A high-resolution self-consistent whole sky foreground model

Abstract

The neutral hydrogen 21cm line is potentially a very powerful probe of the observable universe, and a number of on-going experiments are trying to detect it at cosmological distances. However, the presence of strong foreground radiations such as the galactic synchrotron radiation, galactic free-free emission and extragalactic radio sources make it a very challenging task. For the design of 21cm experiments and analysis of their data, simulation is an essential tool, and good sky foreground model is needed. With existing data the whole sky maps are available only in low angular resolutions or for limited patches of sky, which is inadequate in the simulation of these new 21cm experiments. In this paper, we present the method of constructing a high resolution self-consistent sky model at low frequencies, which incorporates both diffuse foreground and point sources. Our diffuse map is constructed by generating physical foreground components including the galactic synchrotron emission and galactic freefree emission. The point source sample is generated using the actual data from the NRAO VLA Sky Survey (NVSS) and the Sydney University Molonglo Sky Survey (SUMSS) where they are available and complete in flux limit, and mock point sources according to statistical distributions. The entire model is made self-consistent by removing the integrated flux of the point sources from the diffuse map so that this part of radiation is not double counted. We show that with the point sources added, a significant angular power is introduced in the mock sky map, which may be important for foreground subtraction simulations. Our sky maps and point source catalogues are available to download. neutral hydrogen, 21cm line, foreground model, whole sky map, simulation PACS number(s): 95.80.+p, 95.85.Bh, 98.70.Dk, 95.75.Mn, 95.75.Pq Citation: Huang Q Z, Wu F Q & Chen X L, A high-resolution self-consistent whole sky foreground model, Sci. China-Phys. Mech. Astron. ??, 000000 (2018), doi: ? 1) https://lambda.gsfc.nasa.gov/product/foreground/haslam_408.cfm 2)

Imaging sensitivity of a linear interferometer array on lunar orbit

“…A number of extrapolated sky models have been developed, such as the Global Sky Model (GSM) (de Oliveira-Costa et al 2008;Zheng et al 2017), and the Cosmology in the Radio Band (CORA) (Shaw et al 2014(Shaw et al , 2015. In the present work, we make use of the high-resolution Self-consistent whole Sky Model (SSM) (Huang et al 2019). Note that the SSM model used by the current work has not accounted for the absorption effect that would become very significant at 𝜈 < 10 MHz.…”

“…By combining the data from the NRAO VLA Sky Survey (NVSS) at 1.4 GHz (Condon et al 1998) and the Sydney University Molonglo Sky Survey (SUMSS) at 843 MHz (Bock et al 1999;Mauch et al 2003), the SSM model also includes a point source catalogue covering the entire sky, but given at higher frequencies. The source distribution function at 1.4 GHz is given by (Huang et al 2019)…”

“…Here we extrapolate the source count at 1.4 GHz down to below 30 MHz using a spectral index of 𝛼 = 0.8157, which is fitted from sources in the overlap region of SUMSS and NVSS (Huang et al 2019).…”

Exploring the 21 cm cosmology: The Tianlai and Hongmeng experiments

“…(a)为输入天图(该图天空模型基本依据现有的全天射 电观测构建 [50] , 但其中有几个亮点源是为了测试成图 Since the end of the Big Bang, neutral hydrogen has been widely distributed in the universe, providing an important probe for studying the history of the universe from the dark age of the universe to cosmic dawn and reionization epoch, and then down to the post-reionization universe, and for accurately measuring the distribution of matter. But so far, due to the limitation of sensitivity, the observation of neutral hydrogen is mainly limited to the neighboring galaxies.…”

The Tianlai Cylinder Pathfinder array: System functions and basic performance analysis

“…The 21 cm signal is 4-5 orders of magnitude lower than the foreground emission (primarily synchrotron radiation) from Galactic and extra-galactic radio sources (see e.g., ref. [25]), making the detection a great challenge. Extracting the 21 cm signal generally relies on the fact that foreground emissions are smooth functions of frequency, while the 21 cm spectrum has a structure arising from the large-scale distribution of matter along the line of sight [2].…”