1,123 research outputs found
HI Clouds detected towards Virgo with the Arecibo Legacy Fast ALFA Survey
The Arecibo Legacy Fast ALFA survey is in the process of yielding a complete
HI dataset of the Virgo Cluster and its environs (Giovanelli et al. 2007, Kent
et al., in preparation). Assuming a distance to Virgo of 16.7 Mpc, the minimum
detectable HI mass by ALFALFA is of order 2 x 10^7 Msun. A number of the HI
detections appear to have interesting properties. Some appear associated with,
but offset from, low surface brightness optical counterparts; others, at larger
spatial offsets, may be tidally related to optical counterparts. Yet another
class includes detections which are not identifiable with any optical
counterparts. We present the ALFALFA results on these objects in the Virgo
region, as well as followup aperture synthesis observations obtained with the
VLA.Comment: To appear in Proceedings of IAU Symp #244, "Dark Galaxies and Lost
Baryons", June 2007, 10 pages including 7 figures and 1 tabl
NGC 4254: An Act of Harassment Uncovered by the Arecibo Legacy Fast ALFA Survey
We present an HI map constructed from the Arecibo Legacy Fast ALFA (ALFALFA)
survey of the surroundings of the strongly asymmetric Virgo cluster Sc galaxy
NGC 4254. Noted previously for its lopsided appearance, rich interstellar
medium, and extradisk HI emission, NGC 4254 is believed to be entering the
Virgo environment for the first time and at high speed. The ALFALFA map clearly
shows a long HI tail extending ~250 kpc northward from the galaxy. Embedded as
one condensation within this HI structure is the object previously identified
as a "dark galaxy": Virgo HI21 (Davies et al. 2004). A body of evidence
including its location within and velocity with respect to the cluster and the
appearance and kinematics of its strong spiral pattern, extra-disk HI and
lengthy HI tail is consistent with a picture of "galaxy harassment" as proposed
by Moore et al. (1996a,b; 1998). The smoothly varying radial velocity field
along the tail as it emerges from NGC 4254 can be used as a timing tool, if
interpreted as resulting from the coupling of the rotation of the disk and the
collective gravitational forces associated with the harassment mechanism.Comment: accepted for publication in Ap.J.(Lett.). higher resolution figure
available at http://egg.astro.cornell.edu/alfalfa/pubs/figs/n4254_f1.ep
Clouds Toward the Virgo Cluster Periphery: Gas-rich Optically Inert Galaxies
Aperture synthesis observations of two HI cloud complexes located in the
periphery of the Virgo galaxy cluster are presented. These low HI-mass clouds
( 10) are seen projected on the M region of the western Virgo
cluster, where the galaxy population is thought to lie behind the main A
cluster surrounding M87. The kinematic measurements of both unresolved Arecibo
and resolved VLA-C observations are in good agreement. The HI detections cannot
be identified with any optical, IR, or UV emission from available archival
imaging. They are inert at these wavelengths. The HI masses of the individual
VLA detections range from 7.28 log( 7.85. The total
dynamical mass estimates are several times their HI content, ranging from 7.00
log( 9.07, with the assumption that the clouds are
self-gravitating and in dynamical equilibrium. We report the observed
parameters derived from the VLA observations. One of these HI clouds appears to
be the most isolated optically inert detection observed in the outer reaches of
Virgo.Comment: 20 pages, 6 tables, 8 figures, accepted for publication in The
Astrophysical Journa
A Digital Archive of HI 21 cm Line Spectra of Optically-targeted Galaxies
We present a homogeneous compilation of HI spectral parameters extracted from
global 21 cm line spectra for some 9000 galaxies in the local universe
(heliocentric velocity -200 < V_Sun < 28,000 km/s) obtained with a variety of
large single dish radio telescopes but reanalyzed using a single set of
parameter extraction algorithms. Corrections to the observed HI line flux for
source extent and pointing offsets and to the HI line widths for instrumental
broadening and smoothing are applied according to model estimates to produce a
homogenous catalog of derived properties with quantitative error estimates.
