Continuum sources from the THOR survey between 1 and 2 GHz

Abstract

We carried out a large program with the Karl G. Jansky Very Large Array (VLA): "THOR: The HI, OH, Recombination line survey of the Milky Way". We observed a significant portion of the Galactic plane in the first quadrant of the Milky Way in the 21cm HI line, 4 OH transitions, 19 radio recombination lines, and continuum from 1 to 2 GHz. In this paper we present a catalog of the continuum sources in the first half of the survey (l=14.0-37.9deg and l=47.1-51.2deg, |b|<1.1deg) at a spatial resolution of 10-25", with a spatially varying noise level of ~0.3-1 mJy/beam. The catalog contains ~4400 sources. Around 1200 of these are spatially resolved, and ~1000 are possible artifacts, given their low signal-to-noise ratios. Since the spatial distribution of the unresolved objects is evenly distributed and not confined to the Galactic plane, most of them are extragalactic. Thanks to the broad bandwidth of the observations from 1 to 2 GHz, we are able to determine a reliable spectral index for ~1800 sources. The spectral index distribution reveals a double-peaked profile with maxima at spectral indices of alpha = -1 and alpha = 0 , corresponding to steep declining and flat spectra, respectively. This allows us to distinguish between thermal and non-thermal emission, which can be used to determine the nature of each source. We examine the spectral index of ~300 known HII regions, for which we find thermal emission with spectral indices around alpha = 0. In contrast, supernova remnants (SNR) show non-thermal emission with alpha = -0.5 and extragalactic objects generally have a steeper spectral index of alpha = -1. Using the spectral index information of the THOR survey, we investigate potential SNR candidates. We classify the radiation of four SNR candidates as non-thermal, and for the first time, we provide strong evidence for the SNR origin of these candidates.

24 pages, 34 figures, accepted for publication in A&A

References in corpus (6)

• The Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey
• The UKIDSS Galactic Plane Survey
• The VLA Galactic Plane Survey
• IR Dust Bubbles: Probing the Detailed Structure and Young Massive Stellar Populations of Galactic HII Regions
• FellWalker - a Clump Identification Algorithm
• Quasi-simultaneous multi-frequency observations of inverted-spectrum GPS candidate sources

Cited by in corpus (38)

• SEDIGISM: Structure, excitation, and dynamics of the inner Galactic interstellar medium
• Galactic Supernova Remnant Candidates Discovered by THOR
• Metallicity Structure in the Milky Way Disk Revealed by Galactic HII Regions
• The HI/OH/Recombination line survey of the inner Milky Way (THOR): data release 2 and HI overview
• Histogram of oriented gradients: a technique for the study of molecular cloud formation
• A Census of Early Phase High-Mass Star Formation in the Central Molecular Zone
• A Green Bank Telescope Survey of Large Galactic HII Regions
• GLOSTAR -- Radio Source Catalog I: $28^{\circ }<\text{l}<36^{\circ }$ and $|b|<1^{\circ }$
• H2O Southern Galactic Plane Survey (HOPS): Paper III - Properties of Dense Molecular Gas across the Inner Milky Way
• A VLA Search for Radio Signals from M31 and M33
• A population of hypercompact HII regions identified from young HII regions
• Radio continuum emission in the northern Galactic plane: Sources and spectral indices from the THOR survey
• A search for hypercompact HII regions in the Galactic Plane
• Strong excess Faraday rotation on the Inside of the Sagittarius spiral arm
• New insights in the HII region G18.88-0.49: hub-filament system and accreting filaments
• OH absorption in the first quadrant of the Milky Way as seen by THOR
• The GBT Diffuse Ionized Gas Survey (GDIGS): Survey Overview and First Data Release
• The Southern HII Region Discovery Survey I: The Bright Catalog
• A global view on star formation: The GLOSTAR Galactic plane survey IV. Radio continuum detections of young stellar objects in the Galactic Centre region
• Large-scale Map of Millimeter-wavelength Hydrogen Radio Recombination Lines around a Young Massive Star Cluster
• Confirmation Of Two Galactic Supernova Remnant Candidates Discovered By THOR
• ATLASGAL -- Relationship between dense star forming clumps and interstellar masers
• A global view on star formation: The GLOSTAR Galactic plane survey. IX. Radio Source Catalog III: 2<l<28, 36<l<40, 56<l<60 and |b|<1, VLA B-configuration
• A global view on star formation: The GLOSTAR Galactic plane survey X. Galactic HII region catalog using radio recombination lines
• High-resolution Very Large Array observations of 18 MIPSGAL bubbles
• Characterization of unresolved and unclassified sources detected in radio continuum surveys of the Galactic plane
• Search for and Identification of Young Compact Galactic Supernova Remnants Using THOR
• Searching for Magnetar Binaries Disrupted by Core-Collapse Supernovae
• Unraveling the inner substructure of new candidate hub-filament system in the HII region G25.4NW
• Probing the physical conditions and star formation processes in the Galactic HII region S305
• Early Science with the Large Millimetre Telescope: Fragmentation of molecular clumps in the Galaxy
• SCOTCH -- Search for Clandestine Optically Thick Compact HIIs
• Structural and spectral properties of Galactic plane variable radio sources
• Metrewave Galactic Plane with the uGMRT (MeGaPluG) Survey: Lessons from the Pilot Study
• Investigating the physical conditions in extended system hosting mid-infrared bubble N14
• The population of compact radio sources in M 17
• Astrometry of variable compact radio sources: A search for Galactic black hole X-ray binaries
• A VLA Census of the Galactic H II Region Population