arXiv subjects

G. Zamorani

Publications and source records attributed to G. Zamorani.

At least 109 records · Page 6Linked to original sources

arXiv2020

The VANDELS survey: the relation between UV continuum slope and stellar metallicity in star-forming galaxies at z~3

The estimate of stellar metallicities (Z*) of high-z galaxies are of paramount importance in order to understand the complexity of dust effects and the reciprocal interrelations among stellar mass, dust attenuation, stellar age, and metallicity. Benefiting from uniquely deep FUV spectra of >500 star-forming galaxies at redshifts 2<z<5 extracted from the VANDELS survey and stacked in bins of stellar mass (M*) and UV continuum slope (beta), we estimate their stellar metallicities Z* from stellar photospheric absorption features at 1501 and 1719 Angstrom, which are calibrated with Starburst99 models and are largely unaffected by stellar age, dust, IMF, nebular continuum or interstellar absorption. Comparing them to photometric based spectral slopes in the range 1250-1750 Angstrom, we find that the stellar metallicity increases by ~0.5 dex from beta ~ -2 to beta ~ -1 (1 < A(1600) < 3.2), and a dependence with beta holds at fixed UV absolute luminosity M(UV) and stellar mass up to 10^(9.65) Msun. As a result, the metallicity is a fundamental ingredient for properly rescaling dust corrections based on M(UV) and M*. Using the same absorption features, we analyze the mass-metallicity relation (MZR) and find it is consistent with the previous VANDELS estimation based on a global fit of the FUV spectra. Similarly, we do not find a significant evolution between z=2 and z=3.5. Finally, the slopes of our MZR and Z*-beta relation are in agreement with the predictions of well-studied semi-analytic models of galaxy formation (SAM), while some tensions with observations remain as to the absolute metallicity normalization. The relation between UV slope and stellar metallicity is fundamental for the exploitation of large volume surveys with next-generation telescopes and for the physical characterization of galaxies in the first billion years of our Universe.

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arXiv2020

The ALPINE-ALMA [C II] Survey: [C II]158micron Emission Line Luminosity Functions at $z \sim 4-6$

We present the [CII]158$μ$m line luminosity functions (LFs) at $z\sim4-6$ using the ALMA observations of 118 sources, which are selected to have UV luminosity $M_{1500A}<-20.2$ and optical spectroscopic redshifts in COSMOS and ECDF-S. Of the 118 targets, 75 have significant [CII] detections and 43 are upper limits. This is by far the largest sample of [CII] detections which allows us to set constraints to the volume density of [CII] emitters at $z\sim4-6$. But because this is a UV-selected sample, we are missing [CII]-bright but UV-faint sources making our constraints strict lower limits. Our derived LFs are statistically consistent with the $z\sim0$ [CII] LF at $10^{8.25} - 10^{9.75}L_\odot$. We compare our results with the upper limits of the [CII] LF derived from serendipitous sources in the ALPINE maps (Loiacono et al. 2020). We also infer the [CII] LFs based on published far-IR and CO LFs at $z\sim4-6$. Combining our robust lower limits with these additional estimates, we set further constraints to the true number density of [CII] emitters at $z\sim 4 - 6$. These additional LF estimates are largely above our LF at $L_{[CII]}>10^9L_{\odot}$, suggesting that UV-faint but [CII]-bright sources likely make a significant contributions to the [CII] emitter volume density. When we include all the LF estimates, we find that available model predictions underestimate the number densities of [CII] emitters at $z\sim4-6$. Finally, we set a constraint on the molecular gas mass density at $z\sim4-6$, with $ρ_{mol} \sim (2-7)\times10^7M_\odot$\,Mpc$^{-3}$. This is broadly consistent with previous studies.

