The tidal tails of NGC 2298

Abstract

We present an implementation of the matched-filter technique to detect tidal tails of globular clusters. The method was tested using SDSS data for the globular cluster Palomar 5 revealing its well known tidal tails. We also ran a simulation of a globular cluster with a tidal tail where we successfully recover the tails for a cluster at the same position and with the same characteristics of NGC 2298. Based on the simulation we estimate that the matched-filter increases the contrast of the tail relative to the background of stars by a factor of 2.5 for the case of NGC 2298. We also present the photometry of the globular cluster NGC 2298 using the MOSAIC2 camera installed on the CTIO 4m telescope. The photometry covers ~ 3deg2 reaching V ~ 23. A fit of a King profile to the radial density profile of NGC 2298 shows that this cluster has a tidal radius of 15.91' \pm 1.07' which is twice as in the literature. The application of the matched-filter to NGC 2298 reveals several extra-tidal structures, including a leading and trailing tail. We also find that NGC 2298 has extra-tidal structures stretching towards and against the Galactic disk, suggesting strong tidal interaction. Finally, we assess how the matched-filter performs when applied to a globular cluster with and without mass segregation taken into account. We find that disregarding the effects of mass segregation may significantly reduce the detection limit of the matched-filter

More on the structure of tidal tails

“…Such features have been observed in numerical simulations before (Dehnen et al 2004; Capuzzo Dolcetta et al 2005; Montuori et al 2007), but have not yet been interpreted as result of epicyclic motion. The streaks may also be the true nature of the multiple tidal tails observed for Galactic satellites like NGC 288, Willman 1 and NGC 2298 (Leon et al 2000; Willman et al 2006; Balbinot et al 2011).…”

“…Variations of the stellar density along the tails have been observed for extended tidal streams such as the Milky Way globular cluster Palomar 5 (Odenkirchen et al 2003). For other Milky Way satellites, such as NGC 288, Willman 1 and NGC 2298, multiple tidal tails have been observed (Leon, Meylan & Combes 2000; Willman et al 2006; Balbinot et al 2011). This substructure should also be somehow linked to the dynamical past of the satellite.…”

Digging deeper into the Southern skies: a compact Milky Way companion discovered in first-year Dark Energy Survey data

“…In the context of astronomy, it has been used to detect low-density features and populations in imaging data (Szabo et al 2011;Rockosi et al 2002). We here use it to search for new star clusters and dwarf galaxies following on the work by Balbinot et al (2011).…”

Exploring the reality of density substructures in the Palomar 5 stellar stream

“…First, to bring out the stars that could belong to the Pal 5 stream, we select the stars from the SDSS DR9 with dereddened g0 < 22.5 and that follow the colour criterion of Odenkirchen et al (2003). We then derive a matched-filter map, which is based on the recipe outlined in Balbinot et al (2011). Since the distance variation of the stream is negligible (Ibata et al 2016), the CMD of the stars along the stream does not change significantly.…”

“…Since the Pal 5 stream is very thin, we construct the spatial distribution of the background (γ bg in Balbinot et al 2011) by fitting a double Legendre polynomial on the borders of the SDSS footprint, represented by the grey regions in Figure 5, since these regions have small chance to be contaminated by the tidal tails. However, in contrast to Balbinot et al (2011), we assume that the CMD of the background does not change over the region of the sky inhabited by the Pal 5 stream. This assumption is reasonable given that the stream lies at high Galactic latitude, and is oriented parallel to the Galactic plane.…”