A Study of Dense Molecular Gas and Star Formation toward the Vela Molecular Ridge with NANTEN

Abstract New observations of the J=1−0 12CO, 13CO, and C18O emission lines have been extensively made toward the Vela Molecular Ridge (VMR) with NANTEN. The most prominent cloud is the giant molecular cloud, corresponding to the VMR-C region (Vela C). The present C18O distribution has been identified as 29 clouds. Among them, the most massive one is included in Vela C, having a total mass of ∼ 4.4 × 104M⊙. The rest of them are smaller C18O clouds of 102-103M⊙. Star formation in the region is almost exclusively occurring in the C18O clouds. The luminosities of the associated protostellar IRAS sources range from 5 L⊙ to 1.1 × 104L⊙, and the luminosity distribution is found to be well represented by the relation dNstar/dLIR ∞ L-1.65±0.14IR. We find that the ratios of the total luminosity of the sources associated with given C18O clouds to the cloud masses are significantly enhanced for those clouds associated with H II regions by an order of magnitude. This is interpreted as meaning that the formation of massive stars is enhanced due to the effects of H II regions, as is consistent with the preceding work. We have also newly found molecular outflow toward IRAS 08588–4347 as well as five possible candidates for outflows.

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Cloud–cloud collision in the DR 21 cloud as a trigger of massive star formation

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psz041 ◽

2019 ◽

Vol 71 (Supplement_1) ◽

Cited By ~ 11

Author(s):

Kazuhito Dobashi ◽

Tomomi Shimoikura ◽

Shou Katakura ◽

Fumitaka Nakamura ◽

Yoshito Shimajiri

Keyword(s):

Star Formation ◽

Numerical Simulations ◽

Massive Star ◽

Massive Stars ◽

The Other ◽

Emission Lines ◽

Molecular Gas ◽

Massive Star Formation ◽

The North ◽

Molecular Lines

AbstractWe report on a possible cloud–cloud collision in the DR 21 region, which we found through molecular observations with the Nobeyama 45 m telescope. We mapped an area of ∼8′ × 12′ around the region with 20 molecular lines including the 12CO(J = 1–0) and 13CO(J = 1–0) emission lines, and 16 of them were significantly detected. Based on the 12CO and 13CO data, we found five distinct velocity components in the observed region, and we call the molecular gas associated with these components “−42,”“−22,” “−3,” “9,” and “17” km s−1 clouds, after their typical radial velocities. The −3 km s−1 cloud is the main filamentary cloud ($\sim 31000\, M_{\odot }$) associated with young massive stars such as DR21 and DR21(OH), and the 9 km s−1 cloud is a smaller cloud ($\sim 3400\, M_{\odot }$) which may be an extension of the W75 region in the north. The other clouds are much smaller. We found a clear anticorrelation in the distributions of the −3 and 9 km s−1 clouds, and detected faint 12CO emission which had intermediate velocities bridging the two clouds at their intersection. These facts strongly indicate that the two clouds are colliding against each other. In addition, we found that DR21 and DR21(OH) are located in the periphery of the densest part of the 9 km s−1 cloud, which is consistent with results of recent numerical simulations of cloud–cloud collisions. We therefore suggest that the −3 and 9 km s−1 clouds are colliding, and that the collision induced the massive star formation in the DR21 cloud. The interaction of the −3 and 9 km s−1 clouds was previously suggested by Dickel, Dickel, and Wilson (1978, ApJ, 223, 840), and our results strongly support their hypothesis of the interaction.

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HII regions and star formation in the Magellanic Clouds

Symposium - International Astronomical Union ◽

10.1017/s0074180900200211 ◽

1991 ◽

Vol 148 ◽

pp. 139-144 ◽

Cited By ~ 2

Author(s):

Robert C. Kennicutt

Keyword(s):

Star Formation ◽

Interstellar Medium ◽

Massive Star ◽

Massive Stars ◽

Hii Regions ◽

Magellanic Clouds ◽

H Ii Regions ◽

Distant Galaxies ◽

Close Range ◽

Mass Functions

The H II regions in the Magellanic Clouds provide an opportunity to characterize the global star formation properties of a galaxy at close range. They also provide a unique laboratory for testing empirical tracers of the massive star formation rates and initial mass functions in more distant galaxies, and for studying the dynamical interactions between massive stars and the interstellar medium. This paper discusses several current studies in these areas.

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

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3525 ◽

2019 ◽

Vol 493 (2) ◽

pp. 2872-2909 ◽

Cited By ~ 44

Author(s):

Mélanie Chevance ◽

J M Diederik Kruijssen ◽

Alexander P S Hygate ◽

Andreas Schruba ◽

Steven N Longmore ◽

...

Keyword(s):

Star Formation ◽

Flux Ratio ◽

Molecular Gas ◽

H Ii Regions ◽

Dynamical Processes ◽

Nearby Star ◽

Star Forming ◽

Spatially Resolved ◽

Stellar Feedback ◽

Disc Galaxies

ABSTRACT It remains a major challenge to derive a theory of cloud-scale ($\lesssim100$ 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-H α 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 $10\!-\!30\,{\rm Myr}$, and exhibit environmental variation, between and within galaxies. At kpc-scale molecular gas surface densities $\Sigma _{\rm H_2}\ge 8\,\rm {M_\odot}\,{{\rm pc}}^{-2}$, the GMC lifetime correlates with time-scales for galactic dynamical processes, whereas at $\Sigma _{\rm H_2}\le 8\,\rm {M_\odot}\,{{\rm pc}}^{-2}$ GMCs decouple from galactic dynamics and live for an internal dynamical time-scale. After a long inert phase without massive star formation traced by H α (75–90 per cent of the cloud lifetime), GMCs disperse within just $1\!-\!5\,{\rm Myr}$ 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 H ii regions are the fundamental units undergoing these lifecycles, with mean separations of $100\!-\!300\,{{\rm pc}}$ in star-forming discs. Future work should characterize the multiscale physics and mass flows driving these lifecycles.

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Stellar feedback from a massive Super Star Cluster in the Antennae merger

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315008984 ◽

2015 ◽

Vol 12 (S316) ◽

pp. 190-195 ◽

Cited By ~ 1

Author(s):

Cinthya N. Herrera ◽

Francois Boulanger

Keyword(s):

Star Formation ◽

Radiation Pressure ◽

Angular Resolution ◽

Massive Stars ◽

Star Cluster ◽

Molecular Gas ◽

Structure And Dynamics ◽

Stellar Feedback ◽

Formation Efficiency ◽

Co Gas

AbstractStellar feedback from massive stars can unbind and disperse large amount of molecular gas, affecting the star formation efficiency. Based on ALMA and VLT observations in the Antennae galaxies we study a massive (~ 107 M⊙) and young (~ 3 Myr) SSC, B1, associated with compact molecular and ionized emission, which suggests that it is embedded in its parent cloud. However, we found contradictories and puzzling results on the structure and dynamics of the matter around the cluster, indicating that SSC B1 is not embedded in its parent cloud after all. We propose that radiation pressure was highly enhanced at the early stages of the SSC formation, disrupting the parent cloud in < 3 Myr. We show evidences of outflowing gas from the parent cloud in the more extended CO gas. Higher angular resolution observations are needed to validate this interpretation and to understand the origin and fate of the component seen to be associated with SSC B1.

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Molecular Clouds and Star Formation in the Southern H II Regions

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/51.6.791 ◽

1999 ◽

Vol 51 (6) ◽

pp. 791-818 ◽

Cited By ~ 53

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.

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The growth of H ii regions around massive stars: the role of metallicity and dust

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3992 ◽

2020 ◽

Author(s):

Ahmad A Ali

Keyword(s):

Star Formation ◽

Radiation Pressure ◽

Massive Stars ◽

Particle Method ◽

Diffuse Radiation ◽

Uv Absorption ◽

Expansion Velocity ◽

H Ii Regions ◽

Metal Line ◽

Neutral Gas

Abstract Gas metallicity Z and the related dust-to-gas ratio fd can influence the growth of H ii regions via metal line cooling and UV absorption. We model these effects in star-forming regions containing massive stars. We compute stellar feedback from photoionization and radiation pressure (RP) using Monte Carlo radiative transfer coupled with hydrodynamics, including stellar and diffuse radiation fields. We follow a 105 M⊙ turbulent cloud with Z/Z⊙ = 2, 1, 0.5, 0.1 and fd = 0.01Z/Z⊙ with a cluster-sink particle method for star formation. The models evolve for at least 1.5Myr under feedback. Lower Z results in higher temperatures and therefore larger H ii regions. For Z ≥ Z⊙, radiation pressure Prad can dominate locally over the gas pressure Pgas in the inner half-parsec around sink particles. Globally, the ratio of Prad/Pgas is around 1 (2Z⊙), 0.3 (Z⊙), 0.1 (0.5Z⊙), and 0.03 (0.1Z⊙). In the solar model, excluding RP results in an ionized volume several times smaller than the fiducial model with both mechanisms. Excluding RP and UV attenuation by dust results in a larger ionized volume than the fiducial case. That is, UV absorption hinders growth more than RP helps it. The radial expansion velocity of ionized gas reaches +15km s−1 outwards, while neutral gas has inward velocities for most of the runtime, except for 0.1Z⊙ which exceeds +4km s−1. Z and fd do not significantly alter the star formation efficiency, rate, or cluster half-mass radius, with the exception of 0.1Z⊙ due to the earlier expulsion of neutral gas.

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On the turbulence driving mode of expanding H ii regions

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa580 ◽

2020 ◽

Vol 493 (4) ◽

pp. 4643-4656 ◽

Cited By ~ 5

Author(s):

Shyam H Menon ◽

Christoph Federrath ◽

Rolf Kuiper

Keyword(s):

Star Formation ◽

Ionizing Radiation ◽

Massive Stars ◽

Parameter Analysis ◽

Ionization Front ◽

H Ii Regions ◽

Driving Mode ◽

Neutral Gas ◽

Natural Mixture ◽

Hydrodynamical Simulations

Abstract We investigate the turbulence driving mode of ionizing radiation from massive stars on the surrounding interstellar medium. We run hydrodynamical simulations of a turbulent cloud impinged by a plane-parallel ionization front. We find that the ionizing radiation forms pillars of neutral gas reminiscent of those seen in observations. We quantify the driving mode of the turbulence in the neutral gas by calculating the driving parameter b, which is characterized by the relation $\sigma _s^2 = \ln ({1+b^2\mathcal {M}^2})$ between the variance of the logarithmic density contrast $\sigma _s^2$ [where s = ln (ρ/ρ0) with the gas density ρ and its average ρ0], and the turbulent Mach number $\mathcal {M}$. Previous works have shown that b ∼ 1/3 indicates solenoidal (divergence-free) driving and b ∼ 1 indicates compressive (curl-free) driving, with b ∼ 1 producing up to ten times higher star formation rates than b ∼ 1/3. The time variation of b in our study allows us to infer that ionizing radiation is inherently a compressive turbulence driving source, with a time-averaged b ∼ 0.76 ± 0.08. We also investigate the value of b of the pillars, where star formation is expected to occur, and find that the pillars are characterized by a natural mixture of both solenoidal and compressive turbulent modes (b ∼ 0.4) when they form, and later evolve into a more compressive turbulent state with b ∼ 0.5–0.6. A virial parameter analysis of the pillar regions supports this conclusion. This indicates that ionizing radiation from massive stars may be able to trigger star formation by producing predominately compressive turbulent gas in the pillars.

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Gas and Dust in M33

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311022472 ◽

2010 ◽

Vol 6 (S277) ◽

pp. 63-66 ◽

Cited By ~ 1

Author(s):

J. Braine ◽

P. Gratier ◽

C. Kramer ◽

B. Mookerjea ◽

M. Xilouris ◽

...

Keyword(s):

Star Formation ◽

Molecular Clouds ◽

Luminosity Function ◽

Massive Stars ◽

Dust Emission ◽

Emission Lines ◽

Neutral Gas ◽

Dust Temperature ◽

Near Future ◽

Co Emission

AbstractWe present results from the Herschel and IRAM projects to map M33 in the dust continuum and main emission lines, particularly C[II] and CO. The temperature of the cool dust decreases with distance from the center of M33 from ~25K to ~13K. The CO emission generally follows the dust temperature and the overall dust emission. However, about 1/6 of the molecular clouds are not associated with massive stars, such that about 1/6th the lifetime of an entity identifiable as a molecular cloud is in a pre-star formation state. These clouds are less CO-bright than those with massive stars. The largest sample of molecular clouds currently available for an external galaxy shows that the cloud CO luminosity function, usually viewed as the cloud H2 mass, steepens with radius such that smaller clouds are more numerous in the outer parts. The observations of the C[II] line with Herschel indicate that the C[II] emission traces on-going star formation rather than the neutral gas. This identification will be tested via velocity-resolved Herschel/HIFI C[II] spectra in the near future.

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Photoionizing feedback in spiral arm molecular clouds

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1293 ◽

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.

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AGN Feedback Driven Molecular Outflow in NGC 1266

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312019485 ◽

2012 ◽

Vol 8 (S290) ◽

pp. 175-176

Author(s):

K. Alatalo ◽

K. E. Nyland ◽

G. Graves ◽

S. Deustua ◽

J. Wrobel ◽

...

Keyword(s):

Star Formation ◽

Brightness Temperature ◽

Significant Role ◽

Molecular Gas ◽

High Brightness ◽

Continuum Source ◽

Low Level ◽

Molecular Outflow ◽

Field Galaxy ◽

Red Sequence

AbstractNGC 1266 is a nearby field galaxy observed as part of the ATLAS3D survey (Cappellari et al. 2011). NGC 1266 has been shown to host a compact (< 200 pc) molecular disk and a mass-loaded molecular outflow driven by the AGN (Alatalo et al. 2011). Very Long Basline Array (VLBA) observations at 1.65 GHz revealed a compact (diameter < 1.2 pc), high brightness temperature continuum source most consistent with a low-level AGN origin. The VLBA continuum source is positioned at the center of the molecular disk and may be responsible for the expulsion of molecular gas in NGC 1266. Thus, the candidate AGN-driven molecular outflow in NGC 1266 supports the picture in which AGNs do play a significant role in the quenching of star formation and ultimately the evolution of the red sequence of galaxies.

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