9-Jan-2012
Zahra Sheikbahaee (2)
Three dimensional Weak Gravitational Lensing Study from COMBO17 Survey
Chair: E. Angelakis
Abstract:
I will present the preliminary results of our weak lensing analysis of a field of two super clusters from the Wide Field Imager at the MPG/ESO 2.2-m telescope at La Silla, Chile. Our goal is to acquire information
regarding the underlying matter distribution along the line of sight extending up to redshifts $z\sim0.3$. One important requirement of the analysis is an accurate determination of the photometric redshifts for the galaxy samples. Decreasing the redshift uncertainty improves the pinning the structures down in the radial direction. We exploit the photometry information from seventeen bands to obtain a more adequate measurement of the photometric redshift. The spurious effects of noise in the weak lensing data is reduced in our analysis by making presumption in our analysis about the structures along the line of sight. We apply a three dimensional discrete halo model which postulates all masses were encapsulated inside a set of haloes. This method computes the Bayesian evidence of the number of haloes needed to describe the three dimensional matter density field.
16-Jan-2012
Sameera Salim (2)
SED Fitting analysis of (sub)millimeter galaxies in the COSMOS-LABOCA survey data
Chair: Zahra Sheikbahaee
Abstract:
Submillimeter galaxies are dust obscured starburst gaaxies at high redshift and are thought to be the main contributors to the cosmic star formation rate density at these redshifts. Since the available single dish
telescopes have a poor resolution,its comparatively difficult to identify counterparts precisely at other wavelengths and to take up subsequent analysis of their physics. In my talk I will concentrate on the various methods to pinpoint counterparts especially the new method we are testing-SED fitting technique, of our recently finished LABOCA 0.87mm COSMOS field survey data.
23-Jan-2012
Fujun Du (3)
Production of interstellar hydrogen peroxide (H2O2) by grain chemistry
Chair: Sameera Salim
Abstract:
I will first give a short introduction to astrochemistry, and then describe my work on modeling the formation of hydrogen peroxide (H2O2) in grain chemistry, which was recently first detected in the interstellar medium towards rho Ophiuchus A.
30-Jan-2012
Monthly Discussion +
6-Feb-2012
Guang-Xing Li (2)
Molecular Outflow as an Entrainment Phenomenon
Chair: Fujun Du
Abstract:
We propose a wind-driven turbulent model for outflow from protostars. We consider the interaction between the wind from the central protostar and the turbulent envelope, and the outflow is the turbulent entrainment layer that is developed between the wind and the envelope. The turbulence of the interstellar medium plays important role in our model by shaping the outflow cavity and by aiding the mass-growth of the outflow. Our model show promising morphology and kinematic structure. It can explain the de-collimation of outflow with time and is physically consistent in the sense that the dynamical effect of supersonic turbulence, which have been neglected in the wind-driven shell model, is taken into account. Further observational tests are discussed.
13-Feb-2012
Fangchun Liu (3)
Title is Water deuterium fractionation in the high-mass hot core G34.26+0.15
Chair: Guang-Xing Li
Abstract:
Water is the main component of the ice mantles of dust grains and thus becomes a unique probe of the warm gas in star-forming cores, where ices evaporate. However, it is almost impossible to observe it from the ground. By measuring the distribution of the deuterium fractionation of water (HDO/H2O), we could trace the distribution and distinguish between the different pathways: grain surface chemistry or high temperature gas chemistry (HDO/H2O is expected to be low for hot chemistry). In this talk, I will present our HDO study towards the high-mass hot core G34.26+0.15. We used the 1-D radiative transfer code RATRAN with two different physical profiles to analyzed five HDO transitions observed with the APEX and SMA.
20-Feb-2012
Rosenmontag
27-Feb-2012
Monthly Disussion
Maryam Habibi (1)
The extinction map of the Arches starburst cluster in the Galactic center
Chair: Fangchun Liu
Abstract:
The Galactic center is the most active site of star formation in the Milky Way Galaxy, where particularly high-mass stars have formed very recently and are still forming today. However, since we are looking at the Galactic center through the galactic disk , knowledge of extinction is crucial to study the region. The Arches cluster is a young, massive starburst cluster, near the Galactic center.
