English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

The halo of M31 shows a wealth of substructures that are consistent withsatellite accretion. Here we report on kinematic and abundance results fromKeck/DEIMOS spectroscopy in the calcium triplet region of over 3500 red giantstar candidates along the minor axis and in off-axis spheroid fields of M31.Our data reach out to large radial distances of 160 kpc. The derived velocitydistributions show a kinematically cold substructure at 17 kpc that has beenreported before. We devise an improved method to measure accurate metallicitiesfrom the calcium triplet in low signal-to-noise spectra using a coaddition ofthe individual lines. The resulting distribution leads us to note an evenstronger gradient in the abundance distribution along M31's minor axis thanpreviously detected. The mean metallicity in the outer halo reaches below -2dex, with individual values as low as -2.6 dex. In the inner spheroid, at 17-19kpc, we find a sharp decline of ~0.5 dex in metallicity, which roughlycoincides with the edge of an extended disk, previously detected from starcount maps. A large fraction of red giants in the most distant fields arelikely members of M33's overlapping halo. A comparison of our velocities withthose predicted by new N-body simulations argues that the event responsible forthe giant Stream is most likely not responsible for the full population of theinner halo; we show further that the abundance distribution of the Stream isdifferent from that of the inner halo, from which it becomes evident that themerger event that formed the outer halo cannot have contributed any significantmaterial to the inner spheroid. All this evidence of severe structure changesin the halo suggests a high degree of infall and stochastic abundance accretiongoverning the build-up of M31's halo. (Abridged)

Kinematic and Chemical constraints on the formation of M31's inner and outer halo