Steep-spectrum AGN in eROSITA Final Equatorial-Depth Survey (eFEDS): Their host galaxies and multi-wavelength properties
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| Autores principales: | , , , , , , , , , , , , , , |
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| Formato: | Preprint |
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2024
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| author | Iwasawa, K. Liu, T. Boller, Th. Buchner, J. Li, J. Kawaguchi, T. Nagao, T. Terashima, Y. Toba, Y. Silverman, J. D. Arcodia, R. Dauser, Th. Krumpe, M. Nandra, K. Wilms, J. |
| author_facet | Iwasawa, K. Liu, T. Boller, Th. Buchner, J. Li, J. Kawaguchi, T. Nagao, T. Terashima, Y. Toba, Y. Silverman, J. D. Arcodia, R. Dauser, Th. Krumpe, M. Nandra, K. Wilms, J. |
| contents | We selected sources with a steep soft-X-ray-band spectrum with a photon index larger than 2.5 -- measured by eROSITA on board the Spectrum-Roentgen-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 L(SX) ~ 1e44 erg/s 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 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 L(SX)>1e45 erg/s, of which black hole masses can be close to 10^9 M_sun. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2402_14135 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Steep-spectrum AGN in eROSITA Final Equatorial-Depth Survey (eFEDS): Their host galaxies and multi-wavelength properties Iwasawa, K. Liu, T. Boller, Th. Buchner, J. Li, J. Kawaguchi, T. Nagao, T. Terashima, Y. Toba, Y. Silverman, J. D. Arcodia, R. Dauser, Th. Krumpe, M. Nandra, K. Wilms, J. Astrophysics of Galaxies High Energy Astrophysical Phenomena We selected sources with a steep soft-X-ray-band spectrum with a photon index larger than 2.5 -- measured by eROSITA on board the Spectrum-Roentgen-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 L(SX) ~ 1e44 erg/s 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 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 L(SX)>1e45 erg/s, of which black hole masses can be close to 10^9 M_sun. |
| title | Steep-spectrum AGN in eROSITA Final Equatorial-Depth Survey (eFEDS): Their host galaxies and multi-wavelength properties |
| topic | Astrophysics of Galaxies High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2402.14135 |