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Register a new userA mapping study of L1174 with 13CO J=2-1 and 12CO J=3-2: star formation triggered by a Herbig Ae/Be star
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J. H. Yuan
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We have carried out a comprehensive study of the molecular conditions and star-forming activities in dark cloud L1174 with multi-wavelength data. Mapping observations of L1174 in $^{13}$CO $J=2-1$ and $^{12}$CO $J=3-2$ were performed using the KOSMA 3-meter telescope. Six molecular cores with masses ranging from 5 to 31 $M_odot$ and sizes ranging from 0.17 to 0.39 pc are resolved. Large area ahead of a Herbig Be star, HD 200775, is in expanding and core 1 is with collapse signature. Large line widths of $^{13}$CO $J=2-1$ indicate the ubiquity of turbulent motions in this region. Spectra of $^{12}$CO $J=3-2$ prevalently show conspicuously asymmetric double-peaked profiles. In a large area, red-skewed profiles are detected and suggestive of a scenario of global expansion. There is a large cavity around the Herbig Be star HD 200775, the brightest star in L1174. The gas around the cavity has been severely compressed by the stellar winds from HD 200775. Feedbacks from HD 200775 may have helped form the molecular cores around the cavity. Seventeen 2MASS potential young stellar objects were identified according to their 2MASS colour indices. The spatial distribution of the these 2MASS sources indicates that some of them have a triggered origin. All these suggest that feedbacks from a Herbig Ae/Be star may also have the potential to trigger star forming activities.
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After 30 Doradus, N11 is the second largest and brightest nebula in the LMC. This large nebula has several OB associations with bright nebulae at its surroundings. N11 was previously mapped at the lowest rotational transitions of $^{12}$CO (J=1--0 and 2--1), and in some particular regions pointings of the $^{13}$CO J=1--0 and 2--1 lines were also performed. Using ASTE we mapped the whole extension of the N11 nebula in the $^{12}$CO J=3--2 line, and three sub-regions in the $^{13}$CO J=3--2 line. The regions mapped in the $^{13}$CO J=3--2 were selected based on that they may be exposed to the radiation at different ways: a region lying over the nebula related to the OB association LH10 (N11B), another one that it is associated with the southern part of the nebula related to the OB association LH13 (N11D), and finally a farther area at the southwest without any embedded OB association (N11I). We found that the morphology of the molecular clouds lying in each region shows some signatures that could be explained by the expansion of the nebulae and the action of the radiation. Fragmentation generated in a molecular shell due to the expansion of the N11 nebula is suggested. The integrated line ratios $^{12}$CO/$^{13}$CO show evidences of selective photodissociation of the $^{13}$CO, and probably other mechanisms such as chemical fractionation. The CO contribution to the continuum at 870 $mu$m was directly derived. The distribution of the integrated line ratios $^{12}$CO J=3--2/2--1 show hints of stellar feedback in N11B and N11D. The ratio between the virial and LTE mass (M$_{rm vir}$/M$_{rm LTE}$) is higher than unity in all analyzed molecular clumps, which suggests that the clumps are not gravitationally bounded and may be supported by external pressure. A non-LTE analysis suggests that we are mapping gas with densities about a few 10$^{3}$ cm$^{-3}$.
We have carried out 12CO(J =2-1) and 12CO(J =3-2) observations at spatial resolutions of 1.0-3.8 pc toward the entirety of loops 1 and 2 and part of loop 3 in the Galactic center with NANTEN2 and ASTE. These new results revealed detailed distributions of the molecular gas and the line intensity ratio of the two transitions, R3-2/2-1. In the three loops, R3-2/2-1 is in a range from 0.1 to 2.5 with a peak at ~ 0.7 while that in the disk molecular gas is in a range from 0.1 to 1.2 with a peak at 0.4. This supports that the loops are more highly excited than the disk molecular gas. An LVG analysis of three transitions, 12CO J =3-2 and 2-1 and 13CO J =2-1, toward six positions in loops 1 and 2 shows density and temperature are in a range 102.2 - 104.7 cm-3 and 15-100 K or higher, respectively. Three regions extended by 50-100 pc in the loops tend to have higher excitation conditions as characterized by R3-2/2-1 greater than 1.2. The highest ratio of 2.5 is found in the most developed foot points between loops 1 and 2. This is interpreted that the foot points indicate strongly shocked conditions as inferred from their large linewidths of 50-100 km s-1, confirming the suggestion by Torii et al. (2010b). The other two regions outside the foot points suggest that the molecular gas is heated up by some additional heating mechanisms possibly including magnetic reconnection. A detailed analysis of four foot points have shown a U shape, an L shape or a mirrored-L shape in the b-v distribution. It is shown that a simple kinematical model which incorporates global rotation and expansion of the loops is able to explain these characteristic shapes.
