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Register a new userNobeyama 45-m mapping observations toward nearby molecular clouds, Orion A, Aquila Rift, and M17: Project overview
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Fumitaka Nakamura
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We carried out mapping observations toward three nearby molecular clouds, Orion A, Aquila Rift, and M17, using a new 100 GHz receiver, FOREST, on the Nobeyama 45-m telescope. In the present paper, we describe the details of the data obtained such as intensity calibration, data sensitivity, angular resolution, and velocity resolution. Each target contains at least one high-mass star-forming region. The target molecular lines were $^{12}$CO ($J = 1 - 0$), $^{13}$CO ($J = 1 - 0$), C$^{18}$O ($J = 1 - 0$), N$_2$H$^+$ ($J=1-0$), and CCS ($J_N=8_7-7_6$), with which we covered the density range of 10$^2$ cm$^{-3}$ to 10$^6$ cm$^{-3}$ with an angular resolution of $sim 20arcsec$ and a velocity resolution of $sim$ 0.1 km s$^{-1}$. Assuming the representative distances of 414 pc, 436 pc, and 2.1 kpc, the maps of Orion A, Aquila Rift, and M17 cover most of the densest parts with areas of about 7 pc $times$ 15 pc, 7 pc $times$ 7 pc, and 36 pc $times$ 18 pc, respectively. On the basis of the $^{13}$CO column density distribution, the total molecular masses are derived to be $3.86 times 10^4 M_odot$, $2.67 times 10^4 M_odot$, and $8.1times 10^5 M_odot$ for Orion A, Aquila Rift, and M17, respectively. For all the clouds, the H$_2$ column density exceeds the theoretical threshold for high-mass star formation of $gtrsim$ 1 g cm$^{-2}$, only toward the regions which contain current high-mass star-forming sites. For other areas, further mass accretion or dynamical compression would be necessary for future high-mass star formation. This is consistent with the current star formation activity. Using the $^{12}$CO data, we demonstrate that our data have enough capability to identify molecular outflows, and for Aquila Rift, we identify 4 new outflow candidates. The scientific results will be discussed in details in separate papers.
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We conducted an exploration of 12CO molecular outflows in the Orion A giant molecular cloud to investigate outflow feedback using 12CO (J = 1-0) and 13CO (J = 1-0) data obtained by the Nobeyama 45-m telescope. In the region excluding the center of OMC 1, we identified 44 12CO (including 17 newly detected) outflows based on the unbiased and systematic procedure of automatically determining the velocity range of the outflows and separating the cloud and outflow components. The optical depth of the 12CO emission in the detected outflows is estimated to be approximately 5. The total momentum and energy of the outflows, corrected for optical depth, are estimated to be 1.6 x 10 2 M km s-1 and 1.5 x 10 46 erg, respectively. The momentum and energy ejection rate of the outflows are estimated to be 36% and 235% of the momentum and energy dissipation rates of the cloud turbulence, respectively. Furthermore, the ejection rates of the outflows are comparable to those of the expanding molecular shells estimated by Feddersen et al. (2018, ApJ, 862, 121). Cloud turbulence cannot be sustained by the outflows and shells unless the energy conversion efficiency is as high as 20%.
We present results of wide-field $^{12}$CO ($J = 2 - 1$) and $^{13}$CO ($J = 2 - 1$) observations toward the Aquila Rift and Serpens molecular cloud complexes (25$^circ < l < 33^circ$ and $1^circ < b < 6^circ$) at an angular resolution of 3$$.4 ($approx$ 0.25 pc) and at a velocity resolution of 0.079 km s$^{-1}$ with the velocity coverage of $-5$ km s$^{-1} < V_{rm LSR} <$ 35 km s$^{-1}$. We found that the $^{13}$CO emission better traces the structures seen in the extinction map and derived the $X_{rm ^{13}CO}$-factor of this region. Applying texttt{SCIMES} to the $^{13}$CO data cube, we identified 61 clouds and derived their masses, radii, and line widths. The line-width-radius relation of the identified clouds basically follows those of nearby molecular clouds. Majority of the identified clouds are close to virial equilibrium although the dispersion is large. By inspecting the $^{12}$CO channel maps by eye, we found several arcs which are spatially extended to 0.2 $-$ 3 degree in length. In the longitude-velocity diagrams of $^{12}$CO, we also found the two spatially-extended components which appear to converge toward Serpens South and W40 region. The existence of two components with different velocities and arcs suggests that large-scale expanding bubbles and/or flows play a role in the formation and evolution of the Serpens South and W40 cloud.
