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Wave (fuzzy) dark matter ($\psi$DM) consists of ultralight bosons, featuring a solitonic core within a granular halo. Here we extend $\psi$DM to two components, with distinct particle masses $m$ and coupled only through gravity, and investigate the resulting soliton-halo structure via cosmological simulations. Specifically, we assume $\psi$DM contains $75$ per cent major component and $25$ per cent minor component, fix the major-component particle mass to $m_{\rm major}=1\times10^{-22}\,{\rm eV}$, and explore two different minor-component particle masses with $m_{\rm major}:m_{\rm minor}=3:1$ and $1:3$, respectively. For $m_{\rm major}:m_{\rm minor}=3:1$, we find that (i) the major- and minor-component solitons coexist, have comparable masses, and are roughly concentric. (ii) The soliton peak density is significantly lower than the single-component counterpart, leading to a smoother soliton-to-halo transition and rotation curve. (iii) The combined soliton mass of both components follows the same single-component core-halo mass relation. In dramatic contrast, for $m_{\rm major}:m_{\rm minor}=1:3$, a minor-component soliton cannot form with the presence of a stable major-component soliton; the total density profile, for both halo and soliton, is thus dominated by the major component and closely follows the single-component case. To support this finding, we propose a toy model illustrating that it is difficult to form a soliton in a hot environment associated with a deep gravitational potential. The work demonstrates the extra flexibility added to the multi-component $\psi$DM model can resolve observational tensions over the single-component model while retaining its key features., Comment: 19 pages, 24 figures, 1 table, accepted for publication in MNRAS

Low mass galaxies in the Local Group are dominated by dark matter and comprise the well studied “dwarf Spheroidal" (dSph) class, with typical masses of 109−10M⊙ and also the equally numerous “ultra faint dwarfs" (UFD), discovered recently, that are distinctly smaller and denser with masses of only 107−8M⊙. This bimodality amongst low mass galaxies contrasts with the scale free continuity expected for galaxies formed under gravity, as in the standard Cold Dark Matter (CDM) model for heavy particles. Within each dwarf class we find the core radius Rc is inversely related to velocity dispersion σ, quite the opposite of standard expectations, but indicative of dark matter in a Bose-Einstein state, where the Uncertainty Principle requires Rc × σ is fixed by Planks constant, h. The corresponding boson mass, mb = h/Rcσ, differs by one order of magnitude between the UDF and dSph classes, with 10−21.4eV and 10−20.3eV respectively. Two boson species is reinforced by parallel relations seen between the central density and radius of UDF and dSph dwarfs respectively, which both match the steep prediction, ρc ∝ Rc−4, for soliton cores in the ground state. Furthermore, soliton cores accurately fit the stellar profiles of UDF and dSph dwarfs where prominent, dense cores appear surrounded by low density halos, as predicted by our simulations. Multiple bosons may point to a String Theory interpretation for dark matter, where a discrete mass spectrum of axions is generically predicted to span many decades in mass, offering a unifying "Axiverse" interpretation for the physical "diversity" of dark matter dominated dwarf galaxies.

We present a new special relativistic hydrodynamics (SRHD) code capable of handling coexisting ultra-relativistically hot and non-relativistically cold gases. We achieve this by designing a new algorithm for conversion between primitive and conserved variables in the SRHD solver, which incorporates a realistic ideal-gas equation of state covering both the relativistic and non-relativistic regimes. The code can handle problems involving a Lorentz factor as high as 106 and optimally avoid the catastrophic cancellation. In addition, we have integrated this new SRHD solver into the code gamer (https://github.com/gamer-project/gamer) to support adaptive mesh refinement and hybrid OpenMP/MPI/GPU parallelization. It achieves a peak performance of 7 × 107 cell updates per second on a single Tesla P100 GPU and scales well to 2048 GPUs. We apply this code to two interesting astrophysical applications: (a) an asymmetric explosion source on the relativistic blast wave and (b) the flow acceleration and limb brightening of relativistic jets.

Fuzzy dark matter (FDM) has been a promising alternative to standard cold dark matter. The model consists of ultralight bosons with mass $m_b \sim 10^{-22}$ eV and features a quantum-pressure-supported solitonic core that oscillates. In this work, we show that the soliton density oscillations persist even after significant tidal stripping of the outer halo. We report two intrinsic yet distinct timescales associated, respectively, with the ground-state soliton wavefunction $\tau_{00}$ and the soliton density oscillations $\tau_\text{soliton}$, obeying $\tau_\text{soliton} /\tau_{00} \simeq 2.3$. The central star cluster (SC) in Eridanus II has a characteristic timescale $\tau_\text{soliton} / \tau_\text{SC} \sim 2$ to $3$ that deviates substantially from unity. As a result, we demonstrate, both analytically and numerically with three-dimensional self-consistent FDM simulations, that the gravitational heating of the SC owing to soliton density oscillations is negligible irrespective of $m_b$. We also show that the subhalo mass function to form Eridanus II does not place a strong constraint on $m_b$. These results are contrary to the previous findings by Marsh & Niemeyer (2019)., Comment: 19 pages, 19 figures; Accepted for publication in PRD

The evolution of cosmic perturbations in a two-component ultralight axionic universe is investigated. We present the first spectral computation of perturbations in multi-component universes. A particular case composed of light extreme axions and free massive particles offers a possibility for the formation of very high-redshift massive galaxies, which are typically required to host massive early quasars. Our computation retains the information of perturbed velocities for individual axion components, opening a new avenue for setting up initial conditions for future axion dark matter simulations., Comment: 10 pages, 8 figures

