FAST Drift Scan Survey for HI Intensity Mapping. II. Stacking-based Beam Construction of the 19-feed Array at $1.4$ GHz

TL;DR

This paper introduces a stacking-based method to accurately reconstruct the beam patterns of the FAST telescope's 19-feed array, enhancing foreground subtraction in HI intensity mapping for cosmology.

Contribution

It develops a novel stacking and Zernike polynomial modeling pipeline for precise beam reconstruction using drift-scan data, improving HIIM survey accuracy.

Findings

Successfully constructed beam patterns for 19 feeds of FAST.

Achieved more accurate beam models for foreground subtraction.

Enhanced the quality of HI intensity mapping data.

Abstract

Neutral hydrogen (HI) intensity mapping (IM) presents great promise for future cosmological large-scale structure surveys. However, a major challenge for HIIM cosmological studies is to accurately subtract the foreground contamination. An accurate beam model is crucial for improving the quality of foreground subtraction. In this work, we develop a stacking-based beam reconstruction method utilizing the radio continuum point sources within the drift-scan field. Based on the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we employ two sets of drift-scan survey data and merge the measurements to construct the beam patterns of the 19 FAST L-band feeds. To model the beams, we utilize the Zernike polynomial (ZP), which effectively captures asymmetric features of the main beam and the different side lobes. Due to the symmetric location of the beams, the main features of the beams are closely related to the distance from the center of the feed array, e.g., as the distance increases, side lobes become more pronounced. This modeling pipeline leverages the stable drift-scan data to extract beam patterns while accounting for and excluding the reflector's changing effects. It provides a more accurate measurement beam and a more precise model beam for FAST HIIM cosmology surveys.