Jacob Noel-Storr

Space telescope imaging spectrograph spectroscopy of the emission-line gas in the nuclei of nearby FR-I galaxies

We present the results of the analysis of a set of medium-resolution spectra, obtained by the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, of the emission-line gas present in the nuclei of a complete sample of 21 nearby, early-type galaxies with radio jets (the UGC FR-I Sample). For each galaxy nucleus we present spectroscopic data in the region of Hα and the derived kinematics. We find that in 67% of the nuclei the gas appears to be rotating and, with one exception, the cases where rotation is not seen are either face-on or have complex central morphologies. We find that in 62% of the nuclei the fit to the central spectrum is improved by the inclusion of a broad component. The broad components have a mean velocity dispersion of 1349 ± 345 km s-1 and are redshifted from the narrow line components (assuming an origin in Hα) by 486 ± 443 km s-1.

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.

Gas disks and supermassive black holes in nearby radio galaxies

We present the initial results of our analysis of line emission produced in gas disks found at the centers of a sample of nearby radio galaxies with radio jets. We obtained data using STIS (The Space Telescope Imaging Spectrograph) at three parallel slit positions on the nucleus of each galaxy. This allows us to map the Hα +( Nii) flux, the gas radial velocity and the velocity dispersion. We found that we cannot rule out a rotating disk model for the gas in any case. We found that for 62% of the galaxies the fit is improved in the nucleus by the inclusion of an additional broad component. By comparing the observed central kinematics to model gas disks we were able to estimate the masses of nuclear black holes in 12 of the sample galaxies.

The nuclei of nearby radio-loud ellipticals

We have observed a complete sample of 21 nearby (D < 70hMpc) Fanaroff & Riley Type I galaxies with HST/WFPC2 and detected dust disks and lanes in 19 of them. The radio jets are roughly perpendicular to the dust which is used to constrain the Doppler boosting factors of the radio jet and cores. The VLBA core flux correlates with the central Hα+[NII] flux which might indicate that the VLBA core is dominated by an isotropic component. Twelve galaxies show nuclear optical sources. We discuss various possible origins for this emission.