Jurgen Stutzki

High spatial resolution isotopic CO and CS observations of M17 SW - The clumpy structure of the molecular cloud core

This paper presents high-angular-resolution maps of the M17 SW cloud core in the C(O-18) J = 2-1 (13 arcsec FWHM beam) and C(S-34) J = 2-1 (27 arcsec FWHM), 3-2 (17 arcsec FWHM) lines obtained with the IRAM 30 m telescope. These maps directly reveal the clumpy structure of the entire cloud core down to linear scales of 13 arcsec and below. Individual clumps have line widths as small as 0.5 km/s, compared to a line width of 3-5 km/s observed with lower angular resolution in the same lines. The C(O-18) 2-1 line reaches a peak brightness temperature of 24 K in the 13-arcsec beam and is probably slightly optically thick in several locations. Spectra in the more abundant CO isotopes obtained toward several selected positions show strong self-absorption notches and peak brightness temperatures in between these notches of about 100 K. 65 refs.

Aperture synthesis observations of the circumnuclear ring in the Galactic center

Aperture synthesis observations with the Hat Creek millimeter-wave interferometer have been used to study the circumnuclear neutral gas ring in the Galactic center at high spatial and spectral resolution. The resulting data demonstrate the existence of a highly inclined, thin, and clumpy ring or disk of molecular material centered on IRS 16 and the radio point source. The molecular gas is dynamically coupled to ionized gas in the central cavity. The dominant large-scale velocity pattern of most of the molecular gas in the inner 5 pc is rotation. The rotation appears to be perturbed by a large local velocity dispersion, by warping of the structure, and by at least one cloud probably located in the ring but not participating in the rotation.

GREAT: the SOFIA high-frequency heterodyne instrument

We describe the design and construction of GREAT (German REceiver for Astronomy at Terahertz frequencies) operated on the Stratospheric Observatory For Infrared Astronomy (SOFIA). GREAT is a modular dual-color heterodyne instrument for highresolution far-infrared (FIR) spectroscopy. Selected for SOFIA’s Early Science demonstration, the instrument has successfully performed three Short and more than a dozen Basic Science flights since first light was recorded on its April 1, 2011 commissioning flight. We report on the in-flight performance and operation of the receiver that – in various flight configurations, with three different detector channels – observed in several science-defined frequency windows between 1.25 and 2.5 THz. The receiver optics was verified to be diffraction-limited as designed, with nominal efficiencies; receiver sensitivities are state-of-the-art, with excellent system stability. The modular design allows for the continuous integration of latest technologies; we briefly discuss additional channels under development and ongoing improvements for Cycle 1 observations. GREAT is a principal investigator instrument, developed by a consortium of four German research institutes, available to the SOFIA users on a collaborative basis.

Anatomy of the photodissociation region in the orion bar.

Much of the interstellar gas resides in photodissociation regions whose chemistry and energy balance is controlled by the flux of far-ultraviolet radiation upon them. These photons can ionize and dissociate molecules and heat the gas through the photoelectric effect working on dust grains. These regions have been extensively modeled theoretically, but detailed observational studies are few. Mapping of the prominent Orion Bar photodissociation region at wavelengths corresponding to the carbon-hydrogen stretching mode of polycyclic aromatic hydrocarbons, the 1-0 S(1) line of molecular hydrogen, and the J = 1-0 rotational line of carbon monoxide allows the penetration of the far-ultraviolet radiation into the cloud to be traced. The results strongly support the theoretical models and show conclusively that the incident far-ultraviolet radiation field, not shocks as has sometimes been proposed, is responsible for the emission in the Orion Bar.

158 micron forbidden C II mapping of the Orion molecular cloud

A fully sampled, 1000-point, 1-arcmin-resolution map of the inner 6.5 x 10 arcmin (alpha x delta) regions of the Orion Nebula in the 157.7409-micron forbidden fine-structure line is constructed. Large-scale strip maps in forbidden C II across the face of the Orion molecular cloud, and CO(17-16), (14-13), and (7-6) spectra are obtained at selected positions in the Orion H II region/molecular cloud interface. Strong forbidden C II line emission is observed across the face of the Orion molecular. The total forbidden C II luminosity from the Orion molecular cloud is about 1500 solar luminosities, or 0.3 percent of the FIR luminosity. The extended forbidden C II emission probably arises in either the UV-exposed surface of the molecular cloud or from the surfaces of UV-exposed clumps within the molecular cloud.

Quantification of molecular cloud structure using the

We present a detailed study of the Δ -variance as a method to quantify molecular cloud structure. The Δ -variance was introduced by Stutzki et al. (1998) to analyze the drift behaviour of scalar functions and is used to characterize the spatial structure of observed molecular cloud images. For fractional Brownian motion structures ( fBm-fractals ), characterized by a power law power spectrum and random phases, the Δ -variance allows to determine the power spectral index β . We present algorithms to determine the Δ -variance for discretely sampled maps and study the influence of white noise, beam smoothing and the finite spatial extent of the maps. We find that for images with

\Delta

\beta> 3

-variance

, edge effects can bias the structure parameters when determined by means of a Fourier transform analysis. In contrast, the Δ -variance provides a reliable estimate for the spectral index β , if determined in the spatial domain. The effects of noise and beam smoothing are analytically represented in a leading order approximation. This allows to use the Δ -variance of observed maps even at scales where the influence of both effects becomes significant, allowing to derive the spectral index β over a wider range and thus more reliably than possible otherwise. The Δ -variance is applied to velocity integrated spectral line maps of several clouds observed in rotational transitions of 12 CO and 13 CO. We find that the spatial structure of the emission is well characterized by a power law power spectrum in all cases. For linear scales larger than ∼ 0.5 pc the spectral index is remarkably uniform for the different clouds and transitions observed (

Atomic Carbon in M82: Physical Conditions Derived from Simultaneous Observations of the [C I] Fine-Structure Submillimeter-Wave Transitions

2.5\le\beta\le2.8

First observations of the CO J=6-5 transition in starburst galaxies

). Significantly larger values (