The space density of the various classes of cataclysmic variables ( CVs ) could only be weakly constrained in the past .
Reasons were the small number of objects in complete X-ray flux-limited samples and the difficulty to derive precise distances to CVs .
The former limitation still exists .
Here the impact of Gaia parallaxes and implied distances on the space density of X-ray selected complete , flux-limited samples is studied .
The samples are described in the literature , those of non-magnetic CVs are based on ROSAT ( RBS – ROSAT Bright Survey & NEP – North Ecliptic Pole ) , that of the Intermediate Polars stems from Swift/BAT .
All CVs appear to be rarer than previously thought , although the new values are all within the errors of past studies .
Upper limits at 90 % confidence for the space densities of non-magnetic CVs are \rho _ { RBS } < 1.1 \times 10 ^ { -6 } pc ^ { -3 } and \rho _ { RBS + NEP } < 5.1 \times 10 ^ { -6 } pc ^ { -3 } for an assumed scale height of h = 260 pc and \rho _ { IPs } < 1.3 \times 10 ^ { -7 } pc ^ { -3 } for the long-period Intermediate Polars at a scale height of 120 pc .
Most of the distances to the IPs were under-estimated in the past .
The upper limits to the space densities are only valid in the case where CVs do not have lower X-ray luminosities than the lowest-luminosity member of the sample .
These results need consolidation by larger sample sizes , soon to be established through sensitive X-ray all-sky surveys to be performed with eROSITA on the Spektrum-X-Gamma mission .