Spin and the Thermal Equilibrium Distribution of Wave Functions

Consider a quantum system $S$ weakly interacting with a very large but finite system $B$ called the heat bath, and suppose that the composite $S\cup B$ is in a pure state $\Psi$ with participating energies between $E$ and $E+\delta$ with small $\delta$. Then, it is known that for most $\Psi$ the reduced density matrix of $S$ is (approximately) equal to the canonical density matrix. That is, the reduced density matrix is universal in the sense that it depends only on $S$'s Hamiltonian and the temperature but not on $B$'s Hamiltonian, on the interaction Hamiltonian, or on the details of $\Psi$. It has also been pointed out that $S$ can also be attributed a random wave function $\psi$ whose probability distribution is universal in the same sense. This distribution is known as the "Scrooge measure" or "Gaussian adjusted projected (GAP) measure"; we regard it as the thermal equilibrium distribution of wave functions. The relevant concept of the wave function of a subsystem is known as the "conditional wave function". In this paper, we develop analogous considerations for particles with spin. One can either use some kind of conditional wave function or, more naturally, the "conditional density matrix", which is in general different from the reduced density matrix. We ask what the thermal equilibrium distribution of the conditional density matrix is, and find the answer that for most $\Psi$ the conditional density matrix is (approximately) deterministic, in fact (approximately) equal to the canonical density matrix.Comment: 13 pages, no figures; v2 minor improvement

A Comprehensive Archival Chandra Search for X-ray Emission from Ultracompact Dwarf Galaxies

We present the first comprehensive archival study of the X-ray properties of ultracompact dwarf (UCD) galaxies, with the goal of identifying weakly-accreting central black holes in UCDs. Our study spans 578 UCDs distributed across thirteen different host systems, including clusters, groups, fossil groups, and isolated galaxies. Of the 336 spectroscopically-confirmed UCDs with usable archival Chandra imaging observations, 21 are X-ray-detected. Imposing a completeness limit of $L_X>2\times10^{38}$ erg s$^{-1}$, the global X-ray detection fraction for the UCD population is $\sim3\%$. Of the 21 X-ray-detected UCDs, seven show evidence of long-term X-ray time variability on the order of months to years. X-ray-detected UCDs tend to be more compact than non-X-ray-detected UCDs, and we find tentative evidence that the X-ray detection fraction increases with surface luminosity density and global stellar velocity dispersion. The X-ray emission of UCDs is fully consistent with arising from a population of low-mass X-ray binaries (LMXBs). In fact, there are fewer X-ray sources than expected using a naive extrapolation from globular clusters. Invoking the fundamental plane of black hole activity for SUCD1 near the Sombrero galaxy, for which archival Jansky Very Large Array imaging at 5 GHz is publicly available, we set an upper limit on the mass of a hypothetical central black hole in that UCD to be $\lesssim10^5M_{\odot}$. While the majority of our sources are likely LMXBs, we cannot rule out central black holes in some UCDs based on X-rays alone, and so we address the utility of follow-up radio observations to find weakly-accreting central black holes.Comment: 20 pages, 6 figures, re-submitted to ApJ after minor revision

IQ-Collaboratory 1.1: The Star-forming Sequence of Simulated Central Galaxies

A tightly correlated star formation rate (SFR)–stellar mass relation of star-forming galaxies, or star-forming sequence (SFS), is a key feature in galaxy property-space that is predicted by modern galaxy formation models. We present a flexible data-driven approach for identifying this SFS over a wide range of SFRs and stellar masses using Gaussian mixture modeling (GMM). Using this method, we present a consistent comparison of the z = 0 SFSs of central galaxies in the Illustris, Evolution and Assembly of GaLaxies and their Environment, and MUFASA hydrodynamic simulations and the Santa Cruz semianalytic model (SC-SAM), alongside data from the Sloan Digital Sky Survey. We find, surprisingly, that the amplitude of the SFS varies by up to ∼0.7 dex (factor of ∼5) among the simulations with power-law slopes ranging from 0.7 to 1.2. In addition to the SFS, our GMM method also identifies subcomponents in the SFR–stellar mass plane corresponding to starburst, transitioning, and quiescent subpopulations

Comparison of various Post-systems in endodontically treated teeth

Summary: This study aims to compare various post-systems used in endodontically treated teeth. A comprehensive literature review was conducted to identify studies that compared different post systems in endodontically treated teeth. The inclusion criteria included studies comparing two or more post-systems regarding clinical and/or radiographic outcomes. The studies included in the review evaluated different types of post systems, including prefabricated metal posts, custom-made metal posts, fibre-reinforced posts, and zirconia posts. The outcomes evaluated included retention rates, fracture rates, and marginal adaptation. Cast posts offer customization benefits but need multiple appointments, while prefabricated posts are widely used for their various material, size, shape, and aesthetic options. Fibre posts share dentin\u27s elasticity, biocompatibility, aesthetic appeal, and comparable failure rates to metal posts

Exploring the Milky Way Circumgalactic Medium in a Cosmological Context with a Semi-Analytic Model

We combine the Santa-Cruz Semi-Analytic Model (SAM) for galaxy formation and evolution with the circumgalactic medium (CGM) model presented in Faerman et al. (2020) to explore the CGM properties of $L^{*}$ galaxies. We use the SAM to generate a sample of galaxies with halo masses similar to the Milky Way (MW) halo, $M_{\rm vir} \approx 10^{12}~{\rm M_{sun}}$, and find that the CGM mass and mean metallicity in the sample are correlated. We use the CGM masses and metallicities of the SAM galaxies as inputs for the FSM20 model, and vary the amount of non-thermal support. The density profiles in our models can be approximated by power-law functions with slopes in the range of $0.75 < a_n < 1.25$, with higher non-thermal pressure resulting in flatter distributions. We explore how the gas pressure, dispersion measure, OVI-OVIII column densities, and cooling rates behave with the gas distribution and total mass. We show that for CGM masses below $\sim 3 \times 10^{10}~{\rm M_{sun}}$, photoionization has a significant effect on the column densities of OVI and OVIII. The combination of different MW CGM observations favors models with similar fractions in thermal pressure, magnetic fields/cosmic rays, and turbulent support, and with $M_{\rm gas} \sim 3-10 \times 10^{10}~{\rm M_{sun}}$. The MW OVI column requires $t_{\rm cool}/t_{\rm dyn} \sim 4$, independent of the gas distribution. The AGN jet-driven heating rates in the SAM are enough to offset the CGM cooling, although exact balance is not required in star-forming galaxies. We provide predictions for the columns densities of additional metal ions - NV, NeVIII, and MgX.Comment: Submitted to ApJ. 19 pages, 15 figures (+ appendix

The MASSIVE Survey - III. Molecular gas and a broken Tully-Fisher relation in the most massive early-type galaxies

In this work we present CO(1-0) and CO(2-1) observations of a pilot sample of 15 early-type galaxies (ETGs) drawn from the MASSIVE galaxy survey, a volume-limited integral-field spectroscopic study of the most massive ETGs ($M_* >10^{11.5}M_\odot$) within 108 Mpc. These objects were selected because they showed signs of an interstellar medium and/or star formation. A large amount of gas ($>$2$\times$10$^8$ M$_{\odot}$) is present in 10 out of 15 objects, and these galaxies have gas fractions higher than expected based on extrapolation from lower mass samples. We tentatively interpret this as evidence that stellar mass loss and hot halo cooling may be starting to play a role in fuelling the most massive galaxies. These MASSIVE ETGs seem to have lower star-formation efficiencies (SFE=SFR/M$_{\rm H2}$) than spiral galaxies, but the SFEs derived are consistent with being drawn from the same distribution found in other lower mass ETG samples. This suggests that the SFE is not simply a function of stellar mass, but that local, internal processes are more important for regulating star formation. Finally we used the CO line profiles to investigate the high-mass end of the Tully-Fisher relation (TFR). We find that there is a break in the slope of the TFR for ETGs at high masses (consistent with previous studies). The strength of this break correlates with the stellar velocity dispersion of the host galaxies, suggesting it is caused by additional baryonic mass being present in the centre of massive ETGs. We speculate on the root cause of this change and its implications for galaxy formation theories.Comment: 13 pages, 7 figures, accepted by MNRA

