Evidence for substructure in Ursa Minor dwarf spheroidal galaxy using a Bayesian object detection method

Pace, Andrew B.; Martinez, Gregory D.; Kaplinghat, Manoj; Muñoz, Ricardo R.

Abstract

We present a method for identifying localized secondary populations in stellar velocity data using Bayesian statistical techniques. We apply this method to the dwarf spheroidal galaxy Ursa Minor and find two secondary objects in this satellite of the Milky Way. One object is kinematically cold with a velocity dispersion of 4.25 +/- A 0.75 km s(-1) and centred at (9.1 arcmin +/- 1.5, 7.2 arcmin +/- 1.2) in relative RA and Dec. with respect to the centre of Ursa Minor. The second object has a large velocity offset of -12.8(-1.5)(+1.75) km s(-1) compared to Ursa Minor and centred at (-14.0 arcmin(-5.8)(+2.4), -2.5 arcmin(-1.0)(+0.4)). The kinematically cold object has been found before using a smaller data set, but the prediction that this cold object has a velocity dispersion larger than 2.0 km s(-1) at 95 per cent confidence level differs from previous work. We use two- and three-component models along with the information criteria and Bayesian evidence model selection methods to argue that Ursa Minor has additional localized secondary populations. The significant probability for a large velocity dispersion in each secondary object raises the intriguing possibility that each has its own dark matter halo, that is, it is a satellite of a satellite of the Milky Way.

Más información

Título según WOS: Evidence for substructure in Ursa Minor dwarf spheroidal galaxy using a Bayesian object detection method
Título según SCOPUS: Evidence for substructure in Ursa minor dwarf spheroidal galaxy using a Bayesian object detection method
Título de la Revista: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volumen: 442
Número: 2
Editorial: OXFORD UNIV PRESS
Fecha de publicación: 2014
Página de inicio: 1718
Página final: 1730
Idioma: English
DOI:

10.1093/mnras/stu938

Notas: ISI, SCOPUS - ISI