Formation Of Globular Cluster Systems Research Articles

Formation of globular cluster systems – II. Impact of the cut-off of the cluster initial mass function

Observations of young star clusters reveal that the high-mass end of the cluster initial mass function (CIMF) deviates from a pure power-law and instead truncates exponentially. We investigate the effects of this truncation on the formation of globular cluster (GC) systems by updating our analytic model for cluster formation and evolution, which is based on dark matter halo merger trees coupled to empirical galactic scaling relations, and has been shown in previous work to match a wide array of observational data. The cutoff masses of $M_c=10^{6.5} M_{\odot}$ or $10^{7}M_{\odot}$ match many scaling relations: between the GC system mass and host halo mass, between the average metallicity of the GC system and host halo mass, and the distribution of cluster masses. This range of $M_c$ agrees with indirect measurements from extragalactic GC systems. Models with $M_c<10^{6.5}M_{\odot}$ cannot reproduce the observed GC metallicity and mass distributions in massive galaxies. The slope of the mass-metallicity relation for metal-poor clusters (blue tilt) for all $M_c$ models is consistent with observations within their errors, when measured using the same method. We introduce an alternative, more robust fitting method, which reveals a trend of increasing tilt slope for lower $M_c$. In our model the blue tilt arises because the metal-poor clusters form in relatively low-mass galaxies which lack sufficient cold gas to sample the CIMF at highest masses. Massive blue clusters form in progressively more massive galaxies and inherit their higher metallicity. The metal-rich clusters do not exhibit such a tilt because they form in significantly more massive galaxies, which have enough cold gas to fully sample the CIMF.

Formation of globular cluster systems: from dwarf galaxies to giants

Globular cluster (GC) systems around galaxies of a vast mass range show remarkably simple scaling relations. The combined mass of all GCs is a constant fraction of the total galaxy mass and the mean metallicity and metallicity dispersion of the GC system scale up weakly with galaxy mass. The metallicity of massive, metal-poor (‘blue’) clusters increases with cluster mass, while that of metal-rich (‘red’) clusters does not. A significant age–metallicity relation emerges from analysis of resolved stellar populations in Galactic GCs and unresolved populations in nearby galaxies. Remarkably, all these trends can be explained by a simple merger-based model developed in previous work and updated here using recent observations of galaxy scaling relations at high redshift. We show that the increasing dispersion of GC metallicity distributions with galaxy mass is a robust prediction of the model. It arises from more massive galaxies having more mergers that combine satellite GC systems. The average metallicity also increases by 0.6 over 3 dex in halo mass. The models show a non-linear trend between the GC system mass and host galaxy mass that is consistent with the data. The model does not consider GC self-enrichment, yet predicts a correlation between cluster mass and metallicity for massive blue clusters. The age–metallicity relation is another robust prediction of the model. Half of all clusters are predicted to form within the redshift range 5 < |$z$| < 2.3, corresponding to ages of 10.8–12.5 Gyr, in haloes of masses |$10^{11}\!-\!10^{12.5}\, \mathrm{M}_{\odot }$|⁠.

NONLINEAR COLOR-METALLICITY RELATIONS OF GLOBULAR CLUSTERS. V. NONLINEAR ABSORPTION-LINE INDEX VERSUS METALLICITY RELATIONS AND BIMODAL INDEX DISTRIBUTIONS OF M31 GLOBULAR CLUSTERS

Recent spectroscopy on the globular cluster (GC) system of M31 with unprecedented precision witnessed a clear bimodality in absorption-line index distributions of old GCs. Such division of extragalactic GCs, so far asserted mainly by photometric color bimodality, has been viewed as the presence of merely two distinct metallicity subgroups within individual galaxies and forms a critical backbone of various galaxy formation theories. Given that spectroscopy is a more detailed probe into stellar population than photometry, the discovery of index bimodality may point to the very existence of dual GC populations. However, here we show that the observed spectroscopic dichotomy of M31 GCs emerges due to the nonlinear nature of metallicity-to-index conversion and thus one does not necessarily have to invoke two separate GC subsystems. We take this as a close analogy to the recent view that metallicity-color nonlinearity is primarily responsible for observed GC color bimodality. We also demonstrate that the metallicity-sensitive magnesium line displays non-negligible metallicity-index nonlinearity and Balmer lines show rather strong nonlinearity. This gives rise to bimodal index distributions, which are routinely interpreted as bimodal metallicity distributions, not considering metallicity-index nonlinearity. Our findings give a new insight into the constitution of M31's GC system, which could change much of the current thought on the formation of GC systems and their host galaxies.

