Gijs A. Verdoes Kleijn

Core Radio and Optical Emission in the Nuclei of Nearby FR I Radio Galaxies

In this paper we analyze the relation between radio, optical continuum and H?+[N II] emission from the cores of a sample of 21 nearby Fanaroff and Riley type I galaxies as observed with the VLBA and HST. The emission arises inside the inner tens of parsecs of the galaxies. Core radio emission is observed in 19/20 galaxies, optical core continuum emission is detected in 12/21 galaxies and H?+[N II] core emission is detected in 20/21 galaxies. We confirm the recently detected linear correlation between radio and optical core emission in FR I galaxies and show that both core emissions also correlate with central H?+[N II] emission. The tight correlations between radio, optical, and H?+[N II] core emission constrain the bulk Lorentz factor to ? ~ 2?5 and ? 2 for a continuous jet and a jet consisting of discrete blobs, respectively, assuming jet-viewing angles in the range 30??90?. Radio and optical core emissions are likely to be synchrotron radiation from the inner jet, possibly with a significant contribution from emission by an accretion disk and/or flow. Elliptical galaxies with LINER nuclei without large-scale radio jets seem to follow the core emission correlations found in FR I galaxies. This suggests that the central engines could be very similar for the two classes of active galactic nuclei.

Gas Kinematics and the Black Hole Mass at the Center of the Radio Galaxy NGC 4335

We investigate the kinematics of the central gas disk of the radio-loud elliptical galaxy NGC 4335, derived from Hubble Space Telescope (HST) long-slit spectroscopic observations of Hα + [N II] along three parallel slit positions. The observed mean velocities are consistent with a rotating thin disk. We model the gas disk in the customary way, taking into account the combined potential of the galaxy and a putative black hole with mass M•, as well as the influence on the observed kinematics of the point-spread function and finite slit width. This sets a 3 σ upper limit of 108 M⊙ on M•. The velocity dispersion at r 05 is in excess of that predicted by the thin rotating disk model. This does not invalidate the model if the excess dispersion is caused by localized turbulent motion in addition to bulk circular rotation. However, if instead the dispersion is caused by the black hole (BH) potential then the thin disk model provides an underestimate of M•. A BH mass M• ~ 6 × 108 M⊙ is inferred by modeling the central gas dispersion as due to an isotropic spherical distribution of collisionless gas cloudlets. The stellar kinematics for NGC 4335 are derived from a ground-based (William Herschel Telescope/ISIS) long-slit observation along the galaxy major axis. A two-integral model of the stellar dynamics yields M• 3 × 109 M⊙. However, there is reason to believe that this model overestimates M•. Reported correlations between black hole mass and inner stellar velocity dispersion σ predict M• to be ≥5.4 × 108 M⊙ in NGC 4335. If our standard thin disk modeling of the gas kinematics is valid, then NGC 4335 has an unusually low M• for its velocity dispersion. If, on the other hand, this approach is flawed and provides an underestimate of M•, then black hole masses for other galaxies derived from HST gas kinematics with the same assumptions should be treated with caution. In general, a precise determination of the M•-σ relation and its scatter will benefit from (1) joint measurements of M• from gas and stellar kinematics in the same galaxies and (2) a better understanding of the physical origin of the excess velocity dispersion commonly observed in nuclear gas disks of elliptical galaxies.

[ITAL]HUBBLE SPACE TELESCOPE[/ITAL][ITAL]Hubble Space Telescope[/ITAL] Observations of Nearby Radio-Loud Early-Type Galaxies

We present and analyse HST/WFPC2 broad- and narrow-band observations of the central regions of 19 nearby radio-loud early-type galaxies. Together with two more galaxies they form a complete sample of Fanaroff & Riley Type I galaxies. We obtained V- and I-band images and narrow-band images centered on the HalphaNII emission lines. We use archival data for six galaxies. nWe describe the data reduction, give isophotal fits and analyse the central emission-line gas and dust distributions. Our main conclusions are the following. Although obscuration by dust inhibits a direct determination of central cusp slopes, the data suggest most but not all galaxies have shallow cores. Dust is detected in all but two galaxies. There is a wide variety of central dust morphologies, ranging from central disks to lanes and irregular distributions. The analysis suggests the difference between disks and lanes is intrinsic and not due to different viewing angles. Central emission-line gas is detected in all galaxies. Extended low-surface-brightness emission is always associated with the dust features. In a subsequent paper we will present a detailed analysis of the relation between these central properties and the nuclear activity.

