39 research outputs found
Atlas of CO-Line Shells and Cavities around Galactic Supernova Remnants with FUGIN
A morphological} search for molecular shells and cavities was performed
around 63 Galactic supernova remnants (SNR) at ,
using the FUGIN (FOREST Unbiased Galactic Imaging survey with
the Nobeyama 45-m telescope) CO line data at high angular () and velocity
(1.3 km s) resolutions. The results are presented as supplementary data
for general purpose for investigations of the interaction between SNRs and
interstellar matter in the form of an atlas of CO-line maps superposed on radio
continuum maps at 20 cm along with a list of their kinematic distances
determined from CO-line radial velocities.
(Full atlas including all figures is available in this URL:
https://nro-fugin.github.io/2020-apjs-CO-Shell-Atlas-SNR-FUGIN-IX.pdf)Comment: 49 pages, 51 figures, accepted for ApJ. Supp
Cluster formation induced by a cloud--cloud collision in [DBS2003]179
[DBS2003]179 is a super star cluster in the Galaxy discovered by deep near
infrared observations. We carried out CO J=1-0 and J=3-2 observations of the
region of [DBS2003]179 with NANTEN2, ASTE and the Mopra 22m telescope. We
identified and mapped two molecular clouds which are likely associated with the
cluster. The association is evidenced by the spatial correlation with the 8
micron Spitzer image, and a high ratio of the two transitions of 12CO (J=3-2 to
J=1-0). The two clouds show complementary distribution in space and bridge
features connecting them in velocity. We frame a hypothesis that the two clouds
collided with each other 1-2 Myr ago, and the collision compressed the
interface layer, triggering the formation of the cluster. This offers an
additional piece of evidence for a super star cluster formed by cloud--cloud
collision alongside of the four super star clusters including Wd2, NGC3603,
RCW38 and R136. The findings indicate that the known super star clusters having
closely associated dust emission are formed by cloud-cloud collision, lending
support for the important role of cloud--cloud collision in high-mass star
formation.Comment: 32 pages, 16 figure
Molecular clouds toward three Spitzer bubbles S116, S117 and S118: Evidence for the cloud-cloud collision which formed the three \HII \ regions and a 10-pc scale molecular cavity
We carried out a molecular line study toward the three Spitzer bubbles S116,
S117 and S118 which show active formation of high-mass stars. We found
molecular gas consisting of two components with velocity difference of { \kms}. One of them, the small cloud, has typical velocity of { \kms} \
and the other, the large cloud, has that of \kms. The large cloud has a
nearly circular intensity depression whose size is similar to the small cloud.
We present an interpretation that the cavity was created by a collision between
the two clouds and the collision compressed the gas into a dense layer
elongated along the western rim of the small cloud. In this scenario, the O
stars including those in the three Spitzer bubbles were formed in the interface
layer compressed by the collision. By assuming that the relative motion of the
clouds has a tilt of \timeform{45D} to the line of sight, we estimate that the
collision continued over the last 1 Myr at relative velocity of 10 \kms.
In the S116--117--118 system the \HII \ regions are located outside of the
cavity. This morphology is ascribed to the density-bound distribution of the
large cloud which made the \HII \ regions more easily expand toward the outer
part of the large cloud than inside of the cavity. The present case proves that
a cloud-cloud collision creates a cavity without an action of O star feedback,
and suggests that the collision-compressed layer is highly filamentary.Comment: 23 pages, 10 figure
Molecular clouds in the NGC 6334 and NGC 6357 region; Evidence for a 100 pc-scale cloud-cloud collision triggering the Galactic mini-starbursts
We carried out new CO (1-0, 2-1 and 3-2) observations with NANTEN2 and
ASTE in the region of the twin Galactic mini-starbursts NGC 6334 and NGC 6357.
