scholarly journals On Schmidt's Conjecture and Star Formation Scaling Laws

2014 ◽  
Vol 10 (S309) ◽  
pp. 31-38 ◽  
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.

Molecular Clouds

1977 ◽  
Vol 75 ◽  
pp. 37-54 ◽  
Author(s):  
P. Thaddeus
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Molecular Clouds ◽  
Physical State ◽  
Molecular Gas ◽  
Spectroscopic Techniques ◽  
Low Density ◽  
Recombination Line ◽  
Interstellar Gas ◽  
Impossible Task

To attempt to understand star formation without knowing the physical state of the dense interstellar molecular gas from which stars are made is an almost impossible task. Star formation has developed late as a branch of astrophysics largely for lack of observational data, and in particular, has lagged badly behind the study of the atomic and ionized components of the interstellar gas because spectroscopic techniques which work well at low density have an unfortunate tendency to fail when the density is high. Optical spectroscopy, which has been applied to the interstellar medium for over 70 years, has made little progress in regions of high density because of obscuration, and the same is true a fortiori of spacecraft spectroscopy in the UV; radio 21-cm and recombination line observations, although unhampered by obscuration, are unsatisfactory because the dense condensations are almost entirely molecular in composition.

scholarly journals CO in the Large Magellanic Cloud

1984 ◽  
Vol 108 ◽  
pp. 401-402 ◽  
Author(s):  
R. Cohen ◽  
J. Montani ◽  
M. Rubio
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Gas Content ◽  
Previous Survey ◽  
Interstellar Gas

In our galaxy molecular clouds account for about half the total interstellar gas and are probably the sites of all star formation. The high gas content and widespread star formation in the Large Magellanic Cloud would therefore suggest a high molecular content. Very little however is actually known about molecules in the LMC. The most extensive previous survey (see Israel in this volume) found CO in half of the 22 points observed but covered less than 10−4 of the LMC area.

scholarly journals Influence of velocity dispersions on star-formation activities in galaxies

2020 ◽  
Vol 641 ◽  
pp. A24
Author(s):  
Tsan-Ming Wang ◽  
Chorng-Yuan Hwang
Keyword(s):  
Star Formation ◽  
High Velocity ◽  
Surface Density ◽  
Molecular Clouds ◽  
Velocity Dispersion ◽  
Power Index ◽  
Molecular Gas ◽  
Additional Parameter ◽  
Star Formation Activity ◽  
Nearby Galaxies

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.

scholarly journals The Scaling of Star Formation: from Molecular Clouds to Galaxies

2014 ◽  
Vol 10 (S309) ◽  
pp. 121-128
Author(s):  
Daniela Calzetti
Keyword(s):  
Star Formation ◽  
Recent Work ◽  
Molecular Clouds ◽  
Gas Content ◽  
Scaling Relations ◽  
Scaling Relation ◽  
The Past ◽  
Tremendous Progress ◽  
Observing Techniques

AbstractThis is a review of the extant literature and recent work on the scaling relation(s) that link the gas content of galaxies to the measured star formation rates. A diverse array of observing techniques and underlying physical assumptions characterize the determination of these relations at different scales, that range from the tens of parsec sizes of molecular clouds to the tens of kpc sizes of whole galaxies. Different techniques and measurements, and a variety of strategies, have been used by many authors to compare the scaling relations, both within and across galaxies. Although the picture is far from final, the past decade has seen tremendous progress in this field, and more progress is expected over the next several years.

scholarly journals The Bell Laboratories CO Survey: Star Formation in Spiral Arms

1987 ◽  
Vol 115 ◽  
pp. 495-499
Author(s):  
A. A. Stark ◽  
J. Bally ◽  
G. R. Knapp ◽  
A. Krahnert ◽  
A. A. Penzias ◽  
...  
Keyword(s):  
Star Formation ◽  
Survey Data ◽  
Noise Level ◽  
Molecular Clouds ◽  
Spiral Structure ◽  
Giant Molecular Clouds ◽  
Interstellar Gas ◽  
Spiral Arms ◽  
The Difference ◽  
Spiral Arm

