Cosmological simulations are power houses to understand the formation of structures through cosmic time, from the largest collapsed structures of galaxy clusters to individual galaxies, from early redshifts as high as
z=10 to present day. However, comparisons to observations at different times are needed to test the accuracy of the implemented models, and to connect the observables at varying redshifts to the evolution pathways of
structures. Using one of the largest state-of-the-art hydrodynamical cosmological simulation suites, Magneticum Pathfinder, we analyze how structure formation is imprinted in present-day properties, from the
distribution of substructure in galaxy clusters down to the internal properties of galaxies within their half-mass radius.

Starting with the evolution of protoclusters and their galaxies, we show that they evolve into a large range of halos at present day, and only rarely into the most massive clusters observed at low redshifts. Using present-day properties
as a lens into the past, we demonstrate that some of the best tracers of formation pathways are the substructure distribution in galaxy clusters, the presence of shells, streams, and satellite planes around galaxies, and
the central kinematics of galaxies. The latter can even be used to infer the fractions of accreted stars, which we find to be much more difficult when employing radial stellar density distributions. Finally, we provide comparisons to observations from the SLUGGS and SAMI surveys, MATLAS, and the Hubble Frontier fields.

The study of cosmology with the weak gravitational lensing of large-scale structures, so-called ‘cosmic shear’, requires accurate and precise measurement of galaxy shapes and ensemble redshift distributions. For the latter, current and future wide-area surveys (such as the Kilo-Degree Survey, KiDS) are moving inexorably toward machine learning calibration methods. These efforts have lead to cosmological estimates of current (so-called ’Stage-III’) surveys that are statistics-limited, meaning that the precision of the current analyses are limited statistical rather than systematic uncertainties. However, current analysis methods are likely to fail to meet the challenge of next generation (so-called 'Stage-IV’) surveys, like Euclid and Rubin LSST. In this colloquium I will provide an overview of cosmic shear, its use in cosmological inference, and the important systematics considerations required to perform these analyses. I will discuss the state-of-the-art in machine-learning redshift distribution calibration, and describe the sort of pitfalls that will cause these methods to fail in the limit of Stage-IV statistical power.

High-redshift supernovae (SNe) are important probes of stellar evolution in the early Universe. They can provide constraints on stellar evolution in low-metallicity environments that plays a critical role in shaping the compact remnant mass distributions observed by gravitational waves. In particular, pair-instability SNe (PISNe), theorized explosions of massive stars leaving neither neutron stars nor black holes, are predicted to exist exclusively at low metallicity environments. No PISNe, however, have been confidentially identified so far. In this talk, we first introduce our high-redshift SN survey conducted by Subaru/Hyper Suprime-Cam (HSC) and discuss our high-redshift SN discoveries so far. Although we discovered several high-redshift SNe up to z = 2.4, we did not find any PISN candidates. In order to discover PISNe at high redshifts, it is ideal to conduct transient surveys in near-infrared because of redshift. I will discuss high-redshift transient surveys with two upcoming wide-field near-infrared observatories, Euclid and Roman. We argue that Euclid would be able to discover dozens of PISNe up to z ~ 3.5. Having the redder bands, Roman will allow us to observe PISNe at even higher redshifts entering the Epoch of Reionization – up to z ~ 7. Through high-redshift SN discoveries, Euclid and Roman would revolutionize our view on massive star death in the early Universe.

Short bursts, flares, scintillation and other radio time-domain phenomena usually imply extreme astrophysical environments (e.g. strong magnetic fields) that are difficult to achieve on Earth. This time-domain parameter space, however, is relatively unexplored historically, mainly limited by instrumental sensitivity and field-of-view (FoV). In this talk I will present unusual time-domain transient events I have discovered with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope, including extreme scintillation, flaring stars, and pulsars.

