Monday Seminar for the year 2011

    The presentations are shown in order of incerasing time.












    Sameera Salim (1)

    Multi-wavelength Analysis of (Sub)millimetre Galaxies in the COSMOS Survey Data

    Chair: E. Angelakis

Submillimeter galaxies (SMGs) are ultra-luminous, dusty starbursting systems with extreme star formation rates in the range of ~ 100 − 1000 M⊙ yr−1. The bulk of this population lies at redshifts between 2 and 3 and they are thought to be the main contributors to the cosmic star formation rate density at these redshifts.Even though hundreds of SMGs have been discovered using single dish telescopes at low resolution (10 to 30 arcsec), precise counterpart identification at other wavelengths and subsequent detailed analysis of their physics is still at its early stage.

    The COSMOS field provides the largest cosmological deep field to date (2 deg2), spanning a wavelength range that extends from x-ray to radio making it ideal to do multi-wavelength studies of the SMGs. It has been surveyed in the (sub-)mm wavelength regime by four independent instruments (MAMBO,LABOCA, AzTEC, BOLOCAM) and also data from Herschel is going to be available soon.

    In my talk I will concentrate on our recently finished LABOCA .87mm COSMOS field survey and the various methods to pinpoint the counterparts, in order to give a multi-wavelength view of the detected sources.






    Aarti Nagarajan (1)

                                                                  Observing with APEX-SZ and reducing the SZ data

    Chair: Sameera Salim

 Galaxy clusters are the largest collapsed structures in the Universe.The Intra Cluster Medium (ICM) forms a large portion of the visible matter in  these structures. Typical temperatures of ICM are of the orders of 10^6 K. The CMB photons, when interacting with the ICM undergoes inverse Compton scattering known as Sunyaev-Zel’dovich Effect (SZE).

    APEX-SZ  is a Bolometer Array receiver used (now out of commission from Dec 2010) to observe the SZE at 150 GHz at the APEX Telescope, Chajnantor. The last set of observations with APEX-SZ was taken in November-December 2010.  In my talk , I will address the observation procedure followed in taking the data and discuss the reduction method of reducing  the raw data using BoA.



    Monthly discussion     






    Fujun Du (2)

                                    A hybrid moment equation approach to gas-grain chemistry modeling

    Chair: Aarti Nagarajan

 Complementary to the gas phase chemistry, chemical processes happening on the grain surfaces are important for the overall interstellar matter repository.  Due to their discrete and stochastic nature, however, usually surface chemistry cannot be accurately modeled by the rate equations. Various methods have been proposed, including the modified rate equation approach (Caselli et al. 1998; Garrod 2008), master equation approach with cutoff (Stantcheva et al. 2002), moment equation approach with cutoff (Lipshtat and Biham 2003; Barzel and Biham 2007), multiplane approach (Barzel et al. 2007), and the exact Monte Carlo approach (Vasyunin et al. 2009). The Monte Carlo approach would produce the most accurate results if it is repeated for many times; however, it is computationally heavy, and eventually impractical when a large chemical network is being modeled. On the other hand, a consistent and automatic algorithm is needed to handle a generic system in which both the gas phase and grain surface processes are included. In the present work, we propose a moment equation approach in which the generating function machinery is used to generate the equations automatically (up to any prescribed order), and a cut-off-and-switch scheme is implemented to approximate the infinite system of equations. Comparisons are made between the results of this method and those from the exact Monte Carlo simulations for several commonly used systems. The agreement is usually satisfactory, while the speed of our method is not much slower than the rate equation approach. Further issues include the numerical stability of this method (when higher order moments are included), how to control the errors quantitatively, and how to select those mostly needed terms to limit the number of variables and lower the computational burden.






    Monthly discussion






    Guang-Xing Li (1)

    Modeling Molecular Outflow


    Chair: Fujun Du

 Molecular outflow is a prominent phenomenon happening during star formation.  Interferometer observations of molecular outflows using spectral lines such as CO gives us spacial and velocity information of molecular outflows. I will talk about our effort to modelling the special and velocity structure of molecular outflows and present some preliminary results.






    Cherry Ng (1)

    The title of my talk will be: The High Time Resolution Legacy Survey


    Chair: Guang-Xing Li

 I would talk about the standard searching pipeline of pulsar and the current status of the all-sky pulsar survey: the High Time Resolution Legacy Survey. I would also discuss briefly the challenges of the High Time Resolution Legacy Survey and our current progresses in the survey.












