Core Concepts
Variations in the Hubble Space Telescope's (HST) temperature, particularly in its pick-off mirror and main mirrors, introduce a systematic uncertainty in diffuse light measurements, but these variations are small and result in updated diffuse light limits of 21, 32, and 25 nW m−2 sr−1 in the F125W, F140W, and F160W filters, respectively.
Abstract
Bibliographic Information:
McIntyre, I. A., Carleton, T., O’Brien, R., Windhorst, R. A., Caddy, S., Cohen, S. H., Jansen, R. A., MacKenty, J., & Kenyon, S. J. (2024). SKYSURF VI: The Impact of Thermal Variations of HST on Background Light Estimates. arXiv. https://doi.org/10.48550/arXiv.2407.12290v2
Research Objective:
This research paper investigates the impact of thermal variations in the Hubble Space Telescope (HST) on measurements of diffuse light, aiming to improve the accuracy of extragalactic background light (EBL) and diffuse light estimations from the SKYSURF project.
Methodology:
The authors analyzed archival WFC3/IR engineering data from HST, focusing on temperature variations in different components, particularly the pick-off mirror, as a function of time, orbital phase, Earth-Sun distance, and year. They developed an empirical model to describe these variations and used it to correct diffuse light measurements from the SKYSURF project.
Key Findings:
- The pick-off mirror temperature (TPOM) varies by less than 1 Kelvin throughout HST's orbit and in relation to time since Earth occultation.
- TPOM exhibits a yearly variation of approximately 1 Kelvin, correlating with the Earth-Sun distance, being cooler when Earth is farthest from the Sun.
- Empirical analysis suggests a ±3.5K variation in the primary and secondary mirror temperatures over a year, likely due to their direct exposure to Earth's radiation.
- After correcting for thermal background variations, the updated diffuse light limits are 21, 32, and 25 nW m−2 sr−1 in the F125W, F140W, and F160W filters, respectively.
Main Conclusions:
- While HST's thermal variations introduce a systematic uncertainty in diffuse light measurements, these variations are relatively small and well-characterized.
- The updated diffuse light limits, after accounting for thermal variations, are lower than previous estimations, refining the constraints on the EBL.
- The remaining diffuse sky signal observed in SKYSURF data might be attributable to a faint Zodiacal light source, potentially originating from icy dust in the inner Solar System.
Significance:
This research significantly contributes to the field of observational cosmology by improving the accuracy of diffuse light measurements, which are crucial for understanding the EBL and the history of galaxy formation. The findings have implications for interpreting observations from future space telescopes, such as the James Webb Space Telescope (JWST).
Limitations and Future Research:
- The study primarily focuses on the WFC3/IR instrument on HST. Further investigation into thermal variations in other instruments is necessary.
- The exact nature of the remaining diffuse sky signal requires further investigation, potentially through modeling the Zodiacal light contribution from icy dust.
Stats
The pick-off mirror temperature (TPOM) changes by less than one Kelvin.
The primary and secondary mirror temperatures vary by ±3.5K over a year.
The updated diffuse light limits are 21 nW m−2 sr−1, 32 nW m−2 sr−1, and 25 nW m−2 sr−1 in the F125W, F140W, and F160W filters, respectively.
Conservative lower limits on diffuse emission are 12 nW m−2 sr−1, 20 nW m−2 sr−1, and 2 nW m−2 sr−1 in F125W, F140W, and F160W, respectively.
Quotes
"The thermal background changes by less than one Kelvin in the WFC3 pick-off mirror, one of the most important contributors to the thermal background."
"Based on this improved modeling, we provide new upper limits on the level of diffuse light of 21 nW m−2 sr−1, 32 nW m−2 sr−1, and 25 nW m−2 sr−1 for F125W, F140W, and F160W."