4,395 research outputs found
Counter Rotating Open Rotor Animation using Particle Image Velocimetry
This article describes the two accompanying fluid dynamics videos for the
"Counter rotating open rotor flow field investigation using stereoscopic
Particle Image Velocimetry" presented at the 64th Annual Meeting of the APS
Division of Fluid Dynamics in Baltimore, Maryland, November 20-22, 2011.Comment: Videos are include
Globular Cluster Systems in Brightest Cluster Galaxies. III: Beyond Bimodality
We present new deep photometry of the rich globular cluster (GC) systems
around the Brightest Cluster Galaxies UGC 9799 (Abell 2052) and UGC 10143
(Abell 2147), obtained with the HST ACS and WFC3 cameras. For comparison, we
also present new reductions of similar HST/ACS data for the Coma supergiants
NGC 4874 and 4889. All four of these galaxies have huge cluster populations (to
the radial limits of our data, comprising from 12000 to 23000 clusters per
galaxy). The metallicity distribution functions (MDFs) of the GCs can still be
matched by a bimodal-Gaussian form where the metal-rich and metal-poor modes
are separated by ~0.8 dex, but the internal dispersions of each mode are so
large that the total MDF becomes very broad and nearly continuous from [Fe/H] =
-2.4 to Solar. There are, however, significant differences between galaxies in
the relative numbers of \emph{metal-rich} clusters, suggesting that they
underwent significantly different histories of mergers with massive, gas-rich
halos. Lastly, the proportion of metal-poor GCs rises especially rapidly
outside projected radii R > 4 R_eff, suggesting the importance of accreted
dwarf satellites in the outer halo. Comprehensive models for the formation of
GCs as part of the hierarchical formation of their parent galaxies will be
needed to trace the systematic change in structure of the MDF with galaxy mass,
from the distinctly bimodal form in smaller galaxies up to the broad continuum
that we see in the very largest systems.Comment: In press for Astrophysical Journa
Tidal dwarfs in the M81 group: the second generation?
We derive quantitative star formation histories of the four suspected tidal
dwarf galaxies in the M81 group, HolmbergIX, BK3N, Arp-loop (A0952+69), and
Garland, using Hubble Space Telescope/Wide Field Planetary Camera2 images in
F606W and F814W obtained as part of a Snapshot survey of dwarf galaxies in the
Local Universe. We consider the spatial distribution and ages of resolved
stellar populations in these dwarf irregular galaxies. We use synthetic
color-magnitude diagrams to derive the ages of the major star formation
episodes, star formation rates, and approximate metallicity ranges. All the
galaxies show evidence of continuous star formation between about 20 and 200
Myr ago with star formation rates in the range 7.5*10^(-3)- 7.6*10^(-4)
M(sun)/yr. The metallicity of the detected stars spans a wide range, and have
lower than solar abundance. A possible scenario is that all four dwarf galaxies
were formed from material in the metal-poor outer part of the giant spiral
galaxy M81 after the tidal interaction between M81, M82, and NGC3077 about 200
Myr ago. While we do not directly detect pronounced old stellar populations,
the photometric limits of our data are such that the presence of such a
population is not entirely ruled out
Transient Oscillation of Currents in Quantum Hall Effect of Bloch Electrons
We consider the quantum Hall effect of two-dimensional electrons with a
periodic potential and study the time dependence of the Hall and longitudinal
currents when the electric field is applied abruptly. We find that the currents
oscillate in time with very large frequencies because of quantum fluctuation
and the oscillations eventually vanish, for their amplitudes decay as 1/t.Comment: 16 pages and 8 figure
Anchors for the Cosmic Distance Scale: the Cepheid QZ Normae in the Open Cluster NGC 6067
Cepheids are key to establishing the cosmic distance scale. Therefore it's
important to assess the viability of QZ Nor, V340 Nor, and GU Nor as
calibrators for Leavitt's law via their purported membership in the open
