The Tilt of the Fundamental Plane: Three-quarters Structural Nonhomology, One-quarter Stellar Population

The variation of the mass-to-light ratios M/L of early type galaxies as function of their luminosities L is investigated. It is shown that the tilt beta=0.27 (in the B--band) of the fundamental plane relation M/L ~ L^{beta} can be understood as a combination of two effects: about one-quarter (i.e. dbeta =0.07) is a result of systematic variations of the stellar population properties with increasing luminosity. The remaining three-quarters (i.e. dbeta =0.2) can be completely attributed to nonhomology effects that lead to a systematic change of the surface brightness profiles with increasing luminosity. Consequently, the observed tilt in the K-band (beta=0.17) where stellar population effects are negligible, is explained by nonhomology effects alone. After correcting for nonhomology, the mean value of the mass-to-light ratio of elliptical galaxies (M/L_B) is 7.1+-2.8 (1 sigma scatter).Comment: 8 pages, 3 figures, ApJL, 600, 39, minor changes made to match the published versio

Globular clusters and dwarf galaxies in Fornax - I. Kinematics in the cluster core from multi-object spectroscopy

We acquired radial velocities of a significant number of globular clusters (GCs) on wide fields between galaxies in the nearby Fornax cluster of galaxies, in order to derive their velocity dispersion radial profile and to probe the dynamics of the cluster. We used FLAMES on the VLT to obtain accurate velocities for 149 GCs, within a ~500x150 kpc strip centered on NGC 1399, the Fornax central galaxy. These objects are at the very bright tail (M_V < -9.5) of the GC luminosity function, overlapping the so-called ``ultra-compact dwarfs'' magnitude range. Eight of the brightest FLAMES-confirmed members indeed show hints of resolution in the subarcsecond pre-imaging data we used for selecting the ~500 targets for FLAMES spectroscopy. Ignoring the GCs around galaxies by applying 3d_25 diameter masks, we find 61 GCs of 20.0 < V < 22.2 lying in the intra-cluster (IC) medium. The velocity dispersion of the population of ICGCs is 200 km/s at ~150 kpc from the central NGC 1399 and rises to nearly 400 km/s at 200 kpc, a value which compares with the velocity dispersion of the population of dwarf galaxies, thought to be infalling from the surroundings of the cluster.Comment: To be published in A&A Letters. 4 pages, 3 figures, 3 table

Kinematics and stellar population of NGC 4486A

NGC 4486A is a low-luminosity elliptical galaxy harbouring an edge-on nuclear disk of stars and dust. It is known to host a super-massive black hole. We study its large-scale kinematics and stellar population along the major axis to investigate the link between the nuclear and global properties. We use long-slit medium-resolution optical spectra that we fit against stellar population models. The SSP-equivalent age is about 12 Gyr old throughout the body of the galaxy, and its metallicity decreases from [Fe/H] = 0.18 near the centre to sub-solar values in the outskirts. The metallicity gradient is -0.24 dex per decade of radius within the effective isophote. The velocity dispersion is 132+-3 km/s at 1.3 arcsec from the centre and decreases outwards. The rotation velocity reaches a maximum V_max >~ 115+-5 km/s at a radius 1.3 < r_max < 2 arcsec. NGC\,4486A appears to be a typical low-luminosity elliptical galaxy. There is no signature in the stellar population of the possible ancient accretion/merging event that produced the disk.Comment: Astronomy and Astrophysics, in pres

The X-shooter Spectral Library (XSL): I. DR1. Near-ultraviolet through optical spectra from the first year of the survey

We present the first release of XSL, the X-Shooter Spectral Library. This release contains 237 stars spanning the wavelengths 3000--10200 \AA\ observed at a resolving power $R \equiv \lambda / \Delta\lambda \sim 10000$. The spectra were obtained at ESO's 8-m Very Large Telescope (VLT). The sample contains O -- M, long-period variable (LPV), C and S stars. The spectra are flux-calibrated and telluric-corrected. We describe a new technique for the telluric correction. The wavelength coverage, spectral resolution and spectral type of this library make it well suited to stellar population synthesis of galaxies and clusters, kinematical investigation of stellar systems and studying the physics of cool stars.Comment: 41 pages, 38 figures, 5 tables. Accepted for publication in A&A. Webpage: http://xsl.u-strasbg.fr

Clues on the Physical Origin of the Fundamental Plane from Self-consistent Hydrodynamical Simulations

We report on a study of the parameters characterizing the mass and velocity distributions of two samples of relaxed elliptical-like objects (ELOs) identified, at z=0, in a set of self-consistent hydrodynamical simulations operating in the context of a concordance cosmological model. Star formation (SF) has been phenomenologically implemented in the simulations in the framework of the turbulent sequential scenario through a threshold gas density and an efficiency parameter. Each ELO sample is characterized by the values these parameters take. We have found that the (logarithms of the) ELO stellar masses, projected stellar half-mass radii, and stellar central line-of-sight (LOS) velocity dispersions define dynamical fundamental planes (FPs). Zero points depend on the particular values that the SF parameters take, while slopes do not change. The ELO samples have been found to show systematic trends with the mass scale in both the relative content and the relative distributions of the baryonic and the dark mass ELO components. The physical origin of these trends lies in the systematic decrease, with increasing ELO mass, of the relative dissipation experienced by the baryonic mass component along ELO mass assembly, resulting in a tilt of the dynamical FP relative to the virial plane. The dynamical FPs shown by the two ELO samples are consistent with that shown by the SDSS elliptical sample in the same variables, with no further need for any relevant contribution from stellar population effects to explain the observed tilt. These effects could, however, have contributed to the scatter of the observed FP, as the dynamical FPs have been found to be thinner than the observed one. The results we report on hint, for the first time, at a possible way to understand the tilt of the observed FP in a cosmological context.Comment: 12 pages, 1 figure. Accepted to Astrophysical Journal Letter

The Diffuse Emission and a Variable ULX in the Elliptical Galaxy NGC 3379

A Chandra observation of the intermediate luminosity (M_B=-20) elliptical galaxy NGC 3379 resolves 75% of the X-ray emission within the central 5kpc into point sources. Spectral analysis of the remaining unresolved emission within the central 770pc indicates that 90% of the emission probably arises from undetected point sources, while 10% arises from thermal emission from kT=0.6keV gas. Assuming a uniform density distribution in the central region of the galaxy gives a gas mass of 5.0e5 Mo.Such a small amount of gas can be supplied by stellar mass loss in only 1.0e7 years. Thus, the gas must be accreting into the central supermassive black hole at a very low radiative efficiency as in the ADAF or RIAF models, or is being expelled in a galactic wind driven by the same AGN feedback mechanism as that observed in cluster cooling flows. If the gas is being expelled in an AGN driven wind, then the ratio of mechanical to radio power of the AGN must be 1.0e4, which is comparable to that measured in cluster cooling flows which have recently been perturbed by radio outbursts. The brightest point source in NGC 3379 is located 360pc from the central AGN with a peak luminosity of 3.5e39 ergs/s, which places it in the class of ultra-luminous X-ray point sources (ULX). Analysis of an archival ROSAT HRI observation of NGC 3379 shows that this source was at a comparable luminosity 5 years prior to the Chandra observation. During the Chandra observation, the source intensity smoothly varies by a factor of two with the suggestion of an 8-10 hour period