ABSTRACT

Gradients in the stellar populations (SP) of galaxies – e.g. in age, metallicity, stellar initial mass function (IMF) – can result in gradients in the stellar-mass-to-light ratio, M*/L. Such gradients imply that the distribution of the stellar mass and light is different. For old SPs, e.g. in early-type galaxies at z ∼ 0, the M*/L gradients are weak if driven by variations in age and metallicity, but significantly larger if driven by the IMF. A gradient which has larger M*/L in the centre increases the estimated total stellar mass (M*) and reduces the scale which contains half this mass (Re,*), compared to when the gradient is ignored. For the IMF gradients inferred from fitting MILES simple SP models to the H β, 〈Fe〉, [MgFe], and TiO2SDSS absorption lines measured in spatially resolved spectra of early-type galaxies in the MaNGA survey, the fractional change in Re,* can be significantly larger than that in M*, especially when the light is more centrally concentrated. The Re,*–M* correlation which results from accounting for IMF gradients is offset to smaller sizes by 0.3 dex compared to when these gradients are ignored. Comparisons with ‘quiescent’ galaxies at higher z must account for evolution in SP gradients (especially age more »

Authors:
; ; ; ; ;
Publication Date:
NSF-PAR ID:
10383041
Journal Name:
Monthly Notices of the Royal Astronomical Society
Volume:
518
Issue:
3
Page Range or eLocation-ID:
p. 3494-3508
ISSN:
0035-8711
Publisher:
Oxford University Press
In this work, we publish stellar velocity dispersions, sizes, and dynamical masses for eight ultramassive galaxies (UMGs;$log(M*/M⊙)$> 11),z≳ 3) from the Massive Ancient Galaxies Atz> 3 NEar-infrared (MAGAZ3NE) Survey, more than doubling the number of such galaxies with velocity dispersion measurements at this epoch. Using the deep Keck/MOSFIRE and Keck/NIRES spectroscopy of these objects in theHandKbandpasses, we obtain large velocity dispersions of ∼400 km s−1for most of the objects, which are some of the highest stellar velocity dispersions measured and ∼40% larger than those measured for galaxies of similar mass atz∼ 1.7. The sizes of these objects are also smaller by a factor of 1.5–3 compared to this samez∼ 1.7 sample. We combine these large velocity dispersions and small sizes to obtain dynamical masses. The dynamical masses are similar to the stellar masses of these galaxies, consistent with a Chabrier initial mass function (IMF). Considered alongside previous studies of massive quiescent galaxies across 0.2 <z< 4.0, there is evidence for an evolution in the relation between the dynamical mass–stellar mass ratio and velocity dispersion as a function of redshift. This implies an IMF with fewer low-mass stars (e.g., Chabrier IMF) for massive quiescentmore »