( ( For ( ( the ( low ratio ) ) ( of ( ( I ( Zw 36 ) ) ( on ( the ( galactic scale ) ) ) ) ) ) ) ( , ( ( ( a ( large fraction ) ) ( of ( neutral ( interstellar gas ) ) ) ) ( ( should ( have ( a ( high density ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN For) (NP (NP (DT the) (JJ low) (NN ratio)) (PP (IN of) (NP (NP (CD I) (NNP Zw) (CD 36)) (PP (IN on) (NP (DT the) (JJ galactic) (NN scale))))))) (, ,) (NP (NP (DT a) (JJ large) (NN fraction)) (PP (IN of) (NP (JJ neutral) (NN interstellar) (NN gas)))) (VP (MD should) (VP (VB have) (NP (DT a) (JJ high) (NN density)))) (. .)))
For the low ratio of I Zw 36 on the galactic scale, a large fraction of neutral interstellar gas should have a high density.
(ROOT (S (NP (NNS Gases)) (VP (VBP have) (NP (DT the) (JJS lowest) (NN density))) (. .)))