Search

Equation of state for Bose-Einstein condensate is evaluated in two cases: non-interacting particles and particles interacting via potential possessing a non-trivial minimum. In astrophysical context, the first case becomes equivalent to cold dark matter, while the second case – to dark energy. A particular cosmological scenario with dark matter injection from quasi-black holes to galactic halo, followed by Bose-Einstein condensation in the intergalactic medium is considered. [ABSTRACT FROM AUTHOR]

In the determination of location of Lagrangian points, the mass ratio of primaries in Restricted Three Body Problem (RTBP) plays an important role. Due to change in the value of mass ratio, the corresponding variations in different parameters of Halo Orbits (HO) are studied. It has been observed that halo orbits around L1 move towards the first primary, X altitude, AX , corresponding to a fixed Z altitude, AZ , and period around L1 decreases whereas X altitude, AX , corresponding to a fixed Z altitude, AZ , and period around L2 increases with the increase in mass ratio. Further, orbits around L2 move away from the second primary until μ≈ 0.17894 and then move towards the primaries with the increase in mass ratio. Variations in other parameters such as the initial distance from the origin of a spacecraft and its initial velocity in a halo orbit around L1 and L2 are also obtained corresponding to variation in mass ratio. The results are validated by comparing with the data obtained for various Sun-Planet systems. Also, different parameters of halo orbits around the Sun-Earth and the Sun-Earth+Moon system are compared. [ABSTRACT FROM AUTHOR]

In the determination of location of Lagrangian points, the mass ratio of primaries in Restricted Three Body Problem (RTBP) plays an important role. Due to change in the value of mass ratio, the corresponding variations in different parameters of Halo Orbits (HO) are studied. It has been observed that halo orbits around L1 move towards the first primary, X altitude, AX , corresponding to a fixed Z altitude, AZ , and period around L1 decreases whereas X altitude, AX , corresponding to a fixed Z altitude, AZ , and period around L2 increases with the increase in mass ratio. Further, orbits around L2 move away from the second primary until μ≈ 0.17894 and then move towards the primaries with the increase in mass ratio. Variations in other parameters such as the initial distance from the origin of a spacecraft and its initial velocity in a halo orbit around L1 and L2 are also obtained corresponding to variation in mass ratio. The results are validated by comparing with the data obtained for various Sun-Planet systems. Also, different parameters of halo orbits around the Sun-Earth and the Sun-Earth+Moon system are compared. [ABSTRACT FROM AUTHOR]

The reactions involving fusion-fission of compound nuclei 244,247Cm* formed in low energy heavy ion collisions of 12,15C projectiles with actinide target 232Th have been investigated within dynamical cluster-decay model (DCM). We have probed the effects of transition from a paired to an unpaired valence neutron or halo nature of projectile (15C) on the fusion-fission cross sections (σFF) of decay of compound nuclei (CN) 244,247Cm*, formed in these reactions. The calculations are performed using spherical shape of nuclei at touching configuration at near-barrier energies (Ec.m.= 68-70 MeV) where experimental data is already available. The dynamical behaviour of these reactions is explored via fragmentation potential (V), preformation probability (P0), summed up preformation probability over angular momenta (ℓ) values (ΣP0) and penetrability (P) for fusion-fission fragments (FF) having mass numbers (ACN/2) ±20. It is observed that the overall pattern of fragmentation potential, V(MeV) at different ℓ values remains unaffected, but the potential energy surface (PES) for FF fragments show peculiar behavior with increase in mass of CN. These characteristics of the FF fragments are presented in terms of preformation probability (P0), explicitly. The effect of halo configuration of projectile is evident in the summed-up preformation probabilities (ΣP0) of various FF fragments, which means that the relevant structure information is duly explored. The DCM calculated, normalized values, of σFF are found to be consistent with the experimental data. The observation of enhancement in the magnitude of σFF for neutron-rich matter reveals the modification of nuclear behaviour, as we move towards region close to the drip line. [ABSTRACT FROM AUTHOR]

The DAMA/LIBRA experiment (∼ 250 kg sensitive mass composed by highly radio-pure NaI(Tl)) is in data taking underground in the Gran Sasso Laboratory. Its first phase (DAMA/LIBRA–phase1) and the former DAMA/NaI experiment (∼ 100 kg of highly radio-pure NaI(Tl)) collected data for 14 independent annual cycles, exploiting the model-independent Dark Matter (DM) annual modulation signature (total exposure 1.33 ton × yr). A DM annual modulation effect has been observed at 9.3 σ C.L., supporting the presence of DM particles in the galactic halo. No systematic or side reaction able to mimic the observed DM annual modulation has been found or suggested by anyone. Recent analyses on possible diurnal effects and on possible interpretation in terms of Mirror DM will be mentioned. At present DAMA/LIBRA is running in its phase2 with increased sensitivity. [ABSTRACT FROM AUTHOR]

The theory of universal extra dimensions involves Kaluza-Klein (KK) particles. The lightest KK particle (LKP) is one of the good candidates for cold dark matter. Annihilation of LKP dark matter in the Galactic halo produces high-energy gamma-rays. The gamma-ray spectrum shows a characteristic peak structure around the LKP mass. This paper investigates the observability of this peak structure by present and near-future detectors taking account of their energy resolution, and calculates the expected count spectrum of the gamma-ray signal. Then, the maximum likelihood analysis is employed to judge whether the count spectrum contains the LKP signal. In the case where the signal is not detected, we set some constraints on the boost factor which is a product of the annihilation cross section relative to the thermal one and an uncertain factor dependent on the substructure of the LKP distribution in the Galactic halo. The constraints can be regarded as comparable with the results of analysis based on the HESS data. The observational data for the TeV or higher energy region are still limited, and the possible LKP signal is not conclusive. Thus, we expect near-future missions with better sensitivity will clarify whether the LKP dark matter should exist or not. [ABSTRACT FROM AUTHOR]

If dark matter is composed of weakly interacting particles, Earth's orbital motion induces a small annual variation in the rate at which these particles interact in a terrestrial detector. The DAMA collaboration has identified at a 9.3σ confidence level (CL) such an annual modulation in their event rate over two detector iterations, DAMA/NaI and DAMA/LIBRA, each with about 7 years of observations. We examine the nature of this modulation signal and find the modulation amplitude for the two detectors is inconsistent at the 3σ CL over 2-6 keVee. Such a time-dependence in the modulation amplitude is unexpected behavior for a dark matter signal, at least for dark matter halo morphologies consistent with the DAMA signal. We also find unusual behavior over the 5-6 keVee energy range that might indicate problems with the data. [ABSTRACT FROM AUTHOR]

Recent experiments with pure electron plasmas in a Malmberg-Penning trap have observed the algebraic damping of m = 1 and m = 2 diocotron modes. Transport due to small field asymmetries produces a low density halo of electrons moving radially outward from the plasma core, and the mode damping begins when the halo reaches the resonant radius Rm, where there is a matching of ωm = mωE(Rm) for the mode frequency ωm and ExB-drift rotation frequency ωE. The damping rate is proportional to the flux of halo particles through the resonant layer. The damping is related to, but distinct from, spatial Landau damping, in which a linear wave-particle resonance produces exponential damping. This new mechanism of damping is due to transfer of canonical angular momentum from the mode to halo particles, as they are swept around the "cat's eye" orbits of the resonant wave-particle interaction. This paper provides a simple derivation of the time dependence of the mode amplitudes. [ABSTRACT FROM AUTHOR]

The Cold Dark Matter (CDM) paradigm still presents a few problematic issues concerning structure formation at small scales. Predictions like the cusp format of the central density profile and the excess of small satelites are, in some sense, connected to a excess of clustering of the CDM component. Here, we model dark matter as a viscous-dissipative fluid where the non-adiabatic effects lead to a suppressed growth of dark matter structures. Due to such feature the viscous dark matter halos become a promissing direction for solving the structure formation problems of the standard cosmological model. [ABSTRACT FROM AUTHOR]

The CDMS II experiment ran between 2003 and 2009. A total of 30 germanium and silicon ZIP detectors were operated, producing a high quality set of data that has been analyzed for evidence of and placed leading constraints on standard, low-mass, electron-recoil, and annually modulating WIMP interactions. This article will describe the general operation principles behind the CDMS detectors, report on the results of major Ge and Si detector analyses, and describe the current and future activities of the SuperCDMS program. [ABSTRACT FROM AUTHOR]

The Fermi-LAT and several ground-based air cereknov telescopes (ACTs) are actively searching for gamma-ray signals from dark matter. I review the status of these searches, and the implications of the bounds from several astrophysical targets. I discuss what were are learning from present limits, and the future discovery space. [ABSTRACT FROM AUTHOR]

The substructure content of dark matter halos is interesting because it can be affected by complex galaxy physics and dark matter particle physics. However, observing the small scale structure of dark matter is a challenge. The subhalo abundance (mass function, minimum mass) and morphology (density profile, subhalo shape, subsubstructure) contain information about complex astrophysics (halo formation processes) and new exotic fundamental physics (dark matter interactions). Indirect detection of dark matter annihilation radiation (DMAR) in gamma rays may be the most direct method for observing small scale structure. I outline the ways in which gamma rays may probe halo substructure. If substructure is bountiful, it may be responsible for the eventual discovery of DMAR, for instance in galaxy clusters or the diffuse gamma-ray background. Otherwise, the observation of DMAR in places without much substructure, such as the Galactic center, would lead to strict limits on the properties of small scale structure. Properties of the gamma-ray angular power spectrum will also provide information or constraints on Milky Way halo substructure. [ABSTRACT FROM AUTHOR]

Known populations of QSOs appear to fall short of producing the ionizing flux required for re-ionizing the universe. The alternative, galaxies as sources of ionizing photons, suffers from the problem that known types of galaxies are almost completely opaque to ionizing photons. For reionization to happen, either large numbers of (largely undiscovered) sources are required, or the known populations of galaxies need to have had a much larger escape fraction for ionizing radiation in the past. We discuss recent discoveries of faint z ∼ 3 Lyman α emitters with asymmetric, extended Lyα emission regions, which apparently are related to interacting galaxies. The unusually shaped Lyα line profiles and the underlying stellar populations of these objects suggest the presence of damaged gaseous halos, infall of gas, tidal or stripped stellar features and young populations of hot stars that would all be conducive to the release of ionizing radiation into intergalactic space. As galaxy interactions and mergers increase with redshift, these effects can only become more important at earlier times, and so these interacting z ∼ 3 objects may be late, lower redshift analogues of the sources of reionization. [ABSTRACT FROM AUTHOR]

In this contribution, I will review the most recent developments that concern the transition from a primordial, predominantly massive mode of star formation - the Population III stars - to a mode of star formation characterized by the first low mass and long lived stars - the Population II stars. Although the recent observation of a star in the Galactic Halo with a total metallicity of only Z = 4.5×10-5Z⊙ has demonstrated that stars with masses of approximately ∼ 0.8M⊙ can form even at these extremely low metallicities, there are many aspects of the Pop III/II transition that are still poorly understood and that certainly require further investigation. For this reason, I have organized my contribution into three fundamental questions which I try to address based on the current theoretical and observational indications. [ABSTRACT FROM AUTHOR]

A galaxy's mean metallicity is usually closely correlated with its luminosity and mass. Consequently the most metal-poor galaxies in the local universe are dwarf galaxies. Blue compact dwarfs and tidal dwarfs tend to deviate from the metallicity-luminosity relation by being too metalpoor or too metal-rich for their luminosity, respectively. A less pronounced offset separates dwarf spheroidal (dSph) and dwarf irregular galaxies, making the former too metal-rich for their luminosity, which indicates different formation conditions for these two types of dwarfs. While environment (photo-evaporation through local re-ionization bymassive galaxies, tidal and rampressure stripping) govern the observed morphology-distance relation, intrinsic properties (in particular totalmass) play a decisive role in dwarf galaxy evolution with respect to the time and duration of star formation and the amount of enrichment. The metallicity distribution functions of nearby dwarfs can be understood taking pre-enrichment, gas infall, and winds into account. Many dwarfs show evidence for inhomogeneous, localized enrichment. Ultra-faint dSphs, which may have formed their metal-poor stars at high redshift via H2 cooling, show an overabundance of metal-deficient stars as compared to the (inner) Galactic halo, but may, along with classical dSphs, have contributed significantly to the build-up of the outer halo. The abundance ratios measured in the irregular Large Magellanic Cloud are consistent with the postulated early accretion of irregulars to form the inner Galactic halo. [ABSTRACT FROM AUTHOR]

Galaxies grow hierarchically by accreting smaller objects. The abundance of dark matter substructure in simulated Milky Way like galaxies shows evidence for this assembly process. The luminous satellites of our Galaxy are believed to be the visible counterparts to some of these substructures. Existing high-resolution galactic halo simulations show that the variations in substructure distributions and other properties among Milky Way like halos today are significant (a factor of at least 2-3). This, coupled with a few number of high resolution simulated halos, makes the interpretation of many results cosmic variance limited. In order to quantify the scatter in halo properties in a statistically meaningful way, we have initiated the CaterPillar project to perform zoom-In simulations of at least 60 highly resolved galactic size halos. Here we present our overall science goals. We aim to quantify the uniqueness of the Milky Way, to study the role that dwarf galaxies play in shaping large galaxies, to determine whether there really is a missing satellite problem, and to examine the origin of the old, metal-poor stellar halo of the Galaxy. [ABSTRACT FROM AUTHOR]

A small fraction of the atomic-cooling halos assembling at z < 15 may form out of minihalos that never experienced any prior star formation, and could in principle host small galaxies of chemically unenriched stars. Since the prospects of detecting isolated population III stars appear bleak even with the upcoming James Webb Space Telescope (JWST), these population III galaxies may offer one of the best probes of population III stars in the foreseeable future. By projecting the results from population III galaxy simulations through cluster magnification maps, we predict the fluxes and surface number densities of pop III galaxy galaxies as a function of their typical star formation efficiency. We argue that a small number of lensed population III galaxies in principle could turn up at z ≈ 7-10 in the ongoing Hubble Space Telecope survey CLASH, which covers a total of 25 low-redshift galaxy clusters. [ABSTRACT FROM AUTHOR]

