Live Chat Software by Kayako 
How do I convert flux measurements given in Jy km/s or K km/s into the peak flux density required by the OT?
Posted by Suzanna Randall, Last modified by Suzanna Randall on 29 February 2016 10:11 AM


Suppose you want to observe the CO(10) line in a galaxy for which the integrated CO(10) line flux density is known from previous observations,or estimated based on simulations etc. Let us first assume that the proposed ALMA observations will not spatially resolve the galaxy. From previous observations we know that the total velocity width of the CO profile is 200 km/s and the integral flux density 20 Jy km/s. If the line shape is approximately boxcarshaped, this implies that the peak flux density of the line is 0.1 Jy. Detecting this line at 5 sigma requires an rms noise level (sensitivity) of 20 mJy. If your previous measurement of the CO(10) intensity is based on single dish observations and given in terms of integrated brightness temperature that is in units of K km/s, this value needs to be converted to units of Jy km/s first. See How can I estimate the Peak Flux Density per synthesised beam using flux measurements in Jy or K from other observatories? for more details on this conversion. In short, a K per Jy conversion factor is needed, which is dependent on the single dish antenna diameter and the antenna efficiency. Note that for high redshift molecular line measurements, luminosities are often expressed in units of K km/s pc^{^2}. Such a measurement can be easily converted to integrated flux densities in units of Jy km/s using standard equations. For example, the CO luminosity L’ is related to the CO integrated flux density S_{CO} in units of Jy km/s, using the conversion L′=3.25×10^{^7}(1+z)^{−3} f_{obs}^{−2} S_{CO} D_{L}^{^2}, where D_{L} is the luminosity distance at redshift z, in Mpc, and f_{obs} is the observing frequency in GHz.  
(0 vote(s))
Helpful Not helpful
