273 research outputs found
Star formation efficiency in the Barred Spiral Galaxy NGC 4303
We present new CO(J=1-0) observations of the barred galaxy NGC 4303
using the Nobeyama 45m telescope (NRO45) and the Combined Array for Research in
Millimeter-wave Astronomy (CARMA). The H images of barred spiral
galaxies often show active star formation in spiral arms, but less so in bars.
We quantify the difference by measuring star formation rate and efficiency at a
scale where local star formation is spatially resolved. Our CO map covers the
central 2\farcm3 region of the galaxy; the combination of NRO45 and CARMA
provides a high fidelity image, enabling accurate measurements of molecular gas
surface density. We find that star formation rate and efficiency are twice as
high in the spiral arms as in the bar. We discuss this difference in the
context of the Kennicutt-Schimidt (KS) law, which indicates a constant star
formation rate at a given gas surface density. The KS law breaks down at our
native resolution ( 250 pc), and substantial smoothing (to 500 pc) is
necessary to reproduce the KS law, although with greater scatter.Comment: 17 pages, 10 figures, published by ApJ;
http://adsabs.harvard.edu/abs/2010ApJ...721..383
Characterization and Improvement of the Image Quality of the Data Taken with the Infrared Camera (IRC) Mid-Infrared Channels onboard AKARI
Mid-infrared images frequently suffer artifacts and extended point spread
functions (PSFs). We investigate the characteristics of the artifacts and the
PSFs in images obtained with the Infrared Camera (IRC) onboard AKARI at four
mid-infrared bands of the S7 (7{\mu}m), S11 (11{\mu}m), L15 (15{\mu}m), and L24
(24 {\mu}m). Removal of the artifacts significantly improves the reliability of
the ref- erence data for flat-fielding at the L15 and L24 bands. A set of
models of the IRC PSFs is also constructed from on-orbit data. These PSFs have
extended components that come from diffraction and scattering within the
detector arrays. We estimate the aperture correction factors for point sources
and the surface brightness correction factors for diffuse sources. We conclude
that the surface brightness correction factors range from 0.95 to 0.8, taking
account of the extended component of the PSFs. To correct for the extended PSF
effects for the study of faint structures, we also develop an image
reconstruction method, which consists of the deconvolution with the PSF and the
convolution with an appropriate Gaussian. The appropriate removal of the
artifacts, improved flat-fielding, and image reconstruction with the extended
PSFs enable us to investigate de- tailed structures of extended sources in IRC
mid-infrared images.Comment: 35 pages, 15 figures, accepted for publication in PAS
Gingival Fibroblasts as a Promising Source of Induced Pluripotent Stem Cells
Induced pluripotent stem (iPS) cells efficiently generated from accessible tissues have the potential for clinical applications. Oral gingiva, which is often resected during general dental treatments and treated as biomedical waste, is an easily obtainable tissue, and cells can be isolated from patients with minimal discomfort.We herein demonstrate iPS cell generation from adult wild-type mouse gingival fibroblasts (GFs) via introduction of four factors (Oct3/4, Sox2, Klf4 and c-Myc; GF-iPS-4F cells) or three factors (the same as GF-iPS-4F cells, but without the c-Myc oncogene; GF-iPS-3F cells) without drug selection. iPS cells were also generated from primary human gingival fibroblasts via four-factor transduction. These cells exhibited the morphology and growth properties of embryonic stem (ES) cells and expressed ES cell marker genes, with a decreased CpG methylation ratio in promoter regions of Nanog and Oct3/4. Additionally, teratoma formation assays showed ES cell-like derivation of cells and tissues representative of all three germ layers. In comparison to mouse GF-iPS-4F cells, GF-iPS-3F cells showed consistently more ES cell-like characteristics in terms of DNA methylation status and gene expression, although the reprogramming process was substantially delayed and the overall efficiency was also reduced. When transplanted into blastocysts, GF-iPS-3F cells gave rise to chimeras and contributed to the development of the germline. Notably, the four-factor reprogramming efficiency of mouse GFs was more than 7-fold higher than that of fibroblasts from tail-tips, possibly because of their high proliferative capacity.These results suggest that GFs from the easily obtainable gingival tissues can be readily reprogrammed into iPS cells, thus making them a promising cell source for investigating the basis of cellular reprogramming and pluripotency for future clinical applications. In addition, high-quality iPS cells were generated from mouse GFs without Myc transduction or a specific system for reprogrammed cell selection
The GYF domain protein PSIG1 dampens the induction of cell death during plant-pathogen interactions
The Potential-Density Phase Shift Method for Determining the Corotation Radii in Spiral and Barred Galaxies
We have developed a new method for determining the corotation radii of
density waves in disk galaxies, which makes use of the radial distribution of
an azimuthal phase shift between the potential and density wave patterns. The
approach originated from improved theoretical understandings of the relation
between the morphology and kinematics of galaxies, and on the dynamical
interaction between density waves and the basic-state disk stars which results
in the secular evolution of disk galaxies. In this paper, we present the
