1,814 research outputs found
Evidence for a Massive Dark Object in NGC 4350
In this work we build a detailed dynamic model for a S0 galaxy possibly
hosting a central massive dark object (MDO). We show that the photometric
profiles and the kinematics along the major and minor axes, including the h3
and h4 profiles, imply the presence of a central MDO of mass M = 1.5 - 9.7 10^8
solar masses, i.e. 0.3-2.8% of the mass derived for the stellar spheroidal
component. Models without MDO are unable to reproduce the kinematic properties
of the inner stars and of the rapidly rotating nuclear gas.
The stellar population comprise of an exponential disc (27% of the light) and
a diffuse spheroidal component (73% of the light) that cannot be represented by
a simple de Vaucouleurs profile at any radius. The M/L ratios we found for the
stellar components (respectively 3.3 and 6.6) are typical of those of disc and
elliptical galaxies.Comment: 9 pages, 4 encapsulated postscript figures. Requires mn.sty,
psfig.sty. Accepted for publication in MNRA
On syntheses of the X-ray background with power-law sources
The conditions under which the combined emission from power law sources can mimic the X-ray background (XRB) spectrum in the 3-50 keV range are considered in view of HEAO 1 A-2 experiment measurements, and it is confirmed that a good fit may be obtained. The required spectral properties of the component sources differ, however, from those observed for local active galactic nuclei. Constraints are deduced for both the low luminosity extension and evolution of such local objects, and it is shown that any other class of sources contributing to the X-ray background must be characterized by an energy spectral index lower than about 0.4, which is the mean index of the XRB, and exhibit sleeper spectra at higher energies
CAIRNS: The Cluster And Infall Region Nearby Survey I. Redshifts and Mass Profiles
The CAIRNS (Cluster And Infall Region Nearby Survey) project is a
spectroscopic survey of the infall regions surrounding eight nearby, rich,
X-ray luminous clusters of galaxies. We collect 15665 redshifts (3471 new or
remeasured) within \sim 5-10 Mpc of the centers of the clusters, making it the
largest study of the infall regions of clusters. We determine cluster
membership and the mass profiles of the clusters based on the phase space
distribution of the galaxies. All of the clusters display decreasing velocity
dispersion profiles. The mass profiles are fit well by functional forms based
on numerical simulations but exclude an isothermal sphere. Specifically, NFW
and Hernquist models provide good descriptions of cluster mass profiles to
their turnaround radii. Our sample shows that the predicted infall pattern is
ubiquitous in rich, X-ray luminous clusters over a large mass range. The
caustic mass estimates are in excellent agreement with independent X-ray
estimates at small radii and with virial estimates at intermediate radii. The
mean ratio of the caustic mass to the X-ray mass is 1.03\pm0.11 and the mean
ratio of the caustic mass to the virial mass (when corrected for the surface
pressure term) is 0.93\pm0.07. We further demonstrate that the caustic
technique provides reasonable mass estimates even in merging clusters.Comment: 54 pages, 18 figures, to appear in The Astronomical Journa
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