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D. McLeod

Publications and source records attributed to D. McLeod.

12 recordsLinked to original sources
arXiv2021

The ASTRODEEP-GS43 catalogue: new photometry and redshifts for the CANDELS GOODS-South field

We present ASTRODEEP-GS43, a new multiwavelength photometric catalogue of the GOODS-South field, which builds and improves upon the previously released CANDELS catalogue. We provide photometric fluxes and corresponding uncertainties in 43 optical and infrared bands (25 wide and 18 medium filters), as well as photometric redshifts and physical properties of the 34930 CANDELS $H$-detected objects, plus an additional sample of 178 $H$-dropout sources, of which 173 are $Ks$-detected and 5 IRAC-detected. We keep the CANDELS photometry in 7 bands (CTIO $U$, Hubble Space Telescope WFC3 and ISAAC-$K$), and measure from scratch the fluxes in the other 36 (VIMOS, HST ACS, HAWK-I $Ks$, Spitzer IRAC, and 23 from Subaru SuprimeCAM and Magellan-Baade Fourstar) with state-of-the-art techniques of template-fitting. We then compute new photometric redshifts with three different software tools, and take the median value as best estimate. We finally evaluate new physical parameters from SED fitting, comparing them to previously published ones. Comparing to a sample of 3931 high quality spectroscopic redshifts, for the new photo-$z$'s we obtain a normalized median absolute deviation (NMAD) of 0.015 with 3.01$\%$ of outliers (0.011, 0.22$\%$ on the bright end at $I814$<22.5), similarly to the best available published samples of photometric redshifts, such as the COSMOS UltraVISTA catalogue. The ASTRODEEP-GS43 results are in qualitative agreement with previously published catalogues of the GOODS-South field, improving on them particularly in terms of SED sampling and photometric redshift estimates. The catalogue is available for download from the Astrodeep website.

astro-ph.GA↗
arXiv2021

The VANDELS ESO public spectroscopic survey: final Data Release of 2087 spectra and spectroscopic measurements

VANDELS is an ESO Public Spectroscopic Survey designed to build a sample of high signal to noise, medium resolution spectra of galaxies at redshift between 1 and 6.5. Here we present the final Public Data Release of the VANDELS Survey, comprising 2087 redshift measurements. We give a detailed description of sample selection, observations and data reduction procedures. The final catalogue reaches a target selection completeness of 40% at iAB = 25. The high Signal to Noise ratio of the spectra (above 7 in 80% of the spectra) and the dispersion of 2.5Å allowed us to measure redshifts with high precision, the redshift measurement success rate reaching almost 100%. Together with the redshift catalogue and the reduced spectra, we also provide optical mid-IR photometry and physical parameters derived through SED fitting. The observed galaxy sample comprises both passive and star forming galaxies covering a stellar mass range 8.3< Log(M*/Msolar)<11.7. All catalogues and spectra are accessible through the survey database (http://vandels.inaf.it) where all information can be queried interactively, and via the ESO Archive (https://www.eso.org/qi/).

astro-ph.GA↗
arXiv2019

Through Andromeda and Beyond: AGN Optical Transient 'Sharov21' Revisited

We revisit a notable AGN known as `Sharov21', seen to undergo a dramatic outburst in 1992, brightening by a factor of thirty over a period of approximately one year. A simple microlensing model fit to the event lightcurve provides a constraint on the distance of the lensing object which is consistent with the distance to M31, strongly suggesting that this is the correct explanation. Archival XMM/Hubble/Spitzer data show that this AGN can be considered an otherwise unremarkable type-I AGN. Our analysis of the expected rate of background AGN being microlensed by a factor of two or more due to stellar-mass objects in M31 shows that events of this nature should only occur on average every half century. It is thus perhaps surprising that we have uncovered evidence for two more events that are qualitatively similar. A systematic search for new and archival events, with follow-up spectroscopy, is thus warranted.

astro-ph.GA↗
arXiv2019

The Intergalactic medium transmission towards z>4 galaxies with VANDELS and the impact of dust attenuation