    >>> Exceptionally the seminar will take place at 11:00 <<<

    Arturo Gomez (3) 

    The warm gas in HH211 revealed by APEX/CHAMP+ observations


    Chair: Cherry Ng

 In this talk I will continue presenting the sources of the project "warm  gas in rotostellar outflows". H211 is the other class 0 low-mass  protostar we have studied in CO 6-5/7-6 with CHAMP+ at APEX. I will first  introduce the source and describe its characteristic obtained by previous  low-J CO and SiO observations. Then I will present our mid-J CO  observations and contrast them with these traditional shock tracers.  Finally I will show the physical parameters we have obtained by using all  data available in the literature (e.g. from low-J to high-J CO) and give a  comparison with the class 0 source I presented in previous talk (L1448).  






    Natasa Tsitali (1)

    The dynamical state of  the  starless cores in Chamaeleon I and the ‘First Hydrostatic Core’ candidate


    Chair: Arturo Gomez

 In this talk I will introduce my PhD project and summarize our work so far. A 870 micron LABOCA survey of Chamaeleon I has revealed a population of approximately 60 starless cores. Combining this continuum map along with heterodyne observations we aim to explore the nature of these condensations.  Are these cores gravitationally bound and unstable, and therefore going to form stars in the future? Or are they never going to become pre-stellar thus potentially signifying the end of star formation in Chamaeleon I?  A discovery of a very young source in one of these cores has also led us to investigate whether it could be at the phase of the ‘ first hydrostatic core’ (FHC), the missing link between the pre-stellar and the Class 0 (protostar) phase in the low-mass star formation scenarios. So is this object a FHC and will it help us shed some light into this,  theoretically predicted, short-lived phase of star formation?






    Monthly discussion     






    Ewan Barr (2)

    The current status of pulsar searches with Effelsberg

    Chair: Natasa Tsitali

 The massive collecting area of the Effelsberg telescope makes it a remarkable instrument for pulsar observations and especially pulsar surveys. In the past Effelsberg has been underused by the pulsar community but now, with advances in backend and frontend technology, we are working to rectify Effelsbergs pulsar deficiency by conducting two large scale pulsar surveys. Here I will present the status of both current surveys and our future expectations for each.

    Targeted search of unidentified Fermi catalog sources:

    The Fermi satellite in its first 18 months of observations produced a catalog of ~1600 sources which could not be identified as either AGN, blazars, pulsars or pulsar wind nebulae. Many of these sources exhibit characteristics that can be associated with currently know gamma-ray emitting pulsars. These sources were ranked based on a system of logistical regression with predictor variables of curvature and variability and the top 289 sources were observed multiple times at different depths and at different epochs. Here I will present the results, follow-up and continuing work on this project.

    The High Time Resolution Universe - North survey:

    The HTRU-North survey represents the Effelsberg and MPIfR half of the HTRU all sky pulsar survey. Conducted in tandem with the Parkes telescope in Australia, this survey will cover the entire sky with time and frequency resolution that was previously unachievable. To date 6% of the survey has been observed and 1% processed. Here I will give a brief overview of the survey before discussing the current methods by which we excise RFI and by which we sort and select candidates to view.






    Fangchun Liu (2)

