SDSS-IV MaNGA: the spatially resolved stellar initial mass function in ∼400 early-type galaxies

Abstract

MaNGA provides the opportunity to make precise spatially resolved measurements of the IMF slope in galaxies owing to its unique combination of spatial resolution, wavelength coverage and sample size. We derive radial gradients in age, element abundances and IMF slope analysing optical and near-infrared absorption features from stacked spectra out to the half-light radius of 366 early-type galaxies with masses 9.9 − 10.8 log M/M . We find flat gradients in age and [α/Fe] ratio, as well as negative gradients in metallicity, consistent with the literature. We further derive significant negative gradients in the [Na/Fe] ratio with galaxy centres being well enhanced in Na abundance by up to 0.5 dex. Finally, we find a gradient in IMF slope with a bottomheavy IMF in the centre (typical mass excess factor of 1.5) and a Milky Way-type IMF at the half-light radius. This pattern is mass-dependent with the lowest mass galaxies in our sample featuring only a shallow gradient around a Milky Way IMF. Our results imply the local IMF-σ relation within galaxies to be even steeper than the global relation and hint towards the local metallicity being the dominating factor behind the IMF variations. We also employ different stellar population models in our analysis and show that a radial IMF gradient is found independently of the stellar population model used. A similar analysis of the Wing-Ford band provides inconsistent results and further evidence of the difficulty in measuring and modelling this particular feature.

Combining stellar populations with orbit-superposition dynamical modelling: the formation history of the lenticular galaxy NGC 3115

“…Similarly, it appears that regardless of the degree of freedom in λ z as in Sample II, the fits are unable to reproduce the SFH, in particular the metallicity. This reaffirms the existence of radial gradients in stellar populations, with these gradients being stronger in metallicity, as has been seen by many studies previously both in general (for example, see Sarzi et al 2018;Parikh et al 2018;Poetrodjojo et al 2018) and specifically for NGC 3115 (for example, see Strom et al 1976;Pastorello et al 2014). However, we can additionally conclude here that these gradients must exist within each component even at fixed λ z .…”

Galaxy properties as revealed by MaNGA – II. Differences in stellar populations of slow and fast rotator ellipticals and dependence on environment

“…These findings are in qualitative agreement with previous work (e.g. La Barbera et al 2013;Martín-Navarro et al 2015a; La Barbera et al 2016;van Dokkum et al 2017;Tang & Worthey 2017;Parikh et al 2018). However, in Paper I we also found that Es with 200 ≤ σ0 ≤ 250 km s −1 and −21.5 ≤ Mr ≤ −22.5 tend to be the oldest in the sample, even though they are neither the largest σ nor the largest Lr.…”

Initial Mass Function Variation in Two Elliptical Galaxies Using Near-infrared Tracers

“…The IMFs measured in this paper give further support to the observed trend of increasingly bottom-heavy IMFs in ETGs with higher central σ v (CvD12b). Recently, Parikh et al (2018) measured correlations of varying degrees between the low mass (≤ 0.5 M ) IMF slope and galactic properties such as σ v , [Z/H], [Na/Fe], galactic radius, and stellar age in a sample of ∼400 ETGs. Our best-fit x 1 slope for M85 and M87 is consistent with their IMF-σ v correlation.…”