We combine a new, comprehensive database for globular cluster populations in all types of galaxies with a new calibration of galaxy halo masses based entirely on weak lensing. Correlating these two sets of data, we find that the mass ratio $η\equiv M_{GCS}/M_{h}$ (total mass in globular clusters, divided by halo mass) is essentially constant at $\langle η\rangle \sim 4 \times 10^{-5}$, strongly confirming earlier suggestions in the literature. Globular clusters are the only known stellar population that formed in essentially direct proportion to host galaxy halo mass. The intrinsic scatter in $η$ appears to be at most 0.2 dex; we argue that some of this scatter is due to differing degrees of tidal stripping of the globular cluster systems between central and satellite galaxies. We suggest that this correlation can be understood if most globular clusters form at very early stages in galaxy evolution, largely avoiding the feedback processes that inhibited the bulk of field-star formation in their host galaxies. The actual mean value of $η$ also suggests that about $1/4$ of the \emph{initial} gas mass present in protogalaxies collected into GMCs large enough to form massive, dense star clusters. Finally, our calibration of $\langle η\rangle$ indicates that the halo masses of the Milky Way and M31 are $(1.2\pm0.5)\times 10^{12} M_{\odot}$ and $(3.9\pm1.8)\times 10^{12} M_{\odot}$ respectively.
We use a sample of newly-discovered globular clusters from the Pan-Andromeda Archaeological Survey (PAndAS) in combination with previously-catalogued objects to map the spatial distribution of globular clusters in the M31 halo. At projected radii beyond ~30 kpc, where large coherent stellar streams are readily distinguished in the field, there is a striking correlation between these features and the positions of the globular clusters. Adopting a simple Monte Carlo approach, we test the significance of this association by computing the probability that it could be due to the chance alignment of…
Based upon a metallicity selection, we identify a significant sub-population of the inner halo globular clusters in the Andromeda Galaxy which we name the Dulais Structure. It is distinguished as a co-rotating group of 10-20 globular clusters which appear to be kinematically distinct from, and on average more metal-poor than, the majority of the inner halo population. Intriguingly, the orbital axis of this Dulais Structure is closely aligned with that of the younger accretion event recently identified using a sub-population of globular clusters in the outer halo of Andromeda, and this is stron…
We use Hubble Space Telescope imaging to show that the nearby dwarf starburst galaxy NGC 4449 has an unusual abundance of luminous red star clusters. Joint constraints from integrated photometry, low-resolution spectroscopy, dynamical mass-to-light ratios, and resolved color-magnitude diagrams provide evidence that some of these clusters are old globular clusters. Spectroscopic data for two massive clusters suggest intermediate metallicities ([Fe/H] ~ -1) and subsolar Mg enhancement ([Mg/Fe] ~ -0.1 to -0.2). One of these clusters may be the nucleus of a tidally disrupting dwarf galaxy; the oth…
Small distortions in the images of Einstein rings or giant arcs offer the exciting prospect of detecting dark matter haloes or subhaloes of mass below $10^9$M$_{\odot}$, most of which are too small to have made a visible galaxy. A very large number of such haloes are predicted to exist in the cold dark matter model of cosmogony; in contrast other models, such as warm dark matter, predict no haloes below a mass of this order which depends on the properties of the warm dark matter particle. Attempting to detect these small perturbers could therefore discriminate between different kinds of dark m…
We investigate analytically whether in a close encounter with a star, a Dark Matter particle can be accelerated above the escape speed of a Globular Cluster and be ejected. We find that this mechanism is not sufficient to eject a massive, extended Dark Matter halo by the present time. Combined with observations of isolated Globular Clusters that may not have had their halos tidally stripped, these results cast doubt on the scenario in which Globular Clusters formed in Dark Matter halos.
