arXiv subjects

J. Pforr

Publications and source records attributed to J. Pforr.

At least 19 recordsLinked to original sources

arXiv2021

The Size and Pervasiveness of Ly$α$-UV Spatial Offsets in Star-Forming Galaxies at $z\sim6$

We study the projected spatial offset between the ultraviolet continuum and Ly$α$ emission for 65 lensed and unlensed galaxies in the Epoch of Reionization ($5\leq z\leq7$), the first such study at these redshifts, in order to understand the potential for these offsets to confuse estimates of the Ly$α$ properties of galaxies observed in slit spectroscopy. While we find that ~40% of galaxies in our sample show significant projected spatial offsets ($|Δ_{Lyα-UV}|$), we find a modest average offset of 0.61$\pm$0.08 kpc. A small fraction of our sample, ~10%, exhibits offsets of 2-4 kpc, sizes that are larger than the effective radii of typical galaxies at these redshifts. An internal comparison and a comparison to studies at lower redshift yielded no significant evidence of evolution of $|Δ_{Lyα-UV}|$ with redshift. In our own sample, UV-bright galaxies showed offsets a factor of three greater than their fainter counterparts, 0.89$\pm$0.18 vs. 0.27$\pm$0.05 kpc, respectively. We argue that offsets are likely not the result of merging processes, but are rather due to internal anisotropic processes resulting from stellar feedback facilitates Ly$α$ fluorescence and/or backscattering from nearby or outflowing gas. The reduction in the Ly$α$ flux due to offset effects for various observational setups was quantified through mock observations of simple simulations. It was found that the loss of Ly$α$ photons for galaxies with average offsets is not, if corrected for, a limiting factor for all but the narrowest slit widths (<0.4''). However, for the largest offsets, if such offsets are mostly perpendicular to the slit major axis, slit losses were found to be extremely severe in cases where slit widths of $\leq$1'' were employed, such as those planned for James Webb Space Telescope/NIRSpec observations. (abridged)

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arXiv2020

A Spitzer survey of Deep Drilling Fields to be targeted by the Vera C. Rubin Observatory Legacy Survey of Space and Time

The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will observe several Deep Drilling Fields (DDFs) to a greater depth and with a more rapid cadence than the main survey. In this paper, we describe the ``DeepDrill'' survey, which used the Spitzer Space Telescope Infrared Array Camera (IRAC) to observe three of the four currently defined DDFs in two bands, centered on 3.6 $μ$m and 4.5 $μ$m. These observations expand the area which was covered by an earlier set of observations in these three fields by the Spitzer Extragalactic Representative Volume Survey (SERVS). The combined DeepDrill and SERVS data cover the footprints of the LSST DDFs in the Extended Chandra Deep Field-South field (ECDFS), the ELAIS-S1 field (ES1), and the XMM Large-Scale Structure Survey field (XMM-LSS). The observations reach an approximate $5σ$ point-source depth of 2 $μ$Jy (corresponding to an AB magnitude of 23.1; sufficient to detect a 10$^{11} M_{\odot}$ galaxy out to $z\approx 5$) in each of the two bands over a total area of $\approx 29\,$deg$^2$. The dual-band catalogues contain a total of 2.35 million sources. In this paper we describe the observations and data products from the survey, and an overview of the properties of galaxies in the survey. We compare the source counts to predictions from the SHARK semi-analytic model of galaxy formation. We also identify a population of sources with extremely red ([3.6]$-$[4.5] $>1.2$) colours which we show mostly consists of highly-obscured active galactic nuclei.