We detected two velocity molecular components of 12 km s velocity
separation, which is continuous over 3 degrees along the plane. In NGC 6334 the
two components show similar two-peaked intensity distributions toward the young
HII regions and are linked by a bridge feature. In NGC 6357 we found spatially
complementary distribution between the two velocity components as well as a
bridge feature in velocity. Based on these results we hypothesize that the two
clouds in the two regions collided with each other in the past few Myr and
triggered formation of the starbursts over 100 pc. We suggest that the
formation of the starbursts happened toward the collisional region of
10-pc extents with initial high molecular column densities. For NGC 6334 we
present a scenario which includes spatial variation of the colliding epoch due
to non-uniform cloud separation. The scenario possibly explains the apparent
age difference among the young O stars in NGC 6334 raging from yrs to
yrs; the latest collision happened within yrs toward the youngest
stars in NGC 6334 I(N) and I which exhibit molecular outflows without HII
regions. For NGC 6357 the O stars were formed a few Myrs ago, and the cloud
dispersal by the O stars is significant. We conclude that cloud-cloud collision
offers a possible explanation of the min-starburst over a 100-pc scale.Comment: 24 pages, 14 figures, 2 tables, accepted for publication in PAS
Formation of the young compact cluster GM 24 triggered by a cloud-cloud collision
High-mass star formation is an important step which controls galactic
evolution. GM 24 is a heavily obscured star cluster including a single O9 star
with more than 100 lower mass stars within a 0.3 pc radius toward
(350.5, 0.96), close to the Galactic
min-starburst NGC 6334. We found two velocity components associated with the
cluster by new observations of CO 2-1 emission, whereas the cloud
was previously considered to be single. We found the distribution of the two
components of km s separation shows complementary distribution which
fits well with each other, if a relative displacement of 3 pc is applied along
the Galactic plane. A position-velocity diagram of the GM 24 cloud is explained
by a model based on the numerical simulations of two colliding clouds, where an
intermediate velocity component created by collision is taken into account. We
estimate the collision time scale to be Myr in projection of a relative
motion titled to the line of sight by 45 degrees. The results lend further
support for cloud-cloud collision as a major mechanism of high-mass star
formation in the Carina-Sagittarius Arm.Comment: 13 pages, 7 figures, 3 tables, accepted for publication in PAS
A systematic study of Galactic infrared bubbles along the Galactic plane with AKARI and Herschel
Galactic infrared (IR) bubbles, which have shell-like structures in the
mid-IR wavelengths, are known to contain massive stars near their centers. IR
bubbles in inner Galactic regions (l 65, b
1) have so far been studied well to understand the massive star
formation mechanisms. In this study, we expand the research area to the whole
Galactic plane (0 l 360, b 5),
using the AKARI all-sky survey data. We limit our study on large bubbles with
angular radii of to reliably identify and characterize them. For the 247
IR bubbles in total, we derived the radii and the covering fractions of the
shells, based on the method developed in \citet{Hattori2016}. We also created
their spectral energy distributions, using the AKARI and Herschel photometric
data, and decomposed them with a dust model, to obtain the total IR luminosity
and the luminosity of each dust component, i.e., polycyclic aromatic
hydrocarbons (PAHs), warm dust and cold dust. As a result, we find that there
are systematic differences in the IR properties of the bubbles between inner
and outer Galactic regions. The total IR luminosities are lower in outer
Galactic regions, while there is no systematic difference in the range of the
shell radii between inner and outer Galactic regions. More IR bubbles tend to
be observed as broken bubbles rather than closed ones and the fractional
luminosities of the PAH emission are significantly higher in outer Galactic
regions. We discuss the implications of these results for the massive stars and
the interstellar environments associated with the Galactic IR bubbles.Comment: 39 pages, 12 figures, accepted for publication in PAS
The formation of a Spitzer bubble RCW79 triggered by cloud-cloud collision
Understanding the mechanism of O star formation is one of the most important
issues in current astrophysics. It is also an issue of keen interest how O
stars affect their surroundings and trigger secondary star formation. An
H\,\emissiontype{II} region RCW79 is one of the typical Spitzer bubbles
alongside of RCW120. New observations of CO 1--0 emission with Mopra and
NANTEN2 revealed that molecular clouds are associated with RCW79 in four
velocity components over a velocity range of 20 km s. We hypothesize
that two of the clouds collided with each other and the collision triggered the
formation of 12 O stars inside of the bubble and the formation of 54 low mass
young stellar objects along the bubble wall. The collision is supported by
observational signatures of bridges connecting different velocity components in
the colliding clouds. The whole collision process happened in a timescale of
1 Myr. RCW79 has a larger size by a factor of 30 in the projected area
than RCW120 with a single O star, and the large size favored formation of the
12 O stars due to the larger accumulated gas in the collisional shock
compression.Comment: 21 pages, 8 figure
A new view of the giant molecular cloud M16 (Eagle Nebula) in 12CO J=1-0 and 2-1 transitions with NANTEN2
M16, the Eagle Nebula, is an outstanding HII region where extensive high-mass
star formation is taking place in the Sagittarius Arm, and hosts the remarkable
"pillars" observed with HST. We made new CO observations of the region in the
12CO J=1--0 and J=2--1 transitions with NANTEN2. These observations revealed
for the first time that a giant molecular cloud of \Msun
\ is associated with M16, which is elongated vertically to the Galactic plane
over 35 pc at a distance of 1.8 kpc. We found a cavity of the molecular gas of
pc diameter toward the heart of M16 at \lbeq (16.95\degree,
0.85\degree), where more than 10 O-type stars and stars are
associated, in addition to a close-by molecular cavity toward a Spitzer bubble
N19 at \lbeq (17.06\degree, 1.0\degree). We found three velocity components
which show spatially complementary distribution in the entire M16 giant
molecular cloud (GMC) including NGC6611 and N19, suggesting collisional
interaction between them. Based on the above results we frame a hypothesis that
collision between the red-shifted and blue-shifted components at a relative of
\kms \ triggered formation of the O-type stars in the M16 GMC in the
last 1-2 Myr. The collision is two fold in the sense that one of the
collisional interactions is major toward the M16 cluster and the other toward
N19 with a RCW120 type, the former triggered most of the O star formation with
almost full ionization of the parent gas, and the latter an O star formation in
N19.Comment: 20 pages, 10 figures, submitted to PAS
High-mass star formation possibly triggered by cloud-cloud collision in the HII region RCW 34
We report a possibility that the high-mass star located in the HII region RCW
34 was formed by a triggering induced by a collision of molecular clouds.
