We present CO, H2, H i and HISA (H i self-absorption) distributions from a set of simulations of grand design spirals including stellar feedback, self-gravity, heating and cooling. We replicate the emission of the second galactic quadrant by placing the observer inside the modelled galaxies and post-process the simulations using a radiative transfer code, so as to create synthetic observations. We compare the synthetic data cubes to observations of the second quadrant of the Milky Way to test the ability of the current models to reproduce the basic chemistry of the Galactic interstellar medium (ISM), as well as to test how sensitive such galaxy models are to different recipes of chemistry and/or feedback. We find that models which include feedback and self-gravity can reproduce the production of CO with respect to H2 as observed in our Galaxy, as well as the distribution of the material perpendicular to the Galactic plane. While changes in the chemistry/feedback recipes do not have a huge impact on the statistical properties of the chemistry in the simulated galaxies, we find that the inclusion of both feedback and self-gravity are crucial ingredients, as our test without feedback failed to reproduce all of the observables. Finally, even though the transition from H2 to CO seems to be robust, we find that all models seem to underproduce molecular gas, and have a lower molecular to atomic gas fraction than is observed. Nevertheless, our fiducial model with feedback and self-gravity has shown to be robust in reproducing the statistical properties of the basic molecular gas components of the ISM in our Galaxy.
We present $^{12}$CO, $^{13}$CO and C$^{18}$O (J=3$-$2) observations of a new cluster of outflows in the Vulpecula Rift with HARP-B on the JCMT. The mass associated with the outflows, measured using the $^{12}$CO HARP-B observations and assuming a distance to the region of 2.3 kpc, is 129 \msol{}, while the mass associated with the dense gas from C$^{18}$O observations is 458 \msol{} and the associated sub-millimeter core has a mass of 327 $\pm$ 112 \msol{} independently determined from Bolocam 1.1mm data. The outflow-to-core mass ratio is therefore $\sim$0.4, making this region one of the most efficient observed thus far with more than an order of magnitude more mass in the outflow than would be expected based on previous results. The kinetic energy associated with the flows, 94$\times10^{45}$ ergs, is enough to drive the turbulence in the local clump, and potentially unbind the local region altogether. The detection of SiO (J=8$-$7) emission toward the outflows indicates that the flow is still active, and not simply a fossil flow. We also model the SEDs of the four YSOs associated with the molecular material, finding them all to be of mid to early B spectral type. The energetic nature of the outflows and significant reservoir of cold dust detected in the sub-mm suggest that these intermediate mass YSOs will continue to accrete and become massive, rather than reach the main sequence at their current mass.
The Gould Belt Legacy Survey on the James Clerk Maxwell Telescope's has observed a region of 260 arcmin2 in 12CO J= 3 → 2 emission, and a 190 arcmin2 subset of this in 13CO and C18O towards the Serpens molecular cloud. We examine the global velocity structure of the non-outflowing gas, and calculate excitation temperatures and opacities. The large-scale mass and energetics of the region are evaluated, with special consideration for high-velocity gas. We find the cloud to have a mass of 203 M⊙, and to be gravitationally bound, and that the kinetic energy of the outflowing gas is approximately 70 per cent of the turbulent kinetic energy of the cloud. We identify compact outflows towards some of the submillimetre Class 0/I sources in the region.
We have generated a molecular cloud catalog from the Five College Radio Astronomy Observatory Outer Galaxy Survey of 12CO (J = 1-0) emission using a two-phase object identification procedure. The first phase consists of grouping pixels into contiguous structures above a radiation temperature threshold of 0.8 K. The second phase decomposes the first-phase objects by an enhanced version of the CLUMPFIND algorithm, using dynamic thresholding, and again with a threshold of 0.8 K used for discrimination. A detailed comparison of our method with the CLUMPFIND algorithm is given, highlighting the advantages of the use of dynamic (rather than quantized) thresholding. Basic attributes of the clouds—coordinates, bounding boxes, integrated intensities, peak observed temperatures—are tabulated in the catalog. A two-dimensional elliptical Gaussian is fitted to the velocity-integrated map of each cloud; the major and minor axis sizes and major axis position angles thus derived are included in the catalog. To the spatially integrated emission line of each cloud, a Gaussian profile is fitted to measure the global linewidth. Model Gaussian clouds, truncated at 0.8 K, are examined to determine the effects of biases on measured quantities, induced by truncation. Coupled with detailed analysis of the cataloged clouds, statistical corrections for the effects of truncation on measured sizes, linewidths, and integrated intensities are derived and applied, along with corrections for the effects of finite resolution on the measured attributes. The cataloged emission accounts for 76.4% of the total emission in the Outer Galaxy Survey. The deficit is shown to arise mainly from low-intensity emission on the periphery of larger objects, rather than from a large number of small and/or low-intensity features.