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arXiv2020

The VIMOS Ultra-Deep Survey: the Ly$α$ emission line morphology at $2 < z < 6$

The Lyman-$α$ (Ly$α$) emission line has been ubiquitously used to confirm and study high redshift galaxies. We report on the line morphology as seen in the 2D spectra from the VIMOS Ultra Deep Survey in a sample of 914 Ly$α$ emitters from a parent sample of 4192 star-forming galaxies at $2<z_\mathrm{spec}\lesssim6$. The study of the spatial extent of Ly$α$ emission provides insight into the escape of Ly$α$ photons from galaxies. We classify the line emission as either non-existent, coincident, projected spatial offset, or extended with respect to the observed 2D UV continuum emission. The line emitters in our sample are classified as ~45% coincident, ~24% extended and ~11% offset emitters. For galaxies with detected UV continuum, we show that extended Ly$α$ emitters (LAEs) correspond to the highest equivalent width galaxies (with an average $W_\mathrm{Lyα}\sim-22$Å). This means that this class of objects is the most common in narrow-band selected samples, which usually select high equivalent width LAEs, $<-20$Å. Extended Ly$α$ emitters are found to be less massive, less star-forming, with lower dust content, and smaller UV continuum sizes ($r_{50}\sim0.9$kpc) of all the classes considered here. We also find that galaxies with larger UV-sizes have lower fractions of Ly$α$ emitters. By stacking the spectra per emitter class we find that the weaker Ly$α$ emitters have stronger low ionization inter-stellar medium (ISM) absorption lines. Interestingly, we find that galaxies with Ly$α$ offset emission (median separation of $1.1_{-0.8}^{+1.3}$kpc from UV continuum) show similar velocity offsets in the ISM as those with no visible emission (and different from other Ly$α$ emitting classes). This class of objects may hint at episodes of gas accretion, bright offset clumps, or on-going merging activity into the larger galaxies.

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arXiv2019

The UV and Ly$α$ Luminosity Functions of galaxies and the Star Formation Rate Density at the end of HI reionization from the VIMOS Ultra-Deep Survey (VUDS)

We establish a robust statistical description of the star-forming galaxy population at the end of cosmic HI reionization ($5.0\le{}z\le6.6$) from a large sample of 52 galaxies with spectroscopically confirmed redshifts from the VIMOS UltraDeep Survey. We identify galaxies with Ly$α$ either in absorption or in emission, at variance with most spectroscopic samples in the literature where Ly$α$ emitters dominate. We find that star-forming galaxies at these redshifts are distributed along a main sequence in the stellar mass vs. SFR plane. We report a flat evolution of the sSFR(z) in 3 2. The bright end of the Ly$α$ luminosity function has a high number density, indicating a significant star formation activity concentrated in the brightest Ly$α$ emitters (LAE) at these redshifts. LAE with EW>25Å~contribute to about 75\% of the total UV-derived SFRD. While our analysis favors a low dust content in 5.0<z<6.6, uncertainties on the dust extinction correction and associated degeneracies in spectral fitting will remain an issue to estimate the total SFRD until future survey extending spectroscopy to the NIR rest-frame spectral domain, e.g. with JWST.

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arXiv2018

The progeny of a Cosmic Titan: a massive multi-component proto-supercluster in formation at z=2.45 in VUDS

[Abridged] We unveil the complex shape of a proto-supercluster at z~2.45 in the COSMOS field using the spectroscopic redshifts of the VIMOS Ultra-Deep Survey (VUDS), complemented by the zCOSMOS-Deep sample and high-quality photometric redshifts. The method relies on a 2D Voronoi tessellation in overlapping redshift slices that is converted into a 3D density field. The galaxy distribution is constructed using a statistical treatment of spectroscopic and photometric redshifts. We identify a proto-supercluster, dubbed "Hyperion" for its immense size and mass, which extends over a volume of ~60x60x150 comoving Mpc^3 and has an estimated total mass of ~4.8x 10^15 M_sun. This immensely complex structure contains at least 7 density peaks within 2.4 < z < 2.5, connected by filaments. Based on the peaks average matter density, we estimate their total mass, M_tot, and find a range of masses from ~0.1x10^14 M_sun to ~2.7x10^14 M_sun. By using spectroscopic members of each peak, we obtain the velocity dispersion of the galaxies in the peaks, and then their virial mass M_vir (under the strong assumption that they are virialised). The agreement between M_vir and M_tot is surprisingly good, considering that almost all the peaks are probably not yet virialised. According to the spherical collapse model, the 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 heterogeneous galaxy samples. With VUDS, we obtain 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. This provides us the unique possibility to study a rich supercluster in formation.

