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Images of an 8 square minute region around the Orion KL source have been made in the J=7-6 (806 GHz) and J=4-3 (461 GHz) lines of CO with angular resolutions of 13 and 18. These data were taken employing on-the-fly mapping and position switching techniques. Our J=7-6 data set is the largest image of Orion with the highest sensitivity and resolution obtained so far in this line. Most of the extended emission arises from a Photon Dominated Region (PDR), but 8% is associated with the Orion ridge. For the prominent Orion KL outflow, we produced ratios of the integrated intensities of our J=7-6 and 4-3 data to the J=2-1 line of CO. Large Velocity Gradient (LVG) models fit the outflow ratios better than PDR models. The LVG models give H_2 densities of ~10^5 per ccm. The CO outflow is probably heated by shocks. In the Orion S outflow, the CO line intensities are lower than for Orion KL. The 4-3/2-1 line ratio is 1.3 for the blue shifted wing and 0.8 for the red shifted wing. Emission in the jet feature extending 2 to the SW of Orion S was detected in the J=4-3 but not the J=7-6 line; the average 4-3/2-1 line ratio is ~1. The line ratios in the Orion S outflow and jet features are consistent with both PDR and LVG models. Comparisons of the intensities of the J=7-6 and J=4-3 lines from the Orion Bar with PDR models show that the ratios exceed predictions by a factor of 2. Either clumping or additional heating by mechanisms such as shocks, may be the cause of this discrepancy.
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We present observations towards one of the closest regions of high mass star formation, Orion BN/KL, performed at both low resolution mode (grating mode) and high resolution mode (Fabry-Perot) with the Long Wavelength Spectrometer on board the Infrared Space Observatory. We detected the CO rotational lines from Jup = 15 to Jup = 45. While the lines with Jup<= 32 are spectrally unresolved, the higher lying lines show a broadened profile. Finally, we detected two 13CO lines, namely at Jup = 18 and 24, from which we could derive the opacities of the relative 12CO lines. The LVG analysis of the observed line spectrum allows to distinguish three main physical components with different temperatures, densities and column densities: 1) lines with Jup< 20 originate mainly in the diffuse photodissociation region surrounding the source; 2) lines with Jup between 20 and 30 originate in the high velocity outflow (plateau) emanating from IrC2; 3) lines with Jup > 32 originate in the hot and dense gas of the shocked component of the outflow. We discuss how future observations with HIFI, onboard the Far Infrared Space Telescope (FIRST) will allow to spectrally and spatially disentangle the three components, and, consequently, characterise more precisely the Orion BN/KL star forming region.
12CO 1-0,2-1,4-3,7-6, and 13CO 1-0, 2-1, and 3-2 line was mapped with angular resolutions of 13 - 22 toward the nuclear region of starburst galaxy M82. The difference of lobe spacings in submillimeter (~15) and millimeter (~26) lines indicates the presence of a `low and a `high CO excitation component. An LVG excitation analysis of the submillimeter lines leads to inconsistencies, since area and volume filling factors are almost the same, resulting in cloud sizes along the lines-of-sight that match the entire size of the M82 starburst region. Nevertheless, LVG column densities agree with estimates derived from the dust emission in the far infrared and at submillimeter wavelengths. Accounting for high UV fluxes and variations in kinetic temperature and assuming that the observed emission arises from photon dominated regions (PDRs) resolves the problems related to an LVG treatment of the radiative transfer. 12CO/13CO line intensity ratios > 10 indicate that the bulk of the CO emission arises in UV-illuminated diffuse cloud fragments of small column density and sub-parsec cloud sizes with area filling factors >> 1. Thus CO arises from quite a different gas component than the classical high density tracers. The dominance of such a diffuse molecular interclump medium also explains observed high [CI}/CO line intensity ratios. PDR models do not allow a determination of the relative abundances of 12CO to 13CO. Ignoring magnetic fields, the CO gas appears to be close to the density limit for tidal disruption. A warm diffuse ISM not only dominates the CO emission in the starburst region of M82 but is also ubiquitous in the central region of our Galaxy, where tidal stress, cloud-cloud collisions, shocks, high gas pressure, and high stellar densities may all contribute to the formation of a highly fragmented molecular debris.
