The SAMI Galaxy Survey: stellar population gradients of central galaxies

We examine the stellar population radial gradients (age, metallicity, and [α/Fe]) of 96 passive central galaxies up to ∼2 Re in the SAMI Galaxy Survey. The targeted groups have a halo mass range of 11<log(M200/M⊙)<15 . The main goal of this work is to determine whether central galaxies have different stellar population properties when compared to similarly massive satellite galaxies. For the whole sample, we find negative metallicity radial gradients, which show evidence of becoming shallower with increasing stellar mass. The age and [α/Fe] gradients are slightly positive and consistent with zero, respectively. The [α/Fe] gradients become more negative with increasing mass, while the age gradients do not show any significant trend with mass. We do not observe a significant difference between the stellar population gradients of central and satellite galaxies at fixed stellar mass. The mean metallicity gradients are Δ[Z/H]/Δlog(r/Re)=−0.25±0.03 for central galaxies and Δ[Z/H]/Δlog(r/Re)=−0.30±0.01 for satellites. The mean age and [α/Fe] gradients are consistent between central and satellite galaxies, within the uncertainties, with a mean value of Δlog(Age/Gyr)/Δlog(r/Re)=0.13±0.03 for centrals and Δlog(Age/Gyr)/Δlog(r/Re)=0.17±0.01 for satellites and Δ[α/Fe]/Δlog(r/Re)=0.01±0.03 for centrals and Δ[α/Fe]/Δlog(r/Re)=0.08±0.01 for satellites. The stellar population gradients of central and satellite galaxies show no difference as a function of halo mass. This evidence suggests that the inner regions of central passive galaxies form in a similar fashion to those of satellite passive galaxies, in agreement with a two-phase formation scenario.

Publication Date: 
June 2020