Molecular gas distributions of the CO and CO 2-1, and
CO 3-2 lines toward RCW 34 were measured by using the NANTEN2 and
ASTE telescopes. We found two clouds with the velocity ranges of 0-10 km
s and 10-14 km s. Whereas the former cloud as massive as ~2.7 x
10 Msun has a morphology similar to the ring-like structure observed in
the infrared wavelengths, the latter cloud with the mass of ~10 Msun,
which has not been recognized by previous observations, distributes just likely
to cover the bubble enclosed by the other cloud. The high-mass star with the
spectral types of O8.5V is located near the boundary of the two clouds. The
line intensity ratio of CO 3-2 / 2-1 yields high values (~1.5)
in the neighborhood of the high-mass star, suggesting that these clouds are
associated with the massive star. We also confirmed that the obtained
position-velocity diagram shows a similar distribution with that derived by a
numerical simulation of the supersonic collision of two clouds. Using the
relative velocity between the two clouds (~5 km s), the collisional time
scale is estimated to be 0.2 Myr with the assumption of the distance of
2.5 kpc. These results suggest that the high-mass star in RCW 34 was formed
rapidly within a time scale of ~0.2 Myr via a triggering of cloud-cloud
collision.Comment: 18 pages, 10 figures, 2 tables, accepted for Publications of the
Astronomical Society of Japan (PASJ
FOREST Unbiased Galactic Plane Imaging Survey with the Nobeyama 45-m Telescope (FUGIN) V: Dense gas mass fraction of molecular gas in the Galactic plane
Recent observations of the nearby Galactic molecular clouds indicate that the
dense gas in molecular clouds have quasi-universal properties on star
formation, and observational studies of extra galaxies have shown a
galactic-scale correlation between the star formation rate (SFR) and surface
density of molecular gas. To reach a comprehensive understanding of both
properties, it is important to quantify the fractional mass of the dense gas in
molecular clouds f_DG. In particular, for the Milky Way (MW), there are no
previous studies resolving the f_DG disk over a scale of several kpc. In this
study, the f_DG was measured over 5kpc in the first quadrant of the MW, based
on the CO J=1-0 data in l=10-50 deg obtained as part of the FOREST Unbiased
Galactic Plane Imaging Survey with the Nobeyama 45-m Telescope (FUGIN) project.
The total molecular mass was measured using 12CO, and the dense gas mass was
estimated using C18O. The fractional masses including f_DG in the region within
~30% of the distances to the tangential points of the Galactic rotation (e.g.,
the Galactic Bar, Far-3kpc Arm, Norma Arm, Scutum Arm, Sagittarius Arm, and
inter-arm regions) were measured. As a result, an averaged f_DG of
2.9^{+2.6}_{-2.6} % was obtained for the entirety of the target region. This
low value suggests that dense gas formation is the primary factor of
inefficient star formation in galaxies. It was also found that the f_DG shows
large variations depending on the structures in the MW disk. The f_DG in the
Galactic arms were estimated to be ~4-5%, while those in the bar and inter-arm
regions were as small as ~0.1-0.4%. These results indicate that the
formation/destruction processes of the dense gas and their timescales are
different for different regions in the MW, leading to the differences in SFRs.Comment: 36 pages, 22 figures, 1 table, accepted for publication in PAS