510 research outputs found
Caenorhabditis elegans Muscleblind homolog mbl-1 functions in neurons to regulate synapse formation
<p>Abstract</p> <p>Background</p> <p>The sequestration of Muscleblind splicing regulators results in myotonic dystrophy. Previous work on Muscleblind has largely focused on its roles in muscle development and maintenance due to the skeletal and cardiac muscle degeneration phenotype observed in individuals with the disorder. However, a number of reported nervous system defects suggest that Muscleblind proteins function in other tissues as well.</p> <p>Results</p> <p>We have identified a mutation in the <it>Caenorhabditis elegans </it>homolog of Muscleblind, <it>mbl-1</it>, that is required for proper formation of neuromuscular junction (NMJ) synapses. <it>mbl-1 </it>mutants exhibit selective loss of the most distal NMJ synapses in a <it>C. elegans </it>motorneuron, DA9, visualized using the vesicle-associated protein RAB-3, as well as the active zone proteins SYD-2/liprin-α and UNC-10/Rim. The proximal NMJs appear to have normal pre- and postsynaptic specializations. Surprisingly, expressing a <it>mbl-1 </it>transgene in the presynaptic neuron is sufficient to rescue the synaptic defect, while muscle expression has no effect. Consistent with this result, <it>mbl-1 </it>is also expressed in neurons.</p> <p>Conclusions</p> <p>Based on these results, we conclude that in addition to its functions in muscle, the Muscleblind splice regulators also function in neurons to regulate synapse formation.</p
The Rest-frame Submillimeter Spectrum of High-redshift, Dusty, Star-forming Galaxies
We present the average rest-frame spectrum of high-redshift dusty, star-forming galaxies from 250 to 770 GHz. This spectrum was constructed by stacking Atacama Large Millimeter/submillimeter Array (ALMA) 3 mm spectra of 22 such sources discovered by the South Pole Telescope and spanning z = 2.0-5.7. In addition to multiple bright spectral features of ^(12)CO, [C I], and H_2O, we also detect several faint transitions of ^(13)CO, HCN, HNC, HCO^+, and CN, and use the observed line strengths to characterize the typical properties of the interstellar medium of these high-redshift starburst galaxies. We find that the ^(13)CO brightness in these objects is comparable to that of the only other z > 2 star-forming galaxy in which ^(13)CO has been observed. We show that the emission from the high-critical density molecules HCN, HNC, HCO^+, and CN is consistent with a warm, dense medium with T_(kin) ~ 55 K and n_H_2 ≳ 10^(5.5) cm^(–3). High molecular hydrogen densities are required to reproduce the observed line ratios, and we demonstrate that alternatives to purely collisional excitation are unlikely to be significant for the bulk of these systems. We quantify the average emission from several species with no individually detected transitions, and find emission from the hydride CH and the linear molecule CCH for the first time at high redshift, indicating that these molecules may be powerful probes of interstellar chemistry in high-redshift systems. These observations represent the first constraints on many molecular species with rest-frame transitions from 0.4 to 1.2 mm in star-forming systems at high redshift, and will be invaluable in making effective use of ALMA in full science operations
ALMA observations of atomic carbon in z~4 dusty star-forming galaxies
We present ALMA [CI]() (rest frequency 492 GHz) observations for a
sample of 13 strongly-lensed dusty star-forming galaxies originally discovered
at 1.4mm in a blank-field survey by the South Pole Telescope. We compare these
new data with available [CI] observations from the literature, allowing a study
of the ISM properties of extreme dusty star-forming galaxies spanning
a redshift range . Using the [CI] line as a tracer of the molecular
ISM, we find a mean molecular gas mass for SPT-DSFGs of
M. This is in tension with gas masses derived via low- CO
and dust masses; bringing the estimates into accordance requires either (a) an
elevated CO-to-H conversion factor for our sample of and a gas-to-dust ratio , or (b) an high carbon abundance . Using observations of a range of additional atomic
and molecular lines (including [CI], [CII], and multiple transitions of CO), we
use a modern Photodissociation Region code (3D-PDR) to assess the physical
conditions (including the density, UV radiation field strength, and gas
temperature) within the ISM of the DSFGs in our sample. We find that the ISM
within our DSFGs is characterised by dense gas permeated by strong UV fields.