rationales behind the method, and the first application of it to several
representative barred and grand-design spiral galaxies, using near-infrared
images to trace the mass distributions, as well as to calculate the potential
distributions used in the phase shift calculations. We compare our results with
those from other existing methods for locating the corotations, and show that
the new method both confirms the previously-established trends of bar-length
dependence on galaxy morphological types, as well as provides new insights into
the possible extent of bars in disk galaxies. Application of the method to a
larger sample and the preliminary analysis of which show that the phase shift
method is likely to be a generally-applicable, accurate, and essentially
model-independent method for determining the pattern speeds and corotation
radii of single or nested density wave patterns in galaxies. Other implications
of this work are: most of the nearby bright disk galaxies appear to possess
quasi-stationary spiral modes; that these density wave modes and the associated
basic state of the galactic disk slowly transform over time; and that
self-consistent N-particle systems contain physics not revealed by the passive
orbit analysis approaches.Comment: 48 pages, 16 figures. Accepted for publication in the Astronomical
Journa
Star Formation on Subkiloparsec Scale Triggered by Non-linear Processes in Nearby Spiral Galaxies
We report a super-linear correlation for the star formation law based on new CO(J = 1-0) data from the CARMA and NOBEYAMA Nearby-galaxies (CANON) CO survey. The sample includes 10 nearby spiral galaxies, in which structures at sub-kpc scales are spatially resolved. Combined with the star formation rate surface density traced by Hα and 24 μm images, CO(J = 1-0) data provide a super-linear slope of N = 1.3. The slope becomes even steeper (N = 1.8) when the diffuse stellar and dust background emission is subtracted from the Hα and 24 μm images. In contrast to the recent results with CO(J = 2-1) that found a constant star formation efficiency (SFE) in many spiral galaxies, these results suggest that the SFE is not independent of environment, but increases with molecular gas surface density. We suggest that the excitation of CO(J = 2-1) is likely enhanced in the regions with higher star formation and does not linearly trace the molecular gas mass. In addition, the diffuse emission contaminates the SFE measurement most in regions where the star formation rate is law. These two effects can flatten the power-law correlation and produce the apparent linear slope. The super-linear slope from the CO(J = 1-0) analysis indicates that star formation is enhanced by non-linear processes in regions of high gas density, e.g., gravitational collapse and cloud-cloud collisions
Temperature Variations of the Cold Dust in the Triangulum Galaxy M33
We present wide-field 1.1 mm continuum imaging of the nearby spiral galaxy M
33, conducted with the AzTEC bolometer camera on ASTE. We show that the 1.1 mm
flux traces the distribution of dust with T ~20 K. Combined with far-infrared
imaging at 160um, we derive the dust temperature distribution out to a galactic
radius of ~7 kpc with a spatial resolution of ~100 parsecs. Although the 1.1 mm
flux is observed predominantly near star forming regions, we find a smooth
radial temperature gradient declining from ~20 K to ~13 K, consistent with
recent results from the Herschel satellite. Further comparison of individual
regions show a strong correlation between the cold dust temperature and the Ks
band brightness, but not with the ionizing flux. The observed results imply
that the dominant heating source of cold dust at few hundred parsec scales are
due to the non-OB stars, even when associated with star forming regions.Comment: Accepted for publication in PAS
The Schmidt-Kennicutt Law of Matched-Age Star Forming Regions; Pa-alpha Observations of the Early-Phase Interacting Galaxy Taffy I
In order to test a recent hypothesis that the dispersion in the
Schmidt-Kennicutt law arises from variations in the evolutionary stage of star
forming molecular clouds, we compared molecular gas and recent star formation
in an early-phase merger galaxy pair, Taffy I (UGC\ 12915/UGC\ 12914, VV\ 254)
which went through a direct collision 20 Myr ago and whose star forming regions
are expected to have similar ages. Narrow-band Pa-alpha image is obtained using
the ANIR near-infrared camera on the mini-TAO 1m telescope. The image enables
us to derive accurate star formation rates within the galaxy directly. The
total star formation rate, 22.2 M_sun/yr, was found to be much higher than
previous estimates. Ages of individual star forming blobs estimated from
equivalent widths indicate that most star forming regions are ~7 Myr old,
except for a giant HII region at the bridge which is much younger. Comparison
between star formation rates and molecular gas masses for the regions with the
same age exhibits a surprisingly tight correlation, a slope of unity, and star
formation efficiencies comparable to those of starburst galaxies. These results
suggest that Taffy I has just evolved into a starburst system after the
collision, and the star forming sites are at a similar stage in their evolution
from natal molecular clouds except for the bridge region. The tight
Schmidt-Kennicutt law supports the scenario that dispersion in the star
formation law is in large part due to differences in evolutionary stage of star
forming regions.Comment: Accepted for publication in Astrophysical Journa
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