scholarly journals The interaction of an Hii region with a fractal molecular cloud

2010 ◽  
Vol 6 (S270) ◽  
pp. 323-326
Author(s):  
Steffi Walch ◽  
Ant Whitworth ◽  
Thomas Bisbas ◽  
Richard Wünsch ◽  
David Hubber
Keyword(s):  
Fractal Dimension ◽  
Star Formation ◽  
Molecular Clouds ◽  
Density Field ◽  
Scaling Relations ◽  
Principal Mechanism ◽  
Hii Region ◽  
Left Behind ◽  
Collapse Mode ◽  
High Fractal Dimension

AbstractWe describe an algorithm for constructing fractal molecular clouds that obeys prescribed mass and velocity scaling relations.The algorithm involves a random seed, so that many different realisations corresponding to the same fractal dimension and the same scaling relations can be generated. It first generates all the details of the density field, and then position the SPH particles, so that the same simulation can be repeated with different numbers of particles to explore convergence. It can also be used to initialise finite-difference simulations. We then present preliminary numerical simulations of Hii regions expanding into such clouds, and explore the resulting patterns of star formation. If the cloud has low fractal dimension, it already contains many small self-gravitating condensations, and the principal mechanism of star formation is radiatively driven implosion. This results in star formation occurring quite early, throughout the cloud. The stars resulting from the collapse and fragmentation of a single condensation are often distributed in a filament pointing radially away from the source of ionising radiation; as the remainder of the condensation is dispersed, these stars tend to get left behind in the Hii region. If the cloud has high fractal dimension, the cloud does not initially contain dense condensations, and star formation is therefore delayed until the expanding Hii region has swept up a sufficiently massive shell. The shell then becomes gravitationally unstable and breaks up into protostars. In this collect-and-collapse mode, the protostars are distributed in tangential arcs, they tend to be somewhat more massive, and as the expansion of the shell stalls they move ahead of the ionisation front.

scholarly journals Head-on collisions: how to bring large quantities of gas out of inner disks

2004 ◽  
Vol 217 ◽  
pp. 420-421
Author(s):  
Jonathan Braine ◽  
U. Lisenfeld ◽  
P.-A. Duc
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Intergalactic Medium ◽  
Spiral Galaxies ◽  
Molecular Gas ◽  
Hii Region ◽  
Neutral Gas ◽  
Dense Cores ◽  
Clear Cases ◽  
Formation Efficiency

Head-on collisions of spiral galaxies can bring large quantities of gas out of spiral disks and into the intergalactic medium. Only two clear cases (UGC 12914/5 and UGC 813/6) of such collisions are known (Condon et al. 1993, 2002) and in both cases several 109 M⊙ of neutral gas is found in the bridge between the two galaxies which are now separating. About half of the gas is molecular. The gas, atomic or molecular, is brought out by collisions between clouds, which then acquire an intermediate velocity and end up between the galaxies. The bridges contain no old stars and in each case only one HII region despite the large masses of molecular gas, such that the star formation efficiency is very low in the bridges. The collisions occurred 20 – 50 million years ago, much greater than the collapse time for dense cores. We (Braine et al. 2003, 2004) show that collisions between molecular clouds, and not only between atomic gas clouds, bring gas into the bridges. It is not currently known whether the galaxies and bridges are bound or whether they will continue to separate, releasing several 109 M⊙ of neutral gas into the intergalactic medium.

scholarly journals Physical properties and scaling relations of molecular clouds: the impact of star formation

2020 ◽  
Vol 500 (3) ◽  
pp. 3552-3568
Author(s):  
Kearn Grisdale
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Milky Way ◽  
Free Fall ◽  
Scaling Relations ◽  
Formation Method ◽  
Hydrodynamical Simulations ◽  
Formation Efficiency ◽  
The Impact ◽  
Very High

ABSTRACT Using hydrodynamical simulations of a Milky Way-like galaxy, reaching 4.6 pc resolution, we study how the choice of star formation criteria impacts both galactic and giant molecular cloud (GMC) scales. We find that using a turbulent, self-gravitating star formation criteria leads to an increase in the fraction of gas with densities between 10 and $10^{4}{\, \rm {cm^{-3}}}$ when compared with a simulation using a molecular star formation method, despite both having nearly identical gaseous and stellar morphologies. Furthermore, we find that the site of star formation is effected with the the former tending to only produce stars in regions of very high density (${\gt}10^{4}{\, \rm {cm^{-3}}}$) gas, while the latter forms stars along the entire length of its spiral arms. The properties of GMCs are impacted by the choice of star formation criteria with the former method producing larger clouds. Despite the differences, we find that the relationships between clouds properties, such as the Larson relations, remain unaffected. Finally, the scatter in the measured star formation efficiency per free-fall time of GMCs remains present with both methods and is thus set by other factors.

scholarly journals Radio observation of molecular clouds around the W5-East triggered star-forming region

2006 ◽  
Vol 2 (S237) ◽  
pp. 454-454
Author(s):  
Takahiro Niwa ◽  
Yoichi Itoh ◽  
Kengo Tachihara ◽  
Yumiko Oasa ◽  
Kazuyoshi Sunada ◽  
...  
Keyword(s):  
Star Formation ◽  
Physical Properties ◽  
Molecular Clouds ◽  
Mass Density ◽  
Hii Regions ◽  
Radio Observation ◽  
Hii Region ◽  
Star Forming ◽  
Cloud Evolution

It is known that most of stars are formed as clusters (Lada & Lada 2003, ARAA 41, L57) and clusters are formed by triggering. However, the relationships of molecular clouds' conditions and properties of formed stars by triggering is not well studied. To clarify differences between triggered and spontaneous star formation through physical properties of molecular clouds (e.g. mass, density, morphology), we observed the W5-East HII region. The W5-East HII region is located at 2 kpc and has a 10 pc extent of HII region. This region has 3 Bright Rimmed Clouds (BRCs; Sugitani et al. 1991, ApJS 77, S59), which are interface between HII regions and molecular clouds, and known as sites of triggered star formation. The molecular clouds surround the W5-East (Karr et al. 2003, ApJ, 595, 900), thus we expect molecular clouds morphology is affected by the HII region and the cloud evolution is supposed to be dominated by the expanding HII region.

