A stellar overdensity associated with the Small Magellanic Cloud

Pieres, A and Santiago, B X and Drlica-Wagner, A and Bechtol, K and Marel, R P van der and Besla, G and Martin, N F and Belokurov, V and Gallart, C and Martinez-Delgado, D and Marshall, J L and Nöel, N E D and Majewski, S R and Cioni, M R L and Li, T S and Hartley, W and Luque, E and Conn, B C and Walker, A R and Balbinot, E and Stringfellow, G S and Olsen, K A G and Nidever, D and da Costa, L N and Ogando, R and Maia, M and Neto, A F and Abbott, T M C and Abdalla, F B and Allam, S and Annis, J and Benoit-Lévy, A and Rosell, A C and Kind, M C and Carretero, J and Cunha, C E and D'Andrea, C B and Desai, Shantanu and Diehl, H T and Doel, P and Flaugher, B and Fosalba, P and García-Bellido, J and Gruen, D and Gruendl, R A and Gschwend, J and Gutierrez, G and Honscheid, K and James, D J and Kuehn, K and Kuropatkin, N and Menanteau, F and Miquel, R and Plazas, A A and Romer, A K and Sako, M and Sanchez, E and Scarpine, V and Schubnell, M and Sevilla-Noarbe, I and Smith, R C and Soares-Santos, M and Sobreira, F and Suchyta, E and Swanson, M E C and Tarle, G and Tucker, D L and Wester, W (2017) A stellar overdensity associated with the Small Magellanic Cloud. Monthly Notices of the Royal Astronomical Society, 468 (2). pp. 1349-1360. ISSN 0035-8711

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Abstract

We report the discovery of a stellar overdensity 8 degrees north of the centre of the Small Magellanic Cloud (SMC; Small Magellanic Cloud Northern Over-Density; SMCNOD), using data from the first 2 yr of the Dark Energy Survey (DES) and the first year of the MAGellanic SatelLITEs Survey (MagLiteS). The SMCNOD is indistinguishable in age, metallicity and distance from the nearby SMC stars, being primarily composed of intermediate-age stars (6 Gyr, Z=0.001), with a small fraction of young stars (1 Gyr, Z=0.01). The SMCNOD has an elongated shape with an ellipticity of 0.6 and a size of similar to 6 degrees x 2 degrees. It has an absolute magnitude of M-V congruent to -7.7, r(h) = 2.1 kpc, and mu v(r < r(h)) = 31.2 mag arcsec(-2). We estimate a stellar mass of similar to 10(5) M-circle dot, following a Kroupa mass function. The SMCNOD was probably removed from the SMC disc by tidal stripping, since it is located near the head of the Magellanic Stream, and the literature indicates likely recent Large Magellanic Cloud-SMC encounters. This scenario is supported by the lack of significant H-1 gas. Other potential scenarios for the SMCNOD origin are a transient overdensity within the SMC tidal radius or a primordial SMC satellite in advanced stage of disruption.

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