The HI/OH/Recombination line survey of the inner Milky Way (THOR)

Abstract

Context: The past decade has witnessed a large number of Galactic plane surveys at angular resolutions below 20". However, no comparable high-resolution survey exists at long radio wavelengths around 21cm in line and continuum emission. Methods: Employing the Very Large Array (VLA) in the C-array configuration and a large program, we observe the HI 21cm line, four OH lines, nineteen Halpha radio recombination lines as well as the continuum emission from 1 to 2GHz in full polarization over a large part of the first Galactic quadrant. Results: Covering Galactic longitudes from 14.5 to 67.4deg and latitudes between +-1.25deg, we image all of these lines and the continuum at ~20" resolution. These data allow us to study the various components of the interstellar medium (ISM): from the atomic phase, traced by the HI line, to the molecular phase, observed by the OH transitions, to the ionized medium, revealed by the cm continuum and the Halpha radio recombination lines. Furthermore, the polarized continuum emission enables magnetic field studies. In this overview paper, we discuss the survey outline and present the first data release as well as early results from the different datasets. We now release the first half of the survey; the second half will follow later after the ongoing data processing has been completed. The data in fits format (continuum images and line data cubes) can be accessed through the project web-page http://www.mpia.de/thor. Conclusions: The HI/OH/Recombination line survey of the Milky Way (THOR) opens a new window to the different parts of the ISM. It enables detailed studies of molecular cloud formation, conversion of atomic to molecular gas, and feedback from HII regions as well as the magnetic field in the Milky Way. It is highly complementary to other surveys of our Galaxy, and comparing different datasets allows us to address many open questions.

Accepted for Astronomy & Astrophysics, 23 pages, 17 figures, a high-resolution version can be found at http://www.mpia.de/thor

References in corpus (16)

• The VLA Galactic Plane Survey
• From the warm magnetized atomic medium to molecular clouds
• On the Rapid Collapse and Evolution of Molecular Clouds
• CO-dark gas and molecular filaments in Milky Way type galaxies
• The Effelsberg-Bonn HI Survey: Milky Way gas. First data release
• Cooling, Gravity and Geometry: Flow-driven Massive Core Formation
• Resolution of the Distance Ambiguity for Galactic HII Regions
• Large-scale filaments associated with Milky Way spiral arms
• Rapid Molecular Cloud and Star Formation: Mechanisms and Movies
• The Bones of the Milky Way
• CHIMPS: the ${}^{13}$CO/C${}^{18}$O (J=3-2) Heterodyne Inner Milky Way Plane Survey
• The 21-SPONGE HI Absorption Survey I: Techniques and Initial Results
• The formation of the W43 complex: constraining its atomic-to-molecular transition and searching for colliding clouds
• ATLAS 1.4 GHz Data Release 2 -- II. Properties of the faint polarized sky
• An Improved Technique for Measurement of Cold HI in Molecular Cloud Cores
• HI 21 cm opacity fluctuations power spectra towards Cassiopeia A

Cited by in corpus (28)

• Galactic Supernova Remnant Candidates Discovered by THOR
• Tracing the formation of molecular clouds via [CII], [CI] and CO emission
• The SEDIGISM survey: first data release and overview of the Galactic structure
• A global view on star formation: The GLOSTAR Galactic Plane Survey. I. Overview and first results for the Galactic longitude range 28° < l < 36°
• Histogram of oriented gradients: a technique for the study of molecular cloud formation
• The Physical and chemical structure of Sagittarius B2 -- IV. Converging filaments in the high-mass cluster forming region Sgr B2(N)
• GLOSTAR -- Radio Source Catalog I: $28^{\circ }<\text{l}<36^{\circ }$ and $|b|<1^{\circ }$
• A global view on star formation: The GLOSTAR Galactic plane survey. II. Supernova Remnants in the first quadrant of the Milky Way
• H2O Southern Galactic Plane Survey (HOPS): Paper III - Properties of Dense Molecular Gas across the Inner Milky Way
• CHIMPS2: Survey description and ${}^{12}$CO emission in the Galactic Centre
• Synthetic observations of star formation and the interstellar medium
• A search for hypercompact HII regions in the Galactic Plane
• HI-to-H2 Transition Layers in the Star-Forming Region W43
• Strong excess Faraday rotation on the Inside of the Sagittarius spiral arm
• SEDIGISM-ATLASGAL: Dense Gas Fraction and Star Formation Efficiency Across the Galactic Disk
• The diffuse gamma-ray emission toward the Galactic mini starburst W43
• Confirmation Of Two Galactic Supernova Remnant Candidates Discovered By THOR
• ATLASGAL -- Relationship between dense star forming clumps and interstellar masers
• The hydroxyl satellite-line `flip' as a tracer of expanding HII regions
• Extending the view of ArH+ chemistry in diffuse clouds
• Characterization of unresolved and unclassified sources detected in radio continuum surveys of the Galactic plane
• The discovery of the largest gas filament in our Galaxy, or a new spiral arm?
• Search for and Identification of Young Compact Galactic Supernova Remnants Using THOR
• Unraveling the inner substructure of new candidate hub-filament system in the HII region G25.4NW
• Molecular Bow Shock in the 3-kpc Norma Arm
• The warm and dense Galaxy - tracing the formation of dense cloud structures out to the Galactic Center
• Shape Analysis of HII Regions -- II. Synthetic Observations
• Investigating the physical conditions in extended system hosting mid-infrared bubble N14