EMBEDDED STAR FORMATION IN S⁴G GALAXY DUST LANES

Abstract

Star-forming regions that are visible at 3.6 microns and Halpha but not in\nthe u,g,r,i,z bands of the Sloan Digital Sky survey (SDSS), are measured in\nfive nearby spiral galaxies to find extinctions averaging ~3.8 mag and stellar\nmasses averaging ~5x10^4 Msun. These regions are apparently young star\ncomplexes embedded in dark filamentary shock fronts connected with spiral arms.\nThe associated cloud masses are ~10^7 Msun. The conditions required to make\nsuch complexes are explored, including gravitational instabilities in spiral\nshocked gas and compression of incident clouds. We find that instabilities are\ntoo slow for a complete collapse of the observed spiral filaments, but they\ncould lead to star formation in the denser parts. Compression of incident\nclouds can produce a faster collapse but has difficulty explaining the\nsemi-regular spacing of some regions along the arms. If gravitational\ninstabilities are involved, then the condensations have the local Jeans mass.\nAlso in this case, the near-simultaneous appearance of equally spaced complexes\nsuggests that the dust lanes, and perhaps the arms too, are relatively young.\n