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The Subaru Seminar is
usually held in Room 104 of the Hilo Base Facility, adjacent
to the main lobby. Everyone is welcome to attend. If you are
interested in giving a seminar, please contact Subaru seminar organizers
(Tae-Soo Pyo, Sherry Yeh, Nagayoshi Ohashi)
by email : sseminar_at_subaru.naoj.org (please change"_at" to @).
May 05, Thursday, 11:00 am in 104A
" A fundamental constraint on the imaging of molecular gas and dust in the early Universe "
Zhi-Yu Zhang
(IfA/University of Edinburgh/ESO)
Images of dust continuum and CO line emission are powerful tools for
deducing structural characteristics of galaxies such as disk sizes, H2
gas velocity fields, and enclosed H2 and dynamical masses. We report
on a fundamental constraint set by the Cosmic Microwave Background
(CMB) on the observed structural and dynamical characteristics of
galaxies as deduced from dust continuum and CO line imaging at high
redshifts. As the CMB temperature rises in the distant Universe, the
ensuing thermal equilibrium between the CMB and the cold dust and H2
gas progressively erases all spatial and spectral contrasts between
their brightness distributions and the CMB. This strongly biases the
recoverable H2 gas and dust mass distributions, scale lengths, gas
velocity fields, and the dynamical mass estimates, for high redshift
galaxies. This limitation is unique to mm/submm wavelengths, and
unlike its known effect on the global dust continuum and molecular
line emission of galaxies, it cannot be simply addressed. We
nevertheless identify a unique signature of CMB affected continuum and
line brightness distributions, namely a rising rather than diminishing
contrast between such brightness distributions and the CMB once
frequencies beyond the Raleigh-Jeans limit are used for imaging the
cold molecular gas and dust in distant galaxies. Such effects
progressively change the apparent gas and dust distribution and
velocity field, leading to biased size and mass estimates of
high-redshift galaxies, which will be obtained with ALMA, JVLA, and
SKA.