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Register a new userIRAM-30m large scale survey of $^{12}$CO(2-1) and $^{13}$CO(2-1) emission in the Orion molecular cloud
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Using the IRAM 30m telescope we have surveyed a $1times0.8^{circ}$ part of the Orion molecular cloud in the $^{12}$CO and $^{13}$CO (2-1) lines with a maximal spatial resolution of $sim$11 and spectral resolution of $sim$ 0.4 km~s$^{-1}$. The cloud appears filamentary, clumpy and with a complex kinematical structure. We derive an estimated mass of the cloud of 7700 M$_{text{Sun}}$ (half of which is found in regions with visual extinctions $A_V$ below $sim$10) and a dynamical age for the nebula of the order of 0.2 Myrs. The energy balance suggests that magnetic fields play an important role in supporting the cloud, at large and small scales. According to our analysis, the turbulent kinetic energy in the molecular gas due to outflows is comparable to turbulent kinetic energy resulting from the interaction of the cloud with the HII region. This latter feedback appears negative, i.e. the triggering of star formation by the HII region is inefficient in Orion. The reduced data as well as additional products such as the column density map are made available online at http://userpages.irap.omp.eu/~oberne/Olivier_Berne/Data.
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We present results of wide-field $^{12}$CO ($J = 2 - 1$) and $^{13}$CO ($J = 2 - 1$) observations toward the Aquila Rift and Serpens molecular cloud complexes (25$^circ < l < 33^circ$ and $1^circ < b < 6^circ$) at an angular resolution of 3$$.4 ($approx$ 0.25 pc) and at a velocity resolution of 0.079 km s$^{-1}$ with the velocity coverage of $-5$ km s$^{-1} < V_{rm LSR} <$ 35 km s$^{-1}$. We found that the $^{13}$CO emission better traces the structures seen in the extinction map and derived the $X_{rm ^{13}CO}$-factor of this region. Applying texttt{SCIMES} to the $^{13}$CO data cube, we identified 61 clouds and derived their masses, radii, and line widths. The line-width-radius relation of the identified clouds basically follows those of nearby molecular clouds. Majority of the identified clouds are close to virial equilibrium although the dispersion is large. By inspecting the $^{12}$CO channel maps by eye, we found several arcs which are spatially extended to 0.2 $-$ 3 degree in length. In the longitude-velocity diagrams of $^{12}$CO, we also found the two spatially-extended components which appear to converge toward Serpens South and W40 region. The existence of two components with different velocities and arcs suggests that large-scale expanding bubbles and/or flows play a role in the formation and evolution of the Serpens South and W40 cloud.
Strong winds and ultraviolet (UV) radiation from O-type stars disrupt and ionize their molecular core birthplaces, sweeping up material into parsec-size shells. Owing to dissociation by starlight, the thinnest shells are expected to host low molecular abundances and therefore little star formation. Here, we expand previous maps taken with the IRAM 30m telescope and present square-degree 12CO and 13CO (J=2-1) maps of the wind-driven Veil bubble that surrounds the Trapezium cluster and its natal Orion molecular core (OMC). Although widespread and extended CO emission is largely absent from the Veil, we show that several CO globules exist and are embedded in the [CII]158um-bright shell that confines the bubble. This includes the first detection of quiescent CO at negative LSR velocities in Orion. Given the harsh UV irradiation conditions in this translucent material, the detection of CO globules is surprising. These globules are small (R=7,100 AU), not massive (M=0.3M_Sun), and are moderately dense: n_ H=4x10^4 cm^-3 (median values). They are confined by the external pressure of the shell, P_ext/k~10^7 cm^-3 K, and are likely magnetically supported. They are either transient objects formed by instabilities or have detached from pre-existing molecular structures, sculpted by the passing shock associated with the expanding shell and by UV radiation from the Trapezium. Some represent the first stages in the formation of small pillars, others of isolated small globules. Although their masses do not suggest they will form stars, one globule matches the position of a known YSO. The lack of extended CO in the Veil shell demonstrates that feedback from massive stars expels, agitates, and reprocesses most of the disrupted molecular cloud gas, thereby limiting the star-formation rate in the region. The presence of globules is a result of this feedback.
