1,105 research outputs found
UCD Candidates in the Hydra Cluster
NGC 3311, the giant cD galaxy in the Hydra cluster (A1060), has one of the
largest globular cluster systems known. We describe new Gemini GMOS (g',i')
photometry of the NGC 3311 field which reveals that the red, metal-rich side of
its globular cluster population extends smoothly upward into the mass range
associated with the new class of Ultra-Compact Dwarfs (UCDs). We identify 29
UCD candidates with estimated masses > 6x10^6 solar masses and discuss their
characteristics. This UCD-like sequence is the most well defined one yet seen,
and reinforces current ideas that the high-mass end of the globular cluster
sequence merges continuously into the UCD sequence, which connects in turn to
the E galaxy structural sequence.Comment: 5 pages, 3 figures. Accepted for publication in ApJ Letter
From Supermassive Black Holes to Dwarf Elliptical Nuclei: a Mass Continuum
Considerable evidence suggests that supermassive black holes reside at the
centers of massive galactic bulges. At a lower galactic mass range, many dwarf
galaxies contain extremely compact nuclei that structurally resemble massive
globular clusters. We show that both these types of central massive objects
(CMO's) define a single unbroken relation between CMO mass and the luminosity
of their host galaxy spheroid. Equivalently, M_CMO is directly proportional to
the host spheroid mass over 4 orders of magnitude. We note that this result has
been simultaneously and independently identified by Cote et al. (2006), see
also Ferrarese et al. (2006). We therefore suggest that the dE,N nuclei may be
the low-mass analogs of supermassive black holes, and that these two types of
CMO's may have both developed starting from similar initial formation
processes. The overlap mass interval between the two types of CMO's is small,
and suggests that for M_CMO > 10^7 M_sun, the formation of a black hole was
strongly favored, perhaps because the initial gas infall to the center was too
rapid and violent for star formation to occur efficiently.Comment: 4 pages, 2 figures, submitted to ApJ
Probability tree algorithm for general diffusion processes
Motivated by path-integral numerical solutions of diffusion processes,
PATHINT, we present a new tree algorithm, PATHTREE, which permits extremely
fast accurate computation of probability distributions of a large class of
general nonlinear diffusion processes
The Globular Cluster Systems around NGC 3311 and NGC 3309
We present extensive new photometry in (g',i') of the large globular cluster
(GC) system around NGC 3311, the central cD galaxy in the Hydra cluster. Our
GMOS data cover a 5.5' field of view and reach a limiting magnitude i' = 26,
about 0.5 magnitude fainter than the turnover point of the GC luminosity
function. We find that NGC 3311 has a huge population of ~16, 000 GCs, closely
similar to the prototypical high specific frequency Virgo giant M87. The
color-magnitude distribution shows that the metal-poor blue GC sequence and the
metal-richer red sequence are both present, with nearly equal numbers of
clusters. Bimodal fits to the color distributions confirm that the blue
sequence shows the same trend of progressively increasing metallicity with GC
mass that has previously been found in many other large galaxies; the
correlation we find corresponds to a scaling of GC metallicity with mass of Z ~
M^0.6 . By contrast, the red sequence shows no change of mean metallicity with
mass, but it shows an upward extension to much higher than normal luminosity
into the UCD-like range, strengthening the potential connections between
massive GCs and UCDs. The GC luminosity function, which we measure down to the
turnover point at M_I = -8.4, also has a normal form like those in other giant
ellipticals. Within the Hydra field, another giant elliptical NGC 3309 is
sitting just 100" from the cD NGC 3311. We use our data to solve simultaneously
for the spatial structure and total GC populations of both galaxies at once.
Their specific frequencies are S_N (NGC 3311) = 12.5 +/- 1.5 and S_N (NGC 3309)
= 0.6 +/-0.4. NGC 3311 is completely dominant and entirely comparable with
other cD-type systems such as M87 in Virgo.Comment: 15 pages, 15 figures. Accepted to the Astrophysical Journal. Version
with higher resolution figures is available at
http://www.thewehners.net/astro/papers/wehner_n3311_highres.pd
Further Definition of the Mass-Metallicity Relation in Globular Cluster Systems Around Brightest Cluster Galaxies
We combine the globular cluster data for fifteen Brightest Cluster Galaxies
and use this material to trace the mass-metallicity relations (MMR) in their
globular cluster systems (GCSs). This work extends previous studies which
correlate the properties of the MMR with those of the host galaxy. Our combined
data sets show a mean trend for the metal-poor (MP) subpopulation which
corresponds to a scaling of heavy-element abundance with cluster mass Z ~
M^(0.30+/-0.05). No trend is seen for the metal-rich (MR) subpopulation which
has a scaling relation that is consistent with zero. We also find that the
scaling exponent is independent of the GCS specific frequency and host galaxy
luminosity, except perhaps for dwarf galaxies.
