Searching for feedback on ionized ISM in quasar host galaxies

Historically it has been challenging to study the stellar and gas components of quasar host galaxies in the local and distant universe. One of the advantages of integral field spectroscopy (IFS) is that we can construct a point-spread-function (PSF) from our observations, not having to rely on PSF constructed from field stars or a PSF library. The combination of IFS with laser guide star adaptive optics (LGS-AO) provides the necessary contrast and angular resolution required to resolve the galaxies that host these behemoth active galactic nuclei (AGN). The broad emission lines and the continuum emission

Figure 1: Three color composite image of ionized gas in the host galaxy of the quasar 3C 29

in quasar arise from parsec scale regions near the SMBH. These scales will always be unresolved in our data, hence summing the data cube over these spectral features can be used to construct a “pure” quasar image. Details of our PSF construction and subtraction procedure can be found in Vayner et al. 2016. For my thesis, I have been conducting a survey of 11 radio-loud quasars with the OSIRIS instrument at the W.M. Keck Observatory.  Example of a type of analysis and results are showcased in the following paragraphs based on findings published in the Astrophysical Journal (Vayner et al. 2017). Figure 1 on the left shows an example of a PSF subtracted image of ionized gas in the host galaxy of 3C 298 constructed by integrating multiple nebular emission.

Figure 2: Velocity dispersion map of ionized gas in the host galaxy of 3C 298 as traced by the nebular emission line [OIII] 500.7 nm. Synchrotron emission from the extended jet is shown with black contours observed with the VLA.
The Goal of our survey is to detect extended outflows that are driven by the quasar, to understand how they may be regulating the star formation properties of the galaxy. As an example, Figure 2 on the right shows a velocity dispersion map of ionized gas in the host galaxy of 3C 298. Location of the quasar jet aligns well with the broadest (velocity dispersion up to 700 km/s) emission, signaling a powerful quasar driven outflows across the host galaxy, with an ionized outflow rate of 1500 Solar masses per year. Over the outflow regions, we see no evidence for narrow Hα emission consistent with star formation, down to a star formation rate density of 0.3 Mkpc2.

We are interested in understanding the sources of ionization (quasar, star formation, or shocks) across each quasar host galaxy. As such our survey targets multiple nebular emission lines (Hβ, [OIII], Hα, [NII] and [SII]) to construct resolved BPT diagrams. Figure 3 shows an example of resolved ionization diagnostics across the host galaxy of 3C 298.

Figure 3: Resolved BPT photoionization diagnostic diagram for the host galaxy of 3C 298. Distinct photoionization regions are color coded to the dominant source of ionization.