Impact of extragalactic point sources on the low-frequency sky spectrum and cosmic dawn global 21-cm measurements
ABSTRACT The contribution of resolved and unresolved extragalactic point sources to the low-frequency sky spectrum is a potentially non-negligible part of the astrophysical foregrounds for cosmic dawn 21-cm experiments. The clustering of such point sources on the sky, combined with the frequency dep...
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Veröffentlicht in: | Monthly notices of the Royal Astronomical Society 2024-10, Vol.534 (2), p.1317-1328 |
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The contribution of resolved and unresolved extragalactic point sources to the low-frequency sky spectrum is a potentially non-negligible part of the astrophysical foregrounds for cosmic dawn 21-cm experiments. The clustering of such point sources on the sky, combined with the frequency dependence of the antenna beam, can also make this contribution chromatic. By combining low-frequency measurements of the luminosity function and the angular correlation function of extragalactic point sources, 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 ${\gt} 10^{-6}$ 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 measurements 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) project. We find that the contribution of point sources to the resultant spectrum is ${\sim}\, 0.4 {{\, \rm per\, cent}}$ of the total foregrounds, but still larger by at least an order of magnitude than the standard predictions for the cosmological 21-cm signal. As a result, not accounting for the point-source contribution leads to a systematic bias in 21-cm signal recovery. We show, however, that in the REACH case, this reconstruction bias can be removed by modelling the point-source contribution as a power law with a running spectral index. We make our code publicly available as a python package labelled epspy. |
doi_str_mv | 10.1093/mnras/stae2111 |
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The contribution of resolved and unresolved extragalactic point sources to the low-frequency sky spectrum is a potentially non-negligible part of the astrophysical foregrounds for cosmic dawn 21-cm experiments. The clustering of such point sources on the sky, combined with the frequency dependence of the antenna beam, can also make this contribution chromatic. By combining low-frequency measurements of the luminosity function and the angular correlation function of extragalactic point sources, 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 ${\gt} 10^{-6}$ 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 measurements 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) project. We find that the contribution of point sources to the resultant spectrum is ${\sim}\, 0.4 {{\, \rm per\, cent}}$ of the total foregrounds, but still larger by at least an order of magnitude than the standard predictions for the cosmological 21-cm signal. As a result, not accounting for the point-source contribution leads to a systematic bias in 21-cm signal recovery. We show, however, that in the REACH case, this reconstruction bias can be removed by modelling the point-source contribution as a power law with a running spectral index. We make our code publicly available as a python package labelled epspy.</description><identifier>ISSN: 0035-8711</identifier><identifier>EISSN: 1365-2966</identifier><identifier>DOI: 10.1093/mnras/stae2111</identifier><language>eng</language><publisher>London: Oxford University Press</publisher><subject>Angular correlation ; Beams (radiation) ; Bias ; Clustering ; Directivity ; Flux density ; Frequency measurement ; Log spiral antennas ; Luminosity ; Point sources ; Signal reconstruction ; Spiral antennas</subject><ispartof>Monthly notices of the Royal Astronomical Society, 2024-10, Vol.534 (2), p.1317-1328</ispartof><rights>2024 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. 2024</rights><rights>2024 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society.</rights><lds50>peer_reviewed</lds50><oa>free_for_read</oa><woscitedreferencessubscribed>false</woscitedreferencessubscribed><cites>FETCH-LOGICAL-c226t-d1c2f2e2eaacd26fa672959f0fba7665141fe58aa1019f88f1bea16da38e5aea3</cites><orcidid>0000-0002-0247-618X ; 0000-0003-1742-7417 ; 0000-0001-8530-6989 ; 0000-0001-5829-4716</orcidid></display><links><openurl>$$Topenurl_article</openurl><openurlfulltext>$$Topenurlfull_article</openurlfulltext><thumbnail>$$Tsyndetics_thumb_exl</thumbnail><link.rule.ids>314,776,780,860,1598,27901,27902</link.rule.ids></links><search><creatorcontrib>Mittal, Shikhar</creatorcontrib><creatorcontrib>Kulkarni, Girish</creatorcontrib><creatorcontrib>Anstey, Dominic</creatorcontrib><creatorcontrib>de Lera Acedo, Eloy</creatorcontrib><title>Impact of extragalactic point sources on the low-frequency sky spectrum and cosmic dawn global 21-cm measurements</title><title>Monthly notices of the Royal Astronomical Society</title><description>ABSTRACT
The contribution of resolved and unresolved extragalactic point sources to the low-frequency sky spectrum is a potentially non-negligible part of the astrophysical foregrounds for cosmic dawn 21-cm experiments. The clustering of such point sources on the sky, combined with the frequency dependence of the antenna beam, can also make this contribution chromatic. By combining low-frequency measurements of the luminosity function and the angular correlation function of extragalactic point sources, 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 ${\gt} 10^{-6}$ 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 measurements 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) project. We find that the contribution of point sources to the resultant spectrum is ${\sim}\, 0.4 {{\, \rm per\, cent}}$ of the total foregrounds, but still larger by at least an order of magnitude than the standard predictions for the cosmological 21-cm signal. As a result, not accounting for the point-source contribution leads to a systematic bias in 21-cm signal recovery. We show, however, that in the REACH case, this reconstruction bias can be removed by modelling the point-source contribution as a power law with a running spectral index. 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The contribution of resolved and unresolved extragalactic point sources to the low-frequency sky spectrum is a potentially non-negligible part of the astrophysical foregrounds for cosmic dawn 21-cm experiments. The clustering of such point sources on the sky, combined with the frequency dependence of the antenna beam, can also make this contribution chromatic. By combining low-frequency measurements of the luminosity function and the angular correlation function of extragalactic point sources, 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 ${\gt} 10^{-6}$ 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 measurements 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) project. We find that the contribution of point sources to the resultant spectrum is ${\sim}\, 0.4 {{\, \rm per\, cent}}$ of the total foregrounds, but still larger by at least an order of magnitude than the standard predictions for the cosmological 21-cm signal. As a result, not accounting for the point-source contribution leads to a systematic bias in 21-cm signal recovery. We show, however, that in the REACH case, this reconstruction bias can be removed by modelling the point-source contribution as a power law with a running spectral index. We make our code publicly available as a python package labelled epspy.</abstract><cop>London</cop><pub>Oxford University Press</pub><doi>10.1093/mnras/stae2111</doi><tpages>12</tpages><orcidid>https://orcid.org/0000-0002-0247-618X</orcidid><orcidid>https://orcid.org/0000-0003-1742-7417</orcidid><orcidid>https://orcid.org/0000-0001-8530-6989</orcidid><orcidid>https://orcid.org/0000-0001-5829-4716</orcidid><oa>free_for_read</oa></addata></record> |
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subjects | Angular correlation Beams (radiation) Bias Clustering Directivity Flux density Frequency measurement Log spiral antennas Luminosity Point sources Signal reconstruction Spiral antennas |
title | Impact of extragalactic point sources on the low-frequency sky spectrum and cosmic dawn global 21-cm measurements |
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