Extremely light bosonic wave dark matter ($\psi$DM) is an emerging dark matter candidate contesting the conventional cold dark matter paradigm and a model subject to intense scrutiny of late. This work for the first time reports testable salient features pertinent to gravitational lenses of $\psi$DM halos. $\psi$DM halos are distinctly filled with large-amplitude, small-scale density fluctuations with $\delta\rho/\rho_{\rm halo}\sim 1$ in form of density granules. This halo yields ubiquitous flux ratio anomalies of a few tens of percent, as is typically found for lensed quasars, and may also produce rare hexad and octad images, for sources located in well-defined caustic zones. We have found new critical features appearing in the highly de-magnified lens center when the halo has sufficiently high surface density near a very compact massive core., Comment: 6 pages, 4 figures

Wave dark matter ($\psi$DM) predicts a compact soliton core and a granular halo in every galaxy. This work presents the first simulation study of an elliptical galaxy by including both stars and $\psi$DM, focusing on the systematic changes of the central soliton and halo granules. With the addition of stars in the inner halo, we find the soliton core consistently becomes more prominent by absorbing mass from the host halo than that without stars, and the halo granules become "non-isothermal", "hotter" in the inner halo and "cooler" in the outer halo, as opposed to the isothermal halo in pure $\psi$DM cosmological simulations. Moreover, the composite (star+$\psi$DM) mass density is found to follow a $r^{-2}$ isothermal profile near the half-light radius in most cases. Most striking is the velocity dispersion of halo stars that increases rapidly toward the galactic center by a factor of at least 2 inside the half-light radius caused by the deepened soliton gravitational potential, a result that compares favorably with observations of elliptical galaxies and bulges in spiral galaxies. However in some rare situations we find a phase segregation turning a compact distribution of stars into two distinct populations with high and very low velocity dispersions; while the high-velocity component mostly resides in the halo, the very low-velocity component is bound to the interior of the soliton core, resembling stars in faint dwarf spheroidal galaxies., Comment: 15 pages, 11 figures

Wave dark matter ($\psi \rm{DM}$) composed of extremely light bosons ($m_{\psi} \sim 10^{-22}\,\rm eV$), with quantum pressure suppressing structures below a kpc-scale de Broglie wavelength, has become a viable dark matter candidate. Compared to the conventional free-particle $\psi {\rm DM}$ (${\rm FP} \psi {\rm DM}$), the extreme-axion $\psi \rm{DM}$ model (${\rm EA} \psi {\rm DM}$) proposed by Zhang & Chiueh (2017) features a larger cut-off wavenumber and a broad spectral bump in the matter transfer function. Here we conduct cosmological simulations to compare the halo abundances and assembly histories at $z=4-11$ between three different scenarios: ${\rm FP} \psi {\rm DM}$, ${\rm EA} \psi {\rm DM}$, and cold dark matter (CDM). We show that ${\rm EA} \psi {\rm DM}$ produces significantly more abundant low-mass haloes than ${\rm FP} \psi {\rm DM}$ with the same $m_{\psi}$, and therefore could alleviate the tension in $m_{\psi}$ required by the Ly$\alpha$ forest data and by the kpc-scale dwarf galaxy cores. We also find that, compared to the CDM counterparts, massive ${\rm EA} \psi {\rm DM}$ haloes are on average $3-4$ times more massive at $z=10-11$ due to their earlier formation, undergo a slower mass accretion at $7 \lesssim z \lesssim 11$, and then show a rapidly rising major merger rate exceeding CDM by $\sim 50\%$ at $4 \lesssim z \lesssim 7$. This fact suggests that ${\rm EA} \psi {\rm DM}$ haloes may exhibit more prominent starbursts at $z \lesssim 7$., Comment: 5 pages, 4 figures, only minor updates (accepted for publication in MNRAS letters)

Although still under debate, observations generally suggest that dwarf spheroidal (dSph) galaxies exhibit large constant-density cores in the centers, which can hardly be explained by dissipationless cold dark matter simulations without baryonic feedback. Wave dark matter (${\psi {\rm DM}}$), characterized by a single parameter, the dark matter particle mass $m_{\psi}$, predicts a central soliton core in every galaxy arising from quantum pressure against gravity. Here we apply Jeans analysis assuming a soliton core profile to the kinematic data of eight classical dSphs so as to constrain $m_{\psi}$, and obtain $m_{\psi}=1.18_{-0.24}^{+0.28}\times10^{-22}{\,\rm eV}$ and $m_{\psi}=1.79_{-0.33}^{+0.35}\times10^{-22}{\,\rm eV}~(2\sigma)$ using the observational data sets of Walker et al. (2007) and Walker et al. (2009b), respectively. We show that the estimate of $m_{\psi}$ is sensitive to the dSphs kinematic data sets and is robust to various models of stellar density profile. We also consider multiple stellar subpopulations in dSphs and find consistent results. This mass range of $m_{\psi}$ is in good agreement with other independent estimates, such as the high-redshift luminosity functions, the reionization history, and the Thomson optical depth to the cosmic microwave background., Comment: 12 pages, 11 figures, 2 tables, add appendix B about the joint analysis, submitted to MNRAS

Simulations of ultralight, $\sim 10^{-22}\,\rm eV$, bosonic dark matter exhibit rich wave-like structure, including a soliton core within a surrounding halo that continuously self-interferes on the de Broglie scale. We show here that as an inherent consequence, the soliton undergoes a confined random walk at the base of the halo potential. This is significant for the fate of the ancient central star cluster in Eridanus II, as the agitated soliton gravitationally shakes the star cluster in and out of the soliton on a time scale of $\sim 100\,\rm Myr$, so complete tidal disruption of the star cluster can occur within $\sim 1\,\rm Gyr$. This destructive effect can be mitigated by tidal stripping of the halo of Eridanus II, thereby reducing the agitation, depending on its orbit around the Milky Way. Our simulations show the Milky Way tide affects the halo much more than the soliton, so the star cluster in Eridanus II can survive for over $5\,\rm Gyr$ within the soliton if it formed after significant halo stripping., Comment: Accepted for publication in Phys. Rev. Lett. 6 pages, 4 figures

