Steep-spectrum AGN in eROSITA Final Equatorial-Depth Survey (eFEDS): Their host galaxies and multi-wavelength properties

Iwasawa K, Liu T, Boller T, Buchner J, Li J, Kawaguchi T, Nagao T, Terashima Y, Toba Y, Silverman JD, Arcodia R, Dauser T, Krumpe M, Nandra K, Wilms J (2024)

Publication Type: Journal article

Publication year: 2024

Journal

Astronomy & Astrophysics EDP Sciences

Book Volume: 684

Article Number: A153

DOI: 10.1051/0004-6361/202348311

Abstract

We selected sources with a steep soft-X-ray-band spectrum with a photon index of F > 2.5 - measured by eROSITA on board the Spectrum-Röntgen-Gamma (SRG) - from the eFEDS AGN catalogue as candidates of highly accreting supermassive black holes, and investigated their multi-wavelength properties. Among 601 bright AGN with 0.2-5 keV counts of greater than 100, 83 sources (≈14%) are classified as steep-spectrum sources. These sources have typical 0.5-2 keV luminosities of LSX ≈ 1044 erg s-1 and the majority of them are found at redshifts below z = 1. In comparison with sources with flatter spectra, these sources have, on average, a UV (or optical) to 2 keV luminosity ratio that is larger by ~0.3 dex and bluer optical-to-UV continuum emission. They also appear to be radio quiet based on the detection rate in the FIRST and VLASS surveys. Their host galaxies - at least in the redshift range of z = 0.2 - 0.8, where the AGN- galaxy decomposition results from the Subaru Hyper Suprime-Cam imaging are available - tend to be late-type and have smaller stellar masses (M∗ ~ 1010.5~M⊙) than those of sources with flatter spectra. These properties are similar to those found in nearby narrow-line Seyfert 1 galaxies, in agreement with the picture that they are AGN with elevated accretion rates and are in the early growth phase of black hole and galaxy co-evolution. However, the steep-spectrum sources are not exclusively narrow-line Seyfert 1 galaxies; indeed many are broad-line Seyfert 1 galaxies, as found by a catalogue search. This suggests that these steep-spectrum sources may be black holes generally with high accretion rates but of a wide mass range, including a few objects emitting at LSX ≥ 1045 erg s-1, of which black hole masses can be close to 109 M⊙

Authors with CRIS profile

Thomas Dauser Dr.Karl-Remeis-Sternwarte Bamberg, Astronomisches Institut Jörn Wilms Professur für Astronomie und Astrophysik

Involved external institutions

Universitat de Barcelona (UB) / University of Barcelona ES Spain (ES) Max-Planck-Institut für extraterrestrische Physik (MPE) / Max Planck Institute for Extraterrestrial Physics DE Germany (DE) University of Illinois at Urbana-Champaign US United States (USA) (US) Onomichi City University JP Japan (JP) Ehime University / 愛媛大学 JP Japan (JP) University of Tokyo JP Japan (JP) Leibniz Institute for Astrophysics Potsdam / Leibniz-Institut für Astrophysik Potsdam DE Germany (DE)

How to cite

APA:

Iwasawa, K., Liu, T., Boller, T., Buchner, J., Li, J., Kawaguchi, T.,... Wilms, J. (2024). Steep-spectrum AGN in eROSITA Final Equatorial-Depth Survey (eFEDS): Their host galaxies and multi-wavelength properties. Astronomy & Astrophysics, 684. https://doi.org/10.1051/0004-6361/202348311

MLA:

Iwasawa, K., et al. "Steep-spectrum AGN in eROSITA Final Equatorial-Depth Survey (eFEDS): Their host galaxies and multi-wavelength properties." Astronomy & Astrophysics 684 (2024).

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