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For refcode 1997AJ....114.1771F:
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1997AJ....114.1771F THE CENTERS OF EARLY-TYPE GALAXIES WITH HST. IV. CENTRAL PARAMETER RELATIONS S. M. FABER UCO/Lick Observatory. Board of Studies in Astronomy and Astrophysics, University of California, Santa Cruz, California 95064 Electronic mail: faberOucolick.org SCOTT TREMAINE CIAR Cosmology and Gravity Program, Canadian Institute for Theoretical Astrophysics, University of Toronto, 60St. George Street, Toronto M5S 3H8, Canada Electronic mail: tremaine@cita.utoronto.ca EDWARD A. AJHAR Kitt Peak National Observatory, National Optical Astronomy Observatories,2 P.O. Box 26732, Tucson, Arizona 85726 Electronic mail: ajhar@noao.edu YONG-IK BYUN Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, Hawaii 96822, Electronic mail: byun@haneul.phy.ncu.edu.tw ALAN DRESSLER The Observatories of the Carnegie Institution, 813 Santa Barbara Street, Pasadena, California 91101, Electronic mail: dressler@ociw.edu KARL GEBHARDT Department of Astronomy, University of Michigan, Ann Arbor, Michigan 48109, Electronic mail: gebhardt@ucolick.org CARL GRILLMAIR UCO/Lick Observatory, Board of Studies in Astronomy and Astrophysics, University of California, Santa Cruz, California 95064, Electronic mail: carl@grandpa.jpl.nasa.gov JOHN KORMENDY Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, Hawaii 96822, Electronic mail: kormendy@oort.ifa.hawali.edu TOD R. LAUER Kitt Peak National Observatory, National Optical Astronomy Observatories,2 P.O. Box 26732, Tucson, Arizona 85726, Electronic mail: lauer@noao.edu DOUGLAS RICHSTONE Department of Astronomy, University of Michigan, Ann Arbor, Michigan 48109, Electronic mail: dor@astro.lsa.umich.edu Received 1996 October 9; revised 1997 August 5; accepted 1997 August 5 ABSTRACT We analyze Hubble Space Telescope surface-brightness profiles of 61 elliptical galaxies and spiral bulges (hereafter 'hot' galaxies). The profiles are parameterized by break radius r_b_ and break surface brightness I_b_. These are combined with central velocity dispersions, total luminosities, rotation velocities, and isophote shapes to explore correlations among central and global properties. Luminous hot galaxies (M_v_ < -22) have cuspy cores with steep outer power-law profiles that break at r ~ r_b_ to shallow inner profiles 1 is proportional to r^- {gamma}^ with {gamma} <= 0.3. Break radii and core luminosities for these objects are approximately proportional to effective radii and total luminosities. Scaling relations are presented for several core parameters as a function of total luminosity. Cores follow a fundamental plane that parallels the global fundamental plane for hot galaxies but is 30% thicker. Some of this extra thickness may be due to the effect of massive black holes (BHs) on central velocity dispersions. Faint hot galaxies (M_v_ > - 20.5) show steep, largely featureless power-law profiles that lack cores. Measured values of r_b_ and I_b_ for these galaxies are limits only. At a limiting radius of 10 pc, the centers of power-law galaxies are up to 1000 times denser in mass and luminosity than the cores of large galaxies. At intermediate magnitudes (-22 < M_v_ < -20.5), core and power-law galaxies coexist, and there is a range in r_b_ at a given luminosity of at least two orders of magnitude. Here, central properties correlate strongly with global rotation and shape: core galaxies tend to be boxy and slowly rotating, whereas power-law galaxies tend to be disky and rapidly rotating. A search for inner disks was conducted to test a claim in the literature, based on a smaller sample, that power laws originate from edge-on stellar disks. We find only limited evidence for such disks and believe that the difference between core and power-law profiles reflects a real difference in the spatial distribution of the luminous spheroidal component of the galaxy. The dense power-law centers of disky, rotating galaxies are consistent with their formation in gas-rich mergers. The parallel proposition, that cores are the by-products of gas-free stellar mergers, is less compelling for at least two reasons: (l) dissipationless hierarchical clustering does not appear to produce core profiles like those seen; (2) core galaxies accrete small, dense, gas-free galaxies at a rate sufficient to fill in their low-density cores if the satellites survived and sank to the center (whether the satellites survive is still an open question). An alternative model for core formation involves the orbital decay of massive BHs that are accreted in mergers: the decaying BHs may heat and eject stars from the center, eroding a power law if any exists and scouring out a core. An average BH mass per spheroid of 0.002 times the stellar mass yields cores in fair agreement with observed cores and is consistent with the energetics of AGNs and the kinematic detection of BHs in nearby galaxies. An unresolved issue is why power-law galaxies also do not have cores if this process operates in all hot galaxies.
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