Wednesday, 5th of July

Location: Mason theatre, ground floor

Zoom link: https://macquarie.zoom.us/j/82321436522

Slack channel: #asa2023-galaxies

Chair: Cristina Martinez-Lombilla, Co-Chair: Samuel Lai

11:00am: The Tully-Fisher relation in the nearby Universe: Physical causes of scatter and evolution at different galactocentric radii - Andrei Ristea*†, ICRAR/UWA

The Tully-Fisher (TF) relation is a fundamental correlation between the mass and rotational velocity of galaxies. Its slope, intercept, and scatter encode valuable information on the processes driving galaxy evolution. While the relation between baryonic mass and circular velocity is known to exhibit low scatter, the stellar mass TF relation (for stellar and gas rotation separately) contains insight into the effect of different evolutionary processes on galaxy kinematics. However, the drivers of scatter in these relations at different radii and for different galaxy morphologies remain poorly understood in the nearby Universe, and the dependence of the TF relation on the baryonic component tracers has never been investigated for a representative galaxy sample. In this talk, I will present a detailed analysis of the stellar and ionised gas TF relation for the largest representative sample of galaxies with stellar and gas kinematics ever assembled, extracted from the final data release of the MaNGA galaxy survey. I will discuss how the slope, scatter, and intercept of the TF relation dramatically depend on the phase traced, the radius used to measure velocity, and on various galaxy properties and environmental metrics. I will reveal how these findings shed additional light on the evolution of nearby galaxies and are also critical for a correct interpretation of higher redshift studies of the TF relation and for a proper comparison with state-of-the-art cosmological simulations.

11:15am: The connection between galaxy angular momentum and gas fraction in both observations and simulations - Jennifer Hardwick*†, ICRAR-UWA/ASTRO-3D

Understanding angular momentum (AM) is crucial for studying galaxies, as it is linked to their formation, evolution, gas content, and morphology. Despite its importance, many questions about AM scaling relations remain unanswered, as most AM studies focus on small samples of galaxies or just the inner regions of galaxies. This can also lead to samples that are biased to gas-rich disk galaxies. To address this, I will present an investigation into the robustness of AM scaling relations for large diverse samples using the xGASS observational sample, which has deep HI observations of over 500 galaxies in the local universe, and compare this to state-of-the-art cosmological simulations; EAGLE and IllustrisTNG. Our analysis finds a tight planar relationship between a galaxy's AM, mass, and atomic gas fraction, which is different from previous gravitational stability models. Remarkably, the same planar relationship is found when analysing the EAGLE and IllustrisTNG simulations, despite using different subgrid prescriptions and hydrodynamic codes. This is interesting, as the two simulations have very different predictions for the gas properties of galaxies, which further emphasises the importance of its connection to AM. Additionally, the simulations allow for testing of this relationship in the extremely gas-poor regime, which is not possible with current observations. These results will impact the development of future theories about galaxy stability, AM, and gas fraction.

11:30am: Cosmic star formation and AGN activity over 13 billion years - Jordan D’Silva*, ICRAR/UWA

Star formation and the growth of super massive black holes are two of the main processes that shape the observed light distributions of galaxies. Yet studies of star formation tend to only focus on the blue, star forming galaxies and disregard those galaxies that host active galactic nuclei (AGN), and vice-versa for the AGN. In doing so, we can never learn about the union of star formation and AGN activity in galaxies. In this work we aim to break the dichotomy of star formers and AGN, and instead consider only galaxies. We investigate this topic with the cosmic star formation and bolometric AGN luminosity history. We use the Galaxy and Mass Assembly Survey and the Deep Extragalactic Visible Legacy Survey to compute these quantities from z=0 to z=5, where the flux associated with stars and AGN has been self-consistently accounted for in fitting the light distributions. We find that star formation and AGN activity have been coeval for 11 billion years up to the present, implying that the same gas used for star formation is also feeding the AGN. With GAMA and DEVILS, we can take this analysis to a maximum of only ~11 billion years into the past as beyond this the data is most significantly limited by selection effects. As such, we will supplement our analysis with observations from the James Webb Space Telescope. The result of these combined efforts are worthy insights into galaxy evolution from the first few billion years since the Big Bang to the present.

11:45am: Angular Momentum of Dwarf Galaxies - Simon Deeley, UQ

The relation between a galaxy’s mass and specific angular momentum, known as the Fall relation, has been increasingly recognised as forming a tight fundamental scaling relation. This relation is expected to arise from tidal torques between halos in the early Universe and therefore provides a stringent test for our understanding of galaxy formation. The Fall relation has been well-studied for galaxies above 10^9 solar masses, however whether the relation extends down to dwarf galaxies remains uncertain. Here we use H-alpha observations of 49 dwarf galaxies to test the Fall relation down to 10^7 solar masses. We surprisingly found that dwarf galaxies below 10^8 solar masses have lower angular momentum than predicted by the Fall relation. We followed this up with the IllustrisTNG cosmological simulation, creating mock observations which allowed us to determine the angular momentum in the same way as was done for the observations, and we found the same deviation in the dwarf galaxies. We then used the simulation to follow galaxies back in time, and found that the lower angular momentum of dwarf galaxies is due to the absence of a sudden divergence in the evolution of angular momentum experienced by higher-mass galaxies.

