Chemical fingerprints of star forming regions and active galaxies

This thesis is devoted to the study of the physical conditions of the interstellar medium (ISM) in active galactic nuclei (AGNs) and Galactic star-forming regions, using mostly single-dish millimeter observations. I first study the excitation conditions of dense gas in a group of Seyfert galaxies using radiative transfer models (Chapter 2). I then study the galaxy NGC 1068, and try to distinguish signatures of the contributions from the AGN and the starburst ring by incorporating observations of high-J transitions of dense gas tracers (Chapter 3). Later, I venture into the mid-infrared spectral region to study different aspects of the AGN and starburst components in the galaxy NGC 4945 (Chapter 4). In Chapter 5 I delve into theoretical aspects of the dynamical evolution of gas in an AGN torus. I use a 3D hydrodynamic simulation with chemical abundances driven by X-rays. The aim is to understand the effects of X-ray irradiation by the AGN on the temperature, formation and destruction of the molecular gas. I finally explore a Galactic star-forming region, the Omega Nebula, with high resolution single dish observations, to study the properties of the warm gas and to constrain chemical models (Chapters 6 and 7).

Extremely high spectral resolution measurements of the 450 µm atmospheric window at Chajnantor with APEX,

International audienceGround-based telescopes observing at millimeter (mm) and submillimeter (submm) wavelengths have to deal with a line-rich and highly variable atmospheric spectrum, both in space and time. Models of this spectrum play an important role in planning observations that are appropriate for the weather conditions and also calibrating those observations. Through magnetic dipolar (M1) rotational transitions and electric dipolar (E1) transitions O 2 and H 2 O, respectively, dominate the atmospheric opacity in this part of the electromagnetic spectrum. Although O 2 lines, and more generally the so-called dry opacity, are relatively constant, the absorption related to H 2 O can change by several orders of magnitude leading from a totally opaque atmosphere near sea level with high H 2 O columns to frequency windows with good transmission from high and dry mountain sites. Other minor atmospheric gases, such as O 3 and N 2 O among others, are present in the atmospheric spectrum which also includes nonresonant collision-induced absorption due to several mechanisms. The aim of our research is to improve the characterization of the mm/submm atmospheric spectrum using very stable heterodyne receivers with excellent sideband separation and extremely high (kHz) spectral resolutions at the 5000 m altitude Chajnantor site in northern Chile. This last aspect (spectral resolution) is the main improvement (by more than three orders of magnitude) in the presented data with respect to our previous work conducted ∼20 yr ago from Mauna Kea in Hawai'i. These new measurements have enabled us to identify slight modifications needed in the Atmospheric Transmission at Microwaves (ATM) model to better take into account minor constituent vertical profiles, include a few missing lines, and adjust some high-energy O 3 line frequencies. After these updates, the ATM model is highly consistent with all data sets presented in this work (within ∼2% at 1 GHz resolution)