Werner W. Zeilinger

The external origin of the gas in S0 galaxies

In this Letter we present three new cases of S0 galaxies, namely NGC 2768, NGC 4379, and IC 4889, out of a sample of 15, in which the gas is counterrotating or strongly kinematically decoupled with respect to the stellar body of the galaxy. Assuming gas infall with randomly oriented angular momentum, this result implies that in 40% of the galaxies in our sample, the ionized gas is of external origin. However, several pieces of evidence suggest that the acquisition of external gas in S0 galaxies can be even more general

Formation and evolution of dwarf elliptical galaxies – II. Spatially resolved star formation histories

We present optical Very Large Telescope spectroscopy of 16 dwarf elliptical galaxies (dEs) comparable in mass to NGC 205, and belonging to the Fornax cluster and to nearby groups of galaxies. Using full-spectrum fitting, we derive radial profiles of the SSP-equivalent ages and metallicities. We make a detailed analysis with ulyss and steckmap of the star formation history in the core of the galaxies and in an aperture of one effective radius. We resolved the history into one to four epochs. The statistical significance of these reconstructions was carefully tested; the two programs give remarkably consistent results. The old stellar population of the dEs, which dominates their mass, is likely coeval with that of massive ellipticals or bulges, but the star formation efficiency is lower. Important intermediate age (1–5 Gyr) populations and frequently tails of star formation until recent times are detected. These histories are reminiscent of their lower mass dwarf spheroidal counterparts of the Local Group. Most galaxies (10/16) show significant metallicity gradients, with metallicity declining by 0.5 dex over one half-light radius on average. These gradients are already present in the old population. The flattened (or discy), rotating objects (6/16) have flat metallicity profiles. This may be consistent with a distinct origin for these galaxies or it may be due to their geometry. The central single stellar population equivalent age varies between 1 and 6 Gyr, with the age slowly increasing with radius in the vast majority of objects. The group and cluster galaxies have similar radial gradients and star formation histories. The strong and old metallicity gradients place important constraints on the possible formation scenarios of dEs. Numerical simulations of the formation of spherical low-mass galaxies reproduce these gradients, but they require a longer time for them to build up. A gentle depletion of the gas, by ram pressure stripping or starvation, could drive the gas-rich, star-forming progenitors to the present dEs.

Pressure-supported Ionized Gas in S0 Galaxies*

Rotation curves and velocity dispersion profiles are presented for both the stellar and gaseous components of a sample of S0 galaxies. In all galaxies the central velocity dispersion of the ionized gas exceeds 150 km s-1. In some galaxies the gas dispersion remains as high as the stellar one over an extended radial range, showing that random motions are crucial for the dynamical support of the gas. Such a pressure support may explain why the observed gas rotation curves in galaxy bulges often fall short of the circular velocity predicted from the stellar kinematic models. It is suggested that, in addition to the acquisition of external material, some of the observed gas in S0 galaxies may have been shed from bulge stars.

Toward an Alternative Way of Looking at Elliptical Galaxies: Case Studies for NGC 4649 and NGC 7097

In this paper we consider three-integral axisymmetric models for NGC 4649 and NGC 7097, addressing the question of the presence of dark matter in these elliptical galaxies. The data for NGC 7097 can be modeled without a dark matter halo. The central region of NGC 4649 could be hosting a black hole. The kinematical data of NGC 4649 are not inconsistent with a constant mass-to-light ratio model, but a dynamical model with a moderate amount of dark matter better reproduces the observed anisotropy on the major axis. In addition, we look more closely at the issue of the classification of elliptical galaxies. Both galaxies can be placed in different families of elliptical galaxies based on the isophote shape. In this paper we set out to investigate whether the kinematic information can be used to specify a second classification parameter. We propose the use of normalized distribution functions, which are the three-integral distribution functions divided by the two-integral model (constructed from photometry alone), and argue why this is an efficient way of presenting the dynamics of elliptical galaxies. We show that they can be used to characterize the rotational state of a galaxy in a more specific way than merely indicating the amount of rotation or counterrotation. Furthermore, the distribution function for NGC 7097 suggests that the counterrotation is caused by stars spread over large radii in the galaxy, implying that this phenomenon is not related to a compact group of stars. Hence, the origin of the counterrotation should not be found in a recent merger in the first place. This shows that it is important to construct dynamic models with a distribution function. The distribution function is the tool used to visualize structure in phase space, which is the only stellar dynamic remnant of galaxy formation.

