A systematic search for IRAS galaxies behind the Milky Way

We have completed a systematic search for visible IRAS galaxies with 60 μm flux densities larger than 0.6 Jy behind the whole Milky Way region at |b| ≤ 15°, using the Palomar Observatory Sky Survey prints and the UK Schmidt Atlas and SERC IIIa-J plates. A total of 2323 galaxies were identified. The number densities are 0.33 deg^-2 at 10° ≤ |b| ≤ 15°, 0.21 deg^-2 at 5° ≤ |b| ≤ 10°, and 0.08 deg^-2 at 0° ≤ |b| ≤ 5°, showing exponential decrease with increasing H I column density. The average of the entire surveyed region is 0.22 deg^-2, about half the value of the whole-sky average. Among the 2323 galaxies, 93% are identified in the region with H I column densities lower than 5 × 10²¹ cm^-2, the area of which covers 76% of the whole Milky Way region. The distribution of the 60 μm flux densities of the identified galaxies is similar to that of IRAS galaxies outside the Milky Way, consistent with the fact that the far-infrared luminosities of spiral galaxies are almost independent of the optical luminosities. We find six high-density filamentary structures of galaxy distribution across the Milky Way, which correspond to the main clusterings of galaxies in an ∼20 h^-1 Mpc scale within a radius of cz ∼ 6000 km s^-1 along the supergalactic SGX-SGZ plane. The high-density structures in the -SGX and -SGZ directions are located closer to the Local Group than those in the +SGX and +SGZ directions, respectively.