# Convert from Jy/beam km/s to W/m$^2$

I need to compare some ALMA observations of a protoplanetary disk to disk-integrated fluxes obtained from a model.

The ALMA observations are upper limits of non-detected spectral lines, where the RMS is measured from moment 0 maps, given in Jy/beam km/s. The disk integrated fluxes from the model are given in W/m$$^2$$.

How can I convert the measured RMS from the observations to a disk integrated flux given in W/m$$^2$$?

Previous similar questions here and here are related but not quite what I'm looking for.

• Isn't your first link what you're looking for, except the other way? Or is it the "per beam" that confuses you? I think both "Jy km/s" and "W/m²" are integrated over the source, i.e. both are "per beam", no?
– pela
Aug 11 at 13:42
• @pela yes I am unsure how to work with the 'per beam' aspect. The synthesised beam size for the observation is 0.09x0.06arcsec. But since there is no detection, do I just choose an area that is roughly size of the disk, measure its size, then divide this by the number of synthesised beams that could fit within this area? I've added an image to the question to try to better explain what I need to do. Aug 11 at 15:26
• Okay I see the difference now, but I'll refrain from answering this, because I have zero experience with radio astronomy and I don't fully understand this Fourier-transforming back and forth in interferometry, especially when it comes to limits rather than detections.
– pela
Aug 12 at 9:13