We generate synthetic HI Galactic plane surveys from spiral galaxy simulations which include stellar feedback processes. Compared to a model without feedback we find an increased scale height of HI emission (in better agreement with observations) and more realistic spatial structure (including supernova blown bubbles). The synthetic data show HI self-absorption with a morphology similar to that seen in observations. The density and temperature of the material responsible for HI self-absorption is consistent with observationally determined values, and is found to be only weakly dependent on absorption strength and star formation efficiency.
As part of a James Clerk Maxwell Telescope (JCMT) Legacy Survey of star formation in the Gould Belt, we present early science results for Taurus. CO J= 3 –2 maps have been secured along the north-west ridge and bowl, collectively known as L 1495, along with deep 13CO and C18O J= 3 –2 maps in two subregions. With these data, we search for molecular outflows, and use the distribution of flows, Herbig–Haro (HH) objects and shocked H2 line-emission features, together with the population of young stars, protostellar cores and starless condensations to map star formation across this extensive region. In total, 21 outflows are identified. It is clear that the bowl is more evolved than the ridge, harbouring a greater population of T Tauri stars and a more diffuse, more turbulent ambient medium. By comparison, the ridge contains a much younger, less widely distributed population of protostars which, in turn, is associated with a greater number of molecular outflows. We estimate the ratio of the numbers of pre-stellar to protostellar cores in L 1495 to be ∼1.3–2.3, and of gravitationally unbound starless cores to (gravitationally bound) pre-stellar cores to be ∼1. If we take previous estimates of the protostellar lifetime of ∼5 × 105 yr, this indicates a pre-stellar lifetime of 9(±3) × 105 yr. From the number of outflows, we also crudely estimate the star formation efficiency in L 1495, finding it to be compatible with a canonical value of 10–15 per cent. We note that molecular outflow-driving sources have redder near-infrared colours than their HH jet-driving counterparts. We also find that the smaller, denser cores are associated with the more massive outflows, as one might expect if mass build-up in the flow increases with the collapse and contraction of the protostellar envelope.
We present Spitzer, near-IR (NIR) and millimetre observations of the massive star-forming regions W5-east, S235, S252, S254-S258 and NGC 7538. Spitzer data is combined with NIR observations to identify and classify the young population while 12CO and 13CO observations are used to examine the parental molecular cloud. We detect in total 3021 young stellar objects (YSOs). Of those, 539 are classified as Class I, and 1186 as Class II sources. YSOs are distributed in groups surrounded by a more scattered population. Class I sources are more hierarchically organized than Class II and associated with the most dense molecular material. We identify in total 41 embedded clusters containing between 52 and 73 per cent of the YSOs. Clusters are in general non-virialized, turbulent and have star formation efficiencies between 5 and 50 per cent. We compare the physical properties of embedded clusters harbouring massive stars (MEC) and low-mass embedded clusters (LEC) and find that both groups follow similar correlations where the MEC are an extrapolation of the LEC. The mean separation between MEC members is smaller compared to the cluster Jeans length than for LEC members. These results are in agreement with a scenario where stars are formed in hierarchically distributed dusty filaments where fragmentation is mainly driven by turbulence for the more massive clusters. We find several young OB-type stars having IR-excess emission which may be due to the presence of an accretion disc.
Two potential sites of H2 formation have been discovered in diffuse gas at high Galactic latitude through examining the far-infrared (FIR) H i ratio and looking for an excess over that expected from an atomic medium. We call these the Spider and Ursa Major fields. New 12CO and 13CO Five College Radio Astronomical Observatory observations are presented for both regions (53 936 spectra in the Spider and 23 517 spectra in Ursa Major). Although there is a correlation between FIR excess and CO emission, we find that the FIR excess peaks do not coincide with the 12CO emission peaks, indicating that CO might be a poor tracer of H2 in diffuse regions. This implies (i) that the density is too small to allow CO excitation, (ii) that the CO self-shielding is insufficient or (iii) local variations of the dust properties. The 12CO observations are compared with H i observations from the Dominion Radio Astrophysical Observatory. We decompose the 10 000 H i profiles of the Spider and the 20 302 H i profiles of Ursa Major into Gaussian components. We always find at most two narrow components and one broad component. CO always seems to appear where two H i velocity components merge or where there is a H i velocity-shear.
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