National Astronomy Meeting Poster Exhibition

The distribution of stellar metallicities within and across galaxies is an excellent relic of the chemical evolution across cosmic time. Spatially resolved spectroscopic surveys offer the unique opportunity to study global and local drivers of stellar populations in galaxies. In this talk, I present results from a detailed analysis of spatially resolved stellar populations based on > 2.6 million spatial bins from 8109 nearby galaxies in the SDSS-IV MaNGA survey. Our study goes beyond the well-known global mass-metallicity relation and radial metallicity gradients by providing a statistically sound exploration of local relations between stellar metallicity, stellar surface mass density (SMD) and galactocentric distance in the global mass-morphology plane. We find a significant resolved SMD-metallicity relation for galaxies of all types and masses. The spread of the relation is mainly attributed to different radial distances. In particular, we find that at fixed SMD metallicity increases with radius. This result calls for a driver of metallicity in addition to SMD that promotes chemical enrichments in the outer parts of galaxies more strongly than in the inner parts.

The MaNGA Firefly Value-Added-Catalogue (VAC) provides measurements of spatially resolved stellar population properties in MaNGA galaxies. It is built upon and complements the MaNGA data analysis pipeline (DAP; Westfall et al. 2019) and employs the full spectral fitting code Firefly to derive parameters such as stellar ages, metallicities, masses, star formation histories and dust attenuation. In addition to Voronoi-binned measurements, it also provides global properties, such as central values and radial gradients. Here, we present an update on the MaNGA Firefly VAC that now doubled in sample size as compared to the version published in SDSS DR15 and comprises the complete final MaNGA sample (10,010 galaxies). One of the major new additions is the choice to select the results from fits that used either the MILES (Maraston & Strömbäck 2011) or the novel MaStar (Maraston et al. 2020) stellar population models, the later of which allow to constrain the fit over the whole MaNGA wavelength range.

The hydrodynamical interactions between galaxies and their surrounding gas in clusters is a major driver of galaxy evolution, and nowhere is this interaction more dramatically demonstrated than for narrow-angle tail radio sources (NATs); active galaxies whose radio jets are bent back to an acute angle by their motion through the intracluster medium of galaxy clusters. As such, they offer us an interesting diagnostic of these systems’ orbital motion to study their interaction with the gas. We have therefore used the Low-Frequency Array (LOFAR) Two-metre Sky Survey first data release to compile the largest ever sample of 255 NATs matched to clusters, based on both photometric and spectroscopic redshifts. The spectroscopic subset confirms that line-of-sight contamination remains modest out to 7R_500, so we use a sample that excludes BCGs but extends out to these radii, and find a large excess of galaxies with their tails pointing away from the cluster centre. The spectroscopic subsample indicates that this excess persists to at least 15R_500. At small radii, we also find a small excess of jets bent toward the cluster centre. The large-radii results are very surprising, as the effects are found far beyond the cluster virial radius where we might expect such hydrodynamical phenomena to occur. They indicate that infalling filaments are dense enough to start to experience hydrodynamic deceleration, and perhaps preferentially trigger AGN activity. We seem to be seeing AGN as they fall radially in down such filaments, and emerge after passing pericentre, making NATs a potential indicator not just for the location of clusters, but also for the filaments that connect them.

We use a 2.5D model to investigate the propagation of Alfven waves and their interaction with the solar wind. In the absence of waves, the dipole field is stretched into a helmet streamer by the solar wind. The wind speeds near the equator are lower than those near the poles. We next inject monochromatic Alfven waves with a period of 1000 s at the coronal base and investigate their propagation at different azimuthal angles. The result is a moderate acceleration and heating of the background plasma. Enhanced wave amplitudes are seen in the region between 1.4 Rsun and 14 Rsun. This region remains fixed in time and it shows features of forward and backward propagating modes. The width of the region increases with an increase in the period of the Alfven waves.
When the period equals 4000 s, we find enhanced acceleration and heating of the solar wind plasma. The amplitudes of the Alfv\'en waves remain large up to 20 Rsun. However, the width of this region changes with time. Beyond the threshold radii, the wave amplitudes are small. Possible scenarios of wave energy conversion are studied to understand the mechanisms of solar wind acceleration by the long period Alfven waves.

Young massive clusters (YMCs) are recently formed astronomical objects with unusually high star formation rates. We propose the collision of giant molecular clouds (GMCs) as a likely formation mechanism of YMCs, consistent with the YMC conveyor-belt formation mode concluded by other authors. We conducted smoothed particle hydrodynamical simulations of cloud-cloud collisions, and show that greater collision speed, greater initial cloud density, and lower turbulence increase the overall star formation rate. These conditions produce clusters with greater cluster mass, some even resembling the observed Milky Way YMCs. We also investigate grouped star formation, whereby sink particles are grouped as larger star-forming regions, then are used to sample the initial mass function of stars. Having individual stars in the simulations will prepare us for the inclusion of stellar feedback in our colliding clouds simulations in the future.

