Line Emission Mapper: an X-ray probe mission concept to study the cosmic ecosystems and the physics of galaxy formation

In the 2020 Astrophysics Decadal Survey, the National Academies identified cosmic feedback and structure formation as a key question that should drive research in the upcoming decade. In response to this recommendation, NASA released a call for X-ray and IR probe-class missions, with a $1B cost cap. The line emission mapper (LEM) is a mission concept designed in response to this call. LEM is a single-instrument X-ray telescope that consists of a Wolter–Schwarzschild type I X-ray optic with a 4 m focal length, coupled with an X-ray microcalorimeter with a 30′ field of view (FoV), 15″ angular resolution, and 2.5 eV energy resolution [full-width half maximum (FWHM)], with a 1.3 eV FWHM energy resolution central subarray. The high throughput X-ray mirror combined with the large FoV and excellent energy resolution allows for efficient mapping of extended emission-line dominated astrophysical objects from megaparsecs to sub-pc scales to study cosmic ecosystems and unveil the physical drivers of galaxy formation.