Aims. Our aim is to estimate the intergalactic medium transmission towards UV-selected star-forming galaxies at redshift 4 and above and study the effect of the dust attenuation on these measurements. Methods. The ultra-violet spectrum of high redshift galaxies is a combination of their intrinsic emission and the effect of the Inter-Galactic medium (IGM) absorption along their line of sight. Using data coming from the unprecedented deep spectroscopy from the VANDELS ESO public survey carried out with the VIMOS instrument we compute both the dust extinction and the mean transmission of the IGM as well as its scatter from a set of 281 galaxies at z>3.87. Because of a degeneracy between the dust content of the galaxy and the IGM, we first estimate the stellar dust extinction parameter E(B-V) and study the result as a function of the dust prescription. Using these measurements as constraint for the spectral fit we estimate the IGM transmission Tr(Lyalpha). Both photometric and spectroscopic SED fitting are done using the SPectroscopy And photometRy fiTting tool for Astronomical aNalysis (SPARTAN) that is able to fit the spectral continuum of the galaxies as well as photometric data. Results. Using the classical Calzetti's attenuation law we find that E(B-V) goes from 0.11 at z=3.99 to 0.08 at z=5.15. These results are in very good agreement with previous measurements from the literature. We estimate the IGM transmission and find that the transmission is decreasing with increasing redshift from Tr(Lyalpha)=0.53 at z=3.99 to 0.28 at z=5.15. We also find a large standard deviation around the average transmission that is more than 0.1 at every redshift. Our results are in very good agreement with both previous measurements from AGN studies and with theoretical models.

astro-ph.CO↗
arXiv2018

The VANDELS ESO public spectroscopic survey: observations and first data release

This paper describes the observations and the first data release (DR1) of the ESO public spectroscopic survey "VANDELS, a deep VIMOS survey of the CANDELS CDFS and UDS fields". VANDELS' main targets are star-forming galaxies at 2.4<z<5.5 and massive passive galaxies at 1<z<2.5. By adopting a strategy of ultra-long exposure times, from 20 to 80 hours per source, VANDELS is designed to be the deepest ever spectroscopic survey of the high-redshift Universe. Exploiting the red sensitivity of the VIMOS spectrograph, the survey has obtained ultra-deep spectra covering the wavelength 4800-10000 A with sufficient signal-to-noise to investigate the astrophysics of high-redshift galaxy evolution via detailed absorption line studies. The VANDELS-DR1 is the release of all spectra obtained during the first season of observations and includes data for galaxies for which the total (or half of the total) scheduled integration time was completed. The release contains 879 individual objects with a measured redshift and includes fully wavelength and flux-calibrated 1D spectra, the associated error spectra, sky spectra and wavelength-calibrated 2D spectra. We also provide a catalog with the essential galaxy parameters, including spectroscopic redshifts and redshift quality flags. In this paper we present the survey layout and observations, the data reduction and redshift measurement procedure and the general properties of the VANDELS-DR1 sample. We also discuss the spectroscopic redshift distribution, the accuracy of the photometric redshifts and we provide some examples of data products. All VANDELS-DR1 data are publicly available and can be retrieved from the ESO archive. Two further data releases are foreseen in the next 2 years with a final release scheduled for June 2020 which will include improved re-reduction of the entire spectroscopic data set. (abridged)

astro-ph.GA↗
arXiv2016

MUSE integral-field spectroscopy towards the Frontier Fields cluster Abell S1063: II. Properties of low luminosity Lyman alpha emitters at z>3

In spite of their conjectured importance for the Epoch of Reionization, the properties of low-mass galaxies are currently still under large debate. In this article, we study the stellar and gaseous properties of faint, low-mass galaxies at z>3. We observed the Frontier Fields cluster Abell S1063 with MUSE over a 2 arcmin^2 field, and combined integral-field spectroscopy with gravitational lensing to perform a blind search for intrinsically faint Lya emitters (LAEs). We determined in total the redshift of 172 galaxies of which 14 are lensed LAEs at z=3-6.1. We increased the number of spectroscopically-confirmed multiple-image families from 6 to 17 and updated our gravitational-lensing model accordingly. The lensing-corrected Lya luminosities are with L(Lya) <= 10^41.5 erg/s among the lowest for spectroscopically confirmed LAEs at any redshift. We used expanding gaseous shell models to fit the Lya line profile, and find low column densities and expansion velocities. This is to our knowledge the first time that gaseous properties of such faint galaxies at z>=3 are reported. We performed SED modelling to broadband photometry from the U-band through the infrared to determine the stellar properties of these LAEs. The stellar masses are very low (10^{6-8} Msun), and are accompanied by very young ages of 1-100 Myr. The very high specific star formation rates (~100 Gyr^-1) are characteristic of starburst galaxies. The UV-continuum slopes beta are low in our sample, with beta<-2 for all galaxies with M_star<10^8 Msun. We conclude that our low-mass galaxies at 3<z<6 are forming stars at higher rates when correcting for stellar mass effects than seen locally or in more massive galaxies. The young stellar populations with high star-formation rates and low HI column densities lead to continuum slopes and LyC-escape fractions expected for a scenario where low mass galaxies reionise the Universe.

