2008/05/31 by Massimiliano Bonamente, Douglas Swartz, Douglas A. Swartz +4
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Flux (metallurgy) #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy cluster #Limit (mathematics) #Optics #Photon #Physics #Swift #Virgo Cluster #astro-ph
paper · pdf · doi:10.1086/592819
ApJL in press, accepted version
arxiv created 2008/09/23 · openalex publication_date 2008/09/23 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Swift XRT observations of the H I line source VIRGOHI 21 were performed on 2008 April 22 and 26 for a total exposure time of 9.2 ks. This is the first pointed X-ray observation of VIRGOHI 21, a putative dark galaxy in the Virgo Cluster, and no photons were detected from this source. The nondetection of extended X-ray emission within the angular extent of the H I source corresponds to a 99% confidence upper limit of 2.1 × 10 −14 ergs cm −2 s −1 in the 0.3-2.0 keV band. The equivalent upper limit to the amount of diffuse hot gas associated with VIRGOHI 21 is in the range 4 × 10 7 -2 × 10 8 M ☉ for a hot gas temperature between 0.1 and 1 keV. The nondetection also corresponds to a 99% confidence upper limit on the flux from a pointlike source of 8 × 10 −15 ergs cm −2 s −1 in the 0.3-2.0 keV band. We discuss the constraints on the nature of VIRGOHI 21 imposed by these observations and the theoretical implications of these results.