313 research outputs found
The Black Hole Mass - Spheroid Luminosity relation
The differing M_bh-Luminosity relations presented in McLure & Dunlop, Marconi
& Hunt and Erwin et al. have been investigated. A number of issues have been
identified and addressed in each of these studies, including but not limited
to: the removal of a dependency on the Hubble constant; a correction for dust
attenuation in the bulges of disc galaxies; the identification of lenticular
galaxies previously treated as elliptical galaxies; and application of the same
(Y|X) regression analysis. These adjustments result in relations which now
predict similar black hole masses. The optimal K-band relation is
log(M_bh/M_sun) = -0.37(+/-0.04)[M_K +24] + 8.29(+/-0.08), with a total (not
intrinsic) scatter in log M_bh equal to 0.33 dex. This level of scatter is
similar to the value of 0.34 dex from the M_bh-sigma relation of Tremaine et
al. and compares favourably with the value of 0.31 dex from the M_bh-n relation
of Graham & Driver. Using different photometric data, consistent relations in
the B- and R-band are also provided, although we do note that the small (N=13)
R-band sample used by Erwin et al. is found here to have a slope of
-0.30(+/-0.06) and a total scatter of 0.31 dex. Performing a symmetrical
regression on the larger K-band sample gives a slope of -0.40, implying M_bh ~
L^{1.00}. Implications for galaxy-black hole coevolution, in terms of dry
mergers, are briefly discussed, as are predictions for intermediate mass black
holes. Finally, as previously noted by Tundo et al., a potential bias in the
galaxy sample used to define the M_bh-L relations is shown and a corrective
formula provided.Comment: 12 pages, to appaer in MNRA
Comment on "A Non-Parametric Estimate of Mass 'Scoured' in Galaxy Cores" (arXiv:1006.0488)
This comment is in response to the article titled "A Non-Parametric Estimate
of Mass Scoured in Galaxy Cores" (arXiv:1006.0488) written by Hopkins and
Hernquist. This comment politely mentions two relevant papers in which the main
conclusion from Hopkins & Hernquist had already been published six years ago
using the core-Sersic model. It then explains why Hopkins & Hernquist's concern
about the core-Sersic model is not valid.Comment: 1 page of text, plus reference
Quantifying the Coexistence of Massive Black Holes and Dense Nuclear Star Clusters
In large spheroidal stellar systems, such as elliptical galaxies, one
invariably finds a 10^6-10^9 M_Sun supermassive black hole at their centre. In
contrast, within dwarf elliptical galaxies one predominantly observes a
10^5-10^7 M_Sun nuclear star cluster. To date, few galaxies have been found
with both type of nuclei coexisting and even less have had the masses
determined for both central components. Here we identify one dozen galaxies
housing nuclear star clusters and supermassive black holes whose masses have
been measured. This doubles the known number of such hermaphrodite nuclei -
which are expected to be fruitful sources of gravitational radiation. Over the
host spheroid (stellar) mass range from 10^8 to 10^11 M_Sun, we find that a
galaxy's nucleus-to-spheroid (baryon) mass ratio is not a constant value but
decreases from a few percent to ~0.3 percent such that log[(M_BH+M_NC)/M_sph] =
-(0.39+/-0.07)log[M_sph/10^10 M_Sun] -(2.18+/-0.07). Once dry merging has
commenced by M_sph ~ 10^11 M_Sun and the nuclear star clusters have
disappeared, this ratio is expected to become a constant value.
As a byproduct of our investigation, we have found that the projected flux
from resolved nuclear star clusters can be well approximated with Sersic
functions having a range of indices from ~0.5 to ~3, the latter index
describing the Milky Way's nuclear star cluster.Comment: To appear in MNRA
The local supermassive black hole mass density: corrections for dependencies on the Hubble constant
We have investigated past measurements of the local supermassive black hole
mass density, correcting for hitherto unknown dependencies on the Hubble
constant, which, in some cases, had led to an underestimation of the mass
density by factors of ~2. Correcting for this, we note that the majority of
past studies yield a local supermassive black hole mas density that is
consistent with the range 4.4-5.9 x 10^5 f(H_0) M_Sun / Mpc^3 (when using H_0 =
70 km/s/Mpc). In addition, we address a number of ways in which these past
estimates can be further developed. In particular, we tabulate realistic
bulge-to-total flux ratios which can be used to estimate the luminosity of
bulges and subsequently their central black hole masses.Comment: MNRAS, accepte
An investigation into the prominence of spiral galaxy bulges
From a diameter-limited sample of 86 `face-on' spiral galaxies, the
bulge-to-disk size and luminosity ratios, and other quantitative measurements
for the prominence of the bulge are derived. The bulge and disk parameters have
been estimated using a seeing convolved Sersic r^(1/n) bulge and a seeing
convolved exponential disk. In general, early-type spiral galaxy bulges have
Sersic values of n>1, and late-type spiral galaxy bulges have values of n<1. In
the B-band, only 8 galaxies have a bulge shape parameter n consistent with the
exponential value of 1, and only 5 galaxies do in the K-band. Application of
the r^(1/n) bulge models results in a larger mean r_e/h ratio for the
early-type spiral galaxies than the late-type spiral galaxies. Although, this
result is shown not to be statistically significant. The mean B/D luminosity
ratio is, however, significantly larger (> 3-sigma) for the early-type spirals
than the late-type spirals. This apparent contradiction with the r_e/h values
can be explained with an iceberg-like scenario, in which the bulges in
late-type spiral galaxies are relatively submerged in their disk. This can be
achieved by varying the relative bulge/disk stellar density while maintaining
the same effective bulge-to-disk size ratio.
The absolute bulge magnitude - log(n) diagram is used as a diagnostic tool
for comparative studies with dwarf elliptical and ordinary elliptical galaxies.
At least in the B-band, these objects occupy distinctly different regions of
this parameter space. While the dwarf ellipticals appear to be the faint
extension to the brighter elliptical galaxies, the bulges of spiral galaxies
are not.Comment: 33 pages (includes 27 figures, 4 tables). To be published in AJ
(tentatively scheduled for Feb 2001
Invoking the virial theorem to understand the impact of (dry) mergers on the - relation
While dry mergers can produce considerable scatter in the (black hole mass,
)-(spheroid stellar mass, ) and -(spheroid half-light radius, ) diagrams, the virial theorem
is used here to explain why the scatter about the -(velocity
dispersion, ) relation remains low in the face of such mergers. Its
small scatter has been claimed as evidence of feedback from active galactic
nuclei (AGNs). However, it is shown that galaxy mergers also play a significant
role. The major merger of two S0 galaxies with
M advances a system along a slope of 5 in the - diagram. However, a major EE galaxy merger moves a system
(slightly) along a trajectory with a slope of 9, while mergers of
lower-mass S0 galaxies with M move
(slightly) along a trajectory with a slope of 3. This produces a steeper
distribution for the E (and Es,e) galaxies in the -
diagram, reported here to have a slope of 7.270.91, compared to the S0
galaxies which have a slope of 5.680.60. This result forms an important
complement to the AGN feedback models like that from Silk and Rees, providing a
more complete picture of galaxy/(black hole) coevolution. It also has important
implications for nanohertz gravitational wave research. Abridged.Comment: To appear in MNRAS (12 pages, including 7 figures and a 2 page
Appendix
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