842 research outputs found
Dynamical modelling of luminous and dark matter in 17 Coma early-type galaxies
Dynamical models for 17 Coma early-type galaxies are presented. The galaxy
sample consists of flattened, rotating as well as non-rotating early-types
including cD and S0 galaxies with luminosities between M=-18.79 and M=-22.56.
Kinematical long-slit observations cover at least the major and minor axis and
extend to 1-4 effective radii. Axisymmetric Schwarzschild models are used to
derive stellar mass-to-light ratios and dark halo parameters. In every galaxy
models with a dark matter halo match the data better than models without. The
statistical significance is over 95 percent for 8 galaxies, around 90 percent
for 5 galaxies and for four galaxies it is not significant. For the highly
significant cases systematic deviations between observed and modelled
kinematics are clearly seen; for the remaining galaxies differences are more
statistical in nature. Best-fit models contain 10-50 percent dark matter inside
the half-light radius. The central dark matter density is at least one order of
magnitude lower than the luminous mass density. The central phase-space density
of dark matter is often orders of magnitude lower than in the luminous
component, especially when the halo core radius is large. The orbital system of
the stars along the major-axis is slightly dominated by radial motions. Some
galaxies show tangential anisotropy along the minor-axis, which is correlated
with the minor-axis Gauss-Hermite coefficient H4. Changing the balance between
data-fit and regularisation constraints does not change the reconstructed mass
structure significantly. Model anisotropies tend to strengthen if the weight on
regularisation is reduced, but the general property of a galaxy to be radially
or tangentially anisotropic, respectively, does not change. (abridged)Comment: 31 pages, 34 figures; accepted for publication in MNRA
Photoelectric and CCD Photometry of E and S0 Galaxies
We present BR photoelectric photometry for 352 E and S0 galaxies that are part of a large survey of the properties and peculiar motions of galaxies in distant clusters. Repeat measurements show our internal errors to be 2 â 3 per cent in B and R and 1 â 2 per cent in Bâ R. Comparisons of BR and BVR reductions for 10 galaxies also observed in V show small systematic errors due to differences between the spectral energy distributions of stars and galaxies. External comparisons with Bâ V colours in the literature confirm that these colours are good to 1 per cent. We also describe R-band CCD observations for 95 of the galaxies and place these on a BR photometric system for photoelectric and CCD photometry, with a common zero-point good to better than 1 per cent. We find the rms precision of both our photoelectric and CCD R magnitudes to be 2 â 3 per cent for galaxies as faint as R â 15. Errors in galaxy magnitudes of this order introduce errors of âČ 2 per cent into Dn â Ï distance estimates, corresponding to errors in peculiar velocities for single galaxies of âČ 200 km s-1 at a distance of 10000 km s-1
Spatially Resolved Spectroscopy of Coma Cluster EarlyâType Galaxies
We present long slit spectra for a magnitude limited sample of 35 E and S0 galaxies of the Coma cluster. The high quality of the data allowed us to derive spatially resolved spectra for a substantial sample of Coma galaxies for the first time. From these spectra we obtained rota- tion curves, the velocity dispersion profiles and the H3 and H4 coefficients of the Hermite decomposition of the line of sight velocity distribution. Moreover, we derive the radial line index profiles of Mg, Fe and HÎČ line indices out to R â 1re â 3re with high signal-to-noise ratio. We describe the galaxy sample, the observations and data re- duction, and present the spectroscopic database. Ground- based photometry for a subsample of 8 galaxies is also presented
The Chemistry of Extragalactic Globular Clusters
We present preliminary results of VLT/FORS spectroscopy of globular clusters
in nearby early-type galaxies. Our project aims at studying the chemistry and
determine the ages of globular cluster (sub-)populations. First results
indicate that the different galaxies host from little to significant
intermediate-age populations, and that the latter have alpha-element over iron
ratios closer to solar than the old population that show an alpha-element
enhancement similar to the diffuse stellar light.Comment: 4 pages (incl 2 figures) to appear in the proceedings of
"Extragalactic Globular Cluster Systems", ed.M.Kissler-Patig, Springer; see
also related contributions by T.H.Puzia and M.Hempel et a
The Fundamental Plane of Early-Type Galaxies as a Confounding Correlation
Early-type galaxies are characterized by many scaling relations. One of them,
the so-called fundamental plane is a relatively tight correlation between three
variables, and has resisted a clear physical understanding despite many years
of intensive research. Here, we show that the correlation between the three
variables of the fundamental plane can be the artifact of the effect of another
parameter influencing all, so that the fundamental plane may be understood as a
confounding correlation. Indeed, the complexity of the physics of galaxies and
of their evolution suggests that the main confounding parameter must be related
to the level of diversification reached by the galaxies. Consequently, many
scaling relations for galaxies are probably evolutionary correlations
Spatially resolved spectroscopy of Coma cluster early-type galaxies IV. Completing the dataset
The long-slit spectra obtained along the minor axis, offset major axis and
diagonal axis are presented for 12 E and S0 galaxies of the Coma cluster drawn
from a magnitude-limited sample studied before. The rotation curves, velocity
dispersion profiles and the H_3 and H_4 coefficients of the Hermite
decomposition of the line of sight velocity distribution are derived. The
radial profiles of the Hbeta, Mg, and Fe line strength indices are measured
too. In addition, the surface photometry of the central regions of a subsample
of 4 galaxies recently obtained with Hubble Space Telescope is presented. The
data will be used to construct dynamical models of the galaxies and study their
stellar populations.Comment: 40 pages, 7 figures, 6 tables. Accepted for publication in ApJ
Observing the build-up of the colour-magnitude relation at redshift ~0.8
We analyse the rest-frame (U-V) colour-magnitude relation for 2 clusters at
redshift 0.7 and 0.8, drawn from the ESO Distant Cluster Survey. By comparing
with the population of red galaxies in the Coma cluster, we show that the high
redshift clusters exhibit a deficit of passive faint red galaxies. Our results
show that the red-sequence population cannot be explained in terms of a
monolithic and synchronous formation scenario. A large fraction of faint
passive galaxies in clusters today has moved onto the red sequence relatively
recently as a consequence of the fact that their star formation activity has
come to an end at z<0.8.Comment: 5 pages, 2 figures, to appear in Proc. of IAU Colloq. 195: "Outskirts
of Galaxy Clusters: Intense Life in the Suburbs" -- minor typos correcte
Spatially resolved spectroscopy of Coma cluster early-type galaxies - II:the minor axis dataset
We present minor axis, off set major axis and one diagonal long slit spectra for 10 E and S0 galaxies of the Coma cluster drawn from a magnitude-limited sample studied before. We derive rotation curves, velocity dispersion profiles and the H-3 and H-4 coefficients of the Hermite decomposition of the line of sight velocity distribution. Moreover, we derive the line index profiles of Mg, Fe and Hbeta line indices and assess their errors. The data will be used to construct dynamical models of the galaxies and study their stellar populations
- âŠ