Talks, Seminars, Events

# Talks, Seminars, Events

A list of all Physics & Astronomy talks and seminars taking place in Heidelberg can be found at HePhySTO.

### Upcoming events

2017-11-20
11:15
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EMPIRE: Probing the dense, star-forming gas across nearby disk galaxies
Maria Jesus Jimenez (ZAH/ITA)
ITA "blackboard" Colloquium ( Hephysto link )
Philosophenweg 12, 106
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Abstract
I will present results from a comprehensive and systematic study of the fraction of dense gas and its star formation efficiency as traced by several high critical density molecular lines. The results are based on the IRAM-30m large program EMPIRE, a ~500h survey that provides full maps of high critical density tracers like HCN or HCO+ across the entire star forming disks of 9 nearby disk galaxies. My thesis work aims to understand how dense gas fractions and star formation efficiencies vary across and among galaxies. Another particular focus is to relate the fraction of star forming gas and its ability to form stars to local ISM conditions such as stellar surface density or ISM pressure. I furthermore present results of analyzing optically thin isotopologues (e.g. H13CN) and high signal-to-noise 13CO and C18O in EMPIRE and ancillary ALMA data, to constrain optical depths of high critical density tracers and abundance variations in our disk galaxies. Both quantities are crucial to understand the ISM density distribution

2017-11-21
16:15
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The chemical composition of globular clusters throughout the Local Group
Søren Larsen (Univ. Nijmegen, NL)
Philosophenweg 12, großer Hörsaal
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Abstract
I will discuss results from our recent work on the detailed chemistry of globular clusters (GCs) in Local Group galaxies. This work is based on a combination of integrated-light spectroscopy at high resolution and resolved imaging with HST in colour combinations that are sensitive to light-element abundance variations. Through the resolved imaging studies, it is now clear that the abundance anomalies that are the hallmark of multiple stellar populations are not restricted to old GCs, but are also found in LMC/SMC clusters as young as 2 Gyrs. This rules out formation mechanisms that were unique to the high redshift Universe. More generally, we find that GCs in dwarfs are, on average, more metal-poor than those in larger galaxies, although no clusters more metal-poor than [Fe/H]\approx-2.5 have been found so far. Overall, a large fraction of the most metal-poor stars in dwarf galaxies tend to belong to GCs. This has important implications for scenarios that invoke heavy cluster mass loss to account for the large fractions of enriched "second-generation" stars in GCs, as well as for globular cluster disruption and its contribution to the field star populations in halos in general.

2017-11-23
11:15
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Young, metal-enriched cores in early-type dwarf galaxies in the Virgo cluster
Linda Urich (ARI)
ARI Institute Kolloquium ( Hephysto link )
ARI Moenchhofstrasse 12-14, Seminarraum 1
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Abstract
Early-type dwarf galaxies are not simply featureless, old objects, but were found to be much more diverse, hosting substructures and a variety of stellar population properties. To explore the stellar content of faint early-type galaxies, and to investigate in particular those with recent central star formation, we study colours and colour gradients within one effective radius in optical and near-infrared bands for 120 Virgo cluster early-type galaxies. Twelve galaxies turn out to have blue cores and we find them to have the strongest age gradients, i.e., the youngest central regions. Moreover, the metallicity gradients of almost all early-type dwarf galaxies are found to be negative, indicating metal-enriched central regions. A cluster environment is expected to influence such low-mass galaxies through tidal forces through interactions with other galaxies (harassment) as well as through the ram-pressure of its hot intracluster medium (ram-pressure stripping). Therefore, we are comparing the observed stellar population gradients with model predictions, in order to investigate how ram-pressure stripping and harassment can affect a galaxy's star formation activity and stellar population distribution depending on the galaxy's orbit and the time it entered the cluster.

