Thomas M. Bania

GLIMPSE. I. An SIRTF Legacy Project to Map the Inner Galaxy

ABSTRACT The Galactic Legacy Infrared Mid‐Plane Survey Extraordinaire (GLIMPSE), a Space Infrared Telescope Facility (SIRTF) Legacy Science Program, will be a fully sampled, confusion‐limited infrared survey of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

The Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey

\frac{2}{3}

FIRST GLIMPSE RESULTS ON THE STELLAR STRUCTURE OF THE GALAXY

\end{document} of the inner Galactic disk with a pixel resolution of ∼1 \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \u...

The Structure of Four Molecular Cloud Complexes in the BU-FCRAO Milky Way Galactic Ring Survey

The Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey is a new survey of Galactic 13CO J = 1 → 0 emission. The survey used the SEQUOIA multipixel array on the Five College Radio Astronomy Observatory 14 m telescope to cover a longitude range of l = 18°-557 and a latitude range of |b| 40°. At the velocity resolution of 0.21 km s-1, the typical rms sensitivity is σ(T) ~ 0.13 K. The survey comprises a total of 1,993,522 spectra. We show integrated intensity images (zeroth moment maps), channel maps, position-velocity diagrams, and an average spectrum of the completed survey data set. We also discuss the telescope and instrumental parameters, the observing modes, the data reduction processes, and the emission and noise characteristics of the data set. The Galactic Ring Survey data are available to the community online or in DVD form by request.

Resolving the Kinematic Distance Ambiguity toward Galactic H II Regions

The GLIMPSE (Galactic Legacy Mid-Plane Survey Extraordinaire) Point Source Catalog of ~30 million mid-infrared sources toward the inner Galaxy, 10° ≤ |l| ≤ 65° and |b| ≤ 1°, was used to determine the distribution of stars in Galactic longitude, l, latitude, b, and apparent magnitude, m. The counts versus longitude can be approximated by the modified Bessel function N = N0(l/l0)K1(l/l0), where l0 is insensitive to limiting magnitude, band choice, and side of Galactic center: l0 = 17°-30° with a best-fit value in the 4.5 μm band of l0 = 24° ± 4°. Modeling the source distribution as an exponential disk yields a radial scale length of H* = 3.9 ± 0.6 kpc. There is a pronounced north-south asymmetry in source counts for |l| 30°, with ~25% more stars in the north. For l = 10°-30°, there is a strong enhancement of stars of m = 11.5-13.5 mag. A linear bar passing through the Galactic center with half-length Rbar = 4.4 ± 0.5 kpc, tilted by = 44° ± 10° to the Sun-Galactic center line, provides the simplest interpretation of these data. We examine the possibility that enhanced source counts at l = 26°-28°, 315-34°, and 306°-309° are related to Galactic spiral structure. Total source counts are depressed in regions where the counts of red objects (mK-m[8.0] > 3) peak. In these areas, the counts are reduced by extinction due to molecular gas, high diffuse backgrounds associated with star formation, or both.

RCW 49 at Mid-Infrared Wavelengths: A GLIMPSE from the Spitzer Space Telescope

We present a study of the structure of four molecular clouds from the Milky Way Galactic Ring Survey (GRS), a Boston University and Five College Radio Astronomy Observatory collaboration. The GRS is a new high-resolution survey in the 13CO J = 1 → 0 spectral line of the inner Galaxy and the 5 kpc ring, the Milky Ways dominant star-forming structure. Because of the smaller line widths of 13CO compared to 12CO, we can avoid velocity crowding and establish accurate kinematic distances to the clouds. The kinematic distance ambiguity in the first Galactic quadrant is resolved using self-absorption in complementary high-resolution atomic hydrogen data. The four clouds are selected to span a large range of star formation activity, from the quiescent cloud GRSMC 45.60+0.30, which shows no signs of high-mass star formation, to W49, the most luminous star-forming region in the Galaxy. We use a three-dimensional Gaussian clump decomposition to identify clumps in the clouds and to investigate their properties. Each cloud has the same clump mass spectrum, dN/dM ∝ M-1.8, independent of star formation activity. We do not find significant differences in the slopes of the relations of density, line width, and clump mass as a function of clump size among the clouds. The size-density and size-line width relations show considerable scatter. Compared to the conventional Larson scaling laws, we find systematically flatter slopes for the size-density and size-line width relations and a higher power-law index for the size-mass relation. In particular, the clump line widths for the most quiescent cloud GRSMC 45.60+0.30 are independent of clump size. While the clouds as a whole are gravitationally bound, most of the clumps are not; only a small fraction of the total number of clumps is self-gravitating. The active star-forming clouds have a higher fraction of gravitationally bound clumps and a higher mean cloud volume density than the more quiescent clouds. The gravitationally unbound clumps are possibly confined by the weight of the self-gravitating complex. The pressures needed to bind these clumps are largest for the active star-forming clouds, which have a much higher weight than the quiescent clouds. Alternatively, a high number of the gravitationally unbound clumps may be transient.

