The Incidence of Active Galactic Nuclei in Pure Disk Galaxies: The Spitzer View - Astrophysics > Cosmology and Nongalactic AstrophysicsReportar como inadecuado




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Abstract: We have conducted a high-resolution spectroscopic study using Spitzer of 18bulgeless Sd-Sdm galaxies that show no definitive signatures of nuclearactivity in their optical spectra. This is the first systematic mid-IR searchfor weak or hidden AGNs in a statistically significant sample of bulgeless diskgalaxies. Based on the detection of the high-ionization NeV line, we reportthe discovery of an AGN in one out of the 18 galaxies in the sample. Thisgalaxy, NGC 4178, is a nearby edge-on Sd galaxy, which likely hosts a prominentnuclear star cluster NSC. The bolometric luminosity of the AGN inferred fromthe NeV luminosity is ~ 8e41 ergs-s. This is almost two orders of magnitudegreater than the luminosity of the AGN in NGC 4395, the best studied AGN in abulgeless disk galaxy. Assuming that the AGN in NGC 4178 is radiating below theEddington limit, the lower mass limit for the black hole is ~ 6e3M sun. Thefact that none of the other galaxies in the sample shows any evidence for anAGN demonstrates that while the AGN detection rate based on mid-IR diagnosticsis high 30-40% in optically quiescent galaxies with pseudobulges, it dropsdrastically in Sd-Sdm galaxies. Our observations therefore confirm that AGNs incompletely bulgeless disk galaxies are not hidden in the optical but truly arerare. Of the three Sd galaxies with AGNs known so far, all have prominent NSCs,suggesting that in the absence of a well-defined bulge, the galaxy must possessa NSC in order to host an AGN. While the presence of a NSC appears to be arequirement for hosting an AGN in bulgeless galaxies, neither the properties ofthe NSC nor those of the host galaxy appear exceptional in late-type AGN hosts.The recipe for forming and growing a central black hole in a bulgeless galaxytherefore remains unknown.



Autor: S. Satyapal, T. Boeker, W. Mcalpine, M. Gliozzi, N. P. Abel, T. Heckman

Fuente: https://arxiv.org/







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