2,200 research outputs found
High Density Molecular Gas in the IR-bright Galaxy System VV114
New high resolution CO(3-2) interferometric map of the IR-bright interacting
galaxy system VV114 observed with the Submillimeter Array (SMA) reveal a
substantial amount of warm and dense gas in the IR-bright but optically
obscured galaxy, VV114E, and the overlap region connecting the two nuclei. A
1.8 x 1.4 kpc concentration of CO(3-2) emitting gas with a total mass of 4 x
10^9 Msun coincides with the peaks of NIR, MIR, and radio continuum emission
found previously by others, identifying the dense fuel for the AGN and/or the
starburst activity there. Extensive CO(2-1) emission is also detected,
revealing detailed distribution and kinematics that are consistent with the
earlier CO(1-0) results. The widely distributed molecular gas traced in CO(2-1)
and the distributed discrete peaks of CO(3-2) emission suggest that a spatially
extended intense starbursts may contribute significantly to its large IR
luminosity. These new observations further support the notion that VV114 is
approaching its final stage of merger, when violent central inflow of gas
triggers intense starburst activity possibly boosting the IR luminosity above
the ultraluminous threshold.Comment: 11 pages, 2 figures, accepted for publication in ApJ
Luminous Infrared Galaxies With the Submillimeter Array. III. The Dense Kiloparsec Molecular Concentrations of Arp 299
We have used high resolution (~2.3") observations of the local (D = 46 Mpc)
luminous infrared galaxy Arp 299 to map out the physical properties of the
molecular gas which provides the fuel for its extreme star formation activity.
The 12CO J=3-2, 12CO J=2-1 and 13CO J=2-1 lines were observed with the
Submillimeter Array and the short spacings of the 12CO J=2-1 and J=3-2
observations have been recovered using James Clerk Maxwell Telescope single
dish observations. We use the radiative transfer code RADEX to estimate the
physical properties (density, column density and temperature) of the different
regions in this system. The RADEX solutions of the two galaxy nuclei, IC 694
and NGC 3690, are consistent with a wide range of gas components, from warm
moderately dense gas with T_{kin} > 30 K and n(H_{2}) ~ 0.3 - 3 x 10^{3}
cm^{-3} to cold dense gas with T_{kin} ~ 10-30 K and n(H_{2}) > 3 x 10^{3}
cm^{-3}. The overlap region is shown to have a better constrained solution with
T_{\rm{kin}}$ ~ 10-50 K and n(H_{2}) ~ 1-30 x 10^{3} cm^{-3}. We estimate the
gas masses and star formation rates of each region in order to derive molecular
gas depletion times. The depletion times of all regions (20-60 Myr) are found
to be about 2 orders of magnitude lower than those of normal spiral galaxies.
This rapid depletion time can probably be explained by a high fraction of dense
gas on kiloparsec scales in Arp 299. We estimate the CO-to-H_{2} factor,
\alpha_{co} to be 0.4 \pm 0.3 (3 x 10^{-4}/ x_{CO}) M_{sol} (K km s^{-1}
pc^{2})^{-1} for the overlap region. This value agrees well with values
determined previously for more advanced merger systems.Comment: 24 pages, 4 figures, ApJ accepte
Two-dimensional imaging of edge-localized modes in KSTAR plasmas unperturbed and perturbed by n=1 external magnetic fields
The temporal evolution of edge-localized modes (ELMs) has been studied using a 2-D electron cyclotron emission imaging system in the KSTAR tokamak. The ELMs are observed to evolve in three distinctive stages: the initial linear growth of multiple filamentary structures having a net poloidal rotation, the interim state of regularly spaced saturated filaments, and the final crash through a short transient phase characterized by abrupt changes in the relative amplitudes and distance among filaments. The crash phase, typically consisted of multiple bursts of a single filament, involves a complex dynamics, poloidal elongation of the bursting filament, development of a fingerlike bulge, and fast localized burst through the finger. Substantial alterations of the ELM dynamics, such as mode number, poloidal rotation, and crash time scale, have been observed under external magnetic perturbations with the toroidal mode number n = 1. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3694842]X1125sciescopu
Optical identification of ISO far-infrared sources in the Lockman Hole using a deep VLA 1.4 GHz continuum survey
By exploiting the far-infrared(FIR) and radio correlation, we have performed
the Likelihood-Ratio analysis to identify optical counterparts to the
far-infrared sources in the Lockman Hole. Using the likelihood ratio analysis
and the associated reliability, 44 FIR sources have been identified with radio
sources. Redshifts have been obtained for 29 out of 44 identified sources. One
hyper-luminous infrared galaxy (HyLIRG) with and four ultraluminous infrared
galaxies (ULIRGs) are identified in our sample. The space density of the FIR