12:00pm: The role of AGN in regulating galaxy evolution in massive z~3-4 galaxies - Monserrat Martínez-Marín*, Swinburne

The recent analysis of massive galaxies in the early universe (z~3-4) presents challenges for the theory of galaxy evolution. Compared to simulations, an excess of massive quiescent galaxies (MQGs) is found at high redshifts. MQGs at this epoch suggest their stellar content was already in place in the first 1.5 Gyr of the Universe. These findings indicate that MQGs must have experienced an event that caused rapid quenching. Active galactic nucleus (AGN) feedback is the most suitable candidate for quenching these galaxies, although observational evidence is scarce. In this talk, we present a sample of massive galaxies ( 10 <log(𝑀★/𝑀⊙ )< 11 ) at 3 < 𝑧 < 4 from the ZFOURGE survey that presents broad [OIII] and H𝛽 emission lines in their spectra. We analyze the deep H and K–band spectra of the Keck/MOSFIRE and VLT/KMOS near-infrared finding high-velocity dispersion of order 𝜎 ∼ 255 km/s and compared our sample with quiescent massive galaxies at different redshifts. Our spectroscopic analysis finds evidence for AGN in these galaxies. We note that none of our galaxies were detected as AGN previously in the ZFOURGE sample, reflecting the need for spectroscopy in studying critical stages of galaxies in the early universe. Future observation with the JWST can provide better constraints for the structural and emission line measurements for massive galaxies with AGNs, providing a feasible explanation for the rapid quenching of massive galaxies in the early universe.

12:15pm: Statistical gravitational lensing effects on high redshift galaxies - Giovanni Ferrami*, University of Melbourne/ASTRO-3D

The bright end of the rest-frame UV luminosity function (UVLF) of high-redshift galaxies is modified by gravitational lensing around foreground structures. This effect is known as magnification bias. In this talk, I will present how the finite size of bright high-redshift galaxies together with lens ellipticity significantly suppresses magnification bias, producing an observed bright end that declines more sharply than the power-law resulting from the assumption of point sources. By assuming a luminosity-size relation for the source population and comparing it with the observed z = 6 galaxy luminosity function from Harikane et al. (2022), I will show that the UVLF can be used to set mild constraints on the galaxies' intrinsic size, favouring smaller galaxies compared to the fiducial luminosity-size relation, and how future wide surveys using Euclid and Roman Space Telescope will place stronger constraints.

Poster sparklers in this session:

P4: Yi Shuen Christine Lee*, University Of Melbourne/OzGrav

P25: Tomas Rutherford, USyd

P53: Aman Khalid*, UNSW

P77: Andrew Sullivan*, ICRAR/UWA

Location: T2, second floor

Zoom link: https://macquarie.zoom.us/j/81099211834

Slack channel: #asa2023-gw-transients

Chair: Jimi Green, Co-Chair: Neelesh Amrutha

11:00am: Localising high energy transients with the SpIRIT + HERMES nano-satellite constellation - Matt Thomas*†, University of Melbourne/ASTRO-3D

Observations of the transient sky to detect cosmic explosions critically rely on orbiting telescopes to cover the large range of wavelengths where atmospheric absorption and/or emission precludes the use of ground facilities. With funding from the Australian Space Agency and in partnership with the Italian Space Agency, the University of Melbourne is building SpIRIT, Australia's first space telescope, expected to be operational in 2023. SpIRIT is a gamma and X-ray nano-satellite that will operate as part of the HERMES technologic/scientific pathfinder constellation (HERMES-TP/SP) to localise Gamma Ray Bursts (GRBs) and Gravitational Wave counterparts. We find that the inclusion of SpIRIT is able to increase the localisation capabilities of the HERMES-TP/SP by a factor of 5 due to SpIRIT's high inclination Polar orbit, which gives it a large baseline perpendicular to the equatorial orbit of the HERMES satellites. Further improvement by an additional factor of 4 can be achieved by launching 6 SpIRIT-like satellites into a Polar orbit, which would be an ideal next step towards achieving an all-sky X-ray/gamma-ray monitor based on distributed aperture detectors to complement future gravitational wave detection campaigns.