The sizes of entire systems of globular clusters (GCs) depend on the formation and destruction histories of the GCs themselves, but also on the assembly, merger and accretion history of the dark matter (DM) haloes that they inhabit. Recent work has shown a linear relation between total mass of globular clusters in the globular cluster system and the mass of its host dark matter halo, calibrated from weak lensing. Here we extend this to GC system sizes, by studying the radial density profiles of GCs around galaxies in nearby galaxy groups. We find that radial density profiles of the GC systems …
Globular clusters are unique tracers of ancient star formation. We determine the formation efficiencies of globular clusters across cosmic time by modeling the formation and dynamical evolution of the globular cluster population of a Milky Way type galaxy in hierarchical cosmology, using the merger tree from the Via Lactea II simulation. All of the models are constrained to reproduce the observed specific frequency and initial mass function of globular clusters in isolated dwarfs. Globular cluster orbits are then computed in a time varying gravitational potential after they are either accreted…
The conjecture that the ancient globular clusters (GCs) formed at the center of their own dark matter halos was first proposed by Peebles (1984), and has recently been revived to explain the puzzling abundance patterns observed within many GCs. In this paper we demonstrate that the outer stellar density profile of isolated GCs is very sensitive to the presence of an extended dark halo. The GCs NGC 2419, located at 90 kpc from the center of our Galaxy, and MGC1, located at ~200 kpc from the center of M31, are ideal laboratories for testing the scenario that GCs formed at the centers of massive …
We explore the kinematics and orbital properties of a sample of red giants in the halo system of the Milky Way that are thought to have formed in globular clusters, based on their anomalously strong UV/blue CN bands. The orbital parameters of the CN-strong halo stars are compared to those of the inner- and outer-halo populations as described by Carollo et al., and to the orbital parameters of globular clusters with well-studied Galactic orbits. The CN-strong field stars and the globular clusters both exhibit kinematics and orbital properties similar to the inner-halo population, indicating tha…
High mass galaxies, with halo masses $M_{200} \ge 10^{10} M_{\odot}$, reveal a remarkable near-linear relation between their globular cluster (GC) system mass and their host galaxy halo mass. Extending this relation to the mass range of dwarf galaxies has been problematic due to the difficulty in measuring independent halo masses. Here we derive new halo masses based on stellar and HI gas kinematics for a sample of nearby dwarf galaxies with GC systems. We find that the GC system mass--halo mass relation for galaxies populated by GCs holds from halo masses of $M_{200} \sim 10^{14} M_{\odot}$ d…
In the hierarchical formation scenario in which the outer halo of the Milky Way is the result of the continuous accretion of low-mass galaxies, a fraction of the Galactic globular cluster system might have originated in and been accreted with already extinct dwarf galaxies. In this context, we expect that the remnants of these progenitor galaxies might be still populating the surroundings of those accreted globulars. In this work, we present wide-field photometry of a sample of 23 globular clusters in the Galactocentric distance range 10 < Rg < 40kpc, which we use to search for remnants of the…
I discuss a search for red giant stars in the Galactic halo with light-element abundances similar to second-generation globular cluster stars, and discuss the implications of such a population for globular cluster formation models and the balance between in situ star formation and accretion for the assembly of the Galactic halo.
We re-investigate the Fornax cusp-core problem using observational results on the spatial and mass distributions of globular clusters (GCs) in order to put constraints on the dark matter profile. We model Fornax using high-resolution N-body simulations with entirely live systems, i.e. self-gravitating systems composed of stars and dark matter, which account correctly for dynamical friction and tidal effects between Fornax and the globular clusters. We test two alternative hypotheses, which are a cored and a cuspy halo for Fornax by exploring a reasonable range of initial conditions on globular…
We present the first kinematic analysis of the far outer halo globular cluster (GC) population in the Local Group galaxy M31. Our sample contains 53 objects with projected radii of ~20-130 kpc, of which 44 have no previous spectroscopic information. GCs with projected radii >30 kpc are found to exhibit net rotation around the minor axis of M31, in the same sense as the inner GCs, albeit with a smaller amplitude of 79 +/-19 km/s. The rotation-corrected velocity dispersion of the full halo GC sample is 106 +/-12 km/s, which we observe to decrease with increasing projected radius. We find compell…