sources at z = 0.3-0.6 is 4.6\times 10^{-5}Mpc^{-3}, implying a rapid evolution
of the ULIRG population. Most of \ISO FIR sources have their FIR-radio ratios
similar to star-forming galaxies ARP 220 and M82. At least seven of our FIR
sources show evidence for the presence of an active galactic nucleus (AGN) in
optical emission lines, radio continuum excess, or X-ray activity. Three out of
five (60%) of the ULIRG/HyLIRGs are AGN galaxies. Five of the seven AGN
galaxies are within the ROSAT X-ray survey field, and two are within the
XMM-Newton survey fields. X-ray emission has been detected in only one source,
1EX030, which is optically classified as a quasar. The non-detection in the
XMM-Newton 2-10 keV band suggests a very thick absorption obscuring the central
source of the two AGN galaxies. Several sources have an extreme FIR luminosity
relative to the optical R-band, L(90\mu\mathrm{m})/L(R) > 500, which is rare
even among the local ULIRG population. While source confusion or blending might
offer an explanation in some cases, they may represent a new population of
galaxies with an extreme activity of star formation in an undeveloped stellar
system -- i.e., formation of bulges or young ellipticals.Comment: 55 pages, 16 figures. To appear in A
CO Luminosity Functions For FIR and B-band Selected Galaxies and the First Estimate for Omega_{HI+H2}
We derive a non-parametric CO luminosity function using a FIR and an optical
B-band selected sample of the galaxies included in the FCRAO Extragalactic CO
Survey. The FIR selected sample is defined using the IRAS Bright Galaxy Surveys
(BGS; IRAS 60 micron flux density >= 5.24 Jy). Although our CO sample is not
complete, the normalization using the BGS reproduces the IRAS 60 micron
luminosity function in excellent agreement with those found in the literature.
Similarly, a B-band selected sample defined using the Revised Shapley-Ames
(RSA) catalog is used to derive a CO luminosity function for a comparison. A
Schechter function describes the both derived CO luminosity functions
reasonably well. Adopting the standard CO-to-H2 conversion factor, we derive a
molecular gas density of rho_{H2}=(3.1\pm 1.2)*10^7h Mo Mpc^{-3} for the local
volume. Combining with the measurements of the local HI mass density and the
helium contribution, we estimate that the total mass density of cold neutral
gas in the local universe is Omega_{gas} =(4.3 \pm 1.1)*10^{-4} h^{-1}, which
is about 20% of the total stellar mass density Omega_{stars}.Comment: 16 pages, 11 figures uses aastex.cls and emulateapj5.sty. Accepted
for publication in Ap
Molecular Basis for Certain Neuroprotective Effects of Thyroid Hormone
The pathophysiology of brain damage that is common to ischemia–reperfusion injury and brain trauma include disodered neuronal and glial cell energetics, intracellular acidosis, calcium toxicity, extracellular excitotoxic glutamate accumulation, and dysfunction of the cytoskeleton and endoplasmic reticulum. The principal thyroid hormones, 3,5,3′-triiodo-l-thyronine (T3) and l-thyroxine (T4), have non-genomic and genomic actions that are relevant to repair of certain features of the pathophysiology of brain damage. The hormone can non-genomically repair intracellular H+ accumulation by stimulation of the Na+/H+ exchanger and can support desirably low [Ca2+]i.c. by activation of plasma membrane Ca2+–ATPase. Thyroid hormone non-genomically stimulates astrocyte glutamate uptake, an action that protects both glial cells and neurons. The hormone supports the integrity of the microfilament cytoskeleton by its effect on actin. Several proteins linked to thyroid hormone action are also neuroprotective. For example, the hormone stimulates expression of the seladin-1 gene whose gene product is anti-apoptotic and is potentially protective in the setting of neurodegeneration. Transthyretin (TTR) is a serum transport protein for T4 that is important to blood–brain barrier transfer of the hormone and TTR also has been found to be neuroprotective in the setting of ischemia. Finally, the interesting thyronamine derivatives of T4 have been shown to protect against ischemic brain damage through their ability to induce hypothermia in the intact organism. Thus, thyroid hormone or hormone derivatives have experimental promise as neuroprotective agents
A complete view of galaxy evolution: panchromatic luminosity functions and the generation of metals
When and how did galaxies form and their metals accumulate? Over the last
decade, this has moved from an archeological question to a live investigation:
there is now a broad picture of the evolution of galaxies in dark matter halos:
their masses, stars, metals and supermassive blackholes. Galaxies have been
found and studied in which these formation processes are taking place most
vigorously, all the way back in cosmic time to when the intergalactic medium
