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BEGIN:VEVENT
DTSTART;TZID=Atlantic/Canary:20120607T000000
DTEND;TZID=Atlantic/Canary:20120607T010000
UID:iactalks-393
X-WR-CALNAME: IAC Talks: Open Astronomy Seminars
X-ORIGINAL-URL: /iactalks/Talks/view/393
CREATED:2012-06-07T00:00:00+01:00
X-WR-CALDESC: IAC Talks upcomming talks
SUMMARY:Living on the Edge: Superthin Galaxies and the Cosmic UV Background
DESCRIPTION:Living on the Edge: Superthin Galaxies and the Cosmic UV Backgr
 ound\nDr. Juan Uson\n\nSuperthin galaxies are bulgeless, late-type spiral 
 galaxies seen  edge-on.  HI synthesis observations probe the kinemati
 c structure of  their interstellar medium.  Observations of these iso
 lated, quiescent  galaxies have reached column densities as low as few x&n
 bsp;1018  atoms . cm-2 .   The simple structure o
 f the superthins makes them ideal cosmological  laboratories (Uson and Mat
 thews 2003). The  strength of the cosmic UV background has a strong influe
 nce on the  formation of structure in the Universe, from the inhibition of
  the  collapse of small haloes to the ionizing escape fraction in galaxies
  to  the global star formation history.  We have used the VIRUS-P  in
 tegral-field spectrometer on the University of Texas McDonald  Observatory
  2.7m telescope to observe the edge of the superthin  galaxies UGC732
 1 and UGC1281 in the Hα emission line, limiting the  stren
 gth of the local UV background below theoretical expectations  (Adams et a
 l., 2011).  New,  observations  (March 2011) have improved the s
 ensitivity significantly.  The Hα layer  shows a peak brig
 htness of  Σ = 1.0 x 10-19 erg s-1 cm-2 arc
 sec-2 Å-1 (~7σ)   for spectra smoothed with a 1
 5″ spatial kernel.  This leads to a  measurement of the co
 smic UV background induced HI photoionization rate Γ  = 2.0 x 10-14&
 nbsp;s-1 (~7σ, preliminary absolute  calibration, Uson et al, B
 AAS 44, 312-01, 2012).  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 signi
 ficant smoothing over spatial  elements and a sky background model th
 at accounts for variations in the  spectral resolution of our instrument.
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