Infrared reflection nebula in W75N

Abstract

A new infrared reflection nebula is identified in the W75N region. The K-band polarization map shows a centrosymmetric pattern of the vectors extending over a region 2 arcmin in size, with large values of degrees of polarization, up to 50 per cent. The illuminating source is identified with the ultracompact H II region W75N(B) which is located at the center of polarization pattern. The intensity peak, IRS-1, is not a self-luminous source but is rather a bright knot in the reflection nebula. The northern peak, IRS-4, located on a second ultracompact H II region, W75N(A), extends for more than 30 arcsec and is less polarized (5-10 percent). The near-infrared light of IRS-4 is attributed to thermal emission from small (about 10 A) dust grains. The different polarization and spatial distribution of the near-infrared emission around these two ultracompact H II regions are explained by the different dust densities around them, probably due to their different evolutionary stages.