A radio-polarisation and rotation measure study of the Gum Nebula and its environment

Abstract

The Gum Nebula is 36 degree wide shell-like emission nebula at a distance of only 450 pc. It has been hypothesised to be an old supernova remnant, fossil HII region, wind-blown bubble, or combination of multiple objects. Here we investigate the magneto-ionic properties of the nebula using data from recent surveys: radio-continuum data from the NRAO VLA and S-band Parkes All Sky Surveys, and H-alpha data from the Southern H-Alpha Sky Survey Atlas. We model the upper part of the nebula as a spherical shell of ionised gas expanding into the ambient medium. We perform a maximum-likelihood Markov chain Monte-Carlo fit to the NVSS rotation measure data, using the H-halpha data to constrain average electron density in the shell $n_e$. Assuming a latitudinal background gradient in RM we find $n_e=1.3_{-0.4}^{+0.4}{\mathrm{cm}}^{-3}$, angular radius ${\varphi }_{\mathrm{outer}}=22.7_{-0.1}^{+0.1}\mathrm{deg}$, shell thickness $dr=18.5_{-1.4}^{+1.5}\mathrm{pc}$, ambient magnetic field strength $B_0=3.9_{-2.2}^{+4.9}\mu \mathrm{G}$ and warm gas filling factor $f=0.3_{-0.1}^{+0.3}$. We constrain the local, small-scale (~260 pc) pitch-angle of the ordered Galactic magnetic field to $+7^{\circ }\lesssim \wp \lesssim +44^{\circ }$, which represents a significant deviation from the median field orientation on kiloparsec scales (~-7.2${}^{\circ }$). The moderate compression factor $X=6.0{}_{-2.5}^{+5.1}$ at the edge of the H-alpha shell implies that the 'old supernova remnant' origin is unlikely. Our results support a model of the nebula as a HII region around a wind-blown bubble. Analysis of depolarisation in 2.3 GHz S-PASS data is consistent with this hypothesis and our best-fitting values agree well with previous studies of interstellar bubbles.

arXiv comment33 pages, 16 figures. Accepted by The Astrophysical Journal

References in corpus (71)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• Astropy: A Community Python Package for Astronomy
• emcee: The MCMC Hammer
• Validation of the new Hipparcos reduction
• The ATNF Pulsar Catalogue
• Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Final Maps and Results
• Planck 2013 results. I. Overview of products and scientific results
• The ATNF Pulsar Catalogue
• A Hipparcos census of the nearby OB associations
• The Murchison Widefield Array: the Square Kilometre Array Precursor at low radio frequencies
• The Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey
• A New Model of the Galactic Magnetic Field
• A Full-Sky H-alpha Template for Microwave Foreground Prediction
• Three Dimensional Structure of the Milky Way Disk
• Supernova remnants: the X-ray perspective
• A Robotic Wide-Angle H-Alpha Survey of the Southern Sky
• The Wisconsin H-Alpha Mapper Northern Sky Survey
• Radio observational constraints on Galactic 3D-emission models
• Pulsar rotation measures and the large-scale structure of Galactic magnetic field
• GASS: The Parkes Galactic All-Sky Survey. I. Survey Description, Goals, and Initial Data Release
• The Vertical Structure of Warm Ionised Gas in the Milky Way
• Dispersion of Magnetic Fields in Molecular Clouds. I
• The observed spiral structure of the Milky Way
• An improved map of the Galactic Faraday sky
• Science With The Australian Square Kilometre Array Pathfinder
• The Vela Pulsar's proper motion and parallax derived from VLBI observations
• Giant Magnetized Outflows from the Centre of the Milky Way
• Pulsar rotation measures and the magnetic structure of our Galaxy
• Modeling the Magnetic Field in the Galactic Disk using New Rotation Measure Observations from the Very Large Array
• The Escape of Ionizing Photons from OB Associations in Disk Galaxies: Radiation Transfer Through Superbubbles
• Radio polarization from the inner Galaxy at arcminute resolution
• Low-Mach-number turbulence in interstellar gas revealed by radio polarization gradients
• A Survey of Extragalactic Faraday Rotation at High Galactic Latitude: The Vertical Magnetic Field of the Milky Way towards the Galactic Poles
• Radiation-magnetohydrodynamic simulations of HII regions and their associated PDRs in turbulent molecular clouds
• Magnetic fields in barred galaxies. IV. NGC 1097 and NGC 1365
• Galactic dynamo and helicity losses through fountain flow
• Magnetohydronamic Evolution of HII Regions in Molecular Clouds: Simulation Methodology, Tests, and Uniform Media
• Modelling the Galactic Magnetic Field on the Plane in 2D
• Combining cosmological datasets: hyperparameters and Bayesian evidence
• The magnetic field of M31 from multi-wavelength radio polarization observations
• Hierarchical Triggering of Star Formation by Superbubbles in W3/W4
• Magnetic Fields in Large Diameter HII Regions Revealed by the Faraday Rotation of Compact Extragalactic Radio Sources
• Systematic errors in cosmic microwave background polarization measurements
• Analysis of spiral arms using anisotropic wavelets: gas, dust and magnetic fields in M51
• Predictions on high frequency polarization properties of extragalactic radio sources and implications for CMB polarization measurements
• A New 1.4GHz Radio Continuum Map of the Sky South of Declination +25 deg
• Properties of Interstellar Turbulence from Gradients of Linear Radio Polarization Maps
• Clumpy Ultracompact HII Regions I: Fully Supersonic Wind-blown Models
• Constraining models of the large scale Galactic magnetic field with WMAP5 polarization data and extragalactic Rotation Measure sources
• The Interstellar Magnetic Field Close to the Sun II
• Observational study of sites of triggered star formation: CO and mid-infrared observations
• The Ophiuchus Superbubble: A Gigantic Eruption from the Inner Disk of the Milky Way
• Bayesian `Hyper-Parameters' Approach to Joint Estimation: The Hubble Constant from CMB Measurements
• Galactic interstellar turbulence in the southern sky seen through spatial gradients of the polarization vector
• Detection of a Large Arc of Ionized Hydrogen Far Above the Cas OB6 Association: A Superbubble Blowout into the Galactic Halo?
• Particle acceleration in supernova-remnant shocks
• Detection of a radio bridge in Abell 3667
• Magnetic field transport from disk to halo via the galactic chimney process in NGC 6946
• Polarization shadows of extragalactic sources by the local magneto-ionic ISM
• Scatter broadening of pulsars in the direction of the Gum nebula
• Antenna Instrumental Polarization and its Effects on E- and B-Modes for CMBP Observations
• The Parkes Galactic Meridian Survey (PGMS): observations and CMB polarization foreground analysis
• Confirmation of a Faraday Rotation Measure Anomaly in Cygnus
• The Evolution of Mass Loaded Supernova Remnants. II. Temperature Dependent Mass Injection Rates
• Canals in Milky Way radio polarization maps
• Probing the Rosette Nebula Stellar Bubble with Faraday Rotation
• Radio observations and spectral index study of SNR G126.2+1.6
• Testing Galactic Magnetic Field Models using Near-Infrared Polarimetry
• GSH 006-15+7: A local Galactic supershell featuring transition from HI emission to absorption
• The C-Band All-Sky Survey: Instrument design, status, and first-look data
• Kinematics of the Young Stellar Objects associated with the Cometary Globules in the Gum Nebula

