December 16, 2024
Understanding the evolution of galaxies from the Big Bang to the present day is a difficult task, both observationally and theoretically. In this talk, I describe how, despite these challenges, we have been able to make significant progress in this field of research over the last 20 years, thanks in particular to the accurate measurement of the star formation rate, gas mass, and morphology of thousands of high-redshift galaxies using infrared/submillimetre observations from Spitzer, Herschel, ALMA, and JWST/MIRI. These measurements have led to the emergence of a new paradigm on the universality of star formation: the majority of stars in the Universe have formed in long, continuous phases, driven by the secular transformation into stars of gas accreted by galaxies from the cosmic web. In this talk, I will begin by summarizing our current knowledge of the cosmic density of star formation and molecular gas, and discuss how the simultaneous variation of these quantities with redshift (rising from early cosmic time, peaking at z~2, and decaying sharply to the present day) suggests a common mode of star formation, controlled by the availability of molecular gas in galaxies. I will then introduce the main sequence of star-forming galaxies and discuss how the study of galaxy properties in this context has led to the development of this new paradigm of a universal, secular mode of star formation across cosmic time, which is well described by so-called gas regulator models. I will conclude by describing some prospects in this area of research, based in particular on new observatories such as Euclid, SKA, CCAT-prime, and possibly AtLAST.
Benjamin Magnelli
CEA Paris-Saclay, France
“An infrared/submillimeter view on the universality of star-formation across cosmic time”
December 9, 2024
SPHEREx, an upcoming NASA satellite mission, is set to launch in early 2025. With its all-sky near-infrared spectral imaging survey covering 0.75–5 μm, SPHEREx will address key questions in cosmology, galaxy formation, and the origins of biogenic signatures, using its low-resolution spectroscopic catalog and near-infrared spectral images. In this talk, I will provide an overview of the SPHEREx mission, its main science targets in cosmology and galaxy evolution, and discuss additional opportunities with the SPHEREx dataset.
Yun-Ting Cheng
Research Scientist in astrophysics and cosmology at Jet Propulsion Laboratory/California Institute of Technology
“Studying Cosmology and Galaxy Evolution with SPHEREx”
November 28, 2024
Observations of spectral lines are performed to improve our understanding of the interstellar medium (ISM). However, assessing quantitatively the potential of a line to constrain the physical conditions of the ISM is complex, even more so for combinations of lines. Observation campaigns thus usually observe as many lines as possible for as long as possible.
Lucas Einig
IRAM
“Quantifying the informativity of emission lines to infer physical conditions in giant molecular clouds”
In this paper, we propose an approach that quantifies how well observing one or more lines can constrain a physical parameter. To do so, we resort to information theory and in particular mutual information. In fact, this statistic quantifies the average reduction in uncertainty on a given physical parameter resulting from the observation of a given set of lines. We illustrate our approach on synthetic observations — produced from an fast emulator of the Meudon PDR code and a simulator of IRAM 30m observations — to constrain the cloud visual extinction Av and the intensity of the incident UV field G0. We study how mutual information evolves with integration time, which could allow observers to optimize their proposals to achieve the highest constraining power with the minimum time budget. We also propose visualizations, called “information maps”, of how mutual information evolves as a function of the physical regime (Av, G0) for a given line or set of lines. We show that combining lines provides information in regimes where none of the individual lines is informative, thanks to line complementarities. Finally, we compare mutual information values for multiple lines and sets of lines to determine which one best constrains a physical parameter. This could allow observers to select the most suitable lines to observe for a given physical environment. Due to line complementarities, the most informative set of lines does not necessarily combine the most informative individual lines.”
November 18, 2024
The observed eRosita bubbles — massive, bi-lobed structures extending above and below the Milky Way’s disk — have shed new light on the complex dynamics in the galaxy’s center and raised questions about their origin and energy source. These bubbles, reminiscent of the previously observed Fermi bubbles, provide a unique laboratory to understand energetic processes in the galactic center. In this talk, I will present results from state-of-the art 3D magnetohydrodynamic (MHD) simulations of Milky Way-like galaxies, carefully constructed to include a realistic gravitational potential of the central galactic region. These simulations reveal that supernova (SN) driven explosions can indeed produce large-scale outflows comparable in size, dynamics, energetics, and X-ray emission characteristics to the observed eRosita bubbles. However, they fall short of reproducing the gamma-ray emission observed in similar structures, highlighting shortcomings of the included physical processes in current
Philipp Girichidis
Institute for theoretical Astrophysics (ITA), University of Heidelberg
“eRosita bubbles in Milky Way galaxies”
simulations. I will illustrate the physical mechanisms by which these bubbles are generated and discuss future paths to explore a more detailed comparison to observations via gamma rays.
September 17, 2024
Stars, particularly massive ones, are ubiquitous visible light sources in the universe and drive galactic chemical evolution by dramatically altering their surrounding environments through radiation, stellar winds, and supernova explosions. Therefore, understanding the properties of stars is crucial, and numerical modeling has been employed to grasp their complex characteristics. In this talk, the speaker, the lead developer of the Japanese stellar evolution code HOSHI, will present recent research conducted using the HOSHI code. The main topics include the incorporation of large-scale stellar magnetic fields in a general stellar evolution and the disk accretion evolution in the protostellar phase, with brief discussions on the gravitational collapse of massive stars.
Koh Takahashi
Division of Science, National Observatory of Japan
“Research on Stellar Evolution Using the HOSHI Code”