Is Crater II disrupting?

TL;DR

This study confirms the presence of tidal tails around Crater II galaxy, revealing detailed RR Lyrae star distributions and gradients, indicating ongoing disruption and providing insights into its structure and stellar populations.

Contribution

The paper provides the first detailed mapping of Crater II's tidal tails using deep multi-band and multi-epoch observations, identifying RR Lyrae stars and their spatial gradients.

Findings

Confirmed tidal tails extending from Crater II.

Detected 97 variable stars, including 37 RR Lyrae.

Identified a strong distance gradient in RR Lyrae stars.

Abstract

Crater~II (CraII) is a very intriguing, low-surface brightness and extended galaxy in the vicinity of our Milky Way. Motivated by its huge area and the number of RR Lyrae stars (RRLS) detected near to its core, we performed a follow-up campaign to get deep multi-band ($g,i$) and multi-epoch DECam observations in the outskirts of CraII, covering up to 8$r_h$ in the North-East direction and up to 13$r_h$ in the South-West direction (spanning almost 10 degr in the sky across the galaxy). We confirm the existence of tails coming out from CraII. In our survey, we detected a total of 97 periodic variable stars, of which 46 are CraII members [37 RRLS and 7 anomalous Cepheids (AC)]. The RRLS show a strong gradient in distance of 3.7~kpc/deg, which follows the relation: $d (\rm {kpc}) = (-3.70\pm 0.21)\, \xi' + (116.2 \pm 0.32)$ (where $\xi'$ is the planar coordinate rotated to fit the CraII tails). We also found an indication that the gradient in distance in the distant part of the near-side tail (North-East) may be less steep than it is in the inner $5\deg$. The leading tail also displays a significant over-density of RRLS located $\sim 3.25$ deg from the center of CraII. Despite covering a smaller area than previous works, our deeper photometry has allowed us to unveil more variable stars in the region and better define the tidal tails of CraII.