Chris Churchill's Home Page

CHRISTOPHER W CHURCHILL
PROFESSOR
DEPARTMENT OF ASTRONOMY
NEW MEXICO STATE UNIVERSITY

My graduate-level text book is finally completed! This two-volume set, published by Cambridge University Press, provides a comprehensive and detailed treatment of the topic of quasar absorption lines, including its historical development, scientific findings, theoretical foundations, and methods of analysis. Volume 1 (695 pages, 227 figures; 2575 references) chronicles six decades of quasar spectroscopy. The book details the nature of the Lyα forest, Lyman limit systems, damped Lyα absorbers, deuterium (D/H), 21-cm absorbers, HI and HeII reionization, the WHIM, and the multiple ionization phases of metal line absorbers. Galaxies and their connections to these absorbers are treated in depth, as are the taxonomy and classes of AGN/quasar spectra and their associated absorption lines. Volume 2 (621 pages, 188 figures; 518 references) treats the theory and analysis of absorption lines, including the physics of atomic transitions, gas and ionization physics, the cosmological model, radiative transfer, spectrograph design, analysis of spectra, and multi-component, multiphase chemical-ionization modeling. Pragmatic approaches to conducting and assessing absorber counts in large absorption line surveys is presented. Throughout, objective analysis methods are emphasized and presented for clarity of practical application.

Quasar Absorption Lines
Volume 1: Introduction Discoveries, and Methods
Volume 2: Astrophysics, Analysis, and Modeling

(book cover images) these are mock up covers; the final covers will resembles these, but will not be exact.

For more information, a detailed website qsoAbsLines has been created. At that site, you can obtain a full chapter listing, read detailed chapter abstracts, take a peek inside, join the mailing list, and learn about pre-ordering your copy. The book is expected to start delivering in Janaury 2026.

I study the evolution of galaxies by examining their circumgalactic medium (CGM), a gaseous reservoir of dynamically complex, multi-phase, metal enriched gas that surrounds galaxies. The gas is observed in absorption using the technique of quasar absorption lines. When a quasar resides behind a galaxy, the GCM gas imprints absorption patterns in the spectrum of the quasar. From these we measure the gas temperature, metallicity, kinematics, etc. We aim to learn about the role of the cycle of gas (called the baryon cycle) in governing the formation and evolution of galaxies.

(left) A QSO quasar spectrum with emission lines annotated and (across the top) with spectral regions annotated for the various ions that can be observed in absorption. (right) A combined optical and radio image of the galaxy M81. The radio emission (orange) shows how the gas is dstributed around the stars (white).