School of Physics
The Melbourne Astro group has weekly colloquia, group meetings, and journal clubs. Normal times and places can be found on the calendar here.
A list of recent colloquia, with slides in some cases, can be found here
Wednesday 14 Sep 2022 @ 12:00 p.m., Level 6 Geoff Opat(+Zoom)
Madeline Howell, Monash; Email: Madeline.Howell1[at]monash.edu
Mass loss remains a major uncertainty in stellar modelling. In low-mass stars, mass loss is most significant on the red giant branch, and will impact the star’s evolutionary path and final stellar remnant. Directly measuring the mass difference of stars in various phases of evolution represents one of the best ways to quantify mass loss. Globular clusters are ideal objects for this, because they contain stars with essentially identical initial masses, metallicities and ages, and hence easily distinguishable evolutionary phases. M4 is currently the only globular cluster for which asteroseismic data exists for stars in multiple phases of evolution. The advent of space-based photometric missions have provided the opportunity to measure stellar masses with unprecedented accuracy using asteroseismology. Using photometry from the K2 mission, we report asteroseismic masses for 75 red giants in M4, the largest seismic sample in a globular cluster to date. From this sample, we measured a prec
ise integrated red giant branch mass loss. Our results for initial mass, horizontal branch mass, Reimers’ coefficient, and integrated red giant branch mass loss show a remarkable agreement with previous studies, but with higher precision through using asteroseismology. We also report preliminary detections of solar-like oscillations in a second globular cluster, M80. Because this cluster is more metal-poor than M4, we can test the potential mass loss-metallicity trend. We emphasise the importance of seismic studies of globular clusters which could potentially allow us to resolve major uncertainties in our understanding of stellar evolution. We discuss the prospects of using photometry from current and future space-based telescopes for this science objective.
Wednesday 07 Sep 2022 @ 12:00 p.m., Level 6 Geoff Opat(+Zoom)
Dr Aditi Vijayan, ANU; Email: Aditi.Vijayan[at]anu.edu.au
Outflows, generated either due to supernova (SN) activity in the disc of a star-forming disc or through the SMBH activity in a larger galaxy, are critical in understanding galaxy evolution. Such outflows are a complex phenomenon which I have studied using HD simulations. In this talk, I will discuss 3-D HD simulations that I ran that study the properties of outflows in a Milky Way-type star-forming galaxy. I will discuss how feedback creates multiphase outflows and how they appear in X-rays. I will share what I found about diffuse X-ray emission from the CGM and its relationship with the underlying gas properties.
Wednesday 31 Aug 2022 @ 12:00 p.m., Laby Theatre(+Zoom)
Dr Giulia Santucci, ICRAR/UWA; Email: g.santucci[at]unsw.edu.au
Galaxy mergers are thought to play an important role in how galaxies evolve over time, however, extragalactic astronomers do not yet completely understand that merger process, its timing and dependence on galaxy mass. The internal kinematic structures of galaxies are driven by their merger histories, therefore, we expect that the internal kinematic structures of galaxies might show different characteristics depending on their merging history. We apply Schwarzschild orbit-superposition models to passive galaxies in the SAMI Galaxy Survey in order to reconstruct their internal kinematic structure and intrinsic properties. We find that these intrinsic properties correlate strongly with stellar mass and that environment plays a secondary role: at fixed stellar mass, galaxies in the densest regions are more radially anisotropic. Central galaxies and galaxies in high local densities rotate more slowly. We also find suggestions of a possible trend of the fractions of orbits with environment
for lower-mass galaxies. Our results demonstrate that after stellar mass, environment does play a role in shaping present-day galaxies.
Wednesday 17 Aug 2022 @ 12:00 p.m., Laby Theatre(+Zoom)
A Prof Yuan-Sen Ting, ANU; Email: yuan-sen.ting@anu.edu.au
Astronomy today is fundamentally different than it was even just a decade ago. Our increasing ability to collect a large amount of data from ever more powerful instrumental has enabled many new opportunities. However, such opportunity also comes with new challenges. The bottleneck stems from the fact that most astronomical observations are inherently high dimension — from “imaging” the Universe at the finest details to fully characterising tens of millions of spectra consisting of tens of thousands of wavelength pixels. In this regime, classical astrostatistics approaches struggle.
