Xenia - A Probe of Cosmic Chemical Evolution
Tracing Cosmic Chemical Evolution from the Reionization Epoch to the Present
“We are stardust, we are golden; we are billion-year-old carbon; and we got to get ourselves back to the garden.” Joni Mitchell, Woodstock 1969
Xenia is a concept study for a medium-size cosmology mission addressing the Cosmic Origins key objective of NASA’s Science Plan.
OVERVIEW
You, I, the air we breathe, the stars, and the other "normal" matter in the universe are all composed of protons, neutrons, and electrons. These are the ingredients that make all elements from hydrogen to iron and beyond. Astronomers call elements heavier than hydrogen and helium “metals.”
Metals are essential for star formation and their subsequent evolution, and ultimately for the formation of planets and development of life as we know it. To understand the history and evolution of metals is an essential part for our understanding of the universe. Using X-ray imaging and spectroscopy, Xenia will read the metal diaries of the universe to explore and reconstruct the cosmic history of metals reaching from the first population of stars to the processes involved in the formation of galaxies and clusters of galaxies.
How will Xenia accomplish this task?
Xenia's wide-field monitors will watch the sky for gamma-ray bursts, and when they spot one of these spectacular explosions, the spacecraft will turn and point its telescopes at it in less than a minute. Each burst’s brilliance will illuminate the intervening cosmic structures – galaxies, galaxy clusters, and the areas between clusters, together called the cosmic web – for Xenia’s wide-field X-ray imager to capture. Then the spacecraft's wide-field spectrometer will identify the chemical fingerprints, or line features, from key elements that help us trace the cosmic chemical evolution.
Most “normal” matter in the universe resides in the seemingly empty areas between the galaxies and between the galaxy clusters throughout the cosmic web and is predicted to trace the vast filamentary structures created by Dark Matter and Dark Energy. With Xenia's X-ray spectroscopy, astronomers can probe all the metals (carbon through iron) simultaneously, in all ionization stages and all binding states (atomic, molecular, and solid), and thus achieve a unique, model-independent perspective. Xenia will map the gases and collect essential information on galaxy clusters, such as density, temperature and composition, helping astronomers address the questions listed below.
SCIENCE GOALS
Planned as a 5-year mission, Xenia will address the following fundamental questions:
- When were the first metals created?
- How does metallicity change on cosmic time scales?
- How is the matter in clusters and cosmic filaments distributed?
- What are the physical conditions in large-scale structures?
Cosmic Tracers Used by Xenia to Read the Metal Diaries of the Cosmos
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High Angular Resolution Imager
The wide field of view and low background of the WFI allow studies of extended low surface brightness objects such as the outer regions of clusters.
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Transient Event Detector
When one of Xenia's wide-field monitors spots a gamma-ray burst, the spacecraft will turn and point its telescopes at it in less than a minute.
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Cryogenic Imaging Spectrometer
Xenia will survey the nearby universe for emissions from a large sample of galaxy clusters. Her wide-field imaging and spectroscopy detectors will measure surface brightness, temperature, and metal abundances, all the way to the outer regions of many clusters.
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GENERAL INFO AND DISCUSSIONS
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Meaning of Xenia
Xenia is the Greek word for ‘hospitality.' The concept of Xenia evolved in parallel with the Explorer of Diffuse Emission and GRB Explosions (EDGE), a mission proposed by a multinational collaboration to the ESA Cosmic Vision 2015. Xenia incorporates the European and Japanese collaborators into a U.S.-led mission that builds on the scientific objectives and technological readiness of EDGE.
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Mission Profile
Xenia's fast repointing (1 deg/s) requires a compact satellite. With a densely packed payload, this is compatible with the Falcon 9 launcher. Xenia requires a low Earth equatorial orbit. It will enter a circular orbit 600 kilometers from the Earth at a 5 degree inclination.
The mission's lifetime is planned for 5 years with a possible extension to 10 years, appropriate to realize the major goals of the mission with a modest guest observer program.
Xenia will make her observations with fast reaction to gamma-ray bursts, thus allowing high-resolution spectroscopy.
Xenia will observe and survey, through X-ray telescopes with wide field of view and low background (high angular and high spectral resolution), extended sources, like galaxy clusters and the WHIM.
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Cosmic Tracers Used by Xenia to Read the Metal Diaries
Warm Hot Intergalactic Medium (WHIM)
Thanks to her unique observational capabilities, Xenia will be able to study the gaseous matter in the universe from the early epochs, through gamma-ray burst (GRB) explosions, through the period of cluster formation, down to the present.
High resolution spectroscopy of bright, distant continuum sources in the soft X-ray band will reveal the metals in the WHIM. Xenia will use bright GRB afterglows as ‘backlight’ sources, or beacons. GRBs are an unlimited ‘renewable resource’ and occur out to very large distances, back to the time when the universe was only a fraction of its present age.
Complementary to the absorption spectroscopy, Xenia will image the WHIM and the outskirts of clusters in the emission lines of key elements such as Carbon, Oxygen, Neon, and Iron.
Galaxy Clusters
Galaxy clusters still carry the imprints of primordial cosmological fluctuations and, inside these clusters, prodigious amounts of energy are being converted from one form to another.
Xenia will survey the nearby universe for emissions from a large sample of galaxy clusters. Her wide-field imaging and spectroscopy detectors will measure surface brightness, temperature, and metal abundances, all the way to the outer regions of many clusters.
Gamma-Ray Bursts
It is well established that most long-duration GRBs are caused by the explosive deaths of massive stars and, due to their enormous brightness, they can be seen throughout the universe. GRBs produce copious amounts of penetrating high-energy photons and can probe the gaseous regions of the universe, which are not accessible in the optical band.
Xenia will gather a sample of about 400 bright GRB X-ray afterglows in 5 years, measure their redshift, and identify metal lines (chemical fingerprints) associated with matter along their line of sight. Using high-resolution X-ray spectroscopy, the mission will study the history of metals in both the close GRB environments and their host galaxies back to the early epoch of the universe. Xenia will also quickly relay the GRB coordinates to the scientific community to enable multi-wavelength follow-up campaigns.
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