing with 61 coeval galaxies with spectroscopic redshifts in the same volume, we find that the galaxy positions are clearly biased toward regions with enhanced intergalactic medium (IGM) absorption in the tomographic map. We find an extended IGM overdensity with deep absorption troughs at z= 2.45 associated with a recently discovered galaxy protocluster at the same redshift. Based on simulations matched to our data, we estimate the enclosed dark matter mass within this IGM overdensity to be M sub(dm)(z=2.45 )=(1.1 + or - 0.6) x 10 super(14) h super(-1)M sub(middot in circle), and argue based on this mass and absorption strength that it will form at least one z~ 0 galaxy cluster with M (z=0)=(3 + or - 1.5) x 10 super(14)h super(-1)M sub(middot in circle), although its elongated nature suggests that it will likely collapse into two separate clusters. We also point out a compact overdensity of six MOSDEF galaxies at z= 2.30 within a r~ 1 h super(-1) radius and Delta z~ 0.006, which does not appear to have a large associated IGM overdensity. These results demonstrate the potential of Ly alpha forest tomography on larger volumes to study galaxy properties as a function of environment, as well as revealing the large-scale IGM overdensities associated with protoclusters or other features of large-scale structure.
We explore the simple inter-relationships between mass, star formation rate, and environment in the SDSS, zCOSMOS, and other deep surveys. We take a purely empirical approach in identifying those ...features of galaxy evolution that are demanded by the data and then explore the analytic consequences of these. We show that the differential effects of mass and environment are completely separable to z {approx} 1, leading to the idea of two distinct processes of 'mass quenching' and 'environment quenching'. The effect of environment quenching, at fixed over-density, evidently does not change with epoch to z {approx} 1 in zCOSMOS, suggesting that the environment quenching occurs as large-scale structure develops in the universe, probably through the cessation of star formation in 30%-70% of satellite galaxies. In contrast, mass quenching appears to be a more dynamic process, governed by a quenching rate. We show that the observed constancy of the Schechter M* and {alpha}{sub s} for star-forming galaxies demands that the quenching of galaxies around and above M* must follow a rate that is statistically proportional to their star formation rates (or closely mimic such a dependence). We then postulate that this simple mass-quenching law in fact holds over a much broader range of stellar mass (2 dex) and cosmic time. We show that the combination of these two quenching processes, plus some additional quenching due to merging naturally produces (1) a quasi-static single Schechter mass function for star-forming galaxies with an exponential cutoff at a value M* that is set uniquely by the constant of proportionality between the star formation and mass quenching rates and (2) a double Schechter function for passive galaxies with two components. The dominant component (at high masses) is produced by mass quenching and has exactly the same M* as the star-forming galaxies but a faint end slope that differs by {Delta}{alpha}{sub s} {approx} 1. The other component is produced by environment effects and has the same M* and {alpha}{sub s} as the star-forming galaxies but an amplitude that is strongly dependent on environment. Subsequent merging of quenched galaxies will modify these predictions somewhat in the denser environments, mildly increasing M* and making {alpha}{sub s} slightly more negative. All of these detailed quantitative inter-relationships between the Schechter parameters of the star-forming and passive galaxies, across a broad range of environments, are indeed seen to high accuracy in the SDSS, lending strong support to our simple empirically based model. We find that the amount of post-quenching 'dry merging' that could have occurred is quite constrained. Our model gives a prediction for the mass function of the population of transitory objects that are in the process of being quenched. Our simple empirical laws for the cessation of star formation in galaxies also naturally produce the 'anti-hierarchical' run of mean age with mass for passive galaxies, as well as the qualitative variation of formation timescale indicated by the relative {alpha}-element abundances.
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![The ALPINE–ALMA [C II] survey](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-6361/small "The ALPINE–ALMA [C II] survey")
