ABSTRACT
We present a Bayesian full-spectral-fitting analysis of 75 massive ($M_* \gt 10^{10.3} \, \mathrm{M_\odot }$) UVJ-selected galaxies at redshifts of 1.0 < z < 1.3, combining extremely deep ...rest-frame ultraviolet spectroscopy from VANDELS with multiwavelength photometry. By the use of a sophisticated physical plus systematic uncertainties model, constructed within the bagpipes code, we place strong constraints on the star-formation histories (SFHs) of individual objects. We first constrain the stellar mass versus stellar age relationship, finding a steep trend towards earlier average formation time with increasing stellar mass (downsizing) of $1.48^{+0.34}_{-0.39}$ Gyr per decade in mass, although this shows signs of flattening at $M_* \gt 10^{11} \, \mathrm{M_\odot }$. We show that this is consistent with other spectroscopic studies from 0 < z < 2. This relationship places strong constraints on the AGN-feedback models used in cosmological simulations. We demonstrate that, although the relationships predicted by simba and illustristng agree well with observations at z = 0.1, they are too shallow at z = 1, predicting an evolution of ≲0.5 Gyr per decade in mass. Secondly, we consider the connections between green-valley, post-starburst, and quiescent galaxies, using our inferred SFH shapes and the distributions of galaxy physical properties on the UVJ diagram. The majority of our lowest-mass galaxies ($M_* \sim 10^{10.5} \, \mathrm{M_\odot }$) are consistent with formation in recent (z < 2), intense starburst events, with time-scales of ≲500 Myr. A second class of objects experience extended star-formation epochs before rapidly quenching, passing through both green-valley and post-starburst phases. The most massive galaxies in our sample are extreme systems: already old by z = 1, they formed at z ∼ 5 and quenched by z = 3. However, we find evidence for their continued evolution through both AGN and rejuvenated star-formation activity.
In this work, we compare the star formation rates (SFRs) and star formation histories (SFHs) of active galactic nucleus (AGN) and non-AGN galaxies. We explore these aspects across different density ...fields and over three orders of magnitude in X-ray luminosity ( L X ). For that purpose, we employed X-ray AGNs detected in the XMM-XXL field and constructed a galaxy control sample, using sources from the VIPERS catalogue. We applied strict photometric and quality selection criteria to ensure that only sources with robust (host) galaxy measurements were included in the analysis. Our final samples consist of 149 X-ray AGNs with 42 < log, L X ,2#x2212;10 keV (erg s −1 ) < 45 and 3488 non-AGN systems. The sources span a redshift range of 0.5 < z < 1.0 and have stellar masses within, 10.5 < log M * ( M ⊙ ) < 11.5. For these systems, we adopted the available measurements for their local densities and their spectral lines ( D n 4000) from the VIPERS catalogue. To compare the SFRs of these two populations, we calculated the SFR norm parameter. The latter is defined as the ratio of the SFRs of AGNs to the SFRs of non-AGN galaxies with similar M * and redshift. Our findings reveal that low- and moderate- L X AGNs (42 < log, L X ,2#x2212;10 keV (erg s −1 ) < 44) that reside in low-density fields have a nearly flat SFR norm - L X relation. In contrast, the AGNs of similar L X values that reside in high-density environments present an increase in SFR norm with L X . These results are in line with previous studies. Notably, our results suggest that the most luminous of the AGNs (log, L X ,2#x2212;10 keV (erg s −1 ) > 44) exhibit an increased SFR in comparison to non-AGN galaxies. This trend appears to be independent of the density of the environment. Furthermore, for AGNs with similar L X , those in high-density regions tend to have higher SFR norm values compared to their counterparts in low-density areas. Comparisons of the D n 4000 spectral index, which serves as a proxy for the age of the stellar population, reveals that low- and moderate- L X AGNs reside in galaxies with comparable stellar populations with non-AGN systems, regardless of the density field they are situated in. However, the most luminous X-ray sources tend to reside in galaxies that have younger stellar populations, as compared to non-AGN galaxies, regardless of the galaxy’s environment.
