Paper: astro-ph/0605239
Date: Tue, 9 May 2006 19:52:51 GMT (498kb)

Title: Unveiling the Boxy Bulge and Bar of the Andromeda Spiral Galaxy

Authors: Rachael L. Beaton, Steven R. Majewski, Puragra Guhathakurta, Michael
F. Skrutskie, Roc M. Cutri, John Good, Richard J. Patterson, E. Athanassoula,
and Martin Bureau

Comments: Suibmitted to Astrophysical Journal Letters
\\
A new, 2.8 deg^2 J,H,K_s infrared survey from the 2MASS 6x program across the
extent of the optical disk of the Andromeda (M31) galaxy provides a clear view
of the M31 center almost completely unfettered by dust extinction, and reveals
a high contrast bulge with extremely boxy isophotes dominating the NIR light to
a semi-major axis of ~700''(2.6 kpc). The inner bulge (<~50'') is relatively
circular, but shows some isophotal twisting. Beyond this, the ellipticity and
boxiness of the bulge increase with radius -- achieving a boxiness that rivals
that of any other known disk galaxy observed in the near infrared -- and the
position angle is constant at ~50 deg, which is about 10 deg higher than the
position angle of the M31 disk. Boxy bulges in highly inclined disks have been
shown to be the vertical structure of bars, and self-consistent, N-body
modeling specific to the NIR images presented here can reproduce the observed
NIR M31 features with a combination of a classical bulge and a boxy bulge/bar.
Beyond the boxy bulge region and nearly along the 40 deg position angle of the
disk a narrow ridge of infrared flux, which can be identified with the thin
part of the bar, more or less symmetrically extends into the inner disk at
semi-major axis radii of 700'' to 1200'' or more. Little variation in the
morphology or relative brightnesses of these various M31 structures is seen
across the NIR bands (i.e., no color gradients are seen). These new data verify
that M31 is a barred spiral galaxy like the Milky Way.

\\ ( http://arXiv.org/abs/astro-ph/0605239 , 498kb)