The DAMA/LIBRA experiment, running at the Gran Sasso National Laboratory of the I.N.F.N. in Italy, has a sensitive mass of about 250 kg highly radiopure NaI(Tl). It is mainly devoted to the investigation of Dark Matter (DM) particles in the Galactic halo by exploiting the model independent DM annual modulation signature. The present DAMA/LIBRA experiment and the former DAMA/NaI one (the first generation experiment having an exposed mass of about 100 kg) have released so far results corresponding to a total exposure of 1.17 ton×yr over 13 annual cycles. They provide a model independent evidence of the presence of DM particles in the galactic halo at 8.9 σ C.L. on the basis of the investigated DM signature. Few aspects of the obtained results are shortly summarized and perspectives for the experiment are briefly addressed. [ABSTRACT FROM AUTHOR]

We study the viability of a a complex scalar field χ with self-interacting potential V = m0χ/2|χ|2+h|χ|4 as dark matter. Due to the self interaction, the scalar field forms a Bose-Einstein condensate at early times that represents dark matter. The self interaction is also responsible of quantum corrections to the scalar field mass that naturally give the dark matter domination at late times without any fine tuning on the energy density of the scalar field at early times. Finally the properties of the spherically symmetric dark matter halos are also discussed. [ABSTRACT FROM AUTHOR]

In this work we present a hydrodynamic-type model in order to study dark matter halos of galaxies. We start with the Einstein-Hilbert Lagrangian in which we have added a complex scalar field minimally coupled to the geometry. We consider that dark matter halos are well described by the Newtonian limit of this theory. This set of equations can be written in the form of Euler equations for a fluid by making a transformation, where the self-interaction potential of the fluid and a quantum-like potential is present. We study the Jeans' instability of the fluid which gives a limit for the unstable halos and is a way for computing the mass of the scalar field. [ABSTRACT FROM AUTHOR]

The Galactic magnetic fields are a key agent for the cosmic rays to propagate. There have been many models for the Galactic magnetic fields, which have been used for the cosmic ray propagation studies. Here, I review the measurements of the magnetic fields in the disk, in the halo and near the center of our Milky Way galaxy. I emphasize that the measurements in the very limited Galactic volume leave a large parameter space for various models. We examined the deflection of ultra-high energy cosmic rays by different components of the modeled Galactic magnetic fields, and concluded that the unknown magnetic fields in the vast interstellar space are important to identify the source of ultra-high energy cosmic rays. [ABSTRACT FROM AUTHOR]

We report the detection of a planetary companion around HIP 13044, a metal-poor star on the red Horizontal Branch. The detection is based on radial velocity observations with FEROS, a high-resolution spectrograph at the 2.2-m MPG/ESO telescope, located at ESO La Silla observatory in Chile. The periodic radial velocity variation of P = 16.2 days can be distinguished from the periods of the stellar activity indicators. We computed a minimum planetary mass of 1.25 MJup and an orbital semi-major axis of 0.116 AU for the planet. This discovery is unique in three aspects: First, it is the first planet detection around a star with a metallicity much lower than few percent of the solar value; second, the planet host star resides in a stellar evolutionary stage that is still unexplored in the exoplanet surveys; third, the star HIP 13044 belongs to one of the most significant stellar halo streams in the solar neighborhood, implying an extragalactic origin of the planetary system HIP 13044 in a disrupted former satellite of the Milky Way. [ABSTRACT FROM AUTHOR]

We present results of a survey of post-asymptotic giant branch stars (post-AGBs) at high galactic latitude. To date, few post-AGB stars are known throughout the Galaxy and the number of known members of the older populations like the galactic halo is even smaller. This study looks at the number of post-AGB stars which are produced using different synthetic population methods and compare the results with observations. The resulting synthetic populations are compared to observational results from a complete and studied subsample from the photographic Palomar-Green (PG) survey (with high resolution spectroscopic follow-up for post-AGB candidates) and the SDSS spectroscopic database. The results show only two candidate post-AGB stars in a complete subsample of the PG survey spanning 4200 deg2 and one in the SDSS database. We discuss and explore any observational biases which may cause the result. If found to be truely representative of the halo population, one can expect the majority of Population II stars to fail to ascend the AGB and evolve through other evolutionary channels such as the extended horizontal branch. [ABSTRACT FROM AUTHOR]

We report on ancient white dwarfs found in the proper motion survey we are conducting at the Bok and USNO telescopes. To date we have surveyed approximately 2800 square degrees of sky and identified numerous WDs with Teff ≤6000. A subset of these WDs are high velocity objects that most likely belong to the Galactic halo population. Where possible, we are acquiring trigonometric parallaxes to constrain the WD masses. We apply a new Bayesian modeling approach to these WDs that consistently incorporates precursor evolutionary timescales, the initial-final mass relation, WD interior and atmosphere models, and uses the observed magnitudes, distances, etc. to derive the distribution of WD age as a function of uncertainties in the observational parameters. [ABSTRACT FROM AUTHOR]

