Constraining Dark Matter Density Profiles in UFDs with Wide Binaries: Forecast for the Chinese Space Station Survey Telescope

TL;DR

This study forecasts the Chinese Space Station Telescope's ability to detect wide binary stars in ultra-faint dwarf galaxy Segue 1 to probe dark matter density profiles, emphasizing detection limits and observational requirements.

Contribution

It introduces a method to assess CSST's capability to characterize wide binaries in UFDs, linking binary detection to dark matter profile constraints.

Findings

CSST can detect wide binaries with a binary fraction as low as 1% for samples of over 2300 stars.

Distinguishing between cusped and cored dark matter profiles requires larger samples of over 6000 stars.

Detection of wide binaries is feasible at the 3σ level under realistic observational conditions.

Abstract

The internal structure of dark matter halos on sub-galactic scales remains a key open question, particularly in the context of the core-cusp problem. Ultra-faint dwarf galaxies (UFDs), owing to their extreme dark matter dominance, provide a promising laboratory to probe these density profiles through stellar tracers. In this work, we assess the capability of the Chinese Space Station Telescope (CSST) to detect and characterize wide binary stars in the nearby UFD Segue 1, using mock observations. We generate mock binary populations based on our existing $N$-body simulations and incorporate realistic CSST observational conditions, including the expected deep-field limiting magnitude ($g \sim 27.5$ mag) and a photometric completeness of approximately $90\%$. The two-point correlation function (2PCF) of stellar pairs is used as a statistical tool to recover the binary fraction under these assumptions. We find that CSST can robustly detect wide binaries at the $3\sigma$ level for binary fractions as low as $f_b \gtrsim 0.01$, provided a stellar sample size of $N_{\mathrm{star}} \gtrsim 2300$. However, distinguishing between cusped and cored dark matter profiles is significantly more demanding, requiring $N_{\mathrm{star}} \gtrsim 6000$ and $f_b \gtrsim 0.1$ within $\sim 40\mathrm{kpc}$.