Globular Clusters In Elliptical Galaxies Research Articles

Extremely α‐Enriched Globular Clusters in Early‐Type Galaxies: A Step toward the Dawn of Stellar Populations?

We compare (� /Fe), metallicity, and age distributions of globular clusters in elliptical, lenticular, and spiral gal- axies, which we derive from Lick line index measurements. We find a large number of globular clusters in elliptical galaxies that reach significantly higher (� /Fe) values (½� /Fe� > 0:5) than any clusters in lenticular and spiral gal- axies. Most of these extremely � -enriched globular clusters are old (t > 8 Gyr), and cover the metallicity range � 1P ½Z/HP0.Acomparisonwithsupernovayieldmodelssuggeststhattheprogenitorgascloudsofthese globular clustersmusthavebeenpredominantlyenrichedbymassivestars(k20 M� ),withlittlecontributionfromlowermass stars. The measured (� /Fe) ratios are also consistent with yields of very massive pair-instability supernovae (� 130Y190 M� ). Both scenarios imply that the chemical enrichment of the progenitor gas was completed on ex- tremely short timescales of the order of a few Myr. Given the lower (� /Fe) average ratios of the diffuse stellar popu- lation in early-type galaxies, our results suggest that these extremely � -enhanced globular clusters could be members of the very first generation of star clusters formed, and that their formation epochs would predate the formation of the majority of stars in giant early-type galaxies. Subject headingg galaxies: evolution — galaxies: formation — galaxies: star clusters — globular clusters: general

ON THE FORMATION OF GIANT ELLIPTICAL GALAXIES AND GLOBULAR CLUSTERS

I review the current status of understanding when, how long, and how giant elliptical galaxies formed, focusing on the globular clusters. Several observational evidences show that massive elliptical galaxies formed at z > 2 (> 10 Gyr ago). Giant elliptical galaxies show mostly a bimodal color distribution of globular clusters, indicating a factor of <TEX>$\approx$</TEX> 20 metallicity difference between the two peaks. The red globular clusters (RGCs) are closely related with the stellar halo in color and spatial distribution, while the blue globular clusters (BGCs) are not. The ratio of the number of the RGCs and that of the BGCs varies depending on galaxies. It is concluded that the BGCs might have formed 12-13 Gyr ago, while the RGCs and giant elliptical galaxies might have formed similarly 10-11 Gyr ago. It remains now to explain the existence of a gap between the RGC formation epoch and the BGC formation epoch, and the rapid metallicity increase during the gap (<TEX>${\Delta}t{\approx}$</TEX> 2 Gyr). If hierarchical merging can form a significant number of giant elliptical galaxies > 10 Gyr ago, several observational constraints from stars and globular clusters in elliptical galaxies can be explained.

X-Ray Binaries and Globular Clusters in Elliptical Galaxies

The X-ray emission from normal elliptical galaxies has two major components: soft emission from diffuse gas and harder emission from populations of accreting (low-mass) stellar X-ray binaries (LMXB). If LMXB populations are tied to the field stellar populations in galaxies, their total X-ray luminosities should be proportional to the optical luminosities of galaxies. However, recent ASCA and Chandra X-ray observations show that the global luminosities of LMXB components in ellipticals exhibit significant scatter at a given optical luminosity. This scatter may reflect a range of evolutionary stages among LMXB populations in ellipticals of different ages. If so, the ratio of the global LMXB X-ray luminosity to the galactic optical luminosity, L_LMXB/L_opt, may be used to determine when the bulk of stars were formed in individual ellipticals. To test this, we compare variations in L_LMXB/L_opt for LMXB populations in ellipticals to optically-derived estimates of stellar ages in the same galaxies. We find no correlation, implying that L_LMXB/L_opt variations are not good age indicators for ellipticals. Alternatively, LMXBs may be formed primarily in globular clusters (through stellar tidal interactions), rather than in the stellar fields of galaxies. Since elliptical galaxies exhibit a wide range of globular cluster populations for a given galaxian luminosity, this may induce a dispersion in the LMXB populations of ellipticals with similar optical luminosities. Indeed, we find that L_LMXB/L_opt ratios for LMXB populations are strongly correlated with the specific globular cluster frequencies in elliptical galaxies. This suggests that most LMXBs were formed in globular clusters.

Globular Clusters in Elliptical Galaxies: Constraints on Mergers

There exists a relationship between globular cluster mean metallicity and parent galaxy luminosity (e.g. Brodie &amp; Huchra 1991; Forbes et al. 1996), which appears to be similar to that between stellar metallicity and galaxy luminosity. The globular cluster relation has a similar slope but is offset by about 0.5 dex to lower metallicity. The similarity of these relations suggests that both the globular cluster system and their parent galaxy have shared a common chemical enrichment history. If we can understand the formation and evolution of the globulars, we will also learn something about galaxy formation. With this aim in mind we have created the SAGES (Study of the Astrophysics of Globular clusters in Extragalactic Systems) project. Project members include Brodie, Elson, Forbes, Freeman, Grillmair, Huchra, Kissler–Patig and Schroder. We are using HST Imaging and Keck spectroscopy to study extragalactic globular cluster systems. Further details are given at http://www.ucolick.org/~mkissler/Sages/sages.html.