Population III star formation during the dark ages shifted from minihalos (∼106 M⊙) cooled by molecular hydrogen to more massive halos (∼108 M⊙) cooled by Ly-α emission as Lyman-Werner backgrounds progressively quenched molecular hydrogen cooling. Eventually, both modes of primordial star formation were suppressed by the chemical enrichment of the IGM. We present a comprehensive model for following the modes of Population III star formation that is based on a combination of analytical calculations and cosmological simulations. We characterize the properties of the transition from metal-free star formation to the first Population II clusters for an average region of the Universe and for the progenitors of the Milky Way. Finally, we highlight the possibility of observing the explosion of Population III stars within Ly-α cooled halos at redshift z∼6 in future deep all sky surveys such as LSST. [ABSTRACT FROM AUTHOR]

We present an overview of recent work that focuses on understanding the radiative feedback processes that are potentially important during Population III star formation. Specifically, we examine the effect of the Lyman-Werner (photodissociating) background on the early stages of primordial star formation, which serves to delay the onset of star formation in a given halo but never suppresses it entirely. We also examine the effect that both photodissociating and ionizing radiation in I-fronts from nearby stellar systems have on the formation of primordial protostellar clouds. Depending on the strength of the incoming radiation field and the central density of the halos, Pop III star formation can be suppressed, unaffected, or even enhanced. Understanding these and other effects is crucial to modeling Population III star formation and to building the earliest generations of galaxies in the Universe. [ABSTRACT FROM AUTHOR]

Low mass axions are an attractive candidate for making up dark matter. While there are several models for how the Axion couples with other matter, were they to be the majority of the local galactic dark matter halo, they would have a number density on the order of 1014 cm-3. The Axion Dark Matter eXperiment (ADMX) is a microwave cavity experiment searching for axion Dark Matter via the axion's electromagnetic coupling. While the original ADMX did not see evidence of axions, the experiment is planned to go through two phases of upgrades to expand its sensitivity and provide a definitive search for axion dark matter. The first phase established the use of a SQUID amplifier which can reduce the amplifier noise temperature to the 100 mK range. In the second phase we will first move the experiment from LLNL to CENPA at the University of Washington. Once the experiment has been moved successfully we will install a dilution refrigerator to cool the cavity to the 100 mK range thus increasing the sensititivity to the level required to scan the remainder of the allowed model space. [ABSTRACT FROM AUTHOR]

We make use of the generation-regeneration or 'light shining through a wall' technique in searches for optical-wavelength photons mixing with hypothetical hidden-sector paraphotons in the mass range between 10-5 and 10-2 electron volts for a mixing parameter greater than 10-7 and in sensitive searches for scalar and pseudoscalar coupling of photons to light neutral bosons in the mass range of approximately 1.0 milli-electron volts and coupling strength greater than 10-6 GeV-1. Additionally, there is an effort underway to use photons in the microwave region using this same technique to make a more sensitive measurement in the mass range of approximately 0.1 milli-electron volts. The equipment in the latter effort will be used to search for galactic halo axions in this same mass range. [ABSTRACT FROM AUTHOR]

The continuous infall of dark matter with low velocity dispersion in galactic halos leads to the formation of high density structures called caustics. Dark matter caustics are of two kinds : outer and inner. Outer caustics are thin spherical shells surrounding galaxies while inner caustics have a more complicated structure that depends on the dark matter angular momentum distribution. The presence of a dark matter caustic in the plane of the galaxy modifies the gas density in its neighborhood which may lead to observable effects. Caustics are also relevant to direct and indirect dark matter searches. [ABSTRACT FROM AUTHOR]

We report on two quantitative, morphological estimators of the filamentary structure of the Cosmic Web, the so-called global and local skeletons. The first, based on a global study of the matter density gradient flow, allows us to study the connectivity between a density peak and its surroundings, with direct relevance to the anisotropic accretion via cold flows on galactic halos. From the second, based on a local constraint equation involving the derivatives of the field, we can derive predictions for powerful statistics, such as the differential length and the relative saddle to extrema counts of the Cosmic web as a function of density threshold (with application to percolation of structures and connectivity), as well as a theoretical framework to study their cosmic evolution through the onset of gravity-induced non-linearities. [ABSTRACT FROM AUTHOR]

We report on some results on the mass function and the bias of dark matter halos. Focusing on the limit of rare massive halos, we point out that exact analytical results can be obtained for the large-mass tail of the halo mass function. This is most easily seen from a steepest-descent approach, that becomes asymptotically exact for rare events. We also revisit the traditional derivation of the bias of massive halos, associated with overdense regions in the primordial density field, paying attention to the Lagrangian-Eulerian mapping (i.e. corrections associated with the motions of halos). This allows us to improve the standard analytical formula for the bias of massive halos without introducing any free parameter. Next, we briefly note that this approach can be extended to non-Gaussian initial conditions. We again obtain a good agreement with numerical simulations. Moreover, the nonlinear real-space expression we obtain for the halo correlation clearly shows how the baryon acoustic oscillation at ∼100 h-1 Mpc is amplified by the bias of massive halos and modified by primordial non-Gaussianity. At smaller scales, 30

