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We test cosmological hydrodynamical simulations of galaxy formation regarding the properties of the blue cloud (BC), green valley (GV), and red sequence (RS), as measured on the 4000Å break strength versus stellar mass plane at z  = 0.1. We analyse the RefL0100N1504 run of EAGLE and the TNG100 run of IllustrisTNG project, by comparing them with the Sloan Digital Sky Survey (SDSS), while taking into account selection bias. Our analysis focuses on the GV, within stellar mass |$\log \, \mathrm{{\it M}_\star /M_{\odot }} \simeq 10\!-\!11$|⁠ , selected from the bimodal distribution of galaxies on the D n (4000) versus stellar mass plane, following Angthopo et al. methodology. Both simulations match the fraction of AGN in the GV. However, they overproduce quiescent GV galaxies with respect to observations, with IllustrisTNG yielding a higher fraction of quiescent GV galaxies than EAGLE. In both, GV galaxies have older luminosity-weighted ages with respect to the SDSS, while a better match is found for mass-weighted ages. We find EAGLE GV galaxies quench their star formation early, but undergo later episodes of star formation, matching observations. In contrast, IllustrisTNG GV galaxies have a more extended star formation history, and quench more effectively at later cosmic times, producing the excess of quenched galaxies in GV compared with SDSS, based on the 4000Å break strength. These results suggest the AGN feedback subgrid physics, more specifically, the threshold halo mass for black hole input and the black hole seed mass, could be the primary cause of the overproduction of quiescent galaxies found with respect to the observational constraints. [ABSTRACT FROM AUTHOR]

Massive quiescent compact galaxies have been discovered at high redshifts, associated with rapid compaction and cessation of star formation (SF). In this work, we set out to quantify the time-scales in which SF is quenched in compact galaxies at intermediate redshifts. For this, we select a sample of green valley galaxies within the COSMOS field in the midst of quenching their SF at 0.5 < |$z$| < 1.0 that exhibit varying degrees of compactness. Based on the Hδ absorption line and the 4000 Å break of coadded zCOSMOS spectra for subsamples of normal-sized and compact galaxies we determine quenching time-scales as a function of compactness. We find that the SF quenching time-scales in green valley compact galaxies are much shorter than in normal-sized ones. In an effort to understand this trend, we use the Illustris simulation to trace the evolution of the SF history, the growth rate of the central super massive black hole (SMBH), and the AGN feedback in compact and normal-sized galaxies. We find that the difference in SF quenching time-scales is due to the mode of the AGN feedback. In the compact galaxies the kinematic-mode is dominant, being highly efficient at quenching the SF by depleting the internal gas. For normal-sized galaxies, the prevailing thermal-mode injects energy into the circumgalactic gas, preventing cold gas accretion and quenching SF via the slower strangulation mechanism. These results are consistent with the violent disc instability and gas-rich mergers scenarios, followed by strong AGN and stellar feedback. Although this kind of event is most expected to occur at |$z$|  = 2–3, we find evidences that the formation of compact quiescent galaxies can occur at |$z$| < 1. [ABSTRACT FROM AUTHOR]

Recent results on the non-universality of the Initial Mass Function (IMF) have shown strong evidence of IMF variations with galaxy velocity dispersion, with a corresponding impact on other stellar population parameters, line indices and colours. Using a set of stellar population models with varying IMF slopes, we provide additional caveats on the assumption of a universal IMF. This study shows that the derived star formation histories of early-type galaxies vary significantly with the IMF slope. For instance, a steepening in the slope of a single power-law IMF decreases substantially, by a factor of up to 4, the contribution of the old stellar populations to the total light/mass. This trend is milder for a segmented-like IMF shape, where the contribution of the very low mass stars is decreased. It is also shown that, by tuning each IMF slope to its prescribed value according to each galaxy velocity dispersion, a sample of early-type galaxies covering a range of masses yield comparable star formation histories. On the one hand, a small contribution from relatively young stellar populations appears in the star formation histories of most massive elliptical galaxies when adopting a steep IMF. In addition, we find that low-mass early-type galaxies that look like genuinely young objects with a standard IMF (i.e. ‘baby elliptical galaxies’) turn out to be older when a slightly flatter IMF is employed. In summary, the use of a non-universal IMF, tuned according to the velocity dispersion of the galaxy, seems to provide more consistent results. [ABSTRACT FROM AUTHOR]

We analyse the Fundamental Plane (FP) relation of 39 993 early-type galaxies (ETGs) in the optical ( griz) and 5080 ETGs in the near-infrared (NIR; YJHK) wavebands, forming an opticalNIR sample of galaxies. We focus on the analysis of the FP as a function of the environment where galaxies reside. We characterize the environment using the largest group catalogue, based on 3D data, generated from the Sloan Digital Sky Survey at low redshift . We find that the intercept '' of the FP decreases smoothly from high- to low-density regions, implying that galaxies at low density have on average lower mass-to-light ratios than their high-density counterparts. The '' also decreases as a function of the mean characteristic mass of the parent galaxy group. However, this trend is weak and completely accounted for by the variation of '' with local density. The variation of the FP offset is the same in all wavebands, implying that ETGs at low density have younger luminosity-weighted ages than cluster galaxies, consistent with the expectations of semi-analytical models of galaxy formation. We measure an age variation of dex per cent) per decade of local galaxy density. This implies an age difference of about per cent between galaxies in the regions of highest density and the field. We find the metallicity decreasing, at , from low to high density. We also find evidence that the variation in age per decade of local density augments, up to a factor of 2, for galaxies residing in massive relative to poor groups. The velocity dispersion slope of the FP, , tends to decrease with local galaxy density, with galaxies in groups having smaller than those in the field, independent of the waveband used to measure the structural parameters. Environmental effects (such as tidal stripping) may elucidate this result, producing a steeper variation of dark-matter fraction and/or non-homology along the ETG's sequence at higher density. In the optical, the surface brightness slope, , of the FP increases with local galaxy density, being larger for group relative to field galaxies. The difference vanishes in the NIR, as field galaxies show a small per cent) but significant increase of from through , while group galaxies (particularly those in rich clusters) do not. The trend of with the environment results from galaxies residing in more massive clusters, since for groups no variation of with local density is detected. A possible explanation for these findings is that the variation of stellar population properties with mass in ETGs is shallower for galaxies at high density, resulting from tidal stripping and quenching of star formation in galaxies falling into the group's potential well. We do not detect any dependence of the FP coefficients on the presence of substructures in parent galaxy groups. [ABSTRACT FROM AUTHOR]

