Molecular clouds and supernova remnants in the outer galaxy

Huang, Y. L.; Thaddeus, P.

doi:10.1086/164649

Cited by 75 publications

(73 citation statements)

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“…In conjunction with radio continuum, infrared, and optical observations of H II regions, OB associations, and other Population I objects, they have demonstrated that virtually all star formation occurs in molecular clouds, and highresolution CO observations of dense cloud cores and molecular outÑows have contributed greatly to our under- Dame et al 1987 ;(2) Bitran et al 1997 ;(3) Ungerechts et al 2000 ;(8) Huang & Thaddeus 1986 ;(9) Heithausen et al 1993 ; present work (778 additional scans in Polaris, 1738 in Camelopardalis) ; (10) S. T. Megeath, T. M. Dame, & P. Thaddeus, 2001, in preparation ; (11) Stacy & Thaddeus 1991 ;(12) Lang et al 2000 ;(13) Oliver et al 1996 ;(14) B. A.Wilson 2001b, in preparation ;(15) May et al, 1993 ;(16) J. May, D. C. Murphy, M. Sahu, H. Alvarez, & L. Bronfman, 2001, in preparation ;(17) Grabelsky et al 1987 ;(18) Boulanger et al 1998 ;(19) Nyman, Bronfman, & Thaddeus 1989 ;(20) Bronfman et al 1989 ;(21) de Geus, Bronfman, & Thaddeus 1990. standing of how stars form.…”

Section: Introductionmentioning

confidence: 95%

The Milky Way in Molecular Clouds: A New Complete CO Survey

Dame

Hartmann

Thaddeus

2001

ApJ

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2,146

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2,713

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New large-scale CO surveys of the Ðrst and second Galactic quadrants and the nearby molecular cloud complexes in Orion and Taurus, obtained with the CfA 1.2 m telescope, have been combined with 31 other surveys obtained over the past two decades with that instrument and a similar telescope on Cerro Tololo in Chile, to produce a new composite CO survey of the entire Milky Way. The survey consists of 488,000 spectra that Nyquist or beamwidth sample the entire Galactic plane over a (1 8 ¡) strip 4¡È10¡ wide in latitude, and beamwidth or sample nearly all large local clouds at higher lati-1 4 ¡ tudes. Compared with the previous composite CO survey of Dame et al. (1987), the new survey has 16 times more spectra, up to 3.4 times higher angular resolution, and up to 10 times higher sensitivity per unit solid angle. Each of the component surveys was integrated individually using clipping or moment masking to produce composite spatial and longitude-velocity maps of the Galaxy that display nearly all of the statistically signiÐcant emission in each survey but little noise.The composite maps provide detailed information on individual molecular clouds, suggest relationships between clouds and regions widely separated on the sky, and clearly display the main structural features of the molecular Galaxy. In addition, since the gas, dust, and Population I objects associated with molecular clouds contribute to the Galactic emission in every major wavelength band, the precise kinematic information provided by the present survey will form the foundation for many large-scale Galactic studies.A map of molecular column density predicted from complete and unbiased far-infrared and 21 cm surveys of the Galaxy was used both to determine the completeness of the present survey and to extrapolate it to the entire sky at o b o \ 32¡. The close agreement of the observed and predicted maps implies that only D2% of the total CO emission at o b o \ 32¡ lies outside our current sampling, mainly in the regions of Chamaeleon and the Gum Nebula. Taking into account this small amount of unobserved emission, the mean molecular column density decreases from D3 ] 1020 cm~2 at o b o \ 5¡ to D0.1 ] 1020 cm~2 at o b o \ 30¡ ; this drop is D6 times steeper than would be expected from a planeparallel layer, but is consistent with recent measurements of the mean molecular column density at higher latitudes.The ratio of the predicted molecular column density map to the observed CO intensity map provides a calibration of the mass conversion factor Out of the Galactic plane, X shows little systematic variation with latitude from a mean value of (1.8^0.3) ] 1020 cm~2 K~1 km~1 s. Given the large sky area and large quantity of CO data analyzed, we conclude that this is the most reliable measurement to date of the mean X value in the solar neighborhood.

