EROSITAwiki: EcProposal_DemkeSDSS

EroAGN EC Proposal Delvin Demke

• Proposed: 25.03.2026
• Changed: 13/04/2026 by Johannes Buchner

This project was initiated within SDSS and the EC request extends to all SDSS-only participants.

Scientific Proposal

The aim of the project is to combine SDSS data on an X-ray-selected AGN sample (largely based on the SPIDERS programme in SDSS), with eROSITA observations to study the presences of outflows in AGN.

Active Galactic Nuclei (AGNs) are among the most powerful engines in the Universe. A cen- tral open question is how accretion physics, obscuration, and feedback are intertwined in shaping these systems. In Demke et al. (in prep), we were able to detect a weak negative cor- relation between X-ray weakness (relative to mid-infrared luminosity via eROSITA and WISE) and the [O III] outflow strength (via SDSS) in quasars. We aim to investigate the physical ori- gin of this correlation, in particular whether it is driven by obscuration effects associated with outflows or by intrinsic changes in the X-ray emission. For this project, we make use of the eROSITA and SDSS-V DL1 (IPL-3) data products, which provide X-ray fluxes in the 0.2–2.3 keV band. The updated catalogue increases the sample size to over 30,000 quasars with high-quality SDSS spectra and an eROSITA detection likelihood >20.

To quantify X-ray weakness, it is essential to derive intrinsic rest-frame 2–10 keV luminosi- ties. To derive intrinsic rest-frame 2–10 keV luminosities, it is necessary to constrain both the spectral shape and absorption. This cannot be achieved reliably using catalogue fluxes alone and requires spectral fitting of the eRASS5 data. We therefore propose to use eRASS5 spectra to determine basic spectral parameters, namely the photon index (Γ) and hydrogen column density (N_H), through uniform spectral fitting. These parameters will allow us to compute intrinsic X-ray luminosities for the full sample.

For completeness, the original proposal text (before limitation in sample), is attached EC_DemkeSDSS.pdf.

Required data, supporting datasets and/or tools

We request X-ray spectral analyses of the all-sky survey data products for 30,000 sources inside IPL-4 with z<1.

The distribution of the work (as relates to the proprietary eROSITA data) within the project is planned to be as follows. JB will the only one to access the eROSITA data directly, perform- ing the spectral extraction, as well as spectral fitting. However, in order to discuss the spec- tral analysis, intermediate results such as plots of spectra and modelling will be shared with Delvin Demke and Dominika Wylezalek, who are the external leads of this project. Higher- level results, such as potential plots for the publication, may be circulated among the other SDSS-only ECs.

Expected Outcome

These results will be part of the master’s thesis of Delvin Demke.

Expected duration of the project

The Thesis will be submitted by October 2026.

==== Responsibility of the eROSITA member sponsor of the project ==== JB, as sponsoring member, will ensure that eROSITA data are accessed and used for the purposes of this project only, and not in a way that would negatively affect the scientific interests of existing collaboration members.

List of Potential Collaborators within eROSITA_DE

Mara Salvato, Catarina Aydar, Andrea Merloni, Peter Boorman, Carolina Andonie