Seminars and Colloquia at ESO Garching and on the campus

The main DESI redshift surveys have now collected 3 years of data and analysis of the Year-1 data set is almost complete. While concentrating  on the analysis of the Bright Galaxy Survey (BGS) in which I'm most directly involved  I plan to review the main cosmological results from other components of DESI. The BGS is a magnitude-limited (r<19.5) galaxy redshift survey and so rather like the SDSS main survey but about two magnitudes deeper. As such it is not only a useful cosmological probe but also a powerful probe of the local galaxy population and so a constraint on galaxy formation and the galaxy dark matter connection. I will present an analysis of how galaxy clustering depends on galaxy properties and the galaxy luminosity function depends on environment.

Thanks to the recent deep observations, some massive galaxies are known to stop their star formation even just 1-2 Gyrs from the Big Bang. These early massive quiescent galaxies are likely to have obtained their stellar mass by bursty star formation within a short period and suddenly got quenched. However, their statistical properties and quenching mechanisms are still unclear. In this talk, I will introduce our recent studies to characterize massive quiescent galaxies using data from ground-based and space telescopes. 

In the first part of this talk, I will present the result of characterizing the morphology of quiescent galaxies at z>3 using the high-resolution imaging of JWST/NIRCam. We derived their sizes and Sérsic index of ~30 quiescent galaxies. For the first time, we have shown that the size is larger for more massive quiescent galaxies at z>3, as seen at z<3. Their typical sizes are ~0.6kpc at Mstar~5x10^10Msun, smaller than that at z<3; thus, significant size evolution occurred for quiescent galaxies over the last 10 Gyrs.

In the second part of this talk, I will present our study investigating the connection between quenching and AGNs at z~3-5. Using the Chandra data and the multi-band photometry of the ground-based telescopes, we conduct the stacking analysis of X-ray images of ~500 quiescent galaxies. For the first time, we detected the average X-ray emission of quiescent galaxies at z~3-5 and found that they typically have low-luminosity AGNs. Their X-ray luminosity is higher than that of star-forming galaxies, suggesting the possible connection between AGNs and quenching. Also, I will introduce our ongoing work on the detailed characterization of X-ray-detected quiescent galaxies at z~2.

On their way from the main sequence to the final supernova explosion, massive stars lose a substantial fraction of their mass through line-driven winds. Recent decades have witnessed significant advancements in both observational and theoretical studies of these winds that sail on starlight. The advancements in our understanding of radiative driving lead to progressively more accurate estimates of mass-loss rates from massive stars. In this talk, we will outline the key ingredients necessary for reliable predictions of mass-loss rates from numerical simulations, and demonstrate how state-of-the-art theoretical mass-loss rate estimates compare with observational results.

It is creativity/novelty that drives scientific breakthroughs and societal progress, but the journey from a novel scientific idea to a practical solution can be long and winding. Debates also persist regarding whether and how science contributes to practical solutions. In his talk, Jian will explore the complex relationship between novelty and impact in science and technological innovation. Furthermore, he will examine concerns that the current science funding system is increasingly risk-averse and favours short-term, safe projects over long-term, risky and novel projects. He will also present empirical evidence about whether major funding agencies are biased against novelty in their project selection process, and whether receiving funding enables grantees to engage more in novel research. Finally, he will discuss strategies that scientists can use to boost creativity, such as how to structure the professor-PhD student relationship, collaboration teams, and broader collaboration networks.

You can find the abstract and a short bio by the speaker at:

https://indico.euro-fusion.org/event/2559/page/18-highlight-topic-creativity-in-science

High resolution, hydrodynamic galaxy simulations can be used to investigate the inherent variation of dark matter around the Solar Circle of a Milky Way-type galaxy. These simulations self consistently include both the baryonic back-reaction as well as assembly history of substructures, all of which may have lasting impacts on the dark matter’s spatial and velocity distributions, creating `gusts’ of dark matter wind around the Solar Circle, potentially complicating interpretations of direct detection experiments on Earth. Direct detection is a key experimental goal to advance the microscopic understanding of the dark matter that fills the Universe. We investigate how dark matter substructure, simulated in halos analogous to our own Milky Way, impacts the shape, summary statistics, and interpretation of results from terrestrial dark matter direct detectors.

Implementing a new numerical integration technique, our work generates bespoke predictions for terrestrial underground detection, finding large uncertainties arising in the expected signals of direct detection experiments. Having developed a realistic end-to-end pipeline for studying these effects, we discuss the implications of these astrophysical variations in the dark matter distribution of the solar neighbourhood on current and future particle physics searches for dark matter.

The Central Molecular Zone (CMZ) is an extreme environment in the inner few hundred parsecs of the Milky Way Galaxy, with temperatures, pressures, and densities exceeding those measured in the Galactic disk. At a distance of ~8.2 kpc, it has previously been difficult to perform large surveys of the CMZ at high resolution, limiting most studies to individual molecular clouds. ACES (the ALMA CMZ Exploration Survey) is a large ALMA program with high sensitivity observations covering the entire area of the CMZ at high spatial and spectral resolution at 3mm in both continuum and spectral lines. ACES data will be used to determine the overall distribution and chemical composition of mass in the inner Galaxy, from the sub-parsec scales of star formation, to the large-scale global processes that influence it. In addition, spectral line data will be used to create a comprehensive picture of gas kinematics in the CMZ, unveiling how gas flows from galactocentric radii of a few hundred pc down to the vicinity of the central supermassive black hole. Observations and high resolution hydrodynamical simulations will be used in tandem to determine how different physical processes impact the evolution of gas at different scales. We present early science results from the ACES team, including an overview of the data products, the properties of compact sources extracted using ACES continuum data, the rich chemical composition identified in the CMZ, and the characterization of gas kinematics in the CMZ.