scholarly journals Reproducing the CO-to-H2 conversion factor in cosmological simulations of Milky-Way-mass galaxies

2020 ◽  
Vol 499 (1) ◽  
pp. 837-850
Author(s):  
Laura C Keating ◽  
Alexander J Richings ◽  
Norman Murray ◽  
Claude-André Faucher-Giguère ◽  
Philip F Hopkins ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Milky Way ◽  
Conversion Factor ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Giant Molecular Clouds ◽  
Post Processing ◽  
Subgrid Model ◽  
Local Sources ◽  
Molecular Abundances

ABSTRACT We present models of CO(1–0) emission from Milky-Way-mass galaxies at redshift zero in the FIRE-2 cosmological zoom-in simulations. We calculate the molecular abundances by post-processing the simulations with an equilibrium chemistry solver while accounting for the effects of local sources, and determine the emergent CO(1–0) emission using a line radiative transfer code. We find that the results depend strongly on the shielding length assumed, which, in our models, sets the attenuation of the incident UV radiation field. At the resolution of these simulations, commonly used choices for the shielding length, such as the Jeans length, result in CO abundances that are too high at a given H2 abundance. We find that a model with a distribution of shielding lengths, which has a median shielding length of ∼3 pc in cold gas (T < 300 K) for both CO and H2, is able to reproduce both the observed CO(1–0) luminosity and inferred CO-to-H2 conversion factor at a given star formation rate compared with observations. We suggest that this short shielding length can be thought of as a subgrid model, which controls the amount of radiation that penetrates giant molecular clouds.

scholarly journals Star Formation and the Properties of Giant Molecular Clouds in Global Simulations

2010 ◽  
Vol 6 (S270) ◽  
pp. 377-380
Author(s):  
Elizabeth J. Tasker ◽  
Jonathan C. Tan
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Mass Distribution ◽  
Molecular Clouds ◽  
Milky Way ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Type Ii ◽  
Giant Molecular Clouds

AbstractWe simulated an isolated quiescent Milky Way-type galaxy with a maximum effective resolution of 7.8 pc. Clouds formed in the interstellar medium through gravitational fragmentation and became the sites for star formation. We tracked the evolution of the clouds through 300 Myr in the presence of star formation, photoelectric heating and feedback from Type II supernovae. The cloud mass distribution agreed well with observational results. Feedback suppressed star formation but did not destroy the surrounding cloud. Collisions between clouds were found to be sufficiently frequent to be a significant factor in determining the star formation rate.

scholarly journals The role of galactic dynamics in shaping the physical properties of giant molecular clouds in Milky Way-like galaxies

2020 ◽  
Vol 498 (1) ◽  
pp. 385-429 ◽  
Author(s):  
Sarah M R Jeffreson ◽  
J M Diederik Kruijssen ◽  
Benjamin W Keller ◽  
Mélanie Chevance ◽  
Simon C O Glover
Keyword(s):  
Molecular Clouds ◽  
Large Scale ◽  
Milky Way ◽  
Gravitational Instability ◽  
Formation Rate ◽  
Tangential Velocity ◽  
Galactic Rotation ◽  
H Ii Regions ◽  
Giant Molecular Clouds

ABSTRACT We examine the role of the large-scale galactic-dynamical environment in setting the properties of giant molecular clouds in Milky Way-like galaxies. We perform three high-resolution simulations of Milky Way-like discs with the moving-mesh hydrodynamics code arepo, yielding a statistical sample of ${\sim}80\, 000$ giant molecular clouds and ${\sim}55\, 000$ H i clouds. We account for the self-gravity of the gas, momentum, and thermal energy injection from supernovae and H ii regions, mass injection from stellar winds, and the non-equilibrium chemistry of hydrogen, carbon, and oxygen. By varying the external gravitational potential, we probe galactic-dynamical environments spanning an order of magnitude in the orbital angular velocity, gravitational stability, mid-plane pressure, and the gradient of the galactic rotation curve. The simulated molecular clouds are highly overdense (∼100×) and overpressured (∼25×) relative to the ambient interstellar medium. Their gravoturbulent and star-forming properties are decoupled from the dynamics of the galactic mid-plane, so that the kpc-scale star formation rate surface density is related only to the number of molecular clouds per unit area of the galactic mid-plane. Despite this, the clouds display clear, statistically significant correlations of their rotational properties with the rates of galactic shearing and gravitational free-fall. We find that galactic rotation and gravitational instability can influence their elongation, angular momenta, and tangential velocity dispersions. The lower pressures and densities of the H i clouds allow for a greater range of significant dynamical correlations, mirroring the rotational properties of the molecular clouds, while also displaying a coupling of their gravitational and turbulent properties to the galactic-dynamical environment.