    Water deuterium fractionation in the low-mass protostar NGC1333-IRAS2A

    Chair: Ewan Barr

 Although deuterium enrichment of water may provide an essential piece of information in the understanding of the formation of comets and protoplanetary systems, only a few studies up to now have aimed at deriving the HDO/H2O ratio in low-mass star forming regions. Previous  tudies of the molecular deuteration toward the solar-type class 0 protostar, IRAS 16293-2422, have shown that the D/H ratio of water is significantly lower than other grain-surface-formed molecules. It is not clear if this property is general or particular to this source. In order to see if the results toward IRAS 16293-2422 are particular, we aimed at studying water deuterium fractionation in a second low-mass solar-type protostar, NGC1333-IRAS2A. Using the 1-D radiative transfer code RATRAN, we analyzed five HDO transitions observed with the IRAM 30m, JCMT, and APEX telescopes. We assumed that the abundance profile of HDO in the envelope is a step function, with two different values in the inner warm (T>100 K) and outer cold (T<100 k="" regions="" of="" the="" protostellar="" envelope="" inner="" and="" outer="" abundance="" hdo="" is="" found="" to="" be="" well="" constrained="" at="" 3="" sigma="" level="" obtained="" fractional="" abundances="" are="" x_in="6.6e-8" -="" 1e-7="" x_out="9e-11" 1="" 8e-9="" these="" values="" close="" those="" in="" iras="" 16293-2422="" which="" suggests="" that="" may="" formed="" by="" same="" mechanisms="" two="" solar-type="" protostars="" taking="" into="" account="" rather="" poorly="" h2o="" profile="" deduced="" from="" herschel="" observations="" derived="" larger="" than="" it="" 0="" 9="" -18="" more="" one="" order="" magnitude="" higher="" what="" measured="" comets="" if="" ratios="" apply="" protosolar="" nebula="" this="" would="" imply="" there="" some="" efficient="" reprocessing="" material="" between="" cometary="" phases="" could="" further="" an="" analysis="" newer="" high-energy="" h18o="" lines="" new="" required="" understand="" water="" fractionation="" detail="" p="">






    Zeinab Shafiee (1)

    Mass Reconstruction of Clusters of Galaxies within Weak Gravitational Lensing

    Chair: Fangchun Liu

 As a prediction of Albert Einstein's General Theory of Relativity, a distribution of matter such as a cluster of galaxies between a distant source and an observer is capable of bending the light from the source. This effect is known as gravitational lensing and may show itself in strong regime by producing giant arcs or multiple images. However, in most cases the lensing is so weak that it is impossible to detect the deflection in a single background source. Here in weak gravitational lensing regime, a statistical measurement is needed to find a systematic alignment of background sources around the lensing mass. Weak gravitational lensing provides a way to measure the masses of astronomical objects without requiring assumptions about their composition or dynamical state. It is emerging as a powerful technique to measure large-scale structure and to map the distribution of Dark
Matter on various scales. In this talk I introduce my PhD project in which I will study the mass reconstruction of clusters of galaxies with weak gravitational lensing methods.













    Monthly discussion






    Ioannis Nestoras(3)

    cm to Sub-mm Monitoring of Fermi –GST Gamma-ray Blazars The first four years of the

    F-GAMMA program

    Chair: Zeinab Shafiee

 The F -GAMMA program is a coordinated effort of several observing facilities to understand the AGN/blazar phenomenon via a multi-frequency approach, especially in the era of Fermi-GST. Since 2007, we are performing this Fermi-dedicated monthly monitoring program and are collecting (quasi-) simultaneous and high-precision broad-band (cm/mm/sub-mm) variability data for about 65 gamma-ray blazars.

    Here, we present the first four years of observations, data analysis as well as the results obtained so far. In particular, the statistical properties of the sample are presented with emphasis on the variability/spectral characteristics including variability times scales, amplitudes, spectral evolution and corresponding physical parameters. Also we present a phenomenological classification of our sources and we find that the observed variability can be unified to only two fundamentally different ways: (i) spectral evolution dominated variability, (ii) almost achromatic variability. The first four years of data imply that only two physical mechanisms produce the observed variability.






    Brenda Ocejo(2) Cancelled






    Frank Schinzel (3)

    The parsec-scale jet of 3C345 and its connection to emission at GeV energies


    Chair: I. Nestoras or B. Ocejo







    Mar Mezcua (3)

    The parsec-scale of Active Galactic Nuclei


    Chair: F. Schinzel

 LINERs (Low-Ionization Nuclear Emission Regions) constitute the lowest-luminosity class of AGN. Their intrinsic low luminosity is debated between lack of fueling material around the central black hole, a non-standard accretion disk, or simply not being AGN.

    In order to disentangle the true nature of LINERs their innermost region (few parsecs) can be studied by means of near-infrared high spatial resolution spectroscopy, in particular using the Integral Field Spectroscopy (IFS) technique.

    I will present recent results of the molecular gas distribution and kinematics of a sample of LINERs based on IFS observations with SINFONI/VLT.