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arXiv2018

GOODS-ALMA: 1.1 mm galaxy survey - I. Source catalogue and optically dark galaxies

We present a 69 arcmin$^2$ ALMA survey at 1.1mm, GOODS-ALMA, matching the deepest HST-WFC3 H-band part of the GOODS-South field. We taper the 0"24 original image with a homogeneous and circular synthesized beam of 0"60 to reduce the number of independent beams - thus reducing the number of purely statistical spurious detections - and optimize the sensitivity to point sources. We extract a catalogue of galaxies purely selected by ALMA and identify sources with and without HST counterparts down to a 5$σ$ limiting depth of H=28.2 AB (HST/WFC3 F160W). ALMA detects 20 sources brighter than 0.7 mJy in the 0"60 tapered mosaic (rms sensitivity =0.18 mJy/beam) with a purity greater than 80%. Among these detections, we identify three sources with no HST nor Spitzer-IRAC counterpart, consistent with the expected number of spurious galaxies from the analysis of the inverted image; their definitive status will require additional investigation. An additional three sources with HST counterparts are detected either at high significance in the higher resolution map, or with different detection-algorithm parameters ensuring a purity greater than 80%. Hence we identify in total 20 robust detections. Our wide contiguous survey allows us to push further in redshift the blind detection of massive galaxies with ALMA with a median redshift of $z$=2.92 and a median stellar mass of M$_{\star}$ = 1.1 $\times 10^{11}$M$_\odot$. Our sample includes 20% HST-dark galaxies (4 out of 20), all detected in the mid-infrared with IRAC. The near-infrared based photometric redshifts of two of them $z\sim$4.3 and 4.8) suggest that these sources have redshifts $z$>4. At least 40% of the ALMA sources host an X-ray AGN, compared to 14% for other galaxies of similar mass and redshift. The wide area of our ALMA survey provides lower values at the bright end of number counts than single-dish telescopes

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arXiv2018

A subarcsecond near-infrared view of massive galaxies at z > 1 with Gemini Multiconjugate Adaptive Optics

We present images taken using the Gemini South Adaptive Optics Imager (GSAOI) with the Gemini Multiconjugate Adaptive Optics System (GeMS) in three 2 arcmin$^2$ fields in the Spitzer Extragalactic Representative Volume Survey. These GeMS/GSAOI observations are among the first $\approx 0.1^{''}$ resolution data in the near-infrared spanning extragalactic fields exceeding $1.5^{\prime}$ in size. We use these data to estimate galaxy sizes, obtaining results similar to those from studies with the Hubble Space Telescope, though we find a higher fraction of compact star forming galaxies at $z>2$. To disentangle the star-forming galaxies from active galactic nuclei (AGN), we use multiwavelength data from surveys in the optical and infrared, including far-infrared data from Herschel, as well as new radio continuum data from the Australia Telescope Compact Array and Very Large Array. We identify ultraluminous infrared galaxies (ULIRGs) at $z \sim 1-3$, which consist of a combination of pure starburst galaxies and Active Galactic Nuclei (AGN)/starburst composites. The ULIRGs show signs of recent merger activity, such as highly disturbed morphologies and include a rare candidate triple AGN. We find that AGN tend to reside in hosts with smaller scale sizes than purely star-forming galaxies of similar infrared luminosity. Our observations demonstrate the potential for MCAO to complement the deeper galaxy surveys to be made with the James Webb Space Telescope.

