An extended Pal 5 stream in Gaia DR2

Abstract

We present the results of a detailed search for members of the Pal 5 tidal tail system in Gaia Data Release 2 (DR2). Tidal tails provide a sensitive method for measuring the current and past gravitational potential of their host galaxy as well as for testing predictions for the abundance of dark matter subhalos. The Pal 5 globular cluster and its associated tails are an excellent candidate for such analysis; however, only ∼23°o f arc are currently known, with in particular the leading tail much shorter than the trailing. Using Gaia DR2 and its precise astrometry, we extend the known extent of the Pal 5 tail to ∼30°, 7 degrees of which are newly detected along the leading arm. The detected leading and trailing arms are symmetric in length and remain near constant width. This detection constrains proposed models in which the Galactic bar truncates Pal 5's leading arm. Follow-up spectroscopic observations are necessary to verify the candidate stream stars are consistent with the known tidal tails. If confirmed, this Pal 5 stream extension opens up new possibilities to constrain the Galactic potential.

Forward and Back: Kinematics of the Palomar 5 Tidal Tails

“…As a result, we proceed with stars that lie within 2 mas yr −1 of the main body PM of Pal 5 5 : (𝜇 * 𝛼 , 𝜇 𝛿 ) = (−2.75, −2.65) mas yr −1 (Vasiliev 2019). This is a more conservative estimate than the 3 mas yr −1 threshold used by Starkman et al (2020), which is large enough to include contamination from the Sgr stream. Indeed, using the model of in the region 223 • < 𝛼 < 229.5 • deg and −20 • < 𝛿 < 10 • , we find that the Sgr stream in this direction has a PM of (𝜇 * 𝛼 , 𝜇 𝛿 ) ≈ (−1.1, −0.5) mas yr −1 (see Fig.…”

“…Such fanning could indicate triaxiality in the potential (Pearson et al 2015) or the effect of a rotating bar (see Pearson et al 2017;Bonaca et al 2020). On the other hand, Starkman et al (2020) analyse Gaia DR2 data and suggest that the leading tail can be traced nearly as far as the trailing tail in that dataset. However this analysis is based on main sequence turn-off stars with magnitudes at the faint limit of the survey and the assumption of a cluster metallicity of [Fe/H]=-3.1 dex compared to the measured value of [Fe/H]=-1.5 dex (Koch & Côté 2017).…”

The structure of accreted stellar streams

“…The Gaia mission (Gaia Collaboration et al 2016) with its exquisite five-dimensional kinematic data and photometric data, has made the discovery of many new streams and of many new features of known streams possible (e.g., Malhan & Ibata 2018;Price-Whelan & Bonaca 2018;Palau & Miralda-Escudé 2019;Starkman et al 2020;Ibata et al 2021). Aside from finding the archetypical cold streams of which many examples were already known before Gaia, the Gaia data in combination with auxiliary data have revealed additional structure associated with known stellar streams, in particular around the GD-1 stream (Grillmair & Dionatos 2006).…”

Variation in the Stellar Mass Function Along Stellar Streams

“…In order to explore the applicability of our results to globular clusters with observed tidal tails, we further apply our analysis to an N-body simulation of the Milky-Way globular cluster Pal 5 and its tidal tails. The mock Pal 5 stream is generated using the same direct N-body code as our suite of simulations, NBODY6 (Aarseth 2003); this simulation was originally presented in Starkman et al (2020). The simulation consists of initially 100,00 stars in the form of a Plummer model (Plummer 1911) with a half-mass radius of 10 pc.…”