Browsing by Author "Ho, Anna Y. Q."

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    On the origin of the Monoceros Ring - I. Kinematics, proper motions, and the nature of the progenitor
    (2018) Guglielmo, Magda; Lane, Richard R.; Conn, Blair C.; Ho, Anna Y. Q.; Ibata, Rodrigo A.; Lewis, Geraint F.
    The Monoceros Ring (MRi) structure is an apparent stellar overdensity that has been postulated to entirely encircle the Galactic plane and has been variously described as being due to line-of-sight effects of the Galactic warp and flare or of extragalactic origin (via accretion). Despite being intensely scrutinized in the literature for more than a decade, no studies to date have been able to definitively uncover its origins. Here we use N-body simulations and a genetic algorithm to explore the parameter space for the initial position, orbital parameters, and, for the first time, the final location of a satellite progenitor. We fit our models to the latest Pan-STARRS data to determine whether an accretion scenario is capable of producing an in-plane ring-like structure matching the known parameters of the MRi. Our simulations produce streams that closely match the location, proper motion, and kinematics of the MRi structure. However, we are not able to reproduce the mass estimates from earlier studies based on Pan-STARRS data. Furthermore, in contrast to earlier studies, our best-fitting models are those for progenitors on retrograde orbits. If the MRi was produced by satellite accretion, we find that its progenitor has an initial mass upper limit of similar to 10(10) M-circle dot and the remnant is likely located behind the Galactic bulge, making it difficult to locate observationally. While our models produce realistic MRi-like structures, we cannot definitively conclude that the MRi was produced by the accretion of a satellite galaxy.
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    The Atacama cosmology telescope: flux upper limits from a targeted search for extragalactic transients
    (2024) Hervias-Caimapo, Carlos; Naess, Sigurd; Hincks, Adam D.; Calabrese, Erminia; Devlin, Mark J.; Dunkley, Jo; Duenner, Rolando; Gallardo, Patricio A.; Hilton, Matt; Ho, Anna Y. Q.; Huffenberger, Kevin M.; Ma, Xiaoyi; Madhavacheril, Mathew S.; Niemack, Michael D.; Orlowski-Scherer, John; Page, Lyman A.; Partridge, Bruce; Puddu, Roberto; Salatino, Maria; Sifon, Cristobal; Staggs, Suzanne T.; Vargas, Cristian; Vavagiakis, Eve M.; Wollack, Edward J.
    We have performed targeted searches of known extragalactic transient events at millimetre wavelengths using nine seasons (2013-2021) of 98, 150, and 229 GHz Atacama Cosmology Telescope (ACT) observations that mapped similar to 40 per cent of the sky for most of the data volume. Our data cover 88 gamma-ray bursts (GRBs), 12 tidal disruption events (TDEs), and 203 other transients, including supernovae (SNe). We stack our ACT observations to increase the signal-to-noise ratio of the maps. In all cases but one, we do not detect these transients in the ACT data. The single candidate detection (event AT2019ppm), seen at similar to 5 sigma significance in our data, appears to be due to active galactic nuclei activity in the host galaxy coincident with a transient alert. For each source in our search we provide flux upper limits. For example, the medians for the 95 per cent confidence upper limits at 98 GHz are 15, 18, and 16 mJy for GRBs, SNe, and TDEs, respectively, in the first month after discovery. The projected sensitivity of future wide-area cosmic microwave background surveys should be sufficient to detect many of these events using the methods described in this paper.