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Register a new userFormation Efficiencies of Old Globular Clusters - from Dwarf to Giant Galaxies
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For the full galaxy mass range, we find that previously observed trends of globular cluster (GC) system scaling parameters (number, luminosity or mass of all GCs in a galaxy normalized to the host galaxy luminosity or mass, e.g. S_L) as a function of galaxy mass, holds irrespective of galaxy type or environment. The S_L-value of early-type galaxies is, on average, twice that of late-types. We derive theoretical predictions which describe remarkably well the observed GC system scaling parameter distributions given an assumed GC formation efficiency ({eta}), i.e. the ratio of total mass in GCs to galaxy halo mass. It has a mean value of {eta}=5.5e-5 , and an increasing scatter toward low galaxy mass. The excess {eta}-values of some massive galaxies compared to expectations from the mean model prediction, may be attributed to an efficient GC formation, inefficient production of field stars, accretion of low-mass high-{eta} galaxies or likely a mixture of all these effects.
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We present a study of the old globular clusters (GC) using archival F606W and F814W HST/ACS images of 19 Magellanic-type dwarf Irregular (dIrr) galaxies found in nearby (2 - 8 Mpc) associations of only dwarf galaxies. All dIrrs have absolute magnitudes fainter than or equal to the SMC (Mv = -16.2 mag). We detect 50 GC candidates in 13 dIrrs, of which 37 have (V-I) colors consistent with blue (old, metal-poor) GCs (bGC). The luminosity function (LF) of the bGCs in our sample peaks at Mv = -7.41 +/- 0.22 mag, consistent with other galaxy types. The width of the LF is sigma = 1.79 +/- 0.31 which is typical for dIrrs, but broader than the typical width in massive galaxies. The half-light radii and ellipticities of the GCs in our sample (rh ~ 3.3 pc, e ~ 0.1) are similar to those of old GCs in the Magellanic Clouds and to those of Old Halo (OH) GCs in our Galaxy, but not as extended and spherical as the Galactic Young Halo (YH) GCs (rh ~ 7.7 pc, e ~ 0.06). The e distribution shows a turnover rather than a power law as observed for the Galactic GCs. This might suggest that GCs in dIrrs are kinematically young and not fully relaxed yet. The present-day specific frequencies (SN) span a broad range: 0.3 < SN < 11. Assuming a dissipationless age fading of the galaxy light, the SN values would increase by a factor of ~ 2.5 to 16, comparable with values for early-type dwarfs (dE/dSphs). A bright central GC candidate, similar to nuclear clusters of dEs, is observed in one of our dIrrs: NGC 1959. This nuclear GC has luminosity, color, and structural parameters similar to that of wCen and M54, suggesting that the latter might have their origin in the central regions of similar Galactic building blocks. A comparison between properties of bGCs and Galactic YH GCs, suspected to have originated from similar dIrrs, is performed.
In a purely cold dark matter universe, the initial matter power spectrum and its subsequent gravitational growth contain no special mass- or time-scales, and so neither do the emergent population statistics of internal dark matter (DM) halo properties. Using 1.5 million halos from three IllustrisTNG realizations of a LambdaCDM universe, we show that galaxy formation physics drives non-monotonic features (wiggles) into DM property statistics across six decades in halo mass, from dwarf galaxies to galaxy clusters. We characterize these features by extracting the halo mass-dependent statistics of five DM halo properties -- velocity dispersion, NFW concentration, density- and velocity-space shapes, and formation time -- using kernel-localized linear regression (KLLR). Comparing precise estimates of normalizations, slopes, and covariances between realizations with and without galaxy formation, we find systematic deviations across all mass-scales, with maximum deviations of 25% at the Milky-Way mass of 1e12 Msun. The mass-dependence of the wiggles is set by the interplay between different cooling and feedback mechanisms, and we discuss its observational implications. The property covariances depend strongly on halo mass and physics treatment, but the correlations are mostly robust. Using multivariate KLLR and interpretable machine learning, we show the halo concentration and velocity-space shape are principal contributors, at different mass, to the velocity dispersion variance. Statistics of mass accretion rate and DM surface pressure energy are provided in an appendix. We publicly release halo property catalogs and KLLR parameters for the TNG runs at twenty epochs up to z = 12.
We present an analysis of the large set of microlensing events detected so far toward the Galactic center with the purpose of investigating whether some of the dark lenses are located in Galactic globular clusters. We find that in four cases some events might indeed be due to lenses located in the globular clusters themselves. We also give a rough estimate for the average lens mass of the events being highly aligned with Galactic globular cluster centers and find that, under reasonable assumptions, the deflectors could most probably be either brown dwarfs, M-stars or stellar remnants.
We performed the photometric analysis of M2 and M92 globular clusters in g and r bands of SLOAN photometric system. We transformed these g and r bands into BV bands of Johnson-Cousins photometric system and built the color magnitude diagram (CMD). We estimated the age, and metallicity of both the clusters, by fitting Padova isochrones of different age and metallicities onto the CMD. We studied Einstein and de Sitter model, bench mark model, the cosmological parameters by WMAP and Planck surveys. Finally, we compared estimated age of globular clusters to the ages from the cosmological models and cosmological parameters values of WMAP and Planck surveys.
Aims: We describe our newly developed approach to detailed abundance analysis from integrated-light high-dispersion spectra of star clusters. As a pilot project, we measure abundances of several elements for three globular clusters (GCs) in the Fornax dSph, using VLT/UVES spectra. Methods: We divide the cluster colour-magnitude diagrams into about 100 bins and compute synthetic spectra for each bin. The individual model spectra are co-added and the abundances are iteratively adjusted until the best match to the observed spectra is achieved. Results: We find [Fe/H] = -2.3, -1.4 and -2.1 for Fornax 3, 4 and 5, with +/-0.1 dex uncertainties. Fornax 3 and 5 are thus similar in metallicity to the most metal-poor Milky Way GCs and fall near the extreme metal-poor end of the field star metallicity distribution in Fornax. The [alpha/Fe] ratios, as traced by Ca and Ti, are enhanced with respect to the Solar composition at the level of about +0.25 dex for Fornax 3 and 5, and possibly slightly less (about +0.12 dex) for Fornax 4. For all three clusters the [Mg/Fe] ratio is significantly less elevated than [Ca/Fe] and [Ti/Fe], possibly an effect of the abundance anomalies that are well-known in Galactic GCs. We thus confirm that Mg may be a poor proxy for the overall alpha-element abundances for GCs. The abundance patterns of heavy elements (Y, Ba and Eu) indicate a dominant contribution to nucleosynthesis from the r-process in all three clusters, with a mean [Ba/Eu]=-0.7, suggesting rapid formation of the GCs. Conclusions: Combining our results with literature data for Fornax 1 and 2, four of the five Fornax GCs fall in the range -2.5<[Fe/H]<-2, while Fornax 4 is substantially more metal-rich than the others. The indications that abundance anomalies are detectable in integrated light are encouraging, particularly for the prospects of detecting such anomalies in young, massive star clusters.
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