27,887 research outputs found
Wandering globular clusters: the first dwarf galaxies in the universe?
In the last decade we witness an advent of new types of dwarf stellar systems
in cluding ultra-compact dwarfs, ultra-faint dwarf spheroidals, and exotic
globular clusters, breaking the old simple paradigm for dwarf galaxies and
globular clusters. These objects become more intriguing, and understanding of
these new findings be comes more challenging. Recently we discovered a new type
of large scale structure in the Virgo cluster of galaxies: it is composed of
globular clusters. Globular clusters in Virgo are found wandering between
galaxies (intracluster globular clusters) as well as in galaxies. These
intracluster globular clusters fill a significant fraction in the area of the
Virgo cluster and they are dominated by blue globular clusters. These
intracluster globular clusters may be closely related with the first dwarf
galaxies in the universe.Comment: 6 pages, 3 figures, Conference Proceedings: "A Universe of Dwarf
Galaxies", 14-18 June 2010, Lyon, Franc
Spectroscopy of globular clusters in the low-luminosity spiral galaxy NGC 45
CONTEXT: Extragalactic globular clusters have been studied in elliptical
galaxies and in a few luminous spiral galaxies, but little is known about
globular clusters in low-luminosity spirals.
AIMS: Past observations with the ACS have shown that NGC 45 hosts a large
population of globular clusters (19), as well as several young star clusters.
In this work we aim to confirm the bona fide globular cluster status for 8 of
19 globular cluster candidates and to derive metallicities, ages, and
velocities.
METHODS: VLT/FORS2 multislit spectroscopy in combination with the Lick/IDS
system was used to derive velocities and to constrain metallicities and
[alpha/Fe] element ratio of the globular clusters.
RESULTS: We confirm the 8 globular clusters as bona fide globular clusters.
Their velocities indicate halo or bulge-like kinematics, with little or no
overall rotation. From absorption indices such as H_beta, H_gamma, and H_delta
and the combined [MgFe]' index, we found that the globular clusters are
metal-poor [Z/H]<=-0.33 dex and [alpha/Fe]<=0.0 element ratio. These results
argue in favor of a population of globular clusters formed during the
assembling of the galaxy.Comment: Accepted for publication in Astronomy and Astrophysics. 10 pages, 6
figures. Table 6 and Fig. 6 will only be published in the electronic edition
of the A&A journa
The Globular Cluster System of M60 (NGC 4649). I. CFHT MOS Spectroscopy and Database
We present the measurement of radial velocities for globular clusters in M60,
giant elliptical galaxy in the Virgo cluster. Target globular cluster
candidates were selected using the Washington photometry based on the deep
16\arcmin \times 16\arcmin images taken at the KPNO 4m and using the
photometry derived from the HST/WFPC2 archive images. The spectra of the target
objects were obtained using the Multi-Object Spectrograph (MOS) at the
Canada-France-Hawaii Telescope (CFHT). We have measured the radial velocity for
111 objects in the field of M60: 93 globular clusters (72 blue globular
clusters with and 21 red globular clusters with
), 11 foreground stars, 6 small galaxies, and the nucleus of
M60. The measured velocities of the 93 globular clusters range from
km s to km s, with a mean value of
km s, which is in good agreement with the velocity of the nucleus of M60
( km s). Combining our results with data in the
literature, we present a master catalog of radial velocities for 121 globular
clusters in M60. The velocity dispersion of the globular clusters in the master
catalog is found to be km s for the entire sample,
km s for 83 blue globular clusters, and
km s for 38 red globular clusters.Comment: 29 pages, 8 figures. To appear in Ap
The ellipticities of Galactic and LMC globular clusters
The globular clusters of the LMC are found to be significantly more
elliptical than Galactic globular clusters, but very similar in virtually all
other respects. The ellipticity of the LMC globular clusters is shown not be
correlated with the age or mass of those clusters. It is proposed that the
ellipticity differences are caused by the different strengths of the tidal
fields in the LMC and the Galaxy. The strong Galactic tidal field erases
initial velocity anisotropies and removes angular momentum from globular
clusters making them more spherical. The tidal field of the LMC is not strong
enough to perform these tasks and its globular clusters remain close to their
initial states.Comment: 3 pages LaTeX file with 3 figures incorporated accepted for
publication in MNRAS. Also available by e-mailing spg, or by ftp from
ftp://star-www.maps.susx.ac.uk/pub/papers/spg/ellip.ps.
