The ACS Fornax Cluster Survey. V. Measurement and Recalibration of Surface Brightness Fluctuations and a Precise Value of the Fornax--Virgo Relati

📝 Abstract

We present g-z color and z-band surface brightness fluctuations (SBF) measurements for 43 early-type galaxies in the Fornax cluster imaged with HST/ACS. These are combined with measurements for Virgo cluster galaxies to derive a revised, nonlinear calibration of the z-band SBF absolute magnitude as a function of g-z. In all, we tabulate recalibrated SBF distances for 134 galaxies in Virgo, Fornax, the Virgo W’ group, and NGC4697 in the Virgo Southern Extension. The calibration procedure yields a precise relative distance modulus for Fornax with respect to Virgo of 0.42+/-0.03 mag, or a distance ratio 1.214 +/- 0.017. The resulting Fornax distance modulus is 31.51 +/-0.03 +/-0.15 mag, 20.0 +/-0.3 +/-1.4 Mpc, where the second set of error bars reflects systematic uncertainty from our assumed Virgo distance of 16.5 Mpc. The rms distance scatter for the early-type Fornax galaxies is 0.49^{+0.11}_{-0.15} Mpc, consistent with its compact appearance on the sky. This translates to a depth scatter smaller than the intrinsic, or “cosmic”, scatter sigma_cosmic in the SBF calibration, unlike in Virgo. As a result, we are able to place the first tight constraints on the value of sigma_cosmic, finding 0.06 +/- 0.01 mag, with a firm upper limit of sigma_cosmic<0.08 mag, at least for galaxies with g-z>1.02. We also present an alternative SBF calibration based on the `fluctuation count’ parameter Nbar, a proxy for galaxy mass, which gives a consistent relative distance. Finally, we find no evidence for systematic trends of the galaxy distances with position or velocity (e.g., no current infall); the Fornax cluster appears both compact and well virialized.[abridged]

💡 Analysis

We present g-z color and z-band surface brightness fluctuations (SBF) measurements for 43 early-type galaxies in the Fornax cluster imaged with HST/ACS. These are combined with measurements for Virgo cluster galaxies to derive a revised, nonlinear calibration of the z-band SBF absolute magnitude as a function of g-z. In all, we tabulate recalibrated SBF distances for 134 galaxies in Virgo, Fornax, the Virgo W’ group, and NGC4697 in the Virgo Southern Extension. The calibration procedure yields a precise relative distance modulus for Fornax with respect to Virgo of 0.42+/-0.03 mag, or a distance ratio 1.214 +/- 0.017. The resulting Fornax distance modulus is 31.51 +/-0.03 +/-0.15 mag, 20.0 +/-0.3 +/-1.4 Mpc, where the second set of error bars reflects systematic uncertainty from our assumed Virgo distance of 16.5 Mpc. The rms distance scatter for the early-type Fornax galaxies is 0.49^{+0.11}_{-0.15} Mpc, consistent with its compact appearance on the sky. This translates to a depth scatter smaller than the intrinsic, or “cosmic”, scatter sigma_cosmic in the SBF calibration, unlike in Virgo. As a result, we are able to place the first tight constraints on the value of sigma_cosmic, finding 0.06 +/- 0.01 mag, with a firm upper limit of sigma_cosmic<0.08 mag, at least for galaxies with g-z>1.02. We also present an alternative SBF calibration based on the `fluctuation count’ parameter Nbar, a proxy for galaxy mass, which gives a consistent relative distance. Finally, we find no evidence for systematic trends of the galaxy distances with position or velocity (e.g., no current infall); the Fornax cluster appears both compact and well virialized.[abridged]

