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John Kormendy

Publications and source records attributed to John Kormendy.

At least 73 records · Page 4Linked to original sources
arXiv2003

Kinematics of Ten Early-Type Galaxies from HST and Ground-Based Spectroscopy

We present stellar kinematics for a sample of 10 early-type galaxies observed using the STIS aboard the Hubble Space Telescope, and the Modular Spectrograph on the MDM Observatory 2.4-m telescope. The spectra are used to derive line-of-sight velocity distributions (LOSVDs) of the stars using a Maximum Penalized Likelihood method. We use Gauss-Hermite polynomials to parameterize the LOSVDs and find predominantly negative h4 values (boxy distributions) in the central regions of our galaxies. One galaxy, NGC 4697, has significantly positive central h4 (high tail weight). The majority of galaxies have a central velocity dispersion excess in the STIS kinematics over ground-based velocity dispersions. The galaxies with the strongest rotational support, as quantified with v_MAX/sigma_STIS, have the smallest dispersion excess at STIS resolution. The best-fitting, general, axisymmetric dynamical models (described in a companion paper) require black holes in all cases, with masses ranging from 10^6.5 to 10^9.3 Msun. We replot these updated masses on the BH/sigma relation, and show that the fit to only these 10 galaxies has a slope consistent with the fits to larger samples. The greatest outlier is NGC 2778, a dwarf elliptical with relatively poorly constrained black hole mass. The two best candidates for pseudobulges, NGC 3384 and 7457, do not deviate significantly from the established relation between black hole and sigma. Neither do the three galaxies which show the most evidence of a recent merger, NGC 3608, 4473, and 4697.

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arXiv2003

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.

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arXiv2002

Axisymmetric Dynamical Models of the Central Regions of Galaxies

We present axisymmetric, orbit superposition models for 12 galaxies using data taken with the Hubble Space Telescope (HST) and ground-based observatories. In each galaxy, we detect a central black hole (BH) and measure its mass to accuracies ranging from 10% to 70%. We demonstrate that in most cases the BH detection requires both the HST and ground-based data. Using the ground-based data alone does provide an unbiased measure of the BH mass (provided they are fit with fully general models), but at a greatly reduced significance. The most significant correlation with host galaxy properties is the relation between the BH mass and the velocity dispersion of the host galaxy; we find no other equally strong correlation, and no second parameter that improves the quality of the mass-dispersion relation. We are also able to measure the stellar orbital properties from these general models. The most massive galaxies are strongly biased to tangential orbits near the BH, consistent with binary BH models, while lower-mass galaxies have a range of anisotropies, consistent with an adiabatic growth of the BH.

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arXiv2002

Galaxies with a Central Minimum in Stellar Luminosity Density

We used HST WFPC2 images to identify six early-type galaxies with surface- brightness profiles that decrease inward over a limited range of radii near their centers. The implied luminosity density profiles of these galaxies have local minima interior to their core break radii. NGC 3706 harbors a high surface brightness ring of starlight with radius ~20 pc. Its central structure may be related to that in the double-nucleus galaxies M31 and NGC 4486B. NGC 4406 and NGC 6876 have nearly flat cores that on close inspection are centrally depressed. Colors for both galaxies imply that this is not due to dust absorption. The surface brightness distributions of both galaxies are consistent with stellar tori that are more diffuse than the sharply defined system in NGC 3706. The remaining three galaxies are the brightest cluster galaxies in A260, A347, and A3574. Color information is not available for these objects, but they strongly resemble NGC 4406 and NGC 6876 in their cores. The thin ring in NGC 3706 may have formed dissipatively. The five other galaxies resemble the endpoints of some simulations of the merging of two gas-free stellar systems, each harboring a massive nuclear black hole. In one version of this scenario, diffuse stellar tori are produced when stars initially bound to one black hole are tidally stripped away by the second black hole. Alternatively, some inward-decreasing surface-brightness profiles may reflect the ejection of stars from a core during the hardening of the binary black hole created during the merger.

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arXiv2002

The slope of the black-hole mass versus velocity dispersion correlation

Observations of nearby galaxies reveal a strong correlation between the mass of the central dark object M and the velocity dispersion sigma of the host galaxy, of the form log(M/M_sun) = a + b*log(sigma/sigma_0); however, published estimates of the slope b span a wide range (3.75 to 5.3). Merritt & Ferrarese have argued that low slopes (<4) arise because of neglect of random measurement errors in the dispersions and an incorrect choice for the dispersion of the Milky Way Galaxy. We show that these explanations account for at most a small part of the slope range. Instead, the range of slopes arises mostly because of systematic differences in the velocity dispersions used by different groups for the same galaxies. The origin of these differences remains unclear, but we suggest that one significant component of the difference results from Ferrarese & Merritt's extrapolation of central velocity dispersions to r_e/8 (r_e is the effective radius) using an empirical formula. Another component may arise from dispersion-dependent systematic errors in the measurements. A new determination of the slope using 31 galaxies yields b=4.02 +/- 0.32, a=8.13 +/- 0.06, for sigma_0=200 km/s. The M-sigma relation has an intrinsic dispersion in log M that is no larger than 0.3 dex. In an Appendix, we present a simple model for the velocity-dispersion profile of the Galactic bulge.