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arXiv2018

The VIMOS Ultra Deep Survey: Emerging from the Dark, a Massive Proto-Cluster at z~4.57

Using spectroscopic observations taken for the VIMOS Ultra-Deep Survey (VUDS) we report here on the discovery of PCl J1001+0220, a massive proto-cluster located at $z_{spec}\sim4.57$ in the COSMOS field. The proto-cluster was initially detected as a $\sim12σ$ 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 that statistically combines spectroscopic and photometric redshifts, the latter derived from a recent compilation of deep multi-band imaging. Through various methods, the descendant halo mass of PCl J1001+0220 is estimated to be $\log(M_{h}/M_{\odot})_{z=0}\sim14.5-15$ with a large amount of mass apparently already in place at $z\sim4.57$. Tentative evidence is found for a fractional excess of older and more massive galaxies within the proto-cluster, an observation which suggests the pervasive early onset of vigorous star formation. No evidence is found for the differences in the star formation rates of member and a matched sample of coeval field galaxies either through rest-frame ultraviolet methods or through stacking extremely deep Very Large Array 3 GHz imaging. Additionally, no evidence for pervasive strong active galactic nuclei (AGN) activity is observed. Analysis of Hubble Space Telescope images provides weak evidence for for an elevated incidence of galaxy-galaxy interaction within the proto-cluster. The spectral properties of the two samples are compared, with a definite suppression of Ly$α$ seen in the average member galaxy relative to the coeval field ($f_{esc,Lyα}=1.8^{+0.3}_{-1.7}$% and $4.0^{+1.0}_{-0.8}$%, 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.

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arXiv2017

The VIMOS Ultra Deep Survey. Luminosity and stellar mass dependence of galaxy clustering at z~3

We present the study of the dependence of galaxy clustering on luminosity and stellar mass in the redshift range 2$<$z$<$3.5 using 3236 galaxies with robust spectroscopic redshifts from the VIMOS Ultra Deep Survey (VUDS). We measure the two-point real-space correlation function $w_p(r_p)$ for four volume-limited stellar mass and four luminosity, M$_{UV}$ absolute magnitude selected, sub-samples. We find that the scale dependent clustering amplitude $r_0$ significantly increases with increasing luminosity and stellar mass indicating a strong galaxy clustering dependence on these properties. This corresponds to a strong relative bias between these two sub-samples of $Δ$b/b$^*$=0.43. Fitting a 5-parameter HOD model we find that the most luminous and massive galaxies occupy the most massive dark matter haloes with $\langle$M$_h$$\rangle$ = 10$^{12.30}$ h$^{-1}$ M$_{\odot}$. Similar to the trends observed at lower redshift, the minimum halo mass M$_{min}$ depends on the luminosity and stellar mass of galaxies and grows from M$_{min}$ =10$^{9.73}$ h$^{-1}$M$_{\odot}$ to M$_{min}$=10$^{11.58}$ h$^{-1}$M$_{\odot}$ from the faintest to the brightest among our galaxy sample, respectively. We find the difference between these halo masses to be much more pronounced than is observed for local galaxies of similar properties. Moreover, at z~3, we observe that the masses at which a halo hosts, on average, one satellite and one central galaxy is M$_1$$\approx$4M$_{min}$ over all luminosity ranges, significantly lower than observed at z~0 indicating that the halo satellite occupation increases with redshift. The luminosity and stellar mass dependence is also reflected in the measurements of the large scale galaxy bias, which we model as b$_{g,HOD}$($>$L)=1.92+25.36(L/L$^*$)$^{7.01}$. We conclude our study with measurements of the stellar-to-halo mass ratio (SHMR).