We look at the Arches cluster in a wider area around the core using Ks band imaging data obtained with NAOS/CONICA at the VLT combined with Subaro/Cisco J band data to obtain the extinction map of the Arches cluster. We established the importance of extinction knowledge by deriving the individual extinction values and masses by assuming two commonly used extinction laws presented by Rieke & Lebofskey (1985) and Nishiyama et al.(2009). We show that the difference can reach up to 30% in extracted initial mass and 0.93 magnitude in acquired k band extinction ,corresponding to a visual extinction difference of up to 10 mag, while the initial mass function slope does not change dramatically.
5-Mar-2012
Natasa Tsitali (2)
The dynamical state of the ‘ First Hydrostatic Core Candidate’ Cha-MMS1
Chair: E. Angelakis
Abstract:
A 870 micron LABOCA survey of Chamaeleon I has revealed a population of approximately 60 starless cores. A discovery of a very young source in one of these cores has led us to investigate whether it could be at the phase of the ‘ first hydrostatic core’ (FHSC), the missing link between the pre-stellar and the Class 0 (protostar) phase in the low-mass star formation scenarios. We look at the dynamics and kinematics of this source using heterodyne observations and employ radiative transfer models in order to determine its physical characteristics. So is this object a FHSC and will it help us shed some light into this, theoretically predicted, short-lived phase of star formation?
12-Mar-2012
Lisa Zimmermann (2)
19-Mar-2012
Sandra Burkutean (2)
Sunyaev-Zel'dovich observations of galaxy clusters
Chair: Lisa Zimmermann
Abstract:
In this talk I will discuss how multi-wavelength observations of galaxy clusters will help to constrain their 3D triaxiality. Particular emphasis will be put on the Sunyaev Zel'dovich effect and its use in constraining
the pressure profile of the intra-cluster gas. The Sunyaev-Zel’dovich effect in galaxy clusters is caused by inverse Compton scattering of Cosmic Microwave Background photons off thermal electrons in the intra-cluster gas. In the light of a newly accepted proposal, I will also present a discussion on the combination of bolometric APEX-SZ data with interferometric measurements.
Rebekka Schmidt (2)
Probing AGN physics via broad-band monitoring of gamma-ray blazars
Chair: Lisa Zimmermann
Abstract:
The F-GAMMA program (Fermi-GST AGN Multi-frequency Monitoring Allicance) is a highly coordinated effort to probe the AGN physics via multi-frequency monitoring studies. It observes monthly a sample of approximately 65 Fermi detectable blazars at a total of 12 frequencies. The core program utilizes the 100-m Effelsberg telescope (2.6 – 42 GHz), the 30-m IRAM telescope (86, 145, 240 GHz) and occasionally the 12-m APEX telescope oberving at 345 GHz. The coherency of the combined spectra is kept within 10 days.
One of the most prominent characteristics of blazars is the intense variability. In this talk, we present the first results of the F-GAMMA program. Then we review the most discussed mechanisms proposed to explain the variability. Subsequently, we discuss a novel approach to the spectral decomposition of the observed broad-band radio spectra into individual spectral components. This method allows the model-independent study of the evolution of those components as well as that of the physical parameters associated with flaring events (i.e. magnetic fields and particle densities).
26-Mar-2012
Monthly Discussions
2-Apr-2012
Ewan Barr (3)
Radio observations of unidentified Fermi LAT sources
Chair: Sandra Burkutean
Abstract:
In the 4 years since its launch, the Large Area Telescope (LAT) aboard Fermi has revolutionised gamma-ray astronomy. However, due to a low number of incident gamma-ray photons, it is not possible to identify many of the sources discovered by the LAT. This is especially true for binary pulsars, where orbital motion may obfuscate periodicities. Our solution is to perform sensitive pulsar searches at radio wavelengths
at the position of the gamma-ray source, a technique which has, to date, found 36 new millisecond pulsars (MSP).
