Session KK03: V: Mini-Symposium: Cosmology and Galaxies

Protoplanetary accretion discs, planet formation, and gravitational instability.

Since ALMA began operations in 2015, we have been availed of a plethora of resolved millimetre images of protoplanetary discs. We have realised that substructure in these discs, such as rings, spirals and gaps, are the norm rather than the exception. This talk discusses the state of the field and highlights recent developments, particularly the move away from using continuum images to infer the underlying properties of the disc, and instead relying on kinematic detections of substructure and new AI methods to find it.   

Supermassive Black Hole Spins in Seyfert I AGN via Principal Component Analysis

The general-relativistic frame-dragging caused by a spinning supermassive black hole (SMBH) has geometric effects on the inner accretion disk, which can be traced in the X-rays reflected from the disk. Modeling the relativistically broadened X-ray emission reflected from the innermost accretion flows at the centers of active galactic nuclei (AGN) allows us to measure the SMBH spins. Since the supermassive black hole's spin is constant over the course of human history, changes in X-ray sources in AGN should not have an impact on our spin measurement. To evaluate the reliability of our spin constraint, we perform principal component analysis (PCA) on time-segmented XMM-Newton and Suzaku observations of a sample of Seyfert I AGN that have been found to contain the relativistically widened iron lines at 6.4 keV, such as NGC 3783, NGC 4051, and MCG-6-30-15. Our PCA analyses of all the available multi-epoch archival data show that the main component mostly causing X-ray variations is linked to the continuum of a power-law emitting source. The higher-order PCA components involve the trivial contributions from a relativistically redshifted, blurred reflection (<2%). The minimal variations in the relativistic X-ray reflection could potentially result from light-bending phenomena near the event horizon and have no impact on the spin constraints made by using all multi-epoch data.   

Dust in High-Redshift Galaxies: Reconciling UV Attenuation and IR Emission

Dust is a key component of galaxies, but its properties during the earliest eras of structure formation remain elusive. Here we present a simple semi-analytic model of the dust distribution in galaxies at $z \gtrsim 5$. We calibrate the free parameters of this model to estimates of the UV attenuation (using the IRX-$\beta$ relation between infrared emission and the UV spectral slope) and to ALMA measurements of dust emission. We find that the observed dust emission requires that most of the dust expected in these galaxies is retained (assuming a similar yield to lower-redshift sources), but if the dust is spherically distributed, the modest attenuation requires that it be significantly more extended than the stars. Interestingly, the retention fraction is larger for less massive galaxies in our model. However, the required radius is a significant fraction of the host's virial radius and is larger than the estimated extent of dust emission from stacked high-$z$ galaxies. These can be reconciled if the dust is distributed anisotropically, with typical covering fractions of $\sim 0.2$--0.7 in bright galaxies and $\lesssim 0.1$ in fainter ones.   

Detection of solar dark massive particles with micro-mechanical sensor.

We report the direct detection of solar dark massive particles in an Earth-based laboratory with the help of a micro-mechanical detector, which does not require electrical or chemical interactions. When an external massive particle propagates inside such a sensor it may influence the original dynamics of sensor atoms, and in this way can be noticed. Detected particles are electrically neutral with a non-zero rest mass of (5.6 ± 1.7) ×10^-21 kg. The detections of solar dark particles during different dates and times are discussed. The sensors are micro-weight crystals suspended as a bob of the pendulum, which oscillates when solar dark particles hit it. The oscillations may be optically registered with a laser Doppler vibrometer (2023 April APS meeting). Another independent registration is detecting changes in high-frequency electrical current through the crystal-sensor. The detection data from both channels of registration are discussed.  The detection is sensitive to the space orientation of the crystallographic axes of the crystal-sensor. Dark particles are detected when the normal to-crystal surface crystallographic axis is oriented along the solar azimuth. Dark particles are detected only when the Sun is above the horizon. It means they all are absorbed by Earth. The theoretical calculations and experimental data from two registration channels return similar masses of discovered solar dark particles. These particles are undetectable and dark to existing astrophysical and high-energy physics instruments.   

