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Title: To the Edge of M87 and Beyond: Spectroscopy of Intracluster Globular Clusters and Ultracompact Dwarfs in the Virgo Cluster

Abstract

We present the results of a wide-field spectroscopic survey of globular clusters (GCs) in the Virgo cluster. We obtain spectra for 201 GCs and 55 ultracompact dwarfs (UCDs) using Hectospec on the Multiple-Mirror Telescope and derive their radial velocities. We identify 46 genuine intracluster GCs (IGCs), not associated with any Virgo galaxies, using the 3D GMM test on the spatial and radial velocity distribution. They are located at a projected distance 200 kpc≲R ≲500 kpc from the center of M87. The radial velocity distribution of these IGCs shows two peaks, one at v{sub r} = 1023 km s{sup −1}, associated with the Virgo main body, and another at v {sub r}=36 km s{sup −1}, associated with the infalling structure. The velocity dispersion of the IGCs in the Virgo main body is σ{sub GC}∼314 km s{sup −1}, which is smoothly connected to the velocity dispersion profile of M87 GCs but is much lower than that of dwarf galaxies in the same survey field, σ {sub dwarf}∼608 km s{sup −1}. The UCDs are more centrally concentrated on massive galaxies - M87, M86, and M84. The radial velocity dispersion of the UCD system is much smaller than that of dwarf galaxies. Our resultsmore » confirm the large-scale distribution of Virgo IGCs indicated by previous photometric surveys. The color distribution of the confirmed IGCs shows a bimodality similar to that of M87 GCs. This indicates that most IGCs are stripped off dwarf galaxies and some off massive galaxies in the Virgo.« less

Authors:
; ;  [1];  [2]; ; ;  [3];  [4];  [5]
  1. Astronomy Program, Department of Physics and Astronomy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826 (Korea, Republic of)
  2. Quantum Universe Center, Korea Institute for Advanced Study, 85 Hoegiro, Dongdaemun-gu, Seoul 02455 (Korea, Republic of)
  3. Korea Astronomy and Space Science Institute, 776 Daedeokdae-Ro, Yuseong-Gu, Daejeon 34055 (Korea, Republic of)
  4. Department of Astronomy, Peking University, Beijing 100871 (China)
  5. Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States)
Publication Date:
OSTI Identifier:
22663896
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 835; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COLOR; DISPERSIONS; DISTRIBUTION; GALAXIES; GALAXY CLUSTERS; MIRRORS; RADIAL VELOCITY; SPECTRA; SPECTROSCOPY; STAR CLUSTERS; STARS; TELESCOPES