In order to find the possible progenitors of Milky Way globular clusters, we perform orbit integrations to track the orbits of 170 Galactic globular clusters and the eleven classical Milky Way satellite galaxies backwards in time for 11 Gyr in a Milky-Way-plus-satellites potential including the response of the MW to the infall of the Large Magellanic Cloud and the effect of dynamical friction on the satellites. To evaluate possible past associations, we devise a globular-cluster--satellite binding criterion based on the satellite's tidal radius and escape velocity and we test it on globular cl…
We seek to differentiate dynamical and morphological attributes between globular clusters (GCs) that were formed inside their own dark matter (DM) mini-halo, and those who were not. We employ high resolution full N-body simulations on GPU of GCs with and without a DM mini-halo, orbiting a Fornax-like dwarf galaxy. For GCs with DM, we observe that this dark extra mass triggers a tidal radius growth that allows the mini-halo to act as a protective shield against tidal stripping, being itself stripped beforehand the stars. We demonstrate that this shielding effect becomes negligible when the tida…
We use a fully GPU $N$-body code to demonstrate that dark matter minihalos, as a new component of globular clusters, resolve both the timing and cusp-core problems in Fornax if the five (or six) globular clusters were recently accreted ($\leq$ 3 Gyr ago) by Fornax. Under these assumptions, infall of these globular clusters does not occur and no star clusters form in the centre of Fornax in accordance with observations. We find that crossings of globular clusters that have DM minihalos near the Fornax centre induce a cusp-to-core transition of the dark matter halo and hence resolve the cusp-cor…
Stellar dynamical model globular clusters are introduced into reconstituted versions of the dark matter halos of the Via-Lactea II (VL-2) simulation to follow the star cluster tidal mass loss and stellar stream formation. The clusters initially evolve within their local sub-galactic halo, later being accreted into the main halo. Stars are continually removed from the clusters, but those that emerged in the sub-galactic halos are dispersed in a wide stream when accreted into the main halo. Thin tidal streams that survive to the present can begin to form once a cluster is in the main halo. A hig…
The globular cluster systems of galaxies are well-known to extend to large galactocentric radii. Here we quantify the size of GC systems using the half number radius of 22 GC systems around early-type galaxies from the literature. We compare GC system sizes to the sizes and masses of their host galaxies. We find that GC systems typically extend to 4$\times$ that of the host galaxy size, however this factor varies with galaxy stellar mass from about 3$\times$ for M$^{\ast}$ galaxies to 5$\times$ for the most massive galaxies in the universe. The size of a GC system scales approximately linearly…
We propose that the observed stellar halo around the globular cluster (GC) NGC 1851 is evidence for its formation in the central region of its defunct host dwarf galaxy. We numerically investigate the long-term dynamical evolution of a nucleated dwarf galaxy embedded in a massive dark matter halo under the strong tidal field of the Galaxy. The dwarf galaxy is assumed to have a stellar nucleus (or a nuclear star cluster) that could be the progenitor for NGC 1851. We find that although the dark matter halo and the stellar envelope of the host dwarf of NGC 1851 can be almost completely stripped d…
We examine various implications from a dynamical and chemical model of globular clusters (GCs), which successfully reproduces the observed abundance patterns and the multiple populations of stars in these systems assuming chemical enrichment from fast rotating massive stars. Using the model of Decressin et al. (2007) we determine the ratio between the observed, present-day mass of globular clusters and their initial stellar mass as a function of the stellar initial mass function (IMF). We also compute the mass of low-mass stars ejected, and the amount of hydrogen ionising photons emitted by th…
We present new identifications of five red giant stars in the Galactic halo with chemical abundance patterns that indicate they originally formed in globular clusters. Using data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) Survey available through Sloan Digital Sky Survey Data Release 12 (DR12), we first identify likely halo giants, and then search those for the well-known chemical tags associated with globular clusters, specifically enrichment in nitrogen and aluminum. We find that 2% of the halo giants in our sample have this chemical signature, in agreement with…
This is a "biased" review because I will show recent evidence on the contribution of globular clusters (GCs) to the halo of our Galaxy seen through the lens of the new paradigm of multiple populations in GCs. I will show a few examples where the chemistry of multiple populations helps to answer hot questions including whether and how much GCs did contribute to the halo population, if we have evidence of the GCs-halo link, what are the strengths and weak points concerning this contribution.