11:15am: MWA rapid follow-up of gravitational wave transients: prospects for detecting prompt radio counterparts - Jun Tian†, Curtin University

In this talk I will present the prospects for the detection of the coherent radio counterparts of gravitational wave (GW) events using Murchison Widefield Array (MWA) triggered observations. The rapid-response system of the MWA, combined with its buffering mode, enables us to catch any radio signals produced from seconds prior to a compact binary merger to hours after the merger. The large field of view of the MWA and its location under the high sensitivity sky region of the GW detector network forecast a high chance of being on-target for a GW event. We consider three observing modes for the MWA to follow up GW events, including a single dipole per tile, the full array, and four sub-arrays, and perform a population synthesis of binary systems to predict the radio detectable fraction of GW events using these modes. We find that four sub-arrays is the best compromise between sky coverage and sensitivity, and capable of placing meaningful constraints on the radio emission from 12.6% of GW detections. Based on the timescales of the various coherent emission models relative to the evolution of a binary neutron star merger, we propose an observing strategy to target each of them, i.e. triggering the buffering mode for any emission prior to or during the merger and continuing recording for up to six hours for any post-merger emission.

11:30am: Nuclear physics with gravitational waves from neutron stars disrupted by black holes  - Teagan Clarke*, Monash University/OzGrav

Gravitational waves from neutron star + black hole mergers provide an avenue to study the equation of state of neutron stars and hence the behaviour of matter at its most extreme densities. Sometimes the neutron star will be tidally disrupted during the inspiral, the details of which are encoded in the neutron star equation of state. The disruption could be measured in the gravitational-wave data of some systems. This, along with other binary parameters like mass and spin, allows us to measure the neutron star radius and probe the equation of state. In this talk I present a phenomenological model for the gravitational waveform of a neutron star disrupted by a merging black hole. I demonstrate how we can measure the time of tidal disruption in order to place constraints on the radius of the neutron star and hence, the equation of state of nuclear matter. I discuss the constraints we will gain from this method in third generation gravitational-wave observatories. 

11:45am: The core-collapse supernova explosion mechanism - Jade Powell, Swinburne

Gravitational waves are emitted from deep within the inner core of a core-collapse supernova, which may enable us to determine the mechanism of the explosion from a gravitational-wave detection. Previous studies have shown how the gravitational-wave signal will enable us to determine if the explosion mechanism is neutrino-driven or magneto-rotationally powered. However, long duration magneto-rotational waveforms, that cover the full explosion phase, were not available during the time of those studies, and explosions were just assumed to be magneto-rotational if the model was rapidly rotating. Therefore, we perform an updated study using new 3D long-duration magneto-rotational core-collapse supernova waveforms that cover the full explosion phase. We also, for the first time, include failed explosions in our signal classification results. We add our waveforms into simulated noise for the Advanced LIGO, Einstein Telescope and NEMO gravitational-wave detectors. We then determine the explosion mechanism of the signals using three different methods: Bayesian model selection, dictionary learning, and convolutional neural networks.

12:00pm: Merging binary black holes formed through chemically homogeneous evolution - Simon Stevenson, Swinburne

After more than 3 years without new gravitational-wave data, the fourth LIGO-Virgo-KAGRA observing run should be ongoing by the time of this meeting, with an expected yield of hundreds of binary black hole mergers. The properties of these binaries (their masses, spins, and merger rate) provide tantalising clues to their origins. In this presentation I will present recent work modelling the formation of merging binary black holes from close, tidally locked binary stars ('chemically homogeneous evolution'). The models are updated to include a number of physical processes that are important for massive, helium rich, metal poor, rapidly rotating stars. The models are compared to the catalogue of gravitational-wave observations to constrain the model inputs.  

12:15pm: An Untargeted Search for Short-duration Gamma-Ray Burst Afterglows - James Freeburn*, Swinburne/OzGrav

Gamma-ray bursts (GRBs) continue to be an active area of research in the decades since their serendipitous discovery.  Despite this, the physics and nature of their progenitors are still poorly understood.  While GRBs have multiple formation channels, they are all thought to be produced in ultra-relativistic jets.  Constraining the properties of these jets could be the key to understanding these highly energetic events.  GW 170817 and GRB 170817A marked the first combined detection of gravitational wave and electromagnetic emission from a binary neutron star merger.  The unexpected properties of the GRB have sparked an interest in GRB jet structure.  With some models of GRB jet structure, we can predict a population of short-timescale afterglows multiple times larger than the GRB population.  Previous surveys lacked the cadence necessary to probe this theoretical population.  However, the Deeper, Wider, Faster Programme’s (DWF) deep, wide-field, fast-cadenced, multi-wavelength dataset is uniquely suited to a search of this kind.  Using DWF data collected with the Dark Energy Camera, mounted on the Victor M. Blanco telescope, we conduct an untargeted search for GRB afterglows.  This search will constrain the parameter space that GRB jets inhabit and shed light on the mysteries of GRB progenitors.  While the DWF search is ongoing, multiple candidates have been found in the data that beg for further investigation.

Poster sparklers in this session:

P4: Yi Shuen Christine Lee*, University Of Melbourne/OzGrav

P25: Tomas Rutherford, USyd

P53: Aman Khalid*, UNSW

P77: Andrew Sullivan*, ICRAR/UWA

Location: Mason theatre, ground floor

Zoom link: https://macquarie.zoom.us/j/82321436522

Slack channel: #asa2023-cosmology

Chair: Hyein Yoon, Co-Chair: Anthony Carr

2:30pm: Ho’oleilana: An Individual Baryon Acoustic Oscillation? - Cullen Howlett, UQ

Baryon Acoustic Oscillations (BAO) are pressure waves that travelled through the plasma of the early Universe when photons and baryons were coupled. The statistical detection of the remnants of these oscillations in the clustering of galaxies has become routine over the last 15 years, and the size of the statistical BAO has hence come to provide some of the strongest constraints on the cosmology of our Universe. In this talk, I will present evidence for the first ever detection of an individual BAO remnant at z=0.06. This remarkable structure, which we name Ho’oleilana, consists of a clear 3D shell of galaxies, ~300 Mpc across, centred on the Boötes Supercluster. This makes it one of the largest known structures in our Universe, and one which connects several other well-known structures such as the Sloan Great Wall, CFA Great Wall and Hercules supercluster complex. We use galaxy simulations matching the geometry and clustering of our data to verify that the chance of such an alignment occurring randomly is <1%. Interpreting Ho’oleilana as representative of the statistical BAO population, we find that its size implies a value of the Hubble Constant of 75.2_{-4.8}^{+4.1} km/s/Mpc, more consistent with constraints from other local Universe probes than from the Cosmic Microwave Background.

2:45pm: Superluminous supernovae in the UV - Potential as cosmological probes - Nandita Khetan, UQ/DARK Cosmology Centre

Superluminous-supernovae (SLSNe) have been detected to z~4 and can be detected to  z~15 with upcoming facilities. These are extremely luminous in ultraviolet (UV), thus high redshift SLSNe are detected exclusively via their rest-frame UV using optical and infrared telescopes. SLSNe offer an appealing tool to study stellar and galactic evolution, and could potentially be used as high redshift cosmological probes to distinguish various dark energy models. This talk explores the use of SLSNe type-I as distance indicators in their rest-frame UV. Using a sample of SLSNe-I in the redshift range 1<z<3, we investigate correlations between their peak absolute magnitude in UV and their light curve (LC) properties such as rise time, colour and decline rate. We observe promising correlations between LC properties along with insights into the sub-populations of SLSN like those having early bumps in their light curves. The results encourage the use of SLSNe as cosmological probes at high redshifts using standardising relations in the UV. This is particularly important in the view of future instruments which will significantly populate high redshift SLSNe detections.

3:00pm: Galaxy cluster cosmology via CMB cluster lensing - Behzad Ansarinejad, University of Melbourne/SPT collaboration

As galaxy clusters are the culmination of structure growth processes, their observed abundance as a function of mass and redshift - i.e. the halo mass function (HMF) - is a powerful tool for constraining cosmological models. HMF measurements are also a key tool in investigating the tension in the measurements of the cosmological parameter σ_8 obtained from Cosmic Microwave Background (CMB) and optical Weak Lensing (WL) and clustering analyses. However, measuring the HMF requires precise and accurate calibration of cluster mass-observable scaling relations. Here, I present cluster mass measurements for the Dark Energy Survey (DES) year 3 redMaPPer sample, using the lensing of CMB maps from the latest South Pole Telescope (SPT) data. We obtain a ~7% measurement of the normalization of the cluster mass-richness scaling relation, which is ~3x more precise than  previous measurements and significantly more competitive with WL constraints. We then investigate any redshift/richness dependence of the scaling relation and explore whether WL systematics or cluster contamination was the main contributing factor to the lower-than-expected value of the Matter Density parameter (Ω_m) obtained in the DES year 1 WL and cluster counts analysis.

3:15pm: Constraining astrophysics and cosmology via the kinematic Sunyaev-Zel’dovich effect - Eduardo Schiappucci*, University of Melbourne

The kinematic SZ Sunyaev-Zel’dovich (kSZ) effect is produced by the peculiar motion of electrons in galaxy cluster when they scatter off cosmic microwave background (CMB) photons. As such, the kSZ effect carries information about the cosmic velocity field on large-scales and the gastrophysics of galaxy clusters, providing potentially powerful tests of gravity and structure formation. Measuring this signal is challenging due to its small amplitude and spectral degeneracy with the CMB temperature fluctuations, however the kSZ imprint can be isolated by cross-correlating CMB maps with large-scale structure datasets. I will present a 4.1 sigma measurement of the kSZ effect using a catalog of optically-selected galaxy clusters from the Year-3 Dark Energy Survey data and CMB temperature maps from SPT-3G, the third generation receiver on the South Pole Telescope. This measurement is based on a pairwise statistical approach that allows to extract the kSZ signal as function of the comoving separation between clusters pairs. By comparing the recovered signal to theoretical expectations, we can infer the mean optical depth of the cluster sample, an important quantity that relates to the clusters' mean thermal SZ (tSZ) effect. Finally, I will also provide a comparison between the optical depths inferred from the tSZ effect, showing that external measurements of the optical depth will enable accurate cosmological constraints from future surveys, as well as future prospects from CMBS4.