The Formation of Globular Cluster Systems in Massive Elliptical Galaxies: Globular Cluster Multimodality from Radial Variation of Stellar Populations

The most massive elliptical galaxies show a prominent multi-modality in their globular cluster system color distributions. Understanding the mechanisms which lead to multiple globular cluster sub-populations is essential for a complete picture of massive galaxy formation. By assuming that globular cluster formation traces the total star formation and taking into account the radial variations in the composite stellar populations predicted by the Pipino & Matteucci (2004) multi-zone photo-chemical evolution code, we compute the distribution of globular cluster properties as a function of galactocentric radius. We compare our results to the spectroscopic measurements of globular clusters in nearby early-type galaxies by Puzia et al. (2006) and show that the observed multi-modality in globular cluster systems of massive ellipticals can be, at least partly, ascribed to the radial variation in the mix of stellar populations. Our model predicts the presence of a super-metal-rich population of globular clusters in the most massive elliptical galaxies, which is in very good agreement with the spectroscopic observations. Furthermore, we investigate the impact of other non-linear mechanisms that shape the metallicity distribution of globular cluster systems, in particular the role of merger-induced globular cluster formation and a non-linear color-metallicity transformation, and discuss their influence in the context of our model (abridged)

Search for Formation Criteria of Globular Cluster Systems

The research of early evolution stages and formation of galaxies requires creation of appropriate non-linear theory. The formation process of globular cluster systems (GCS) covers the long period of time as probably one begins from a dark matter state. So far it is difficult to simulate formation of GCS and galaxies ab initio. That’s why it is necessary to construct exact analytically solvable models of non-linear non-stationary early stages of evolution of self-gravitating systems and revealing the instabilities on a background of non-equilibrium states. The formation and evolution of GCS at early stage of collapsing dark matter (or protogalaxy) can be explained by instability of the modes of the high oscillation degrees (Nuritdinov et al., 2000), which corresponds to rather small-scale perturbations of the density of collapsing system. The mode degree defines on the average the number of clusters.

On the formation of globular cluster systems in a hierarchical Universe

ABSTRA C T We have investigated the formation of globular cluster (GC) systems in the fiducial semianalytic model of galaxy formation of Cole et al., by assuming that GCs are formed at high redshifts ﷿z . 5fi in protogalactic fragments, and during the subsequent gas-rich merging of these fragments. Under these assumptions we have simulated the GC systems of 450 elliptical galaxies, and find that the majority (93 per cent) are intrinsically bimodal in metallicity. We find that, in the mean, the metal-rich GC subpopulations are younger than the metal-poor GC subpopulations, with ages of 9 and 12 Gyr respectively, and that the mean ages of the metalrich GCs are dependent upon host galaxy luminosity and environment (halo circular velocity), whereas the metal-poor GCs are not. We find that the continued gaseous merging of the protogalactic fragments leads to significant age-structure amongst the metal-rich GCs. These GCs exhibit a large age-range (5 to 12 Gyr), which increases for low-luminosity galaxies, and for galaxies in low circular velocity haloes. Moreover, the metal-rich GCs associated with low-luminosity field and/or group ellipticals are , 2 Gyr younger than the metal-rich GCs in luminous cluster ellipticals. We find that the total GC populations scale with host galaxy luminosity as NGC / L 1:25 V;gal , a result in agreement with observations of luminous elliptical galaxies. This scaling is due to a systematic increase in the M/L ratios of the galaxy haloes with luminosity for LV;gal . L * galaxies in the model. A comparison between the luminosity growth of the model ellipticals and their GC formation indicates that mergers do not significantly affect SN at z , 2. We find the mean colours of the both the metal-rich and metal-poor GCs exhibit only a weak dependence upon host galaxy luminosity, a result consistent with contemporary observations. We conclude that gaseous merging, the bulk of which occurs at 1 # z # 4i n ourLCDM model, leads to the formation of the metalrich peak of the GC systems of elliptical galaxies. We suggest that the formation and subsequent truncation of the metal-poor GCs in the protogalactic fragments is closely related to the star formation rate in these fragments, which may have been significantly higher at very early times.

Formation Scenarios for Globular Clusters and Their Host Galaxies

This review focuses on how galaxies and their globular cluster systems form. I first discuss the now fairly convincing evidence that some globular clusters form in galaxy starbursts/mergers. One way these observations are valuable is they place important constraints on the physics of the formation of globular clusters. Moreover, it is natural to associate the typically metal-rich clusters forming in mergers with the substantial metal-rich population of globulars around ellipticals, thereby implying an important role for galaxy mergers in the evolution of elliptical galaxies. I also highlight some new observational efforts aimed at constraining how and when elliptical galaxies and their globular cluster systems formed. These include systematic studies of the number of globular clusters around galaxies as a function of morphological type, studies of the kinematics of globular cluster populations in elliptical galaxies, and a variety of observational programs aimed at constraining the relative ages of globular clusters within galaxies as a function of cluster metallicity. The understanding of the formation of globular cluster systems and their host galaxies has grown dramatically in recent years, and the future looks equally promising.

