We present Herschel observations of the core of the Perseus cluster of galaxies .
Especially intriguing is the network of filaments that surround the brightest cluster galaxy , NGC 1275 , previously imaged extensively in H \alpha and CO .
In this work , we report detections of far-infrared ( FIR ) lines , in particular , [ C ii ] 158 \mu m , [ O i ] 63 \mu m , [ N ii ] 122 \mu m , [ O ib ] 145 \mu m and [ O iii ] 88 \mu m , with Herschel .
All lines are spatially extended , except [ O iii ] , with the [ C ii ] line emission extending up to 25 kpc from the core .
[ C ii ] emission is found to be cospatial with H \alpha and CO .
Furthermore , [ C ii ] shows a similar velocity distribution to CO , which has been shown in previous studies to display a close association with the H \alpha kinematics .
The spatial and kinematical correlation among [ C ii ] , H \alpha and CO gives us confidence to model the different components of the gas with a common heating model .

With the help of FIR continuum Herschel measurements , together with a suite of coeval radio , submm and infrared data from other observatories , we performed a spectral energy distribution fitting of NGC 1275 using a model that contains contributions from dust emission as well as synchrotron AGN emission .
This has allowed us to accurately estimate the dust parameters .
The data indicate a low dust emissivity index , \beta \approx 1 , a total dust mass close to 10 ^ { 7 } ~ { } M _ { \odot } , a cold dust component with temperature 38 \pm 2 K and a warm dust component with temperature of 116 \pm 9 K. The FIR-derived star formation rate ( SFR ) is 24 \pm 1 ~ { } M _ { \odot } ~ { } \mathrm { yr } ^ { -1 } , which is in agreement with the FUV-derived SFR in the core , determined after applying corrections for both Galactic and internal reddening .
The total infrared luminosity in the range 8 \mu m to 1000 \mu m is inferred to be 1.5 \times 10 ^ { 11 } ~ { } L _ { \odot } , making NGC 1275 a luminous infrared galaxy ( LIRG ) .

We investigated in detail the source of the Herschel FIR and H \alpha emissions emerging from a core region 4 ~ { } kpc in radius .
Based on simulations conducted using the radiative transfer code , cloudy , a heating model comprising old and young stellar populations is sufficient to explain these observations .
The optical line ratios indicate that there may be a need for a second heating component .
However , stellar photoionization seems to be the dominant mechanism .

We have also detected [ C ii ] in three well-studied regions of the filaments .
Herschel , with its superior sensitivity to FIR emission , can detect far colder atomic gas than previous studies .
We find a [ O i ] / [ C ii ] ratio about 1 dex smaller than predicted by the otherwise functional Ferland ( 2009 ) model .
That study considered optically thin emission from a small cell of gas and by design did not consider the effects of reasonable column densities .
The line ratio suggests that the lines are optically thick , as is typical of galactic PDRs , and implies that there is a large reservoir of cold atomic gas .
This was not included in previous inventories of the filament mass and may represent a significant component .