Cited by in corpus (34)

• A New Electron Density Model for Estimation of Pulsar and FRB Distances
• Stars, Gas, and Dark Matter in the Solar Neighborhood
• Strong-field Gravity Tests with the Double Pulsar
• S-band Polarization All Sky Survey (S-PASS): survey description and maps
• New constraints on the magnetization of the cosmic web using LOFAR Faraday rotation observations
• A ring in a shell: the large-scale 6D structure of the Vela OB2 complex
• The Galactic Faraday depth sky revisited
• Constraints from Faraday rotation on the magnetic field structure in the Galactic halo
• Detecting stellar-wind bubbles through infrared arcs in HII regions
• Illuminating the past 8 billion years of cold gas towards two gravitationally lensed quasars
• The start of the Sagittarius spiral arm (Sagittarius origin) and the start of the Norma spiral arm (Norma origin) - model-computed and observed arm tangents at galactic longitudes -20 degrees < l < +23 degrees
• Strong excess Faraday rotation on the Inside of the Sagittarius spiral arm
• Cosmic Magnetism in Centimeter and Meter Wavelength Radio Astronomy
• The POlarised GLEAM Survey (POGS) I: First Results from a Low-Frequency Radio Linear Polarisation Survey of the Southern Sky
• The Global Magneto-Ionic Medium Survey: Polarimetry of the Southern Sky from 300 to 480 MHz
• S-PASS/ATCA: a window on the magnetic universe in the southern hemisphere
• The POlarised GLEAM Survey (POGS) II: Results from an All-Sky Rotation Measure Synthesis Survey at Long Wavelengths
• Interacting Large-Scale Magnetic Fields and Ionised Gas in the W50/SS433 System
• A Broadband Spectro-polarimetric View of the NVSS Rotation Measure Catalogue I: Breaking the nπ-ambiguity
• Far UV and Optical Emissions from Three Very Large Supernova Remnants Located at Unusually High Galactic Latitudes
• The Complex Large-scale Magnetic Fields in the First Galactic Quadrant as Revealed by the Faraday Depth Profile Disparity
• Disentangling the Faraday rotation sky
• A Faraday Rotation Study of the Stellar Bubble and HII Region Associated with the W4 Complex
• Denser Sampling of the Rosette Nebula with Faraday Rotation Measurements: Improved Estimates of Magnetic Fields in HII Regions
• A Broadband Spectro-polarimetric View of the NVSS Rotation Measure Catalogue II: Effects of Off-axis Instrumental Polarisation
• Interstellar Polarization Survey III: Relation Between Optical Polarization and Reddening in the General Interstellar Medium
• Synthetic observations of spiral arm tracers of a simulated Milky Way analog
• A new perspective on turbulent Galactic magnetic fields through comparison of linear polarisation decomposition techniques
• NE2025: An Updated Electron Density Model for the Galactic Interstellar Medium
• Ghost of a Shell: Magnetic Fields of Galactic Supershell GSH 006$-$15$+$7
• The Galactic latitude dependency of Faraday complexity in the S-PASS/ATCA RM catalogue
• Distant probes of RM structure -- Where is the Faraday Rotation towards the Magellanic Leading Arm?
• Associations Between Scattering Screens and Interstellar Medium Filaments
• On the Potential of Faraday Tomography to Identify Shock Structures in Supernova Remnants