We note that previous efforts to characterise PDR regions in DSFGs may have
significantly underestimated the density of the ISM. Combined, our analysis
suggests that the ISM of extreme dusty starbursts at high redshift consists of
dense, carbon-rich gas not directly comparable to the ISM of starbursts in the
local Universe.Comment: 21 pages, 12 figures. Accepted for publication in MNRA
SPT0346-52: Negligible AGN Activity in a Compact, Hyper-starburst Galaxy at z = 5.7
We present Chandra ACIS-S and ATCA radio continuum observations of the
strongly lensed dusty, star-forming galaxy SPT-S J034640-5204.9 (hereafter
SPT0346-52) at = 5.656. This galaxy has also been observed with ALMA, HST,
Spitzer, Herschel, APEX, and the VLT. Previous observations indicate that if
the infrared (IR) emission is driven by star formation, then the inferred
lensing-corrected star formation rate ( 4500 M_{\sun} yr) and
star formation rate surface density ( 2000 M_{\sun}
{yr^{-1}} {kpc^{-2}}) are both exceptionally high. It remained unclear from
the previous data, however, whether a central active galactic nucleus (AGN)
contributes appreciably to the IR luminosity. The {\it Chandra} upper limit
shows that SPT0346-52 is consistent with being star-formation dominated in the
X-ray, and any AGN contribution to the IR emission is negligible. The ATCA
radio continuum upper limits are also consistent with the FIR-to-radio
correlation for star-forming galaxies with no indication of an additional AGN
contribution. The observed prodigious intrinsic IR luminosity of (3.6
0.3) 10 L_{\sun} originates almost solely from vigorous star
formation activity. With an intrinsic source size of 0.61 0.03 kpc,
SPT0346-52 is confirmed to have one of the highest of any known
galaxy. This high , which approaches the Eddington limit for a
radiation pressure supported starburst, may be explained by a combination of
very high star formation efficiency and gas fraction.Comment: 8 pages, 6 figures, accepted for publication in Ap
Recommended from our members
Scientific rationale of a Saturn probe mission
We describe the main scientific goals to be addressed by future in situ exploration of Saturn
Scientific Value of a Saturn Atmospheric Probe Mission
Atmospheric entry probe mISSions to the giant planets can uniquely discriminate between competing theories of solar system formation and the origin and evolution of the giant planets and their atmospheres. This provides for important comparative studies of the gas and ice giants, and to provide a laboratory for studying the atmospheric chemistries, dynamics, and interiors of all the planets including Earth. The giant planets also represent a valuable link to extrasolar planetary systems. As outlined in the recent Planetary Decadal Survey, a Saturn Probe mission - with a shallow probe - ranks as a high priority for a New Frontiers class mission [1]
The Rest-Frame Submillimeter Spectrum of High-Redshift, Dusty, Star-Forming Galaxies
We present the average rest-frame spectrum of high-redshift dusty,
star-forming galaxies from 250-770GHz. This spectrum was constructed by
stacking ALMA 3mm spectra of 22 such sources discovered by the South Pole
Telescope and spanning z=2.0-5.7. In addition to multiple bright spectral
features of 12CO, [CI], and H2O, we also detect several faint transitions of
13CO, HCN, HNC, HCO+, and CN, and use the observed line strengths to
characterize the typical properties of the interstellar medium of these
high-redshift starburst galaxies. We find that the 13CO brightness in these
objects is comparable to that of the only other z>2 star-forming galaxy in
which 13CO has been observed. We show that the emission from the high-critical
density molecules HCN, HNC, HCO+, and CN is consistent with a warm, dense
medium with T_kin ~ 55K and n_H2 >~ 10^5.5 cm^-3. High molecular hydrogen
densities are required to reproduce the observed line ratios, and we
demonstrate that alternatives to purely collisional excitation are unlikely to
be significant for the bulk of these systems. We quantify the average emission
from several species with no individually detected transitions, and find
emission from the hydride CH and the linear molecule CCH for the first time at
high redshift, indicating that these molecules may be powerful probes of
interstellar chemistry in high-redshift systems. These observations represent
the first constraints on many molecular species with rest-frame transitions
from 0.4-1.2mm in star-forming systems at high redshift, and will be invaluable
in making effective use of ALMA in full science operations.Comment: 19 pages, 10 figures (2 in appendices); accepted for publication in
Ap
The redshift distribution of dusty star forming galaxies from the SPT survey
We use the Atacama Large Millimeter/submillimeter Array (ALMA) in Cycle 1 to
determine spectroscopic redshifts of high-redshift dusty star-forming galaxies
(DSFGs) selected by their 1.4mm continuum emission in the South Pole Telescope
(SPT) survey. We present ALMA 3mm spectral scans between 84-114GHz for 15
galaxies and targeted ALMA 1mm observations for an additional eight sources.
