We present results from SPH-cosmological simulations, including self-consistent modelling of SN feedback and chemical evolution, of galaxies belonging to two clusters and twelve groups. We reproduce the mass-metallicity (ZM) relation of galaxies classified in two samples according to their star-forming activity, as parametrized by their sSFR, across a redshift range up to z=2.
Its slope shows irrelevant evolution in the passive sample, being steeper in groups than in clusters. However, the sub-sample of high-mass passive galaxies only is characterized by a steep increase of the slope with redshift, from which it can be inferred that the bulk of the slope evolution of the ZM relation is driven by the more massive passive objects. (...ABRIDGED...)
The ZM relation for the star-forming sample reveals an increasing scatter with redshift, indicating that it is still being built at early epochs. The star-forming galaxies make up a tight sequence in the SFR-M_* plane at high redshift, whose scatter increases with time alongside with the consolidation of the passive sequence. We also confirm the anti-correlation between sSFR and stellar mass, pointing at a key role of the former in determining the galaxy downsizing, as the most significant means of diagnostics of the star formation efficiency. Likewise, an anti-correlation between sSFR and metallicity can be established for the star-forming galaxies, while on the contrary more active galaxies in terms of simple SFR are also metal-richer.
We discuss these results in terms of the mechanisms driving the evolution within the high- and low-mass regimes at different epochs: mergers, feedback-driven outflows and the intrinsic variation of the star formation efficiency.
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…
(Abridged) We explored 18 clusters from LoCuSS at z~0.2 with ACReS spectra of ~1800 cluster members at R<R200 in a mass-complete sample. The metallicities of SF cluster galaxies with R<R200 were found to be enhanced with respect to the MZR of coeval field SF galaxies. This metallicity enhancement is limited to lower-mass satellites of the 9 clusters with a passive BCG. Many of the SF galaxies with enhanced metallicities are found in the core regions of the phase-space diagram expected for virialized populations. We find a higher fraction of higher mass SF galaxies at R<R500 in clusters with ac…
The efficient use of Type Ia supernovae (SNIa) for cosmological studies requires knowledge of any parameter that can affect their luminosity in either systematic or statistical ways. Observational samples of SNIa commonly use the metallicity of the host galaxy, Z_host, as an estimator of the supernova progenitor metallicity, Z_Ia, that is one of the primary factors affecting SNIa magnitude. Here, we present a theoretical study of the relationship between Z_Ia and Z_host. We follow the chemical evolution of homogeneous galaxy models together with the evolution of the supernova rates in order to…
We report the detection of color gradients in six massive (stellar mass > 10^{10} M_{sun}) and passively evolving (specific SFR < 10^{-11}/yr) galaxies at redshift 1.3<z<2.5 identified in the HUDF using HST ACS and WFC3/IR images. After matching different PSFs, we obtain color maps and multi-band optical/near-IR photometry (BVizYJH) in concentric annuli, from the smallest resolved radial (~1.7 kpc) up to several times the H-band effective radius. We find that the inner regions of these galaxies have redder rest-frame UV--optical colors than the outer parts. The slopes of the color gradients mi…
We study the dwarf spheroidal galaxies in the nearby M81 group in order to construct their photometric metallicity distributions and to investigate the potential presence of population gradients. We select all the dwarf spheroidals with available Hubble Space Telescope / Advanced Camera for Surveys archival observations, nine in total. We interpolate isochrones so as to assign a photometric metallicity to each star within a selection box in the color-magnitude diagram of each dwarf galaxy. We assume that the dwarf spheroidals contain mainly an old stellar population. In order to search for met…
Towards Bayesian Photometric Cosmic Chronometers: Application to VIPERS
Institute of Space Sciences (ICE, CSIC)（空间科学研究所）；Institut d´Estudis Espacials de Catalunya (IEEC)（加泰罗尼亚空间研究学院）；Institute of Cosmology and Gravitation (ICG), University of Portsmouth（朴茨茅斯大学宇宙学与引力研究所）；Department of Astronomy, Tsinghua University（清华大学天文系）；Instituto de Astrofísica de Canarias (IAC)（加那利天体物理研究所）；Universidad de La Laguna (ULL)（拉古纳大学）；European Space Agency (ESA)（欧洲航天局）；European Space Astronomy Centre (ESAC)（欧洲空间天文中心）