astro-ph.GA↗
arXiv2015

Participant and spectator scaling of spectator fragments in Au+Au and Cu+Cu collisions at sqrt(sNN) = 19.6 and 22.4 GeV

Spectator fragments resulting from relativistic heavy ion collisions, consisting of single protons and neutrons along with groups of stable nuclear fragments up to Nitrogen (Z=7), are measured in PHOBOS. These fragments are observed in Au+Au (sqrt(sNN)=19.6 GeV) and Cu+Cu (22.4 GeV) collisions at high pseudorapidity ($η$). The dominant multiply-charged fragment is the tightly bound Helium ($α$), with Lithium, Beryllium, and Boron all clearly seen as a function of collision centrality and pseudorapidity. We observe that in Cu+Cu collisions, it becomes much more favorable for the $α$ fragments to be released than Lithium. The yields of fragments approximately scale with the number of spectator nucleons, independent of the colliding ion. The shapes of the pseudorapidity distributions of fragments indicate that the average deflection of the fragments away from the beam direction increases for more central collisions. A detailed comparison of the shapes for $α$ and Lithium fragments indicates that the centrality dependence of the deflections favors a scaling with the number of participants in the collision.

nucl-ex↗
arXiv2010

Phobos results on charged particle multiplicity and pseudorapidity distributions in Au+Au, Cu+Cu, d+Au, and p+p collisions at ultra-relativistic energies

Pseudorapidity distributions of charged particles emitted in $Au+Au$, $Cu+Cu$, $d+Au$, and $p+p$ collisions over a wide energy range have been measured using the PHOBOS detector at RHIC. The centrality dependence of both the charged particle distributions and the multiplicity at midrapidity were measured. Pseudorapidity distributions of charged particles emitted with $|η|<5.4$, which account for between 95% and 99% of the total charged-particle emission associated with collision participants, are presented for different collision centralities. Both the midrapidity density, $dN_{ch}/dη$, and the total charged-particle multiplicity, $N_{ch}$, are found to factorize into a product of independent functions of collision energy, $\sqrt{s_{_{NN}}}$, and centrality given in terms of the number of nucleons participating in the collision, $N_{part}$. The total charged particle multiplicity, observed in these experiments and those at lower energies, assumes a linear dependence of $(\ln s_{_{NN}})^2$ over the full range of collision energy of $\sqrt{s_{_{NN}}}$=2.7-200 GeV.

nucl-ex↗
arXiv2004

Production of phi Mesons in Au+Au Collisions at 11.7 A GeV/c

We report on a measurement of phi-meson production in Au+Au collisions at a beam momentum of 11.7 A GeV/c by Experiment E917 at the AGS. The measurement covers the midrapidity region 1.2 < y < 1.6. Transverse-mass spectra and the rapidity distribution are presented as functions of centrality characterized by the number of participant projectile nucleons. The yield of phi's per participant projectile nucleon increases strongly in central collisions in a manner similar to that observed for kaons.

nucl-ex↗
arXiv2001

Baryon Rapidity Loss in Relativistic Au+Au Collisions

An excitation function of proton rapidity distributions for different centralities is reported from AGS Experiment E917 for Au+Au collisions at 6, 8, and 10.8 GeV/nucleon. The rapidity distributions from peripheral collisions have a valley at midrapidity which smoothly change to distributions that peak at midrapidity for central collisions. The mean rapidity loss increases with increasing beam energy, whereas the fraction of protons consistent with isotropic emission from a thermal source at midrapidity decreases with increasing beam energy.

nucl-ex↗
arXiv2001

Antilambda production in Au+Au collisions at 11.7 A GeV/c

We present results from Experiment E917 for antilambda and antiproton production in Au+Au collisions at 11.7 A GeV. We have measured invariant spectra and yields for both species in central and peripheral collisions. We find that the antilambda/antiproton ratio near mid-rapidity increases from 0.26+0.19-0.15 in peripheral collisions to 3.6+4.7-1.8 in central collisions, a value that is substantially larger than current theoretical estimates.

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