2017-11-27
11:15
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Cosmic ray driven galactic winds and their dependence on halo mass
Jacob Svenja (H-ITS)
ITA "blackboard" Colloquium ( Hephysto link )
Philosophenweg 12, 106
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Abstract
Galactic winds are commonly observed in starburst galaxies and play an important role in modelling realistic galaxies. However, the mechanism that drives these winds remains poorly understood. Cosmic rays provide one possibility to launch the outflows. To improve our understanding of cosmic ray driven winds, I use a set of hydrodynamic simulations of isolated galaxies to study how the wind properties change with halo mass.

2017-11-28
16:15
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Exoplanets and the search for extraterrestrial life
Ignas Snellen (Univ. Leiden, NL)
Philosophenweg 12, großer Hörsaal
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Abstract
Placing the solar system in the context of other planetary systems is one of the central objectives driving the study of extrasolar planets. One of the most fascinating questions in modern science is whether other life-bearing planets exist. In this talk I will review the current state of the art of exoplanet research and discuss future ways to probe biomarker gases in Earth-like exoplanets that could point to biological activity.

2017-11-30
11:15
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nn
Eric Pellegrini (ITA)
ARI Institute Kolloquium ( Hephysto link )
ARI Moenchhofstrasse 12-14, Seminarraum 1
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Abstract
nn

2017-12-04
11:15
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tpd
Fabian Klein (ZAH/ARI)
ITA "blackboard" Colloquium ( Hephysto link )
Philosophenweg 12, 106

2017-12-04
11:15
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Disk Fragmentation as a Planet Formation Scenario
Hans Baehr (MPIA)
ITA "blackboard" Colloquium ( Hephysto link )
Philosophenweg 12, 106
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Abstract
Circumstellar disks are likely gravitationally unstable early in their lifetimes when massive and still accreting from their surrounding envelopes. These gravitational instabilities will form spirals and possibly fragment into dense clumps of gas which may result in gas giant planets and low-mass stars. My research uses hydrodynamic simulations to focus on what disk conditions result in the formation of planets and do so over various resolutions to ensure convergence.

2017-12-05
16:15
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Zooming in on planet-forming zones of disks around young stars
Ewine F. van Dishoeck (Leiden Obs., NL / MPE Garching)
Philosophenweg 12, großer Hörsaal
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Abstract
Protoplanetary disks are the birthplaces of planets but the spatial resolution at long wavelengths has so far been insufficient to resolve the critical 5-30 AU region. The Atacama Large Millimeter Array (ALMA) now allows us to zoom in to nearby disks and determine the physical and chemical structure associated with planet formation. This talk will provide examples of recent work on observations and models of protoplanetary disks in various stages of evolution. Surveys of large numbers of disks provide insight into typical masses and sizes, revealing surprisingly weak gas emission. Special attention will be given to transitional disks, which are a subset of disks with evidence for sharp-rimmed cavities (gaps or holes). They are the best candidate sources for harboring just-formed giant planets. ALMA allows imaging of both the gas and dust in these disks, providing constraints on the properties of any young planets. Some prospects for JWST will be mentioned.

2017-12-07
11:15
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Small-scale cosmology with dwarf galaxies
Oliver Müller (Universität Basel)
ARI Institute Kolloquium ( Hephysto link )
ARI Moenchhofstrasse 12-14, Seminarraum 1
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Abstract
Dwarf galaxies are tracers of the fine-structure of the large-scale structure of the universe, but their predicted abundance and distribution from simulations is in conflict with observations in the Local Group, today's best studied group of galaxies. Recently, two planes of satellites were discovered around Centaurus A, providing a unique opportunity to test cosmological predictions beyond the Local Group. We surveyed the complete Centaurus Group with the Dark Energy Camera, doubling the census of dwarf galaxies in the group. We found evidence that these satellite planes are co-rotating, posing a challenge to LambdaCDM. Comparison with high-resolution dark matter simulations shows that this finding is highly significant. Furthermore, I will connect this to the recently established and unexpected relation between the number of dwarf galaxies and the size of the bulge of the host galaxy in the context of LambdaCDM cosmology and MOND.

