arXiv subjects

H. J. McCracken

Publications and source records attributed to H. J. McCracken.

At least 55 records · Page 3Linked to original sources

arXiv2022

The evolution of the galaxy UV luminosity function at redshifts z ~ 8-15 from deep JWST and ground-based near-infrared imaging

We reduce and analyse the available James Webb Space Telescope (JWST) ERO and ERS NIRCam imaging (SMACS0723, GLASS, CEERS) in combination with the latest deep ground-based near-infrared imaging in the COSMOS field (provided by UltraVISTA DR5) to produce a new measurement of the evolving galaxy UV luminosity function (LF) over the redshift range $z = 8 - 15$. This yields a new estimate of the evolution of UV luminosity density ($ρ_{\rm UV}$), and hence cosmic star-formation rate density ($ρ_{\rm SFR}$) out to within $< 300$\, Myr of the Big Bang. Our results confirm that the high-redshift LF is best described by a double power-law (rather than a Schechter) function up to $z\sim10$, and that the LF and the resulting derived $ρ_{\rm UV}$ (and thus $ρ_{\rm SFR}$), continues to decline gradually and steadily up to $z\sim15$ (as anticipated from previous studies which analysed the pre-existing data in a consistent manner to this study). We provide details of the 61 high-redshift galaxy candidates, 47 of which are new, that have enabled this new analysis. Our sample contains 6 galaxies at $z \ge 12$, one of which appears to set a new redshift record as an apparently robust galaxy candidate at $z \simeq 16.4$, the properties of which we therefore consider in detail. The advances presented here emphasize the importance of achieving high dynamic range in studies of early galaxy evolution, and re-affirm the enormous potential of forthcoming larger JWST programmes to transform our understanding of the young Universe.

astro-ph.GA↗

arXiv2022

Euclid preparation. XXI. Intermediate-redshift contaminants in the search for $z>6$ galaxies within the Euclid Deep Survey

(Abridged) The Euclid mission is expected to discover thousands of z>6 galaxies in three Deep Fields, which together will cover a ~40 deg2 area. However, the limited number of Euclid bands and availability of ancillary data could make the identification of z>6 galaxies challenging. In this work, we assess the degree of contamination by intermediate-redshift galaxies (z=1-5.8) expected for z>6 galaxies within the Euclid Deep Survey. This study is based on ~176,000 real galaxies at z=1-8 in a ~0.7 deg2 area selected from the UltraVISTA ultra-deep survey, and ~96,000 mock galaxies with 25.3$\leq$H<27.0, which altogether cover the range of magnitudes to be probed in the Euclid Deep Survey. We simulate Euclid and ancillary photometry from the fiducial, 28-band photometry, and fit spectral energy distributions (SEDs) to various combinations of these simulated data. Our study demonstrates that identifying z>6 with Euclid data alone will be very effective, with a z>6 recovery of 91(88)% for bright (faint) galaxies. For the UltraVISTA-like bright sample, the percentage of z=1-5.8 contaminants amongst apparent z>6 galaxies as observed with Euclid alone is 18%, which is reduced to 4(13)% by including ultra-deep Rubin (Spitzer) photometry. Conversely, for the faint mock sample, the contamination fraction with Euclid alone is considerably higher at 39%, and minimized to 7% when including ultra-deep Rubin data. For UltraVISTA-like bright galaxies, we find that Euclid (I-Y)>2.8 and (Y-J)<1.4 colour criteria can separate contaminants from true z>6 galaxies, although these are applicable to only 54% of the contaminants, as many have unconstrained (I-Y) colours. In the most optimistic scenario, these cuts reduce the contamination fraction to 1% whilst preserving 81% of the fiducial z>6 sample. For the faint mock sample, colour cuts are infeasible.

