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.
Measuring environment for large numbers of galaxies in the distant Universe is an open problem in astrophysics, as environment is important in determining many properties of galaxies during their ...formation and evolution. In order to measure galaxy environments, we need galaxy positions and redshifts. We study how photometric redshifts affect the measurement of galaxy environment and how the reconstruction of the density field may limit an analysis of the galaxy stellar mass function (GSMF) in different environments. We varied the parameters defining the fixed aperture volume and explored different configurations. This work allows us several useful considerations on how to interpret results of an analysis of the GSMF in different environments when the density field is measured with photometric redshifts and represents a preparatory study for future wide area photometric redshift surveys, such as the Euclid Survey. We plan to apply the result of this work to an environmental analysis of the GSMF in the UltraVISTA Survey in future work.
Aims. We present the results of the GMRT cluster radio halo survey. The main purposes of our observational project are to measure what fraction of massive galaxy clusters in the redshift range z ...=0.2-0.4 host a radio halo, and to constrain the expectations of the particle re-acceleration model for the origin of the non-thermal radio emission. Methods. We selected a complete sample of 50 clusters in the X-ray band from the REFLEX (27) and the eBCS (23) catalogues. We present Giant Metrewave Radio Telescope (GMRT) observations at 610 MHz for all clusters still lacking high sensitivity radio information, i.e. 16 eBCS and 7 REFLEX clusters, thus completing the radio information for the whole sample. The typical sensitivity in our images is in the range 1 sigma sim 35-100 similar to \muJy b super(-1). Results. We found a radio halo in A 697, a diffuse peripheral source of unclear nature in A 781, a core-halo source in Z 7160, a candidate radio halo in A 1682 and "suspect" central emission in Z 2661. Including the literature information, a total of 10 clusters in the sample host a radio halo. A very important result of our work is that 25 out of the 34 clusters observed with the GMRT do not host extended central emission at the sensitivity level of our observations, and for 20 of them firm upper limits to the radio power of a giant radio halo were derived. The GMRT Radio Halo Survey shows that radio halos are not common, and our findings on the fraction of giant radio halos in massive clusters are consistent with the statistical expectations based on the re-acceleration model. Our results favour primary to secondary electron models.
Utilizing spectroscopic observations taken for the VIMOS Ultra-Deep Survey (VUDS), new observations from Keck/DEIMOS, and publicly available observations of large samples of star-forming galaxies, we ...report here on the relationship between the star-formation rate (SFR) and the local environment (
δ
gal
) of galaxies in the early universe (2 <
z
< 5). Unlike what is observed at lower redshifts (
z
≲ 2), we observe a definite, nearly monotonic increase in the average SFR with increasing galaxy overdensity over more than an order of magnitude in
δ
gal
. The robustness of this trend is quantified by accounting for both uncertainties in our measurements and galaxy populations that are either underrepresented or not present in our sample (e.g., extremely dusty star-forming and quiescent galaxies), and we find that the trend remains significant under all circumstances. This trend appears to be primarily driven by the fractional increase of galaxies in high-density environments that are more massive in their stellar content and are forming stars at a higher rate than their less massive counterparts. We find that, even after stellar mass effects are accounted for, there remains a weak but significant SFR–
δ
gal
trend in our sample implying that additional environmentally related processes are helping to drive this trend. We also find clear evidence that the average SFR of galaxies in the densest environments increases with increasing redshift. These results lend themselves to a picture in which massive gas-rich galaxies coalesce into proto-cluster environments at
z
≳ 3, interact with other galaxies or with a forming large-scale medium, subsequently using or losing most of their gas in the process, and begin to seed the nascent red sequence that is present in clusters at slightly lower redshifts.