We unveil the complex shape of a proto-supercluster at z ∼ 2.45 in the COSMOS field exploiting the synergy of both spectroscopic and photometric redshifts. Thanks to the spectroscopic redshifts of ...the VIMOS Ultra-Deep Survey (VUDS), complemented by the zCOSMOS-Deep spectroscopic sample and high-quality photometric redshifts, we compute the three-dimensional (3D) overdensity field in a volume of ∼100 × 100 × 250 comoving Mpc3 in the central region of the COSMOS field, centred at z ∼ 2.45 along the line of sight. The method relies on a two-dimensional (2D) Voronoi tessellation in overlapping redshift slices that is converted into a 3D density field, where the galaxy distribution in each slice is constructed using a statistical treatment of both spectroscopic and photometric redshifts. In this volume, we identify a proto-supercluster, dubbed “Hyperion” for its immense size and mass, which extends over a volume of ∼60 × 60 × 150 comoving Mpc3 and has an estimated total mass of ∼4.8 × 1015 M⊙. This immensely complex structure contains at least seven density peaks within 2.4 ≲ z ≲ 2.5 connected by filaments that exceed the average density of the volume. We estimate the total mass of the individual peaks, Mtot, based on their inferred average matter density, and find a range of masses from ∼0.1 × 1014 M⊙ to ∼2.7 × 1014 M⊙. By using spectroscopic members of each peak, we obtain the velocity dispersion of the galaxies in the peaks, and then their virial mass Mvir (under the strong assumption that they are virialised). The agreement between Mvir and Mtot is surprisingly good, at less than 1−2σ, considering that (almost all) the peaks are probably not yet virialised. According to the spherical collapse model, these peaks have already started or are about to start collapsing, and they are all predicted to be virialised by redshift z ∼ 0.8−1.6. We finally perform a careful comparison with the literature, given that smaller components of this proto-supercluster had previously been identified using either heterogeneous galaxy samples (Lyα emitters, sub-mm starbursting galaxies, CO emitting galaxies) or 3D Lyα forest tomography on a smaller area. With VUDS, we obtain, for the first time across the central ∼1 deg2 of the COSMOS field, a panoramic view of this large structure, that encompasses, connects, and considerably expands in a homogeneous way on all previous detections of the various sub-components. The characteristics of this exceptional proto-supercluster, its redshift, its richness over a large volume, the clear detection of its sub-components, together with the extensive multi-wavelength imaging and spectroscopy granted by the COSMOS field, provide us the unique possibility to study a rich supercluster in formation.
Using spectroscopic observations taken for the Visible Multi-Object Spectrograph (VIMOS) Ultra-Deep Survey (VUDS) we report here on the discovery of PCl J1001+0220, a massive proto-cluster of ...galaxies located at zspec ~ 4.57 in the COSMOS field. With nine spectroscopic members, the proto-cluster was initially detected as a ~12σ spectroscopic overdensity of typical star-forming galaxies in the blind spectroscopic survey of the early universe (2 < z ≲ 6) performed by VUDS. It was further mapped using a new technique developed which statistically combines spectroscopic and photometric redshifts, the latter derived from a recent compilation of incredibly deep multi-band imaging performed on the COSMOS field. Through various methods, the descendant mass of PCl J1001+0220 is estimated to be log (Mh/M⊙)z=0 $\log(\mathcal{M}_{h}/\mathcal{M}_{\odot})_{z=0}$log(Mh/M⊙)z=0 ~ 14.5–15 with a large amount of mass apparently already in place at z ~ 4.57. An exhaustive comparison was made between the properties of various spectroscopic and photometric member samples and matched samples of galaxies inhabiting less dense environments at the same redshifts. Tentative evidence is found for a fractional excess of older galaxies more massive in their stellar content amongst the member samples relative to the coeval field, an observation which suggests the pervasive early onset of vigorous star formation for proto-cluster galaxies. No evidence is found for the differences in the star formation rates (SFRs) of member and coeval field galaxies either through estimating by means of the rest-frame ultraviolet or through separately stacking extremely deep Very Large Array 3 GHz imaging for both samples. Additionally, no evidence for pervasive strong active galactic nuclei (AGN) activity is observed in either environment. Analysis of Hubble Space Telescope images of both sets of galaxies as well as their immediate surroundings provides weak evidence for an elevated incidence of galaxy–galaxy interaction within the bounds of the proto-cluster. The stacked and individual spectral properties of the two samples are compared, with a definite suppression of Lyα seen in the average member galaxy relative to the coeval field ( fesc, Lyα = 1.8−1.7+0.3 $f_{esc, \, \textrm{Ly}\alpha} = 1.8^{+0.3}_{-1.7}$fesc, Lyα=1.8−1.7+0.3% and 4.0−0.8+1.0 $4.0^{+1.0}_{-0.8}$4.0−0.8+1.0%, respectively). This observation along with other lines of evidence leads us to infer the possible presence of a large, cool, diffuse medium within the proto-cluster environment evocative of a nascent intracluster medium forming in the early universe.