Accurate and precise measurements of the Hubble constant are critical for testing our current standard cosmological model and revealing possibly new physics. With Hubble Space Telescope (HST) imaging, each strong gravitational lens system with measured time delays can allow one to determine the Hubble constant with an uncertainty of $\sim 7\%$. Since HST will not last forever, we explore adaptive-optics (AO) imaging as an alternative that can provide higher angular resolution than HST imaging but has a less stable point spread function (PSF) due to atmospheric distortion. To make AO imaging useful for time-delay-lens cosmography, we develop a method to extract the unknown PSF directly from the imaging of strongly lensed quasars. In a blind test with two mock data sets created with different PSFs, we are able to recover the important cosmological parameters (time-delay distance, external shear, lens mass profile slope, and total Einstein radius). Our analysis of the Keck AO image of the strong lens system RXJ1131-1231 shows that the important parameters for cosmography agree with those based on HST imaging and modeling within 1-$\sigma$ uncertainties. Most importantly, the constraint on the model time-delay distance by using AO imaging with $0.045"$resolution is tighter by $\sim 50\%$ than the constraint of time-delay distance by using HST imaging with $0.09"$when a power-law mass distribution for the lens system is adopted. Our PSF reconstruction technique is generic and applicable to data sets that have multiple nearby point sources, enabling scientific studies that require high-precision models of the PSF., Comment: 20 pages, 15 figures

Wave dark matter ($\psi$DM), which satisfies the Schr\"odinger-Poisson equation, has recently attracted substantial attention as a possible dark matter candidate. Numerical simulations have in the past provided a powerful tool to explore this new territory of possibility. Despite their successes to reveal several key features of $\psi$DM, further progress in simulations is limited, in that cosmological simulations so far can only address formation of halos below $\sim 2\times 10^{11} M_\odot$ and substantially more massive halos have become computationally very challenging to obtain. For this reason, the present work adopts a different approach in assessing massive halos by constructing wave-halo solutions directly from the wave distribution function. This approach bears certain similarity with the analytical construction of particle-halo (cold dark matter model). Instead of many collisionless particles, one deals with one single wave that has many non-interacting eigenstates. The key ingredient in the wave-halo construction is the distribution function of the wave power, and we use several halos produced by structure formation simulations as templates to determine the wave distribution function. Among different models, we find the fermionic King model presents the best fits and we use it for our wave-halo construction. We have devised an iteration method for constructing the nonlinear halo, and demonstrate its stability by three-dimensional simulations. A Milky-Way-sized halo has also been constructed, and the inner halo is found flatter than the NFW profile. These wave-halos have small-scale interferences both in space and time producing time-dependent granules. While the spatial scale of granules varies little, the correlation time is found to increase with radius by one order of magnitude across the halo., Comment: 14 pages, 7 figures, accepted by PRD

A 17.4-GHz 1-b sampling spectrum analyzer is built to demonstrate the working principle for a much faster spectrometer, where noise dithering and sine transformation are two key features of the principle. While the noise dithering can suppress the harmonics of signals, the sine transformation is shown to restore the noise. Measurements of this instrument reveal that the newly proposed novel scheme works as it should, with no technical showstopper for a much faster device.

Linear perturbations of the wave dark matter, or $\psi$ dark matter ($\psi$DM), of particle mass $\sim 10^{-22}$eV in the radiation-dominant era are analyzed, and the matter power spectrum at the photon-matter equality is obtained. We identify four phases of evolution for $\psi$DM perturbations, where the dynamics can be vastly different from the counterparts of cold dark matter (CDM). While in late stages after mass oscillation long-wave $\psi$DM perturbations are almost identical to CDM perturbations, some subtle differences remain, let alone intermediate-to-short waves that bear no resemblance with those of CDM throughout the whole evolutionary history. The dissimilarity is due to quantum mechanical effects which lead to severe mode suppression. We also discuss the axion model with a cosine field potential. The power spectrum of axion models are generally almost identical to those of $\psi$DM, but in the extreme case when the initial axion angle is near the field potential top, this axion model predict a power excess over a range of wave number and a higher spectral cutoff than $\psi$DM as if $\psi$DM had a higher particle mass., Comment: 20 pages, 7 figures

A new approximation method for inverting the Poisson's equation is presented for a continuously distributed and finite-sized source in an unbound domain. The advantage of this image multipole method arises from its ability to place the computational error close to the computational domain boundary, making the source region almost error free. It is contrasted to the modified Green's function method that has small but finite errors in the source region. Moreover, this approximation method also has a systematic way to greatly reduce the errors at the expense of somewhat greater computational efforts. Numerical examples of three-dimensional and two-dimensional cases are given to illustrate the advantage of the new method., 7 pages, 6 figures

We present the implementation and performance of a class of directionally unsplit Riemann-solver-based hydrodynamic schemes on Graphic Processing Units (GPU). These schemes, including the MUSCL-Hancock method, a variant of the MUSCL-Hancock method, and the corner-transport-upwind method, are embedded into the adaptive-mesh-refinement (AMR) code GAMER. Furthermore, a hybrid MPI/OpenMP model is investigated, which enables the full exploitation of the computing power in a heterogeneous CPU/GPU cluster and significantly improves the overall performance. Performance benchmarks are conducted on the Dirac GPU cluster at NERSC/LBNL using up to 32 Tesla C2050 GPUs. A single GPU achieves speed-ups of 101(25) and 84(22) for uniform-mesh and AMR simulations, respectively, as compared with the performance using one(four) CPU core(s), and the excellent performance persists in multi-GPU tests. In addition, we make a direct comparison between GAMER and the widely-adopted CPU code Athena (Stone et al. 2008) in adiabatic hydrodynamic tests and demonstrate that, with the same accuracy, GAMER is able to achieve two orders of magnitude performance speed-up., Comment: 16 pages, 5 figures, accepted for publication in International Journal of High Performance Computing Applications (IJHPCA)

