An accurate estimate of the interstellar gas density distribution is crucial to understanding the interstellar medium ( ISM ) and Galactic cosmic rays ( CRs ) .
To comprehend the ISM and CRs in a local environment , a study of the diffuse \gamma -ray emission in a mid-latitude region of the third quadrant was performed .
The \gamma -ray data in the 0.1–25.6 GeV energy range of the Fermi Large Area Telescope ( LAT ) and other interstellar gas tracers such as the HI4PI survey data and the Planck dust thermal emission model were used , and the northern and southern regions were analyzed separately .
The variation of the dust emission D _ { \mathrm { em } } with the total neutral gas column density N _ { \mathrm { H } } was studied in high dust-temperature areas , and the N _ { \mathrm { H } } / D _ { \mathrm { em } } ratio was calibrated using \gamma -ray data under the assumption of a uniform CR intensity in the studied regions .
The measured integrated \gamma -ray emissivities above 100 MeV are ( 1.58 \pm 0.04 ) \times 10 ^ { -26 } ~ { } \mathrm { photons~ { } s ^ { -1 } ~ { } sr ^ { -1 } ~ { } H \mbox { - } % atom ^ { -1 } } and ( 1.59 \pm 0.02 ) \times 10 ^ { -26 } ~ { } \mathrm { photons~ { } s ^ { -1 } ~ { } sr ^ { -1 } ~ { } H \mbox { - } % atom ^ { -1 } } in the northern and southern regions , respectively , supporting the existence of a uniform CR intensity in the vicinity of the solar system .
While most of the gas can be interpreted to be H i with a spin temperature of T _ { \mathrm { S } } = 125 ~ { } \mathrm { K } or higher , an area dominated by optically thick H i with T _ { \mathrm { S } } \sim 40 ~ { } \mathrm { K } was identified .