Monday Seminar for the year 2016

The presentations are shown in order of increasing time.

4-Jan-2016

 

No Seminar

11-Jan-2016

 

Andrew Cameron (2) and Monthly Discussion

chair: N. Porayko

Adventures in Space and Timing: The latest news from HTRU-S-LowLat

Pulsars, rapidly-rotating highly-magnetised neutron stars, are fantastic natural laboratories and allow for a wide range of fundamental scientific applications. To date, over 2500 pulsars have been found, and the search to find more is constantly ongoing, with the development of new surveys and search techniques pushing the boundaries of what we are able to observe and discover. In this talk, I will present an overview of and the latest progress from the High Time Resolution Universe South Low-Latitude (HTRU-S LowLat) survey, a highly sensitive survey taken using the 64m Parkes Radio Telescope in Australia, which represents the deepest large-scale pulsar search conducted in the Galactic plane region to date. This talk will involve highlighting some of the more interesting pulsars recently discovered as part of the survey, as well a brief exploration of some of the techniques involved in timing newly discovered pulsars.

18-Jan-2016

 

 SPECIAL! 1st Lab Visit: The Digital Lab of the MPIfR (Introduction: Prof. Bernd Klein) 

meeting place: Seminar Room 0.01

25-Jan-2016

 

 Vivien Thiel (1)

chair: A. Cameron

High-angular-resolution absorption studies along the line of sight of Sgr B2

The giant molecular cloud Sagittarius B2 (Sgr B2) in the Galactic center region is one of the most massive star forming regions in our galaxy. Due to the strong continuum emission in the millimeter wavelength regime it is possible to study the diffuse envelope of Sgr B2 and the diffuse molecular clouds along the line of sight to Sgr B2 in absorption. These diffuse molecular clouds are not well-known so far. Previous absorption line studies were performed with single-dish telescopes. For this project ALMA data are available, which have an one order of magnitude better resolution and sensitivity than the single-dish data used before. This unbiased interferometric line survey offers an excellent opportunity to study the small-scale physical and chemical structure of the diffuse molecular clouds and to improve our understanding of these structures.
In this talk I will give an overview over the project and present first results of the investigated molecules.

 

 

 

 

 

 

1-Feb-2016

 

Monthly Discussion

8-Feb-2016

 

Rosenmontag

15-Feb-2016

 

 F. Jaron

chair: V. Thiel

Radio characteristics of LS I +61 303

The stellar binary system LS I +61 303 is composed of a Be type star and a compact object of still unknown nature, i.e., either a black hole or a neutron star. This object features periodic emission all over the
electromagnetic spectrum, the physical processes responsible for the non-thermal emission still being a matter of debate. Because of the eccentricity of the orbit, the emission from this source is predicted
to be modulated by the orbital period P1 = 26.4960 +/- 0.0028 days, which has indeed been found in the radio emission along with another period, Plong = 1667 days, for which the responsible mechanism
remained unclear. Timing analysis of archived radio data reveals a period P2 = 26.92 +/- 0.07 days, close to the orbital one and compatible with the precession period of a jet determined from the
astrometry of VLBA images. The presence of these two periods, P1 and P2, has since been confirmed by other observations. The long-term period can consequently be explained as a beating between the orbital
modulation and the precession of a relativistic jet, giving rise to variable Doppler boosting. Further analysis of the radio data show that the radio outbursts indeed do not occur with P1 but with the
average period between P1 and P2, in agreement with the beating model, leading to a straightforward prediction of the radio outbursts of the source. A physical model of a self-absorbed jet, precessing with P2
and periodically refilled with relativistic particles every orbit (P1) reproduces the observed radio characteristics.

22-Feb-2016

 

A. Ridolfi (3)

Latest news from 47 Tucanae

chair: F. Jaron

Pulsars are fast rotating, magnetized neutron stars that turn out to be outstanding natural laboratories for testing fundamental Physics. Many of them are found in binary systems, with a great variety of companion types. Globular clusters (GCs), spherical groups of stars that are gravitationally bound, are very efficient pulsar binary "factories", thanks to their very high stellar densities which favor two- or three-body gravitational interactions. Many exotic binary systems are indeed seen in GCs. 47 Tucanae is a globular cluster in the southern hemisphere that ranks 2nd for the number of pulsars hosted, with 25 objects currently known. They all have spin periods of less than 8 ms, and the majority of them are found in binary systems. I will present a study of 4 amongst the faintest binary pulsars in 47 Tuc. Because of their faintness they turn out to be very difficult to detect and, thus, to investigate. I will show the techniques that have been used to search and detect them, as well as the results that we obtained. In particular, one of the pulsars, 47 Tuc X, is a very peculiar object compared to rest of the 47 Tuc pulsar population and will be discussed in detail.

