The Tidal Tails of Globular Cluster Palomar 5 Based on Neural Networks Method

TL;DR

This paper employs neural networks on SDSS data to identify and analyze the tidal tails of globular cluster Palomar 5, revealing detailed tail structures and substructures, and confirming their origin from the cluster.

Contribution

It introduces a neural network-based method to detect and map tidal tails of Palomar 5 using SDSS data, providing detailed structural insights.

Findings

Tails extend 5.42° north and 3.77° south of Palomar 5.

Detected substructures within the tidal tails.

Tidal radius of Palomar 5 is 14.28 arcminutes.

Abstract

The Sixth Data Release (DR6) in the Sloan Digital Sky Survey (SDSS) provides more photometric regions, new features and more accurate data around globular cluster Palomar 5. A new method, Back Propagation Neural Network (BPNN), is used to estimate the probability of cluster member to detect its tidal tails. Cluster and field stars, used for training the networks, are extracted over a $40\times20$ deg$^2$ field by color-magnitude diagrams (CMDs). The best BPNNs with two hidden layers and Levenberg-Marquardt (LM) training algorithm are determined by the chosen cluster and field samples. The membership probabilities of stars in the whole field are obtained with the BPNNs, and contour maps of the probability distribution show that a tail extends $5.42\dg$ to the north of the cluster and a tail extends $3.77\dg$ to the south. The whole tails are similar to those detected by \citet{od03}, but no longer debris of the cluster is found to the northeast of the sky. The radial density profiles are investigated both along the tails and near the cluster center. Quite a few substructures are discovered in the tails. The number density profile of the cluster is fitted with the King model and the tidal radius is determined as $14.28'$. However, the King model cannot fit the observed profile at the outer regions ($R > 8'$) because of the tidal tails generated by the tidal force. Luminosity functions of the cluster and the tidal tails are calculated, which confirm that the tails originate from Palomar 5.