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

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.