Star formation in unbound giant molecular clouds: the origin of OB associations?

Clark, Paul; Bonnell, Ian A.; Zinnecker, H.; Bate, Matthew R.

doi:10.1111/j.1365-2966.2005.08942.x

Cited by 113 publications

(122 citation statements)

References 62 publications

(93 reference statements)

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“…However, we cannot rule out that some clouds may also be completely destroyed, e.g., in the manner described in the previous section; mass loss might follow from shear, which is non-zero at these radii, or through the process of star formation itself, which might consume a large fraction of the cloud mass. In some models, the star formation efficiency per free-fall time can be as high as 0.2-0.3 (e.g., Klessen & Burkert 2000;Bonnell et al 2003;Vazquez-Semadeni et al 2003;Clark et al 2005). …”

Section: Transformation Via Feedbackmentioning

confidence: 99%

SHORT GMC LIFETIMES: AN OBSERVATIONAL ESTIMATE WITH THE PdBI ARCSECOND WHIRLPOOL SURVEY (PAWS)

Meidt

Hughes

Dobbs

et al. 2015

ApJ

107

113

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We describe and execute a novel approach to observationally estimate the lifetimes of giant molecular clouds (GMCs). We focus on the cloud population between the two main spiral arms in M51 (the inter-arm region) where cloud destruction via shear and star formation feedback dominates over formation processes. By monitoring the change in GMC number densities and properties across the inter-arm, we estimate the lifetime as a fraction of the inter-arm travel time. We find that GMC lifetimes in M51ʼs inter-arm are finite and short, 20-30 Myr. Over most of the region under investigation shear appears to regulate the lifetime. As the shear timescale increases with galactocentric radius, we expect cloud destruction to switch primarily to feedback at larger radii. We identify a transition from shear-to feedback-dominated disruption, finding that shear is more efficient at dispersing clouds, whereas feedback transforms the population, e.g., by fragmenting high-mass clouds into lower mass pieces. Compared to the characteristic timescale for molecular hydrogen in M51, our short lifetimes suggest that gas can remain molecular while clouds disperse and reassemble. We propose that galaxy dynamics regulates the cycling of molecular material from diffuse to bound (and ultimately star-forming) objects, contributing to long observed molecular depletion times in normal disk galaxies. We also speculate that, in extreme environments like elliptical galaxies and concentrated galaxy centers, star formation can be suppressed when the shear timescale is short enough that some clouds will not survive to form stars.

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Section: Transformation Via Feedbackmentioning

confidence: 99%

SHORT GMC LIFETIMES: AN OBSERVATIONAL ESTIMATE WITH THE PdBI ARCSECOND WHIRLPOOL SURVEY (PAWS)

Meidt

Hughes

Dobbs

et al. 2015

ApJ

107

113

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“…The larger mass clouds which formed in more turbulent conditions, are more resistant to the disruptive effects of young stars, i.e., can sustain a higher star-forming efficiency. Clark et al (2005) investigated the formation of star clusters in unbound giant molecular clouds (GMCs), where the cloud tend to form a series of star clusters and disperse quickly, within a rapid star formation process (∼10Myr). They also proposed that the clusters that form in the unbound GMCs may be progenitors of the OB associations.…”

Section: Possible Formation Scenarios Of the Yscs In Arp 24mentioning

confidence: 99%

Multiwavelength Study of Young Massive Star Clusters in the Interacting Galaxy Arp 24

