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Search Results: 1 - 10 of 404218 matches for " R. P. van der Marel "
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Black holes and central surface brightness cusps
R. P. van der Marel
Physics , 1998,
Abstract: HST observations show that the surface brightness profiles of early-type galaxies have central cusps. I summarize here the results of van der Marel (1999), which show that the observed characteristics of these cusps are consistent with the hypothesis that all early-type galaxies have central black holes (BHs) that grew adiabatically in homogeneous isothermal cores. The models suggest a roughly linear correlation between BH mass and V-band galaxy luminosity, log M_BH = -1.83 + log L in solar units, similar to the relation suggested by kinematical BH detections in nearby galaxies.
The black hole mass distribution in early-type galaxies: cusps in HST photometry interpreted through adiabatic black hole growth
R. P. van der Marel
Physics , 1998, DOI: 10.1086/300730
Abstract: The surface brightness profiles of early-type galaxies have central cusps. Two characteristic profile types are observed with HST: `core' profiles have a break at a resolved radius and logarithmic cusp slope gamma < 0.3 inside that radius; `power-law' profiles have no clear break and gamma > 0.3. With few exceptions, galaxies with M_V < -22 have core profiles, and galaxies with M_V > -20.5 have power-law profiles. Both profile types occur in galaxies with -22 < M_V < -20.5. We show that these results are consistent with the hypothesis that: (i) all early-type galaxies have black holes (BHs) that grew adiabatically in homogeneous isothermal cores; and (ii) these `progenitor' cores followed scaling relations similar to those of the fundamental plane. The models studied here are the ones first proposed by Young. Models with BH masses and progenitor cores that obey established scaling relations predict (at Virgo) that galaxies with M_V < -21.2 have core profiles and galaxies with M_V > -21.2 have power-law profiles. This reproduces both the sense and the absolute magnitude of the observed transition. Intrinsic scatter in BH and galaxy properties can explain why both types of galaxies are observed around the transition magnitude. The observed bimodality in cusp slopes may be due to a bimodality in M_bh/L, with rapidly rotating disky galaxies having larger M_bh/L than slowly rotating boxy galaxies. Application to individual galaxies with HST photometry yields a roughly linear correlation between BH mass and V-band galaxy luminosity, log M_bh = -1.83 + log L (solar units). This agrees with the average relation for nearby galaxies with kinematically determined BH masses, and also with predictions from quasar statistics (shortened abstract).
Nuclear Brightness Profiles of Merger Remnants: Constraints on the Formation of Ellipticals by Mergers
R. P. van der Marel,D. Zurek
Physics , 1999,
Abstract: We present preliminary results of an HST/NICMOS program to image merger remnants in the J, H and K bands. The nuclear brightness profiles for most sample galaxies are similar to those typical for elliptical galaxies, but some (including the well-studied NGC 3921 and 7252) have an unusually high luminosity density at small radii. This is consistent with the prediction of N-body simulations that gas flows to the center during a merger and forms new stars.
Evidence for a 3 x 10^8 solar mass black hole in NGC 7052 from HST observations of the nuclear gas disk
R. P. van der Marel,F. C. van den Bosch
Physics , 1998, DOI: 10.1086/300593
Abstract: We present an HST study of the nuclear region of the E4 radio galaxy NGC 7052, which has a nuclear disk of dust and gas. The WFPC2 was used to obtain B, V and I broad-band images and an H_alpha+[NII] narrow-band image. The FOS was used to obtain H_alpha+[NII] spectra along the major axis, using a 0.26 arcsec diameter circular aperture. The observed rotation velocity of the ionized gas is V = 155 +/- 17 km/s at r = 0.2 arcsec from the nucleus. The Gaussian dispersion of the emission lines increases from sigma = 70 km/s at r=1 arcsec, to sigma = 400 km/s on the nucleus. To interpret the gas kinematics we construct axisymmetric models in which the gas and dust reside in a disk in the equatorial plane of the stellar body. It is assumed that the gas moves on circular orbits, with an intrinsic velocity dispersion due to turbulence. The circular velocity is calculated from the combined gravitational potential of the stars and a possible nuclear black hole (BH). Models without a BH predict a rotation curve that is shallower than observed (V_pred = 92 km/s at r = 0.2 arcsec), and are ruled out at > 99% confidence. Models with a BH of 3.3^{+2.3}_{-1.3} x 10^8 solar masses provide an acceptable fit. NGC 7052 can be added to the list of active galaxies for which HST spectra of a nuclear gas disk provide evidence for the presence of a central BH. The BH masses inferred for M87, M84, NGC 6251, NGC 4261 and NGC 7052 span a range of a factor 10, with NGC 7052 falling on the low end. By contrast, the luminosities of these galaxies are identical to within 25%. Any relation between BH mass and luminosity, as suggested by independent arguments, must therefore have a scatter of at least a factor 10.
