129 research outputs found
Superwind-driven Intense H Emission in NGC 6240 II: Detailed Comparison of Kinematical and Morphological Structures of the Warm and Cold Molecular Gas
We report on our new analysis of the spatial and kinematical distribution of
warm and cold molecular gas in NGC 6240, which was undertaken to explore the
origin of its unusually luminous H emission. By comparing three-dimensional
emission-line data (in space and velocity) of CO (J=2-1) in the radio and H
in the near infrared, we are able to study the H emitting efficiency,
defined in terms of the intensity ratio of H to CO [(H)/(CO)], as
a function of velocity. The integrated H emitting efficiency is calculated
by integrating the velocity profile of H emitting efficiency in blue, red,
and total (blue + red) velocity regions of the profile. We find that (1) both
the total H emitting efficiency and the blue-to-red ratio of the efficiency
are larger in regions surrounding the CO and H intensity peaks, and (2) the
H emitting efficiency and the kinematical conditions in the warm molecular
gas are closely related to each other. A collision between the molecular gas
concentration and the external superwind outflow from the southern nucleus
seems plausible to explain these characteristics, since it can reproduce the
enhanced emitting efficiency of blueshifted H around the molecular gas
concentration, if we assume that the superwind blows from the southern nucleus
toward us, hitting the entire gas concentration from behind. In this model,
internal cloud-cloud collisions within the molecular gas concentration are
enhanced by the interaction with the superwind outflow, and efficient and
intense shock-excited H emission is expected as a result of the
cloud-crushing mechanism.Comment: 12 pages, 6 figures, accepted for publication in A
What Controls the Star Formation in Luminous Starburst Mergers ?
In order to understand what controls the star formation process in luminous
starburst mergers (e.g., NGC 6240, Arp 220, and so on), we investigate
observational properties of two samples of high-luminosity starburst galaxies
mapped in CO(=1--0) independently using both the Owens Valley Radio
Observatory (Scoville et al. 1991) and the IRAM interferometer (Downes &
Solomon 1998). We find that the surface density of far-infrared luminosity,
(FIR), is proportional linearly to the H surface mass density,
(H), for the two samples; (FIR) (H) with a correlation coefficient of 0.96. It is
often considered that (FIR) provides a good measure of the star
formation rate per unit area, (SFR). It is also known that molecular
gas is dominated in circumnuclear regions in the luminous starburst mergers;
i.e., (gas) (H). Therefore, the above relationship
suggests a star formation law; (SFR) (gas). We suggest
that this star formation law favors the gravitational instability scenario
rather than the cloud-cloud collision one.Comment: 14 pages, 2 figures. The Astrophysical Journal (Letters), in pres
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