The MAGellanic Inter-Cloud (MAGIC) project – II. Slicing up the Bridge

Abstract

The origin of the gas in between the Magellanic Clouds (MCs), known as the Magellanic Bridge, has always been the subject of controversy. To shed light into this, we present the results from the MAGellanic Inter-Cloud II (MAGIC II) project aimed at probing the stellar populations in 10 large fields located perpendicular to the main ridge-line of H I in the Inter-Cloud region. We secured these observations of the stellar populations in between the MCs using the WFI (Wide Field Imager) camera on the 2.2 m telescope in La Silla. Using colour-magnitude diagrams, we trace stellar populations across the Inter-Cloud region. In good agreement with MAGIC I, we find significant intermediate-age stars in the Inter-Cloud region as well as young stars of a similar age to the last pericentre passage in between the MCs (∼200 Myr ago). We show here that the young, intermediate-age and old stars have distinct spatial distributions. The young stars correlate well with the H I gas suggesting that they were either recently stripped from the Small Magellanic Cloud (SMC) or formed in situ. The bulk of intermediate-age stars are located mainly in the Bridge region where the H I column density is higher, but they are more spread out than the young stars. They have very similar properties to stars located ∼2 kpc from the SMC centre, suggesting that they were tidally stripped from this region. Finally, the old stars extend to some 8 kpc from the SMC supporting the idea that all galaxies have a large extended metal-poor stellar halo.

The Properties of the Magellanic Bridge Based on OGLE IV RR Lyrae Variables

“…By examining the Bridge between the LMC and SMC, we gain insight into the structure of the system and their history of interactions. Studies have shown that the young and intermediate age stars in the MB have a clumpy, non-uniform distribution (Noël et al 2013(Noël et al , 2015Skowron et al 2014). The asymmetric locations of these stellar populations suggest that either they formed in situ or were stripped from the LMC or the SMC during an interaction.…”

“…Such an interaction is thought to have triggered star formation in the MB, as pointed out by Grondin, Demers & Kunkel (1992); Mizuno et al (2006); Skowron et al (2014); Chen et al (2014). However, based on their ages, the young stars could have either formed in situ in the MB, or formed in the SMC and been tidally stripped from it in the past ∼ 200 Myr (Noël et al 2015). Skowron et al (2014) find that although the young stellar populations in the MB tend to be concentrated near the SMC, there is evidence for a continuity of a young population throughout the Bridge region, consistent with the HI densities.…”

“…Some studies suggest that interactions between the LMC and SMC stem from multiple pericentric passages of the galaxies as they orbit our Galaxy, with the inter-galactic features resulting from tidal stripping and ram pressure (Růžička, Theis & Palouš 2009). Other work suggests that the Magellanic clouds have only begun interacting with each other and the Milky Way during two recent encounters, estimated to have occurred ∼2 Gyr and ∼250 Myr ago (Kallivayalil et al 2013;Noël et al 2015).…”

The VMC Survey - XXIV. Signatures of tidally stripped stellar populations from the inner Small Magellanic Cloud

“…Earlier studies by Demers & Battinelli (1998) and Harris (2007) did not find the presence of intermediate-age/old stellar populations in fields centred on the H i ridge line of the MB. However, recent studies (Bagheri, Cioni & Napiwotzki 2013;Noël et al 2013Noël et al , 2015Skowron et al 2014) found evidence of the presence of intermediate-age/old stellar populations in the central and western regions of the MB.…”

“…These authors suggested that it is the tidally stripped stellar counterpart of the H i in the MB. From their analysis of a few fields in the MB, Noël et al (2013Noël et al ( , 2015 found from the synthetic colour-magnitude diagram (CMD) fitting technique that the intermediate-age population in the MB has similar properties to stars in the inner ∼ 2.5 kpc region of the SMC and suggested that they were tidally stripped from the inner SMC region. Meanwhile, Skowron et al (2014), who studied a more complete region of the MB, explained the presence of intermediate-age stars as the overlapping haloes of the MCs.…”