1,386 research outputs found
Phase decorrelation, streamwise vortices and acoustic radiation in mixing layers
Several direct numerical simulations were performed and analyzed to study various aspects of the early development of mixing layers. Included are the phase jitter of the large-scale eddies, which was studied using a 2-D spatially-evolving mixing layer simulation; the response of a time developing mixing layer to various spanwise disturbances; and the sound radiation from a 2-D compressible time developing mixing layer
Mapping the Polarization of the Radio-Loud Ly Nebula B3 J2330+3927
Lya nebulae, or "Lya blobs", are extended (up to ~100 kpc), bright (L[Lya] >
10^43 erg/s) clouds of Lya emitting gas that tend to lie in overdense regions
at z ~ 2--5. The origin of the Lya emission remains unknown, but recent
theoretical work suggests that measuring the polarization might discriminate
among powering mechanisms. Here we present the first narrowband, imaging
polarimetry of a radio-loud Lya nebula, B3 J2330+3927 at z=3.09, with an
embedded active galactic nucleus (AGN). The AGN lies near the blob's Lya
emission peak and its radio lobes align roughly with the blob's major axis.
With the SPOL polarimeter on the 6.5m MMT telescope, we map the total (Lya +
continuum) polarization in a grid of circular apertures of radius 0.6"
(4.4kpc), detecting a significant (>2sigma) polarization fraction P in nine
apertures and achieving strong upper-limits (as low as 2%) elsewhere. P
increases from <2% at ~5kpc from the blob center to ~17% at ~15-25kpc. The
detections are distributed asymmetrically, roughly along the nebula's major
axis. The polarization angles theta are mostly perpendicular to this axis.
Comparing the Lya flux to that of the continuum, and conservatively assuming
that the continuum is highly polarized (20-100%) and aligned with the total
polarization, we place lower limits on the polarization of the Lya emission
P(Lya) ranging from no significant polarization at ~5 kpc from the blob center
to ~ 3--17% at 10--25kpc. Like the total polarization, the Lya polarization
detections occur more often along the blob's major axis.Comment: 9 pages, 7 figures, accepted for publication in Ap
Restoration of Sp4 in Forebrain GABAergic Neurons Rescues Hypersensitivity to Ketamine in Sp4 Hypomorphic Mice.
BackgroundKetamine produces schizophrenia-like behavioral phenotypes in healthy people. Prolonged ketamine effects and exacerbation of symptoms after the administration of ketamine have been observed in patients with schizophrenia. More recently, ketamine has been used as a potent antidepressant to treat patients with major depression. The genes and neurons that regulate behavioral responses to ketamine, however, remain poorly understood. Sp4 is a transcription factor for which gene expression is restricted to neuronal cells in the brain. Our previous studies demonstrated that Sp4 hypomorphic mice display several behavioral phenotypes relevant to psychiatric disorders, consistent with human SP4 gene associations with schizophrenia, bipolar disorder, and major depression. Among those behavioral phenotypes, hypersensitivity to ketamine-induced hyperlocomotion has been observed in Sp4 hypomorphic mice.MethodsIn the present study, we used the Cre-LoxP system to restore Sp4 gene expression, specifically in either forebrain excitatory or GABAergic inhibitory neurons in Sp4 hypomorphic mice. Mouse behavioral phenotypes related to psychiatric disorders were examined in these distinct rescue mice.ResultsRestoration of Sp4 in forebrain excitatory neurons did not rescue deficient sensorimotor gating nor ketamine-induced hyperlocomotion. Restoration of Sp4 in forebrain GABAergic neurons, however, rescued ketamine-induced hyperlocomotion, but did not rescue deficient sensorimotor gating.ConclusionsOur studies suggest that the Sp4 gene in forebrain GABAergic neurons regulates ketamine-induced hyperlocomotion
The Diversity of Diffuse Ly Nebulae around Star-Forming Galaxies at High Redshift
We report the detection of diffuse Ly emission, or Ly halos
(LAHs), around star-forming galaxies at and in the NOAO
Deep Wide-Field Survey Bo\"otes field. Our samples consist of a total of
1400 galaxies, within two separate regions containing spectroscopically
confirmed galaxy overdensities. They provide a unique opportunity to
investigate how the LAH characteristics vary with host galaxy large-scale
environment and physical properties. We stack Ly images of different
samples defined by these properties and measure their median LAH sizes by
decomposing the stacked Ly radial profile into a compact galaxy-like
and an extended halo-like component. We find that the exponential scale-length
of LAHs depends on UV continuum and Ly luminosities, but not on
Ly equivalent widths or galaxy overdensity parameters. The full
samples, which are dominated by low UV-continuum luminosity Ly emitters
(), exhibit LAH sizes of 5kpc. However, the
most UV- or Ly-luminous galaxies have more extended halos with
scale-lengths of 7kpc. The stacked Ly radial profiles decline
more steeply than recent theoretical predictions that include the contributions
from gravitational cooling of infalling gas and from low-level star formation
in satellites. On the other hand, the LAH extent matches what one would expect
for photons produced in the galaxy and then resonantly scattered by gas in an
outflowing envelope. The observed trends of LAH sizes with host galaxy
properties suggest that the physical conditions of the circumgalactic medium
(covering fraction, HI column density, and outflow velocity) change with halo
mass and/or star-formation rates.Comment: published in ApJ, minor proof corrections applie
Spectroscopic Properties of the z=4.5 Lyman-alpha Emitters
We present Keck/LRIS optical spectra of 17 Lya-emitting galaxies and one
Lyman break galaxy at z=4.5 discovered in the Large Area Lyman Alpha (LALA)
survey. The survey has identified a sample of ~350 candidate Lya-emitting
galaxies at z=4.5 in a search volume of 1.5 x 10^6 comoving Mpc^3. We targeted
25 candidates for spectroscopy; hence, the 18 confirmations presented herein
suggest a selection reliability of 72%. The large equivalent widths (median
W(rest)~80 A) but narrow physical widths (v < 500 km/s) of the Lya emission
lines, along with the lack of accompanying high-ionization state emission
lines, suggest that these galaxies are young systems powered by star formation
rather than by AGN activity. Theoretical models of galaxy formation in the
primordial Universe suggest that a small fraction of Lya-emitting galaxies at
z=4.5 may still be nascent, metal-free objects. Indeed, we find with 90%
confidence that 3 to 5 of the confirmed sources show W(rest) > 240 A, exceeding
the maximum Lya equivalent width predicted for normal stellar populations.
Nonetheless, we find no evidence for HeII 1640 emission in either individual or
composite spectra, indicating that though these galaxies are young, they are
not truly primitive, Population III objects.Comment: 12 pages, Accepted to Ap
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