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arXiv2020

SUPER III. Broad Line Region properties of AGN at z$\sim$2

The SINFONI survey for Unveiling the Physics and Effect of Radiative feedback (SUPER) was designed to conduct a blind search for AGN-driven outflows on X-ray selected AGN at redshift z$\sim$2 with high ($\sim$2 kpc) spatial resolution, and correlate them to the properties of the host galaxy and central black hole. The main aims of this paper are: a) to derive reliable estimates for the BH mass and accretion rates for the Type-1 AGN in this survey; b) to characterize the properties of the AGN driven winds in the BLR. We analyzed rest-frame optical and UV spectra of 21 Type-1 AGN. We found that the BH masses estimated from H$α$ and H$β$ lines are in agreement. We estimate BH masses in the range Log(M$\rm_{BH}/M_{\odot}$)=8.4-10.8 and Eddington ratios $\rmλ_{Edd}$ =0.04-1.3. We confirm that the CIV line width does not correlate with the Balmer lines and the peak of the line profile is blue-shifted with respect to the [OIII]-based systemic redshift. These findings support the idea that the CIV line is tracing outflowing gas in the BLR, with velocities up to $\sim$4700 km/s. We confirm the strong dependence of the BLR wind velocity with the UV-to-Xray continuum slope, L$\rm_{Bol}$ and $\rmλ_{Edd}$. We inferred BLR mass outflow rates in the range 0.005-3 M$_{\odot}$/yr, showing a correlation with the bolometric luminosity consistent with that observed for ionized winds in the NLR and X-ray winds detected in local AGN, and kinetic power $\sim$10$^{[-7:-4]}\times$ L$\rm_{Bol}$. Finally, we found an anti-correlation between the equivalent width of the [OIII] line with respect to the CIV shift, and a positive correlation with [OIII] outflow velocity. These findings, for the first time in an unbiased sample of AGN at z$\sim$2, support a scenario where BLR winds are connected to galaxy scale detected outflows, and are capable of affecting the gas in the NLR located at kpc scale.

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arXiv2020

The ALPINE-ALMA [CII] survey: Dust attenuation properties and obscured star formation at z~4.4-5.8

We present dust attenuation properties of spectroscopically confirmed star forming galaxies on the main sequence at a redshift of ~4.4-5.8. Our analyses are based on the far infrared continuum observations of 118 galaxies at rest-frame 158μm obtained with the Atacama Large Millimeter Array (ALMA) Large Program to INvestigate [CII] at Early times (ALPINE). We study the connection between the ultraviolet (UV) spectral slope ($β$), stellar mass (M_*), and infrared excess (IRX=L_IR/L_UV). Twenty-three galaxies are individually detected in the continuum at >3.5 sigma significance. We perform a stacking analysis using both detections and nondetections to study the average dust attenuation properties at z~4.4-5.8. The individual detections and stacks show that the IRX-$β$ relation at z~5 is consistent with a steeper dust attenuation curve than typically found at lower redshifts (z<4). The attenuation curve is similar to or even steeper than that of the extinction curve of the Small Magellanic Cloud (SMC). This systematic change of the IRX-$β$ relation as a function of redshift suggests an evolution of dust attenuation properties at z>4. Similarly, we find that our galaxies have lower IRX values, up to 1dex on average, at a fixed mass compared to previously studied IRX-M_* relations at z<4, albeit with significant scatter. This implies a lower obscured fraction of star formation than at lower redshifts. Our results suggest that dust properties of UV-selected star forming galaxies at z>4 are characterised by (i) a steeper attenuation curve than at z<4, and (ii) a rapidly decreasing dust obscured fraction of star formation as a function of redshift. Nevertheless, even among this UV-selected sample, massive galaxies (log M_*/$M_\odot$>10) at z~5-6 already exhibit an obscured fraction of star formation of ~45%, indicating a rapid build-up of dust during the epoch of reionization.

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arXiv2020

The ALPINE-ALMA [CII] Survey: The nature, luminosity function and star formation history of dusty galaxies up to z~6

We present the detailed characterisation of a sample of 56 sources serendipitously detected in ALMA band 7, as part of the ALMA Large Program to INvestigate CII at Early Times (ALPINE) in COSMOS and ECDFS. These sources have been used to derive the total infrared luminosity function (LF) and to estimate the cosmic star formation rate density (SFRD) up to z=6. We have looked for counterparts in all the available multi-wavelength and photometric redshift catalogues, and in deeper near- and mid-IR source lists and maps, to identify optically dark sources with no matches in the public catalogues. Our ALMA blind survey allows us to push further the study of the nature and evolution of dusty galaxies at high-z, identifying luminous and massive sources to redshifts and faint luminosities never probed before by any far-infrared surveys. The ALPINE data are the first ones to sample the faint-end of the infrared LF, showing little evolution from z=2.5 to z=6, and a flat slope up to the highest redshifts. The SFRD obtained by integrating the luminosity function remains almost constant between z=2 and 6, and significantly higher than the optical/UV derivations, showing an important contribution of dusty galaxies and obscured star formation up to high-z. About 14 per cent of the ALPINE serendipitous continuum sources are optically+near-IR dark (six show a counterpart only in the mid-IR and no HST or near-IR identification, while two are detected as [CII] emitters at z=5). The six HST and near-IR dark galaxies with mid-IR counterpart contribute for about 17 per cent of the total SFRD at z=5 and dominate the high-mass end of the stellar mass function at z>3.

