Finding halo streams with a pencil-beam survey

New wraps in the Sagittarius stream

Leiden Observatory, Leiden University Oort Building, Niels Bohrweg 2 2333 CA Leiden The Netherlands
e-mail: piladiez@strw.leidenuniv.nl; kuijken@strw.leidenuniv.nl; jelte@strw.leidenuniv.nl; hoekstra@strw.leidenuniv.nl; vdburg@strw.leidenuniv.nl

Received: 6 November 2013
Accepted: 18 February 2014

Abstract

We use data from two CFHT-MegaCam photometric pencil-beam surveys in the g′ and the r′ bands to measure distances to the Sagittarius, the Palomar 5 and the Orphan stream. We show that, using a cross-correlation algorithm to detect the turnoff point of the main sequence, it is possible to overcome the main limitation of a two-bands pencil-beam survey, namely the lack of adjacent control-fields that can be used to subtract the foreground and background stars to enhance the signal on the colour−magnitude diagrams. We describe the cross-correlation algorithm and its implementation. We combine the resulting main sequence turnoff points with theoretical isochrones to derive photometric distances to the streams. Our results (31 detections on the Sagittarius stream and one each for the Palomar 5 and the Orphan streams) confirm the findings by previous studies, expand the distance trend for the Sagittarius faint southern branch and trace the Sagittarius faint branch of the northern-leading arm out to 56 kpc. In addition, they show evidence for nearby substructures. We argue that these detections trace the continuation of the Sagittarius northern-leading arm into the southern hemisphere, and the northern wrap of the Sagittarius trailing arm. We provide accurate distance measurements to these detections.