I will present two different machine learning approaches to quantify complex systems in astronomy. (1) Reductionist approach: I will discuss how machine learning can optimally compress information and extract higher-order moment information in stochastic processes. (2) A generative approach: I will discuss how generative models, such as normalising flow, allow us to properly model the vast astronomy data set, enabling the study of complex astronomy systems directly in their raw dimensional space.
Wednesday 10 Aug 2022 @ 12:00 p.m., Zoom
Dr Anita Petzler, CSIRO; Email: Anita.Petzler[at]csiro.au
The molecular gas of the interstellar medium provides the raw material for star formation, yet its principle component – molecular hydrogen – is essentially invisible at radio wavelengths. Instead we must infer its presence and properties through the study of other tracer molecules, such as hydroxyl (OH). OH, with its four ground-rotational transitions at 1612, 1665, 1667 and 1720 MHz is a challenging molecule to observe due both to the weakness of its lines and the complexity of their excitation. However, the complex excitation of OH holds valuable information about the host molecular gas. The satellite lines at 1612 and 1720 MHz in particular, with their ubiquitous anomalous excitation, are much more sensitive to local conditions than the main lines which rarely diverge from their expected excitation at local thermodynamic equilibrium (LTE). In this talk I will discuss my PhD research which focused on exploring the utility of this interesting molecule. I will also introduce my current project which is to monitor the time-variability of high-gain OH masers in star forming regions.
Wednesday 03 Aug 2022 @ 12:00 p.m., Laby Theatre(+Zoom)
A Prof Deanne B. Fisher, Swinburne University; Email: dfisher[at]swin.edu.au
Over 2/3 of all star formation in the Universe occurs in gas-rich, super-high pressure clumpy galaxies in the epoch of redshift z~1-3. However, because these galaxies are so distant we are limited in the information available to study the properties of star formation and gas in these systems. I will present results using a sample of extremely rare, nearby galaxies (from the DYNAMO survey and the new DUVET survey) that are very well matched to high-z main-sequence galaxies. We use these galaxies as laboratories to study the processes inside galaxies in the dominate mode of star formation in the Universe. In this talk I will report on results that are aimed at testing models of star formation in galaxies, which are designed to simultaneously explain star formation and kinematics. I will discuss very recent efforts to connect the regulation of gas via outflows to the picture of how galaxies maintain their star formation rates, and outlook for the future with the new Australian led large ESO program, GECKOS.
Wednesday 27 Jul 2022 @ 12:00 p.m., Laby Theatre(+Zoom)
Associate Professor Jeff Cooke, Swinburne University; Email: jeffreycooke[at]swin.edu.au
In this talk, I will I first discuss work by our group on identifying and studying high-redshift (z ~ 3-5) star forming galaxies with massive stars that are leaking Lyman continuum photons to better understand the sources responsible for reionising the Universe. Secondly, I will present the first observational method to directly measure massive star cloud collapse timescales and progenitor star lifetimes of gamma-ray bursts and superluminous supernovae. These observational efforts include our Hubble Space Telescope and Keck program data, along with other telescope data, and have important implications for, and can directly benefit from, large-scale cosmological simulations, JWST and 30m-class telescopes, and 21 cm mapping of reionisation by the Square Kilometre Array.
Wednesday 20 Jul 2022 @ 12:00 p.m., Laby Theatre(+Zoom)
Dr Sven Buder, ANU; Email: sven.buder[at]anu.edu.au
The life-story of our Milky Way is missing key pages! In our ever-evolving Galaxy, our best hope is to use long-lived stars as time capsules.
The industrial revolution of equipment in Galactic archaeology allows us to survey the stars of our Milky Way in unprecedented depth and detail. The Gaia satellite monitors the positions and motions of billions of stars, while ground-based surveys like our Australian-led GALAH survey take millions of stellar spectra.
I will present the innovative tools that we have developed to extract information for millions of high-resolution optical spectra and how we can use stellar chemistry, dynamics, and ages to tell apart populations in the Milky Way and even identify stellar survivors of previous mergers. Putting these findings into an extragalactic and cosmological context will forge the connections to understand galaxy evolution across the Universe.
