Issue |
A&A
Volume 661, May 2022
The Early Data Release of eROSITA and Mikhail Pavlinsky ART-XC on the SRG mission
|
|
---|---|---|
Article Number | A16 | |
Number of page(s) | 17 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/202141641 | |
Published online | 18 May 2022 |
The eROSITA Final Equatorial-Depth Survey (eFEDS)
Presenting the demographics of X-ray emission from normal galaxies
1
NASA Goddard Space Flight Center,
Code 662,
Greenbelt,
MD
20771,
USA
e-mail: nvulic@uwo.ca
2
Department of Astronomy, University of Maryland,
College Park,
MD
20742-2421,
USA
3
Center for Research and Exploration in Space Science and Technology, NASA/GSFC,
Greenbelt,
MD
20771,
USA
4
Eureka Scientific, Inc.,
2452 Delmer Street, Suite 100,
Oakland,
CA
94602-3017,
USA
5
Department of Physics and Astronomy, Johns Hopkins University,
3400 N. Charles Street,
Baltimore,
MD
21218,
USA
6
Max-Planck-Institut für extraterrestrische Physik,
Gießenbachstraße 1,
85748
Garching,
Germany
7
Department of Physics, University of Maryland Baltimore County,
Baltimore,
MD
21250,
USA
8
Physics Department & Institute of Theoretical & Computational Physics, University of Crete,
71003
Heraklion,
Crete,
Greece
9
Harvard-Smithsonian Center for Astrophysics,
60 Garden Street,
Cambridge,
MA
02138,
USA
10
Institute of Astrophysics, Foundation for Research and Technology-Hellas,
GR-71110
Heraklion,
Greece
11
Dr. Karl Remeis-Observatory and Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg,
Sternwartstr. 7,
96049
Bamberg,
Germany
12
Department of Physics and Astronomy, University of Southampton,
Southampton
SO17 1BJ,
UK
13
Leibniz Institut für Astrophysik,
An der Sternwarte 16,
14482
Potsdam,
Germany
14
Institut für Astronomie und Astrophysik Tübingen, Universität Tübingen,
Sand 1,
72076
Tübingen,
Germany
Received:
25
June
2021
Accepted:
21
September
2021
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.
Key words: surveys / galaxies: starburst / galaxies: dwarf / galaxies: statistics / X-rays: galaxies / X-rays: binaries
© ESO 2022
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