cluster NGC 6067. The following suite of evidence confirms that QZ Nor and V340
Nor are members of NGC 6067, whereas GU Nor likely lies in the foreground: (i)
existing radial velocities for QZ Nor and V340 Nor agree with that established
for the cluster (-39.4+-1.2 km/s) to within 1 km/s, whereas GU Nor exhibits a
markedly smaller value; (ii) a steep velocity-distance gradient characterizes
the sight-line toward NGC 6067, thus implying that objects sharing common
velocities are nearly equidistant; (iii) a radial profile constructed for NGC
6067 indicates that QZ Nor is within the cluster bounds, despite being 20' from
the cluster center; (iv) new BVJH photometry for NGC 6067 confirms the cluster
lies d=1.75+-0.10 kpc distant, a result that matches Wesenheit distances
computed for QZ Nor/V340 Nor using the Benedict et al. (2007, HST parallaxes)
calibration. QZ Nor is a cluster Cepheid that should be employed as a
calibrator for the cosmic distance scale.Comment: To appear in ApS
The Globular Cluster Systems of NGC 1400 and NGC 1407
The two brightest elliptical galaxies in the Eridanus A group, NGC 1400 and
NGC 1407, have been observed in both the Washington T_1 and Kron-Cousins I
filters to obtain photometry of their globular cluster systems (GCSs). This
group of galaxies is of particular interest due to its exceptionally high M/L
value, previously estimated at ~3000h, making this cluster highly
dark-matter-dominated. NGC 1400's radial velocity (549 km/s) is extremely low
compared to that of the central galaxy of Eridanus A (NGC 1407 with =
1766 km/s) and the other members of the system, suggesting that it is a
foreground galaxy projected by chance onto the cluster. Using the shapes of the
globular cluster luminosity functions, however, we derive distances of 17.6 +/-
3.1 Mpc to NGC 1407 and 25.4 +/- 7.0 Mpc to NGC 1400. These results support
earlier conclusions that NGC 1400 is at the distance of Eridanus A and
therefore has a large peculiar velocity. Specific frequencies are also derived
for these galaxies, yielding values of S_N = 4.0 +/- 1.3 for NGC 1407 and S_N =
5.2 +/- 2.0 for NGC 1400. In this and other respects, these two galaxies have
GCSs which are consistent with those observed in other galaxies.Comment: 14 pages (AASTeX), 3 postscript figures, submitted to the
Astronomical Journa
Extragalactic Globular Clusters in the Near-Infrared: V. IC 4051 and NGC 3311
We present the results of combined optical and near-infrared photometry for
the globular cluster systems of the giant ellipticals IC 4051 and NGC 3311. We
use the reduced age-metallicity degeneracy in (V-I) vs.(V-H) color-color
diagrams to derive the cumulative age distribution within the red
sub-population of globular clusters and to search for age sub-populations. The
age distribution is then compared to the one determined for simulated globular
cluster systems in order to set constraints on the relative age and size of
these globular cluster sub-populations. In both galaxies we find a significant
fraction of globular clusters with ages between 2- 5 Gyr. We also investigate
the metallicity distribution in both systems. Small number statistics prevent
us from making any definite statements concerning NGC 3311, but we find that
the derived metallicity distribution of the IC 4051 clusters strongly depends
on the assumed age distribution. Based on our most likely result that finds a
large number of young/intermediate age clusters (~2 Gyr) within the selected
globular cluster sample, we find metallicity peaks at -0.2 for the old
clusters and +0.8 for the young clusters. Only few very metal poor clusters are
found. However, the metallicity distribution within the young/intermediate
globular cluster population is significantly affected by our choice of the
applied Single Stellar Population model. The mean metallicity of the second
generation of globular clusters changes from the above mentioned and extremely
high +0.8 dex to +0.2 dex. Note that the model dependency becomes less severe
with an increasing age of the cluster population.Comment: 21 pages, 21 figures, A&A, accepte
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