A continuum of structure and stellar content from Virgo cluster early-type dwarfs to giants?

Based on the wealth of multiwavelength imaging data from the SDSS, we investigate whether dwarf and giant early-type galaxies in the Virgo cluster follow a continuum in their structural parameters and their stellar population characteristics. More specifically we study the relation between size and brightness for the galaxies and their color magnitude relation. In both cases, we find noticeable deviations from a simple joint behavior of dwarfs and giants. We discuss these findings in the light of the different formation mechanisms commonly assumed for dwarf and giant early types, thereby taking into account the existence of several distinct early-type dwarf subclasses. By comparing our results to a semianalytic model of galaxy formation, we argue that the analyzed relations might be reproduced by processes that form dwarfs and giants altogether. The work presented here is based on Janz & Lisker 2008, 2009.Comment: 7 pages, 3 figures, to be published in Astronomische Nachrichten (proceedings of Symposium 6 of the JENAM 2008, Vienna

Near-infrared imaging and spectroscopy of the nuclear region of the disturbed Virgo cluster spiral NGC 4438

We present near-infrared VLT ISAAC imaging and spectroscopy of the peculiar Virgo galaxy NGC 4438, whose nucleus has been classified as a LINER. The data are supplemented by mid-infrared imaging, and compared to previous WFPC2 HST broadband images. Images and position-velocity maps of the [Fe II] and H2 line emissions are presented and compared with the distribution of the optical narrow-line region and radio features. Our results show that shocks (possibly driven by a radio jet) contribute to an important fraction of the excitation of [Fe II], while X-ray heating from a central AGN may be responsible for the H2 excitation. We address the question whether the outflow has an AGN or a starburst origin by providing new estimates of the central star formation rate and the kinetic energy associated with the gas. By fitting a Sersic bulge, an exponential disc and a compact nuclear source to the light distribution, we decomposed NGC 4438's light distribution and found an unresolved nuclear source at 0.8 arcsec resolution with M_K = -18.7 and J-H = 0.69. Our measured bulge velocity dispersion, 142 km/s, together with the standard M_bh-sigma relation, suggests a central black hole mass of log(M_bh/Msun) ~ 7.0. The stellar kinematics measured from the near-infrared CO lines shows a strong peak in the velocity dispersion of 178 km/s in the central 0.5 arcsec, which is possible kinematic evidence of a central black hole. We calculated a general expression for the integrated Sersic profile flux density in elliptical geometry, including the case of 'disky' isophotes.Comment: 13 pages, 12 figures. Affiliation added. Higher resolution image

Line-of-sight velocity dispersions and a mass distribution model of the Sa galaxy NGC 4594

In the present paper we develop an algorithm allowing to calculate line-of-sight velocity dispersions in an axisymmetric galaxy outside of the galactic plane. When constructing a self-consistent model, we take into account the galactic surface brightness distribution, stellar rotation curve and velocity dispersions. This algorithm is applied to a Sa galaxy NGC 4594 = M 104, for which there exist velocity dispersion measurements outside of the galactic major axis. The mass distribution model is constructed in two stages. In the first stage we construct a luminosity distribution model, where only galactic surface brightness distribution is taken into account. Thereafter, in the second stage we develop on the basis of the Jeans equations a detailed mass distribution model and calculate line-of-sight velocity dispersions and the stellar rotation curve. Here a dark matter halo is added to visible components. Calculated dispersions are compared with observations along different slit positions perpendicular and parallel to the galactic major axis. In the best-fitting model velocity dispersion ellipsoids are radially elongated. Outside the galactic plane velocity dispersion behaviour is more sensitive to the dark matter density distribution and allows to estimate dark halo parameters.Comment: 12 pages, 13 figures, accepted for publication in MNRA