Institute of Astronomy

Illuminating the Dark Universe with quasar-induced Ly-alpha emission

SpeakerTalk DateTalk Series
Sebastiano Cantalupo (UC Santa Cruz)15 February 2013Institute of Astronomy Galaxies Discussion Group


Galaxy formation occurs along the densest part of the filamentary
Intergalactic Medium where the gas can collapse and form stars. The
proto-galactic phases preceding substantial star-formation are however
unobservable - in emission - in most of the studies conducted so far
and thus poorly constrained. Recent theoretical models have suggested
that gas-rich, low-mass haloes at high redshift may have indeed very
low or absent star formation, as a consequence of lower gas
metallicity, H2 self-regulation effects or reduced cooling accretion
due photoionization. These "dark" galaxies may represent an important
gas baryonic reservoir for later star-formation in more massive
systems and a crucial ingredient in order to reproduce the properties
of current galaxy population. In this talk, I will present the result
of a an ongoing, successful program that uses a new approach to
directly detect and study these "dark" phases of galaxy formation: the
key idea is to use an external ``source of illumination'', a bright
quasar, to light up with fluorescent Ly-alpha emission dark, proto-
galactic clouds and dense streams around galaxies in a large
cosmological volume. In the first part of the talk, I will discuss our
pilot project based on deep narrow-band imaging on VLT/FORS centered
on a z=2.4 hyper-luminous quasar: how we identified and characterized
the physical properties of the first sample of high-redshift, "dark"
galaxy candidates. In the second part of the talk, I will present the
detection of fluorescent emission from the Circumgalactic Medium of
star forming galaxies and very recent, spectacular results obtained
with Keck/LRIS of the detection of hundred-kpc scale filaments
surrounding bright quasars.


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