We have used ASKAP to probe timescales of seconds to hours, searching for rapidly varying radio sources. With the advantage of the large FoV, we discovered a group of fast-scintillating galaxies arranged linearly on the sky, spanning approximately 2 degrees. Using this unlikely sky distribution we inferred the presence of a nearby, straight, and high-pressured plasma filament between the Earth and those galaxies, which produces extreme scintillation. Circular polarisation is another poorly explored parameter-space. With ASKAP dual-polarisation beams, we identified a new pulsar (rapidly rotating neutron star) PSR J0523-7125 through its strong circularly polarised emission and variable behaviour. PSR J0523-7125 shows many unusual properties (e.g., upturn spectrum shape), which may shed light on the as-yet-unknown pulsar coherent emission mechanism.

Our discovery has filled gaps in this unexplored time-domain parameter space, and highlighted a new way of finding unusual pulsars – useful for future space-time experiments. The existence of a nearby, high-pressured plasma filament also changes our understanding of the origins of extreme scintillation, and requires new models to explain the underlying phenomenon, as existing theoretical models are incompatible with the structure we measured.

Understanding Gas Flows in-and-around Galaxies

https://swinburne.zoom.us/j/756407223?pwd=RHk2TEF2MFZJZDNhL1FwckxDUUpSZz09
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Since time immemorial, Aboriginal and Torres Strait Islander communities have been looking up to pristine dark skies and fostering an intricate understanding of their dynamics. Indigenous knowledge systems observe the complex interrelations between Sky Country above and natural cycles of the land, informing community on local food economics, weather events, seasonal variation, long-distance navigation, and native plant and animal cycles.

In this talk, Krystal will be presenting an overview of the book she co-authored with Karlie Noon, Astronomy: Sky Country, which offers an introduction to the world of Indigenous astronomy through the lens of two Gamilaroi astronomers.

Variability offers a unique opportunity to study both intrinsic properties of sources as well as the intervening media between source and observer, informing on properties from the ionised interstellar medium of the host galaxy through to the structure of the intervening media in the Milky Way. Unfortunately, determining the origins of radio variability of extragalactic sources has, until recently, largely been limited to small populations and/or single frequencies. However, large population studies with significant spectral and temporal coverage have only recently become available with the development of radio telescopes like the Murchison Widefield Array (MWA). In this talk, I will show the results of two spectral variability surveys: a blind search using the two epochs of the Galactic and Extragalactic All-sky MWA (GLEAM) Survey and a targeted monitoring programme combining the MWA and the Australia Telescope Compact Array (ATCA). I will demonstrate how spectral variability can determine the absorption mechanism of compact peaked AGN and inform on their local environments, where previous attempts to do so have remained inconclusive. Lastly, I will talk about the future of variability surveys and with the upcoming GLEAM-eXtended (GLEAM-X) survey.

Molecular gas is the fuel for star formation in galaxies. Using observations from the mm-Wave Interferometric Survey of Dark Object Masses (WISDOM) survey, that spatially resolve (1-30 pc) individual molecular clouds across the Hubble sequence, we reveal a clear dependence of the nature of the molecular interstellar medium of
galaxies on Hubble type, and present a simple diagnostic of cloud formation. In particular, we highlight the shortcomings of the usual virial approach to clouds as self-gravitating objects, and stress the importance of the external galactic potential and in-plane shear to regulate the dynamical states of clouds. We also introduce a simple but powerful cloud-cloud collision formalism that accounts for the cloud properties in both nearby and high-redshift systems. Finally, we discuss the impact of these different mechanisms on the star formation efficiency of the clouds and thus the quenching of star formation, particularly in galaxy nuclei and spheroids (morphological quenching).

CoC review- Millisecond Pulsar Timing with SKA
Pathfinder MeerKAT

I will provide a brief update on the SKA Observatory as a whole, the fundamental science drivers, and the expected design and scope for the SKA-Low telescope in Australia. I will then provide an update on the progress of the growing SKAO entity in Australia, including the Science and Engineering Operations Centres, and the roll out plan of the SKA-Low telescope. I'll outline the plan for the science operations team, the breakdown between commissioning, verification and operations, and highlight pathways for involvement (from students through science engagement to employment opportunities).