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arXiv2001

M33: A Galaxy with No Supermassive Black Hole

Galaxies that contain bulges appear to contain central black holes whose masses correlate with the velocity dispersion of the bulge. We show that no corresponding relationship applies in the pure disk galaxy M33. Three-integral dynamical models fit Hubble Space Telescope WFPC2 photometry and STIS spectroscopy best if the central black hole mass is zero. The upper limit is 1500 M_sun. This is significantly below the mass expected from the velocity dispersion of the nucleus and far below any mass predicted from the disk kinematics. Our results suggest that supermassive black holes are associated only with galaxy bulges and not with their disks.

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arXiv2001

The Nuclear Disk in the Dwarf Elliptical Galaxy NGC 4486A

Many ellipticals contain nuclear disks of dust and gas. Some ellipticals contain nuclear disks of stars that are distinct from the rest of the galaxy. We show that the dwarf E2 galaxy NGC 4486A contains both -- it is a "Rosetta stone" object that tells us how nuclear disks evolve. Its properties suggest that, as accreted gas dissipates and settles toward the center, it forms stars and builds a stellar disk. Secular growth may explain not only the most distinct nuclear disks such as those in NGC 4486A but also some of the disky distortions that are commonly seen in elliptical galaxies. That is, density distributions may grow secularly cuspier. This would result in chaotic mixing of stellar orbits in phase space and would tend to make an elliptical galaxy evolve toward a more nearly axisymmetric shape.

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arXiv2001

Supermassive Black Holes in Nuclei of Galaxies

We review the motivation and search for supermassive black holes (BHs) in galaxies. Energetic nuclear activity provides indirect but compelling evidence for BH engines. Ground-based dynamical searches for central dark objects are reviewed in Kormendy & Richstone (1995, ARA&A, 33, 581). Here we provide an update of results from the HST. As of 2001 March, dynamical BH detections are available for at least 37 galaxies. The demographics of these objects lead to the following conclusions: (1) BH mass correlates with the luminosity of the bulge component of the host galaxy. The median BH mass fraction is 0.13% of the mass of the bulge. (2) BH mass correlates with the mean velocity dispersion of the bulge inside its effective radius. For the best mass determinations, the scatter is consistent with the measurement errors. (3) BH mass correlates with the luminosity of the high-density central component in disk galaxies independent of whether this is a real bulge (a mini-elliptical, believed to form via a merger-induced dissipative collapse and starburst) or a ``pseudobulge'' (believed to form by inward transport of disk material). (4) BH mass does not correlate with the luminosity of galaxy disks. If pure disks contain BHs, then their masses are much smaller than 0.13% of the mass of the disk. We conclude that present observations show no dependence of BH mass on the details of whether BH feeding happens rapidly during a collapse or slowly via secular evolution of the disk. The above results increasingly support the hypothesis that the major events that form a bulge or elliptical galaxy and the main growth phases of its BH -- when it shone like a quasar -- were the same events.

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arXiv2000

Black Hole Mass Estimates from Reverberation Mapping and from Spatially Resolved Kinematics

Black hole (BH) masses that have been measured by reverberation mapping in active galaxies fall significantly below the correlation between bulge luminosity and BH mass determined from spatially resolved kinematics of nearby normal galaxies. This discrepancy has created concern that one or both techniques suffer from systematic errors. We show that BH masses from reverberation mapping are consistent with the recently discovered relationship between BH mass and galaxy velocity dispersion. Therefore the bulge luminosities are the probable source of the disagreement, not problems with either method of mass measurement. This result underscores the utility of the BH mass -- velocity dispersion relationship. Reverberation mapping can now be applied with increased confidence to galaxies whose active nuclei are too bright or whose distances are too large for BH searches based on spatially resolved kinematics.