scholarly journals Turbulence, feedback, and slow star formation

2006 ◽  
Vol 2 (S237) ◽  
pp. 378-383
Author(s):  
Mark R. Krumholz
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Free Fall ◽  
Giant Molecular Clouds ◽  
Star Forming ◽  
Striking Result ◽  
Wide Range ◽  
Individual Cluster

AbstractOne of the outstanding puzzles about star formation is why it proceeds so slowly. Giant molecular clouds convert only a few percent of their gas into stars per free-fall time, and recent observations show that this low star formation rate is essentially constant over a range of scales from individual cluster-forming molecular clumps in the Milky Way to entire starburst galaxies. This striking result is perhaps the most basic fact that any theory of star formation must explain. I argue that a model in which star formation occurs in virialized structures at a rate regulated by supersonic turbulence can explain this observation. The turbulence in turn is driven by star formation feedback, which injects energy to offset radiation from isothermal shocks and keeps star-forming structures from wandering too far from virial balance. This model is able to reproduce observational results covering a wide range of scales, from the formation times of young clusters to the extragalactic IR-HCN correlation, and makes additional quantitative predictions that will be testable in the next few years.

scholarly journals Star Formation in the Local Milky Way

2015 ◽  
Vol 10 (S314) ◽  
pp. 8-15
Author(s):  
Charles J. Lada
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Milky Way ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Young Stars ◽  
Molecular Gas ◽  
Physical Processes ◽  
Star Forming ◽  
Star Forming Regions

AbstractStudies of molecular clouds and young stars near the sun have provided invaluable insights into the process of star formation. Indeed, much of our physical understanding of this topic has been derived from such studies. Perhaps the two most fundamental problems confronting star formation research today are: 1) determining the origin of stellar mass and 2) deciphering the nature of the physical processes that control the star formation rate in molecular gas. As I will briefly outline here, observations and studies of local star forming regions are making particularly significant contributions toward the solution of both these important problems.

scholarly journals The Ballistic Particle Model

1983 ◽  
Vol 100 ◽  
pp. 133-134
Author(s):  
Frank N. Bash
Keyword(s):  
Radial Velocity ◽  
Gravitational Potential ◽  
Molecular Clouds ◽  
Milky Way ◽  
Terminal Velocity ◽  
Particle Model ◽  
The Sun ◽  
Giant Molecular Clouds ◽  
Spiral Pattern ◽  
Armed Spiral

Bash and Peters (1976) suggested that giant molecular clouds (GMC's) can be viewed as ballistic particles launched from the two-armed spiral-shock (TASS) wave with orbits influenced only by the overall galactic gravitational potential perturbed by the spiral gravitational potential in the arms. For GMC's in the Milky Way, the model predicts that the radial velocity observed from the Sun increases with age (time since launch). We showed that the terminal velocity of CO observed from l ≃ 30° to l ≃ 60° can be understood if all GMC's are born in the spiral pattern given by Yuan (1969) and live 30 × 106 yrs. Older GMC's were predicted to have radial velocities which exceed observed terminal velocities.

