From molecules to young stellar clusters: the star formation cycle across the disk of M 33

Corbelli, E.; Braine, J.; Bandiera, R.; Brouillet, N.; Combes, F.; Druard, C.; Gratier, P.; Mata, J.; Schuster, K.; Xilouris, E. M.; Palla, F.

doi:10.1051/0004-6361/201630034

Cited by 103 publications

(231 citation statements)

References 41 publications

(90 reference statements)

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“…If these regional variations arise from individual GMCs, the H I-CO line widths may indicate changes in the local environment or the evolutionary state of the cloud. If the latter is true, the lack of a radial trend is consistent with the radial distribution of cloud evolution types from Corbelli et al (2017), which are well-mixed in the inner 6 kpc (see also Gratier et al 2012).…”

Section: Regional Variations In the H I-co Line Widthssupporting

confidence: 65%

Relationship between the line width of the atomic and molecular ISM in M33

Koch

Rosolowsky

Schruba

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We investigate how the spectral properties of atomic (H I) and molecular (H 2 ) gas, traced by CO(2-1), are related in M33 on 80 pc scales. We find the H I and CO(2-1) velocity at peak intensity to be highly correlated, consistent with previous studies. By stacking spectra aligned to the velocity of H I peak intensity, we find that the CO line width (σ HWHM = 4.6 ± 0.9 km s −1 ; σ HWHM is the effective Gaussian width) is consistently smaller than the H I line width (σ HWHM = 6.6 ± 0.1 km s −1 ), with a ratio of ∼0.7, in agreement with Druard et al. (2014). The ratio of the line widths remains less than unity when the data are smoothed to a coarser spatial resolution. In other nearby galaxies, this line width ratio is close to unity which has been used as evidence for a thick, diffuse molecular disk that is distinct from the thin molecular disk dominated by molecular clouds. The smaller line width ratio found here suggests that M33 has a marginal thick molecular disk. From modelling individual lines-ofsight, we recover a strong correlation between H I and CO line widths when only the H I located closest to the CO component is considered. The median line width ratio of the lineof-sight line widths is 0.56 ± 0.01. There is substantial scatter in the H I-CO(2-1) line width relation, larger than the uncertainties, that results from regional variations on < 500 pc scales, and there is no significant trend in the line widths, or their ratios, with galactocentric radius. These regional line width variations may be a useful probe of changes in the local cloud environment or the evolutionary state of molecular clouds.

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Section: Regional Variations In the H I-co Line Widthssupporting

confidence: 65%

Relationship between the line width of the atomic and molecular ISM in M33

Koch

Rosolowsky

Schruba

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…Other studies, most of which rely on different methodological approaches, have also found evidence that GMCs are dispersed within a few Myr after the onset of massive star formation (e.g. Kawamura et al 2009;Whitmore et al 2014;Hollyhead et al 2015;Corbelli et al 2017;Grasha et al 2019;Hannon et al 2019;Hygate et al 2019a). A detailed comparison between the measured feedback time-scales and theoretical expectations for different feedback mechanisms is investigated in more detail in a companion paper (M. Chevance et al in prep.).…”

Section: Feedback Time-scalementioning

confidence: 96%

The lifecycle of molecular clouds in nearby star-forming disc galaxies

Chevance

Kruijssen

Hygate

et al. 2019

Monthly Notices of the Royal Astronomical Society

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It remains a major challenge to derive a theory of cloud-scale ( 100 pc) star formation and feedback, describing how galaxies convert gas into stars as a function of the galactic environment. Progress has been hampered by a lack of robust empirical constraints on the giant molecular cloud (GMC) lifecycle. We address this problem by systematically applying a new statistical method for measuring the evolutionary timeline of the GMC lifecycle, star formation, and feedback to a sample of nine nearby disc galaxies, observed as part of the PHANGS-ALMA survey. We measure the spatially-resolved (∼ 100 pc) CO-to-Hα flux ratio and find a universal de-correlation between molecular gas and young stars on GMC scales, allowing us to quantify the underlying evolutionary timeline. GMC lifetimes are short, typically 10−30 Myr, and exhibit environmental variation, between and within galaxies. At kpc-scale molecular gas surface densities Σ H 2 8 M pc −2 , the GMC lifetime correlates with time-scales for galactic dynamical processes, whereas at Σ H 2 8 M pc −2 GMCs decouple from galactic dynamics and live for an internal dynamical time-scale. After a long inert phase without massive star formation traced by Hα (75−90 per cent of the cloud lifetime), GMCs disperse within just 1−5 Myr once massive stars emerge. The dispersal is most likely due to early stellar feedback, causing GMCs to achieve integrated star formation efficiencies of 4−10 per cent. These results show that galactic star formation is governed by cloud-scale, environmentally-dependent, dynamical processes driving rapid evolutionary cycling. GMCs and HII regions are the fundamental units undergoing these lifecycles, with mean separations of 100−300 pc in star-forming discs. Future work should characterise the multi-scale physics and mass flows driving these lifecycles.

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“…If Ω = 0.1 km s −1 pc −1 is an appropriate gradient, then the rotation period is T = 2π/Ω = 61 Myr. Even allowing for projection effects and the correction below, the rotation period is greater than typical GMC lifetimes of ∼ 15Myr (e.g., Corbelli et al 2017). Figure 4 shows the specific angular momenta of the clouds as a histogram.…”

Section: Rotational Versus Binding Energymentioning

confidence: 99%

Rotation of molecular clouds in M 51

Braine

Hughes

Rosolowsky

et al. 2019

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The grand-design spiral galaxy M 51 was observed at 40pc resolution in CO(1-0) by the PAWS project. A large number of molecular clouds were identified and we search for velocity gradients in two high signal-to-noise subsamples, containing 682 and 376 clouds. The velocity gradients are found to be systematically prograde oriented, as was previously found for the rather flocculent spiral M 33. This strongly supports the idea that the velocity gradients reflect cloud rotation, rather than more random dynamical forces, such as turbulence. Not only are the gradients prograde, but their ∂v ∂x and ∂v ∂y coefficients follow galactic shear in sign, although with a lower amplitude. No link is found between the orientation of the gradient and the orientation of the cloud. The values of the cloud angular momenta appear to be an extension of the values noted for galactic clouds despite the orders of magnitude difference in cloud mass. Roughly 30% of the clouds show retrograde velocity gradients. For a strictly rising rotation curve, as in M 51, gravitational contraction would be expected to yield strictly prograde rotators within an axisymmetric potential. In M 51, the fraction of retrograde rotators is found to be higher in the spiral arms than in the disk as a whole. Along the leading edge of the spiral arms, a majority of the clouds are retrograde rotators. While this work should be continued on other nearby galaxies, the M 33 and M 51 studies have shown that clouds rotate and that they rotate mostly prograde, although the amplitudes are not such that rotational energy is a significant support mechanism against gravitation. In this work, we show that retrograde rotation is linked to the presence of a spiral gravitational potential.

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From molecules to young stellar clusters: the star formation cycle across the disk of M 33

Cited by 103 publications

References 41 publications

Relationship between the line width of the atomic and molecular ISM in M33

Relationship between the line width of the atomic and molecular ISM in M33

The lifecycle of molecular clouds in nearby star-forming disc galaxies

Rotation of molecular clouds in M 51

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