Wednesday 13 Jul 2022 @ 12:00 p.m., Laby Theatre(+Zoom)
Dr Manisha Caleb, The University of Sydney; Email: manisha.caleb[at]sydney.edu.au
Fast radio bursts (FRBs) have a story which has been told and retold many times over the past few years as they have sparked excitement and controversy since the pioneering discovery in 2007. The FRB class encompasses a number of microsecond-millisecond duration pulses occurring at Galactic to cosmological distances with energies spanning several orders of magnitude. Many radio telescopes around the world are currently undertaking wide area surveys and targeted searches to discover and localise FRBs, as their true potential can only be realised up host galaxy identification and association. Significant effort is being put into localising FRBs to sub-arcsecond precision by radio interferometers around the globe. The MeerTRAP project at the MeerKAT telescope in South Africa has been operational since 2019 and has discovered ~25 FRBs and localised a handful of them to host galaxies, including an FRB localised to sub-arcsecond precision at z~1. In my talk, I will present the recent discoveries and the multi-wavelength follow-up efforts from the MeerTRAP project.
Wednesday 06 Jul 2022 @ 12:00 p.m., Level 6 Geoff Opat(+Zoom)
Professor Chris Matzner, University of Toronto; Email: matzner[at]astro.utoronto.ca
I will cover three topics:
1. “Bells not Whistles”: Some massive stars undergo shock-driven outbursts before the cores collapse. I will show that nonlinear acoustics rules out a standard explanation for how these events are driven, a result that deepens the mystery of their origin.
2. “Do crashes make flashes?”: Compact supernovae can be aspherical enough to fling ejecta sideways, causing collisions outside the progenitor. I address the open question: can a circumstellar collision ever be visible from afar, or will it be smothered by the ejecta surrounding it?
3. “The LUVS small satellite concept.” This would be an instrument to perform rapid ultraviolet alert follow-up and chase binary neutron star coalescence signals. It is also a testbed for fast, cheap, off-the-shelf mission development in the New Space paradigm, intended to show that scaling laws, which say space must be hard, can be broken.
Wednesday 06 Jul 2022 @ 12:00 p.m., Laby Theatre(+Zoom)
Professor Chris Matzner, University of Toronto; Email: matzner[at]astro.utoronto.ca
I will cover three topics:
1. “Bells not Whistles”: Some massive stars undergo shock-driven outbursts before the cores collapse. I will show that nonlinear acoustics rules out a standard explanation for how these events are driven, a result that deepens the mystery of their origin.
2. “Do crashes make flashes?”: Compact supernovae can be aspherical enough to fling ejecta sideways, causing collisions outside the progenitor. I address the open question: can a circumstellar collision ever be visible from afar, or will it be smothered by the ejecta surrounding it?
3. “The LUVS small satellite concept.” This would be an instrument to perform rapid ultraviolet alert follow-up and chase binary neutron star coalescence signals. It is also a testbed for fast, cheap, off-the-shelf mission development in the New Space paradigm, intended to show that scaling laws, which say space must be hard, can be broken.
Wednesday 15 Jun 2022 @ 12:00 p.m., Laby Theatre(+Zoom)
A Prof. Julia Bryant, The University of Sydney; Email: julia.bryant[at]sydney.edu.au
Hector is a new optical integral field spectrograph (IFS) instrument that has recently been commissioned on the Anglo-Australian Telescope (AAT). It will undertake a 15,000-galaxy IFS survey of nearby z<0.1 galaxies. Fundamentally new science will be achieved compared to existing instruments due to Hector’s capability to do the largest IFS galaxy survey to date, with the highest spectral resolution, and imaging 2 effective radii on most galaxies.
The high fill-factor imaging fibre bundles `hexabundles’ of the type used on the SAMI instrument, have been improved and enlarged to cover up to 27-arcsec diameter. Hector has 21 hexabundles over a 2-degree field feeding both the new ‘Spector’ spectrograph and existing AAOmega spectrograph. The new dual-arm spectrograph has the highest spectral resolution of any large IFS nearby galaxy survey of 1.3 Angstrom. This is the key to enable higher order stellar kinematics to be measured on a larger fraction of galaxies, and to link those galaxies to the large-scale environments in which they form to test formation models of galaxies.
