Fading AGN Candidates: AGN Histories and Outflow Signatures^∗

Abstract

We consider the energy budgets and radiative history of eight fading AGN, identified from an energy shortfall between the requirements to ionize very extended (radius > 10 kpc) ionized clouds and the luminosity of the nucleus as we view it directly. All show evidence of significant fading on ≈ 50, 000-year timescales. We explore the use of minimum ionizing luminosity Q ion derived from photoionization balance in the brightest pixels in Hα at each projected radius. Tests using presumably constant Palomar-Green (PG) QSOs, and one of our targets with detailed photoionization modeling, suggest that we can derive useful histories of individual AGN, with the caveat that the minimum ionizing luminosity is always an underestimate and subject to uncertainties about fine structure in the ionized material. These consistency tests suggest that the degree of underestimation from the upper envelope of reconstructed Q ion values is roughly constant for a given object and therefore does not prevent such derivation. The AGN in our sample show a range of behaviors, with rapid drops and standstills; the common feature is a rapid drop in the last ≈ 2 × 10 4 years before the direct view of the nucleus. The e-folding timescales for ionizing luminosity are mostly in the thousands of years, with a few episodes as short as 400 years. In the limit of largely obscured AGN, we find additional evidence for fading from the shortfall between even the lower limits from recombination balance and the maximum luminosities derived from from infrared fluxes. We compare these long-term light curves, and the occurrence of these fading objects among all optically identified AGN, to simulations of AGN accretion; the strongest variations on these timespans are seen in models with strong and local (parsec-scale) feedback. We present Gemini integral-field optical spectroscopy, which shows a very limited role for outflows in these ionized structures. While rings and loops of emission, morphologically suggestive of outflow, are common, their kinematic structure shows some to be in regular rotation. UGC 7342 exhibits local signatures of outflows < 300 km s −1 , largely associated with very diffuse emission, and possibly entraining gas in one of the clouds seen in HST images. Only in the Teacup AGN do we see outflow signatures of order 1000 km s −1 . In contrast to the extended emission regions around many radio-loud AGN, the clouds around these fading AGN consist largely of tidal debris being externally illuminated but not displaced by AGN outflows.

An Interacting Galaxy Pair at the Origin of a Light Echo

“…Similar time-scales are obtained by Keel et al (2015) (∼ 5×10 4 yr) and Keel et al (2017) (∼ 2 × 10 4 yr). It is of course impossible to predict whether the ShaSS 073-622 system will turn into the kind of objects belonging to the family of GBs or HV-like objects, but it appears that all ingredients are already in place.…”

Quasar Feedback in the Ultraluminous Infrared Galaxy F11119+3257: Connecting the Accretion Disk Wind with the Large-scale Molecular Outflow

“…Given the well-known short-and long-term variability of F11119+3257 (T15) and AGN in general (e.g., Schawinski et al 2010Schawinski et al , 2015Keel et al 2012aKeel et al , 2012bKeel et al , 2015Keel et al , 2017, it is perhaps surprising to find in Table 4 that the time-averaged mass, momentum, and energy outflow rates derived from the CO data are similar to the time-averaged values derived from the OH data. This suggests that the efficiency of the quasar at driving the molecular outflow on large scales in F11119+3257 has been relatively stable over the past few × 10 6 yrs.…”

Ionized gas outflow signatures in SDSS-IV MaNGA active galactic nuclei

“…A particularly intriguing possibility is that some of the AGN candidates are relic AGN. In such objects the nuclear activity subsided some time ago, but the photo-ionisation signatures at large distances persist for 10 4 − 10 5 years due to light-travel delays and radiative timescales of emitting gas (Lintott et al 2009;Schawinski et al 2015b;Sartori et al 2016;Keel et al 2017). In relic AGN, kinematic signatures of previous AGN activity may be longer lived than nuclear photoionisation signatures (Ishibashi & Fabian 2015).…”