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arXiv2022

Revealing Galaxy Candidates out to $z \sim 16$ with JWST Observations of the Lensing Cluster SMACS0723

One of the main goals of the JWST is to study the first galaxies in the Universe. We present a systematic photometric analysis of very distant galaxies in the first JWST deep field towards the massive lensing cluster SMACS0723. As a result, we report the discovery of two galaxy candidates at $z\sim16$, only $250$ million years after the Big Bang. We also identify two candidates at $z\sim 12$ and 6 candidates at $z\sim 9-11$. Our search extended out to $z\lesssim21$ by combining color information across seven NIRCam and NIRISS filters. By modelling the Spectral Energy Distributions (SEDs) with \texttt{EAZY} and \texttt{BEAGLE}, we test the robustness of the photometric redshift estimates. While their intrinsic (un-lensed) luminosity is typical of the characteristic luminosity L$^*$ at $z>10$, our high-redshift galaxies typically show small sizes and their morphologies are consistent with disks in some cases. The highest-redshift candidates have extremely blue UV-continuum slopes $-3 < β<-2.4$, young ages $\sim 10-100$\,Myr, and stellar masses around $\log(M_{\star}/\mathrm{M}_{\odot})=8.8$ inferred from their SED modeling, which indicate a rapid build-up of their stellar mass. Our search clearly demonstrates the capabilities of JWST to uncover robust photometric candidates up to very high redshifts, and peer into the formation epoch of the first galaxies.

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arXiv2022

COSMOS2020: Identification of High-z Protocluster Candidates in COSMOS

We conduct a systematic search for protocluster candidates at $z \geq 6$ in the COSMOS field using the recently released COSMOS2020 source catalog. We select galaxies using a number of selection criteria to obtain a sample of galaxies that have a high probability of being inside a given redshift bin. We then apply overdensity analysis to the bins using two density estimators, a Weighted Adaptive Kernel Estimator and a Weighted Voronoi Tessellation Estimator. We have found 15 significant ($>4σ$) candidate galaxy overdensities across the redshift range $6\le z\le7.7$. The majority of the galaxies appear to be on the galaxy main sequence at their respective epochs. We use multiple stellar-mass-to-halo-mass conversion methods to obtain a range of dark matter halo mass estimates for the overdensities in the range of $\sim10^{11-13}\,M_{\rm \odot}$, at the respective redshifts of the overdensities. The number and the masses of the halos associated with our protocluster candidates are consistent with what is expected from the area of a COSMOS-like survey in a standard $Λ$CDM cosmology. Through comparison with simulation, we expect that all the overdensities at $z\simeq6$ will evolve into a Virgo-/Coma-like clusters at present (i.e., with masses $\sim 10^{14}-10^{15}\,M_{\rm \odot}$). Compared to other overdensities identified at $z \geq 6$ via narrow-band selection techniques, the overdensities presented appear to have $\sim10\times$ higher stellar masses and star-formation rates. We compare the evolution in the total star-formation rate and stellar mass content of the protocluster candidates across the redshift range $6\le z\le7.7$ and find agreement with the total average star-formation rate from simulations.

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arXiv2022

Euclid preparation: XX. The Complete Calibration of the Color-Redshift Relation survey: LBT observations and data release

The Complete Calibration of the Color-Redshift Relation survey (C3R2) is a spectroscopic programme designed to empirically calibrate the galaxy color-redshift relation to the Euclid depth (I_E=24.5), a key ingredient for the success of Stage IV dark energy projects based on weak lensing cosmology. A spectroscopic calibration sample as representative as possible of the galaxies in the Euclid weak lensing sample is being collected, selecting galaxies from a self-organizing map (SOM) representation of the galaxy color space. Here, we present the results of a near-infrared H- and K-bands spectroscopic campaign carried out using the LUCI instruments at the LBT. For a total of 251 galaxies, we present new highly-reliable redshifts in the 1.3<= z <=1.7 and 2<= z<=2.7 ranges. The newly-determined redshifts populate 49 SOM cells which previously contained no spectroscopic measurements and almost double the occupation numbers of an additional 153 SOM cells. A final optical ground-based observational effort is needed to calibrate the missing cells in particular in the redshift range 1.7<= z<=2.7 that lack spectroscopic calibration. In the end, Euclid itself will deliver telluric-free NIR spectra that can complete the calibration.

