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

Abstract

The Pan-Andromeda Archaeological Survey is a survey of > 400 square degrees centered on the Andromeda (M31) and Triangulum (M33) galaxies that has provided the most extensive panorama of a L ⋆ galaxy group to large projected galactocentric radii. Here, we collate and summarise the current status of our knowledge of the substructures in the stellar halo of M31, and discuss connections between these features. We estimate that the 13 most distinctive substructures were produced by at least 5 different accretion events, all in the last 3 or 4 Gyrs. We suggest that a few of the substructures furthest from M31 may be shells from a single accretion event. We calculate the luminosities of some prominent substructures for which previous estimates were not available, and we estimate the stellar mass budget of the outer halo of M31. We revisit the problem of quantifying the properties of a highly structured dataset; specifically, we use the OPTICS clustering algorithm to quantify the hierarchical structure of M31's stellar halo, and identify three new faint structures. M31's halo, in projection, appears to be dominated by two "mega-structures", that can be considered as the two most significant branches of a merger tree produced by breaking M31's stellar halo into smaller and smaller structures

The Satellite Luminosity Function of M101 into the Ultra-faint Dwarf Galaxy Regime

“…We consider the M101 luminosity function to be 90% complete down to MV ≈−7.7 mag, and 50% complete down to MV ≈−7.4 mag (hollow symbol; we also mark the magnitude range between these two values with a dashed line); see Section 4 for details. The data for the other luminosity functons come from Smercina et al (2018) for M94, Crnojević et al (2019) for Cen A, Chiboucas et al (2013) and Smercina et al (2017) for M81, Martin et al (2016) & McConnachie et al (2018 for M31 and McConnachie (2012) for the MW. Note that this is a lower limit for the MW due to incomplete spatial coverage; no attempt was made to correct any luminosity function for incompleteness.…”

“…As the four faint dwarf candidates that we have imaged were the only remaining viable members in the M101 sample of Bennet et al (2017), we can use their status as background objects to extend the M101 satellite luminosity function to fainter magnitudes. As we discuss below, M101 is now only the third MWsized halo with a near-complete luminosity function that pushes into the ultra-faint dwarf galaxy regime; after the MW (McConnachie 2012) and M31 (Martin et al 2016;McConnachie et al 2018). Such information is vital, as the number of such satellites is smaller than expected from dark matter only simulations (Moore et al 1999;Klypin et al 1999).…”

A correlation between the number of satellites and the bulge-to-total baryonic mass ratio extending beyond the Local Group

“…• The LG galaxies: we refer to McConnachie (2012) and McConnachie et al (2018), for the information about MW and M31 satellites, respectively 2 .…”

A detailed study of Andromeda XIX, an extreme local analogue of ultradiffuse galaxies

“…For And XIX, stars were selected as targets for each of our DEIMOS observations using the Subaru Suprime-Cam imaging. For the stream feature, we used imaging from the Pan-Andromeda Archaeological suvey (McConnachie et al 2018). In both, we isolate the region of colour-magnitude space that the RGB of And XIX is located in using its colour magnitude diagram (CMD, fig.…”