1,010 research outputs found
2MASS Galaxies in the Fornax Cluster Spectroscopic Survey
The Fornax Cluster Spectroscopic Survey (FCSS) is an all-object survey of a
region around the Fornax Cluster of galaxies undertaken using the 2dF
multi-object spectrograph on the Anglo-Australian Telescope. Its aim was to
obtain spectra for a complete sample of all objects with 16.5 < b_j < 19.7
irrespective of their morphology (i.e. including `stars', `galaxies' and
`merged' images). We explore the extent to which (nearby) cluster galaxies are
present in 2MASS. We consider the reasons for the omission of 2MASS galaxies
from the FCSS and vice versa. We consider the intersection (2.9 square degrees
on the sky) of our data set with the infra-red 2 Micron All-Sky Survey (2MASS),
using both the 2MASS Extended Source Catalogue (XSC) and the Point Source
Catalogue (PSC). We match all the XSC objects to FCSS counterparts by position
and also extract a sample of galaxies, selected by their FCSS redshifts, from
the PSC. We confirm that all 114 XSC objects in the overlap sample are
galaxies, on the basis of their FCSS velocities. A total of 23 Fornax Cluster
galaxies appear in the matched data, while, as expected, the remainder of the
sample lie at redshifts out to z = 0.2 (the spectra show that 61% are early
type galaxies, 18% are intermediate types and 21% are strongly star
forming).The PSC sample turns out to contain twice as many galaxies as does the
XSC. However, only one of these 225 galaxies is a (dwarf) cluster member. On
the other hand, galaxies which are unresolved in the 2MASS data (though almost
all are resolved in the optical) amount to 71% of the non-cluster galaxies with
2MASS detections and have redshifts out to z=0.32.Comment: 5 pages, accepted by A&A, resubmitted due to missing reference
Galaxy threshing and the origin of intracluster stellar objects
We numerically investigate dynamical evolution of non-nucleated dwarf
elliptical/spiral galaxies (dE) and nucleated ones (dE,Ns) in clusters of
galaxies in order to understand the origin of intracluster stellar objects,
such as intracluster stars (ICSs), GCs (ICGCs), and ``ultra-compact dwarf''
(UCDs) recently discovered by all-object spectroscopic survey centred on the
Fornax cluster of galaxies. We find that the outer stellar components of a
nucleated dwarf are removed by the strong tidal field of the cluster, whereas
the nucleus manages to survive as a result of its initially compact nature. The
developed naked nucleus is found to have physical properties (e.g., size and
mass) similar to those observed for UCDs. We also find that the UCD formation
processes does depend on the radial density profile of the dark halo in the
sense that UCDs are less likely to be formed from dwarfs embedded in dark
matter halos with central `cuspy' density profiles. Our simulations also
suggest that very massive and compact stellar systems can be rapidly and
efficiently formed in the central regions of dwarfs through the merging of
smaller GCs. GCs initially in the outer part of dE and dE,Ns are found to be
stripped to form ICGCs.Comment: 6 pages and 3 figures (JPG file for Fig. 1), in the proceedings of
IAU 217 ``Recycling intergalactic and interstellar matter'
The evolution and star formation of dwarf galaxies in the Fornax Cluster
We present the results of a spectroscopic survey of 675 bright (16.5<Bj<18)
galaxies in a 6 degree field centred on the Fornax cluster with the FLAIR-II
spectrograph on the UK Schmidt Telescope. We measured redshifts for 516
galaxies of which 108 were members of the Fornax Cluster. 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 virialised. Our spectral data reveal a higher rate of
star formation among the dwarf galaxies than suggested by morphological
classification: 35 per cent have H-alpha emission indicative of star formation
but only 19 per cent were morphologically classified as late-types. 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. 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 5 dwarfs with detected HI emission: these are long (of order 10 Gyr),
indicating that active gas removal must be involved if they are transformed
into gas-poor dwarfs as they fall further into the cluster. In agreement with
our previous results, we find no compact dwarf elliptical (M32-like) galaxies
in the Fornax Cluster.Comment: To appear in Monthly Notices of the Royal Astronomical Societ
High surface brightness dwarf galaxies in the Fornax cluster
We describe a search for compact dwarf galaxies in the Fornax cluster using
the FLAIR spectrograph on the UK Schmidt Telescope. We measured radial
velocities of 453 compact galaxies brighter than Bt=17.3 and found seven new
compact dwarf cluster members that were not classified in previous surveys as
members of the cluster. These are amongst the most compact, high surface
brightness dwarf galaxies known.
The inclusion of these galaxies in the cluster does not change the total
luminosity function significantly but they are important because of their
extreme nature; one in particular appears to be a high (normal) surface
brightness dwarf spiral. Three of the new dwarfs have strong emission lines and
appear to be blue compact dwarfs (BCDs), doubling the number of confirmed BCDs
in the cluster. We also determined that none of the compact dwarf elliptical
(M32-like) candidates are in the cluster, down to an absolute magnitude
Mb=-13.2. We have investigated the claim of Irwin et al. (1990) that there is
no strong relation between surface brightness and magnitude for the cluster
members and find some support for this for the brighter galaxies (Bt<17.3) but
fainter galaxies still need to be measured.Comment: Submitted to Monthly Notices of the Royal Astronomical Society, 5
pages; a LaTeX file (uses mn.sty) and 5 eps figure
Ultra-compact dwarf galaxies: a new class of compact stellar system discovered in the Fornax Cluster
We have used the 2dF spectrograph on the Anglo-Australian Telescope to obtain
a complete spectroscopic sample of all objects in the magnitude range, Bj= 16.5
to 19.8, regardless of morphology, in an area centred on the Fornax Cluster of
galaxies. Among the unresolved targets are five objects which are members of
the Fornax Cluster. They are extremely compact stellar systems with scale
lengths less than 40 parsecs. These ultra-compact dwarfs are unlike any known
type of stellar system, being more compact and significantly less luminous than
other compact dwarf galaxies, yet much brighter than any globular cluster.Comment: To appear in IAU Symposium 207: Extragalactic Star Cluster
The Surface Brightness and Colour-Magnitude Relations for Fornax Cluster Galaxies
We present BVI photometry of 190 galaxies in the central region of the Fornax
Cluster observed with the Michigan Curtis Schmidt Telescope. The cluster
members exhibit a strong surface brightness-magnitude relation in our data:
both giant and dwarf ellipticals decrease in surface brightness as luminosity
decreases. However the surface brightness-magnitude relation is no longer a
reliable method for determining cluster membership at surface brightnesses
fainter than 22 mag/sq.arcsec. The newly discovered ultra-compact dwarf
galaxies (UCDs) lie well off the normal surface brightness-magnitude relation.
We present the colour-magnitude relation for a sample of 113 cluster galaxies
as a function of morphological type. The UCDs also lie off the locus of this
relation. Their mean V-I colours are redder than dwarf galaxies of similar
luminosity, but similar to those of globular clusters associated with NGC 1399.
The location of the UCDs on both surface brightness and colour-magnitude plots
supports the hypothesis that they are the remnants of tidally stripped
nucleated dwarf elliptical galaxies.Comment: 14 pages, 8 figures. accepted for publication to MNRAS,
low-resolution version of some images, changes made in response to referee's
repor
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