Browsing by Author "Kissler-Patig, M"
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- ItemExtragalactic globular clusters in the near infrared - I. A comparison between M87 and NGC 4478(2002) Kissler-Patig, M; Brodie, JP; Minniti, DWe compare optical and near infrared colours of globular clusters in M87, the central giant elliptical in Virgo, and NGC 4478, an intermediate luminosity galaxy in Virgo, close in projection to M87. Combining V and I photometry obtained with the WFPC2 on HST and K-s photometry obtained with the NIRC on Keck 1, we find the broad range in colour and previously detected bi-modality in M87. We confirm that NGC 4478 only hosts a blue sub-population of globular clusters and now show that these clusters' V-I and V-K colours are very similar to those of the halo globular clusters in Milky Way and M31. Most likely, a metal-rich sub-population never formed around this galaxy (rather than having formed and been destroyed later), probably because its metal-rich gas was stripped during its passage through the centre of the Virgo cluster.
- ItemExtragalactic globular clusters in the near-infrared - II. The globular clusters systems of NGC 3115 and NGC 4365(2002) Puzia, TH; Zepf, SE; Kissler-Patig, M; Hilker, M; Minniti, D; Goudfrooij, PWe combine near-infrared photometry obtained with the VLT/ISAAC instrument and archival HST/WFPC2 optical images to determine VIK magnitudes and colours of globular clusters in two early-type galaxies, NGC 3115 and NGC 4365. The combination of near-IR and optical photometry provides a way to lift the age-metallicity degeneracy. For NGC 3115, the globular cluster colours reveal two major sub-populations, consistent with previous studies. By comparing the V-I, V-K colours of the NGC 3115 globular clusters with stellar populations models, we find that the colour difference between the two greater than or similar to 10 Gyr old major sub-populations is primarily due to a difference in metallicity. We find Delta[Fe/H] = 1.0 +/- 0.3 dex and the blue (metal-poor) and red (metal-rich) globular cluster sub-populations being coeval within 3 Gyr. In contrast to the NGC 3115 globular clusters, the globular cluster system in NGC 4365 exhibits a more complex age and metallicity structure. We find a significant population of intermediate-age very metal-rich globular clusters along with an old population of both metal-rich and metal-poor clusters. Specifically, we observe a large population of globular clusters with red V K colours but intermediate V I colours, for which all current stellar population models give ages and metallicities in the range similar to2-8 Gyr and similar to0.5 Z(.) -3 Z(.), respectively. After 10 Gyr of passive evolution, the intermediate-age globular clusters in NGC 4365 will have colours which are consistent with the very metal-rich population of globular clusters in giant elliptical galaxies, such as M 87. Our results for both globular cluster systems are consistent with previous age and metallicity studies of the diffuse galactic light. In addition to the major globular cluster populations in NGC 3115 and NGC 4365 we report on the detection of objects with extremely red colours (V-K greater than or similar to3.8 mag), whose nature could not ultimately be revealed with the present data.
- ItemHubble Space Telescope observations of globular cluster systems along the Hubble sequence of spiral galaxies(2003) Goudfrooij, P; Strader, J; Brenneman, L; Kissler-Patig, M; Minniti, D; Huizinga, JEWe have studied the globular cluster systems of seven giant, edge-on spiral galaxies using Hubble Space Telescope imaging in V and I . The galaxy sample covers the Hubble types Sa to Sc, allowing us to study the variation of the properties of globular cluster systems along the Hubble sequence. The photometry reaches similar to1.5 mag beyond the turn-over magnitude of the globular cluster luminosity function for each galaxy. Specific frequencies of globular clusters (S-N values) were evaluated by comparing the numbers of globular clusters found in our WFPC2 pointings with those in our Milky Way that would be detected in the same spatial region if placed at the distance of the target galaxies. Results from this method were found to be consistent with the more commonly used method of constructing radial distribution functions of globular clusters. The S-N values of spirals with B /T less than or similar to 0.3 (i.e. spirals with a Hubble type later than about Sb) are consistent with a value of S-N = 0.55 +/- 0.25. We suggest that this population of globular clusters represents a 'universal', old halo population that is present around each galaxy. Most galaxies in our sample have S-N values that are consistent with a scenario in which globular cluster systems are made up of (i) the aforementioned halo population plus (ii) a population that is associated with bulges, which grows approximately linearly with the mass of the bulge. Such scenarios include the 'merger scenario' for the formation of elliptical galaxies as well as the 'multi-phase collapse' scenario, but it seems inconsistent with the 'secular evolution' scenario of Pfenniger & Norman, in which bulges are formed from disc stars by means of the redistribution of angular momentum through bar instabilities and/or minor perturbations. However, there is one bulge-dominated spiral galaxy in our sample (NGC 7814) with a low S-N value that is consistent with those of the latest-type spirals. This means that the 'secular evolution' scenario can still be viable for some bulge-dominated spirals. Thus, our results suggest that the formation histories of galaxy bulges of early-type spirals can be significantly different from one galaxy to another.
- ItemThe central region of the Fornax cluster I. A catalog and photometric properties of galaxies in selected CCD fields(1999) Hilker, M; Kissler-Patig, M; Richtler, T; Infante, L; Quintana, HWe 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 square degrees in total. The limiting surface brightness is around 24 mag arcsec(-2), similar to that of Ferguson's (1989) catalog, whereas our limiting total magnitude is around V similar or equal to 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 (Appendix A)(1). The properties and fit parameters of the surface brightness profiles for a sub-sample are presented as a second catalog (Appendix B)(1).
- ItemToward an understanding of the globular cluster overabundance around the central giant elliptical galaxy NGC 1399(1999) Kissler-Patig, M; Grillmair, CJ; Meylan, G; Brodie, JP; Minniti, D; Goudfrooij, PWe investigate the kinematics of a combined sample of 74 globular clusters around NGC 1399. Their high velocity dispersion, increasing with radius, indicates their association with the gravitational potential of the galaxy cluster rather than with that of NGC 1399 itself. We find no evidence for rotation in the full sample, although there is some indication of rotation in the outer regions. The data do not allow us to detect differences between the kinematics of the blue and red subpopulations of globular clusters. A comparison of the globular cluster systems of NGC 1399 and those of NGC 1404 and NGC 1380 indicates that the globular clusters in all three galaxies are likely to have formed via similar mechanisms and at similar epochs. The only property that distinguishes the NGC 1399 globular cluster system from these others is that it is 10 times more abundant. We summarize the evidence for associating these excess globular clusters with the galaxy cluster rather than with NGC 1399 itself and suggest that the overabundance can be explained by tidal stripping, at an early epoch, of neighboring galaxies and subsequent accumulation of globular clusters in the gravitational potential of the galaxy cluster.