It is shown that broad-line region (BLR) line profiles ranging from the classic "logarithmic" profile to double-peaked, disk-like profiles are readily explained by the distribution of BLR gas proposed by Gaskell, Klimek, & Nazarova (2007; GKN) without any need to invoke fundamental differences in the AGNs other than differing viewing angles. It is argued that the highly-variable thermal energy generation in AGNs originates off axis in regions that cannot be axially symmetric. This off-axis model readily explains the varying degrees of temporal correlation found in multi-wavelength variability studies, the strong, variable asymmetry of BLR line profiles, the varying time delays in the response of the BLR to different continuum events, how narrow velocity ranges of line profiles will often appear to respond differently or not at all to continuum variability, complex changes in the Balmer decrement with velocity, inconsistent and variable inflow/outflow signatures found in velocity-resolved reverberation mapping, the diversity of velocity-dependent polarizations observed, and polarization variability. The fundamentally non-axisymmetric nature of AGN continuum variability severely limits what can be learned from reverberation mapping. In particular, high-fidelity reverberation mapping is not possible. There will be systematic orientation-dependent errors in black hole mass determinations. The effects of off-axis emission will mask subtle signatures of possible close supermassive black hole binaries. Some tests of the off-axis-variability model are proposed.
Galaxy clusters pose a "cooling-flow problem", where the X-ray emission from their cores is not accompanied by enough cold gas or star formation. This requires a continuous energy source that balances the cooling rate over the whole core volume. We address the feasibility of a gravitational heating mechanism, utilizing the gravitational energy released by the gas that streams into the potential well of the cluster dark-matter halo. We focus here on a specific form of gravitational heating in which the energy is transferred to the medium thorough the drag exerted on inflowing gas clumps. Using spheri-symmetric hydro simulations with a subgrid representation of these clumps, we confirm our earlier estimates that in haloes >=10^13 solar masses the gravitational heating is more efficient than the cooling everywhere. The worry was that this could overheat the core and create an instability that might push it away from equilibrium. However, we find that the overheating does not change the global halo properties, and that convection can stabilize the cluster by carrying energy away from the overheated core. In a typical rich cluster of 10^{14-15} solar masses, with ~5% of the accreted baryons in gas clumps of 10^8 solar masses, the simulated temperature and entropy profiles are consistent with those observed in cool-core clusters, and so are the predicted density and mass of cold gas and the level of turbulence.
We use WIRC, IR images of the Antennae (NGC 4038/4039) together with the extensive catalogue of 120 X-ray point sources (Zezas et al. 2006) to search for counterpart candidates. Using our proven frame-tie technique, we find 38 X-ray sources with IR counterparts, almost doubling the number of IR counterparts to X-ray sources first identified in Clark et al. (2007). In our photometric analysis, we consider the 35 IR counterparts that are confirmed star clusters. We show that the clusters with X-ray sources tend to be brighter, K_s ~16 mag, with (J-K_s) = 1.1 mag. We then use archival HST images of the Antennae to search for optical counterparts to the X-ray point sources. We employ our previous IR-to-X-ray frame-tie as an intermediary to establish a precise optical-to-X-ray frame-tie with <0.6 arcsec rms positional uncertainty. Due to the high optical source density near the X-ray sources, we determine that we cannot reliably identify counterparts. Comparing the HST positions to the 35 identified IR star cluster counterparts, we find optical matches for 27 of these sources. Using Bruzual-Charlot spectral evolutionary models, we find that most clusters associated with an X-ray source are massive, ~10^6 M_sun, young, ~10^6 yr, with moderate metallicities, Z=0.05.
We study the behaviour of multiple radiative cooling algorithms implemented in six Semi-Analytic Models (SAMs) of galaxy formation, including a new model we propose in this paper. We use versions of the models without feedback and apply them to dark matter haloes growing in a cosmological context, which have final masses that range from 10^{11}Msun to 10^{14}Msun. First, using simplified smoothly-growing halo models, we demonstrate that the different algorithms predict cooling rates and final cold gas masses that differ by a factor of ~5 for massive haloes (>10^{12}Msun). The algorithms are in better agreement for less massive haloes because they cool efficiently and, therefore, their cooling rates are largely limited by the halo accretion rate. However, for less massive haloes, all the SAMs predict less cooling than corresponding 1D hydrodynamic models. Second, we study the gas accretion history of the central galaxies of dark matter haloes using merger trees. The inclusion of mergers alters the cooling history of haloes by locking up gas in galaxies within small haloes at early times. For realistic halo models, the dispersion in the cold gas mass predicted by the algorithms is 0.5 dex for high mass haloes and 0.1 dex for low mass haloes, while the dispersion in the accretion rate is about two times larger. Comparing to cosmological SPH simulations, we find that most SAMs systematically under-predict the gas accretion rates for low-mass haloes but over-predict the gas accretion rates for massive haloes. Although the models all include both "rapid" and "slow" mode accretion, the transition between the two accretion modes varies between models and also differs from the simulations. Finally, we construct a new model that explicitly incorporates cold halo gas to illustrate that such a class of models can better match the results from cosmological hydrodynamic simulations.