With the aim of quantifying the contribution of the environment on the evolution of galaxies at z = 0 we have used the DR7 catalogue of the Sloan Digital Sky Survey (SDSS) to reconstruct the 3-D ...distribution of 4132 galaxies in 420 square degrees of the Coma supercluster, containing two rich clusters (Coma and A1367), several groups, and many filamentary structures belonging to the “Great Wall”, at the approximate distance of 100 Mpc. At this distance the galaxy census is complete to Mi = –17.5 mag, i.e. ~4 mag fainter than M*. The morphological classification of galaxies into early- (ellipticals) and late-types (spirals) was carried out by inspection of individual SDSS images and spectra. The density around each galaxy was determined in cylinders of 1 Mpc radius and 1000 km s-1 half length. The color-luminosity relation was derived for galaxies in bins morphological type and in four thresholds of galaxy density-contrast, ranging from δ1,1000 ≤ 0 (UL = the cosmic web); 0 < δ1,1000 ≤ 4 (L = the loose groups); 4 < δ1,1000 ≤ 20 (H = the large groups and the cluster's outskirts) and δ1,1000 > 20 (UH = the cluster's cores). The fraction of early-type galaxies increases with the log of the over-density. A well defined “red sequence” composed of early-type galaxies exists in all environments at high luminosity, but it lacks of low luminosity (dwarf) galaxies in the lowest density environment. Conversely low luminosity isolated galaxies are predominantly of late-type. In other words the low luminosity end of the distribution is dominated by red dE galaxies in clusters and groups and by dwarf blue amorphous systems in the lowest density regions. At z = 0 we find evidence for strong evolution induced by the environment (Nurture). Transformations take place mostly at low luminosity when star forming dwarf galaxies inhabiting low density environments migrate into amorphous passive dwarf ellipticals in their infall into denser regions. The mechanism involves suppression of the star formation due to gas stripping, without significant mass growth, as proposed by Boselli et al. (2008a, ApJ, 674, 742). This process is more efficient and fast in ambients of increasing density. In the highest density environments (around clusters) the truncation of the star formation happens fast enough (few 100 Myr) to produce the signature of post-star-burst in galaxy spectra. PSB galaxies, that are in fact found significantly clustered around the largest dynamical units, represent the remnants of star forming isolated galaxies that had their star formation violently suppressed during their infall in clusters in the last 0.5–1.5 Gyrs, and the progenitors of future dEs.