The Black Hole in IC 1459 from [ITAL]HUBBLE SPACE TELESCOPE[/ITAL][ITAL]Hubble Space Telescope[/ITAL] Observations of the Ionized Gas Disk

The peculiar elliptical galaxy IC 1459 (MV = -21.19, D = 16.5 h-1 Mpc) has a fast counterrotating stellar core, stellar shells and ripples, a blue nuclear point source, and strong radio core emission. We present results of a detailed Hubble Space Telescope study of IC 1459, and in particular its central gas disk, aimed at constraining the central mass distribution. We obtained WFPC2 narrowband imaging centered on the Hα+[N II] emission lines to determine the flux distribution of the gas emission at small radii, and we obtained FOS spectra at six aperture positions along the major axis to sample the gas kinematics. We construct dynamical models for the Hα+[N II] and Hβ kinematics that include a supermassive black hole and in which the stellar mass distribution is constrained by the observed surface brightness distribution and ground-based stellar kinematics. In one set of models we assume that the gas rotates on circular orbits in an infinitesimally thin disk. Such models adequately reproduce the observed gas fluxes and kinematics. The steepness of the observed rotation velocity gradient implies that a black hole must be present. There are some differences between the fluxes and kinematics for the various line species that we observe in the wavelength range 4569–6819 A. Species with higher critical densities generally have a flux distribution that is more concentrated toward the nucleus, and have observed velocities that are higher. This can be attributed qualitatively to the presence of the black hole. There is some evidence that the gas in the central few arcsec has a certain amount of asymmetric drift, and we therefore construct alternative models in which the gas resides in collisionless cloudlets that move isotropically. All models are consistent with a black hole mass in the range M• = 1–4 × 108 M⊙, and models without a black hole are always ruled out at high confidence. The implied ratio of black holes mass to galaxy mass is in the range 0.4–1.5 × 10-3, which is not inconsistent with results obtained for other galaxies. These results for the peculiar galaxy IC 1459 and its black hole add an interesting data point for studies on the nature of galactic nuclei.

Hubble Space Telescope observations of nearby radio-loud early-type galaxies

We present and analyse HST/WFPC2 broad- and narrow-band observations of the central regions of 19 nearby radio-loud early-type galaxies. Together with two more galaxies they form a complete sample of Fanaroff & Riley Type I galaxies. We obtained V- and I-band images and narrow-band images centered on the HalphaNII emission lines. We use archival data for six galaxies. nWe describe the data reduction, give isophotal fits and analyse the central emission-line gas and dust distributions. Our main conclusions are the following. Although obscuration by dust inhibits a direct determination of central cusp slopes, the data suggest most but not all galaxies have shallow cores. Dust is detected in all but two galaxies. There is a wide variety of central dust morphologies, ranging from central disks to lanes and irregular distributions. The analysis suggests the difference between disks and lanes is intrinsic and not due to different viewing angles. Central emission-line gas is detected in all galaxies. Extended low-surface-brightness emission is always associated with the dust features. In a subsequent paper we will present a detailed analysis of the relation between these central properties and the nuclear activity.

The Black Hole in IC 1459 from Hubble Space Telescope Observations of the Ionized Gas Disk

The peculiar elliptical galaxy IC 1459 (MV = -21.19, D = 16.5 h-1 Mpc) has a fast counterrotating stellar core, stellar shells and ripples, a blue nuclear point source, and strong radio core emission. We present results of a detailed Hubble Space Telescope study of IC 1459, and in particular its central gas disk, aimed at constraining the central mass distribution. We obtained WFPC2 narrowband imaging centered on the Hα+[N II] emission lines to determine the flux distribution of the gas emission at small radii, and we obtained FOS spectra at six aperture positions along the major axis to sample the gas kinematics. We construct dynamical models for the Hα+[N II] and Hβ kinematics that include a supermassive black hole and in which the stellar mass distribution is constrained by the observed surface brightness distribution and ground-based stellar kinematics. In one set of models we assume that the gas rotates on circular orbits in an infinitesimally thin disk. Such models adequately reproduce the observed gas fluxes and kinematics. The steepness of the observed rotation velocity gradient implies that a black hole must be present. There are some differences between the fluxes and kinematics for the various line species that we observe in the wavelength range 4569–6819 A. Species with higher critical densities generally have a flux distribution that is more concentrated toward the nucleus, and have observed velocities that are higher. This can be attributed qualitatively to the presence of the black hole. There is some evidence that the gas in the central few arcsec has a certain amount of asymmetric drift, and we therefore construct alternative models in which the gas resides in collisionless cloudlets that move isotropically. All models are consistent with a black hole mass in the range M• = 1–4 × 108 M⊙, and models without a black hole are always ruled out at high confidence. The implied ratio of black holes mass to galaxy mass is in the range 0.4–1.5 × 10-3, which is not inconsistent with results obtained for other galaxies. These results for the peculiar galaxy IC 1459 and its black hole add an interesting data point for studies on the nature of galactic nuclei.