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Section: Introductionmentioning

confidence: 95%

The Milky Way in Molecular Clouds: A New Complete CO Survey

Dame

Hartmann

Thaddeus

2001

ApJ

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2,146

178

2,713

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“…A large region encompassing Sh 2-217, Sh 2-219, and the supernova remnant HB9 was mapped with an 8. 7 beam by Huang & Thaddeus (1986), who found a total mass for the complex (several degrees in size) of 3.0 × 10 5 M (scaled to a distance of 4.2 kpc).…”

Section: Presentation Of Sh 2-217mentioning

confidence: 99%

Triggered star formation at the borders of the H ii region Sh 2-217

Brand

Massi

Zavagno

et al. 2011

A&A

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Context. This paper is part of our ongoing study of star formation at the borders of Galactic H ii regions. In this paper, we report our observations and analysis of Sharpless 217 (Sh 2-217). Aims. We study the stars and gas in and around H ii regions to see if the various physical parameters derived from the data (such as column densities, masses, sizes, and timescales) are consistent with the predictions of a simple model of the collect-and-collapse mechanism. This should indicate whether stars forming in molecular gas at the borders of the H ii regions could have been triggered by the expansion of the ionized gas. Methods. We observed the emission of various molecules and transitions towards Sh 2-217, and obtained both near-infrared photometry in the H and K bands, and near-infrared images in [Fe ii] and H 2 narrow-band filters of the stars in a molecular condensation at the edge of the H ii region, where an UC H ii region is also located. For the atomic and ionized hydrogen gas, we used literature data. Results. Several molecular condensations are found on the borders of Sh 2-217 and both behind and in front of the ionized emission. We find signs of star formation (an UC H ii region, outflows, and water masers). The masses of the larger molecular condensations, derived from 13 CO-data, are > ∼ 330−1100 M , while smaller clumps or cores within them have up to several tens of solar masses. The morphology of the atomic and molecular gas associated with Sh 2-217, especially the condensations of molecular gas on its border, and the presence of star forming activity within them, is strongly indicative of it being the result of star formation triggered by the expansion of the ionized region, following the collect-and-collapse scenario. Application of a simple model illustrates that the present radii of both Sh 2-217 and the UC H ii region, the masses of the condensations, and the timescales needed to sweep up these amounts of gas and allow massive stars to form in them, are consistent with the model predictions. Conclusions. We show that it is highly plausible that the expansion of Sh 2-217 has swept-up the ambient interstellar medium, and that it has taken about 4 Myr to reach its present radius. About 1 Myr ago, the most massive gas condensation became unstable and produced a cluster of stars. The most massive of these stars gave rise to the UC H ii region, which took about 0.5 Myr to reach its present size.

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“…Ratios are ≥ 3 in IC443, and higher than ∼ 1 in W44, which also shows broadened line profiles indicating disrupted molecular material (Figure 1, right). Huang and Thaddeus (1986) carried out a search for possible SNR/MC associations in the outer Galaxy, within a limited region of the northern hemisphere, finding about 13 possible associations based on spatial coincidences (out of 26 SNRs investigated). More recently, Chen et al (2013) reported CO observations towards a number of SNRs possibly interacting with MCs.…”

Section: Molecular Emissionmentioning

confidence: 99%

Supernova Remnants Interacting with Molecular Clouds: X-Ray and Gamma-Ray Signatures

et al. 2014

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The giant molecular clouds (MCs) found in the Milky Way and similar galaxies play a crucial role in the evolution of these systems. The supernova explosions that mark the death of massive stars in these regions often lead to interactions between the supernova remnants (SNRs) and the clouds. These interactions have a profound effect on our understanding of SNRs. Shocks in SNRs should be capable of accelerating particles to cosmic ray (CR) energies with efficiencies high enough to power Galactic CRs. X-ray and γ-ray studies have established the presence of relativistic electrons and protons in some SNRs and provided strong evidence for diffusive shock acceleration as the primary acceleration mechanism, including strongly amplified magnetic fields, temperature and ionization effects on the shock-heated plasmas, and modifications to the dynamical evolution of some systems. Because protons dominate the overall energetics of the CRs, it is crucial to understand this hadronic component even though electrons are much more efficient radiators and it can be difficult to identify the hadronic component. However, near MCs the densities are sufficiently high to allow the γ-ray emission to be dominated by protons. Thus, these interaction sites provide some of our best opportunities to constrain the overall energetics of these particle accelerators. Here we summarize some key properties of interactions between SNRs and MCs, with an emphasis on recent X-ray and γ-ray studies that are providing important constraints on our understanding of cosmic rays in our Galaxy.

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Molecular clouds and supernova remnants in the outer galaxy

Cited by 75 publications

References 0 publications

The Milky Way in Molecular Clouds: A New Complete CO Survey

The Milky Way in Molecular Clouds: A New Complete CO Survey

Triggered star formation at the borders of the H ii region Sh 2-217

Supernova Remnants Interacting with Molecular Clouds: X-Ray and Gamma-Ray Signatures

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