Galactic Model Parameters and Space Density of Cataclysmic Variables in Gaia Era: New Constraints to Population Models

TL;DR

This study uses Gaia DR3 data to refine the Galactic distribution, scale height, and space density of cataclysmic variables, revealing larger scale heights and a significant discrepancy with population models.

Contribution

It provides new constraints on CV population models by analyzing a large Gaia-based sample and estimating their spatial distribution and luminosity function.

Findings

Scale height of CVs increases near the period gap

Measured space densities are 1-2 orders of magnitude higher than models

Luminosity function of CVs matches that of white dwarfs when scaled by 500 times

Abstract

The spatial distribution, Galactic model parameters and luminosity function of cataclysmic variables (CVs) are established using re-estimated trigonometric parallaxes of {\it Gaia} DR3. The data sample of 1,587 CVs in this study is claimed to be suitable for Galactic model parameter estimation as the distances are based on trigonometric parallaxes and the {\it Gaia} DR3 photometric completeness limits were taken into account when the sample was created. According to the analysis, the scale height of All CVs increases from 248$\pm$2 to 430$\pm$4 pc towards shorter periods near the lower limit of the period gap and suddenly drops to 300$\pm$2 pc for the shortest orbital period CVs. The exponential scale heights of All CVs and magnetic systems are found to be 375$\pm$2 and 281$\pm$3 pc, respectively, considerably larger than those suggested in previous observational studies. The local space density of All CVs and magnetic systems in the sample are $6.8^{+1.3}_{-1.1}\times$10$^{-6}$ and $2.1^{+0.5}_{-0.4}\times10^{-6}$ pc$^{-3}$, respectively. Our measurements strengthen the 1-2 order of magnitude discrepancy between CV space densities predicted by population synthesis models and observations. It is likely that this discrepancy is due to objects undetected by CV surveys, such as the systems with very low $\dot{M}$ and the ones in the period gap. The comparisons of the luminosity function of white dwarfs with the luminosity function of All CVs in this study show that 500 times the luminosity function of CVs fits very well to the luminosity function of white dwarfs. We conclude that the estimations and data sample in this study can be confidently used in further analysis of CVs.