arXiv subjects

Gijs Verdoes Kleijn

Publications and source records attributed to Gijs Verdoes Kleijn.

44 records · Page 3Linked to original sources

arXiv2006

Understanding the Nuclear Gas Dispersion in Early-Type Galaxies in the Context of Black Hole Demographics

(abridged) We analyze and model HST /STIS observations of a sample of 27 galaxies; 16 Fanaroff & Riley Type I radio galaxies and 11 (more) normal early-type galaxies. We focus here on what can be learned from the nuclear velocity dispersion (line width) of the gas as a complement to the many studies dealing with gas rotation velocities. We find that the dispersion in a STIS aperture of ~0.1''-0.2'' generally exceeds the large-scale stellar velocity dispersion of the galaxy. This is qualitatively consistent with the presence of central BHs, but raises the question whether the excess gas dispersion is of gravitational or non-gravitational origin and whether the implied BH masses are consistent with our current understanding of BH demography(as predicted by the M-sigma relation between BH mass and stellar velocity dispersion). To address this we construct dynamical models for the gas, both thin disk models and models with more general axis ratios and velocity anisotropies. For the normal galaxies the nuclear gas dispersions are adequately reproduced assuming disks around BHs with masses that follow the M-sigma relation. In contrast, the gas dispersions observed for the radio galaxies generally exceed those predicted by any of the models. We attribute this to the presence of non-gravitational motions in the gas that are similar to or larger than the gravitational motions. The non- gravitational motions are presumably driven by the active galactic nucleus (AGN), but we do not find a relation between the radiative output of the AGN and the non-gravitational dispersion. It is not possible to uniquely determine the BH mass for each galaxy from its nuclear gas dispersion. However, for the sample as a whole the observed dispersions do not provide evidence for significant deviations from the M-sigma relation.

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arXiv2005

A dichotomy in radio jet orientations

We examine the relative orientations of radio jets, central dust and stars in low-power (i.e., FR I and FR I/II) radio galaxies. We use the position angles of jet and dust to constrain the three-dimensional angle $θ_{\rm DJ}$ between jet and dust. For galaxies with filamentary dust 'lanes' (which tend to be misaligned with the galaxy major axis) the jet is approximately perpendicular to the dust structure, while for galaxies with elliptical dust distributions (typically aligned with the galaxy major axis) there is a much wider distribution of $θ_{\rm DJ}$. nThe dust ellipses are consistent with being nearly circular thin disks viewed at random viewing angles. The lanes are likely warped, unsettled dust structures. We consider two scenarios to explain the dust/jet orientation dichotomy.

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arXiv2005

The HST view of the nuclear emission line region in low luminosity radio-galaxies

We study the properties of the emission line regions in two samples of low luminosity radio-galaxies (LLRG), focusing on the compact emission line region (CELR) revealed to be a characteristic feature of these objects by HST narrow-band imaging. We find a strong correlation between line and optical continuum nuclear emission, suggesting that the optical cores (most likely of non thermal origin) can be directly associated to the source of ionizing photons, i.e. that we are seeing a jet-ionized narrow line region. A photon budget argument indicates that the optical nuclear sources produce a sufficient photon flux provided that the covering factor of the circum-nuclear gas is rather large, on average ~ 0.3. Analysis of HST images and spectra suggests that the CELR may take the form of a pc-scale, high filling factor, structure, possibly an optically thin torus. Estimates of the CELR mass lead to values as small as 10 - 1000 solar masses and photon counting sets a limit to the BLR mass of 0.01 solar masses. When considered together with the low accretion rate and the tenuous torus structure, a general paucity of gas in the innermost regions of LLRG emerges as the main characterizing difference from more powerful AGN.

