1,518 research outputs found
Systematic trends in total-mass profiles from dynamical models of early-type galaxies
We study trends in the slope of the total mass profiles and dark matter
fractions within the central half-light radius of 258 early-type galaxies,
using data from the volume-limited ATLAS survey. We use three
distinct sets of dynamical models, which vary in their assumptions and also
allow for spatial variations in the stellar mass-to-light ratio, to test the
robustness of our results. We confirm that the slopes of the total mass
profiles are approximately isothermal, and investigate how the total-mass slope
depends on various galactic properties. The most statistically-significant
correlations we find are a function of either surface density, , or
velocity dispersion, . However there is evidence for a break in the
latter relation, with a nearly universal logarithmic slope above
\log_{10}[\sigma_e/(\si{km~s^{-1}})]\sim 2.1 and a steeper trend below this
value. For the 142 galaxies above that critical value, the total
mass-density logarithmic slopes have a mean value
(
error) with an observed rms scatter of only . Considering the observational errors, we estimate an intrinsic scatter
of . These values are
broadly consistent with those found by strong lensing studies at similar radii
and agree, within the tight errors, with values recently found at much larger
radii via stellar dynamics or HI rotation curves (using significantly smaller
samples than this work).Comment: 17 pages, 11 figures, 3 tables. Published in MNRA
Two channels of supermassive black hole growth as seen on the galaxies mass-size plane
We investigate the variation of black hole masses (Mbh) as a function of
their host galaxy stellar mass (Mstar) and half-light radius (Re). We confirm
that the scatter in Mbh within this plane is essentially the same as that in
the Mbh - sigma relation, as expected from the negligible scatter reported in
the virial mass estimator sigma_v^2=GxMstar/(5xRe). All variation in Mbh
happens along lines of constant sigma_v on the (Mstar, Re) plane, or Mstar
Re for Mstar <2x10^11 Msun. This trend is qualitatively the same as
those previously reported for galaxy properties related to stellar populations,
like age, metallicity, alpha enhancement, mass-to-light ratio and gas content.
We find evidence for a change in the Mbh variation above the critical mass of
Mcrit ~ 2x10^11 Msun. This behaviour can be explained assuming that Mbh in
galaxies less massive than Mcrit can be predicted by the Mbh - sigma relation,
while Mbh in more massive galaxies follow a modified relation which is also
dependent on Mstar once Mstar >Mcrit. This is consistent with the scenario
where the majority of galaxies grow through star formation, while the most
massive galaxies undergo a sequence of dissipation-less mergers. In both
channels black holes and galaxies grow synchronously, giving rise to the black
hole - host galaxy scaling relations, but there is no underlying single
relation that is universal across the full range of galaxy masses.Comment: 11 pages, 5 figures; MNRAS accepted (minor text changes
VLT Diffraction Limited Imaging and Spectroscopy in the NIR: Weighing the black hole in Centaurus A with NACO
We present high spatial resolution near-infrared spectra and images of the
nucleus of Centaurus A (NGC 5128) obtained with NAOS-CONICA at the VLT. The
adaptive optics corrected data have a spatial resolution of 0.06" (FWHM) in K-
and 0.11" in H-band, four times higher than previous studies. The observed gas
motions suggest a kinematically hot disk which is orbiting a central object and
is oriented nearly perpendicular to the nuclear jet. We model the central
rotation and velocity dispersion curves of the [FeII] gas orbiting in the
combined potential of the stellar mass and the (dominant) black hole. Our
physically most plausible model, a dynamically hot and geometrically thin gas
disk, yields a black hole mass of M_bh = (6.1 +0.6/-0.8) 10^7 M_sun. As the
physical state of the gas is not well understood, we also consider two limiting
cases: first a cold disk model, which completely neglects the velocity
dispersion; it yields an M_bh estimate that is almost two times lower. The
other extreme case is to model a spherical gas distribution in hydrostatic
equilibrium through Jeans equation. Compared to the hot disk model the best-fit
black hole mass increases by a factor of 1.5. This wide mass range spanned by
the limiting cases shows how important the gas physics is even for high
resolution data. Our overall best-fitting black hole mass is a factor of 2-4
lower than previous measurements. With our revised M_bh estimate, Cen A's
offset from the M_bh-sigma relation is significantly reduced; it falls above
this relation by a factor of ~2, which is close to the intrinsic scatter of
this relation. (Abridged)Comment: 12 pages, 14 figures, including minor changes following the referee
report; accepted for publication in The Astrophysical Journa
The Quest for the Dominant Stellar Population in the Giant Elliptical NGC 5018
Newly obtained HST/WFPC2 images of the disturbed elliptical galaxy NGC 5018
