103 research outputs found
13CO(J=1-0) On-the-fly Mapping of the Giant HII Region NGC 604: Variation in Molecular Gas Density and Temperature due to Sequential Star Formation
We present 13CO(J=1-0) line emission observations with the Nobeyama 45-m
telescope toward the giant HII region NGC 604 in the spiral galaxy M 33. We
detected 13CO(J=1-0) line emission in 3 major giant molecular clouds (GMCs)
labeled as GMC-A, B, and C beginning at the north. We derived two line
intensity ratios, 13CO(J=1-0)/12CO(J =1-0), R13/12, and 12CO(J=3-2)/12CO(J
=1-0), R31, for each GMC at an angular resolution of 25" (100 pc). Averaged
values of R13/12 and R31 are 0.06 and 0.31 within the whole GMC-A, 0.11 and
0.67 within the whole GMC-B, and 0.05 and 0.36 within the whole GMC-C,
respectively. In addition, we obtained R13/12=0.09\pm0.02 and R31=0.76\pm0.06
at the 12CO(J=1-0) peak position of the GMC-B. Under the Large Velocity
Gradient approximation, we determined gas density of 2.8 \times10^3 cm^-3 and
kinetic temperature of 33+9-5 K at the 12CO(J=1-0) peak position of the GMC-B.
Moreover, we determined 2.5 \times10^3 cm^-3 and 25\pm2 K as averaged values
within the whole GMC-B. We concluded that dense molecular gas is formed
everywhere in the GMC-B because derived gas density not only at the peak
position of the GMC but also averaged over the whole GMC exceeds 10^3 cm^-3. On
the other hand, kinetic temperature averaged over the whole GM-B, 25 K, is
significantly lower than that at the peak position, 33 K. This is because HII
regions are lopsided to the northern part of the GMC-B, thus OB stars can heat
only the northern part, including the 12CO(J=1-0) peak position, of this GMC.Comment: 16 pages, 7 figures, PASJ in pres
Modulation of Corticospinal Excitability during Acquisition of Action Sequences by Observation
Excitability of the corticospinal pathway increases during observation of an action. However, how corticospinal excitability changes during observation of sequential actions in the course of acquiring novel skills (observational learning) remains unexplored. To investigate this, we used a previously unpracticed sequence of ten hand postures. Participants were asked to repeat observation and replication of the sequence. This block of observation and replication was repeated 5 times. During observation of a given hand posture (OK sign), motor-evoked potentials (MEPs) elicited by transcranial magnetic stimulation were recorded from hand muscles. In experiment 1, the OK sign appeared in the 9th position of the sequence. Almost all participants could replicate the OK sign only at the 5th block of the experiment. MEP amplitude was greater than that in the control, and decreased with the stages. This suggested that during observational learning of sequential hand postures MEP changed with the progress of the learning. To evaluate this idea, we performed two additional experiments. In experiment 2, the OK sign appeared in the 2nd position. Almost all participants replicated the OK sign even in the 1st block. The MEP amplitude did not change across stages. In experiment 3, the OK sign appeared in the 9th position, but the order of other signs was randomized in every stage. Many participants were not able to replicate the OK sign even during the 5th block of the experiment. The MEP amplitude did not change across stages. These results suggest that: (1) During observational learning modulation of corticospinal excitability is associated with the learning process. (2) Corticospinal excitability decreases as learning progresses
Corticospinal excitability modulation in resting digit muscles during cyclical movement of the digits of the ipsilateral limb
We investigated how corticospinal excitability of the resting digit muscles was modulated by the digit movement in the ipsilateral limb. Subjects performed cyclical extension-flexion movements of either the right toes or fingers. To determine whether corticospinal excitability of the resting digit muscles was modulated on the basis of movement direction or action coupling between ipsilateral digits, the right forearm was maintained in either the pronated or supinated position. During the movement, the motor evoked potential (MEP) elicited by transcranial magnetic stimulation was measured from either the resting right finger extensor and flexor, or toe extensor and flexor. For both finger and toe muscles, independent of forearm position, MEP amplitude of the flexor was greater during ipsilateral digit flexion as compared to extension, and MEP amplitude of the extensor was greater during ipsilateral digit extension as compared to flexion. An exception was that MEP amplitude of the toe flexor with the supinated forearm did not differ between during finger extension and flexion. These findings suggest that digit movement modulates corticospinal excitability of the digits of the ipsilateral limb such that the same action is preferred. Our results provide evidence for a better understanding of neural interactions between ipsilateral limbs, and may thus contribute to neurorehabilitation after a stroke or incomplete spinal cord injury
NRO M33 All-Disk Survey of Giant Molecular Clouds (NRO MAGiC): II. Dense Gas Formation within Giant Molecular Clouds in M33
We report the results of our observations of the 12CO (J=1-0) and 12CO
(J=3-2) line emission of 74 major giant molecular clouds (GMCs) within the
galactocentric distance of 5.1 kpc in the Local Group galaxy M33. The
observations have been conducted as part of the Nobeyama Radio Observatory M33
All-disk survey of Giant Molecular Clouds project (NRO MAGiC). The spatial
resolutions are 80 pc for 12CO (J=1-0) and 100 pc for 12CO (J=3-2). We detect
12CO (J=3-2) emission of 65 GMCs successfully. Furthermore, we find that the
correlation between the surface density of the star formation rate, which is
derived from a linear combination of Halpha and 24um emissions, and the 12CO
(J=3-2) integrated intensity still holds at this scale. This result show that
the star-forming activity is closely associated with warm and dense gases that
are traced with the 12CO (J=3-2) line, even in the scale of GMCs. We also find
that the GMCs with a high star-forming activity tend to show a high integrated
intensity ratio (R3-2/1-0). Moreover, we also observe a mass-dependent trend of
R3-2/1-0 for the GMCs with a low star-forming activity. From these results, we
speculate that the R3-2/1-0 values of the GMCs with a low star-forming activity
mainly depend on the dense gas fraction and not on the temperature, and
therefore, the dense gas fraction increases with the mass of GMCs, at least in
the GMCs with a low star-forming activity.Comment: 17 pages, 5 figures, Accepted for publication in PASJ, 2012, Vol. 64,
No.
