2026-04-18T04:04:13Zhttps://recercat.cat/oai/request

oai:recercat.cat:2445/2182602026-04-03T01:10:06Zcom_2072_1057col_2072_478904col_2072_478917

00925njm 22002777a 4500 dc Iwasawa, Kazushi author Liu, T. author Boller, T. author Buchner, J. author Li, Jun author Kawaguchi, T. author Nagao, T. author Terashima, Y. author Toba, Y. author Silverman, John D. author Arcodia, R. author Dauser, T. author Krumpe, M. author Nandra, K. author Wilms, J. author 2025-01-30T17:21:24Z 2025-01-30T17:21:24Z 2024 2025-01-30T17:21:24Z We selected sources with a steep soft-X-ray-band spectrum with a photon index of Γ > 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⊙. Galàxies Astronomia de raigs X Aixecaments topogràfics Galaxies X-ray astronomy Surveys Steep-spectrum AGN in eROSITA Final Equatorial-Depth Survey (eFEDS): Their host galaxies and multi-wavelength properties