29-Feb-2016

 

Special!: 2nd Lab Visit: The VLBI Korrelator, Introduction: Dr. H. Rottmann

 

 

 

 

 

 

 

 

 

7-Mar-2016

 

Monthly Discussion

14-Mar-2016

 

 Victoria Yankelevich (1)

chair: A. Ridolfi

Cosmology with the bispectrum

The last decades witnessed huge progress in understanding the large-scale structure of the Universe. While homogeneous and isotropic on the largest scales, the matter and galaxy distributions display complex patterns on smaller scales where we observe elongated filaments, compact clusters and volume-filling underdense regions. These features are not captured by studies of two-point statistics like the power spectrum that does not retain information on the phases of the Fourier modes of the density field. Therefore, higher-order statistics like the bispectrum should provide additional information. However, the potential of the bispectrum as a mean to extract additional cosmological information has never been explored. This work will be devoted to quantify this potential using the Fisher-matrix formalism.

Michal Zajacek (2)

Understanding the Galactic centre in a broader perspective

chair: V. Yankelevich

I will present recent results of my research of galactic nuclei. In the first part, I will provide an update about the monitoring of the Dusty S-cluster object (G2) that is observed primarily in near-infrared L (3.8 mikrons) and K bands (2.2 mikrons). This object exhibits a near-infrared excess and is moving on a highly-elliptical orbit (e=0.98) around the supermassive black hole associated with compact radio source Sgr A*. Its pericentre velocity has reached 6000 km/s and the distance from the black hole was only 150 AU (about 2000 Schwarzschild radii). The source remains compact in both continuum and emission in its post-pericentre phase. We also detect broad emission lines, in particular Br-gamma (2.17 mikrons), whose FWHM is of the order of 100 km/s. All these basic observational characteristics may be reconciled within a model of dust-enshrouded young star that can be still in an accretion phase that I will describe in a more detail. If the further monitoring confirms the character of the object, it will be the first star of different spectral type than B in the S cluster and the young age would confirm the theory of continuing star formation in the Galactic centre.

In the second part, I will summarize main results of the continuing project of analysing radio-optical properties of a sample of 400 galaxiess (joint SDSS-FIRST sample). In particular, I will discuss the radio spectral index distribution in the optical emission-line diagnostic diagrams. This project is complementary to the first, Galactic centre project, since it helps us to understand why our Galactic centre is currently underluminous and what the overall galaxy evolution may look like.

21-Mar-2016

 

Carlos Durán: 3rd  Lab-visit: The MPIfR Sub-mm Lab

28-Mar-2016

 

Easter Monday

 

 

 

4-Apr-2016

 

R. Angioni (1)

Multi-band studies of radio-loud AGN

Radio galaxies provide us with a way to study AGN jets which is not heavily affected by relativistic effects. Unfortunately, this also means that these sources are relatively faint at γ-ray energies, where they make up only 1-2% of all AGN detected by Fermi-LAT. This is to be compared with aligned, heavily Doppler-boosted radio-loud AGN (i.e. blazars), which are the dominant population. The recent implementation of the Fermi-LAT Pass8 data analysis holds substantial potential to expand the LAT radio galaxy sample.
In addition, the milliarcsecond radio structure of many southern-hemisphere radio galaxies, in particular, has been poorly studied so far.
During my PhD I am characterizing the milliarcsecond-scale properties of the radio galaxies in TANAMI, a monitoring program of extragalactic jets in the southern hemisphere which includes Very Long Baseline Interferometry (VLBI) monitoring and and extensive multi-wavelength coverage, including Fermi-LAT data. Using radio imaging, we obtain high-resolution maps at 8.4 and 22 GHz. By combining these, we also produce spectral index maps for our sources. Finally, we constrain characteristic source parameters like jet speed and inclination angle from multi-epoch imaging and kinematic analysis. This is the first systematic sample study of southern-hemisphere radio galaxies at high angular resolution.
I will also attempt to expand the γ-ray radio galaxy sample by analyzing LAT Pass8 data on a sample of candidate sources, with particular focus on the young sources in the TANAMI sample. Additionally, I will study the SED of the TANAMI AGN which are not detected in γ-rays, to search for common properties that might explain why they are still missed by the LAT.

