2007/10/29 by David R. Silva, D. R. Silva, H. Kuntschner +3 · 67 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Brightest cluster galaxy #Elliptical galaxy #Fornax Cluster #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy cluster #Metallicity #Stars #Stellar population #Stellar, planetary, and galactic studies #Surface brightness fluctuation #astro-ph
paper · pdf · doi:10.1086/524869
published in The Astrophysical Journal 674(1), 194-208 (IOP Publishing) · 47 pages, 16 figures, ApJ accepted
arxiv created 2007/10/29 · openalex publication_date 2008/02/07 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The strong spectral features near 2.2 μm in early-type galaxies remain relatively unexplored. Yet, they open a tightly focused window on the coolest giant stars in these galaxies—a window that can be used to explore both age and metallicity effects. Here, new measurements of K -band spectral features are presented for 11 early-type galaxies in the nearby Fornax galaxy cluster. Based on these measurements, the following conclusions have been reached: (1) in galaxies with no signatures of a young stellar component, the K -band Na I index is highly correlated with both the optical metallicity indicator [MgFe]' and the central velocity dispersion σ; (2) in the same galaxies, the K -band Fe features saturate in galaxies with σ > 150 km s −1 , while Na I (and [MgFe]') continues to increase; (3) [Si/Fe] (and possibly [Na/Fe]) is larger in all observed Fornax galaxies than in Galactic open clusters with near-solar metallicity; (4) in various near-IR diagnostic diagrams, galaxies with signatures of a young stellar component (strong Hβ, weak [MgFe]') are clearly separated from galaxies with purely old stellar populations; furthermore, this separation is consistent with the presence of an increased number of M-giant stars (most likely to be thermally pulsating AGB stars); (5) the near-IR Na I versus σ or ⟨Fe I⟩ versus σ diagrams discussed here seem as efficient for detecting putatively young stellar components in early-type galaxies as the more commonly used age/metallicity diagnostic plots using optical indices (e.g., Hβ vs. [MgFe]'). The combination of these spectral indices near 2.2 μm with high spatial resolution spectroscopy from ground-based or space-based observatories promises to provide new insights into the nature of stellar populations in the central regions of distant early-type galaxies.