1997A&A...325..915N

We have studied the faint luminous parts of the disk of NGC 4565 in the radial and z-directions. The semi-major axis profiles follow exponentials until a break in the luminosity profiles occurs. Beyond the breaks the luminosity distributions are well fitted by steeper exponentials and continue with a constant slope to the limit of the data around µ_V=28mag/arcsec². A recent discovery of a faint luminous halo in NGC 5907 has raised the question whether there is a luminous population tracing the dark mass in spiral galaxies. The vertical profiles of NGC 4565 fall off less steeply than those of NGC 5907 which to a large extent is explained by the combination of a thin disk and a photometric thick disk. The outer profiles are more shallow, in agreement with previous studies, giving a hint of a third component or of the response of the inner parts to the dark-halo mass. The constancy of scaleheight with radius in the outer parts is confirmed. The marginal NW stellar warp is also confirmed, but more interestingly there is a faint extension of this optical warp, which coincides with the HI warp, and therefore most likely is physically connected to the galaxy. This finding indicates that star formation may occur outside the disk cutoff in spiral galaxies.