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Title: Tidal stripping stellar substructures around four metal-poor globular clusters in the galactic bulge

Abstract

We investigate the spatial density configuration of stars around four metal-poor globular clusters (NGC 6266, NGC 6626, NGC 6642, and NGC 6723) in the Galactic bulge region using wide-field deep J, H, and K imaging data obtained with the Wide Field Camera near-infrared array on the United Kingdom Infrared Telescope. A statistical weighted filtering algorithm for the stars on the color–magnitude diagram is applied in order to sort cluster member candidates from the field star contamination. In two-dimensional isodensity contour maps of the clusters, we find that all four of the globular clusters exhibit strong evidence of tidally stripped stellar features beyond the tidal radius in the form of tidal tails or small density lobes/chunks. The orientations of the extended stellar substructures are likely to be associated with the effect of dynamic interaction with the Galaxy and the cluster's space motion. The observed radial density profiles of the four globular clusters also describe the extended substructures; they depart from theoretical King and Wilson models and have an overdensity feature with a break in the slope of the profile at the outer region of clusters. The observed results could imply that four globular clusters in the Galactic bulge region have experiencedmore » strong environmental effects such as tidal forces or bulge/disk shocks of the Galaxy during the dynamical evolution of globular clusters. These observational results provide further details which add to our understanding of the evolution of clusters in the Galactic bulge region as well as the formation of the Galaxy.« less

Authors:
 [1]; ; ;  [2]
  1. Yonsei University Observatory, Seoul (Korea, Republic of)
  2. Department of Astronomy, Yonsei University, Seoul 120-749 (Korea, Republic of)
Publication Date:
OSTI Identifier:
22342155
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (New York, N.Y. Online); Journal Volume: 149; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALGORITHMS; COLOR; CONFIGURATION; DENSITY; EVOLUTION; FILTERS; GALAXIES; INTERACTIONS; MAPS; METALS; NEAR INFRARED RADIATION; SPACE; STAR CLUSTERS; STARS; STRIPPING; TELESCOPES; TWO-DIMENSIONAL CALCULATIONS

