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Diffuse Baryons in Space

Final Report Summary - DIFFUSE BARYONS (Diffuse Baryons in Space)

The aim of this project was to shed light on the properties of dilute gas in the halos of galaxies with direct implications for their formation, as well as the evolution of the surrounding intergalactic medium. As such environs, on accounts of their extremely low densities, are poor emitters of radiation, the approach taken in this work seeks to study them in absorption, whose signal scales linearly with density. In particular, we focused on the properties of active vs. non-active galaxy halos, thereby shedding light on the origin of the gas and feedback mechanisms in galaxy formation.

In the course of the project, a large set of quasar-quasar and quasar-galaxy pairs has been compiled, where the spectra of the background quasars are used to probe the environs of the foreground objects. Follow-up ground- and space-based observations have been carried out leading to the following conclusions (based on tracers of cool gas such as Hydrogen and singly ionized Magnesium): a) there are no profound differences in the circumgalactic medium of active vs. non-active sources hence consistent with the notion of secular processes as the main triggering mechanism for black hole activity, b) the brightest quasars have larger envelopes with higher velocity dispersions possibly reflecting on the denser environs in which they reside, c) cool gas on large scales around a nearby (active) galaxy is consistent with an extended rotating gaseous disk with considerable implications for the origin of metal-rich intervening systems, feedback physics, and galaxy halo structure.

A further objective of the project was to bridge the gap between the theory of dilute metal-rich photoionized media and (spectroscopic) observations in the general astrophysical context, and to pave the way for a self-consistent modeling scheme that accounts for photoionization and photo-heating processes at the atomic scale and the global gas dynamics. Over the course of the IRG, a large database of the relevant atomic data has been compiled to facilitate state-of-the-art thermal calculations and synthetic absorption spectra predictions, and the effects of the gas microphysics on its global dynamical properties have been quantified. The work continues beyond the IRG term to provide the community with a general purpose computer code that self-consistently solves these physical processes on the fly (for optically-thin media) using additional secured funds, and a newly purchased high-performance computer cluster.

As part of the IRG, emphasis has been put on public outreach. Specifically, public talks have been given with a special emphasis on exposing minority groups within the Israeli society to up-to-date scientific topics (especially in Astronomy). Further, a new course in "order-of-magnitude physics" has been prepared and given to physics teachers with the aim of explaining everyday natural phenomena using simple physical arguments thus better engaging high-school students in science.

Thanks to IRG funding (with complementary support from external resources) the newly established astrophysics group at the University of Haifa has considerably expanded in 4 years, and was able to attract several graduate students, three postdocs, and research assistants. The group has also ventured to new research fields, studying the properties of photoionized gas around quasars using a new (photometric) reverberation mapping technique, which has since been adopted by several groups in Europe and the US. New research collaborations have been formed with several groups in Israel, US, Germany, and Switzerland, and additional funding to sustain the group has been secured.

The group's webpage is available at: