Monday Seminar for the year 2014

    The presentations are shown in order of increasing time.



    Monthly Discussion



    Abhijeet Borkar (2)

    Monitoring the Galactic Center with ATCA

    Chair: E. Angelakis

The center of the Milky Way hosts a highly variable radio, NIR & X-ray source, Sagittarius A* (Sgr A*) which is associated with a 4 million solar mass super-massive black hole (SMBH). Sgr A* is known to have a ?aring activity occurring from a few hours to few days which has been observed at X-ray and NIR wavelengths with radio/sub-mm ?are following approximately 100 min later. This suggests that Sgr A* undergoes accretion events sporadically. Recently, Gillessen et. al. (2012) reported a dusty object (DSO/G2) approaching Sgr A* with its pericenter passage in mid-September 2013. The ?y-by of this object could result in the enhanced accretion and hence could lead to an elevated ?ux and variability of Sgr A*. We report the results of our recent observations of the Galactic Center with the Australian Telescope Compact Array (ATCA).


    H. Saghiha (3)

    3rd-order galaxy-matter correlation: A new approach to study galaxy formation (models)

    Chair: E. Angelakis





    Banafsheh Shahzamanian (3) + Kostas Markakis (2)






    Monthly Discussion



    Nicolas Caballero (3)

    How noise processes in pulsar timing interfere with Gravitational Wave detection efforts

    Chair: E. Angelakis

 Millisecond (radio) pulsars (MSPs) have remarkable rotational stabilities that allows them to be used as accurate cosmic clocks. Among their many applications in astrophysics and fundamental physics, is the use of an array or MSPs, a Pulsar Timing Array, to directly detect Gravitational Waves. However, MSPs are not perfect timers and many challenges remain on the way to the GW detection. In this talk I'll explain the sources of noise in pulsar timing data and the challenge they impose to GW detection. I will conclude with preliminary results from the  European Pulsar Timing Array project.






    Milan  den Heijer (2)

    Hi kinematics of the Bluedisk ensemble of 50 galaxies selected from the Sloan Digital Sky Survey

    Chair: Nicolas Caballero

In this presentation I will present results of the second and introduce the third project of my thesis work.  In the second project, I study the H i kinematics of the Bluedisk ensemble of 50 galaxies selected from the Sloan Digital Sky Survey and observed in H i with the Westerbork Synthesis Radio Telescope. The sample consists of 25 galaxies with a high H i mass fraction and an equally large control sample including galaxies of comparable stellar mass, stellar mass surface density, redshift and inclination. By studying the H i velocity fields of these galaxies, I investigate whether there are indications of ongoing gas accretion: i.e. global asymmetries and signatures such as warping and kinematical lopsidedness. In addition, I compare the K-band Tully-Fisher and the baryonic Tully-Fisher relations found for both groups. I find no enhanced kinematical asymmetries between the H i-rich sample and the control sample galaxies, indicating no significant difference in kinematical signatures such as warping and lopsidedness. Furthermore, I find no difference in position angle and systemic velocity offset with respect to the optical between the sub-samples. I therefore do not find clear evidence for enhanced global asymmetry of the H i-excess galaxies in comparison to the control sample galaxies. The baryonic Tully-Fisher relation does not show a clear difference between the samples and reveals a comparable scatter to the K-band Tully-Fisher relation. In the third project I investigate systematics in the analysis of H i kinematics. In the first part I will study the effect of zero-spacing correction on the observed kinematics of a nearby spiral galaxy (NGC 2403). This galaxy has been analysed in great detail and is known to contain anomalous gas. In this part I will investigate the effect of the zero-spacing correction on parameters such as the gas inflow rate. Secondly, I will investigate systematic effects of several factors such as zero-spacing correction, Milky-Way confusion, beam-smearing etc. have on the data products used to study kinematics. Instead of using data, this study will focus on 3-dim. simulations of H i kinematics.



     Franz Kirsten (3)

    Standard VLBI and beyond

    Chair: Milan  den Heijer

 In the first part of this talk I will discuss the final results of our multi-epoch VLBI observations of the globular cluster M15. Besides measuring the proper motion of the brightest pulsars in this cluster with unprecedented precision we also determine the nature of two preciously known but unclassified sources within the field of view. Our observations also allow us to constrain the spectral index of the pulsars in M15 and to test the pulsar luminosity function. In the second part I will present the principles and first results of a phased-array mode for the software correlator SFXC.






