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

Invoking the virial theorem to understand the impact of (dry) mergers on the MbhM_{\rm bh}-σ\sigma relation

While dry mergers can produce considerable scatter in the (black hole mass, $M_{\rm bh}$)-(spheroid stellar mass, $M_{\rm *,sph}$) and $M_{\rm bh}$-(spheroid half-light radius, $R_{\rm e,sph}$) diagrams, the virial theorem is used here to explain why the scatter about the $M_{\rm bh}$-(velocity dispersion, $\sigma$) 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 $M_{\rm *,sph}\sim10^{11}$ M$_\odot$ advances a system along a slope of $\sim$5 in the $M_{\rm bh}$-$\sigma$ diagram. However, a major E$+$E galaxy merger moves a system (slightly) along a trajectory with a slope of $\sim$9, while mergers of lower-mass S0 galaxies with $M_{\rm *,sph}\sim10^{10}$ M$_\odot$ move (slightly) along a trajectory with a slope of $\sim$3. This produces a steeper distribution for the E (and Es,e) galaxies in the $M_{\rm bh}$-$\sigma$ diagram, reported here to have a slope of 7.27$\pm$0.91, compared to the S0 galaxies which have a slope of 5.68$\pm$0.60. 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

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