55 research outputs found
Tracing the relation between black holes and dark haloes
We present new velocity dispersion measurements for a set of 12 spiral
galaxies and use them to derive a more accurate V_c - sigma relation which
holds for a wide morphological range of galaxies. Combined with the M_BH -
sigma relation, this relation can be used as a tool to estimate supermassive
black hole (SMBH) masses by means of the asymptotic circular velocity. Together
with the Tully-Fisher relation, it serves as a constraint for galaxy formation
and evolution models.Comment: 2 pages, 2 figures, to appear in Proc. IAU Symp. 220, "Dark Matter in
Galaxies" eds. S. Ryder, D.J. Pisano, M. Walker, & K. Freeman (San Francisco:
ASP
Completely analytical families of anisotropic gamma-models
We present new analytical distribution functions for anisotropic spherical
galaxies. They have the density profiles of the gamma-models, which allow a
wide range of central density slopes, and are widely used to fit elliptical
galaxies and the bulges of spiral galaxies. Most of our models belong to two
two-parameter families. One of these parameters is the slope gamma of the
central density cusp. The other allows a wide range of varying radial and
tangential anisotropies, at either small or large radii. We give analytical
formulas for their distribution functions, velocity dispersions, and the manner
in which energy and transverse velocity are distributed between orbits. We also
give some of their observable properties, including line-of-sight velocity
profiles which have been computed numerically. Our models can be used to
provide a useful tool for creating initial conditions for N-body and Monte
Carlo simulations.Comment: 21 pages, 15 figures, accepted for publication in MNRA
Dynamical models linking BH masses and DM content
We investigate the relation between the dark matter distribution of galaxies
and their central supermassive black holes which is suggested by the v_c-sigma
relation. Since early-type galaxies appear to have larger black holes than
late-type ones, we look for an equivalent pattern in the dark matter
distribution as a function of Hubble type. To achieve our goal we use a
state-of-the-art modelling code that allows a variety of geometries to be
fitted to a combination of radio and optical observations of galaxies with
different morphology.Comment: 2 pages, 2 figures, contributed paper to Proceedings of the
Conference "Growing Black Holes" held in Garching, Germany, June 21-25, 2004,
edited by A. Merloni, S. Nayakshin and R. Sunyaev, Springer-Verlag series of
"ESO Astrophysics Symposia
FCC046: a candidate gaseous polar ring dwarf elliptical galaxy in the Fornax Cluster
FCC046 is a Fornax Cluster dwarf elliptical galaxy. Optical observations have
shown that this galaxy, besides an old and metal-poor stellar population, also
contains a very young centrally concentrated population and is actively forming
stars, albeit at a very low level. Here, we report on 21cm observations of
FCC046 with the Australia Telescope Compact Array (ATCA) which we conducted in
the course of a small survey of Fornax Cluster early-type dwarf galaxies. We
have discovered a ~10^7 Mo HI cloud surrounding FCC046. We show that the
presence of this significant gas reservoir offers a concise explanation for
this galaxy's optical morphological and kinematical properties. Surprisingly,
the HI gas, as evidenced by its morphology and its rotational motion around the
galaxy's optical major axis, is kinematically decoupled from the galaxy's
stellar body. This is the first time such a ring of gaseous material in
minor-axis rotation is discovered around a dwarf galaxy.Comment: 5 pages, 4 figures, published in Astrophysical Journal Letter
Observational evidence for a connection between SMBHs and dark matter haloes
We investigate the relation between circular velocity vc and bulge velocity
dispersion sigma in spiral galaxies, based on literature data and new
spectroscopic observations. We find a strong, nearly linear vc-sigma
correlation with a negligible intrinsic scatter, and a striking agreement with
the corresponding relation for elliptical galaxies. The least massive galaxies
(sigma < 80 km/s) significantly deviate from this relation. We combine this
vc-sigma correlation with the well-known MBH-sigma relation to obtain a tight
correlation between circular velocity and supermassive black hole mass, and
interpret this as observational evidence for a close link between supermassive
black holes and the dark matter haloes in which they presumably formed. Apart
from being an important ingredient for theoretical models of galaxy formation
and evolution, the relation between MBH and circular velocity has the potential
to become an important practical tool in estimating supermassive black hole
