James Webb Space Telescope Feed Post

Predictions of the 21cm global signal in the JWST and ALMA era Published: 6/5/2023 9:04:22 PM Updated: 6/5/2023 9:04:22 PM

Paper abstract: We calculate the redshift evolution of the global 21cm signal in the firstbillion years using a semi-analytic galaxy formation model, DELPHI, thatjointly tracks the assembly of dark matter halos and their constituent baryonsincluding the impact of supernova feedback and dust enrichment. Employing onlytwo redshift- and mass-independent free parameters, our model predicts galaxypopulations in accord with data from both the James Webb Space Telescope (JWST)and the Atacama Large Millimetre Array (ALMA) at z ~ 5-12. In addition tothis ``fiducial" model, which fully incorporates the impact of dustattenuation, we also explore an unphysical ``maximal" model wherein galaxiescan convert a 100\% of their gas into stars instantaneously (and supernovafeedback is ignored) required to explain JWST data at z >=13. We also explorea wide range of values for our {\it 21cm} parameters that include the impact ofX-ray heating (f_{\rm X,h} =0.02-2.0) and the escape fraction of Lyman Alphaphotons (f_\alpha = 0.01-1.0). Our key findings are: (i) the fiducial modelpredicts a global 21cm signal which reaches a minimum brightness temperature of T_{\rm b, min}~ -215 mK at a redshift z_{\rm min} ~ 14; (ii) sincethe impact of dust on galaxy properties (such as the star formation ratedensity) only becomes relevant at z <= 8, dust does not have a sensibleimpact on the global 21cm signal; (iii) the ``maximal" model predicts T_{\rmb, min}= -210 mK as early as z_{\rm min} ~ 18; (iv) galaxy formation and21cm parameters have a degenerate impact on the global 21cm signal. Acombination of the minimum temperature and its redshift will therefore becrucial in constraining galaxy formation parameters and their coupling to the21cm signal at these early epochs.