Studies of Molecular Clouds associated with H II Regions: S175

We are studying the impact of HII regions on star formation in their associated molecular clouds. In this paper we present JCMT RxA molecular line observations of S175 and environs. This is the first within a sample of ten HII regions and their surrounding molecular clouds selected for our study. We first make 7'x 7' maps in $^{12}$CO(2-1), which are used to investigate the structure of the cloud and to identify individual clumps. Single point observations were made in $^{13}$CO(2-1) and CS(5-4) at the peak of the $^{12}$CO(2-1) emission within each clump in order to measure the physical properties of the gas. Densities, temperatures, clump masses, peak velocities, and line widths were measured and calculated using these observations. We have identified two condensations (S175A and S175B) in the molecular cloud associated with this HII region. S175A is adjacent to the ionization front and is expected to be affected by the HII region while S175B is too distant to be disturbed. We compare the structure and gas properties of these two regions to investigate how the molecular gas has been affected by the HII region. S175A has been heated by the HII region and partially compressed by the ionized gas front, but contrary to our expectation it is a quiescent region while S175B is very turbulent and dynamically active. Our investigation for the source of turbulence in S175B resulted in the detection of an outflow within this region.Comment: 33 pages, 11 figures, 6 tables, accepted for publication in Astronomical Journa

Observational Determination of the Turbulent Ambipolar Diffusion Scale and Magnetic Field Strength in Molecular Clouds

We study the correlation of the velocity dispersion of the coexisting molecules H13CN and H13CO+ and the turbulent energy dissipation scale in the DR21(OH) star-forming region. The down-shift of the H13CO+ spectrum relative to H13CN is consistent with the presence of ambipolar diffusion at dissipation length scales that helps the process of turbulent energy dissipation, but at a different cut-off for ions compared to the neutrals. We use our observational data to calculate a turbulent ambipolar diffusion length scale L'\simeq17 mpc and a strength of B_{pos}\simeq1.7 mG for the plane of the sky component of the magnetic field in DR21(OH)

Spectral Cube Visualisation and Explorer Tool from the Herschel Interactive Processing Environment (HIPE)

We present the interactive tool for visualizing and exploring spectral cubes of the Herschel Interactive Processing Environment (HIPE). With this GUI tool, one can easily plot the spectra within the cube, compare several cubes from the same region of the sky, and run a number of analysis tasks on them (such as computing velocity/dispersion maps or position-velocity diagrams). The tool is integrated within the Spectral Explorer from HIPE, which offers additional functionality such as an interface to the spectral fitter tool. All the actions with HIPE tools produce Python code, which can later be reused in scripts for automation. Various results can be saved as FITS files and loaded into other astronomical analysis tools

A precessing jet in the NGC2264G outflow

We (Teixeira et al., 2008) present IRAC imaging of the NGC 2264 G protostellar outflow region. A jet in the red (eastern) outflow lobe is clearly detected in all four IRAC bands, and is shown to continuously extend over the entire length of the red outflow lobe as seen in CO. The easternmost part of the jet exhibits multiple changes of direction, which we find can be largely explained by a slowly precessing jet. The changes in the jet direction may be sufficient to account for a significant fraction of the broadening of the outflow lobe, as observed in CO emission.</p

A spectroscopic study of the giant infrared jet powering NGC 2264 G

We propose to obtain Spitzer IRS spectral maps of the jet associated with the NGC 2264 G outflow. Our analysis of Spitzer IRAC observations revealed the jet to continuously extend along the entire (~1 pc) length of the redshifted lobe of this very young and highly collimated CO outflow (Teixeira et al., 2007). We found the jet to undergo multiple changes in direction as a result of either precession or deflection. We intend to use the proposed IRS observations in conjunction with shock models to quantitatively evaluate how the physical conditions (temperature, column density, ionization) vary along the jet. In doing so we hope to test the hypothesis that the narrow jet we observed in the IRAC images has sufficient energy and momentum to both broaden and drive the molecular outflow. The second goal of this proposal is to obtain detailed mid-infrared diagnostics of the Class 0 driving source of the outflow, VLA2, and a nearby Class I source, VLA1 which is not driving an outflow. These two protostars have formed under similar conditions and their study will help us further understand how protostellar envelopes are modified by jets