We have developed an analytic formulation for axially symmetric GNFW lens model with parametrized cusp slope (α). The lensing theory has several implications, for example strong lensing is very difficult without cusped mass profile. Required cusp strength for strong lensing depends on the lens object mass and concentration. Exceedingly high concentrations are required for profiles, that have α>-1 in order to produce multiple lensed images. We study mass profiles of lens objects with double image lenses, since they are resilient against deviations from axial symmetry, perturbations from microlensing, and halo substructure. The statistics of the observed image flux ratios is connected to the general properties of the of the lens mass density profiles. Our analysis is based on a limiting value for the shallowest cusp slope αCSL able to produce the observed flux ratio with any lens geometry and lens-source alignment. The cusp slope limit (CSL) does not depend on cosmology, total lens mass, concentration or redshifts of the the lens and the lensed object. In case of axial symmetry the limiting value is depending only on the magnification ratio (observed flux ratio of the images). This removes uncertainties in the lens and source distributions from the statistical analysis. Distribution of these threshold values reveals existence of halo population(s) with similar profiles in the sample; most of the halos have cusp slope α = -1.95±0.02. We have also found an imprint of a second population with a cusp slope value α = -1.49±0.09. There is about 99 per cent estimated probability, that the observed feature in the distribution is produced by the second population of lenses, with their own characteristic density profile. We analyze error sources in our analysis with mock catalogues, and discuss about alternative explanations for the second population signature. [ABSTRACT FROM AUTHOR]

Galaxies are composed of baryonic stars and gas embedded in dark matter halos. Here I briefly review two aspects of the connection between baryons and their halos. (1) The observed baryon content of galaxies falls short of the cosmic baryon fraction by an amount that varies systematically with mass. Where these missing baryons now reside is unclear. (2) The characteristic acceleration in disk galaxies correlates strongly with their baryonic mass surface density. This implies a close coupling between the gravitational dynamics, which is presumably dominated by dark matter, and the purely baryonic components of galaxies. [ABSTRACT FROM AUTHOR]

Physical processes influencing the properties of galaxies can be traced by the dependence and evolution of galaxy properties on their environment. A detailed understanding of this dependence can only be gained through comparison of observations with models, with an appropriate quantification of the rich parameter space describing the environment of the galaxy. We present a new, multiscale parameterization of galaxy environment which retains an observationally motivated simplicity whilst utilizing the information present on different scales. We examine how the distribution of galaxy (u-r) colours in the Sloan Digital Sky Survey (SDSS), parameterized using a double gaussian (red plus blue peak) fit, depends upon multiscale density. This allows us to probe the detailed dependence of galaxy properties on environment in a way which is independent of the halo model. Nonetheless, cross-correlation with the group catalogue constructed by Yang et al., 2007 shows that galaxy properties trace environment on different scales in a way which mimics that expected within the halo model. This provides independent support for the existence of virialized haloes, and important additional clues to the role played by environment in the evolution of the galaxy population. This work is described in full by Wilman et al., 2010, MNRAS, in press. [ABSTRACT FROM AUTHOR]

We summarize recent developments in the use of spectral methods for analyzing large numbers of orbits in N-body simulations to obtain insights into the global phase space structure of dark matter halos. The fundamental frequencies of oscillation of orbits can be used to understand the physical mechanism by which the shapes of dark matter halos evolve in response to the growth of central baryonic components. Halos change shape primarily because individual orbits change their shapes adiabatically in response to the growth of a baryonic component, with those at small radii become preferentially rounder. Chaotic scattering of orbits occurs only when the central point mass is very compact and is equally effective for centrophobic long-axis tube orbits as it is for centrophilic box orbits. [ABSTRACT FROM AUTHOR]

Extremely metal-poor (EMP) stars in the Galactic halo are the remaining survivors of the early generations of stars. Their surface element abundances are signature of the nucleosynthesis in the first and second generation of stars. From comparison between the observationsof EMP stars and calculations of stellar evolution, it is suggested that typical mass of EMP stars are much higher than more metal-rich one and the majority of observed EMP stars are formed in binary systems. I review the effect of binarity and difference of initial mass function on the EMP stars and chemical evolution of galaxy. We calculate chemical enrichment history in the context of hierarchical Galaxy formation with high mass IMF and binary contribution. We compare resultant abundance distributions with observations. Additionally, I discuss the origin of the most metal-deficient stars known to date. [ABSTRACT FROM AUTHOR]

