Spiral arms in near-infrared bands - Broad- and narrow-band NIR photometry

We investigate the contribution of Br gamma and H-2 emission due to young o bjects in the arms of spiral galaxies observed in the K' filter. Out of a s ample of disk galaxies for which we obtained deep surface photometry in bro ad- and narrow-band near-infrared filters, we selected two grand design spi rals (NGC 5861, NGC 7412), which clearly have sharp knots along their arms both ill optical and NIR images. For these galaxies we estimate the amount of light coming from Br? and Hz emission and we conclude that it represents only a few percent of the observed K' light. For comparison we used the sp iral galaxy NGC 4603, which has high recessional velocity. In this case the emission lines we study are practically shifted out of the narrow-band fil ter. Comparing its flux with what we found in the two former cases, we conc lude that a major contribution from young objects in K' comes from continuu m radiation which in the arm regions can amount to 20%.