Zusammenfassung
Many techniques have been used in the literature for determining which
particles or cells in a hydrodynamic simulation are attached to a galaxy. Often
these invoke a spherical aperture that defines the boundary between the galaxy
and the rest of its parent (sub)halo, sometimes coupled with, or alternatively
involving, the use of a subhalo finder and gas property restrictions. Using the
suite of high-resolution zoom re-simulations of individual haloes by Martig et
al., and the large-scale simulation MassiveBlack-II, we examine the differences
in measured galaxy properties from techniques with various aperture
definitions. We perform techniques popular in the literature and present a new
technique of our own, based on the baryonic mass profiles of simulated
(sub)haloes. For the average Milky-Way-mass system, we find the two most
popular techniques in the literature return differences of order 30 per cent
for stellar mass, a factor of 3 for gas mass, 40 per cent for star formation
rate, and factors of several for gas accretion and ejection rates. Individual
cases can show variations greater than this, with the severity dependent on the
concentration of a given system. The average difference in integrated
properties for a more general galaxy population are not as striking, but are
still significant for stellar and gas mass. The large differences that can
occur are problematic for comparing results from various publications. We
stress the importance of both defining and justifying a technique choice and
discourage using popular apertures that use an exact fraction of the virial
radius, due to the unignorable variation in galaxy-to-(sub)halo size. Finally,
we note that technique choice does not greatly affect simulated galaxies from
lying within the scatter of observed scaling relations, but it can alter the
derived best-fit slope for the Kennicutt-Schmidt relation.
Beschreibung
[1404.4053] Where do galaxies end? A study of hydrodynamic-simulation galaxies and their integrated properties
Links und Ressourcen
Tags