We present an analysis of the H I and CO gas in conjunction with the Planck / IRAS sub-mm/far-infrared dust properties toward the most outstanding high latitude clouds ( catalog MBM 53 , 54 , 55 ) and ( catalog HLCG $ 92-35 $ ) at b = { - } 30 ^ { \circ } to { - } 45 ^ { \circ } .
The CO emission , dust opacity at 353 \mathrm { GHz } ( \tau _ { 353 } ) , and dust temperature ( T _ { \mathrm { d } } ) show generally good spatial correspondence .
On the other hand , the correspondence between the H I emission and the dust properties is less clear than in CO .
The integrated H I intensity W _ { \mbox { { \scriptsize H } { \tiny I } } } and \tau _ { 353 } show a large scatter with a correlation coefficient of \sim 0.6 for a T _ { \mathrm { d } } range from 16 \mathrm { K } to 22 \mathrm { K } .
We find however that W _ { \mbox { { \scriptsize H } { \tiny I } } } and \tau _ { 353 } show better correlation for smaller ranges of T _ { \mathrm { d } } every 0.5 \mathrm { K } , generally with a correlation coefficient of 0.7 \mbox { - - } 0.9 .
We set up a hypothesis that the H I gas associated with the highest T _ { \mathrm { d } } \geq 21.5 \mathrm { K } is optically thin , whereas the H I emission is generally optically thick for T _ { \mathrm { d } } lower than 21.5 \mathrm { K } .
We have determined a relationship for the optically thin H I gas between atomic hydrogen column density and \tau _ { 353 } , N _ { \mbox { { \scriptsize H } { \tiny I } } } ( \mathrm { cm ^ { -2 } } ) = ( 1.5 \times 10 ^ { 26 } ) % \cdot \tau _ { 353 } , under the assumption that the dust properties are uniform , and applied it to estimate N _ { \mbox { { \scriptsize H } { \tiny I } } } from \tau _ { 353 } for the whole cloud . N _ { \mbox { { \scriptsize H } { \tiny I } } } was then used to solve for T _ { \mathrm { s } } and \tau _ { \mbox { { \scriptsize H } { \tiny I } } } over the region .
The result shows that the H I is dominated by optically thick gas having low spin temperature of 20 \mathrm { K } \mbox { - - } 40 \mathrm { K } and density of 40 \mathrm { cm ^ { -3 } } \mbox { - - } 160 \mathrm { cm ^ { -3 } } .
The H I envelope has a total mass of \sim 1.2 \times 10 ^ { 4 } M _ { \odot } , an order of magnitude larger than that of the CO clouds . The H I envelope properties derived by this method do not rule out a mixture of H I and \mbox { H } _ { 2 } in the dark gas , but we present indirect evidence that most of the gas mass is in the atomic state .