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

scholarly journals Evolution of the star formation efficiency in galaxies

2012 ◽  
Vol 10 (H16) ◽  
pp. 341-341
Author(s):  
Jonathan Braine
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Conversion Factor ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Molecular Gas ◽  
Present Evidence ◽  
Ngc 6822 ◽  
Physical And Chemical ◽  
Formation Efficiency

AbstractThe physical and chemical evolution of galaxies is intimately linked to star formation, We present evidence that molecular gas (H2) is transformed into stars more quickly in smaller and/or subsolar metallicity galaxies than in large spirals – which we consider to be equivalent to a star formation efficiency (SFE). In particular, we show that this is not due to uncertainties in the N(H2)/Ico conversion factor. Several possible reasons for the high SFE in galaxies like the nearby M33 or NGC 6822 are proposed which, separately or together, are the likely cause of the high SFE in this environment. We then try to estimate how much this could contribute to the increase in cosmic star formation rate density from z = 0 to z = 1.

scholarly journals The manifestation of secondary bias on the galaxy population from IllustrisTNG300

2020 ◽  
Vol 496 (2) ◽  
pp. 1182-1196 ◽  
Author(s):  
Antonio D Montero-Dorta ◽  
M Celeste Artale ◽  
L Raul Abramo ◽  
Beatriz Tucci ◽  
Nelson Padilla ◽  
...  
Keyword(s):  
Surface Density ◽  
Star Formation Rate ◽  
Statistical Significance ◽  
Formation Rate ◽  
Mass Range ◽  
Halo Formation ◽  
Subgrid Model ◽  
High Statistical Significance ◽  
The Galaxy ◽  
Galaxy Population

ABSTRACT We use the improved IllustrisTNG300 magnetohydrodynamical cosmological simulation to revisit the effect that secondary halo bias has on the clustering of the central galaxy population. With a side length of 205 h−1 Mpc and significant improvements on the subgrid model with respect to previous Illustris simulations, IllustrisTNG300 allows us to explore the dependencies of galaxy clustering over a large cosmological volume and halo mass range. We show at high statistical significance that the halo assembly bias signal (i.e. the secondary dependence of halo bias on halo formation redshift) manifests itself on the clustering of the galaxy population when this is split by stellar mass, colour, specific star formation rate, and surface density. A significant signal is also found for galaxy size: at fixed halo mass, larger galaxies are more tightly clustered than smaller galaxies. This effect, in contrast to the rest of the dependencies, seems to be uncorrelated with halo formation time, with some small correlation only detected for halo spin. We also explore the transmission of the spin bias signal, i.e. the secondary dependence of halo bias on halo spin. Although galaxy spin retains little information about the total halo spin, the correlation is enough to produce a significant galaxy spin bias signal. We discuss possible ways to probe this effect with observations.

scholarly journals THE ADF AND THE t2 FORMALISM IN H II REGIONS BASED ON THE UPPER MASS LIMIT OF THE IMF FOR THE MW

2020 ◽  
Vol 56 (2) ◽  
pp. 235-244
Author(s):  
L. Carigi ◽  
A. Peimbert ◽  
M. Peimbert ◽  
G. Delgado-Inglada
Keyword(s):  
Milky Way ◽  
Spiral Galaxies ◽  
Star Formation Rate ◽  
Direct Method ◽  
Formation Rate ◽  
Mass Function ◽  
Initial Mass Function ◽  
H Ii Regions ◽  
Mass Limit ◽  
Better Than

We study in depth the abundance discrepancy problem in H II regions, this time from a different perspective than the usual one: by studying the effect of the upper mass limit (Mup) of the initial mass function (IMF) on the O, C, and He predicted by chemical evolution models for the Milky Way. We use abundances determined with the direct method (DM) and with the temperature independent method (TIM). We compare the predicted abundances at the present time with observations of Orion, M17, and M8 to determine the Mup value of the galactic IMF. From the DM abundances, the models predict an Mup = 25 − 45 M⨀, while from the TIM, CEMs derive an Mup = 70 − 110 M⨀. Spiral galaxies with the stellar mass and star formation rate of the MW are predicted to have an Mup ≈ 100 M⨀. These results support that abundances derived from the TIM are better than those derived from the DM.

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