Superdense galaxies and the mass-size relation at low redshift

We search for massive and compact galaxies (superdense galaxies, hereafter SDGs) at z=0.03-0.11 in the Padova-Millennium Galaxy and Group Catalogue, a spectroscopically complete sample representative of the local Universe general field population. We find that compact galaxies with radii and mass densities comparable to high-z massive and passive galaxies represent 4.4% of all galaxies with stellar masses above 3 X 10^10 M_sun, yielding a number density of 4.3 X 10^-4 h^3 Mpc^-3. Most of them are S0s (70%) or ellipticals (23%), are red and have intermediate-to-old stellar populations, with a median luminosity-weighted age of 5.4 Gyr and a median mass-weighted age of 9.2 Gyr. Their velocity dispersions and dynamical masses are consistent with the small radii and high stellar mass estimates. Comparing with the WINGS sample of cluster galaxies at similar redshifts, the fraction of superdense galaxies is three times smaller in the field than in clusters, and cluster SDGs are on average 4 Gyr older than field SDGs. We confirm the existence of a universal trend of smaller radii for older luminosity-weighted ages at fixed galaxy mass. On top of the well known dependence of stellar age on galaxy mass, the luminosity-weighted age of galaxies depends on galaxy compactness at fixed mass, and, for a fixed mass and radius, on environment. This effect needs to be taken into account in order not to overestimate the evolution of galaxy sizes from high- to low-z. Our results and hierarchical simulations suggest that a significant fraction of the massive compact galaxies at high-z have evolved into compact galaxies in galaxy clusters today. When stellar age and environmental effects are taken into account, the average amount of size evolution of individual galaxies between high- and low-z is mild, a factor ~1.6. (abridged)Comment: ApJ, in pres

The evolution of galaxy sizes

We present a study of galaxy sizes in the local Universe as a function of galaxy environment, comparing clusters and the general field. Galaxies with radii and masses comparable to high-z massive and compact galaxies represent 4.4% of all galaxies more massive than 3 X 10^{10} M_sun in the field. Such galaxies are 3 times more frequent in clusters than in the field. Most of them are early-type galaxies with intermediate to old stellar populations. There is a trend of smaller radii for older luminosity-weighted ages at fixed galaxy mass. We show the relation between size and luminosity-weighted age for galaxies of different stellar masses and in different environments. We compare with high-z data to quantify the evolution of galaxy sizes. We find that, once the progenitor bias due to the relation between galaxy size and stellar age is removed, the average amount of size evolution of individual galaxies between high- and low-z is mild, of the order of a factor 1.6.Comment: to appear in the proceedings of the IAU S295: The intriguing life of massive galaxies, editors D. Thomas, A. Pasquali & I. Ferrera

Surface photometry of WINGS galaxies with GASPHOT

Aims. We present the B-, V- and K-band surface photometry catalogs obtained running the automatic software GASPHOT on galaxies from the WINGS cluster survey having isophotal area larger than 200 pixels. The catalogs can be downloaded at the Centre de Donnees Astronomiques de Strasbourg (CDS). Methods. We outline the GASPHOT performances and compare our surface photometry with that obtained by SExtractor, GALFIT and GIM2D. This analysis is aimed at providing statistical information about the accuracy generally achieved by the softwares for automatic surface photometry of galaxies. Results. For each galaxy and for each photometric band the GASPHOT catalogs provide the parameters of the Sersic law best-fitting the luminosity profiles. They are: the sky coordinates of the galaxy center (R:A:; DEC:), the total magnitude (m), the semi-major axis of the effective isophote (Re), the Sersic index (n), the axis ratio (b=a) and a flag parameter (QFLAG) giving a global indication of the fit quality. The WINGS-GASPHOT database includes 41,463 galaxies in the B-band, 42,275 in the V-band, and 71,687 in the K-band. We find that the bright early-type galaxies have larger Sersic indices and effective radii, as well as redder colors in their center. In general the effective radii increase systematically from the K- to the V- and B-band. Conclusions. The GASPHOT photometry turns out to be in fairly good agreement with the surface photometry obtained by GALFIT and GIM2D, as well as with the aperture photometry provided by SExtractor. The main advantages of GASPHOT with respect to other tools are: (i) the automatic finding of the local PSF; (ii) the short CPU time of execution; (iii) the remarkable stability against the choice of the initial guess parameters. All these characteristics make GASPHOT an ideal tool for blind surface photometry of large galaxy samples in wide-field CCD mosaics.Comment: 14 pages, 9 figure