Strong lensing images provide a wealth of information about both the magnified source and the mass distribution in the lens, allowing dark matter models to be constrained. However, due to the degeneracies inherent to lensing, making inferences about substructure requires very accurate and precise, yet flexible, reconstruction of the source. In anticipation of future high-resolution datasets, in this work we leverage a range of recent developments in machine learning to present a new end-to-end differentiable GPU-accelerated Bayesian strong lensing image analysis pipeline. We have also developed a new statistically principled source model based on an efficient approximation to Gaussian processes that also takes into account pixelisation effects. Using variational inference and stochastic gradient descent, we simultaneously derive approximate posteriors for tens of thousands of lens and source parameters, while also optimising hyperparameters. Besides efficient and accurate parameter estimation and uncertainty quantification, the main aim of the pipeline is the generation of training data for targeted simulation-based inference of dark matter substructure.

The presence of a prograde jet at the equator in a planetary atmosphere is often referred to as super-rotation. On Mars, the strength of the equatorial jet is dynamically coupled to the amount of dust in the atmosphere; strengthening of the equatorial jet by the presence of dust affects dust transport in the tropics, which in turn determines the locations of further dust-driven heating. We used data assimilation to study the interaction between dust and the equatorial jet during the 2018 Mars global dust storm (GDS). The data assimilation scheme integrated temperature and dust information from instruments aboard the Mars Reconnaissance Orbiter and ExoMars Trace Gas Orbiter satellites into a numerical model of the Martian atmosphere, creating a better representation of the atmospheric state than could be achieved from observations or models alone. We found that super-rotation increased by a factor of two at the peak of the GDS, due to enhanced winds in the tropics. A strong westerly jet formed in the tropical lower atmosphere, and easterlies were strengthened above 60 km, as a result of momentum transport by dust-driven thermal tides. We found that the atmosphere was in a state of enhanced super-rotation even before the onset of the GDS, as a result of equatorward advection of dust from the southern mid-latitudes into the tropics. The redistribution of dust across the hemispheres resulted in a more uniform dust distribution across the tropics, leading to a symmetric Hadley cell with a tropical upwelling branch that was closely aligned to the vertical. We argue that the symmetrical circulation and enhanced super-rotation would have been important environmental factors that encouraged the development of the GDS in 2018.

We infer the radial gravitational acceleration around isolated galaxy-galaxy lenses from KiDS-1000 weak lensing convergence measurements. We extend the radial acceleration relation (RAR), conventionally measured using galaxy rotation curves, by 2 decades in acceleration. We compare the measurements with mock lensing "observations" of the MICE N-body + semi-analytic galaxy formation simulation, and the BAHAMAS cosmological hydrodynamical simulations. We find MICE predictions to be in excellent agreement with our measurements, but these simulations fail to reproduce y expected bias in the stellar-to-halo-mass ratio of isolated galaxies. Conversely, the BAHAMAS simulations do reproduce this bias, but this causes the RAR to shift well away from the measured trend. We also compare to predictions of two modified gravity models, MOND and Emergent Gravity, finding these to be consistent with the overall measured RAR. However, we find a significant difference in the RAR of early- and late-type galaxies, which these theories do not predict, but is straightforwardly accommodated in dark matter models. Our interpretation of our measurements is limited primarily by uncertainty in the distribution of hot, circumgalactic gas.

We combine orbital information from N-body simulations with an analytic model for star formation quenching and SDSS observations to infer the differential effect of the group/cluster environment on star formation in satellite galaxies. We also consider a model for gas stripping, using the same input supplemented with H I <br /> fluxes from the ALFALFA survey. The models are motivated by and tested on the Hydrangea cosmological hydrodynamical simulation suite. We recover the characteristic times when satellite galaxies are stripped and quenched. Stripping in massive (Mvir ∼ 10^14.5 Msun) clusters typically occurs at or just before the first pericentric passage. Lower mass (∼10^13.5 Msun) groups strip their satellites on a significantly longer (by ∼ 3 Gyr) time-scale. Quenching occurs later: Balmer <br /> emission lines typically fade ∼ 3.5 Gyr (5.5 Gyr) after first pericentre in clusters (groups), followed a few hundred Myr later by reddenning in (g − r) colour. These ‘delay time-scales’ are remarkably constant across the entire satellite stellar mass range probed (∼10^9.5 –10^11 Msun ), a feature closely tied to our treatment of ‘group pre-processing’. The lowest mass groups in our sample (∼ 10^12.5 Msun) strip and quench their satellites extremely inefficiently: typical time-scales may approach the age of the Universe. Our measurements are qualitatively consistent with the ‘delayed-then-rapid’ quenching scenario advocated for by several other studies, but we find significantly longer delay times. Our combination of a homogeneous analysis and input catalogues yields new insight into the sequence of events leading to quenching across wide intervals in host and satellite mass.

Current sheets play a key role in solar flares and coronal mass ejections as they are the locations where magnetic energy is liberated through reconnection and is converted to other forms. Yet, their formation and evolution during the impulsive phase of a flare remain elusive. In this talk, we will report new observations of a current sheet formation and subsequent evolution in the early stages of an eruptive solar flare. In particular, we will present multiphase evolution of a dynamic current sheet from its formation to quasi-stable evolution and disruption. Implications for the onset and evolution of reconnection will be discussed.