VANDELS is a deep spectroscopic survey, performed with the VIMOS instrument at VLT, aimed at studying in detail the physical properties of high-redshift galaxies. VANDELS targeted ~2100 sources at 1 ...<
z <
6.5 in the CANDELS
Chandra
Deep-Field South (CDFS) and Ultra-Deep Survey (UDS) fields. In this paper, we present the public release of the spectroscopic measurement catalogues from this survey, featuring emission and absorption line centroids, fluxes, and rest-frame equivalent widths obtained through a Gaussian fit, as well as a number of atomic and molecular indices (e.g. Lick) and continuum breaks (e.g. D4000), and including a correction to be applied to the error spectra. We describe the measurement methods and the validation of the codes that were used.
Aims. The aim of this work is to study the contribution of the Lyα emitters to the star formation rate density (SFRD) of the Universe in the interval 2 < z < 6.6. Methods. We assembled a sample of ...217 Lyα emitters (LAE) from the Vimos-VLT Deep Survey (VVDS) with secure spectroscopic redshifts in the redshift range 2 < z < 6.62 and fluxes down to F ~ 1.5 × 10-18 erg/s/cm2. Of those Lyα emitters, 133 are serendipitous identifications in the 22 arcmin2 total slit area surveyed with the VVDS-Deep and the 3.3 arcmin2 from the VVDS Ultra-Deep survey, and 84 are targeted identifications in the 0.62 deg2 surveyed with the VVDS-DEEP and 0.16 deg2 from the Ultra-Deep survey. Among the serendipitous targets we estimate that 90% of the emission lines are most probably Lyα, while the remaining 10% could be either OII3727 or Lyα. We computed the luminosity function (LF) and derived the star-formation rate density using this sample of LAE. Results. The VVDS-LAE sample reaches faint line fluxes F(Lyα) = 1.5 × 10-18 erg/s/cm2 (corresponding to L(Lyα) ~ 1041 erg/s at z ~ 3), allows the faint-end slope of the luminosity function to be constrained to α ~ −1.6 ± 0.12 at redshift z ~ 2.5 and to \hbox{$\alpha\sim-1.78^{0.10}_{-0.12}$}α~−1.78-0.120.10 at redshift ~4, placing trends found in previous LAE studies on firm statistical grounds, and indicating that sub-L ∗ LAE (LLy − α ≲ 1042.5 erg/s) contribute significantly to the SFRD. The projected number density and volume density of faint LAE in 2 ≤ z ≤ 6.6 with F > 1.5 × 10-18 erg/s/cm2 are 33 galaxies/arcmin2 and ~4 × 10-2 Mpc-3, respectively. We find that the observed luminosity function (LF) of LAEs does not evolve from z = 2 to z = 6. This implies that, after correction for the redshift-dependent IGM absorption, the intrinsic luminosity function must have evolved significantly over 3 Gyr. The SFRD from LAE contributes around 20% of the SFRD at z = 2−3, while the LAE appear to be the dominant source of star formation producing ionizing photons in the early universe z ~ > 5−6, equivalent to Lyman Break galaxies.
Context. The advent of deep, multi-wavelength surveys, together with the availability of extensive numerical simulations, now allow us for the systematic search and study of (proto)clusters and their ...surrounding environment as a function of redshift. Aims. We aim to define the environment and to identify overdensities in the VANDELS Chandra Deep Field-South (CDFS) and UKIDSS Ultra Deep Survey (UDS) fields. We want to investigate whether we can use Lyα emission to obtain additional information of the environment properties and whether Lyα emitters show different characteristics as a function of their environment. Methods. We estimated local densities using a three-dimensional algorithm which works in the RA-dec-redshift space. We took advantage of the physical parameters of all the sources in the VANDELS fields to study their properties as a function of environment. In particular, we focused on the rest-frame U − V color to evaluate the stage of evolution of the galaxies located in the overdensities and in the field. Then we selected a sample of 131 Lyα-emitting galaxies (EW(Lyα) > 0 Å), unbiased with respect to environmental density, from the first two seasons of the VANDELS survey to study their location with respect to the over- or under-dense environment and infer whether they are useful tracers of overdense regions. Results. We identify 13 (proto)cluster candidates in the CDFS and nine in the UDS at 2 < z < 4, based on photometric and spectroscopic redshifts from VANDELS and from all the available literature. No significant difference is observed in the rest-frame U − V color between field and galaxies located within the identified overdensities, but the star-forming galaxies in overdense regions tend to be more massive and to have low specific SFRs than in the field. We study the distribution of the VANDELS Lyα emitters (LAEVs) and we find that Lyα emitters lie preferentially outside of overdense regions as the majority of the galaxies with spectroscopic redshifts from VANDELS. The LAEVs in overdense regions tend to have low Lyα equivalent widths and low specific SFRs, and they also tend to be more massive than the LAEVs in the field. Their stacked Lyα profile shows a dominant red peak and a hint of a blue peak. There is evidence that their Lyα emission is more extended and offset with respect to the UV continuum. Conclusions. LAEVs are likely to be influenced by the environment. In fact, our results favour a scenario that implies outflows of low expansion velocities and high HI column densities for galaxies in overdense regions. An outflow with low expansion velocity could be related to the way galaxies are forming stars in overdense regions; the high HI column density can be a consequence of the gravitational potential of the overdensity. Therefore, Lyα-emitting galaxies can provide useful insights on the environment in which they reside.