    Gabriele Surcis (3)

    High resolution magnetic field measurements in high-mass star-forming regions


    Chair: M. Mezcua

 Three different scenarios have been proposed to explain the formation of high-mass stars. In one of these scenarios, core accretion, massive stars form through gravitational collapse, which involves disc-assisted accretion to overcome radiation pressure. This scenario is similar to the favored picture of low-mass star-formation, in which magnetic fields are thought to play an important role by removing excess angular momentum, thereby allowing accretion to continue onto the star. However, the role of magnetic fields during the protostellar phase of high-mass star-formation is still a debated topic. In particular, it is still unclear how magnetic fields influence the formation and dynamics of discs and outflows. Most current information on magnetic fields close to high-mass protostars comes from polarized maser emissions, which allow us to investigate the magnetic field on small scales by using interferometers, such as EVN, MELIN, and VLBA. In this talk I will show the results obtained during my Ph.D. in which I have investigated the magnetic field of 7 massive star-forming regions by using the polarized emissions of methanol and water masers.












    Sandra Burkutean (1)

    Sunyaev-Zel’dovich observations of galaxy clusters with interferometry and single dish


    Chair: G. Surcis

 The Sunyaev-Zel’dovich effect in galaxy cluster is caused by inverse Compton scattering of Cosmic Microwave Background photons off thermal electrons in the intra-cluster gas. With new or improved interferometers like ALMA,  EVLA and CARMA being available, this opens up the possibility to make high resolution Sunyaev_Zel’dovich observations. In order to re-construct the pressure profile of the intra-cluster gas at a wide range of spatial scales, zero-spacing information is needed however. In this talk, I will give an introduction to the Sunyaev-Zel’dovich effect as well as discuss possible methods for the combination of  interferometric and bolometric measurements of the Sunyaev-Zel’dovich effect.






    Rebekka Schmidt (1) 

    Probing AGN physics via broad-band monitoring of gamma-ray blazars


    Chair: Sandra Burkutean

 The F-GAMMA program (Fermi-GST AGN Multi-frequency Monitoring Alliance) is a monitoring program which observes roughly 65 Fermi-GST detectable blazars each month. The core program involves observations with the 100-m Effelsberg telescope at 8 frequencies between 2.6 and 43 GHz, the 30-m IRAM telescope at 86, 145 and 240 GHz and the APEX 12-m telescope at 345 GHz. Spectra simultaneous within a week are produced for cross-band studies.

    In this talk I will introduce the classicfication of the spectra which can be grouped in only 9 phenomenological classes of spectral variability pattern. Seven of these classes are clearly dominated by spectral evolution and can be interpreted as a quiescent optically thin spectrum with a super-imposed flaring event. The other 2 classes vary self-similarly with almost no apparent shift of the peak frequency implying that a totally different mechanism is at work. None of the sources has swichted classes so far.

    I will present the most famous models which try to explain the observed variability. Then I will give a short overview about synchrotron self-absorption and introduce our ansatz to investigate the spectra. It is our aim to reject or verify the models and to find some physical parameters of the sources.






    Monthly discussion     






    Alex Kreplin (3, moved from Feb. 14) Cancelled. New date to be decided!  C. (2)






    Lisa Zimmermann (1)

    Variability of radio and TeV emitting X-ray binaries: The case of LS I +61303  

    Chair: E. Angelakis

 Radio and TeV emitting X-ray binaries are a class of rare and enigmatic objects. The hunt for a better understanding of the emission processes in these sources is ongoingly extensive.  LS I +61303 is a high mass X-ray binary, where a compact object of unknown nature travels on an eccentric orbit around a Be star, and has been detected at high and very high energies with e.g. Fermi-Lat, MAGIC and VERITAS. The most peculiar radio characteristics of LS I +61303 are two periodicities. A large periodic radio outburst which exhibits the same period as the orbit of 26.5 d (Phi). A second periodicity of 4.6 yr (Theta) modulates the orbital phase and amplitude of this large outburst. Two models have been proposed for this source, a two-peak microquasar and a millisecond pulsar model. Furthermore, the emission processes leading to the high and very high energy emission in this source are still under debate. Recent results indicate that radio spectral index data, folded with the two periodicities, is a new important tool, when used together with high energy observations, to distinguish between the two models and to yield new insights into the emission processes.






    Michael Marks (3)      



    Constraining the initial conditions of young star clusters using their binary populations  


 Binary Populations in young star clusters show multiplicity fractions both lower and up to twice as high than that observed in the Galactic field. It is shown that evolving a population of binary stars in dense or loose star clusters, starting with an invariant initial binary distribution and a multiplicity fraction of unity, can explain diverse binary properties in star clusters, such as in the 1 Myr old and sparse Taurus-Auriga region, the same-aged but much denser Orion Nebula Cluster and the 100 Myr old Pleiades. The evolved theoretical semi-major axis distributions are highly-probable parent distributions for the observed ones. Given the present model, birth conditions (mass and size) for the young star clusters' progenitors and the overall present-day binary fractions are constrained. It is concluded that dynamics play an important role in shaping the present characteristics of binary populations in star clusters.