The Black Hole in IC 1459 from Hubble Space TelescopeObservations of the IonizedGas DiskBased on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Incorporated, underNASA contract NAS5-26555.

The peculiar elliptical galaxy IC 1459 (MV = -21.19, D = 16.5 h-1 Mpc) has a fast counterrotating stellar core, stellar shells and ripples, a blue nuclear point source, and strong radio core emission. We present results of a detailed Hubble Space Telescope study of IC 1459, and in particular its central gas disk, aimed at constraining the central mass distribution. We obtained WFPC2 narrowband imaging centered on the Hα+[N II] emission lines to determine the flux distribution of the gas emission at small radii, and we obtained FOS spectra at six aperture positions along the major axis to sample the gas kinematics. We construct dynamical models for the Hα+[N II] and Hβ kinematics that include a supermassive black hole and in which the stellar mass distribution is constrained by the observed surface brightness distribution and ground-based stellar kinematics. In one set of models we assume that the gas rotates on circular orbits in an infinitesimally thin disk. Such models adequately reproduce the observed gas fluxes and kinematics. The steepness of the observed rotation velocity gradient implies that a black hole must be present. There are some differences between the fluxes and kinematics for the various line species that we observe in the wavelength range 4569–6819 A. Species with higher critical densities generally have a flux distribution that is more concentrated toward the nucleus, and have observed velocities that are higher. This can be attributed qualitatively to the presence of the black hole. There is some evidence that the gas in the central few arcsec has a certain amount of asymmetric drift, and we therefore construct alternative models in which the gas resides in collisionless cloudlets that move isotropically. All models are consistent with a black hole mass in the range M• = 1–4 × 108 M⊙, and models without a black hole are always ruled out at high confidence. The implied ratio of black holes mass to galaxy mass is in the range 0.4–1.5 × 10-3, which is not inconsistent with results obtained for other galaxies. These results for the peculiar galaxy IC 1459 and its black hole add an interesting data point for studies on the nature of galactic nuclei.

Hubble SpaceTelescope Observations of Nearby Radio-LoudEarly-Type Galaxies*

We present and analyse HST/WFPC2 broad- and narrow-band observations of the central regions of 19 nearby radio-loud early-type galaxies. Together with two more galaxies they form a complete sample of Fanaroff & Riley Type I galaxies. We obtained V- and I-band images and narrow-band images centered on the HalphaNII emission lines. We use archival data for six galaxies. nWe describe the data reduction, give isophotal fits and analyse the central emission-line gas and dust distributions. Our main conclusions are the following. Although obscuration by dust inhibits a direct determination of central cusp slopes, the data suggest most but not all galaxies have shallow cores. Dust is detected in all but two galaxies. There is a wide variety of central dust morphologies, ranging from central disks to lanes and irregular distributions. The analysis suggests the difference between disks and lanes is intrinsic and not due to different viewing angles. Central emission-line gas is detected in all galaxies. Extended low-surface-brightness emission is always associated with the dust features. In a subsequent paper we will present a detailed analysis of the relation between these central properties and the nuclear activity.

Hubble SpaceTelescope Observations of Nearby Radio-LoudEarly-Type GalaxiesBased on observations with the NASA/ESA HubbleSpace Telescope obtained at the Space Telescope Science Institute,which is operated by the Association of Universities for Research inAstronomy, Incorporated, under NASA contract NAS5-26555.

We present and analyse HST/WFPC2 broad- and narrow-band observations of the central regions of 19 nearby radio-loud early-type galaxies. Together with two more galaxies they form a complete sample of Fanaroff & Riley Type I galaxies. We obtained V- and I-band images and narrow-band images centered on the HalphaNII emission lines. We use archival data for six galaxies. nWe describe the data reduction, give isophotal fits and analyse the central emission-line gas and dust distributions. Our main conclusions are the following. Although obscuration by dust inhibits a direct determination of central cusp slopes, the data suggest most but not all galaxies have shallow cores. Dust is detected in all but two galaxies. There is a wide variety of central dust morphologies, ranging from central disks to lanes and irregular distributions. The analysis suggests the difference between disks and lanes is intrinsic and not due to different viewing angles. Central emission-line gas is detected in all galaxies. Extended low-surface-brightness emission is always associated with the dust features. In a subsequent paper we will present a detailed analysis of the relation between these central properties and the nuclear activity.