We present the results of CO(J=3-2) on-the-fly mappings of two nearby non-barred spiral galaxies NGC 628 and NGC 7793 with the Atacama Submillimeter Telescope Experiment at an effective angular resolution of 25. We successfully obtained global distributions of CO(J=3-2) emission over the entire disks at a sub-kpc resolution for both galaxies. We examined the spatially-resolved (sub-kpc) relationship between CO(J=3-2) luminosities (LCO(3-2)) and infrared (IR) luminosities (LIR) for NGC 628, NGC 7793, and M 83, and compared it with global luminosities of JCMT Nearby Galaxy Legacy Survey sample. We found a striking linear LCO(3-2)-LIR correlation over the 4 orders of magnitude, and the correlation is consistent even with that for ultraluminous infrared galaxies and submillimeter selected galaxies. In addition, we examined the spatially-resolved relationship between CO(J=3-2) intensities (ICO(3-2)) and extinction-corrected star formation rates (SFRs) for NGC 628, NGC 7793, and M 83, and compared it with that for GMCs in M 33 and 14 nearby galaxy centers. We found a linear ICO(3-2)-SFR correlation with 1 dex scatter. We conclude that the CO(J=3-2) star formation law (i.e., linear LCO(3-2)-LIR and ICO(3-2)-SFR correlations) is universally applicable to various types and spatial scales of galaxies, from spatially-resolved nearby galaxy disks to distant IR-luminous galaxies, within 1 dex scatter.
New 12CO J=4-3 and 13CO J=3-2 observations of the N159 region in the Large Magellanic Cloud have been made. The 12CO J=4-3 distribution is separated into three clumps. These new measurements toward the three clumps are used in coupled calculations of molecular rotational excitation and line radiation transfer, along with other transitions of the 12CO as well as the isotope transitions of 13CO. The temperatures and densities are determined to be ~70-80K and ~3x10^3 cm-3 in N159W and N159E and ~30K and ~1.6x10^3 cm-3 in N159S. These results are compared with the star formation activity. The N159E clump is associated with embedded cluster(s) as observed at 24 micron and the derived high temperature is explained as due to the heating by these sources. The N159E clump is likely responsible for a dark lane in a large HII region by the dust extinction. The N159W clump is associated with embedded clusters mainly toward the eastern edge of the clump only. These clusters show offsets of 20-40 from the 12CO J=4-3 peak and are probably responsible for heating indicated by the derived high temperature. The N159W clump exhibits no sign of star formation toward the 12CO J=4-3 peak position and its western region. We suggest that the N159W peak represents a pre-star-cluster core of ~105M_sol which deserves further detailed studies. Note that recent star formation took place between N159W and N159E as indicated by several star clusters and HII regions, while the natal molecular gas toward the stars have already been dissipated by the ionization and stellar winds of the OB stars. The N159S clump shows little sign of star formation as is consistent with the lower temperature and somewhat lower density. The N159S clump is also a candidate for future star formation.
We have made new CO observations of two molecular clouds, which we call jet and arc clouds, toward the stellar cluster Westerlund 2 and the TeV gamma-ray source HESS J1023-575. The jet cloud shows a linear structure from the position of Westerlund 2 on the east. In addition, we have found a new counter jet cloud on the west. The arc cloud shows a crescent shape in the west of HESS J1023-575. A sign of star formation is found at the edge of the jet cloud and gives a constraint on the age of the jet cloud to be ~Myrs. An analysis with the multi CO transitions gives temperature as high as 20 K in a few places of the jet cloud, suggesting that some additional heating may be operating locally. The new TeV gamma-ray images by H.E.S.S. correspond to the jet and arc clouds spatially better than the giant molecular clouds associated with Westerlund 2. We suggest that the jet and arc clouds are not physically linked with Westerlund 2 but are located at a greater distance around 7.5 kpc. A microquasar with long-term activity may be able to offer a possible engine to form the jet and arc clouds and to produce the TeV gamma-rays, although none of the known microquasars have a Myr age or steady TeV gamma-rays. Alternatively, an anisotropic supernova explosion which occurred ~Myr ago may be able to form the jet and arc clouds, whereas the TeV gamma-ray emission requires a microquasar formed after the explosion.
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