Smash 1: A Very Faint Globular Cluster Disrupting in the Outer Reaches of the Lmc?

Abstract

We present the discovery of a very faint stellar system, SMASH 1, that is potentially a satellite of the Large Magellanic Cloud. Found within the Survey of the MAgellanic Stellar History (SMASH), SMASH 1 is a compact ( r 9.1 pc h 3.4 5.9) and very low luminosity ( M) stellar system that is revealed by its sparsely populated main sequence and a handful of red giant branch candidate member stars. The photometric properties of these stars are compatible with a metal-poor ( Fe H 2.2 [ ] ) and old (13 Gyr) isochrone located at a distance modulus of ∼18.8, i.e., a distance of 57 kpc. Situated at 11°. 3 from the LMC in projection, its three-dimensional distance from the Cloud is 13 kpc, consistent with a connection to the LMC, whose tidal radius is at least 16 kpc. Although the nature of SMASH 1 remains uncertain, its compactness favors it being a stellar cluster and hence dark-matter free. If this is the case, its dynamical tidal radius is only 19 pc at this distance from the LMC, and smaller than the system's extent on the sky. Its low luminosity and apparent high ellipticity ( 0.62 0.21 0.17 ) with its major axis pointing toward the LMC may well be the tell-tale sign of its imminent tidal demise.

The Pristine Dwarf-Galaxy survey – II. In-depth observational study of the faint Milky Way satellite Sagittarius II

“…Among the 123 globular clusters presented here, the properties of 116 were extracted from Harris (1996) catalog, revised in 2010. For the remaining ones (Kim 1, Kim 2, Kim 3, Laevens 1, Balbinot 1, Munoz 1 and SMASH 1) parameters of the discovery publications were used , , Kim et al (2016), Laevens et al (2014), Balbinot et al (2013), Muñoz et al (2012) and Martin et al (2016b)). Globular cluster metallicity spread measurements are taken from Willman & Strader (2012) and references therein: Carretta et al (2006, 2011), Cohen et al (2010, Gratton et al (2007), Johnson & Pilachowski (2010), and Marino et al (2011).…”

“…We use our MC photometry to refine the structural properties of Sgr II previously studied by L15 and M18 and determine its main stellar properties through a CMD and spatial distribution fitting procedure. The formalism of this analysis is detailed in Martin et al (2016a) and L18. Though the main steps will be briefly detailed below, we refer the reader to these two references for more details.…”

“…To avoid aliasing effects, especially at the bright end of our models where the photometric uncertainties are unrealistically low, we add 0.01 in quadrature to the photometric uncertainties. Finally, each PDF is degraded to the completeness of the data estimated by following the method of Martin et al (2016a). The 50 per cent completeness is reached at g0 ∼ 24.2 and i0 ∼ 23.4 mag.…”

Stellar Cluster Candidates Discovered in the Magellanic System

“…We preferred those reprojected images which have been corrected for distortion, etc, and are better astrometrically fixed. Finally, we filtered g images with exposure times longer than 267 sec; the deepest images obtained by the DECam (Martin et al 2016;Drlica-Wagner et al 2016;Kim et al 2016). Then we run the DAOFIND routine within the DAOPHOT suite of programs (Stetson et al 1990) to produce photometric catalogs of each ∼ 2.2 deg FOV image down to g ∼ 24.0 mag.…”

“…As stellar clusters are considered, some recent outcomes have shown that there are still a substantial number of extreme low luminosity stellar clusters undetected in the wider MS periphery and the MW halo (Kim et al 2015;Pieres et al 2016;Martin et al 2016). Furthermore, streams of gas and stars that might harbor stellar clusters have also been detected Belokurov et al 2016;Deason et al 2016).…”