Over the last decade, ALMA has opened up our view of the fuel for star formation in distant galaxies, by probing the emission from cold, molecular gas and dust. Multiple surveys of dust and CO emission have provided a view of how the total gas content evolves from z~4 to today, and how this relates to the build up of stellar mass in galaxies. However, zooming in to individual galaxies remains a challenge. How is star-forming gas distributed relative to the existing stars? And, what are the physical conditions within the gas? In this seminar, I will provide a short overview of the current highest-resolution view of cold gas in galaxies at Cosmic Noon and what indicates about the structures of these early galaxies compared to local galaxies. I will also highlight how we are probing the turbulence, temperature and density of this cold gas, from galaxies at Cosmic Noon to the EoR, and how some of these conditions may be changing. Throughout the talk, I will highlight the current challenges and give some perspective for the next decade of studies of star-forming gas in distant galaxies.

Low surface brightness galaxies (LSBs) are extremely dark matter-dominated, faint objects hardly distinguishable from the night sky. In the last decade, it has become clear that large numbers of LSB galaxies exist, including the recently discovered Ultra-Diffuse Galaxies (UDGs), opening a new window on galaxy evolution and formation. How do such diffuse galaxies form and evolve? How are they linked to their dark matter haloes, and how do they fit within the current cosmological model of galaxy formation? I will review current results coming from state-of-the-art, sophisticated hydrodynamical cosmological simulations to try to answer these questions: insights on the formation of such elusive galaxies will be provided, as well as on our understanding of the role of baryonic feedback in galaxy formation.

Our understanding of the Milky Way is in the midst of a revolution with large-scale spectroscopic surveys such as APOGEE and GALAH, along with the Gaia satellite providing information on billions of stars across the Galaxy. I will give an overview of the current chemodynamic structure of the Milky Way from these massive surveys, ranging from the bulge to the edge of the disk, and the role that secular processes and mergers have played in the evolution of the disk.

I will describe our detailed chemical evolution models, which are the first to reproduce the global chemoydnamic structures of the Galaxy. These models incorporate many physical processes that govern the evolution of the disk, including gas physics as accretion, cooling, and heating, along with stellar evolution and state of the art yields, and as well as secular evolution to account for radial mixing of stars and gas within the disk. I will also describe our upcoming work to use the Milky Way as a benchmark for galaxy evolution, such as producing IFU data cubes of the Milky Way with a range of properties (inclination, extinction model, spatial and spectral resolution, etc.) to enable direct comparisons of our Galaxy to external systems, along with the GECKOS program on MUSE.

There are a few main ways in which breakthrough astronomy gets done. You can build a new widget for observing that opens up an entirely new area of observation phase space (think IRAS, Chandra, WISE, JWST, LIGO), so that everything you observe has never been seen before. Alternatively build a new widget that that gives you data much like you had before - but massively scales up the rate of production - so that you can do unprecedented surveys (think 2dF, SDSS). Or you can open up new observational phase space by pushing available techniques to unprecedented levels of precision and accuracy (think HIPARCOS, Gaia, HARPS).

I think of these two paths as being “Galilliean” vs “Tychonian”. Both Galileo and Tycho were directly responsible for breakthrough outcomes in astronomy - one by deploying a radical new technology (the telescope), the other by pushing the precision of the available technology (naked-eye astrometry) to unprecedented levels.

Personally, I’ve always found the “Tycho” strategy the most personally satisfying. So I’ll try to explain why details matter. And why I’ve spent the pandemic years trying to understand the details of the new Veloce instrument on the AAT, in an effort to achieve m/s-level velocity precisions at a fraction of the cost of equivalent facilities elsewhere.

In the last few decades, our view of the cosmos has changed a lot. High-resolution data from both ground- and space-based telescopes have enabled us to observe unprecedented details in stellar systems such as stellar binaries and star clusters. On the theoretical side, however, stellar evolution remains highly approximated in most population synthesis codes. While this may have been sufficient to reproduce observations of stellar systems in the past, an improved and up-to-date treatment of stellar evolution is required for the current and upcoming observations, especially for stars more massive than 9 Msun. In this talk, I will present results from a new approach, the Method of Interpolation for Single Star Evolution (METISSE). It can readily make use of stellar models computed with different stellar evolution codes and approximate evolution parameters for a population of stars. I will further shed light on the lives of massive stars and discuss how various physical ingredients used in modeling their evolution, such as the treatment of their radiation-dominated envelopes, can lead to differences in their evolutionary properties. Finally, I will show that by using METISSE with population synthesis codes, we can better understand the impact of these differences on the evolution of stellar systems and the formation of gravitational-wave progenitors.

