Bibcode
Beckman, J. E.; Erwin, P.; Gutiérrez, L.
Referencia bibliográfica
Highlights of Astronomy, Volume 16, pp. 361-361
Fecha de publicación:
3
2015
Número de citas
0
Número de citas referidas
0
Descripción
Azimuthally averaged surface brightness profiles of disc galaxies
provide a most useful practical classification scheme which gives
insights into their evolution. Freeman (1970) first classified disc
profiles into Type I, with a single exponential decline in surface
brightness, and Type II, having a split exponential profile, whose inner
radial portion is shallower than its outer section. Van der Kruit &
and Searle, (1981) drew attention to sharply truncated profiles of outer
discs observed edge-on, but more recently Pohlen et al. (2004) showed
that if these same galaxies were observed face-on their profiles would
be of Type II. Finally in Erwin, Beckman and Pohlen (2005) we found a
significant fraction of profiles with inner portion steeper than the
outer portion, which we termed ``antitruncations`` or Type III profiles.
In Erwin, Pohlen and Beckman (2008), we produced a refined
classification, taking into account those Type II's produced by
dynamical effects at the outer Lindblad resonance, and those Type III's
caused by the presence of an outer stellar halo. In Gutiérrez et
al. (2011) we showed the distribution of the three main profile types
along the Hubble sequence. In early type discs Types I and III
predominate, while in late types, Sc and later, Type II predominates.
The evolution of Type II's over cosmic time was studied by Azzollini et
al. (2008a, 2008b) who obtained four key results: (a) between z = 1 and
z = 0 the break radius between the inner (shallower) and outer (steeper)
profile has increased systematically, by a factor 1.3; (b) the inner
profile has steepened while the outer profile is shallower at lower z;
(c) the extrapolated central surface brightness has fallen by over two
magnitudes; (d) the discs in the full redshift interval are always
bluest at the break radius. While this behaviour can be qualitatively
explained via evolutionary models including stellar migration plus gas
infall, such as that by Roskar et al. (2008), and while Type III
profiles may have a qualitative explanation via mergers and/or
accretion, the widespread existence of Type I's is still a major
conceptual challenge.