Based on ALMA Band 3 observations of the CO(2→1) line transition, we report the discovery of three new gas-rich (
M
H
2
∼ 1.5 − 4.8 × 10
10
M
⊙
) galaxies in an overdense region at
z
= 1.7 that ...already contains eight spectroscopically confirmed members. This leads to a total of 11 confirmed overdensity members within a projected distance of ∼1.15 Mpc and in a redshift range of Δ
z
= 0.012. Under simple assumptions, we estimate that the system has a total mass of ≥3 − 6 × 10
13
M
⊙
, and show that it will likely evolve into a ≳10
14
M
⊙
cluster at
z
= 0. The overdensity includes a powerful Compton-thick Fanaroff-Riley type II (FRII) radio galaxy, around which we discovered a large molecular gas reservoir (
M
H
2
∼ 2 × 10
11
M
⊙
). We fit the FRII resolved CO emission with a 2D Gaussian model with a major (minor) axis of ∼27 (∼17) kpc, which is a factor of ∼3 larger than the optical rest-frame emission. Under the assumption of a simple edge-on disk morphology, we find that the galaxy interstellar medium produces a column density toward the nucleus of ∼5.5 × 10
23
cm
−2
. A dense interstellar medium like this may then contribute significantly to the total nuclear obscuration measured in the X-rays (
N
H, X
∼ 1.5 × 10
24
cm
−2
) in addition to a small, paresec-scale absorber around the central engine. The velocity map of this source unveils a rotational motion of the gas that is perpendicular to the radio jets. All ALMA sources have a dust-reddened counterpart in deep
Hubble
Space Telescope images (bands
i
,
z
,
H
), while we do not detect any molecular gas reservoir around the known UV-bright, star-forming members discovered by MUSE. This highlights the capability of ALMA of tracing gas-rich members of the overdensity. For the MUSE sources, we derive 3
σ
upper limits to the molecular gas mass of
M
H
2
≤ 2.8 − 4.8 × 10
10
M
⊙
. We derive star formation rates in the range ∼5 − 100
M
⊙
yr
−1
for the three new ALMA sources. The FRII is located at the center of the projected spatial distribution of the structure members, and its velocity offset from the peak of the redshift distribution is well within the velocity dispersion of the structure. All this, coupled with the large amount of gas around the FRII, its stellar mass of ∼3 × 10
11
M
⊙
, star formation rate of ∼200 − 600
M
⊙
yr
−1
, and powerful radio-to-X-ray emission, suggests that this source is the likely progenitor of the future brightest cluster galaxy.
ABSTRACT
We present a sample of 151 massive (M* > 1010 M⊙) quiescent galaxies at 2 < z < 5, based on a sophisticated Bayesian spectral energy distribution fitting analysis of the CANDELS UDS and ...GOODS-South fields. Our sample includes a robust sub-sample of 61 objects for which we confidently exclude low-redshift and star-forming solutions. We identify 10 robust objects at z > 3, of which 2 are at z > 4. We report formation redshifts, demonstrating that the oldest objects formed at z > 6; however, individual ages from our photometric data have significant uncertainties, typically ∼0.5 Gyr. We demonstrate that the UVJ colours of the quiescent population evolve with redshift at z > 3, becoming bluer and more similar to post-starburst galaxies at lower redshift. Based upon this, we construct a model for the time evolution of quiescent galaxy UVJ colours, concluding that the oldest objects are consistent with forming the bulk of their stellar mass at z ∼ 6–7 and quenching at z ∼ 5. We report spectroscopic redshifts for two of our objects at z = 3.440 and 3.396, which exhibit extremely weak Ly α emission in ultra-deep VANDELS spectra. We calculate star formation rates based on these line fluxes, finding that these galaxies are consistent with our quiescent selection criteria, provided their Ly α escape fractions are >3 and >10 per cent, respectively. We finally report that our highest redshift robust object exhibits a continuum break at λ ∼ 7000 Å in a spectrum from VUDS, consistent with our photometric redshift of $z_\mathrm{phot}=4.72^{+0.06}_{-0.04}$. If confirmed as quiescent, this object would be the highest redshift known quiescent galaxy. To obtain stronger constraints on the times of the earliest quenching events, high-SNR spectroscopy must be extended to z ≳ 3 quiescent objects.
Abstract
Fast and energetic winds are invoked by galaxy formation models as essential processes in the evolution of galaxies. These outflows can be powered either by star formation (SF) and/or active ...galactic nucleus (AGN) activity, but the relative dominance of the two mechanisms is still under debate. We use spectroscopic stacking analysis to study the properties of the low-ionization phase of the outflow in a sample of 1330 star-forming galaxies (SFGs) and 79 X-ray-detected (1042 < L
X < 1045 erg s−1) Type 2 AGN at 1.7 < z < 4.6 selected from a compilation of deep optical spectroscopic surveys, mostly zCOSMOS-Deep and VIMOS Ultra Deep Survey (VUDS). We measure mean velocity offsets of ∼− 150 km s−1 in the SFGs, while in the AGN sample the velocity is much higher (∼− 950 km s−1), suggesting that the AGN is boosting the outflow up to velocities that could not be reached only with the SF contribution. The sample of X-ray AGN has on average a lower SF rate than non-AGN SFGs of similar mass: this, combined with the enhanced outflow velocity in AGN hosts, is consistent with AGN feedback in action. We further divide our sample of AGN into two X-ray luminosity bins: we measure the same velocity offsets in both stacked spectra, at odds with results reported for the highly ionized phase in local AGN, suggesting that the two phases of the outflow may be mixed only up to relatively low velocities, while the highest velocities can be reached only by the highly ionized phase.