    Monthly Discussion


    Axel Buddendiek (2)

    Constraining Cosmology using Galaxy-Galaxy Lensing and Galaxy Clustering

    Chair: Franz Kirsten

    Abstract: In order to constrain cosmological parameters we need to compare theoretical predictions with observations. Those predictions are easiest made for the statistical properties of the dark matter distribution in our Universe. Unfortunately, this distribution cannot be observed directly, instead we need to use tracers like galaxies or gravitational lensing. Because galaxies are only a biased tracer and cosmic shear measurements are complicated in many ways I will in this talk introduce a different estimator for the statistics of the dark matter distribution and present the status of my thesis research, which makes use of two large optical data sets: the Kilo Degree Survey and the Red Cluster Sequence Lensing Survey.




    Alessandro Ridolfi (1)

    Timing of pulsars in the globular cluster M15

    Chair: Axel Buddendiek

 Globular clusters (GCs) are spherical, gravitationally bound groups of stars which are very often home of a number of pulsars. Their very high densities, especially near their cores, make GCs also ideal environments for the formation (and disruption) of binary systems and for the spin-up of pulsars through accretion processes. M15 is the fourth-richest globular cluster in terms of the number of pulsars, boasting 7 isolated pulsars and 1 binary pulsar in a double neutron star system (M15C). This latter is of particular interest because it shows evidence of geodetic precession occurring. In this talk I will highlight the most remarkable features of the pulsars hosted in M15 with particular emphasis on M15C. I will outline the current status of the analysis of data previously taken at Arecibo and describe our plans for future observations and consequent studies.



    Alice Pasetto (2) 


    Chair: Alessandro Ridolfi




    Biagina Boccardi (2)

    High resolution mm-VLBI observations of the radiogalaxy Cygnus A

    Chair: Chair: Alessandro Ridolfi

The prototypical radio galaxy Cygnus A is an ideal target for high resolution mm-VLBI studies aimed at a deeper understanding of the mechanism of launching, acceleration and collimation of relativistic jets. Due to its relatively close proximity (z=0.056, DL=247 Mpc, 1 mas=1.07 pc), CygA can be imaged with mm-VLBI reaching a spatial resolution of up to ∼ 200 Schwarzschild radii, providing aunique opportunity to test MHD jet models in the vicinity of the central engine. Results from a kinematic and spectral study at 15, 43 and 86 GHz are shown here. They suggest the presence of a frequency-dependent stratification in the double sided jet, both in flux density (double ridge line at 7 mm) and in velocity (faster layers emerge at higher frequency in the inner jet). The spectral index profile reveals deviations from the typical optically thin synchrotron emission of an expanding jet. The flatter spectrum on the counter-jet side is likely caused by free-free absorption of a torus, partially obscuring the counter-jet but not the jet.



    Patrick Lazarus (3)

    Searching for Radio Pulsars with the PALFA Survey

    Chair: B. Bocccardi / A. Pasetto 

Pulsars, rapidly rotating, highly magnetized neutron stars, are frequently used as tools to probe physics in extreme conditions inaccessible to terrestrial experiments. Many of the >2000 known pulsars have been successfully used to test relativistic gravity, study the interstellar medium, constrain the equation-of-state of ultra-dense matter, etc. For this reason, huge amounts of data produced by several large-scale projects are being combed through using specialized algorithms to identify the faint characteristic emission of radio pulsars. Using the on-going PALFA survey as a case-study, I will give an overview of the basic steps used to find a radio pulsars. I will also provide an update on the status of the PALFA survey, and highlight some interesting pulsars it has recently discovered.