Poster sparklers in this session:

P9: Natasha Van Bemmel*, Swinburne 

P12: Bailey Martin*, ANU

P16: Sonja Panjkov*, University of Melbourne

P45: Adnaan Thakur*, University of Adelaide

Location: T2, second floor

Zoom link: https://macquarie.zoom.us/j/81099211834

Slack channel: #asa2023-gw-transients

Chair: Jade Powell, Co-Chair: Teagan Clarke

2:30pm: Unveiling a population of prompt radio-emitting tidal disruption events - Adelle Goodwin, Curtin Uni./ICRAR

When a star passes too close to a supermassive black hole (SMBH) it can be destroyed, temporarily increasing the accretion rate onto the SMBH. Such tidal disruption events (TDEs) produce bright flares across the electromagnetic spectrum that provide a unique window into the central region of a galaxy, including the previously dormant black hole. Radio observations of TDEs are essential for probing synchrotron emission from electrons that are accelerated in the shocks formed from outflows, however, <20 TDEs have published radio detections to date. Thus, the origin of outflows is uncertain with scenarios including accretion disk winds, weak radio jets launched by accretion onto the SMBH, or collisions between debris streams. I will present results from detailed radio monitoring campaigns we have been conducting of 6 TDEs over 3 to 4 years, enabling detailed insight into the evolution of the outflows that were produced, as well as predictions about the circumnuclear environment of the host galaxies. Interestingly, it seems that there is a population of prompt radio-emitting TDEs, which narrows down the possible scenarios for the outflow mechanism. This work contributes to understanding the underlying mechanism that launches jets and outflows from black holes, the circumnuclear environment of distant galaxies, and the accretion process in strong gravitational fields.

2:45pm: Stellar Radio Bursts - Joshua Pritchard*, USyd

Stellar radio bursts are produced in powerful magnetic reconnection and transient mass loss events, and are projected to account for the majority of radio transients detectable with current, millijansky sensitivity radio surveys. The non-thermal radio emission produced by these source classes is often associated with strong magnetic fields - providing a unique window into processes associated with space weather, stellar mass loss, and magnetic dynamo mechanisms. Population studies of these events have primarily been limited to targeted observations of the most active stars, while unbiased, widefield searches for stellar radio bursts have so far been dominated by false-positive associations between foreground stars and background active galactic nuclei. The biases inherent in these surveys impact the inference of key population metrics such as the the surface density, rates, and energetics of stellar radio bursts. In this talk I will present a sample of 60 stars detected in a circular polarisation search of the Rapid ASKAP Continuum Survey and VAST phase 1 pilot survey at 888 MHz. We use repeat detection of stars in these surveys to infer the statistical properties of stellar radio bursts and find that at least 20% of Mdwarfs should produce radio bursts detectable by ASKAP.

3:00pm: Classifying light-curves for Rubin  - Anais Möller, Swinburne

Vera C. Rubin Observatory will open a new era for optical astronomy by imaging the Southern Sky at unprecedented depths. Rubin LSST will detect millions of transients and variables every night. In preparation for this data avalanche, it is imperative to develop methods for processing and selecting the most promising events for a variety of science cases. In this talk I will present results on light-curve classification of simulated light-curves from the The Extended LSST Astronomical Time-series Classification Challenge (ELAsTiCC). This simulation includes 30 astrophysical transients and variable models, including predicted events that have never been observed. I will present the results on different classification algorithms in a Rubin broker targeting kilonovae, supernovae, AGNs and other events. 

3:15pm: Finding AGN with Peculiar Accretion Rates using Lightcurves - Neelesh Amrutha*, ANU

Changing-look AGN (CLAGN) are a recent discovery of a rare subset of AGN where the accretion onto the central black hole turns on and off on timescales of months or years, which is much shorter than the viscous timescale of the accretion disk (~1000 yrs). Even with the advent of systematic searches for CLAGN in the past few years, less than 300 CLAGN are currently known. A bottleneck in CLAGN searches is that identifying them requires comparison of spectra from two epochs. ~20% of the known CLAGN sample is from the southern sky, with a majority of them identified by our group using photometric colours. Here, we use high cadence NASA Asteroid Terrestrial Impact Last Alert System (ATLAS) lightcurve data from the past 6 years to identify discrepancies in expected lightcurve behaviour based on their 6dFGS spectra to identify 200 CLAGN candidates. We further confirm these candidates spectroscopically using ANU 2.3m WiFeS instrument. We observe 62 candidates and find 24 CLAGN, resulting in a 39% success rate.

