The Observable Thermal and Kinetic Sunyaev-Zel'dovich Effect in Merging Galaxy Clusters

The advent of high-resolution imaging of galaxy clusters using the Sunyaev-Zel'dovich Effect (SZE) provides a unique probe of the astrophysics of the intracluster medium (ICM) out to high redshifts. To investigate the effects of cluster mergers on resolved SZE images, we present a high-resolution cosmological simulation of a 1.5E15 M_sun adiabatic cluster using the TreeSPH code ChaNGa. This massive cluster undergoes a 10:3:1 ratio triple merger accompanied by a dramatic rise in its integrated Compton-Y, peaking at z = 0.05. By modeling the thermal SZE (tSZ) and kinetic SZE (kSZ) spectral distortions of the Cosmic Microwave Background (CMB) at this redshift with relativistic corrections, we produce various mock images of the cluster at frequencies and resolutions achievable with current high-resolution SZE instruments. The two gravitationally-bound merging subclusters account for 10% and 1% of the main cluster's integrated Compton-Y, and have extended merger shock features in the background ICM visible in our mock images. We show that along certain projections and at specific frequencies, the kSZ CMB intensity distortion can dominate over the tSZ due to the large line of sight velocities of the subcluster gas and the unique frequency-dependence of these effects. We estimate that a one-velocity assumption in estimation of line of sight velocities of the merging subclusters from the kSZ induces a bias of ~10%. This velocity bias is small relative to other sources of uncertainty in observations, partially due to helpful bulk motions in the background ICM induced by the merger. Our results show that high-resolution SZE observations, which have recently detected strong kSZ signals in subclusters of merging systems, can robustly probe the dynamical as well as the thermal state of the ICM.Comment: MNRAS, accepted. 13 pages, 9 figure

Consequences of fine-scale heterogeneity on predictions of the carbon cycle using lidar data and a height-structured ecosystem model

To more accurately predict carbon stocks and fluxes in forests, it is important to measure fine-scale heterogeneity in ecosystem structure across the landscape, and incorporate the underlying mechanisms responsible for the observed heterogeneity in ecosystem models. This study used large-footprint lidar and a height-structured ecosystem model to estimate carbon stocks and fluxes at Hubbard Brook Experimental Forest (HBEF). At HBEF elevation gradients yield a decline in aboveground carbon stock, due to changes in net growth rates and disturbance at higher elevations. Lidar and a height structured ecosystem model can accurately quantified aboveground carbon stocks. Estimates of aboveground carbon fluxes depended on the availability of lidar data, the representation of fine-scale heterogeneity in climate and soil inputs, and the simulation of spatial variation in disturbance. Predictions of forest structure depended strongly on simulating the mechanisms that drive heterogeneity in forest structure across the landscape

Off the Beaten Path: A New Approach to Realistically Model The Orbital Decay of Supermassive Black Holes in Galaxy Formation Simulations

We introduce a force correction term to better model the dynamical friction (DF) experienced by a supermassive black hole (SMBH) as it orbits within its host galaxy. This new approach accurately follows the orbital decay of a SMBH and drastically improves over commonly used advection methods. The force correction introduced here naturally scales with the force resolution of the simulation and converges as resolution is increased. In controlled experiments we show how the orbital decay of the SMBH closely follows analytical predictions when particle masses are significantly smaller than that of the SMBH. In a cosmological simulation of the assembly of a small galaxy, we show how our method allows for realistic black hole orbits. This approach overcomes the limitations of the advection scheme, where black holes are rapidly and artificially pushed toward the halo center and then forced to merge, regardless of their orbits. We find that SMBHs from merging dwarf galaxies can spend significant time away from the center of the remnant galaxy. Improving the modeling of SMBH orbital decay will help in making robust predictions of the growth, detectability, and merger rates of SMBHs, especially at low galaxy masses or at high redshift.Comment: 8 pages, 4 figure, Accepted by MNRA

Astrophysical Effects of Scalar Dark Matter Miniclusters

We model the formation, evolution and astrophysical effects of dark compact Scalar Miniclusters (``ScaMs''). These objects arise when a scalar field, with an axion-like or Higgs-like potential, undergoes a second order phase transition below the QCD scale. Such a scalar field may couple too weakly to the standard model to be detectable directly through particle interactions, but may still be detectable by gravitational effects, such as lensing and baryon accretion by large, gravitationally bound miniclusters. The masses of these objects are shown to be constrained by the Ly$\alpha$ power spectrum to be less than $\sim 10^4 M_\odot$, but they may be as light as classical axion miniclusters, of the order of $10^{-12} M_\odot$. We simulate the formation and nonlinear gravitational collapse of these objects around matter-radiation equality using an N-body code, estimate their gravitational lensing properties, and assess the feasibility of studying them using current and future lensing experiments. Future MACHO-type variability surveys of many background sources can reveal either high-amplification, strong lensing events, or measure density profiles directly via weak-lensing variability, depending on ScaM parameters and survey depth. However, ScaMs, due to their low internal densities, are unlikely to be responsible for apparent MACHO events already detected in the Galactic halo. A simple estimate is made of parameters that would give rise to early structure formation; in principle, early stellar collapse could be triggered by ScaMs as early as recombination, and significantly affect cosmic reionization.Comment: 13 pages, 12 figures. Replaced to reflect published versio