NDLI: Fraction of the X-ray selected AGNs with optical emission lines in galaxy groups

Content Provider	Springer Nature Link
Author	Li, Feng Yuan, Qirong Bian, Weihao Chen, Xi Yan, Pengfei
Copyright Year	2017
Abstract	Compared with numerous X-ray dominant active galactic nuclei (AGNs) without emission-line signatures in their optical spectra, the X-ray selected AGNs with optical emission lines are probably still in the high-accretion phase of black hole growth. This paper presents an investigation on the fraction of these X-ray detected AGNs with optical emission-line spectra in 198 galaxy groups at $z<1$ in a rest frame 0.1–2.4 keV luminosity range $41.3 < \log(L_{\mathrm{X}}/\mbox{erg}\,\mbox{s}^{-1}) < 44.1$ within the Cosmological Evolution Survey (COSMOS) field, as well as its variations with redshift and group richness. For various selection criteria of member galaxies, the numbers of galaxies and the AGNs with optical emission lines in each galaxy group are obtained. It is found that, in total 198 X-ray groups, there are 27 AGNs detected in 26 groups. AGN fraction is on average less than $4.6 (\pm1.2)\%$ for individual groups hosting at least one AGN. The corrected overall AGN fraction for whole group sample is less than $0.98 (\pm0.11) \%$ . The normalized locations of group AGNs show that 15 AGNs are found to be located in group centers, including all 6 low-luminosity group AGNs ( $L_{\mbox{ 0.5--2~keV}} < 10^{42.5} \mbox{erg}\,\mbox{s}^{-1}$ ). A week rising tendency with $z$ are found: overall AGN fraction is 0.30–0.43% for the groups at $z<0.5$ , and 0.55–0.64% at $0.5 < z < 1.0$ . For the X-ray groups at $z>0.5$ , most member AGNs are X-ray bright, optically dull, which results in a lower AGN fractions at higher redshifts. The AGN fraction in isolated fields also exhibits a rising trend with redshift, and the slope is consistent with that in groups. The environment of galaxy groups seems to make no difference in detection probability of the AGNs with emission lines. Additionally, a larger AGN fractions are found in poorer groups, which implies that the AGNs in poor groups might still be in the high-accretion phase, whereas the AGN population in rich clusters is mostly in the low-accretion, X-ray dominant phase.
Starting Page	1
Ending Page	9
Page Count	9
File Format	PDF
ISSN	0004640X
Journal	Astrophysics and Space Science
Volume Number	362
Issue Number	4
e-ISSN	1572946X
Language	English
Publisher	Springer Netherlands
Publisher Date	2017-03-30
Publisher Place	Dordrecht
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Galaxies: active Galaxies: nuclei Galaxies: groups Galaxies: field Quasars: emission lines Astrophysics and Astroparticles Astronomy, Observations and Techniques Cosmology Space Sciences (including Extraterrestrial Physics, Space Exploration and Astronautics) Astrobiology
Content Type	Text
Resource Type	Article
Subject	Astronomy and Astrophysics Space and Planetary Science

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1	Ministry of Education (GoI), Department of Higher Education	Sanctioning Authority	https://www.education.gov.in/ict-initiatives
2	Indian Institute of Technology Kharagpur	Host Institute of the Project: The host institute of the project is responsible for providing infrastructure support and hosting the project	https://www.iitkgp.ac.in
3	National Digital Library of India Office, Indian Institute of Technology Kharagpur	The administrative and infrastructural headquarters of the project	Dr. B. Sutradhar bsutra@ndl.gov.in
4	Project PI / Joint PI	Principal Investigator and Joint Principal Investigators of the project	Dr. B. Sutradhar bsutra@ndl.gov.in Prof. Saswat Chakrabarti will be added soon
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