Poster sparklers in this session:

P9: Natasha Van Bemmel*, Swinburne 

P12: Bailey Martin*, ANU

P16: Sonja Panjkov*, University of Melbourne

P45: Adnaan Thakur*, University of Adelaide

Location: Mason theatre, ground floor

Zoom link: https://macquarie.zoom.us/j/82321436522

Slack channel: #asa2023-cosmology

Chair: Cullan Howlett, Co-Chair: Kateryna Andrych

4:00pm: The Dark Energy Survey's 5-year results: Methodology and future directions - Patrick Armstrong*†, ANU

The Dark Energy Survey (DES) is preparing their final 5-year supernova results, the largest and deepest supernova sample acquired from a single survey to date. This sample also represents the first large-scale survey which relies on photometrically classified supernovae, an important step in the transition to the next generation of supernova cosmology surveys, like the Rubin Observatory's LSST. In this talk, we present Pippin, the end-to-end cosmological pipeline used by DES. We also present the methodology of the DES analysis, with special attention paid to how DES treats statistical and systematic uncertainties. Additionally, alternative analysis methods are presented, such as forward modelling and Approximate Bayesian Computation, which could become vital to supernova cosmology as the scale of cosmological surveys expand.

4:15pm: Can we see Pop III and mini-halos through EoR? - Emanuele Maria Ventura*†, University of Melbourne/ASTRO-3D

In this work we investigated the first episodes of star formation in mini-halos and what is their imprint on the main observables during the EoR such as the 21cm global signal and power spectrum. The main tool used for this project is Meraxes, a semi-analytical model of galaxy formation that we run on top of a N-body simulation of L = 10 cMpc/h. In order to study the first episodes of star formation we implemented a number of effect including: (i) molecular hydrogen cooling functions for mini-halos, (ii) photo-dissociation of H2 molecules from the Lyman-Werner background and (iii) the chemical evolution of the intergalactic medium. This latter effect has been implemented assuming that metals are released through supernova explosions within a bubble that expands accordingly to the Sedov-Taylor model. We found that these bubbles are generally small with radii typically of 50-100 comoving kpc at z = 6. The main consequence of this results is that it is still possible to form Pop III stars during EoR inside pockets of pristine gas. The implementation of both internal and external metal enrichment allows us to understand whether a galaxy will form Pop III or Pop II stars and thus to quantify the effect of Pop III star formation on the reionization and on the chemical enrichment of the Universe. 

4:30pm: Using the peculiar velocities of galaxies for cosmology and particle physics  - Abbe Whitford*, UQ

In this talk I will explain how the peculiar velocities of galaxies contain useful information for understanding gravity and cosmology which is complementary to information obtained from the spatial distribution of galaxies. Further to this, I will present a bulk flow measurement I have made using the CosmicFlows-4 dataset that includes ~55,000 peculiar velocity measurements (in preparation for publication) and the implications these results have for the Lambda-CDM model.  The results confirm a bulk flow that is larger than expected, in agreement with the results by Watkins et al (2023). However, using extensive simulations we have shown that some bulk flow estimators tend to underestimate the uncertainty on the measurement, and accounting for this reduces the significance of the anomaly. I will also discuss how galaxy peculiar motions contain information on the sum of neutrino masses and can help improve constraints obtainable from redshift surveys and Cosmic Microwave Background data (published in MNRAS).

4:45pm: Faster cosmological analysis with power spectrum without simulations - Yan Lai*, UQ

State-of-the-art galaxy redshift surveys will provide the most detailed mapping of the universe and the tightest constraints on the cosmological parameters. However, the huge amount of data also presents a computational challenge. For instance, it may take several months to produce thousands of simulations to estimate the covariance matrix which measures the uncertainty of our measurements. Furthermore, our constraints on the cosmological parameters are weakened because of the noises and biases in the simulation. In this talk, I will present my new work on using data compression and analytical models to dramatically reduce the computational cost and noise associated with this procedure. I validated my approach with the largest and most constraining state-of-the-art galaxy surveys and found computing the analytical covariance matrix for these surveys can be done within a day while simulations will generally take several months. The data compression reduces the length of the data vector and speeds up the likelihood evaluation by a factor of two. Furthermore, I find even without knowing the best-fit parameters a priori, the analytical covariance matrix returns similar constraints on the cosmological parameters to the simulated covariance matrix. My method can significantly speed up the analysis for future surveys such as DESI and Euclid.