Internal Dynamics, Structure and Formation of Dwarf Elliptical Galaxies: II. Rotating Versus Non-Rotating Dwarfs
M. Geha,P. Guhathakurta,R. van der Marel
Physics , 2003, DOI: 10.1086/377624
Abstract: We present spatially-resolved internal kinematics and stellar chemical abundances for a sample of dwarf elliptical (dE) galaxies in the Virgo Cluster observed with Keck/ESI. We find that 4 out of 17 dEs have major axis rotation velocities consistent with rotational flattening, while the remaining dEs have no detectable major axis rotation. Despite this difference in internal kinematics, rotating and non-rotating dEs are remarkably similar in terms of their position in the Fundamental Plane, morphological structure, stellar populations, and local environment. We present evidence for faint underlying disks and/or weak substructure in a fraction of both rotating and non-rotating dEs, but a comparable number of counter-examples exist for both types which show no evidence of such structure. Absorption-line strengths were determined based on the Lick/IDS system (Hbeta, Mgb, Fe5270, Fe5335) for the central region of each galaxy. We find no difference in the line-strength indices, and hence stellar populations, between rotating and non-rotating dE galaxies. The best-fitting mean age and metallicity for our 17 dE sample are 5 Gyr and Fe/H = -0.3 dex, respectively, with rms spreads of 3 Gyr and 0.1 dex. The majority of dEs are consistent with solar alpha/Fe abundance ratios. By contrast, the stellar populations of classical elliptical galaxies are, on average, older, more metal rich, and alpha-enhanced relative to our dE sample. The local environments of both dEs types appear to be diverse in terms of their proximity to larger galaxies in real or velocity space within the Virgo Cluster. Thus, rotating and non-rotating dEs are remarkably similar in terms of their structure, stellar content, and local environments, presenting a significant challenge to theoretical models of their formation. (abridged)
Dynamical stability of N-body models for M32 with a central black hole
R. P. van der Marel,S. Sigurdsson,L. Hernquist
Physics , 1997, DOI: 10.1086/304605
Abstract: We study the stability of stellar dynamical equilibrium models for M32. Kinematic observations show that M32 has a central black hole of 3x10^6 solar masses, and a phase-space distribution function that is close to the `two-integral' form f=f(E,L_z). M32 is also rapidly rotating; 85-90% of the stars have the same sense of rotation around the symmetry axis. Previous work has shown that flattened, rapidly rotating two-integral models can be bar-unstable. We have performed N-body simulations to test whether this is the case for M32. Particle realizations with N=512,000 were studied for two representative inclinations, i=90 (edge-on) and i=55, corresponding to intrinsic axial ratios of q=0.73 and q=0.55, respectively. The time evolution of the models was calculated with a `self-consistent field' code on a Cray T3D parallel supercomputer. We find both models to be dynamically stable. This implies that they provide a physically meaningful description of M32, and that the inclination of M32 (and hence its intrinsic flattening) cannot be strongly constrained through stability arguments. Previous work on the stability of f(E,L_z) models has shown that the bar-mode is the only possibly unstable mode for systems rounder than q=0.3, and that the likelihood for this mode to be unstable increases with flattening and rotation rate. The f(E,L_z) models studied for M32 are stable, and M32 has a higher rotation rate than nearly all other elliptical galaxies. This suggests that f(E,L_z) models constructed to fit data for real elliptical galaxies will generally be stable for q>0.55, and possibly for flatter systems as well.