The origin of the stellar Initial Mass Function (IMF) and its variation with cosmic time or with diverse environmental conditions still lack a complete physical interpretation. Observationally, the present-day stellar IMF appears to have an almost universal profile, characterized by a power-law at large masses and flattening below a characteristic mass of ∼1 M⊙. Among the many proposed explanations, the origin of the characteristic stellar mass and the broad peak of the IMF are best attributed to gravitational fragmentation, which sets the mean Jeans mass at cloud fragmentation. We present the results of a self-consistent study of the response of the mean Jeans mass at cloud fragmentation to metal line-cooling, dust-cooling and the Cosmic Microwave Background (CMB) based on a semi-analytic model of the thermal evolution of clouds with varying initial metal-licities and dust contents at different redshifts. We then discuss the implications of our findings for observational samples of very metal poor stars observed in the halo of our Galaxy. [ABSTRACT FROM AUTHOR]

Following our long-erm work on development of model-independent data analysis methods for reconstructing the one-dimensional velocity distribution function of halo WIMPs as well as for determining their mass and couplings on nucleons by using data from direct Dark Matter detection experiments directly, we combined the simulation programs to a compact system: AMIDAS (A Model-Independent Data Analysis System). For users’ convenience an online system has also been established at the same time. AMIDAS has the ability to do full Monte Carlo simulations, faster theoretical estimations, as well as to analyze (real) data sets recorded in direct detection experiments without modifying the source code. In this article, I give an overview of functions of the AMIDAS code based on the use of its website. [ABSTRACT FROM AUTHOR]

A public talk given at CEPANP 2009 on Dark Matter and Massive Compact Halo Objects (MACHOs). [ABSTRACT FROM AUTHOR]

We examine dark matter annihilation in galaxy halos. By considering annihilation into all Standard Model particles we show that the least detectable final states, namely neutrinos, define a strong general upper bound on the total cross section. This limit implies annihilation cannot significantly modify dark matter halo density profiles. We also consider dark matter annihilation into charged particles, which is necessarily accompanied by gamma rays, produced via radiative corrections. Internal bremsstrahlung from the final state particles produce hard gamma rays up to the dark matter mass, with an approximately model-independent spectrum, allowing robust upper bounds on the dark matter self annihilation cross section to e± to be determined from Galactic gamma ray data. [ABSTRACT FROM AUTHOR]

In cold dark matter cosmologies, the most massive dark matter halos undergo rapid growth between a redshift of z = 1 and z = 0, corresponding to the past 7 billion years of cosmic time. There is thus an expectation that the stellar masses of the most massive galaxies will also rapidly grow via merging over this redshift range. While there are examples of massive merging galaxies at low redshift, recent observations show that the stellar masses of massive galaxies have grown by only ∼30% since z = 1. Some of the literature claims that the slow growth of massive galaxies is contrary to the ΛCDM paradigm, although this is not necessarily the case. To determine why massive galaxies are not growing rapidly, we have modeled how galaxies populate dark matter halos. To do this, we have measured the space density and spatial clustering of redshift z<1 galaxies in the Boötes field of the NOAO Deep Wide-Field Survey. We have then modeled the observations using the halo occupation distribution (HOD) formalism. We find that the stellar masses of the largest galaxies are proportional to dark matter halo mass to the power of a third. In the most massive dark matter halos, we also find that the stellar mass is distributed mostly among “satellite” galaxies. As a consequence, the stellar masses of large galaxies are expected to increase relatively slowly, even though they reside within rapidly growing dark matter halos. [ABSTRACT FROM AUTHOR]

The properties of the hot gas in the Milky Way’s halo are reviewed. The plasma’s distribution is discerned from observations of O VI ions and 1/4 keV and 3/4 keV X-rays. Most of the hot gas is located within a few kpc of the disk. The T∼3×105 K gas has a patchy distribution, while the T = 2 to 3×106 K gas has a smoother distribution. The density and pressure of the hot gas above the Galactic disk have been determined (ne∼0.01 to ∼0.02 cm-3 and Pth/k∼7000 to 10,000 K cm-3, respectively). With its large pressure, the gas above the disk significantly compresses the gas in the disk. The plasma’s cooling rate has been found to be large, suggesting that the hot halo plasma acts as a radiator for the disk/halo system. Several possible sources for the hot gas are considered. These include superbubbles and supernova remnants, Galactic winds, accreting IGM, and infalling high velocity clouds. Multiple mechanisms are probably at work. The review ends with a highlight of new trends. [ABSTRACT FROM AUTHOR]

New observations from the Hubble ultra deep field suggest that the star formation rate at z>7 drops off faster than previously thought. Using the newly determined star formation rate for the normal mode of PopII/I stars we compute the Thomson optical depth. We also investigate the consequences of PopIII stars on the local metallicity distribution function of the Galactic halo and on the evolution of C, O abundances as a function of [Fe/H], with special emphasis on carbon-enhanced metal-poor stars (CEMPS). The metallicity distribution function shape is well reproduced at low redshift ([Fe/H]>=-4), in agreement with other studies. However, the Hamburg/ESO survey hints at a sharp decrease of the number of low-mass stars at very low iron abundance, which is not reproduced in models with only PopII/I stars. The presence of PopIII stars helps in reproducing this feature, leading to a prompt initial enrichment before the onset of PopII/I stars. Finally, we show that the nucleosynthetic yields of PopIII stars leads to abundance patterns in agreement with those observed in extremely metal-poor stars. This can be evidenced by the transition discriminant (a criterion for low-mass star formation taking into account the cooling due to C II and O I). In this simple approach for cosmic evolution, PopIII stars prove to be a compulsory ingredient, and extremely metal poor stars are found to be born at high redshift. [ABSTRACT FROM AUTHOR]

We derive an expression for the entropy of a present dark matter halo described by a Navarro-Frenk-White modified model with a central core. We obtain an expression for the relic abundance of neutralinos by comparing this entropy of the halo with the value it had during the freeze-out era. Using WMAP observations, we constrain the parameter space for mSUGRA models. Combining our results with the usual abundance criteria, we are able to discriminate clearly among different validity regions for tan β values. For this, we require both criteria to be consistent within a 2σ bound of the WMAP observations for the relic density: 0.112<Ωh2<0.122. We find that for sgn μ = +1, small values of tan β are not favored; only for tan β∼50 are both criteria significantly consistent. Both criteria allow us to put a lower bound on the neutralino mass, mχ>=141 GeV. [ABSTRACT FROM AUTHOR]

We analyze the dark matter problem in the context of supersymmetric, U(1)B-L model. In this model, the lightest neutalino can be B-L gaugino ZB-L or Higgsinos χ1,2 dominated. We examine the thermal relic abundance of these particles and discuss the prospects for their direct detection if they form part of our galactic halo. [ABSTRACT FROM AUTHOR]

We have detected about 40 new, extremely faint (i>21) high proper motion (μ>0.14 arcsec/yr) objects from deep multi-epoch Sloan Digital Sky Survey (SDSS) imaging data in a 110×2.5 = 275 square degrees area on the celestial equator (SDSS stripe 82). According to their location in a reduced proper motion diagram and from comparison with known objects, these objects are representatives of three different classes: 1) L and T dwarfs, 2) ultracool (>sdM7) subdwarfs, 3) cool white dwarfs. Low-resolution optical spectroscopy with the VLT has confirmed this classification and provided preliminary spectroscopic distance estimates. The resulting tangential velocities give first hints on the membership of these nearby low-luminosity objects in the Galactic disk or halo populations. [ABSTRACT FROM AUTHOR]

The last years saw numerous detections of substructure in the Galactic halo, largely due to wide area surveys like the Sloan Digital Sky Survey (SDSS) or the Two Micron All Sky Survey (2MASS). The analysis of SDSS data revealed the ‘Field of Streams’ which encompasses, among other features, the broad and extended Sagittarius tidal stream as well as the Monoceros and Orphan stellar streams. In this contribution we present first results from our analysis of Galactic tidal streams based on SDSS Data Release 6 (DR6) stellar photometry. We use the F star method to derive stellar density maps for various distance intervals. These maps reveal a heliocentric distance to the Sagittarius stream near the Galactic anticenter of ∼13 kpc which is lower than previously claimed. The value also is smaller than predicted by current state-of the art N-body simulations of the disruption of the Sagittarius dwarf galaxy in the Galactic halo. Our maps furthermore yield a distance between 13 kpc and 16 kpc to the nearest part of the Virgo overdensity. Rather surprisingly, we found evidence for a discontinuity in the Orphan stream. The ‘disconnected’ region extends over a projected length of ∼6 degrees and appears at distances exceeding ∼25 kpc. If confirmed, this feature would pose strong constraints on theoretical models trying to explain the origin of the Orphan stream. [ABSTRACT FROM AUTHOR]

Large scale surveys are providing vast amounts of data that can help us understand and study tidal debris more easily and accurately. A maximum likelihood method for determining the spatial properties of this tidal debris and the stellar Galactic spheroid has been developed to take advantage of these huge datasets. We present the results of studying the Sagittarius dwarf tidal stream in two SDSS stripes taken in the southern Galactic Cap using this method. This study was done using stars with the colors of blue F turnoff stars in SDSS. We detected Sagittarius debris at the positions (l,b,R) = (163.311°,-48.400°,30.23 kpc) and (l,b,R) = (34.775°,-72.342°,26.08 kpc). These debris pieces were found to have a FWHM of 6.53±0.54 kpc and 5.71±0.26 kpc and also to contain ≈9,500 and ≈16,700 F turnoff stars, respectively. The debris pieces were also found to have (spatial) directions of (X,Ŷ,Z) = (0.758,0.254,-0.600) and (X,Ŷ,Z) = (0.982,0.945,0.167), respectively. Using the results of the algorithm, we have also probabilistically separated the tidal debris from the stellar spheroid and present those results as well. [ABSTRACT FROM AUTHOR]