Diffuse Stellar Light at 100 Kiloparsec Scales in M87

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Abstract
In a new survey of nearby galaxies from stacked photographic images, seemingly regular galaxies of several types show amorphous, often asymmetrical features at very faint levels (28 mag arcsec-2). In M87, a diffuse fan of stellar material extends along the projected southeast (major) axis out to about 100 kpc. We suggest that accretion of a small spheroidal galaxy into a larger potential is the most likely explanation for the diffuse structure. The orbit is required to pass close to the center of the potential in order to produce a fan that is nearly aligned with the major axis and has a large opening angle, as seen in M87. Our simulations include a rigid primary potential with characteristics similar to those derived for M87 and a populated secondary potential. We investigate the structure of the dark matter at large galactic radii by representing M87 with different potentials. The morphologies of the debris of intruder spheres and disks of different masses and orbital parameters limit the possible accretion scenarios. The total luminosity of the fan and the kinematics of debris in the center of the primary potential are analyzed and compared with substructure in M87. The short lifetimes (tfan 5 × 108 yr) of the simulated diffuse fans and lack of observed shells indicates either that we are seeing M87 at a "special time" during its evolution or that infall from small intruder galaxies is common. Our simulations indicate that several accretion events could be hidden in galaxies. For many orbits, intruder material is quickly spread out to very low light levels. Observations of the high specific frequency of globular clusters in M87 provide evidence that the galaxy may experience frequent accretions of this type.
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