Aims. We use the first release of the VImos Public Extragalactic Redshift Survey of galaxies (VIPERS) of ~50 000 objects to measure the biasing relation between galaxies and mass in the redshift ...range z= 0.5,1.1 . Methods. We estimate the 1-point distribution function PDF of VIPERS galaxies from counts in cells and, assuming a model for the mass PDF, we infer their mean bias relation. The reconstruction of the bias relation is performed through a novel method that accounts for Poisson noise, redshift distortions, inhomogeneous sky coverage. and other selection effects. With this procedure we constrain galaxy bias and its deviations from linearity down to scales as small as 4 h super(-1) Mpcand out to z= 1.1. Results. We detect small (up to 2%) but statistically significant (up to 3sigma) deviations from linear bias. The mean biasing function is close to linear in regions above the mean density. The mean slope of the biasing relation is a proxy to the linear bias parameter. This slope increases with luminosity, which is in agreement with results of previous analyses. We detect a strong bias evolution only for z> 0.9, which is in agreement with some, but not all, previous studies. We also detect a significant increase of the bias with the scale, from 4 to 8 h super(-1) Mpc, now seen for the first time out to z= 1. The amplitude of non-linearity depends on redshift, luminosity, and scale, but no clear trend is detected. Owing to the large cosmic volume probed by VIPERS, we find that the mismatch between the previous estimates of bias at z~ 1 from zCOSMOS and VVDS-Deep galaxy samples is fully accounted for by cosmic variance. Conclusions. The results of our work confirm the importance of going beyond the over-simplistic linear bias hypothesis showing that non-linearities can be accurately measured through the applications of the appropriate statistical tools to existing datasets like VIPERS.
The ALPINE-ALMA [CII] survey Ginolfi, M; Jones, G C; Béthermin, M ...
Astronomy and astrophysics (Berlin),
11/2020, Letnik:
643
Journal Article
Recenzirano
Odprti dostop
We present ALMA observations of a merging system at z ∼ 4.57, observed as a part of the ALMA Large Program to INvestigate CII at Early times (ALPINE) survey. Combining ALMA CII158 μm and far-infrared ...continuum data with multi-wavelength ancillary data, we find that the system is composed of two massive (M⋆ ≳ 1010 M⊙) star-forming galaxies experiencing a major merger (stellar mass ratio rmass ≳ 0.9) at close spatial (∼13 kpc; projected) and velocity (Δv < 300 km s−1) separations, and two additional faint narrow CII-emitting satellites. The overall system belongs to a larger scale protocluster environment and is coincident to one of its overdensity peaks. Additionally, ALMA reveals the presence of CII emission arising from a circumgalactic gas structure, extending up to a diameter-scale of ∼30 kpc. Our morpho-spectral decomposition analysis shows that about 50% of the total flux resides between the individual galaxy components, in a metal-enriched gaseous envelope characterised by a disturbed morphology and complex kinematics. Similarly to observations of shock-excited CII emitted from tidal tails in local groups, our results can be interpreted as a possible signature of interstellar gas stripped by strong gravitational interactions, with a possible contribution from material ejected by galactic outflows and emission triggered by star formation in small faint satellites. Our findings suggest that mergers could be an efficient mechanism of gas mixing in the circumgalactic medium around high-z galaxies, and thus play a key role in the galaxy baryon cycle at early epochs.