astro-ph.CO↗

arXiv2022

Euclid: Searching for pair-instability supernovae with the Deep Survey

Pair-instability supernovae are theorized supernovae that have not yet been observationally confirmed. They are predicted to exist in low-metallicity environments. Because overall metallicity becomes lower at higher redshifts, deep near-infrared transient surveys probing high-redshift supernovae are suitable to discover pair-instability supernovae. The Euclid satellite, which is planned to be launched in 2023, has a near-infrared wide-field instrument that is suitable for a high-redshift supernova survey. The Euclid Deep Survey is planned to make regular observations of three Euclid Deep Fields (40 deg2 in total) spanning the Euclid's 6 year primary mission period. While the observations of the Euclid Deep Fields are not frequent, we show that the predicted long duration of pair-instability supernovae would allow us to search for high-redshift pair-instability supernovae with the Euclid Deep Survey. Based on the current observational plan of the Euclid mission, we conduct survey simulations in order to estimate the expected numbers of pair-instability supernova discoveries. We find that up to several hundred pair-instability supernovae at z < ~ 3.5 can be discovered within the Euclid Deep Survey. We also show that pair-instability supernova candidates can be efficiently identified by their duration and color that can be determined with the current Euclid Deep Survey plan. We conclude that the Euclid mission can lead to the first confirmation of pair-instability supernovae if their event rates are as high as those predicted by recent theoretical studies. We also update the expected numbers of superluminous supernova discoveries in the Euclid Deep Survey based on the latest observational plan.

astro-ph.HE↗

arXiv2022

COSMOS2020: UV selected galaxies at $z\geq7.5$

This paper presents a new search for $z\geq7.5$ galaxies using the COSMOS2020 photometric catalogues. Finding galaxies at the reionization epoch through deep imaging surveys remains observationally challenging. The larger area covered by ground-based surveys like COSMOS enables the discovery of the brightest galaxies at these high redshifts. Covering $1.4$deg$^2$, our COSMOS catalogues were constructed from the latest UltraVISTA data release (DR4) combined with the final Spitzer/IRAC COSMOS images and the Hyper-Suprime-Cam Subaru Strategic Program DR2 release. We identify $17$ new $7.5<z<10$ candidate sources, and confirm $15$ previously published candidates. Using deblended photometry extracted by fitting surface brightness models on multi-band images, we select four candidates which would be rejected using fixed aperture photometry. We test the robustness of all our candidates by comparing six different photometric redshift estimates. Finally, we compute the galaxy UV luminosity function in three redshift bins centred at $z=8,9,10$. We find no clear evolution of the number density of the brightest galaxies $M_\text{UV}<-21.5$, in agreement with previous works. Rapid changes in the quenching efficiency or attenuation by dust could explain such lack of evolution between $z\sim 8$ and $z\sim 9. A spectroscopic confirmation of the redshifts, already planned with JWST and the Keck telescopes, will be essential to confirm our results.

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arXiv2022

COSMOS2020: The cosmic evolution of the stellar-to-halo mass relation for central and satellite galaxies up to z~5

