We present Herschel Space Telescope observations of the nearby Fornax cluster at 100 , 160 , 250 , 350 and 500 \mu m with a spatial resolution of 7 - 36 arc sec ( 10 ” \approx 1 kpc at d _ { Fornax } = 17.9 Mpc ) .
We define a sample of eleven bright galaxies , selected at 500 \mu m , 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 three , in Fornax compared to Virgo , consistent with the higher number density of galaxies .
The 100 \mu m ( 42.5-122.5 \mu m ) luminosity is two orders of magnitude larger in Fornax than in the local field as measured by IRAS .
We calculate stellar ( L _ { 0.4 - 2.5 } ) and far-infrared ( L _ { 100 - 500 } ) luminosities for each galaxy and use this to estimate a mean optical depth of \tau = 0.4 \pm 0.1 - the same value as we previously found for Virgo cluster galaxies .
For ten of the eleven galaxies ( NGC1399 excepted ) we fit a modified blackbody curve ( \beta = 2.0 ) to our observed flux densities to derive dust masses and temperatures of 10 ^ { 6.54 - 8.35 } M _ { \odot } and T=14.6-24.2K 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 and 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 over densities 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 and Virgo , NGC1365 is also detected by Planck .
The Planck data fit the PACS/SPIRE SED out to 1382 \mu m with no evidence of other sources of emission ( ’ spinning dust ’ , free-free , synchrotron ) .
At the opposite end of the scale NGC1399 is detected only at 500 \mu m with the emission probably arising from the nuclear radio source rather than inter-stellar dust .