We study the environment of wet, dry, and mixed galaxy mergers at 0.75 < z < 1.2 using close pairs in the DEEP2 Galaxy Redshift Survey. We find that the typical environment of mixed and dry merger candidates is denser than that of wet mergers, mostly due to the color-density relation. While the galaxy companion rate (Nc) is observed to increase with overdensity, using N-body simulations we find that the fraction of pairs that will eventually merge decreases with the local density, predominantly because interlopers are more common in dense environments. After taking into account the merger probability of pairs as a function of local density, we find only marginal environment dependence of the fractional merger rate for wet mergers over the redshift range we have probed. On the other hand, the fractional dry merger rate increases rapidly with local density due to the increased population of red galaxies in dense environments. We also find that the environment distribution of K+A galaxies is similar to that of wet mergers alone and of wet+mixed mergers, suggesting a possible connection between K+A galaxies and wet and/or wet+mixed mergers. We conclude that, as early as z ~ 1, high-density regions are the preferred environment in which dry mergers occur, and that present-day red-sequence galaxies in overdense environments have, on average, undergone 1.2+-0.3 dry mergers since this time, accounting for (38+-10)% of their mass accretion in the last 8 billion years. Our findings suggest that dry mergers are crucial in the mass-assembly of massive red galaxies in dense environments, such as Brightest Cluster Galaxies (BCGs) in galaxy groups and clusters., 14 pages, 7 figures, 2 tables, submitted to ApJ, revised according to the referee's comments

GAMER, a parallel Graphic-processing-unit-accelerated Adaptive-MEsh-Refinement hydrodynamic code, has been extended to support magnetohydrodynamics (MHD) with both the corner-transport-upwind (CTU) and MUSCL-Hancock schemes and the constraint transport (CT) technique. The divergent preserving operator for adaptive mesh refinement (AMR) has been applied to reinforce the divergence-free constraint on the magnetic field. GAMER-MHD has fully exploited the concurrent executions between the GPU MHD solver and other CPU computation pertinent to AMR. We perform various standard tests to demonstrate that GAMER-MHD is both second-order accurate and robust, producing results as accurate as those given by high-resolution uniform-grid runs. We also explore a new 3D MHD test, where the magnetic field assumes the Arnold-Beltrami-Childress (ABC) configuration, temporarily becomes turbulent with current sheets and finally settles to a lowest-energy equilibrium state. This 3D problem is adopted for the performance test of GAMER-MHD. The single-GPU performance reaches $1.2\times 10^8$ and $5.5\times 10^7$ cell-updates/sec for the single- and double-precision calculations, respectively, on Tesla P100. We also demonstrate a parallel efficiency of $\sim 70\%$ for both weak and strong scaling using $1,024$ XK nodes on the Blue Waters supercomputers., Comment: 29 pages, 22 figures, 1 table. GAMER-MHD will soon become available at https://github.com/gamer-project/gamer

We present the newly developed code, GAMER (GPU-accelerated Adaptive MEsh Refinement code), which has adopted a novel approach to improve the performance of adaptive mesh refinement (AMR) astrophysical simulations by a large factor with the use of the graphic processing unit (GPU). The AMR implementation is based on a hierarchy of grid patches with an oct-tree data structure. We adopt a three-dimensional relaxing TVD scheme for the hydrodynamic solver, and a multi-level relaxation scheme for the Poisson solver. Both solvers have been implemented in GPU, by which hundreds of patches can be advanced in parallel. The computational overhead associated with the data transfer between CPU and GPU is carefully reduced by utilizing the capability of asynchronous memory copies in GPU, and the computing time of the ghost-zone values for each patch is made to diminish by overlapping it with the GPU computations. We demonstrate the accuracy of the code by performing several standard test problems in astrophysics. GAMER is a parallel code that can be run in a multi-GPU cluster system. We measure the performance of the code by performing purely-baryonic cosmological simulations in different hardware implementations, in which detailed timing analyses provide comparison between the computations with and without GPU(s) acceleration. Maximum speed-up factors of 12.19 and 10.47 are demonstrated using 1 GPU with 4096^3 effective resolution and 16 GPUs with 8192^3 effective resolution, respectively.

An alternative bosonic dark matter model is examined in detail via high-resolution simulations. These bosons have particle mass of order $10^{-22}eV$ and are non-interacting. If they do exist and can account for structure formation, these bosons must be condensed into the Bose-Einstein state and described by a coherent wave function. This matter, also known as Fuzzy Dark Matter (Hu, Barkana & Gruzinov 2000),, is speculated to be able, first, to eliminate the sub-galactic halos to solve the problem of over-abundance of dwarf galaxies, and, second, to produce flat halo cores in galaxies suggested by some observations. Our simulation results show that although this extremely light bosonic dark matter indeed suppresses low-mass halos, it can, to the contrary of expectation, yield singular halo cores. The density profile of the singular halo is almost identical to the halo profile of Navarro, Frenk & White (1997). Such a profile seems to be universal, in that it can be produced via either accretion or merger., 21 pages, 10 figures

The Y.T. Lee Array for Microwave Background Anisotropy (AMiBA) started scientific operation in early 2007. This work describes the optimization of the system performance for the measurements of the Sunyaev-Zel'dovich effect for six massive galaxy clusters at redshifts $0.09 - 0.32$. We achieved a point source sensitivity of $63\pm 7$ mJy with the seven 0.6m dishes in 1 hour of on-source integration in 2-patch differencing observations. We measured and compensated for the delays between the antennas of our platform-mounted interferometer. Beam switching was used to cancel instrumental instabilities and ground pick up. Total power and phase stability were good on time scales of hours, and the system was shown to integrate down on equivalent timescales of 300 hours per baseline/correlation, or about 10 hours for the entire array. While the broadband correlator leads to good sensitivity, the small number of lags in the correlator resulted in poorly measured bandpass response. We corrected for this by using external calibrators (Jupiter and Saturn). Using Jupiter as the flux standard, we measured the disk brightness temperature of Saturn to be $149^{+5}_{-12}$ K., 9 pages, 7 figures, 1 table, accepted for publication in ApJ