Where the redshift is available from optical studies, we also provide flux
measurements for an additional 156 galaxies classified as marginal HI
detections and rms noise limits for 494 galaxies classified as nondetections.
Given the diverse nature of the observing programs contributing to it, the
characteristics of the combined dataset are heterogeneous, and as such, the
compilation is neither integrated HI line flux nor peak flux limited. However,
because of the large statistical base and homogenous reprocessing, the spectra
and spectral parameters of galaxies in this optically targeted sample can be
used to complement data obtained at other wavelengths to characterize the
properties of galaxies in the local universe and to explore the large scale
structures in which they reside.Comment: 13 pages, 9 figures, 3 external online tables, accepted for
publication in ApJ
Motor deficits in schizophrenia quantified by nonlinear analysis of postural sway.
Motor dysfunction is a consistently reported but understudied aspect of schizophrenia. Postural sway area was examined in individuals with schizophrenia under four conditions with different amounts of visual and proprioceptive feedback: eyes open or closed and feet together or shoulder width apart. The nonlinear complexity of postural sway was assessed by detrended fluctuation analysis (DFA). The schizophrenia group (n = 27) exhibited greater sway area compared to controls (n = 37). Participants with schizophrenia showed increased sway area following the removal of visual input, while this pattern was absent in controls. Examination of DFA revealed decreased complexity of postural sway and abnormal changes in complexity upon removal of visual input in individuals with schizophrenia. Additionally, less complex postural sway was associated with increased symptom severity in participants with schizophrenia. Given the critical involvement of the cerebellum and related circuits in postural stability and sensorimotor integration, these results are consistent with growing evidence of motor, cerebellar, and sensory integration dysfunction in the disorder, and with theoretical models that implicate cerebellar deficits and more general disconnection of function in schizophrenia
Are Newly Discovered HI High Velocity Clouds Minihalos in the Local Group?
A set of HI sources extracted from the north Galactic polar region by the
ongoing ALFALFA survey has properties that are consistent with the
interpretation that they are associated with isolated minihalos in the
outskirts of the Local Group (LG). Unlike objects detected by previous surveys,
such as the Compact High Velocity Clouds of Braun & Burton (1999), the HI
clouds found by ALFALFA do not violate any structural requirements or halo
scaling laws of the LambdaCDM structure paradigm, nor would they have been
detected by extant HI surveys of nearby galaxy groups other than the LG. At a
distance of d Mpc, their HI masses range between $5 x 10^4 d^2 and 10^6 d^2
solar and their HI radii between <0.4d and 1.6 d kpc. If they are parts of
gravitationally bound halos, the total masses would be on order of 10^8--10^9
solar, their baryonic content would be signifcantly smaller than the cosmic
fraction of 0.16 and present in a ionized gas phase of mass well exceeding that
of the neutral phase. This study does not however prove that the minihalo
interpretation is unique. Among possible alternatives would be that the clouds
are shreds of the Leading Arm of the Magellanic Stream.Comment: 4 pages, 3 figures, 1 table; to appear Ap.J. Letter
Foraging Distance of the Argentine Ant in California Vineyards.
Argentine ants, Linepithema humile (Mayr) (Hymenoptera: Formicidae), form mutualisms with hemipteran pests in crop systems. In vineyards, they feed on honeydew produced by mealybugs and soft scales, which they tend and protect from natural enemies. Few options for controlling Argentine ants are available; one of the more effective approaches is to use liquid baits containing a low dose of an insecticide. Knowledge of ant foraging patterns is required to estimate how many bait stations to deploy per unit area. To measure how far ants move liquid bait in vineyards, we placed bait stations containing sugar water and a protein marker in plots for 6 d, and then collected ants along transects extending away from bait stations. The ants moved an average of 16.08 m and 12.21 m from bait stations in the first and second years of the study, respectively. Marked ants were found up to 63 m from bait stations; however, proportions of marked ants decreased exponentially as distance from the bait station increased. Results indicate that Argentine ants generally forage at distancesvineyards, thus suggesting that insecticide bait stations must be deployed at intervals of 36 m or less to control ants. We found no effect of insecticide on distances that ants moved the liquid bait, but this may have been because bait station densities were too low to affect the high numbers of Argentine ants that were present at the study sites
The Arecibo Legacy Fast ALFA Survey: VIII. HI Source Catalog of the Anti-Virgo Region at dec = +25 deg
We present a fourth catalog of HI sources from the Arecibo Legacy Fast ALFA
(ALFALFA) Survey. We report 541 detections over 136 deg2, within the region of
the sky having 22h < R.A. < 03h and 24 deg < Dec. < 26 deg . This complements a
previous catalog in the region 26 deg < Dec. < 28 deg (Saintonge et al. 2008).
