Filamentary structure in the Orion molecular cloud

Bally, John; Stark, A. A.; Wilson, R. W.; Langer, W. D.

doi:10.1086/184817

Cited by 484 publications

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“…120 to the south and NGC 1977 to the north. The Orion A molecular cloud has been mapped in 12CO J \ 1 ] 0 (Kutner et al 1977 ;Maddalena et al 1986), 12CO J \ 2 ] 1 (Sakamoto et al 1994), 13CO (Bally et al 1987 ;Castets et al 1990), CS J \ 1 ] 0 (Tatematsu et al 1993), C18O (Dutrey et al 1993), and (Batrla et al 1983 ;Cesaroni & Wilson NH 3 1994). Bally et al (1987) discovered that the Orion A cloud narrows into an "" integral-shaped ÏÏ Ðlament 30@ south of OMC-1 and continuing toward OMC-2 and OMC-3 to the north.…”

Section: Observationsmentioning

confidence: 99%

A Multiwavelength Study of Outflows in OMC-2/3

Billawala

Smith

et al. 2000

The Astronomical Journal

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We present new v \ 1È0 S(1) 12CO J \ 2 ] 1, and 12CO J \ 3 ] 2 observations of the star-H 2 , forming clouds OMC-2 and OMC-3, one of the densest known groupings of outÑows from low-mass young stellar objects (YSOs) in the sky. High-velocity 12CO J \ 2 ] 1 gas in this region suggests that previously discoveredÑows are driving and entraining molecular outÑows. However, the large H 2 number of sources and Ñows within the narrow molecular Ðlament means it is difficult to make a Ðrm association of molecular outÑow gas with Ñows, except for in the case of the bipolar east-west H H 2 Ñow. A number of Herbig-Haro (HH) objects, including ones far to the west and east of the main ridge, are identiÐed with knots. High-resolution spectroscopy in the v \ 1È0 S(1) line of 10 knots shows H 2 H 2 line proÐles consistent with dual forward and reverse shocks. C-shock modeling suggest that asymmetries seen in suspected bow shocks could be evidence of varying magnetic Ðeld orientations throughout the cloud. One of the bow shocks in the H Ñow, YBD-5, can be successfully modeled by a 100 km s~1 C-shock propagating into a magnetized, 106 cm~3 medium, although the observations and limitations within the computer code itself do not entirely rule out J-shocks. Mass spectra of the H Ñow are broken power laws, which might be evidence for a jet that has two entrainment mechanisms for accelerating ambient molecular gas into the outÑow. The luminosity in this Ñow is many times smaller than H 2 the CO mechanical luminosity, but this fact cannot rule out the possibility that a narrow highly collimated jet drives the molecular outÑow, owing to uncertainties in extinction, outÑow dynamic times, cooling contributions from other lines, and the wind model used. OutÑows from OMC-2/3 are likely to contribute to the turbulent pumping of gas within the molecular ridge north of the Orion Nebula. Highvelocity gas clumps north of the sources investigated here may represent evidence of additional undiscovered outÑows from young stars.

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Section: Observationsmentioning

confidence: 99%

A Multiwavelength Study of Outflows in OMC-2/3

Billawala

Smith

et al. 2000

The Astronomical Journal

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“…Clearly, the gas is organized in filamentary and clumpy structures that allow the penetration of FUV photons to very large distances from the illuminating stars. On a parsec scale, the Orion molecular cloud consists of a highly nonuniform complex of filaments and clumps (Bally et al, 1987). Second, maps in many molecular species (i.e., 13 CO, C 18 O, CS, NH 3 , HCO ϩ , HCN, H 2 , and PAHs) show direct evidence for clumping 13 in PDRs with a surface filling factor of Ӎ0.1.…”

Section: Fig 22 the Luminosity In The [Cii] Andmentioning

confidence: 96%

“…Therefore even a fairly attenuated far-ultraviolet field can appreciably photodissociate CO and produce C and C ϩ deep into the cloud. Photodissociation of CO has been studied in detail by Bally and Langer (1982), Glassgold et al (1985), , Viala et al (1988), and Lee et al (1996). High-resolution laboratory studies show that CO photodissociation occurs through discrete absorption into predissociating bound states, implying that CO is also affected by self-shielding (Eidelsberg et al, 1992).…”