The Hector survey is aligned to the 4MOST WAVES-North and WAVES-South regions. The WAVES data will give the environment metrics necessary to relate how local and global environments influence galaxy growth through gas accretion, star formation and spins measured with Hector. The WALLABY ASKAP survey will trace HI gas across the Hector fields, which in combination with Hector will give a complete view of gas accretion and star formation.
This talk will discuss what makes Hector scientifically unique and the new opportunities it offers Australian astronomers.
Wednesday 08 Jun 2022 @ 12:00 p.m., Laby Theatre(+Zoom)
Dr Stefania Barsanti, ANU; Email: Stefania.Barsanti[at]anu.edu.au
The study of the interplay between galaxy angular momentum and structures in the cosmic web is a powerful tool to constrain galaxy evolution scenarios. I will present the alignments of galaxies’ spin axes with respect to nearby cosmic web filaments as a function of various properties of the galaxies and their constituent bulges and discs. I will exploit the SAMI Galaxy Survey to identify 3D spin axes from spatially-resolved stellar kinematics for galaxies and their kinematic bulge and disc components. The mass of the bulge is found to be the primary parameter of correlation with spin-filament alignments. I will discuss our findings in terms of possible formation pathways for the galaxies, bulges and discs.
Friday 03 Jun 2022 @ 10:00 a.m., Laby Theatre(+Zoom)
Prof. Jean-Pierre Barriot, The University of French Polynesia; Email: jean-pierre.barriot[at]upf.pf
We will discuss in this seminar how radio links in deep space make it possible to test general relativity and to probe gravitational waves, with three examples: a/ The NASA/ESA Cassini mission to Saturn, active in space for almost 20 years (1997-2017), which was equipped with an extremely precise radio system, and provided data capable of constraining the post-Newtonian gamma parameter to an unprecedented level of 1 + (2.1 ± 2.3)×10−5, and also gave upper bounds on the amplitude of gravitational waves at low frequency passing through the solar system. b/ The ESA/JAXA BepiColombo mission, launched on October 20, 2018, which is carrying out a seven-year journey to the smallest and closest to the Sun terrestrial planet, Mercury. It is equipped with a state-of-the-art radio system inherited from Cassini, with the aim of improving the accuracy of gamma determination by at least a factor of 10. c/ The LISA (Laser Interferometer Space Antenna), which will be a set of three spacecraft flying in a triangular formation about 50 million kilometers from the Earth, whose launch is scheduled for 2034. It was recently approved for Phase A study by the European Space Agency after results from the successful precursor LISA-Pathfinder mission in 2016 proved the concept feasible.
Wednesday 18 May 2022 @ 12:00 p.m., Laby Theatre(+Zoom)
Associate Prof. Ivo Labbe, Swinburne University; Email: ilabbe[at]swin.edu.au
The formation of the first galaxies is one of the most exciting and elusive frontiers in astronomy. In only a few months this field is about to be revolutionized when the James Webb Space Telescope starts operations. JWST will deliver ultra-sensitive observations at previously inaccessible infrared wavelengths. Among the many exciting programs in Webb’s first year is the Treasury program UNCOVER which will take ultradeep NIRCam imaging and NIRSpec spectroscopy boosted by the gravitational lensing cluster Frontier Field Abell 2744. I will look ahead and discuss the science goals of this public program, such as finding First Light galaxies during the Dark Ages at z>10 and studying the ultra-low luminosity galaxies at later times that were responsible for reionization. The program will support a broad array of additional science including stellar mass complete studies to z=10, the role of dust obscuration at high redshift, and the various pathways of quenching star formation.
Wednesday 11 May 2022 @ 12:00 p.m., Laby Theatre(+Zoom)
Professor Duncan A. Forbes, Swinburne University; Email: dforbes[at]swin.edu.au
Ultra Diffuse Galaxies (UDGs) were first identified using the Dragonfly Telescope Array in 2015. Their extreme properties (of low surface brightness, large size, and in some cases rich globular cluster systems) continue to present challenges for standard cosmological simulations. UDGs may represent galaxies with a range of properties: from puffed-up dwarfs to failed galaxies, from those with overly massive dark matter halos to some that are dark matter free. In my talk I will present new observations, and contrast these with the latest simulations, summarising our current understanding of this extreme class of galaxy.