We present observations, analysis, and results for the first-year operation of Array for Microwave Background Anisotropy (AMiBA), an interferometric experiment designed to study cosmology via the measurement of cosmic microwave background (CMB). AMiBA is the first CMB interferometer operating at 3 mm to have reported successful results, currently with seven close-packed antennas of 60 cm diameter giving a synthesized resolution of around 6'. During 2007, AMiBA detected the Sunyaev-Zel'dovich effects (SZEs) of six galaxy clusters at redshift 0.091 ≤ z ≤ 0.322. An observing strategy with on-off-source switching is used to minimize the effects from electronic offset and ground pickup. Planets were used to test the observational capability of AMiBA and to calibrate the conversion from correlator time-lag data to visibilities. The detailed formalism for data analysis is given. We summarize our early tests including observations of planets and quasars, and present images, visibility profiles, the estimated central coordinates, sizes, and SZE amplitudes of the galaxy clusters. Scientific implications are summarized. We also discuss possible systematic effects in the results.

AMiBA is the largest hexapod astronomical telescope in current operation. We present a description of this novel hexapod mount with its main mechanical components -- the support cone, universal joints, jack screws, and platform -- and outline the control system with the pointing model and the operating modes that are supported. The AMiBA hexapod mount performance is verified based on optical pointing tests and platform photogrammetry measurements. The photogrammetry results show that the deformations in the inner part of the platform are less than 120 micron rms. This is negligible for optical pointing corrections, radio alignment and radio phase errors for the currently operational 7-element compact configuration. The optical pointing error in azimuth and elevation is successively reduced by a series of corrections to about 0.4 arcmin rms which meets our goal for the 7-element target specifications., Comment: Accepted for ApJ, 33 pages, 15 figures

We discuss the observation, analysis, and results of the first-year science operation of AMiBA, an interferometric experiment designed to study cosmology via the measurement of Cosmic Microwave Background (CMB). In 2007, we successfully observed 6 galaxy clusters (z < 0.33) through the Sunyaev-Zel'dovich effect. AMiBA is the first CMB interferometer operating at 86–102 GHz, currently with 7 close-packed antennas of 60 cm in diameter giving a synthesized resolution of around 6 arcminutes. An observing strategy with on-off-source modulation is used to remove the effects from electronic offset and ground pickup. Formalism of the analysis is given and preliminary science results are summarized. Tests for systematic effects are also addressed. We also discuss the expansion plan.

The Array for Microwave Background Anisotropy is a 7-element interferometer sited on Mauna Loa, Hawaii. The seven 60cm telescopes are mounted on a 6-meter platform, and operates at 3mm wavelength. In October 2006, the telescope was officially dedicated and renamed as the Y. T. Lee AMiBA. During 2007, scientific operations have begun, after a long process of calibration and testing. At the time of this meeting, six clusters of galaxies have been detected and mapped via the inverse Compton scattering of the Cosmic Microwave Background radiation, also known as the Sunyaev-Zel'dovich Effect.

The observed far greater number of giant arcs than that predicted by the ΛCDM cosmology has been a long-standing puzzle. We adopt high-resolution cosmological simulations to assess this problem and quantitatively show that this issue can be resolved by inclusion of high-redshift source galaxies. Our ΛCDM results reveal a much higher giant-arc probability (>10-5) for source galaxies of z > 2 than that for z < 2. Together with the source redshift distribution derived from the NTT catalogs, we obtain the predicted giant-arc number counts, which turn out to be consistent with most observations. The fact that the high-redshift (z ≥ 1.5) galaxies are preferentially magnified by the foreground lenses with a surprisingly high efficiency explains why previous theoretical work substantially underestimated the giant-arc number density. In previous work, the source galaxies were assumed to be mostly around z = 1, an assumption commonly adopted in weak-lensing studies. In addition, although the lens mergers have been found to yield enhanced lensing cross sections, we find that merely 5% of giant arcs are associated with merging lenses. Our results support not only the ΛCDM cosmology but also the long-standing anticipation that galaxy clusters, mostly formed below z = 1, are powerful gravitational telescopes for probing the high-redshift protogalaxies. We illustrate how the patchy dust regions in interacting galaxies at z = 4 may appear as filamentary structures within a giant arc when observed at the submillimeter wave band.

We report an instantaneous heating scheme at z=2 that can produce bound objects obeying the observed mass-temperature and luminosity-temperature relations. Such heating reduces the Sunyaev–Zeldovich (SZ) flux by a factor 3–2 on scale of 4–6 arcminutes. It exacerbates the need for the matter-fluctuation normalization to σ8 to assume an exceedingly high value (~1.2), if the several-arcminute excess anisotropy detected by the CBI experiment is entirely caused by the SZ effect of inter-galactic hot gas. By contrast, we find that the several-arcminute excess detected by ACBAR can be consistent with the preheated SZ signals of σ8=1.

The Array for Microwave Background Anisotropy is a 7-element interferometer to be sited on Mauna Loa, Hawaii. The seven 1.2m telescopes are mounted on a 6-meter platform, and operates at 3mm wavelength. At the time of this meeting, the telescope is under construction at the Vertex factory in Germany. It is due to be delivered in the middle of 2004. A 2-element prototype instrument has already been deployed to Mauna Loa where initial tests are underway.

Due to the finite-size beam, interferometry observations of the CMB polarization tend to measure a mixture of E and B modes arising from uw-space smearing. We propose an interferometry observation strategy that can disentangle the polarization E and B modes in a clean manner. This strategy employs a similar principle as that of the single-dish observation proposed earlier, but requiring additional linear combinations of signals measured from different baselines. In this work, we consider a hexagonally packed interferometry array as an example to demonstrate the ultility and efficiency of the proposed method. The measurement from a unit cell of equilateral triangular baselines in interferometry measurement is found to be comparable to that from a single dish in single-dish measurements.

