CVs and AM CVn binaries eRASS1/Gaia X-match

We construct X-ray luminosity functions that, for the first time, flatten out at LX~10^30^erg/s. We infer average number, mass, and luminosity densities of {rho}_N,CV_=(3.7+/-0.7)x10^-6^pc^-3^, {rho}_M_=(5.0+/-1.0)x10^-5^M_{sun}_^-1^, and {rho}_LX_=(2.3+.-0.4)x10^26^erg/s/M_{sun}_, respectively, in the solar neighborhood. Our uniform selection method also allows us to place meaningful estimates on the space density of AM CVns, {rho}_N,AM-CVn_=(5.5+/-3.7)x10^-7^pc^-3^.

Magnetic CVs and period bouncers make up 35% and 25% of our sample, respectively. This work, through a novel discovery technique, shows that the observed number densities of CVs and AM CVns, as well as the fraction of period bouncers, are still in tension with population synthesis estimates.