Robert Lang

Publications (3)12.05 Total impact

• Article: 21 cm Synthesis Observations of VIRGOHI 21—A Possible Dark Galaxy in the Virgo Cluster

  Robert Minchin, Jonathan Davies, Michael Disney, Marco Grossi, Sabina Sabatini, Peter Boyce, Diego Garcia, Chris Impey, Christine Jordan, Robert Lang, Andrew Marble, Sarah Roberts, and Wim van Driel
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  ABSTRACT: Many observations indicate that dark matter dominates the extragalactic universe, yet no totally dark structure of galactic proportions has ever been convincingly identified. Previously, we have suggested that VIRGOHI 21, a 21 cm source we found in the Virgo Cluster using Jodrell Bank, was a possible dark galaxy because of its broad line width (~200 km s-1) unaccompanied by any visible gravitational source to account for it. We have now imaged VIRGOHI 21 in the neutral hydrogen line and find what could be a dark, edge-on, spinning disk with the mass and diameter of a typical spiral galaxy. Moreover, VIRGOHI 21 has unquestionably been involved in an interaction with NGC 4254, a luminous spiral with an odd one-armed morphology, but lacking the massive interactor normally linked with such a feature. Numerical models of NGC 4254 call for a close interaction ~108 yr ago with a perturber of ~1011 M☉. This we take as additional evidence for the massive nature of VIRGOHI 21, as there does not appear to be any other viable candidate. We have also used the Hubble Space Telescope to search for stars associated with the H I and find none down to an I-band surface brightness limit of 31.1 ± 0.2 mag arcsec-2.
  The Astrophysical Journal 12/2008; 670(2):1056. · 6.02 Impact Factor
• Source

  Available from: Robert F. Minchin

  Article: A Dark Hydrogen Cloud in the Virgo Cluster

  Robert Minchin, Jonathan Davies, Michael Disney, Peter Boyce, Diego Garcia, Christine Jordan, Virginia Kilborn, Robert Lang, Sarah Roberts, Sabina Sabatini, and Wim van Driel
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  ABSTRACT: VIRGOHI 21 is an H I source detected in the Virgo Cluster survey of Davies et al. that has a neutral hydrogen mass of 108 M☉ and a velocity width of ΔV20 = 220 km s-1. From the Tully-Fisher relation, a galaxy with this velocity width would be expected to be 12 mag or brighter; however, deep CCD imaging has failed to turn up a counterpart down to a surface brightness level of 27.5 B mag arcsec-2. The H I observations show that it is extended over at least 16 kpc, which, if the system is bound, gives it a minimum dynamical mass of ~1011 M☉ and a mass-to-light ratio of Mdyn/LB > 500 M☉/L☉. If it is tidal debris, then the putative parents have vanished; the remaining viable explanation is that VIRGOHI 21 is a dark halo that does not contain the expected bright galaxy. This object was found because of the low column density limit of our survey, a limit much lower than that achieved by all sky H I surveys such as those carried out at Parkes and Jodrell Bank. Further such sensitive surveys might turn up a significant number of the dark matter halos predicted by galaxy formation models.
  The Astrophysical Journal 12/2008; 622(1):L21. · 6.02 Impact Factor
• Source

  Available from: Robert F. Minchin

  Article: 21-cm synthesis observations of VIRGOHI 21 - a possible dark galaxy in the Virgo Cluster

  Robert Minchin, Jonathan Davies, Michael Disney, Marco Grossi, Sabina Sabatini, Peter Boyce, Diego Garcia, Chris Impey, Christine Jordan, Robert Lang, Andrew Marble, Sarah Roberts, Wim van Driel
  [show abstract] [hide abstract]
  ABSTRACT: Many observations indicate that dark matter dominates the extra-galactic Universe, yet no totally dark structure of galactic proportions has ever been convincingly identified. Previously we have suggested that VIRGOHI 21, a 21-cm source we found in the Virgo Cluster using Jodrell Bank, was a possible dark galaxy because of its broad line-width (~200 km/s) unaccompanied by any visible gravitational source to account for it. We have now imaged VIRGOHI 21 in the neutral-hydrogen line and find what could be a dark, edge-on, spinning disk with the mass and diameter of a typical spiral galaxy. Moreover, VIRGOHI 21 has unquestionably been involved in an interaction with NGC 4254, a luminous spiral with an odd one-armed morphology, but lacking the massive interactor normally linked with such a feature. Numerical models of NGC 4254 call for a close interaction ~10^8 years ago with a perturber of ~10^11 solar masses. This we take as additional evidence for the massive nature of VIRGOHI 21 as there does not appear to be any other viable candidate. We have also used the Hubble Space Telescope to search for stars associated with the HI and find none down to an I band surface brightness limit of 31.1 +/- 0.2 mag/sq. arcsec. Comment: 8 pages, accepted to ApJ, uses emulateapj.cls. Mpeg animation (Fig. 2) available at ftp://ftp.naic.edu/pub/publications/minchin/video2.mpg
  06/2007;