We present a spectroscopic search for halo field stars that originally formed in globular clusters. Using moderate-resolution SDSS-III/SEGUE-2 spectra of 561 red giants with typical halo metallicities (-1.8 < [Fe/H] < -1.0), we identify 16 stars, 3% of the sample, with CN and CH bandstrength behavior indicating depleted carbon and enhanced nitrogen abundances relative to the rest of the data set. Since globular clusters are the only environment known in which stars form with this pattern of atypical light-element abundances, we claim that these stars are second-generation globular cluster star…
We present evidence for the contribution of high-mass globular clusters to the stellar halo of the Galaxy. Using SDSS-II/SEGUE spectra of over 1900 G- and K-type halo giants, we identify for the first time a subset of stars with CN bandstrengths significantly larger, and CH bandstrengths lower, than the majority of halo field stars, at fixed temperature and metallicity. Since CN bandstrength inhomogeneity and the usual attendant abundance variations are presently understood as a result of star formation in globular clusters, we interpret this subset of halo giants as a result of globular clust…
We perform an evolutionary multivariate analysis of a sample of 54 Galactic globular clusters with high-quality colour-magnitude diagrams and well-determined ages. The four parameters adopted for the analysis are: metallicity, age, maximum temperature on the horizontal branch, and absolute V magnitude. Our cladistic analysis breaks the sample into three novel groups. An a posteriori kinematical analysis puts groups 1 and 2 in the halo, and group 3 in the thick disc. The halo and disc clusters separately follow a luminosity-metallicity relation of much weaker slope than galaxies. This property …
While recent sky surveys have uncovered large numbers of ever fainter Milky Way satellites, their classification as star clusters, low-luminosity galaxies, or tidal overdensities remains often unclear. Likewise, their contributions to the build-up of the halo is yet debated. In this contribution we will discuss the current knowledge of the stellar populations and chemo-dynamics in these puzzling satellites, with a particular focus on dwarf spheroidal galaxies and the globular clusters in the outer Galactic halo. Also the question of whether some of the outermost halo objects are dynamically as…
Color-magnitude diagrams (CMDs) derived from Hubble Space Telescope (HST) Advanced Camera for Surveys F606W,F814W photometry of 6 globular clusters (GCs) are presented. The six GCs form two loose groupings in Galactocentric distance (Rgc): IC 4499, NGC 6426, and Ruprecht 106 at ~15-20 kpc and NGC 7006, Palomar 15, and Pyxis at ~40 kpc. The CMDs allow the ages to be estimated from the main sequence turnoff in every case. In addition, the age of Palomar 5 (Rgc ~ 18 kpc) is estimated using archival HST Wide Field Planetary Camera 2 V,I photometry. The age analysis reveals the following: IC 4499, …
NGC 2419 is a massive outer halo Galactic globular cluster whose stars have previously been shown to have somewhat peculiar abundance patterns. We have observed seven luminous giants that are members of NGC 2419 with Keck/HIRES at reasonable SNR. One of these giants is very peculiar, with an extremely low [Mg/Fe] and high [K/Fe] but normal abundances of most other elements. The abundance pattern does not match the nucleosynthetic yields of any supernova model. The other six stars show abundance ratios typical of inner halo Galactic globular clusters, represented here by a sample of giants in t…
In Martell & Grebel (2010) we reported the discovery in the Sloan Digital Sky Survey-II/SEGUE spectroscopic database of a small subset of halo red giants, 2.5%, with CN and CH band strengths indicative of globular-cluster-like carbon and nitrogen abundances. Because the formation of stars with unusual light-element abundances is thought to be restricted to high-density environments like globular clusters, this result has strong implications for both cluster formation processes and the assembly history of the Galactic halo. Here we discuss two efforts to expand upon that work.
