The Sources of Excitation of the Optical Emission in X-ray-Selected Galaxies

• Applicant: Dr. Nadiia Pulatova
• Subject Area: Astrophysics and Astronomy
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 527508779

The physical processes behind the multi-wavelength emission from galaxies, especially those with Active Galactic Nuclei, are not fully understood and remain an important topic of research. The X-ray emission from galaxies is most likely to come from the hot parts of accretions disks. But when the accretion disk around the central supermassive black hole (SMBH) dominates, accretion processes in compact binaries dominate is not clear. Most galaxies that have X-ray emission also show optical emission lines (Balmer lines, oxygen, nitrogen, sulfur, etc.) lines, emitted mostly by ionized gas. This emission may be powered by (X-ray-emitting) accretion or by hot stars, with their UV radiation and their winds. Here we propose a project to quantify in which X-ray detected galaxies the optical emission lines are powered by the X-ray emitting sources, or by star formation; and, if the former is the case, whether it is the SMBH or X-ray binaries that cause the excitation. Our project will be based on new and emerging spectroscopy from SDSS-V of an unprecedented set of X-ray-selected galaxies from the 1-st eROSITA hemisphere data release. This data release will reflect the initial results from the first imaging all-sky survey in the medium energy X-ray range up to 10 keV, with an unprecedented spectral and angular resolution. In preliminary work, based on SDSS DR17, we found an indication that the optical line-ratio diagnostics in the so-called BPT-diagram, (whether a galaxy is AGN or HII depends on the X-ray/Hα ratio). In the proposed project, we plan to continue our investigation with all advantages from the SDSS-V phase and eROSITA mission. SDSS-V will be the first large-area ’’quick-look’’ survey of eROSITA sources, making this a timely project and a unique data set. Work program: • Checking individual galaxies and re-analyse their SDSS spectra using more sophisticated emission line models of eROSITA X-ray sources in eFEDS.• For galaxies with Broad Emission Lines we will separate the narrow and broad components of the line and we will find the position of these galaxies on BPT plots according to their narrow emission line components. • We will carefully check all individual galaxies with peculiarities, for example, unusual positions on the BPT diagrams, and check their optical and X-ray spectra.• For some individual galaxies we will estimate the central Black Hole masses • For the brightest X-ray sources, we will analyze the X-ray spectra with some basic models and investigate the relation between X-ray spectral properties and optical emission lines • We will investigate the connection of X-ray hardness ratio with optical emission lines parameters.

• DFG Programme: WBP Position