The Stellar-Dynamical Search for Supermassive Black Holes in Galactic Nuclei

The robustness of stellar-dynamical black hole (BH) mass measurements is illustrated using 7 galaxies that have results from independent groups. Derived masses have remained constant to a factor of about 2 as spatial resolution has improved by factors of 2 - 330 and as the analysis has improved from spherical, isotropic models to axisymmetric, three-integral models. This gives us confidence that the masses are reliable and that the galaxies do not indulge in a wide variety of perverse orbital structures. Constraints on BH alternatives are also improving. In M31, Hubble Space Telescope (HST) spectroscopy shows that the central massive dark object (MDO) is in a tiny cluster of blue stars embedded in the P2 nucleus of the galaxy. The MDO must be less than about 0.06 arcsec in radius. M31 becomes the third galaxy in which dark clusters of brown dwarf stars or stellar remnants can be excluded. In our Galaxy, observations of almost-complete stellar orbits show that the MDO radius is less than about 0.0006 pc. Among BH alternatives, this excludes even neutrino balls. Therefore, measurements of central dark masses and the conclusion that these are BHs have both stood the test of time. Confidence in the BH paradigm for active galactic nuclei is correspondingly high. Compared to the radius of the BH sphere of influence, BHs are discovered at similar spatial resolution with HST as in ground-based work. The reason is that HST is used to observe more distant galaxies. Large, unbiased samples are accessible. As a result, HST has revolutionized the study of BH demographics.Comment: 20 pages, 5 figures + 2 tables embedded as figures, LaTeX2e with wrapping fixed, uses ociwsymp1.sty; To appear in "Carnegie Observatories Astrophysics Series, Vol. 1: Coevolution of Black Holes and Galaxies," ed. L. C. Ho (Cambridge: Cambridge Univ. Press

Internal Secular Evolution in Disk Galaxies: The Growth of Pseudobulges

Observational and theoretical evidence that internal, slow ("secular") evolution reshapes galaxy disks is reviewed in Kormendy & Kennicutt (2004, ARAA, 42, 603). This update has three aims. First, I emphasize that this evolution is very general -- it is as fundamental to the evolution of galaxy disks as (e.g.) core collapse is to globular clusters, as the production of hot Jupiters is to the evolution of protoplanetary disks, and as evolution to red giants containing proto-white-dwarfs is to stellar evolution. One consequence for disk galaxies is the buildup of dense central components that get mistaken for classical (i.e., merger-built) bulges but that were grown out of disk stars and gas. We call these pseudobulges. Second, I review new results on pseudobulge star formation and structure and on the distinction between boxy and disky pseudobulges. Finally, I highlight how these results make a galaxy formation problem more acute. How can hierarchical clustering produce so many pure disk galaxies with no evidence for merger-built bulges?Comment: 6 pages, 7 Postscript figures; requires iaus.cls; to appear in Formation and Evolution of Galaxy Bulges, Proceedings IAU Symposium No. 245, 2007, M. Bureau et al. eds., in pres

Structural Analogs of the Milky Way Galaxy: Stellar Populations in the Boxy Bulges of NGC 4565 and NGC 5746

We present NGC 4565 and NGC 5746 as structural analogs of our Milky Way. All three are giant, SBb - SBbc galaxies with two pseudobulges, i. e., a compact, disky, star-forming pseudobulge embedded in a vertically thick, "red and dead", boxy pseudobulge that really is a bar seen almost end-on. The stars in the boxy bulge of our Milky Way are old and enhanced in alpha elements, indicating that star formation finished within ~ 1 Gyr of when it started. Here, we present Hobby-Eberly Telescope spectroscopy of the boxy pseudobulges of NGC 4565 and NGC 5746 and show that they also are made of old and alpha-element-enhanced stars. Evidently it is not rare that the formation of stars that now live in bars finished quickly and early, even in galaxies of intermediate Hubble types whose disks still form stars now. Comparison of structural component parameters leads us to suggest that NGC 4565 and NGC 5746 are suitable analogs of the Milky Way, because they show signatures of similar evolution processes.Comment: 6 pages, 3 figures, 1 postscript table, accepted by ApJ after tweaks in response to referee and after improving notation in figures; no conclusions change