(IGM) was still largely neutral. However, the details of how and why the
interstellar medium (ISM) in distant galaxies cools, is processed, recycled and
enriched in metals by stars, and fuels active galactic nuclei (AGNs) remain
uncertain. In particular, the cooling of gas to fuel star formation, and the
chemistry and physics of the most intensely active regions is hidden from view
at optical wavelengths, but can be seen and diagnosed at mid- & far-infrared
(IR) wavelengths. Rest-frame IR observations are important first to identify
the most luminous, interesting and important galaxies, secondly to quantify
accurately their total luminosity, and finally to use spectroscopy to trace the
conditions in the molecular and atomic gas out of which stars form. In order to
map out these processes over the full range of environments and large-scale
structures found in the universe - from the densest clusters of galaxies to the
emptiest voids - we require tools for deep, large area surveys, of millions of
galaxies out to z~5, and for detailed follow-up spectroscopy. The necessary
tools can be realized technically. Here, we outline the requirements for
gathering the crucial information to build, validate and challenge models of
galaxy evolution.Comment: A whitepaper submitted on 15th February 2009 in response to the call
from the Astro2010 panel: astro2010.org; uploaded as an 8-page pdf fil
Luminous Infrared Galaxies with the Submillimeter Array: I. Survey Overview and the Central Gas to Dust Ratio
We present new data obtained with the Submillimeter Array for a sample of
fourteen nearby luminous and ultraluminous infrared galaxies. The galaxies were
selected to have luminosity distances D < 200 Mpc and far-infrared luminosities
log(L_FIR) > 11.4. The galaxies were observed with spatial resolutions of order
1 kpc in the CO J=3-2, CO J=2-1, 13CO J=2-1, and HCO+ J=4-3 lines as well as
the continuum at 880 microns and 1.3 mm. We have combined our CO and continuum
data to measure an average gas-to-dust mass ratio of 120 +/- 28 (rms deviation
109) in the central regions of these galaxies, very similar to the value of 150
determined for the Milky Way. This similarity is interesting given the more
intense heating from the starburst and possibly accretion activity in the
luminous infrared galaxies compared to the Milky Way. We find that the peak H_2
surface density correlates with the far-infrared luminosity, which suggests
that galaxies with higher gas surface densities inside the central kiloparsec
have a higher star formation rate. The lack of a significant correlation
between total H_2 mass and far-infrared luminosity in our sample suggests that
the increased star formation rate is due to the increased availability of
molecular gas as fuel for star formation in the central regions. In contrast to
previous analyses by other authors, we do not find a significant correlation
between central gas surface density and the star formation efficiency, as trace
by the ratio of far-infrared luminosity to nuclear gas mass. Our data show that
it is the star formation rate, not the star formation efficiency, that
increases with increasing central gas surface density in these galaxies.Comment: 66 pages, 39 figures, aastex preprint format; to be published in ApJ
Supplements. Version of paper with full resolution figures available at
http://www.physics.mcmaster.ca/~wilson/www_xfer/ULIRGS_publi
Saponin Inhibits Hepatitis C Virus Propagation by Up-regulating Suppressor of Cytokine Signaling 2
Saponins are a group of naturally occurring plant glycosides which possess a wide range of pharmacological properties, including anti-tumorigenic and antiviral activities. To investigate whether saponin has anti-hepatitis C virus (HCV) activity, we examined the effect of saponin on HCV replication. HCV replication was efficiently inhibited at a concentration of 10 µg/ml of saponin in cell culture grown HCV (HCVcc)-infected cells. Inhibitory effect of saponin on HCV replication was verified by quantitative real-time PCR, reporter assay, and immunoblot analysis. In addition, saponin potentiated IFN-α-induced anti-HCV activity. Moreover, saponin exerted antiviral activity even in IFN-α resistant mutant HCVcc-infected cells. To investigate how cellular genes were regulated by saponin, we performed microarray analysis using HCVcc-infected cells. We demonstrated that suppressor of cytokine signaling 2 (SOCS2) protein level was distinctively increased by saponin, which in turn resulted in inhibition of HCV replication. We further showed that silencing of SOCS2 resurrected HCV replication and overexpression of SOCS2 suppressed HCV replication. These data imply that saponin inhibits HCV replication via SOCS2 signaling pathway. These findings suggest that saponin may be a potent therapeutic agent for HCV patients
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