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 3.27. Millimeter-wave continuum observation of galaxies

1998 ◽  
Vol 184 ◽  
pp. 143-144 ◽  
Author(s):  
H. Matsuo ◽  
N. Kuno ◽  
B. Vila-Vilaro ◽  
H. Kashihara ◽  
T. Kawabata
Keyword(s):  
Star Formation ◽  
Millimeter Wave ◽  
Molecular Clouds ◽  
Dust Emission ◽  
Synchrotron Emission ◽  
Diffuse Component ◽  
Hii Region ◽  
Continuum Observation

Continuum observation of galaxies in millimeter-wave gives informations on dust emission from molecular clouds, free-free emission from HII region and synchrotron emission from SNR and diffuse component. The free-free emission can be observed only at millimeter-wave frequencies and their emission is optically thin, it can be a good indicator of their star-formation activities.

scholarly journals Remnant Molecular Clouds in the Ori OB 1 Association

1998 ◽  
Vol 15 (1) ◽  
pp. 91-98 ◽  
Author(s):  
Katsuo Ogura ◽  
Koji Sugitani
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Hii Region ◽  
Reflected Light ◽  
Ob Associations ◽  
T Tau

AbstractWe suggest and give some evidence that as an HII region expands and the O stars evolve into B giants, remains of the molecular clouds first appear as bright-rimmed clouds, then as cometary globules and finally as small clouds which are visible by the reflected light from the B giants. We propose to call the last of these ‘reflection clouds’ and all three categories collectively ‘remnant clouds’. A list is presented of about 80 objects of these remnant clouds in the Ori OB 1 association. In the Belt region there is a beautiful spatial sequence from bright-rimmed clouds through cometary globules to reflection clouds. We suspect that retarded star formation in remnant clouds can explain the presence of so-called dispersed T Tau stars in the peripheries of OB associations.

scholarly journals STAR FORMATION RATES IN MOLECULAR CLOUDS AND THE NATURE OF THE EXTRAGALACTIC SCALING RELATIONS

2012 ◽  
Vol 745 (2) ◽  
pp. 190 ◽  
Author(s):  
Charles J. Lada ◽  
Jan Forbrich ◽  
Marco Lombardi ◽  
João F. Alves
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Scaling Relations

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.

scholarly journals Testing the star formation scaling relations in the clumps of the North American and Pelican nebulae cloud complex

2020 ◽  
Vol 500 (3) ◽  
pp. 3123-3141
Author(s):  
Swagat R Das ◽  
Jessy Jose ◽  
Manash R Samal ◽  
Shaobo Zhang ◽  
Neelam Panwar
Keyword(s):  
Star Formation ◽  
Surface Density ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Free Fall ◽  
Scaling Relations ◽  
Time Model ◽  
Fall Time ◽  
The North ◽  
Crossing Time

ABSTRACT The processes that regulate star formation within molecular clouds are still not well understood. Various star formation scaling relations have been proposed as an explanation, one of which is to formulate a relation between the star formation rate surface density $\rm \Sigma _{SFR}$ and the underlying gas surface density $\rm \Sigma _{gas}$. In this work, we test various star formation scaling relations, such as the Kennicutt–Schmidt relation, the volumetric star formation relation, the orbital time model, the crossing time model and the multi free-fall time-scale model, towards the North American Nebula and Pelican Nebula and in the cold clumps associated with them. Measuring stellar mass from young stellar objects and gaseous mass from CO measurements, we estimate the mean $\rm \Sigma _{SFR}$, the star formation rate per free-fall time and the star formation efficiency for clumps to be 1.5 $\rm M_{\odot}\, yr^{-1}\, kpc^{-2}$, 0.009 and 2.0 per cent, respectively, while for the whole region covered by both nebulae (which we call the ‘NAN’ complex) the values are 0.6 $\rm M_{\odot}\, yr^{-1}\, kpc^{-2}$, 0.0003 and 1.6 per cent, respectively. For the clumps, we notice that the observed properties are in line with the correlation obtained between $\rm \Sigma _{SFR}$ and $\rm \Sigma _{gas}$, and between $\rm \Sigma _{SFR}$ and $\rm \Sigma _{gas}$ per free-fall time and orbital time for Galactic clouds. At the same time, we do not observe any correlation with $\rm \Sigma _{gas}$ per crossing time and multi free-fall time. Even though we see correlations in the former cases, however, all models agree with each other within a factor of 0.5 dex. It is not possible to discriminate between these models because of the current uncertainties in the input observables. We also test the variation of $\rm \Sigma _{SFR}$ with the dense gas but, because of low statistics, a weak correlation is seen in our analysis.

scholarly journals Molecular Clouds and Star Formation Rate in Disk Galaxies

2016 ◽  
Vol 25 (3) ◽  
Author(s):  
E. O. Vasiliev ◽  
S. A. Khoperskov ◽  
A. V. Khoperskov
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Disk Galaxies

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