Seminars and Colloquia at ESO Garching and on the campus

Historically, the search for the inter-galactic medium (IGM) motivated the search for  the Far Ultraviolet (<0.2 micron; FUV) background which in turn led to a number of experiments and missions.  Decades later the focus shifted to FUV as the primary heating and ionizing agent of the atomic phases (warm and cold neutral medium).  On the observational side, it was realized that at high Galactic latitudes, the diffuse FUV has three components: FUV light from hot stars in the Galactic plane reflected by dust grains (diffuse galactic light or DGL), FUV from other galaxies (extra-galactic background light, EBL) and a component of unknown origin.  This view has been amply confirmed by later GALEX observations. During the eighties, there was conisderable discussion that decaying dark matter particles produced FUV radiation.  In my talk I systematically investigate production of FUV photons from all major sources capable of producing FUV emission. I conclude that two thirds to perhaps all of the third component can be explained by the sum of Galactic Hot Ionized Medium (line emission), two photon emission from the  Warm Ionized Medium, low velocity shocks in the Galaxy and Lyman fluorescence in the Solar System (the interplanetary medium and  the exosphere of Earth).

Recent JWST observations of Type Ia supernovae (SNe Ia) during the late-time nebular phase (>200 days post explosion) have paved the way for spectroscopic studies extending all the way to the mid-infrared range, and with it the hope to better constrain SN Ia explosion mechanisms. The first SN Ia spectrum obtained with JWST unveiled for the first time the 2.5-5 micron wavelength range and revealed kinematic offsets of several 1000 km/s in a subset of emission lines, hinting at possible ejecta and composition asymmetries. The second SN Ia displayed a prominent line due to once-ionised neon ([Ne II] 12.8 micron), never observed before in spectra of such events and associated with the violent merger of two WDs. I will present the results of radiative-transfer simulations that were used to interpret these data, and discuss the impact of ejecta asymmetries, ionisation effects and uncertainties in the atomic data on the predicted spectra. These models suggest that key physical ingredients are missing from either the explosion models, or the radiative-transfer post-processing, or both. Nonetheless, they also show the potential of the near- and mid-infrared to uncover new spectroscopic diagnostics of SN Ia explosion mechanisms.

We employ natural language processing algorithms with attention, repurposed to receive QSO spectra to predict unseen spectra, broad lines, and super massive black hole masses. We find that the trained algorithm is able to reproduce with high significance masked broad lines and/or continua in QSO spectra, highlighting an ability to learn from and leverage physical information imprinted amongst the entire spectrum. A key implication is that this information may help to refine physical properties such as single-epoch black hole masses. We tested the algorithm’s ability to directly predict black hole masses, with no spectral fitting or decomposition, finding reasonable success to reproduce single-epoch prescriptions. Finally, the algorithm is able to reconstruct broad UV lines such as C IV and Ly-alpha in the presence of broad absorption lines or intervening IGM. We will discuss the attention mechanism, which allows us to peek inside and probe what information is being used to make the above predictions and several broad future applications that we envision.

I will present recent and ongoing explorations regarding cold clouds in the circumgalactic media of (simulated) z=0 Milky Way-like galaxies. We find that these CGMs are typically filled with >~100s-1000s of such cold gas structures, possibly analogs of high-velocity clouds (HVCs) observed in the Milky Way sky. These objects primarily originate as a result of cold gas outflows from the central galaxy and/or precipitation of the warm-hot phase of the CGM. Clouds arising as a result of stripping of cold gas from satellites are rare in our sample (<5%). Lastly, we find that properties of clouds are diverse, and may furthermore depend closely on their source of origin.

Stellar multiplicity is ubiquitous at early stages of star formation. This unavoidably modifies the initial conditions of protoplanetary discs and hence planet formation. The high level of stellar multiplicity translates into a high number of binaries and triple stellar systems in active star forming regions. In this lunch talk, we will briefly cover disc dynamics within multiple stellar systems, mainly binaries and triples. In addition, based on numerical simulations, we will discuss how to interpret complex disc morphologies such as spirals, warps, and streamers as signposts of ongoing gravitational interaction between young stars. We will illustrate these claims with representative examples of observed multiple stellar systems with discs (e.g. ALMA, VLT, GRAVITY, Gaia). To conclude, we will briefly discuss the current open question regarding planet formation in multiple stellar systems given the emergence of planetary architectures in such systems.