An H i/Optical Atlas of H II Galaxies and Their Companions: Erratum

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view Abstract Citations (36) References (1) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An H i/Optical Atlas of H II Galaxies and Their Companions: Erratum Taylor, Christopher L. ; Brinks, Elias ; Grashuis, Randy M. ; Skillman, Evan D. Abstract In the paper "An H I/Optical Atlas of H II Galaxies and Their Companions" by C. L. Taylor, E. Brinks, R. M. Grashuis, & E. D. Skillman (ApJS, 99,427(1995]), three objects were erroneously identified as being H I companion objects. The majority of the companion objects are unambiguously identified with optical counterparts and are considered to be genuine. For six objects we reported that no optical counterparts were present at about the 23 mag arcsec^-2^ level. Three of the six appear partially merged with their parent galaxies and will require VLA C-configuration observations to confirm their reality; the other three were well separated from the parent H II galaxy. Although these three objects met the same selection criteria as used to find the genuine companion objects, recent observations conducted to confirm their reality detected only one out of three: the companions UM 483A and UM 491B were not recovered and are taken to be false detections in the original observations, whereas the companion UM 422C was detected at the expected level and is confirmed as a genuine companion object. Further observations showed that UM 323A, for which we have no optical data, is a spurious detection as well. The spurious detections were caused by the presence of solar interference during the H I observations. Such interference is time- variable and frequency-dependent, and the measures described in the original paper were inadequate to entirely remove the effects of the interference in the instances of the false detections. As solar interference can be spatially correlated from channel to channel, the selection criteria, which assume random Gaussian noise, failed in the presence of the nonrandom residual interference. The residual interference mimicked a low-mass, H I-rich object as it would appear in observations of low spatial and velocity resolution. The process of companion candidate identification was designed to be followed up with confirmation observations, but it was only recently that we were given any VLA time to accomplish this. The new observations were carried out on 1995 June 6 and at night so as to avoid solar interference. In addition, the new data have ~50% lower noise, so any real objects ought to have been readily visible in the channel maps. The statistics of the companion frequency now change as follows in the light of the new observations. The frequency with which H II galaxies are observed to have nearby companions is 12/21 = 0.57, rather than the 14/21 originally reported. Using this new detection rate to recalculate the lower limit on the frequency of companion occurrence results in a value of ρ = 0.37. The corresponding upper limit is 0.76, but, as discussed in the paper, this is not nearly as strong a limit as is the lower limit, and we cannot rule out an upper limit of ρ = l. The lower and upper limits calculated from the original detection rate of 14/21 are 0.46 and 0.84, respectively. We present a new version of Figure 22 from the original paper, showing the histograms for the H I mass and total mass distributions of the companion object population. The histograms are not greatly changed as a result of omitting the three spurious objects. We should like to emphasize that most of the material presented in the original paper is reliable and that none of the discussion is significantly changed. We thank John Salzer, Renzo Sancisi, and Jacqueline van Gorkom for bringing to our attention the possibility of false detections caused by solar interference, and Miller Goss and Barty Clark for allocating time for the follow-up observations. Publication: The Astrophysical Journal Supplement Series Pub Date: January 1996 DOI: 10.1086/192256 Bibcode: 1996ApJS..102..189T full text sources ADS |