arXiv subjects
Publications and source records attributed to C. Maraston.
We present the results of TNG near-IR low resolution spectroscopy of two (S7F5-254 and S7F5-45) sources belonging to a complete sample of 15 EROs with K'<18 and R-K'>5 selected from the MUNICS Survey. Both the spectra show a sharp drop in the continuum which can be ascribed only to the Balmer break. This places them at 1.2 3.5 and z_f>2 for the two EROs respectively.
We present kinematics and stellar population properties of 17 dwarf early-type galaxies in the luminosity range -14> M_B> -19. Our sample fills the gap between the intensively studied giant elliptical and Local Group dwarf spheroidal galaxies. The dwarf ellipticals of the present sample have constant velocity dispersion profiles within their effective radii and do not show significant rotation, hence are clearly anisotropic. The dwarf lenticulars, instead, rotate faster and are, at least partially, supported by rotation. From optical Lick absorption indices, we derive metallicities and element abundances. Combining our sample with literature data of the Local Group dwarf spheroidals and giant ellipticals, we find a surprisingly tight linear correlation between metallicity and luminosity over a wide range: -8> M_B> -22. The alpha/Fe ratios of our dwarf ellipticals are significantly lower than the ones of giant elliptical galaxies, which is in agreement with spectroscopy of individual stars in Local Group dwarf spheroidals. Our results suggest the existence of a clear kinematic and stellar population dichotomy between dwarf and giant elliptical galaxies. This result is important for theories of galaxy formation, because it implies that present-day dwarf ellipticals are not the fossiled building blocks of giant ellipticals.
We present preliminary results of VLT/FORS spectroscopy of globular clusters in nearby early-type galaxies. Our project aims at studying the chemistry and determine the ages of globular cluster (sub-)populations. First results indicate that the different galaxies host from little to significant intermediate-age populations, and that the latter have alpha-element over iron ratios closer to solar than the old population that show an alpha-element enhancement similar to the diffuse stellar light.
The Munich Near-IR Cluster Survey (MUNICS) is a wide-area, medium-deep, photometric survey selected in the K' band. The project's main scientific aims are the identification of galaxy clusters up to redshifts of unity and the selection of a large sample of field early-type galaxies up to z < 1.5 for evolutionary studies. We created a Large Scale Structure catalog, using a new structure finding technique specialized for photometric datasets, that we developed on the basis of a friends-of-friends algorithm. We tested the plausibility of the resulting galaxy group and cluster catalog with the help of Color-Magnitude Diagrams (CMD), as well as a likelihood- and Voronoi-approach.
A near-IR low-resolution spectroscopic follow-up of a complete sample of K<18.5 EROs has started at the 3.5 m Telescopio Nazionale Galileo (TNG, La Palma, Canary Islands) by using a prism disperser AMICI. The sample has been selected from the Munich Near-IR Cluster Survey (MUNICS). The project aims at revealing massive galaxies at z>1.2 and at estimating their spatial density to put constraints on the galaxy formation and evolution models. In this proceeding, the preliminary analysis of the first spectra obtained is presented.
We derive the number density evolution of massive field galaxies in the redshift range 0.4 < z < 1.2 using the K-band selected field galaxy sample from the Munich Near-IR Cluster Survey (MUNICS). We rely on spectroscopically calibrated photometric redshifts to determine distances and absolute magnitudes in the rest-frame K-band. To assign mass-to-light ratios, we use two different approaches. First, we use an approach which maximizes the stellar mass for any K-band luminosity at any redshift. We take the mass-to-light ratio of a Simple Stellar Population (SSP) which is as old as the universe at the galaxy's redshift as a likely upper limit. Second, we assign each galaxy a mass-to-light ratio by fitting the galaxy's colours against a grid of composite stellar population models and taking their M/L. We compute the number density of galaxies more massive than 2 x 10^10 h^-2 Msun, 5 x 10^10 h^-2 Msun, and 1 x 10^11 h^-2 Msun, finding that the integrated stellar mass function is roughly constant for the lowest mass limit and that it decreases with redshift by a factor of ~ 3 and by a factor of ~ 6 for the two higher mass limits, respectively. This finding is in qualitative agreement with models of hierarchical galaxy formation, which predict that the number density of ~ M* objects is fairly constant while it decreases faster for more massive systems over the redshift range our data probe.
We derive the number density evolution of massive field galaxies in the redshift range 0.4 < z < 1.2 using the K-band selected field galaxy sample from the Munich Near-IR Cluster Survey (MUNICS). We rely on spectroscopically calibrated photometric redshifts to determine distances and absolute magnitudes in the rest-frame K-band. To assign mass-to-light ratios, we use an approach which maximizes the stellar mass for any K-band luminosity at any redshift. We take the mass-to-light ratio, M/L_K, of a Simple Stellar Population (SSP) which is as old as the universe at the galaxy's redshift as a likely upper limit. This is the most extreme case of pure luminosity evolution and in a more realistic model M/L_K will probably decrease faster with redshift due to increased star formation. We compute the number density of galaxies more massive than 2 10^10 h^-2 solar masses, 5 10^10 h^-2 solar masses, and 1 10^11 h^-2 solar masses, finding that the integrated stellar mass function is roughly constant for the lowest mass limit and that it decreases with redshift by a factor of roughly 3 and by a factor of roughly 6 for the two higher mass limits, respectively. This finding is in qualitative agreement with models of hierarchical galaxy formation, which predict that the number density of ~ M* objects is fairly constant while it decreases faster for more massive systems over the redshift range our data probe.
