{"ID":23603864,"CreatedAt":"2026-09-18T06:00:06.305330393Z","UpdatedAt":"2026-09-18T06:00:06.305330393Z","DeletedAt":null,"paper_url":"https://arxiv.org/abs/2609.20810","arxiv_id":"2609.20810","title":"A near-IR survey of luminous asymptotic giant branch stars in the satellites and stellar halo of M31","abstract":"We investigate the dwarf spheroidal (dSph) satellites and stellar halo of M31 using near-infrared imaging from the Wide-Field Camera on the UKIRT 3.8 m telescope. Our homogeneous analysis covers the stellar extents of 12 dSphs, as well as their surrounding halo field populations. We identify carbon-rich (C) and oxygen-rich (M) thermally-pulsing AGB stars (TP-AGBs) using colour-magnitude and colour-colour diagrams, which also allows for effective contaminant rejection. TP-AGB stars are detected in eight of the 12 dSphs, indicating small intermediate-age populations in a substantial fraction of the sample; they are also found in considerable numbers throughout most of M31's stellar halo. By combining 316 new detections with a revised classification of objects previously reported in the literature, we increase the TP-AGB candidate population in the dSphs from 82 to 359. We use the resulting dSph and halo AGB samples to compute C/M ratios and infer metallicities in the dSphs and adjacent halo fields with non-zero AGB counts. A clear metallicity gradient is observed in the M31 stellar halo out to ~150 kpc, consistent with that found using other tracers. Using literature star formation histories from main-sequence turn-off photometry, we find a tight correlation between the number of C stars in the dSphs and the stellar mass formed in the last 0.5--3 Gyr. This study underscores the promise of AGB stars as quantitative tracers of intermediate-age star formation, particularly in intrinsically faint systems, and provides a catalogue of candidate TP-AGB stars for follow-up.","short_abstract":"We investigate the dwarf spheroidal (dSph) satellites and stellar halo of M31 using near-infrared imaging from the Wide-Field Camera on the UKIRT 3.8 m telescope. Our homogeneous analysis covers the stellar extents of 12 dSphs, as well as their surrounding halo field populations. We identify carbon-rich (C) and oxygen-...","url_abs":"https://arxiv.org/abs/2609.20810","url_pdf":"https://arxiv.org/pdf/2609.20810v1","authors":"[\"Jess M. Howell\",\"Annette M. N. Ferguson\",\"Olivia C. Jones\",\"Mike. J. Irwin\",\"Maria-Rosa L. Cioni\",\"Geraint F. Lewis\",\"Nicolas. F. Martin\",\"Alan. W. McConnachie\"]","published":"2026-09-17T17:58:39Z","proceeding":"astro-ph.GA","tasks":"[\"astro-ph.GA\"]","methods":"[]","has_code":false}