Cao

2007

Astron J

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We made a multi-wavelength study of young massive star clusters (YSCs) in the interacting galaxy ARP 24, using the optical and ultraviolet images from Hubble Space Telescope (HST), Sloan Digital Sky Survey, and Galaxy Evolution Explorer; the mid-infrared images from Spitzer Space Telescope; and the narrowband Hα image and optical spectra from the NAOC 2.16 m telescope. Based on the HST images, we found that the brightest infrared knot in ARP 24 is associated with a complex of five young massive star clusters, within a region of ∼ 0.95 ′′ radius (127pc) in size. The ages and masses of the star clusters in this complex and other regions were estimated using HST broadband photometries and the Starburst99 synthesis models. The star clusters in this complex are very young (within ages of ∼ 3-5 Myr) and massive (masses of ∼10 5 M ⊙ ). The ionization parameter and metallicity of the complex were estimated using the emission line ratios, and the star formation rates were calculated using monochromatic 24µm, FUV, and Hα line luminosities. We speculate that ARP 24 may formed by a retrograde fly-by encounter indicated by its one-armed appearance and fanlike structure, and the formation of the YSCs in this galaxy is triggered by the interaction. The clusters in the YSC complex may formed in a single giant molecular cloud simultaneously. From the ultraviolet to mid-infrared spectral energy distributions, we found that the region of the YSC complex is relatively bluer in optical and has higher 24µm dust emission relative to the starlight and 8µm emission. This warm infrared color may due to strong UV radiation field or other mechanisms (e.g., shocks) within this region which may destroy the Polycyclic Aromatic Hydrocarbons and enhance the small grain emission at 24µm.

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“…After 5-10 Myr, 90% of the embedded clusters do not evolve to become bound open clusters, like the Pleiades, but rather disperse into the field (Lada & Lada 2003). This happens because the cluster forms in an unbound state or becomes unbound during a ∼10 Myr timeframe from the dynamical evolution of stars within the cluster (Clark et al 2005;Carpenter 2000;Adams & Myers 2001;Lada & Lada 2003), because of the expulsion of residual gas left over from star formation (e.g., Hills 1980;Lada et al 1984;, because of the tidal heating from nearby giant molecular clouds (Elmegreenalso affects planet formation because of frequent stellar encounters in crowded regions (e.g., Adams & Laughlin 2001;Parker & Quanz 2012), stellar multiplicity through dynamical interactions and the orbital separation distribution of binary systems , and mass segregation towards the cluster core (Parker & Reggiani 2013). A detailed study of dynamical states of clusters in a variety of environments is needed in order to understand the evolution of stellar clusters and the relative importance of these processes.…”

Section: Introductionmentioning

confidence: 99%

TheGaia-ESO Survey: Dynamical analysis of the L1688 region in Ophiuchus

Rigliaco

Wilking

Meyer

et al. 2016

A&A

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The Gaia ESO Public Spectroscopic Survey (GES) is providing the astronomical community with high-precision measurements of many stellar parameters including radial velocities (RVs) of stars belonging to several young clusters and star-forming regions. One of the main goals of the young cluster observations is to study their dynamical evolution and provide insight into their future, revealing whether they will eventually disperse to populate the field rather than evolve into bound open clusters. In this paper we report the analysis of the dynamical state of L1688 in the ρ Ophiuchi molecular cloud using the dataset provided by the GES consortium. We performed the membership selection of the more than 300 objects observed. Using the presence of the lithium absorption and the location in the Hertzspung-Russell diagram, we identify 45 already known members and two new association members. We provide accurate RVs for all 47 confirmed members. A dynamical analysis, after accounting for unresolved binaries and errors, shows that the stellar surface population of L1688 has a velocity dispersion σ ∼ 1.14 ± 0.35 km s −1 that is consistent with being in virial equilibrium and is bound with a ∼80% probability. We also find a velocity gradient in the stellar surface population of ∼1.0 km s −1 pc −1 in the northwest-southeast direction, which is consistent with that found for the pre-stellar dense cores, and we discuss the possibility of sequential and triggered star formation in L1688.

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Star formation in unbound giant molecular clouds: the origin of OB associations?

Cited by 113 publications

References 62 publications

SHORT GMC LIFETIMES: AN OBSERVATIONAL ESTIMATE WITH THE PdBI ARCSECOND WHIRLPOOL SURVEY (PAWS)

SHORT GMC LIFETIMES: AN OBSERVATIONAL ESTIMATE WITH THE PdBI ARCSECOND WHIRLPOOL SURVEY (PAWS)

Multiwavelength Study of Young Massive Star Clusters in the Interacting Galaxy Arp 24

TheGaia-ESO Survey: Dynamical analysis of the L1688 region in Ophiuchus

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