Mounting evidence from $x$-ray observations reveals that bound objects should receive some form of energy in the past injected from non-gravitaional sources. We report that an instantaneous heating scheme, for which gases in dense regions were subjected to a temperature jump of 1keV at $z=2$ whereas those in rarified regions remained intact, can produce bound objects obeying the observed mass-temperature and luminosity-temperature relations. Such preheating lowers the peak Sunyaev-Zeldovich (SZ) power by a factor of 2 and exacerbates the need for the normalization of matter fluctuations $\sigma_8$ to assume an extreme high value $(\sim 1.1)$ for the SZ signals to account for the excess anisotropy on 5-arcminute scale detected by the Cosmic Background Imager in the cosmic microwave background radiation.

Although it has previously been recognized that the CMB polarization measurement on a sky ring is able to separate the B and E-mode patterns, we show that the rotational symmetry of the CMB polarization measurement is indeed unique, in that it enables the B and E modes to be separately measured in a simple and clean manner. The separation of B and E modes can in principle be achieved even with a single-polarization detector of arbitrary beam pattern. Based on this premise, a specific observing strategy is suggested, where the telescope scans along a sky circle with the polarimeter axis always oriented to a fixed direction with respect to the radial direction of the sky circle. The observational strategy for B-mode measurements can further be refined by choosing appropriate beam sizes to suppress the accidental E-mode leakage. We present the expected variances of the measured E and B-mode surface-brightness fluctuations as functions of the sky annulus radius and beam size. The measured peak power is expected to be up to 10% of the total power contained in the CMB polarization fluctuations for both B and E modes. The temperature-polarization, or T-E, correlation can be measured by the present method as well. By adopting this strategy, the AMiBA experiment is expected to detect, in a single sky annulus, a 1\sigma$ B-mode signal in 340 hours.

Nonspherical collapse is modelled, under the Zeldovich approximation, by six-dimensional random walks of the initial deformation tensor field. The collapse boundary adopted here is a slightly-modified version of that proposed by Chiueh and Lee (2001). Not only the mass function agrees with the fitting formula of Sheth and Tormen (1999), but the bias function and conditional mass function constructed by this model are also found to agree reasonably well with the simulation results of Jing (1998) and Somerville et al. (2000), respectively. In particular, by introducing a small mass gap, we find a fitting formula for the conditional mass function, which works well even at small time intervals between parent and progenitor halos during the merging history., Comment: 28 pages, 11 figures, section 3.2 complemented, Fig.1 and Fig. 4 modified, version accepted for publication in ApJ

We make use of a catalog of 1600 Pan-STARRS1 groups produced by the probability friends-of-friends algorithm to explore how the galaxy properties, i.e. the specific star formation rate (SSFR) and quiescent fraction, depend on stellar mass and group-centric radius. The work is the extension of Lin et al. (2014). In this work, powered by a stacking technique plus a background subtraction for contamination removal, a finer correction and more precise results are obtained than in our previous work. We find that while the quiescent fraction increases with decreasing group-centric radius the median SSFRs of star-forming galaxies in groups at fixed stellar mass drop slightly from the field toward the group center. This suggests that the major quenching process in groups is likely a fast mechanism. On the other hand, a reduction in SSFRs by ~0.2 dex is seen inside clusters as opposed to the field galaxies. If the reduction is attributed to the slow quenching effect, the slow quenching process acts dominantly in clusters. In addition, we also examine the density-color relation, where the density is defined by using a sixth-nearest neighbor approach. Comparing the quiescent fractions contributed from the density and radial effect, we find that the density effect dominates over the massive group or cluster galaxies, and the radial effect becomes more effective in less massive galaxies. The results support mergers and/or starvation as the main quenching mechanisms in the group environment, while harassment and/or starvation dominate in clusters., 19 pages, 11 figures, accepted to ApJ

We study Sunyaev-Zeldovich Effect (SZE) cluster counts in different cosmologies. It is found that even without the full knowledge of the redshift distribution of SZE clusters, one can still readily distinguish a flat universe with a cosmological constant from an open universe. We divide clusters into a low redshift group (with redshift z 1), and compute the relation r=N(z 1), where N is the number of flux-limited (S_lim) SZE clusters. With about the same total number of SZE clusters N(z>0), the r-value for a flat universe with a consmological constant and that for an open universe occupy different regions in the S_lim -- r plot for the most likely cosmological parameters 0.25

We demonstrate the photonic generation of an ultra-wideband millimeter-wave (MMW) signal (white-light), which covers the full W-band (75-110 GHz). A W-band photonic emitter (PE) with a wide 3-dB optical-to-electrical bandwidth (30 GHz, 80-110 GHz), constructed by integrating a planar quasi-yagi radiator for feeding the WR-10 waveguide-based horn antenna and a high-power near-ballistic uni-traveling-carrier photodiode, serves as the key component in our system. Two different kinds of optical sources are adopted to excite our emitter, one is a broadband amplified-spontaneous-emission source and the other is a fast-sweeping wavelength laser for simultaneous and very-fast scanning (35 GHz/ms) MMW white-light generation, respectively. Compared with the traditional solid-state MMW white-light (noise) generator and reported photonic approach, our demonstrated solution has the advantages of simpler configuration, higher output MMW power density, and a much faster scanning rate, due to excellent high-power performance of our wideband PE.

As the angular momentum of visible matter in a spiral galaxy is derived from the host cloud, the dark matter halo left behind in the cloud is likely to be in rotation also. In the merging model of galaxy formation, it is shown that the conservation of mass and angular momentum yields a spin parameter within the halo increasing toward the core as r-1/3 for an isothermal halo and as r-1/2 for a halo with the universal density profile. Hence, almost corotation between the halo and disk can become possible in the inner galaxy for a relatively high angular momentum halo. Much like normal galaxies, the high angular momentum, low surface brightness galaxies have been observed to exhibit a wide variety of spiral patterns. In this work we explore a mechanism by which disk density waves are excited by corotation resonance between disk and halo, even in disks with a Toomre Q exceeding unity by a sizable margin. Apart from the resonant condition, the effectiveness of disk-halo coupling is found to be determined also by the halo scale height, and enhanced excitation of disk density waves occurs only when the halo scale height is sufficiently small. The spiral-arm pitch angles depend on the halo scale height as well, with the more loosely wound arms associated with smaller halo scale height.