& Monthly Discussion

11-Apr-2016

 

 Michael Mattern (2)

ATLASGAL filaments in SEDIGISM

chair: R. Angioni

It has been proposed that filaments in clouds are a crucial step towards star formation. Filaments are found within almost every molecular cloud. The current paradigm of star formation states a two-step process of clouds forming filaments fragmenting into dense cores, as the sites of star formation. However, the processes leading to filament formation and fragmentation are still not well understood. To fully understand the mechanisms in cloud evolution it is necessary to study a comprehensive, unbiased sample, which is provided by the ATLASGAL filament catalog (Li et al. submitted). This Galactic-wide catalog includes 517 filaments identified in the ATLASGAL 870 µm dust emission survey by the DisPerSE algorithm and are confirmed visually by 5 people.
 
The SEDIGISM survey covers about 300 filaments of the catalog and will trace the larger, diffuse structure of the filaments. This will allow us to connect them to the larger scale Galactic structure. With the 13CO data cubes we will be able to analyze the kinematic properties of these targets. It is important to verify whether structures identified in continuum maps are coherent in velocity. Additionally, we can estimate the distance, the physical size and the mass of the filaments, which will be used to determine the mass per unit length (m/l), which is a measurement of the gravitational stability. The critical line mass is estimated from the velocity dispersion sig_v, a measurement of the gas turbulence, which counteracts gravity (m/l)cr = 2sig_v^2/G. Also, we will search for extensions to the filaments in line emission. Starting with velocity components identified along the backbones traced by dust emission, we will search in position-position-velocity space around these components using friends-of-friends analysis.

18-Apr-2016

 

Fateme Kamali (2)


Radio Continuum of Water-Disk-Megamaser Galaxies

chair: M. Mattern

Water-disk-megamasers in the very central region of active galaxies, with the circumnuclear disk being viewed edge-on, provide a unique sample of targets for studying the accretion disk surrounding the super massive black holes.  In my PhD project we search for jets from the active galaxies where the water-disk-megamaser emission has been observed from the accretion disk. The goal is to investigate the nuclear environment of water-disk-maser and to relate the maser properties with those of the radio continuum.
Preliminary result of JVLA 33 GHz observations demonstrates that 87% of galaxies in our sample exhibit radio continuum emission at 4 sigma or higher level. The follow-up higher resolution observation of the detected sources will reveal the nature of these compact radio emissions.

Jae-Young Kim (1)

High-resolution VLBI study of the jet base of M87

chair: F. Kamali

Physical understanding of collimated relativistic jets emanating from the center of active galaxies is an integral part of the study of AGN.
The jet formation, acceleration of the outflowing plasma, and the high level of collimation are especially important issues regarding their origins and the evolution over long distances.  Nearby jet systems with massive black holes such as M87, Cygnus A, 3C 84, and NGC 1052 are the best laboratory to examine and provide supports for the theoretical model.  Now, regular operation of the global VLBI network at 3mm has made it possible to explore the physical conditions of the jet base at around 50 micro arc-seconds resolution.  Especially for M87, this resolution corresponds to only 6 Rsch, which is yet the highest spatial resolution achievable for any of jet systems harboring SMBHs.
In this talk, I will provide a brief review of previous studies about the jet in M87 and will present new results from a GMVA observation of M87 performed in May 2015.
Owing to the addition of the sensitive mm-VLBI telescopes, including both IRAM telescopes and the GBT, the observation reveals new details of the complex jet and core morphology.  The preliminary results from the observation will be discussed in the context of the ongoing PhD thesis project.

25-Apr-2016

 

 Ana Mikler (2)

Pressure Profile of Galaxy Clusters with the APEX-SZ Survey

chair J.-Y. Kim

Hundreds of galaxy clusters have been found trough recent Sunyaev-Zel’dovich (SZ) surveys. These surveys allow us to identify, in an unbiased way, galaxy clusters which are powerful tools for cosmological and dark energy studies. In this work we use the data from the APEX-SZ survey to study the generalised Navarro, Frank and White (gNFW) pressure profile that describes the galaxy clusters, assuming spherical symmetry and hydrostatic equilibrium. The survey observed X-ray selected targets permitting us  to carry on multi-wavelenght analyses on the future. Specifically we are looking to obtain a better method for retrieving information about the profile from the observations and to further constrain some of its parameters, specially the concentration parameter. For these purpose we use a Markov Chain Monte Carlo (MCMC) fitting of the data with the gNFW model. Currently, we are in the stage of modelling the data and the noise in order to understand the limits to which we can use the observations. Furthermore, we are testing the fitting of the parameters using (MCMC) in simulated data which mimics the original survey data.