We use the COSMOS2020 catalogue to measure the stellar-to-halo mass relation (SHMR) divided by central and satellite galaxies from $z=0.2$ to $z = 5.5$. Starting from accurate photometric redshifts we measure the near-infrared selected two-point angular correlation and stellar mass functions in ten redshift bins and fit them with an HOD-based model. At each redshift, we measure the ratio of stellar mass to halo mass, $M_*/M_h$, which shows the characteristic strong dependence of halo mass with a peak at $M_h^{\rm peak} \sim 10^{12}\, M_{\odot}$. Our results are in accordance with the scenario in which the peak of star-formation efficiency moves towards more massive halos at higher redshifts. We also measure the fraction of satellites as a function of stellar mass and redshift. For all stellar mass thresholds the satellite fraction decreases at higher redshifts. At a given redshift there is a higher fraction of low-mass satellites. The satellite contribution to the total stellar mass budget in halos becomes more important than centrals at halo masses of about $M_h > 10^{13} \, M_{\odot}$ and always stays below by peak, indicating that quenching mechanisms are present in massive halos that keep the star-formation efficiency low. Finally, we compare our results with three hydrodynamical simulations Horizon-AGN, Illustris-TNG-100 and EAGLE. We find that the most significant discrepancy is at the high mass end, where the simulations generally show that satellites have a higher contribution to the total stellar mass budget than the observations. This, together with the finding that the fraction of satellites is higher in the simulations, indicates that the feedback mechanisms acting in group-and cluster-scale halos appear to be less efficient in quenching the mass assembly of satellites, and/or that quenching occurs much later in the simulations.

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arXiv2022

COSMOS2020: Manifold Learning to Estimate Physical Parameters in Large Galaxy Surveys

We present a novel method to estimate galaxy physical properties from spectral energy distributions (SEDs), alternate to template fitting techniques and based on self-organizing maps (SOM) to learn the high-dimensional manifold of a photometric galaxy catalog. The method has been previously tested with hydrodynamical simulations in Davidzon et al. (2019) while here is applied to real data for the first time. It is crucial for its implementation to build the SOM with a high quality, panchromatic data set, which we elect to be the "COSMOS2020" galaxy catalog. After the training and calibration steps with COSMOS2020, other galaxies can be processed through SOM to obtain an estimate of their stellar mass and star formation rate (SFR). Both quantities result to be in good agreement with independent measurements derived from more extended photometric baseline, and also their combination (i.e., the SFR vs. stellar mass diagram) shows a main sequence of star forming galaxies consistent with previous studies. We discuss the advantages of this method compared to traditional SED fitting, highlighting the impact of having, instead of the usual synthetic templates, a collection of empirical SEDs built by the SOM in a "data-driven" way. Such an approach also allows, even for extremely large data sets, an efficient visual inspection to identify photometric errors or peculiar galaxy types. Considering in addition the computational speed of this new estimator, we argue that it will play a valuable role in the analysis of oncoming large-area surveys like Euclid or the Legacy Survey of Space and Time at the Vera Cooper Rubin Telescope.

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arXiv2021

Euclid preparation: XVIII. Cosmic Dawn Survey. Spitzer observations of the Euclid deep fields and calibration fields

We present a new infrared survey covering the three Euclid deep fields and four other Euclid calibration fields using Spitzer's Infrared Array Camera (IRAC). We have combined these new observations with all relevant IRAC archival data of these fields in order to produce the deepest possible mosaics of these regions. In total, these observations represent nearly 11% of the total Spitzer mission time. The resulting mosaics cover a total of approximately 71.5deg$^2$ in the 3.6 and 4.5um bands, and approximately 21.8deg$^2$ in the 5.8 and 8um bands. They reach at least 24 AB magnitude (measured to sigma, in a 2.5 arcsec aperture) in the 3.6um band and up to ~ 5 mag deeper in the deepest regions. The astrometry is tied to the Gaia astrometric reference system, and the typical astrometric uncertainty for sources with 16<[3.6]<19 is <0.15 arcsec. The photometric calibration is in excellent agreement with previous WISE measurements. We have extracted source number counts from the 3.6um band mosaics and they are in excellent agreement with previous measurements. Given that the Spitzer Space Telescope has now been decommissioned these mosaics are likely to be the definitive reduction of these IRAC data. This survey therefore represents an essential first step in assembling multi-wavelength data on the Euclid deep fields which are set to become some of the premier fields for extragalactic astronomy in the 2020s.