The environmental dark matter mass around clusters is investigated by taking into account dark halo-cluster correlations. We find that while the surrounding dark matter significantly increases the lensing amplification factor as compared to that caused by foreground clusters only, the total enhancement factor for background QSOs still remains quite insufficient to explain the observed strong QSO-cluster associations. Effects of the environmental matter on the cluster mass estimates through the inversion of weak-lensing distortions of background galaxies are also studied. For relatively small clusters, the existence of the environmental dark matter would lead to an overestimate of the cluster mass, whereas for large clusters, their mass would be underestimated.

With a new analytical method, we present a static model for quiescent solar prominences of inverse polarity. These prominences have a plasma β slightly below unity and correspond to those located in the lower corona. Although this static model cannot address the helmet-like features at the top of the prominences, which are believed to be associated with the open-field topology and driven by outflows, the model may nevertheless capture several characteristic features of the solar prominences. These features include the sheetlike gas condensation hanging above an asymptotically weak magnetic cusp, the sheared magnetic arcades/loops, the coronal cavity, radio dark strips cospatial with the Hα filaments, bright radio ribbons located on both sides of the dense prominence sheet, and the increasing magnetic field strength with height along the prominence sheet. In our model, the densest gas is contained within a narrow field-free tube immediately above the prominence sheet. Thermally insulated by the surrounding strong fields, this narrow tube may be a natural site for housing the cool gas (≥104 K) siphoned from the lower solar atmosphere. We also find that there are hot spots (≤107 K) located on the sides of the prominence loop, which might be the source of thermal X-ray emission in the quiet Sun.

A semi-analytical model is proposed for understanding the quasi-periodic vertical structures in a plasma crystal, which are shown to be sustained by the combined effects of an ion flow, gravity and horizontal bonds of the dust particles. These structures are the manifestations of large-amplitude standing wake fields that lead to strong vertical bonds for the formation of an oriented hexagonal lattice. The orientational symmetry breaking is caused by a gravity-induced thick sheath, which can preferentially accelerate a supersonic ion flow in the vertical direction. The electron and streaming ion densities and the electric potential are found to be all in phase in the plasma crystal, whereas the dust density is 180 degrees out of phase. With each dust layer playing a similar role as the plasma wall, the Bohm sheath criterion is also found to be satisfied. Crystal melting may also be qualitatively described by the present model when the horizontal bonds of the dust particles are sufficiently weakened.

We present a critical examination of the ideal MHD model for the stationary Crab pulsar wind, which has a terminal flow Lorentz factor γ∞ ~ 106 and may have a terminal ratio of Poynting flux to kinetic energy flux as low as σ ~ 10-2-10-3. We first show that transitions to a low-σ configuration cannot occur gradually in regions well beyond the light cylinder where the flow has already become ultrarelativistic. This is because the poloidal field lines do not expand sufficiently beyond the fast critical point to convert the electromagnetic energy into flow kinetic energy. As an alternative, we consider whether the acceleration may proceed abruptly, with the flow rapidly passing through the fast critical point and expanding into a low-σ configuration. Such rapid expansion of field lines, analogous to that in a de Laval nozzle, requires the poloidal fields to be highly compressed upstream of the fast critical point. We categorize the rapid field expansion generally into two prototypes: sheetlike and fountain-like, with the former being a spontaneous transition and the latter requiring external pressure supports. Unfortunately, it is shown that both types of rapid acceleration fail to satisfy either the energy and momentum conservation or the MHD flux-freezing condition. Nevertheless, we have pinned down the only situation where a stationary, ideal-MHD low-σ wind may exist. It requires almost the entire wind acceleration to occur in the immediate neighborhood of the light cylinder. Moreover, it also demands drastic modifications to the conventional picture of the pulsar dipole magnetosphere, in that the outer magnetosphere must be dominated by the toroidal fields and that the pulsar wind is carried by only a small fraction of the magnetospheric field lines emerging from the star.

As the observations of highly flattened galaxies, including the Milky Way, and gravitational N-body simulations show, the central parts of these systems at distances of, say, r Fg. The latter condition is none other than the condition of the so-called firehose electromagnetic instability in collisionless plasmas. The source of free energy in the instability is the intrinsic anisotropy of a velocity dispersion ("temperature"). It seems reasonable that this is a natural mechanism for building a snake-shaped radio structure, which has recently been observed by Zhao and coworkers in the central region of the spiral starburst galaxy NGC 2146 with the Very Large Array at an angular resolution of 2''. In the current paper, in order to investigate the dynamics of the central region, N-body simulations of the firehose-type bending instability are presented for this galaxy. Use of concurrent computers has enabled us to make long simulation runs using a sufficiently large number of particles in the direct summation code, N ~ 20,000. In contrast to all previous N-body simulations of bending instabilities, we show how bending structures may be longer lived in real starburst galaxies than in the computer models. The simulations clearly confirm the qualitative picture and, moreover, are in fair quantitative agreement with the theory. A theoretical prediction is confirmed that the instability is driven by an excess of plane kinetic energy of random motions of stars, when the ratio of the dispersion of radial velocities of stars in the plane cr to the velocity dispersion in the perpendicular direction cz is large enough, cr 0.6cz, in other words, if the thickness of the stellar disk h ∝ cz is small enough. The extent to which our results on the stability of the disk can have a bearing on observable spiral galaxies with a high star formation rate in the central parts is discussed.