2017-12-12
16:15
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Charting new physics territories with time-domain astronomy
Ariel Goobar (Univ. Stockholm)
Philosophenweg 12, großer Hörsaal

2017-12-14
11:15
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nn
Kseniia Sysoliatina (ARI)
ARI Institute Kolloquium ( Hephysto link )
ARI Moenchhofstrasse 12-14, Seminarraum 1
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Abstract
nn

2017-12-19
16:15
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Cassini at Saturn: Mission accomplished
Tilmann Denk (Univ. Berlin)
Philosophenweg 12, großer Hörsaal
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Abstract
After two decades of flying through space and more than 13 years orbiting Saturn, the journey of the Cassini spacecraft ended in mid-September with an intended crash into the atmosphere of the ring planet. The months before brought an absolute highlight: In the "Grand Finale" of the mission, Cassini crossed the narrow gap between the rings and the atmosphere of the planet 22 times. What has the spacecraft experienced in these 20 years and especially in the Grand Finale, what have we learned about Saturn, its rings and the numerous moons? After having worked with Cassini throughout its entire journey, I will give you a small insight into the most interesting and exciting events and results, garnished with images of huge storms, complex ring structures, intricate tectonics, Germany-sized seas of methane, water eruption "plumes" hundreds of kilometers high, gigantic mountains, objects that look like flying saucers, or in short: pictures of Saturn, its rings and its moons.

2017-12-21
11:15
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nn
Gergely Hajdu (ARI)
ARI Institute Kolloquium ( Hephysto link )
ARI Moenchhofstrasse 12-14, Seminarraum 1
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Abstract
nn

2018-01-08
11:15
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The Edge of Galaxy Formation: Simulating the smallest galaxies in our Universe
Jonas Frings (MPIA)
ITA "blackboard" Colloquium ( Hephysto link )
Philosophenweg 12, 106
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Abstract
The satellites of the Milky Way and Andromeda represent the smallest galaxies we can observe in our Universe. Because of the large range of mass and spatial scales it is quite challenging to resolve such objects properly in simulations. I will present a new hybrid method that we used to investigate satellites of Milky Way mass halos in hydrodynamical simulations and the effects of the satellite-host galaxy interaction that we can observe therein.

2018-01-09
16:15
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Nucleosynthesis and the origin of stardust grains
Maria Lugaro (Konkoly Obs., HU)
Philosophenweg 12, großer Hörsaal

2018-01-11
11:15
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nn
Clio Bertelli Motta (ARI)
ARI Institute Kolloquium ( Hephysto link )
ARI Moenchhofstrasse 12-14, Seminarraum 1
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Abstract
nn

2018-01-15
11:15
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Search for Dark Matter produced in association with a Higgs boson decaying to $b\bar{b}$ at the ATLAS detector
Daniel Narrias Villar (KIP)
ITA "blackboard" Colloquium ( Hephysto link )
Philosophenweg, 12, 106

2018-01-16
16:15
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Black hole mass growth across cosmic time: Insights from radio surveys
Vernesa Smolcic (Univ. Zagreb)
Philosophenweg 12, großer Hörsaal

2018-01-18
11:15
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nn
Carolin Wittmann (ARI)
ARI Institute Kolloquium ( Hephysto link )
ARI Moenchhofstrasse 12-14, Seminarraum 1
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Abstract
nn

2018-01-22
11:15
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The two worlds of photometric redshift estimation: feature-based and fully automatic models
Disanto Antonio (H-ITS)
ITA "blackboard" Colloquium ( Hephysto link )
Philosophenweg 12, 106
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Abstract
Redshift estimation is a fundamental task in astronomy. In particular, it serves as distance indicator in the cosmological field. As opposed to the expensive and time consuming redshift estimation via spectra, the use of photometry has emerged as a popular and practical alternative. In order to process the ever increasing number of sources, the use of machine learning methods has become mandatory. Manual feature extraction is the standard approach to train machine learning models. However, thanks to recent developments in GPU computing, it is now possible to perform massive feature selection, computing thousands of features combinations and selecting the best performing ones through a greedy forward selection scheme. On the other hand, the application of deep learning technologies and of convolutional neural networks allows estimating photometric redshifts directly from images, in a fully probabilistic way, precluding the need of pre-classification and feature extraction. In this framework, the process of feature extraction and selection is fully automatized. The success of several upcoming projects, such as the EUCLID mission, LOFAR, PANSTARRS and many more, requires the availability of highly affordable photometric redshifts. We believe that methods, along the ones presented here, will fulfill this requirement.

