RII Track-4:@NASA: Bluer and Hotter: From Ultraviolet to X-ray Diagnostics of the Circumgalactic Medium

The brilliant spiral appearances of galaxies have dazzled humanity since their discovery through the first telescopes. However, this picture of galaxies is highly incomplete, containing only their starlight. Those stars, like our Sun must form out of an enormous gas supply, both inside and outside the galaxy, that cannot be seen in light visible by human eyes.

Thus, understanding how and why new generations of stars may or may not form (i.e., whether galaxies 'live' or 'die') requires observations over an enormous range of wavelengths, as the gas reservoirs in and around galaxies may span a factor of 100,000 in temperature. We now know that gas flows in and out of galaxies engage in a complex interplay, like ecosystems often encountered in nature.

The mechanics of these ecosystems lies at the core of our own cosmic origins. The National Academy of Sciences has set these 'cosmic ecosystems' as a key national priority for astrophysics research over the next decade and beyond. The Principal Investigator's (PI) research group has been focused on the cooler gas in cosmic ecosystems, those detectable at ultraviolet and visible wavelengths, but the hotter phases requiring X-rays to observe play a critical role.

This fellowship will equip the PI's research group at New Mexico State University to address this national priority from a comprehensive multi-wavelength perspective. The project will leverage the X-ray expertise at the NASA Goddard Space Flight Center to train the PI and a graduate student in X-ray astronomical observations. The research team will engage in three key investigations that couple our current expertise with the newly acquired X-ray techniques while employing X-ray facilities receiving substantial U.S. investment.

The gas permeating cosmic ecosystems has been primarily characterized observationally at ultraviolet (UV) and optical wavelengths, which are sensitive to cool (10^4 K) and warm-hot (10^5−10^6 K) gas. However, galaxy formation theory is increasingly pointing towards the hotter phases (> 10^6 K) observed in X-rays as holding the answers to the critical processes within cosmic ecosystems.

We stand at an exciting juncture with the imminent data release of the eROSITA All Sky Survey (eRASS), the U.S.- and Japanese-led high spectral resolution XRISM X-ray telescope launching in 2023, and the X-ray community tirelessly developing mission concepts for the next X-ray space telescope to be launched by the U.S. within the next decade (another National Academy recommendation). In partnership with astrophysicists at NASA Goddard Space Flight Center, the research team will build the necessary research infrastructure at New Mexico State University (NMSU) to seize these emerging opportunities.

Towards this end, we will conduct research projects that involve the key facets of X-ray analysis. 1) We will employ the eRASS X-ray imaging to unveil the interactions between the hot intragroup and circumgalactic medium (IGrM; CGM) in galaxy groups. 2) After the launch of XRISM, we will measure precise hot intracluster medium velocities within galaxy clusters and compare with the cool-phase H I velocity distribution from existing UV absorption line observations to characterize high-velocity, multiphase gas flows. 3) Looking towards the future, we will employ state-of-the-art galaxy formation simulations to generate mock X-ray microcalorimeter spectra and mock UV absorption and emission spectra of spatially coincident regions in the CGM. We will then propagate this expertise back through our NMSU Astronomy Department, as X-ray observations are used in every subfield of astronomy studied by the NMSU faculty, but X-rays are missing from our observational skill portfolio.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.