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Astron. Astrophys. 325, 915-922 (1997)

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Surface photometry of the edge-on spiral NGC 4565 *

I. V-band data and the extended optical warp

Magnus Näslund and Steven Jörsäter

Stockholm Observatory, S-133 36 Saltsjöbaden, Sweden (magnus@astro.su.se, steven@astro.su.se)

Received 5 July 1996 / Accepted 13 January 1997


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 [FORMULA].

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 H I 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.

Key words: galaxies: halos – galaxies: NGC 4565 – galaxies: photometry – galaxies: spiral – galaxies: structure – dark matter

* Based on observations collected at the Nordic Optical Telescope, La Palma, Spain

Send offprint requests to: M. Näslund

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© European Southern Observatory (ESO) 1997

Online publication: April 28, 1998