Urmila Chadayammuri, Lukas Eisert, Annalisa Pillepich
et al.
The physical properties of the intracluster medium (ICM) reflect signatures of the underlying gravitational potential, mergers and strong interactions with other halos and satellite galaxies, as well as galactic feedback from supernovae and supermassive black holes (SMBHs). Traditionally, clusters have been characterized in terms of summary statistics, such as halo mass, X-ray luminosity, cool-core state, luminosity of AGN, and number of merging components. In this paper of the Extracting Reality from Galaxy Observables with Machine Learning series (ERGO-ML), we instead consider the full information content available in maps of X-ray emission from the ICM. We employ Nearest Neighbour Contrastive Learning (NNCLR) to identify and populate a low-dimensional representation space of such images. Using idealized X-ray maps of the 352 clusters of the TNG-Cluster cosmological magnetohydrodynamical simulation suite, we take three orthogonal projections of each cluster at eight snapshots within the redshift range $0\leq z<1$, resulting in a dataset of $\sim$8,000 images. Our findings reveal that this representation space forms a continuous distribution from relaxed to merging objects, and from centrally-peaked to flat emission profiles. The representation also exhibits clear trends with redshift, with halo, gas, stellar, and SMBH mass, with time since a last major merger, and with indicators of dynamical state. We show that an 8-dimensional representation can be used to predict a variety of cluster properties, find analogs, and identify correlations between physical properties, thereby suggesting causal relationships. Our analysis demonstrates that contrastive learning is a powerful tool for characterizing galaxy clusters from their images alone, allowing us to derive constraints on their physical properties and formation histories using cosmological hydrodynamical galaxy simulations.
AbstractWe extend Einstein’s theory of general relativity by introducing stochastic elements in addition to the usual fields and apply it to explore late-time redshift. The stochastic perturbation of spacetime enforces an effective minimum length (ML) to give us a cosmological constant naturally derived from the diffusive nature of spacetime and a redshift driven by both the geometry of spacetime as well as its diffusive nature. In this new theory, “dark energy” is the manifestation of fundamental uncertainty caused by ML of spacetime. The new theory converges to the minimalΛ\LambdaCDM model in the era after the Big Bang, when the geometry dominates over the diffusive character of spacetime. However, as the Hubble parameter decreases in value over time, there is a period during which the diffusive effects play an increasingly important role. For later times, as the universe approaches its minimum total energy density, the resulting redshift obtains significant contributions from both the geometry, captured by the Hubble parameter “HH,” and spacetime diffusion, captured by a new parameter “DD,” the diffusive equivalent toHH. Hence, the new theory presented here is particularly important during the later times in whichHHdiminishes and becomes comparable toDD. The theory suggests that the Hubble tension might be relieved by the diffusive character of spacetime. In order to compare the early time Hubble parameter estimates to the late-time estimates, we must recognize the contribution diffusion makes to the redshift observations and further reformulate luminosity distance and its kinematic expression to account for the effects of diffusion in addition to geometry. We perform a simple analysis of Type Ia supernovae observations with distances calibrated using Cepheids to obtain estimates for the new diffusion parameter. Based on these results, the new theory places the universe well inside a vacuum-dominated regime with a small and diminishing diffusion parameter.
Motivated by previous studies in literature about the potential importance of relativistic corrections to galaxy cluster hydrostatic masses, we calculate the masses of 12 relaxed clusters (with Chandra X-ray data) using the Tolman-Oppenheimer-Volkov (TOV) equation of hydrostatic equilibrium and the ideal gas equation of state. Analytical formulae for gas density and temperature profiles for these clusters, previously derived by Vikhlinin et al (astro-ph/0507092) were used to obtain these masses. We compare the TOV-based masses with those obtained using the corresponding Newtonian equation of hydrostatic equilibrium. We find that the fractional relative difference between the two masses are negligible, corresponding to $\sim \mathcal{O}(10^{-5})$.
We present a new set of models for intermediate mass AGB stars (4.0, 5.0 and, 6.0 Msun) at different metallicities (-2.15<=Fe/H]<=+0.15). This integrates the existing set of models for low mass AGB stars (1.3<=M/M<=3.0) already included in the FRUITY database. We describe the physical and chemical evolution of the computed models from the Main Sequence up to the end of the AGB phase. Due to less efficient third dredge up episodes, models with large core masses show modest surface enhancements. The latter is due to the fact that the interpulse phases are short and, then, Thermal Pulses are weak. Moreover, the high temperature at the base of the convective envelope prevents it to deeply penetrate the radiative underlying layers. Depending on the initial stellar mass, the heavy elements nucleosynthesis is dominated by different neutron sources. In particular, the s-process distributions of the more massive models are dominated by the \nean~reaction, which is efficiently activated during Thermal Pulses. At low metallicities, our models undergo hot bottom burning and hot third dredge up. We compare our theoretical final core masses to available white dwarf observations. Moreover, we quantify the weight that intermediate mass models have on the carbon stars luminosity function. Finally, we present the upgrade of the FRUITY web interface, now also including the physical quantities of the TP-AGB phase of all the models included in the database (ph-FRUITY).
