Аннотация
We present ALMA band 3 observations of the CO(6-5), CO(7-6), and CI
369micron emission lines in three of the highest redshift quasar host galaxies
at 6.6<z<6.9. These measurements constitute the highest-redshift CO detections
to date. The target quasars have previously been detected in CII 158micron
emission and the underlying far-infrared (FIR) dust continuum. We detect
(spatially unresolved, at a resolution of >2", or >14kpc) CO emission in all
three quasar hosts. In two sources, we detect the continuum emission around
400micron (rest-frame), and in one source we detect CI at low significance.
We derive molecular gas reservoirs of (1-3)x10^10 M_sun in the quasar hosts,
i.e. approximately only 10 times the mass of their central supermassive black
holes. The extrapolated CII-to-CO(1-0) luminosity ratio is 2500-4200,
consistent with measurements in galaxies at lower redshift. The detection of
the CI line in one quasar host galaxy and the limit on the CI emission in
the other two hosts enables a first characterization of the physical properties
of the interstellar medium in z~7 quasar hosts. In the sources, the derived
global CO/CII/CI line ratios are consistent with expectations from
photodissociation regions (PDR), but not X-ray dominated regions (XDR). This
suggest that quantities derived from the molecular gas and dust emission are
related to ongoing star-formation activity in the quasar hosts, providing
further evidence that the quasar hosts studied here harbor intense starbursts
in addition to their active nucleus.
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