Identifying RR Lyrae in the ZTF DR3 dataset

TL;DR

This paper presents a comprehensive catalogue of 71,755 RR Lyrae stars from the ZTF DR3 and Gaia EDR3 data, using a multi-step classification pipeline, revealing halo structures and Oosterhoff fraction variations.

Contribution

The paper introduces a new, large RR Lyrae catalogue combining ZTF DR3 and Gaia data with a novel classification pipeline, improving completeness and coverage of the Galactic halo.

Findings

Catalogue contains 71,755 RR Lyrae stars with high completeness and purity.

Reveals known halo over-densities like Virgo and Hercules-Aquila.

Finds variation in Oosterhoff fractions across the Galactic halo.

Abstract

We present a RR Lyrae (RRL) catalogue based on the combination of the third data release of the Zwicky Transient Facility (ZTF DR3) and \textit{Gaia} EDR3. We use a multi-step classification pipeline relying on the Fourier decomposition fitting to the multi-band ZTF light curves and random forest classification. The resulting catalogue contains 71,755 RRLs with period and light curve parameter measurements and has completeness of 0.92 and purity of 0.92 with respect to the SOS \textit{Gaia} DR2 RRLs. The catalogue covers the Northern sky with declination $\geq -28^\circ$, its completeness is $\gtrsim 0.8$ for heliocentric distance $\leq 80$~kpc, and the most distant RRL at 132~kpc. Compared with several other RRL catalogues covering the Northern sky, our catalogue has more RRLs around the Galactic halo and is more complete at low Galactic latitude areas. Analysing the spatial distribution of RRL in the catalogue reveals the previously known major over-densities of the Galactic halo, such as the Virgo over-density and the Hercules-Aquila Cloud, with some evidence of an association between the two. We also analyse the Oosterhoff fraction differences throughout the halo, comparing it with the density distribution, finding increasing Oosterhoff I fraction at the elliptical radii between 16 and 32 kpc and some evidence of different Oosterhoff fractions across various halo substructures.