An Infrared Study of the Extended Interstellar Medium of Extreme, Luminous Infrared Galaxies

Cristina Lofaro
University of Crete
Tuesday, March 19, 2024
4:00 pm
NS2 1201

Abstract: The most powerful events in the Universe do not take place within star-forming galaxies. Instead, they unfold within extreme systems characterised by nuclear starbursts and luminous active galactic nuclei. Despite not being the primary drivers of overall cosmic star formation rate or black hole accretion, these phenomena still contribute significantly to both of them, up to 30% at any given time. They bring about significant changes in galaxies shape, turning them into elliptical forms, while slowing down star formation and black hole growth due to feedback from their powerful energy sources. It is crucial to study these extreme galaxies to fully understand how galaxies evolve, as they represent a critical component of the overall picture. These extreme galaxies often result from mergers between gas-rich galaxies in the nearby Universe. They are typically hidden by dust, emitting infrared (IR) light, making them challenging to observe yet essential subjects for research. Over the past few decades, many studies have focused on examining the nuclear activity in nearby luminous (LIRGs, LIR > 10^11 solar luminosities) and ultra-luminous infrared galaxies (ULIRGs, LIR > 10^12 solar luminosities), yet the impact of their nuclear activity on the surrounding interstellar medium (ISM) remains largely unexplored.  Whether the extended ISM is affected (and if so, how and up to which distance) by the nuclear region or whether the density and/or the ionisation state of the gas is related to the merger stage are still open questions. To address those questions, we use Spitzer and Herschel spectral map observations encompassing the most prominent ionised emission lines across the mid- and far-infrared wavelengths, providing insight into a wide spectral range of ionisation strengths and gas density conditions. We used spectral cubes from the Spitzer/IRSA archive and Herschel/PACS observations in at least three emission lines: [OI]63um,  [OIII]88um, [CII]158um (including also [NII]122um for some sources) for more than 60 galaxies from the Great Observatories All-sky LIRG Survey (GOALS) sample.  After performing the extraction of the emission line fluxes from the Spitzer and Hershel datasets, we analysed the radial profile of the most useful emission lines ratios to address the main physical processes in the different phases of the extended ISM.


Paul Robertson