The Effelsberg-Bonn HI Survey: Data reduction

TL;DR

The paper presents the data reduction software and initial results of the EBHIS, a large-scale 21-cm survey of the northern sky using advanced FPGA spectrometers and RFI mitigation techniques.

Contribution

It introduces a comprehensive data reduction pipeline for EBHIS, including RFI detection, calibration, stray-radiation removal, and gridding, applied to large sky areas.

Findings

Successful application to large sky areas (~2000 sq. deg.)

High data quality demonstrated for Milky Way observations

First data release planned for 2011

Abstract

Starting in winter 2008/2009 an L-band 7-Feed-Array receiver is used for a 21-cm line survey performed with the 100-m telescope, the Effelsberg-Bonn HI survey (EBHIS). The EBHIS will cover the whole northern hemisphere for decl.>-5 deg comprising both the galactic and extragalactic sky out to a distance of about 230 Mpc. Using state-of-the-art FPGA-based digital fast Fourier transform spectrometers, superior in dynamic range and temporal resolution to conventional correlators, allows us to apply sophisticated radio frequency interference (RFI) mitigation schemes. In this paper, the EBHIS data reduction package and first results are presented. The reduction software consists of RFI detection schemes, flux and gain-curve calibration, stray-radiation removal, baseline fitting, and finally the gridding to produce data cubes. The whole software chain is successfully tested using multi-feed data toward many smaller test fields (1--100 square degrees) and recently applied for the first time to data of two large sky areas, each covering about 2000 square degrees. The first large area is toward the northern galactic pole and the second one toward the northern tip of the Magellanic Leading Arm. Here, we demonstrate the data quality of EBHIS Milky Way data and give a first impression on the first data release in 2011.