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We study the relationships between stellar mass, size, and age within the quiescent population, using two mass-complete spectroscopic samples with log10(M⋆/M⊙) > 10.3, taken from VANDELS at 1.0 < z < 1.3, and LEGA-C at 0.6 < z < 0.8. Using robust Dn4000 values, we demonstrate that the well-known ‘downsizing’ signature is already in place by z ≃ 1.1, with Dn4000 increasing by ≃ 0.1 across a ≃ 1 dex mass interval for both VANDELS and LEGA-C. We then proceed to investigate the evolution of the quiescent galaxy stellar mass–size relation from z ≃ 1.1 to z ≃ 0.7. We find the median size increases by a factor of 1.9 ± 0.1 at log10(M⋆/M⊙) = 10.5, and see tentative evidence for flattening of the relation, finding slopes of α = 0.72 ± 0.06 and α=0.56±0.04 for VANDELS and LEGA-C, respectively. We finally split our sample into galaxies above and below our fitted mass–size relations, to investigate how size and Dn4000 correlate. For LEGA-C, we see a clear difference, with larger galaxies found to have smaller Dn4000 at fixed stellar mass. Due to the faintness and smaller numbers of the VANDELS sample, we cannot confirm whether a similar relation exists at z ≃ 1.1. We consider whether differences in stellar age or metallicity are most likely to drive this size–Dn4000 relation, finding that any metallicity differences are unlikely to fully explain the observed offset, meaning smaller galaxies must be older than their larger counterparts. We find the observed evolution in size, mass, and Dn4000 across the ≃ 2 Gyr from z ∼ 1.1 to z ∼ 0.7 can be explained by a simple toy model in which VANDELS galaxies evolve passively whilst experiencing a series of minor mergers.

We present the results of a new study investigating the relationship between observed Ly α equivalent width (Wλ(Ly α)) and the metallicity of the ionizing stellar population ( Z⋆) for a sample of 768 star-forming galaxies at 3 ≤ z ≤ 5 drawn from the VANDELS survey. Dividing our sample into quartiles of rest-frame Wλ(Ly α) across the range $-58 \,\rm {\mathring{\rm A}} \lesssim$ Wλ(Ly α) $\lesssim 110 \,\rm {\mathring{\rm A}}$ , we determine Z⋆ from full spectral fitting of composite far-ultraviolet spectra and find a clear anticorrelation between Wλ(Ly α) and Z⋆. Our results indicate that Z⋆ decreases by a factor ≳ 3 between the lowest Wλ(Ly α) quartile (λ(Ly α) $\rangle =-18\,\rm {\mathring{\rm A}}$ ) and the highest Wλ(Ly α) quartile (λ(Ly α) $\rangle =24\,\rm {\mathring{\rm A}}$ ). Similarly, galaxies typically defined as Lyman alpha emitters (LAEs; Wλ(Ly α) $\gt 20\,\rm {\mathring{\rm A}}$ ) are, on average, metal poor with respect to the non-LAE galaxy population (Wλ(Ly α) $\le 20\,\rm {\mathring{\rm A}}$ ) with Z⋆non-LAE ≳ 2 × Z⋆LAE. Finally, based on the best-fitting stellar models, we estimate that the increasing strength of the stellar ionizing spectrum towards lower Z⋆ is responsible for ${\simeq}15{-}25{{\ \rm per\ cent}}$ of the observed variation in Wλ(Ly α) across our sample, with the remaining contribution ( ${\simeq}75{-}85{{\ \rm per\ cent}}$ ) being due to a decrease in the H I/dust covering fractions in low- Z⋆ galaxies.

The Euclid mission will observe well over a billion galaxies out to $z\sim6$ and beyond. This will offer an unrivalled opportunity to investigate several key questions for understanding galaxy formation and evolution. The first step for many of these studies will be the selection of a sample of quiescent and star-forming galaxies, as is often done in the literature by using well known colour techniques such as the `UVJ' diagram. However, given the limited number of filters available for the Euclid telescope, the recovery of such rest-frame colours will be challenging. We therefore investigate the use of observed Euclid colours, on their own and together with ground-based u-band observations, for selecting quiescent and star-forming galaxies. The most efficient colour combination, among the ones tested in this work, consists of the (u-VIS) and (VIS-J) colours. We find that this combination allows users to select a sample of quiescent galaxies complete to above $\sim70\%$ and with less than 15$\%$ contamination at redshifts in the range $0.7565\%$ completeness level and contamination below 20$\%$ at $1, Comment: 19 pages, 15 figures, 5 tables, accepted for publication in MNRAS

We present the results of a study utilising ultra-deep, rest-frame UV, spectroscopy to quantify the relationship between stellar mass and stellar metallicity for 681 star-forming galaxies at $2.5, Comment: 21 pages (+ appendix), 13 figures, MNRAS accepted