F. Jaron

Physical processes behind the periodic emission from LS I +61°303

chair: A. Mikler

The X-ray binary LS I +61°303 consists of a Be type star and a compact object. Bondi-Hoyle accretion along the eccentric orbit of the system is predicted to peak twice, once at periastron and once towards apastron. Radio outbusts occur once per orbit during phases around apastron, and modulated by two periods P1 = 26.5 d and P2 = 26.9 d. P1 is associated to the orbit, P2 is the precessing period of a relativistic jet. Timing analysis of GeV data from Fermi-LAT observations results in the periastron data to be modulated by the orbital period P1, while the apastron emission is modulated not only by P1 but also by the slightly larger P2. In the first part of the talk, I will present a physical model of a precessing conical jet (P2), periodically refilled with relativistic particles (P1) twice along the orbit. We find that the timing characteristics of the GeV emission are reproduced by the model, the jet velocity at periastron resulting to be significantly smaller than at apastron. In the second part of the talk, I will report on radio observations of LS I +61°303 at 5, 8, and 10 GHz with the 100-m telescope in Effelsberg covering the decline of a radio outburst. I will present results on short-term variability on time-scales of ~10 hours.

 

 

 

2-May-2016

 

Monthly Discussion

9-May-2016

 

 A. Schootemeijer (1)

SMC Wolf-Rayet stars as products of chemically (quasi-)homogeneous evolution

chair: F. Jaron

Theory predicts rotational mixing in massive stars. Rapid rotation can cause mixing of the inner and outer layers in stellar models of some tens of solar masses and more. As a result, these chemically (quasi-)homogeneous stars remain hot and compact during their evolution, in contrast to slow rotators which are known to expand and cool. Perhaps the most intriguing implication of chemically homogeneous evolution is that through this channel, two massive stars in a close binary could evolve into a close black hole binary that can merge within a Hubble time. This makes this channel a possible progenitor of GW150914.
However, unambiguous observational evidence of rotational mixing is still absent. The aim of this project is to test the theory of rotational mixing on the Wolf-Rayet stars in the Small Magellanic Cloud. These stars are candidates for rotational mixing since they are hot, luminous and hydrogen-depleted.

Jason Wu (3)

Gamma-ray pulsar survey among 3FGL unidentified sources with Einstein@Home

chair: A. Schootemeier

The Third Fermi Large Area Telescope (LAT) Point Source Catalog (3FGL) describes the properties of 3033 gamma-ray sources detected in the 100 MeV - 300 GeV range. The 3FGL catalog is based on the first four years of science data from the Fermi LAT, the main instrument of the Fermi satellite. Over one third of the catalogued sources do not have obvious counterparts at other wavelengths, which are thought to be mainly AGNs or Pulsars. Over the course of its seven-year mission, the LAT detected more than 200 pulsars in gamma-rays, revolutionizing pulsar astronomy. While the majority of these pulsars were first found in radio, 40 of them have been discovered through blind searches of the LAT data. A list of 118 unidentified Fermi LAT sources from the 3FGL catalog was constructed based on the known gamma-ray emission properties of pulsars and using the Machine Learning algorithm - Gaussian mixture model. The list provided the seeds for a gamma-ray pulsar blind search survey using the Einstein@Home volunteer computing system, in collaboration with the Albert Einstein Institute (AEI) in Hanover. In this talk I will summarizes the survey and new gamma-ray pulsars found in this survey.

16-May-2016

 

Pfingstmontag

23-May-2016

 

 N. Grin (1)

The Mass Discrepancy in Massive Stars

chair: Jason Wu

Massive stars are powerful cosmic engines that, through their strong stellar winds and explosive final deaths provide important feedback to their immediate environment. The evolution of stars on the main-sequence (the core hydrogen-burning phase) is determined by their initial mass, and as such it is important to be able to estimate the masses of observed stars. Several methods are employed for this purpose, however, they tend to disagree. Specifically, the evolutionary mass, where one compares evolutionary computations with observed quantities, is systematically higher than the spectroscopic mass, where one measures the surface gravity from the spectrum yielding a mass estimate. Sometimes this discrepancy between the masses amounts for over a factor 2. We explore from the theoretical side how to alter evolutionary computations to reconcile the two mass estimates. In a preliminary study, we find that it is very difficult to explain the discrepancy as being a consequence of uncertain input physics such as mass-loss and convective-overshooting. It may well be possible that alternative explanations such as binary evolution have to be invoked in order to alleviate the situation.

