{Context. The main element of the observing program of the Spectrum-Roentgen-Gamma orbital observatory is a four-year all-sky survey, in the course of which the entire sky will be scanned eight times. <BR /> Aims: We analyze the statistical properties of active galactic nuclei (AGN) and quasars/quasi-stellar objects (QSOs ) that are expected to be detected in the course of the eROSITA all-sky survey (eRASS). <BR /> Methods: According to the currently planned survey strategy and based on the parameters of the Galactic and extragalactic X-ray background as well as on the results of the recent calculations of the eROSITA instrumental background, we computed a sensitivity map of the eRASS. Using the best available redshift-dependent AGN X-ray luminosity function (XLF), we computed various characteristics of the eRASS AGN sample, such as their luminosity- and redshift distributions, and the brightness distributions of their optical counterparts. <BR /> Results: After four years of the survey, a sky-average sensitivity of about 1 {\times} 10$^{-14 }$ergs$^{-1}$ cm$^{-2}$ will be achieved in the 0.5-2.0 keV band. With this sensitivity, eROSITA is expected to detect about 3 million AGN on the extragalactic sky (|b| {\gt} 10{\deg}). The median redshift of the eRASS AGN will be z {\ap} 1 with approximately 40\% of the objects in the z = 1-2 redshift range. About 10$^{4}$-10$^{5}$ AGN are predicted beyond redshift z = 3 and about 2000-30 000 AGN beyond redshift z = 4, the exact numbers depend on the poorly known behavior of the AGN XLF in the high-redshift and high-luminosity regimes. Of the detected AGN, the brightest 10\% will be detected with more than {\ap}38 counts per point-spread-function (half-energy width), while the faintest 10\% will have fewer than {\ap}9 counts. The optical counterparts of approximately 95\% of the AGN will be brighter than I$_{AB}$ = 22.5 mag. The planned scanning strategy will allow one to search for transient events on a timescale of half a year and a few hours with a 0.5-2.0 keV sensitivity of {\ap}2 {\times} 10$^{-14}$ to {\ap}2 {\times} 10$^{-13 }$ergs$^{-1}$ cm$^{-2}$, respectively. }

### AGN and QSOs in the eROSITA All-Sky Survey. I. Statistical properties

#### Abstract

{Context. The main element of the observing program of the Spectrum-Roentgen-Gamma orbital observatory is a four-year all-sky survey, in the course of which the entire sky will be scanned eight times.
Aims: We analyze the statistical properties of active galactic nuclei (AGN) and quasars/quasi-stellar objects (QSOs ) that are expected to be detected in the course of the eROSITA all-sky survey (eRASS).
Methods: According to the currently planned survey strategy and based on the parameters of the Galactic and extragalactic X-ray background as well as on the results of the recent calculations of the eROSITA instrumental background, we computed a sensitivity map of the eRASS. Using the best available redshift-dependent AGN X-ray luminosity function (XLF), we computed various characteristics of the eRASS AGN sample, such as their luminosity- and redshift distributions, and the brightness distributions of their optical counterparts.
Results: After four years of the survey, a sky-average sensitivity of about 1 {\times} 10$^{-14 }$ergs$^{-1}$ cm$^{-2}$ will be achieved in the 0.5-2.0 keV band. With this sensitivity, eROSITA is expected to detect about 3 million AGN on the extragalactic sky (|b| {\gt} 10{\deg}). The median redshift of the eRASS AGN will be z {\ap} 1 with approximately 40\% of the objects in the z = 1-2 redshift range. About 10$^{4}$-10$^{5}$ AGN are predicted beyond redshift z = 3 and about 2000-30 000 AGN beyond redshift z = 4, the exact numbers depend on the poorly known behavior of the AGN XLF in the high-redshift and high-luminosity regimes. Of the detected AGN, the brightest 10\% will be detected with more than {\ap}38 counts per point-spread-function (half-energy width), while the faintest 10\% will have fewer than {\ap}9 counts. The optical counterparts of approximately 95\% of the AGN will be brighter than I$_{AB}$ = 22.5 mag. The planned scanning strategy will allow one to search for transient events on a timescale of half a year and a few hours with a 0.5-2.0 keV sensitivity of {\ap}2 {\times} 10$^{-14}$ to {\ap}2 {\times} 10$^{-13 }$ergs$^{-1}$ cm$^{-2}$, respectively. }
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A. Kolodzig;M. Gilfanov;R. Sunyaev;S. Sazonov;M. Brusa
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11585/229687
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