TBD

The top recommendation for a large space mission in the US 2010 Decadal Survey was the Nancy Grace Roman Space Telescope (formerly known as WFIRST), which is now on schedule for launch in 2026. Similarities in hardware requirements between proposed dark energy cosmology, exoplanet microlensing, and near infrared surveyor missions allowed for a single mission that would accomplish all three goals. The gift of an existing 2.4 meter telescope to NASA by another US government agency enhanced the capability of Roman and allowed for the addition of a coronagraph that will take images and spectra of nearby exoplanets; this instrument will be a technological stepping stone to imaging other Earths in a future NASA flagship mission. I will give an overview of Roman's instrumentation, science goals, implementation plan, and plans to engage the worldwide community in designing surveys.

Accretion and outflows are fundamental drivers of galaxy evolution, where galaxies must obtain metal-poor gas to form new stars and eject metal-rich gas to quench their growth. These baryon cycle processes pass through and contribute to the massive gaseous reservoir known as the circumgalactic medium (CGM). Interactions between galaxies in group environments further distribute gas widely through the CGM, resulting in gas with larger kinematic spreads out to larger distances than in isolated galaxies. New integral field spectrographs like VLT/MUSE and Keck/KCWI are currently revolutionising CGM studies by allowing observers to quickly obtain a census of all galaxies in close projection to background quasars to study the CGM in absorption. They also make mapping the CGM in emission to low surface brightness limits possible. I will highlight two results from programs with KCWI: 1) The complex intragroup medium around a compact group of galaxies at z=2.43. We used a new method to model the cloud-by-cloud kinematics and physical conditions of the multiphase absorbing gas, which found evidence for outflows, accretion, and tidal streams around this group. 2) CGM emission line mapping around a nearby starbursting galaxy that is undergoing a significant accretion event. KCWI revealed emission to over 30 kpc away and curious sub-kpc sized knots.

The fate of a neutron star merger plays a critical role in the multi-messenger signatures expected from a merger. I will discuss the theoretical diversity of electromagnetic and gravitational-wave signals from neutron star binary mergers and how we can leverage the rapidly growing catalogue of transient observations to confront our models and learn about the lives and deaths of neutron star binaries. I will also discuss the challenges we need to solve to maximise the promise of gravitational-wave multi-messenger astronomy and the tools we need to make these challenges solvable.

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.

Time: Jul 5, 2022 02:00 PM Australia/Melbourne
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Galaxies show a wide range of kinematic properties according to galaxy types. We aim to quantitatively understand the intrinsic distribution of bulge and disk kinematics, and how two components describe the overall distribution of stellar kinematics of galaxies. The spatially-resolved rotation velocity and the velocity dispersion of bulge and disk components have been simultaneously estimated for the SAMI 3D spectroscopy data using the penalised pixel fitting method. Kinematic scaling relations demonstrate that the galaxy stellar mass scales with kinematics for both bulge and disk components of all galaxy types, which suggests kinematics of two components are less dependent on galaxy populations and largely determined by the mass. We quantitatively show that the bulge and disk components are kinematically distinct: the two components show scaling relations with similar slopes, but different intercepts; the spin parameter λR indicates bulges (disks) are pressure(rotation)-dominated systems. Our findings suggest that the relative contributions of bulge and disk components explain, at least to first order, the complex kinematic behaviour of galaxies according to galaxy type. On the other hand, kinematics of ionized gas are significantly impacted by power sources (e.g. star formation, AGN, and old stars), unlike stellar kinematics. For star-forming galaxies, the stellar velocity dispersion tends to be larger than the gas velocity dispersion, suggesting that stars are, in general, dynamically hotter than the ionised gas (asymmetric drift). However, AGN show gas velocity dispersions comparable to stellar ones, implying their gas kinematics have been dynamically heated by AGN activities (e.g. outflows).


