ESA - Science Press Note - released 17 Aug 1999

the detection of molecular hydrogen in the disk of NGC 891

Optical photograph of NGC 891 thanks to Blair Savage, Chris Howk (U. Wisconsin)/N.A.Sharp (NOAO)/AURA/NSF
ISO-SWS data from Valentijn and van der Werf / SRON

A true colour photograph of the edge-on Spiral galaxy NGC 891 (field of view is 6.7 x 6.7 arcminutes). The dark band running through the center of the disk is caused by the effect of large dust clouds in this galaxy. At 8 positions in this disk, even beyond the field of this photo, the ISO-SWS has detected the signal from molecular hydrogen gas (H2). The graphical inset shows the signal of the H2 lines at 17.0 and 28.2 micrometer wavelength, detected at the outermost position of the survey, at a distance 12 kilo parsec (37000 light-years) from the center, a position where other observations of lines of molecules, like the CO molecule, are trailing into the noise. From the ratio of the signal strength of these lines a Temperature of the gas of about 80K is derived. This gas has never been seen before, is quite massive and provides, at least for this galaxy, a solution to the missing mass problem.

Press release by Space Research Organization Netherlands
ISO satelliet detecteert signaal van ontbrekende materie
SRON press release in Dutch

further links:
electronic publication by the Astrophysical Journal, 522, L29, September 1, 1999

1580 x 1580 8-bit color TIFF image full size tiff image can be down-loaded

more down-loadable colour photographs of NGC 891 can be found here

First extra galactic detection of pure rotational H2 lines at 17.0 and 28.2 micrometer wavelength in the center of the nearby galaxy NGC 6946 The photograph on the left is taken from the ESA press release on Early results of the ISO satellite., 14 February 1996

    ................Optical + SWS (Valentijn et al)................................................ ISOCAM (Malhotra et al).................. ISOPHOT (Tuffs et al) ....................

    Postscript (gzipped) versions of related papers ( PREPRINTS and REPRINTS)

  1. Discovery paper:
    First extra-galactic direct detection of large scale Molecular Hydrogen in the disk of NGC 891
    E.A. Valentijn and P.P. van der Werf
    1999, Astrophysical Journal Letters, 522, L29
    download postscript version of paper
    download postscript-gzipped version of paper

  2. Early report on molecular hydrogen survey in the disks of NGC 891 and NGC 6946, presented at ESA conference 'The Universe as seen by ISO', October 1998 Paris.
    The ISO-SWS Survey for Molecular Hydrogen in Galaxies
    E.A. Valentijn and P.P. van der Werf
    1999, Proceedings of the Conference "The Universe as seen by ISO", Paris, France, 20-23 October 1998 (ESA SP-427, March 1999) Edts P.Cox, M.F. Kessler,

  3. Discovery paper: First extra galactic detection of rotational lines at 17 and 28 micrometer wavelength in the center of the nearby galaxy NGC 6946
    The SWS survey for rotational H2 lines in late-type galaxies. Observations of the central regions of NGC6946
    Valentijn, Edwin A., Van der Werf, Paul P., De Graauw, Th., & De Jong, T.
    1996, Astron. & Astrophys. 315, L145

  4. Technical Paper: improving the sensitivity of the ISO-SWS by removing the various effects of cosmic ray impacts (cosmic weather)- self calibration techniques
    ISO's Short Wavelength spectrometer - Ultimate sensitivity
    E.A. Valentijn and W.F.Thi
    1999, Experimental Astronomy in press

  5. Technical paper: characterizing the wavelength calibration and the spectral resolution of the ISO-SWS.
    The wavelength calibration and resolution of the SWS
    Valentijn, E.A., Feuchtgruber, H., Kester, D.J.M., Roelfsema, P.R., Barr, P., Bauer, O.H., Beintema, D.A., Boxhoorn, D.R., Graauw,, Haser, L.N., Heske, A., Heras, A.M., Katterloher, R.O., Lahuis, F., Lutz, D., Leech, K.J., Morris, P.W., Salama, A., Schaeidt, S.G., Spoon, H.W.W., Vandenbussche, B., Wieprecht, E., Luinge, W., Wildeman, K.J.
    1996, Astron. Astrophys. 315, L60