Aims. The aim of this work is twofold: first, to assess whether the population of elliptical galaxies in cluster at z~ 1.3 differs from the population in the field and whether their intrinsic ...structure depends on the environment where they belong; second, to constrain their properties 9 Gyr back in time through the study of their scaling relations. Methods. We compared a sample of 56 cluster elliptical galaxies selected from three clusters at 1.2 <z< 1.4 with elliptical galaxies selected at comparable redshift in the GOODS-South field (~30), in the COSMOS area (~180), and in the CANDELS fields (~220). To single out the environmental effects, we selected cluster and field elliptical galaxies according to their morphology. We compared physical and structural parameters of galaxies in the two environments and we derived the relationships between effective radius, surface brightness, stellar mass, and stellar mass density capital sigma Re within the effective radius and central mass density capital sigma sub(1 kpc), within 1 kpc radius. Results. We find that the structure and the properties of cluster elliptical galaxies do not differ from those in the field: they are characterized by the same structural parameters at fixed mass and they follow the same scaling relations. On the other hand, the population of field elliptical galaxies at z~ 1.3 shows a significant lack of massive (M sub(*)> 2 x 10 super(11)M sub(middot in circle)) and large (R sub(e)> 4-5 kpc) elliptical galaxies with respect to the cluster. Nonetheless, at M sub(*)< 2 x 10 super(11)M sub(middot in circle), the two populations are similar. The size-mass relation of cluster and field ellipticals at z~ 1.3 clearly defines two different regimes, above and below a transition mass m sub(t)Asymptotically = to 2-3 x 10 super(10)M sub(middot in circle): at lower masses the relation is nearly flat (R sub(e)is proportional to Mu sub(*) super(-0.1+ or -0.2)), the mean radius is nearly constant at ~1 kpc and, consequenly, capital sigma ReAsymptotically = to capital sigma sub(1 kpc) while, at larger masses, the relation is R sub(e)is proportional to Mu sub(*) super(0.64+ or -0.09). The transition mass marks the mass at which galaxies reach the maximum stellar mass density. Also the capital sigma sub(1 kpc)-mass relation follows two different regimes, above and below the transition mass ( capital sigma sub(1 kpc)is proportional to Mu sub(*) sub(1.07<mt) super(0.64>mt)) defining a transition mass density capital sigma sub(1 kpc)Asymptotically = to 2-3 x 10 super(3)M sub(middot in circle) pc super(-2). The effective stellar mass density capital sigma Re does not correlate with mass; dense/compact galaxies can be assembled over a wide mass regime, independently of the environment. The central stellar mass density, capital sigma sub(1 kpc), besides being correlated with the mass, is correlated to the age of the stellar population: the higher the central stellar mass density, the higher the mass, the older the age of the stellar population. Conclusions. While we found some evidence of environmental effects on the elliptical galaxies as a population, we did not find differences between the intrinsic properties of cluster and field elliptical galaxies at comparable redshift. The structure and the shaping of elliptical galaxies at z~ 1.3 do not depend on the environment. However, a dense environment seems to be more efficient in assembling high-mass large ellipticals, much rarer in the field at this redshift. The correlation found between the central stellar mass density and the age of the galaxies beside the mass shows the close connection of the central regions to the main phases of mass growth.
The aim of the present paper is to quantify the dependence of the estimates of luminosities and stellar mass content of early-type galaxies on the different models and model parameters which can be ...used to analyse the observational data. The paper is organized in two parts. The first one analyses the dependence of the ratios and of the k-corrections in different bands on model parameters (initial mass function, metallicity, star formation history, age), assuming some among the most popular spectrophotometric codes usually adopted to study the evolutionary status of galaxies: Bruzual & Charlot (BC03), Charlot & Bruzual (CB08), Maraston (Ma05), Fioc & Rocca-Volmerange (PEGASE), Silva et al. (GRASIL). The second part of our work is dedicated to quantify the reliability and systematics affecting the mass and luminosity estimates obtained by means of the best-fitting technique applied to the photometric spectral energy distributions (SEDs) of early-type galaxies at 1 < z < 2. To this end, we apply the best-fitting technique to some mock catalogues built on the basis of a wide set of models of early-type galaxies. We then compare the luminosity and the stellar mass estimated from the SED fitting with the true known input values. The goodness of the mass estimate is found to be dependent on the mass estimator adopted to derive it, but masses cannot anyhow be retrieved better than within a factor of 2–3, depending on the quality of the available photometric data and/or on the distance of the galaxies since more distant galaxies are fainter on average and thus affected by larger photometric errors. Finally, we present a new empirical mass estimator based on the K-band apparent magnitude and on the observed(V−K) colour. We show that the reliability of the stellar mass content derived with this new estimator for early-type galaxies and its stability are even higher than those achievable with the best classic estimators, with the not negligible advantage that it does not need any multiwavelength data fitting.
