105 research outputs found

    NH3 in the Galactic Center is formed in Cool Conditions

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    It is an open question why the temperature of molecular gas in the Galactic center region is higher than that of dust. To address this problem, we made simultaneous observations in the NH_3 (J,K) = (1,1), (2,2), and (3,3) lines of the central molecular zone (CMZ) using the Kagoshima 6 m telescope. The ortho-to-para ratio of NH_3 molecules in the CMZ is 1.5--3.5 at most observed area. This ratio is higher than the statistical equilibrium value, and suggests that the formation temperature of NH_3 is 11--20 K. This temperature is similar to the dust temperature estimated from the submillimeter and infrared continuum. This result suggests that the NH_3 molecules in the CMZ were produced on dust grains with the currently observed temperature (11--20 K), and they were released into the gas phase by supernova shocks or collisions of dust particles. The discrepancy between warm molecular gas and cold dust can be explained by the transient heating of the interstellar media in the CMZ approximately 10^5 years ago when the NH_3 molecules were released from the dust.Comment: 19 pages, 12 figures, accepted for PAS

    A Complete Survey of the Central Molecular Zone in NH3

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    We present a map of the major part of the central molecular zone (CMZ) of simultaneous observations in the NH3 (J,K) = (1,1) and (2,2) lines using the Kagoshima 6-m telescope. The mapped area is -1.000 < l < 1.625 deg, -0.375 < b < +0.250 deg. The kinetic temperatures derived from the (2,2) to (1,1) intensity ratios are 20--80 K or exceed 80 K. The gases corresponding to temperature of 20--80 K and > 80 K contain 75% and 25% of the total NH3 flux, respectively. These temperatures indicate that the dense molecular gas in the CMZ is dominated by gas that is warmer than the majority of the dust present there. A comparison with the CO survey by Sawada et al. (2001) shows that the NH3 emitting region is surrounded by a high pressure region on the l-v plane. Although NH3 emission traces dense gas, it is not extended into a high pressure region. Therefore, the high pressure region is less dense and has to be hotter. This indicates that the molecular cloud complex in the Galactic center region has a ``core'' of dense and warm clouds which are traced by the NH3 emission, and an ``envelope'' of less dense and hotter gas clouds. Besides heating by ambipolar diffusion, the hot plasma gas emitting the X-ray emission may heat the hot ``envelope''.Comment: 21 pages, 14 figures, accepted for PAS

    Trigonometric distance and proper motions of H2O maser bowshocks in AFGL 5142

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    We present the results of multi-epoch VLBI observations of water masers in the AGFL 5142 massive star forming region. We measure an annual parallax of π=0.467±0.010\pi=0.467 \pm 0.010 mas, corresponding to a source distance of D=2.140.049+0.051D=2.14^{+0.051}_{-0.049} kpc. Proper motion and line of sight velocities reveal the 3D kinematics of masers in this region, most of which associate with millimeter sources from the literature. In particular we find remarkable bipolar bowshocks expanding from the most massive member, AFGL 5142 MM1, which are used to investigate the physical properties of its protostellar jet. We attempt to link the known outflows in this region to possible progenitors by considering a precessing jet scenario and we discuss the episodic nature of ejections in AFGL 5142

    Propagation of Highly Efficient Star Formation in NGC 7000

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    We surveyed the (1,1), (2,2), and (3,3) lines of NH3 and the H2O maser toward the molecular cloud L935 in the extended HII region NGC 7000 with an angular resolution of 1.6' using the Kashima 34-m telescope. We found five clumps in the NH3 emission with a size of 0.2--1 pc and mass of 9--452 M_sun. The molecular gas in these clumps has a similar gas kinetic temperature of 11--15 K and a line width of 1--2 km/s. However, they have different star formation activities such as the concentration of T-Tauri type stars and the association of H2O maser sources. We found that these star formation activities are related to the geometry of the HII region. The clump associated with the T-Tauri type star cluster has a high star formation efficiency of 36--62%. This clump is located near the boundary of the HII region and molecular cloud. Therefore, we suggest that the star formation efficiency increases because of the triggered star formation.Comment: 19 pages, 15 figures, accepted for PASJ Vol.63 No.