Mon. Not. R. Astron. Soc., 428, 834-844 (2013/January-1)
The Herschel Fornax Cluster Survey - I. The bright galaxy sample.
DAVIES J.I., BIANCHI S., BAES M., BOSELLI A., CIESLA L., CLEMENS M., DAVIS T.A., DE LOOZE I., DI SEREGO ALIGHIERI S., FULLER C., FRITZ J., HUNT L.K., SERRA P., SMITH M.W.L., VERSTAPPEN J., VLAHAKIS C., XILOURIS E.M., BOMANS D., HUGHES T., GARCIA-APPADOO D. and MADDEN S.
Abstract (from CDS):
We present Herschel Space Telescope observations of the nearby Fornax cluster at 100, 160, 250, 350 and 500µm with a spatial resolution of 7-36 arcsec (10arcsec ~ 1kpc at dFornax = 17.9Mpc). We define a sample of 11 bright galaxies, selected at 500µm, that can be directly compared with our past work on the Virgo cluster. We check and compare our results with previous observations made by IRAS and Planck, finding good agreement. The far-infrared luminosity density is higher, by about a factor of 3, in Fornax compared to Virgo, consistent with the higher number density of galaxies. The 100µm (42.5-122.5µm) luminosity is two orders of magnitude larger in Fornax than in the local field as measured by IRAS. We calculate stellar (L0.4-2.5) and far-infrared (L100-500) luminosities for each galaxy and use these to estimate a mean optical depth of τ = 0.4±0.1 - the same value as we previously found for Virgo cluster galaxies. For 10 of the 11 galaxies (NGC 1399 excepted), we fit a modified blackbody curve (β = 2.0) to our observed flux densities to derive dust masses and temperatures of 106.54-8.35 M☉ and T =14.6-24.2 K, respectively, values comparable to those found for Virgo. The derived stars-to-gas(atomic) and gas(atomic)-to-dust ratios vary from 1.1-67.6 to 9.8-436.5, respectively, again broadly consistent with values for Virgo. Fornax is a mass overdensity in stars and dust of about 120 when compared to the local field (30 for Virgo). Fornax and Virgo are both a factor of 6 lower overdensities in gas(atomic) than in stars and dust indicating loss of gas, but not dust and stars, in the cluster environment. We consider in more detail two of the sample galaxies. As the brightest source in either Fornax or Virgo, NGC 1365 is also detected by Planck. The Planck data fit the PACS/SPIRE spectral energy distribution out to 1382µm with no evidence of other sources of emission (`spinning dust', free-free, synchrotron). At the opposite end of the scale, NGC 1399 is detected only at 500µm with the emission probably arising from the nuclear radio source rather than interstellar dust.
© 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society (2012)
Galaxies: clusters individual: Fornax - Galaxies: ISM
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