Globular clusters (GCs) have been at the heart of many longstanding questions in many sub-fields of astronomy and, as such, systematic identification of GCs in external galaxies has immense impacts. In this study, we take advantage of M87’s well-studied GC system to implement supervised machine learning (ML) classification algorithms — specifically random forest and neural networks — to identify GCs from foreground stars and background galaxies using ground-based photometry from the Canada-France-Hawai’i Telescope (CFHT). We compare these two ML classification methods to studies of ‘human-selected’ GCs and find that the best performing random forest model can reselect 61.2 per cent ± 8.0 per cent of GCs selected from HST data (ACSVCS) and the best performing neural network model reselects 95.0 per cent ± 3.4 per cent. When compared to human-classified GCs and contaminants selected from CFHT data — independent of our training data — the best performing random forest model can correctly classify 91.0 per cent ± 1.2 per cent and the best performing neural network model can correctly classify 57.3 per cent ± 1.1 per cent. ML methods in astronomy have been receiving much interest as Vera C. Rubin Observatory prepares for first light. The observables in this study are selected to be directly comparable to early Rubin Observatory data and the prospects for running ML algorithms on the upcoming dataset yields promising results.
Ultraluminous X-ray Sources (ULXs) in globular clusters are low mass X-ray binaries that achieve high X-ray luminosities through a currently uncertain accretion mechanism. Using archival Chandra and Hubble Space Telescope (HST) observations, we perform a volume-limited search (≲ 70 Mpc) of 21 of the most massive (>1011.5M⊙) early-type galaxies to identify ULXs hosted by globular cluster (GC) candidates. We find a total of 34 ULX candidates above the expected background within 5 times the effective radius of each galaxy, with 10 of these ($\sim 29.4\%$) potentially hosted by a GC. A comparison of the spatial and luminosity distributions of these new candidate GC ULXs with previously identified GC ULXs shows that they are similar: both samples peak at LX ∼ a few × 1039 erg/s and are typically located within a few effective radii of their host galaxies.
We present X-ray analysis of three short Chandra observations of M87. The basis of this analysis is the search for possible new ultraluminous X-ray sources (ULXs) in M87's globular clusters (GCs) and attempt to quantify possible variability within the observations. We searched Chandra ObsIDs 1808 (2000 July 30, 14 ks) Wilson & Yang, 3975 (2002 November 17, 5 ks) and 3977 (2003 February 4, 5 ks) Harris et al. and identified one previously discovered GC ULX, and two new GC ULX candidates. Analysis of the light-curves revealed no new evidence of variability in these sources for the duration of the observations.
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