We explore the relation between colour and specific star formation rate (derived from optical spectra obtained by SDSS DR4) of over 6,000 galaxies (M_r<=-20.5) in and around low redshift (z<0.12) clusters. Even though most red galaxies have little or no ongoing star formation, and most blue galaxies are currently forming stars, there are significant populations of red star-forming (SF) and blue passive galaxies. This paper examines various properties of galaxies belonging to the latter two categories. These properties include morphological parameters, internal extinction, spectral features suc…
Using deep V, B-V wide-field photometry, we have conducted a new study of stellar over-densities in the Fornax dwarf spheroidal galaxy by determining detailed Star Formation Histories from Colour-Magnitude Diagram analysis. We have concentrated on the relatively young stellar component (<4 Gyr old), and compared this to the underlying Fornax field population. We have studied in more detail the previously known inner shell-like structure and shown that it has a well-defined age-metallicity relation with a peak at ~1.5 Gyr, [Fe/H]=-0.6 dex. Comparison to the Fornax centre shows that the over-den…
Aim: We establish the mean metallicity from high-resolution spectroscopy for the recently found dwarf spheroidal galaxy Bootes I and test whether it is a common feature for ultra-faint dwarf spheroidal galaxies to show signs of inhomogeneous chemical evolution (e.g. as found in the Hercules dwarf spheroidal galaxy). Methods: We analyse high-resolution, moderate signal-to-noise spectra for seven red giant stars in the Bootes I dSph galaxy using standard abundance analysis techniques. In particular, we assume local thermodynamic equilibrium and employ spherical model atmospheres and codes that t…
A recent observational study of haloes of nearby Milky Way-like galaxies shows that only half (four out of eight) of the current sample exhibits strong negative metallicity ([Fe/H]) gradients. This is at odds with predictions from hydrodynamical simulations where such gradients are ubiquitous. In this Letter, we use high resolution cosmological hydrodynamical simulations to study the [Fe/H] distribution of galactic haloes. We find that kinematically selected stellar haloes, including both in-situ and accreted particles, have an oblate [Fe/H] distribution. Spherical [Fe/H] radial profiles show …
We analyze the projected axial ratio distribution, p(b/a), of galaxies that were spectroscopically selected from the Sloan Digital Sky Survey (DR6) to have low star-formation rates. For these quiescent galaxies we find a rather abrupt change in p(b/a) at a stellar mass of ~10^{11} M_sol: at higher masses there are hardly any galaxies with b/a<0.6, implying that essentially none of them have disk-like intrinsic shapes and must be spheroidal. This transition mass is ~3-4 times higher than the threshold mass above which quiescent galaxies dominate in number over star-forming galaxies, which sugge…
The increasing abundance of passive "red-sequence" galaxies since z=1-2 is mirrored by a coincident rise in the number of galaxies with spheroidal morphologies. In this paper, however, we show that in detail the correspondence between galaxy morphology and color is not perfect, providing insight into the physical origin of this evolution. Using the COSMOS survey, we study a significant population of red sequence galaxies with disk-like morphologies. These passive disks typically have Sa-Sb morphological types with large bulges, but they are not confined to dense environments. They represent ne…
We present abundances for seven stars in the (extremely) low-metallicity tail of the Sculptor dwarf spheroidal galaxy, from spectra taken with X-shooter on the ESO VLT. Targets were selected from the Ca II triplet (CaT) survey of the Dwarf Abundances and Radial Velocities Team (DART) using the latest calibration. Of the seven extremely metal-poor candidates, five stars are confirmed to be extremely metal-poor (i.e., [Fe/H]<-3 dex), with [Fe/H]=-3.47 +/- 0.07 for our most metal-poor star. All are around or below [Fe/H]=-2.5 dex from the measurement of individual Fe lines. These values are in ag…
Scaling relations of metallicity (O/H), star formation rate (SFR), and stellar mass give important insight on galaxy evolution. They are obeyed by most galaxies in the Local Universe and also at high redshift. In a companion paper, we compiled a sample of ~1100 galaxies from redshift 0 to ~3, spanning almost two orders of magnitude in metal abundance, a factor of $\sim10^6$ in SFR, and of ~10^5 in stellar mass. We have characterized empirically the star-formation "main sequence" (SFMS) and the mass-metallicity relation (MZR) for this sample, and also identified a class of low-metallicity starb…