We present a galactic survey which to date consists of 47,000 positions covering −3° < l < 122°, −1° < b < 1°, observed in the J= 1→ 0 line of 13CO to an rms noise level of 0.15 K in 0.68 km s−1 channels, using the 7 m antenna at Crawford Hill. Maps made from the survey data show a clear difference between spiral arm and interarm regions. The signature of spiral structure on kiloparsec scales is the presence in galactic survey data of voids in l, b, v space which contain many times fewer Giant Molecular Clouds (GMCs) than do adjacent regions of similar size. The difference between arm and interarm regions in the inner galaxy is manifested only in the GMCs — small clouds are present throughout. These results are based on catalogs of clouds and their estimated sizes in 13CO. We suggest that GMCs are formed as interstellar gas enters a spiral arm, and that they break up into small molecular or atomic clouds as the gas leaves the arm.

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

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.

scholarly journals The Single-Cloud Star Formation Relation

2020 ◽  
Author(s):  
Riwaj Pokhrel
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Dynamic Range ◽  
Formation Rate ◽  
Free Fall ◽  
High Dynamic Range ◽  
Young Stellar Objects ◽  
Interstellar Gas ◽  
Stellar Objects ◽  
Fall Time

Abstract One of the most important and well-established empirical results in astronomy is the so-called Kennicutt-Schmidt (KS) relation between the density of interstellar gas and the rate at which that gas forms stars. While a tight correlation between these quantities has long been measured at galactic scales, the difficulty of measuring star formation rates and gas densities over a large dynamic range at sub-galactic scales has thus far precluded a definitive determination of whether the same relationship holds within individual star-forming clouds. In this article we use a new, high-accuracy catalogue of young stellar objects from Spitzer combined with new, high-dynamic range maps of twelve nearby ($<$1.5 kpc) molecular clouds from Herschel to re-examine the KS relation within individual molecular clouds. We find a tight, linear correlation between clouds' star formation rate per unit area and their gas surface density normalised by the gas free-fall time. The measured relation extends over more than two orders of magnitude within each cloud, and is nearly identical in each of the twelve clouds, implying a constant star formation efficiency per free-fall time eff≈0.026$. The finding of a universal correlation within individual molecular clouds, including clouds that contain no massive stars or massive stellar feedback, favours models in which star formation is regulated by local processes such as turbulence or protostellar outflows, and disfavours models in which star formation is regulated primarily by galaxy properties or supernova feedback on galactic scales.

scholarly journals Bird’s eye view of molecular clouds in the Milky Way

2021 ◽  
Vol 653 ◽  
pp. A63
Author(s):  
Andri Spilker ◽  
Jouni Kainulainen ◽  
Jan Orkisz
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Scaling Laws ◽  
Milky Way ◽  
Probability Distributions ◽  
Young Stellar Objects ◽  
Density Contrast ◽  
Stellar Objects ◽  
Size Scale ◽  
Star Formation Activity

Context. Describing how the properties of the interstellar medium are combined across various size scales is crucial for understanding star formation scaling laws and connecting Galactic and extragalactic data of molecular clouds. Aims. We describe how the statistical structure of the clouds and its connection to star formation changes from sub-parsec to kiloparsec scales in a complete region within the Milky Way disk. Methods. We built a census of molecular clouds within 2 kpc from the Sun using data from the literature. We examined the dust-based column density probability distributions (N-PDFs) of the clouds and their relation to star formation as traced by young stellar objects (YSOs). We then examined our survey region from the outside, within apertures of varying sizes, and describe how the N-PDFs and their relation to star formation changes with the size scale. Results. We present a census of the molecular clouds within 2 kpc distance, including 72 clouds and YSO counts for 44 of them. The N-PDFs of the clouds are not well described by any single simple model; use of any single model may bias the interpretation of the N-PDFs. The top-heaviness of the N-PDFs correlates with star formation activity, and the correlation changes with Galactic environment (spiral- and inter-arm regions). We find that the density contrast of clouds may be more intimately linked to star formation than the dense gas mass fraction. The aperture-averaged N-PDFs vary with the size scale and are more top-heavy for larger apertures. The top-heaviness of the aperture N-PDFs correlates with star formation activity up to roughly 0.5 kpc, depending on the environment. Our results suggest that the relations between cloud structure and star formation are environment specific and best captured by relative quantities (e.g. the density contrast). Finally, we show that the density structures of individual clouds give rise to a kiloparsec-scale Kennicutt-Schmidt relation as a combination of sampling effects and blending of different galactic environments.