The Munich Near-IR Cluster Survey (MUNICS) is a wide-area, medium-deep, photometric survey selected in the K' band. It covers an area of roughly one square degree in the K' and J near-IR pass-bands. The survey area consists of 16 6' x 6' fields targeted at QSOs with redshifts 0.5 < z < 2 and 7 28' x 13' stripes targeted at `random' high Galactic latitude fields. Ten of the QSO fields were additionally imaged in R and I, and 0.6 square degrees of the randomly selected fields were also imaged in the V, R, and I bands. The resulting object catalogues were strictly selected in K', having a limiting magnitude (50 per cent completeness) of K' ~ 19.5 mag and J ~ 21 mag, sufficiently deep to detect passively evolving systems up to a redshift of z ~ 1.5 and luminosity of 0.5 L*. The optical data reach a depth of roughly R ~ 23.5 mag. The project's main scientific aims are the identification of galaxy clusters at redshifts around unity and the selection of a large sample of field early-type galaxies at 0 < z < 1.5 for evolutionary studies. In this paper - the first in a series - we describe the survey's concept, the selection of the survey fields, the near-IR and optical imaging and data reduction, object extraction, and the construction of photometric catalogues. Finally, we show the J-K' vs. K' colour-magnitude diagramme and the R-J vs. J-K', V-I vs. J-K', and V-I vs. V-R colour-colour diagrammes for MUNICS objects, together with stellar population-synthesis models for different star-formation histories, and conclude that the data set presented is suitable for extracting a catalogue of massive field galaxies in the redshift range 0.5 < z < 1.5 for evolutionary studies and follow-up observations.
We have extended the study of the young star clusters observed in the merger remnant galaxy NGC 7252 by obtaining K band photometry for these clusters. Our K band data significantly complement the optical photometry and spectroscopy in the literature: K band data are fundamental to study the Asymptotic Giant Branch (AGB) population of these clusters, since the AGB phase transition (occuring between the age of 200 Myr and 1 Gyr) causes abrupt changes in the near-infrared luminosity of the clusters while producing only small changes in the optical. Therefore, the e.g. V-K colour is ideal to study this evolutionary phase of stellar populations. For the present analysis we present models for Simple Stellar Populations which include the contribution of the AGB stellar phase, calibrated with the young and intermediate age star clusters of the Magellanic Clouds. The comparison with the colour distribution of the NGC 7252 star clusters shows that they are indeed intermediate age clusters undergoing the AGB phase transition. The AGB phase transition is observed for the first time outside the Local Group. Most of the studied clusters span the very narrow age range 300-500 Myr, and likely have metallicities 0.5-1 Z_{\odot}. A very important exception is the cluster W32, which has already completed its AGB epoch, its colours being consistent with an age of 1-2 Gyr. This impacts on the duration of the merger-induced starburst. The strengths of the magnesium and iron lines in the spectrum of the best observed cluster W3, and in the spectrum of the diffuse central light of NGC 7252, do not show an overabundance in alpha-elements, in contrast to the bulk stellar population of elliptical galaxies.
We investigate the origin of color gradients in cluster early-type galaxies to probe whether pure age or pure metallicity gradients can explain the observed data in local and distant (z approx 0.4) samples. We measure the surface brightness profiles of the 20 brightest early-type galaxies of CL0949+44 (hereafter CL0949) at redshift z=0.35-0.38 from HST WF2 frames taken in the filters F555W, F675W, F814W. We determine the color profiles (V-R)(r), (V-I)(r), and (R-I)(r) as a function of the radial distance r in arcsec, and fit logarithmic gradients in the range -0.2 to 0.1 mag per decade. These values are similar to what is found locally for the colors (U-B), (U-V), (B-V) which approximately match the (V-R), (V-I), (R-I) at redshift approx 0.4. We analyse the results with up to date stellar population models. We find that passive evolution of metallicity gradients (approx 0.2 dex per radial decade) provides a consistent explanation of the local and distant galaxies' data. Invoking pure age gradients (with fixed metallicity) to explain local color gradients produces too steep gradients at redshifts z approx 0.4. Pure age gradients are consistent with the data only if large present day ages (>=15 Gyr) are assumed for the galaxy centers.
In the first contribution the basic problems posed by the existence of the Fundamental Plane (FP), and its relations with the Virial Theorem are discussed. Various possibilities are presented that can produce the observed uniform departure from homology and/or from a constant stellar mass-to-light ratio. The role of orbital anisotropy and its relation with the FP thickness are also discussed. In the second contribution the observational evidence for the existence of a FP for galaxy clusters, analogous to that of ellipticals, is presented and discussed. In the third contribution the dynamical properties of $R^{1/m}$ spherical galaxies with variable orbital anisotropy are discussed. The stability of the models against radial--orbit instability is studied, and the consequences on the FP tilt and thickness are discussed. An innovative tool for the construction of Evolutionary Synthesis models of Stellar Populations is described in the fourth contribution. As an illustrative example, the evolution of the stellar mass-to-light ratios has been computed and the implications on the FP of elliptical galaxies are briefly discussed. Finally, in the fifth contribution, with the aid of the first large sample of X-ray emitting early-type galaxies with known kinematics, the effect of rotation on the X-ray emission, particularly with regard to the X-ray underluminosity of flat systems is discussed. The role of structural parameters as the ellipticity, the isophotal shape parameter $a_4/a$, and the inner slope of the surface brightness profile recently measured by HST are also investigated.