* Astronomy

Spectacular Hubble View of Centaurus A

The NASA/ESA Hubble Space Telescope has produced a close-up view of the galaxy Centaurus A. Hubble's out-of-this-world location and world-class Wide Field Camera 3 instrument reveal a dramatic picture of a dynamic galaxy in flux.
Centaurus A, also known as NGC 5128, is well known for its dramatic dusty lanes of dark material. Hubble's observations, using its most advanced instrument, the Wide Field Camera 3, are the most detailed ever made of this galaxy. They have been combined here in a multi-wavelength image that reveals never-before-seen detail in the dusty portion of the galaxy.
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Firestorm of Star Birth in the Active Galaxy Centaurus A


Credit NASA

Resembling looming rain clouds on a stormy day, dark lanes of dust crisscross the giant elliptical galaxy Centaurus A. Hubble's panchromatic vision, stretching from ultraviolet through near-infrared wavelengths, reveals the vibrant glow of young, blue star clusters and a glimpse into regions normally obscured by the dust. This image was taken in July 2010 with Hubble's Wide Field Camera 3.
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Title: The Cepheids of Centaurus A (NGC 5128) and Implications for H0
Authors: Daniel J. Majaess
(Version, v2)

An analysis based on new OGLE observations reaffirms Ferrarese et al. discovery of 5 Type II Cepheids in NGC 5128. The distance to that comparatively unreddened population is d=3.8±0.4(se) Mpc. The classical Cepheids in NGC 5128 are the most obscured in the extragalactic sample (n=30) surveyed, whereas groups of Cepheids tied to several SNe host galaxies feature negative reddenings. Adopting an anomalous extinction law for Cepheids in NGC 5128 owing to observations of SN 1986G (Rv~2.4) is not favoured, granted SNe Ia may follow small Rv. The distances to classical Cepheids in NGC 5128 exhibit a dependence on colour and CCD chip, which may arise in part from photometric contamination. Applying a colour cut to mitigate contamination yields d~3.5 Mpc (V-I<1.3), while the entire sample's mean is d~3.1 Mpc. The distance was established via the latest VI Galactic Wesenheit functions that include the 10 HST calibrators, and which imply a shorter distance scale than Sandage et al.2004 by ~>10% at P~25d. HST monitored classical Cepheids in NGC 5128, and the SNe hosts NGC 3021 & NGC 1309, follow a shallower VI Wesenheit slope than ground-based calibrations of the Milky Way, LMC, NGC 6822, SMC, and IC 1613. The discrepancy is unrelated to metallicity since the latter group share a common slope over a sizeable abundance baseline (a=-3.34±0.08,d[Fe/H]~1). A negligible distance offset between OGLE Cepheids and RR Lyr variables in the LMC, SMC, and IC 1613 bolsters assertions that VI-based Wesenheit functions are relatively insensitive to chemical abundance. In sum, a metallicity effect (VI) is not the chief source of uncertainty associated with the Cepheid distance to NGC 5128 or the establishment of Hubble's constant, but rather it may be the admittedly challenging task of obtaining precise, commonly standardized, multiepoch, multiband, comparatively uncontaminated extragalactic Cepheid photometry.

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Title: The Distance to NGC 5128 (Centaurus A)
Authors: Gretchen L. H. Harris, Marina Rejkuba, William E. Harris

In this paper we review the various high precision methods that are now available to determine the distance to NGC 5128. These methods include: Cepheids, TRGB (tip of the red giant branch), PNLF (planetary nebula luminosity function), SBF (surface brightness fluctuations) and Long Period Variable (LPV) Mira stars. From an evaluation of these methods and their uncertainties, we derive a best-estimate distance of 3.8 ± 0.1 Mpc to NGC 5128 and find that this mean is now well supported by the current data. We also discuss the role of NGC 5128 more generally for the extragalactic distance scale as a testbed for the most direct possible comparison among these key methods.

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