Here we present an overview of the current efforts to further understand the population of radio selected LAT pulsars, with particular focus on a 1.4 GHz targeted search in LAT error boxes performed with the 100-m Effelsberg telescope. This search, the largest of its type, covered 289 unidentified sources with > 200 hours of telescope time.
In addition to the discovery of the "Black Widow" MSP, PSR J1745+1017, this survey has provided strong luminosity and spectral index limits on several newly detected radio and gamma-ray pulsars.
Furthermore, with the large number of sources covered in this work we have performed a statistical analysis of the population distribution of radio selected LAT pulsars.
9-Apr-2012
Ostermontag
16-Apr-2012
Zeinab Shafiee (2)
23-Apr-2012
Nicolas Caballero (1)
It only works if the timing is right! High-precision (millisecond) pulsar timing and the European Pulsar Timing Array
Chair: Zeinab Shafiee
Abstract:
Millisecond (radio) pulsars (MSPs) have remarkable rotational stabilities that allows them to be used as accurate cosmic clocks. Pulsar Timing relies on measuring the times of arrival of the pulses, and using them to construct a model for the pulsar's rotation. High-precision timing of an sample of pulsars, a Pulsar Timing Array, could lead to the first direct detection of gravitational waves beginning an era of gravitational wave astronomy. Furthermore, timing of individual MSPs is used as a tool for a number of applications such as tests of gravity theories, interstellar weather monitoring and the equation-of-state of super-dense matter in pulsars. In this talk, I will explain how pulsar timing is performed and discuss the work carried out in the framework of the European Pulsar Timing Array, that combines the MSP timing programmes of the largest European single-dish radio telescopes, including the 100-m Effelsberg radio telescope.
30-Apr-2012
Patrick Lazarus (1)
Searching for Pulsars
Chair: Nicolas Caballero
Abstract:
Searching for pulsars is a computationally intensive task, taking days to analyse minutes of telescope data. Additionally, performing a large-scale pulsar survey requires a sizable amount of infrastructure and organization to deal with huge amounts of data. However, the endeavour is very rewarding (and in more than the usual "soulful/inner peace" kind of way); pulsars, being extreme astrophysical objects, enable tests of physics in extreme environments. This presentation will describe how data from blind radio pulsar survey pointings are analysed. Then, as a case study, I will present the on-going Pulsar-ALFA survey being conducted at the Arecibo Observatory and outline its current status and future plans
7-May-2012
Lijing Shao(1)
Gravity experiments with pulsar timing
Chair: Patrick Lazarus
Abstract:
Pulsars provide superb testing grounds for fundamental physics from many aspects, notably in tests of general relativity and alternative gravity theories. In this respect, one of the most important results is the (indirect) evidence of the existence of gravitational waves (Nobel Prize in Physics, 1993). We will review the idea behind gravity experiments with pulsar timing. Furthermore, we propose two new tests of the possible existence of a preferred reference frame for the gravitational interaction. New constraints of two preferred frame parameters are obtained from our new methods, which surpass current best limits for strongly self-gravitating masses, and one of which also surpasses the best limit obtained in the weak gravitational field of the Solar system.
14-May-2012
21-May-2012
Monthly Discussion +
Christian Fromm (3)
Spectral evolution in Blazars -Observation and Theory-
Chair: Lijing Shao
Abstract:
The spectral evolution in Blazars is presently being studied in the high energy regime (X-rays to Gamma-rays) and explained by single zone models within conical jets. In contrast to these studies, we concentrate on the spectral evolution in the radio regime, using single dish and high-resolution multi-frequency VLBI observations. We present the analysis of multi-band light curves and high-resolution VLBI observations from which we extracted the temporal and spatial evolution of the physical parameters and tested the shock-in-jet model.
In order to better understand the highly non-linear effects involved in the spectral evolution we perform several eRHD simulations. In the second part of my talk I will present first results these simulations and discuss the influence energy losses on the observed emission.
