Radio observational constraints on Galactic 3D-emission models

By Xiao-Hui Sun, W. Reich, A. Waelkens, Torsten A. Ensslin. 2007

321 citations recorded by the source corpus.

Context. Our position inside the Galaxy requires 3D-modelling to obtain the distribution of the Galactic magnetic field, cosmic- ray (CR) electrons and thermal electrons. Aims. Our intention is to find a Galactic 3D-model which agrees best with available radio observations. Methods. We constrain simulated all-sky maps in total intensity, lin ear polarization, and rotation measure (RM) by observations. For the simulated maps as a function of frequency we integrate in 15 ′ wide cones the emission along the line of sight calculated from Galactic 3D-models. We test a number of large-scale magnetic field configurations and take the properties of the warm inte rstellar medium into account. Results. From a comparison of simulated and observed maps we are able to constrain the regular large-scale Galactic magnetic field in the disk and the halo of the Galaxy. The local regular fi eld is 2� G and the average random field is about 3 � G. The known local excess of synchrotron emission originating either fr om enhanced CR electrons or random magnetic fields is able to e xplain the observed high-latitude synchrotron emission. The thermal electron model (NE2001) in conjunction with a proper fill ing factor accounts for the observed optically thin thermal emission and low frequency absorption by optically thick emission. A coupling factor between thermal electrons and the random magnetic field comp onent is proposed, which in addition to the small filling fact or of thermal electrons increases small-scale RM fluctuations an d thus accounts for the observed depolarization at 1.4 GHz. Conclusions. We conclude that an axisymmetric magnetic disk field configur ation with reversals inside the solar circle fits available observations best. Out of the plane a strong toroidal magnetic field with di fferent signs above and below the plane is needed to account for the observed high-latitude RMs. The large field strength is a consequence of the small thermal electron scale height of 1 kpc, which also limits the CR electron extent up to a height of 1 kpc not to contradict with the observed synchrotron emission out of the plane. Our preferred 3D-model fits the observed Galactic total intensi ty and polarized emission better than other models over a wide frequency range and also agrees with the observed RM from extragalactic sources.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/2563b9378a4189a3678907413adcfacd6efb61ca

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Citations in the corpus

The Vertical Structure of Warm Ionised Gas in the Milky Way (2008, methodology): “As discussed by Sun et al. (2008), the NE2001 model cannot successfully predict the free-free emission see at 23 GHz by theWMAP experiment, but incorporating the functionf(z) derived by BMM06 (see Eqn.”
DEVELOPMENT OF THE MODEL OF GALACTIC INTERSTELLAR EMISSION FOR STANDARD POINT-SOURCE ANALYSIS OF FERMI LARGE AREA TELESCOPE DATA (2016, background): “Figure 7 of Sun et al. (2008) shows that NE2001 does not reproduce the structures of the free–free emission from the Wilkinson Microwave Anisotropy Probe (WMAP) observations.”
CRPropa 3—a public astrophysical simulation framework for propagating extraterrestrial ultra-high energy particles (2016, methodology): “Galactic magnetic fields Toroidal Halo Toroidal halo field model adopted from [24, 25].”
Cosmic-ray propagation with DRAGON2: I. numerical solver and astrophysical ingredients (2016, methodology): “Sun2007 ASS/BSS In this model the disk field takes the form of a coplanar and constant pitch angle spiral field with components [100]”
Science with the Murchison Widefield Array (2012, background): “Because many Galactic HII regions have well-constrained distance estimates, MWA measurements of the synchrotron absorption features will allow for a threedimensional map of the relativistic gas content in the Milky Way (e.g. Sun et al. 2008).”
An improved map of the Galactic Faraday sky (2011, methodology): “…(2008), Han et al. (2006), and Men et al. (2008) relied entirely on pulsar rotation measures for estimating the Galactic magnetic field, while Sun et al. (2008), Jansson et al. (2009), and Jaffe et al. (2010) used rotation measures of extragalactic sources in combination with synchrotron…”
THE GALACTIC MAGNETIC FIELD (2012, methodology): “…χ2 per degree of freedom of 1.096 for the 6605 observables (pixels of RM, Q and U) while the fit is much worse for other recent models in the literature, with χ2dof of 2.663 & 4.971 for Pshirkov et al. (2011) BSS & ASS respectively and 1.672 for Sun et al. (2008), with their 2010 parameter update.”
The Nine Lives of Cosmic Rays in Galaxies (2015, methodology): “The study of Galactic synchrotron radiation was extended to full-sky spatial distribution and polarization data by Orlando & Strong (2013), Sun et al. (2008) using a range of magnetic field models from the literature.”
Magnetic Fields in Supernova Remnants and Pulsar-Wind Nebulae (2011, methodology): “We have used the model of Sun et al. (2008) to compute the expected variation of the azimuthal field in the Galaxy at the location of SN 1006.”
Magnetic fields and spiral arms in the galaxy M51 (2010, background): “A field reversal between the regular fields in the disc and the inner halo has also been suggested in the Milky Way (Sun et al. 2008), perhaps similar to the northern half of M51 (Fig.”
Cosmological Magnetic Fields: Their Generation, Evolution and Observation (2013, methodology): “…uncertainties in the measurements of Galactic magnetic field and discrepancies between the existing measurements and existing theoretical models (Sun et al 2008; Jansson et al 2009; Jansson and Farrar 2012a,b) do not allow to predict the deflection angle and direction of deflection for…”
DERIVING THE GLOBAL STRUCTURE OF THE GALACTIC MAGNETIC FIELD FROM FARADAY ROTATION MEASURES OF EXTRAGALACTIC SOURCES (2011, methodology): “The original values of the parameters in the model of Sun et al. (2008) were: BH0 = 10 µG, R H 0 = 4 kpc, zH0 = 1.5 kpc and z H 1 = 0.2 kpc for |z| < zH0 , otherwise zH1 = 0.4 kpc ( z H 1(1) = 0.2 kpc and z H 1(2) = 0.4 kpc).”
GIANT GAMMA-RAY BUBBLES FROM FERMI-LAT: ACTIVE GALACTIC NUCLEUS ACTIVITY OR BIPOLAR GALACTIC WIND? (2010, methodology): “However, models with a non-exponential halo magnetic field, as discussed by e.g. Alvarez-Muñiz et al. (2002); Sun et al. (2008), can have ∼ 10 µG fields well off the plane.”
Reionization and the Cosmic Dawn with the Square Kilometre Array (2012, methodology): “More detailed simulations of Galactic emission were developed by Sun et al. (2008); Waelkens et al. (2009); Sun & Reich (2009); Jelić et al. (2010a), while maps of the extragalactic emission were developed by Jackson (2005); Wilman et al. (2008).”
Galactic synchrotron emission with cosmic ray propagation models (2013, methodology): “The electron spectrum used by Sun et al. (2008) and Sun & Reich (2010) is a factor of 2 higher than the one used in our analysis.”
A NEW MODEL OF THE GALACTIC MAGNETIC FIELD (2012, methodology): “Our GMF has a χ2/dof = 1.1 compared to χ2/dof = 1.3 for the best previous form, the Sun et al. model (Sun et al. 2008; Sun & Reich 2010), after optimizing that models’ parameters to give the best fit to the same set of observables.”
COrE (Cosmic Origins Explorer) A White Paper (2011, unknown): “Data from [183, 175, 181] and figures from [180].”