High spatial resolution low-J 12CO observations have shown that the wide-angle outflow seen in the Orion BN/KL region correlates with the famous H2 fingers. Recently, high-resolution large-scale mappings of mid- and higher-J CO emissions have been reported toward the Orion molecular cloud 1 core region using the APEX telescope. Therefore, it is of interest to investigate this outflow in the higher-J 12CO emission, which is likely excited by shocks. The observations were carried out using the dual-color heterodyne array CHAMP+ on the APEX telescope. The images of the Orion BN/KL region were obtained in the 12CO J=6-5 and J=7-6 transitions with angular resolutions of 8.6 and 7.4 arcsec, respectively. The results show a good agreement between our higher-J 12CO emission and SMA low-J 12CO data, which indicates that this wide-angle outflow in Orion BN/KL is likely the result of an explosive event that is related to the runaway objects from a dynamically decayed multiple system. From our observations, we estimate that the kinetic energy of this explosive outflow is about 1-2x10^47 erg. In addition, a scenario has been proposed where part of the outflow is decelerated and absorbed in the cloud to explain the lack of CO bullets in the southern part of BN/KL, which in turn induces the methanol masers seen in this region.
We present the result of a systematic search for the iron Kalpha fluorescent line at 6.4 keV among 1616 X-ray sources detected by ultra-deep Chandra observations of the Orion Nebula Cluster and the obscured Orion Molecular Cloud 1 population as part of the Chandra Orion Ultra-deep Project (COUP). Seven sources are identified to have an excess emission at 6.4 keV among 127 control sample sources with significant counts in the 6.0-9.0 keV band. These seven sources are young stellar objects (YSOs) characterized by intense flare-like flux variations, thermal spectra, and near-infrared (NIR) counterparts. The observed equivalent widths of the line cannot be attributed to the fluorescence by interstellar or circumstellar matter along the line of sight. The X-ray spectral fits and NIR colors of the 6.4 keV sources show that these sources have X-ray absorption of > 1x10^22 cm^(-2) and NIR excess emission, which is not expected when the fluorescence occurs at the stellar photosphere. We therefore conclude that the iron fluorescent line of YSOs arises from reflection off of circumstellar disks, which are irradiated by the hard X-ray continuum emission of magnetic reconnection flares.
A high density portion of the Orion Molecular Cloud 1 (OMC-1) contains the prominent, warm Kleinmann-Low (KL) nebula that is internally powered by an energetic event plus a farther region in which intermediate to high mass stars are forming. Its outside is affected by ultraviolet radiation from the neighboring Orion Nebula Cluster and forms the archetypical photon-dominated region (PDR) with the prominent bar feature. Its nearness makes the OMC-1 core region a touchstone for research on the dense molecular interstellar medium and PDRs. Using the Atacama Pathfinder Experiment telescope (APEX), we have imaged the line emission from the multiple transitions of several carbon monoxide (CO) isotopologues over the OMC-1 core region. Our observations employed the 2x7 pixel submillimeter CHAMP+ array to produce maps (~ 300 arcsec x 350 arcsec) of 12CO, 13CO, and C18O from mid-J transitions (J=6-5 to 8-7). We also obtained the 13CO and C18O J=3-2 images toward this region. The 12CO line emission shows a well-defined structure which is shaped and excited by a variety of phenomena, including the energetic photons from hot, massive stars in the nearby Orion Nebulas central Trapezium cluster, active high- and intermediate-mass star formation, and a past energetic event that excites the KL nebula. Radiative transfer modeling of the various isotopologic CO lines implies typical H2 densities in the OMC-1 core region of ~10^4-10^6 cm^-3 and generally elevated temperatures (~ 50-250 K). We estimate a warm gas mass in the OMC-1 core region of 86-285 solar masses.
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