2019/09/11 by Kevin A. Pimbblet, K. A. Pimbblet, Jacob P. Crossett +3
Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Cluster (spacecraft) #Emission spectrum #Equivalent width #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy cluster #Physics #Spectral line #Spiral galaxy #Stars #Stellar, planetary, and galactic studies #astro-ph.GA
paper · pdf · doi:10.1093/mnras/stz2549
14 pages, 9 figures, accepted for publication in MNRAS
arxiv created 2019/09/11 · openalex publication_date 2019/09/11 · arxiv updated 2019/09/12 · openalex created_date 2019/09/19 · openalex updated_date 2026/08/05
ABSTRACT The ratio of calcium ii H plus Hϵ to calcium ii K inverts as a galaxy stellar population moves from being dominated by older stars to possessing more A and B class stars. This ratio – the H:K ratio – can serve as an indicator of stellar populations younger than 200 Myr. In this work, we provide a new method to determine H:K, and apply it to spectra taken of cluster galaxies in Abell 3888. Although H:K is on average systematically lower for the cluster than for a wider field sample, we show that H:K does not have a simple relationship with other indices such as the equivalent widths of Hδ and [O ii] beyond having a high value for strong [O ii] emission. Moreover, strongly inverted galaxies with H:K > 1.1 have no preferred location within the cluster and are only slightly lower in their velocity dispersions around the cluster compared to strongly emitting [O ii] galaxies. Our results indicate that selecting galaxies on H:K inversion results in a heterogeneous sample formed via a mixture of pathways that likely includes, but may not be limited to, merging spiral galaxies, and quiescent galaxies accreting lower mass, gas-rich companions. In concert with other selection criteria, H:K can provide a means to select a more ‘pure’ passive sample or to aid in the selection of highly star-forming galaxies, especially where other spectral line indicators such as H α may not have been observed.