STAR FORMATION IN DISK GALAXIES. I. FORMATION AND EVOLUTION OF GIANT MOLECULAR CLOUDS VIA GRAVITATIONAL INSTABILITY AND CLOUD COLLISIONS

By Elizabeth J. Tasker, Jonathan C. Tan. 2008

219 citations recorded by the source corpus.

We investigate the formation and evolution of giant molecular clouds (GMCs) in a Milky-Way-like disk galaxy with a flat rotation curve. We perform a series of three-dimensional adaptive mesh refinement numerical simulations that follow both the global evolution on scales of ∼20 kpc and resolve down to scales ≲10 pc with a multiphase atomic interstellar medium. In this first study, we omit star formation and feedback, and focus on the processes of gravitational instability and cloud collisions and interactions. We define clouds as regions with nH ⩾ 100 cm-3 and track the evolution of individual clouds as they orbit through the galaxy from their birth to their eventual destruction via merger or via destructive collision with another cloud. After ∼140 Myr a large fraction of the gas in the disk has fragmented into clouds with masses ∼106 M☉ and a mass spectrum similar to that of Galactic GMCs. The disk settles into a quasi-steady-state in which gravitational scattering of clouds keeps the disk near the threshold of global gravitational instability. The cloud collision time is found to be a small fraction, ∼1/5, of the orbital time, and this is an efficient mechanism to inject turbulence into the clouds. This helps to keep clouds only moderately gravitationally bound, with virial parameters of order unity. Many other observed GMC properties, such as mass surface density, angular momentum, velocity dispersion, and vertical distribution, can be accounted for in this simple model with no stellar feedback.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

