Michael G. Richer
Association of Universities for Research in Astronomy
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Publication
Featured researches published by Michael G. Richer.
The Astronomical Journal | 2003
Henry Lee; Marshall L. McCall; Michael G. Richer
The impact of the cluster environment on the evolution of dwarf galaxies is investigated by comparing the properties of a sample of dwarf irregular galaxies (dI’s) in the Virgo Cluster with a control sample of nearby (‘‘ field ’’) dI’s having oxygen abundances derived from [O iii] � 4363 measurements and measured distances from resolved stellar constituents. Spectroscopic data are obtained for H ii regions in 11 Virgo dI’s distributed in the central and outer regions of the cluster. To ensure that oxygen abundances are derived in a homogeneous manner, oxygen abundances for field and Virgo dI’s are computed using the bright-line method and compared with abundances directly obtained from [O iii] � 4363, where available. They are found to agree to within about 0.2 dex, with no systematic offset. At a given optical luminosity, there is no systematic difference in oxygen abundance between the sample of Virgo dI’s and the sample of nearby dI’s. However, five of the 11 Virgo dI’s exhibit much lower baryonic gas fractions than field dI’s at comparable oxygen abundances. Using field dI’s as a reference, a gas-deficiency index for dI’s is constructed, making it possible quantitatively to identify which galaxies have lost gas. For the Virgo sample, some of the dwarfs are gas-deficient by a factor of 30. The gas deficiency correlates roughly with the X-ray surface brightness of the intracluster gas. Ram pressure stripping can best explain the observed gas-poor dI’s in the cluster sample. Together with the lack of significant fading and reddening of the gas-poor dI’s compared with gas-normal dI’s, these observations suggest that the gas-poor dI’s in Virgo have recently encountered the intracluster medium for the first time. Faded remnants of gas-poor dI’s in Virgo will resemble bright dwarf elliptical galaxies currently seen in the cluster core.
Archive | 2007
M. A. Pena; Michael G. Richer; Grazyna Stasinska
Archive | 2007
Gaghik H. Tovmassian; John A. Tomsick; R. Napiwotzki; Lev R. Yungelson; Grazyna Stasinska; M. A. Pena; Michael G. Richer
Archive | 2005
Grazyna Stasinska; Corinne Charbonnel; R. Napiwotzki; Miriam Peña; Michael G. Richer; R. Szczerba; Gaghik H. Tovmassian
Symposium - International Astronomical Union | 2003
Michael G. Richer; Marshall L. McCall
Proceedings of The International Astronomical Union | 2003
Marshall L. McCall; Michael G. Richer
Archive | 2003
Grazyna Stasinska; Gaghik H. Tovmassian; Michael G. Richer
Archive | 2002
Heejo Lee; Marshall L. McCall; Michael G. Richer
Archive | 1998
Grazyna Stasinska; Michael G. Richer; Marshall L. McCall
Archive | 1996
Michael G. Richer; Grazyna Stasinska; Marshall L. McCall