30-May-2016

 

 Elvijs Matrozis (3)

Evolution of carbon-enhanced metal-poor stars with rotation

chair: N. Grin

About 20% of all metal-poor stars in the Galaxy are enriched in carbon, most of which also show enhanced s-process element abundances. Radial velocity measurements are consistent with all of these so-called CEMP-s stars being in binaries, suggesting that binarity factors in their abundance anomalies. Thus, the currently preferred model for explaining these anomalies is mass accretion from an asymptotic giant branch (AGB) companion. Surface abundances of CEMP-s stars are therefore often used to infer the nucleosynthesis occurring in low-metallicity AGB stars, which played an important role in the chemical evolution of galaxies and stellar clusters. To infer the processes in the AGB star in this way, the extent and nature of mixing of the accreted material in the secondary has to be understood. In this talk I will discuss some of the mixing mechanisms that should be operating in CEMP-s stars and their impact on the stars' surface abundances. In particular, I will show that models with atomic diffusion predict abundances that are clearly at odds with observations, demonstrating that we must be missing a crucial piece of the puzzle. Finally, I will sketch how stellar rotation might help reconcile the models with observations.

 

 

 

 

 

 

 

 

 

6-June-2016

 

Monthly Discussion

13-June-2016

 

 Mélisse Bonfand (1)

Exploring Molecular Complexity with ALMA: Characterizing the hot core population in Sgr B2(N

chair: E. Matrozis

Located close to the Galactic center, Sagittarius B2 (Sgr B2) is one of the most prominent high-mass star-forming regions in our Galaxy. Thanks to its immense column density, it is also one of the best targets to search for Complex Organic Molecules (COMs) and probe interstellar chemistry. The search for COMs is mainly motivated by the discovery  of amino acids (building blocks of proteins) in meteorites fallen to Earth. Today the pathways that lead to the formation of such molecules are still not completely understood. The aim of my PhD project is to use the high sensitivity of ALMA to better characterize the star formation process in Sgr B2(N) investigating the detected COMs.
This talk will report the discovery of three new hot cores in the Sgr B2 region and I will explain how to characterize these star-forming cores investigating their chemical composition.

20-June-2016

 

 Carlos Durán (1)

4Great : When SOFIA meets HERSCHEL

chair: M. Bonfand

The German REceiver for Astronomy at Terahertz frequencies has been successfully in service onboard SOFIA since 2011. GREAT, with its modular approach, is composed of a group of cryostats containing detectors for different frequency bands between 1.25 and 4.7 THz. Individual cryostats are then grouped in pairs.
 
4GREAT, a new member of the GREAT constellation, is a four-color single-pixel-detector. Two channels, CH1 and CH2, are implemented using spare mixers of Herschel-Heterodyne Instrument for the Far-Infrared: HIFI-channel 1 (492– 635 GHz) and HIFI-channel 4 (892-1100 GHz). The third channel makes use of the current GREAT L1 detector, while the fourth covers the frequency range of GREAT L2, using one of the upGREAT LFA spare mixers. All channels are all co-aligned on sky in a single closed cycle cooled cryostat.

This four color instrument offers the possibility to observe several lines, including multiple transitions from the same molecule simultaneously, which is necessary to better constrain the physical conditions. Some of the potentially interesting transitions include Ammonia, (NH3), Carbon monosulfide (CS), the Methylidyne radical (CH), Hydroxyl (OH), and Carbon Monoxide (CO and 13CO) among many others.

When 4GREAT will be fully integrated by Q2-2018, it will offer a compact and powerful system. It could be used simultaneously with GREAT-M or upGREAT-HFA.

Jackie Ma (1)

Broadband Radio Polarimetry of Magnetised Gas --- from Local Universe to Active Galactic Nuclei

chair. C. Durán

The NVSS Rotation Measure (RM) Catalogue (Taylor et al. 2009) presents the RMs of over 37,000 polarised sources, serving as an invaluable window to the study of both Galactic and extragalactic magnetic fields. The results in the catalogue were derived from measurements at two closely separated bands at about 1400 MHz. Despite efforts to minimise the effect of the nπ-ambiguity using depolarisation information and the median RM values in surrounding regions, the nπ-ambiguity may not yet be completely ruled out. A plausible consequence is that the listed RM values of some of the sources could deviate from the true value by several hundreds of rad m-2, and this can propagate to magnetic field studies that are based on the NVSS RMs.

From this vast sample, we have selected a small set of 23 extragalactic sources that are away from the Galactic plane (|b| > 10°) and with high NVSS |RM| (> 300 rad m-2). We observed them with the Karl G. Jansky Very Large Array (JVLA) with the upgraded broadband receiver in L-band (1-2 GHz) to verify their RM values. In this talk, I will present the preliminary results of this study.