We present new photometry in (g',i') obtained with Gemini/GMOS for the
globular cluster populations around the southern giant ellipticals NGC 5193 and
IC 4329. Both galaxies have rich cluster populations which show up as normal,
bimodal sequences in the colour-magnitude diagram.
We test the observed MMRs and argue that they are statistically real, and not
an artifact caused by the method we used. We also argue against asymmetric
contamination causing the observed MMR as our mean results are no different
from other contamination-free studies. Finally, we compare our method to the
standard bimodal fitting method (KMM or RMIX) and find our results are
consistent.
Interpretation of these results is consistent with recent models for globular
cluster formation in which the MMR is determined by GC self-enrichment during
their brief formation period.Comment: 35 pages, 20 figures. Accepted by Astronomical Journal. Complete
preprint including high resolution figures available at
http://www.physics.mcmaster.ca/~cockcroft/MMRpape
On the connection between Complementarity and Uncertainty Principles in the Mach-Zehnder interferometric setting
We revisit, in the framework of Mach-Zehnder interferometry, the connection
between the complementarity and uncertainty principles of quantum mechanics.
Specifically, we show that, for a pair of suitably chosen observables, the
trade-off relation between the complementary path information and fringe
visibility is equivalent to the uncertainty relation given by Schr\"odinger
and Robertson, and to the one provided by Landau and Pollak as well. We also
employ entropic uncertainty relations (based on R\'enyi entropic measures) and
study their meaning for different values of the entropic parameter. We show
that these different values define regimes which yield qualitatively different
information concerning the system, in agreement with findings of [A. Luis,
Phys. Rev. A 84, 034101 (2011)]. We find that there exists a regime for which
the entropic uncertinty relations can be used as criteria to pinpoint non
trivial states of minimum uncertainty.Comment: 7 pages, 2 figure
X-ray, Optical, and Infrared Imaging and Spectral Properties of the 1 Ms Chandra Deep Field North Sources
We present the optical, near-infrared, submillimeter, and radio follow-up
catalog of the X-ray selected sources from the 1 Ms Chandra observation of the
Hubble Deep Field North region. We have B, V, R, I, and z' magnitudes for the
370 X-ray point sources, HK' magnitudes for 276, and spectroscopic redshifts
for 182. We present high-quality spectra for 175 of these. The redshift
distribution shows indications of structures at z=0.843 and z=1.0175 (also
detected in optical surveys) which could account for a part of the
field-to-field variation seen in the X-ray number counts. The flux
contributions separated into unit bins of redshift show that the z<1
spectroscopically identified sources already contribute about one-third of the
total flux in both the hard and soft bands. We find from ratios of the X-ray
counts that the X-ray spectra are well-described by absorption of an intrinsic
Gamma=1.8 power-law, with log NH values ranging from 21 to 23.7. We estimate
that the Chandra sources that produce 87% of the HEAO-A X-ray background (XRB)
at 3 keV produce 57% at 20 keV, provided that at high energies the spectral
shape of the sources continues to be well-described by a Gamma=1.8 power-law.
However, when the Chandra contributions are renormalized to the BeppoSAX XRB at
3 keV, the shape matches fairly well the observed XRB at both energies. Thus,
whether a substantial population of as-yet undetected Compton-thick sources is
required to completely resolve the XRB above 10 keV depends critically on how
the currently discrepant XRB measurements in the 1-10 keV energy range tie
together with the higher energy XRB. (Abridged)Comment: October 2002 issue of The Astronomical Journal, 19 pages + Table 1,
Figs 2 and 6 can be found at http://www.astro.wisc.edu/~barger/cdfn.htm
Desert Ants Learn Vibration and Magnetic Landmarks
The desert ants Cataglyphis navigate not only by path integration but also by using visual and olfactory landmarks to pinpoint the nest entrance. Here we show that Cataglyphis noda can additionally use magnetic and vibrational landmarks as nest-defining cues. The magnetic field may typically provide directional rather than positional information, and vibrational signals so far have been shown to be involved in social behavior. Thus it remains questionable if magnetic and vibration landmarks are usually provided by the ants' habitat as nest-defining cues. However, our results point to the flexibility of the ants' navigational system, which even makes use of cues that are probably most often sensed in a different context
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