Spatial Distribution Of Globular Clusters Research Articles

The spatial distribution of globular clusters in dwarf spheroidal galaxies and the timing problem

ABSTRACT The dynamical friction time-scale of massive globular clusters (GCs) in the inner regions of cuspy dark haloes in dwarf spheroidal (dSph) galaxies can be much shorter than the Hubble time. This implies that a small fraction of the GCs is expected to be caught close to the centre of these galaxies. We compare the radial distribution of GCs predicted in simple Monte Carlo models with that of a sample of 38 spectroscopically confirmed GCs plus 17 GC candidates associated mainly with low-luminosity dSph galaxies. If dark matter haloes follow an NFW profile, the observed number of off-centre GCs at projected distances less than one-half the galaxy effective radius is significantly higher than the models predict. This timing problem can be viewed as a fine-tuning of the starting GC distances. As a result of the short sinking time-scale for GCs in the central regions, the radial distribution of GCs is expected to evolve significantly during the next 1–2 Gyr. However, dark matter haloes with cores of size comparable to the galaxy effective radii can lead to a slow orbital inspiral of GCs in the central regions of these galaxies, providing a simple solution to the timing problem. We also examine any indication of mass segregation in the summed distribution of our sample of GCs.

Effect of the Galactic Disk and Satellite Galaxies on the Spatial Distribution of Globular Clusters

The distribution anisotropy in systems of globular clusters (GCs) in satellite galaxies of the Milky Way is considered using the inertia tensor. The statistical significance of the results is estimated by repeating this analysis for random catalogs. This method reproduces a known planar structure in the distribution of satellite galaxies; however, the significance of this structure is slightly lower than that for other methods used in the literature. For the GCs at distances 2 < R < 10 kpc, the structure is coplanar with the galactic plane. At large distances, the structure orientation is close to the orientations of the satellite galaxies, i.e., is perpendicular to the Galaxy plane. The probability of stochastic realization of such distribution is 1.7%. The GC distribution anisotropy is also measured without the GCs belonging to the Sagittarius tidal stream. Measurements show that the effect of the stream on the GC perturbation is weak.

A Wide-field Map of Intracluster Globular Clusters in Coma

Abstract The large-scale distribution of globular clusters in the central region of the Coma cluster of galaxies is derived through the analysis of Hubble Space Telescope/Advanced Camera for Surveys data. Data from three different HST observing programs are combined in order to obtain a full surface density map of globular clusters in the core of Coma. A total of 22,426 Globular cluster candidates were selected through a detailed morphological inspection and the analysis of their magnitude and colors in two wavebands, F475W (Sloan g) and F814W (I). The spatial distribution of globular clusters defines three main overdensities in Coma that can be associated with NGC 4889, NGC 4874, and IC 4051 but have spatial scales five to six times larger than individual galaxies. The highest surface density of globular clusters in Coma is spatially coincidental with NGC 4889. The most extended overdensity of globular clusters is associated with NGC 4874. Intracluster globular clusters also form clear bridges between Coma galaxies. Red globular clusters, which agglomerate around the center of the three main subgroups, reach higher surface densities than blue ones.

Spatial distribution of globular clusters in the Galaxy

The Milky Way's satellite galaxies and Globular Clusters (GCs) are known to exhibit an anisotropic spatial distribution. We examine in detail this anisotropy by the means of the inertia tensor. We estimate the statistical significance of the results by repeating this analysis for random catalogues which use the radial distribution of the real sample. Our method reproduces the well-known planar structure in the distribution of the satellite galaxies. We show that for GCs several anisotropic structures are observed. The GCs at small distances, $2<R<10$ kpc, show a structure coplanar with the Galactic plane. At smaller and larger distances the whole sample of GCs shows quite weak anisotropy. Nevertheless, at largest distances the orientation of the structure is close to that of the satellite galaxies, i.e. perpendicular to the Galactic plane. We estimate the probability of random realization for this structure of 1.7%. The Bulge-Disk GCs show a clear disk-like structure lying within the galactic disk. The Old Halo GCs show two structures: a well pronounced polar elongated structure at $R<3$ kpc which is perpendicular to the galactic plane, and a less pronounced disk-like structure coplanar with the galactic disk at $6<R<20$ kpc. The Young Halo GCs do not show significant anisotropy.