Ellipticals with Kinematically Distinct Cores: WFPC2 Imaging of Globular Clusters

view Abstract Citations (103) References (60) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Ellipticals with Kinematically Distinct Cores: WFPC2 Imaging of Globular Clusters Forbes, Duncan A. ; Franx, Marijn ; Illingworth, Garth D. ; Carollo, C. M. Abstract New globular clusters may form in the merger of two galaxies. Perhaps the best examples of merger remnants are the set of ellipticals with kinematically distinct cores. Here we present Hubble Space Telescope (HST) Wide Field and Planetary Camera 2 (WFPC2) imaging of 14 kinematically distinct core ellipticals to examine their globular cluster systems. In particular, we probe the galaxy central regions, for which we might expect to see the strongest signatures of some formation and destruction processes. These data increase substantially the number of extragalactic globular cluster systems studied to date. We have developed a method for galaxy subtraction and selection of globular clusters which results in about 200 globulars per galaxy to a limiting magnitude of V ~ 25. Simulations of artificial globulars are described also. We find that the globular cluster luminosity, and color, vary only weakly, if at all, with galactocentric distance. The mean colors of globular clusters are constant with globular cluster magnitude. Several clear trends are also present. First, globular cluster colors are bluer (more metal poor by ~0.5 dex) than the underlying galaxy starlight at any given galactocentric distance. Second, we find a good correlation over roughly 10 magnitudes between the mean globular cluster metallicity and parent galaxy luminosity of the form Z is proportional to L^0.4^. This relationship includes dwarf ellipticals, spiral galaxy bulges, and giant ellipticals. Third, we find that globular cluster surface density distribution can be described by a core model, for which the core radius correlates with galaxy luminosity. Last, for the sample as a whole, the globular cluster systems are closely aligned with the galaxy major axis and are slightly rounder than the galaxy itself, although their are some notable exceptions. Our results favor scenarios in which ellipticals form from massive, gas rich progenitors at early epochs. Detailed simulations of the formation of globular cluster systems would be valuable to draw firmer conclusions. Publication: The Astrophysical Journal Pub Date: August 1996 DOI: 10.1086/177589 arXiv: arXiv:astro-ph/9604146 Bibcode: 1996ApJ...467..126F Keywords: GALAXIES: ELLIPTICAL AND LENTICULAR; CD; GALAXIES: KINEMATICS AND DYNAMICS; GALAXIES: NUCLEI; GALAXIES: STAR CLUSTERS; Astrophysics E-Print: text only is given here, 13 figures are available at http://www.ucolick.org/~forbes/home.html Paper accepted for publication in the Astrophysical Journal full text sources arXiv | ADS | data products SIMBAD (33) NED (14) MAST (1) ESA (1)

The Formation of Globular Cluster Systems. I. The Luminosity Function

view Abstract Citations (95) References (97) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Formation of Globular Cluster Systems. I. The Luminosity Function McLaughlin, Dean E. ; Pudritz, Ralph E. Abstract We present a numerical model for the globular cluster luminosity function (GCLF) which characterizes globular cluster systems (GCSs) around galaxies. This model is based on the idea that globular clusters formed in the cores of self-gravitating, magnetized, supergiant molecular clouds (SGMCs). A distribution of core masses is built up through a series of collisions within a parent SGMC. Massive cores are assumed to be destroyed (at a mass-dependent rate) by the act of star formation, allowing for the establishment of a unique, steady state mass spectrum. The model, which allows only for coalescent collisions between cores, fits observed GCS mass spectra very well above the GCLF peak mass m* ≃ 1.6 × 105 Msun, which is remarkably constant from galaxy to galaxy. We suggest that it represents the critical mass above which the cores of SGMCs become susceptible to internal disruption. Our fits to the mass spectra of the Milky Way, M31, and M87 GCSs predict that, in a given SGMC, the lifetimes of such cores should decrease at higher masses. The crucial factor in determining the shape of the GCLF is the ratio β of characteristic core disruption and collision timescales. It is shown that β does not differ between SGMCs in a single protogalaxy; this accounts for observations that GCLFs are independent of galactocentric radius. However, p does differ, and the overall shape of the GCLF along with it, between GCSs. Finally, our model suggests an "inside-out" sequence of GCS formation. Publication: The Astrophysical Journal Pub Date: February 1996 DOI: 10.1086/176754 Bibcode: 1996ApJ...457..578M Keywords: GALAXIES: FORMATION; GALAXIES: STAR CLUSTERS; GALAXY: GLOBULAR CLUSTERS: GENERAL; GALAXIES: LUMINOSITY FUNCTION; MASS FUNCTION full text sources ADS | data products SIMBAD (9) NED (2)

The Formation of Globular Cluster Systems: how, when, and where?

Globular clusters, as fossil remnants of the protogalactic era, provide unique traces of the earliest events of galaxy formation. However, new observations – especially from HST – are showing that massive, globular-like star clusters belong not only to the pregalactic era but can form right up to the present day under the right circumstances. Appropriate interpretation may now let us learnsimultaneouslyabout the process of cluster formation as well as the nature of the gaseous fragments from which the galaxies were assembled.

Supergiant molecular clouds and the formation of globular cluster systems

Supergiant molecular clouds and the formation of globular cluster systems