Citation Formats

Ko, Youkyung, Lee, Myung Gyoon, Jang, In Sung, Hwang, Ho Seong, Park, Hong Soo, Hwang, Narae, Park, Byeong-Gon, Lim, Sungsoon, and Sohn, Jubee, E-mail: ykko@astro.snu.ac.kr, E-mail: mglee@astro.snu.ac.kr. To the Edge of M87 and Beyond: Spectroscopy of Intracluster Globular Clusters and Ultracompact Dwarfs in the Virgo Cluster. United States: N. p., 2017. Web. doi:10.3847/1538-4357/835/2/212.
Ko, Youkyung, Lee, Myung Gyoon, Jang, In Sung, Hwang, Ho Seong, Park, Hong Soo, Hwang, Narae, Park, Byeong-Gon, Lim, Sungsoon, & Sohn, Jubee, E-mail: ykko@astro.snu.ac.kr, E-mail: mglee@astro.snu.ac.kr. To the Edge of M87 and Beyond: Spectroscopy of Intracluster Globular Clusters and Ultracompact Dwarfs in the Virgo Cluster. United States. doi:10.3847/1538-4357/835/2/212.
Ko, Youkyung, Lee, Myung Gyoon, Jang, In Sung, Hwang, Ho Seong, Park, Hong Soo, Hwang, Narae, Park, Byeong-Gon, Lim, Sungsoon, and Sohn, Jubee, E-mail: ykko@astro.snu.ac.kr, E-mail: mglee@astro.snu.ac.kr. Wed . "To the Edge of M87 and Beyond: Spectroscopy of Intracluster Globular Clusters and Ultracompact Dwarfs in the Virgo Cluster". United States. doi:10.3847/1538-4357/835/2/212.
@article{osti_22663896,
title = {To the Edge of M87 and Beyond: Spectroscopy of Intracluster Globular Clusters and Ultracompact Dwarfs in the Virgo Cluster},
author = {Ko, Youkyung and Lee, Myung Gyoon and Jang, In Sung and Hwang, Ho Seong and Park, Hong Soo and Hwang, Narae and Park, Byeong-Gon and Lim, Sungsoon and Sohn, Jubee, E-mail: ykko@astro.snu.ac.kr, E-mail: mglee@astro.snu.ac.kr},
abstractNote = {We present the results of a wide-field spectroscopic survey of globular clusters (GCs) in the Virgo cluster. We obtain spectra for 201 GCs and 55 ultracompact dwarfs (UCDs) using Hectospec on the Multiple-Mirror Telescope and derive their radial velocities. We identify 46 genuine intracluster GCs (IGCs), not associated with any Virgo galaxies, using the 3D GMM test on the spatial and radial velocity distribution. They are located at a projected distance 200 kpc≲R ≲500 kpc from the center of M87. The radial velocity distribution of these IGCs shows two peaks, one at v{sub r} = 1023 km s{sup −1}, associated with the Virgo main body, and another at v {sub r}=36 km s{sup −1}, associated with the infalling structure. The velocity dispersion of the IGCs in the Virgo main body is σ{sub GC}∼314 km s{sup −1}, which is smoothly connected to the velocity dispersion profile of M87 GCs but is much lower than that of dwarf galaxies in the same survey field, σ {sub dwarf}∼608 km s{sup −1}. The UCDs are more centrally concentrated on massive galaxies - M87, M86, and M84. The radial velocity dispersion of the UCD system is much smaller than that of dwarf galaxies. Our results confirm the large-scale distribution of Virgo IGCs indicated by previous photometric surveys. The color distribution of the confirmed IGCs shows a bimodality similar to that of M87 GCs. This indicates that most IGCs are stripped off dwarf galaxies and some off massive galaxies in the Virgo.},
doi = {10.3847/1538-4357/835/2/212},
journal = {Astrophysical Journal},
number = 2,
volume = 835,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}
  • The origin of ultra-compact dwarfs (UCDs; r{sub h} ≳ 10 pc)—objects larger and more massive than typical globular clusters (GCs), but more compact than typical dwarf galaxies—has been hotly debated in the 15 years since their discovery. Even whether UCDs should be considered galactic in origin, or simply the most extreme star clusters, is not yet settled. We present the dynamical properties of 97 spectroscopically confirmed UCDs and 911 GCs associated with the central cD galaxy of the Virgo cluster, M87. Our UCDs, of which 89% have M {sub *} ≳ 2× 10{sup 6} M {sub ☉} and 92% are as blue asmore » the classic blue GCs, nearly triple the confirmed sample of Virgo UCDs, providing by far the best opportunity for studying global dynamics of a UCD system. We found that (1) UCDs have a surface number density profile that is shallower than that of blue GCs in the inner ∼70 kpc and as steep as that of red GCs at larger radii; (2) UCDs exhibit a significantly stronger rotation than GCs, and blue GCs seem to have a velocity field that is more consistent with that of the surrounding dwarf ellipticals than with that of UCDs; (3) UCDs have an orbital anisotropy profile that is tangentially biased at radii ≲40 kpc and radially biased farther out, whereas blue GCs become more tangentially biased at larger radii beyond ∼40 kpc; (4) GCs with M {sub *} ≳ 2 × 10{sup 6} M {sub ☉} have rotational properties indistinguishable from the less massive ones, suggesting that it is the size, instead of mass, that differentiates UCDs from GCs as kinematically distinct populations. We conclude that most UCDs in M87 are not consistent with being merely the most luminous and extended examples of otherwise normal GCs. The radially biased orbital structure of UCDs at large radii is in general agreement with the 'tidally threshed dwarf galaxy' scenario.« less
