A search for diffuse hydrogen alpha emission from Lyman alpha absorption clouds toward 3C 273

Details A search for diffuse hydrogen alpha emission from Lyman alpha absorption clouds toward 3C 273 A search for diffuse hydrogen alpha emission from Lyman alpha absorption clouds toward 3C 273

Dec 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...437l..95b&link_type=abstract

Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 437, no. 2, p. L95-L98

Astronomy and Astrophysics

Astronomy

17

Absorption Spectra, Emission Spectra, H Alpha Line, Intergalactic Media, Lyman Alpha Radiation, Lyman Spectra, Ultraviolet Astronomy, Absorption Spectroscopy, Charge Coupled Devices, Fabry-Perot Interferometers, Hubble Space Telescope, Radial Velocity

Scientific paper

The Hubble Space Telescope (HST) has identified a series of low-velocity Lyman alpha absorption lines in the direction of 3C 273. We have investigated a recent claim (williams & Schommer 1993) that there is diffuse hydrogen alpha emission with surface brightness 1.2 x 10-18 ergs/sq cm/s/sq arcsec at a radial velocity within 130 km/s of one of these Lyman alpha features. The observations were made with the TAURUS-2 imaging Fabry-Perot interferometer and a Tek 1024 squared CCD at the 3.9 m Anglo-Australian Telescope. We do not detect hydrogen alpha emission at the claimed wavelength lambda 6600.3 down to a 3 sigma upper limit of 4 x 10-19 ergs/sq cm/s/arcsec squared (em approximately 0.2 cm-6 pc), nor do we detect emission at the absorption-line velocity. We show that the Jacquinot advantage of spectroscopic interferometers makes 3 sigma detection thresholds as low as Em(hydrogen alpha) = 0.02 cm-6 pc quite feasible. Even at this very deep limit, it is unlikely that Lyman alpha absorbers irradiated by the UVX background will be detectable in optical line emission at any redshift. However, our sensitivity limit now brings other important detections into the realm of possibility for the first time, in particular, the detection of ionized disks beyond the H I truncation radius in spiral galaxies.

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