    Jason Wu (1)

    Fermi-LAT guided pulsar searches

    Chair: B. Bocccardi / A. Pasetto 








    Monthly Discussion



    Maria Strandent (2)

    Spectral Energy Distributions of Lensed Dusty Star Forming Galaxies

    Chair: Patrick Lazarus 

 A formally unknown population of rare (n~0.1 deg^2) and extremely bright (S1.4mm > 20 mJy) mm-selected high redshift galaxies has been uncovered with the South Pole Telescope (SPT) from a 2500 deg^2 survey at 1.4 & 2.0 mm.  I will present follow-up observations with APEX (LABOCA) and Herschel (SPIRE and PACS). With this data we can beautifully sample the thermal dust emission for all the sub-millimeter galaxies with S1.4mm >  20 mJy in the 2500 deg2 field yielding information about their star formation rates, dust content, and photometric redshifts.The LABOCA observations provide a crucial piece of data (besides contributing importantly to the SEDs) as only these maps allow us to determine securely the SPIRE counterpart to the 1.4mm emission given the poor spatial resolution of the SPT (1′ ). In my talk I will present an analysis of the dust spectral energy distribution of ~100 SPT selected submm-galaxies including their photometric redshift distribution.


    Denise Keller (2)

    Spectral Survey of IRC+10216 with the JVLA

    Chair: Patrick Lazarus 

 Most intermediate-mass stars become red giants and go through the asymptotic giant branch (AGB) phase during their evolution. AGB stars are important contributors to the chemical evolution of galaxies by providing dust and metal-enriched gas to interstellar molecular clouds in which new stars form, and they are fundamentally important to constrain the formation channels of molecules in the Universe. We observe the emission of molecules in the circumstellar envelopes (CSEs) through their rotational and vibrational transitions in the far-infrared and submillimetre wavelength domain. In many cases the molecular spatial distribution in CSEs departs from spherical symmetry and shows a clumpy structure. In carbon-rich CSEs, the chemistry of carbon-bearing molecules is particularly interesting. I focus on the carbon-rich and high-mass loss AGB star IRC+10216, also known as CW Leonis. Due to its proximity (~130 pc), IRC+10216 is an exemplary object. About 80 molecules have been identified in its CSE, so it is one of the richest and most complex astronomical sources. However, there is no global view on the morphology of its CSE on different scales. I will talk about the new spectral survey of IRC+10216 from the JVLA I am working on. Not only does this survey include a spectral scan from about 18 to 45 GHz that has not been covered before with such a good sensitivity, but also mapping of the molecular distribution on arc second level is done. I perform the calibration and imaging synthesis with the data reduction program CASA. I will present first results of identified spectral lines and example images of the cyanopolyynes HC3N, HC5N and HC7N and will briefly discuss future work. 






    Behnam Javanmardi (2)

    Is cosmic acceleration isotropic?

    Chair: D. Keller

Cosmological Principle requires the Universe to be homogeneous and isotropic on large scales. In an isotropic Universe, the expansion and its acceleration are expected to be (statistically) equal in all directions. In this work, we develop a new method to search for any direction dependency of the cosmic acceleration using Type Ia Supernovae (SNe Ia) data and compare it with the directions of cosmic microwave background anomalies that were detected by WMAP and confirmed by Planck data.


    Elvijs Matrozis (1)


    Chair: D. Keller









    Monthly Discussion


    Gerrit  Schellenberger (2)

    X-ray Cross Calibration and Scaling Relations for Galaxy Groups

    Chair: Elvijs Matrozis & B. Javanmardi

 Cosmological constraints from clusters rely on accurate gravitational mass estimates, which strongly depend on cluster gas temperature measurements. Therefore, systematic calibration differences may result in biased, instrument-dependent cosmological constraints. I quantify in detail the systematics and uncertainties of the cross-calibration of the effective area between five X-ray instruments, EPIC-MOS1/MOS2/PN onboard XMM-Newton and ACIS-I/S onboard Chandra, and the influence on temperature measurements. Performing spectral fitting in the full energy band I find that best-fit temperatures determined with XMM-Newton/EPIC are significantly lower than Chandra/ACIS temperatures. I conclude that using XMM-Newton/EPIC, instead of Chandra/ACIS to derive full energy band temperature profiles for cluster mass determination results in an 8% shift towards lower OmegaM values and <1% shift towards higher sigma8 values in a cosmological analysis of a complete sample of galaxy clusters. 

    X-ray scaling relations are of high importance for the upcoming eROSITA mission in order to constrain cluster masses from observables. In the second part of this talk I demonstrate, how scaling relations are different on galaxy group scales and what selection effects have to be accounted for. I will show in detail which steps have to be performed to
correct for the Malmquist bias and how this changes the resulting scaling relation. 



