PKS 1814-637: a powerful radio-loud AGN in a disk galaxy

Abstract

We present a detailed study of PKS 1814-637, a rare case of powerful radio source (P 5 GHz = 4.1 × 10 25 W Hz −1 ) hosted by a disk galaxy. Optical images have been used to model the host galaxy morphology confirming it to be dominated by a strong (and warped) disk component that is observed close to edge-on to the line of sight. This is the first radio galaxy found to reside in a disk dominated galaxy with radio luminosity equivalent to powerful FRII objects. At radio wavelengths, PKS 1814-637 is about 480 pc in diameter and it is classified as a compact steep spectrum (CSS) source; such sources are usually considered to be radio sources observed in the early stages of their evolution. However, the optical and mid-IR spectroscopic properties of PKS1814-637 show more in common with Seyfert galaxies than they do with radio galaxies, with the detection of H 2 , and PAH emission features, along with HI and silicate absorption features, providing evidence for a rich ISM which is likely to be related to the disk morphology of the host galaxy. We argue that the interaction between the radio plasma and the rich ISM in this and similar objects may have boosted their radio emission, allowing them to more easily enter flux limited samples of radio sources. In this case, PKS 1814-637 represents a type of "imposter": an intrinsically low power object that is selected in a radio flux limited sample because of the unusually efficient conversion of jet power into radio emission. This would make PKS 1814-637 an extreme example of the effects of jet-cloud interactions in galaxies containing a rich ISM, and perhaps a missing link between radio galaxies and radio-loud Seyfert galaxies. However, it is unlikely that jet-cloud interactions alone can account for the unusually powerful radio emission compared to Seyfert galaxies, and it is probable that the jet in PKS 1814-637 is also intrinsically more powerful than in typical Seyfert galaxies, perhaps due to a higher bulge and black hole mass. The estimated BH mass is indeed higher than the majority of Seyfert galaxies in the local Universe. We speculate that sources similar to PKS1814-637 are likely to be more common at high redshifts, because of the enhanced probability at earlier epochs of triggering radio sources in moderately massive bulges that are also gas-rich.

Compact steep-spectrum sources as the parent population of flat-spectrum radio-loud narrow-line Seyfert 1 galaxies

“…Therefore it is possible that CSS/HERGs are also hosted in disk galaxies, as NLS1s. An example of a disk host for a powerful CSS was found by Morganti et al (2011). Moreover in a very large sample of AGN, Best & Heckman (2012) found that HERGs host galaxies have different properties than those of LERGs and, in particular, these authors found that they are bluer with lower mass, lower 4000 Å break, and a higher star formation rate.…”

Discovery of a Pseudobulge Galaxy Launching Powerful Relativistic Jets

“…systems (e.g., Ledlow et al 1998;Hota et al 2011;Morganti et al 2011;Bagchi et al 2014;Kaviraj et al 2015;Mao et al 2015;Singh et al 2015), and among them, PKS 2004-447 is the only gamma-ray-emitting radio galaxy in which a disky pseudobulge and a stellar bar have been found. Since there is solid observational evidence pointing to the presence of fully developed relativistic jets emanating from PKS2004-447 Schulz et al 2016), it arises that the same spinning black hole conditions that enable the production of prominent relativistic jets can be met, even if non-major merger related black hole fueling mechanisms have ignited the AGN.…”

J1649+2635: a grand-design spiral with a large double-lobed radio source

“…Powerful radio sources that are hosted by spiral and disk-dominated galaxies are known to exist at lowredshift, although to-date there are only a few tens of examples (e.g Morganti et al 2011), most of which are hosted by disk-dominated or lenticular galaxies (e.g. NGC612, Ekers et al 1978).…”