AGN Feedback and Outflows
Many observations in the past decades have now made it clear that the active (quasar) phase of black hole evolution can have profound effects on the formation of the galaxy. One idea – quasar feedback – seeks to simultaneously explain several major observational findings and open issues in galaxy formation theory such as the observed relations between black holes and their hosts. However, specific examples of quasar-driven feedback in action have been surprisingly hard to come by, and it is far from clear how exactly the coupling between accretion energy and matter on galactic scales is established. Understanding the mechanism, the physics of quasar feedback and its impact on the quasar host galaxy has been the subject of intense observational effort. Luminous type-2 quasars in which the glow from the central black hole is obscured by dust are ideal targets for studying the host galaxies of powerful quasars and the quasars’ effect on galaxy evolution. Such feedback appears to ubiquitous luminous obscured quasars where quasi-spherical, high velocity ionized nebulae have been found.
Our group is making substantial progress in this direction by combining unique data sets using different techniques such as resolved kinematic information from IFU observations, photometry and classical spectroscopy from several space-based observatories (such as HST, WISE and Herschel) and ground-based observatories (Gemini, SDSS) that will allow us to better measure and quantify the galaxy-wide impact of actively accreting black holes. Furthermore, we have been developing novel techniques to determine the geometry of the galaxies’ nuclear regions where the black holes are located. These measurements of structure and geometry of winds driven by active black holes hold the potential to reshape our understanding of galaxy formation.
MaNGA is a new survey that began in July 2014 as part of SDSS-IV with the aim of obtaining integral field spectroscopy for an unprecedented sample of 10,000 nearby galaxies, among which several hundred AGN. The unprecedented sample size and coverage of luminosity, redshift and morphology ranges, allows us to map and measure spatially resolvd gas kinematics and probe both the launching quasar winds and the impact of the wind on the host galaxy.
(see Wylezalek et al. 2017, 2016a,b, Obied et al. 2016, Zakamska et al. 2015, Wylezalek et al. in prep.)
Galaxy Clusters at high redshift
Emerging from the cosmic web, galaxy clusters are the most massive gravitationally bound structures in the universe. Thought to have begun their assembly at 2 < z < 3, clusters provide insights into the growth of large-scale structure as well as the physics that drives galaxy evolution. But how and when did the most massive galaxies assemble their stellar mass? When did they stop forming stars? How did they acquire their observed morphologies that we observe today? These remain outstanding questions that we have been tackling with various projects in the last years.
We have made a major contribution to this field with a 400 hr targeted Warm Spitzer program surveying 421 radio-loud AGN at 1.3 < z < 3.2 across the full sky, Clusters Around Radio- Loud AGN (CARLA). Extensive literature over several decades shows that powerful radio-loud AGN preferentially reside in overdense environments. From this survey, we have identified a very promising sample of ∼ 200 galaxy cluster candidates, the largest high-z cluster candidate sample to date. Using the newest generation of instruments on the VLT and Keck observatories and with HST, we have been confirming several of our candidates already.
This large (proto-)cluster sample also allows us for the first time at these redshifts, to systematically measure the build-up of mass in these systems. The results are consistent with cosmic downsizing and as these clusters were all found in the vicinity of radio-loud AGN — which have proven to be preferentially located in massive dark matter halos in the richest environments at high redshift — they may therefore be older and more evolved systems than the general protocluster population.
Clusters can also be used as powerful probes of cosmology. The single detection of one, very massive galaxy cluster at high redshift could challenge cosmological models which give firm predictions on the number of massive clusters that should exist in the universe at certain redshifts. The Massive and Distant Clusters of WISE Survey (MaDCoWS) is a new IR-selected galaxy cluster survey based on the all-sky catalogs of the Wide-field Infrared Survey Explorer (WISE). The combination of WISE infrared and SDSS optical photometry allows us to robustly isolate galaxy clusters at z > 1 in the northern hemisphere. With MaDCoWs, we have successfully found a number of massive clusters at z > 1 and are working on several projects regarding masses, gas/baryon fractions, morphologies to understand the population of the most massive structures in the universe.
(see e.g. Wylezalek et al. 2013a,b, 2014, Brodwin et al. 2015, Gonzalez et al. 2015)