See you again: an $80^\circ$ NGC~5466 stellar stream and its constraints on the Galactic dark halo mass

Abstract

Using \textit{Gaia} Data Release 3 combined with Dark Energy Spectroscopic Instrument Legacy Imaging Survey Data Release 9 and Panoramic Survey Telescope and Rapid Response System Data Release 2, we apply a modified matched filter method to obtain a weighted stellar map in the surrounding of the globular cluster NGC~5466. Our results support that the tidal stream of NGC~5466 extends around $80^\circ$ on the sky, and the leading tail seemingly exhibits an upward deviation in the range of $180^\circ \lesssim α\lesssim 190^\circ$, which supports previous claim that the Large Magellanic Cloud (LMC) may have caused dynamical perturbations to the stream. Based on the 308 highly-weighted member candidates of the NGC~5466 stream, we try to measure the mass distribution of the Milky Way dark matter halo along with the mass of LMC. By comparing the observed stream candidate members to a series of model streams generated under different potential parameters, we obtain the posterior distributions of the parameters: the circular velocity at the solar radius $V_{\rm c} = 239.56^{+1.46}_{-1.44}\ \mathrm{km\ s^{-1}}$, the density flattening of the halo $q = 1.08^{+0.07}_{-0.07}$, the scale radius of the halo density profile $r_s = 12.97^{+3.02}_{-2.18}\ \mathrm{kpc}$ and the total mass of the LMC $M_{\rm LMC} = 9.63^{+1.89}_{-2.00}\times 10^{10}$ $\mathrm{M_\odot}$. The enclosed mass of the Milky Way within the stream apocenter radius of $\sim$ 50 kpc is calculated as $M_{\rm MW}(<50~\mathrm{kpc}) = 4.59^{+0.48}_{-0.37} \times 10^{11}$ $\mathrm{M_\odot}$.