Metallicity Distributions in Extragalactic Globular Cluster Systems: Constraints on Globular Cluster and Galaxy Formation

The merger model for elliptical galaxy formation has received increasing attention since it was first suggested by Toomre &amp; Toomre (1972). Van den Bergh (1984) pointed out a problem with the idea that elliptical galaxies were formed by simply combining two, or more, spiral galaxies. He noted that the specific frequency (SN, number of globular clusters per unit galaxy light) is systematically lower for spirals than for ellipticals. Schweizer (1987) suggested that globular clusters (GCs) might be expected to form in the merger process, thereby alleviating or possibly eliminating the SN problem. Ashman &amp; Zepf (1992) developed this idea into a merger model for GC formation with testable predictions.We recently examined this model in the light of new HST and ground-based imaging data on the blue and red sub-populations of GCs in elliptical galaxies (Forbes, Brodie &amp; Grillmair 1997). We concluded that the merger model for GC formation has serious problems, particularly in explaining the characteristics of GCs in giant elliptical galaxies with high SN. A multi-phase collapse scenario was suggested as more consistent with the available evidence.

Specific frequencies of globular clusters in elliptical galaxies - A new test of the extragalactic distance scale

view Abstract Citations (9) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Specific Frequencies of Globular Clusters in Elliptical Galaxies: A New Test of the Extragalactic Distance Scale de Vaucouleurs, G. Abstract The specific frequencies of globular clusters in elliptical galaxies, S, being the ratio of their (extrapolated) total number, N_t_, to the absolute luminosity of the galaxy, depend on the adopted distance scale. If the distance is derived from the redshift and some assumed value of h = H/100, the optimum value, h_m_, may be derived for a sample of normal E galaxies covering a sufficient range of distances by finding the value of h (or of log h) which minimizes either the dispersion σ(S) or σ(log S) or, better, the relative dispersion F(S) = σ(S)/(S>. Application to a sample of nine E galaxies for which Harris and van den Bergh calculated S for h = 0.50, 0.75, and 1.00, gives H_m_ = (85 +/- 4) km s^-1^ Mpc^-1^. This is also the value which optimizes the agreement between the different methods and minimizes <S> = 4.7 +/- 0.7. The mean Hubble ratio predicted by the original short scale (EDS VII) for the same nine objects was <H^*^> = 87 +/- 3 (Appendix A). Because all nine objects are in the north Galactic hemisphere where the apparent Hubble ratio is known to be about 20%-30% less than in the south Galactic hemisphere, the corresponding all-sky average could be as high as H = 95, in close agreement with the short-scale value. An alternative use of the errors by means of linear relations and correlation coefficients with the Hubble modulus HM makes little difference to the solutions. The frequency function of 28 solutions is very nearly Gaussian with mode <H_m_> = 86 +/- 2 and dispersion σ(H_m_) = 12 (Appendix B). A suggestion to use weighted means is tested, but although agreeing in the mean (84.5 +/- 6) with the unweighted solutions, it leads to a much larger scatter and is contraindicated (Appendix C). A larger, more precise and more homogeneous collection of counts, magnitudes, and extinction corrections over a bigger range of distances will be necessary to better evaluate the errors and potential precision of the method. Publication: The Astrophysical Journal Pub Date: September 1993 DOI: 10.1086/173139 Bibcode: 1993ApJ...415...33D Keywords: Elliptical Galaxies; Galactic Structure; Globular Clusters; Hubble Constant; Distance; Lenticular Bodies; Scaling; Astrophysics; COSMOLOGY: DISTANCE SCALE; GALAXIES: ELLIPTICAL AND LENTICULAR; CD; GALAXY: GLOBULAR CLUSTERS: GENERAL full text sources ADS | data products SIMBAD (9) NED (9)

On the origin of globular clusters in elliptical galaxies

Multivariate statistical analysis is used to correlate the estimated total numbers of globular clusters in elliptical galaxies (N sub gc), and the numbers per unit luminosity (S sub N), with a variety of observed properties of the host galaxies. Both N sub gc and S sub N are correlated with the so-called fundamental plane of elliptical galaxies, suggesting that the processes which determine global properties of ellipticals also largely determine their globular cluster content, although a considerable residual scatter remians. The redder (presumably more metal-rich) galaxies were found to have more globular clusters, implying that a dissipative formation mechanism was involved. Galaxies which have more anisotropic velocity distributions were also found to have more clusters, suggesting that mergers may have been important in the production of globular systems.