Beliebiger Eintrag,
Evidence for a constant IMF in early-type galaxies based on their X-ray binary populations
(2014)cite arxiv:1401.3405Comment: 12 pages, 5 figures, 2 tables, submitted to ApJ, revised following initial referees report.
Zusammenfassung
A number of recent studies have proposed that the stellar initial mass
function (IMF) of early type galaxies varies systematically as a function of
galaxy mass, with higher mass galaxies having steeper IMFs. These steeper IMFs
have more low-mass stars relative to the number of high mass stars, and
therefore naturally result in proportionally fewer neutron stars and black
holes. In this paper, we specifically predict the variation in the number of
black holes and neutron stars in early type galaxies based on the IMF variation
required to reproduce the observed mass-to-light ratio trends with galaxy mass.
We then test whether such variations are observed by studying the field
low-mass X-ray binary populations (LMXBs) of nearby early-type galaxies. In
these binaries, a neutron star or black hole accretes matter from a low-mass
donor star. Their number is therefore expected to scale with the number of
black holes and neutron stars present in a galaxy. We find that the number of
LMXBs per K-band light is similar among the galaxies in our sample. These data
are consistent with an invariant IMF but inconsistent with proposals that the
IMF varies from a Kroupa/Chabrier like IMF at low masses to a steeper IMF (with
slope x=2.8) at high masses. We discuss how these observations constrain the
possible forms of the IMF variations and how future Chandra observations can
enable sharper tests of the IMF.