27-June-2016

 

 M. Tiwari (1)

Unveiling the remarkable PDR of M8 and its link to Diffuse Interstellar Bands

chair: Jackie Ma

The study of photodissociation dissociation regions (PDRs) is the study of the effects of stellar farultraviolet (FUV) photons on the structure, chemistry, thermal balance, evolution of the neutral interstellar medium of galaxies and understanding the process of star formation. Also, they are good searching grounds for the carriers of diffuse infrared bands (DIBs). The most suspected carriers of DIBs are the polycyclic aromatic hydrocarbons (PAHs). PAHs are suggested to undergo fragmentation to smaller hydrocarbons when exposed to high energy FUV photons which might be responsible for some of the observed DIBs. We intend to do a comprehensive survey of Messier 8 which is one of the brightest PDRs in our galaxy with APEX, IRAM 30m and SOFIA telescopes. Our aim is to characterize M8 as a PDR and to find an explanation to the observed DIBs along it. In this talk, I will introduce my project and will present the preliminary results of this study.

Ka Tat Wong (3)

Resolving the extended atmosphere and the inner wind of the AGB star Mira (omicron Ceti) with long ALMA baselines

chair: M. Tiwari

The dust condensation sequence and physical conditions close to the stellar photosphere in oxygen-rich asymptotic giant branch (AGB) stars are still poorly understood. The high angular resolution and high sensitivity offered by the Atacama Large Millimeter/submillimeter Array (ALMA) allow us to probe the dust formation zone and the extended atmosphere of evolved stars at an unprecedented detail.

I will present the ALMA Science Verification observation of the AGB star, omi Cet (Mira), in the 2014 ALMA Long Baseline Campaign. The long ALMA baselines up to 15 km produce images of SiO and H2O emission/absorption at an angular resolution of ~30 mas at 220 GHz, which clearly resolve the wind of this prototypical Mira variable within the dust condensation radius. Very unique in the dataset is that molecular transition lines are seen in absorption towards the continuum source, allowing detailed studies of the physical conditions and chemistry along the line of sight. I have modelled the 28SiO J=5-4 v=0, 2 and H2O ν2=1 J(Ka,Kc)=5(5,0)-6(4,3) emission and absorption. In this talk, I will focus on comparing our models with existing hydrodynamical models of dynamic atmospheres and current knowledge on the dust condensation process of oxygen-rich AGB stars.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4-July-2016

 

Monthly Discussion

11-July-2016

 

 Nina Brinkmann (1)

The physical and chemical conditions of molecular clouds on large scales

chair: Ka Tat Wong

With a distance of just ~ 414 pc, OMC-1 offers the opportunity to differentiate in a complex high-mass star forming cloud several, physically distinct regions, such as PDRs, outflows and the well-studied Orion Hot Core. The diverse conditions are distinguishable through variations in molecular content and excitation, but also through line shapes and velocities. I present APEX observations with the new PI230 receiver and give a first impression of the chemical diversity towards this prominent high-mass star forming region. I will also give an overview of some of the characteristics of the PI230, as it will soon become available to all observers.

Dominik Klaes (3)

Weak lensing with XCS galaxy clusters in KiDS


chair: Nina Brinkmann


Galaxy clusters are the most massive structures in the universe with typically M_200 = 10
^14
 - 10
^15
 M_sol. As they are tracers for the matter distribution in our universe, they are very sensitive to the underlying cosmology. While the mass estimation via e.g. X-Ray (cluster gas) is biased and only about 9% of the mass is measured, weak lensing, the bending of light by matter, is insensitive to the actual type and state of matter (gas, dark matter, ...) and thus can deliver an unbiased mass estimate. On the other side, the weak lensing signal is noisy and thus we need to carefully process the optical data of the Kilo Degree Survey (KiDS) and can only calculate the cluster masses statistically via an ensemble of galaxy clusters. I will present the ongoing work towards the mass estimation via weak lensing, combining the cluster candidates from the XMM-Newton Cluster Survey (XCS), weak lensing shear information and photometric redshifts of the clusters and background galaxies, both from KiDS. Furthermore I will introduce our "blinding scheme"

14-July-2016

Special! Lab Visit to Effelsberg. 9:30 by bus. Meeting at the MPIfR main entrance.

