2002/10/05 by Joseph B. Jensen, J. Tonry, John L. Tonry +8 · 3 citations
Engineering · Physics and Astronomy · #CCD and CMOS Imaging Sensors #Galaxies: Formation, Evolution, Phenomena #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/345430
published as Astrophys.J.583:712-726,2003 · 38 pages, 8 figures; accepted for publication in ApJ
arxiv created 2002/10/05 · openalex publication_date 2003/02/01 · arxiv updated 2011/05/05 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
To empirically calibrate the IR surface brightness fluctuation (SBF) distance scale and probe the properties of unresolved stellar populations, we measured fluctuations in 65 galaxies using NICMOS on the Hubble Space Telescope . The early-type galaxies in this sample include elliptical and S0 galaxies and spiral bulges in a variety of environments. Absolute fluctuation magnitudes in the F160W (1.6 μm) filter ( F160W ) were derived for each galaxy using previously measured I -band SBF and Cepheid variable star distances. F160W SBFs can be used to measure distances to early-type galaxies with a relative accuracy of ~10%, provided that the galaxy color is known to ~0.035 mag or better. Near-IR fluctuations can also reveal the properties of the most luminous stellar populations in galaxies. Comparison of F160W fluctuation magnitudes and optical colors to stellar population model predictions suggests that bluer elliptical and S0 galaxies have significantly younger populations than redder ones and may also be more metal-rich. There are no galaxies in this sample with fluctuation magnitudes consistent with old, metal-poor ( t > 5 Gyr, [Fe/H] < -0.7) stellar population models. Composite stellar population models imply that bright fluctuations in the bluer galaxies may be the result of an episode of recent star formation in a fraction of the total mass of a galaxy. Age estimates from the F160W fluctuation magnitudes are consistent with those measured using the Hβ Balmer-line index. The two types of measurements make use of completely different techniques and are sensitive to stars in different evolutionary phases. Both techniques reveal the presence of intermediate-age stars in the early-type galaxies of this sample.