Characterizing the Palomar 5 Stream: HDBSCAN Analysis and Galactic Halo Constraints

Abstract

We utilize the DESI Legacy Imaging Surveys DR10 to investigate the previously undetected faint extension of the Palomar 5 stellar stream. By applying the HDBSCAN clustering algorithm, we identify stream members and successfully extend the leading arm of the stream to approximately $\mathrm{DEC}\sim -15^{\circ }$. Combining the fully detected stream with a suite of mock stream simulations, we conduct a detailed comparison to constrain both the intrinsic properties of the stream and the dynamical parameters of the Milky Way (MW) halo. Our analysis yields a best-fit model characterized by eight parameters: $M_{\mathrm{halo}}=5.67\times 10^{11}{M}_{\odot }$, $r_{s,\mathrm{halo}}=28.94\mathrm{kpc}$, $q_z=0.93$, $M_{\mathrm{gc}}=4.31\times 10^3{M}_{\odot }$, $d{M}_{\mathrm{gc}}/dt=1.81M_{\odot }{\mathrm{Myr}}^{-1}$, $\hat{I}{¼}_{\hat{I}}\pm \cos \hat{I}´=-2.28{\mathrm{mas}\mathrm{yr}}^{-1}$, $\hat{I}{¼}_{\hat{I}}´=-2.26{\mathrm{mas}\mathrm{yr}}^{-1}$, and $D=23.25\mathrm{kpc}$. Notably, our constraints on the halo shape indicate that the MW's dark matter halo exhibits a flattened potential, with a minor-to-major axis ratio of $q_z=0.93$. This finding aligns well with theoretical expectations and previous observational estimates. Additionally, the best-fit model accurately reproduces the observed stream morphology and dynamics, providing a more precise understanding of both the evolution of the stream and the overall structure of the Galactic halo.

Submitted to Research in Astronomy and Astrophysics (RAA). Comments welcome