Recalibrating the Wide-field Infrared Survey Explorer (WISE) W4 Filter

TL;DR

This paper recalibrates the WISE W4 infrared filter by revising its effective wavelength and response curve, improving the accuracy of photometric measurements for galaxies and planetary nebulae.

Contribution

The study provides a revised effective wavelength and modified response curve for the WISE W4 filter based on empirical comparisons, enhancing photometric calibration accuracy.

Findings

Effective wavelength revised from 22.1 to 22.8 microns.

Discrepancies up to 0.3 mag for galaxies and 1 mag for planetary nebulae.

A modified response curve model achieves better agreement with observed data.

Abstract

We present a revised effective wavelength and photometric calibration for the Wide-field Infrared Survey Explorer (WISE) W4 band, including tests of empirically motivated modifications to its pre-launch laboratory-measured relative system response curve. We derived these by comparing measured W4 photometry with photometry synthesised from spectra of galaxies and planetary nebulae. The difference between measured and synthesised photometry using the pre-launch laboratory-measured W4 relative system response can be as large as 0.3 mag for galaxies and 1 mag for planetary nebulae. We find the W4 effective wavelength should be revised upward by 3.3%, from 22.1 micron to 22.8 micron, and the W4 AB magnitude of Vega should be revised from m = 6.59 to m = 6.66. In an attempt to reproduce the observed W4 photometry, we tested three modifications to the pre-launch laboratory-measured W4 relative system response curve, all of which have an effective wavelength of 22.8 micron. Of the three relative system response curve models tested, a model that matches the laboratory-measured relative system response curve, but has the wavelengths increased by 3.3% (or 0.73 micron) achieves reasonable agreement between the measured and synthesised photometry.