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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.

Cosmological simulations have become an essential tool for testing structure formation theories. The advances in both observational and computational techniques over the years ultimately have allowed us to pick LCDM as the standard model of cosmology. Nevertheless, cosmological simulations highlight the intrinsic degeneracy between alternative dark matter models and the baryonic prescriptions we use in LCDM simulations. In order to break this degeneracy, we have to consider a series of challenges to our analysis and design our tests accordingly. In this talk I will present some of my previous research into galaxy formation problems within LCDM, and the outline of the simulating alternative dark matter models collaboration I recently started.

Studying absorption and emission lines in the spectra of nearby galaxies is an invaluable tool for learning about their stars. Whilst spectroscopy has a long history, the arrival of large integral field unit surveys in the past few decades has allowed astronomers to obtain exquisitely detailed ‘three dimensional’ data for thousands of nearby galaxies for the first time. I will give an overview of my research into the stellar populations of galaxies, including an investigation of the low-mass end of the initial mass function, whilst also discussing the prospects for studying stellar populations in the coming years.

The twin Keck 10m telescopes on Maunakea, Hawaii are amongst the most productive facilities for ground-based optical/IR astronomy in the world, with the highest scientific impact in ground-based OIR research. In their over 25 years of operation, discoveries made using the Keck telescopes have resulted in major advances in astronomy, and have played a leading role in the awarding of two Nobel prizes. Over the next decade, substantial new research facilities will come online worldwide and in space, and the Keck Observatory is adapting to continue to be a forefront research tool for the most challenging astronomy questions.

This talk will discuss the current status of the Keck Observatory operations and instrumentation, new instrumentation and capabilities currently under development, and aspirations for the coming decade.

The recent releases of data from the Gaia satellite have been transformational for galactic astronomy. The unprecedented accuracy with which stellar positions and velocities can be determined with Gaia means we are getting a fresh understanding of the structure, composition and history of the Milky Way. The new data shows that the Milky Way underwent several major merger events which shaped the kinematic structure of its stellar halo in surprising ways. As the stellar halo and the dark matter halo are closely linked, this new evidence will have important consequences for experiments searching for dark matter on Earth. In some cases, like underground searches for particle-like dark matter, Gaia allows us to update the standard halo assumptions used in modelling expected signals. In other cases, notably searches for wave-like dark matter, the relics of our Milky Way's past may be much more readily observable.

Time: Apr 26, 2022 10:30 AM Australia/Melbourne
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One of the principal systematic constraints on the Epoch of Reionisation (EoR) experiment is the accuracy of the foreground calibration model. Recent results have shown that highly accurate models of extended foreground sources, and including models for sources in both the primary beam and its sidelobes, are necessary for reducing foreground power. To improve the source models in the EoR fields observed by the Murchison Widefield Array (MWA), we conducted the Long Baseline Epoch of Reionisation Survey. This survey consists of multi-frequency observations, spanning 104-230 MHz, of the MWA EoR fields and their eight neighbouring fields using the MWA Phase II extended array. These observations provide high-resolution, UV-components to compliment the existing UV-plane sampling of these fields. Additionally, due to the better imaging capabilities of the MWA Phase II extended array, this survey improves upon the sensitivity of the GLEAM survey by roughly a factor of 5 in the EoR fields. This talk will present results from the first half of the LoBE survey and discuss the next steps for foreground modelling for the MWA EoR experiment.

In this colloquium, I will talk about my experiences with transitioning from an academic PhD to a job as a programmer in industry.

I will give an overview of the reasons why I felt leaving academia was necessary; what the skills are that industry is looking for (and how these align with what you learn as an astrophysics PhD student); and what my current job entails.
This colloquium functions both as just an overview talk of what is possible outside of academia, which should be of interest to most students, but also as an update of what I have been up to lately (as most at Swinburne will still remember me).