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arXiv2021

COSMOS2020: A panchromatic view of the Universe to $z\sim10$ from two complementary catalogs

The Cosmic Evolution Survey (COSMOS) has become a cornerstone of extragalactic astronomy. Since the last public catalog in 2015, a wealth of new imaging and spectroscopic data has been collected in the COSMOS field. This paper describes the collection, processing, and analysis of this new imaging data to produce a new reference photometric redshift catalog. Source detection and multi-wavelength photometry is performed for 1.7 million sources across the $2\,\mathrm{deg}^{2}$ of the COSMOS field, $\sim$966,000 of which are measured with all available broad-band data using both traditional aperture photometric methods and a new profile-fitting photometric extraction tool, The Farmer, which we have developed. A detailed comparison of the two resulting photometric catalogs is presented. Photometric redshifts are computed for all sources in each catalog utilizing two independent photometric redshift codes. Finally, a comparison is made between the performance of the photometric methodologies and of the redshift codes to demonstrate an exceptional degree of self-consistency in the resulting photometric redshifts. The $i<21$ sources have sub-percent photometric redshift accuracy and even the faintest sources at $25<i<27$ reach a precision of $5\,\%$. Finally, these results are discussed in the context of previous, current, and future surveys in the COSMOS field. Compared to COSMOS2015, reaches the same photometric redshift precision at almost one magnitude deeper. Both photometric catalogs and their photometric redshift solutions and physical parameters will be made available through the usual astronomical archive systems (ESO Phase 3, IPAC IRSA, and CDS).

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arXiv2020

The ROSAT Raster Survey in the North-Ecliptic Pole Field: X-ray Catalogue and Optical Identifications

The North-Ecliptic Pole is an important region for extragalactic surveys. Deep/wide contiguous surveys are being performed by several space observatories. We analyse all ROSAT pointed and survey observations within 40 deg2 around the NEP, restricting the field-of-view to the inner 30' radius. We obtain an X-ray catalogue of 805 sources with 0.5-2 keV fluxes >2.9E-15 cgs, a factor of three deeper than the ROSAT All-Sky Survey in this field. The sensitivity and angular resolution of our data are comparable to the eROSITA All-Sky Survey expectations. We use HEROES optical and near-infrared imaging photometry from Subaru and CFHT telescopes together with literature catalogues and a new deep and wide Spitzer survey in the field to identify X-ray sources and calculate photometric redshifts for the candidate counterparts. In particular we utilize mid-IR colours to identify AGN X-ray counterparts. Despite relatively large error circles and faint counterparts, confusion and systematic errors, we obtain a rather reliable catalogue of 766 optical counterparts, redshifts and optical classifications. We find a new population of luminous absorbed X-ray AGN at large redshifts, not recognized in previous X-ray surveys, but identified in our work due to the unique combination of survey solid angle, X-ray sensitivity and multiwavelength photometry. We also use the WISE and Spitzer photometry to identify a sample of 185 AGN selected purely through mid-IR colours, most of which are not detected by ROSAT. Their redshifts and upper limits to X-ray luminosity and X-ray to optical flux ratios are even higher than for the new class of X-ray selected luminous AGN2. This unique dataset is important as reference for future deep surveys in the NEP region. Most of the absorbed distant AGN should be readily picked up by eROSITA, but they require sensitive mid-IR imaging to be recognized as optical counterparts.

astro-ph.CO↗

arXiv2020

A lack of evolution in the very bright-end of the galaxy luminosity function from z = 8-10