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28-May-2012
Pfingsmontag
4-Jun-2012
Cherry Ng (2)
Conducting the deepest all-sky pulsar survey ever: The High Time Resolution Universe Survey
Chair: C. Fromm
Abstract:
The extreme conditions found in and around pulsars make them fantastic natural laboratories, providing insights to a rich variety of aspects of fundamental physics and astronomy. To discovery more pulsars we have begun the High Time Resolution Universe (HTRU) survey; a blind survey of the northern sky with the 100-m Effelsberg radio telescope in Germany and a twin survey of the southern sky with the 64-m Parkes radio telescope in Australia. Blind pulsar surveys are the only way to significantly increase the known population of pulsars in an unbiased way. In particular, the HTRU survey uses multi-beam receivers and backends constructed with recent advancements in technology, providing unprecedentedly high time and frequency resolution to probe deeper into the Galaxy than ever before. In my talk I will emphasize the challenges, strategies and status of the survey in the Galactic Plane region. As the deepest large-scale survey ever attempted, I will provide an overview of the pulsar searching pipeline and the computational challenges arising from the processing of the petabyte-sized HTRU survey data. I will present an innovative segmented search technique which aims to increase our chances of discoveries of highly accelerated relativistic binary systems, including the potential pulsar-black-hole binaries.
11-Jun-2012
Frau Pott (IMPRS assistant)
Thesis Submission Procedure
Special Seminar
18-Jun-2012
Banafsheh Shahzamanian (1)
Near Infrared Emission of SgrA*
Chair:
Abstract:
In this talk I will discuss about recent near infrared observations of the supermassive black hole at the Galactic Center, Sagittarius A*, which is the most extreme example of low-luminosity AGN accessible to observation. The observations have been carried out using the NACO adaptive optics instrument at the European Southern Observatory's Very Large Telescope. The polarization measurements of Sagittarius A* show that its emission is polarized during its frequent radiation outbursts. High level of linear polarization at 2.2 micron and its strong variations can provide clues about the physical conditions at the accretion flow around this SMBH.
25-Jun-2012
Monthly Disussion +
2-Jul-2012
Cancelled
9-Jul-2012
Aarti Nagarajan (3)
Modelling of intra cluster gas medium using APEX-SZ and studying correlation of radio halos with Sunyaev Zel'dovich effect
Chair:
Abstract:
I shall be talking on two topics today as I am working on two projects currently. The first one being the modelling of the intra cluster gas medium in the galaxy clusters using the observational data obtained from the APEX telescope with the APEX-SZ instrument at 150 GHz. In the second part of the talk I shall talk about radio halos observed in some clusters that indicate presence of relativistic electrons in the intra cluster gas. The mechanism for the source of radio emission in the cluster scale is not well understood. The radio halos are known to be correlated with the X-ray luminosity and hence indicating a correlation between radio halos and the mass of the cluster. However, another way to understand them could be from studying the correlation between SZ intensity and the radio halos, since SZ effect also correlates with the cluster mass.
16-Jul-2012
L. Flöer (2)
Exploration of the Local Universe in HI
Chair: Aarti Nagarajan
Abstract:
Since fall of 2008, the Effelsberg-Bonn HI Survey (EBHIS) is carried out with the 7 feed array at the Effelsberg 100-m telescope. This survey will cover the whole sky north of declination -5° and maps both the galactic and extragalactic HI emission out to a redshift of 0.07. This enables EBHIS to be the complement to two surveys, already carried out on the southern hemisphere: The Galactic All Sky Survey, GASS, for the galactic and the HI Parkes All Sky Survey, HIPASS, for the extragalactic HI emission.
In my talk I will briefly summarize my results regarding source finding and then move on to describe the challenges of an automated parameterization pipeline, needed to extract parameters from the detected sources. I'll highlight the problems with unsupervised measurement of profile widths and total flux of galaxies and present my solutions to both problems. Finally I'll show, that a completely unsupervised pipeline is able to deliver results comparable to supervised parameterization, as employed in past and future HI surveys.
