The eROSITA Final Equatorial Depth Survey (eFEDS)

We present one of the largest uniform optical spectroscopic surveys of X-ray selected sources to date that were observed as a pilot study for the Black Hole Mapper (BHM) survey. The BHM program of the Sloan Digital Sky Survey (SDSS)-V is designed to provide optical spectra for hundreds of thousands of X-ray selected sources from the SRG/eROSITA all-sky survey. This significantly improves our ability to classify and characterise the physical properties of large statistical populations of X-ray emitting objects. Our sample consists of 13 079 sources in the eROSITA eFEDS performance verification field, 12 011 of which provide reliable redshifts from 0 ≲ z ≤ 5.8. The vast majority of these objects were detected as point-like sources (X-ray flux limit F 0.5 − 2 keV ≳ 6.5 × 10 −15 erg/s/cm 2 ) and were observed for about 20 years with fibre-fed SDSS spectrographs. After including all available redshift information for the eFEDS sources from the dedicated SDSS-V plate programme and archival data, we visually inspected the SDSS optical spectra to verify the reliability of these redshift measurements and the performance of the SDSS pipeline. The visual inspection allowed us to recover reliable redshifts (for 99% of the spectra with a signal-to-noise ratio of > 2) and to assign classes to the sources, and we confirm that the vast majority of our sample consists of active galactic nuclei (AGNs). Only ∼3% of the eFEDS/SDSS sources are Galactic objects. We analysed the completeness and purity of the spectroscopic redshift catalogue, in which the spectroscopic completeness increases from 48% (full sample) to 81% for a cleaner, brighter ( r AB < 21.38) sample that we defined by considering a high X-ray detection likelihood, a reliable counterpart association, and an optimal sky coverage. We also show the diversity of the optical spectra of the X-ray selected AGNs and provide spectral stacks with a high signal-to-noise ratio in various sub-samples with different redshift and optical broad-band colours. Our AGN sample contains optical spectra of (broad-line) quasars, narrow-line galaxies, and optically passive galaxies. It is considerably diverse in its colours and in its levels of nuclear obscuration.

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Publication Details

Journal
Astronomy and Astrophysics
Published
2025-04-24
DOI
https://doi.org/10.1051/0004-6361/202554372
Citations
2
Primary Topic
Astronomy and Astrophysical Research
Type
article
Field-Weighted Citation Impact
2.38
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article

The eROSITA Final Equatorial Depth Survey (eFEDS)

J. Buchner, C. A. Negrete, M. Salvato, C. Pizarro et al.
2 citations
Astronomy and Astrophysics
Astronomy and Astrophysical Research
2.38
article

The eROSITA Final Equatorial Depth Survey (eFEDS)

J. Buchner, C. A. Negrete, M. Salvato, C. Pizarro, W. N. Brandt, B. Musiimenta, Sophia G. H. Waddell, T. Miyaji, Juna A. Kollmeier, F. E. Bauer, A. Malyali, Y. P. Shen, S.F. Anderson, P.J. Green, J. Ider-Chitham, Kaike Pan, G. Lamer, J. Wolf, Catarina Aydar, R. Arcodia, Joseph N. Burchett, Johan Comparat, Anton M. Koekemoer, Y. Díaz, Qingling Ni, Dmitry Bizyaev, Carolina Andonie, T. Dwelly, M. Krumpe, T. Urrutia, A. Georgakakis, L. Hernández-García, Jonathan R. Trump, K. Nandra, Michael R. Blanton, Kevin R. Covey, Sean J. Morrison, Pulak K. Chakraborty, José Sánchez-Gallego, M. Brusa, A. Schwope, Tingting Liu, D. P. Schneider, Dong Wook Kim, A. Merloni, Boris T. Gänsicke, C. Ricci, H. Ibarra
article en
2 citations

Abstract

We present one of the largest uniform optical spectroscopic surveys of X-ray selected sources to date that were observed as a pilot study for the Black Hole Mapper (BHM) survey. The BHM program of the Sloan Digital Sky Survey (SDSS)-V is designed to provide optical spectra for hundreds of thousands of X-ray selected sources from the SRG/eROSITA all-sky survey. This significantly improves our ability to classify and characterise the physical properties of large statistical populations of X-ray emitting objects. Our sample consists of 13 079 sources in the eROSITA eFEDS performance verification field, 12 011 of which provide reliable redshifts from 0 ≲ z ≤ 5.8. The vast majority of these objects were detected as point-like sources (X-ray flux limit F 0.5 − 2 keV ≳ 6.5 × 10 −15 erg/s/cm 2 ) and were observed for about 20 years with fibre-fed SDSS spectrographs. After including all available redshift information for the eFEDS sources from the dedicated SDSS-V plate programme and archival data, we visually inspected the SDSS optical spectra to verify the reliability of these redshift measurements and the performance of the SDSS pipeline. The visual inspection allowed us to recover reliable redshifts (for 99% of the spectra with a signal-to-noise ratio of > 2) and to assign classes to the sources, and we confirm that the vast majority of our sample consists of active galactic nuclei (AGNs). Only ∼3% of the eFEDS/SDSS sources are Galactic objects. We analysed the completeness and purity of the spectroscopic redshift catalogue, in which the spectroscopic completeness increases from 48% (full sample) to 81% for a cleaner, brighter ( r AB < 21.38) sample that we defined by considering a high X-ray detection likelihood, a reliable counterpart association, and an optimal sky coverage. We also show the diversity of the optical spectra of the X-ray selected AGNs and provide spectral stacks with a high signal-to-noise ratio in various sub-samples with different redshift and optical broad-band colours. Our AGN sample contains optical spectra of (broad-line) quasars, narrow-line galaxies, and optically passive galaxies. It is considerably diverse in its colours and in its levels of nuclear obscuration.

Astronomy and AstrophysicsVol. 698
Openalex Percentile: Top 12%
Astronomy and Astrophysical Research
2.38
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