We utilise the final catalogue from the Pan-Andromeda Archaeological Survey to investigate the links between the globular cluster system and field halo in M31 at projected radii $R_p=25-150$ kpc. In this region the cluster radial density profile exhibits a power-law decline with index $Γ=-2.37\pm0.17$, matching that for the stellar halo component with [Fe/H] $<-1.1$. Spatial density maps reveal a striking correspondence between the most luminous substructures in the metal-poor field halo and the positions of many globular clusters. By comparing the density of metal-poor halo stars local to eac…
Using imaging that shows four magnitudes of main sequence stars, we have discovered that the Galactic globular cluster NGC 1851 is surrounded by a halo that is visible from the tidal radius of 700 arcsec (41 pc) to more than 4500 arcsec (>250 pc). This halo is symmetric and falls in density as a power law of $r^{-1.24}$. It contains approximately 0.1% of the dynamical mass of NGC 1851. There is no evidence for tidal tails. Current models of globular cluster evolution do not explain this feature, although simulations of tidal influences on dwarf spheroidal galaxies qualitatively mimic these res…
Using a cosmological dark matter simulation of a galaxy-cluster halo, we follow the temporal evolution of its globular cluster population. To mimic the red and blue globular cluster populations, we select at high redshift $(z\sim 1)$ two sets of particles from individual galactic halos constrained by the fact that, at redshift $z=0$, they have density profiles similar to observed ones. At redshift $z=0$, approximately 60\% of our selected globular clusters were removed from their original halos building up the intra-cluster globular cluster population, while the remaining 40\% are still gravit…
Using a cosmological N-body numerical simulation of the formation of a galaxy cluster- sized halo, we analyze the temporal evolution of its globular cluster population. We follow the dynamical evolution of 38 galactic dark matter halos orbiting in a galaxy cluster that at redshift z=0 has a virial mass of 1.71 * 10 ^14 Msol h^-1. In order to mimic both "blue" and "red" populations of globular clusters, for each galactic halo we select two different sets of particles at high redshift (z ~ 1), constrained by the condition that, at redshift z=0, their average radial density profiles are similar t…
Many observational studies have revealed the presence of multiple stellar generations in Galactic globular clusters. These studies suggest that second-generation stars make up a significant fraction of the current mass of globular clusters, with the second-generation mass fraction ranging from ~50 to 80 per cent in individual clusters. In this Letter we carry out hydrodynamical simulations to explore the dependence of the mass of second-generation stars on the initial mass and structural parameters and stellar initial mass function (IMF) of the parent cluster. We then use the results of these …
We show that hard encounters in the central regions of globular clusters embedded in dark matter (DM) haloes necessarily lead to the formation of gravitationally-bound stellar envelopes that extend far beyond the nominal tidal radius of the system. Using statistical arguments and numerical techniques we derive the equilibrium distribution function of stars ejected from the centre of a non-divergent spherical potential. Independently of the velocity distribution with which stars are ejected, GC envelopes have density profiles that approach asymptotically $ρ\sim r^{-4}$ at large distances and be…
We construct a model for the Galactic globular cluster system based on a realistic gravitational potential and a distribution function (DF) analytic in the action integrals. The DF comprises disc and halo components whose functional forms resemble those recently used to describe the stellar discs and stellar halo. We determine the posterior distribution of our model parameters using a Bayesian approach. This gives us an understanding of how well the globular cluster data constrain our model. The favoured parameter values of the disc and halo DFs are similar to values previously obtained from f…
We report the results of a systematic photometric survey of the peripheral regions of a sample of fourteen globular clusters in the outer halo of the Milky Way at distances d_GC>25 kpc from the Galactic centre. The survey is aimed at searching for the remnants of the host satellite galaxies where these clusters could originally have been formed before being accreted onto the Galactic halo. The limiting surface brightness varies within our sample, but reaches muV_lim=30-32 mag arcsec^-2. For only two globular clusters (NGC 7492 and Whiting 1; already suggested to be associated with the Sagittar…
