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