154 research outputs found
Nuclear Cusps and Cores in Early-type Galaxies As Relics of Binary Black Hole Mergers
We present an analysis of the central cusp slopes and core parameters of
early-type galaxies using a large database of surface brightness profiles
obtained from Hubble Space Telescope observations. We examine the relation
between the central cusp slopes, core parameters, and black hole masses in
early-type galaxies, in light of two models that attempt to explain the
formation of cores and density cusps via the dynamical influence of black
holes. Contrary to the expectations from adiabatic-growth models, we find that
the cusp slopes do not steepen with increasing black hole mass fraction.
Moreover, a comparison of kinematic black hole mass measurements with the
masses predicted by the adiabatic models shows that they overpredict the masses
by a factor of approximately 3. Simulations involving binary black hole mergers
predict that both the size of the core and the central mass deficit correlate
with the final black hole mass. These relations are qualitatively supported by
the present data.Comment: To appear in ApJ. 8 page
Near infrared and optical morphology of the dusty galaxy NGC972
Near infrared (NIR) and optical surface photometric analyses of the dusty
galaxy NGC972 are presented. The photometric profiles in the BVRJHK bands can
be fitted with a combination of gaussian and exponential profiles,
corresponding to a starburst nucleus and a stellar disk respectively. The
exponential scale length in the B-band is 2.8 times larger than in the K-band,
which implies a central B-band optical depth as high as 11. A bulge is absent
even in the NIR bands and hence the galaxy must be of a morphological type
later than the usually adopted Sb type. Relatively low rotational velocity and
high gas content also favor a later type, probably Sd, for the galaxy. Only one
arm can be traced in the distribution of old stars; the second arm, however,
can be traced in the distribution of dust and HII regions. Data suggest a short
NIR bar, which ends inside the nuclear ring. The slowly rising nature of the
rotation curve rules out a resonance origin of the the nuclear ring. The ring
is most likely not in the plane of the galaxy, given its circular appearance in
spite of the moderately high inclination of the galaxy. The off-planar nature
of the star forming ring, the unusually high fraction (30%) of the total mass
in molecular form, the presence of a nuclear starburst and the asymmetry of
spiral arms, are probably the result of a merger with a gas-rich companion
galaxy.Comment: Uses aas2pp4.sty and epsfig.sty, 12 pages To appear in Astronomical
Journal, October 199
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