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  The eROSITA Final Equatorial-Depth Survey (eFEDS) - Presenting the demographics of X-ray emission from normal galaxies

Vulic, N., Hornschemeier, A. E., Haberl, F., Basu-Zych, A. R., Kyritsis, E., Zezas, A., et al. (2022). The eROSITA Final Equatorial-Depth Survey (eFEDS) - Presenting the demographics of X-ray emission from normal galaxies. Astronomy and Astrophysics, 661: A16. doi:10.1051/0004-6361/202141641.

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Vulic, N., Author
Hornschemeier, A. E., Author
Haberl, F.1, Author           
Basu-Zych, A. R., Author
Kyritsis, E., Author
Zezas, A., Author
Salvato, M.1, Author           
Ptak, A., Author
Bogdan, A., Author
Kovlakas, K., Author
Wilms, J., Author
Sasaki, M., Author
Liu, T.1, Author           
Merloni, A.1, Author           
Dwelly, T., Author
Brunner, H.1, Author           
Lamer, G., Author
Maitra, C.1, Author           
Nandra, K.1, Author           
Santangelo, A., Author
1High Energy Astrophysics, MPI for Extraterrestrial Physics, Max Planck Society, ou_159890              


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 Abstract: Context. The eROSITA Final Equatorial Depth Survey (eFEDS), completed in survey mode during the calibration and performance verification phase of the eROSITA instrument on Spectrum Roentgen Gamma, delivers data at and beyond the final depth of the 4-yr eROSITA all-sky survey (eRASS:8), f0.5–2 keV = 1.1 × 10−14 erg s−1 cm−2, over 140 deg2. It provides the first view of normal galaxy X-ray emission from X-ray binaries (XRBs) and the hot interstellar medium at the full depth of eRASS:8.
Aims. We used the Heraklion Extragalactic Catalogue (HECATE) of galaxies to correlate with eFEDS X-ray sources and identify X-ray detected normal galaxies. This flux-limited X-ray survey is relatively free from selection effects and enables the study of integrated normal galaxy X-ray emission and its relation to galaxy parameters such as the stellar mass, star formation rate (SFR), and metallicity.
Methods. We cross-correlated 32 646 eFEDS X-ray sources to 1181 HECATE normal galaxies and obtained 94 matches. We classified galaxies as star-forming, early-type, composite, and active galactic nuclei (AGN) using Sloan Digital Sky Survey (SDSS) and Six-degree Field (6dF) optical spectroscopy.
Results. The eFEDS field harbours 37 normal galaxies: 36 late-type (star-forming) galaxies and one early-type galaxy. There are 1.9 times as many normal galaxies as predicted by scaling relations via simulations, with an overabundance of late-type galaxies and a dearth of early-type galaxies. When compared with empirical relations, eFEDS dwarf galaxies with a high specific SFR have elevated LX/SFR at a fixed specific SFR and metallicity, indicating an increase in XRB emission due to low metallicity. We expect that eRASS:8 will detect 12 500 normal galaxies, the majority of which will be star-forming, with the caveat that there are unclassified sources in eFEDS and galaxy catalogue incompleteness issues that could increase the actual number of detected galaxies over these current estimates.
Conclusions. eFEDS observations detected a rare population of galaxies – the metal-poor dwarf starbursts – that do not follow known scaling relations. eRASS is expected to discover significant numbers of these high-redshift analogues, which are important for studying the heating of the intergalactic medium at high redshift. Further investigation of the hot gas emission from normal galaxies and stochastic effects in the dwarf galaxy population are required to constrain their X-ray output.


Language(s): eng - English
 Dates: 2022-05-18
 Publication Status: Published online
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1051/0004-6361/202141641
 Degree: -



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Source 1

Title: Astronomy and Astrophysics
  Other : Astron. Astrophys.
Source Genre: Journal
Publ. Info: Les Ulis Cedex A France : EDP Sciences
Pages: - Volume / Issue: 661 Sequence Number: A16 Start / End Page: - Identifier: ISSN: 1432-0746
ISSN: 0004-6361
CoNE: https://pure.mpg.de/cone/journals/resource/954922828219_1