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 most astronomical observations are inherently high dimension - from "imaging" the Universe at the finest details to fully characterizing tens of millions of spectra which consists 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 normalizing flow, allow us to properly model the vast astronomy data set, enabling the study of complex astronomy systems directly in their raw dimension.

The ASKAP Variables and Slow Transients survey will give us an unprecedented opportunity to investigate the sky at radio wavelengths for highly variable and transient sources on timescales as short as 5 seconds. ASKAP’s wide-field survey capabilities will enable the discovery and investigation of variable and transient phenomena from the local to the cosmological including flare stars, intermittent pulsars, X-ray binaries, magnetars, extreme scattering events, intra-day variables, radio supernovae and the orphan afterglows of gamma-ray bursts.

In 2021 we completed the VAST Phase I and Phase II Pilot Surveys, in preparation for full survey operations in 2022. I will present the first results from the pilot surveys, including the discovery of a new Galactic Centre Radio Transient, and discuss our plans for the upcoming full survey.

**Note special time** 9am start for Brodie's DTR

Matt Miles's mid-candidature review.

The Dark Energy Survey (DES) was designed to investigate the dynamics of the cosmic expansion. During five years, the DES Supernova Program (DES-SN) obtained light curves for tens of thousands of extragalactic transients including thousands type Ia supernovae (SNe Ia) for cosmology. In collaboration with DES, OzDES obtained spectroscopic redshifts with spectra of SNe Ia host-galaxies using the AAT.

In this talk, I will introduce analysis updates from the DES-SN survey. I will present cosmology constraints obtained from data that were taken during the first three years of the survey, containing 207 spectroscopically confirmed SNe Ia. I will then summarise work that is being done now to analyse the full dataset. I will highlight key features of our current cosmology analysis including photometric classifiers and our efforts on systematic uncertainties control.

Zoom Link: https://swinburne.zoom.us/j/82931943032?pwd=Z0p3NzhTejA3NDAzdVExZHFtOFJQUT09

The exciting field of fast radio bursts (FRBs) has rapidly evolved, but their origin(s) remain unknown. Thanks to new radio telescopes with large fields of view, the number of known FRBs has increased drastically in recent years, ushering us into an era where the phenomena may be studied as a population. FRB 121102, on the other hand, is the first source known to repeat and its precise localisation has enabled unprecedented studies of a single source. In the first part of this talk, I show what we’ve learned over the years using sensitive Arecibo observations. In the second part of my talk, I will describe the possible connection between FRBs and neutron star mergers. In particular, I will show how we can use localised FRBs to constrain merger-related FRB models. Then, tackling the hypothesis from a different angle, I show how we are triggering the Low-Frequency Array (LOFAR) within minutes to catch prompt radio emission associated with short Gamma-ray bursts that are detected by Swift. In the final part of my talk, I will describe the LOFAR gravitational wave merger follow-up campaign of which I am PI. Here, I will discuss the later-time incoherent afterglows of merger events at low frequencies. The biggest challenge associated with detecting the electromagnetic counterpart of gravitational wave (GW) merger events, however, is the large uncertainty (tens of square degrees) on their locations. I will present our strategy which applies LOFAR’s high sensitivity and large field of view to search for GW merger radio counterparts. I will also show our latest results from O3, the last gravitational wave observing run. Finally, the wide coverage of our observations should probe most of the localisation region for binary neutron star merger events detected in the upcoming GW observing run.

Gas, dust and stars make a galaxy. In the disk-shaped spiral galaxies, gas constantly feeds to star formation. Massive stars die and stir the gas, which results in turbulent motions. Later, along with gravitational instabilities, it creates fragments of isolated gas clouds, some of which overcome the pressure from thermal motion and turbulence and collapse to form a new generation of stars. We observe 21-cm spectral line emission from the neutral hydrogen gas in galaxies to probe the statistical characteristics of the structures in the column density and velocity in the interstellar medium (ISM). Our investigations show that the energy input in the interstellar medium originates at scales comparable to the size of the galaxy and cascades down to smaller scales, where it thereby influences the star formation. The methodology used to access the statistics of the column density and velocity structure, interpretation of the measurements and their importance in ISM physics will be discussed.