Unveiling the Boxy Bulge and Bar of the Andromeda Spiral Galaxy

摘要: A new, 2.8 deg^2 J, H, Ks near-infrared (NIR) survey from the 2MASS 6X program across extent of optical disk Andromeda (M31) galaxy provides a clear view M31 center almost completely unfettered by dust extinction and reveals high-contrast bulge with very boxy isophotes dominating NIR light to semimajor axis ~700" (2.6 kpc). The inner (≾50") are relatively circular but show some twisting. Beyond this, (1) ellipticity increases, (2) its position angle is constant at ~50°, or about 10° higher than disk, (3) boxiness increases degree (~3%-4%) comparable other renowned examples bulges observed in NIR. In companion paper, self-consistent N-body simulations classical plus bar shown reproduce features presented here. region nearly along 40° narrow ridge flux, which can be identified thin part bar, more less symmetrically extends into radii 700"-1200" more. Little variation morphology relative brightnesses these various structures seen bands (e.g., no color gradients seen). These new data verify that barred spiral like Milky Way.