Signatures of AGN Feedback: The Post-SOFIA Era

 A list of archival public SOFIA data on AGN and hosts is available here. 

Executive Summary:

The event presented some of the most impressive SOFIA results relevant to AGN research (and the Milky Way as a likely site of former AGN activity), showing how SOFIA picked up where Spitzer and Herschel had left. Of particular note, talks showed how the FIFI-LS instrument uncovered “anomalous arms” formed by gas shocked by jets from the central black hole, and how HAWC+ polarization mapping revealed new links between magnetic field orientation and radio brightness. Speakers emphasized how the next frontier in IR observations will be addressed by collecting more data on fainter, more obscured, and more distant objects with the ultimate goal of obtaining statistical samples of dust-emitting objects, both in total and polarized infrared light, and studying emission line gas tracers of RL and RQ AGN across cosmic time. This matches results from our questionnaire to the attendees, which emphasized some of the next big questions for AGN-feedback research, including: the modalities of energy-deposition by AGN feedback (timescales, single or multiple events), the energy balance across AGN evolutionary stages (turbulence/ kinetic / radiation/ magnetic), the nature of jets and triggering mechanisms for ignition and quenching, AGN evolutionary models as related to host galaxy properties (relation between obscuration and evolutionary stage), the importance of observational classifications and possible selection biases (reframing radio-loud and radio-quiet concepts, untangling the effect of orientation), and the role of the magnetic fields in AGN accretion and feedback to the host galaxy.  A list of archival public SOFIA data on AGN and hosts is available here.

Considering the current gap in far-IR coverage in the post-SOFIA era (30-200 um), future investigations will be driven by how IR probes will be designed. The need for deep continuum surveys (ideally sensitive enough to see a Milky Way type galaxy at z~2), and possibly on timescales allowing for monitoring, was highlighted as a need to effectively de-bias AGN hosts statistics. While JWST is not a survey mission and may not significantly contribute to such an effort, all-sky spectroscopic surveys such as, LSST, SPHEREx at <5 um that were designed with cosmological goals, could potentially inform FIR surveys. However, highly obscured AGN and cold and dense dust and gas emission will be missing on these surveys. In the radio and submm, the ngVLA and ALMA Wideband Sensitivity Upgrade will greatly enhance our ability to study the cold, molecular gas component and its interaction with AGN jets, but again, these are not survey instruments, so targets for follow-up will need to be identified from FIR survey missions.

Fine-structure line spectroscopy mapping (50-200 um) on a large number of sources is the best way to characterize energy transfer across a galaxy and cooling efficiency; using spectroscopy is a way to alleviate confusion concerns. High spectral resolution (of 10000 order) can also enable component separation on unresolved sources. JWST only covers the spectrum at <30 um, so for a large range of redshifts, this is an area uniquely covered by FIR facilities. It was noted that far-IR is the best way to capture both dust and ionized gas for galaxies at cosmic noon. Another spectroscopic topic is silicate feature tracing, which requires moderate resolution of at least a few hundreds in the MIR.

Polarimetric capabilities in the far-IR must be available to capture the highly wavelength-dependent dust polarization signal at different temperatures in order to investigate the dust composition and formation across cosmic time, as well as study the effect of B-fields in galaxy evolution and star formation activity. Far-IR total and polarized continuum traces outflows and components that would not appear in ALMA data. Some of these investigations could be covered by ground based 1-20 micron polarimeters (for pc-scale mapping), but availability of such instruments on 8m class telescopes is very limited, which could stymie their availability on future large ground or space based missions.

Finally, the need for coordinated collaboration between modeling and observational efforts was noted, as it can help to define the key measurements for testing hypotheses linked to evolution models. This includes for example quantities (physical scales, field amplitudes, temperatures, velocities, magnetic fields) which could inform jet and torus simulations.