Ruprecht-Karls-Universität Heidelberg
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


2018-01-16
16:15
Add to calendar (ics)
Black hole mass growth across cosmic time: Insights from radio surveys
Vernesa Smolcic (Univ. Zagreb)
Heidelberg Joint Astronomical Colloquium ( Home pageHephysto link )
Philosophenweg 12, großer Hörsaal
Show/hide abstract

Abstract
Understanding how galaxies form and evolve through cosmic time, and how these processes are influenced by active galactic nuclei (AGN) are important goals of modern astrophysics. In this context, “radio-mode AGN feedback” is a regular ingredient in cosmological models, yet from an observational perspective still rather poorly understood. It is considered to be a key feedback mechanism, related to central supermassive black hole mass growth, at work in the latest phases of massive galaxy formation, and controlling the galaxy’s stellar mass build-up. Over the past decades our understanding of radio AGN was significantly advanced by panchromatic look-back sky surveys, and we have recently entered a “golden age” of radio astronomy thanks to upgraded and new facilities delivering now an order of magnitude increase in sensitivity. The VLA-COSMOS 3 GHz Large Project is based on 384 hours of observations with the upgraded, Karl G. Jansky Very Large Array (VLA) at 3 GHz (10 cm) toward the two square degree COSMOS field. The survey, reaching a median rms of 2.3 uJy/beam over the two square degrees at an angular resolution of 0.75′′, contains 10,830 radio sources down to 5 times the rms. It simultaneously provides the largest and deepest radio continuum survey at such angular resolution to-date, bridging the gap between last-generation and next-generation radio surveys. These radio data, in conjunction with the panchromatic COSMOS data sets, allowed us to study the physical properties, composite nature (i.e., star-formation vs. AGN related contributions to the total radio emission of the sources), and cosmic evolution of radio AGN out to a redshift of about 6, which can directly be linked to the radio-mode feedback, as postulated in cosmological models.

2018-01-18
11:15
Add to calendar (ics)
Were the most compact and most diffuse stellar systems in galaxy clusters both formed by tidal stripping?
Carolin Wittmann (ARI)
ARI Institute Kolloquium ( Hephysto link )
ARI Moenchhofstrasse 12-14, Seminarraum 1
Show/hide abstract

Abstract
We use deep optical wide field imaging data of the nearby Perseus and Fornax galaxy clusters to analyse the most compact and most diffuse stellar systems for signs of tidal stripping. In the Fornax cluster core we examine a population of spectroscopically confirmed ultra-compact dwarf galaxies (UCDs) and probe whether they could be the remnant nuclei of destroyed nucleated early-type dwarfs. Although we do not detect diffuse tidal debris around any of the UCDs, a significant fraction of our sample exhibits distorted outer structures. In the core of Perseus we identify a population of low-surface brightness dwarf galaxy candidates of the kind named 'ultra-diffuse galaxies'. We investigate whether they show signs of current tidal disruption or whether they might be protected by a large dark matter content. Our sample seems surprisingly intact, with only very few candidates showing possible signs of current disruption. We discuss the importance of tidal stripping for the formation of both the compact and the diffuse cluster populations by comparison to the predicted timescales and frequency of disruption events from simulations.

2018-01-22
11:15
Add to calendar (ics)
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
Show/hide abstract

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
Add to calendar (ics)
The circumgalactic medium of high redshift galaxies in emission
Lutz Wisotzki (Leibniz Institut für Astrophysik, Potsdam)
Heidelberg Joint Astronomical Colloquium ( Home pageHephysto link )
Philosophenweg 12, großer Hörsaal
Show/hide abstract

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
Add to calendar (ics)
nn
Andreas Koch (ARI)
ARI Institute Kolloquium ( Hephysto link )
ARI Moenchhofstrasse 12-14, Seminarraum 1
Show/hide abstract

Abstract
nn

2018-01-29
11:15
Add to calendar (ics)
Chemical properties of Galactic open clusters
Clio Bertelli Motta (ARI)
ITA "blackboard" Colloquium ( Hephysto link )
Philosophenweg 12, 106
Show/hide abstract

Abstract
TBD

2018-01-30
16:15
Add to calendar (ics)
Black holes in the era of gravitational wave astronomy
Frans Pretorius (Perimeter Inst., Princeton, USA)
Heidelberg Joint Astronomical Colloquium ( Home pageHephysto link )
Philosophenweg 12, großer Hörsaal
Show/hide abstract

Abstract
Black holes are one of the more astonishing predictions of the theory of General Relativity. The Schwarzschild black hole solution was discovered within months of Einstein publishing the field equations of general relativity, though for decades after was regarded more as a mathematical curiosity than a plausible description of any real object in the universe. This began to change in the 1960's, both through theoretical and observational discoveries, and finally in 2015 the LIGO gravitational wave detectors found the first direct evidence for the existence of black holes, having measured a signal consistent with the inspiral and merger of two black holes. In this talk I will give an overview of black holes in general relativity, the LIGO observations, and what we can hope to learn about black holes in the coming decade as a plethora of new data is gathered from ground based gravitational wave detectors, the Event Horizon Telescope, and pulsar timing arrays.

2018-02-01
11:15
Add to calendar (ics)
nn
Yasna Ordenes (PUC Chile, ARI)
ARI Institute Kolloquium ( Hephysto link )
ARI Moenchhofstrasse 12-14, Seminarraum 1
Show/hide abstract

Abstract
nn

2018-02-06
16:15
Add to calendar (ics)
Gravitational-wave emission and their multi-messenger signatures
Alessandra Buonanno (MPI Gravitationsphysik, Potsdam)
Heidelberg Joint Astronomical Colloquium ( Home pageHephysto link )
Philosophenweg 12, großer Hörsaal
Show/hide abstract

Abstract
The detection of gravitational waves has opened a new era of scientific discovery, as it permits a new kind of observation of the cosmos, quite different from electromagnetic and particle observations. In this talk I will review the gravitational-wave signals detected up to now by LIGO and Virgo, and discuss the theoretical groundwork that allows to identify and interpret those signals. I will also highlight how those new astronomical messengers are unveiling the properties of the most extreme astrophysical objects in the universe and probe fundamental physics.

2018-02-08
11:15
Add to calendar (ics)
nn
Fayezeh Shabani (ARI)
ARI Institute Kolloquium ( Hephysto link )
ARI Moenchhofstrasse 12-14, Seminarraum 1
Show/hide abstract

Abstract
nn

2018-02-12
11:15
Add to calendar (ics)
Improving star cluster survival with centrally peaked star-formation efficiency profile
Bekdaulet Shukirgaliyev (ARI)
ITA "blackboard" Colloquium ( Hephysto link )
Philosophenweg, 12, 106
Show/hide abstract

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.

Editor: Webmaster
zum Seitenanfang/up