Tearing instability is shown to be greatly enhanced by ambipolar diffusion near the locations where two-dimensional magnetic fields reverse signs. The growth time is found to be on the order of the ambipolar diffusion timescale, independent of electrical resistivity. Consistent with the earlier works, the enhancement in the reconnection of field lines indeed arises from the development of a singular current perturbation. Such magnetic reconnection is driven by the steepening effect of ambipolar diffusion on the magnetic fields near the field-reversal lines. Although the background magnetic fields are evolving on a similar timescale as the perturbations, we show that magnetic reconnection proceeds substantially faster than the steepening of the background fields. In contrast to the conventional tearing instabilities in three dimensions, where the magnetic reconnection occurs only in the flux surfaces that contain the free energy, a positive Δ', the three-dimensional extension of this new tearing instability can occur only in regions where the Lorentz force reverses the sign. This report outlines how the three-dimensional reconnection may proceed in a similar fashion as the two-dimensional counterpart does.

The investigation of the first papers of the present series (Griv, Planet. Space Sci. 44 , 579–589 , 1996; Griv and Yuan, Planet. Space Sci. 44 , 1185–1190, 1996) is extended to include the effect of spatial inhomogeneity, i.e. the surface density gradient of Saturn's ring disk of mutual-gravitating identical particles. The model of an infinitely thin inhomogeneous disk with rare physical (inelastic) collisions between particles is considered. Similar to the investigation of the first papers, the well-elaborated mathematical methods of plasma linear kinetic theory are utilized. The influence of disk inhomogeneity on the oscillation spectrum of different small-amplitude oscillations in the Saturnian ring system is studied. Estimates are made for the frequencies and the growth rate of the oscillations. It is shown that, as a rule, in Saturn's A ring the spatial inhomogeneity reinforces the growth rate of the oscillating instability (or the resonant self-excitation of density waves), and weakens the growth rate both in the C ring and in the inner portions of the B ring. In addition, the investigation of waves and their instabilities in the plane of Saturn's rings is extended by taking into account the density wave excitation/absorption at Lindblad's resonances and the weak effect of the finite but not large ring disk thickness.

Nonlinear gravitational sound waves within an expanding collisionless background matter are investigated. Under the assumptions of power-law time dependence and an equation of state for collisionless particles, two classes of nonlinear waves are identified: solitons and solitary wave trains. The soliton solutions may describe physically how the high-density sheets evolve immediately after the formation of caustics in the disk-collapse scenario of large-scale structure formation. The solutions can describe either that a discoid continuously loses matter that is expelled by the high pressure of the disk, reaching supersonic speeds and presumably blended into the background Hubble flow, or that the disk collects matter from the low-density background and becomes ever-increasingly massive. We also find that the multiple-mass-shell solutions, generally believed to be caused by the crossing of mass shells after the gravitational collapse, exist in the form of solitons.

A class of nonrelativistic magnetosonic soliton, where the charge-separation electric field can be as large as the background magnetic field, is discovered in a strongly magnetized cold plasma, where the electron cyclotron frequency is much larger than the electron plasma frequency. We study how the Mach number of such a soliton is changed by the presence of a gentle background density gradient. An effective Hamiltonian for the soliton trajectory is derived, with which one can show that the soliton Mach number increases as the soliton travels to a background of increasing density, or equivalently, decreasing Alfven speed. The soliton can generally exchange its energy, momentum, and mass with the background plasmas. Our results also show that the soliton may undergo wave breaking at a finite background Alfven speed. {copyright} {ital 1997} {ital The American Physical Society}

Aims: We performed a detailed photometric analysis of the lensed system UM673 (Q0142-100) and an analysis of the tentative lens models. Methods: High-resolution adaptive optics images of UM673 taken with the Subaru telescope in the H band were examined. We also analysed the J, H and K-band observational data of UM673 obtained with the 1.3m telescope at the CTIO observatory. Results: We present photometry of quasar components A and B of UM673, the lens, and the nearby bright galaxy using H-band observational data obtained with the Subaru telescope. Based on the CTIO observations of UM673, we also present J- and H-band photometry and estimates of the J, H and K-band flux ratios between the two UM673 components in recent epochs. The near-infrared fluxes of the A and B components of UM673 and their published optical fluxes are analysed to measure extinction properties of the lensing galaxy. We estimate the extinction-corrected flux ratio between components A and B to be about 2.14 mag. We discuss lens models for the UM673 system constrained with the positions of the UM673 components, their flux ratio, and the previously measured time delay, Comment: Submitted to A&A, 10 pages, 9 figures, 7 tables

A variety of methods have been proposed to define and to quantify galaxy environments. While these techniques work well in general with spectroscopic redshift samples, their application to photometric redshift surveys remains uncertain. To investigate whether galaxy environments can be robustly measured with photo-z samples, we quantify how the density measured with the nearest neighbor approach is affected by photo-z uncertainties by using the Durham mock galaxy catalogs in which the 3D real-space environments and the properties of galaxies are exactly known. Furthermore, we present an optimization scheme in the choice of parameters used in the 2D projected measurements which yield the tightest correlation with respect to the 3D real-space environments. By adopting the optimized parameters in the density measurements, we show that the correlation between the 2D projected optimized density and real-space density can still be revealed, and the color-density relation is also visible out to $z \sim 0.8$ even for a photo-z uncertainty ($\sigma_{\Delta_{z}/(1+z)}$) up to 0.06. We find that at the redshift $0.3 < z < 0.5$ a deep ($i \sim 25$) photometric redshift survey with $\sigma_{\Delta_{z}/(1+z)} = 0.02$ yields a comparable performance of small-scale density measurement to a shallower $i \sim$ 22.5 spectroscopic sample with $\sim$ 10% sampling rate. Finally, we discuss the application of the local density measurements to the Pan-STARRS1 Medium Deep survey, one of the largest deep optical imaging surveys. Using data from $\sim5$ square degrees of survey area, our results show that it is possible to measure local density and to probe the color-density relation with 3$\sigma$ confidence level out to $z \sim 0.8$ in the PS-MDS. The color-density relation, however, quickly degrades for data covering smaller areas., Comment: ApJ accepted; 29 figures