We present a deep and wide $I$ luminosity function for galaxies in Abell 1689 ($z=0.183$) from a mosaic of HST WFPC2 images covering $10'$ on the side. The main result of this work is the detection of a steep upturn in the dwarf galaxy LF, with $\alpha \sim -2$. The dwarf to giant ratio appears to increase outwards, but this is because giant galaxies are missing in the cluster outskirts, indicating luminosity segregation. The red sequence LF has the same parameters, within errors, as the total LF, showing that the faint end upturn consists of red quiescent galaxies. We speculate that the upturn is connected to the `filling-in' of the red sequence at $z < 0.4$ and may represent the latest installment of `downsizing' as the least massive galaxies are being quenched at the present epoch.
We present a study of protoclusters associated with high redshift radio galaxies. We imaged MRC1017-220 (z=1.77) and MRC0156-252 (z=2.02) using the near-infrared wide-field (7.5'x7.5') imager VLT/HAWK-I in the Y, H and Ks bands. We present the first deep Y-band galaxy number counts within a large area (200 arcmin2). We then develop a purely near-infrared colour selection technique to isolate galaxies at 1.6<z<3 that may be associated with the two targets, dividing them into (i) red passively evolving or dusty star-forming galaxies or (ii) blue/star-formation dominated galaxies with little or no dust. Both targeted fields show an excess of star-forming galaxies with respect to control fields. No clear overdensity of red galaxies is detected in the surroundings of MRC1017-220 although the spatial distribution of the red galaxies resembles a filament-like structure within which the radio galaxy is embedded. In contrast, a significant overdensity of red galaxies is detected in the field of MRC0156-252, ranging from a factor of 2-3 times the field density at large scales (2.5Mpc, angular distance) up to a factor of 3-4 times the field density within a 1Mpc radius of the radio galaxy. Half of these red galaxies have colours consistent with red sequence models at z~2, with a large fraction being bright (Ks<21.5, i.e. massive). In addition, we also find a small group of galaxies within 5" of MRC0156-252 suggesting that the radio galaxy has multiple companions within ~50 kpc. We conclude that the field of MRC0156-252 shows many remarkable similarities with the well-studied protocluster surrounding PKS1138-262 (z=2.16) suggesting that MRC0156-252 is associated with a galaxy protocluster at z~2.
Using the Sloan Digital Sky Survey (SDSS) and the FIRST (Faint Images of the Radio Sky at Twenty Centimeters) catalogs, we examined the optical environments around double-lobed radio sources. Previous studies have shown that multi-component radio sources exhibiting some degree of bending between components are likely to be found in galaxy clusters. Often this radio emission is associated with a cD-type galaxy at the center of a cluster. We cross-correlated the SDSS with the FIRST catalog and measured the richness of the cluster environments surrounding both bent and straight multi-component sources. This led to the discovery and classification of a large number of galaxy clusters out to a redshift of z ~ 0.5. We divided our sample into smaller subgroups based on their optical and radio properties. We find that FR I radio sources are more likely to be found in galaxy clusters than FR II sources. Further, we find that bent radio sources are more often found in galaxy clusters than non-bent radio sources. We also examined the environments around single-component radio sources and find that single-component radio sources are less likely to be associated with galaxy clusters than extended, multi-component radio sources. Bent, visually-selected sources are found in clusters or rich groups ~78% of the time. Those without optical hosts in SDSS are likely associated with clusters at even higher redshifts, most with redshifts of z > 0.7.
The discovery of quasars with redshifts higher than six has prompted a great deal of discussion in the literature regarding the role of quasars, both as sources of reionization, and as probes of the ionization state of the IGM. However the extreme ultra-violet (EUV) spectral index cannot be measured directly for high redshift quasars owing to absorption at frequencies above the Lyman limit, and as a result, studies of the impact of quasars on the intergalactic medium during reionization must assume a spectral energy distribution in the extreme ultra-violet based on observations at low redshift, z<1. In this paper we use regions of high Ly-alpha transmission (near-zones) around the highest redshift quasars to measure the quasar EUV spectral index at z~6. We jointly fit the available observations for variation of near-zone size with both redshift and luminosity, and propose that the observed relation provides evidence for an EUV spectral index that varies with absolute magnitude in the high redshift quasar sample, becoming softer at higher luminosity. Using a large suite of detailed numerical simulations we find that the typical value of spectral index for a luminous quasar at z~6 is constrained to be alpha=1.3+/-0.4 for a specific luminosity of the form L\propto\nu^{-alpha}. We find the scatter in spectral index among individual quasars to be in the range ~0.75-1.25. These values are in agreement with direct observations at low redshift, and indicate that there has been no significant evolution in the EUV spectral index of quasars over 90% of cosmic time.
In this paper, we will use $\delta \mathcal{N}$-formalism to calculate the primordial curvature perturbation for the curvaton model with a Lagrange multiplier field. We calculate the non-linearity parameters $f_{NL}$ and $g_{NL}$ in the sudden-decay approximation in this kind of model, and we find that one could get a large non-Gaussinity even if the curvaton dominates the total energy density before it decays, and this property will make the curvaton model much richer. We also calculate the probability density function of the primordial curvature perturbation in the sudden-decay approximation, as well as some moments of it.