Internal Dynamics, Structure and Formation of Dwarf Elliptical Galaxies: I. A Keck/HST Study of Six Virgo Cluster Dwarfs
M. Geha,P. Guhathakurta,R. van der Marel
Physics , 2002, DOI: 10.1086/344764
Abstract: Keck/ESI spectroscopy is presented for six Virgo Cluster dwarf elliptical (dE) galaxies. The mean line-of-sight velocity and velocity dispersion are resolved as a function of radius along the major axis of each galaxy, nearly doubling the total number of dEs with spatially-resolved stellar kinematics. None of the observed objects shows evidence of strong rotation: upper limits on v_rot/sigma are well below those expected for rotationally-flattened objects. Such limits place strong constraints on dE galaxy formation models. Although these galaxies continue the trend of low rotation velocities observed in Local Group dEs, they are in contrast to recent observations of large rotation velocities in slightly brighter cluster dEs. Using WFPC2 surface photometry and spherically-symmetric dynamical models, we determine global mass-to-light ratios 3 < M/L_V < 6. These ratios are comparable to those expected for an intermediate-age stellar population and are broadly consistent with the (V-I) colors of the galaxies. This implies that these dEs do not have a significant dark matter component inside an effective radius. Central black holes more massive than 10^7 M_sun can be ruled out. For the 5 nucleated dEs in our sample, we determine kinematic and photometric properties for the central nucleus separately from the underlying host dE galaxy. These nuclei are as bright or brighter than the most luminous Galactic globular clusters and lie near the region of Fundamental Plane space occupied by globular clusters. In this space, the Virgo dE galaxies lie in the same general region as Local Group and other nearby dEs, although non-rotating dEs appear to have a slightly higher mean mass and mass-to-light ratio than their rotating counterparts.
Keck Spectroscopy of Dwarf Elliptical Galaxies in the Virgo Cluster
M. Geha,P. Guhathakurta,R. van der Marel
Physics , 2001,
Abstract: Keck spectroscopy is presented for four dwarf elliptical galaxies in the Virgo Cluster. At this distance, the mean velocity and velocity dispersion are well resolved as a function of radius between 100 to 1000 pc, allowing a clear separation between nuclear and surrounding galaxy light. We find a variety of dispersion profiles for the inner regions of these objects, and show that none of these galaxies is rotationally flattened.
CO-bandhead spectroscopy of IC 342: mass and age of the nuclear star cluster
T. Boeker,R. P. van der Marel,W. D. Vacca
Physics , 1999, DOI: 10.1086/300985
Abstract: We have used the NASA Infra-Red Telescope Facility (IRTF) to observe the nuclear stellar cluster in the nearby, face-on, giant Scd spiral IC 342. From high resolution (R = 21500) spectra at the 12CO (2-0) bandhead at 2.3 micron we derive a line-of-sight stellar velocity dispersion sigma = (33 +- 3) km/s. To interpret this observation we construct dynamical models based on the Jeans equation for a spherical system. The light distribution of the cluster is modeled using an isophotal analysis of an HST V-band image from the HST Data Archive, combined with new ground-based K-band imaging. Under the assumption of an isotropic velocity distribution, the observed kinematics imply a K-band mass-to-light ratio M/L_K = 0.05, and a cluster mass M ~ 6 times 10^6 Msun. We model the mass-to-light ratio with the `starburst99' stellar population synthesis models of Leitherer and collaborators, and infer a best-fitting cluster age in the range 63-630 Myears. Although this result depends somewhat on a number of uncertainties in the modeling (e.g., the assumed extinction along the line-of-sight towards the nucleus, the IMF of the stellar population model, and the velocity dispersion anisotropy of the cluster), none of these can be plausibly modified to yield a significantly larger age. We discuss the implications of this result on possible scenarios for the frequency of nuclear starbursts and their impact on secular evolution of spiral galaxy nuclei. As a byproduct of our analysis, we infer that IC 342 cannot have any central black hole more massive than 0.5 million solar masses. This is ~ 6 times less massive than the black hole inferred to exist in our Galaxy, consistent with the accumulating evidence that galaxies with less massive bulges harbor less massive black holes.
Velocity profiles of Osipkov-Merritt models
C. M. Carollo,P. T. de Zeeuw,R. P. van der Marel
Physics , 1995, DOI: 10.1093/mnras/276.4.1131
Abstract: A simple algorithm is presented for the calculation of the projected line-of-sight velocity profiles (VPs) of non-rotating anisotropic spherical stellar dynamical models with a phase-space distribution function of the Osipkov-Merritt type. The velocity distribution in these models is isotropic inside the anisotropy radius r_a and becomes increasingly radially biased at larger radii. VP shape parameters are presented for a family of models in which the luminous mass density has an r^{-gamma} power-law cusp at small radii and an r^{-4} power-law fall-off at large radii. Self-consistent models and models in which the luminous matter is embedded in a dark halo are discussed. The effects of changes in the cusp slope gamma and in the anisotropy radius r_a are documented, and the area in the (gamma,r_a)-plane that contains physical models is delineated. The shapes of the VPs of the models show a considerable (and observable) variation with projected galactocentric radius. These models will be useful for interpreting the data on the VP shapes of elliptical galaxies that are now becoming available.
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