Spiral arms in near-infrared bands

Free access article

Issue		A&A Volume 370, Number 3, May II 2001


Page(s)		875 - 880
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20010270

A&A 370, 875-880 (2001)
DOI: 10.1051/0004-6361:20010270

Broad- and narrow-band NIR photometry

P. A. Patsis^{1, 2, 3}, Ph. Héraudeau³ and P. Grosbøl⁴

¹ Research Center for Astronomy, Academy of Athens, 14 Anagnostopoulou St., 10673, Athens, Greece
² Astronomisches Rechen-Institut Heidelberg, Mönchhofstrasse 13, 69120 Heidelberg, Germany
³ Max-Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁴ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany

(Received 31 October 2000 / Accepted 15 February 2001 )

Abstract
We investigate the contribution of Br $\gamma$ and H₂ emission due to young objects in the arms of spiral galaxies observed in the $K^\prime$ filter. Out of a sample of disk galaxies for which we obtained deep surface photometry in broad- and narrow-band near-infrared filters, we selected two grand design spirals (NGC 5861, NGC 7412), which clearly have sharp knots along their arms both in optical and NIR images. For these galaxies we estimate the amount of light coming from Br $\gamma$ and H₂ emission and we conclude that it represents only a few percent of the observed $K^\prime$ light. For comparison we used the spiral galaxy NGC 4603, which has high recessional velocity. In this case the emission lines we study are practically shifted out of the narrow-band filter. Comparing its flux with what we found in the two former cases, we conclude that a major contribution from young objects in $K^\prime$ comes from continuum radiation which in the arm regions can amount to 20% .

Key words: galaxies: photometry -- galaxies: spiral -- galaxies: structure -- infrared: galaxies

Offprint request: P. A. Patsis, ppatsis@cc.uoa.gr

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