Simulated square kilometre array maps from Galactic 3D-emission models

Abstract

Context. Planning of the Square Kilometre Array (SKA) requires simulations of the expected sky emission at arcsec angular resolution to evaluate its scientific potential, to constrain its technical realization in the best possible way, and to guide the observing strategy. Aims. We simulate high-resolution total intensity, polarization, and rotation measure (RM) maps of selected fields based on our recent global 3D-model of Galactic emission.Methods. Simulations of diffuse Galactic emission were conducted using the hammurabi code modified for arcsec angular resolution patches towards various Galactic directions. The random magnetic field components are set to follow a Kolmogorov-like power-law spectrum. We analysed the simulated maps in terms of their probability density functions (PDFs) and structure functions.Results. We present maps for various Galactic longitudes and latitudes at 1.4 GHz, which is the frequency where deep SKA surveys are proposed. The maps are about 1.• 5 in size and have an angular resolution of about 1. 6. Total intensity emission is smoother in the plane than at high latitudes because of the different contributions from the regular and random magnetic field. The high-latitude fields show more extended polarized emission and RM structures than those in the plane, where patchy emission structures dominate on very small scales. The RM PDFs in the plane are close to Gaussians, but clearly deviate from that at high latitudes. The RM structure functions show smaller amplitudes and steeper slopes towards high latitudes. These results emerge from much more turbulent cells being passed through by the line-of-sights in the plane. Although the simulated random magnetic field components distribute in 3D, the magnetic field spectrum extracted from the structure functions of RMs conforms to 2D in the plane and approaches 3D at high latitudes. This is partly related to the outer scale of the turbulent magnetic field, but mainly to the different lengths of the lines-ofsight. Conclusions. The significant scatter of the simulated RM distributions agrees with the large scatter of observed RMs of pulsars and extragalactic sources in the Galactic plane and also at high Galactic latitudes. A very dense grid of RMs from extragalactic sources is required to trace and separate Galactic RM foreground fluctuations. Even at high latitudes, total intensity and polarized emission is highly structured, which will contaminate sensitive high-resolution extragalactic observations with the SKA and have to be separated in an appropriate way.

A Sino-Germanλ6 cm polarization survey of the Galactic plane

“…As shown by high angular resolution simulations by Sun & Reich (2009), turbulent magnetic fields with a Kolmogorov-like spectrum produce polarized features without corresponding total intensity. In the anti-centre region, the cosmic-ray electron density is low and the polarized intensities contributed by individual turbulent field cells is also small.…”

“…The quantity Kn e bL is roughly equal to σ RM and l is about the spatial scale resolved by the beam for a distance L. For this λ6 cm survey section, the polarization horizon in the Galactic plane was estimated to be about 4 kpc based on simulations described by Sun & Reich (2009) (see Fig. 4).…”

“…The simulations were based on the hammurabi code developed by Waelkens et al (2009) and the new Galactic 3D-emission model developed by Sun et al (2008) using modifications for high-resolution simulations of selected patches by Sun & Reich (2009), where a Kolmogorov spectrum for the random magnetic fields was included. For each line of sight, the complex polarization P was calculated following Sun et al (2008) as…”

“…As explained by Sun & Reich (2009), the coordinates of the target patches for simulations had to be adapted to the HEALPix (Górski et al 2005) projection scheme. The polarized intensities at 22.8 GHz were scaled to 4.8 GHz with a spectral index detailed in Sect.…”

“…We apply structure functions to study the properties of the polarized patches following the approach by Sun & Reich (2009). It is yet unknown how the turbulent magnetic field properties are reflected in structure functions.…”