Recent theoretical and observational studies on the assembly of early-type galaxies (ETGs) point towards an inside-out growth of their stellar mass characterized by extended low-mass-density haloes ...grown around compact and dense cores. Models can form ETGs at high-z as compact spheroids that then grow in size through dry minor mergers. Dry mergers would affect mainly the outskirts of the galaxy, enlarging the size (i.e. the effective radius), keeping the inner parts and the total stellar mass nearly unchanged. Hence, the central stellar mass density will not change with time, in contrast to the stellar mass density within the effective radius, which should decrease with time as the effective radius increases. Some previous observations are interpreted as supporting inside-out growth, as the central stellar mass density of high-z ETGs is found to be similar to that of local ETGs. In this paper we derive the central stellar mass density within a fixed radius and the effective stellar mass density within the effective radius for a complete sample of 34 ETGs morphologically selected at 0.9 < z
spec < 2 and compare them with those derived for a sample of ∼900 local ETGs in the same mass range. We find that the central stellar mass density of high-z ETGs spans just an order of magnitude and is similar to that of local ETGs, as found in previous studies. However, we find that the effective stellar mass density of high-z ETGs spans three orders of magnitude, exactly as the local ETGs, and that it is similar to the effective stellar mass density of local ETGs, showing that it has not changed since z∼ 1.5, in the last 9-10 Gyr. Thus, the wide spread of the effective stellar mass density observed up to z∼ 1.5 must originate earlier, at z > 2. Furthermore, we show that the small scatter of the central mass density of ETGs compared with the large scatter of the effective mass density is simply a peculiar feature of the Sérsic profile and hence is independent of redshift and of any assembly history experienced by galaxies. Thus, it has no connection with the possible inside-out growth of ETGs. Finally, we show a tight correlation between the central stellar mass density and the total stellar mass of ETGs in the sense that the central mass density increases with mass as
. This implies that the fraction of the central stellar mass of ETGs decreases with the mass of the galaxy. These correlations are valid for the whole population of ETGs considered, independently of their redshift, suggesting that they originate in the early phases of their formation.
We present a study based on a sample of 62 early-type galaxies (ETGs) at 0.9 < z
spec < 2 aimed at constraining their past star formation and mass assembly histories. The sample is composed of normal ...ETGs having effective radii comparable to the mean radius of local ones and of compact ETGs having effective radii from two to six times smaller. We do not find evidence of a dependence of the compactness of ETGs on their stellar mass. The best fit to their spectral energy distribution at known redshift has allowed us to constrain the epoch at which the stellar mass formed. We find that the stellar mass of normal ETGs formed at z
form≲ 3, while the stellar content of compact ETGs formed over a wider range of redshift (2 < z
form < 10) with a large fraction of them characterized by z
form > 5. Earlier stars, those formed at z
form > 5, are assembled in compact and more massive (
M⊙) ETGs, while stars formed later (z
form≲ 3) or resulting from subsequent episodes of star formation are assembled both in compact and in normal ETGs. Thus, the older the stellar population, the higher the mass of the hosting galaxy but not vice versa. This suggests that the epoch of formation may play a role in the formation of massive ETGs rather than the mass itself. We show that the possible general scheme in which normal ETGs at 〈z〉≃ 1.5 are descendants of compact spheroids assembled at higher redshift is not compatible with the current models. Indeed, we find that the number of dry mergers expected in a hierarchical model is almost two orders of magnitude lower than that needed to enlarge a compact ETG up to a normal-size ETG. Moreover, we do not find evidence supporting a dependence of the compactness of galaxies on their redshift of assembly, a dependence expected in the hypothesis that the compactness of a galaxy is due to the higher density of the Universe at earlier epochs. Finally, we propose a simple scheme of formation and assembly of the stellar mass of ETGs based on dissipative gas-rich merger, which can qualitatively account for the coexistence of normal and compact ETGs observed at 〈z〉≃ 1.5 in spite of the same stellar mass, the lack of normal ETGs with high z
form and the absence of correlation between compactness, stellar mass and formation redshift.
