Images, Maps, Spectra and SEDs

X-Ray data

PKS0320-37

Optical spectrum taken with ESO telescopes.

Tadhunter et al. (1993)

0.005

03 22 41.7

-37 12 30

WLRG

FRI

Fornax A

N

E

UK Schmidt image, λ4680A, width 8 arcmins.

Notes

    One of the closest and most famous radio sources in the southern hemisphere. The nearby FRI radio elliptical/S0 galaxy Fornax A shows a prominent, kpc-scale dust lane, as well as shells and other features on a larger scale. It is situated towards the edge of the Fornax cluster of galaxies, but it is not the dominant E/cD galaxy in the cluster. A line index analysis by Kuntschner (2000) gives a luminosity-weighted age of 2 Gyr for the stellar populations emitting the diffuse light of the galaxy. This is consistent with the 3 ± 0.5 Gyr obtained by Goudfrooij et al. (2001) using spectroscopic observations of three luminous clusters in the galaxy halo. Overall, the morphological and spectroscopic evidence supports the idea that this galaxy was involved in a major galaxy merger ∼2–3 Gyr ago, associated with a period of enhanced star formation that formed the current intermediate-age stellar populations.

    In order to attempt to learn more about the star formation history of Fornax A, we have carried out spectral synthesis modelling of our deep optical NTT spectrum of this source taken in 2003. Following the approach outlined in Holt et al. (2007) we have modelled the optical continuum SED using a combination of old (12.5 Gyr) and young (<5 Gyr) stellar populations, allowing for the possibility of reddening in the YSP. We find that, while YSPs are required to model the detailed shape of the continuum in the blue/near-UV, their flux contribution is relatively minor (<10 per cent at 4720 A for a single burst YSP with age <1.0 Gyr). In consequence, the age and reddening of the YSP are not well constrained. For example, our fits to both the detailed absorption features and the overall SEDs are consistent with an old stellar population plus a minor (<5 per cent at 4720 A) contribution from a YSP of age <0.1 Gyr, but they are also consistent with old stellar populations plus a more significant (>20 per cent at 4720 A) contribution from an older YSP with age >1 Gyr (see Fig. A2); no range of ages for the YSP is ruled out. Wider spectral coverage data, extending further into the UV, would be required to obtain more accurate results for Fornax A.

    The radio image shows two ‘flat’, low-brightness lobes and a weak core in the middle. These lobes are extremely filamentary at high resolution. It is presumably an FRI, but no very typical. No [OIII] emission lines are detected. The continuum appears to be typical of early type galaxies.