The Incidence of Active Galactic Nuclei in Pure Disk Galaxies: The Spitzer View

Details The Incidence of Active Galactic Nuclei in Pure Disk Galaxies: The Spitzer View The Incidence of Active Galactic Nuclei in Pure Disk Galaxies: The Spitzer View

2009-08-13

arxiv.org/abs/0908.1820v1

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

17 pages, 8 figures, accepted for publication in ApJ

Scientific paper

We have conducted a high-resolution spectroscopic study using Spitzer of 18 bulgeless (Sd/Sdm) galaxies that show no definitive signatures of nuclear activity in their optical spectra. This is the first systematic mid-IR search for weak or hidden AGNs in a statistically significant sample of bulgeless disk galaxies. Based on the detection of the high-ionization [NeV] line, we report the discovery of an AGN in one out of the 18 galaxies in the sample. This galaxy, NGC 4178, is a nearby edge-on Sd galaxy, which likely hosts a prominent nuclear star cluster (NSC). The bolometric luminosity of the AGN inferred from the [NeV] luminosity is ~ 8e41 ergs/s. This is almost two orders of magnitude greater than the luminosity of the AGN in NGC 4395, the best studied AGN in a bulgeless disk galaxy. Assuming that the AGN in NGC 4178 is radiating below the Eddington limit, the lower mass limit for the black hole is ~ 6e3M_sun. The fact that none of the other galaxies in the sample shows any evidence for an AGN demonstrates that while the AGN detection rate based on mid-IR diagnostics is high (30-40%) in optically quiescent galaxies with pseudobulges, it drops drastically in Sd/Sdm galaxies. Our observations therefore confirm that AGNs in completely bulgeless disk galaxies are not hidden in the optical but truly are rare. 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 possess a NSC in order to host an AGN. While the presence of a NSC appears to be a requirement for hosting an AGN in bulgeless galaxies, neither the properties of the 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 galaxy therefore remains unknown.

Affiliated with

Also associated with

No associations

Rating

The Incidence of Active Galactic Nuclei in Pure Disk Galaxies: The Spitzer View does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with The Incidence of Active Galactic Nuclei in Pure Disk Galaxies: The Spitzer View, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Incidence of Active Galactic Nuclei in Pure Disk Galaxies: The Spitzer View will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-699954