This is the first paper of a series presenting the Spheroids Panchromatic Investigation in Different Environmental Regions (SPIDER). The sample of spheroids consists of 5080 bright () early-type galaxies (ETGs), in the redshift range of 0.05 to 0.095, with optical () photometry and spectroscopy from the Sloan Digital Sky Survey Data Release 6 (SDSS-DR6) and near-infrared () photometry from the UKIRT Infrared Deep Sky Survey-Large Area Survey (UKIDSS-LAS) (DR4). We describe how homogeneous photometric parameters (galaxy colours and structural parameters) are derived using wavebands. We find no systematic steepening of the colour-magnitude relation when probing the baseline from to , implying that internal colour gradients drive most of the mass-metallicity relation in ETGs. As far as structural parameters are concerned we find that the mean effective radius of ETGs smoothly decreases, by 30 per cent, from g through K, while no significant dependence on waveband is detected for the axial ratio, Sersic index and a parameters. Furthermore, velocity dispersions are remeasured for all the ETGs using and compared to those obtained by SDSS. The velocity dispersions are rederived using a combination of simple stellar population models as templates, hence accounting for the kinematics of different galaxy stellar components. We compare our () measurements of total magnitude, effective radius and mean surface brightness with those obtained as part of the SDSS pipeline (). Significant differences are found and reported, including comparisons with a third and independent part. A full characterization of the sample completeness in all wavebands is presented, establishing the limits of application of the characteristic parameters presented here for the analysis of the global scaling relations of ETGs. [ABSTRACT FROM AUTHOR]

We present a complete analysis of the Fundamental Plane (FP) of early-type galaxies (ETGs) in the nearby Universe . The sample, as defined in Paper I, comprises 39 993 ETGs located in environments covering the entire domain in local density (from field to cluster). We derive the FP in the wavebands with a detailed discussion on fitting procedure, bias due to selection effects and bias due to correlated errors on the effective parameters, and , as key factors in obtaining meaningful FP coefficients. Studying the Kormendy relation (KR) we find that its slope varies from through implying that smaller size ETGs have a larger ratio of optical to near-infrared (NIR) radii than galaxies with larger . We also examine the Faber-Jackson (FJ) relation and find that its slope is similar for all wavebands, within the uncertainties, with a mean value of . Writing the FP equation as , we find that the '' varies from in to in , implying a per cent variation across the wavelength baseline. The corresponding variation of '' is negligible , while '' varies by per cent. We show that the waveband dependence of the FJ and KR results from the complex variation of the distribution of galaxies in the face-on projection of the FP as well as by the change of FP coefficients with waveband. We find that '' and '' become smaller for higher Sersic index and larger axial ratios, independent of the waveband. This suggests that these variations are likely to be related to differences in structural and dynamical (rather than stellar population) properties of ETGs. It is noticeable that galaxies with bluer colours and disc-like isophotes have smaller '', with the effect decreasing smoothly from through . Considering a power-law relation between mass-to-light ratio and (dynamical) mass, , we estimate from the FP coefficients in . The decreases from in to in band. Using the values, we estimate the variation of age and metallicity of the stellar populations present in massive galaxies per decade in stellar mass. This analysis shows that in the NIR the tilt of the FP is not due to stellar population variation, and that ETGs have coeval stellar populations with an age variation of a few per cent per decade in mass, and a corresponding metallicity increase of 23 per cent. We also show that current semi-analytical models of galaxy formation reproduce very well these amounts of variation of age and metallicity with respect to stellar mass. [ABSTRACT FROM AUTHOR]

MNRAS 502, 3703 (2021) doi:10.1093/mnras/staa3697 Erratum: Evaluating hydrodynamical simulations with green valley galaxies by J. Angthopo, 1‹ A. Negri, 2,3 I. Ferreras, 2,3,4 I. G. de la Rosa, 2,3 C. Dalla Vecchia 2,3 and A. Pillepich 5 1 Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK 2 Instituto de Astrof' isica de Canarias, Calle V' ia L' actea s/n, E-38205 La Laguna, Tenerife, Spain 3 Departamento de Astrof' isica, Universidad de La Laguna (ULL), E-38206 La Laguna, Tenerife, Spain 4 Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK 5 Max-Planck-Institut f ur Astronomie, K onigstuhl 17, D-69117 Heidelberg, Germany Key words: errata, addenda - galaxies: evolution - galaxies: formation - galaxies: interactions - galaxies: stellar content. This paper has been typeset from a Microsoft Word file prepared by the author. [Extracted from the article]