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arXiv2020

MOONRISE: The Main MOONS GTO Extragalactic Survey

The MOONS instrument possesses an exceptional combination of large multiplexing, high sensitivity, broad simultaneous spectral coverage (from optical to near-infrared bands), large patrol area and high fibre density. These properties provide the unprecedented potential of enabling, for the very first time, SDSS-like surveys around Cosmic Noon (z~1-2.5), when the star formation rate in the Universe peaked. The high-quality spectra delivered by MOONS will sample the same nebular and stellar diagnostics observed in extensive surveys of local galaxies, providing an accurate and consistent description of the evolution of various physical properties of galaxies, and hence a solid test of different scenarios of galaxy formation and transformation. Most importantly, by spectroscopically identifying hundreds of thousands of galaxies at high redshift, the MOONS surveys will be capable of determining the environments in which primeval galaxies lived and will reveal how such environments affected galaxy evolution. In this article, we specifically focus on the main Guaranteed Time Observation (GTO) MOONS extragalactic survey, MOONRISE, by providing an overview of its scientific goals and observing strategy.

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arXiv2020

The VLA-COSMOS 3 GHz Large Project: Average radio spectral energy distribution of active galactic nuclei

As the SKA is expected to be operational in the next decade, investigations of the radio sky in the range of 100 MHz to 10 GHz have become important for simulations of the SKA observations. In determining physical properties of galaxies from radio data, the radio SED is often assumed to be described by a simple power law, usually with a spectral index of 0.7 for all sources. Even though radio SEDs have been shown to exhibit deviations from this assumption, both in differing spectral indices and complex spectral shapes, it is often presumed that their individual differences cancel out in large samples. We constructed the average radio SED of radio-excess active galactic nuclei (RxAGN), defined as those that exhibit a 3 $σ$ radio luminosity excess with respect to the value expected only from contribution from star formation, out to z~4. We combined VLA observations of the COSMOS field at 1.4 GHz and 3 GHz with GMRT observations at 325 MHz and 610 MHz. To account for nondetections in the GMRT maps, we employed the survival analysis technique. We selected a sample of RxAGN out to z~4. We find that a sample of RxAGN can be described by a spectral index of $α_1=0.28\pm0.03$ below the break frequency $ν_b=(4.1\pm0.2)$ GHz and $α_2=1.16\pm0.04$ above, while a simple power-law model yields a single spectral index of $α=0.64\pm0.07$. By binning in 1.4 GHz radio luminosity and redshift, we find that the power-law spectral index, as well as broken power-law spectral indices, may increase for larger source sizes, while the power-law spectral index and lower-frequency (<4 GHz) broken power-law spectral index are additionally positively correlated with redshift.

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arXiv2020

SUPER-II: Spatially resolved ionized gas kinematics and scaling relations in z~2 AGN host galaxies

The SINFONI survey for Unveiling the Physics and Effect of Radiative feedback (SUPER) aims at tracing and characterizing ionized gas outflows and their impact on star formation in a statistical sample of X-ray selected Active Galactic Nuclei (AGN) at z$\sim$2. We present the first SINFONI results for a sample of 21 Type-1 AGN spanning a wide range in bolometric luminosity (log $\mathrm{L_{bol}}$ = 45.4-47.9 erg/s). The main aims of this paper are determining the extension of the ionized gas, characterizing the occurrence of AGN-driven outflows, and linking the properties of such outflows with those of the AGN. We use Adaptive Optics-assisted SINFONI observations to trace ionized gas in the extended narrow line region using the [OIII]5007 line. We classify a target as hosting an outflow if its non-parametric velocity of the [OIII] line, $\mathrm{w_{80}}$, is larger than 600 km/s. We study the presence of extended emission using dedicated point-spread function (PSF) observations, after modelling the PSF from the Balmer lines originating from the Broad Line Region. We detect outflows in all the Type-1 AGN sample based on the $\mathrm{w_{80}}$ value from the integrated spectrum, which is in the range 650-2700 km/s. There is a clear positive correlation between $\mathrm{w_{80}}$ and the AGN bolometric luminosity (99% correlation probability), but a weaker correlation with the black hole mass (80% correlation probability). A comparison of the PSF and the [OIII] radial profile shows that the [OIII] emission is spatially resolved for $\sim$35% of the Type-1 sample and the outflows show an extension up to $\sim$6 kpc. The relation between maximum velocity and the bolometric luminosity is consistent with model predictions for shocks from an AGN driven outflow. The escape fraction of the outflowing gas increase with the AGN luminosity, although for most galaxies, this fraction is less than 10%.