THE EXTENDED SPATIAL DISTRIBUTION OF GLOBULAR CLUSTERS IN THE CORE OF THE FORNAX CLUSTER

ABSTRACT We report the discovery of a complex extended density enhancement in the Globular Clusters (GCs) in the central &sim; 0.5 ( &deg; ) 2 ?> ( &sim; 0.06 ?> Mpc2) of the Fornax cluster, corresponding to &sim; 50 &percnt; ?> of the area within 1 core radius. This overdensity connects the GC system of NGC 1399 to most of those of neighboring galaxies within &sim; 0 &fdg; 6 ?> ( &sim; 210 ?> kpc) along the W–E direction. The asymmetric density structure suggests that the galaxies in the core of the Fornax cluster experienced a lively history of interactions that have left a clear imprint on the spatial distribution of GCs. The extended central dominant structure is more prominent in the distribution of blue GCs, while red GCs show density enhancements that are more centrally concentrated on the host galaxies. We propose that the relatively small-scale density structures in the red GCs are caused by galaxy–galaxy interactions, while the extensive spatial distribution of blue GCs is due to stripping of GCs from the halos of core massive galaxies by the Fornax gravitational potential. Our investigations are based on density maps of candidate GCs extracted from the multi-band VLT Survey Telescope (VST) survey of Fornax (FDS), identified in a three-dimensional color space and further selected based on their g-band magnitude and morphology.

Globular cluster clustering and tidal features around ultra-compact dwarf galaxies in the halo of NGC 1399

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 the halo of NGC1399, the central galaxy of the Fornax cluster, by analysing theirsurface brightness profiles. We derived the structural parameters of 13 extended UCDs modelling them with a single Sersic function and decomposing them into composite King and Sersic profiles. We find evidence for faint stellar envelopes at mu=~26 mag\arcsec^-2 surrounding the UCDs up to an extension of 90pc in radius. We also show new evidence for faint asymmetric structures and tidal tail-like features surrounding several of these UCDs, a possible tracer of their origin and assembly history within their host galaxy halos. In particular, we present evidence for the first discovery of a significant tidal tail with an extension of ~350pc around UCD-FORS2. We searched for local overdensities in the spatial distribution of globular clusters within the halo of NGC1399, to see if they are related to the positions of the UCDs. We found a local overabundance of globular clusters on a scale of <1kpc around UCDs, when we compare it to the distribution of globulars from the host galaxy. This effect is strongest for the metal-poor blue GCs. We discuss how likely it is that these clustered globulars were originally associated with the UCD.

Optical-near-IR analysis of globular clusters in the IKN dwarf spheroidal: a complex star formation history

Age, metallicity and spatial distribution of globular clusters (GCs) provide a powerful tool to reconstruct major star-formation episodes in galaxies. IKN is a faint dwarf spheroidal (dSph) in the M81 group of galaxies. It contains five old GCs, which makes it the galaxy with the highest known specific frequency (SN=126). We estimate the photometric age, metallicity and spatial distribution of the poorly studied IKN GCs. We search SDSS for GC candidates beyond the HST field of view, which covers half of IKN. To break the age-metallicity degeneracy in the V-I colour we use WHT/LIRIS Ks-band photometry and derive photometric ages and metallicities by comparison with SSP models in the V,I,Ks colour space. IKN GCs' VIKs colours are consistent with old ages ($\geq\!8$ Gyr) and a metallicity distribution with a higher mean than typical for such a dSph ([Fe/H$]\!\simeq\!-1.4_{-0.2}^{+0.6}$ dex). Their photometric masses range ($0.5 <{\cal M_{\rm GC}}<4\times10^5M_\odot$) implies a high mass ratio between GCs and field stars, of $10.6\%$. Mixture model analysis of the RGB field stars' metallicity suggests that 72\% of the stars may have formed together with the GCs. Using the most massive GC-SFR relation we calculate a SFR of $\sim\!10M_\odot/$yr during its formation epoch. We note that the more massive GCs are closer to the galaxy photometric centre. IKN GCs also appear spatially aligned along a line close to the IKN major-axis and nearly orthogonal to the plane of spatial distribution of galaxies in the M81 group. We identify one new IKN GC candidate based on colour and PSF analysis of the SDSS data. The evidence towards i) broad and high metallicity distribution of the field IKN RGB stars and its GCs, ii) high fraction and iii), spatial alignment of IKN GCs, supports a scenario for tidally triggered complex IKN's SFH in the context of interactions with galaxies in the M81 group.

