The evolution and star formation of dwarf galaxies in the Fornax Cluster

Drinkwater, M. J., Gregg, M. D., Holman, B. A. and Brown, M. J. I. (2001) The evolution and star formation of dwarf galaxies in the Fornax Cluster. Monthly Notices of The Royal Astronomical Society, 326 3: 1076-1094. doi:10.1046/j.1365-8711.2001.04646.x


Author Drinkwater, M. J.
Gregg, M. D.
Holman, B. A.
Brown, M. J. I.
Title The evolution and star formation of dwarf galaxies in the Fornax Cluster
Journal name Monthly Notices of The Royal Astronomical Society   Check publisher's open access policy
ISSN 0035-8711
1365-2966
Publication date 2001
Sub-type Article (original research)
DOI 10.1046/j.1365-8711.2001.04646.x
Open Access Status DOI
Volume 326
Issue 3
Start page 1076
End page 1094
Total pages 19
Place of publication Oxford, United Kingdom
Publisher Oxford University Press
Language eng
Abstract We present the results of a spectroscopic survey of 675 bright (16.5 < b(J) < 18) galaxies in a 6 degrees field centred on the Fornax cluster with the FLAIR-II spectrograph on the UK Schmidt Telescope. Three galaxy samples were observed: compact galaxies to search for new blue compact dwarfs, candidate M 32-like compact dwarf ellipticals, and a subset of the brightest known cluster members in order to study the cluster dynamics. We measured redshifts for 516 galaxies, of which 108 were members of the Fornax Cluster. Defining dwarf galaxies to be those with b(J) greater than or equal to 15 (M-B greater than or equal to - 16.5), there are a total of 62 dwarf cluster galaxies in our sample. Nine of these are new cluster members previously misidentified as background galaxies. The cluster dynamics show that the dwarf galaxies are still falling into the cluster whereas the giants are virialized. We classified the observed galaxies as late-type if we detected H alpha emission at an equivalent width greater than 1 Angstrom. The spectra were obtained through fixed apertures, so they reflect activity in the galaxy cores, but this does not significantly bias the classifications of the compact dwarfs in our sample. The new classifications reveal a higher rate of star formation among the dwarf galaxies than suggested by morphological classification: 35 per cent have significant H alpha emission indicative of star formations but only 19 per cent were morphologically classified as late-types. The star-forming dwarf galaxies span the full range of physical sizes and we find no evidence in our data for a distinct class of star-forming blue compact dwarf (BCD) galaxy. The distribution of scale sizes is consistent with evolutionary processes which transform late-type dwarfs to early-type dwarfs. The fraction of dwarfs with active star formation drops rapidly towards the cluster centre: this is the usual density-morphology relation confirmed here for dwarf galaxies. The star-forming dwarfs are concentrated in the outer regions of the cluster, the most extreme in an infalling subcluster. We estimate gas depletion time-scales for five dwarfs with detected Hi emission: these are long (of order 10(10) yr), indicating that an active gas removal process must be involved if they are transformed into gas-poor dwarfs as they fall further into the cluster. Finally, in agreement with our previous results, we find no compact dwarf elliptical (M 32-like) galaxies in the Fornax Cluster.
Keyword Astronomy & Astrophysics
Stars
Galaxies
Galaxies
Galaxies
Surface-brightness Galaxies
Virgo Cluster
Elliptical Galaxies
Catalog
Photometry
Spectroscopy
Field
Velocities
Population
Sample
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Unknown

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Physical Sciences Publications
 
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Created: Mon, 13 Aug 2007, 12:34:37 EST