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arXiv2020

The VANDELS survey: Discovery of massive overdensities of galaxies at z>2

We want to investigate whether we can use Lyalpha emission to obtain information on the environment properties and whether Lyalpha emitters show different characteristics as a function of their environment. We estimated local densities in the VANDELS Chandra Deep Field-South (CDFS) and UKIDSS Ultra Deep Survey (UDS) fields, by using a three-dimensional algorithm which works in the RA-dec-redshift space. We selected a sample of 131 Lyalpha-emitting galaxies (EW(Lyalpha)>0 A), unbiased with respect to environmental density, to study their location with respect to the over- or under-dense environment. 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. We find that VANDELS Lyalpha emitters (LAEVs) 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 Lyalpha equivalent widths and low specific SFRs, and they also tend to be more massive than the LAEVs in the field. Their stacked Lyalpha profile shows a dominant red peak and a hint of a blue peak. Our results show that LAEVs are likely to be influenced by the environment and favour a scenario with 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, Lyalpha-emitting galaxies can provide useful insights on the environment in which they reside.

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arXiv2020

The ALPINE-ALMA [CII] Survey: CGM pollution and gas mixing by tidal stripping in a merging system at z~4.57

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 [CII] 158 micron and far-infrared continuum data with multi-wavelength ancillary data we find that the system is composed of two massive (Mstar >~ 10^10 Msun) star-forming galaxies experiencing a major merger (stellar mass ratio r_mass ~ 0.9) at close spatial (~13 kpc; projected) and velocity (delta_v < 300 km/s) 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. ALMA reveals also 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 characterized 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.

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arXiv2020

The ALPINE-ALMA [CII] Survey: data processing, catalogs, and statistical source properties

The ALPINE-ALMA large program targets the [CII] 158 $μ$m line and the far-infrared continuum in 118 spectroscopically confirmed star-forming galaxies between z=4.4 and z=5.9. It represents the first large [CII] statistical sample built in this redshift range. We present details of the data processing and the construction of the catalogs. We detected 23 of our targets in the continuum. To derive accurate infrared luminosities and obscured star formation rates, we measured the conversion factor from the ALMA 158 $μ$m rest-frame dust continuum luminosity to the total infrared luminosity (L$_{\rm IR}$) after constraining the dust spectral energy distribution by stacking a photometric sample similar to ALPINE in ancillary single-dish far-infrared data. We found that our continuum detections have a median L$_{\rm IR}$ of 4.4$\times 10^{11}$ L$_\odot$. We also detected 57 additional continuum sources in our ALMA pointings. They are at lower redshift than the ALPINE targets, with a mean photometric redshift of 2.5$\pm$0.2. We measured the 850 $μ$m number counts between 0.35 and 3.5 mJy, improving the current interferometric constraints in this flux density range. We found a slope break in the number counts around 3 mJy with a shallower slope below this value. More than 40 % of the cosmic infrared background is emitted by sources brighter than 0.35 mJy. Finally, we detected the [CII] line in 75 of our targets. Their median [CII] luminosity is 4.8$\times$10$^8$ L$_\odot$ and their median full width at half maximum is 252 km/s. After measuring the mean obscured SFR in various [CII] luminosity bins by stacking ALPINE continuum data, we find a good agreement between our data and the local and predicted SFR-L$_{\rm [CII]}$ relations of De Looze et al. (2014) and Lagache et al. (2018).

