THE LONGITUDINAL DEPENDENCE OF THE LOCAL I-60-MU-M-I-100-MU-M FLUX-DENSITY RATIO AT HIGH GALACTIC LATITUDE

We have studied the local 60 mu m and 100 mu m emission for a region i n the northern half of the first two quadrants of the Galaxy (42 degre es less than or equal to l less than or equal to 146 degrees & 22 degr ees less than or equal to b less than or equal to 50 degrees), using t he IRAS Sky Survey Atlas. We have unfolded the 100 mu m data and have determined a dust layer vertical scale height of 117 pc. We find the a verage I-60 mu m-I-100 mu m flux density ratio in this region to be 0. 19 (+/- 0.01), in excellent agreement with values previously presented in the literature. We also find what appears to be a longitudinal dep endence of the local I-60 mu m-I-100 mu m flux density ratio. For the galactic longitude range of 42 degrees less than or equal to l less th an or equal to 100 degrees, the average flux density ratio is found to be 0.25 (+/- 0.02) while for the longitude range of 101 degrees less than or equal to l less than or equal to 146 degrees it is found to be 0.16 (+/- 0.02). We find that a change in the UV fraction of the inte rstellar radiation held can explain the change in the infrared flux de nsity ratio. Further, we find the higher flux density ratio region to have a vertical scale height similar to 20% less than the scale height associated with the lower flux density ratio region. A change in the thickness of the dust layer may be the cause of the altered radiation field at these high latitudes. (C) 1996 American Astronomical Society.