67 research outputs found
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
Analytical galactic models with mild stellar cusps
In the past two decades, it has been established by high-resolution
observations of early-type galaxies that their nuclear surface brightness and
corresponding stellar mass densities are characterized by cusps. In this paper,
we present a new spherical analytical model family describing mild cuspy
centres. We study isotropic and anisotropic models of Osipkov-Merritt type. It
is shown that the associated distribution functions and intrinsic velocity
dispersions can be represented analytically in a unified way in terms of
hypergeometric series, allowing thus a straightforward comparison of these
important global quantities for galaxies having underlying mass densities which
may differ significantly in their degree of central cuspiness or radial
falloff.Comment: 9 pages, 2 figures; accepted for publication in MNRAS; different
format than previous versio
The HI content of E+A galaxies
We present deep single-dish HI observations of a sample of six nearby E+A
galaxies (0.05<z<0.1). A non-negligible fraction of a local sample of E+As are
detected in HI. In four galaxies, we have detected up to a few times 10^9 Msun
of neutral gas. These E+A galaxies are almost as gas-rich as spiral galaxies
with comparable luminosities. There appears to exist no direct correlation
between the amount of HI present in an E+A galaxy and its star-formation rate
as traced by radio continuum emission. Moreover, the end of the starburst does
not necessarily require the complete exhaustion of the neutral gas reservoir.
Most likely, an intense burst of star formation consumed the dense molecular
clouds, which are the sites of massive star formation. This effectively stops
star formation, even though copious amounts of diffuse neutral gas remain. The
remaining HI reservoir may eventually lead to further episodes of star
formation. This may indicate that some E+As are observed in the inactive phase
of the star-formation duty cycle.Comment: Accepted for publication in ApJ, 9 pages, 3 figures (reduced in
resolution
The Herschel Virgo Cluster Survey: VII. Dust in cluster dwarf elliptical galaxies
We use the Science Demonstration Phase data of the Herschel Virgo Cluster
Survey to search for dust emission of early-type dwarf galaxies in the central
regions of the Virgo Cluster as an alternative way of identifying the
interstellar medium.We present the first possible far-infrared detection of
cluster early-type dwarf galaxies: VCC781 and VCC951 are detected at the 10
sigma level in the SPIRE 250 micron image. Both detected galaxies have dust
masses of the order of 10^5 Msun and average dust temperatures ~20K. The
detection rate (less than 1%) is quite high compared to the 1.7% detection rate
for Hi emission, considering that dwarfs in the central regions are more Hi
deficient. We conclude that the removal of interstellar dust from dwarf
galaxies resulting from ram pressure stripping, harassment, or tidal effects
must be as efficient as the removal of interstellar gas.Comment: Letter accepted for publication in A&A (Herschel special issue
Ocrelizumab versus Interferon Beta-1a in Relapsing Multiple Sclerosis
Supported by F. Hoffmann–La Roche
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