Barun Kumar Dhar, Liliya L. R. Williams
{Abridged} We show that the surface brightness (SB) profiles of elliptical
galaxies can be parametrized using a linear superposition of 2-3 components,
described by functions developed in Dhar & Williams as the 2D projections of a
3D Einasto profile. For a sample of 23 ellipticals with -24 < Mv < -15, our
multi-component models span a range of up to 10^6 in SB and 10^5 in radius,
have a median rms of 0.032 mag arcsec^-2, and are statistically justified at
>3{\sigma}. Our models indicate that i) the central component is more
concentrated than the outer component; and ii) the central component of 'core'
galaxies is much more luminous, extended and concentrated than that of 'cuspy'
galaxies, with their near exponential central profiles indicating disk-like
systems whose existence must be verified spectroscopically. While such central
excess components are not necessarily contrary to the notion of a mass deficit
in 'core' galaxies, we show that the existence, amount, radial extent and sign
of mass deficits disagree substantially in the literature, both for a given
galaxy and on an average over a sample. We discuss possible implications and
suggest that SMBH binaries are unlikely to be the sole mechanism for producing
the large 'cores'.
We also deduce conditions under which the 3D light density can be described
with a multi-component Einasto model for both cuspy and core galaxies;
indicating an universality in the functional form of the 3D density of light in
galaxies and dark matter in LCDM N-body haloes. Finally, we show that our
result - the outer component of the SB profiles of massive galaxies has 5 < n <
8 - could imply i) a common feature of collisionless systems; and ii) that
galaxies with such n for their outer component are dark matter dominated.
View original:
http://arxiv.org/abs/1112.3120
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