Wednesday 25 May 2022 @ 12:00 p.m., Laby Theatre(+Zoom)
Dr Susan Wei, UniMelbourne; Email: susan.wei[at]unimelb.edu.au
In contrast to regular models, singular statistical models lack identifiability and a positive definite Fisher information matrix. Singular models are in fact ubiquitous in modern machine learning, with neural networks serving as a prominent example. Coinciding with the resurgence of interest in Bayesian neural networks, this work sets out to characterize the approximation gap in variational inference for the posterior distribution over neural network weights. The result rests on a central insight from singular learning theory according to which the posterior distribution over the parameters of a singular model, following an algebraic-geometrical transformation known as a desingularization map, is asymptotically a mixture of so-called standard forms. We proceed to demonstrate that a generalized gamma mean-field family, following desingularization, can recover the leading order term of the model evidence. The theoretical results are accompanied by a set of experiments in which we employ affine coupling layers to learn the unknown desingularization map.
Wednesday 04 May 2022 @ 12:00 p.m., Laby Theatre(+Zoom)
Prof Alan Duffy, Swinburne University; Email: aduffy[at]swinburne.edu.au
For over half a century the nature of dark matter has remained a mystery despite enormous advances in astronomical observations, numerical simulations, and direct detection efforts. I will convey some of the ongoing research efforts at Swinburne as we seek a holistic approach to constraining the potential dark matter candidate, from microlensing by theorised nano-planet mass blackholes to ultra-light axion candidates, and particles of masses in between all in partnership with colleagues across Australia and beyond. While conveying the science of these experiments I will also try to share ways in which I try to explain it to the public as ideas for others to explore using in their own science communication efforts.
Wednesday 27 Apr 2022 @ 12:00 p.m., David Caro building, Level 7 Conference Room (+Zoom)
Prof. Darren Croton, Swinburne University; Email: dcroton[at]astro.swin.edu.au
Much progress has been made in recent years in our understanding of the co-evolution of galaxies and supermassive black holes, and their connection to the underlying large-scale dark matter structure. In this talk I will discuss simulation and modelling techniques that bridge theories of galaxy and black hole formation with the properties of observed galaxy populations. In addition, I will discuss a number of open questions important for extra-galactic astronomy and cosmology, and explain how future large-scale surveys and galaxy formation models may jointly address them.
Wednesday 20 Apr 2022 @ 12:00 p.m., David Caro building, Level 7 Conference Room (+Zoom)
Professor Matthew Bailes, Swinburne University; Email: mbailes[at]swin.edu.au
Although Fast Radio Bursts (FRBs) were discovered in 2007, the last couple of years has seen an explosion of recorded events and breakthroughs in the field. In this talk I will tell the story of FRBs and their impact on potential source models and cosmology.
Wednesday 06 Apr 2022 @ 12:00 p.m., Zoom
Dr Yisheng Qiu, Zhejiang University; Email: yishengq[at]126.com
In this talk, I will introduce Starduster, a supervised deep learning model that predicts the multi-wavelength SED from galaxy geometry parameters and star formation history by emulating dust radiative transfer simulations. The model is comprised of three specifically designed neural networks, which take into account the features of dust attenuation and emission. We utilise the Skirt radiative transfer simulation to produce data for the training data of neural networks. Each neural network can be trained using ∼4000−5000 samples. Compared with the direct results of the Skirt simulation, our deep learning model produces 0.1−0.2 mag errors in FUV to FIR wavelengths. At some bands, the uncertainty is only 0.01 mag. As an application, we fit our model to the observed SEDs of IC4225 and NGC5166. Our model can reproduce the observations, and successfully predicts that both IC4225 and NGC5166 are edge-on galaxies. However, the predicted geometry parameters are different from image-fitting studies. Our analysis implies that the inconsistency is mainly due to the degeneracy in the star formation history of the stellar disk and bulge. In addition, we find that the predicted fluxes at 20μm−80μm by our SED model are correlated with bulge radius. Our SED code is public available and can be applied to both SED-fitting and SED-modelling of galaxies from semi-analytic models.