    Alex Kreplin (3)



    Probing the circumstellar environment of three Herbig Ae/Be stars in the near-infrared with VLTI/AMBER  


 Young stellar objects (YSOs) are surrounded by matter accumulated from its natal envelope, which is bound in circumstellar dust and gas disks. Observations of circumstellar disks are therefore well suited to study the star formation process. Near-infrared observations trace the hot dust and gas in the innermost region of the circumstellar disk near the dust sublimation radius. In the case of intermediate-mass YSOs, the Herbig Ae/Be stars, the inner dust rim is expected to form a "puffed-up" inner rim, which often dominates the near-infrared emission. Interferometric methods provide the required high angular resolution to study these innermost regions at a few AU from the central star. With the near-infrared interferometric instrument VLTI/AMBER, the innermost region of the circumstellar environment of the YSO candidate V921 Sco and the two Herbig Ae stars HD144432 and KK Oph has been spatially resolved. In this talk, I will briefly discuss the concept of the AMBER instrument, the data reduction, the observational AMBER results, and the simultaneous modeling of the visibilities and SED.










    Aarti Nagarajan (2)



    Model fitting of ICM using APEX SZ data  


 Galaxy clusters are the largest collapsed structures in the Universe.The Intra Cluster Medium (ICM) forms a large portion of the visible matter in these structures. This hot ICM inverse Compton scatters the CMB photons (Sunyaev-Zel’dovich Effect (SZE)). Under the APEX SZ project many clusters have been targeted and observed at 150 GHz. With combined modeling of SZ data and X-ray data, it is possible to derive the density and temperature distribution of the ICM. In my talk, I shall discuss the basics of the model fitting and briefly touch upon the advantages of the non-parametric de-projection method over parametric model fitting.




    Monica Valencia-Schneider (3)



    ooking for the AGN in Sy/SB composite galaxies. The case of IRAS01072+4954  


 Observations of active galactic nuclei (AGN) indicate that their main power supply arises from the accretion onto supermassive black holes (SMBH) and appear to confirm the so called Unified model, according to which the differences between the observed spectra are due to orientation effects with respect to the line of sight. However, low luminous unobscured AGN seem not to fit into the unified scheme: they do not show broad lines in the optical (in some cases, not even in polarized light) but have X-Ray spectra typical of Seyfert 1 galaxies. The starburst/Seyfert composite galaxy IRAS 01072+4954 is one of these objects. It displays a starburst-like spectrum in the optical/infrared and strong emission in X-rays revealing the presence of the AGN.

    I present the results of spectro-photometric observations of the central region of this galaxy in the near infrared (H- and K-bands). We find a that the mass of the SMBH is ~<10^6 M_sun, which places it at the lower end of the BH mass range for AGNs with an Eddington ratio indicative of relatively high accretion rate. The existence of a broad line region is expected but not confirmed. In contrast to the low extinction estimated from X-ray data, we find a central concentration of hot gas which could indicate the presence of a torus.




    Monthly discussion     






    I. Antoniadis (2) moved to Sep. 26






    L. Flöer (1)

    Exploration of the local universe in HI  

    Chair: E. Angelakis

 Since autumn of 2008, the Effelsberg-Bonn HI Survey (EBHIS) is carried out with the 7 feed array at the Effelsberg 100-m telescope.  EBHIS aims to cover the whole sky north of declination -5° and maps both the galactic and extragalactic HI emission out 270 Mpc in parallel. This enables EBHIS to complement the two already performed major surveys towards the southern hemisphere: The Galactic All Sky Survey, (GASS) and the HI Parkes All Sky Survey (HIPASS).

    In my talk I will briefly introduce EBHIS and then discuss the general issue of automatic source finding for spectroscopic surveys. Until this day, there is no go-to solution for this problem, especially in the face of the three dimensional data, as is obtained by these surveys. I will discuss my approach to the problem using wavelet denoising techniques and show the results of simulations that were carried out to assess the performance of this technique as a source finder.