scholarly journals Volumetric star formation prescriptions in vertically resolved edge-on galaxies

2020 ◽  
Vol 494 (3) ◽  
pp. 4558-4575
Author(s):  
Kijeong Yim ◽  
Tony Wong ◽  
Richard J Rand ◽  
Eva Schinnerer
Keyword(s):  
Star Formation ◽  
Surface Density ◽  
Formation Rate ◽  
Volume Density ◽  
Gas Pressure ◽  
Molecular Gas ◽  
Strongly Correlated ◽  
Interstellar Gas ◽  
Significant Difference ◽  
Galaxy Sample

ABSTRACT We measure the gas disc thicknesses of the edge-on galaxy NGC 4013 and the less edge-on galaxies (NGC 4157 and 5907) using CO (CARMA/OVRO) and/or H i (EVLA) observations. We also estimate the scale heights of stars and/or the star formation rate (SFR) for our sample of five galaxies using Spitzer IR data (3.6 and 24 µm). We derive the average volume densities of the gas and the SFR using the measured scale heights along with radial surface density profiles. Using the volume density that is more physically relevant to the SFR than the surface density, we investigate the existence of a volumetric star formation law (SFL), how the volumetric SFL is different from the surface-density SFL, and how the gas pressure regulates the SFR based on our galaxy sample. We find that the volumetric and surface SFLs in terms of the total gas have significantly different slopes, while the volumetric and surface SFLs in terms of the molecular gas do not show any noticeable difference. The volumetric SFL for the total gas has a flatter power-law slope of 1.26 with a smaller scatter of 0.19 dex compared to the slope (2.05) and the scatter (0.25 dex) of the surface SFL. The molecular gas SFLs have similar slopes of 0.78 (volume density) and 0.77 (surface density) with similar rms scatters. We show that the interstellar gas pressure is strongly correlated with the SFR but find no significant difference between the correlations based on the volume and surface densities.

scholarly journals Effects of initial density profiles on massive star cluster formation in giant molecular clouds

2021 ◽  
Author(s):  
Yingtian Chen ◽  
Hui Li ◽  
Mark Vogelsberger
Keyword(s):  
Angular Momentum ◽  
Star Formation ◽  
Molecular Clouds ◽  
Globular Clusters ◽  
Cluster Formation ◽  
Initial Density ◽  
Giant Molecular Clouds ◽  
Density Profiles ◽  
Stellar Feedback ◽  
Gas Accretion

Abstract We perform a suite of hydrodynamic simulations to investigate how initial density profiles of giant molecular clouds (GMCs) affect their subsequent evolution. We find that the star formation duration and integrated star formation efficiency of the whole clouds are not sensitive to the choice of different profiles but are mainly controlled by the interplay between gravitational collapse and stellar feedback. Despite this similarity, GMCs with different profiles show dramatically different modes of star formation. For shallower profiles, GMCs first fragment into many self-gravitation cores and form sub-clusters that distributed throughout the entire clouds. These sub-clusters are later assembled ‘hierarchically’ to central clusters. In contrast, for steeper profiles, a massive cluster is quickly formed at the center of the cloud and then gradually grows its mass via gas accretion. Consequently, central clusters that emerged from clouds with shallower profiles are less massive and show less rotation than those with the steeper profiles. This is because 1) a significant fraction of mass and angular momentum in shallower profiles is stored in the orbital motion of the sub-clusters that are not able to merge into the central clusters 2) frequent hierarchical mergers in the shallower profiles lead to further losses of mass and angular momentum via violent relaxation and tidal disruption. Encouragingly, the degree of cluster rotations in steeper profiles is consistent with recent observations of young and intermediate-age clusters. We speculate that rotating globular clusters are likely formed via an ‘accretion’ mode from centrally-concentrated clouds in the early Universe.

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