23-Jul-2012
M. Broockamp (2)
Growth processes of the least and most massive black holes
Chair: L. Flöer
Abstract:
There is a broad consensus that the evolution of galaxies and their central SMBHs are closely related. Black hole growth processes at the extreme ends of the SMBH mass function are investigated in this talk. The tidal disruption rate of the least massive black holes up to a few million solar masses are constrained with direct N-body simulations for several types of galaxies. The implications for black hole growth processes (beyond standard gas accretion scenarios) are discussed.
In the second part of this talk a highly sophisticated N-body software for simulating extremely massive black holes (>5e9 M_sun) is presented. It is designed for obtaining the growth processes and dynamics of black holes inside massive elliptical galaxies with different shapes (spherical, oblate, prolate and triaxial) and density profiles. I will explain the physics behind this software, the integration of the relativistic black hole feature and the model generation of realistic elliptical galaxies. First results are presented.
30-Jul-2012
Monthly Disussion
Florent Mertens (1)
Novel method for ridge-lines detection in the jet of AGN
Chair: Michael Broockamp
Abstract:
Study of ridge lines of radio images of many AGN reveal us helical structure in the jet. This structure can be explained by Kelvin-Helmholtz instability in the the plasma of the jet. We propose a novel method for this ridge lines detection and analysis. Using curvelet transform, we believe that we will be able to precisely reveal with high sensibility ridges along the jet. Based on the wavelet transform and the radon transfrom, curvelets provide a good representation of images which are smooth apart from singularities along smooth curves. In this presentation I will show you the current status of the development of this analysis tool.
6-Aug-2012
Philip Schmidt (1)
Continuum Halos in Nearby Galaxies - an EVLA Survey (CHANG-ES)
Chair: Florent Mertens
Abstract:
The CHANG-ES project aims to map the radio continuum halos of 35 edge-on spiral galaxies at 1.5 GHz and 6 GHz, the primary goals being to characterize the nature and prevalence of radio halos, their magnetic fields and the cosmic rays that illuminate those fields. The survey is exploiting the new wide bandwidth capabilities of the newly dedicated Karl G. Jansky Very Large Array (JVLA, or Expanded Very Large Array (EVLA)) in a variety of array configurations (B, C, and D) in order to achieve unprecedented sensitivity limits and to compile the most comprehensive data set yet obtained for the study of radio halo properties. This is also the first survey of this kind to include all polarization products. I will talk about the scientific motivation of the project, the observations, and also provide a brief glimpse of some very fresh results.
13-Aug-2012
Sandra Martin (1)
Model for Common Dark Matter Halos of Galaxy Pairs from Galaxy-Galaxy-Galaxy Lensing
Chair: Philip Schmidt
Abstract:
Third-order galaxy-galaxy lensing (GGGL) promises to be the next generation tool in gravitational lensing for investigating the dark matter/galaxy connection. GGGL can readily be measured from existing data. However, we still lack a deeper understanding of what exactly is reflected in the new correlation functions of GGGL. Today I want to give you insight into the state of art concerning GGGL.
20-Aug-2012
Vassilis Karamanavis (1)
Broad-band emission and structure dynamics of the γ-ray blazar PKS1502+106
Chair: Sandra Martin
Abstract:
Blazars are the most variable and most broad-band emitters of radiation in the Universe. The processes that give rise to those characteristics, though, remain still unclear. In this talk an introduction to the blazar phenomenon will be given. The tools used in their study will also be introduced, namely broad-band variability studies and the F-GAMMA program, but also the Very Long Baseline Interferometry technique will be discussed. Then I will give an account of the scope of my thesis which is the application of both techniques to PKS1502+106, a prominent Fermi detected γ-ray blazar.
27-Aug-2012
Monthly Disussion
Katharina Immer (1)
The massive star forming complex W33 - Closer than expected?
Chair: Vassilis Karamanavis
Abstract:
The massive star forming complex W33 consists of several molecular clouds in different stages of star formation, from quiescent, infrared-dark clouds to highly active HII regions. Ammonia and radio recombination line observations show two velocity components at ~36 and ~58 km/s, spread over opposite parts of the complex. Two explanations were suggested for this peculiar kinematic structure: 1) a single region, located at a near-kinematic distance of 3.7 kpc, that is expanding with large internal motions or 2) a line of sight superposition of two unrelated regions at different distances.