    Katharina  Borm  (2)

    Studying Cosmology with Galaxy Clusters – the Example of eROSITA

    Chair: Gerrit  Schellenberger

 eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the German core instrument aboard the Russian Spektrum-Roentgen-Gamma satellite which is scheduled for launch in 2015. The main driver for eROSITA is studying the nature of dark energy, which is especially imprinted in the redshift and mass distribution of galaxy clusters. eROSITA is expected to detect around 100 thousand clusters of galaxies in X-rays up to redshifts of z~2.0.
My talk gives an overview of how cosmology can be studied with the help of galaxy clusters and how exactly this study will look like for the future eROSITA data. For this, I introduce the distribution of galaxy clusters with mass and redshift as it is expected to be observed during eROSITA’s all-sky survey. Furthermore, I present forecasts for the observation power of this instrument, by quantifying the accuracy and the precision with which eROSITA will determine the temperature of the intra-cluster medium. According to these predictions, eROSITA will increase the current cluster sample with precise temperatures by a factor of 5-10.  According to these results and the first cosmological forecasts, eROSITA is a very promising instrument for studying the nature of dark energy.






    Ka Tat Wong (1)

    Ammonia Emission from Oxygen-rich Circumstellar Envelopes

    Chair: Katharina Borm 

    Abstract: Evolved stars lose mass to their immediate circumstellar environment and form circumstellar envelopes (CSEs) containing various molecular species. These molecules will eventually return to the interstellar medium and enrich the chemistry in galaxies. However, the physics and chemistry of the formation of molecules are not well understood. One outstanding problem is the abundance of ammonia (NH3) molecules. Observations suggest that the molecular abundance of NH3 in oxygen-rich CSEs is orders of magnitude higher than values predicted by thermodynamic equilibrium chemistry. In order to probe the physical conditions of NH3-forming regions, multiple rotational and inversion transitions were observed towards CSEs of various evolved stars. My work focuses on four oxygen-rich evolved stars (IK Tau, OH 231.8+4.2, VY CMa and IRC+10420) which are the representative samples in their respective evolution stages. In my talk, I will present the spectra and maps of ammonia emission observed with the Herschel Space Observatory and the Very Large Array. I will also discuss the preliminary modelling results using the radiative transfer code RATRAN.






    Marina Berezina (2)

    Pulsar searches with Effelsberg

    Chair: Ka Tat Wong

    Abstract: Pulsars are highly magnetized rapidly rotating neutron stars. The discovery of new pulsars holds great scientific potential because they are valuable probes of fundamental physics in extreme conditions, inaccessible in terrestrial experiments. In my talk I will give an overview of basic steps we need to perform to find a radio pulsar. I will provide an update on the status of the HTRU-North (High-Time Resolution Universe) pulsar survey being done with the 100-m Effelsberg telescope. I will also mention a targeted search for relativistic binaries and touch a bit testing of theories of gravity with the Double Pulsar.






    Monthly discussion






    Florent Mertens (3)  

    Longitudinal and transverse velocity fields in parsec-scale jets

    Chair: Marina Berezina

    Abstract: Radio-loud AGN typically manifest powerful relativistic jets extending up to millions of light years and often showing superluminal motions organised in a complex kinematic pattern. A number of physical models are still competing to explain the jet structure and kinematics revealed by radio images using the VLBI technique. Robust measurements of

    longitudinal and transverse velocity field in the jets would provide crucial information for these models. This is a difficult task, particularly for transversely resolved jets in objects like 3C273 and M87. To address this task, we have developed a new technique for identifying significant structural patterns (SSP) of smooth, transversely resolved flows and obtaining a velocity field from cross-correlation of these regions in multi-epoch observations. Detection of individual SSP is performed using the wavelet decomposition and multiscale segmentation of the observed structure. The cross-correlation algorithm combines structural information on different scales of the wavelet decomposition, providing a robust and reliable identification of related SSP in multi-epoch images. The algorithm enables recovering structural evolution on scales down to 0.25 FWHM of the image PSF. We present here the results from application of this algorithm to obtaining the first detailed transverse velocity fields and studying the kinematic evolution in the parsec-scale jets in 3C273 and M87.

    Rebekka Azulay (1)

    Binary stars in moving groups: AB Dor B and HD 160934

    chair: Florent Mertens

    Abstract: We are going to present radio interferometric data of the binary systems AB Doradus B and HD 160934, members of the AB Doradus moving group. We observed these targets with the LBA at 8.4GHz between 2007 and 2013 and with the EVN at 5GHz between 2012 and 2014, respectively. In both cases it was possible to detect, for the first time, radio emission of the two components of the binary. This has allowed us to mesure the relative orbital motion and to estimate the orbital parameters and the masses of the objects. The study of these two binaries, along with other stars of the same association, will help to calibrate the pre-main sequence (PMS) stellar evolution models for low-mass stars, which is essential, because the contrast with empirical data reveals some discordances.






    Luca Grassitelli (1) & Monthly Discussion

    Observational diagnostic of convective envelopes of Wolf-Rayet stars

    chair: R. Azulay

    Abstract: Wolf-Rayet stars are the late stages of evolved massive star, showing strong mass loss rates. We investigate envelopes of massive pure helium stars (He-star), where the instability to convection is due to the iron opacity peak and where the envelope in some cases is unstable against pulsations. We determine the physical parameters and especially the average convective velocities in the Fe convective regions. We then estimate the velocity amplitude of the perturbations caused by the rising convective elements which propagate through the upper radiative layer to the last hydrostatic surface which potentially lead to the formation of structures and variability observed in the wind of Wolf-Rayet stars. We model the He-stars using the Bonn stellar evolution code. We investigate He-ZAMS stars in the range 2-17Msun with solar metallicity. The code predicts convective regions in the envelope of these stars, using the Mixing Length Theory and OPAL opacities.The results show  the occurrence of sub-surface convective regions which generate  mostly gravity waves. Small surface velocity amplitude are found for model masses below 10Msun and of the order of ten km/s for M>10Msun. Moreover the occurrence of pulsations may drive enhanced mass loss rates in the range 8..14Msun.
The results of this study can relate the surface velocity amplitude to the formation of structures, clumping, in the inner part of the wind. We predict the surface velocity amplitude to become significant for WR stars with mass M>10Msun and we compare our prediction with some observed spectral variability.



     Vassilis Karamanavis (3 moved up) - Cosmos Yeh (2)

     Ultra-high resolution VLBI and broadband radio study  of the prominent gamma-ray blazar PKS 1502+106

    chair: Luca Grassitelli

    Abstract: Blazars are among the most variable and most broad-band emitters of radiation in the Universe. The detailed processes that give rise to those characteristics though, remain still unclear. In August 2008, Fermi/LAT discovered the blazar PKS 1502+106 showing a rapid and strong gamma-ray outburst followed by bright and variable flux over the next months. This activity at high energies triggered an intensive multi-wavelength campaign indicating that the outburst was accompanied by a simultaneous flare at optical/UV/X-rays with a significantly delayed counterpart at radio bands as observed by the F-GAMMA program. Taking advantage of the densely sampled 2.6 to 345 GHz light curves and spectra of the F-GAMMA along with broad-band data up to Fermi gamma-ray energies and with the addition of ultra-high angular resolution VLBI imaging at 86 and 43GHz, we attempt to shed light on the physical processes at work during the high-energy flare. Consequently, PKS 1502+106 turns out to be a key source in the framework of detailed studies of the physical connection between the radio and gamma-ray emission, particularly probing the emission mechanism, size and location of the gamma-ray emitting region. In this talk the findings of the mm-VLBI study using the Global Millimeter VLBI Array (GMVA) data between 2009 and 2012, will be presented. Furthermore an initial analysis of the radio light curves and spectra will be discussed.

    Cosmos Yeh (2)

    CO observations of Luminous Star Forming Regions in the Carina Arm

    chair: Vassilis Karamanavis

    Abstract: We present a large-scale CO data cube of one of the massive star-forming regions in the Far Carina Arm. By utilizing FLASH345/460L receiver of the APEX telescope, we observed star forming region G297.50-0.80 with CO(3–2), CO(4–3), and 13CO(3–2) simultaneously. The comparison between Herschel/SPIRE far infrared images and the APEX/CO integrated intensity maps reveals an unprecedented picture of massive star forming clumps and their diffuse, ambient environment. Molecular line mapping without line-of-sight contaminations also indicate that most of the structure of G297.50-0.80 in continuum images are located at the distance of Far Carina Arm. Applying the radius-velocity map and the line intensity profile for the interstellar bubble located at the center of G297.50-0.80 reveals the signature of expanding shell.






    Sandra Martin (3) - Naftali Kimani (2) 

               Using galaxy-galaxy-galaxy lensing to constrain the halo model

    Chair: Cosmos Yeh

    Abstract: A widely accepted model for the distribution and evolution of matter in our Universe is the halo model. It assumes that the whole dark matter content of the Universe is bound to so called halos which host its luminous tracers, the galaxies. The assumptions on which this semi-analytical model is build, can be tested by comparing predictions of the model to real measurements. So far the halo model predictions fit second-order signals quite well, but can it also reproduce third-order correlation functions?

    In my PhD project I use the halo model to forecast the galaxy-galaxy-galaxy lensing signal. I compare the modeled signal with observations to test the assumptions and the physical concepts the model is based on.

    Naftali Kimani (2)

    The Kinematics study of M81-M82 galaxies

    chair: Sandra Martin

    Abstract: Galaxy interaction is a common phenomena which plays an important role in galaxy evolution. In this work, we study the M81 group which shows clear signs of tidal interactions. The goal is to obtain the proper motion of M81 and M82 galaxies, and the tangential motions of M81 and M82 relative to milky Way. To achieve this, the nucleus of M81 and 3 background quasars were observed with a global VLBA array for 3 years. Phase-referencing the background quasars with the compact radio nucleus of M81 (M81*) enables us to find the proper motion of M81 galaxy. We will present the preliminary results of the morphologies of M81* and quasars and the proper motion of M81 galaxy.






    Monthly Discussion









    --- SUMMER BREAK ---









    Monthly Discussion



    Carolina Mora (3)

    NGC4631 with the new EVLA telescope

    chair: Naftali Kimani 

    Abstract: Continuum HAlos in Nearby Galaxies - an EVLA Survey (CHANG-ES) is a new survey of 35 edge-on galaxies to search for both in-disk as well as extra-planar radio continuum emission. The survey is exploiting the new wide bandwidth capabilities of the Expanded Very Large Array (EVLA) telescope  in a variety of array configurations and at 1.5 GHz and 6 GHz, in order to compile the most comprehensive data set yet obtained for the study of galaxy properties. NGC 4631 is an spiral edge-on galaxy with a spectacular radio halo. I will present new images of this galaxy obtained with the EVLA on the total power and polarized emission, spectral index and rotation measure distribution.



    Philip Schmidt (3 moved up) Sebastian Kielhmann (3 moved up)

    Magnetic Field Structure and Spectral Distribution in the Edge-on Galaxies NGC 891 and NGC 4565

    chair: Naftali Kimani

    Abstract: Being two high-priority targets of CHANG-ES (Continuum Halos in Nearby Galaxies – an EVLA Survey), the nearby edge-on galaxies NGC 891 and NGC 4565 are well-suited objects to study the magnetic field structure in galaxy halos as well as cosmic ray transport. The wideband capabilities of the recently upgraded Jansky Very Large Array (JVLA/EVLA) not only provide unprecedented sensitivity limits (which for the first time allow to detect these galaxies at angular resolutions down to 3'' at radio frequencies) but are also of particular advantage for the application of Rotation Measure (RM) Synthesis, in order to probe the line-of-sight magnetic field component. In addition, it is now possible to compute the spectral index across a single frequency band. I will draw a comparison between the spectral index measurements within two such bands (centered around 1.5 GHz and 6 GHz in this case), which allows to put constraints on the thermal fraction and the shape of the synchrotron spectrum at different positions within a galaxy, and will also point out differences in the spectral behaviour of the two galaxies.

    Sebastian Kiehlmann 

    Massive star forming regions

    chair: Philip Schmidt 

    Abstract: In my third IMPRS seminar presentation I will talk about the progress of my PhD project. I will only briefly touch the scientific output and results of analyzing a multi-wavelength photometry and polarimetry data set of a blazar. Instead I am going to focus on the way this project evolved from its original project plan to its current status. I will point out some aspects of self-, time- and project-management and will discuss how scientific work –as a creative process-, to my understanding, is conducted. Aside from my personal view on managing and performing a scientific project I would like to raise a few questions as basis for a discussion with the audience.






    Miriam Ramos Ceja (3)

    Multiwavelength study of distant galaxy clusters

    chair: S. Kiehlmann

    Abstract: In recent years, X-ray and radio observations have revealed the variety and complexity of the physical processes in the Intra-Cluster Medium. In a similar way, a new generation of optical/IR studies of galaxy clusters are extending our knowledge by routinely finding clusters at redshifts above z~1. These high-z studies shed new light on the formation history of the large scale structure. Thus, the combination of multiwavelength observations allows a deep understanding of many properties of galaxy clusters. The XMM-Newton Large Scale Structure (XMM-LSS) and The Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS) belong to these state of the art surveys in X-rays and optical/infrared, respectively. In this talk I will describe a Bayesian technique for X-ray aperture photometry, which allows to put a flux limit on non-detected/faint X-ray galaxy clusters. And I will present how this method is applied to X-ray observations of a SpARCS galaxy cluster sample, and how measure and compare the X-ray/infrared properties of both populations.






    Special Seminar: 

    Dr. Peter A. Schuller

    Job Seeking Outside Academia – A Personal Review 







    Ioannis Miserlis (3) + Tobias Roehser (2)

    Gaining insight of the micro-physics of AGN jet emission elements using high-precision linear and circular radio polarimetry

    chair: Miriam Ramos Ceja

    Abstract: The current picture of the physical characteristics of AGN jets is one with several open questions. We attempt to address the ones that concern their magnetic field magnitude and topology as well as the jet composition through the means of linear and circular radio polarimetry. The accuracy needed though to look at the detailed picture of the theoretically predicted polarization behavior of these sources in the radio bands is of the order of 0.1% for both linear and circular polarization measurements, which is hardly reached using the current practice of radio polarization data reduction. In this talk, I will discuss the methods we developed to reach the needed accuracy and measure the linear and especially the circular radio polarization of AGN jet emission elements in high accuracy using data obtained with the Effelsberg telescope.

    Molecular Gas in Intermediate-Velocity Clouds

    chair: Ioannis Myserlis

    Abstract: Intermediate-Velocity Clouds (IVCs) are HI clouds in the lower galactic halo that are thought to be related to a galactic fountain process. IVCs are predominantly atomic with a small fraction of molecular hydrogen (H_2). However, a few molecular IVCs (MIVCs) are observed with a significant amount of H_2. MIVCs are identified by their far-infrared (FIR) excess, e.g. more FIR emission than inferred from the HI emission alone. Using the HI-FIR correlation with data from the Effelsberg-Bonn HI Survey and the Planck Satellite, we deduce the H_2 distribution towards large galactic latitudes.
    For two particular neighbouring IVCs, a FIR-dim and a FIR-bright cloud, we obtained high-resolution HI data with the Westerbork-Synthesis Radio Telescope and additional 12CO(1-0) and 13CO(1-0) observations with the IRAM 30m telescope. We study the small-scale structure of the different types of clouds as well as the X_CO-factor. MIVCs show significantly lower X_CO-factors than the canonical value known for the Milky Way disk.



    Alberto Doria (3)

    The 400d Cosmological Sample: Weak Lensing Analysis of the IMACS and MegaCam Clusters

    chair: Tobias Röhser

    Abstract: One of the major challenges of today's astrophysics and cosmology is to unveil the mystery of dark energy, leading to a better understanding of the history and evolution of the universe.
    The study of galaxy cluster evolution, in particular of the number density of massive clusters, allows us to constrain cosmological parameters. Considering the importance of cluster mass estimation, the comparison of independent approaches, such as X-ray and gravitational lensing analysis, yields the most accurate results in tracing the cosmic evolution. We are working on the mass reconstruction  of the weak lensing follow-up of the cosmological subsample of the 400d Galaxy Cluster Survey: this is a complete sample of 36 high-redshift (0.35 < z < 0.90) clusters. Providing new mass estimates through weak lensing measurements we will obtain more reliable masses, correcting for possible biases on the X-ray measurements. This will also contribute to improve our understanding of the scaling relation between X-ray luminosity and mass, providing the essential connection between observations and cosmological constraints that will be obtained thanks to the forthcoming eROSITA mission. The previous steps in data reduction and analysis and the current status of the lensing work on a subsample of 8 galaxy clusters observed with IMACS@Magellan and MegaCam@CFHT will be presented, together with a focus on the outlook of the future tasks to be performed on the 400d Cosmological Sample.






    Monthly Discussion 






     Pablo Torne (3) + Eleni Graikou (1)

    High-frequency Radio Observations of the Galactic Centre Magnetar J1745-2900

    chair: A. Doria 

    Abstract: In this talk I will comment on the mystery of pulsar radio emission and present the results of high-frequency observations of the radio loud magnetar J1745-2900. This object is particularly interesting for being very close to SgrA*, the supermassive black hole in the centre of our Milky Way, and can be used to probe the medium between us and the Galactic Centre. Furthermore, the flatter spectral index of radio magnetars with respect to normal pulsars make them unique sources to survey the under-explored region of pulsar spectra at very high radio frequencies and try to test pulsar emission models. Among other interesting results that will be commented, our detections of J1745-2900 and B0355+54 reached 154 and 138 GHz, respectively, setting new records for the detections at radio frequencies of magnetars and normal pulsars.

    Precise pulsar timing

    chair: P. Torres

    Abstract: Pulsars are rotating neutron stars. Especially, millisecond pulsars have a property that make them unique. Their rotational stability is comparable to the stability of atomic clocks in long time scales. The precise measurement of the exact time that their signal arrives to Earth is a technique known as pulsar timing. Pulsar timing provides us with useful information about the characteristics of pulsar (mass, orbital parameters etc.), the interstellar medium and help us test theories of gravity. In this presentation I will try to explain how timing works and why it is important. And finally, I will present the timing parameters of PSR J1933-6211 a millisecond pulsar with a low mass white dwarf companion and a good timing precision.   



    Won Ju Kim (1)

    Hydrogen recombination emissions toward a new sample of galactic massive star-forming clumps


    We do not know still how massive stars are formed but several evolutionary stages
    by a lot of efforts are revealed like the infrared dark cloud, the high-mass proto-stelallar object and the ultracompact HII region (or the hyper compact HII region). In particular, I will talk the ultracompact HII region or the hyper compact HII regions  in today talk. The HII regions are signposts of the massive star formation. In addition, I will explain why ATLASGAL sources are a good sample for the study of evolutionary stages of the massive star formation unlike former criteria of evolutionary stages. And I will show what physical information can be obtained from recombination emissions. Last, I will briefly show preliminary results of millimeter recombination lines observations towards the ATLASGAL sources.






    Special Seminar

    Eduardo Ros

    Abstract: I my talk I will give a general overview to the important aspects to consider about the next logical step in an astronomer’s career after the PhD: a postdoctoral stay or fellowship.  I will give some hints on the strategy for finding a postdoc, the application itself, and some guidelines on further career planning beyond the postdoctoral stay.  Academia, research institutes and other options such as an exit strategy will be considered as well.



    Dhanya G. Nair (1)  - Monthly Discussion

    86 GHz VLBI Survey of Ultracompact Radio Emission in Active Galactic Nuclei

    chair: Won Ju Kim

    Very Long Baseline Interferometry (VLBI) Observations at a frequency of 86 GHz (wavelength of 3 mm) reach a resolution of about 50 microarcseconds and enable detailed studies of ultracompact radio emission in Active Galactic Nuclei. Synchrotron radiation becomes optically thin at millimetre wavelength; making it possible to look deeper into the inner jets of AGN. The data at 86 GHz will sample the scales as small as 103 -104 Schwartzchild radii and uncover the jet regions where accelaration and collimation of the flow takes place. In this context, we are carrying out a survey of 175 ultracompact radio sources (in quasars,radio galaxies and blazars) at 86 GHz to study the morphology and also to estimate the brightness temperature of these sources.
    In this talk, I will present how brightness temperature is measured in this survey and how it will be utilized to study the behaviour of brightness temperature as a function of frequency and also as a function of the linear distance from the central engine of the AGN.  I will also present in brief the calibration methods used for the data reduction of the first epoch of this survey and the preliminary results for the radio images and also the brightness temperature measurements at 86 GHz for the sources 3C273B, J2210+2013, J0046+2456, J0700+1709, 3C345, J0713+1935 , J0956+2515 and J1043+2408.



     Xmas party for the Administration Division










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