(Abridged) In our previous work we found a statistically significant offset Delta V = 27 m/s between the radial velocities of the HC3N(2-1) and NH3(1,1) transitions observed in molecular cores from the Milky Way. This may indicate that the electron-to-proton mass ratio, mu = m_e/m_p, increases by 3x10^{-8} when measured under interstellar conditions with matter densities of more than 10 orders of magnitude lower as compared with laboratory (terrestrial) environments. We now map four molecular cores L1498, L1512, L1517, and L1400K selected from our previous sample in order to estimate systematic effects in Delta V due to possible velocity gradients. We find that in two cores L1498 and L1512 the NH3(1,1) and HC3N(2-1) transitions closely trace the same material and show an offset of Delta V = 26.9 +/- 1.2_stat +/- 3.0_sys m/s throughout the entire clouds. The measured velocity offset, being expressed in terms of Delta mu = (mu_obs - mu_lab)/mu_lab, gives Delta mu = (26 +/- 1_stat +/- 3_sys)x10^{-9}.
The secondary spectra of the gravitons induced by a waterfall-like field are computed and the general bounds on the spectral energy density of the tensor modes of the geometry are translated into explicit constraints on the amplitude and slope of the waterfall spectrum. The obtained results are compared with the primary gravitational wave spectra of the concordance model and of its neighboring extensions as well as with the direct Ligo/Virgo bounds on stochastic backgrounds of relic gravitons. Space-borne interferometers (such as Lisa, Bbo, Decigo) seem to be less relevant but their potential implications are briefly outlined.
The largest uncollapsed inhomogeneity in the observable Universe is statistically represented in the quadrupole signal of the cosmic microwave background (CMB) sky maps as observed by the Wilkinson Microwave Anisotropy Probe (WMAP). The constant temporal offset of -25.6 ms between the timestamps of the spacecraft attitude and observational data records in the time-ordered data (TOD) of the WMAP observations was suspected to imply that previously derived all-sky CMB maps are erroneous, and that the quadrupole is in large part an artefact. The optimal focussing of bright objects in the Galactic Plane plays a key role in showing that no error occurred at the step of mapmaking from the calibrated TOD. Instead, the error had an effect when the uncalibrated TOD were calibrated. Estimates of the high-latitude quadrupole based on the wrongly calibrated WMAP maps are overestimated by about 15-60%.
Our peculiar velocity with respect to the CMB rest frame is known to induce a large dipole in the CMB. However, the motion of an observer has also the effect of distorting the anisotropies at all scales, as shown by Challinor and Van Leeuwen (2002), due to aberration and Doppler effects. We propose to measure independently our local motion by using off-diagonal two-point correlation functions for high multipoles. We study the observability of the signal for temperature and polarization anisotropies. We point out that Planck can measure the velocity $\beta$ with an error of about 10%-20% and the direction with an error of about 5-10 degrees. This method constitutes a cross-check, which can be useful to verify that our CMB dipole is due mainly to our velocity or to disentangle the velocity from other possible intrinsic sources. Although in this paper we focus on our peculiar velocity, a similar effect would result also from other intrinsic vectorial distortion of the CMB which would induce a dipolar lensing. Measuring the off-diagonal correlation terms is therefore a test for a preferred direction on the CMB sky.
We investigate the cosmological perturbations in f(T) gravity. Examining the pure gravitational perturbations, we extract the corresponding dispersion relation, which provides a constraint on the f(T) ansatzes that lead to a theory free of instabilities. Additionally, upon inclusion of the matter perturbations, we derive the fully perturbed equations of motion, and we study the growth of matter overdensities. We show that f(T) gravity with f(T) constant coincides with General Relativity, both at the background as well as at the first-order perturbation level. Applying our formalism to the power-law model we find that on large subhorizon scales (O(100 Mpc) or larger), the evolution of matter overdensity differs markedly from LambdaCDM cosmology.
We phenomenologically put local constraints on the rotation of distant masses by using the planets of the solar system. First, we analytically compute the orbital secular precessions induced on the motion of a test particle about a massive primary by a Coriolis-like force, treated as a small perturbation of first order in the rotation, in the case of a constant angular velocity vector \Psi directed along a generic direction in space. The semimajor axis a and the eccentricity e of the test particle do not secularly precess, contrary to the inclination I, the longitude of the ascending node \Omega, the longitude of the pericenter \varpi and the mean anomaly M. Then, we compare our prediction for <\dot\varpi> with the corrections \Delta\dot\varpi to the usual perihelion precessions of the inner planets recently estimated by fitting long data sets with different versions of the EPM ephemerides. We obtain |\Psi_z| <= 0.0006-0.013 arcsec cty^-1, |\Psi_x| <= 0.1-2.7 arcsec cty-1, |\Psi_y| <= 0.3-2.3 arcsec cty^-1. Interpreted in terms of models of space-time involving cosmic rotation, our results are able to yield constraints on cosmological parameters like the cosmological constant \Lambda and the Hubble parameter H_0 not too far from their values determined with cosmological observations and, in some cases, several orders of magnitude better than the constraints usually obtained so far from space-time models not involving rotation. In the case of the rotation of the solar system throughout the Galaxy, occurring clockwise about the North Galactic Pole, our results for \Psi_z are in disagreement with the expected value of it at more than 3-\sigma level.