Water masers at 22 GHz were detected in three molecular clouds in the complex. In the framework of the BeSSeL project, trigonometric parallax observations of these masers were conducted with the Very Long Baseline Array over the time span of one year.
I will report the parallaxes and proper motions of the water masers in this complex. The results prove that W33 is one expanding star forming complex, located at two thirds of the near-kinematic distance. This is the most accurate distance to W33, and the first one based on an annual astrometric monitoring of the W33 water masers.
3-Sep-2012
>>> CANCELLED <<<
10-Sep-2012
Carolina Mora (1)
Magnetic field structure and halo in NGC 4631
Chair: Ioannis Antoniadis
Abstract:
All edge-on spiral galaxies observed so far present a similar magnetic field configuration, which consists of a plane-parallel field in the disk and an X-shaped field at larger z-distances from the plane of the galaxy. The plane-parallel magnetic field in the disk is the expected edge-on projection of the spiral magnetic field structure observed in face-on galaxies. However, NGC 4631 seems to be the only galaxy with an exceptionally different field orientation in its disk. Along the eastern and western halves of the disk of NGC 4631 the magnetic field orientation is indeed parallel to the galactic plane, but in the central region of the disk a vertical field seems to dominate. In order to clarify whether NGC~4631 has a unique magnetic field configuration in the central region along its disk we present high-resolution Faraday-corrected data.
17-Sep-2012
Franz Kirsten (1)
Pulsar astrometry with global very long baseline interferometry
Chair: Carolina Mora
Abstract:
Global Very Long Baseline Interferometry (VLBI) provides the highestangular resolution achievable with Earth-bound telescopes. Reachingpositional accuracies on the order of microarcseconds, this technique isthe only means to measure model-independent trigonometric parallaxes andproper motions of pulsars. The application of such measurements ismanifold: Pulsars can be traced back to their birth location to studyformation scenarios; the measured parallax and inferred distance can beused to confine electron-density models along the line of sight to thepulsar; pulsar timing models can be improved to perform accurate test ofgeneral relativity.
In this project we observe the globular cluster M15 and measure theproper motion of the pulsars known to reside in the cluster.Furthermore, we analyse the proper motion of three further pulsars withthe goal to constrain their birth location in the Milky Way.
24-Sep-2012
Monthly Disussion +
M. Vitale (2)
Spectroscopic multi-wavelength studies of AGNs: The AGN/starburst connection
Chair: Franz Kirsten
Abstract:
The Sloan Digital Sky Survey (SDSS) allows us to classify galaxies using optical low-ionization emission-line diagnostic diagrams. A cross-correlation of the SDSS data release 7 (DR7), containing spectroscopic data, with the Very Large Array (VLA) survey Faint Images of the Radio Sky at Twenty-centimeters (FIRST), makes it possible to conduct a joined multi-wavelength statistical study of radio-optical galaxy properties on a very large number of sources. Our goal is to improve the study of the combined radio-optical data by investigating whether there is a correlation between the radio luminosity at 20 cm over the luminosity of the optical Hα line (L20 cm/LHα) and line excitation ratios, where the latter provide the spectroscopic classification in Seyferts, low-ionization nuclear emission-line regions (LINERs), and star-forming galaxies.
In this talk I report on the results of my first year as PhD student and our recently published paper. Moreover, I present my current projects and some ideas for the future.
1-Oct-2012
M. Tomassetti (2)
Molecules and galaxy formation
Chair: E. Angelakis
Abstract:
The recent discovery of a much tighter correlation of thestar formation rate density with the molecular hydrogen density ratherthan the total gas density has motivated several attempts to updatethe standard star formation recipe in numerical simulations. Gasdenser than a threshold value it is usually converted into stars, in afree-fall time, with an efficiency of few percents. Although thismodel has proved to successfully reproduce most of the observableproperties of galaxies, its parameters are often tuned to match theKennicutt-Schmidt relation for star formation. I will discuss theimplication of a molecular-regulated star formation prescription inthe morphology and the dynamics of a disk galaxy at z~1, simulatedwith a patched version of the AMR code RAMSES. I will also talk aboutpossible improvement of the model and their implications in futureworks.
