Extragalactic Globular Cluster Systems

Das Ziel dieser Dissertation ist die spektroskopische Studie von extragalaktischen Kugelsternhaufensystemen. Ihre Motivation ist das bessere Verstaendnis der Bildung und Entwicklung dieser Kugelsternhaufensysteme und ihrer Wirtsgalaxien. Zu diesem Zweck werden spektroskopische Linienindices des integrierten Lichts einzelner extragalaktischer Kugelsternhaufen gemessen, aus denen das Alter, die Metallizitaet und das Haeufigkeitsverhaeltnis von alpha-Elementen zu Eisen (im folgenden [alpha/Fe]) abgeleitet werden kann. Dies erlaubt detaillierte Rueckschluesse auf ihre Entstehungsepochen und -mechanismen

Extragalactic Globular Cluster Systems

Das Ziel dieser Dissertation ist die spektroskopische Studie von extragalaktischen Kugelsternhaufensystemen. Ihre Motivation ist das bessere Verstaendnis der Bildung und Entwicklung dieser Kugelsternhaufensysteme und ihrer Wirtsgalaxien. Zu diesem Zweck werden spektroskopische Linienindices des integrierten Lichts einzelner extragalaktischer Kugelsternhaufen gemessen, aus denen das Alter, die Metallizitaet und das Haeufigkeitsverhaeltnis von alpha-Elementen zu Eisen (im folgenden [alpha/Fe]) abgeleitet werden kann. Dies erlaubt detaillierte Rueckschluesse auf ihre Entstehungsepochen und -mechanismen

Old Metal-rich Globular Cluster Populations: Peak Color and Peak Metallicity Trends with Mass of Host Spheroids

We address the problem of the factors contributing to a peak color trend of old metal-rich globular cluster (MRGC) populations with mass of their hosts, early-type galaxies and spheroidal subsystems of spiral ones (spheroids). The color-mass trend is often converted to a metallicity-mass trend under the assumption that age effects are small or negligible. While direct estimates of the ages of MRGC populations neither can rule out nor reliably support the populations' age trend, key data on timing of the formation of spheroids and other indirect evidence imply it in the sense: the more massive spheroid the older on average its MRGC population. We show that the contribution of an allowable age trend of the MRGC populations to their peak color trend can achieve up to ~50 % or so. In this event the comparable value of the color trend, ~30 %, is due to alpha-element ratio systematic variations of the order of Delta[alpha/Fe] ~ 0.1 to 0.2 dex because of a correlation between the [alpha/Fe] ratios and age. Hence a systematic variation of exactly [Fe/H] ratios may turn out to be less significant among the contributors, and its range many times lower, i.e. of the order of Delta[Fe/H] ~ 0.1 or even none, than the corresponding range deduced by assuming no age trend.Comment: 5 pages, 1 figure, accepted for publication in Astronomische Nachrichte

On Collision Course: The Nature of the Binary Star Cluster NGC 2006 / SL 538

The LMC hosts a rich variety of star clusters seen in close projected proximity. Ages have been derived for few of them showing differences up to few million years, hinting at being binary star clusters. However, final confirmation needs to be done through spectroscopic analysis. Here we focus on the LMC cluster pair NGC2006-SL538 and aim to determine whether the star cluster pair is a bound entity (binary star cluster) or a chance alignment. Using the MIKE echelle spectrograph at LCO we have acquired integrated-light spectra for each cluster. We have measured radial velocities by two methods: a) direct line profile measurement yields v$_r=300.3\pm5\pm6$ km/s for NGC2006 and $v_r=310.2\pm4\pm6$ km/s for SL538. b) By comparing observed spectra with synthetic bootstrapped spectra yielding $v_r=311.0\pm0.6$ km/s for NGC2006 and $v_r=309.4\pm0.5$ km/s for SL538. Finally when spectra are directly compared, we find a ${\Delta}v=1.08\pm0.47$ km/s. Full-spectrum SED fits reveal that the stellar population ages lie in the range 13-21 Myr with a metallicity of Z=0.008. We find indications for differences in the chemical abundance patterns as revealed by the helium absorption lines between the two clusters. The dynamical analysis shows that the two clusters are likely to merge within the next $\sim$150 Myr. The NGC2006-SL538 cluster pair shows radial velocities, stellar population and dynamical parameters consistent with a gravitational bound entity. We conclude that this is a genuine binary cluster pair, and we propose that their differences in ages and stellar population chemistry is most likely due to variances in their chemical enrichment history within their environment. We suggest that their formation may have taken place in a loosely bound star-formation complex which saw initial fragmentation but then had its clusters become a gravitationally bound pair by tidal capture.Comment: Accepted for publication in Astronomy & Astrophysics. 15 pages, 10 figures in low resolutio