Formation and evolution of dwarf elliptical galaxies

Abstract

Abstract. This paper is the first in a series in which we present the results of an ESO Large Program on the kinematics and internal dynamics of dwarf elliptical galaxies (dEs). We obtained deep major and minor axis spectra of 15 dEs and broad-band imaging of 22 dEs. Here, we investigate the relations between the parameters that quantify the structure (B-band luminosity L B , half-light radius R e , and mean surface brightness within the half-light radius I e = L B /2πR 2 e ) and internal dynamics (velocity dispersion σ) of dEs. We confront predictions of the currently popular theories for dE formation and evolution with the observed position of dEs in log L B vs. log σ, log L B vs. log R e , log L B vs. log I e , and log R e vs. log I e diagrams and in the (log σ, log R e , log I e ) parameter space in which bright and intermediate-luminosity elliptical galaxies and bulges of spirals define a Fundamental Plane (FP). In order to achieve statistical significance and to cover a parameter interval that is large enough for reliable inferences to be made, we merge the data set presented in this paper with two other recently published, equally large data sets. We show that the dE sequences in the various univariate diagrams are disjunct from those traced by bright and intermediateluminosity elliptical galaxies and bulges of spirals. It appears that semi-analytical models (SAMs) that incorporate quiescent star formation with an essentially z-independent star-formation efficiency, combined with post-merger starbursts and the dynamical response after supernova-driven gas-loss, are able to reproduce the position of the dEs in the various univariate diagrams. SAMs with star-formation efficiencies that rise as a function of redshift are excluded since they leave the observed sequences traced by dEs virtually unpopulated. dEs tend to lie above the FP and the FP residual declines as a function of luminosity. Again, models that take into account the response after supernova-driven mass-loss correctly predict the position of dEs in the (log σ, log R e , log I e ) parameter space as well as the trend of the FP residual as a function of luminosity. While these findings are clearly a success for the hierarchical-merging picture of galaxy formation, they do not necessarily invalidate the alternative "harassment" scenario, which posits that dEs stem from perturbed and stripped late-type disk galaxies that entered clusters and groups of galaxies about 5 Gyr ago.

SUPERMASSIVE BLACK HOLES AND THEIR HOST SPHEROIDS. II. THE RED AND BLUE SEQUENCE IN THE MBH–M*,SPH DIAGRAM

“…One of these is the M BH -s relation (Ferrarese & Merritt 2000;Gebhardt et al 2000), which can be described with a single power law (M BH 5 6 s µ -) over a wide range in velocity dispersion (70 350 km s 1 --, e.g., Graham et al 2011;McConnell et al 2011;. The other is the L sph -s relation, which has long been known to be a "double power law," with L sph 5 6 s µ -at the luminous end 5 (Schechter 1980;Malumuth & Kirshner 1981;Lauer et al 2007b;von der Linden et al 2007;Liu et al 2008)and L sph 2 s µ at intermediate and faint luminosities (Davies et al 1983;Held et al 1992;de Rijcke et al 2005;Matković & Guzmán 2005;Balcells et al 2007;Chilingarian et al 2008;Forbes et al 2008;Cody et al 2009;Tortora et al 2009 When Graham (2012) pointed out this overlooked inconsistency between these linear and bent relations, he identified two different populations of galaxies, namely the core-Sérsic spheroids Trujillo et al 2004) and the Sérsic spheroids 6 , and attributed the change in slope (from super-quadratic to linear) to their different formation mechanisms. In this scenario, core-Sérsic spheroids are built in dry merger events where the black hole and the bulge grow at the same pace, increasing their mass in lock steps (M L BH sph 1 µ ), whereas Sérsic spheroids originate from gas-rich processes in which the mass of the black hole increases more rapidly than the mass of its host spheroid (M L BH sph 2.5 µ ).…”

Kinematics in galactic tidal tails

“…The satellite galaxies are modeled as an adiabatically contracted NFW halo hosting a Hernquist sphere as the spherical baryonic component. The models fulfill the constraints from the Fundamental plane of dE+dSph galaxies given in de Rijcke et al (2005):…”

“…A Hernquist sphere has an effective radius R e 1.82r bulge (Hernquist 1990). For the velocity dispersion σ 0 , in analogy to the dispersion used by de Rijcke et al (2005), we computed the mass-weighted mean of the line-of-sight velocity dispersions in different radial annuli of the visible component. Finally, to relate the luminosity L B to the baryonic mass content of the galaxy we assume a mass-to-light ratio Υ B = 2Υ B, .…”

Formation and evolution of dwarf early-type galaxies in the Virgo cluster

“…Bender et al 1992;Graham & Guzmán 2003;Geha et al 2003;de Rijcke et al 2005;Matković & Guzmán 2005;Kormendy et al 2009), but whether dEs follow the same trends as Es is still unclear. While Kormendy et al (2009) claim that Es and dEs are two different populations of galaxies finding that they follow perpendicular trends in, e.g., the Kormendy relation, other works such as Graham & Guzmán (2003) or Ferrarese et al (2006) find that there is a continuity in the physical properties of dwarf and massive early-types.…”