On the claimed X-shaped structure in the Milky Way bulge

TL;DR

This study critically examines the evidence for an X-shaped structure in the Milky Way bulge, finding that previous claims are heavily influenced by data processing choices and that the structure's stellar density is too low to produce observed features.

Contribution

The paper demonstrates that the claimed X-shaped structure in the Milky Way bulge is not supported by residual analysis after standard dust correction and bulge modeling, challenging prior detections.

Findings

Residuals show no clear X-shape after proper correction and modeling

Dust extinction correction significantly affects residual analysis

The stellar density in the claimed structure is too low for observed features

Abstract

A number of recent studies have claimed that the double red clump (RC) observed in the Milky Way bulge is a consequence of a giant X-shaped structure. In particular, Ness & Lang (2016) reported a direct detection of a faint X-shaped structure from the residual map of the Wide-Field Infrared Survey Explorer (WISE) bulge image. Here we show, however, that their result is affected substantially by whether the conventional dust extinction correction is applied or not and partly by a bulge model subtracted from the original image. We find that the residuals obtained by subtracting either ellipsoidal or boxy bulge models from the dereddened images show no obvious X-shaped structure. We further show that, even if it is real, the stellar density in the claimed X-shaped structure is way too low to be observed as a strong double RC at l=0.