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arXiv2017

The VIMOS Ultra-Deep Survey: A major merger origin for the high fraction of galaxies at $2<z<6$ with two bright clump

(Abridged) The properties of stellar clumps in star forming galaxies and their evolution over the redshift range $2\lesssim z \lesssim 6$ are presented and discussed in the context of the build-up of massive galaxies at early cosmic times. We use HST/ACS images of galaxies with spectroscopic redshifts from the VIMOS Ultra Deep Survey (VUDS) to identify clumps within a 20 kpc radius. We find that the population of galaxies with more than one clump is dominated by galaxies with two clumps, representing $\sim21-25$\% of the population, while the fraction of galaxies with 3, or 4 and more, clumps is 8-11 and 7-9\%, respectively. The fraction of clumpy galaxies is in the range $\sim35-55\%$ over $2<z<6$, increasing at higher redshifts, indicating that the fraction of irregular galaxies remains high up to the highest redshifts. The large and bright clumps (M$_{\star}\sim10^9$ up to $\sim10^{10}$M$_\odot$) are found to reside predominantly in galaxies with two clumps. Smaller and lower luminosity clumps ($\log_{10}\left(M_{\star}/\mathrm{M_\odot}\right)<9$) are found in galaxies with three clumps or more. We interpret these results as evidence for two different modes of clump formation working in parallel. The small low luminosity clumps are likely the result of disc fragmentation, with violent disc instabilities (VDI) forming several long-lived clumps in-situ, as suggested from simulations. A fraction of these clumps is also likely coming from minor mergers. The clumps in the dominating population of galaxies with two clumps are significantly more massive and have properties akin to those in merging pairs observed at similar redshifts; they appear as more massive than the most massive clumps observed in VDI numerical simulations.

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arXiv2017

AGN-enhanced outflows of low-ionization gas in star-forming galaxies at 1.7<z<4.6

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 and/or 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 (42<log(L_X)<45 erg/s) Type 2 AGN at 1.7<z<4.6 selected from a compilation of deep optical spectroscopic surveys, mostly zCOSMOS-Deep and VUDS. We measure mean velocity offsets of -150 km/s in the SFGs while in the AGN sample the velocity is much higher (-950 km/s), suggesting that the AGN is boosting the outflow up to velocities that could not be reached only with the star- formation contribution. The sample of X-ray AGN has on average a lower SFR 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.

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arXiv2017

Evolution of Galaxy Luminosity and Stellar-Mass Functions since $z=1$ with the Dark Energy Survey Science Verification Data

We present the first study of the evolution of the galaxy luminosity and stellar-mass functions (GLF and GSMF) carried out by the Dark Energy Survey (DES). We describe the COMMODORE galaxy catalogue selected from Science Verification images. This catalogue is made of $\sim 4\times 10^{6}$ galaxies at $0<z\lesssim1.3$ over a sky area of $\sim155\ {\rm sq. \ deg}$ with ${\it i}$-band limiting magnitude ${\it i}=23\ {\rm mag}$. Such characteristics are unprecedented for galaxy catalogues and they enable us to study the evolution of GLF and GSMF at $0<z<1$ homogeneously with the same statistically-rich data-set and free of cosmic variance effects. The aim of this study is twofold: i) we want to test our method based on the use of photometric-redshift probability density functions against literature results obtained with spectroscopic redshifts; ii) we want to shed light on the way galaxies build up their masses over cosmic time. We find that both the ${\it i}$-band galaxy luminosity and stellar mass functions are characterised by a double-Schechter shape at $z<0.2$. Both functions agree well with those based on spectroscopic redshifts. The DES GSMF agrees especially with those measured for the GAlaxy Mass Assembly and the PRism MUlti-object Survey out to $z\sim1$. At $0.2<z<1$, we find the ${\it i}$-band luminosity and stellar-mass densities respectively to be constant ($ρ_{\rm L}\propto (1+z)^{-0.12\pm0.11}$) and decreasing ($ρ_{\rm Mstar}\propto (1+z)^{-0.5\pm0.1}$) with $z$. This indicates that, while at higher redshift galaxies have less stellar mass, their luminosities do not change substantially because of their younger and brighter stellar populations. Finally, we also find evidence for a top-down mass-dependent evolution of the GSMF.

