T He Cool Stellar P Opulations of E Arly-T Y Pe G
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Arxiv:Astro-Ph/0304318V1 16 Apr 2003
The Globular Cluster Luminosity Function: New Progress in Understanding an Old Distance Indicator Tom Richtler Astronomy Group, Departamento de F´ısica, Universidad de Concepci´on, Casilla 160-C, Concepci´on, Chile Abstract. I review the Globular Cluster Luminosity Function (GCLF) with emphasis on recent observational data and theoretical progress. As is well known, the turn-over magnitude (TOM) is a good distance indicator for early-type galaxies within the limits set by data quality and sufficient number of objects. A comparison with distances derived from surface brightness fluctuations with the available TOMs in the V-band reveals, however, many discrepant cases. These cases often violate the condition that the TOM should only be used as a distance indicator in old globular cluster systems. The existence of intermediate age-populations in early-type galaxies likely is the cause of many of these discrepancies. The connection between the luminosity functions of young and old cluster systems is discussed on the basis of modelling the dynamical evolution of cluster systems. Finally, I briefly present the current ideas of why such a universal structure as the GCLF exists. 1 Introduction: What is the Globular Cluster Luminosity Function? Since the era of Shapley, who first explored the size of the Galaxy, the distances to globular clusters often set landmarks in establishing first the galactic, then the extragalactic distance scale. Among the methods which have been developed to determine the distances of early-type galaxies, the usage of globular clusters is one of the oldest, if not the oldest. Baum [5] first compared the brightness of the brightest globular clusters in M87 to those of M31. -
The SBF Survey of Galaxy Distances. I. Sample Selection, Photometric
TheSBFSurveyofGalaxyDistances.I. Sample Selection, Photometric Calibration, and the Hubble Constant1 John L. Tonry2 and John P. Blakeslee2 Physics Dept. Room 6-204, MIT, Cambridge, MA 02139; Edward A. Ajhar2 Kitt Peak National Observatory, National Optical Astronomy Observatories, P.O. Box 26732 Tucson, AZ 85726; Alan Dressler Carnegie Observatories, 813 Santa Barbara St., Pasadena, CA 91101 ABSTRACT We describe a program of surface brightness fluctuation (SBF) measurements for determining galaxy distances. This paper presents the photometric calibration of our sample and of SBF in general. Basing our zero point on observations of Cepheid variable stars we find that the absolute SBF magnitude in the Kron-Cousins I band correlates well with the mean (V −I)0 color of a galaxy according to M I =(−1.74 ± 0.07) + (4.5 ± 0.25) [(V −I)0 − 1.15] for 1.0 < (V −I) < 1.3. This agrees well with theoretical estimates from stellar popula- tion models. Comparisons between SBF distances and a variety of other estimators, including Cepheid variable stars, the Planetary Nebula Luminosity Function (PNLF), Tully-Fisher (TF), Dn−σ, SNII, and SNIa, demonstrate that the calibration of SBF is universally valid and that SBF error estimates are accurate. The zero point given by Cepheids, PNLF, TF (both calibrated using Cepheids), and SNII is in units of Mpc; the zero point given by TF (referenced to a distant frame), Dn−σ, and SNIa is in terms of a Hubble expan- sion velocity expressed in km/s. Tying together these two zero points yields a Hubble constant of H0 =81±6 km/s/Mpc. -
April Constellations of the Month
April Constellations of the Month Leo Small Scope Objects: Name R.A. Decl. Details M65! A large, bright Sa/Sb spiral galaxy. 7.8 x 1.6 arc minutes, magnitude 10.2. Very 11hr 18.9m +13° 05’ (NGC 3623) high surface brighness showing good detail in medium sized ‘scopes. M66! Another bright Sb galaxy, only 21 arc minutes from M65. Slightly brighter at mag. 11hr 20.2m +12° 59’ (NGC 3627) 9.7, measuring 8.0 x 2.5 arc minutes. M95 An easy SBb barred spiral, 4 x 3 arc minutes in size. Magnitude 10.5, with 10hr 44.0m +11° 42’ a bright central core. The bar and outer ring of material will require larger (NGC 3351) aperature and dark skies. M96 Another bright Sb spiral, about 42 arc minutes east of M95, but larger and 10hr 46.8m +11° 49’ (NGC 3368) brighter. 6 x 4 arc minutes, magnitude 10.1. Located about 48 arc minutes NNE of M96. This small elliptical galaxy measures M105 only 2 x 2.1 arc minutes, but at mag. 10.3 has very high surface brightness. 10hr 47.8m +12° 35’ (NGC 3379) Look for NGC 3384! (110NGC) and NGC 3389 (mag 11.0 and 12.2) which form a small triangle with M105. NGC 3384! 10hr 48.3m +12° 38’ See comment for M105. The brightest galaxy in Leo, this Sb/Sc spiral galaxy shines at mag. 9.5. Look for NGC 2903!! 09hr 32.2m +21° 30’ a hazy patch 11 x 4.7 arc minutes in size 1.5° south of l Leonis. -