We compare three methods to measure the count-in-cell probability density function of galaxies in a spectroscopic redshift survey. From this comparison we found that, when the sampling is low (the ...average number of object per cell is around unity), it is necessary to use a parametric method to model the galaxy distribution. We used a set of mock catalogues of VIPERS to verify if we were able to reconstruct the cell-count probability distribution once the observational strategy is applied. We find that, in the simulated catalogues, the probability distribution of galaxies is better represented by a Gamma expansion than a skewed log-normal distribution. Finally, we correct the cell-count probability distribution function from the angular selection effect of the VIMOS instrument and study the redshift and absolute magnitude dependency of the underlying galaxy density function in VIPERS from redshift 0.5 to 1.1. We found a very weak evolution of the probability density distribution function and that it is well approximated by a Gamma distribution, independently of the chosen tracers.
We exploit the synergy between low-resolution spectroscopy and photometric redshifts to study environmental effects on galaxy
evolution in slitless spectroscopic surveys from space. As a test case, ...we consider the future Euclid Deep survey (∼40 deg2), which combines a slitless spectroscopic survey limited at Hα flux ≥5 × 10−17 erg cm−2 s−1 and a photometric survey limited in H band (H ≤ 26). We use Euclid-like galaxy mock catalogues, in which we anchor the photometric redshifts to the 3D galaxy distribution of the available spectroscopic redshifts. We then estimate the local density contrast by counting objects in cylindrical cells with radius from 1 to 10 h
−1Mpc, over the redshift range 0.9 < z < 1.8. We compare this density field with the one computed in a mock catalogue with the same depth as the Euclid Deep survey (H = 26) but without redshift measurement errors. We find that our method successfully separates high- from low-density environments (the last from the first quintile of the density distribution), with higher efficiency at low redshift and large cells: the fraction of low-density regions mistaken by high-density peaks is <1 per cent for all scales and redshifts explored, but for scales of 1 h
−1Mpc for which is a few per cent. These results show that we can efficiently study environment in photometric samples if spectroscopic information is available for a smaller sample of objects that sparsely samples the same volume. We demonstrate that these studies are possible in the Euclid Deep survey, i.e. in a redshift range in which environmental effects are different from those observed in the local Universe, hence providing new constraints for galaxy evolution models.
Aims. Strong He II emission is produced by low-metallicity stellar populations. Here, we aim to identify and study a sample of He IIλ1640-emitting galaxies at redshifts of z ∼ 2.5 − 5 in the deep ...VANDELS spectroscopic survey. Methods. We identified a total of 33 Bright He II emitters (S/N > 2.5) and 17 Faint emitters (S/N < 2.5) in the VANDELS survey and used the available deep multi-wavelength data to study their physical properties. After identifying seven potential AGNs in our sample and discarding them from further analysis, we divided the sample of Bright emitters into 20 Narrow (FWHM < 1000 km s−1) and 6 Broad (FWHM > 1000 km s−1) He II emitters. We created stacks of Faint, Narrow, and Broad emitters and measured other rest-frame UV lines such as O III and C III in both individual galaxies and stacks. We then compared the UV line ratios with the output of stellar population-synthesis models to study the ionising properties of He II emitters. Results. We do not see a significant difference between the stellar masses, star-formation rates, and rest-frame UV magnitudes of galaxies with He II and no He II emission. The stellar population models reproduce the observed UV line ratios from metals in a consistent manner, however they under-predict the total number of He II ionising photons, confirming earlier studies and suggesting that additional mechanisms capable of producing He II are needed, such as X-ray binaries or stripped stars. The models favour subsolar metallicities (∼0.1 Z⊙) and young stellar ages (106 − 107 years) for the He II emitters. However, the metallicity measured for He II emitters is comparable to that of non-He II emitters at similar redshifts. We argue that galaxies with He II emission may have undergone a recent star-formation event, or may be powered by additional sources of He II ionisation.
Building on the two-point correlation function analysis of the VIMOS Public Extragalactic Redshift Survey (VIPERS), we investigate the higher-order correlation properties of the same galaxy samples ...to test the hierarchical scaling hypothesis at z ~ 1 and the dependence on galaxy luminosity, stellar mass, and redshift. With this work we also aim to assess possible deviations from the linearity of galaxy bias independently from a previously performed analysis of our survey. The results are compatible with a null nonlinear bias term, but taking into account another analysis for VIPERS and the analysis of other surveys, we argue that there is evidence for a small but nonzero nonlinear bias term.
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