Kavli Affiliate: Roberto Maiolino
| First 5 Authors: , , , ,
| Summary:
We present a theoretical framework for interpreting far-ultraviolet (FUV)
fluorescent emission from molecular hydrogen (H$_2$) in high-redshift galaxies,
motivated by the unique capabilities of the James Webb Space Telescope (JWST)
to probe the rest frame FUV at cosmic dawn. Using the Meudon photodissociation
region (PDR) code, we model the H$_2$ fluorescence spectrum under extreme
interstellar medium (ISM) conditions in terms of high pressure
($10^11~mathrmK~ cm^-3$), high radiation field ($10^6$ $G_0$) combined
with low metallicity ($Z = 0.1~Z_odot$) and high cosmic ionization rate
($zeta = 10^-14~mathrms^-1$), characteristic of early galaxies. As a
case study, we apply this framework to stacked NIRSpec spectra from the JWST
Advanced Deep Extragalactic Survey (JADES) for galaxies at redshifts $zgeq7$.
The stacked spectrum exhibits emission features consistent in profile and
wavelength with the predicted H$_2$ fluorescence lines, including a blue shift
suggestive of an outflow of molecular gas. Although individual features remain
below robust detection thresholds, this demonstration illustrates the
feasibility of using FUV fluorescence modeling to guide and interpret JWST
spectroscopy of the molecular ISM at high redshift. Our framework provides a
foundation for future searches for molecular hydrogen emission and the study of
galactic feedback processes in the early universe.
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