scholarly journals Photoionizing feedback in spiral arm molecular clouds

2020 ◽  
Vol 495 (2) ◽  
pp. 1672-1691
Author(s):  
Thomas J R Bending ◽  
Clare L Dobbs ◽  
Matthew R Bate
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Total Mass ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Rapid Decrease ◽  
H Ii Regions ◽  
Noticeable Effect ◽  
Spiral Arm ◽  
Dense Features

ABSTRACT We present simulations of a 500 pc2 region, containing gas of mass 4 × 106 M⊙, extracted from an entire spiral galaxy simulation, scaled up in resolution, including photoionizing feedback from stars of mass >18 M⊙. Our region is evolved for 10 Myr and shows clustered star formation along the arm generating ≈ 5000 cluster sink particles ≈ 5 per cent of which contain at least one of the ≈ 4000 stars of mass >18 M⊙. Photoionization has a noticeable effect on the gas in the region, producing ionized cavities and leading to dense features at the edge of the H ii regions. Compared to the no-feedback case, photoionization produces a larger total mass of clouds and clumps, with around twice as many such objects, which are individually smaller and more broken up. After this we see a rapid decrease in the total mass in clouds and the number of clouds. Unlike studies of isolated clouds, our simulations follow the long-range effects of ionization, with some already dense gas, becoming compressed from multiple sides by neighbouring H ii regions. This causes star formation that is both accelerated and partially displaced throughout the spiral arm with up to 30 per cent of our cluster sink particle mass forming at distances >5 pc from sites of sink formation in the absence of feedback. At later times, the star formation rate decreases to below that of the no-feedback case.

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

AbstractWe use

Molecular Clouds and Star Formation in the Southern H II Regions

1999 ◽  
Vol 51 (6) ◽  
pp. 791-818 ◽  
Author(s):  
Reiko Yamaguchi ◽  
Hiro Saito ◽  
Norikazu Mizuno ◽  
Yoshihiro Mine ◽  
Akira Mizuno ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Formation Rate ◽  
Point Sources ◽  
Young Stellar Objects ◽  
H Ii Regions ◽  
Stellar Objects ◽  
Order Of Magnitude ◽  
Formation Efficiency ◽  
Active Formation

Abstract We have carried out extensive 13CO(J = 1−0) observations toward 23 southern H II regions associated with bright-rimmed clouds. In total, 95 molecular clouds have been identified to be associated with the H II regions. Among the 95, 57 clouds \ are found to be associated with 204 IRAS point sources which are candidates for young stellar objects. There is a significant increase of star-formation efficiency on the side facing to the H II regions; the luminosity-to-mass ratio, defined as the ratio of the stellar luminosity to the molecular cloud mass, is higher by an order of magnitude on the near side of the H II regions than that on the far side. This indicates that molecular gas facing to the H II regions is more actively forming massive s\ tars whose luminosity is ≳103L⊙. In addition, the number density of the IRAS point sources increases by a factor of 2 on the near side of the H II regions compared with on the far side. These results strongly suggest that the active formation of massive stars on the near side of the H II regions is due to the effects of the H II regions, such as the compression of molecular material by the ionization/shock fronts. For the whole Galaxy, we estimate that the present star-formation rate under such effects is at least 0.2−0.4 M⊙ yr-1, corresponding to a few 10% by mass.

scholarly journals Cosmic Star Formation Rate at z ~ 3 — Metallicity Effect

2001 ◽  
Vol 204 ◽  
pp. 415-415
Author(s):  
H. Hirashita ◽  
A. K. Inoue ◽  
H. Kamaya
Keyword(s):  
Star Formation ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Dust Emission ◽  
Star Formation History ◽  
H Ii Regions ◽  
Formation History ◽  
Ir Emission ◽  
Dust Absorption ◽  
Gas Ratio

Infrared (IR) emission from Galactic dust is frequently used as an indicator of the star formation rate (SFR). Recently, A. K. Inoue, H. Hirashita, & H. Kamaya derived a formula for conversion from the IR luminosity to the SFR based on a physical model of H II regions (PASJ, 52, 539, 2000). They expressed this as SFR/(M⊙ yr−1) = {1.1 x 10-10(1-η)/(0.4–0.22f+0.6∊)}(LIR/L⊙), where f is the fraction of ionizing photons absorbed by hydrogen, ∊ is the efficiency of dust absorption for non-ionizing photons, η is the cirrus fraction of the observed dust luminosity, and LIR is the observed luminosity of dust emission. Since f depends on the dust-to-gas ratio and the dust-to-gas ratio is related to metallicity, we present the dependence of the formula on metallicity.Our metallicity-dependent conversion formula is applied to the cosmic star formation history. Based on a recent model of the cosmic star formation history and metal enrichment history, we find that the photons from OB stars are not efficiently reprocessed in the IR before z ~ 3 because of a low dust-to-gas ratio. This indicates that the star formation rate estimated from the submillimeter luminosity using an empirical formula is significantly underestimated (by at least a factor of 3).