The Antarctic Submillimeter Telescope and Remote Observatory (AST/RO)

Kinematic distance determinations in the inner Galaxy are hampered by the near-far kinematic distance ambiguity. Here we resolve the ambiguity for 49 H II region complexes with known recombination-line velocities in the first Galactic quadrant. We measured the 21 cm H I absorption spectrum toward each source with the Very Large Array in the C array. The maximum velocity of H I absorption was used to discriminate between the near and far kinematic distances. The number ratio of far to near sources, ~3, can be entirely explained as a geometrical effect. The kinematic distances that we derive are compared with previous determinations for the same sources. Although our distance determinations are largely in agreement with previous measurements, there are 22 discrepancies that we discuss. Using our distance determinations, we create a face-on Galactic map of the H II region complexes and compare it with a kinematically derived profile of the distribution of CO-traced molecular hydrogen. The H II region complexes delineate the large-scale features seen in the molecular gas. The 5 kpc molecular ring and the Sagittarius spiral arm are clearly evident, and a few H II region complexes lie in the Perseus arm.

Detection of AU-scale structure in molecular clouds

The luminous, massive star formation region RCW 49, located in the southern Galactic plane, was imaged with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope as part of the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) program. The IRAC bands contain polycyclic aromatic hydro- carbon (PAH) features at 3.3, 6.2, 7.7, and 8.6 � m, as well as the Brline. These features are the major contributors to the diffuse emission from RCW 49 in the IRAC bands. The Spitzer IRAC images show that the dust in RCW 49 is distributed in a network of fine filaments, pillars, knots, sharply defined boundaries, bubbles, and bow shocks. The regions immediately surrounding the ionizing star cluster and W-R stars are evacuated of dust by stellar winds and radiation. The IRAC images of RCW 49 suggest that the dust in RCW 49 has been sculpted by the winds and radiation from the embedded luminous stars in the inner 5 0 (inner � 6 pc) of the nebula. At projected angular radii �> 5 0 from the central ionizing cluster, the azimuthally averaged infrared intensity falls off as � � � 3 . Both high-resolution radio and mid-IR images suggest that the nebula is density bounded along its western boundary. The filamentary structure of the dust in RCW 49 suggests that the nebula has a small dust filling factor and, as a consequence, the entire nebula may be slightly density bounded to H-ionizing photons. Subject headingg astrochemistry — dust, extinction — H ii regions — infrared: ISM — ISM: lines and bands

A GLIMPSE OF STAR FORMATION IN THE GIANT H II REGION RCW 49

The Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) is a 1.7-meter diameter offset Gregorian instrument located at the NSF Amundsen-Scott South Pole Station. This site is exceptionally dry and cold, providing opportunities for Terahertz observations from the ground. Preliminary analysis of recent site testing results shows that the zenith transparency of the 1.5 THz atmospheric window at South Pole frequently exceeds 10% during the Austral winter. Routine observations at 810 GHz have been conducted over the past two years, resulting in large-scale maps of the Galactic Center region and measurements of the (13)C line in molecular clouds. During the next two years, the observatory plans to support two Terahertz instruments: 1) TREND (Terahertz Receiver with Niobium Nitride Device--K. S. Yngvesson, University of Massachusetts, P. I.), and 2) SPIFI (South Pole Imaging Fabry-Perot Interferometer--G. J. Stacey, Cornell University, P. I.). AST/RO could be used in future as an observational test bed for additional prototype Terahertz instruments. Observing time on AST/RO is available on a proposal basis (see this http URL).

H I Self-Absorption and the Kinematic Distance Ambiguity: The Case of the Molecular Cloud GRSMC 45.6+0.3

We have detected significant secular changes in the 4.83 GHz H 2 CO absorption line toward the compact extragalactic radio sources NRAO 150 and 3C 111 with the Very Large Array. In each case the absorption occurs within a molecular cloud in our Galaxy against the submilliarcsecond core or the background radio source. Because of relative motion between Earth and the cloud, the position of the line of sight through each cloud drifts by a transverse distance or ∼4 AU per year. The changes in absorption-line profile over a period of 2.05 yr are interpreted in terms of clumps of size ≤10 AU in the molecular cloud