Probing satellite galaxies in the Local Group by using FAST

TL;DR

This study uses hydrodynamic simulations and observational data to predict the abundance of neutral hydrogen in satellite galaxies of the Local Group, demonstrating FAST's potential to significantly improve detection capabilities and constrain galaxy formation models.

Contribution

It provides the first detailed prediction of HI satellite galaxy counts for the upcoming FAST survey, combining simulations with observational systematic analysis.

Findings

FAST can detect HI satellites down to 10^5 M_sun with 40-minute integration.

Predicted 61 HI satellites in the Local Group, 36 within FAST's survey area.

Current data is an order of magnitude less complete than the forecasted detections.

Abstract

The abundance of neutral hydrogen (HI) in satellite galaxies in the Local Group is important for studying the formation history of our Local Group. In this work, we generated mock HI satellite galaxies in the Local Group using the high mass resolution hydrodynamic \textsc{apostle} simulation. The simulated HI mass function agrees with the ALFALFA survey very well above $10^6M_{\odot}$, although there is a discrepancy below this scale because of the observed flux limit. After carefully checking various systematic elements in the observations, including fitting of line width, sky coverage, integration time, and frequency drift due to uncertainty in a galaxy's distance, we predicted the abundance of HI in galaxies in a future survey that will be conducted by FAST. FAST has a larger aperture and higher sensitivity than the Arecibo telescope. We found that the HI mass function could be estimated well around $10^5 M_{\odot}$ if the integration time is 40 minutes. Our results indicate that there are 61 HI satellites in the Local Group, and 36 in the FAST field above $10^5 M_{\odot}$. This estimation is one order of magnitude better than the current data, and will put a strong constraint on the formation history of the Local Group. Also more high resolution simulated samples are needed to achieve this target.