We searched the Sloan Digital Sky Survey for outer halo globular clusters (GCs) around M31. Our search of non-stellar objects, within the limits 0.3 < (g-i)o < 1.5 and 14.0 < ro < 19.0 concentrated in some remote areas of the extended halo, to a maximum projected distance of 240 kpc, for a total of approximately 200 square degrees. Another roughly 50 square degrees, approximately 5-75 kpc from M31, were surveyed as test areas. In these areas, we identified 39 GCs and 2 GC candidates, 84% of the previously known GCs (93% of the "classical GCs" and 40% of the "halo extended clusters", on the clu…
Intermediate mass black holes (IMBHs) are among the most elusive objects in contemporary astrophysics. Both theoretical and observational evidence of their existence is subject of debate. Conversely, both theory and observations confirm the presence of a large population of millisecond pulsars (MSPs) with low mass companions residing in globular cluster (GC) centers. If IMBHs are common in GC centers as well, then dynamical interactions will inevitably break up many of these binaries, causing the ejection of several fast MSPs in the Galactic halo. Such population of fast halo MSPs, hard to pro…
M3 and M13 are Galactic globular clusters with previous reports of surrounding stellar halos. We present the results of a search for members and extratidal cluster halo stars within and outside of the tidal radius of these clusters in the LAMOST Data Release 1. We find seven candidate cluster members (inside the tidal radius) of both M3 and M13 respectively. In M3 we also identify eight candidate extratidal cluster halo stars at distances up to ~9.8 times the tidal radius, and in M13 we identify 12 candidate extratidal cluster halo stars at distances up to ~13.8 times the tidal radius. These r…
The Galactic halo has a complex assembly history, which can be seen in its wealth of kinematic and chemical substructure. Globular clusters lose stars through tidal interactions with the Galaxy and cluster evaporation processes, meaning that they are inevitably a source of halo stars. These "migrants" from globular clusters can be recognized in the halo field by the characteristic light element abundance anticorrelations that are commonly observed only in globular cluster stars, and the number of halo stars that can be chemically tagged to globular clusters can be used to place limits on the f…
We estimate the mass of the inner ($<20$ kpc) Milky Way and the axis ratio of its dark matter halo using globular clusters as tracers. At the same time, we constrain the phase-space distribution of the globular cluster system. We use the Gaia DR2 catalogue of 75 globular clusters' proper motions and recent measurements of the proper motions of another 20 distant clusters obtained with the Hubble Space Telescope. We describe the globular cluster system with a 2-component distribution function (DF), with a flat, rotating disc and a rounder, more extended halo. While fixing the Milky Way's disc a…
We confirm that the number of globular clusters (GCs), N$_{GC}$, is an excellent tracer of their host galaxy's halo virial mass M$_{vir}$. The simple linear relation M$_{vir} = 5 \times 10^9$ M$_{\odot} \times$ N$_{GC}$ fits the data perfectly from M$_{vir} = 10^{10}$ M$_{\odot}$ to M$_{vir} = 2 \times 10^{15}$ M$_{\odot}$. This result is independent of galaxy morphology and extends statistically into the dwarf galaxy regime with M$_{vir} = 10^8 - 10^{10}$ M$_{\odot}$, including the extreme ultra diffuse galaxy DF44. As this correlation does not depend on GC mass it is ideally suited for high-…
Globular Clusters (GCs) have historically been subdivided in either two (disk/halo) or three (disk/inner-halo/outer-halo) groups based on their orbital, chemical and internal physical properties. The qualitative nature of this subdivision makes it impossible to determine whether the natural number of groups is actually two, three, or more. In this paper we use cluster analysis on the $(\log M, \log σ_0, \log R_e, [Fe/H], \log | Z |)$ space to show that the intrinsic number of GC groups is actually either $k=2$ or $k=3$, with the latter being favored albeit non-significantly. In the $k=2$ case,…
We present $N$-body simulations of globular clusters, exploring the effect of different galactic potentials on cluster sizes, $r_h$. For various galactocentric distances, $R_G$, we assess how cluster sizes change when we vary the virial mass and concentration of the host galaxy's dark-matter halo. We show that sizes of GCs are determined by the local galactic mass density rather than the virial mass of the host galaxy. We find that clusters evolving in the inner haloes of less concentrated galaxies are significantly more extended than those evolving in more concentrated ones, while the sizes o…