New-generation spectroscopic surveys of the Milky Way plane have been revealing the structure of the interstellar medium, allowing the simultaneous study of dense structures from single star-forming objects or systems to entire spiral arms. We present the catalogue of molecular clouds extracted from the $^{13}$CO(1-0) data cubes of the Forgotten Quadrant Survey, which mapped the Galactic plane in the range 220deg<l<240deg, and -2.5deg<b<0deg in $^{12}$CO(1-0) and $^{13}$CO(1-0).The catalogue contains 87 molecular clouds for which the main physical parameters such as area, mass, distance, velocity dispersion, and virial parameter were derived. These structures are overall less extended and less massive than the molecular clouds identified in the $^{12}$CO(1-0) data-set because they trace the brightest and densest part of the $^{12}$CO(1-0) clouds. Conversely, the distribution of aspect ratio, equivalent spherical radius, velocity dispersion, and virial parameter in the two catalogues are similar. The mean value of the mass surface density of molecular clouds is 87$pm$55 M$_{odot}$ pc$^{-2}$ and is almost constant across the galactocentric radius, indicating that this parameter, which is a proxy of star formation, is mostly affected by local conditions.In data of the Forgotten Quadrant Survey, we find a good agreement between the total mass and velocity dispersion of the clouds derived from $^{12}$CO(1-0) and $^{13}$CO(1-0). This is likely because in the surveyed portion of the Galactic plane, the H$_2$ column density is not particularly high, leading to a CO emission with a not very high optical depth. This mitigates the effects of the different line opacities between the two tracers on the derived physical parameters. This is a common feature in the outer Galaxy, but our result cannot be readily generalised to the entire Milky Way.
While molecular gas mass is usually derived from $^{12}$CO($J$=1-0) - the most fundamental line to explore molecular gas - it is often derived from $^{12}$CO($J$=2-1) assuming a constant $^{12}$CO($J$=2-1)/$^{12}$CO($J$=1-0) line ratio ($R_{2/1}$). We present variations of $R_{2/1}$ and effects of the assumption that $R_{2/1}$ is a constant in 24 nearby galaxies using $^{12}$CO data obtained with the Nobeyama 45-m radio telescope and IRAM 30-m telescope. The median of $R_{2/1}$ for all galaxies is 0.61, and the weighted mean of $R_{2/1}$ by $^{12}$CO($J$=1-0) integrated-intensity is 0.66 with a standard deviation of 0.19. The radial variation of $R_{2/1}$ shows that it is high (~0.8) in the inner ~1 kpc while its median in disks is nearly constant at 0.60 when all galaxies are compiled. In the case that the constant $R_{2/1}$ of 0.7 is adopted, we found that the total molecular gas mass derived from $^{12}$CO($J$=2-1) is underestimated/overestimated by ~20%, and at most by 35%. The scatter of a molecular gas surface density within each galaxy becomes larger by ~30%, and at most by 120%. Indices of the spatially resolved Kennicutt-Schmidt relation by $^{12}$CO($J$=2-1) are underestimated by 10-20%, at most 39% in 17 out of 24 galaxies. $R_{2/1}$ has good positive correlations with star-formation rate and infrared color, and a negative correlation with molecular gas depletion time. There is a clear tendency of increasing $R_{2/1}$ with increasing kinetic temperature ($T_{rm kin}$). Further, we found that not only $T_{rm kin}$ but also pressure of molecular gas is important to understand variations of $R_{2/1}$. Special considerations should be made when discussing molecular gas mass and molecular gas properties inferred from $^{12}$CO($J$=2-1) instead of $^{12}$CO($J$=1-0).
We have mapped the Orion-A Giant Molecular Cloud in the CO (J=4-3) line with the Tsukuba 30-cm submillimeter telescope.The map covered a 7.125 deg^2 area with a 9 resolution, including main components of the cloud such as Orion Nebula, OMC-2/3, and L1641-N. The most intense emission was detected toward the Orion KL region. The integrated intensity ratio between CO (J=4-3) and CO (J=1-0) was derived using data from the Columbia-Univ. de Chile CO survey, which was carried out with a comparable angular resolution. The ratio was r_{4-3/1-0} ~ 0.2 in the southern region of the cloud and 0.4-0.8 at star forming regions. We found a trend that the ratio shows higher value at edges of the cloud. In particular the ratio at the north-eastern edge of the cloud at (l, b) = (208.375 deg, -19.0 deg) shows the specific highest value of 1.1. The physical condition of the molecular gas in the cloud was estimated by non-LTE calculation. The result indicates that the kinetic temperature has a gradient from north (Tkin=80 K) to south (20 K). The estimation shows that the gas associated with the edge of the cloud is warm (Tkin~60 K), dense (n_{H_2}~10^4 cm^{-3}), and optically thin, which may be explained by heating and sweeping of interstellar materials from OB clusters.
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