Globular Clusters in Dwarf Galaxies
Data are presently available on the luminosities and half-light radii of 101
globular clusters associated with low-luminosity parent galaxies. The
luminosity distribution of globulars embedded in dwarf galaxies having is found to differ dramatically from that for globular clusters
surrounding giant host galaxies with . The luminosity distribution
of globular clusters in giant galaxies peaks at , whereas that
for dwarfs is found to increases monotonically down to the completeness limit
of the cluster data at . Unexpectedly, the power law
distribution of the luminosities of globular clusters hosted by dwarf galaxies
is seen to be much flatter than the that of bright unevolved part of the
luminosity distribution of globular clusters associated with giant galaxies.
The specific frequency of globular clusters that are fainter than is found to be particularly high in dwarf galaxies. The luminosity
distribution of the LMC globular clusters is similar to that in giant galaxies,
and differs from those of the globulars in dwarf galaxies. The present data
appear to show no strong dependence of globular cluster luminosity on the
morphological types of their parent galaxies. No attempt is made to explain the
unexpected discovery that the luminosity distribution of globular clusters is
critically dependent on parent galaxy luminosity (mass?), but insensitive to
the morphological type of their host galaxy.Comment: Figure 6 replaced to be published in the Astronomical Journa
Intergalactic Globular Clusters
We confirm and extend our previous detection of a population of intergalactic
globular clusters in Abell 1185, and report the first discovery of an
intergalactic globular cluster in the nearby Virgo cluster of galaxies. The
numbers, colors and luminosities of these objects can place constraints on
their origin, which in turn may yield new insights to the evolution of galaxies
in dense environments.Comment: 2 pages, no figures. Talk presented at JD6, IAU General Assembly XXV,
Sydney, Australia, July 2003, to appear in Highlights of Astronomy, Vol. 1
Intracluster Globular Clusters
Globular cluster populations of supergiant elliptical galaxies are known to
vary widely, from extremely populous systems like that of UGC 9799, the
centrally dominant galaxy in Abell 2052, to globular-cluster-poor galaxies such
as NGC 5629 in Abell 2666. Here we propose that these variations point strongly
to the existence of a population of globular clusters that are not bound to
individual galaxies, but rather move freely throughout the cores of clusters of
galaxies. Such intracluster globular clusters may have originated as tidally
stripped debris from galaxy interactions and mergers, or alternatively they may
have formed in situ in some scenarios of globular cluster formation.Comment: 9 pages, uuencoded compressed postscript. Accepted for publication in
the Astrophysical Journal Letter
Some Systematics of Galactic Globular Clusters
The global properties of all known Galactic globular clusters are examined.
The relationship between the luminosities and the metallicities of Galactic
globular clusters is found to be complex. Among luminous clusters there is a
correlation in the sense that the oldest clusters are slightly more metal
deficient than are younger clusters. However, no such clear-cut relationship is
found among the faintest globular clusters. The central concentration index C
of globular clusters is seen to be independent of metallicity. The dependence
of the half-light radii of globular clusters on their Galactocentric distances
can be approximated by the relation . Clusters with
collapsed cores are mostly situated close to the Galactic nucleus. For kpc the luminosities and the radii of clusters appear to be uncorrelated.
The Galaxy differs from the LMC and the SMC in that it appears to lack highly
flattened luminous clusters. Galactic globular clusters with ages 13.0
Gyr are all of Oosterhoff type II, whereas almost all of those with ages
13.0 Gyr have been assigned to Oosterhoff type I. Globular clusters with ages
11.5 Gyr are all located in the outer Galactic halo, have below-average
luminosities and above-average radii. On the other hand the very old globular
cluster NGC 6522 is situated close to the Galactic nucleus.Comment: PASP, in pres
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