Regulation of Star Formation by a Hot Circumgalactic Medium

Galactic outflows driven by supernovae (SNe) are thought to be a powerful regulator of a galaxy's star-forming efficiency. Mass, energy, and metal outflows ($\eta_M$, $\eta_E$, and $\eta_Z$, here normalized by the star formation rate, the SNe energy and metal production rates, respectively) shape galaxy properties by both ejecting gas and metals out of the galaxy and by heating the circumgalactic medium (CGM), preventing future accretion. Traditionally, models have assumed that galaxies self-regulate by ejecting a large fraction of the gas which enters the interstellar medium (ISM), even though such high mass-loadings are in growing tension with observations. To better understand how the relative importance of ejective (i.e. high mass-loading) vs preventative (i.e. high energy-loading) feedback affects the present-day properties of galaxies, we develop a simple gas-regulator model of galaxy evolution, where the stellar mass, ISM, and CGM are modeled as distinct reservoirs which exchange mass, metals, and energy at different rates within a growing halo. Focusing on the halo mass range from $10^{10}$ to $10^{12} M_{\odot}$, we demonstrate that, with reasonable parameter choices, we can reproduce the stellar-to-halo mass relation and the ISM-to-stellar mass relation with low mass-loaded ($\eta_M \sim 0.1-10$) but high energy-loaded ($\eta_E \sim 0.1-1$) winds, with self-regulation occurring primarily through heating and cooling of the CGM. We show that the model predictions are robust against changes to the mass-loading of outflows but are quite sensitive to our choice of the energy-loading, preferring $\eta_E \sim 1$ for the lowest mass halos and $\sim 0.1$ for Milky Way-like halos.Comment: 19 pages, 9 Figures, submitted to Ap

The relationship between galaxy and dark matter halo size from z ∼ 3 to the present

We explore empirical constraints on the statistical relationship between the radial size of galaxies and the radius of their host dark matter haloes from z similar to 0.1-3 using the Galaxy And Mass Assembly (GAMA) and Cosmic Assembly Near Infrared Deep Extragalactic Legacy Survey (CANDELS) surveys. We map dark matter halo mass to galaxy stellar mass using relationships from abundance matching, applied to the Bolshoi-Planck dissipationless N-body simulation. We define SRHR equivalent to r(e)/R-h as the ratio of galaxy radius to halo virial radius, and SRHR lambda equivalent to r(e)/(lambda R-h) as the ratio of galaxy radius to halo spin parameter times halo radius. At z similar to 0.1, we find an average value of SRHR similar or equal to 0.018 and SRHR. similar or equal to 0.5 with very little dependence on stellar mass. Stellar radius-halo radius (SRHR) and SRHR lambda have a weak dependence on cosmic time since z similar to 3. SRHR shows a mild decrease over cosmic time for low-mass galaxies, but increases slightly or does not evolve formoremassive galaxies. We find hints that at high redshift (z similar to 2-3), SRHR. is lower for more massive galaxies, while it shows no significant dependence on stellar mass at z less than or similar to 0.5. We find that for both the GAMA and CANDELS samples, at all redshifts from z similar to 0.1-3, the observed conditional size distribution in stellar mass bins is remarkably similar to the conditional distribution of lambda R-h. We discuss the physical interpretation and implications of these results