5:00pm: Recent results from the Pantheon+/SH0ES collaboration: supernova systematics cannot explain the Hubble tension - Anthony Carr*, UQ

The Hubble tension has reached the 5σ level between local supernova measurements of the expansion rate of the universe and Cosmic Microwave Background measurements. This must either be the result of new physics beyond our standard cosmological model, or systematics in our measurements. In this talk I provide an overview of the results of the Pantheon+/SH0ES joint collaboration with a focus on the often underappreciated effects of redshift biases on supernova cosmology. I will show that, despite their ubiquity, redshift systematics can be thoroughly ruled out as a contributor to the Hubble tension. In fact, supernova systematics in general cannot explain the Hubble tension.

5:15pm: Merging galaxy clusters as a testbed for self-interacting dark matter - Ellen Sirks, USyd

Self-interacting dark matter (SIDM) has been proposed as a solution to some of the tension at small scales between observations and simulations run with a cold dark matter (CDM) model. In the SIDM model, the dark matter is not collisionless but can interact with itself. The scattering rate is proportional to the local dark matter density, so high-density systems like galaxy clusters are an ideal environment to study SIDM. We identify merging galaxy clusters in hydrodynamical simulations of SIDM, and find that they can be used as enormous natural particle colliders. Even if dark matter interacts with standard model particles only via gravity, if its cross-section per unit mass with other dark matter particles exceeds 0.1 cm^2/g, dark matter in clusters spreads out and lags behind galaxies (by about 5% as much as the lag of gas due to ram pressure stripping). The spatial offset from galaxies could be detected with observations of a number well-chosen clusters from the SuperBIT balloon-borne telescope, launched from New Zealand on the 16th of April 2023.

Poster sparklers in this session:

P2: Saurav Mishra*, Macquarie Uni.

P11: Simon C.-C. Ho*, ANU

P48: Susie Tuntipong*, Swinburne 

P99: Jose Bellido Caceres, University of Adelaide 

Location: T2, second floor

Zoom link: https://macquarie.zoom.us/j/81099211834

Slack channel: #asa2023-mw-localuniverse

Chair: Amit Seta, Co-Chair: Madeleine McKenzie

4:00pm: Variable OH masers as a powerful laboratory for high-mass star formation - Anita Hafner, CSIRO

High mass stars are perhaps the most influential inhabitants of a galaxy: they interact with their surroundings through their intense UV radiation, powerful outflows and explosive deaths. Despite this importance, our understanding of how these massive stars form is still shrouded in mystery, due in part to the literal shrouding of young massive stars within their dusty natal clouds. Therefore we must rely on radio and infrared observations to peer through the dust and study these objects. One such method is through the observation of masers: natural lasers that amplify their background radiation and are strongly associated with regions of high-mass star formation. The intensity of hydroxyl (OH) masers is strongly linked to conditions of their local environment, and even minor changes to these conditions can cause the maser intensity to vary. I present the preliminary results of a 2.5 year survey using the 64m Murriyang dish at Parkes NSW to monitor the intensity of 4 OH maser transitions towards 46 high-mass star forming regions in the Milky Way. We identify over 260 individual maser features with significant variability ranging from flares, long term changes and regular periodicity. I will discuss how this variability in intensity can be caused by variability in local environmental conditions, and how this will help us to understand the process by which high-mass stars form.

4:15pm: The sub-critical illusion: synthetic Zeeman effect observations from galactic zoom-in simulations - Zipeng Hu*, ANU

Mass-to-flux ratios measured via the Zeeman effect suggest the existence of a transition from a magnetically sub-critical state in HI clouds to a super-critical state in molecular clouds. However, due to projection, chemical, and excitation effects, Zeeman measurements are subject to a number of biases, and may not reflect the true relations between gravitational and magnetic energies. In this paper, we carry out simulations of the formation of magnetised molecular clouds, zooming in from an entire galaxy to sub-pc scales, which we post-process to produce synthetic HI and OH Zeeman measurements. The mass-to-flux ratios we recover from the simulated observations show a transition in magnetic criticality that closely matches observations, but we find that the gravitational-magnetic energy ratios on corresponding scales are mostly super-critical, even in the HI regime. We conclude that H I clouds in the process of assembling to form molecular clouds are already super-critical even before H2 forms, and that the apparent transition from sub- to super-criticality between HI and H2 is primarily an illusion created by chemical and excitation biases affecting the Zeeman measurements.

