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Relic galaxies, the oldest ultra-compact massive galaxies (UCMGs), contain almost exclusively "pristine" stars formed during an intense star formation (SF) burst at high redshift. As such, they allow us to study in detail the early mechanism of galaxy assembly in the Universe. Using the largest catalogue of spectroscopically confirmed UCMGs for which a degree of relicness (DoR) had been estimated, the INSPIRE catalogue, we investigate whether or not relics prefer dense environments. The objective of this study is to determine if the DoR, which measures how extreme the SF history was, and the surrounding environment are correlated. In order to achieve this goal, we employ the AMICO galaxy cluster catalogue to compute the probability for a galaxy to be a member of a cluster, and measure the local density around each UCMG using machine learning-based photometric redshifts. We find that UCMGs can reside both in clusters and in the field, but objects with very low DoR (< 0.3, i.e., a relatively extended SF history) prefer under-dense environments. We additionally report a correlation between the DoR and the distance from the cluster centre: more extreme relics, when located in clusters, tend to occupy the more central regions of them. We finally outline potential evolution scenarios for UCMGs at different DoR to reconcile their presence in both clusters and field environments, Comment: Accepted for publication on MNRAS, 11 pages, 8 figure, 1 table

The INSPIRE project has built the largest sample of ultra-compact massive galaxies (UCMGs) at 0.12, and the other stellar population parameters.We use the Full-Index-Fitting method to fit the INSPIRE spectra to single stellar population (SSP) models. This allows us to measure, for the first time, the low-mass end slope of the IMF, as well as stellar metallicity [M/H], [Mg/Fe], [Ti/Fe] and [Na/Fe] ratios, and study correlations between them and the DoR. Similarly to normal-sized galaxies, UCMGs with larger stellar masses have overall higher metallicities. We found a correlation between the low-mass end of the IMF slope and the DoR, that, however, breaks down for systems with a more extended SFH. An even stronger dependency is found between the IMF and the fraction of mass formed at high-z. At equal velocity dispersion and metallicity, galaxies with a higher DoR have a dwarf-richer IMF than that of low-DoR counterparts. This might indicate that the cosmic epoch and formation mechanisms influence the fragmentation of the star formation cloud and hence might be the explanation for IMF variations detected in massive ETGs., Comment: 16 pages, 11 figures, submitted to MNRAS

We measure the [${\alpha}$/Fe] abundances for 183 quiescent galaxies at z = 0.60 - 0.75 with stellar masses ranging 10.4 \leq log10 10.4 $\leq$ log10 (M$_*$ /M$_\odot$) $\leq$ 11.6 selected from the LEGA-C survey. We estimate [${\alpha}$/Fe] from the ratio of the spectral indices Mgb (${\lambda} \sim 5177$ {\AA}) and Fe4383, compared to predictions of simple stellar population models. We find that 91% of quiescents in our sample have supersolar [${\alpha}$/Fe], with an average value of [${\alpha}$/Fe] = +0.24 $\pm$ 0.01. We find no significant correlation between [${\alpha}$/Fe] and stellar metallicity, mass, velocity dispersion, and average formation time. Galaxies that formed the bulk of their stellar mass on time scales shorter than 1 Gyr follow the same [${\alpha}$/Fe] distribution as those which formed on longer time scales. In comparison to local early-type galaxies and to stacked spectra of quiescent galaxies at z = 0.38 and z = 0.07, we find that the average [${\alpha}$/Fe] has not changed between z = 0.75 and the present time. Our work shows that the vast majority of massive quiescent galaxies at z $\sim$ 0.7 are ${\alpha}$-enhanced, and that no detectable evolution of the average [${\alpha}$/Fe] has taken place over the last $\sim$ 6.5 Gyr., Comment: 12 pages, 10 figures, 2 tables, 1 appendix

We derived stellar ages and metallicities [Z/H] for $\sim$70 passive early type galaxies (ETGs) selected from VANDELS survey over the redshift range 1.0$<$$z$$<$1.4 and stellar mass range 10$<$log(M$_*$/M$_\odot$)$<$11.6. We find significant systematics in their estimates depending on models and wavelength ranges considered. Using the full-spectrum fitting technique, we find that both [Z/H] and age increase with mass as for local ETGs. Age and metallicity sensitive spectral indices independently confirm these trends. According to EMILES models, for 67 per cent of the galaxies we find [Z/H]$>$0.0, a percentage which rises to $\sim$90 per cent for log(M$_*$/M$_\odot$)$>$11 where the mean metallicity is [Z/H]=0.17$\pm$0.1. A comparison with homogeneous measurements at similar and lower redshift does not show any metallicity evolution over the redshift range 0.0$11.0 host stellar populations with [Z/H]>0.05, formed over short timescales ($\Delta{t50}$$<$1 Gyr) at early epochs (t$_{form}$$<$2 Gyr), implying high star formation rates (SFR$>$100 M$_\odot$/yr) in high mass density regions (log($\Sigma_{1kpc}$)$>$10 M$_\odot$/kpc$^2$). This sharp picture tends to blur at lower masses: log(M$_*$/M$_\odot$)$\sim$10.6 galaxies can host either old stars with [Z/H]$<$0.0 or younger stars with [Z/H]$>$0.0, depending on the duration ($\Delta{t50}$) of the SF. The relations between galaxy mass, age and metallicities are therefore largely set up ab initio as part of the galaxy formation process. Mass, SFR and SF time-scale all contribute to shape up the stellar mass-metallicity relation with the mass that modulates metals retention., Comment: 18 pages + Appendix, 16 figures, 5 tables. Accepted for publication in MNRAS

We present the integral-field kinematics and stellar population properties of 64 galaxies (61 are Early-Type galaxies, ETGs) with Counter-Rotating stellar Disks (CRD) selected from about 4000 galaxies in the MaNGA survey, based on evidence of counter-rotation or two velocity dispersion peaks in the kinematic maps. For 17 CRDs, the counter-rotating components can also be separated spectroscopically. The frequency of CRDs in MaNGA is <5% for ellipticals, <3% for lenticulars and <1% for spirals (at 95% confidence level), consistent with previous estimates. We produced age and metallicity maps, and compared the stellar population properties to those of the general ETGs population. We found that CRDs have similar trends in age and metallicity to ETGs, but are less metallic at low masses, and show flatter age and steeper metallicity gradients, on average. A comparison of the velocity fields of the ionized gas and the stars reveals that in 33 cases the gas corotates with either the inner (15 cases) or outer (18 cases) stellar disk, in 9 cases it is misaligned. In most cases the gas corotates with the younger disk. Evidence of multimodality in the stellar population is found in 31 galaxies, while the 14 youngest and least massive galaxies show ongoing star formation; 14 galaxies, instead, exhibit unimodality, and are the oldest and most massive. As a general result, our work indicates that CRDs form primarily via gas accretion in retrograde rotation with respect to a pre-existing stellar disk., Comment: 26 pages, 22 figures, 1 table. Accepted for publication on December 16, 2021; published as MNRAS 511, 139 (2022)