Heterogeneity of inverted calcium II H:K ratio cluster galaxies

Pimbblet, K. A.; Crossett, J. P.; Fraser-McKelvie, A.

Abstract

© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society The ratio of calcium II H plus H∊ 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.

Citation

Pimbblet, K. A., Crossett, J. P., & Fraser-McKelvie, A. (2019). Heterogeneity of inverted calcium II H:K ratio cluster galaxies. Monthly notices of the Royal Astronomical Society, 490(1), 455-466. https://doi.org/10.1093/mnras/stz2549

• Journal Article Type: Article
• Acceptance Date: Sep 10, 2019
• Online Publication Date: Sep 12, 2019
• Publication Date: 2019-11
• Deposit Date: Nov 26, 2019
• Publicly Available Date: Nov 26, 2019
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 490
• Issue: 1
• Pages: 455-466
• DOI: https://doi.org/10.1093/mnras/stz2549
• Keywords: Space and Planetary Science; Astronomy and Astrophysics
• Public URL: https://hull-repository.worktribe.com/output/2715647