We present here the detections falling into three classes: (a) extragalactic
sources with S/N > 6.5, where the reliability of the catalog is better than
95%; (b) extragalactic sources 5.0 < S/N < 6.5 and a previously measured
optical redshift that corroborates our detection; or (c) High Velocity Clouds
(HVCs), or subcomponents of such clouds, in the periphery of the Milky Way. Of
the 541 objects presented here, 90 are associated with High Velocity Clouds,
while the remaining 451 are identified as extragalactic objects. Optical
counterparts have been matched with all but one of the extragalactic objects.Comment: 26 pages, 5 figures, 1 table, accepted for publication in
Astrophysical Journal Supplement Serie
The Arecibo Legacy Fast ALFA Survey: VI. Second HI Source Catalog of the Virgo Cluster Region
We present the third installment of HI sources extracted from the Arecibo
Legacy Fast ALFA extragalactic survey. This dataset continues the work of the
Virgo ALFALFA catalog. The catalogs and spectra published here consist of data
obtained during the 2005 and 2006 observing sessions of the survey. The catalog
consists of 578 HI detections within the range 11h 36m < R.A.(J2000) < 13h 52m
and +08 deg < Dec.(J2000) < +12 deg, and cz_sun < 18000 km/s. The catalog
entries are identified with optical counterparts where possible through the
examination of digitized optical images. The catalog detections can be
classified into three categories: (a) detections of high reliability with S/N >
6.5; (b) high velocity clouds in the Milky Way or its periphery; and (c)
signals of lower S/N which coincide spatially with an optical object and known
redshift. 75% of the sources are newly published HI detections. Of particular
note is a complex of HI clouds projected between M87 and M49 that do not
coincide with any optical counterparts. Candidate objects without optical
counterparts are few. The median redshift for this sample is 6500 km/s and the
cz distribution exhibits the local large scale structure consisting of Virgo
and the background void and the A1367-Coma supercluster regime at cz_sun ~7000
km/s. Position corrections for telescope pointing errors are applied to the
dataset by comparing ALFALFA continuum centroid with those cataloged in the
NRAO VLA Sky Survey. The uncorrected positional accuracy averages
27 arcsec ~(21 arcsec ~median) for all sources with S/N > 6.5 and is of order
~21 arcsec ~(16 arcsec ~median) for signals with S/N > 12. Uncertainties in
distances toward the Virgo cluster can affect the calculated HI mass
distribution.Comment: 25 pages, 1 Table, 8 figures, Accepted by the Astronomical Journa
Eyeblink Conditioning in Schizophrenia: A Critical Review
There is accruing evidence of cerebellar abnormalities in schizophrenia. The theory of cognitive dysmetria considers cerebellar dysfunction a key component of schizophrenia. Delay eyeblink conditioning (EBC), a cerebellar-dependent translational probe, is a behavioral index of cerebellar integrity. The circuitry underlying EBC has been well characterized by non-human animal research, revealing the cerebellum as the essential circuitry for the associative learning instantiated by this task. However, there have been persistent inconsistencies in EBC findings in schizophrenia. This article thoroughly reviews published studies investigating EBC in schizophrenia, with an emphasis on possible effects of antipsychotic medication and stimulus and analysis parameters on reports of EBC performance in schizophrenia. Results indicate a consistent finding of impaired EBC performance in schizophrenia, as measured by decreased rates of conditioning, and that medication or study design confounds do not account for this impairment. Results are discussed within the context of theoretical and neurochemical models of schizophrenia
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