Galaxy stellar mass functions of different morphological types in clusters, and their evolution between z=0.8 and z=0

We present the galaxy stellar mass function (MF) and its evolution in clusters from z~0.8 to the current epoch, based on the WIde-field Nearby Galaxy-cluster Survey (WINGS) (0.04<z<0.07), and the ESO Distant Cluster Survey (EDisCS) (0.4<z <0.8). We investigate the total MF and find it evolves noticeably with redshift. The shape at M*>10^11 M' does not evolve, but below M*~10^10.8 M' the MF at high redshift is flat, while in the Local Universe it flattens out at lower masses. The population of M* = 10^10.2 - 10^10.8 M' galaxies must have grown significantly between z=0.8 and z=0. We analyze the MF of different morphological types (ellipticals, S0s and late-types), and find that also each of them evolves with redshift. All types have proportionally more massive galaxies at high- than at low-z, and the strongest evolution occurs among S0 galaxies. Examining the morphology-mass relation (the way the proportion of galaxies of different morphological types changes with galaxy mass), we find it strongly depends on redshift. At both redshifts, ~40% of the stellar mass is in elliptical galaxies. Another ~43% of the mass is in S0 galaxies in local clusters, while it is in spirals in distant clusters. To explain the observed trends, we discuss the importance of those mechanisms that could shape the MF. We conclude that mass growth due to star formation plays a crucial role in driving the evolution. It has to be accompanied by infall of galaxies onto clusters, and the mass distribution of infalling galaxies might be different from that of cluster galaxies. However, comparing with high-z field samples, we do not find conclusive evidence for such an environmental mass segregation. Our results suggest that star formation and infall change directly the MF of late-type galaxies in clusters and, indirectly, that of early-type galaxies through subsequent morphological transformations.Comment: MNRAS in press, 24 pages, 19 figures and 8 table

The evolution of early-type galaxies in clusters from z~ 0.8 to z~ 0: the ellipticity distribution and the morphological mix

We present the ellipticity distribution and its evolution for early-type galaxies in clusters from z~0.8 to z~0, based on the WIde-field Nearby Galaxy-cluster Survey (WINGS)(0.04<z<0.07), and the ESO Distant Cluster Survey (EDisCS)(0.4<z<0.8). We first investigate a mass limited sample and we find that, above a fixed mass limit, the ellipticity distribution of early-types noticeably evolves with redshift. In the local Universe there are proportionally more galaxies with higher ellipticity, hence flatter, than in distant clusters. This evolution is due partly to the change of the mass distribution and mainly to the change of the morphological mix with z (among the early types, the fraction of ellipticals goes from ~70% at high to ~40% at low-z). Analyzing separately the ellipticity distribution of the different morphological types, we find no evolution both for ellipticals and S0s. However, for ellipticals a change with redshift in the median value of the distributions is detected. This is due to a larger population of very round (e<0.05) elliptical galaxies at low-z. To compare our finding to previous studies, we also assemble a magnitude-"delimited" sample that consists of early-type galaxies on the red sequence with -19.3>M_B+1.208z>-21. Analyzing this sample, we do not recover exactly the same results of the mass-limited sample. Hence the selection criteria are crucial to characterize the galaxy properties: the choice of the magnitude-delimited sample implies the loss of many less massive galaxies and so it biases the final results. Moreover, although we are adopting the same selection criteria, our results in the magnitude-delimited sample are also not in agreement with those of Holden et al.(2009). This is due to the fact that our and their low-z samples have a different magnitude distribution because the Holden et al.(2009) sample suffers from incompleteness at faint magnitudes.Comment: 19 figures and 9 tables, MNRAS in pres