We categorically point out why the analysis of arXiv:1404.1821 [hep-ph] is incorrect. Here we explicitly show why the sub-Planckian field excursion of the inflaton field can yield large observable tensor-to-scalar ratio, which satisfies both Planck and BICEP constraints.
Hugo Buddelmeijer, Danny Boxhoorn, Edwin A. Valentijn
We present the design of a novel way of handling astronomical catalogs in Astro-WISE in order to achieve the scalability required for the data produced by large scale surveys. A high level of automation and abstraction is achieved in order to facilitate interoperation with visualization software for interactive exploration. At the same time flexibility in processing is enhanced and data is shared implicitly between scientists. This is accomplished by using a data model that primarily stores how catalogs are derived; the contents of the catalogs are only created when necessary and stored only when beneficial for performance. Discovery of existing catalogs and creation of new catalogs is done through the same process by directly requesting the final set of sources (astronomical objects) and attributes (physical properties) that is required, for example from within visualization software. New catalogs are automatically created to provide attributes of sources for which no suitable existing catalogs can be found. These catalogs are defined to contain the new attributes on the largest set of sources the calculation of the attributes is applicable to, facilitating reuse for future data requests. Subsequently, only those parts of the catalogs that are required for the requested end product are actually processed, ensuring scalability. The presented mechanisms primarily determine which catalogs are created and what data has to be processed and stored: the actual processing and storage itself is left to existing functionality of the underlying information system.
We have invented a new algorithm to use with self-gravitating SPH Star Formation codes. The new method is designed to enable SPH simulations to self-regulate their numerical resolution, i.e. the number of SPH particles; the latter is calculated using the Jeans condition (Bate & Burkert 1997) and the local hydrodynamic conditions of the gas. We apply our SPH with Particle Splitting code to cloud-cloud collision simulations. Chapter 2 lists the properties of our standard SPH code. Chapter 3 discusses the efficiency of the standard code as this is applied to simulations of rotating, uniform clouds with m=2 density perturbations. Chapter 4 [astro-ph/0203057] describes the new method and the tests that it has successfully been applied to. It also contains the results of the application of Particle Splitting to the case of rotating clouds as those of Chapter 3, where, with great computational efficiency, we have reproduced the results of FD codes and SPH simulations with large numbers of particles. Chapter 5 gives a detailed account of the cloud-cloud collisions studied, starting from a variety of initial conditions produced by altering the cloud mass, cloud velocity and the collision impact parameter. In the majority of the cases studied, the collisions produced filaments (similar to those observed in ammonia in nearby Star Forming Regions) or networks of filaments; groups of protostellar cores have been produced by fragmentation of the filaments. The accretion rates at these cores are comparable to those of Class 0 objects. Due to time-step constraints the simulations stop early in their evolution. The star formation efficiency of this mechanism is extrapolated in time and is found to be 10-20%.
I give a synopsis of two aspects of the Galactic Cosmic Ray (GCR) acceleration problem: the importance of the medium energy gamma-ray window, and several specific astrophysical sources which merit further investigation. NOTE: figures may be found in the on-line version only: astro-ph/0309758.
The release of the Hipparcos catalogue provides an opportunity to check results from asteroseismology. Here we show that Hipparcos parallaxes for two stars are in good agreement with oscillation results. For eta Boo, a probable detection of solar-like oscillations by Kjeldsen at al. (1994; astro-ph/9411016) gave a frequency splitting in good agreement with the Hipparcos luminosity. For kappa_2 Boo, a delta Scuti variable, the Hipparcos parallax agrees well with the distance derived by Frandsen et al. (1995).
Intergalactic MgII absorbers are known to have structures down to scales ~ 10^{2.5} pc, and there are now indications that they may be fragmented on scales <~ 10^{-2.5} pc (Hao et al., astro-ph/0612409). When a lensed quasar is microlensed, the micro-images of the quasar experience creation, destruction, distortion, and drastic astrometric changes during caustic-crossing. I show that quasar microlensing can effectively probe MgII and other absorption "cloudlets" with sizes ~ 10^{-4.0} - 10^{-2.0} pc by inducing significant spectral variability on the timescales of months to years. With numerical simulations, I demonstrate the feasibility of applying this method to Q2237+0305, and I show that high-resolution spectra of this quasar in the near future would provide a clear test of the existence of such metal-line absorption "cloudlets" along the quasar sight line.