A CCD Hα Survey of Nearby Southern Spiral Galaxies

1991 ◽  
Vol 9 (1) ◽  
pp. 89-90
Author(s):  
Stuart D. Ryder ◽  
Michael A. Dopita
Keyword(s):  
Star Formation ◽  
Observational Data ◽  
Spiral Galaxies ◽  
Star Formation Rate ◽  
Formation Rate ◽  
High Mass ◽  
H Ii Regions ◽  
Mass Star ◽  
Reliable Measure ◽  
Initial Results

AbstractSome initial results of a flux-calibrated CCD Hα imaging program of bright, nearby southern spiral galaxies are presented. Very few southern hemisphere spiral galaxies have ever been completely imaged in Hα, let alone with a CCD. This survey (which mainly uses the MSSSO 1.0-m reflector with an f/3.5 focal reducer) will, when combined with spectrophotometry of the H II regions thus revealed, allow us to trace the chemical evolution of each galaxy. Furthermore, since the absolute Hα flux is a reliable measure of the high-mass star formation rate in a galaxy, such observational data will permit us to test the predictions of the various star formation theories.

scholarly journals Supernova Driving. IV. The Star-formation Rate of Molecular Clouds

2017 ◽  
Vol 840 (1) ◽  
pp. 48 ◽  
Author(s):  
Paolo Padoan ◽  
Troels Haugbølle ◽  
Åke Nordlund ◽  
Søren Frimann
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Star Formation Rate ◽  
Formation Rate

scholarly journals The Mopra DQS survey of the G333 region

2006 ◽  
Vol 2 (S237) ◽  
pp. 404-404
Author(s):  
M. R. Cunningham ◽  
I. Bains ◽  
N. Lo ◽  
T. Wong ◽  
M. G. Burton ◽  
...  
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Standard Model ◽  
Molecular Clouds ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Star Forming ◽  
Successful Model ◽  
The Standard Model ◽  
Forming Efficiency

Any successful model of star formation must be able to explain the low star forming efficiency of molecular clouds in our Galaxy. If the collapse of gas is regulated only by gravity, then the star formation rate should be orders of magnitude larger than the 1 M per year within our galaxy. The standard model invokes magnetic fields to slow down the rate of collapse, but does not explain star formation in cluster mode, or the lack of observed variations in the chemistry of molecular clouds if they are long-lived entities.

scholarly journals The Star Formation Rate of Molecular Clouds

2014 ◽  
Author(s):  
P. Padoan ◽  
C. Federrath ◽  
G. Chabrier ◽  
N. J. Evans II ◽  
D. Johnstone ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Star Formation Rate ◽  
Formation Rate

scholarly journals The star formation rate in the inner Milky Way Galaxy

2012 ◽  
Vol 8 (S292) ◽  
pp. 98-98
Author(s):  
Oscar Cavichia ◽  
Mercedes Mollá ◽  
Roberto D. D. Costa ◽  
Walter J. Maciel
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Star Formation Rate ◽  
Massive Stars ◽  
Galactic Disk ◽  
Formation Rate ◽  
Specific Pattern ◽  
Gas Flows ◽  
Milky Way Galaxy ◽  
Stellar Formation

AbstractThe present star formation rate (SFR) in the inner Galaxy is puzzling for the chemical evolution models (CEM). No static CEM is able to reproduce the peak of the SFR in the 4 kpc ring. The main reason is probably a shortage of gas, which could be due to the dynamical effects produced by the galactic bar, not considered by these models. We developed a CEM that includes radial gas flows in order to mimic the effects of the galactic bar in the first 5 kpc of the galactic disk. In this model, the star formation (SF) is a two-step process: first, the diffuse gas forms molecular clouds. Then, stars form from cloud-cloud collisions or by the interaction between massive stars and the molecular gas. The former is called spontaneous and the latter induced SF. The mass in the different phases of each region changes by the processes associated with the stellar formation and death by: the SF due to spontaneous fragmentation of gas in the halo; formation of gas clouds in the disk from the diffuse gas; induced SF in the disk due to the interaction between massive stars and gas clouds; and finally, the restitution of the diffuse gas associated to these process of cloud and star formation. In the halo, the star formation rate for the diffuse gas follows a Schmidt law with a power n = 1.5. In the disk, the stars form in two steps: first, molecular clouds are formed from the diffuse gas also following a Schmidt law with n=1.5 and a proportionality factor. Including a specific pattern of radial gas flows, the CEM is able to reproduce with success the peak in the SFR at 4 kpc (fig. 1).

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