Aims. The aim of this work is to identify He II emitters at 2 < z < 4.6 and to constrain the source of the hard ionizing continuum that powers the He II emission. Methods. We assembled a sample of ...277 galaxies with a highly reliable spectroscopic redshift at 2 < z < 4.6 from the VIMOS-VLT Deep Survey (VVDS) Deep and Ultra-Deep data, and we identified 39 He II λ1640 emitters. We studied their spectral properties, measuring the fluxes, equivalent widths (EW), and full width at half maximum (FWHM) for most relevant lines, including He II λ1640, Lyα line, Si II λ1527, and C IV λ1549. Results. About 10% of galaxies at z ~ 3 and iAB ≤ 24.75 show He II in emission, with rest frame equivalent widths EW0 ~ 1–7 Å, equally distributed between galaxies with Lyα in emission or in absorption. We find 11 (3.9% of the global population) reliable He II emitters with unresolved He II lines (FWHM0 < 1200 km s-1), 13 (4.6% of the global population) reliable emitters with broad He II emission (FWHM0 > 1200 km s-1), 3 active galactic nuclei (AGN), and an additional 12 possible He II emitters. The properties of the individual broad emitters are in agreement with expectations from a Wolf-Rayet (W-R) model. Instead, the properties of the narrow emitters are not compatible with this model, nor with predictions of gravitational cooling radiation produced by gas accretion, unless this is severely underestimated by current models by more than two orders of magnitude. Rather, we find that the EW of the narrow He II line emitters are in agreement with expectations for a Population III (PopIII) star formation, if the episode of star formation is continuous, and we calculate that a PopIII star formation rate (SFR) of 0.1–10 M⊙ yr-1 alone is enough to sustain the observed He II flux. Conclusions. We conclude that narrow He II emitters are powered either by the ionizing flux from a stellar population rare at z ~ 0 but much more common at z ~ 3, or by PopIII star formation. As proposed by Tornatore and collaborators, incomplete interstellar medium mixing may leave some small pockets of pristine gas at the periphery of galaxies from which PopIII may form, even down to z ~ 2 or lower. If this interpretation is correct, we measure at z ~ 3 a star formation rate density in PopIII stars of 10-6 M⊙ yr-1 Mpc-3, higher than, but qualitatively comparable to the value predicted by Tornatore and collaborators.
ABSTRACT
The Observations of Redshift Evolution in Large-Scale Environments (ORELSE) survey is an ongoing imaging and spectroscopic campaign initially designed to study the effects of environment on ...galaxy evolution in high-redshift (z ∼ 1) large-scale structures. We use its rich data in combination with a powerful new technique, Voronoi tessellation Monte Carlo (VMC) mapping, to search for serendipitous galaxy overdensities at 0.55 < z < 1.37 within 15 ORELSE fields, a combined spectroscopic footprint of ∼1.4 deg2. Through extensive tests with both observational data and our own mock galaxy catalogues, we optimize the method’s many free parameters to maximize its efficacy for general overdensity searches. Our overdensity search yielded 402 new overdensity candidates with precisely measured redshifts and an unprecedented sensitivity down to low total overdensity masses ($\mathcal {M}_{\mathrm{ tot}}\gtrsim5\times 10^{13}$ M⊙). Using the mock catalogues, we estimated the purity and completeness of our overdensity catalogue as a function of redshift, total mass, and spectroscopic redshift fraction, finding impressive levels of both 0.92/0.83 and 0.60/0.49 for purity/completeness at z = 0.8 and z = 1.2, respectively, for all overdensity masses at spectroscopic fractions of ∼20 per cent. With VMC mapping, we are able to measure precise systemic redshifts, provide an estimate of the total gravitating mass, and maintain high levels of purity and completeness at z ∼ 1 even with only moderate levels of spectroscopy. Other methods (e.g. red-sequence overdensities and hot medium reliant detections) begin to fail at similar redshifts, which attests to VMC mapping’s potential to be a powerful tool for current and future wide-field galaxy evolution surveys at z ∼ 1 and beyond.
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