We present spectroscopic metallicities of individual stars in seven gas-rich dwarf irregular galaxies (dIrrs), and we show that dIrrs obey the same mass-metallicity relation as the dwarf spheroidal (dSph) satellites of both the Milky Way and M31: Z_* ~ M_*^(0.30 +/- 0.02). The uniformity of the relation is in contradiction to previous estimates of metallicity based on photometry. This relationship is roughly continuous with the stellar mass-stellar metallicity relation for galaxies as massive as M_* = 10^12 M_sun. Although the average metallicities of dwarf galaxies depend only on stellar mass…
The collapse of dense cores with different metallicities is studied by hydrodynamical calculations coupled with detailed chemical and radiative processes. For this purpose, we construct a simple chemical network with non-equilibrium reactions among 15 chemical species, which reproduces the abundance of important molecular coolants by more detailed network very well. The evolution is followed until the formation of a hydrostatic protostar at the center. In a lower-metallicity gas cloud, the temperature during the collapse remains high owing to less efficient cooling. Using the temperature evolu…
VV124 (UGC 4879) is an isolated, dwarf irregular/dwarf spheroidal (dIrr/dSph) transition-type galaxy at a distance of 1.36 Mpc. Previous low-resolution spectroscopy yielded inconsistent radial velocities for different components of the galaxy, and photometry hinted at the presence of a stellar disk. In order to quantify the stellar dynamics, we observed individual red giants in VV124 with the Keck/DEIMOS spectrograph. We validated members based on their positions in the color-magnitude diagram, radial velocities, and spectral features. Our sample contains 67 members. The average radial velocit…
During the last three decades, many papers have reported the existence of a luminosity-metallicity or mass-metallicity (M-Z) relation for all kinds of galaxies: The more massive galaxies are also the ones with more metal-rich interstellar medium. We have obtained the mass-metallicity relation at different lookback times for the same set of galaxies from the Sloan Digital Sky Survey (SDSS), using the stellar metallicities estimated with our spectral synthesis code STARLIGHT. Using stellar metallicities has several advantages: We are free of the biases that affect the calibration of nebular meta…
(Abridged) We present the spectroscopy of red giant stars in the dwarf spheroidal galaxy LeoI, aimed at further constraining its chemical enrichment history. Intermediate-resolution spectroscopy in the CaII triplet spectral region was obtained for 54 stars in LeoI using FORS2 at the ESO Very Large Telescope. The equivalent widths of CaII triplet lines were used to derive the metallicities of the target stars on the [Fe/H] scale of Carretta & Gratton, as well as on a scale tied to the global metal abundance, [M/H]. The metallicity distribution function for LeoI stars is confirmed to be very nar…
We present a detailed analysis of the global and fine structure of four middle-mass disc galaxies obtained from simulations in a $Λ$CDM scenario. These objects have photometric D/T ratios in good agreement with those observed for late-type spirals, as well as kinematic properties in agreement with the observational Tully-Fisher relation. We identify the different dynamical components at z=0 on the basis of both orbital parameters and the binding energy of stars in the galaxy. In this way, we recognize a slowly rotating centrally concentrated spheroid, and two disc components supported by rotat…
We present an analysis of the large-scale structure of the halo of the Andromeda galaxy, based on the Pan-Andromeda Archeological Survey (PAndAS), currently the most complete map of resolved stellar populations in any galactic halo. Despite copious substructure, the global halo populations follow closely power law profiles that become steeper with increasing metallicity. We divide the sample into stream-like populations and a smooth halo component. Fitting a three-dimensional halo model reveals that the most metal-poor populations ([Fe/H]<-1.7) are distributed approximately spherically (slight…
