Speaker
Alton Padraig
(Durham University)
Description
Massive elliptical galaxies are thought to form in two stages - first, the formation
of a central core via fast dissipative processes by z~2, followed by the accumulation
of mass through (mostly minor) dry mergers. A combination of evidence from
spectroscopy, lensing, and stellar dynamics appears to suggest that in the most
massive central cores stars form according to a 'bottom-heavy' IMF (i.e. an excess of
dwarf stars are formed relative to the Milky-Way stellar populations). This has
implications for the inferred M/L ratio (and thus the SFR estimated for these systems
at high redshift), and also for the future evolution of these systems since the IMF
controls e.g. the SNe rate.
The accumulation of mass via minor mergers ought to introduce radial gradients in the
inferred IMF for present-day massive ellipticals (since lower mass systems are
thought to form stars according to a Milky-Way-like IMF). Likewise, both dissipative
collapse and minor mergers should introduce e.g. radial metallicity gradients. Both
of these are in principle detectable through spatially-resolved spectroscopy. I will
present infrared spectroscopy from VLT-KMOS for a sample of local massive ellipticals
(Alton et al. 2016 - submitted to MNRAS), showing that IMF gradients are not
significant within the half-light radii of these systems (although chemical abundance
gradients are present). Taken in concert with evidence for a bottom-heavy IMF in
these systems, this appears to indicate that minor mergers deposit mass primarily
beyond the present-day half-light radii. Meanwhile, the stellar population within the
effective radius is inferred to be dwarf-enriched throughout.
Primary author
Alton Padraig
(Durham University)