Context. The study of statistically significant samples of star-forming dwarf galaxies (SFDGs) at different cosmic epochs is essential for the detailed understanding of galaxy assembly and chemical ...evolution. However, the main properties of this large population of galaxies at intermediate redshift are still poorly known. Aims. We present the discovery and spectrophotometric characterization of a large sample of 164 faint (iAB~ 23–25 mag) SFDGs at redshift 0.13 ≤ z ≤ 0.88 selected by the presence of bright optical emission lines in the VIMOS Ultra Deep Survey (VUDS). We investigate their integrated physical properties and ionization conditions, which are used to discuss the low-mass end of the mass-metallicity relation (MZR) and other key scaling relations. Methods. We use optical VUDS spectra in the COSMOS, VVDS-02h, and ECDF-S fields, as well as deep multi-wavelength photometry that includes HST-ACS F814W imaging, to derive stellar masses, extinction-corrected star-formation rates (SFR), and gas-phase metallicities of SFDGs. For the latter, we use the direct method and a Te-consistent approach based on the comparison of a set of observed emission lines ratios with the predictions of detailed photoionization models. Results. The VUDS SFDGs are compact (median re~ 1.2 kpc), low-mass (M∗~ 107–109M⊙) galaxies with a wide range of star-formation rates (SFR(Hα) ~ 10-3–101M⊙/yr) and morphologies. Overall, they show a broad range of subsolar metallicities (12 +log (O/H) =7.26–8.7; 0.04 ≲Z/Z⊙≲ 1). Nearly half of the sample are extreme emission-line galaxies (EELGs) characterized by high equivalent widths and emission line ratios indicative of higher excitation and ionization conditions. The MZR of SFDGs shows a flatter slope compared to previous studies of galaxies in the same mass range and redshift. We find the scatter of the MZR is partly explained in the low mass range by varying specific SFRs and gas fractions amongst the galaxies in our sample. In agreement with recent studies, we find the subclass of EELGs to be systematically offset to lower metallicity compared to SFDGs at a given stellar mass and SFR, suggesting a younger starburst phase. Compared with simple chemical evolution models we find that most SFDGs do not follow the predictions of a “closed-box” model, but those from a gas-regulating model in which gas flows are considered. While strong stellar feedback may produce large-scale outflows favoring the cessation of vigorous star formation and promoting the removal of metals, younger and more metal-poor dwarfs may have recently accreted large amounts of fresh, very metal-poor gas, that is used to fuel current star formation.
ABSTRACT
Using the wide multiband photometry available in the Cosmic Evolution Survey (COSMOS) field, we explore the host galaxy properties of a large sample of active galactic nuclei (AGNs; ∼1700 ...objects) with Lbol ranging from 1043 to 1047 erg s−1, obtained by combining X‐ray and optical spectroscopic selections. Based on a careful study of their spectral energy distributions, which have been parametrized using a two‐component (AGN+galaxy) model fit, we have derived dust‐corrected rest‐frame magnitudes, colours and stellar masses of the obscured and unobscured AGN hosts up to high redshift (z≲3). Moreover, for the sample of obscured AGNs, we have also derived reliable star formation rates (SFRs). We find that AGN hosts span a large range of stellar masses and SFRs. No colour‐bimodality is seen at any redshift in the AGN hosts, which are found to be mainly massive, red galaxies. Once we have accounted for the colour–mass degeneracy in well‐defined mass‐matched samples, we find a residual (marginal) enhancement of the incidence of AGNs in redder galaxies with lower specific SFRs. We argue that this result might emerge because of our ability to properly account for AGN light contamination and dust extinction, compared to surveys with a more limited multiwavelength coverage. However, because these colour shifts are relatively small, systematic effects could still be considered responsible for some of the observed trends. Interestingly, we find that the probability for a galaxy to host a black hole that is growing at any given ‘specific accretion rate’ (i.e. the ratio of X‐ray luminosity to the host stellar mass) is almost independent of the host galaxy mass, while it decreases as a power law with LX/M*. By analysing the normalization of such a probability distribution, we show how the incidence of AGNs increases with redshift as rapidly as (1 + z)4, which closely resembles the overall evolution of the specific SFR of the entire galaxy population. We provide analytical fitting formulae that describe the probability of a galaxy of any mass (above the completeness limit of the COSMOS) to host an AGN of any given specific accretion rate as a function of redshift. These can be useful tools for theoretical studies of the growing population of black holes within galaxy evolution models. Although AGN activity and star formation in galaxies do appear to have a common triggering mechanism, at least in a statistical sense, within the COSMOS sample, we do not find any conclusive evidence to suggest that AGNs have a powerful influence on the star‐forming properties of their host galaxies.
