Forecast for FAST: from Galaxies Survey to Intensity Mapping

TL;DR

This paper forecasts the capabilities of FAST for large-scale structure surveys using HI intensity mapping, evaluating measurement errors, and potential cosmological constraints, highlighting the telescope's promising role in dark energy research.

Contribution

It provides detailed forecasts for FAST's HI survey performance and cosmological measurement potential, including the impact of different receiver configurations and survey strategies.

Findings

Measurement errors increase with redshift, reducing galaxy detection.

Intensity mapping enables effective large-scale structure measurement without resolving individual galaxies.

FAST can achieve dark energy constraints comparable to stage IV experiments with advanced receivers.

Abstract

The Five-Hundred-Meter Aperture Spherical Radio Telescope(FAST) is the largest single-dish radio telescope in the world. In this paper, we make forecast on the FAST HI large scale structure survey by mock observations. We consider a drift scan survey with the L-band 19 beam receiver, which may be commensal with the pulsar search and Galactic HI survey. We also consider surveys at lower frequency, either using the current single feed wide band receiver, or a future multi-beam phased array feed (PAF) in the UHF band. We estimate the number density of detected HI galaxies and the measurement error in positions, the precision of the surveys are evaluated using both Fisher matrix and simulated observations. The measurement error in the HI galaxy power spectrum is estimated, and we find that the error is relatively large even at moderate redshifts, as the number of positively detected galaxies drops drastically with increasing redshift. However, good cosmological measurement could be obtained with the intensity mapping technique where the large scale HI distribution is measured without resolving individual galaxies. The figure of merit (FoM) for the dark energy equation of state with different observation times are estimated, we find that with the existing L-band multi-beam receiver, a good measurement of low redshift large scale structure can be obtained, which complements the existing optical surveys. With a PAF in the UHF band, the constraint can be much stronger, reaching the level of a dark energy task force (DETF) stage IV experiment.