Wednesday 06 Apr 2022 @ 12:00 p.m., Zoom
Dr Yisheng Qiu, Zhejiang University; Email: yishengq[at]126.com
In this talk, I will introduce Starduster, a supervised deep learning model that predicts the multi-wavelength SED from galaxy geometry parameters and star formation history by emulating dust radiative transfer simulations. The model is comprised of three specifically designed neural networks, which take into account the features of dust attenuation and emission. We utilise the Skirt radiative transfer simulation to produce data for the training data of neural networks. Each neural network can be trained using ∼4000−5000 samples. Compared with the direct results of the Skirt simulation, our deep learning model produces 0.1−0.2 mag errors in FUV to FIR wavelengths. At some bands, the uncertainty is only 0.01 mag. As an application, we fit our model to the observed SEDs of IC4225 and NGC5166. Our model can reproduce the observations, and successfully predicts that both IC4225 and NGC5166 are edge-on galaxies. However, the predicted geometry parameters are different from image-fitting studies. Our analysis implies that the inconsistency is mainly due to the degeneracy in the star formation history of the stellar disk and bulge. In addition, we find that the predicted fluxes at 20μm−80μm by our SED model are correlated with bulge radius. Our SED code is public available and can be applied to both SED-fitting and SED-modelling of galaxies from semi-analytic models.
Wednesday 30 Mar 2022 @ 12:00 p.m., David Caro building, Level 7 Conference Room (+Zoom) Dr Ben Wibking, ANU; Email: ben.wibking[at]anu.edu.au
Since the discovery of the accelerating expansion of the Universe, a fundamental question for physics has been the nature of this acceleration – is it consistent with a cosmological constant, cold dark matter Universe governed by General Relativity? One of the most precise probes of this is weak gravitational lensing. This can be combined with galaxy clustering and examined on nonlinear scales to obtain very precise measurements of cosmological parameters. I present constraints from galaxy clustering and weak lensing on ~Megaparsec scales using the galaxy catalogue from the Baryon Oscillation Spectroscopic Survey. I show that these data lead to a statistically significant tension in the amplitude of matter fluctuations at low redshift compared to that measured by the Planck cosmic microwave background satellite.
Wednesday 23 Mar 2022 @ 12:00 p.m., David Caro building, Level 2, Hercus Theatre (+Zoom)
A Prof Paul Lasky, Monash University; Email: Paul.Lasky[at]monash.edu
Since the first gravitational-wave detection of a binary black hole merger in 2015, the LIGO and Virgo detectors have observed gravitational waves from almost 100 merging systems. That number is expected to increase significantly over the coming years as these experiments become even more sensitive. The increased number of detections, and the improved sensitivity of these instruments, allows us to probe the ultra-strong regime of gravity, as well as the formation history of these systems. I will discuss ongoing efforts to test general relativity in the ultra strong-field regime, including tests of the no-hair theorem and searches for gravitational-wave memory — a permanent deformation of spacetime following the passage of a gravitational wave. I will also discuss efforts to detect orbital eccentricity in these systems, which has led to potentially the first observation of a second-generation black hole merger.
Wednesday 16 Mar 2022 @ 12:00 p.m., David Caro building, Level 2, Hercus Theatre (+Zoom)
Associate Professor Michelle Cluver, Swinburne University; Email: mcluver[at]swin.edu.au
It’s a tale of three very different surveys: WISE (a mid-infrared imaging survey of the entire sky), 4HS (a newly accepted redshift survey of the southern hemisphere on 4MOST), and MeerHoGS (a pilot HI survey on MeerKAT). This talk will focus on the key science goals of 4HS (which I co-PI with Ned Taylor) and how this connects to my work using WISE and MeerKAT to a) create a benchmark view of the nearby universe, and b) investigate how environment influences the properties of galaxies. Finally, I will illustrate the power of immersive visualisation tools (such as VR) in this intrinsically multi-dimensional space.