Section: Pdr Chemical Network a Oxygen And Carbonmentioning

confidence: 99%

“…CO shielding functions have been tabulated by van and by Lee et al (1996). For low ratios of G 0 /n, the effects of CO self-shielding can lead to isotopic fractionation effects at the borders of clouds, where the rarer CO isotopes are preferentially photodissociated (Bally and Langer, 1982;Chu and Watson, 1983;Glassgold et al, 1985;Viala et al, 1988;Gredel et al, 1994;Warin et al, 1996;Keene, Schilke, et al 1998). However, the location of the C ϩ /C/CO transition in bright PDRs is largely governed by dust extinction.…”

Section: Pdr Chemical Network a Oxygen And Carbonmentioning

confidence: 99%

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Photodissociation regions in the interstellar medium of galaxies

Hollenbach

Tielens²

1999

Rev. Mod. Phys.

740

712

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The interstellar medium of galaxies is the reservoir out of which stars are born and into which stars inject newly created elements as they age. The physical properties of the interstellar medium are governed in part by the radiation emitted by these stars. Far-ultraviolet (6 eVϽh Ͻ13.6 eV) photons from massive stars dominate the heating and influence the chemistry of the neutral atomic gas and much of the molecular gas in galaxies. Predominantly neutral regions of the interstellar medium in which the heating and chemistry are regulated by far ultraviolet photons are termed PhotoDissociation Regions (PDRs). These regions are the origin of most of the non-stellar infrared (IR) and the millimeter and submillimeter CO emission from galaxies. The importance of PDRs has become increasingly apparent with advances in IR and submillimeter astronomy. The IR emission from PDRs includes fine structure lines of C, C ϩ , and O; rovibrational lines of H 2 ; rotational lines of CO; broad mid-IR features of polycyclic aromatic hydrocarbons; and a luminous underlying IR continuum from interstellar dust. The transition of H to H 2 and C ϩ to CO occurs within PDRs. Comparison of observations with theoretical models of PDRs enables one to determine the density and temperature structure, the elemental abundances, the level of ionization, and the radiation field. PDR models have been applied to interstellar clouds near massive stars, planetary nebulae, red giant outflows, photoevaporating planetary disks around newly formed stars, diffuse clouds, the neutral intercloud medium, and molecular clouds in the interstellar radiation field-in summary, much of the interstellar medium in galaxies. Theoretical PDR models explain the observed correlations of the [CII] 158 m with the CO Jϭ1 -0 emission, the CO Jϭ1 -0 luminosity with the interstellar molecular mass, and the [CII] 158 m plus [OI] 63 m luminosity with the IR continuum luminosity. On a more global scale, PDR models predict the existence of two stable neutral phases of the interstellar medium, elucidate the formation and destruction of star-forming molecular clouds, and suggest radiation-induced feedback mechanisms that may regulate star formation rates and the column density of gas through giant molecular clouds. [S0034-6861(99)01001-6] CONTENTS

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“…A new CO survey of this region by the northern telescope (Table 1), just completed during the 1999È2000 observing season, improves on the coverage and sensitivity of the previous survey by Maddalena et al (1986). The entire Orion A cloud has been mapped in 13CO with both the Bell Laboratories 7 m telescope (Bally et al 1987) and the Nagoya 4 m telescopes (Nagahama et al 1998), and both the A and B clouds have been surveyed in the 2È1 transition of the normal isotopic species with the Tokyo-NRO 60 cm telescope (Sakamoto et al 1994). The Mon R2 cloud has been surveyed in the normal 1È0 CO line with the FCRAO 14 m telescope (Xie & Goldsmith 1994).…”

Section: Orion Regionmentioning

confidence: 99%

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

Dame

Hartmann

Thaddeus

2001

ApJ

2,121

178

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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Filamentary structure in the Orion molecular cloud

Cited by 484 publications

References 0 publications

A Multiwavelength Study of Outflows in OMC-2/3

A Multiwavelength Study of Outflows in OMC-2/3

Photodissociation regions in the interstellar medium of galaxies

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

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