The opacity of spiral disks

A. Bosma, Y. Byun, K. C. Freeman, E. Athanassoula

Research output: Contribution to journalArticlepeer-review

59 Citations (Scopus)


The opacity of the disks of spiral galaxies can be evaluated by studying the gaseous component in edge-on galaxies in several wavelength regions. By combining data of the galaxy NGC 891 at 21 cm (H I), 2.6 mm (CO), and Hα, we show that the outer regions are transparent, while the inner regions, out to the radius to which CO is detected, could be optically thick. For the small galaxy NGC 100, such data indicate that this galaxy is by and large transparent, despite the presence of dust patches in the optical image. These results confirm the claim that spiral galaxies are transparent, at least in the outer parts, and clearly contradict the claim by Valentijn (1991) that the dark matter in spiral galaxies resides in the disk, in the form of absorbing clouds particularly abundant in the outer parts.

Original languageEnglish
Pages (from-to)L21-L24
JournalAstrophysical Journal
Issue number1 PART 2
Publication statusPublished - 1992 Nov 20

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


Dive into the research topics of 'The opacity of spiral disks'. Together they form a unique fingerprint.

Cite this