4:30pm: The truncation of the disk of NGC 4565: detected up to z = 4 kpc, with star formation, and affected by the warp - Cristina Martinez-Lombilla, Monash University

The hierarchical model of galaxy formation suggests that galaxies are continuously growing. However, our position inside the Milky Way prevents the study of its disk edges. The whole picture can only be obtained from extragalactic sources with similar properties. In this talk, we show a multi-wavelength vertical analysis of the outer part of the disk of the nearby, edge-on, Milky Way-like galaxy NGC 4565. We use ultra-deep optical data, reaching a surface brightness limit of 30.5 mag arcsec^−2 in g-band, along with near- and far-ultraviolet, Hα, and HI observations. We study the stellar populations of the disk edge well above the NGC 4565 mid-plane (0<z<8 kpc), in unprecedented detail. We also determined the radial and the vertical location of the truncation and thus, establish the actual disk thickness, by exploring their position at different heights above the disk plane. We set a lower limit for the disk growth rate and measure the star formation rate throughout the disk out to R~30 kpc. Finally, we compare these results with theoretical predictions to infer the dominant process in the evolution of the disk of NGC 4565 and the potential implications for the Milky Way. We propose an inside-out growth scenario for the formation of the disk of NGC 4565. Our results point towards the truncation feature being linked to a star-forming threshold and to the onset of the disk warp. 

4:45pm: The 3D Structure & Dynamics of the Galactic Long Bar - Jayender Kumar, CSIRO/UTas

Understanding the 3D structure and associated dynamics of the inner 4-kpc of the Milky Way is very challenging because of high obscuration at optical wavelengths and our ability to accurately measure the distance and 3D motions of sources at these distances. In this work, we measured parallax and proper motions of three 22.2 GHz water masers, each associated with a High-Mass Star-Forming Region in the first quadrant of the Milky Way. With these measurements combined with other BeSSel projects’ published and un-published parallax and proper motion measurements of maser sources associated with HMSFRs within the 4 kpc region of the Galactic centre, we present evidence that the young HMSFRs in the inner galaxy are located in the gases following ’quasi-elliptical’ orbits. These represent the first direct measurements of the dynamics of the Milky Way’s bar.

5:00pm: Relics in the Sky-Remnants of accretion events from the Milky Way’s past - Adithya Gudalur Balasubramaniam*, Macquarie University

Stellar streams- formed through the tidal disruptions and gravitational instabilities of dwarf galaxies and star clusters- can tell us about the nature of their progenitors as well as the distribution of mass inside their orbits. The Southern Stream Stellar Spectroscopic Survey(S5) employs the Anglo-Australian Telescope(AAT) to study stellar streams, using photometric and proper-motion data to identify candidate member stars and AAT spectra to obtain radial velocities and abundance information. Work done by S5 has explored stream membership, orbit models and progenitors in detail. S5 also takes high resolution follow-up spectra for confirmed stream members to analyze their detailed properties and better understand the evolutionary processes of progenitor dwarf galaxies and globular clusters. I will present an in-depth study and comparison of two metal-poor, distant stellar steams originally found in the Dark Energy Survey: Elqui and Turranburra. Elqui is the most distant stream found in the S5 survey, with a Galactocentric distance of almost 52 kpc and an apocenter distance of 60 kpc. Previous work using the line of sight velocity and metallicity dispersions of the streams showed that they had most likely originated as ultrafaint dwarf galaxies. Elqui has a lower limit mass estimate of 3x10^4 solar masses. Its large orbit is sensitive to the gravitational influence of the Large Magellanic Cloud, allowing a look into the dynamics and history of the Local Group. 

5:15pm: Connecting the dots. Link between bars, neutral hydrogen gas content and star formation in barred ring galaxies - Chandrashekar Murugeshan, CSIRO

Bars are believed to play an important role in the evolution of galaxies via their ability to transfer angular momentum (AM) to the outskirts of galaxies while also driving gas towards the galactic centres leading to star formation. Previous studies have shown that barred galaxies appear to be more gas-deficient and quenched compared to non-barred galaxies. In addition to AM transfer and quenching, bars are believed to drive and sustain resonance rings at one or more Lindblad resonance locations. In this talk, I will present a new high-resolution neutral atomic hydrogen (HI) survey of ring galaxies using the Australia Telescope Compact Array (ATCA) to probe the HI gas and star formation properties of ring galaxies. We find that most of the barred ring galaxies in our sample are HI-deficient, alluding to the effects of the bar in driving their HI deficiency. Furthermore, for the secularly evolving barred ring galaxies, we identify rings of HI gas and recent star formation co-located at one or the other major resonances. Lastly, we measure the bar pattern speed for a sub-sample of our galaxies and find that the values range from 10 – 90 km/s per kpc, in good agreement with previous studies. Though this study, we show the importance of high-resolution HI studies of galaxies to better understand the implications of the bar on their gas content, star formation and consequently their evolution.

Poster sparklers in this session:

P2: Saurav Mishra*, Macquarie Uni.

P11: Simon C.-C. Ho*, ANU

P48: Susie Tuntipong*, Swinburne 

P99: Jose Bellido Caceres, University of Adelaide