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SUMMARY:  Impact of extragalactic point sources on the foregrounds and 21-
 cm observations - Shikhar Mittal / Cavendish Laboratory
DTSTART:20250618T124000Z
DTEND:20250618T130500Z
UID:TALK233458@talks.cam.ac.uk
CONTACT:128254
DESCRIPTION:The contribution of resolved and unresolved extragalactic poin
 t sources to the low-frequency sky spectrum is a potentially non-negligibl
 e part of the astrophysical foregrounds for cosmic dawn 21-cm experiments.
  The clustering of such point sources on the sky\, combined with the frequ
 ency dependence of the antenna beam\, can also make this contribution chro
 matic. By combining low-frequency measurements of the luminosity function 
 and the angular correlation function of extragalactic point\nsources\, we 
 develop a model for the contribution of these sources to the low-frequency
  sky spectrum. Using this model\, we find that the contribution of sources
  with flux density >10^-6 Jy to the sky-averaged spectrum is smooth and of
  the order of a few kelvins at 50–200 MHz. We combine this model with me
 asurements of the galactic foreground spectrum and weigh the resultant sky
  by the beam directivity of the conical log-spiral antenna planned as part
  of the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH) proje
 ct. We find that the contribution of point sources to the resultant spectr
 um is ∼ 0.4 per cent of the total foregrounds\, but still larger by at l
 east an order of magnitude than the standard predictions for the cosmologi
 cal 21-cm signal. As a result\, not accounting for the point-source contri
 bution leads to a systematic bias in 21-cm signal recovery. We show\, howe
 ver\, that in the REACH case\, this reconstruction bias can be removed by 
 modelling the point-source contribution as a power law with a running spec
 tral index. We make our code publicly available as a python package labell
 ed epspy.
LOCATION:The Hoyle Lecture Theatre + Zoom 
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