    M. Broockamp (1)

    The disruption rate of stars by supermassive black holes (SMBHs)  

    Chair: L. Flöer

 In this talk the disruption rate of stars by supermassive black holes (SMBHs) will be presented. This rate was calculated numerically for the first time with a direct N-body integrator (a modified version of NBODY6) by performing a very large set of models in order to increase the statistical significance and to infer relaxation driven effects. Only a relatively modest dependence of the tidal disruption rate on the mass of the SMBH is found and the results will be discussed in the context of the $\mbh-\sigma$ relation. This also bears direct consequences for the search and existence of IMBHs

    in globular clusters.






    I. Antoniadis (2) moved from Sep. 05 + Monthly discussion  






    Tag der Deutschen Einheit






    M. Tomassetti (1)

    Numerical simulations of galaxy formation - An Introduction  

    Chair: E. Angelakis

 The Cold Dark Matter (CDM) paradigm has proved to be remarkably successful both in predicting and explaining a variety of observational data. However, there is still a lack of understanding about how gas is converted into stars and how stars impact their environment. The "standard" (local) star formation recipe, which links the local star formation rate (SFR) to the local gas density, requires fine-tuning to match the observed Kennicutt-Schmidt relation. Moreover, several problems stem from troubles with correctly modeling the formation and evolution of low-mass ("dwarf") galaxies. Molecular hydrogen-regulated prescription seems to alleviate some of the dwarf galaxies problems faced by theoretical galaxy formation models (Kuhlen et al. 2011). I will discuss how to incorporate new sub-grid models for star formation and stellar feedback in the Adaptive Mesh Refinement (AMR) code RAMSES (Teyssier et al. 2002).






    M. Vitale(1)



    Spectroscopic studies on AGNs under a multiwavelength approach. A close look at the AGN/starburst connection  

    Chair: M. Tomassetti

 Active Galactic Nuclei (AGNs) can be selected from a galaxy survey thanks to diagnostic techniques like the Baldwin, Phillips & Terlevich (BPT) diagrams, which use the ratios of some optical emission lines to identify which is the main contribution to the ionization inside galaxies – stars or accretion around the black hole. 

    The AGNs selection allows studying these objects at different wavelengths. We need to take into account that the instrument aperture size can affect the final classification on the diagnostic diagram, pointing at the nucleus of the source rather than at the whole galaxy. I will explain the role of diagnostic diagram in selecting AGNs and the way the selection could be biased. 

    Integral Field Spectroscopy (IFS) is a new spectroscopic technique that allow taking spectra of the sky over a 2Dfield of view, in order to obtain a final data cube where every pixel of the source image contains a unit of information in terms of spectra. This is particularly useful when studying the star formation and nuclear activity in different regions of  the galaxy, e.g. the AGN/starburst connection. With a set of SINFONI data, I will show you the very first results of my analysis.




    Cancelled. Departure for the retreat.






    Monthly discussion


    Christian Fromm (2)   



    Shock-Shock-Interaction in jets: Observations and Simulations

    Chair: M. Vitale

 We successfully modeled single dish light curves of the 2006 radio flare in CTA102 with a modified shock-in-jet model including a standing shock wave around 0.2mas (36pc de-projected) away from the core (Fromm et al. 2011). From our multi-frequency VLBI observations (2GHz - 86 GHz) we derived the spatial and temporal evolution of the intrinsic parameters, e.g. magnetic field, particle density and the magnetization of the jet. The result of this analysis supported our assumption of the interaction between a traveling and a standing shock wave. To better understand this highly non-linear interaction between traveling and standing shock waves we performed 2D RHD simulations and calculated the corresponding synchrotron emission.




    Jennifer Piel (2)

    Weak Lensing Analysis of Galaxy Clusters at 0.3 < z <0.55

    Chair: C. M. Fromm

 Weak gravitational lensing is a powerful tool to investigate the properties of galaxy clusters. In this talk, I will present the results of this technique for a sample of five galaxy clusters with very different masses and morphologies at 0.3 < z < 0.55 which were observed with deep ASC@HST mosaics. My method is based on the weak lensing aperture mass statistics which is conveniently used for cluster detection and measuring the significance of their weak lensing signal, among others. I will show that the position where the weak lensing signal attains a maximum value can be used as an alternative definition of the cluster centre besides the X-ray centre or the Brightest Cluster Galaxy (BCG). By fitting four different mass models to the tangential shear profiles, I will further discuss how well these models apply with respect to the morphologies and dynamical states of each cluster.



