6 research outputs found
The Apparent Host Galaxy of PKS 1413+135: HST, ASCA and VLBA Observations
PKS 1413+135 (z=0.24671) is one of very few radio-loud AGN with an apparent
spiral host galaxy. Previous authors have attributed its nearly exponential
infrared cutoff to heavy absorption but have been unable to place tight limits
on the absorber or its location in the optical galaxy. In addition, doubts
remain about the relationship of the AGN to the optical galaxy given the
observed lack of re-emitted radiation. We present new HST, ASCA and VLBA
observations which throw significant new light on these issues. The HST
observations reveal an extrremely red color (V-H = 6.9 mag) for the active
nucleus of PKS 1413+135, requiring both a spectral turnover at a few microns
due to synchrotron aging and a GMC-sized absorber. We derive an intrinsic
column N_H = 4.6^{+2.1}_{-1.6} times 10^{22}cm^{-2} and covering fraction f =
0.12^{+0.07}_{-0.05}. As the GMC is likely in the disk of the optical galaxy,
our sightline is rather unlikely (P ~ 2 times 10^{-4}). The properties of the
GMC typical of GMCs in our own galaxy. The HI absorber appears centered 25
milliarcseconds away from the nucleus, while the X-ray and nearly all of the
molecular absorbers must cover the nucleus, implying a complicated geometry and
cloud structure, with a molecular core along our line of sight to the nucleus.
Interestingly, the HST/NICMOS data require the AGN to be decentered relative to
the optical galaxy by 13 +/- 4 milliarcseconds. This could be interpreted as
suggestive of an AGN location far in the background compared to the optical
galaxy, but it can also be explained by obscuration and/or nuclear structure,
which is more consistent with the observed lack of multiple images.Comment: 27 pages, 8 figures; accepted to A