Star–Gas Surface Density Correlations in 12 Nearby Molecular Clouds. I. Data Collection and Star-sampled Analysis

We investigated the influence of the random velocity of molecular gas on star-formation activities of six nearby galaxies. The physical properties of a molecular cloud, such as temperature and density, influence star-formation activities in the cloud. Additionally, local and turbulent motions of molecules in a cloud may exert substantial pressure on gravitational collapse and thus prevent or reduce star formation in the cloud. However, the influence of gas motion on star-formation activities remains poorly understood. We used data from the Atacama Large Millimeter/submillimeter Array to obtain 12CO(J = 1 − 0) flux and velocity dispersion. We then combined these data with 3.6 and 8 micron midinfrared data from the Spitzer Space Telescope to evaluate the effects of gas motion on star-formation activities in several nearby galaxies. We discovered that relatively high velocity dispersion in molecular clouds corresponds with relatively low star-formation activity. Considering the velocity dispersion as an additional parameter, we derived a modified Kennicutt-Schmidt law with a gas surface density power index of 0.84 and velocity dispersion power index of −0.61.

Download Full-text

The Distribution of Molecular Clouds in Spiral Galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900032356 ◽

1983 ◽

Vol 100 ◽

pp. 35-42

Author(s):

P. M. Solomon

Keyword(s):

Millimeter Wave ◽

Molecular Hydrogen ◽

Surface Density ◽

Molecular Clouds ◽

Spiral Galaxies ◽

Galactic Disk ◽

Giant Molecular Clouds ◽

The Galaxy ◽

Co Emission ◽

Half Thickness

The use of millimeter wave CO emission as a tracer of molecular hydrogen in the Galaxy (Scoville and Solomon 1975) showed that most of the H2 unlike HI is concentrated in the inner part of the Galaxy in a “ring” between 4–8 kpc and in the inner 1 kpc. Subsequent surveys (Gordon and Burton 1976, Cohen and Thaddeus 1977, Solomon etal. 1979) confirmed this picture with more extensive data. The molecular interstellar medium was shown to be dominated by Giant Molecular Clouds with individual masses between 105 and 3·106M⊙ (Solomon etal. 1979, Solomon and Sanders 1980). The GMC's confined to a layer with a half thickness of only 60 pc are an important component of the galactic disk, and the most massive objects in the galaxy. They affect the dynamics of the disk by contributing significantly to the surface density and through their individual gravitational interactions with stars.

Download Full-text

On the probability distribution function of the mass surface density of molecular clouds. II.

Astronomy and Astrophysics ◽

10.1051/0004-6361/201423647 ◽

2014 ◽

Vol 571 ◽

pp. A95 ◽

Cited By ~ 6

Author(s):

Jörg Fischera

Keyword(s):

Distribution Function ◽

Probability Distribution ◽

Probability Distribution Function ◽

Surface Density ◽

Molecular Clouds

Download Full-text

NRO Legacy Project: M33 all Disk Survey of Giant Molecular Clouds with NRO 45-m and ASTE 10-m telescopes

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311022484 ◽

2010 ◽

Vol 6 (S277) ◽

pp. 67-70

Author(s):

N. Kuno ◽

T. Tosaki ◽

S. Onodera ◽

R. Miura ◽

K. Muraoka ◽

...

Keyword(s):

Star Formation ◽

Surface Density ◽

Molecular Clouds ◽

Molecular Gas ◽

Evolutionary Stage ◽

Giant Molecular Clouds ◽

Radio Observatory ◽

Active Star ◽

Star Forming ◽

The Difference

AbstractWe have conducted all disk imaging of M33 in 12CO(1-0) using the 45-m telescope at Nobeyama Radio Observatory. We present preliminary results of this project. The spatial resolution of ~ 80 pc is comparable to the size of GMCs. The identified GMCs show wide variety in star forming activity. The variety can be regarded as the difference of their evolutionary stage. We found that Kennicutt-Schmidt law breaks in GMC scale (~ 80 pc), although it is still valid in 1 kpc scale. The correlation between molecular gas fraction, fmol = Σ(H2)/Σ(HI+H2) and gas surface density shows two distinct sequences and shows that fmol tends to be higher near the center. We also made partial mapping 12CO(3-2) with ASTE telescope. These data show that the variation of physical properties of molecular gas are correlated with the GMC evolution and mass. That is, GMCs with more active star formation and more mass tend to have higher fraction of dense gas.

Download Full-text

On Schmidt's Conjecture and Star Formation Scaling Laws

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314009260 ◽

2014 ◽

Vol 10 (S309) ◽

pp. 31-38 ◽

Cited By ~ 1

Author(s):

Charles J. Lada

Keyword(s):

Star Formation ◽

Surface Density ◽

Molecular Clouds ◽

Scaling Laws ◽

Scaling Law ◽

Empirical Relation ◽

Linear Scaling ◽

Scaling Relation ◽

Interstellar Gas ◽

Physical Relation

AbstractEver since the pioneering work of Schmidt a half-century ago there has been great interest in finding an appropriate empirical relation that would directly link some property of interstellar gas with the process of star formation within it. Schmidt conjectured that this might take the form of a power-law relation between the rate of star formation (SFR) and the surface density of interstellar gas. However recent observations suggest that a linear scaling relation between the total SFR and the amount of dense gas within molecular clouds appears to be the underlying physical relation that most directly connects star formation with interstellar gas from scales of individual GMCs to those encompassing entire galaxies both near and far. Although Schmidt relations are found to exist within local GMCs, there is no Schmidt relation observed between GMCs. The implications of these results for interpreting and understanding the Kennicutt-Schmidt scaling law for galaxies are discussed.

