Polarization shadows of extragalactic sources by the local magneto-ionic ISM

Abstract

We report depolarization of extragalactic sources in the NRAO VLA Sky Survey (NVSS) by local structures in the interstellar medium. The sky density of polarized sources drops by a factor 2 - 4 in regions with angular scales approx. 10 degrees, implying up to 40% depolarization on average per source. Some of these polarization shadows are associated with HII regions, but three are associated with regions of depolarized diffuse Galactic emission. The absence of a correlation between the depth of polarization shadows and H-alpha intensity suggests that some shadows are related to structure in the magnetic field. At least some polarization shadows are caused by partial bandwidth depolarization in the NVSS. Alternatively, some may be caused by regions with small scale (< 1 arcsec) variations in rotation measure.

11 pages, 2 figures. Both figures provided as separate gif images. Accepted for publication in The Astrophysical Journal Letters

References in corpus (18)

• A Full-Sky H-alpha Template for Microwave Foreground Prediction
• A Robotic Wide-Angle H-Alpha Survey of the Southern Sky
• The Wisconsin H-Alpha Mapper Northern Sky Survey
• Pulsar rotation measures and the magnetic structure of our Galaxy
• The magnetic field of the Large Magellanic Cloud revealed through Faraday rotation
• An absolutely calibrated survey of polarized emission from the northern sky at 1.4 GHz
• Radio polarization from the inner Galaxy at arcminute resolution
• A Multiwavelength Optical Emission Line Survey of Warm Ionized Gas in the Galaxy
• A 1.4 GHz radio continuum and polarization survey at medium Galactic latitudes: II. First section
• The Southern Galactic Plane Survey: Polarized Radio Continuum Observations and Analysis
• Structures in the RM sky
• Enhanced small-scale Faraday rotation in the Galactic spiral arms
• Predictions on high frequency polarization properties of extragalactic radio sources and implications for CMB polarization measurements
• Radio Polarization from the Galactic Plane in Cygnus
• Radio polarimetric imaging of the interstellar medium: magnetic field and diffuse ionized gas structure near the W3/W4/W5/HB3 complex
• Estimating the Porosity of the Interstellar Medium from Three-Dimensional Photoionization Modeling of H II Regions
• An Investigation of Diffuse Interstellar Gas toward a Large, Low Extinction Window into the Inner Galaxy
• A Faraday Rotation Template for the Galactic Sky

Cited by in corpus (17)

• An improved map of the Galactic Faraday sky
• The outer scale of turbulence in the magneto-ionized Galactic interstellar medium
• Structure in the Rotation Measure Sky
• A Sino-German 6 cm polarization survey of the Galactic plane III. The region from 10 degree to 60 degree longitude
• Detection Thresholds and Bias Correction in Polarized Intensity
• A radio-polarisation and rotation measure study of the Gum Nebula and its environment
• Degree of Polarization and Source Counts of Faint Radio Sources from Stacking Polarized Intensity
• Three-Dimensional Simulations of Magnetized Superbubbles: New Insights into the Importance of MHD Effects on Observed Quantities
• Strong excess Faraday rotation on the Inside of the Sagittarius spiral arm
• Magnetic field disorder and Faraday effects on the polarization of extragalactic radio sources
• The POlarised GLEAM Survey (POGS) I: First Results from a Low-Frequency Radio Linear Polarisation Survey of the Southern Sky
• S-PASS/ATCA: a window on the magnetic universe in the southern hemisphere
• Heightened Faraday Complexity in the inner 1 kpc of the Galactic Centre
• The Discovery of Diffuse Radio Polarization Structures in the NVSS
• Turbulent magnetic field in the HII region Sh 2-27
• Stacking for Cosmic Magnetism with SKA Surveys
• A new window into the sub-parsec scale magnetic field in the Milky Way? Unveiling small-scale magneto-ionic structures with Faraday complexity