Probing the Outer Galactic halo with RR Lyrae from the Catalina Surveys

TL;DR

This study analyzes over 12,000 RR Lyrae stars from the Catalina Surveys to map the Milky Way's outer halo, revealing detailed structures and comparing observations with galaxy formation models.

Contribution

It provides the largest volume survey of RR Lyrae stars in the Milky Way's outer halo, with precise period, magnitude, and velocity measurements, and compares these with N-body models of the Sagittarius stream.

Findings

Mapped the Sagittarius tidal streams crossing the sky at 20-60 kpc.

Achieved high-precision periods with sigma = 0.002%.

Identified discrepancies between observed structures and model predictions.

Abstract

We present the analysis of 12227 type-ab RR Lyrae found among the 200 million public lightcurves in the Catalina Surveys Data Release 1 (CSDR1). These stars span the largest volume of the Milky Way ever surveyed with RR Lyrae, covering ~20,000 square degrees of the sky (0 < RA < 360, -22 < Dec < 65 deg) to heliocentric distances of up to 60kpc. Each of the RR Lyrae are observed between 60 and 419 times over a six-year period. Using period finding and Fourier fitting techniques we determine periods and apparent magnitudes for each source. We find that the periods at generally accurate to sigma = 0.002% by comparison with 2842 previously known RR Lyrae and 100 RR Lyrae observed in overlapping survey fields. We photometrically calibrate the light curves using 445 Landolt standard stars and show that the resulting magnitudes are accurate to ~0.05 mags using SDSS data for ~1000 blue horizontal branch stars and 7788 of the RR Lyrae. By combining Catalina photometry with SDSS spectroscopy, we analyze the radial velocity and metallicity distributions for > 1500 of the RR Lyrae. Using the accurate distances derived for the RR Lyrae, we show the paths of the Sagittarius tidal streams crossing the sky at heliocentric distances from 20 to 60 kpc. By selecting samples of Galactic halo RR Lyrae, we compare their velocity, metallicity, and distance with predictions from a recent detailed N-body model of the Sagittarius system. We find that there are some significant differences between the distances and structures predicted and our observations.