Further evidence for a time-dependent initial mass function in massive early-type galaxies

Abstract

Spectroscopic analyses of gravity-sensitive line strengths give growing evidence towards an excess of low-mass stars in massive early-type galaxies (ETGs). Such a scenario requires a bottom-heavy initial mass function (IMF). However, strong constraints can be imposed if we take into account galactic chemical enrichment. We extend the analysis of Weidner et al. and consider the functional form of bottom-heavy IMFs used in recent works, where the high-mass end slope is kept fixed to the Salpeter value, and a free parameter is introduced to describe the slope at stellar masses below some pivot mass scale (M<MP=0.5Msun). We find that no such time-independent parameterisation is capable to reproduce the full set of constraints in the stellar populations of massive ETGs - resting on the assumption that the analysis of gravity-sensitive line strengths leads to a mass fraction at birth in stars with mass M<0.5Msun above 60%. Most notably, the large amount of metal-poor gas locked in low-mass stars during the early, strong phases of star formation results in average stellar metallicities [M/H]<-0.6, well below the solar value. The conclusions are unchanged if either the low-mass end cutoff, or the pivot mass are left as free parameters, strengthening the case for a time-dependent IMF.

5 pages, 4 figures, 1 table. MNRAS Letters, in press

References in corpus (5)

• A systematic variation of the stellar initial mass function in early-type galaxies
• Variations of the stellar initial mass function in the progenitors of massive early-type galaxies and in extreme starburst environments
• Variations in the initial mass function in early-type galaxies: A critical comparison between dynamical and spectroscopic results
• Testing the universal stellar IMF on the metallicity distribution in the bulges of the Milky Way and M31
• The star-formation histories of elliptical galaxies across the fundamental plane

Cited by in corpus (8)

• Galaxy And Mass Assembly (GAMA): The galaxy stellar mass function to $z=0.1$ from the r-band selected equatorial regions
• Timing the formation and assembly of early-type galaxies via spatially resolved stellar populations analysis
• The initial mass function of a massive relic galaxy
• IMF and [Na/Fe] abundance ratios from optical and NIR Spectral Features in Early-type Galaxies
• The Initial Mass Function of Early-type Galaxies: no correlation with [Mg/Fe]
• Stellar populations across the black hole mass - velocity dispersion relation
• Evidence of a Bottom-heavy Initial Mass Function in Massive Early-type Galaxies from Near-infrared Metal Lines
• Testing the Universality of the Stellar IMF with Chandra and HST