325 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
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
New atmospheric parameters and spectral interpolator for the MILES cool stars
Context: The full spectrum fitting of stellar spectra against a library of
empirical spectra is a well-established approach to measure the atmospheric
parameters of FGK stars with a high internal consistency. Extending it towards
cooler stars still remains a challenge. Aims: We address this question by
improving the interpolator of the MILES (Medium-resolution INT Library of
Empirical Spectra) library in the low effective temperature regime (Tefff <
4800 K), and we refine the determination of the parameters of the cool MILES
stars. Methods: We use the ULySS package to determine the atmospheric
parameters (Teff, logg and [Fe/H]), and measure the biases of the results with
respect to our updated compilation of parameters calibrated against theoretical
spectra. After correcting some systematic effects, we compute a new
interpolator that we finally use to redetermine the atmospheric parameters
homogeneously and assess the biases. Results: Based on an updated literature
compilation, we determine Teff in a more accurate and unbiased manner compared
to those determined with the original interpolator. The validity range is
extended downwards to about Teff = 2900 K compared to 3500 K previously. The
mean residual biases on Teff, logg, and [Fe/H], with respect to the literature
compilation for the coolest stars (Teff <= 3800 K) computed using the new
interpolator, are -15 K, -0.02 dex, and 0.02 dex respectively. The
corresponding estimations of the external precision are 63 K, 0.23 dex, and
0.15 dex respectively. For the stars with Teff in the range 3800 - 4200 K, the
determinations of Teff and [Fe/H] have been slightly improved. At higher
temperatures, the new interpolator is comparable to the original one. The new
version of the interpolator is publicly available.Comment: A&A Accepted, 30 pages, 10 figure
Origin of the scatter in the X-ray luminosity of early-type galaxies observed with ROSAT
Statistical properties of X-ray luminosity and temperature are studied for 52
early-type galaxies based on the ROSAT PSPC data. All of the X-ray luminous
galaxies show largely extended emission with a radius of a few times of
10, while X-ray faint galaxies do not show such a component. This leads to
a division of early-type galaxies into two categories: X-ray extended and X-ray
compact galaxies. Except for a few galaxies in dense cluster environments, the
luminosity and temperature of X-ray compact galaxies are well explained by a
kinematical heating of the gas supplied by stellar mass loss. In contrast,
X-ray extended galaxies indicate large scatter in the X-ray luminosity. We
discuss that X-ray extended galaxies are the central objects of large potential
structures, and the presence and absence of this potential is the main origin
of the large scatter in the X-ray luminosity.Comment: 35 pages, including 8 figures, Accepted for publication in Ap
Star Formation Histories of Nearby Elliptical Galaxies. II. Merger Remnant Sample
This work presents high spectroscopic observations of a sample of six
suspected merger remnants, selected primarily on the basis of H{\sc i} tidal
debris detections. Single stellar population analysis of these galaxies
indicates that their ages, metallicities, and -enhancement ratios are
consistent with those of a representative sample of nearby elliptical galaxies.
The expected stellar population of a recent merger remnant, young age combined
with low [/Fe], is not seen in any H{\sc i}-selected galaxy. However,
one galaxy (NGC~2534), is found to deviate from the -plane in the sense
expected for a merger remnant. Another galaxy (NGC~7332), selected by other
criteria, best matches the merger remnant expectations.Comment: 12 pages, 10 figures, accepted by A
Generalisations of the Tully-Fisher relation for early and late-type galaxies
We study the locus of dwarf and giant early and late-type galaxies on the
Tully-Fisher relation (TFR), the stellar mass Tully-Fisher relation (sTFR) and
the so-called baryonic or HI gas+stellar mass Tully-Fisher relation (gsTFR). We
show that early-type and late-type galaxies, from dwarfs to giants, trace
different yet approximately parallel TFRs. Surprisingly, early-type and
late-type galaxies trace a single yet curved sTFR over a range of 3.5 orders of
magnitude in stellar mass. Moreover, all galaxies trace a single, linear gsTFR,
over 3.5 orders of magnitude in HI gas+stellar mass. Dwarf ellipticals,
however, lie slightly below the gsTFR. This may indicate that early-type
dwarfs, contrary to the late-types, have lost their gas, e.g. by galactic winds
or ram-pressure stripping. Overall, environment only plays a secondary role in
shaping these relations, making them a rather ``clean'' cosmological tool. LCDM
simulations predict roughly the correct slopes for these relations.Comment: 4 pages, 2 figures, accepted for publication in Astrophysical Journa
Spatially Resolved Stellar Kinematics of Field Early-Type Galaxies at z=1: Evolution of the Rotation Rate
We use the spatial information of our previously published VLT/FORS2
absorption line spectroscopy to measure mean stellar velocity and velocity
dispersion profiles of 25 field early-type galaxies at a median redshift z=0.97
(full range 0.6<z<1.2). This provides the first detailed study of early-type
galaxy rotation at these redshifts. From surface brightness profiles from HST
imaging we calculate two-integral oblate axisymmetric Jeans equation models for
the observed kinematics. Fits to the data yield for each galaxy the degree of
rotational support and the mass-to-light ratio M/L_Jeans. S0 and Sa galaxies
are generally rotationally supported, whereas elliptical galaxies rotate less
rapidly or not at all. Down to M(B)=-19.5 (corrected for luminosity evolution),
we find no evidence for evolution in the fraction of rotating early-type (E+S0)
galaxies between z=1 (63+/-11%) and the present (61+/-5%). We interpret this as
evidence for little or no change in the field S0 fraction with redshift. We
compare M/L_Jeans with M/L_vir inferred from the virial theorem and globally
averaged quantities and assuming homologous evolution. There is good agreement
for non-rotating (mostly E) galaxies. However, for rotationally supported
galaxies (mostly S0) M/L_Jeans is on average ~40% higher than M/L_vir. We
discuss possible explanations and the implications for the evolution of M/L
between z=1 and the present and its dependence on mass.Comment: To appear in ApJ 683 (9 pages, 7 figures). Minor changes included to
match published versio
Damp Mergers: Recent Gaseous Mergers without Significant Globular Cluster Formation?
Here we test the idea that new globular clusters (GCs) are formed in the same
gaseous ("wet") mergers or interactions that give rise to the young stellar
populations seen in the central regions of many early-type galaxies. We compare
mean GC colors with the age of the central galaxy starburst. The red GC
subpopulation reveals remarkably constant mean colors independent of galaxy
age. A scenario in which the red GC subpopulation is a combination of old and
new GCs (formed in the same event as the central galaxy starburst) can not be
ruled out; although this would require an age-metallicity relation for the
newly formed GCs that is steeper than the Galactic relation. However, the data
are also well described by a scenario in which most red GCs are old, and few,
if any, are formed in recent gaseous mergers. This is consistent with the old
ages inferred from some spectroscopic studies of GCs in external systems. The
event that induced the central galaxy starburst may have therefore involved
insufficient gas mass for significant GC formation. We term such gas-poor
events "damp" mergers.Comment: 17 pages, 5 figures, ApJ accepte
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