arXiv subjects

J. L. Donley

Publications and source records attributed to J. L. Donley.

21 records · Page 2Linked to original sources

arXiv2003

A Hubble Space Telescope Survey of Extended [OIII]5007A Emission in a Far-Infrared Selected Sample of Seyfert Galaxies: Observations

We present a Hubble Space Telescope (HST) survey of extended [OIII] emission for a sample of 60 Seyfert galaxies (22 Seyfert 1's and 38 Seyfert 2's), selected based on their far infrared properties. The observations for 42 of these galaxies were done in a snapshot survey with WFPC2. The remaining 18 were obtained from the HST archive, most of which were observed with the same configuration. These observations cover 68% of the objects in the sample defined by Kinney et al. (2000), and create a valuable dataset for the study of the Narrow Line Region (NLR) properties of Seyfert galaxies. In this paper, we present the details of the observations, reductions, and measurements. We also discuss the extended structure of individual sources, and the relation of this emission to the radio and host galaxy morphology. We also address how representative the subsample of [O III]-imaged galaxies is of the entire sample, and possible selection effects that may affect this comparison of the properties of Seyfert 1 and Seyfert 2 galaxies.

astro-ph↗

arXiv2003

A Hubble Space Telescope Survey of Extended [OIII]5007A Emission in a Far-Infrared Selected Sample of Seyfert Galaxies: Results

We present the results of a Hubble Space Telescope (HST) survey of extended [OIII] emission in a sample of 60 nearby Seyfert galaxies (22 Seyfert 1's and 38 Seyfert 2's), selected by mostly isotropic properties. The comparison between the semi major axis size of their [OIII] emitting regions (R_Maj) shows that Seyfert 1's and Seyfert 2's have similar distributions, which seems to contradict Unified Model predictions. We discuss possible ways to explain this result, which could be due either to observational limitations or the models used for the comparison with our data. We show that Seyfert 1 Narrow Line Regions (NLR's) are more circular and concentrated than Seyfert 2's, which can be attributed to foreshortening in the former. We find a good correlation between the NLR size and luminosity, following the relation R_Maj propto L([OIII])^0.33, which is flatter than a previous one found for QSO's and Seyfert 2's. We discuss possible reasons for the different results, and their implications to photoionization models. We confirm previous results which show that the [OIII] and radio emission are well aligned, and also find no correlation between the orientation of the extended [OIII] emission and the host galaxy major axis. This agrees with results showing that the torus axis and radio jet are not aligned with the host galaxy rotation axis, indicating that the orientation of the gas in the torus, and not the spin of the black hole, determine the orientation of the accretion disk, and consequently the orientation of the radio jet.

astro-ph↗

arXiv2002

Large-Amplitude X-ray Outbursts from Galactic Nuclei: A Systematic Survey Using ROSAT Archival Data

In recent years, luminous X-ray outbursts with variability amplitudes as high as ~ 400 have been serendipitously detected from a small number of active and inactive galaxies. These outbursts may result from the tidal disruptions of stars by supermassive black holes as well as accretion-disk instabilities. In order to place the first reliable constraints on the rate of such outbursts in the Universe and test the stellar tidal disruption hypothesis, we have performed a systematic and complete survey for them by cross-correlating ROSAT All-Sky Survey (RASS) and pointed PSPC data. We have detected five galaxies that were in outburst during the RASS, three of which show no signs of nuclear activity; these objects had been reported on individually in previous studies. After making reasonable corrections for the complicated selection effects, we conclude that the rate of large-amplitude X-ray outbursts from inactive galaxies in the local Universe is ~ 9.1 x 10^{-6} galaxy^{-1} yr^{-1}. This rate is consistent with the predicted rate of stellar tidal disruption events in such galaxies. When only the two active galaxies are considered, we find a rate for active galaxies of ~ 8.5 x 10^{-4} galaxy^{-1} yr^{-1}. In order to place tighter constraints on these rates, additional outbursts must be detected.

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