A. Pipino

THE ZURICH ENVIRONMENTAL STUDY OF GALAXIES IN GROUPS ALONG THE COSMIC WEB. I. WHICH ENVIRONMENT AFFECTS GALAXY EVOLUTION

The Zurich Environmental Study (ZENS) is based on a sample of ~1500 galaxy members of 141 groups in the mass range ~1012.5-14.5 M ☉ within the narrow redshift range 0.05 1010 M ☉, satellite galaxies in relaxed and unrelaxed groups have similar size, color, and (specific) star formation rate distributions; at lower galaxy masses, satellites are marginally redder in relaxed relative to unrelaxed groups, suggesting quenching of star formation in low-mass satellites by physical processes active in relaxed halos. Overall, relaxed and unrelaxed groups show similar stellar mass populations, likely indicating similar stellar mass conversion efficiencies. In the enclosed ZENS catalog, we publish all environmental diagnostics as well as the galaxy structural and photometric measurements described in companion ZENS papers II and III.

ZENS. IV. Similar morphological changes associated with mass quenching and environment quenching and the relative importance of bulge growth versus the fading of disks

We use the low-redshift Zurich Environmental Study (ZENS) catalog to study the dependence of the quenched satellite fraction at

The dust content of QSO hosts at high redshift

{10}^{10.0}\;{M}_{\odot }\to {10}^{11.5}\;{M}_{\odot }

THE ZURICH ENVIRONMENTAL STUDY (ZENS) OF GALAXIES IN GROUPS ALONG THE COSMIC WEB. II. GALAXY STRUCTURAL MEASUREMENTS AND THE CONCENTRATION OF MORPHOLOGICALLY CLASSIFIED SATELLITES IN DIVERSE ENVIRONMENTS

, and of the morphological mix of these quenched satellites, on three different environmental parameters: group halo mass, halo-centric distance, and large-scale structure (LSS) overdensity. Within the two mass bins into which we divide our galaxy sample, the fraction of quenched satellites is more or less independent of halo mass and the surrounding LSS overdensity, but it increases toward the centers of the halos, as found in previous studies. The morphological mix of these quenched satellites is, however, constant with radial position in the halo, indicating that the well-known morphology–density relation results from the increasing fraction of quenched galaxies toward the centers of halos. If the radial variation in the quenched fraction reflects the action of two quenching processes, one related to mass and the other to environment, then the constancy with radius of the morphological outcome suggests that both have the same effect on the morphologies of the galaxies. Alternatively, mass and environment quenching may be two reflections of a single physical mechanism. The quenched satellites have larger bulge-to-total ratios (B/T) and smaller half-light radii than the star-forming satellites. The bulges in quenched satellites have very similar luminosities and surface brightness profiles, and any mass growth of the bulges associated with quenching cannot greatly change these quantities. The differences in the light-defined B/T and in the galaxy half-light radii are mostly due to differences in the disks, which have lower luminosities in the quenched galaxies. The difference in galaxy half-light radii between quenched and star-forming satellites is however larger than can be explained by uniformly fading the disks following quenching, and the quenched disks have smaller scale lengths than in star-forming satellites. This can be explained either by a differential fading of the disks with galaxy radius or the disks being generally smaller in the past, both of which would be expected in an inside-out disk growth scenario. The overall conclusion is that, at least at low redshifts, the structure of massive quenched satellites at these masses is produced by processes that operate before the quenching takes place. A comparison of our results with semianalytic models argues for a reduction in the efficiency of group halos in quenching their disk satellites and for mechanisms to increase the B/T of low-mass quenched satellites.

On the relation between specific star formation rate and metallicity

Infrared observations of high-z quasar (QSO) hosts indicate the presence of large masses of dust in the early universe. When combined with other observables, such as neutral gas masses and star formation rates, the dust content of z~6 QSO hosts may help constraining their star formation history. We have collected a database of 58 sources from the literature discovered by various surveys and observed in the FIR. We have interpreted the available data by means of chemical evolution models for forming proto-spheroids, investigating the role of the major parameters regulating star formation and dust production. For a few systems, given the derived small dynamical masses, the observed dust content can be explained only assuming a top-heavy initial mass function, an enhanced star formation efficiency and an increased rate of dust accretion. However, the possibility that, for some systems, the dynamical mass has been underestimated cannot be excluded. If this were the case, the dust mass can be accounted for by standard model assumptions. We provide predictions regarding the abundance of the descendants of QSO hosts; albeit rare, such systems should be present and detectable by future deep surveys such as Euclid already at z>4.

