Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21931201u&link_type=abstract
American Astronomical Society, AAS Meeting #219, #312.01
Astronomy and Astrophysics
Astronomy
Scientific paper
We have used the VIRUS-P integral-field spectrometer on the University of Texas McDonald Observatory 2.7m telescope to observe the edge of the superthin spiral galaxy UGC7321. We detect faint Hα emission as expected from the exposure of the peripheral neutral Hydrogen gas traced by its 21cm radio emission to the metagalactic UV background. Observations of the intensity of the UV background and its redshift evolution are important to the theory and simulations of the evolution of large scale structure in the Universe as the UV background controls the cooling and collapse of small halos and is itself determined by the global histories of quasar and star formation. We have used dithered expositions with three pointings that fill in the gaps in the VIRUS-P detector for essentially full spatial coverage over a field of view of 1.6′ x 1.6′ and a spectral resolution of R = 3860 from 6040 Å to 6740 Å that allows us to resolve bright OH sky lines and geocoronal Hα from our target wavelength of 6574 Å. The Hα layer appears rather thin, with a peak surface brightness of Σ = 1.4 x 10-19 erg s-1 cm-2 arcsec-2 Å-1 for spectra smoothed with a 15″ spatial kernel. This leads to a measurement of the cosmic UV background induced HI photoionization rate Γ = 3.4 x 10-14 s-1 ( 5σ, preliminary absolute calibration). Contrary to past observational attempts, our measurements covered a large, two-dimensional on-sky area. We reach flux limits that are 50 times fainter than the sky background with significant smoothing over spatial elements and applying a sky background model that accounts for variations in the spectral resolution of our instrument. At this writing, we are continuing with the analysis of the data. Final results will be announced at the meeting.
Adams Jeffrey
Hill Gary J.
MacQueen Phillip J.
Uson Juan M.
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