TOWARD A SOLUTION FOR THE Ca II TRIPLET PUZZLE : RESULTS FROM DWARF ELLIPTICAL GALAXIES

We present new estimates of ages and metallicities, based on VLT FORS optical (4400-5500 A) spectroscopy, of 16 dwarf elliptical galaxies (dEs) in the Fornax Cluster and in southern groups. These dEs are more metal-rich and younger than previous estimates based on narrowband photometry and low-resolution spectroscopy. For our sample we find a mean metallicity [Z/H] = -0.33 dex and mean age 3.5 Gyr, consistent with similar samples of dEs in other environments (Local Group, Virgo). Three dEs in our sample show emission lines and very young ages. This suggests that some dEs formed stars until a very recent epoch and were self-enriched by a long star formation history. Previous observations of large near-infrared (~8500 A) Ca II absorption strengths in these dEs are in good agreement with the new metallicity estimates, solving part of the so-called calcium puzzle.

Age and metallicity gradients in fossil ellipticals

Context. Fossil galaxy groups are speculated to be old and highly evolved systems of galaxies that formed early in the universe and had enough time to deplete their L ∗ galaxies through successive mergers of member galaxies, building up one massive central elliptical, but retaining the group X-ray halo. Aims. Considering that fossils are the remnants of mergers in ordi nary groups, the merger history of the progenitor group is ex pected to be imprinted in the fossil central galaxy (FCG). We present for the first time radial gradients of single-stellar popul ation (SSP) ages and metallicites in a sample of FCGs to constrain their formation scenario. We also measure line-strength gradients for the strongest absorption features in these galaxies. Methods. We took deep spectra with the long-slit spectrograph ISIS at the William Herschel Telescope (WHT) for six FCGs. The obtained spectra are fit with Pegase HR SSP models within the ful l-spectrum fitting package ULySS yielding SSP ages and metal licities of the stellar populations. We measure radial gradients of S SP ages and metallicities along the major axes. Lick indices are measured for the strongest absorption features to determine line-st rength gradients and compare with the full-spectrum fitting results. Results. Our sample comprises some of the most massive galaxies in the universe exhibiting an average central velocity dispersio n of �0 = 271± 28 km s −1 . Metallicity gradients are throughout negative with comparatively flat slopes of ∇[Fe/H] =−0.19± 0.08 while age gradients are found to be insignificant (∇age = 0.00± 0.05). All FCGs lie on the fundamental plane, suggesting that they are virialised systems. We find that gradient strengths and central metalli cities are similar to those found in cluster ellipticals of s imilar mass. Conclusions. The comparatively flat metallicity gradients with respect t o those predicted by monolithic collapse (∇Z =−0.5) suggest that fossils are indeed the result of multiple major mergers . Hence we conclude that fossils are not ’failed groups’ that formed with a top heavy luminosity function. The low scatter of gradient slopes suggests a similar merging history for all galaxies in our sample.

Calibrating the fundamental plane with SDSS DR8 data

We present a calibration of the fundamental plane using SDSS Data Release 8. We analysed about 93000 elliptical galaxies up to

Evidence for a triaxial bulge in the spiral galaxy NGC 4845

z<0.2

Revisiting the low-luminosity galaxy population of the NGC 5846 group with SDSS

, the largest sample used for the calibration of the fundamental plane so far. We incorporated up-to-date K-corrections and used GalaxyZoo data to classify the galaxies in our sample. We derived independent fundamental plane fits in all five Sloan filters u, g, r, i and z. A direct fit using a volume-weighted least-squares method was applied to obtain the coefficients of the fundamental plane, which implicitly corrects for the Malmquist bias. We achieved an accuracy of 15% for the fundamental plane as a distance indicator. We provide a detailed discussion on the calibrations and their influence on the resulting fits. These re-calibrated fundamental plane relations form a well-suited anchor for large-scale peculiar-velocity studies in the nearby universe. In addition to the fundamental plane, we discuss the redshift distribution of the elliptical galaxies and their global parameters.

Mixed early and late-type properties in the bar of NGC 6221: Evidence for evolution along the Hubble sequence?

Spectroscopic observations for the Sa galaxy NGC 4845 in five position angles reveal a regular but nonaxisymmetric velocity field for the gas at r of 1.5 kpc or less. Photometry indicates a possible slight twisting between the disk and bulge isophotes. These phenomena are interpreted as a manifestation of a triaxial bulge, and estimates of the ranges of b/a and c/a are obtained. 20 refs.