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arXiv2017

Environmental dependence of the galaxy stellar mass function in the Dark Energy Survey Science Verification Data

Measurements of the galaxy stellar mass function are crucial to understand the formation of galaxies in the Universe. In a hierarchical clustering paradigm it is plausible that there is a connection between the properties of galaxies and their environments. Evidence for environmental trends has been established in the local Universe. The Dark Energy Survey (DES) provides large photometric datasets that enable further investigation of the assembly of mass. In this study we use ~3.2 million galaxies from the (South Pole Telescope) SPT-East field in the DES science verification (SV) dataset. From grizY photometry we derive galaxy stellar masses and absolute magnitudes, and determine the errors on these properties using Monte-Carlo simulations using the full photometric redshift probability distributions. We compute galaxy environments using a fixed conical aperture for a range of scales. We construct galaxy environment probability distribution functions and investigate the dependence of the environment errors on the aperture parameters. We compute the environment components of the galaxy stellar mass function for the redshift range 0.15<z<1.05. For z<0.75 we find that the fraction of massive galaxies is larger in high density environment than in low density environments. We show that the low density and high density components converge with increasing redshift up to z~1.0 where the shapes of the mass function components are indistinguishable. Our study shows how high density structures build up around massive galaxies through cosmic time.

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arXiv2017

Analogs of primeval galaxies two billion years after the Big Bang

Deep observations are revealing a growing number of young galaxies in the first billion year of cosmic time. Compared to typical galaxies at later times, they show more extreme emission-line properties, higher star formation rates, lower masses, and smaller sizes. However, their faintness precludes studies of their chemical abundances and ionization conditions, strongly limiting our understanding of the physics driving early galaxy build-up and metal enrichment. Here we study a rare population of UV-selected, sub$-L^{*}$(z=3) galaxies at redshift 2.4$<z<$3.5 that exhibit all the rest-frame properties expected from primeval galaxies. These low-mass, highly-compact systems are rapidly-forming galaxies able to double their stellar mass in only few tens million years. They are characterized by very blue UV spectra with weak absorption features and bright nebular emission lines, which imply hard radiation fields from young hot massive stars. Their highly-ionized gas phase has strongly sub-solar carbon and oxygen abundances, with metallicities more than a factor of two lower than that found in typical galaxies of similar mass and star formation rate at $z\lesssim$2.5. These young galaxies reveal an early and short stage in the assembly of their galactic structures and their chemical evolution, a vigorous phase which is likely to be dominated by the effects of gas-rich mergers, accretion of metal-poor gas and strong outflows.

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arXiv2016

CANDELS Multiwavelength Catalogs: Source Identification and Photometry in the CANDELS COSMOS Survey Field

We present a multi-wavelength photometric catalog in the COSMOS field as part of the observations by the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). The catalog is based on Hubble Space Telescope Wide Field Camera 3 (HST/WFC3) and Advanced Camera for Surveys (ACS) observations of the COSMOS field (centered at RA: $10^h00^m28^s$, Dec:$+02^{\circ}12^{\prime}21^{\prime\prime}$). The final catalog has 38671 sources with photometric data in forty two bands from UV to the infrared ($\rm \sim 0.3-8\,μm$). This includes broad-band photometry from the HST, CFHT, Subaru, VISTA and Spitzer Space Telescope in the visible, near infrared and infrared bands along with intermediate and narrow-band photometry from Subaru and medium band data from Mayall NEWFIRM. Source detection was conducted in the WFC3 F160W band (at $\rm 1.6\,μm$) and photometry is generated using the Template FITting algorithm. We further present a catalog of the physical properties of sources as identified in the HST F160W band and measured from the multi-band photometry by fitting the observed spectral energy distributions of sources against templates.