Aims. We investigate the global galaxy evolution over ~12 Gyr (0.05 ≤ z ≤ 4.5), from the far ultraviolet (FUV) luminosity function (LF), luminosity density (LD), and star formation rate density ...(SFRD), using the VIMOS-VLT Deep Survey (VVDS), a single deep galaxy redshift survey with a well controlled selection function. Methods. We combine the VVDS Deep (17.5 ≤ IAB ≤ 24.0) and Ultra-Deep (23.00 ≤ i'AB ≤ 24.75) redshift surveys, totalizing ~11 000 galaxies, to estimate the rest-frame FUV LF and LD, using a wide wavelength range of deep photometry (337 < λ < 2310 nm). We extract the dust attenuation of the FUV radiation, embedded in the well-constrained spectral energy distributions. We then derive the dust-corrected SFRD. Results. We find a constant and flat faint-end slope α in the FUV LF at z < 1.7. At z > 1.7, we set α steepening with (1 + z). The absolute magnitude M*FUV steadily brightens in the entire range 0 < z < 4.5, and at z > 2 it is on average brighter than in the literature, while φ∗ is on average smaller. The evolution of our total LD shows a peak at z ≃ 2, clearly present also when considering all sources of uncertainty. The SFRD history peaks as well at z ≃ 2. It first steadily rises by a factor of ~6 during 2 Gyr (from z = 4.5 to z = 2), and then decreases by a factor of ~12 during 10 Gyr down to z = 0.05. This peak is mainly produced by a similar peak within the population of galaxies with −21.5 ≤ MFUV ≤ − 19.5. As times goes by, the total SFRD is dominated by fainter and fainter galaxies. The mean dust attenuation of the global galaxy population rises fast by 1 mag during 2 Gyr from z ≃ 4.5 to z ~ 2, reaches slowly its maximum at z ≃ 1 (AFUV ≃ 2.2 mag), and then decreases by 1.1 mag during 7 Gyr down to z ≃ 0. Conclusions. We have derived the cosmic SFRD history and the total dust amount in galaxies over a continuous period of ~12 Gyr, using a single homogeneous spectroscopic redshift sample. The presence of a clear peak at z ≃ 2 and a fast rise at z > 2 of the SFRD is compelling for models of galaxy formation. This peak is mainly produced by bright galaxies (L ≳ L*z=2), requiring that significant gas reservoirs still exist at this epoch and are probably replenished by cold accretion and wet mergers, while feedback or quenching processes are not yet strong enough to lower the SF. The dust attenuation maximum is reached ~2 Gyr after the SFRD peak, implying a contribution from the intermediate-mass stars to the dust production at z < 2.