We present a novel approach to constrain the formation channels of Ultra-Compact Dwarf Galaxies (UCDs). This inhomogeneous class of objects of remnants of tidally stripped dwarf elliptical galaxies and high mass globular clusters. We use three methods to unravel their nature: 1) we analysed their surface brightness profiles, 2) we carried out a direct search for tidal features around UCDs and 3) we compared the spatial distribution of GCs and UCDs in the halo of their host galaxy. Based on FORS2 observations, we have studied the detailed structural composition of a large sample of 97 UCDs in t…
We report the discovery of tidal tails around the two outer halo globular clusters, Eridanus and Palomar 15, based on $gi$-band images obtained with DECam at the CTIO 4-m Blanco Telescope. The tidal tails are among the most remote stellar streams presently known in the Milky Way halo. Cluster members have been determined from the color-magnitude diagrams and used to establish the radial density profiles, which show, in both cases, a strong departure in the outer regions from the best-fit King profile. Spatial density maps reveal tidal tails stretching out on opposite sides of both clusters, ex…
In our recent investigation of the Oosterhoff dichotomy in the multiple population paradigm (Jang et al. 2014), we have suggested that the RR Lyrae variables in the Oosterhoff groups I, II, and III globular clusters (GCs) are produced mostly by the first, second, and third generation stars (G1, G2, and G3), respectively. Here we show, for the first time, that the observed dichotomies in the inner and outer halo GCs can be naturally reproduced when these models are extended to all metallicity regimes, while maintaining reasonable agreements in the horizontal-branch type versus [Fe/H] correlatio…
We explore a scenario where metal poor globular clusters (GCs) form at the centres of their own dark matter halos in the early universe before reionization. This hypothesis leads to predictions about the abundance, distribution and kinematics of GCs today that we explore using cosmological N-body simulations and analytical modelling. We find that selecting the massive tail of collapsed objects at $z\gtrsim 9$ as GC formation sites leads to four main predictions: i) a highly clustered population of GCs around galaxies today, ii) a natural scaling between number of GCs and halo virial mass that …
We report on Gemini/GMOS observations of two newly discovered globular clusters in the outskirts of M31. These objects, PAndAS-7 and PAndAS-8, lie at a galactocentric radius of ~87 kpc and are projected, with separation ~19 kpc, onto a field halo substructure known as the South-West Cloud. We measure radial velocities for the two clusters which confirm that they are almost certainly physically associated with this feature. Colour-magnitude diagrams reveal strikingly short, exclusively red horizontal branches in both PA-7 and PA-8; both also have photometric [Fe/H] = -1.35 +/- 0.15. At this met…
Spherical systems with polytropic equations of state are of great interest in astrophysics. They are widely used to describe neutron stars, red giants, white dwarfs, brown dwarfs, main sequence stars, galactic halos, and globular clusters of diverse sizes. In this paper we construct analytically a family of self-gravitating spherical models in the post-Newtonian approximation of general relativity. These models present interesting cusps in their density profiles which are appropriate for the modeling of galaxies and dark matter halos. The systems described here are anisotropic in the sense tha…
We determine the elemental abundances of nine red giant stars belonging to Palomar 14 (Pal 14). Pal 14 is an outer halo globular cluster (GC) at a distance of \sim 70 kpc. Our abundance analysis is based on high-resolution spectra and one-dimensional stellar model atmospheres.We derived the abundances for the iron peak elements Sc, V, Cr, Mn, Co, Ni, the α-elements O, Mg, Si, Ca, Ti, the light odd element Na, and the neutron-capture elements Y, Zr, Ba, La, Ce, Nd, Eu, Dy, and Cu. Our data do not permit us to investigate light element (i.e., O to Mg) abundance variations. The neutron-capture el…
The stars SDSS J064655.6+411620.5 and SDSS J193712.01+502455.5 are relatively bright stars that were initially observed as part of the SDSS/MARVELS pre-survey. They were selected, on the basis of their weak CH $G$-bands, along with a total of 60 others, in the range of halo globular cluster metallicities for high-resolution spectroscopic follow-up as a part of the HESP-GOMPA survey (Hanle Echelle SPectrograph -- Galactic survey Of Metal Poor stArs). The stars exhibit typical nucleosynthesis signatures expected from the so-called second-generation stars of globular clusters. The light-element a…