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arXiv2016

Host galaxies of luminous z$\sim$0.6 quasars: Major mergers are not prevalent at the highest AGN luminosities

Galaxy interactions are thought to be one of the main triggers of Active Galactic Nuclei (AGN), especially at high luminosities, where the accreted gas mass during the AGN lifetime is substantial. Evidence for a connection between mergers and AGN, however, remains mixed. Possible triggering mechanisms remain particularly poorly understood for luminous AGN, which are thought to require triggering by major mergers, rather than secular processes. We analyse the host galaxies of a sample of 20 optically and X-ray selected luminous AGN (log($L_{bol}$ [erg/s]) $>$ 45) at z $\sim$ 0.6 using HST WFC3 data in the F160W/H band. 15/20 sources have resolved host galaxies. We create a control sample of mock AGN by matching the AGN host galaxies to a control sample of non-AGN galaxies. Visual signs of disturbances are found in about 25% of sources in both the AGN hosts and control galaxies. Using both visual classification and quantitative morphology measures, we show that the levels of disturbance are not enhanced when compared to a matched control sample. We find no signs that major mergers play a dominant role in triggering AGN at high luminosities, suggesting that minor mergers and secular processes dominate AGN triggering up to the highest AGN luminosities. The upper limit on the enhanced fraction of major mergers is $\leqslant$20%. While major mergers might increase the incidence of (luminous AGN), they are not the prevalent triggering mechanism in the population of unobscured AGN.

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arXiv2016

The impact of the Star Formation Histories on the SFR-M$_{*}$ relation at z$\ge$2

In this paper we investigate the impact of different star formation histories (SFHs) on the relation between stellar mass M$_{*}$ and star formation rate (SFR) using a sample of galaxies with reliable spectroscopic redshift zspec>2 drawn from the VIMOS Ultra-Deep Survey (VUDS). We produce an extensive database of dusty model galaxies, calculated starting from the new library of single stellar population (SSPs) models presented in Cassara' et al. 2013 and weighted by a set of 28 different SFHs based on the Schmidt function, and characterized by different ratios of the gas infall time scale $\tau_{infall}$ to the star formation efficiency $\nu$. The treatment of dust extinction and re-emission has been carried out by means of the radiative transfer calculation. The spectral energy distribution (SED) fitting technique is performed by using GOSSIP+, a tool able to combine both photometric and spectroscopic information to extract the best value of the physical quantities of interest, and to consider the Intergalactic Medium (IGM) attenuation as a free parameter. We find that the main contribution to the scatter observed in the $SFR-M_{*}$ plane is the possibility of choosing between different families of SFHs in the SED fitting procedure, while the redshift range plays a minor role. The majority of the galaxies, at all cosmic times, are best-fit by models with SFHs characterized by a high $\tau_{\rm infall}/\nu$ ratio. We discuss the reliability of the presence of a small percentage of dusty and highly star forming galaxies, in the light of their detection in the FIR.

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arXiv2016

The VIMOS Ultra Deep Survey First Data Release: spectra and spectroscopic redshifts of 698 objects up to z~6 in CANDELS

This paper describes the first data release (DR1) of the VIMOS Ultra Deep Survey (VUDS). The DR1 includes all low-resolution spectroscopic data obtained in 276.9 arcmin2 of the CANDELS-COSMOS and CANDELS-ECFDS survey areas, including accurate spectroscopic redshifts z_spec and individual spectra obtained with VIMOS on the ESO-VLT. A total of 698 objects have a measured redshift, with 677 galaxies, two type-I AGN and a small number of 19 contaminating stars. The targets of the spectroscopic survey are selected primarily on the basis of their photometric redshifts to ensure a broad population coverage. About 500 galaxies have z_spec>2, 48 with z_spec>4, and the highest reliable redshifts reach beyond z_spec=6. This dataset approximately doubles the number of galaxies with spectroscopic redshifts at z>3 in these fields. We discuss the general properties of the sample in terms of the spectroscopic redshift distribution, the distribution of Lyman-alpha equivalent widths, and physical properties including stellar masses M_star and star formation rates (SFR) derived from spectral energy distribution fitting with the knowledge of z_spec. We highlight the properties of the most massive star-forming galaxies, noting the large range in spectral properties, with Lyman-alpha in emission or in absorption, and in imaging properties with compact, multi-component or pair morphologies. We present the catalogue database and data products. All data are publicly available and can be retrieved from a dedicated query-based database available at http://cesam.lam.fr/vuds.

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