2018-01-23
16:15
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The circumgalactic medium of high redshift galaxies in emission
Lutz Wisotzki (Leibniz Institut für Astrophysik, Potsdam)
Philosophenweg 12, großer Hörsaal
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Abstract
I present observations with the MUSE instrument at the ESO-VLT that reveal the ubiquitous presence of extended Ly-alpha emitting envelopes around individual normal (non-AGN) galaxies at redshifts z > 3. These haloes are larger by factors of ~3-20 than the corresponding rest-frame UV continuum sources as seen by HST. Between ~20% and >~95% of the observed total Ly-alpha flux comes from the extended halo component. At the sensitivity level provided by MUSE, a large fraction of the field of view is actually covered with Ly alpha emission from redshifts 3 < z < 6, and I present a spectacular colour image visualising the "Sky in Ly-alpha". Our observations provide direct insights into the spatial distribution of at least partly neutral gas in the circumgalactic medium of low to intermediate mass galaxies at z > 3. I also discuss some implications for the demographics of high-redshift galaxies.

2018-01-25
11:15
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nn
Andreas Koch (ARI)
ARI Institute Kolloquium ( Hephysto link )
ARI Moenchhofstrasse 12-14, Seminarraum 1
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Abstract
nn

2018-01-29
11:15
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Chemical properties of Galactic open clusters
Clio Bertelli Motta (ARI)
ITA "blackboard" Colloquium ( Hephysto link )
Philosophenweg 12, 106
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Abstract
TBD

2018-01-30
16:15
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Black holes in the era of gravitational wave astronomy
Frans Pretorius (Perimeter Inst., Princeton, USA)
Philosophenweg 12, großer Hörsaal

2018-02-01
11:15
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nn
Fayezeh Shabani (ARI)
ARI Institute Kolloquium ( Hephysto link )
ARI Moenchhofstrasse 12-14, Seminarraum 1
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Abstract
nn

2018-02-06
16:15
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Gravitational-wave emission and their multi-messenger signatures
Alessandra Buonanno (MPI Gravitationsphysik, Potsdam)
Philosophenweg 12, großer Hörsaal

2018-02-08
11:15
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nn
Yasna Ordenes (PUC Chile,ARI)
ARI Institute Kolloquium ( Hephysto link )
ARI Moenchhofstrasse 12-14, Seminarraum 1
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nn

2018-02-12
11:15
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Improving star cluster survival with centrally peaked star-formation efficiency profile
Bekdaulet Shukirgaliyev (ARI)
ITA "blackboard" Colloquium ( Hephysto link )
Philosophenweg, 12, 106
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Abstract
We study the formation of the bound clusters after instantaneous gas expulsion, when the cluster forms with centrally peaked star-formation efficiency (SFE) profile. That means our embedded cluster has steeper density profile than that of initial and residual star forming gas at the time of gas expulsion. This is the consequence of star-formation proceeding with a constant SFE per free-fall time in centrally-concentrated spherically-symmetric molecular gas clump according to the local-density-driven cluster formation model by Parmentier and Pfalzner (2013). We assume our embedded cluster in virial equilibrium with the gravitational potential of whole clump (star+gas) at the time of gas expulsion. We perform a grid of direct N-body simulations, starting from instantaneous gas expulsion time with different global SFEs and cluster initial stellar masses. We found that the minimum global SFE needed to survive instantaneous gas expulsion is 13 percent for the isolated cluster and 15 percent for the cluster in the Solar Neighbourhood.

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