Measuring Distances and Probing the Unresolved Stellar Populations of Galaxies Using Infrared Surface Brightness Fluctuations

Abstract

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 (M F160W ) were derived for each galaxy using previouslymeasured 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.To the 1996 Virgo sample, Jensen et al. (1998) added galaxies in the Fornax and Eridanus clusters. Three of the bluest galaxies in their sample showed K-band fluctuation magnitudes that were ∼0.25 mag brighter than the others. Jensen et al. noted that the models implied younger stellar populations in these bluer ellipticals. However, the sample size was small and the range in (V −I) color was limited; hence, the slope they measured was not statistically significant and they adopted a constant K-band SBF calibration. The K-band fluctuations for the bluest galaxy in their sample (NGC 4489) were significantly brighter than the others in the Virgo cluster, but the measurement was not trusted due to its low signal-to-noise (S/N) ratio. Mei, Silva, & Quinn (2001c) subsequently re-observed this galaxy and found comparably bright K-band fluctuations.

New distances of unresolved dwarf elliptical galaxies in the vicinity of the Local Group

“…Our SBF distance to NGC 4150 of 14.4 ± 0.7 Mpc is in good agreement with earlier SBF distances (Tonry et al 2001;Jensen et al 2003) of 13.7 ± 1.7 Mpc and 12.8 ± 1.5 Mpc, Fig. 11.…”

“…The galaxy has a heliocentric velocity of v = 226 ± 22 km s −1 (Fisher et al 1995). Tonry et al (2001) reported a first SBF distance modulus of (m − M) = 30.69 ± 0.25 mag (or 13.7 ± 1.7 Mpc) and Jensen et al (2003) another, corrected SBF distance modulus of (m − M) = 30.53 ± 0.24 mag (or 12.8 ± 1.5 Mpc). We analysed six independent SBF fields across the galaxy's surface but well away from the spiral structures (Fig.…”

UV Excess and AGB Evolution in Elliptical-Galaxy Stellar Populations

“…3. As Hβ basically probes the temperature location of the turn-off point of galaxy main sequence stars (Buzzoni et al, 1994;Jensen et al, 2003), the inferred physical trend confirms that UV-upturn is stronger among Hβ-poor old and super metal-rich galaxies.…”

Detecting cold H2globules in the outer Galactic disc by microlensing towards the Maffei 1 elliptical

“…The observed absolute fluctuation magnitudes of galaxies in IHK as a function of intrinsic colour are: (Tonry et al 1997), (Jensen et al 2003), (Liu et al 2002). Fingerhut et al (2003) report (V−I) 0 = 1.06 ± 0.09 for Maffei 1, which impliesM I = −2.1 andM K s = −6.2 for this galaxy.…”