8-Oct-2012
Miriam Ramos Ceja (1)
Cosmology with X-ray galaxy cluster surveys
Chair: M. Tomasetti
Abstract:
The extended ROentgen Survey with an Imaging Telescope Array(eROSITA) is the next generation of X-ray satellite observatories. It willbe launch in 2014 and will perform the first imaging all-sky survey in themedium energy X-ray range up to 10 keV with an unprecedented spectral andangular resolution. eROSITA will detect the hot intergalactic medium of50-100 thousand galaxy clusters and groups and hot gas in filamentsbetween clusters to map out the large scale structure in the Universe forthe study of cosmic structure evolution. However, the detection of suchobjects represents a challenging task. In this talk I will present thewavelet transformation technique as candidate for the detection procedureof eROSITA.
Alberto Doria (1)
tba
Chair: M. Tomasetti
Abstract:
Tba
15-Oct-2012
Jan Wagner (2) – cancelled -
22-Oct-2012
Semir Smajic (1) – cancelled - + Sebastian Kielhmann (1)
29-Oct-2012
Monthly Disussion +
I. Antoniadis (3) + H. Saghiha (2) (to be rescheduled)
5-Nov-2012
Sandra Burkutean
Sunyaev-Zel'dovich effect in galaxy clusters - new observations and analyses
Chair: tba
Abstract:
The Sunyaev-Zel'dovich effect (SZE) in galaxy clusters is caused by unverse Compton scattering of Cosmic Microwave Background photons off thermal electrons in the intra-cluster gas. I will describe how one can use this SZE information in conjunction with multi-wavelenght observations to put constraints on a galaxy cluster's triaxiality. In light of two newly accepted proposals, preliminary results of interferometric SZ data analyses will be shown. This will be followed by a discussion on the combination of interferometric SZ and bolometric APEX-SZ data. In addition, I will present how combining ALMA/ACA and bolometric single dish information from APEX-SZ will cover the intra-cluster pressure profile over an unprecedented range of spatial scales in SZ, enabling closer investigations into the nature of dynamically relaxed 'cool-core clusters'.
Jan Wagner
Overview of the Megamaser Cosmology Project: Measuring H0
Chair: tba
Abstract:
Tighter constraints on the Hubble constant H0 are needed to improve CMB derived estimates on the Dark Energy equation of state and neutrino mass and curvature of space. The international collaborative Megamaser Cosmology Project (MCP), lead by Jim Braatz, NRAO, aims to directly measure H0 to <3% with nearby water megamaser galaxies (z<0.06) using several PhD students and angular diameter distances to the masing accretion disks around AGN in these galaxies. Like the archetypal NGC 4258 and now UGC 3789, several Sy2 AGN were found to exhibit similar 22 GHz water megamaser emission, tracing the inner parsecs of an AGN accretion disk. This allows H0 to be determined on an almost purely geometric basis, complementing current methods based on CMB, lensing, BAO, SN Ia and Cepheids. In this talk I will present an overview of the MCP project and method, and its current status as well as ongoing work.
12-Nov-2012
Maryam Habibi (3)
Study of an extreme starburst cluster: different star formation or dynamical evolution?
Chair: Burkutean /Wagner
Abstract:
The Galactic Center is the most active site of star formation in the MilkyWay Galaxy, where particularly high-mass stars have formed very recentlyand are still forming today. The Arches cluster is a young, massivestarburst cluster, near the Galactic Center.
We observed the Arches cluster out to its tidal radius to gain a fullunderstanding of the cluster mass distribution. In my previous IMPRS talkI showed that the determination of the mass of the most massive star inthe Arches cluster, which had been used in previous studies to establishan upper-mass limit for the star formation process in the Milky Way,strongly depends on the assumed slope of the extinction law.