Secular Evolution in Disk Galaxies: Pseudobulge Growth and the Formation of Spheroidal Galaxies

Updating Kormendy & Kennicutt (2004, ARAA, 42, 603), we review internal secular evolution of galaxy disks. One consequence is the growth of pseudobulges that often are mistaken for true (merger-built) bulges. Many pseudobulges are recognizable as cold, rapidly rotating, disky structures. Bulges have Sersic function brightness profiles with index n > 2; most pseudobulges have n <= 2. Recognition of pseudobulges makes the biggest problem with cold dark matter galaxy formation more acute: How can hierarchical clustering make so many pure disk galaxies with no evidence for merger-built bulges? E. g., the giant Scd galaxies M101 and NGC 6946 have rotation velocities of V ~ 200 km/s but nuclear star clusters with velocity dispersions of 25 to 40 km/s. Within 8 Mpc of us, 11 of 19 galaxies with V > 150 km/s show no evidence for a classical bulge, while only 7 are ellipticals or have classical bulges. It is hard to understand how bulgeless galaxies could form as the quiescent tail of a distribution of merger histories. Our second theme is environmental secular evolution. We confirm that spheroidal galaxies have fundamental plane (FP) correlations that are almost perpendicular to those for bulges and ellipticals. Spheroidals are not dwarf ellipticals. Rather, their structural parameters are similar to those of late-type galaxies. We suggest that spheroidals are defunct late-type galaxies transformed by internal processes such as supernova-driven gas ejection and environmental processes such as secular harassment and ram-pressure stripping. Minus spheroidals, the FP of ellipticals and bulges has small scatter. With respect to these, pseudobulges are larger and less dense.Comment: 11 pages, 6 Postscript figures; requires asp2006.sty; as published, except with updated references; for a version with full resolution figures, see http://chandra.as.utexas.edu/~kormendy/kormendy-rome.pd

Supermassive Black Holes in Active Galactic Nuclei

This article gives a brief overview of the direct and indirect evidence in support of the standard paradigm that active galactic nuclei are powered by supermassive black holes.Comment: A review to appear in The Encyclopedia of Astronomy and Astrophysics (Institute of Physics Publishing). TeX, 13 pages, including embedded figure

Scaling Laws for Dark Matter Halos in Late-Type and Dwarf Spheroidal Galaxies

Maximum disk mass models fitted to galaxy rotation curves are used to show that dark matter (DM) halos in late-type and dwarf spheroidal (dSph) galaxies satisfy well defined scaling laws. Halos in less luminous galaxies have smaller core radii, higher central densities, and smaller central velocity dispersions. Implications: (1) A single, continuous physical sequence of increasing mass extends from the tiniest dSphs to the most luminous spirals. (2) The high DM densities in dSph galaxies are normal for such dwarf galaxies. Since virialized density depends on collapse redshift z, the smallest dwarfs formed about delta z = 7 earlier than the biggest spirals. (3) The high DM densities of dSphs implies that they are real galaxies formed from primordial density fluctuations. They are not tidal fragments. (4) Because dwarf galaxies become more numerous and more nearly dominated by DM as luminosity decreases, there may be a large population of objects that are completely dark. Such objects are a canonical prediction of cold DM theory. (5) The slopes of the DM parameter correlations provide a measure on galactic mass scales of the slope n of the power spectrum of primordial density fluctuations. Our results not yet corrected for baryonic compression of DM give n = -1.9 +- 0.2. This is consistent with cold DM theory.Comment: 19 pages, 5 Postscript figures; requires IAUS215.sty; to appear in "IAU Symposium 220, Dark Matter in Galaxies", ed. Ryder, Pisano, Walker, and Freeman, San Francisco: ASP, in pres