Browsing by Subject "acs-virgo-cluster"
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Item Correlations Between Supermassive Black Holes, Velocity Dispersions, and Mass Deficits in Elliptical Galaxies with Cores(2009-02) Kormendy, John; Bender, Ralf; Kormendy, JohnHigh-dynamic-range surface photometry in a companion paper makes possible accurate measurement of the stellar light deficits L(def) and mass deficits M(def) associated with the cores of elliptical galaxies. We show that L(def) correlates with velocity dispersions sigma of the host galaxy bulge averaged outside the central region that may be affected by a supermassive black hole (BH). We confirm that L(def) correlates with BH mass M(center dot). Also, the fractional light deficit L(def)/L(*) correlates with M(center dot)/M(*), the ratio of BH mass to the galaxy stellar mass. All three correlations have scatter similar to or smaller than the scatter in the well-known correlation between M(center dot) and sigma. The new correlations are remarkable in view of the dichotomy between ellipticals with cores and those with central extra light. Core light deficit correlates closely with M(center dot) and sigma, but extra light does not. This supports the suggestion that extra light Es are made in wet mergers with starbursts whereas core Es are made in dry mergers. After dry mergers, cores are believed to be scoured by BH binaries that fling stars away as their orbits decay or by BHs that sink back to the center after recoiling from anisotropic gravitational radiation emitted when they merge. Direct evidence for these mechanisms has been elusive. We interpret the new correlations as the "smoking gun" that connects cores with BHs. Together, the M(center dot) - sigma and M(center dot) - L(def) correlations give us two independent ways to estimate BH masses in core Es.Item A Revised Parallel-Sequence Morphological Classification of Galaxies: Structure and Formation of S0 and Spheroidal Galaxies(2012-01) Kormendy, John; Bender, Ralf; Kormendy, JohnWe update van den Bergh's parallel-sequence galaxy classification in which S0 galaxies form a sequence S0a-S0b-S0c that parallels the sequence Sa-Sb-Sc of spiral galaxies. The ratio B/T of bulge-to-total light defines the position of a galaxy in this tuning-fork diagram. Our classification makes one major improvement. We extend the S0a-S0b-S0c sequence to spheroidal ("Sph") galaxies that are positioned in parallel to irregular galaxies in a similarly extended Sa-Sb-Sc-Im sequence. This provides a natural "home" for spheroidals, which previously were omitted from galaxy classification schemes or inappropriately combined with ellipticals. To motivate our juxtaposition of Sph and Im galaxies, we present photometry and bulge-disk decompositions of four rare, late-type S0s that bridge the gap between the more common S0b and Sph galaxies. NGC 4762 is an edge-on SB0bc galaxy with a very small classical-bulge-to-total ratio of B/T = 0.13 +/- 0.02. NGC 4452 is an edge-on SB0 galaxy with an even tinier pseudobulge-to-total ratio of PB/T = 0.017 +/- 0.004. It is therefore an SB0c. VCC 2048, whose published classification is S0, contains an edge-on disk, but its "bulge" plots in the structural parameter sequence of spheroidals. It is therefore a disky Sph. And NGC 4638 is similarly a "missing link" between S0s and Sphs-it has a tiny bulge and an edge-on disk embedded in an Sph halo. In the Appendix, we present photometry and bulge-disk decompositions of all Hubble Space Telescope Advanced Camera for Surveys Virgo Cluster Survey S0s that do not have published decompositions. We use these data to update the structural parameter correlations of Sph, S + Im, and E galaxies. We show that Sph galaxies of increasing luminosity form a continuous sequence with the disks (but not bulges) of S0c-S0b-S0a galaxies. Remarkably, the Sph-S0-disk sequence is almost identical to that of Im galaxies and spiral galaxy disks. We review published observations for galaxy transFormation processes, particularly ram-pressure stripping of cold gas. We suggest that Sph galaxies are transformed, "red and dead" Scd-Im galaxies in the same way that many S0 galaxies are transformed, red and dead Sa-Sc spiral galaxies.Item Structure and Formation of Elliptical and Spheroidal Galaxies(2009-05) Kormendy, John; Fisher, David B.; Cornell, Mark E.; Bender, Ralf; Kormendy, John; Fisher, David B.; Cornell, Mark E.; Bender, RalfNew surface photometry of all known elliptical galaxies in the Virgo cluster is combined with published data to derive composite profiles of brightness, ellipticity, position angle, isophote shape, and color over large radius ranges. These provide enough leverage to show that Sersic log I alpha r(1/n) functions fit the brightness profiles I(r) of nearly all ellipticals remarkably well over large dynamic ranges. Therefore, we can confidently identify departures from these profiles that are diagnostic of galaxy Formation. Two kinds of departures are seen at small radii. All 10 of our ellipticals with total absolute magnitudes M(VT) <= -21.66 have cuspy cores-"missing light"-at small radii. Cores are well known and naturally scoured by binary black holes (BHs) formed in dissipationless ("dry") mergers. All 17 ellipticals with -21.54 <= M(VT) <= -15.53 do not have cores. We find a new distinct component in these galaxies: all coreless ellipticals in our sample have extra light at the center above the inward extrapolation of the outer Sersic profile. In large ellipticals, the excess light is spatially resolved and resembles the central components predicted in numerical simulations of mergers of galaxies that contain gas. In the simulations, the gas dissipates, falls toward the center, undergoes a starburst, and builds a compact stellar component that, as in our observations, is distinct from the Sersic-function main body of the elliptical. But ellipticals with extra light also contain supermassive BHs. We suggest that the starburst has swamped core scouring by binary BHs. That is, we interpret extra light components as a signature of Formation in dissipative ("wet") mergers. Besides extra light, we find three new aspects to the ("E-E") dichotomy into two types of elliptical galaxies. Core galaxies are known to be slowly rotating, to have relatively anisotropic velocity distributions, and to have boxy isophotes. We show that they have Sersic indices n > 4 uncorrelated with M(VT). They also are alpha-element enhanced, implying short star-Formation timescales. And their stellar populations have a variety of ages but mostly are very old. Extra light ellipticals generally rotate rapidly, are more isotropic than core Es, and have disky isophotes. We show that they have n similar or equal to 3 +/- 1 almost uncorrelated with MVT and younger and less alpha-enhanced stellar populations. These are new clues to galaxy Formation. We suggest that extra light ellipticals got their low Sersic indices by forming in relatively few binary mergers, whereas giant ellipticals have n > 4 because they formed in larger numbers of mergers of more galaxies at once plus later heating during hierarchical clustering. We confirm that core Es contain X-ray-emitting gas whereas extra light Es generally do not. This leads us to suggest why the E-E dichotomy arose. If energy feedback from active galactic nuclei (AGNs) requires a "working surface" of hot gas, then this is present in core galaxies but absent in extra light galaxies. We suggest that AGN energy feedback is a strong function of galaxy mass: it is weak enough in small Es not to prevent merger starbursts but strong enough in giant Es and their progenitors to make dry mergers dry and to protect old stellar populations from late star Formation. Finally, we verify that there is a strong dichotomy between elliptical and spheroidal galaxies. Their properties are consistent with our understanding of their different Formation processes: mergers for ellipticals and conversion of late-type galaxies into spheroidals by environmental effects and by energy feedback from supernovae. In an appendix, we develop machinery to get realistic error estimates for Sersic parameters even when they are strongly coupled. And we discuss photometric dynamic ranges necessary to get robust results from Sersic fits.