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arXiv2020

The ALPINE-ALMA [CII] Survey: Obscured Star Formation Rate Density and Main Sequence of star-forming galaxies at z>4

Star formation rate (SFR) measurements at z>4 have relied mostly on rest-frame far-ultraviolet (FUV) observations. The corrections for dust attenuation based on IRX-$β$ relation are highly uncertain and are still debated in the literature. Hence, rest-frame far-infrared (FIR) observations are necessary to constrain the dust-obscured component of the SFR. In this paper, we exploit the rest-frame FIR continuum observations collected by the ALMA Large Program to INvestigate [CII] at Early times (ALPINE) to directly constrain the obscured SFR in galaxies at 4.4<z<5.9. We use stacks of continuum images to measure average infrared (IR) luminosities taking into account both detected and undetected sources. Based on these measurements, we measure the position of the main sequence of star-forming galaxies and the specific SFR (sSFR) at $z\sim4.5$ and $z\sim5.5$. We find that the main sequence and sSFR do not evolve significantly between $z\sim4.5$ and $z\sim5.5$, as opposed to lower redshifts. We develop a method to derive the obscured SFR density (SFRD) using the stellar masses or FUV-magnitudes as a proxy of FIR fluxes measured on the stacks and combining them with the galaxy stellar mass functions and FUV luminosity functions from the literature. We obtain consistent results independent of the chosen proxy. We find that the obscured fraction of SFRD is decreasing with increasing redshift but even at $z\sim5.5$ it constitutes around 61\% of the total SFRD.

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arXiv2020

X-ray properties of He II 1640 emitting galaxies in VANDELS

We explore X-ray emission from a sample of 18 He II 1640 emitting star-forming galaxies at z ~ 2.3-3.6 from the VANDELS survey in the Chandra Deep Field South, to set constraints on the role of X-ray sources in powering the He II emission. We find that 4 He II emitters have tentative detections with S/N ~ 2 and have X-ray luminosities, L_X = 1.5-4.9 x 10^41 erg/s. The stacked luminosity of all 18 He II emitters is 2.6 x 10^41 erg/s, and that of a subset of 13 narrow He II emitters (FHWM(He II) < 1000 km/s) is 3.1 x 10^41 erg/s. We also measure stacked L_X for non-He II emitters through bootstrapping of matched samples, and find L_X = 2.5 x 10^41 erg/s, which is not significantly different from L_X measured for He II emitters. The L_X per star-formation rate for He II emitters (log (L_X/SFR) ~ 40.0) and non-emitters (log (L_X/SFR) ~ 39.9) are also comparable and in line with the redshift evolution and metallicity dependence predicted by models. Due to the non-significant difference between the X-ray emission from galaxies with and without He II, we conclude that X-ray binaries or weak or obscured AGNs are unlikely to be the dominant producers of He II ionising photons in VANDELS star-forming galaxies at z ~ 3. Given the comparable physical properties of both He II emitters and non-emitters reported previously, alternative He II ionising mechanisms such as localised low-metallicity stellar populations, Pop-III stars, etc. may need to be explored.

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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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arXiv2020

The ALPINE-ALMA [CII] survey: Small Lya-[CII] velocity offsets in main-sequence galaxies at 4.4 < z < 6

The Lya line in the UV and the [CII] line in the FIR are widely used tools to identify galaxies and to obtain insights into ISM properties in the early Universe. By combining data obtained with ALMA in band 7 at ~ 320 GHz as part of the ALMA Large Program to INvestigate [CII] at Early Times (ALPINE) with spectroscopic data from DEIMOS at Keck, VIMOS and FORS2 at the VLT, we assembled a unique sample of 53 main-sequence star-forming galaxies at 4.4 < z < 6 in which we detect both the Lya line and the [CII]. We used [CII], observed with ALMA, as a tracer of the systemic velocity of the galaxies, and we find that 90% of the selected objects have Lya-[CII] velocity offsets in the range 0 < Dv_Lya-[CII] < 400 km/s, in line with the few measurements available so far in the early Universe, and significantly smaller than those observed at lower z. We observe ISM-[CII] offsets in the range -500 < Dv_ISM-[CII] < 0 km/s, in line with values at all redshifts. We find significant anticorrelations between Dv_Lya-[CII] and the Lya rest-frame equivalent width EW0(Lya) (or equivalently, the Lya escape fraction f_esc(Lya)). According to available models for the radiative transfer of Lya photons, the escape of Lya photons would be favored in galaxies with high outflow velocities, in agreement with our observations. The uniform shell model would also predict that the Lya escape in galaxies with slow outflows (0 < v_out < 300 km/s) is mainly determined by the neutral hydrogen column density (NHI), while the alternative model by Steidel+10 would favor a combination of NHI and covering fraction as driver of the Lya escape. We suggest that the observed increase in Lya escape that is observed between z~2 and z~6 is not due to a higher incidence of fast outflows at high redshift, but rather to a decrease in average NHI along the line of sight, or alternatively, a decrease in HI covering fraction. [abridged]