We study the quantum measurement problem in the context of an infinite, statistically uniform space, as could be generated by eternal inflation. It has recently been argued that when identical copies of a quantum measurement system exist, the standard projection operators and Born rule method for calculating probabilities must be supplemented by estimates of relative frequencies of observers. We argue that an infinite space actually renders the Born rule redundant, by physically realizing all outcomes of a quantum measurement in different regions, with relative frequencies given by the square of the wave function amplitudes. Our formal argument hinges on properties of what we term the quantum confusion operator, which projects onto the Hilbert subspace where the Born rule fails, and we comment on its relation to the oft-discussed quantum frequency operator. This analysis unifies the classical and quantum levels of parallel universes that have been discussed in the literature, and has implications for several issues in quantum measurement theory. It also shows how, even for a single measurement, probabilities may be interpreted as relative frequencies in unitary (Everettian) quantum mechanics. We also argue that after discarding a zero-norm part of the wavefunction, the remainder consists of a superposition of indistinguishable terms, so that arguably "collapse" of the wavefunction is irrelevant, and the "many worlds" of Everett's interpretation are unified into one. Finally, the analysis suggests a "cosmological interpretation" of quantum theory in which the wave function describes the actual spatial collection of identical quantum systems, and quantum uncertainty is attributable to the observer's inability to self-locate in this collection.
We present an extension of TRAPHIC, the method for radiative transfer of ionising radiation in smoothed particle hydrodynamics simulations that we introduced in Pawlik & Schaye (2008). The new version keeps all advantages of the original implementation: photons are transported at the speed of light, in a photon-conserving manner, directly on the spatially adaptive, unstructured grid traced out by the particles, in a computation time that is independent of the number of radiation sources, and in parallel on distributed memory machines. We extend the method to include multiple frequencies, both hydrogen and helium, and to model the coupled evolution of the temperature and ionisation balance. We demonstrate that close to sources the grey approximation asymptotes to the multi-frequency result if photo-heating rates are computed in the optically thin limit, but that it breaks down everywhere if, as is often done, the optically thick limit is assumed. We test our methods by performing a set of simulations of increasing complexity and including a small cosmological reionisation run. The results are in excellent agreement with exact solutions, where available, and also with results obtained with other codes if we make similar assumptions and account for differences in the atomic rates used.
We introduce a novel method for weak-lensing measurements, which is based on a mathematically exact deconvolution of the moments of the apparent brightness distribution of galaxies from the telescope's PSF. No assumptions on the shape of the galaxy or the PSF are made. The (de)convolution equations are exact for unweighted moments only, while in practice a compact weight function needs to be applied to the noisy images to ensure that the moment measurement yields significant results. We employ a Gaussian weight function, whose centroid and ellipticity are iteratively adjusted to match the corresponding quantities of the source. The change of the moments caused by the application of the weight function can then be corrected by considering higher-order weighted moments of the same source. Because of the form of the deconvolution equations, even an incomplete weighting correction leads to an excellent shear estimation if galaxies and PSF are measured with a weight function of identical size. We demonstrate the accuracy and capabilities of this new method in the context of weak gravitational lensing measurements with a set of specialized tests and show its competitive performance on the GREAT08 challenge data. A complete C++ implementation of the method can be requested from the authors.
The quantum field theoretic prediction for the vacuum energy density leads to a value for the effective cosmological constant that is incorrect by between 60 to 120 orders of magnitude. We review an old proposal of replacing Einstein's Field Equations by their trace-free part (the Trace-Free Einstein Equations), together with an independent assumption of energy--momentum conservation by matter fields. We confirm that while this does not solve the fundamental issue of why the cosmological constant has the value it has, it is indeed a viable theory that resolves the problem of the discrepancy between the vacuum energy density and the observed value of the cosmological constant. We also point out that this proposal may have a valid quantum field theory basis in terms of a spin-2 field theory for the graviton interaction with matter.
The fluid model for the dark sector of the universe (darkon fluid) introduced previously in \cite{PRD} is reformulated as a modified model involving only variables from physical phase space. The Lagrangian of the model does not possess a free particle limit and hence the particles it describes, darkons, exist only as a self-gravitating fluid. This darkon fluid presents a dynamical realisation of the zero-mass Galilean algebra extended by anisotropic dilational symmetry with dynamical exponent $z=\frac{5}{3}$. The model possesses cosmologically relevant solutions which are identical to those of \cite{PRD}. We derive also the equations for the cosmological perturbations at early times and determine their solutions. In addition, we discuss also some implications of adding higher spatial-derivative terms.
The possibility that the stellar initial mass function (IMF) arises mostly from cloud structure is investigated with fractal Brownian motion (fBm) clouds that have power-law power spectra. An fBm cloud with a realistic projected power spectrum slope of $\beta=2.8$ is found to have a mass function for clumps exceeding a threshold density that is a power-law with a slope of $\alpha=2.35$, the same as in the Salpeter IMF. Any hierarchically structured cloud has a clump mass function with about the same slope. This result implies that turbulent interstellar clouds produce dense substructure with the observed pre-stellar core mass function built in from the start. Details of the clump formation processes are not critical. The conversion of clumps into stars involves a second step. A one-to-one correspondence between clump mass and star mass is not necessary to convert the clump mass spectrum into an IMF with the same power-law slope. As long as clumps have an internal stellar IMF from sub-fragmentation, protostellar accretion, coalescence and other processes, and the characteristic mass for this internal IMF scales with the clump mass, then the IMF slope above the minimum characteristic mass will equal the clump mass slope. A detailed review of IMF models illustrates the prominence of cloud structure as a major component in a wide class of theories. Tests are proposed to determine the relative importance of cloud structure and competitive accretion in the IMF.
The assumption that a complete description of an early state of the universe does not privilege any position or direction in space leads to a unified account of probability in cosmology, macroscopic physics, and quantum mechanics. Such a description has a statistical character. Deterministic laws link it to statistical descriptions of the cosmic medium at later times, and because these laws do not privilege any position or direction in space, the same must be true of these descriptions. If the universe is infinite, we can identify the probability that the energy density at a particular instant and a particular point in space (relative to a system of spacetime coordinates in which the postulated spatial symmetries are manifest) lies in a given range with the fractional volume occupied by points where the energy density lies in this range; and similarly with all other probabilities that figure in the statistical description. The probabilities that figure in a complete description of the cosmic medium at any given moment thus have an exact and objective physical interpretation. The statistical entropy and the information associated with each cosmological probability distribution are likewise objective properties of the universe, defined in terms of relative frequencies or spatial averages.
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Population III stars are theoretically expected to be prominent around redshifts z ~ 20, consisting of mainly very massive stars with M_* >~ 10 M_sun$, but there is no direct observational evidence for these objects. They may produce collapsar gamma-ray bursts (GRBs), with jets driven by magnetohydrodynamic processes, whose total isotropic-equivalent energy could be as high as E_iso >~ 10^{57} erg over a cosmological-rest-frame duration of t_d >~ 10^4 s, depending on the progenitor mass. Here we calculate the afterglow spectra of such Pop. III GRBs based on the standard external shock model, and show that they will be detectable with the Swift BAT/XRT and Fermi LAT instruments. We find that in some cases a spectral break due to electron-positron pair creation will be observable in the LAT energy range, which can put constraints on the ambient density of the pre-collapse Pop. III star. Thus, high redshift GRB afterglow observations could be unique and powerful probes of the properties of Pop. III stars and their environments. We examine the detection threshold of the BAT instrument in detail, focusing on the image trigger system, and show that the prompt emission of Pop. III GRBs could also be detected by BAT. Finally we briefly show that the late-time radio afterglows of Pop. III GRBs for typical parameters, despite the large distances, can be very bright: ~ 140 mJy at 1 GHz, which may lead to a constraint on the Pop. III GRB rate from the current radio survey data, and ~2.4 mJy at 70 MHz, which implies that Pop. III GRB radio afterglows could be interesting background source candidates for 21 cm absorption line detections.
It is a longstanding problem that HII regions and very young stellar
populations in the Large Magellanic Cloud (LMC) have the nitrogen abundances
([N/H]) by a factor of ~7 lower than the solar value. We here discuss a new
scenario in which the observed unusually low nitrogen abundances can be closely
associated with recent collision and subsequent accretion of HI high velocity
clouds (HVCs) that surround the Galaxy and have low nitrogen abundances. We
show that if the observed low [N/H] is limited to very young stars with ages
less than ~10^7 yr, then the collision/accretion rate of the HVCs onto the LMC
needs to be ~ 0.2 M_sun/yr (corresponding to the total HVC mass of 10^6-10^7
M_sun) to dilute the original interstellar medium (ISM) before star formation.
The required accretion rate means that even if the typical mass of HVCs
accreted onto the LMC is ~ 10^7 M_sun, the Galaxy needs to have ~2500 massive
HVCs within the LMC's orbital radius with respect to the Galactic center. The
required rather large number of massive HVCs drives us to suggest that the HVCs
are not likely to efficiently dilute the ISM of the LMC and consequently lower
the [N/H]. We thus suggest the transfer of gas with low [N/H] from the Small
Magellanic Cloud (SMC) to the LMC as a promising scenario that can explain the
observed low [N/H].
We investigate dynamics of a flat FRW cosmological model with a barotropic matter and a non-minimally coupled scalar field (both canonical and phantom). In our approach we do not assume any specific form of a potential function for the scalar field and we are looking for generic scenarios of evolution. We show that dynamics of universe can be reduced to a 3-dimensional dynamical system. We have found the set of fixed points and established their character. These critical points represent all important epochs in evolution of the universe : (a) a finite scale factor singularity, (b) an inflation (rapid-roll and slow-roll), (c) a radiation domination, (d) a matter domination and (e) a quintessence era. We have shown that the inflation, the radiation and matter domination epochs are transient ones and last for a finite amount of time. The existence of the radiation domination epoch is purely the effect of a non-minimal coupling constant. We show the existence of a twister type solution wandering between all these critical points.
The mean mass densities of cosmic dark matter is larger than that of baryonic matter by a factor of about 5 in the $\Lambda$CDM universe. Therefore, the gravity on large scales should be dominant by the distribution of dark matter in the universe. However, a series of observations incontrovertibly show that the velocity and density fields of baryonic matter are decoupling from underlying dark matter field. This paper shows our attemps to unveil the physics behind this puzzle. In linear approximation, the dynamics of the baryon fluid is completely governed by the gravity of the dark matter. Consequently, the mass density field of baryon matter $\rho_b({\bf r},t)$ will be proportional to that of dark matter $\rho_{\rm dm}({\bf r},t)$, even though they are different from each other initially. In weak and moderate nonlinear regime, the dynamics of the baryon fluid can be sketched by Burgers equation. A basic feature of the Burgers dynamics is to yield shocks. When the Reynolds number is large, the Burgers fluid will be in the state of Burgers turbulence, which consists of shocks and complex structures. On the other hand, the collisionless dark matter may not show such shock, but a multivalued velocity field. Therefore, the weak and moderate nonlinear evolution leads to the IGM-dark matter deviation. Yet, the velocity field of Burgers fluid is still irrotational, as gravity is curl-free. In fully nonlinear regime, the vorticity of velocity field developed, and the cosmic baryonic fluid will no longer be potential, as the dynamics of vorticity is independent of gravity and can be self maintained by the nonlinearity of hydrodynamics. In this case, the cosmic baryon fluid is in the state of fully developed turbulence, which is statistically and dynamically decoupling from dark matter. This scenario provides a mechanism of cohenent explanation of observations.
Modulated reheating scenario is one of the most attractive models that predict possible detections of not only the primordial non-Gaussianity but also the tensor fluctuation through future CMB observations such as the Planck satellite, the PolarBeaR and the LiteBIRD satellite experiments. We study the baryonic-isocurvature fluctuations in the Affleck-Dine baryogenesis with the modulated reheating scenario. We show that the Affleck-Dine baryogenesis can be consistent with the modulated reheating scenario with respect to the current observational constraint on the baryonic-isocurvature fluctuations.
A sterile neutrino with mass in the eV range, mixing with the electron antineutrino, is allowed and possibly even preferred by cosmology and oscillation experiments. If such eV-mass neutrinos exist they provide a much better target for direct detection in beta decay experiments than the active neutrinos which are expected to have sub-eV masses. Their relatively high mass would allow for an easy separation from the primary decay signal in experiments such as KATRIN.
There exist power contrast in even and odd multipoles of WMAP power spectrum at low and intermediate multipole range. This anomaly is explicitly associated with the angular power spectrum, which are heavily used for cosmological model fitting. Having noted this, we have investigated whether even(odd) multipole data set is consistent with the WMAP concordance model. Our investigation shows WMAP concordance model does not make a good fit for even(odd) multipole data set, and there exist tension between two data subsets. Noting tension is highest in primordial power spectrum parameters, we have additionally considered a running spectral index, but find tension increases to even a higher level. We believe these parametric tensions may be indications of unaccounted contamination or imperfection of the model.
In the last few years there has been some interest in WIMP Dark Matter models featuring a velocity dependent cross section through the Sommerfeld enhancement mechanism. The idea is to have light bosons mediate a force between the WIMPs, which gives rise to a Yukawa-potential. In the first part of this article, we analyse the Sommerfeld enhancement in detail. We find analytic expressions for the boost factor for three different modelpotentials, Coulomb, the spherical well and the spherical cone well and compare with the numerical solution in the Yukawa case. In the second part of the article, we perform a detailed computation of the Dark Matter relic density for models having Sommerfeld enhancement by solving the Boltzmann equation numerically. As an application we compare the expected distortions of the CMB blackbody spectrum to the bounds set by FIRAS.
We carry out a multi-wavelength study of individual galaxies detected by the Balloon-borne Large Aperture Submillimeter Telescope (BLAST) and identified at other wavelengths, using data spanning the radio to the ultraviolet (UV). We develop a Monte Carlo method to account for flux boosting, source blending, and correlations among bands, which we use to derive deboosted far-infrared (FIR) luminosities for our sample. We estimate total star-formation rates for BLAST counterparts with z < 0.9 by combining their FIR and UV luminosities. Star formation is heavily obscured at L_FIR > 10^11 L_sun, z > 0.5, but the contribution from unobscured starlight cannot be neglected at L_FIR < 10^11 L_sun, z < 0.25. We assess that about 20% of the galaxies in our sample show indication of a type-1 active galactic nucleus (AGN), but their submillimeter emission is mainly due to star formation in the host galaxy. We compute stellar masses for a subset of 92 BLAST counterparts; these are relatively massive objects with a median mass of 10^11 M_sun. We argue that BLAST is bridging the mass gap at 0 < z < 2 between the 24um-selected population and the SCUBA objects. The bulk of the BLAST counterparts at z < 0.9 appear to be run-of-the-mill star-forming galaxies, typically spiral in shape, with intermediate stellar masses (< 10^11 M_sun) and constant specific star-formation rates. On the other hand, the high-z, high-mass tail of the BLAST counterparts significantly overlaps with the SCUBA population, in terms of both star-formation rates and stellar masses, with observed trends of specific star-formation rate that support strong evolution and downsizing.
General relativity predicts the existence of black holes, compact objects whose spacetimes depend on only their mass and spin (the famous "no hair" theorem). As various observations probe deeper into the strong fields of black hole candidates, it is becoming possible to test this prediction. Previous work suggested that such tests can be performed by measuring whether the multipolar structure of black hole candidates has the form that general relativity demands, and introduced a family of "bumpy black hole" spacetimes to be used for making these measurements. These spacetimes are black holes with the "wrong" multipoles, where the deviation from general relativity depends on the spacetime's "bumpiness." In this paper, we show how to compute the Geroch-Hansen moments of a bumpy black hole, demonstrating that there is a clean mapping between the deviations used in the bumpy black hole formalism and the Geroch-Hansen moments. We also extend our previous results to define bumpy black holes whose {\it current} moments, analogous to magnetic moments of electrodynamics, deviate from the canonical Kerr value.
Using our new Binary Population and Spectral Synthesis (BPASS) code we explore the affect of binary populations on the integrated spectra of galaxies. We also explore the interplay of binary populations and a varying maximum stellar mass. We compare our synthetic populations to observations of H$\alpha$ emission from isolated clusters and H$\alpha$ and FUV observations of galaxies. We find that observations tend to favour a pure stochastic sampling of the initial mass function although the evidence is not significant. We also find that binaries make a stellar population less susceptible to the stochastic effects of filling the IMF. Therefore making it more difficult to determine if there is a variable maximum stellar mass.
A Lifshitz scalar with the dynamical critical exponent z = 3 obtains scale-invariant, super-horizon field fluctuations without the need of an inflationary era. Since this mechanism is due to the special scaling of the Lifshitz scalar and persists in the presence of unsuppressed self-couplings, the resulting fluctuation spectrum can deviate from a Gaussian distribution. We study the non-Gaussian nature of the Lifshitz scalar's intrinsic field fluctuations, and show that primordial curvature perturbations sourced from such field fluctuations can have large non-Gaussianity of order f_NL = O(100), which will be detected by upcoming CMB observations. We compute the bispectrum and trispectrum of the fluctuations, and discuss their configurations in momentum space. In particular, the bispectrum is found to take various shapes, including the local, equilateral, and orthogonal shapes. Intriguingly, all integrals in the in-in formalism can be performed analytically.
We present the analysis of three XMM observations of the Seyfert 2 galaxy NGC 7590. The source was found to have no X-ray absorption in the low spatial resolution ASCA data. The XMM observations provide a factor of 10 better spatial resolution than previous ASCA data. We find that the X-ray emission of NGC 7590 is dominated by an off-nuclear ULX and extended emission from the host galaxy. The nuclear X-ray emission is rather weak comparing with the host galaxy. Based on its very low X-ray luminosity as well as the small ratio between the 2-10 keV and the [O III] fluxes, we interpret NGC 7590 as Compton-thick rather than being an "unobscured" Seyfert 2 galaxy. Future higher resolution observations such as Chandra are crucial to shed light on the nature of NGC 7590 nucleus.
Combined Spitzer, Chandra, XMM-Newton, and VLA observations of the giant radio galaxy NGC 1316 (Fornax A) show a radio jet and X-ray cavities from AGN outbursts likely triggered by a merger with a late-type galaxy at least 0.4 Gyr ago. We detect a weak nucleus with an SED typical of a low-luminosity AGN with a bolometric luminosity of 2.4x10^42 erg/s. The Spitzer IRAC and MIPS images show dust emission strongest in regions with little or no radio emission. The large infrared luminosity relative to the galaxy's K-band luminosity implies an external origin for the dust. The dust mass implies that the merger spiral galaxy had a stellar mass of 1-6x10^10 M_sun and a gas mass of 2-4x10^9 M_sun. Chandra images show a small ~15"(1.6 kpc) cavity coincident with the radio jet, while the XMM-Newton image shows two large X-ray cavities lying 320"(34.8 kpc) east and west of the nucleus, each approximately 230"(25 kpc) in radius. The radio lobes lie at radii of 14.3'(93 kpc) and 15.6'(101 kcp), more distant from the nucleus than the detected X-ray cavities. The relative morphology of the large scale 1.4 GHz and X-ray emission suggests they were products of two distinct outbursts, an earlier one creating the radio lobes and a later one producing the X-ray cavities. Alternatively, if a single outburst created both the X-ray cavities and the radio lobes, this would require that the morphology is not fully defined by the 1.4 GHz emission. For the more likely two outburst scenario, we use the buoyancy rise times to estimate an age for the more recent outburst of 0.1 Gyr and use the associated PV work done by the expanding plasma to create the X-ray cavities to estimate the outburst's energy of 10^58 ergs. The present size and location of the large radio lobes implies that the AGN outburst that created them happened ~0.4 Gyr ago and released ~5x10^58 ergs. (abridged)
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Using the 12m APEX telescope, we have detected redshifted emission from the 157.74micron [CII] line in the z=4.4074 quasar BRI1335-0417. The linewidth and redshift are in good agreement with previous observations of high-J CO line emission. We measure a [CII] line luminosity, L_[CII] = (16.4 +/- 2.6)x10^9 Lsun, making BRI~1335-0417 the most luminous, unlensed [CII] line emitter known at high-redshift. The [CII]-to-FIR luminosity ratio of (5.3+/-0.8)x10^-4 is ~3x higher than expected for an average object with a FIR luminosity L_FIR = 3.1x10^13 Lsun, if this ratio were to follow the trend observed in other FIR-bright galaxies that have been detected in [CII] line emission. These new data suggest that the scatter in the [CII]-to-FIR luminosity ratio could be larger than previously expected for high luminosity objects. BR1335-0417 has a similar FIR luminosity and [CII]/CO luminosity compared to local ULIRGS and appears to be a gas-rich merger forming stars at a rate of a few thousand solar masses per year.
We explore the cosmological halo-to-halo scatter of the distribution of mass within dark matter halos utilizing a well-resolved statistical sample of clusters from the cosmological Millennium simulation. We find that at any radius, the spherically-averaged dark matter density of a halo (corresponding to the ``smooth-component'') and its logarithmic slope are well-described by a Gaussian probability distribution. At small radii (within the scale radius), the density distribution is fully determined by the measured Gaussian distribution in halo concentrations. The variance in the radial distribution of mass in dark matter halos is important for the interpretation of direct and indirect dark matter detection efforts. The scatter in mass profiles imparts approximately a 25 percent cosmological uncertainty in the dark matter density at the Solar neighborhood and a factor of ~3 uncertainty in the expected Galactic dark matter annihilation flux. The aggregate effect of halo-to-halo profile scatter leads to a small (few percent) enhancement in dark matter annihilation background if the Gaussian concentration distribution holds for all halo masses versus a 10 percent enhancement under the assumption of a log-normal concentration distribution. The Gaussian nature of the cluster profile scatter implies that the technique of ``stacking'' halos to improve signal to noise should not suffer from bias.
Recent work indicates that star-forming early-type galaxies (ETGs) residing in the blue cloud migrate rapidly to the red sequence within around a Gyr, passing through several phases of increasingly strong AGN activity in the process (Schawinski et al. 2007, MNRAS, 382, 1415; S07 hereafter). We show that natural depletion of the gas reservoir through star formation (i.e. in the absence of any feedback from the AGN) induces a blue-to-red reddening rate that is several factors lower than that observed in S07. This is because the gas depletion rate due to star formation alone is too slow, implying that another process needs to be invoked to remove gas from the system and accelerate the reddening rate. We develop a simple phenomenological model, in which a fraction of the AGN's luminosity couples to the gas reservoir over a certain 'feedback timescale' and removes part of the gas mass from the galaxy, while the remaining gas continues to contribute to star formation. We use the model to investigate scenarios which yield migration times consistent with the results of S07. We find that acceptable models have feedback timescales <0.2 Gyrs. The mass fraction in young stars in the remnants is <5% and the residual gas fractions are less than 0.6%, in good agreement with the recent literature. At least half of the initial gas reservoir is removed as the galaxies evolve from the blue cloud to the red sequence. If we restrict ourselves to feedback timescales similar to the typical duty cycles of local AGN (a few hundred Myrs) then a few tenths of a percent of the luminosity of an early-type Seyfert (10^11 LSun) must couple to the gas reservoir in order to produce migration times that are consistent with the observations.
We present the results of our systematic infrared 2.5-5 micron spectroscopy of 60 luminous infrared galaxies (LIRGs) with infrared luminosities L(IR) = 10^11-12 Lsun, and 54 ultraluminous infrared galaxies (ULIRGs) with L(IR) > 10^12 Lsun, using AKARI IRC. AKARI IRC slit-less spectroscopy allows us to probe the full range of emission from these galaxies, including spatially extended components. The 3.3 micron polycyclic aromatic hydrocarbon (PAH) emission features, hydrogen recombination emission lines, and various absorption features are detected and used to investigate the properties of these galaxies. Because of the relatively small effect of dust extinction in the infrared range, quantitative discussion of these dusty galaxy populations is possible. For sources with clearly detectable Br beta (2.63 micron) and Br alpha (4.05 micron) emission lines, the flux ratios are found to be similar to that predicted by case B theory. Starburst luminosities are estimated from both 3.3 micron PAH and Br alpha emission, which roughly agree with each other. In addition to the detected starburst activity, a significant fraction of the observed sources display signatures of obscured AGNs, such as low PAH equivalent widths, large optical depths of dust absorption features, and red continuum emission. The energetic importance of optically elusive buried AGNs in optically non-Seyfert galaxies tends to increase with increasing galaxy infrared luminosity, from LIRGs to ULIRGs.
In this paper we examine the cosmological consequences of fourth order Galileon gravity. We carry out detailed investigations of the underlying dynamics and demonstrate the stability of one de Sitter phase. The stable de Sitter phase contains a Galileon field $\pi$ which is an increasing function of time (\dot{\pi}>0). Using the required suppression of the fifth force, supernovae, BAO and CMB data, we constrain parameters of the model. We find that the $\pi$ matter coupling parameter $\beta$ is constrained to small numerical values such that $\beta$<0.02. We also show that the parameters of the third and fourth order in the action (c_3,c_4) are not independent and with reasonable assumptions, we obtain constrains on them. We investigate the growth history of the model and find that the sub-horizon approximation is not allowed for this model. We demonstrate strong scale dependence of linear perturbations in the fourth order Galileon gravity.
We use archival HST observations of resolved stellar populations to derive the star formation histories (SFHs) of 18 nearby starburst dwarf galaxies. In this first paper we present the observations, color-magnitude diagrams, and the SFHs of the 18 starburst galaxies, based on a homogeneous approach to the data reduction, differential extinction, and treatment of photometric completeness. We adopt a star formation rate (SFR) threshold normalized to the average SFR of the individual system as a metric for classifying starbursts in SFHs derived from resolved stellar populations. This choice facilitates finding not only currently bursting galaxies but also "fossil" bursts increasing the sample size of starburst galaxies in the nearby (D<8 Mpc) universe. