Wed 21st Aug 2019 @12:00 PM, level 7, David Caro Building
Prof. John Lattanzio
Email: john.lattanzio@monash.edu
Abstract
The final 12 minutes of the Apollo 11 moon landing were filled with problems and ample reasons to abort. I will explain what was happening and why, and thus unlock the tension of those last few minutes. While the world watched in awe of the achievement, only Mission Control and the astronauts realised how close they were to aborting…for more than one reason.
Wed 14th Aug 2019 @14:15 PM, level 7, David Caro Building
Alejandro Vigna Gomez
Email: avigna@star.sr.bham.ac.uk
Abstract
Neutron stars have been associated with pulsars, X-ray binaries, Galactic double neutron stars, short gamma-ray bursts, gravitational waves and luminous red novae. In this talk, I will discuss the study of double neutron stars using the COMPAS population synthesis code. I will focus on the orbital properties of the Galactic double neutron star population. I will also discuss the mass transfer episodes leading to common-envelope events for this population, which have been associated to luminous red novae.
Wed 7th Aug 2019 @14:15 PM, level 7, David Caro Building
Dr Anne Hutter
Email: a.k.hutter@rug.nl
Abstract
The Epoch of Reionization represents an important epoch in the history
in the Universe, when the first stars and galaxies gradually ionize the
neutral hydrogen in the intergalactic medium (IGM). Understanding the
nature of the ionizing sources, the associated ionization of the IGM,
and its impact on subsequent structure formation and galaxy evolution by
means of radiative feedback effects, represent key outstanding questions
in current astrophysics.
In the past few years high-redshift galaxy observations and simulations
have significantly extended our knowledge on the nature of high-redshift
galaxies. However, essential properties such as the escape fraction of
ionizing photons from galaxies into the intergalactic medium and their
dependency on galactic properties remain essentially unknown, but
determine significantly the distribution and time evolution of the
ionized regions during reionization. Analysing this ionization topology
by means of the neutral hydrogen sensitive 21cm signal with radio
interferometers such as the Square Kilometre Array (SKA) offers a
complementary and unique opportunity to determine the nature of these
first galaxies and pin down the reionization history.
In this talk, I will discuss how synergising high-redshift galaxy
observations with 21cm signal detections can provide constraints on
reionization. Furthermore, I will show results from a self-consistent
semi-numerical model of galaxy evolution and reionization, and discuss
the potential of inferring galactic properties, as the escape fraction
of ionizing photons, with the 21cm signal by means of its bispectrum.
Thurs 1st Aug 2019 @14:15 PM, level 7, David Caro Building
Adélie Gorce Imperial College London/Institut d’Astrophysique Spatiale
Email: adelie.gorce16@imperial.ac.uk
Abstract
During the Epoch of Reionisation (EoR), the first galaxies and AGNs ionise the neutral atoms surrounding them. Although essential, this period in the history of the Universe is still poorly known. We wonder about the sources: if it is generally admitted that the first stars led the process, more exotic sources such as the bright radiation of quasars might be needed. But also about the chronology: when were the first stars born? How efficient were they to ionise the IGM, what were their properties? Finally, about the topology: were overdense regions ionised first or last?…
In this talk, I’ll give an overview of the different observational ways available to learn about cosmic reionisation, from astrophysics to cosmology, from galaxy and quasar spectra to the 21cm signal. I’ll present the assumptions usually made to model reionisation and how they can impact the interpretation of observations. Finally, I’ll spend some time on the prospects of observing the 21cm signal to learn about the EoR, and in particular, what we can learn from the non-Gaussianity of the signal.
Email: charlotte.mason@cfa.harvard.edu
Abstract
The reionization of intergalactic hydrogen in the universe’s first billion years was likely driven by the first stars and galaxies. The timeline of reionization is currently uncertain but if it is accurately measured it can unveil properties of ‘first light’ sources. I will describe how we can use galaxies at our current observational frontiers to learn about reionization. In particular, Lyman alpha (Lyα) emission from galaxies can be used to probe the intergalactic medium (IGM) at high redshift, but requires modelling physics from pc to Gpc scales. I will describe a forward-modelling Bayesian approach which combines cosmological IGM simulations with empirical interstellar medium models to constrain reionization from observations of galaxies, focusing on Lyα emission at z>6. I will present new measurements which favour a late and relatively rapid reionization, and place these in the context of high redshift galaxy formation. I will discuss the challenges and future prospects in using Lyα emission as a cosmological tool.
Mon 22nd July, 2019 @3:15 PM, level 6, David Caro Building
Akanksha Kapahtia, Indian Institute of Astrophysics
Email: akanksha.kapahtia@iiap.res.in
Abstract
Neutral hydrogen is the dominant component of the universe after recombination with high density regions harbouring the first luminous objects. The radiation from these first luminous objects changes the thermal and ionization state of the intergalactic medium leading to a major transition in the history of the universe called the Epoch of Reionization (EoR). The EoR is marked by the appearance of ionized regions around these collapsed objects which grow and merge until the entire universe is ionized. The growth and topology of these ionized regions depends upon the properties of these first luminous sources. One important observational probe of the EoR is the 21cm spin flip hyperfine transition of the neutral hydrogen. The brightness temperature of this transition encodes the ionization and heating history of the IGM. We introduce real space morphological descriptors, called Minkowski Tensors (MTs) and topological quantities Betti numbers, to probe the morphology of the 21cm brightness temperature field. The MTs provide shape and anisotropy information of the structures in the excursion set of the fields, while Betti numbers describe the topology in terms of the number of connected regions and holes. We obtain different regimes of morphological evolution of brightness temperature, as the universe evolves depending upon different astrophysical settings of the EoR. Therefore, we show that the ionization history of the IGM can be reconstructed using the morphological description of brightness temperature in real space and help us further probe the properties of the first luminous objects.
Thurs 4 July, 2019 @12:00 PM, level 6, David Caro Building
Luke Pratley, Mullard Space Science Laboratory, University College London
Email: luke.pratley@gmail.com
Abstract
The standard methods in radio interferometry for reconstructing images, such as CLEAN and its variants, have served the community well over the last few decades and have survived largely because they are pragmatic. However, they produce reconstructed interferometric images that are limited in quality and scalability for big data. In this work, we demonstrate the use of computationally distributed state-of-the-art sparse image reconstruction algorithms which have been implemented in the PURIFY software package. We do this by applying PURIFY to real interferometric observations from the Very Large Array (VLA) and the Australia Telescope Compact Array (ATCA), where PURIFY out performs CLEAN in modelling structure shown by the residuals. Lastly, we use PURIFY in wide-field imaging at low frequencies, where the w-projection algorithm models wide-fields of view with the non-coplanar w-term.The required accuracy and computational cost of these corrections is one of the largest unsolved challenges facing next generation radio interferometers. We show that the same calculation can be performed with a radially symmetric w-projection kernel, where we use one dimensional adaptive quadrature to calculate the resulting Hankel transform, decreasing the computation required for kernel generation by several orders of magnitude, whilst preserving the accuracy. We demonstrate the potential of our radially symmetric w-projection kernel via sparse image reconstruction, using the software package PURIFY. We develop a distributed w-stacking and w-projection hybrid algorithm where we apply exact w-term corrections for each measurement from observations from the Murchison Widefield Array (MWA), showing that it allows full wide-field correction for real data sets.
Wed 3 July, 2019 @2:15 PM, level 7, David Caro Building
Dr Catherine Watkinson, Imperial College London
Email: c.watkinson11[at]imperial.ac.uk
Abstract
The SKA and HERA are expected to detect the 21cm line of neutral hydrogen from the high-z Universe with great precision. This should allow us to learn about early generations of stars and galaxies, as we observe the impact of their radiation through ionisations and heating of hydrogen in the intergalactic medium.
As theorists, the challenge we face is how to best interpret these observations. Much work has already been done to develop MCMC pipelines using fast semi-numerical simulations. The current pipeline 21cmMC only includes the power spectrum as a metric to compare how similar a given simulation is to the data. I will discuss the benefits of including statistics that are sensitive to non-Gaussianity in the data.
To facilitate this discussion, I will provide an intuitive explanation of the bispectrum, why it might be an interesting statistic for many datasets, and how it is easier to measure than is often thought. I will also touch on some work I have been doing on likelihood-free parameter estimation which allows the researcher to concentrate on forward modelling their problem, rather than working out the appropriate form for the likelihood.
Wed 26th June, 2019 @14:15 PM, level 7, David Caro Building
Tom Binnie, Imperial College London, UK
Email: t.binnie16@imperial.ac.uk
Abstract
We apply Bayesian statistics to perform model selection on different reionisation scenarios via the Multinest algorithm. Initially, we recover the results shown by 21CMMC for the parameter estimation of 21cmFAST models. We proceed to test several toy models of the Epoch of Reionisation (EoR) defined in contrasting morphology and scale. We find that LOFAR observations are unlikely to allow model selection even with long integration times. HERA would require 61 dipoles to perform the same analysis in 1080 hours, and becomes comparable to the SKA with 217 dipoles. We find the SKA requires only 324 hours of observation to conclusively distinguish between our models. Once model selection is achievable, an analysis of observational priors is performed finding that neutral fraction checks at specific redshifts add little to no inference. We show the difficulties in model selection at the level of distinguishing fiducial parameters within a model or distinguishing galaxies with a constant versus power law mass-to-light ratio. Finally, we explore the use of the Savage-Dickey density ratio to show the redundancy of the parameter Rmfp within 21cmFAST.
Wed 12th June 2019 @14:15 PM, level 6, David Caro Building,
Dr. Daniel Reardon, Swinburne University,
Email: dreardon@swin.edu.au
Abstract
Radio pulsars are precise clocks that can be timed using a detailed model of the pulsar, its binary orbit, and the ionised interstellar medium along our line of sight. This timing model can be used to test theories of dense matter, gravity in the strong field, and a set of the most stable pulsars can even be used as a Galactic-scale gravitational wave detector. In this talk I will describe my work to improve the timing models of pulsars through precision pulsar timing and by modelling their scintillation. I will highlight recent results for the nearest and brightest millisecond pulsar PSR J0437-4715, which include precise new distance and mass measurements, and a relativistic binary PSR J1141-6545. Finally, I will describe how these techniques will be useful for next-generation instruments including the Parkes ultra-wideband receiver, and the impressive MeerKAT radio telescope in South Africa.
Wed 5th June, 2019 @14:15 PM, level 7, David Caro Building
Dr Yuxiang Qin, Scuola Normale Superiore, Pisa
Email: yuxiang.qin@sns.it
Abstract
The measurement of the cosmic 21-cm signal with the SKA will transform our understanding of the epochs of reionization and cosmic dawn. The properties of the first stars and galaxies are encoded in the patterns of the signal. Interpreting these patterns requires accurate and efficient models. I will present an update of the 21cmFAST semi-numerical simulation, which separately accounts for star-formation inside the very first galaxies. This unseen and transient population of galaxies obtain their gas through molecular cooling from the intergalactic medium, and could have markedly different properties from the more massive galaxies observed with Hubble and eventually JWST. I demonstrate that if the recently-reported EDGES signal at z~17 is genuinely cosmological, these molecularly-cooled “mini-halo” galaxies must have played a dominant role during Cosmic Dawn.
Wed 29 May, 2019 @14:15 PM, level 7, David Caro Building
Dr Nick Seymour, Curtin University
Email: nick.seymour[at]curtin.edu.au
Abstract
Radio surveys are unique probes of accreting super-massive black holes. Curiously, powerful radio emission is associated with both high and low accretion rates. Broadband radio surveys covering many decades of frequency allow us to select specific radio-loud sources as well as to characterise their jet power. I will present work at both low and high redshift studying the evolution of super-massive black holes selected from radio surveys. From deep multi-wavelength observations of the GAMA 23 survey field, I will present a study of a giant radio galaxy associated with a cluster at z~0.2. Modelling of the radio emission and the high current accretion rate suggests that this source may have had a recent change in its accretion state. I shall also present work using broad-band radio surveys and unique follow-up to identify some of the earliest super-massive black holes in the Universe. The ultimate aim of this project is to study the impact of radio-loud sources within the Epoch of Reionisation.
Wed 15 May, 2019 @14:15 PM, level 7, David Caro Building
Dr Kim-Vy Tran, UNSW
Email: kimvy.tran[at]gmail.com
Abstract
ZFOURGE and MOSEL are deep observational surveys that track how galaxies assemble over cosmic time. ZFOURGE identifies approximately 70,000 objects up to redshifts of z~7 using a custom set of near-infrared imaging filters that provide high precision photometric redshifts. MOSEL targets emergent galaxies from ZFOURGE for spectroscopic follow-up to track this rapidly evolving population. Here I highlight results that include building a library of composite Spectral Energy Distributions and using the SED fitting code Prospector to determine star formation histories for a range of galaxy populations.
Mon 13th May, 2019 @14:15 PM, level 6, David Caro Building
Dr Koki Kakiichi, University College London
Email: k.kakiichi@ucl.ac.uk
Abstract
Study of reionization is now experiencing a surge of new insights, but the long-standing problem ‘what reionized the universe’ still remains unsolved. Hubble observations have placed a now-commonly-held view that the intrinsically faint galaxies are responsible for driving the reionization process, but with a fundamental assumption of large escape fractions >10%. A further puzzle comes from the recent deep spectroscopy of luminous galaxies and the spatial opacity fluctuation of the intergalactic medium (IGM) at z>5.7, which suggests a possibly important role of luminous systems and active galactic nuclei/quasars (QSOs). In the theoretical front, simulating early galaxies and the reionization process and is extremely challenging, requiring the understanding of the physics over a huge dynamic range from the scale of molecular clouds to the intergalactic medium. To shed light on these issues, we introduce a new spectroscopic programme surveying 56 QSO fields and a power of direct 3D mapping of galaxies and the IGM via 21cm tomography, which will be enabled by JWST, ELT, and SKA.
Wed 8th May 2019 @14:15 PM, level 7, David Caro Building
Dr Emma Kerr RMIT
Email: emma.kerr[at]rmit.edu.au
Abstract
The problem posed by space debris has been internationally recognised and many different methods tackling both mitigation and remediation have been proposed. One fundamental challenge though is accurate tracking and position prediction of objects in orbit. Beyond improving technology, the only method for tackling this challenge is in improving orbit propagation method. Orbit propagation allows a user to predict where an object will be in the future given its current position. This research focusses on improving general perturbations methods for orbit propagation. General perturbations methods for orbit propagation are typically considered to be less accurate and/or less useful than their numerical counterparts. The major problem facing these methods in terms of accuracy is that it is very difficult to capture time dependant phenomena such as the solar activity cycle’s effect on atmospheric density in a general perturbation solution. To date very little research on this topic has been published, as computers became more powerful it became less important to study such methods. However, as space debris has become such a prevalent issue, threatening the safety of both current and future missions, it has once again become prudent to look at methods that can allow the propagation of a large catalogue of objects in as computationally inexpensive way as possible.
Fri 3rd May, 2019 @15:15 PM, level 7, David Caro Building
Professor Romeel Davé, University of Edinburgh
Email: rad@roe.ac.uk
Abstract
The growth of black holes and their role in quenching massive galaxies is a key unsolved problem in galaxy formation. I present a new suite of cosmological hydrodynamic simulations called Simba, which builds on our successful Mufasa simulations to include a novel torque-limited black hole accretion model and AGN feedback using observationally-constrained bipolar kinetic jets. I will describe the physical motivations behind our new model, explain why they represent an improvement over other current black hole growth and feedback models, and demonstrate that they yield a galaxy population in very good agreement with numerous observations across cosmic time. These successes set the stage for exploring galaxy–black hole co-evolution towards better understanding the impact of AGN feedback on the baryon cycle along the mass hierarchy.
Wed 1st May, 2019 @14:15 PM, level 7, David Caro Building
Dr Paul Lasky, Monash University
Email: paul.lasky@monash.edu
Abstract
Gravitational-wave astronomy is now a reality. In the first two observing runs of Advanced LIGO and Virgo, there were ten detected black hole collisions, and one spectacular multimessenger detection of a binary neutron star merger. But what is next for this burgeoning field of gravitational-wave astronomy? I will discuss what we hope to learn from both black hole and binary neutron star collisions in the near future. This will include journeys into the exotic world of testing General Relativity in the ultra-strong field regime, and understanding bulk nuclear matter at supranuclear densities. I will also discuss the next generation of gravitational-wave instruments, and Australia’s potential to play a significant part in this global endeavour.
Wed 17 April, 2019 @14:15 PM, level 7, David Caro Building
Dr Rossana Ruggeri, Swinburne University
Email: rruggeri[at]swin.edu.au
Abstract
With the aid of millions of galaxies, cosmology, as a data driven discipline, investigates the physics just after the Big-Bang, when the seeds of anisotropies ( later becoming galaxies through gravity ) were created and the effect of dark energy driving the evolution of the Universe today.
In this talk I will present various ways in which we can use galaxy redshift surveys to test theoretical models. In particular, using observables like Baryon Acoustic Oscillations and Redshift-space distortions, we can measure the cosmological parameters as well as test models of dark energy and modified gravity. The low statistical errors on cosmological parameters promised by future galaxy surveys will only be realised with the development of new, fast, analysis methods that reduce potential systematic problems to low levels. In the second part of my talk, I will present an efficient method for measuring the redshift evolution in the cosmological parameters and its application to measure the latest eBOSS DR14 data.
Mon 1 April 2019 @14:15 PM, level 7, David Caro Building
Dr Sarah Sweet Swinburne University
Email: sarah[at]sarahsweet.com.au
Abstract
How do galaxies evolve from the compact, red nuggets; clumpy, turbulent disks; and complex merging systems of the early Universe to the familiar Hubble types we see today? Their evolution is intimately linked with the environmental conditions and structure of the Universe since cosmic noon. The impact of cumulative tidal torques over a galaxy’s lifetime is traced by its specific angular momentum, which is consequently a fundamental property in its evolutionary history, affecting that galaxy’s size, density and morphology. In this talk I will present research into the relation between specific angular momentum and galaxy morphology for galaxies at the peak of cosmic star formation and galaxies today, critically accounting for the internal spatial distribution of angular momentum and its effect on galaxy evolution.
Wed 27 March 2019 @14:15 PM, level 7, David Caro Building
Dr Amelia Fraser-McKelvie, University of Nottingham
Email: amelia.fraser-mckelvie[at]nottingham.ac.uk
Abstract
Most galaxies consist of a dispersion-dominated bulge region and a regularly rotating disk. These components have built up their mass separately through different processes, yet are evolving together. It has become commonplace to separate the light from bulge and disk regions to better understand their formation and contribution to their host galaxy. The same techniques can also be applied to IFS data of other galaxy components, such as bars and spiral arms. I will detail some of the latest results from the MaNGA galaxy survey, including efforts to study stellar populations in lenticular galaxies within bulge and disk regions, and an investigation into the influence of bars on the secular evolution of disk galaxies.
Mon 25th March, 2019 @14:15 PM, level 7, David Caro Building
Dr Benedetta Vulcani, INAF – Osservatorio Astronomico di Padova
Email: benedetta.vulcani[at]inaf.it
Abstract
Studying galaxies in transition in the different environments give important clues on galaxy evolution. I will present different methods to select galaxies in transition, showing how different approaches can reveal different pathways to quenching.
– Transition galaxies can be identified as outliers in the SFR-mass plane. I will focus on the cluster SFR-mass relation at z=0 and show that in some galaxies the star formation is enhanced, while in some others it is suppressed with respect to the field. The triggering of the star formation is due to fast gas removal processes, such as ram pressure stripping (Vulcani+2018c), while its suppression is due to slow processes, such as strangulation (Paccagnella, Vulcani+2016).
– Transition galaxies can be selected according to their spectral information. I will show how the incidence and the properties of post starburst galaxies, tracers of fast quenching processes, depend on environment (Paccagnella, Vulcani+2017, 2018).
– Transition galaxies can be selected using photometric information. I will also present an analysis of those galaxies that show signs of an ongoing or recent transformation of their star formation activity and/or morphology discussing an evolutionary scenario that links all the different populations at z=0 (Vulcani+15).
These analyses are based on the GAs Stripping Phenomena in galaxies with MUSE (GASP) survey, the WIde-field Nearby Galaxy-cluster Survey (WINGS), its recent extension OmegaWINGS and the Padova Millennium Galaxy Group Catalog (PM2GC).
Mon 18 March 2019 @14:15 PM, level 7, David Caro Building
Prof. Ian Jones University of Southampton, UK
Email: d.i.jones[at]soton.ac.uk
Abstract
In this talk I will describe the physics that determines the spin evolution of millisecond magnetars, early in their lives. The results have implications for their gravitational wave emission, and for the distributions of spins and magnetic field geometries observed in the Galactic magnetar population.
Wed 6 March, 2019 @12:00 PM, level 7, David Caro Building
Dr Matthew Baring, Rice University
Email: baring[at]rice.edu
Abstract
Magnetars are young neutron stars with high surface magnetic fields,
exceeding around 10 TeraGauss. Pulsed, non-thermal quiescent X-ray
emission extending between 10 keV to >150 keV has been observed in about
10 magnetars by RXTE, INTEGRAL, Suzaku, NuSTAR and Fermi-GBM. This talk
describes a model for the generation of such hard X-ray signals, wherein
the emission is produced by resonant Compton upscattering of soft
thermal photons from the neutron star surface. This mechanism is
efficient due to the enhancement of the scattering cross section at the
cyclotron resonance. Spectra that approximately match observations can
be generated by emission volumes within about ten stellar radii of the
magnetar surface. The observed/implied maximum energies of these hard
X-ray signals may require that an attenuation process such as magnetic
photon splitting be active. This prospect can be probed by future
sensitive Compton telescopes with polarimetric capability, for example
the AMEGO concept. Interestingly, key pulsation and spectral signatures
can be used to constrain the viewing geometry and the angle between the
magnetic and spin axes of magnetars, a diagnostic that may improve the
ability to precisely determine the strengths of magnetar fields.
Thurs 28 Feb, 2019 @12:00 PM, level 7, David Caro Building
Dr Natasha Hurley-Walker, ICRAR
Email: nhw[at]icrar.org
Abstract
Using images from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM; MWA) survey, I have discovered 27 new supernova remnants (SNRs) via their non-thermal emission at low radio frequencies. Some of these are quite unusual objects with very low surface brightness, while others were simply hidden from view due to confusion between thermal and non-thermal emission at higher radio frequencies. For six candidates I have suggested pulsar associations and can derive physical characteristics. I will conclude the talk with future prospects for further discoveries using upcoming MWA surveys.
Wed 27 February 2019 @12:00 PM, level 7, David Caro Building
Prof. Ilya Mandel Monash University
Email: ilya.mandel[at]monash.edu
Abstract
The first detections of gravitational waves from compact-object mergers have opened up new opportunities and challenges in astrophysics. I will describe ongoing efforts to extract the astrophysical evolution of massive stellar binaries from observations of gravitational waves emitted during mergers of the stellar remnants.
Mon 25 February, 2019 @14:15 PM, level 7, David Caro Building
Dr Gemma Anderson, ICRAR, Curtin University
Email: gemma.anderson[at]curtin.edu.au
Abstract
The first neutron star gravitational wave merger has been detected and Australia is primed to take the lead in locating their radio afterglows. However, the positional uncertainties make fast localisation of the electromagnetic counterpart extremely difficult. In order to address this concern, I use new rapid-response systems on Australian radio telescopes to rapidly and automatically obtain observations of transients. These systems allow telescopes to “trigger” on transient alerts, causing the telescope to automatically repoint and begin collecting data within minutes of discovery. For example, the Murchison Widefield Array (MWA) can be on-target within 14 seconds of receiving a trigger. Additionally, the Australia Telescope Compact Array (ATCA) can now be on-target within minutes. My main research focus is on the rapid follow-up of transients, particularly short-duration gamma-ray bursts, a known subclass of gravitational wave events that are well localised by the Swift telescope. MWA response times are fast enough to probe for prompt radio signals predicted to be produced by merging neutron star binaries, in-turn allowing us to test neutron star merger models. ATCA can be on-target to probe the reverse shock emission from gamma-ray bursts, allowing us to determine a template of the radio luminosities and temporal behaviour of the gravitational wave events that will be detected by aLIGO/Virgo. In this talk, I will discuss some of the early results from the MWA and ATCA rapid-response observations of transient events and how these experiements will contribute invaluable knowledge towards optimising transient science to be conducted with the Square Kilometre Array.
Thurs 14 February 2019 @12:00 PM, level 7, David Caro Building
Dr Christopher Berrry Northwestern
Email: christopher.berry[at]northwestern.edu
Abstract
The gravitational waves observed by LIGO and Virgo encode unique information about their sources. I will explain how we go from the observed signal to making inferences about the source’s parameters, such as a black hole’s mass and spin. These properties are an insight into the processes that forged these compact objects. With a growing catalogue of observations, we can begin to constrain the properties of the population. This can help to pin down the uncertain physics of binary evolution. Making a binary black hole involves many processes that are currently poorly understood, such as stellar mass loss rates and the kicks imparted in supernova explosions. Once we have large numbers of detections, as expected following the upcoming observing runs, we can use mass and merger rate measurements to constrain the parameters describing these processes to a few percent. Adding in further information, such as the evolution of the merger rate with redshift will provide an even more detailed picture of the physics of binary evolution.
Wed 13 February, 2019 @12:00 PM, level 7, David Caro Building
Assistant Professor Sebastiano Cantalupo, ETH Zurich
Email: cantalupo[at]phys.ethz.ch
Abstract
Our standard cosmological model predicts that most of the matter in the universe is distributed into a network of filaments – the Cosmic Web – in which galaxies form and evolve. Because most of this material is too diffuse to form stars, its direct imaging has remained elusive for several decades leaving fundamental questions about the structure of the universe still open, including: How are galaxies linked to each other? What are the morphological and physical properties of the Cosmic Web on both large and small scales? How do galaxies accrete gas from the Cosmic Web? In this talk, I will tackle these questions using the results of a new program to directly detect and study high-redshift cosmic gas in emission using bright quasars and galaxies as external “sources of illumination’’. In particular, I will show results from ultra-deep narrow-band imaging and integral-field-spectroscopy with both MUSE/VLT and the Keck Cosmic Web Imager (KCWI) that revealed numerous giant Lyman-alpha emitting filaments extending up to several hundred kpc around quasars and bright galaxies. I will discuss how the unexpectedly high luminosities of these systems, together with the constraints from Helium and metal extended emission, represent a challenge for our current understanding of cosmological structure formation. In particular, I will show that current observations suggest that intergalactic gas around high-redshift galaxies and quasars has a much broader density distribution of cold material than expected from cosmological simulations and I will present our first attempts to understand the origin and nature of these structures using high-resolution hydrodynamical models. At the same time, current galaxy formation models lack an efficient mechanism to prevent too much intergalactic gas cooling onto galaxies at later epochs and rely on very strong “ejective” feedback. In the final part of the talk (if time allows), I will show how the interaction between high-energy radiation from star-forming galaxies and the gas surrounding them provides a natural way to prevent “excessive” intergalactic gas cooling onto galaxies and I will discuss HST/COS observations that provide support for the importance of this effect.
Mon 11 February, 2019 @14.15 PM, level 6, Opat Seminar room
Prof Tom Quinn, University of Washington
Email: trq[at]astro.washington.edu
Abstract
The standard model for cosmology states that only 5% of the mass-energy density of the Universe is in ordinary matter. Other than its gravitational properties, the nature of the dark matter is unknown, leading to significant effort on constraining its properties.
I will discuss how effects in the ordinary matter influence the constraints that can be put on the theories of dark matter, and will specifically examine constraints on direct detection of axionic dark matter, and substructure constraints on self-interacting dark matter.
Wed 6 February 2019 @12:00 PM, level 7, David Caro Building
Melanie Kaasinen Max Planck Institute for Astronomy
Email: kaasinen[at]mpia.de
Abstract
One of the outstanding problems in galaxy evolution studies is to link the evolution of the star formation rate of galaxies to their molecular gas content. Observationally, the last decade of studies have led to a clear picture of the cosmic star formation history, which peaked at z~2 and has declined since then. However, it is unclear whether the declining star formation rates are simply the result of lower molecular gas masses, or whether the star formation efficiency has also evolved. In this talk I will discuss how the molecular gas contents of galaxies are measured and highlight the difficulties of doing so at high redshift. I will describe one of the most popular approaches, which relies upon the dust continuum emission, and will present our recent work where we test the validity of the this dust continuum calibration via a unique sample of z~2 galaxies with observations of both dust continuum and CO(1-0) line emission.
Number of posts found: 201