CK Vul (Nova Vul 1670) is one of the most mysterious objects among erupting stellar objects. Past studies have suggested that CK Vul is a final helium-flash object resembling V605 Aql and V4334 Sgr (Sakurai's object). The peculiar outburst light curve of CK Vul, however, had no similar counterpart among the known eruptive objects. Furthermore, the presence of hydrogen in the proposed remnant seems to contradict with the final helium-flash scenario. We propose that the peculiarities of CK Vul can be naturally understood if we consider a merging of main-sequence stars, following a new interpretation by Soker and Tylenda (astro-ph/0210463), which was proposed to explain the peculiar eruptive object V838 Mon. In this case, the 1670 outburst of CK Vul may be best understood as a V838 Mon-like event which occurred in our vicinity.
Lyutikov (astro-ph/0503505) raised a valid point that for shock deceleration of a highly magnetized outflow, the fate of the magnetic fields after shock crossing should be considered. However, his comment that the deceleration radius should be defined by the total energy rather than by the baryonic kinetic energy is incorrect. As strictly derived from the shock jump conditions in Zhang & Kobayashi (2005), during the reverse shock crossing process the magnetic energy is not tapped. As a result, the fireball deceleration radius is defined by the baryonic energy only. The magnetic energy is expected to be transferred to the circumburst medium after the reverse shock disappears. The evolution of the system then mimicks a continuously-fed fireball. As a result, Lyutikov's naive conclusion that the forward shock dynamics is independent on the ejecta content is also incorrect. The shock deceleration dynamics and the reverse shock calculation presented in Zhang & Kobayashi (2005) are robust and correct.
A convincing physical picture for the Lyman-alpha forest has emerged from simulations and related semi-analytic studies of structure formation models. Observations can be be used in the context of this picture to study cosmology using the structure of the forest. With the availability of well motivated predictions, not only has it become possible to test models directly, but the physical processes involved appear to be simple enough that we can attempt to reconstruct aspects of the underlying cosmology from observations. We briefly summarise the method of Croft et al (1997) (astro-ph/9708018) for recovering the primordial mass power spectrum from Lyman-alpha forest data, emphasising the physical reasons that the derived P(k) is independent of unknown "bias factors". We present an illustrative application of the method to four quasar "spectra" reconstructed from published line lists.
Observational tests during the next decade may determine if the evolution of the Universe can be understood from fundamental physical principles, or if special initial conditions, coincidences, and new, untestable physical laws must be invoked. The inflationary model of the Universe is an important example of a predictive cosmological theory based on physical principles. In this talk, we discuss the distinctive fingerprint that inflation leaves on the cosmic microwave background anisotropy. We then suggest a series of five milestone experimental tests of the microwave background which could determine the validity of the inflationary hypothesis within the next decade. The paper is a Review based on a Plenary talk given at the Snowmass Workshop on Particle Astrophysics and Cosmology, 1995 It will appear in the Proceedings edited by E. Kolb and R.Peccei. Software package for computing filter functions and band power estimates available thru world-wide-web at http://dept.physics.upenn.edu/~www/astro-cosmo/ .
The phenomena customly called Dark Matter or Modified Newtonian Dynamics (MOND) have been argued by Bekenstein (2004) to be the consequences of a covariant scalar field, controlled by a free function (related to the MOND interpolating function) in its Lagrangian density. In the context of this relativistic MOND theory (TeVeS), we examine critically the interpolating function in the transition zone between weak and strong gravity. Bekenstein's toy model produces too gradually varying functions and fits rotation curves less well than the standard MOND interpolating function. However, the latter varies too sharply and implies an implausible external field effect (EFE). These constraints on opposite sides have not yet excluded TeVeS, but made the zone of acceptable interpolating functions narrower. An acceptable "toy" Lagrangian density function with simple analytical properties is singled out for future studies of TeVeS in galaxies. We also suggest how to extend the model to solar system dynamics and cosmology, and compare with strong lensing data (see also astro-ph/0509590).
The X-ray emission by hot gas around the central galaxies of galaxy clusters is commonly modeled assuming the existence of steady-state, multiphase cooling flows. The inflowing gas will be chemically enriched by type Ia supernovae and stellar mass loss occurring in the outer parts of the central galaxy. This may give rise to a substantial metallicity enhancement towards the center, whose amplitude is proportional to the ratio of the central galaxy luminosity to the mass inflow rate. The metallicity of the hotter phases is expected to be higher than that of the colder, denser phases. The metallicity profile expected for the Centaurus cluster is in good agreement with the iron abundance gradient recently inferred from ASCA measurements (Fukazawa et al. 1994). However, current data do not rule out alternative models where cooling is balanced by some heat source. In either case, the enhancement expected from injection by type Ia supernovae is roughly as observed. Most of this work is described in more detail in Reisenegger, Miralda-Escudé, \& Waxman (1996; astro-ph/9511044).