Tidal energy effects of dark matter halos on early-type galaxies

Tidal interactions between neighboring objects span across the whole admissible range of lengths in nature: from, say, atoms to clusters of galaxies i.e. from micro to macrocosms. According to current cosmological theories, galaxies are embedded within massive non-baryonic dark matter (DM) halos, which affects their formation and evolution. It is therefore highly rewarding to understand the role of tidal interaction between the dark and luminous matter in galaxies. The current investigation is devoted to Early-Type Galaxies (ETGs), looking in particular at the possibility of establishing whether the tidal interaction of the DM halo with the luminous baryonic component may be at the origin of the so-called "tilt" of the Fundamental Plane (FP). The extension of the tensor virial theorem to two-component matter distributions implies the calculation of the self potential energy due to a selected subsystem, and the tidal potential energy induced by the other one. The additional assumption of homeoidally striated density profiles allows analytical expressions of the results for some cases of astrophysical interest. The current investigation raises from the fact that the profile of the (self + tidal) potential energy of the inner component shows maxima and minima, suggesting the possible existence of preferential scales for the virialized structure, i.e. a viable explanation of the so called "tilt" of the FP. It is found that configurations related to the maxima do not suffice, by themselves, to interpret the FP tilt, and some other relation has to be looked for

Test of Clausius' Virial Dynamical Theory of Fundamental Plane By Homogeneous + \u3b3-Free Two Component Galaxy Model

Introduction: the theory of the Fundamental Plane (FP) proposed by Secco (2000, 2001,2005) is based on the existence of a maximum in the Clausius' Virial potential energy (CV) of a stellar component when it is completely embedded inside a dark matter (DM) halo. At the first order approximation the theory was developed by modeling the two-components with two power-law density profiles and two homogeneous cores. In order to test the extension of the theory to an higher order we explore the effect on an homogeneous stellar component due to a DM halo with a density profile characterized by a inner slope \u3b3free and an outer slope -3, according to high resolution rotation curves of Sps (Garrido et al. 2004). The aim is to investigate the role of the dark to bright mass ratio m and of the halo concentration C[D] in order to produce the maximum of CV. Particular attention is devoted to the slope of the density halo profile at the maximum location, to its height in comparison with the CV value when the two component coincide, V[n.] For all the models we choose \u3b3=0. Method: we follow the general method proposed by Caimmi (1993) for two striated ellipsoidals with Zhao-density profiles. Virial equilibrium is described by tensor virial equations extended to two subcomponents (Caimmi & Secco,1992). The interaction terms are numerically performed for different values of m and C [D] and sequences of CV as function of the ratio baryonic to halo virial semi-axis are taken into account. Results: the special configuration at the CV maximum with all the properties discovered with the theory of first order appears if m is greater than a given threshold.The corresponding slope (in absolute value) on the halo DM profile decreases either as m increases at fixed C[D] or as C[D] decreases at fixed m. The same conspiracy between m and C[D] appears in order to obtain the highest values of V[n]. Discussion: the test is relevant in order to confirm the main results of the first order approach and then to move the description of the main features of galaxy FP toward more realistic models

The 3D Topology of the Clausius Virial for Two Component Dynamical Models of Elliptical Galaxies

Introduction: as found in Secco (2000, 2001), the presence of the dark halo in a two component astrophysical object, can induce a scale length on the visible component trough the appearance of a maximum in the Clausius Virial potential energy (CV), which we expect, in general, to be monotonic. In this investigation the author used two power law density profiles, but we will find that the same occurs for more complex and realistic models. Method: we present a set of three two component dynamical models of elliptical galaxies to investigate the topology of the CV of a stellar spherical component completely embedded in a dark spherical halo. We have chosen Hernquist and Plummer mass density profiles for the two components in three different combinations: Plummer-Plummer, Hernquist-Hernquist, Hernquist-Plummer, where the first term refers to the stellar component, while the second to the dark component. In this way we can evaluate different combinations of cuspy and cored profiles and see their influence on the general behavior of CV. The fact that Plummer profiles are not perfectly describing real elliptical galaxies, and maybe also dark halos, is not so important for our present study, as the aim is to investigate the general trend of the CV. Results: it will be shown that the presence or not of stationary points in the CV are strongly depending on the ratio R between dark halo and stellar component masses, as expected, but are not much depending on the particular choice of the mass density profiles. Indeed all three models present the maximum of CV, with some restrictions on R. In general, cuspy profiles tend to restrain the presence of the CV, which appears for greater R, while cored profiles tend to enhance it. Discussion: with this preliminary study of the CV trend for two component models of elliptical galaxies we have found that the maximums in the CV are present for certain values of R also for more complex models. This can indicate that the stationary points in the CV could have a physical interesting meaning in the dynamics of elliptical galaxies

Violent relaxation of galactic dark matter halos

Simulazione numerica ad alta risoluzione del fenomeno di rilassamento violento di un alone galattico di materia oscura non barionica