We present the discovery of a massive, quiescent galaxy at z=2.99. We have obtained a HST/WFC3 spectrum of this object and measured its redshift from the detection of a deep 4000A break consistent with an old population and a high metallicity. By stellar population modeling of both its grism spectrum and broad-band photometry, we derive an age of ~0.7 Gyr, implying a formation redshift of z>4, and a mass >10^11 Msun. Although this passive galaxy is the most distant confirmed so far, we find that it is slightly less compact than other z>2 early-types of similar mass, being overall more analogou…
Aims. The method of deriving photometric metallicities using red giant branch stars is applied to resolved stellar populations under the common assumption that they mainly consist of single-age old stellar populations. We explore the effect of the presence of mixed-age stellar populations on deriving photometric metallicities. Methods. We use photometric data sets for the five Galactic dwarf spheroidals Sculptor, Sextans, Carina, Fornax, and Leo II in order to derive their photometric metallicity distribution functions from their resolved red giant branches using isochrones of the Dartmouth St…
We derive the dependence of the fraction of passive central galaxies on the mass of their supermassive black holes for a sample of over 400,000 SDSS galaxies at z < 0.2. Our large sample contains galaxies in a wide range of environments, with stellar masses 8 < log(M*/Msun) < 12, spanning the entire morphological spectrum from pure disks to spheroids. We derive estimates for the black hole masses from measured central velocity dispersions and bulge masses, using a variety of published empirical relationships. We find a very strong dependence of the passive fraction on black hole mass, which is…
The chemodynamical evolution of spherical multi-component self-gravitating models for isolated dwarf galaxies is studied. We compare their evolution with and without feedback effects from star formation processes. We find that initially cuspy dark matter profiles flatten with time as a result of star formation, without any special tuning conditions. Thus the seemingly flattened profiles found in many dwarfs do not contradict the cuspy profiles predicted by cosmological models. We also calculate the chemical evolution of stars and gas, to permit comparisons with observational data.
We present a multi-wavelength study of the nature of the SDSS galaxies divided into fine classes based on their morphology, colour and spectral features. The SDSS galaxies are classified into early-type and late-type; red and blue; passive, HII, Seyfert and LINER, which returns a total of 16 fine classes of galaxies. The properties of galaxies in each fine class are investigated from radio to X-ray, using 2MASS, IRAS, FIRST, NVSS, GALEX and ROSAT data. The UV - optical - NIR colours of blue early-type galaxies (BEGs) seem to result from the combination of old stellar population and recent star…
We present three dimensional spectroscopy of eleven E+A galaxies, selected for their strong H-delta absorption but weak (or non-existent) [OII]3727 and H-alpha emission. This selection suggests that a recent burst of star-formation was triggered but subsequently abruptly ended. We probe the spatial and spectral properties of both the young (~1Gyr) and old (few Gyr) stellar populations. Using the H-delta equivalent widths we estimate that the burst masses must have been at least 10% by mass (Mburst~10^10Mo), which is also consistent with the star-formation history inferred from the broad-band S…
Using wide baseline broad-band photometry, we analyse the stellar population properties of a sample of 72 galaxies, spanning a wide range of stellar masses and morphological types, in the nearby spiral-rich and dynamically young galaxy cluster Abell 1367. The sample galaxies are distributed from the cluster centre out to approximately half the cluster Abell radius. The optical/near-infrared colours are compared with simple stellar population synthesis models from which the luminosity-weighted stellar population ages and metallicities are determined. The locus of the colours of elliptical galax…
We make use of Spitzer imaging between 4 and 16 micron and near-infrared data at 2.2 micron to investigate the nature and distribution of the mid-infrared emission in a sample of early-type galaxies in the Virgo cluster. These data allow us to conclude, with some confidence, that the emission at 16 micron in passive ETGs is stellar in origin, consistent with previous work concluding that the excess mid-infrared emission comes from the dusty envelopes around evolved AGB stars. There is little evidence for the mid-infrared emission of an unresolved central component, as might arise in the presen…
