Showing papers by "G. Neugebauer published in 2005"

Far-Infrared Observations of Radio Quasars and FR II Radio Galaxies

Abstract: We report MIPS photometry of 20 radio-loud quasars and galaxies at 24 and 70 μm (and of five at 160 μm). We combine this sample with additional sources detected in the far-infrared by IRAS and ISO for a total of 47 objects, including 23 steep-spectrum type I AGNs: radio-loud quasars and broad-line radio galaxies; and 24 type II AGNs: narrow-line and weak-line FR II radio galaxies. Of this sample, the far-infrared emission of all but 3C 380 appears to be dominated by emission by dust heated by the AGN and by star formation. The AGN appears to contribute more than 50% of the far-infrared luminosity in most of the sources. It is also expected that the material around the nucleus is optically thin in the far-infrared. Thus, the measurements at these wavelengths can be used to test the orientation-dependent unification model. As predicted by the model, the behavior of the sources is consistent with the presence of an obscuring circumnuclear torus; in fact, we find that it may still have significant optical depth at 24 μm. In addition, as expected for the radio-loud quasars, there is a significant correlation between the low-frequency radio (178 MHz) and the 70 μm emission, two presumably isotropic indicators of nuclear activity. This result is consistent with the simple unified scheme. However, there is a population of radio galaxies that are underluminous at 70 μm compared with the radio-loud quasars and hence are a challenge to the simple unified model.

Sub-Arcsecond Mid-Infrared Observations of NGC 6240: Limitations of AGN-Starburst Power Diagnostics

Abstract: In order to examine the relative importance of powerful starbursts and Compton-thick AGNs in NGC 6240, we have obtained mid-infrared images and low-resolution spectra of the galaxy with sub-arcsecond spatial resolution using the Keck Telescopes. Despite the high spatial resolution (~200 pc) of our data, no signature of the hidden AGNs has been detected in the mid-infrared. The southern nucleus, which we show provides 80-90% of the total 8-25 um luminosity of the system, has a mid-infrared spectrum and a mid-/far-infrared spectral energy distribution consistent with starbursts. At the same time, however, it is also possible to attribute up to 60% of the bolometric luminosity to an AGN, consistent with X-ray observations, if the AGN is heavily obscured and emits mostly in the far-infrared. This ambiguity arises because the intrinsic variation of properties among a given galaxy population (e.g., starbursts) introduces at least a factor of a few uncertainty even into the most robust AGN-starburst diagnostics. We conclude that with present observations it is not possible to determine the dominant power source in galaxies when AGN and starburst luminosities are within a factor of a few of each other.

Far Infrared Observations of Radio Quasars and FR II Radio Galaxies

Abstract: We report MIPS photometry of 20 radio-loud quasars and galaxies at 24 and 70 um (and of five at 160 um). We combine this sample with additional sources detected in the far infrared by IRAS and ISO for a total of 47 objects, including 23 steep spectrum Type I AGNs: radio-loud quasars and broad line radio galaxies; and 24 Type II AGNs: narrow line and weak line FR II radio galaxies. Of this sample, the far infrared emission of all but 3C 380 appears to be dominated by emission by dust heated by the AGN and by star formation. The AGN appears to contribute more than 50% of the far infrared luminosity in most of sources. It is also expected that the material around the nucleus is optically thin in the far infrared. Thus, the measurements at these wavelengths can be used to test the orientation-dependent unification model. As predicted by the model, the behavior of the sources is consistent with the presence of an obscuring circumnuclear torus; in fact, we find it may still have significant optical depth at 24 um.In addition, as expected for the radio-loud quasars, there is a significant correlation between the low frequency radio (178 MHz) and the 70 um emission, two presumably isotropic indicators of nuclear activity. This result is consistent with the simple unified scheme. However, there is a population of radio galaxies that are underluminous at 70 um compared with the radio-loud quasars and hence are a challenge to the simple unified model.