NRO M33 All Disk Survey of Giant Molecular Clouds (NRO MAGiC): I. HI to H_2 Transition
We present the results of the Nobeyama Radio Observatory (NRO) M33 All Disk
(30'x30' or 7.3 kpc x 7.3 kpc) Survey of Giant Molecular Clouds (NRO MAGiC)
based on 12CO (1-0) observations using the NRO 45-m telescope. The spatial
resolution of the resultant map is 19".3, corresponding to 81 pc, which is
sufficient to identify each Giant Molecular Cloud (GMC) in the disk. We found
clumpy structures with a typical spatial scale of ~100 pc, corresponding to
GMCs, and no diffuse, smoothly distributed component of molecular gas at this
sensitivity. Closer inspection of the CO and HI maps suggests that not every CO
emission is associated with local HI peaks, particularly in the inner portion
of the disk (r < 2 kpc), although most of CO emission is located at the local
HI peaks in the outer radii. We found that most uncovered GMCs are accompanied
by massive star-forming regions, although the star formation rates (SFRs) vary
widely from cloud to cloud. The azimuthally averaged H{\sc i} gas surface
density exhibits a flat radial distribution. However, the CO radial
distribution shows a significant enhancement within the central 1-2 kpc region,
which is very similar to that of the SFR. We obtained a map of the molecular
fraction, f_mol = Sigma_H_2/(Sigma_HI+Sigma_H_2, at a 100-pc resolution. This
is the first f_mol map covering an entire galaxy with a GMC-scale resolution.
We find that f_mol tends to be high near the center. The correlation between
f_mol and gas surface density shows two distinct sequences. The presence of two
correlation sequences can be explained by differences in metallicity, i.e.,
higher (~ 2-fold) metallicity in the central region (r< 1.5 kpc) than in the
outer parts. Alternatively, differences in scale height can also account for
the two sequences, i.e., increased scale height toward the outer disk.Comment: Accepted for publication in PASJ, See
http://www.juen.ac.jp/lab/tosaki/paper/astro-ph/2011/tosaki2011.pdf for a
version with full resolution figure
ASTE CO(3-2) Mapping toward the Whole Optical Disk of M 83: Properties of Inter-arm GMAs
We present a new on-the-fly (OTF) mapping of CO(J=3-2) line emission with the
Atacama Submillimeter Telescope Experiment (ASTE) toward the 8' x 8' (or 10.5 x
10.5 kpc at the distance of 4.5 Mpc) region of the nearby barred spiral galaxy
M 83 at an effective resolution of 25''. Due to its very high sensitivity, our
CO(J=3-2) map can depict not only spiral arm structures but also spur-like
substructures extended in inter-arm regions. This spur-like substructures in
CO(J=3-2) emission are well coincident with the distribution of massive star
forming regions traced by Halpha luminosity and Spitzer/IRAC 8 um emission. We
have identified 54 CO(J=3-2) clumps as Giant Molecular-cloud Associations
(GMAs) employing the CLUMPFIND algorithm, and have obtained their sizes,
velocity dispersions, virial masses, and CO luminosity masses. We found that
the virial parameter alpha, which is defined as the ratio of the virial mass to
the CO luminosity mass, is almost unity for GMAs in spiral arms, whereas there
exist some GMAs whose alpha are 3 -- 10 in the inter-arm region. We found that
GMAs with higher tend not to be associated with massive star forming
regions, while other virialized GMAs are. Since alpha mainly depends on
velocity dispersion of the GMA, we suppose the onset of star formation in these
unvirialized GMAs with higher alpha are suppressed by an increase in internal
velocity dispersions of Giant Molecular Clouds within these GMAs due to shear
motion.Comment: 42 pages, 16 figures, ApJ in press, version with high resolution
figures is available via
http://www.nro.nao.ac.jp/~kmuraoka/m83paper/m83aste-otf.pd
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