18-July-2016

 

 E. Garaldi (1)

The role of quasars in Cosmic Reionization

chair: Dominik Klaes

The Epoch of Reionization (EoR) is one of the least understood period in the evolution of the Universe, due to severe observational challenges. For this reason analytical and numerical modeling play a fundamental role in extracting informations from the handful of observational constraints currently available. The debated topic of the first sources of Reionization will be addressed, with particular focus on the role of quasars. I ran a suite of cosmological simulations that include radiative-transfer, allowing a realistic and self-consistent treatment of the quasars as the only source of Reionization as well as to produce realistic mock observations to compare with real data. In this talk I will give an overview of the current knowledge about the Epoch of Reionization and present some results from the numerical simulations.

25-July-2016

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1-Aug-2016

 

Monthly Discussion

8-Aug-2016

 

 Joey Martinez (2) & Laura Vega Garcia (1)

15-Aug-2016

 

HOLIDAYS

22-Aug-2016

 

HOLIDAYS

29-Aug-2016

 

HOLIDAYS

 

 

 

 

 

 

 

 

 

 

 

 

5-Sept-2016

 

Monthly Discussion

12-Sept-2016

 

 Marzieh Parsa (2)

chair:

The relativistic motion of stars near super-massive black hole in the Galactic center

The S-stars, the Galactic Center cluster of high velocity stars, have provided us with a laboratory for investigating general relativistic effects. One of the brightest stars in this cluster is S2 with a short period of 15.9 years and a periapse velocity of 0.02 in units of speed of light. Such a high velocity makes the periapse precession to be observable in the upcoming periapse of the star in 2017.9. It is believed that there are many fainter stars within the orbit of S2 to be discovered in near future. These stars will have smaller periapse passage and are consequently more relativistic. In our study, first we aim at finding the gravitational potential parameters of the super-massive black hole at Galactic center using the orbit of three stars simultaneously. Then we simulate the motion of example stars within the orbit of S2 with different semi-major axes and eccentricities using post-Newtonian approximation in order to probe relativistic effects.

19-Sept-2016

 

 Maja Kierdof (2)

chair: tbd

Probing the Magnetized Medium of AGNs using Wideband Polarimetry

Wideband radio polarimetry is a powerful tool to reveal magnetic fields on different scales in different environments: in galaxies and in Active Galactic Nuclei (AGNs). I will introduce RM synthesis and QU-fitting which are excellent tools to interpret wideband polarization data. The aim of my thesis is to use new polarization data with a wide frequency coverage and these tools to map magnetic fields near and far in order to shed new light on the origin of cosmic magnetism. I observed polarized emission from unresolved point sources, selected from the NVSS catalog which seems to have very high fractional polarizations (> 30%). Except for the high degree of polarization, those sources appear to have normal AGN properties. Therefore, they could represent a class of sources with very well ordered magnetic fields. For this, I am conducting a deep, high resolution, broad band polarization survey of around 80 of those sources to make one more step towards understanding the origin of the unusual high degree of polarization. Understanding the intrinsic polarization properties of these objects are crucial since these unresolved point sources are used as background probe of intervening systems in these so-call RM grid experiments.

Eric Faustino (1)

chair: Maja Kierdorf

MOLECULAR GAS IN AZTEC/C159: A STAR-FORMING DISK GALAXY 1.3GYR AFTER THE BIG BANG

The nature of the star formation in high-redshift galaxies remains an open issue. Observational studies of the molecular gas, which fuels the star formation in these galaxies, are paramount to understand galaxy evolution at early cosmic times. We report the detection of CO molecular line emission from the active star forming disk galaxy AzTEC/C159 at z = 4.56702. We secured line detections for the transition levels J =2−1 and J =5−4 using the NRAO Very Large Array (VLA) and the NOEMA (NOrthern Extended Millimeter Array) interferometer, respectively. Its star formation efficiency (SFE) is at least five times higher than that of local spiral galaxies and z ∼0.4−2 Main Sequence galaxies, but similar to those observed in sub-mm selected galaxies. Its CO spectral line energy distribution suggests that this is an unusually high excited galaxy, where the CO(5−4) integrated line flux is only 12% lower than expected for thermal excitation. If, indeed, AzTEC/C159 is not a merger-driven system, our results give evidence that the cold mode accretion can drive star formation as efficiently as observed in high-z starburst galaxies.

26-Sept-2016

 

 Joseph Kuruvilla (1)

chair: Eric Faustino

Redshift-space distortions: Perspectives on streaming model

Peculiar velocities modify the observed redshifts of distant galaxies thus introducing distortions in all statistical measures of the reconstructed large-scale structure. These distortions are in general complex to model. For the first part of this work, we use N-body simulations to test the nature of one of the popular model known as the streaming model. In the latter part, we introduce the Hyperbolic streaming model. This is particularly interesting as the new model works better than the currently used Gaussian streaming model on all scales, thus paving a way to derive a deeper understanding of redshift-space distortions.