We present the results of a ~250 square degrees CO mapping (+26d<l<+50d and -5d<b<+5d) toward the Aquila Rift region at a spatial resolution of ~50 and a grid spacing of 30. The high dynamic range CO maps with a spectral resolution of ~0.2km/s display highly structured molecular cloud (MC) morphologies with valuable velocity information, revealing complex spatial and dynamical features of the local molecular gas. In combination with the MWISP CO data and the Gaia DR2, distances of the main MC structures in the local ISM are well determined toward the Aquila Rift. We find that the total MC mass within 1 kpc is about >4.1x10^5 Msun in the whole region. In fact, the mass of the molecular gas is dominated by the W40 giant molecular cloud (GMC) at ~474 pc (~1.4x10^5 Msun) and the GMC complex G036.0+01.0 at ~560-670 pc (~2.0x10^5 Msun), while the MCs at ~220-260pc have gas masses of 10^2-10^3 Msun. Interestingly, an ~80pc long filamentary MC G044.0-02.5 at a distance of ~404 pc shows a systematic velocity gradient along and perpendicular to the major axis of the filament. The HI gas with the enhanced emission has the similar spatial morphologies and velocity features compared to the corresponding CO structure, indicating that the large-scale converging HI flows are probably responsible for the formation of the MC. Meanwhile, the long filamentary MC consists of many sub-filaments with the lengths ranging from ~0.5 pc to several pc, as well as prevalent networks of filaments in other large-scale local MCs.
The FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45-m telescope (FUGIN) project is one of the legacy projects using the new multi-beam FOREST receiver installed on the Nobeyama 45-m telescope. This project aims to investigate the distribution, kinematics, and physical properties of both diffuse and dense molecular gas in the Galaxy at once by observing 12CO, 13CO, and C18O J=1-0 lines simultaneously. The mapping regions are a part of the 1st quadrant (10d < l < 50d, |b| < 1d) and the 3rd quadrant (198d < l <236d, |b| < 1d) of the Galaxy, where spiral arms, bar structure, and the molecular gas ring are included. This survey achieves the highest angular resolution to date (~20) for the Galactic plane survey in the CO J=1-0 lines, which makes it possible to find dense clumps located farther away than the previous surveys. FUGIN will provide us with an invaluable dataset for investigating the physics of the galactic interstellar medium (ISM), particularly the evolution of interstellar gas covering galactic scale structures to the internal structures of giant molecular clouds, such as small filament/clump/core. We present an overview of the FUGIN project, observation plan, and initial results, which reveal wide-field and detailed structures of molecular clouds, such as entangled filaments that have not been obvious in previous surveys, and large-scale kinematics of molecular gas such as spiral arms.
We surveyed the Aquila Rift complex including the Serpens South and W40 region in the NH$_3$(1,1) and (2,2) transitions making use of the Nanshan 26-m telescope. The kinetic temperatures of the dense gas in the Aquila Rift complex range from 8.9 to 35.0K with an average of 15.3$pm$6.1K. Low gas temperatures associate with Serpens South ranging from 8.9 to 16.8K with an average 12.3$pm$1.7K, while dense gas in the W40 region shows higher temperatures ranging from 17.7 to 35.0K with an average of 25.1$pm$4.9 K. A comparison of kinetic temperatures against HiGal dust temperatures indicates that the gas and dust temperatures are in agreement in the low mass star formation region of Serpens South. In the high mass star formation region W40, the measured gas kinetic temperatures are higher than those of the dust. The turbulent component of the velocity dispersion of NH$_3$(1,1) is found to be positively correlated with the gas kinetic temperature, which indicates that the dense gas may be heated by dissipation of turbulent energy. For the fractional total-NH3 abundance obtained by a comparison with Herschel infrared continuum data representing dust emission we find values from 0.1 to 21$times 10^{-8}$ with an average of 6.9$(pm 4.5)times 10^{-8}$. Serpens South also shows a fractional total-NH3 abundance ranging from 0.2 to 21$times 10^{-8}$ with an average of 8.6($pm 3.8)times 10^{-8}$. In W40, values are lower, between 0.1 and 4.3$times 10^{-8}$ with an average of 1.6($pm 1.4)times 10^{-8}$. Weak velocity gradients demonstrate that the rotational energy is a negligible fraction of the gravitational energy. In W40, gas and dust temperatures are not strongly dependent on the projected distance to the recently formed massive stars. Overall, the morphology of the mapped region is ring-like, with strong emission at lower and weak emission at higher Galactic longitudes.
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