Polarimetric modeling and assessment of science cases for Giant Magellan Telescope-Polarimeter (GMT-Pol)

TL;DR

This paper models the polarimetric capabilities of the upcoming Giant Magellan Telescope, assessing instrumental polarization and crosstalk, and discusses science cases and design options for future polarimetric instruments.

Contribution

It provides the first detailed polarimetric modeling of GMT for different ports, highlighting its advantages and proposing design routes for polarimetric instruments.

Findings

Instrumental polarization is 0.1% (Gregorian) and 3% (folded port).

Linear to circular crosstalk is 0.1% (Gregorian) and 30% (folded port).

Gregorian focus offers a significant advantage for sensitive polarimetry.

Abstract

Polarization observations through the next-generation large telescopes will be invaluable for exploring the magnetic fields and composition of jets in AGN, multi-messenger transients follow-up, and understanding interstellar dust and magnetic fields. The 25m Giant Magellan Telescope (GMT) is one of the next-generation large telescopes and is expected to have its first light in 2029. The telescope consists of a primary mirror and an adaptive secondary mirror comprising seven circular segments. The telescope supports instruments at both Nasmyth as well as Gregorian focus. However, none of the first or second-generation instruments on GMT has the polarimetric capability. This paper presents a detailed polarimetric modeling of the GMT for both Gregorian and folded ports for astronomical B-K filter bands and a field of view of 5 arc minutes. At 500nm, The instrumental polarization is 0.1% and 3% for the Gregorian and folded port, respectively. The linear to circular crosstalk is 0.1% and 30% for the Gregorian and folded ports, respectively. The Gregorian focus gives the GMT a significant competitive advantage over TMT and ELT for sensitive polarimetry, as these telescopes support instruments only on the Nasmyth platform. We also discuss a list of polarimetric science cases and assess science case requirements vs. the modeling results. Finally, we discuss the possible routes for polarimetry with GMT and show the preliminary optical design of the GMT polarimeter.