ABSTRACT
We present spectroscopic observations obtained at the Large Binocular Telescope in the field of the cluster XLSSJ0223−0436 at z = 1.22. We confirm 12 spheroids cluster members and determine ...stellar velocity dispersion for 7 of them. We combine these data with those in the literature for clusters RXJ0848+4453 at z = 1.27 (8 galaxies) and XMMJ2235−2557 at z = 1.39 (7 galaxies) to determine the Fundamental Plane (FP) of cluster spheroids. We find that the FP at z ∼ 1.3 is offset and rotated (∼3σ) with respect to the local FP. The offset corresponds to a mean evolution Δlog(Mdyn/LB) = (−0.5 ± 0.1)z. High-redshift galaxies follow a steeper mass-dependent Mdyn/LB–Mdyn relation than local ones. Assuming Δ log(Mdyn/LB) = Δ log(M*/LB), higher mass galaxies log(Mdyn/M⊙) ≥ 11.5 have a higher formation redshift (zf ≥ 6.5) than lower mass ones zf ≤2 for log(Mdyn/M⊙ ≤ 10), with a median zf ≃ 2.5 for the whole sample. Also, galaxies with higher stellar mass density host stellar populations formed earlier than those in lower density galaxies. At fixed initial mass function, Mdyn/M* varies systematically with mass and mass density. It follows that the evolution of the stellar populations (M*/LB) accounts for the observed evolution of Mdyn/LB for Mdyn > 1011 M⊙ galaxies, while accounts for ∼85 per cent of the evolution at Mdyn < 1011 M⊙. We find no evidence in favour of structural evolution of individual galaxies, while we find evidences that spheroids later added to the population may account for the observed discrepancy between Δlog(Mdyn/LB) and Δ log(M*/LB) at masses <1011 M⊙. Thus, the evolution of the FP of cluster spheroids is consistent with the mass-dependent and mass density-dependent evolution of their stellar populations superimposed to a minor contribution of spheroids joining the population at later times.
Aims. We investigate the stellar mass assembly history of ultramassive (M⋆ ≳ 1011M⊙) dense (Σ = M⋆/2πRe2> 2500M⊙ pc-2) early-type galaxies (ETGs, elliptical and spheroidal galaxies) selected on basis ...of visual classification over the last 9 Gyr. Methods. We traced the evolution of the comoving number density ρ of ultramassive dense ETGs and compared their structural (effective radius Re and stellar mass M⋆) and dynamical (velocity dispersion σe) parameters over the redshift range 0 < z < 1.6. We derived the number density ρ at 1.6 <z< 1 from the MUNICS and GOODS-South surveys, while we took advantage of the COSMOS spectroscopic survey to probe the intermediate redshift range 0.2−1.0. We derived the number density of ultramassive dense local ETGs from the SDSS sample taking all of the selection bias affecting the spectroscopic sample into account. To compare the dynamical and structural parameters, we collected a sample of 11 ultramassive dense ETGs at 1.2 < z < 1.6 for which velocity dispersion measurements are available. For four of these ETGs (plus one at z = 1.91), we present previously unpublished estimates of velocity dispersion, based on optical VLT-FORS2 spectra. We probe the intermediate redshift range (0.2 ≲ z ≲ 0.9) and the local Universe with different ETGs samples. Results. We find that the comoving number density of ultramassive dense ETGs evolves with z as ρ(z) ∝ (1 + z)0.3 ± 0.8 implying a decrease of ~25% of the population of ultramassive dense ETGs since z = 1.6. By comparing the structural and dynamical properties of high-z ultramassive dense ETGs over the range 0 ≲ z < 1.6 in the Re, M⋆, σe plane, we find that all of the ETGs of the high-z sample have counterparts with similar properties in the local Universe. This implies either that the majority (~70%) of ultramassive dense ETGs already completed the assembly and shaping at ⟨ z ⟩ = 1.4, or that, if a significant portion of dense ETGs evolves in size, new ultramassive dense ETGs must form at z < 1.5 to maintain their number density at almost constant. The difficulty in identify good progenitors for these new dense ETGs at z ≲ 1.5 and the stellar populations properties of local ultramassive dense ETGs point towards the first hypothesis. In this case, the ultramassive dense galaxies missing in the local Universe could have joined, in the last 9 Gyr, the so colled non-dense ETGs population through minor mergers, thus contributing to mean size growth. In any case, the comparison between their number density and the number density of the whole population of ultramassive ETGs relegates their contribution to the mean size evolution to a secondary process.