Metallicity field and selection effects in spatial distribution of the Galactic globular cluster system

AbstractThe prospects for using the present‐day data on metallicity of globular clusters (GCs) of the Galaxy to put constraints on the distance to the Galactic center, R0, are considered. We have found that the GCs of the metal‐rich and metal‐poor subsystems separately form a bar‐like structure in metallicity maps whose parameters are very close to those for the Galactic bar. The results indicate the existence of a bar component within both the metal‐rich and metal‐poor subsystems of GCs. The bar GCs could have formed within the already existing Galactic bar or could have later been locked in resonance with the bar. We conclude that substantial constraints on the R0 value can be obtained only with non‐axisymmetric models for the space distribution of GC metallicities with the allowance for the subdivision of GCs into subsystems. We found evidence for a bar extinction component that causes the observational incompleteness of GCs in the far side of the Galactic bar and in the “post‐central” region. This selection effect should be taken into account when determining R0 from the spatial distribution of GCs. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

THE TWO-DIMENSIONAL PROJECTED SPATIAL DISTRIBUTION OF GLOBULAR CLUSTERS. I. METHOD AND APPLICATION TO NGC 4261

We present a new method for the determination of the two-dimensional (2D) projected spatial distribution of globular clusters (GCs) in external galaxies. This method is based on the K-Nearest Neighbor density estimator of Dressler (1980), complemented by MonteCarlo simulations to establish the statistical significance of the results. We apply this method to NGC4261, a "test galaxy" where significant 2D anisotropy in the GC distribution has been reported. We confirm that the 2D distribution of GC is not azimuthally isotropic. Moreover, we demonstrate that the 2D distribution departures from the average GC radial distribution results in highly significant spiral-like or broken shell features. Overall, the same perturbations are found in "red" and "blue" GCs, but with some differences. In particular, we observe a central feature, roughly aligned with the minor axis of NGC4261, composed of red and most luminous GCs. Blue and fainter GCs are more frequent at large radial distances and follow the spiral-like features of the overall density structure. These results suggest a complex merging history for NGC4261.

EVIDENCE FOR AN ACCRETION ORIGIN FOR THE OUTER HALO GLOBULAR CLUSTER SYSTEM OF M31

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 globular clusters smoothly distributed in the M31 halo. We find the likelihood of this possibility is low, below 1%, and conclude that the observed spatial coincidence between globular clusters and multiple tidal debris streams in the outer halo of M31 reflects a genuine physical association. Our results imply that the majority of the remote globular cluster system of M31 has been assembled as a consequence of the accretion of cluster-bearing satellite galaxies. This constitutes the most direct evidence to date that the outer halo globular cluster populations in some galaxies are largely accreted.

The Distance to the Galactic Center Derived from Infrared Photometry of Bulge Red Clump Stars

On the basis of the near infrared observations of bulge red clump stars near the Galactic center, we have determined the galactocentric distance to be R_0 = 7.52 +- 0.10 (stat) +- 0.35 (sys) kpc. We observed the red clump stars at |l| < 1.0 deg and 0.7 deg < |b| < 1.0 deg with the IRSF 1.4 m telescope and the SIRIUS camera in the H and Ks bands. After extinction and population corrections, we obtained (m - M)_0 = 14.38 +- 0.03 (stat) +- 0.10 (sys). The statistical error is dominated by the uncertainty of the intrinsic local red clump stars' luminosity. The systematic error is estimated to be +- 0.10 including uncertainties in extinction and population correction, zero-point of photometry, and the fitting of the luminosity function of the red clump stars. Our result, R_0 = 7.52 kpc, is in excellent agreement with the distance determined geometrically with the star orbiting the massive black hole in the Galactic center. The recent result based on the spatial distribution of globular clusters is also consistent with our result. In addition, our study exhibits that the distance determination to the Galactic center with the red clump stars, even if the error of the population correction is taken into account, can achieve an uncertainty of about 5%, which is almost the same level as that in recent geometrical determinations.