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arXiv2000

Monsters at the Heart of Galaxy Formation

Surveys with the Hubble Space Telescope find supermassive black holes (BHs) of 10**6 to 10**9.5 solar masses in every galaxy that has an elliptical-galaxy-like "bulge" component. BHs appear to be standard equipment in galaxy bulges. At the 2000 June meeting of the American Astronomical Society, two groups announced the discovery of a tight correlation between BH mass and the global velocity dispersion of stars in the host galaxy bulge (astro-ph/0006053 and astro-ph/0006289). Also, BH mass scales with bulge mass; the median BH mass fraction is 0.15 % of the bulge mass. In contrast, BH mass does not scale with disk properties. Pure disk galaxies - ones that lack a bulge component - must have BH mass fractions that are much smaller than the BH mass fractions in bulges. These results imply a close connection between BH growth and bulge (but not disk) formation. Observations increasingly support the hypothesis that the major events that form a bulge or elliptical galaxy and the main growth phases of its BH - when it shone like a quasar - were the same events. These and other results are leading to a profound change in how astronomers view BHs. More than just exotica needed to explain rare active galactic nuclei, they are becoming an integral part of our understanding of galaxy formation.

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arXiv2000

Supermassive Black Holes in Disk Galaxies

Dynamical searches find central dark objects - candidate supermassive black holes (BHs) - in at least 34 galaxies. The demographics of these objects lead to the following conclusions: (1) BH mass correlates with the luminosity of the bulge component of the host galaxy, albeit with considerable scatter. The median BH mass fraction is 0.15 % of the mass of the bulge. The quartiles are 0.09 % and 0.7 %. (2) BH mass correlates with the mean velocity dispersion of the bulge component inside its effective radius, i.e., with how strongly the bulge stars are gravitationally bound to each other. For the best BH mass determinations, the scatter is consistent with the measurement errors. (3) BH mass correlates with the luminosity of the high-density central component in disk galaxies independent of whether this is a real bulge (a mini-elliptical) or a "pseudobulge" (believed to form via inward transport of disk material). (4) BH mass does not correlate with the luminosity of galaxy disks. If pure disks contain BHs (and observations of active nuclei argue that some do), then their BH mass fractions are much smaller than the canonical 0.15 % for bulges. These results lead to the following conclusions: (A) Present observations show no dependence of BH mass on the details of whether BH feeding happens rapidly during a collapse or slowly via secular evolution of the disk. (B) The above results increasingly support the hypothesis that the major events that form a bulge or elliptical galaxy and the main growth phases of its BH -- when it shone as an active nucleus -- were the same events.

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arXiv2000

A Relationship Between Nuclear Black Hole Mass and Galaxy Velocity Dispersion

We describe a correlation between the mass M_BH of a galaxy's central black hole and the luminosity-weighted line-of-sight velocity dispersion sigma_e within the half-light radius. The result is based on a sample of 26 galaxies, including 13 galaxies with new determinations of black hole masses from Hubble Space Telescope measurements of stellar kinematics. The best-fit correlation is M_BH = 1.2 (+-0.2) x 10^8 M_sun (sigma_e/200 km/s)^(3.75 (+-0.3))over almost three orders of magnitude in M_BH; the scatter in M_BH at fixed sigma_e is only 0.30 dex and most of this is due to observational errors. The M_BH-sigma_e relation is of interest not only for its strong predictive power but also because it implies that central black hole mass is constrained by and closely related to properties of the host galaxy's bulge.

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arXiv1999

Axisymmetric, 3-Integral Models of Galaxies: A Massive Black Hole in NGC3379

We fit axisymmetric 3-integral dynamical models to NGC3379 using the line-of-sight velocity distribution obtained from HST/FOS spectra of the galaxy center and ground-based long-slit spectroscopy along four position angles, with the light distribution constrained by WFPC2 and ground-based images. We have fitted models with inclinations from 29 (intrinsic galaxy type E5) to 90 degrees (intrinsic E1) and black hole masses from 0 to 1e9 M_solar. The best-fit black hole masses range from 6e7 to 2e8 M_solar, depending on inclination. The velocity ellipsoid of the best model is not consistent with either isotropy or a two-integral distribution function. Along the major axis, the velocity ellipsoid becomes tangential at the innermost bin, radial in the mid-range radii, and tangential again at the outermost bins. For the acceptable models, the radial to tangential dispersion in the mid-range radii ranges from 1.1 < sigma_r / sigma_t < 1.7. Compared with these 3-integral models, 2-integral isotropic models overestimate the black hole mass since they cannot provide adequate radial motion. However, the models presented in this paper still contain restrictive assumptions-namely assumptions of constant M/L and spheroidal symmetry-requiring yet more models to study black hole properties in complete generality.

