3,919 research outputs found
The central region of the Fornax cluster -- II. Spectroscopy and radial velocities of member and background galaxies
Radial velocities of 94 galaxies brighter than about V_tot = 20 mag in the
direction of the central Fornax cluster have been measured. Except for 8 Fornax
members, all galaxies lie in the background. Among the 8 members, there are 5
nucleated dwarf ellipticals that are already listed in the FCC (Ferguson 1989,
AJ 98, 367). Two of the 3 ``new'' members are very compact and have surface
brightnesses comparable to globular clusters, however their luminosities are in
the range of dwarf elliptical nuclei. The measured line indices (especially
Mg2, H beta, and iron) of the brighter of the compact objects suggest a solar
metallicity, whereas the fainter compact object as well as the dE,Ns have line
indices that are similar to those of old metal-poor globular clusters (GCs).
However, with these data it is not possible to clearly classify the compact
objects either as very bright globular clusters, isolated nuclei of dE,Ns, or
even compact ellipticals. A background galaxy cluster at z = 0.11 has been
found just behind the center of the Fornax cluster. This explains the excess
population of galaxies reported in Paper I. The brightest galaxy of the
background cluster lies only 1.1 arcmin south of NGC 1399 and is comparable in
absolute luminosity with the central Fornax galaxy itself.Comment: 12 pages, LaTeX2e, uses aa.cls, including 9 PostScript figures;
accepted for publication in A&AS, also available at
http://www.astro.puc.cl/~mhilker/publication.htm
The central region of the Fornax cluster -- I. A catalog and photometric properties of galaxies in selected CCD fields
We present a photometric catalog (based on V and I photometry) of galaxies in
the central regions of the Fornax galaxy cluster. Our 11 CCD fields cover 0.17
degrees in total. The limiting surface brightness is around 24 mag arsec^-2,
similar to that of Ferguson's (1989, AJ 98, 367) catalog, whereas our limiting
total magnitude is around V = 22 mag, about two magnitudes fainter. It is the
surface brightness limit, however, that prevents us from detecting the
counterparts of the faintest Local Group dwarf spheroidals. The photometric
properties of all objects are presented as a catalog. The properties and fit
parameters of the surface brightness profiles for a sub-sample are presented as
a second catalog (both catalogs are available in electronic form at the CDS).
We can only add 4 new dwarf galaxies to Ferguson's catalog. However, we confirm
that the dwarf galaxies in Fornax follow a similar surface brightness-magnitude
relation as the Local Group dwarfs. They also follow the color (metallicity) -
relation seen in other galaxy clusters. A formerly suspected excess of dwarf
galaxies surrounding the central cD galaxy NGC 1399 can finally be ruled out.
An enhanced density of objects around NGC 1399 can indeed be seen, but it
appears displaced with respect to the central galaxy and is identified as a
background cluster at z = 0.11 in Paper II of these series, which will discuss
spectroscopic results for our sample.Comment: 15 pages, LaTeX2e, uses aa.cls, including 10 PostScript figures, 1
additional gif figure; accepted for publication in A&AS, also available at
http://www.astro.puc.cl/~mhilker/publication.htm
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