Simulations of the grand design galaxy M51: a case study for analysing tidally induced spiral structure (2009, background): “Several simulations show the formation of giant molecular clouds in this manner (Wada & Norman 1999; Wada, Meurer & Norman 2002; Li, Mac Low & Klessen 2005; Tasker & Bryan 2006; Robertson & Kravtsov 2008), although collisions between clouds may also contribute (Tasker & Tan 2009).”
Is molecular gas necessary for star formation (2011, background): “Models of cloud formation on the scale of the Galactic disk also appear to have no difficulty in producing large cold gas clouds with- c© 0000 RAS, MNRAS 000, 000–000 out needing to invoke molecular cooling (see e.g. Tasker & Tan 2009).”
Star-formation laws in luminous infrared galaxies. New observational constraints on models (2011, background): “Alternatively, other forms of the star formation laws adduce the importance of including explicitlyglobal dynamical time scales tdyn (Elmegreen 1997; Silk 1997; Kennicutt 1998; Elmegreen 2002; Boissier et al. 2003; Tasker & Tan 2009; Tan 2010; Genzel et al. 2010).”
FIRE-2 simulations: physics versus numerics in galaxy formation (2017, background): “…repeatedly shown that almost all star formation occurs in the largest GMC complexes in galaxies (see Evans 1999; Rosolowsky et al. 2003; Blitz & Rosolowsky 2005; Bolatto et al. 2008; Elmegreen 2007; Tasker & Tan 2009; Feldmann & Gnedin 2011; Murray 2011; Harper-Clark & Murray 2011; Hopkins 2012a).”
The exciting lives of giant molecular clouds (2013, background): “Numerical simulations have also investigated the physical mechanisms for GMC formation (Dobbs et al. 2006; Dobbs 2008; Wada 2008; Kim & Ostriker 2002; Kim et al. 2003; Tasker & Tan 2009).”
Turbulent molecular clouds (2012, background): “The second approach treats a whole galactic disk in- cluding the gravity of stars either in a fixed asymmetric potential (e.g. Tasker & Tan 2009), or in a prescribed spiral arm potential (e.g. Dobbs & Bonnell 2007) or with self–consistent dynamics of stars (e.g. Bournaud et al. 2010, Hopkins et al.…”
Self-regulated star formation in galaxies via momentum input from massive stars (2011, background): “The details of feedback on small scales should also not be important, so long as it is sufficient to self-regulate (compare our result to Saitoh et al. 2008).”
The formation of disc galaxies in a ΛCDM universe (2010, background): “Isolated simulations of large spiral galaxies in a non-cosmological setting have successfully reached this resolution (Agertz et al. 2009; Tasker & Tan 2009), albeit with simplified physics.”
ISM properties in hydrodynamic galaxy simulations: turbulence cascades, cloud formation, role of gravity and feedback (2010, methodology): “Journal compilation C© 2010 RAS et al. 2009a; Tasker & Tan 2009) but have not been compared to observational constraints yet, probably because of lacking the required level of realism, both in spatial resolution and in global dynamical modelling (no old stellar components and live dark halo were…”
FORMATION OF MASSIVE GALAXIES AT HIGH REDSHIFT: COLD STREAMS, CLUMPY DISKS, AND COMPACT SPHEROIDS (2009, background): “One particular mechanism of this sort for generating velocity dispersion in the disk is the gravitational en- counters between the bound disk clumps (see Wada et al. 2002; Agertz et al. 2008; Tasker & Tan 2009).”
Star formation in galaxy mergers with realistic models of stellar feedback and the interstellar medium (2012, background): “Numerical simulations of isolated galaxies and galaxy mergers can now achieve the dynamic range required to resolve the formation of GMC and ISM structure, ∼1–10 pc (see e.g. Saitoh et al. 2008; Tasker & Tan 2009; Bournaud et al. 2010; Dobbs, Burkert & Pringle 2011).”
PHYSICAL PROPERTIES AND GALACTIC DISTRIBUTION OF MOLECULAR CLOUDS IDENTIFIED IN THE GALACTIC RING SURVEY (2010, methodology): “On the other hand, simulations by Tasker & Tan (2009) suggest that molecular clouds are gravitationally bound.”
THE PdBI ARCSECOND WHIRLPOOL SURVEY (PAWS): ENVIRONMENTAL DEPENDENCE OF GIANT MOLECULAR CLOUD PROPERTIES IN M51 (2014, background): “…that GMCs also increase their mass through coagulation processes (cloud collisions, accretion of small clouds, mutual coalescence) that are aided by the converging streamlines of the gas flow within the arms (Casoli & Combes 1981; Kwan & Valdes 1983; Tomisaka 1986; Dobbs 2008; Tasker & Tan 2009).”
Why are most molecular clouds not gravitationally bound (2011, methodology): “However with no, or little feedback, the clouds are predominantly bound and quasi-spherical (as found in Run B and by Tasker & Tan 2009), in disagreement with observations.”
Physical Processes in the Interstellar Medium (2014, methodology): “In addition, the coagulation model also can easily produce clouds that are counter-rotating compared to the galactic disk (e.g. Dobbs 2008; Tasker and Tan 2009), explaining why clouds with retrograde rotation appear to be common within the ISM (see e.”
MOLECULAR CLOUDS TOWARD THE SUPER STAR CLUSTER NGC 3603; POSSIBLE EVIDENCE FOR A CLOUD–CLOUD COLLISION IN TRIGGERING THE CLUSTER FORMATION (2013, background): “…between the two clouds may have triggered the formation of the SSC. Theoretical studies have modelled the triggering of star formation via cloud-cloud collisions (Habe & Ohta 1992; Anathpindika – 5 – 2010), and such collisions are believed to be frequent in gas-rich galaxies (Tasker & Tan 2009).”
HYDRODYNAMICS OF HIGH-REDSHIFT GALAXY COLLISIONS: FROM GAS-RICH DISKS TO DISPERSION-DOMINATED MERGERS AND COMPACT SPHEROIDS (2010, methodology): “Highresolution models explicitly including gas cooling could, in principle, resolve the densest gas phases that are actually star-forming (Tasker & Tan 2009; Agertz et al. 2009; Bournaud et al. 2010), but models using an artificially thermalized ISM do not reach such high gas densities and they…”
Star Formation in the Milky Way and Nearby Galaxies (2012, background): “…phase balance, and feedback are providing deeper insights into the physical nature of the star formation scaling laws and thresholds and the life cycles of molecular clouds (e.g., Robertson & Kravtsov 2008; Dobbs 2008; Dobbs & Pringle 2010; Tasker & Tan 2009; Tasker 2011; Brooks et al. 2011).”
The structure of the interstellar medium of star‐forming galaxies (2011, methodology): “This has been seen in other high-resolution disc simulations with- out feedback, as well (Bournaud, Elmegreen & Elmegreen 2007; Dobbs 2008; Tasker & Tan 2009).”