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arXiv1999

HST ultraviolet spectral energy distributions for three ultraluminous infrared galaxies

We present HST Faint Object Camera ultraviolet (230 nm and 140 nm) images of three ultraluminous infrared galaxies (ULIG: L_ir > 10^12 L_sun) selected from the IRAS Revised Bright Galaxy Sample. The purpose is to estimate spectral energy distributions (SEDs) to facilitate the identification of similar objects at high redshift in deep optical, infrared, and submm surveys. All three galaxies (VII Zw031 = IRAS F12112+0305, and IRAS F22491-1808) were well detected at 230 nm. Two of the three were marginally detected at 140 nm. The fluxes, together with ground-based optical and infrared photometry, are used to compute SEDs over a wide wavelength range. The measured SEDs drop from the optical to the ultraviolet, but the magnitude of the drop ranges from a factor of ~3 in IRAS F22491-1808 to a factor of ~100 in VIIZw031. This is most likely due to different internal extinctions. Such an interpretation is also suggested by extrapolating to ultraviolet wavelengths the optical internal extinction measured in VIIZw031. K-corrections are calculated to determine the colors of the sample galaxies as seen at high redshifts. Galaxies like VIIZw031 have very low observed rest-frame UV fluxes which means that such galaxies at high redshift will be extremely red or even missing in optical surveys. On the other hand, galaxies like IRAS F12112+0305 and IRAS F22491-1808, if seen at high redshift, would be sufficiently blue that they would not easily be distinguished from normal field galaxies, and therefore, identified as ULIGs. The implication is then that submillimeter surveys may be the only means of properly identifying the majority of ULIGs at high redshift.

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arXiv1998

The Mass Distribution in the Elliptical Galaxy NGC 3377: Evidence for a 2 x 10**8 Solar Mass Black Hole

We have measured the mass distribution in the central 35" = 1.7 kpc of the E5 galaxy NGC 3377. Stellar rotation velocity and velocity dispersion profiles (seeing sigma_* = 0.20 - 0.56 arcsec) and V-band surface photometry (sigma_* = 0.20 - 0.26 arcsec) have been obtained with the Canada-France-Hawaii Telescope. NGC 3377 is kinematically similar to M32: the central kinematic gradients are steep. The apparent velocity dispersion rises from 95 +- 2 km/s at 1" <= r <= 4" to 178 +- 10 km/s at the center. To search for a central black hole, we derive three-dimensional velocity and velocity dispersion fields that fit our observations and Hubble Space Telescope surface photometry after projection and seeing convolution. Isotropic models imply that the mass-to-light ratio rises by a factor of ~ 4 at r < 2" to M/L_V > 10. If the mass-to-light ratio of the stars is constant with radius, then NGC 3377 contains a central massive dark object (MDO), probably a black hole, of mass (1.8 +- 0.8) x 10**8 M_Sun. Several arguments suggest that NGC 3377 is likely to be nearly isotropic. However, flattened, anisotropic maximum entropy models can fit the data without an MDO. Therefore the MDO detection in NGC 3377 is weaker than those in M31, M32, or NGC 3115. The above MDO mass is corrected for the E5 shape of the galaxy and for the difference between velocity moments and velocities given by Gaussian fits to the line profiles. We show that the latter correction does not affect the strength of the MDO detection, but it slightly reduces the mass and mass-to-light ratio. At 3" <= r <= 35", M/L_V is constant at ~ 2.4. Therefore the inner parts of NGC 3377 are dominated by a normal old stellar population, not by halo dark matter.

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arXiv1997

The Centers of Early-Type Galaxies with HST. IV. Central Parameter Relations

We analyze Hubble Space Telescope surface-brightness profiles of 61 elliptical galaxies and spiral bulges (hot galaxies). Luminous hot galaxies have cuspy cores with steep outer power-law profiles that break at r ~ r_b to shallow inner profiles with logslope less than 0.3. Faint hot galaxies show steep, largely featureless power-law profiles at all radii and lack cores. The centers of power-law galaxies are up to 1000 times denser in mass and luminosity than the cores of large galaxies at a limiting radius of 10 pc. At intermediate magnitudes (-22.0 < 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. Central properties correlate 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. The dense power-law centers of disky, rotating galaxies are consistent with their formation in gas-rich mergers. The parallel proposition that cores are simply the by-products of gas-free stellar mergers is less compelling. For example, core galaxies accrete small, dense, gas-free galaxies at a rate sufficient to fill in low-density cores if the satellites survived and sank to the center. An alternative model for core formation involves the orbital decay of massive black holes (BHs): the BH 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 reasonably good agreement with the masses and radii of observed cores and in addition is consistent with the energetics of AGNs and kinematic detections of BHs in nearby galaxies.

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