Aims. We compute photometric redshifts in the fourth public release of the Canada-France-Hawaii Telescope Legacy Survey. This unique multi-colour catalogue comprises $u^*, g', r', i', z'$ photometry ...in four deep fields of 1 deg2 each and 35 deg2 distributed over three wide fields. Methods. We used a template-fitting method to compute photometric redshifts calibrated with a large catalogue of 16 983 high-quality spectroscopic redshifts from the VVDS-F02, VVDS-F22, DEEP2, and the zCOSMOS surveys. The method includes correction of systematic offsets, template adaptation, and the use of priors. We also separated stars from galaxies using both size and colour information. Results. Comparing with galaxy spectroscopic redshifts, we find a photometric redshift dispersion, $\sigma_{\Delta z/(1+z_{\rm s})}$, of 0.028–0.30 and an outlier rate, $|\Delta z| \ge 0.15\times (1+z_{\rm s})$, of 3–4% in the deep field at $i'_{\rm AB}$ < 24. In the wide fields, we find a dispersion of 0.037–0.039 and an outlier rate of 3–4% at $i'_{\rm AB}$ < 22.5. Beyond $i'_{\rm AB}$ = 22.5 in the wide fields the number of outliers rises from 5% to 10% at $i'_{\rm AB}$ < 23 and $i'_{\rm AB}$ < 24, respectively. For the wide sample the systematic redshift bias stays below 1% to $i'_{\rm AB}$ < 22.5, whereas we find no significant bias in the deep fields. We investigated the effect of tile-to-tile photometric variations and demonstrated that the accuracy of our photometric redshifts is reduced by at most 21%. Application of our star-galaxy classifier reduced the contamination by stars in our catalogues from 60% to 8% at $i'_{\rm AB}$ < 22.5 in our field with the highest stellar density while keeping a complete galaxy sample. Our CFHTLS T0004 photometric redshifts are distributed to the community. Our release includes 592891 ($i'_{\rm AB}$ < 22.5) and 244701 ($i'_{\rm AB}$ < 24) reliable galaxy photometric redshifts in the wide and deep fields, respectively.
ABSTRACT We report the detection of C ii λ158 $\mu$m emission from a system of three closely separated sources in the Cosmic Evolution Survey (COSMOS) field at z ∼ 4.56 , as part of the Atacama Large ...Millimeter/submillimeter Array (ALMA) Large Program to INvestigate C ii at Early times (ALPINE). The two most luminous sources are closely associated, both spatially (1.6 arcsec ∼ 11 kpc) and in velocity (∼100 km s−1), while the third source is slightly more distant (2.8 arcsec ∼ 18 kpc, ∼300 km s−1). The second most luminous source features a slight velocity gradient, while no significant velocity gradient is seen in the other two sources. Using the observed C ii luminosities, we derive a total log$_{10}(\rm SFR_{C\,{\small II}}\, M_{\odot }\, yr^{-1})=2.8\pm 0.2$, which may be split into contributions of 59, 31, and 10 per cent from the central, east, and west sources, respectively. Comparison of these C ii detections to recent zoom-in cosmological simulations suggests an ongoing major merger. We are thus witnessing a system in a major phase of mass build-up by merging, including an ongoing major merger and an upcoming minor merger, which is expected to end up in a single massive galaxy by z ∼ 2.5.
Aims. We present new high sensitivity observations of the radio relic in A 521 carried out using the Giant Metrewave Radio Telescope at 327 MHz and with the Very Large Array at 4.9 and 8.5 GHz. ...Methods. We imaged the relic at these frequencies and carried out a detailed spectral analysis, based on the integrated radio spectrum between 235 MHz and 4.9 GHz, and on the spectral index image in the frequency range 327-610 MHz. In our present analysis we use our new GMRT observations in addition to proprietary and archival data. We search for a possible shock front co-located with the relic on a short archival Chandra X-ray observation of the cluster. Results. The integrated spectrum of the relic is consistent with a single power law; the spectral index image shows a clear trend of steepening going from the outer portion of the relic toward the cluster centre. We discuss the origin of the source in the light of theoretical models for the formation of cluster radio relics. Our results on the spectral properties of the relic are consistent with acceleration of relativistic electrons by a shock in the intracluster medium. This scenario is supported by our detection of an X-ray surface brightness edge coincident with the outer border of the radio relic. This edge is probably a shock front.
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![The ALPINE-ALMA [C ii ] sur...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1745-3925_1745-3933/small "The ALPINE-ALMA [C ii ] survey: a triple merger at z ∼ 4.56")