We analyze the statistical properties of normal galaxies to be detected in the all-sky survey
by the eROSITA X-ray telescope of the Spectrum-X-Gamma observatory. With the current configura-
tion and parameters of the eROSITA telescope, the sensitivity of a 4-year-long all-sky survey will be
≈10 −14 erg s −1 in the 0.5–2 keV band. This will allow ∼(1.5–2) × 10 4 normal galaxies with approximately
the same contribution of star-forming and elliptical galaxies to be detected. All galaxies of the X-ray
survey are expected to enter into the existing far-infrared (IRAS) or near-infrared (2MASS) catalogs; the
sample of star-forming galaxies will be approximately equivalent in sensitivity to the sample of star-forming
galaxies in the IRAS catalog of infrared sources. Thus, a large homogeneous sample of normal galaxies
with measured X-ray, near-infrared, and far-infrared fluxes will be formed. About 90% of the galaxies in
the survey are located within ∼200–400 Mpc. A typical (most probable) galaxy will have a luminosity
log L X ∼ 40.5–41.0, will be located at a distance of ∼70–90 Mpc, and will be either a star-forming galaxy
with a star formation rate of ∼20M
yr −1 whose X-ray emission is produced by ultraluminous X-ray
sources (ULXs) or an elliptical galaxy with a mass log M ∗ ∼ 11.3 emitting through to a hot interstellar gas.
The galaxies within 35 Mpc will collectively contain ∼10 2 ULXs with luminosities log L X > 40, ∼80% of
which will be the only luminous source in the galaxy. Thus, although the angular resolution of the eROSITA
telescope is too low for the luminosity function of compact sources in galaxies to be studied in detail, the
survey data will allow one to investigate its bright end and, possibly, to impose constraints on the maximum
luminosity of ULXs.

EB00000003818K

Available

• Normal Galaxies in the All-Sky Survey by the eROSITA X-ray Telescope of the Spectrum-X-Gamma Observatory