We utilize deep near-infrared survey data from the UltraVISTA fourth data release (DR4) and the VIDEO survey, in combination with overlapping optical and Spitzer data, to search for bright star-forming galaxies at $z \gtrsim 7.5$. Using a full photometric redshift fitting analysis applied to the $\sim 6\,{\rm deg}^2$ of imaging searched, we find 27 Lyman-break galaxies (LBGs), including 20 new sources, with best-fitting photometric redshifts in the range $7.4 < z < 9.1$. From this sample we derive the rest-frame UV luminosity function (LF) at $z = 8$ and $z = 9$ out to extremely bright UV magnitudes ($M_{\rm UV} \simeq -23$) for the first time. We find an excess in the number density of bright galaxies in comparison to the typically assumed Schechter functional form derived from fainter samples. Combined with previous studies at lower redshift, our results show that there is little evolution in the number density of very bright ($M_{\rm UV} \sim -23$) LBGs between $z \simeq 5$ and $z\simeq 9$. The tentative detection of an LBG with best-fit photometric redshift of $z = 10.9 \pm 1.0$ in our data is consistent with the derived evolution. We show that a double power-law fit with a brightening characteristic magnitude ($ΔM^*/Δz \simeq -0.5$) and a steadily steepening bright-end slope ($Δβ/Δz \simeq -0.5$) provides a good description of the $z > 5$ data over a wide range in absolute UV magnitude ($-23 < M_{\rm UV} < -17$). We postulate that the observed evolution can be explained by a lack of mass quenching at very high redshifts in combination with increasing dust obscuration within the first $\sim 1 \,{\rm Gyr}$ of galaxy evolution.

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arXiv2019

Horizon-AGN virtual observatory - 1. SED-fitting performance and forecasts for future imaging surveys

Using the ligthcone from the cosmological hydrodynamical simulation Horizon-AGN, we produced a photometric catalogue over $0<z<4$ with apparent magnitudes in COSMOS, DES, LSST-like, and Euclid-like filters at depths comparable to these surveys. The virtual photometry accounts for the complex star formation history and metal enrichment of Horizon-AGN galaxies, and consistently includes magnitude errors, dust attenuation and absorption by inter-galactic medium. The COSMOS-like photometry is fitted in the same configuration as the COSMOS2015 catalogue. We then quantify random and systematic errors of photometric redshifts, stellar masses, and star-formation rates (SFR). Photometric redshifts and redshift errors capture the same dependencies on magnitude and redshift as found in COSMOS2015, excluding the impact of source extraction. COSMOS-like stellar masses are well recovered with a dispersion typically lower than 0.1 dex. The simple star formation histories and metallicities of the templates induce a systematic underestimation of stellar masses at $z<1.5$ by at most 0.12 dex. SFR estimates exhibit a dust-induced bimodality combined with a larger scatter (typically between 0.2 and 0.6 dex). We also use our mock catalogue to predict photometric redshifts and stellar masses in future imaging surveys. We stress that adding Euclid near-infrared photometry to the LSST-like baseline improves redshift accuracy especially at the faint end and decreases the outlier fraction by a factor $\sim$2. It also considerably improves stellar masses, reducing the scatter up to a factor 3. It would therefore be mutually beneficial for LSST and Euclid to work in synergy.

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arXiv2018

The WIRCam Ultra Deep Survey (WUDS) I. Survey overview and UV luminosity functions at z~5 and z~6

The aim of this paper is to introduce the WIRCam Ultra Deep Survey (WUDS), a near-IR photometric public survey carried out at the CFH Telescope in the field of the CFHTLS-D3 field (Groth Strip). WUDS includes four near-IR bands (Y, J, H and K_s) over a field of view of ~400 arcmin^2. The typical depth of WUDS data reaches between ~26.8 in Y and J, and ~26 in H and K_s (AB, 3 sigma in 1.3 arcsec aperture). The area and depth of this survey were specifically tailored to set strong constraints on the cosmic star formation rate and the luminosity function brighter or around L* in the z~6-10 redshift domain, although these data are also useful for a variety of extragalactic projects.This first paper is intended to present the properties of WUDS: catalog building, completeness and depth, number counts, photometric redshifts, and global properties of the galaxy population. We have also concentrated on the study of galaxy samples at z~[4.5-7] in this field. UV luminosity functions were derived at z~5 and z~6 taking advantage from the fact that WUDS covers a particularly interesting regime at intermediate luminosities, which allows a combined determination of M* and Phi* with increased accuracy. Our results on the luminosity function are consistent with a small evolution of both M* and Phi* between z=5 and z=6, irrespective of the method used to derive them, either photometric redshifts applied to blindly-selected dropout samples or the classical Lyman Break Galaxy color-preselected samples. Our results lend support to higher Phi* determinations at z=6 than usually reported. The selection and combined analysis of different galaxy samples at z>7 will be presented in a forthcoming paper. WUDS is intended to provide a robust database in the near-IR for the selection of targets for detailed spectroscopic studies, in particular for the EMIR/GTC GOYA Survey (Abridged)