    H. Saghiha (1)

    Galaxy-Galaxy Lensing

    Chair: J. Piel

 The gravitational lensing effect provides a significant tool to probe the matter distribution in the universe, from individual galaxies to the cosmic large-scale structure. Weak lensing of galaxies, or Galaxy-Galaxy Lensing (GGL), allows studying the matter distribution associated with galaxies.  Recently, third-order GGL (G3L) has been investigated and applied to the observational data by converting the measurements to a mathematically equivalent aperture statistics . The result of this effort is a significant detection of the third-order aperture signal. In the present work, measurements of the third-order aperture statistics were carried out by  using the Millennium Simulation, with the combination of semi-analytic models of galaxy formation, to infer information about the relative distribution of lens galaxy pairs and the underlying matter.



    Monthly discussion






    Silvia Spezzano (2)    

    High resolution spectroscopy of CO+

    Chair: H. Saghiha

 CO+ is the cation of the second most abundant molecule in space, carbon monoxide. Nevertheless this small cation has been proven not to be as widespread as his neutral counterpart, as it reacts on every collision with H2; indeed his abundance becomes important just in hot layers of photo-dissociation regions PDRs, where hydrogen is mostly atomic.

    Precise rest frequencies are needed in radioastronomy: with new facilities such as Herschel, SOFIA and ALMA a lot of effort has been required to spectroscopists in order to provide very accurate line frequencies in the THz region.

    I will present my results on CO+ in several isotopic substituted species from 300 GHz to 1.3 THz.








    Jana Koehler (1)

    Study of large-scale galactic magnetic fields using rotation measure synthesis at sub-Gigahertz frequencies


    Chair: Silvia Spezzano

 Total intensity maps of the entire sky are well known at frequencies lower than 1GHz. This is not the case in polarisation. With observations from the Low Frequency Array (LOFAR) and the new receiver for the Effelsberg dish (300-900 MHz), I want to study large-scale magnetic fields at low frequencies. Using RM synthesis of the polarised emission will give us the possibility to study the different structures in the Milky Way ISM and the turbulence in the ISM. In this talk I will give an introduction to polarisation, Stokes parameters and RM synthesis. I will also give a short introduction to LOFAR and will show first skymaps made with data from the single LOFAR station in Effelsberg.




    Jan Wagner (1)

    RFI Mitigation for VLBI and Phased Arrays with Applications in HI/OH Surveys and the Megamaser Cosmology Project


    Chair: J Köhler

 Radio frequency interference in the lower radio astronomy frequency bands is a concern in interferometry, phased array and multi-pixel observations. In particular, spectral line observations suffer from local RFI and satellite induced correlated RFI. Excision is a common practice. There exist however strong methods able to suppress RFI in data before and during post-processing. In present work I will report three types of existing and improved RFI suppression methods. These are applicable to interferometry (VLBI), arrays (WSRT, APERTIF PAF), and arrays with RFI reference antennas. I will present technical output with synthetic and actual data from VLBI and APERTIF.

    To excercise RFI mitigation, 18cm VLBI was used in a OH line search in two galaxies (NGC 1068, Cygnus A). We attempt a definite detection of OH J=3/2 ground state transition in the IR-luminous edge-on AGN of Cygnus A, following an earlier tentative 13.424 GHz detection (Impellizzeri, 2006), to trace regions of massive star formation. The second object, the archetypal Seyfert 2 galaxy NGC 1068, exhibits an inner 1-3pc Keplerian disk with H2O maser spots and OH emission (Gallimore 1996) with massive star formation presumed within 120pc inside the obscuring torus (Exposito 2011). I will present the status so far; a non-detection of OH in 1068 and corresponding maser region size constraint.

    Extragalactic megamasers tracing thin Keplerian disks around AGN can also be used to determine accurate angular diameter distances D to galaxies. The method combines high resolution 22 GHz VLBI maps with single-dish observations. Observing recession versus distance D for galaxies in disjoint clusters in the Hubble flow narrows down the Hubble Constant H0 with implications on dark energy. The goal of the Megamaser Cosmology Project (MCP), for which I intend to assist analyze data and test RFI mitigation non-toxicity, is to combine observations of ten H2O megamaser galaxies found by surveys to get a ~3% accurate estimate of H0. I will present a short introduction to the MCP project in this talk.

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