Based on CO ( 2-1 ) public data , we study the monoxide oxygen gas excitation conditions and the magnetic field strength of four spiral galaxies .
For the galaxy outskirts , we found kinetic temperatures in the range of \lesssim 35–38 K , CO column densities \lesssim 10 ^ { 15 } – 10 ^ { 16 } cm ^ { -2 } , and H _ { 2 } masses \lesssim 4 \times 10 ^ { 6 } – 6 \times 10 ^ { 8 } M _ { \odot } .
An H _ { 2 } density \lesssim 10 ^ { 3 } cm ^ { -3 } is suitable to explain the 2 \sigma upper limits of the CO ( 2-1 ) line intensity .
We constrain the magnetic field strength for our sample of spiral galaxies and their outskirts by using their masses and H _ { 2 } densities to evaluate a simplified magneto-hydrodynamic equation .
Our estimations provide values for the magnetic field strength on the order of \lesssim 6–31 \upmu G .