4 research outputs found
NH3 in the Galactic Center is formed in Cool Conditions
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
Propagation of Highly Efficient Star Formation in NGC 7000
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.