Many of the early-type galaxies (ETGs) observed so far at z > 1 turned out to have smaller radii with respect to that of a typical present day ETG with comparable mass. This has generated the ...conviction that in the past ETGs were more compact, hence denser, and that as a consequence, they should have increased their radius across the time to reconcile with the present day ones. However, observations have not yet established whether the population of early types in the early universe was fully represented by compact galaxies nor if they were so much more numerous than in the present day Universe to require an evolution of their sizes. Here we report the results of a study based on a complete sample of 34 ETGs at 0.9 < zspec < 1.92. We find a majority (62 per cent) of normal ETGs, similar to typical local ones, co-existing with compact early types from ∼ two to ∼ six times smaller in spite of the same mass and redshift. The co-existence of normal and compact ETGs at 〈z〈 ≃ 1.5 suggests that their build-up taken place in the first 3–4 Gyr, followed distinct paths. Furthermore, we find that the number density of compact early types at 〈z〈 ≃ 1.5 is consistent with the lower limits of the local number density of compact early types derived from local clusters of galaxies. The similar number of compact early types found in the early and in the present day Universe frustrates the hypothesized effective radius evolution while provides evidence that also compact ETGs were as we see them today 9–10 Gyr ago. Finally, the fact that (at least) most of the compact ETGs at high z are accounted for by compact early types in local cluster of galaxies implies that the former are the direct progenitors of the compact early-type cluster galaxies establishing a direct link between environment and early phases of assembly of ETGs.
Extremely compact massive galaxies at z ∼ 1.4 Trujillo, I.; Feulner, G.; Goranova, Y. ...
Monthly notices of the Royal Astronomical Society,
November 2006, Letnik:
373, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The optical rest-frame sizes of 10 of the most massive (∼5 × 1011 h−270 M⊙) galaxies found in the near-infrared MUNICS survey at 1.2 < z < 1.7 are analysed. Sizes are estimated in both the J and K′ ...filters. These massive galaxies are at least a factor of 4+1.9−1.0 (±1σ) smaller in the rest-frame V-band than local counterparts of the same stellar mass. Consequently, the stellar mass density of these objects is (at least) 60 times larger than that of massive ellipticals today. Although the stellar populations of these objects are passively fading, their structural properties are rapidly changing since that redshift. This observational fact disagrees with a scenario where the more massive and passive galaxies are fully assembled at z∼ 1.4 (i.e. a monolithic scenario) and points towards a dry merger scenario as the responsible mechanism for the subsequent evolution of these galaxies.
ABSTRACT
We derived stellar ages and metallicities Z/H for ∼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⊙) < 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 ∼90 per cent for log(M*/M⊙) > 11 where the mean metallicity is Z/H = 0.17 ± 0.1. A comparison with homogeneous measurements at similar and lower redshift does not show any metallicity evolution over the redshift range 0.0 < z < 1.4. The derived star formation (SF) histories show that the stellar mass fraction formed at early epoch increases with the mass of the galaxy. Galaxies with log(M*/M⊙) > 11.0 host stellar populations with Z/H > 0.05, formed over short time-scales (Δt50 < 1 Gyr) at early epochs (tform < 2 Gyr), implying high star formation rates (SFR > 100 M⊙ yr−1) in high-mass density regions (log(Σ1kpc) > 10 M⊙/kpc2). This sharp picture tends to blur at lower masses: log(M*/M⊙) ∼ 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 (Δt50) 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.
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