We empirically test the relation between the SFR(LIR) derived from the infrared luminosity, LIR, and the SFR(Ha) derived from the Ha emission line luminosity using simple conversion relations. We use a sample of 474 galaxies at z = 0.06 - 0.46 with both Ha detection (from 20k zCOSMOS survey) and new far-IR Herschel data (100 and 160 {\mu}m). We derive SFR(Ha) from the Ha extinction corrected emission line luminosity. We find a very clear trend between E(B - V) and LIR that allows to estimate extinction values for each galaxy even if the Ha emission line measurement is not reliable. We calculate the LIR by integrating from 8 up to 1000 {\mu}m the SED that is best fitting our data. We compare SFR(Ha) with the SFR(LIR). We find a very good agreement between the two SFR estimates, with a slope of m = 1.01 \pm 0.03 in the SFR(LIR) vs SFR(Ha) diagram, a normalization constant of a = -0.08 \pm 0.03 and a dispersion of sigma = 0.28 dex.We study the effect of some intrinsic properties of the galaxies in the SFR(LIR)-SFR(Ha) relation, such as the redshift, the mass, the SSFR or the metallicity. The metallicity is the parameter that affects most the SFR comparison. The mean ratio of the two SFR estimators log[SFR(LIR)/SFR(Ha)] varies by approx. 0.6 dex from metal-poor to metal-rich galaxies (8.1 < log(O/H) + 12 < 9.2). This effect is consistent with the prediction of a theoretical model for the dust evolution in spiral galaxies. Considering different morphological types, we find a very good agreement between the two SFR indicators for the Sa, Sb and Sc morphologically classified galaxies, both in slope and normalization. For the Sd, irregular sample (Sd/Irr), the formal best-fit slope becomes much steeper (m = 1.62 \pm 0.43), but it is still consistent with 1 at the 1.5 sigma level, because of the reduced statistics of this sub-sample.

Bolometric luminosities and Eddington ratios of both X-ray selected broad-line (Type-1) and narrow-line (Type-2) AGN from the XMM-Newton survey in the COSMOS field are presented. The sample is composed by 929 AGN (382 Type-1 AGN and 547 Type-2 AGN) and it covers a wide range of redshifts, X-ray luminosities and absorbing column densities. About 65% of the sources are spectroscopically identified as either Type-1 or Type-2 AGN (83% and 52% respectively), while accurate photometric redshifts are available for the rest of the sample. The study of such a large sample of X-ray selected AGN with a high quality multi-wavelength coverage from the far-infrared (now with the inclusion of Herschel data at 100 micron and 160 micron) to the optical-UV allows us to obtain accurate estimates of bolometric luminosities, bolometric corrections and Eddington ratios. The kbol-Lbol relations derived in the present work are calibrated for the first time against a sizable AGN sample, and rely on observed redshifts, X-ray luminosities and column density distributions. We find that kbol is significantly lower at high Lbol with respect to previous estimates by Marconi et al. (2004) and Hopkins et al. (2007). Black hole masses and Eddington ratios are available for 170 Type-1 AGN, while black hole masses for Type-2 AGN are computed for 481 objects using the black hole mass-stellar mass relation and the morphological information. We confirm a trend between kbol and lambda_Edd, with lower hard X-ray bolometric corrections at lower Eddington ratios for both Type-1 and Type-2 AGN. We find that, on average, Eddington ratio increases with redshift for all Types of AGN at any given Mbh, while no clear evolution with redshift is seen at any given Lbol.

We have studied the evolution of high redshift quiescent galaxies over an effective area of ~1.7 deg^2 in the COSMOS field. Galaxies have been divided according to their star-formation activity and the evolution of the different populations has been investigated in detail. We have studied an IRAC (mag_3.6 1.4 with multi-wavelength coverage. We have derived accurate photometric redshifts (sigma=0.06) and other important physical parameters through a SED-fitting procedure. We have divided our sample into actively star-forming, intermediate and quiescent galaxies depending on their specific star formation rate. We have computed the galaxy stellar mass function of the total sample and the different populations at z=1.4-3.0. We have studied the properties of high redshift quiescent galaxies finding that they are old (1-4 Gyr), massive (log(M/M_sun)~10.65), weakly star forming stellar populations with low dust extinction (E(B-V) 11, while the quiescent population increases from 10% to 50% at the same redshift and mass intervals. We compare the fraction of quiescent galaxies derived with that predicted by theoretical models and find that the Kitzbichler & White (2007) model is the one that better reproduces the data. Finally, we calculate the stellar mass density of the star-forming and quiescent populations finding that there is already a significant number of quiescent galaxies at z > 2.5 (rho~6.0 MsunMpc^-3).

We measure the real-space galaxy power spectrum on large scales at redshifts 0.5 to 1.2 using optical colour-selected samples from the CFHT Legacy Survey. With the redshift distributions measured with a preliminary ~14000 spectroscopic redshifts from the VIMOS Public Extragalactic Redshift Survey (VIPERS), we deproject the angular distribution and directly estimate the three-dimensional power spectrum. We use a maximum likelihood estimator that is optimal for a Gaussian random field giving well-defined window functions and error estimates. This measurement presents an initial look at the large-scale structure field probed by the VIPERS survey. We measure the galaxy bias of the VIPERS-like sample to be b_g=1.38 +- 0.05 (sigma_8=0.8) on scales k

We model the evolution of the mean galaxy occupation of dark-matter halos over the range $0.1 0.1 M_0$ merger event occuring between redshifts of 0.5 and 1.0. Futhermore, we find that more luminous galaxies are found to occupy more massive halos irrespectively of the redshift. Finally, the average number of galaxies per halo shows little increase from redshift z$\sim$ 1.0 to z$\sim$ 0.5, with a sharp increase by a factor $\sim$3 from z$\sim$ 0.5 to z$\sim$ 0.1, likely due to the dynamical friction of subhalos within their host halos.