Galactic and cosmic Type Ia supernova (SNIa) rates: is it possible to impose constraints on SNIa progenitors?

We present structural measurements for the galaxies in the 0.05 1010 M ☉ disk-dominated satellites, which are ~10% more concentrated in high mass groups than in lower mass groups.

The two regimes of the cosmic sSFR evolution are due to spheroids and discs

In this paper we present an exact general analytic expression Z(sSFR) = yZ Λ(sSFR) + I(sSFR) linking the gas metallicity Z to the specific star formation rate (sSFR), that validates and extends the approximate relation put forward by Lilly et al. (2013, L13), where yz is the yield per stellar generation, Λ(sSFR) is the instantaneous ratio between inflow and star formation rate expressed as a function of the sSFR, and I is the integral of the past enrichment history, respectively. We then demonstrate that the instantaneous metallicity of a self-regulating system, such that its sSFR decreases with decreasing redshift, can be well approximated by the first term on the right-hand side in the above formula, which provide an upper bound to the metallicity. The metallicity is well approximated also by Z L13 = Z(sSFR) = yZ 1+η+sSFR/ν (L13 ideal regulator case), which provides a lower bound to the actual metallicity. We compare these approximate analytic formulae to numerical results and infer a discrepancy < 0.1 dex in a range of metallicities (log(Z/Z⊙) ∈ [−1.5, 0], for yz ≡ Z⊙ = 0.02) and almost three orders of magnitude in the sSFR. We explore the consequences of the L13 model on the mass-weighted metallicity in the stellar component of the galaxies. We find that the stellar average metallicity lags ∼ 0.1− 0.2 dex behind the gas-phase metallicity relation, in agreement with the data.

THE ZURICH ENVIRONMENTAL STUDY (ZENS) OF GALAXIES IN GROUPS ALONG THE COSMIC WEB. V. PROPERTIES AND FREQUENCY OF MERGING SATELLITES AND CENTRALS IN DIFFERENT ENVIRONMENTS

We compute the Type Ia supernova rates in typical elliptical galaxies by varying the progenitor models for Type Ia supernovae. To do that a formalism which takes into account the delay distribution function (DTD) of the explosion times and a given star formation history is adopted. Then the chemical evolution for ellipticals with baryonic initial masses 10 10 , 10 11 and 10 12 M⊙ is computed, and the mass of Fe produced by each galaxy is precisely estimated. We also compute the expected Fe mass ejected by ellipticals in typical galaxy clusters (e.g. Coma and Virgo), under different assumptions about Type Ia SN progenitors. As a last step, we compute the cosmic Type Ia SN rate in an unitary volume of the Universe by adopting several cosmic star formation rates and compare it with the available and recent observational data. Unfortunately, no firm conclusions can be derived only from the cosmic SNIa rate, neither on SNIa progenitors nor on the cosmic star formation rate. Finally, by analysing all our results together, and by taking into account previous chemical evolution results, we try to constrain the best Type Ia progenitor model. We conclude that the best progenitor models for Type Ia SNe are still the single degenerate model, the double degenerate wide model, and the empirical bimodal model. All these models require the existence of prompt Type Ia supernovae, exploding in the first 100 Myr since the beginning of star formation, although their fraction should not exceed 15-20% in order to fit chemical abundances in galaxies.

Colour gradients of high-redshift early-type galaxies from hydrodynamical monolithic models

This paper aims at explaining the two phases in the observed specific star formation rate (sSFR), namely the high (>3/Gyr) values at z>2 and the smooth decrease since z=2. In order to do this, we compare to observations the specific star formation rate evolution predicted by well calibrated models of chemical evolution for elliptical and spiral galaxies, using the additional constraints on the mean stellar ages of these galaxies (at a given mass). We can conclude that the two phases of the sSFR evolution across cosmic time are due to different populations of galaxies. At z>2 the contribution comes from spheroids: the progenitors of present-day massive ellipticals (which feature the highest sSFR) as well as halos and bulges in spirals (which contribute with average and lower-than-average sSFR). In each single galaxy the sSFR decreases rapidly and the star formation stops in <1 Gyr. However the combination of different generations of ellipticals in formation might result in an apparent lack of strong evolution of the sSFR (averaged over a population) at high redshift. The z<2 decrease is due to the slow evolution of the gas fraction in discs, modulated by the gas accretion history and regulated by the Schmidt law. The Milky Way makes no exception to this behaviour.

Abundances and Abundance Ratios in Stars and Hot Gas in Elliptical Galaxies

We use the Zurich ENvironmental Study (ZENS) database to investigate the environmental dependence of the merger fraction