Computing the space density of X-ray detected blazars in eRASS at 1 < z < 4.5

Previous works constraining blazar space density evolution over time have reported different space

density peaks when detecting blazars in the X-ray versus the radio bands. Understanding this discrep-

ancy is essential if we are wanting to use blazars as tracers of jetted AGN evolution. Using the newly

released eROSITA All-Sky Survey, we generate a sample of X-ray detected blazars spectroscopically

confirmed in the SDSS Quasar Data Release 16 and with radio flux detections in the Very Large Array

Sky Survey (3 GHz) and FIRST (1.4 GHz). We select only the most luminous blazars with luminosities

above log L(2−10 keV) ∼ 45.85 erg s−1 and compute the space density of our sample across redshift

range z = 1.5−4.5. We identify 48 spectroscopically confirmed flat-radio spectrum blazars detected at

2–10 keV. We report, contrarily to previous works, a space density peak at z ≃ 3.0 which suggest the

presence of an evolution of the X-ray and radio properties of blazars —and thus the general population

of jetted AGN— as a function of redshift