Physical mechanism that gives rise to cosmic inflation in a finite-sized electron model

In order to explain both (i) the anisotropy of the Cosmic Microwave Background (CMB), where thermal fluctuations δT/T ~ 10^-5 to 10^-4, as well as, (ii) the flatness of the Universe, it is normally postulated that the Universe underwent a period of Cosmic Inflation, early in its history, where the Universe experienced an exponential acceleration which increased the scale factor by ~ e⁶⁰. The inflaton scalar field φ that caused this acceleration is currently unknown where, additionally, the corresponding potential energy density ψ(φ) is normally merely surmised. Planck collaboration measurements indicate that the CMB anisotropies are best explained by a ψ(φ) possessing a plateau shape, which terminates abruptly at the end of inflation.

In 2020 the author published the electron Born self-energy (eBse) model for Dark Energy (DE) wherein many features of DE are quantitatively explained by attributing this energy to the electric field energy surrounding a finite-sized electron in the WHIM (Warm-Hot Intergalactic Medium). The current contribution extends the eBse model to very high densities, early in the Universe’s expansion, where electrons and positrons are packed together as close as is physically possible. It is found that this model undergoes a glass transition at a temperature T_G = 1.06x10¹⁷K caused by the electrons and positrons attaining a maximum packing density given by 1/(2R_e)³ where R_e is the electron radius. For temperatures T > T_G, it is impossible to physically increase the packing density above this maximum; the system falls out of photon-electron-positron (γ-e-e+) chemical equilibrium and the potential energy density remains constant at ψ(T_G) = 1.9x10⁵⁰J/m³. A constant ψ(T_G) leads to an accelerated expansion phase, akin to cosmic inflation. For T < T_G  γ-e-e+ equilibrium is restored where the potential energy density ψ(T) is a plateau potential, in agreement with Planck collaboration expectations. In this model the inflaton scalar field is temperature.   

Benchmarking AI-evolved cosmological structure formation and expanding dimensions through parallelization frameworks

The potential of deep learning-based image-to-image translations has recently attracted significant attention, and serves as a potentially powerful alternative to cosmological simulations, useful in contexts such as covariance studies, investigations of systematics, and cosmological parameter inference. To investigate various aspects of learning-based cosmological mappings, we choose two approaches for generation of cosmological matter fields as datasets: the analytical prescription provided by the Zel'dovich approximation, and the numerical N-body Particle-Mesh method.  A comprehensive list of metrics is considered, including higher-order correlation functions, conservation laws, topological indicators, and statistical independence of density fields. We find that a U-Net approach performs well only for some of these physical metrics. 

In addition, we develop strategies to expand the available dynamical range of deep neural networks' output. While conventional studies often showcase the neural network predictions within modest spatial dimensions and particle counts, their practical use requires significantly larger box sizes and number of particles to yield physically relevant predictions for cosmological  structure formation. To achieve this, we harness data and model parallelism frameworks during model training, and a split-and-recombine approach at model deployment for the large simulation box. We are able to achieve box sizes multiple times larger than what is typically found in the existing literature. This opens up the possibility of overcoming a number of computational bottlenecks.   

Limits on Non-Relativistic Matter During Big-Bang Nucleosynthesis

Big-bang nucleosynthesis (BBN) probes cosmic mass-energy at temperatures ~1 to ~0.1 MeV. Here we consider the effect of a cosmic matter-like species that is non-relativistic and pressureless during BBN. Such a component must decay; doing so during BBN can alter the baryon-to-photon ratio η and the effective number of neutrino species N_ν. We use light element abundances and the cosmic microwave background (CMB) constraints on η and N_ν to place constraints on such a matter component. We find that electromagnetic decays heat the photons relative to neutrinos, and thus dilute the effective number of relativistic species for the case of three Standard Model neutrinos. Intriguingly, likelihood results based on Planck CMB data alone find N_ν = 2.800 ± 0.294, and when combined with standard BBN and the observations of D and ⁴He give N_ν = 2.898 ± 0.141. While both results are consistent with the Standard Model, we find that a nonzero abundance of electromagnetically decaying matter gives a better fit to these results. Our best-fit is for a matter species that decays entirely electromagnetically with a lifetime τ_X = 0.89 s and pre-decay density that is a fraction ξ = (ρ_X/ρ_rad)_10MeV = 0.0026 of the radiation energy density at 10 MeV; similarly good fits are found over a range of constant ξτ^1/2. On the other hand, decaying matter often spoils the BBN+CMB concordance, and we present limits in the (τ_X, ξ) plane for both electromagnetic and invisible decays. We end with a brief discussion of the impact of future measurements including CMB-S4.