51 research outputs found
The relation of H2CO, 12CO, and 13CO in molecular clouds
Aims. We seek to understand how the 4.8 GHz formaldehyde absorption line is
distributed in the MON R2, S156, DR17/L906, and M17/M18 regions. More
specifically, we look for the relationship among the H2CO, 12CO, and 13CO
spectral lines. Methods. The four regions of MON R2 (60'x90'), S156 (5'0x70'),
DR17/L906 (40'x60'), and M17 /M18 (70'x80')were observed for H2CO (beam 10'),
H110a recombination (beam 10'), 6 cm continuum (beam 10'), 12CO (beam 1'), and
13CO (beam 1'). We compared the H2CO,12CO,13CO, and continuum distributions,
and also the spectra line parameters of H2CO,12CO, and 13CO. Column densities
of H2CO,13CO, and H2 were also estimated. Results. We found out that the H2CO
distribution is similar to the 12CO and the 13CO distributions on a large
scale. The correlation between the 13 CO and the H2CO distributions is better
than between the 12CO and H2CO distributions. The H2CO and the 13CO tracers
systematically provide consistent views of the dense regions. T heir maps have
similar shapes, sizes, peak positions, and molecular spectra and present
similar centr al velocities and line widths. Such good agreement indicates that
the H2CO and the 13CO arise from similar regions.Comment: 21 pages, 12 figures published, 201
Filament L1482 in the California molecular cloud
Aims. The process of gravitational fragmentation in the L1482 molecular
filament of the California molecular cloud is studied by combining several
complementary observations and physical estimates. We investigate the kinematic
and dynamical states of this molecular filament and physical properties of
several dozens of dense molecular clumps embedded therein.
Methods. We present and compare molecular line emission observations of the
J=2--1 and J=3--2 transitions of 12CO in this molecular complex, using the
KOSMA 3-meter telescope. These observations are complemented with archival data
observations and analyses of the 13CO J=1--0 emission obtained at the Purple
Mountain Observatory 13.7-meter radio telescope at Delingha Station in QingHai
Province of west China, as well as infrared emission maps from the Herschel
Space Telescope online archive, obtained with the SPIRE and PACS cameras.
Comparison of these complementary datasets allow for a comprehensive
multi-wavelength analysis of the L1482 molecular filament.
Results. We have identified 23 clumps along the molecular filament L1482 in
the California molecular cloud. All these molecular clumps show supersonic
non-thermal gas motions. While surprisingly similar in mass and size to the
much better known Orion molecular cloud, the formation rate of high-mass stars
appears to be suppressed in the California molecular cloud relative to that in
the Orion molecular cloud based on the mass-radius threshold derived from the
static Bonnor Ebert sphere. Our analysis suggests that these molecular
filaments are thermally supercritical and molecular clumps may form by
gravitational fragmentation along the filament. Instead of being static, these
molecular clumps are most likely in processes of dynamic evolution.Comment: 10 pages, 9 figures, 2 tables, accepted to Astronomy and Astrophysic
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