Wednesday 09 Mar 2022 @ 16:00 p.m., Zoom
Unnikrishnan Sureshkumar, Jagiellonian University; Email: ukp1513[at]gmail.com
Galaxies live in dark matter haloes and hence the galaxy properties are majorly defined by the properties of the haloes. Thus the environmental dependence of dark matter halo properties prompts a correlation between galaxy properties and the environment. In this talk, I will discuss the results from our recent works (arXiv:2102.04177 and arXiv:2201.10480) that explored how luminosities in various passbands and the associated galaxy properties are correlated with the environment. We used a set of 3.4 micro-m luminosity-selected and stellar mass-selected galaxies from the Galaxy and Mass Assembly (GAMA) survey. We made use of the galaxy two-point correlation functions and marked correlation functions to investigate the environmental correlations. I will also discuss the impact of various selection effects on the galaxy clustering measurements.
Wednesday 02 Mar 2022 @ 2:00 p.m., Zoom
Assistant Prof Yuichi Harikane, Institute for Cosmic Ray Research, the University of Tokyo; Email: hari[at]icrr.u-tokyo.ac.jp
Studying the statistical properties of high redshift galaxies is crucial for understanding the overall picture of galaxy formation and evolution. In this talk, I will present our latest results from ~4,000,000 galaxies at z~2-7 identified in the Subaru/Hyper Suprime-Cam survey. This large sample has allowed us to reveal 1) rest-frame UV luminosity functions in a very wide luminosity range, 2) the number density excess of bright galaxies beyond the classical Schechter function, and 3) the almost constant star formation efficiency at z~2-7, suggesting that the evolution of the cosmic star formation rate density is primarily driven by the structure formation and the cosmic expansion. Extrapolation of this result to higher redshifts suggests a sharp decline of the star formation rate density at z>10, which is consistent with our recent finding of z~13 galaxy candidates and will be directly tested with JWST. Finally, I will briefly introduce our planned JWST Cycle 1 observations.
Wednesday 23 Feb 2022 @ 12:00 p.m., Zoom
Dr Stevanus K. Nugroho, Astrobiology Center, National Institutes of Natural Sciences (NINS), Japan; Email: stevanus.nugroho[at]nao.ac.jp
Using high-resolution spectroscopy, the atomic/molecular bands in the spectrum of an exoplanet are resolved into individual absorption lines. The variation of Doppler shifts caused by the planet’s orbital motion enables absorption lines in the exoplanet spectrum to be distinguished from telluric lines. By combining thousands of unique absorption (or emission) lines, the atomic/molecular signatures can be identified unambiguously and detected at high significance. As it is sensitive to the position of the lines, it also allows us to measure the planetary rotation and wind velocity, as well as search for atmospheric variability and inhomogeneity during the transit. In this talk, I will give a review on how we characterise the atmosphere of exoplanets using high-resolution spectroscopy including some of the latest discoveries in the atmosphere of ultra-hot Jupiters.
Wednesday 16 Feb 2022 @ 12:00 p.m., Zoom
Associate Prof. Christoph Federrath, ANU; Email: christoph.federrath[at]anu.edu.au
The formation of stars is controlled by the interplay between gravity, interstellar turbulence, magnetic fields, and stellar feedback. In this talk, I will try to explain the link between these processes and how they shape the structure of molecular clouds, paving the way towards star formation. A lot of this is based on supercomputer simulations and theoretical models, however, the design of the simulations and theoretical models is ultimately guided by observational evidence.
Wednesday 01 Dec 2021 @ 12:00 p.m., Zoom
Dr Anitha Ravishankar, University of Calgary; Email: anitha.ravishanka1[at]ucalgary.ca
An accurate understanding of the propagation of coronal mass ejections (CMEs) is crucial in the prediction of space weather. CMEs generate geomagnetic storms causing catastrophic damages to power grids on Earth and are serious radiation threat to satellites on low-Earth orbit and their crew during spacewalks. Basic parameters such as their velocity and acceleration varying with time and heliospheric distance away from the Sun gives researchers the opportunity to predict their arrival time in the vicinity of the Earth. Once these clouds of charged particles reach the Earth, aurorae or Northern/Southern lights are generated at higher latitudes. Extreme geomagnetic storms (kp>4) are a matter of concern and also contribute to a beautiful sight with intense auroras. Ground based riometers have proven to be an efficient way to detect these KeV electron precipitation in the ionosphere during auroral formation. Absorption profiles offer a good approach towards studying various associated par
ameters and eventually help in building a model for predicting these events. In today’s talk I shall cover the cause & effect of these geomagnetic storms and touch base on our University’s research approach.
Number of posts found: 201