masses in spiral galaxies.Comment: 4 pages, 1 figure, to appear in "The Interplay among Black Holes,
Stars and ISM in Galactic Nuclei", IAU Symposium 222, eds. Th. Storchi
Bergmann, L.C. Ho & H.R. Schmit
The CO content of the Local Group dwarf irregular galaxies IC5152, UGCA438, and the Phoenix dwarf
We present a search for CO(1->0) emission in three Local Group dwarf
irregular galaxies: IC5152, the Phoenix dwarf, and UGCA438, using the ATNF
Mopra radio telescope. Our scans largely cover the optical extent of the
galaxies and the stripped HI cloud West of the Phoenix dwarf. Apart from a
tentative but non-significant emission peak at one position in the Phoenix
dwarf, no significant emission was detected in the CO spectra of these
galaxies. For a velocity width of 6 km/s, we derive 4sigma upper limits of 0.03
K km/s, 0.04 K km/s and 0.06 K km/s for IC5152, the Phoenix dwarf and UGCA438,
respectively. This is an improvement of over a factor of 10 compared with
previous observations of IC5152; the other two galaxies had not yet been
observed at millimeter wavelengths. Assuming a Galactic CO-to-H_2 conversion
factor, we derive upper limits on the molecular gas mass of 6.2 x 10^4 M_sun,
3.7 x 10^3 M_sun and 1.4 x 10^5 M_sun for IC5152, the Phoenix dwarf and
UGCA438, respectively. We investigate two possible causes for the lack of CO
emission in these galaxies. On the one hand, there may be a genuine lack of
molecular gas in these systems, in spite of the presence of large amounts of
neutral gas. However, in the case of IC5152 which is actively forming stars,
molecular gas is at least expected to be present in the star forming regions.
On the other hand, there may be a large increase in the CO-to-H_2 conversion
factor in very low-metallicity dwarfs (-2 <= [Fe/H] <= -1), making CO a poor
tracer of the molecular gas content in dwarf galaxies.Comment: 7 pages, 5 figures, 2 tables, accepted for publication in MNRA
EA01A/B : high-resolution HI imaging of an interacting pair of post-starburst (E+A) galaxies
We present high spatial resolution 21cm HI observations of EA01A and EA01B, a
pair of interacting post-starburst, or E+A, galaxies at z = 0.0746. Based on
optical HST/WFPC2 images, both galaxies are known to display disturbed
morphologies. They also appear to be linked by a bridge of stars. Previous HI
observations Chang et al. (2001) had already uncovered sizable quantities of
neutral gas in or near these galaxies but they lacked the spatial resolution to
locate the gas with any precision within this galactic binary system. We have
analysed deep, high resolution archival VLA observations of the couple. We find
evidence for three gaseous tidal tails; one connected to EA01A and two
emanating from EA01B. These findings confirm, independently from the optical
imaging, that (i) EA01A and EA01B are actively interacting, and that, as a
consequence, the starbursts that occurred in these galaxies were most likely
triggered by this interaction, and that (ii) 6.6+-0.9 10^9 Msun of neutral gas
are still present in the immediate vicinity of the optical bodies of both
galaxies. The HI column density is lowest at the optical positions of the
galaxies, suggesting that most of the neutral gas that is visible in our maps
is associated with the tidal arms and not with the galaxies themselves. This
might provide an explanation for the apparent lack of ongoing star formation in
these galaxies.Comment: 5 pages, 3 figures (lowered resolution), accepted for publication in
ApJ
Observational evidence for a connection between supermassive black holes and dark matter haloes
We present new velocity dispersion measurements of sample of 12 spiral
galaxies for which extended rotation curves are available. These data are used
to refine a recently discovered correlation between the circular velocity and
the central velocity dispersion of spiral galaxies. We find a slightly steeper
slope for our larger sample, we confirm the negligible intrinsic scatter on
this correlation, and we find a striking agreement with a corresponding
relation for elliptical galaxies. We combine this correlation with the
well-known MBH-sigma relation to obtain a tight correlation between the
circular velocities of galaxies and the masses of the supermassive black holes
they host. This correlation is the observational evidence for an intimate link
between dark matter haloes and supermassive black holes. Apart from being an
important ingredient for theoretical models of galaxy formation and evolution,
the relation between MBH and circular velocity can serve as a practical tool to
estimate black hole masses in spiral galaxies.Comment: 5 pages, 2 figures, accepted for publication in MNRAS pink page
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