📄 Content

arXiv:0901.1138v1 [astro-ph.CO] 8 Jan 2009 DRAFT VERSION OCTOBER 22, 2018 Preprint typeset using LATEX style emulateapj v. 08/22/09 THE ACS FORNAX CLUSTER SURVEY. V. MEASUREMENT AND RECALIBRATION OF SURFACE BRIGHTNESS FLUCTUATIONS AND A PRECISE VALUE OF THE FORNAX–VIRGO RELATIVE DISTANCE1 JOHN P. BLAKESLEE2,3, ANDRÉS JORDÁN4,5, SIMONA MEI6,7, PATRICK CÔTÉ2, LAURA FERRARESE2, LEOPOLDO INFANTE5, ERIC W. PENG8, JOHN L. TONRY9, AND MICHAEL J. WEST10 Draft version October 22, 2018 ABSTRACT We present (g475−z850) color and z850-band surface brightness fluctuations (SBF) measurements for 43 early- type galaxies in the Fornax cluster imaged with the Hubble Space Telescope Advanced Camera for Surveys. These are combined with our earlier measurements for Virgo cluster galaxies to derive a revised, nonlinear calibration of the z850-band SBF absolute magnitude Mz as a function of (g475−z850) color, valid for the AB color range 0.8 < (g475−z850) < 1.6. In all, we tabulate recalibrated SBF distances for 134 galaxies in Virgo, Fornax, the VirgoW ′ group, and NGC 4697 in the Virgo Southern Extension. The calibration procedure yields a highly precise relative distance modulus for Fornax with respect to Virgo of ∆(m−M)FV = 0.42±0.03 mag, or a distance ratio dF/dV = 1.214±0.017. The resulting Fornax distance modulus is (m−M)For = 31.51±0.03±0.15 mag, corresponding to dF = 20.0±0.3±1.4 Mpc, where the second set of error bars reflects the total systematic uncertainty from our assumed Virgo distance of 16.5 Mpc. The rms distance scatter for the early-type Fornax cluster galaxies is σd = 0.49+0.11 −0.15 Mpc, or a total line-of-sight depth of 2.0+0.4 −0.6 Mpc, consistent with its compact appearance on the sky. This translates to a depth scatter smaller than the intrinsic, or “cosmic,” scatter σcos in the SBF calibration, unlike the case for the larger Virgo cluster. As a result, we are able to place the first tight constraints on the value of σcos. We find σcos = 0.06 ± 0.01 mag, with a firm upper limit of σcos < 0.08 mag, for the subsample of galaxies with (g475−z850) > 1.02, but it is about twice as large for bluer galaxies. We also present an alternative SBF calibration based on the ‘fluctuation count’ parameter N = m−mtot, a proxy for galaxy mass. This gives a consistent relative distance but with larger intrinsic scatter, and we adopt the result from the calibration on (g475−z850) because of its basis in stellar population properties alone. Finally, we find no evidence for systematic trends of the galaxy distances with position or velocity (e.g., no current infall); the Fornax cluster appears both compact and well virialized. Subject headings: galaxies: clusters: individual (Fornax, Virgo) — galaxies: distances and redshifts — galax- ies: elliptical and lenticular, cD — large-scale structure of the universe

1. INTRODUCTION It is now more than twenty years since Tonry & Schnei- der (1988) first quantified the surface brightness fluctuations (SBF) method for determining extragalactic distances. That paper envisioned SBF potentially being used to measure dis- tances to elliptical galaxies out to 20 Mpc from the ground and being calibrated from stellar evolution models tied to Galac- tic clusters with distances from main sequence fitting. Tonry & Scheider noted that the absolute fluctuation magnitude M would vary with the age and metallicity of a stellar popula- tion, but they predicted that the mean color of a galaxy could 1 Based on observations with the NASA/ESA Hubble Space Telescope ob- tained at the Space Telescope Science Institute, which is operated by the As- sociation of Universities for Research in Astronomy, Inc., under NASA con- tract NAS 5-26555 2 Dominion Astrophysical Observatory, Herzberg Institute of Astro- physics, National Research Council of Canada, Victoria, BC V9E 2E7, Canada; John.Blakeslee@nrc.ca 3 Department of Physics and Astronomy, Washington State University, Pullman, WA 99163-2814 4 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 5 Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Santiago 22, Chile 6 University of Paris Denis Diderot, 75205 Paris Cedex 13, France 7 GEPI, Observatoire de Paris, Section de Meudon, 5 Place J. Janssen, 92195 Meudon Cedex, France 8 Department of Astronomy, Peking University, Beijing 100871, China 9 Institute for Astronomy, University of Hawaii, Honolulu, HI 96822 10 European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile be used to constrain M to within 0.4 mag, allowing galaxy distance measurements accurate to at least ∼20%. The first major application of the fully developed SBF method was by Tonry et al. (1990), who applied it to a sam- ple of Virgo cluster galaxies in the VRI bandpasses. They calibrated the M zero point from measurements in M31 and M32, assuming the Cepheid distance to M31. The depth of Virgo, including the unexpected discovery that the giant elliptical NGC 4365 apparently lay in the back

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