Citation Formats

Chun, Sang-Hyun, Kang, Minhee, Jung, DooSeok, and Sohn, Young-Jong, E-mail: shchun@galaxy.yonei.ac.kr. Tidal stripping stellar substructures around four metal-poor globular clusters in the galactic bulge. United States: N. p., 2015. Web. doi:10.1088/0004-6256/149/1/29.
Chun, Sang-Hyun, Kang, Minhee, Jung, DooSeok, & Sohn, Young-Jong, E-mail: shchun@galaxy.yonei.ac.kr. Tidal stripping stellar substructures around four metal-poor globular clusters in the galactic bulge. United States. doi:10.1088/0004-6256/149/1/29.
Chun, Sang-Hyun, Kang, Minhee, Jung, DooSeok, and Sohn, Young-Jong, E-mail: shchun@galaxy.yonei.ac.kr. 2015. "Tidal stripping stellar substructures around four metal-poor globular clusters in the galactic bulge". United States. doi:10.1088/0004-6256/149/1/29.
@article{osti_22342155,
title = {Tidal stripping stellar substructures around four metal-poor globular clusters in the galactic bulge},
author = {Chun, Sang-Hyun and Kang, Minhee and Jung, DooSeok and Sohn, Young-Jong, E-mail: shchun@galaxy.yonei.ac.kr},
abstractNote = {We investigate the spatial density configuration of stars around four metal-poor globular clusters (NGC 6266, NGC 6626, NGC 6642, and NGC 6723) in the Galactic bulge region using wide-field deep J, H, and K imaging data obtained with the Wide Field Camera near-infrared array on the United Kingdom Infrared Telescope. A statistical weighted filtering algorithm for the stars on the color–magnitude diagram is applied in order to sort cluster member candidates from the field star contamination. In two-dimensional isodensity contour maps of the clusters, we find that all four of the globular clusters exhibit strong evidence of tidally stripped stellar features beyond the tidal radius in the form of tidal tails or small density lobes/chunks. The orientations of the extended stellar substructures are likely to be associated with the effect of dynamic interaction with the Galaxy and the cluster's space motion. The observed radial density profiles of the four globular clusters also describe the extended substructures; they depart from theoretical King and Wilson models and have an overdensity feature with a break in the slope of the profile at the outer region of clusters. The observed results could imply that four globular clusters in the Galactic bulge region have experienced strong environmental effects such as tidal forces or bulge/disk shocks of the Galaxy during the dynamical evolution of globular clusters. These observational results provide further details which add to our understanding of the evolution of clusters in the Galactic bulge region as well as the formation of the Galaxy.},
doi = {10.1088/0004-6256/149/1/29},
journal = {Astronomical Journal (New York, N.Y. Online)},
number = 1,
volume = 149,
place = {United States},
year = 2015,
month = 1
}
  • Wide-field deep g'r'i' images obtained with the Megacam of the Canada-France-Hawaii Telescope are used to investigate the spatial configuration of stars around five metal-poor globular clusters M15, M30, M53, NGC 5053, and NGC 5466, in a field-of-view {approx}3 deg. Applying a mask filtering algorithm to the color-magnitude diagrams of the observed stars, we sorted cluster's member star candidates that are used to examine the characteristics of the spatial stellar distribution surrounding the target clusters. The smoothed surface density maps and the overlaid isodensity contours indicate that all of the five metal-poor globular clusters exhibit strong evidence of extratidal overdensity featuresmore » over their tidal radii, in the form of extended tidal tails around the clusters. The orientations of the observed extratidal features show signatures of tidal tails tracing the clusters' orbits, inferred from their proper motions, and effects of dynamical interactions with the Galaxy. Our findings include detections of a tidal bridge-like feature and an envelope structure around the pair of globular clusters M53 and NGC 5053. The observed radial surface density profiles of target clusters have a deviation from theoretical King models, for which the profiles show a break at 0.5-0.7r{sub t} , extending the overdensity features out to 1.5-2r{sub t} . Both radial surface density profiles for different angular sections and azimuthal number density profiles confirm the overdensity features of tidal tails around the five metal-poor globular clusters. Our results add further observational evidence that the observed metal-poor halo globular clusters originate from an accreted satellite system, indicative of the merging scenario of the formation of the Galactic halo.« less
  • Using wide-field J, H, and K{sub s} images obtained with the WIRCam near-infrared camera on the Canada-France-Hawaii Telescope, we investigated the spatial density configuration of stars within the tidal radius of metal-poor globular cluster NGC 6626, which is known to be located near the bulge region and have a thick-disk orbit motion. In order to trace the stellar density around a target cluster, we sorted the cluster's member stars using a mask-filtering algorithm and weighted the stars on the color-magnitude diagram. From the weight-summed surface density map, we found that the spatial density distribution of stars within the tidal radiusmore » is asymmetric with distorted overdensity features. The extending overdensity features are likely associated with the effects of the dynamic interaction with the Galaxy and the cluster's space motion. An interesting finding is that the prominent overdensity features extend toward the direction of the Galactic plane. This orientation of stellar density distribution can be interpreted with the result of the disk-shock effect of the Galaxy, previously experienced by the cluster. Indeed, the radial surface density profile accurately describes this overdensity feature with a break in the slope inside the tidal radius. Thus, the observed results indicate that NGC 6626 experienced a strong dynamical interaction with the Galaxy. Based on the result of strong tidal interaction with the Galaxy and previously published results, we discussed possible origins and evolutions of the cluster: (1) the cluster might have formed in satellite galaxies that were merged and created the Galactic bulge region in the early universe, after which time its dynamical properties were modified by dynamical friction, or (2) the cluster might have formed in primordial and rotationally supported massive clumps in the thick disk of the Galaxy.« less
  • We calculate orbits, tidal radii, and bulge-bar and disk shocking destruction rates for 63 globular clusters in our Galaxy. Orbits are integrated in both an axisymmetric and a nonaxisymmetric Galactic potential that includes a bar and a three-dimensional model for the spiral arms. With the use of a Monte Carlo scheme, we consider in our simulations observational uncertainties in the kinematical data of the clusters. In the analysis of destruction rates due to the bulge-bar, we consider the rigorous treatment of using the real Galactic cluster orbit instead of the usual linear trajectory employed in previous studies. We compare resultsmore » in both treatments. We find that the theoretical tidal radius computed in the nonaxisymmetric Galactic potential compares better with the observed tidal radius than that obtained in the axisymmetric potential. In both Galactic potentials, bulge-shocking destruction rates computed with a linear trajectory of a cluster at its perigalacticons give a good approximation of the result obtained with the real trajectory of the cluster. Bulge-shocking destruction rates for clusters with perigalacticons in the inner Galactic region are smaller in the nonaxisymmetric potential than those in the axisymmetric potential. For the majority of clusters with high orbital eccentricities (e > 0.5), their total bulge+disk destruction rates are smaller in the nonaxisymmetric potential.« less
  • It is suggested that the X-ray sources of the galactic bulge and those in globular clusters are of the same type. This is supported by the similarity of the respective stellar populations and the observed incidence of luminous sources. Evolutionary considerations suggest that it is the high stellar density that favors X-ray source formation in those regions. If the correspondence is correct, there must be approx.100 additional weak sources in the bulge which have so far eluded detection because of source confusion. (AIP)
  • With the aim of finding evidence of tidal stripping of globular clusters (GCs) we analyzed a sample of 13 elliptical galaxies taken from the ACS Virgo Cluster Survey (VCS). These galaxies belong to the main concentration of the Virgo Cluster (VC) and present absolute magnitudes -18.5 < M{sub z} < -22.5. We used the public GC catalog of Jordan et al. and separated the GC population into metal poor (blue) and metal rich (red) according to their integrated colors. The galaxy properties were taken from Peng et al. We found the following. (1) The specific frequencies (S{sub N} ) ofmore » total and blue GC populations increase as a function of the projected galaxy distances r{sub p} to M87. A similar result is observed when three-dimensional distances r {sub 3D} are used. The same behaviors are found if the analysis is made using the number of GCs per 10{sup 9} M{sub odot} (T). No correlations between S{sub N} or T and r{sub p} or r {sub 3D} is observed for the red GC population. The correlations for the blue GCs (typically more extended) and the lack of correlations for the red GCs (more concentrated) with the clustocentric distance of the host galaxy are interpreted as evidence of GCs stripping due to tidal forces. (2) No correlation is found between the slope of GC density profiles of host galaxies and the galaxy distance to M87 (Virgo central galaxy). The lack of such a correlation is interpreted in terms of a shrinkage of the GC distribution after the stripping of GCs in the outermost region of galaxies. (3) We also computed the local density of GCs ({rho}{sub out}) located further than 6.2 kpc from the galaxy center for nine galaxies of our sample. We find that the GC population around most of these galaxies is mainly composed of blue GCs. The two highest values of {rho}{sub out} are found in the core of the VC (up to 100 kpc) and correspond to the two lowest values of S{sub N} . Our results suggest that the number and the fraction of blue and red GCs observed in elliptical galaxies located near the centers of massive clusters could be significantly different from the underlying GC population. These differences could be explained by tidal stripping effects that occur as galaxies approach the centers of clusters.« less