Our observations yield 30 new line detections from CO, [CI] , [NII] , H_2O and
NH_3. We further present APEX [CII] and CO mid-J observations for seven sources
for which only a single line was detected in spectral-scan data from ALMA Cycle
0 or Cycle 1. We combine the new observations with previously published and new
mm/submm line and photometric data of the SPT-selected DSFGs to study their
redshift distribution. The combined data yield 39 spectroscopic redshifts from
molecular lines, a success rate of >85%. Our sample represents the largest data
set of its kind today and has the highest spectroscopic completeness among all
redshift surveys of high-z DSFGs. The median of the redshift distribution is
z=3.9+/-0.4, and the highest-redshift source in our sample is at z=5.8. We
discuss how the selection of our sources affects the redshift distribution,
focusing on source brightness, selection wavelength, and strong gravitational
lensing. We correct for the effect of gravitational lensing and find the
redshift distribution for 1.4mm-selected sources with a median redshift of
z=3.1+/-0.3. Comparing to redshift distributions selected at shorter
wavelengths from the literature, we show that selection wavelength affects the
shape of the redshift distribution
Observations of neutral carbon in 29 high-z lensed dusty star forming galaxies and the comparison of gas mass tracers
The nature and evolution of high-redshift dusty star-forming galaxies (high-z
DSFGs) remain an open question. Their massive gas reservoirs play an important
role in driving the intense star-formation rates hosted in these galaxies. We
aim to estimate the molecular gas content of high-z DSFGs by using various gas
mass tracers such as the [CI], CO, [CII] emission lines and the dust content.
These tracers need to be well calibrated as they are all limited by
uncertainties on factors such as aCO, XCI, aCII and GDR, thereby affecting the
determination of the gas mass accurately. The main goal of our work is to check
the consistency between the gas mass tracers and cross-calibrate the uncertain
factors. We observe the two [CI] line transitions for 29 SPT-SMGs with the
ALMA-ACA. Additionally, we also present new APEX observations of [CII] line for
9 of these galaxies. We find a nearly linear relation between the infrared
luminosity and [CI] luminosity if we fit the starbursts and main-sequence
galaxies separately. We measure a median [CI]-derived excitation temperature of
34.5+/-2.1 K. We probe the properties of the interstellar medium (ISM) such as
density and radiation field intensity using [CI] to mid- or high-J CO lines and
[CI] to infrared luminosity ratio, and find similar values to the SMG
populations in literature. Finally, the gas masses estimated from [CI], CO,
dust, and [CII] do not exhibit any significant trend with the infrared
luminosity or the dust temperature. We provide the various cross-calibrations
between these tracers. Our study confirms that [CI] is a suitable tracer of the
molecular gas content, and shows an overall agreement between all the classical
gas tracers used at high redshift. However, their absolute calibration and thus
the gas depletion timescale measurements remain uncertain.Comment: Accepted for publication in A&A, 25 pages, 11 figures, 6 table
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