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arXiv2005

A dichotomy in the orientation of dust and radio jets in nearby low-power radio galaxies

We examine the properties of central dust in nearby quiescent and active early-type galaxies. The active galaxies are low-power radio galaxies with Fanaroff & Riley Type I or I/II radio jets. We focus on the comparison of the dust distributions in the active and quiescent galaxy samples and the relation between the radio jet and dust orientations. Our main observational conclusions are: (a) radio galaxies contain a higher fraction of regular dust 'ellipses' compared to quiescent galaxies which contain more often irregular dust distributions; (b) the morphology, size and orientation of dust ellipses and lanes in quiescent early-types and active early-types with kpc-scale radio jets is very similar; (c) dust ellipses are aligned with the major axis of the galaxy, dust lanes do not show a preferred alignment except for large (>kpc) dust lanes which are aligned with the minor axis of the galaxy. Dust morphologies can be classified as regular 'ellipses' and filamentary 'lanes'. We show that the dust ellipses are consistent with being nearly circular thin disks viewed at random viewing angles. The lanes are likely warped dust structures, which may be in the process of settling down to become regular disks or are being perturbed by a non-gravitational force. We use the observed dust-jet orientations to constrain the three-dimensional angle $θ_{\rm DJ}$ between jet and dust. For dust-lane galaxies, the jet is approximately perpendicular to the dust structure, while for dust-ellipse galaxies there is a much wider distribution of $θ_{\rm DJ}$. We discuss two scenarios that could explain the dust/jet/galaxy orientation dichotomy. (abridged)

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arXiv2004

A dichotomy in dust-jet orientation in radio galaxies

We have analyzed the position angle (PA) differences between radio jets and dust distributions in the centers of Fanaroff & Riley Type 1 (FRI) radio galaxies. We model the observed PA differences to infer the three-dimensional relative orientation of jet and dust. Our main conclusion is that there is a dichotomy in dust-jet-galaxy orientation both in projection and in three-dimensional space. The orientation dichotomy can explain the contradictory results obtained in previous studies. We briefly mention scenarios that might explain the dichotomy.

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arXiv2003

STIS 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 H-alpha and the dervived 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 and are redshifted from the narrow line components (assuming an origin in H-alpha) by 486 +/- 443 km\s.

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arXiv2002

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

(abridged) We investigate the kinematics of the central gas disk of the radio-loud elliptical galaxy NGC 4335, derived from HST/STIS long-slit spectroscopic observations of Halpha+[NII] along 3 parallel slit positions. The observed mean velocities are consistent with a rotating thin disk. We model the gas disk in the customary way. This sets a 3 sigma upper limit of 10^8 Msun on black hole mass, Mbh. The velocity dispersion at r <0.5'' 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 BH potential then a mass Mbh ~ 6x10^8 Msun 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 (WHT/ISIS) long-slit observation along the galaxy major axis. A two-integral model of the stellar dynamics yields Mbh >= 3x10^9 Msun. However, there is reason to believe that this model overestimates Mbh. Reported correlations between black hole mass and inner stellar velocity dispersion sigma predict Mbh to be >= 5.4x10^8 Msun in NGC 4335. If our standard thin disk modeling of the gas kinematics is valid, then NGC 4335 has an unusually low Mbh for its velocity dispersion. If, on the other hand, this approach is flawed, and provides an underestimate of Mbh, then black hole masses for other galaxies derived from HST gas kinematics with the same assumptions should be treated with caution.

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arXiv2001

Core Radio and Optical Emission in Nearby FR I Radio Galaxies

In this paper we analyze the relation between radio, optical continuum and Halpha+[NII] emission from the cores of a sample of 21 nearby Fanaroff & Riley type I galaxies as observed with the VLBA and HST. The emission arises inside the inner tens of parsec of the galaxies. Core radio emission is observed in 19/20 galaxies, optical core continuum emission is detected in 12/21 galaxies and Halpha+[NII] 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 Halpha+[NII] emission. The tight correlations between radio, optical and Halpha+[NII] core emission constrain the bulk Lorentz factor to gamma ~ 2-5 and gamma =< 2 for a continuous jet and a jet consisting of discrete blobs, respectively, assuming jet viewing angles in the range [30deg,90deg]. 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 AGNs.

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