arXiv subjects

M. Hilker

Publications and source records attributed to M. Hilker.

130 records · Page 8Linked to original sources

arXiv1998

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.

astro-ph↗

arXiv1998

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.

astro-ph↗

arXiv1997

NGC 1427A - an LMC type galaxy in the Fornax Cluster

We have discovered that the Fornax irregular galaxy NGC 1427A is in very many respects a twin of the Large Magellanic Cloud. Based on B, V, I, and H alpha images, we find the following. The light of the galaxy is dominated by high surface brightness regions in the south-west that are superimposed by a half-ring of OB associations and H II regions indicating recent star formation. The colors of the main stellar body are (V-I) = 0.8 mag and (B-V) = 0.4 mag, comparable to the LMC colors. A low surface brightness cloud north of the main body as well as a LSB tail in the west have colors (V-I = 0.2 mag) that are more typical for blue compact dwarf galaxies. We identified a system of cluster candidates with mean ages < 2 Gyr (assuming a LMC metallicity) comprising the richest cluster system in an irregular galaxy observed up to now outside the Local Group. In X-ray wavelengths NGC 1427A appears with a relatively soft and complex spectrum.

astro-ph↗

arXiv1996

Globular cluster systems of early--type galaxies in Fornax

We studied the properties of the globular cluster systems of five early--type galaxies in the Fornax galaxy cluster: NGC 1374, NGC 1379, NGC 1387, NGC 1427, and the central giant elliptical NGC 1399. From the investigation of their number of globular clusters, specific frequency, color distribution, surface density profile, and spatial distribution, we conclude that our faint ellipticals have no more globular clusters than spirals of the same mass, and neither differ in their other properties. For these galaxies there is no need to imply a different formation scenario of the globular cluster system. The central giant elliptical has far more globular clusters and show signatures of a different history in the building up of its globular cluster system.

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