Correcting the extended-source calibration for the Herschel-SPIRE Fourier-transform spectrometer

Valtchanov, I., Hopwood, R., Bendo, G., Benson, C., Conversi, L., Fulton, T., Griffin, Matthew J. ORCID: https://orcid.org/0000-0002-0033-177X, Joubaud, T., Lim, T., Lu, N., Marchili, N., Makiwa, G., Meyer, R.A., Naylor, D. A., North, Christopher, Papageorgiou, Andreas, Pearson, C., Polehampton, E.T., Scott, J., Schulz, B., Spencer, L.D., Van der Wiel, M.H.D. and Wu, R. 2018. Correcting the extended-source calibration for the Herschel-SPIRE Fourier-transform spectrometer. Monthly Notices of the Royal Astronomical Society 475 (1) , pp. 321-330. 10.1093/mnras/stx3178

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Abstract

We describe an update to the Herschel-SPIRE Fourier-Transform Spectrometer (FTS) calibration for extended sources, which incorporates a correction for the frequency-dependent far-field feedhorn efficiency, ηFF. This significant correction affects all FTS extended-source calibrated spectra in sparse or mapping mode, regardless of the spectral resolution. Line fluxes and continuum levels are underestimated by factors of 1.3-2 in the Spectrometer Long-Wavelength band (SLW, 447-1018 GHz; 671-294 μm) and 1.4-1.5 in the Spectrometer Short-Wavelength band (SSW, 944-1568 GHz; 318-191 μm). The correction was implemented in the FTS pipeline version 14.1 and has also been described in the SPIRE Handbook since Feb 2017. Studies based on extended-source calibrated spectra produced prior to this pipeline version should be critically reconsidered using the current products available in the Herschel Science Archive. Once the extended-source calibrated spectra are corrected for ηFF, the synthetic photometry and the broadband intensities from SPIRE photometer maps agree within 2-4% -- similar levels to the comparison of point-source calibrated spectra and photometry from point-source calibrated maps. The two calibration schemes for the FTS are now self-consistent: the conversion between the corrected extended-source and point-source calibrated spectra can be achieved with the beam solid angle and a gain correction that accounts for the diffraction loss.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Physics and Astronomy
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Publisher:	Oxford University Press
ISSN:	0035-8711
Date of First Compliant Deposit:	6 December 2017
Date of Acceptance:	5 December 2017
Last Modified:	04 May 2023 20:52
URI:	https://orca.cardiff.ac.uk/id/eprint/107297

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