  • We use imaging from the Next Generation Virgo cluster Survey (NGVS) to present a comparative study of ultra-compact dwarf (UCD) galaxies associated with three prominent Virgo sub-clusters: those centered on the massive red-sequence galaxies M87, M49, and M60. We show how UCDs can be selected with high completeness using a combination of half-light radius and location in color–color diagrams (u*iK{sub s} or u*gz). Although the central galaxies in each of these sub-clusters have nearly identical luminosities and stellar masses, we find large differences in the sizes of their UCD populations, with M87 containing ∼3.5 and 7.8 times more UCDs thanmore » M49 and M60, respectively. The relative abundance of UCDs in the three regions scales in proportion to sub-cluster mass, as traced by X-ray gas mass, total gravitating mass, number of globular clusters (GCs), and number of nearby galaxies. We find that the UCDs are predominantly blue in color, with ∼85% of the UCDs having colors similar to blue GCs and stellar nuclei of dwarf galaxies. We present evidence that UCDs surrounding M87 and M49 may follow a morphological sequence ordered by the prominence of their outer, low surface brightness envelope, ultimately merging with the sequence of nucleated low-mass galaxies, and that envelope prominence correlates with distance from either galaxy. Our analysis provides evidence that tidal stripping of nucleated galaxies is an important process in the formation of UCDs.« less
  • We report on a large-scale study of the distribution of globular clusters (GCs) throughout the Virgo cluster, based on photometry from the Next Generation Virgo Cluster Survey (NGVS), a large imaging survey covering Virgo's primary subclusters (Virgo A = M87 and Virgo B = M49) out to their virial radii. Using the g{sub o}{sup ′}, (g' – i') {sub o} color-magnitude diagram of unresolved and marginally resolved sources within the NGVS, we have constructed two-dimensional maps of the (irregular) GC distribution over 100 deg{sup 2} to a depth of g{sub o}{sup ′} = 24. We present the clearest evidence tomore » date showing the difference in concentration between red and blue GCs over the full extent of the cluster, where the red (more metal-rich) GCs are largely located around the massive early-type galaxies in Virgo, while the blue (metal-poor) GCs have a much more extended spatial distribution with significant populations still present beyond 83' (∼215 kpc) along the major axes of both M49 and M87. A comparison of our GC maps to the diffuse light in the outermost regions of M49 and M87 show remarkable agreement in the shape, ellipticity, and boxiness of both luminous systems. We also find evidence for spatial enhancements of GCs surrounding M87 that may be indicative of recent interactions or an ongoing merger history. We compare the GC map to that of the locations of Virgo galaxies and the X-ray intracluster gas, and find generally good agreement between these various baryonic structures. We calculate the Virgo cluster contains a total population of N {sub GC} = 67, 300 ± 14, 400, of which 35% are located in M87 and M49 alone. For the first time, we compute a cluster-wide specific frequency S {sub N,} {sub CL} = 2.8 ± 0.7, after correcting for Virgo's diffuse light. We also find a GC-to-baryonic mass fraction ε {sub b} = 5.7 ± 1.1 × 10{sup –4} and a GC-to-total cluster mass formation efficiency ε {sub t} = 2.9 ± 0.5 × 10{sup –5}, the latter values slightly lower than but consistent with those derived for individual galactic halos. Taken as a whole, our results show that the production of the complex structures in the unrelaxed Virgo cluster core (including the production of the diffuse intracluster light) is an ongoing and continuing process.« less
  • 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
  • We use a highly homogeneous set of data from 132 early-type galaxies in the Virgo and Fornax clusters in order to study the properties of the globular cluster luminosity function (GCLF). The globular cluster system of each galaxy was studied using a maximum likelihood approach to model the intrinsic GCLF after accounting for contamination and completeness effects. The results presented here update our Virgo measurements and confirm our previous results showing a tight correlation between the dispersion of the GCLF and the absolute magnitude of the parent galaxy. Regarding the use of the GCLF as a standard candle, we havemore » found that the relative distance modulus between the Virgo and Fornax clusters is systematically lower than the one derived by other distance estimators, and in particular, it is 0.22 mag lower than the value derived from surface brightness fluctuation measurements performed on the same data. From numerical simulations aimed at reproducing the observed dispersion of the value of the turnover magnitude in each galaxy cluster we estimate an intrinsic dispersion on this parameter of 0.21 mag and 0.15 mag for Virgo and Fornax, respectively. All in all, our study shows that the GCLF properties vary systematically with galaxy mass showing no evidence for a dichotomy between giant and dwarf early-type galaxies. These properties may be influenced by the cluster environment as suggested by cosmological simulations.« less