Formation of the Andromeda giant stream: asymmetric structure and disc progenitor

Abstract

We focus on the evidence of a past minor merger discovered in the halo of the Andromeda galaxy (M31). Previous N-body studies have enjoyed moderate success in producing the observed giant stellar stream (GSS) and stellar shells in M31's halo. The observed distribution of stars in the halo of M31 shows an asymmetric surface brightness profile across the GSS; however, the effect of the morphology of the progenitor galaxy on the internal structure of the GSS requires further investigation in theoretical studies. To investigate the physical connection between the characteristic surface brightness in the GSS and the morphology of the progenitor dwarf galaxy, we systematically vary the thickness, rotation velocity and initial inclination of the disc dwarf galaxy in N-body simulations. The formation of the observed structures appears to be dominated by the progenitor's rotation. Besides reproducing the observed GSS and two shells in detail, we predict additional structures for further observations. We predict the detectability of the progenitor's stellar core in the phase-space density distribution, azimuthal metallicity gradient of the western shell-like structure and an additional extended shell in the north-western direction that may constrain the properties of the progenitor galaxy.

The Large-scale Structure of the Halo of the Andromeda Galaxy. II. Hierarchical Structure in the Pan-Andromeda Archaeological Survey

“…Thus, it is a relatively young feature. The spatial morphology of the stream, in particular the relatively well-defined northern edge and the "fanning" of material to the south, suggests that the progenitor might have been a disk galaxy (Fardal et al 2008;Kirihara et al 2017b). It is worth noting that the age of the stream is reasonably close to the age of the star forming ring in M31 Dalcanton et al 2012).…”

Elemental Abundances in M31: Gradients in the Giant Stellar Stream*

“…The similarity of the photometric metallicity and age distributions of stellar populations in the SE shelf and GSS (Brown et al 2003(Brown et al , 2006Gilbert et al 2007) further bolstered the hypothesis that the SE shelf and GSS were tidal debris from the same event. The prediction of the SE shelf illustrates that minor merger models for the formation of the GSS (M å ∼ (1 − 5) × 10 9 M e ; Fardal et al 2006Fardal et al , 2007Fardal et al , 2008Fardal et al , 2013Mori & Rich 2008;Kirihara et al 2014;Sadoun et al 2014;Kirihara et al 2017;Miki et al 2016) can successfully reproduce the broad morphological and kinematical features of the stream while accounting for diffuse shell-like features such as the Northeast (Ferguson et al 2002(Ferguson et al , 2005 and West (W; Fardal et al 2007) shelves as part of the forward continuation of the stream. In further support of this hypothesis, Fardal et al (2012) showed that the kinematics of the W shelf were strikingly similar to predictions for the feature and that the shelf's metallicity was consistent with that of the GSS.…”

The nature of the progenitor of the M31 north-western stream: globular clusters as milestones of its orbit

“…Since this analysis does not consider the evolution of the tidal debris, a comprehensive survey by N-body simulations including the effects of a progenitor's morphology, a live disc and the density profile of the DMH is necessary for further analysis (cf. Mori & Rich 2008;Kirihara, Miki & Mori 2014;Miki, Mori & Rich 2016;Kirihara et al 2017).…”