In this talk I will show that the derived present-day mass function of thecluster increase from a flat slope of αN ishi =−1.76 ± 0.22 inthe core , compare to the Salpeter IMF, increasing from a flat slope ofNishi =1.76 0.22 in the core to αN ishi = −2.23 ± 0.27 in theintermediate annulus and become high mass depleted , αN ishi =−2.95 ± 0.26, in the outer annulus. Steepenig of the mass functiontoward the outskirt of the cluster guide us to investigate the dynamicalstate of the cluster. I compared the derived slope of the mass functionsin different annuli of the cluster with a series of dynamical N-bodysimulations with different models and initial conditions performed byHarfst et al. (2010). The derived slope from a Salpeter IMF model at theradius of 1 pc was in good agreement with our finding (Fig.1, right).Therefor, we concluded that the observed mass function of the Archescluster is consistent with dynamical evolution of the cluster, and that notop-heavy IMF is required to explain the present cluster mass function.
I will also present my current project on study of the distribution ofejected sources in the simulations and its comparison to thedistribution of isolated massive sources in the Galactic center region.
19-Nov-2012
Ioannis Miserlis (1)
Linear and circular radio and optical polarization studies as a probe of AGN physics
Chair: Habibi
Abstract:
In this talk, I include a brief introduction of the F-GAMMA program, which monitors the radio flux density and polarization characteristics of 60 selected γ-ray blazars and the RoboPol program, which will do the same in the optical regime. Such data can be used for the investigation of the wealth of their physical properties, such as the topology and magnitude of their magnetic field, the composition of their jets or the physical mechanisms that produce their observed variability. Subsequently, the focus will be put on the intrinsic polarization characteristics of an incoherent synchrotron source as well as second order, Faraday effects that can take place in magnetized plasmas that we usually observe in space. For the 100-m Effelsberg radio telescope polarization data, I will discuss: (a) the necessary formalism, (b) describe method used for the necessary determination of the instrumental polarization in terms of obtaining the 4x4 Müller matrix that realizes the instrumental effects as a transfer function between the 4-vectors of the actual and the observed Stokes parameters and (c) show first results of our preliminary work on linear and circular radio polarization which show a consistency of our calibrators' polarization characteristics before and after the correction as well as the detection of high circular polarization percentage from some of the observed sources. Finally, I will brief the results of the exploratory optical observations that have been conducted for the formation of the target sample of the imminent RoboPol program.
26-Nov-2012
Monthly Disussion
3-Dec-2012
Zahra Sheikbahaee (3) + Silvia Spezzano (3)
10-Dec-2012
Jana Koehler (2)
Study of large-scale galactic magnetic fields at low frequencies
Chair: E. Angelakis
Abstract:
The main aim of this project is to map out the large-scale total and polarized emission of the entire northern sky, concentrating on the Faraday spectrum of the polarized emission. In this way the polarization properties of the Milky Way can be studied, as well as special targets like CasA, CygA and TauA. The use of RM synthesis will help to study the structures and turbulent regions in the Milky Way ISM. With the use of LOFAR it is now possible to study polarization below 250 MHz, which gives the oppertunity to study the weak magnetic fields in the Galactic halo and outer disc, about which little has been measured to date. In this talk I will first give an short overview about what we already know about large-scale structures in total and polarized intensity. Then I will talk about the polarization calibration of LOFAR Single Station data and will show some results from my data reduction.
17-Dec-2012
Pablo Torne (1)
SKA-technology for the Effelsberg 100-m
Chair: Jana Koehler
Abstract:
Single large dish telescopes suffer from a narrow field-of-view (FoV) and this is translated into a slow survey speed. This limitation can be addressed by a new generation of receivers available to the scientific community thanks to the investigations and developments towards the Square Kilometer Array (SKA) telescope. In this presentation I will give an overview of the survey speed problem, the SKA, its pathfinders, and the new derived receivers: the Ultra-Wide-Band and Phased Array Feeds. Our efforts to apply these new technologies to the Effelsberg 100-m will also be discussed, together with the main challenges they impose.
Bindu Rani (1)
Radio to Gamma-ray Variability study of blazar S5 0716+714
Chair: Jana Koehler
Abstract:
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