Download Full-text

Motions of neutral hydrogen at high latitudes

Symposium - International Astronomical Union ◽

10.1017/s0074180900101068 ◽

1967 ◽

Vol 31 ◽

pp. 265-278 ◽

Cited By ~ 1

Author(s):

A. Blaauw ◽

I. Fejes ◽

C. R. Tolbert ◽

A. N. M. Hulsbosch ◽

E. Raimond

Keyword(s):

Surface Density ◽

Velocity Dispersion ◽

Neutral Hydrogen ◽

Hydrogen Gas ◽

High Latitudes ◽

Low Velocity

Earlier investigations have shown that there is a preponderance of negative velocities in the hydrogen gas at high latitudes, and that in certain areas very little low-velocity gas occurs. In the region 100° <l< 250°, + 40° <b< + 85°, there appears to be a disturbance, with velocities between - 30 and - 80 km/sec. This ‘streaming’ involves about 3000 (r/100)2solar masses (rin pc). In the same region there is a low surface density at low velocities (|V| < 30 km/sec). About 40% of the gas in the disturbance is in the form of separate concentrations superimposed on a relatively smooth background. The number of these concentrations as a function of velocity remains constant from - 30 to - 60 km/sec but drops rapidly at higher negative velocities. The velocity dispersion in the concentrations varies little about 6·2 km/sec. Concentrations at positive velocities are much less abundant.

Download Full-text

Electron Diffraction of Wet Biological Membranes

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100050809 ◽

1974 ◽

Vol 32 ◽

pp. 158-159

Author(s):

S.W. Hui ◽

D.F. Parsons

Keyword(s):

Electron Diffraction ◽

Data Collection ◽

Biological Membranes ◽

Small Areas ◽

Electron Diffraction Technique ◽

Electron Microscopes ◽

Collection Time ◽

Camera Length

The development of the hydration stages for electron microscopes has opened up the application of electron diffraction in the study of biological membranes. Membrane specimen can now be observed without the artifacts introduced during drying, fixation and staining. The advantages of the electron diffraction technique, such as the abilities to observe small areas and thin specimens, to image and to screen impurities, to vary the camera length, and to reduce data collection time are fully utilized. Here we report our pioneering work in this area.

Download Full-text

Automated electron tomography: from data collection to image processing

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100136507 ◽

1995 ◽

Vol 53 ◽

pp. 26-27

Author(s):

Weiping Liu ◽

Jennifer Fung ◽

W.J. de Ruijter ◽

Hans Chen ◽

John W. Sedat ◽

...

Keyword(s):

Image Processing ◽

Data Collection ◽

Structural Information ◽

Imaging Technique ◽

Electron Tomography ◽

Ccd Camera ◽

Automated Data Collection ◽

Full Control ◽

Transmission Electron ◽

Amorphous Structures

Electron tomography is a technique where many projections of an object are collected from the transmission electron microscope (TEM), and are then used to reconstruct the object in its entirety, allowing internal structure to be viewed. As vital as is the 3-D structural information and with no other 3-D imaging technique to compete in its resolution range, electron tomography of amorphous structures has been exercised only sporadically over the last ten years. Its general lack of popularity can be attributed to the tediousness of the entire process starting from the data collection, image processing for reconstruction, and extending to the 3-D image analysis. We have been investing effort to automate all aspects of electron tomography. Our systems of data collection and tomographic image processing will be briefly described.To date, we have developed a second generation automated data collection system based on an SGI workstation (Fig. 1) (The previous version used a micro VAX). The computer takes full control of the microscope operations with its graphical menu driven environment. This is made possible by the direct digital recording of images using the CCD camera.

Download Full-text

Productivity of Emerging Word Combinations in Toddlers With Specific Expressive Language Impairment

American Journal of Speech-Language Pathology ◽

10.1044/1058-0360.0604.34 ◽

1997 ◽

Vol 6 (4) ◽

pp. 34-47 ◽

Cited By ~ 6

Author(s):

Steven H. Long ◽

Lesley B. Olswang ◽

Julianne Brian ◽

Philip S. Dale

Keyword(s):

Data Collection ◽

Young Children ◽

Language Impairment ◽

Treatment Approach ◽

Expressive Language ◽

Semantic Consistency ◽

Session Analysis

This study investigated whether young children with specific expressive language impairment (SELI) learn to combine words according to general positional rules or specific, grammatic relation rules. The language of 20 children with SELI (4 females, 16 males, mean age of 33 months, mean MLU of 1.34) was sampled weekly for 9 weeks. Sixteen of these children also received treatment for two-word combinations (agent+action or possessor+possession). Two different metrics were used to determine the productivity of combinatorial utterances. One metric assessed productivity based on positional consistency alone; another assessed productivity based on positional and semantic consistency. Data were analyzed session-by-session as well as cumulatively. The results suggest that these children learned to combine words according to grammatic relation rules. Results of the session-by-session analysis were less informative than those of the cumulative analysis. For children with SELI ready to make the transition to multiword utterances, these findings support a cumulative method of data collection and a treatment approach that targets specific grammatic relation rules rather than general word combinations.

Download Full-text