show that the average amount of internal reddening due to the its complex
``dust web'' is as low as E(B-V)~0.02 within the IUE aperture, thus implying
that its observed and intrinsic energy distributions do not differ
significantly down to UV wavelengths. This, in turn, is quite relevant to the
current debate on the age of its dominant stellar population.Comment: 2 pages, 1 figure. Proceedings of the conference "Galaxy Disks and
Disk Galaxies", ASP Conference Series, eds. J.G. Funes, S.J. and E.M. Corsin
Systematic Uncertainties in Stellar Mass Estimation for Distinct Galaxy Populations
We show that different stellar-mass estimation methods yield overall mass
scales that disagree by factors up to ~2 for the z=0 galaxy population, and
more importantly, relative mass scales that sometimes disagree by factors >~3
between distinct classes of galaxies (spiral/irregular types, classical E/S0s,
and E/S0s whose colors reflect recent star formation). This comparison
considers stellar mass estimates based on (a) two different calibrations of the
correlation between K-band mass-to-light ratio and B-R color (Bell et al.,
Portinari et al.) and (b) detailed fitting of UBRJHK photometry and optical
spectrophotometry using two different population synthesis models
(Bruzual-Charlot, Maraston), with the same initial mass function in all cases.
We also compare stellar+gas masses with dynamical masses. This analysis offers
only weak arguments for preferring a particular stellar-mass estimation method,
given the plausibility of real variations in dynamical properties and dark
matter content. These results help to calibrate the systematic uncertainties
inherent in mass-based evolutionary studies of galaxies, including comparisons
of low and high redshift galaxies.Comment: 5 pages including 2 enlarged figures, ApJ Letters, accepte
Measuring the low mass end of the Mbh - sigma relation
We show that high quality laser guide star (LGS) adaptive optics (AO)
observations of nearby early-type galaxies are possible when the tip-tilt
correction is done by guiding on nuclei while the focus compensation due to the
changing distance to the sodium layer is made 'open loop'. We achieve
corrections such that 40% of flux comes from R<0.2 arcsec. To measure a black
hole mass (Mbh) one needs integral field observations of both high spatial
resolution and large field of view. With these data it is possible to determine
the lower limit to Mbh even if the spatial resolution of the observations are
up to a few times larger than the sphere of influence of the black hole.Comment: 4 pages, 2 figures, LaTeX. To appear in "Hunting for the Dark: The
Hidden Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P.
Debattista and C.C. Popescu, AIP Conf. Ser., in pres
Monster black holes
A combination of ground-based and spacecraft observations has uncovered two
black holes of 10 billion solar masses in the nearby Universe. The finding
sheds light on how these cosmic monsters co-evolve with galaxies.Comment: 2 pages, 1 figure, LaTeX. Published in Nature "News & Views
Selection bias in the M_BH-sigma and M_BH-L correlations and its consequences
It is common to estimate black hole abundances by using a measured
correlation between black hole mass and another more easily measured observable
such as the velocity dispersion or luminosity of the surrounding bulge. The
correlation is used to transform the distribution of the observable into an
estimate of the distribution of black hole masses. However, different
observables provide different estimates: the Mbh-sigma relation predicts fewer
massive black holes than does the Mbh-L relation. This is because the sigma-L
relation in black hole samples currently available is inconsistent with that in
the SDSS sample, from which the distributions of L or sigma are based: the
black hole samples have smaller L for a given sigma or have larger sigma for a
given L. This is true whether L is estimated in the optical or in the NIR. If
this is a selection rather than physical effect, then the Mbh-sigma and Mbh-L
relations currently in the literature are also biased from their true values.
We provide a framework for describing the effect of this bias. We then combine
it with a model of the bias to make an estimate of the true intrinsic
relations. While we do not claim to have understood the source of the bias, our
simple model is able to reproduce the observed trends. If we have correctly
modeled the selection effect, then our analysis suggests that the bias in the
relation is likely to be small, whereas the relation is
biased towards predicting more massive black holes for a given luminosity. In
addition, it is likely that the Mbh-L relation is entirely a consequence of
more fundamental relations between Mbh and sigma, and between sigma and L. The
intrinsic relation we find suggests that at fixed luminosity, older galaxies
tend to host more massive black holes.Comment: 12 pages, 7 figures. Accepted by ApJ. We have added a figure showing
that a similar bias is also seen in the K-band. A new appendix describes the
BH samples as well as the fits used in the main tex
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