C. Chidiac (1)

chair: J. Kuruvilla

Dense gas in nearby galaxies

The galaxies M 82 and IC 342 are the two most prominent molecular lighthouses in the northern Hemisphere. M 82 is a late type starburst galaxy,
while IC 342 is a barred spiral galaxy, like the Milky Way,  seen face-on. These two galaxies show similar characteristics to the Milky Way.
However, the star formation in these three galaxies is very different. They exhibit different chemical fingerprints that reflects different
star formation stages. Their chemistry is complex and different. This work aims to map the innermost few hundreds pc of M 82 and IC 342, covering
the entire 3-mm range in order to get a complete spatially resolved inventory of the molecular content of galaxies, which is still missing.
Moreover, using the Principle component analysis (PCA), we will study the kinematics of the lines found in the survey. Finally, we will further
investigate the possible NH3 maser emission that is observed in IC 342. This work will help us identify the different chemistries in these
galaxies and associate them with different locations, as well identify reliable indicators or tracers of star formation.

 

 

 

 

 

 

 

 

 

 

 

 

3-Oct-2016

 

Tag der deutschen Einheit (Day of German reunification)

10-Oct-2016

 

Monthly Discussion 

17-Oct-2016

 

 No seminar

24-Oct-2016

 

 

31-Oct-2016

 

  Jens Erler (2)

chair: C. Chidiac

Planck's view on the spectrum of the Sunyaev-Zel'dovich effect (II)

The Sunyaev-Zel'dovich effect (SZE) is a powerful tool to study galaxy clusters through their hot intracluster medium. Its signal is not dimmed with redshift and is proportional to the line of sight integral of the electron pressure of the gas, i.e. the product of electron density and temperature. In its relativistic formulation, corrections to the spectral shape of the effect introduce a temperature dependence, which beaks the degeneracy between electron density and temperature, allowing a complete thermodynamical description of the intracluster medium similar to X-ray observations.
Although the relativistic corrections have been known for almost 40 years, no robust measurement has been made so far. My work focuses on an attempt to detect these corrections with data from the Planck mission. With its nine frequency channels, Planck allows to probe the entire spectrum of the SZE. Of particular interest are the high frequencies (353 to 875 GHz) that are difficult to access from the ground but where the relativistic corrections are particularly strong. The main challenge is to account for the different galactic and extra-galactic foregrounds. My work aims to quantitatively demostrate the possibilities and limitations of current generation instruments, as well as future instruments like the Cerro Chajnantor Atacama Telescope Pathfinder (CCATp).

 

 

 

 

 

 

 

 

 

7-Nov-2016

 

Monthly Discussion

14-Nov-2016

 

 Elaheh Hosseini (1)

Near Infrared Observations of faint sources in the Galactic Center

chairing: Jens Erler

The Galactic Center (GC) is the closest laboratory to study galactic nuclei. There are some faint sources close to the Super Massive Black Hole (SMBH) at the center of our galaxy such as the DSO/G2 and OS1. There are different theories about the nature of these sources, and their importance lies in the fact that they are detected within the inner tenth of a parsec of the GC. We are going to probe for these sources in different wavelengths to help understand them better, and study their interaction with their surroundings and the central black hole, Sgr A*.

Eleni Graikou (3)

High precision pulsar timing

chairing: E. Hosseini

Pulsars - a special kind of neutron starts, emits periodic -- or repeating -- bursts of radio waves, X-rays or gamma rays. Millisecond pulsars, a subset of the pulsar population, having a rotational stability compared to atomic clocks, are ideal for studying a wide range of physical and astrophysical phenomena, which allow us to investigate the interstellar medium and test theories of gravity. In this talk I will present how by using timing (the precise measurement of the exact time that the signal of pulsars arrives to Earth) we can understand the evolution of PSR J1933–6211: a millisecond pulsar with a white dwarf companion and investigate the emission beam geometry in the double neutron star system PSR B1913+16 by studying the geodetic precession.

21-Nov-2016

 

 Conversation with new students

28-Nov-2016

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5-Dec-2016

 

Monthly Discussion

12-Dec-2016

 

 Ann Kathrin Baczko (1)

19-Dec-2016

 

 Elaheh Hosseini (1)

26-Dec-2016

 

2nd Christmas Holiday

 
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