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arXiv2018

The Spitzer Matching Survey of the UltraVISTA Ultra-deep Stripes (SMUVS): the Evolution of Dusty and Non-Dusty Galaxies with Stellar Mass at z=2-6

The Spitzer Matching Survey of the UltraVISTA Ultra-deep Stripes (SMUVS) has obtained the largest ultra-deep Spitzer maps to date in a single field of the sky. We considered the sample of about 66,000 SMUVS sources at $z=2-6$ to investigate the evolution of dusty and non-dusty galaxies with stellar mass through the analysis of the galaxy stellar mass function (GSMF). We further divide our non-dusty galaxy sample with rest-frame optical colours to isolate red quiescent (`passive') galaxies. At each redshift, we identify a characteristic stellar mass in the GSMF above which dusty galaxies dominate, or are at least as important as non-dusty galaxies. Below that stellar mass, non-dusty galaxies comprise about 80% of all sources, at all redshifts except at $z=4-5$. The percentage of dusty galaxies at $z=4-5$ is unusually high: 30-40% for $M_{*}=10^9 - 10^{10.5} \, \rm M_\odot$ and $>80\%$ at $M_*>10^{11} \, \rm M_\odot$, which indicates that dust obscuration is of major importance in this cosmic period. The overall percentage of massive ($\log_{10} (M_*/M_\odot)>10.6$) galaxies that are quiescent increases with decreasing redshift, reaching $>30\%$ at $z\sim2$. Instead, the quiescent percentage among intermediate-mass galaxies (with $\log_{10} (M_*/M_\odot)=9.7-10.6$) stays roughly constant at a $\sim 10\%$ level. Our results indicate that massive and intermediate-mass galaxies clearly have different evolutionary paths in the young Universe, and are consistent with the scenario of galaxy downsizing.

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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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arXiv2018

Starburst to quiescent from HST/ALMA: Stars and dust unveil minor mergers in submillimeter galaxies at $z \sim 4.5$

Dust-enshrouded, starbursting, submillimeter galaxies (SMGs) at $z \geq 3$ have been proposed as progenitors of $z \geq 2$ compact quiescent galaxies (cQGs). To test this connection, we present a detailed spatially resolved study of the stars, dust and stellar mass in a sample of six submillimeter-bright starburst galaxies at $z \sim 4.5$. The stellar UV emission probed by HST is extended, irregular and shows evidence of multiple components. Informed by HST, we deblend Spitzer/IRAC data at rest-frame optical finding that the systems are undergoing minor mergers, with a typical stellar mass ratio of 1:6.5. The FIR dust continuum emission traced by ALMA locates the bulk of star formation in extremely compact regions (median $r_{\rm{e}} = 0.70 \pm 0.29$ kpc) and it is in all cases associated with the most massive component of the mergers (median $\log (M_{*}/M_{\odot}) = 10.49 \pm 0.32$). We compare spatially resolved UV slope ($β$) maps with the FIR dust continuum to study the infrared excess ($\rm{IRX} = L_{\rm{IR}}/L_{\rm{UV}}$)-$β$ relation. The SMGs display systematically higher $\rm{IRX}$ values than expected from the nominal trend, demonstrating that the FIR and UV emissions are spatially disconnected. Finally, we show that the SMGs fall on the mass-size plane at smaller stellar masses and sizes than cQGs at $z = 2$. Taking into account the expected evolution in stellar mass and size between $z = 4.5$ and $z = 2$ due to the ongoing starburst and mergers with minor companions, this is in agreement with a direct evolutionary connection between the two populations.

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