# Astronomical data convertion from Jy/pixel to MJy/sr?

I'm in the middle of collecting infrared data of various wavelengths. My problem is the following: SPIRE data (250µm) are in MJy/sr and PACS data (100µm) are in Jy/pixel. I would like to combine these data, but I'm a bit lost with these units... So I would have several questions:

1. How can we switch from Jy/pixel to MJy/sr?
2. Is "Jy/beam" equivalent to "Jy/deg^2" or "Jy/sr"?

1. How can we switch from Jy/pixel to MJy/sr? The Jy -> MJy part is just a factor of $$10^{6}$$ Jy/MJy. The pixel -> sr (steradian) part requires that you know the angular size of a pixel on the sky. For PACS it looks like the pixel size is different for different wavelengths; see Table 3.1. Once you know the pixel size in arcseconds, then the conversion is 206265 arcseconds / radian (or more precisely, 3600*180/pi). Square the size in radians to get the area in steradians. You also may be able to find the pixel size for your data by looking in the FITS header, if you have FITS images.