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arXiv2020

Timing the earliest quenching events with a robust sample of massive quiescent galaxies at 2 < z < 5

We present a sample of 151 massive ($M_* > 10^{10}\mathrm{M_\odot}$) 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 $\sim0.5$ 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 $z\sim6-7$ and quenching at $z\sim5$. 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 $λ\sim7000$A 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 $z\gtrsim3$ quiescent objects.

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arXiv2020

The ALPINE-ALMA [CII] survey. Little to no evolution in the [CII]-SFR relation over the last 13 Gyr

The [CII] 158 micron line is one of the strongest IR emission lines, which has been shown to trace the star-formation rate (SFR) of galaxies in the nearby Universe and up to $z \sim 2$. Whether this is also the case at higher redshift and in the early Universe remains debated. The ALPINE survey, which targeted 118 star-forming galaxies at $4.4 < z< 5.9$, provides a new opportunity to examine this question with the first statistical dataset. Using the ALPINE data and earlier measurements from the literature we examine the relation between the [CII] luminosity and the SFR over the entire redshift range from $z \sim 4-8$. ALPINE galaxies, which are both detected in [CII] and dust continuum, show a good agreement with the local L([CII])-SFR relation. Galaxies undetected in the continuum with ALMA are found to be over-luminous in [CII], when the UV SFR is used. After accounting for dust-obscured star formation, by an amount SFR(IR)$\approx$SFR(UV) on average, which results from two different stacking methods and SED fitting, the ALPINE galaxies show an L([CII])-SFR relation comparable to the local one. When [CII] non-detections are taken into account, the slope may be marginally steeper at high-z, although this is still somewhat uncertain. When compared in a homogeneous manner, the $z>6 $ [CII] measurements (detections and upper limits) do not behave very differently from the $z \sim 4-6$ data. We find a weak dependence of L([CII])/SFR on the Lyman-alpha equivalent width. Finally, we find that the ratio L([CII])/LIR $\sim (1-3) \times 10^{-3}$ for the ALPINE sources, comparable to that of "normal" galaxies at lower redshift. Our analysis, which includes the largest sample ($\sim 150$ galaxies) of [CII] measurements at $z>4$ available so far, suggests no or little evolution of the L([CII])-SFR relation over the last 13 Gyr of cosmic time.

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arXiv2020

The ALPINE-ALMA [CII] Survey: Size of Individual Star-Forming Galaxies at z=4-6 and their Extended Halo Structure

We present the physical extent of [CII] 158um line-emitting gas from 46 star-forming galaxies at z=4-6 from the ALMA Large Program to INvestigate CII at Early Times (ALPINE). Using exponential profile fits, we measure the effective radius of the [CII] line (r_e,[CII]) for individual galaxies and compare them with the rest-frame ultra-violet (UV) continuum (r_e,UV) from Hubble Space Telescope images. The effective radius r_e,[CII] exceeds r_e,UV by factors of ~2-3 and the ratio of r_e,[CII]/r_e,UV increases as a function of M_star. We do not find strong evidence that [CII] line, the rest-frame UV, and FIR continuum are always displaced over ~ 1-kpc scale from each other. We identify 30% of isolated ALPINE sources as having an extended [CII] component over 10-kpc scales detected at 4.1$σ$-10.9$σ$ beyond the size of rest-frame UV and far-infrared (FIR) continuum. One object has tentative rotating features up to ~10-kpc, where the 3D model fit shows the rotating [CII]-gas disk spread over 4 times larger than the rest-frame UV-emitting region. Galaxies with the extended [CII] line structure have high star-formation rate (SFR), stellar mass (M_star), low Lya equivalent-width, and more blue-shifted (red-shifted) rest-frame UV metal absorption (Lya line), as compared to galaxies without such extended [CII] structures. Although we cannot rule out the possibility that a selection bias towards 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 [CII] line structures are ubiquitous to high-z star-forming galaxies.

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