On the shape of elliptical galaxies

We propose a test for the existence of prolate elliptical galaxies based on the properties of the photometric parameters introduced in the Córdoba surface photometry.     

Feedback and late star formation in elliptical galaxies

We present a one-zone model of star formation in elliptical galaxies that includes thermal feedback from supernovae and a temperature dependent star formation efficiency. The modulation of feedback with the total mass results in the triggering of late episodes of star formation in low-mass galaxies. These small `bursts' can occur as late as at redshifts z ∼ 0.5 but they do not change significantly the optical and NIR color-magnitude relation (CMR) of cluster galaxies, both locally and out to moderate redshifts, in agreement with the observations. However, they introduce a large scatter at the faint end of the NUV-Optical CMR, as recently found in cluster Abell 851 (z = 0.41). This revised version was published online in August 2006 with corrections to the Cover Date.     

Line-of-sight velocity distributions of low-luminosity elliptical galaxies

The shape of the line-of-sight velocity distribution (LOSVD) is measured for a sample of 14 elliptical galaxies, predominantly low-luminosity ellipticals. The sample is dominated by galaxies in the Virgo cluster but also contains ellipticals in nearby groups and low-density environments. The parametrization of the LOSVD given by Gerhard and van der Marel & Franx is adopted, which measures the asymmetrical and symmetrical deviations of the LOSVD from a Gaussian by the amplitudes h ₃ and h ₄ of the Gauss–Hermite series. Rotation, velocity dispersion, h ₃ and h ₄ are determined as a function of radius for both major and minor axes. Non-Gaussian LOSVDs are found for all galaxies along the major axes. Deviations from a Gaussian LOSVD along the minor axis are of much lower amplitude if present at all. Central decreases in velocity dispersion are found for three galaxies. Two galaxies have kinematically decoupled cores: NGC 4458 and the well-known case of NGC 3608.     

Recent star-forming activity in local elliptical galaxies

The formation and evolution of elliptical galaxies (EGs) are still an open question. In particular, recent observations suggest that EGs are not only simple spheroidal systems of old stars. In this paper, we analyse a sample of EGs selected from the Sloan Digital Sky Survey in order to study the star-forming activity in local EGs. Among these 487 ellipticals, we find that 13 EGs show unambiguous evidence of recent star formation activity betrayed by conspicuous nebular emission lines. Using the evolutionary stellar population synthesis models and Lick absorption line indices, we derive stellar ages, metallicities and α-element abundances, and thus reconstruct the star formation and chemical evolution history of the star-forming elliptical galaxies (SFEGs) in our sample.
We find that SFEGs have relative younger stellar population age, higher metallicity and lower stellar mass, and that their star formation history can be well described by a recent minor and short starburst superimposed on old stellar component. We also detect 11 E+A galaxies whose stellar population properties are closer to those of quiescent (normal) ellipticals than to star-forming ones. However, from the analysis of their absorption line indices, we note that our E+A galaxies show a significant fraction of intermediate-age stellar populations, remarkably different from the quiescent galaxies. This might suggest an evolutionary link between E+As and star-forming ellipticals. Finally, we confirm the relations between age, metallicity, α-element abundance and stellar mass for local EGs.     

Young nuclei in dwarf elliptical galaxies

We report the discovery of young embedded structures in three diffuse elliptical galaxies (dE) in the Virgo cluster: IC 783, IC 3468, and IC 3509. We performed 3D spectroscopic observations of these galaxies with the MPFS spectrograph at the 6-m Special Astrophysical Observatory telescope and obtained spatially resolved distributions of kinematic and stellar population parameters by fitting high-resolution PEGASE. HR synthetic single stellar populations (SSP) in pixel space. In all three galaxies, the luminosity-weighted age of the nuclei (∼4 Gyr) is considerably younger than that of the population in the outer regions of the galaxies. We discuss two possibilities for the formation of such structures—a dissipative merger event and a different ram pressure stripping efficiency during two consecutive crossings of the Virgo cluster centre. The article was translated by the authors.     

Evidence of fast rotation in dwarf elliptical galaxies

In this letter we investigate the kinematical properties of early-type dwarfs by significantly enlarging the scarce observational sample so far available. We present rotation curves and mean velocity dispersions for four bright dwarf ellipticals and two dwarf lenticular galaxies in the Virgo cluster. Most of these galaxies exhibit conspicuous rotation curves. In particular, five out of the six new galaxies are found to be close to the predictions for oblate spheroids flattened by rotation. Therefore, and contrary to the previous observational hints, the present data suggest that an important fraction of dwarf early-type galaxies may be rotationally supported.     

Ages of elliptical galaxies: single- versus multi-population interpretation

New calibrations of spectrophotometric indices of elliptical galaxies as functions of spectrophotometric indices are presented, permitting estimates of mean stellar population ages and metallicities. These calibrations are based on evolutionary models including a two-phase interstellar medium, infall and a galactic wind. Free parameters were fixed by requiring that models reproduce the mean trend of data in the colour–magnitude diagram as well as in the plane of indices  Hβ–Mg₂  and  Mg₂–〈Fe〉  . To improve the location of faint ellipticals  ( M _B > −20)  in the  Hβ–Mg₂  diagram, downsizing was introduced. An application of our calibrations to a sample of ellipticals and a comparison with results derived from single stellar population models are given. Our models indicate that mean population ages span an interval of 7–12 Gyr and are correlated with metallicities, which range from approximately half up to three times solar.     

Infrared–red cores in nearby elliptical galaxies

We present the Spitzer Space Telescope Infrared Array Camera observations for a sample of local elliptical galaxies to study later stages of active galactic nucleus (AGN) activity. A sample of 36 elliptical galaxies is selected from the Palomar spectroscopic survey. We detect nuclear non-stellar infrared emission in nine of them. There is unambiguous evidence of circumnuclear dust in these nine galaxies in their optical images. We also find a remarkable correlation between the infrared excess emission and the nuclear radio/X-ray emission, suggesting that infrared excess emission is tightly related to nuclear activity. The possible origin of infrared excess emission from hot dust heated by the central AGN is supported by the spectral indices of the infrared excess emission.     

Supermassive black holes, star formation and downsizing of elliptical galaxies

The overabundance of Mg relative to Fe, observed in the nuclei of bright ellipticals, and its increase with galactic mass, poses a serious problem for all current models of galaxy formation. Here, we improve on the one-zone chemical evolution models for elliptical galaxies by taking into account positive feedback produced in the early stages of supermassive central black hole growth. We can account for both the observed correlation and the scatter if the observed anti-hierarchical behaviour of the AGN population couples to galaxy assembly and results in an enhancement of the star formation efficiency which is proportional to galactic mass. At low and intermediate galactic masses, however, a slower mode for star formation suffices to account for the observational properties.