3,593 research outputs found
Virgo Galaxies with Long One-Sided HI Tails
In a new HI imaging survey of Virgo galaxies (VIVA: VLA Imaging of Virgo
galaxies in Atomic gas), we find 7 spiral galaxies with long HI tails. The
morphology varies but all the tails are extended well beyond the optical radii
on one side. These galaxies are found in intermediate-low density regions
(0.6-1 Mpc in projection from M87). The tails are all pointing roughly away
from M87, suggesting that these tails may have been created by a global cluster
mechanism. While the tidal effects of the cluster potential are too small, a
rough estimate suggests that simple ram-pressure stripping indeed could have
formed the tails in all but two cases. At least three systems show HI
truncation to within the stellar disk, providing evidence for a gas-gas
interaction. Although most of these galaxies do not appear disturbed optically,
some have close neighbors, suggesting that tidal interactions may have moved
gas outwards making it more susceptible to the ICM ram-pressure or viscosity.
Indeed, a simulation study of one of the tail galaxies, NGC 4654, suggests that
the galaxy is most likely affected by the combined effect of a gravitational
interaction and ram-pressure stripping. We conclude that these one-sided HI
tail galaxies have recently arrived in the cluster, falling in on highly radial
orbits. It appears that galaxies begin to lose their gas already at
intermediate distances from the cluster center through ram-pressure or
turbulent viscous stripping and tidal interactions with neighbours, or a
combination of both.Comment: 4 pages, 3 figures (including 1 plate), accepted for accepted for
publication in ApJ Letter (vol. 659, L115), a version with full resolution
Plate 1 is available from
http://www.astro.umass.edu/~achung/astro-ph/viva_tail.pd
Yield modeling of acoustic charge transport transversal filters
This paper presents a yield model for acoustic charge transport transversal filters. This model differs from previous IC yield models in that it does not assume that individual failures of the nondestructive sensing taps necessarily cause a device failure. A redundancy in the number of taps included in the design is explained. Poisson statistics are used to describe the tap failures, weighted over a uniform defect density distribution. A representative design example is presented. The minimum number of taps needed to realize the filter is calculated, and tap weights for various numbers of redundant taps are calculated. The critical area for device failure is calculated for each level of redundancy. Yield is predicted for a range of defect densities and redundancies. To verify the model, a Monte Carlo simulation is performed on an equivalent circuit model of the device. The results of the yield model are then compared to the Monte Carlo simulation. Better than 95% agreement was obtained for the Poisson model with redundant taps ranging from 30% to 150% over the minimum
Temporal Development of Electric Field Structures in Photoconductive GaAs Switches
The temporal development of the electric field distribution in semi‐insulating GaAs photoconductive switches operated in the linear and lock‐on mode has been studied. The field structure was obtained by recording a change in the absorption pattern of the switch due to the Franz–Keldysh effect at a wavelength near the band edge of GaAs. In the linear mode, a high field layer develops at the cathode contact after laser activation. With increasing applied voltage, domainlike structures become visible in the anode region and the switch transits into the lock‐on state, a permanent filamentary electrical discharge. Calibration measurements show the field intensity in these domains to exceed 40 kV/cm, which is greater than three times the value of the average applied field
CO Distribution and Kinematics Along the Bar in the Strongly Barred Spiral NGC 7479
We report on the 2.5 arcsec (400 pc) resolution CO (J = 1 -> 0) observations
covering the whole length of the bar in the strongly barred late-type spiral
galaxy NGC 7479. CO emission is detected only along a dust lane that traverses
the whole length of the bar, including the nucleus. The emission is strongest
in the nucleus. The distribution of emission is clumpy along the bar outside
the nucleus, and consists of gas complexes that are unlikely to be
gravitationally bound. The CO kinematics within the bar consist of two separate
components. A kinematically distinct circumnuclear disk, < 500 pc in diameter,
is undergoing predominantly circular motion with a maximum rotational velocity
of 245 km/s at a radius of 1 arcsec (160 pc). The CO-emitting gas in the bar
outside the circumnuclear disk has substantial noncircular motions which are
consistent with a large radial velocity component, directed inwards. The CO
emission has a large velocity gradient across the bar dust lane, ranging from
0.5 to 1.9 km/s/pc after correcting for inclination, and the projected velocity
change across the dust lane is as high as 200 km/s. This sharp velocity
gradient is consistent with a shock front at the location of the bar dust lane.
A comparison of H-alpha and CO kinematics across the dust lane shows that
although the H-alpha emission is often observed both upstream and downstream
from the dust lane, the CO emission is observed only where the velocity
gradient is large. We also compare the observations with hydrodynamic models
and discuss star formation along the bar.Comment: 16 pages, including 10 figures. Accepted for publication in Ap
Hubble Space Telescope Imaging of the Ultra-Compact High Velocity Cloud AGC 226067: A stripped remnant in the Virgo Cluster
We analyze the optical counterpart to the ultra-compact high velocity cloud
AGC 226067, utilizing imaging taken with the Advanced Camera for Surveys (ACS)
on the Hubble Space Telescope. The color magnitude diagram of the main body of
AGC 226067 reveals an exclusively young stellar population, with an age of
7--50 Myr, and is consistent with a metallicity of [Fe/H]0.3 as
previous work has measured via HII region spectroscopy. Additionally, the color
magnitude diagram is consistent with a distance of 17 Mpc,
suggesting an association with the Virgo cluster. A secondary stellar system
located 1.6' (8 kpc) away in projection has a similar stellar
population. The lack of an old red giant branch (5 Gyr) is contrasted
with a serendipitously discovered Virgo dwarf in the ACS field of view (Dw
J122147+132853), and the total diffuse light from AGC~226067 is consistent with
the luminosity function of the resolved 7--50 Myr stellar population. The
main body of AGC~226067 has a =11.30.3, or
=5.41.310 given the stellar population.
We searched 20 deg of imaging data adjacent to AGC~226067 in the Virgo
Cluster, and found two similar stellar systems dominated by a blue stellar
population, far from any massive galaxy counterpart -- if this population has
similar star formation properties as AGC~226067, it implies 0.1
yr in Virgo intracluster star formation. Given its unusual
stellar population, AGC~226067 is likely a stripped remnant and is plausibly
the result of compressed gas from the ram pressure stripped M86 subgroup
(350 kpc away in projection) as it falls into the Virgo Cluster.Comment: 9 pages, 4 figures, 1 table. Accepted by the Astrophysical Journa
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