712 research outputs found
The sigma - L correlation in Nearby Early-Type Galaxies
Early-type galaxy velocity dispersions and luminosities are correlated. The
correlation estimated in local samples (< 100 Mpc) differs from that measured
more recently in the SDSS. This is true even when systematics in the SDSS
photometric and spectroscopic parameters have been accounted-for. We show that
this is also true for the ENEAR sample if galaxy luminosities are estimated
using distances which have been corrected for peculiar motions. We then show
that, because the estimate of the `true' distance is derived from a correlation
with velocity dispersion, in this case the D_n-sigma relation, using it in the
sigma-L relation leads to an artificially tight relation with a biased slope.
Making no correction for peculiar velocities results in a sigma-L relation
which is very similar to that of the SDSS, although with larger scatter. We
also measure the sigma-L correlation in a mock ENEAR catalog, in which the
underlying galaxy sample has the same sigma-L correlation as seen in the SDSS.
The mock catalog produces the same D_n-sigma relation as the data, the same
biased slope when D_n-sigma distances are used to estimate luminosities, and
good agreement with the input sigma-L relation when redshift is used as the
distance indicator. This provides further evidence that the true sigma-L
relation of ENEAR galaxies is indeed very similar to that of SDSS early-types.
Our results suggest that local sigma-L relations which are based on Fundamental
Plane distances should also be re-evaluated. Our findings also have important
implications for black hole demographics; the best direct estimates of the
masses of supermassive black holes come from local galaxies, so estimates of
the black hole mass function are more safely made by working with the Mbh-sigma
correlation than with Mbh-L.Comment: 9 pages, 9 figures. Accepted by AJ. A new appendix describes
systematics effects we found in the SDSS velocity dispersion measurements
(sigmas < 150 km/s are biased towards larger values; this bias was not
present in the Bernardi et al. 2003 sample) and luminosity measurement
Tidal distortions in pairs of early-type galaxies
The authors are conducting an imaging survey of pairs of elliptical galaxies which has already produced interesting results. Some pairs present a common pattern of distortion interpreted in terms of tidal effects (Davoust and Prugniel, 1988; Prugniel et al., 1989). Other examples drawn from the literature (Borne and Hoessel, 1988; Colina and Perez-Fournon, 1990) share the same morphology. New cases and lists of the characteristics of 24 such systems. The authors' pairs are drawn from a sample of binary and multiple galaxies which has in turn been extracted from the CGCG, UGC (Nilson, 1973) and VV (Vorontsov-Velyaminov, 1959) catalogues. This sample includes that of Karachentsev (1972). It contains 1800 pairs, among which 700 are S - S or mixed morphology pairs. The authors are working on the remainder to produce a sample of close physical pairs of elliptical galaxies (they also include bulge dominated SO's since the morphological discrimination from ellipticals is often ambiguous, in particular for interacting galaxies). One of the interests of this work is to provide a sample selected on purely optical criteria, at variance with other works (e.g., Valentijn and Casertano, 1988). This will allow statistical studies of non-optical properties of these pairs (in particular radio emission). The authors have so far obtained charge-coupled device (CCD) images of 125 pairs with a 2m telescope and velocities' differences of 78 pairs were obtained using the 1.93 meter telescope of Observatoire de Haute Provence and from the literature. One is an optical pair (VV 190). Eighteen of our pairs present the morphological effect described in Davoust and Prugniel (1988): the external parts of each member are stretched in opposite senses in a direction rougly perpendicular to the pair axis. The proportion of 15 plus or minus 4 percent distorted pairs confirms previous estimates. Except for a few cases involving flattened galaxies with nearly aligned major axes which deserve careful detailed analysis (Prugniel, 1989), the apparent distortions do correspond to physical distortions. We have searched the literature for isophote maps showing this effect. In the survey of radio galaxies by Colina and Perez-Fournon (1990), 7 out of 20 pairs show this characteristic distortion
Nuclear Activity and the Dynamics of Elliptical Galaxies
This paper looks for any correlation between the internal dynamics of
elliptical galaxies and the relatively mild nuclear activity found in many such
systems. We show that there is such a relation in the sense that the active
ellipticals tend to be significantly less rotationally supported than their
inactive cousins. The correlation can partly be related to the galaxies'
luminosities: the brightest galaxies tend to be more active and less
rotationally supported. However, even at lower luminosities the active and
inactive galaxies seem to have systematically different dynamics. This
variation suggests that there are significant large-scale structural
differences between active and inactive elliptical galaxies, and hence that the
existence of both types of system cannot just be the result of random sporadic
nuclear activity.Comment: 5 pages, 3 figures. Accepted for publication in MNRA
Structure and stellar content of dwarf galaxies. III: B and R photometry of dwarf galaxies in the M101 group and the nearby field
We have carried out CCD photometry in the Cousins B and R bands of 21 dwarf
galaxies in and around the M101 group. Eleven are members and suspected members
of the group and ten are field galaxies in the projected vicinity of the group.
We have derived total magnitudes, effective radii, effective surface
brightnesses, as well as galaxy diameters at various isophotal levels in both
colours. Best-fitting exponential parameters and colour gradients are also
given for these galaxies. Some of the galaxies show a pronounced luminosity
excess above the best-fitting exponential at large radii, or surface
brightnesses fainter than approx 26 mag/sq_arcsec in R. This feature, while
non-significant for a single case and technically difficult to interpret, might
be an indication of the existence of an extended old stellar halo in dwarf
irregulars. The photometric parameters of the galaxies presented here will be
combined with previously published data for nearby dwarf galaxies and
statistically analysed in a forthcoming paper.Comment: 15 pages, 4 tables and 13 figures. For a full resolution version see
http://www.astro.unibas.ch/galaxies/papers.html To appear in A&A
Structure and stellar content of dwarf galaxies IV. B and R photometry of dwarf galaxies in the CVnI cloud
We have carried out CCD photometry in the Cousins B and R bands of 15
galaxies in the Canes Venatici I cloud. Total magnitudes, effective radii,
effective surface brightnesses, as well as galaxy radii at various isophotal
levels in both colors were determined. Best-fitting exponential parameters and
color gradients are also given for these galaxies. The photometric parameters
presented here will analyzed in a forthcoming paper, together with previously
published data for nearby dwarf galaxies.Comment: 10 pages, submitted to A&AS. For a full resolution version see
ftp://merkur.astro.unibas.ch/pub/bremnes/canesv.ps.g
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