Low‐Mass X‐Ray Binaries and Globular Clusters in Early‐Type Galaxies

A high fraction of the low-mass X-ray binaries (LMXBs) in early-type galaxies are associated with globular clusters (GCs). Here we discuss the correlations between LMXBs and GCs in a sample of four early-type galaxies with X-ray source lists determined from Chandra observations. There is some evidence that the fraction of LMXBs associated with GCs (fX-GC) increases along the Hubble sequence from spiral bulges (or spheroids) to S0s to Es to cDs. On the other hand, the fraction of GCs that contain X-ray sources appears to be roughly constant at fGC-X ~ 4%. There is a strong tendency for the X-ray sources to be associated with the optically more luminous GCs. However, this correlation is consistent with a constant probability of finding an LMXB per unit optical luminosity; that is, it seems to result primarily from the larger number of stars in optically luminous GCs. The probability of finding a bright LMXB per unit optical luminosity in the GCs is about 1.5 ? 10-7 LMXBs per L?,I for LX 1 ? 1038 ergs s-1 (0.3-10 keV) and rises to about 2.0 ? 10-7 LMXBs per L?,I at lower X-ray luminosities, LX 3 ? 1037 ergs s-1. This frequency appears to be roughly constant for different galaxies, including the bulges of the Milky Way and M31. There is a tendency for the X-ray sources to be found preferentially in redder GCs, which is independent of optical luminosity correlation. This seems to indicate that the evolution of X-ray binaries in a GC is affected by either the metallicity or the age of the GC, with younger and/or more metal rich GCs having more LMXBs. There is no strong difference in the X-ray luminosities of GC and non-GC LMXBs. There is a weak tendency for the brightest LMXBs, whose luminosities exceed the Eddington luminosity for a 1.4 M? neutron star, to avoid GCs. That may indicate that black hole X-ray binaries are somewhat less likely to be found in GCs, as seems to be true in our Galaxy. On the other hand, there are some luminous LMXBs associated with GCs. There is no clear evidence that the X-ray spectra or variability of GC and non-GC X-ray sources differ. We also find no evidence for a difference in the spatial distribution of GC and non-GC LMXBs. Many of these results are similar to those found in NGC 1399 and NGC 4472 by Angelini et al. and Kundu et al., respectively.

Hubble Space Telescope Imaging of the Globular Cluster System Around NGC 5846

view Abstract Citations (51) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hubble Space Telescope Imaging of the Globular Cluster System Around NGC 5846 Forbes, Duncan A. ; Brodie, Jean P. ; Huchra, John Abstract Bimodal globular cluster metallicity distributions have now been seen in a handful of large ellipticals. Here we report the discovery of a bimodal distribution in the dominant group elliptical NGC 5846, using the Hubble Space Telescope's Wide Field and Planetary Camera 2 (WFPC2). The two peaks are located at V-I=0.96 and 1.17, which roughly correspond to metallicities of [Fe/H]=-1.2 and -0.2, respectively. The luminosity functions of the blue and red subpopulations appear to be the same, indicating that luminosity does not correlate with metallicity within an individual galaxy's globular cluster system. Our WFPC2 data cover three pointings allowing us to examine the spatial distribution of globular clusters out to 30 kpc (or 2.5 galaxy effective radii). We find a power law surface density with a very fiat slope, and a tendency for globular clusters to align close to the galaxy minor axis. An extrapolation of the surface density profile, out to 50 kpc, gives a specific frequency SN=4.3±1.1 Thus NGC 5846 has a much lower specific frequency than other dominant ellipticals in clusters but is similar to those in groups. The central galaxy regions reveal some filamentary dust features, presumably from a past merger or accretion of a gas-rich galaxy. This dust reaches to the very nucleus and so provides an obvious source of fuel for the radio core. We have searched for proto-globular clusters that may have resulted from the merger/accretion and find none. Finally, we briefly discuss the implications of our results for globular cluster formation mechanisms. Publication: The Astronomical Journal Pub Date: March 1997 DOI: 10.1086/118308 arXiv: arXiv:astro-ph/9612172 Bibcode: 1997AJ....113..887F Keywords: Astrophysics E-Print: 22 pages, Latex. To be published in the Astronomical Journal. Full paper available at http://www.ucolick.org/~forbes/home.html full text sources arXiv | ADS | data products SIMBAD (5) NED (1) MAST (1) ESA (1)

Spatial Distribution of Globular Clusters in M 31

The spatial distribution of globular clusters in M 31 has been analyzed using the catalogues of Sargent et al. (1977) and Crampton et al. (1985). It is concluded that the globular clusters within the distance of 54′ from the center of M 31 show an elliptical distribution aligned to the major axis of the disk. This is similar to the distribution of metal-rich clusters in our galaxy.