Highlights from eROSITA AGN Studies

Speaker

Dr. Johannes Buchner (Max Planck Institute for Extraterrestrial Physics )

Abstract

I will summarize some recent results enabled by the large AGN samples discovered by eROSITA's X-ray all-sky survey. Taken within four days, the pilot survey of eROSITA, eFEDS, revealed a diverse sample of over 20000 AGN. SDSS spectroscopy combined with sophisticated modelling techniques gives access to black hole mass estimates. The new multi-wavelength SED analysis code GRAHSP yields unbiased host stellar mass estimates even for luminous AGN. Combining these techniques reveals over-massive black holes (OMBHs) with 10x larger black hole masses than typical Milky-Way-mass galaxies. The discovery of abundant OMBHs at z<1 is at odds with an interpretation of OMBHs as seed remnants and the tight correlations in galaxy evolution simulations. The subsequent 2 years of data taken in the eROSITA all-sky survey also provided a wealth of X-ray data. Rest-frame X-ray spectral stacks of SDSS quasars revealed the soft excess spectrum as a function of black hole mass, Eddington ratio, X-ray to UV luminosity ratio. The future is bright: With 4MOST, SphereX, Euclid and LSST, AGN multiwavelength & spectroscopic surveys enable precision AGN-galaxy co-evolution studies and can reveal unusual modes of AGN accretion.

A New Population of Spatially Resolved Mid-IR Dual AGNs In the DESI Legacy Survey Fields

Speaker

Dr. Ryan Pfeifle (US Naval Observatory) 

Abstract

Theoretical studies predict that dual AGNs are a critical stage of galaxy merger-driven supermassive black hole growth. Systematic searches for dual AGNs typically target late-stage mergers (<10 kpc nuclear separations) and select AGNs based on optical diagnostics. However, simulations predict both that obscuration can occur early in the merger sequence, and that a significant fraction of dual AGNs can be found beyond 10 kpc. In this talk, we discuss our multiwavelength investigation of spatially resolved mid-IR dual AGN candidates within the Dark Energy Survey Instrument Legacy Survey (DESI LS) fields. 155 candidates were selected based upon their spatially resolved W1-W2 mid-IR colors, and their host galaxies were morphologically identified as galaxy merger candidates using optical DESI LS imaging. 77 candidates have so far been confirmed to reside in galaxy mergers, and roughly 40% of these systems constitute multi-mergers involving three or more galaxies. Optical spectra are revealing a diversity in BPT optical classifications, and 13 mid-IR dual AGNs have so far been confirmed using optical spectra or radio imaging. Over 50% of these dual AGN candidates exhibit projected separations >50 kpc. The diversity in AGN properties and environments identified in this work highlights the importance of multiwavelength selection strategies and analyses in the quest to holistically understand dual AGNs as a population.

Seminar Connection

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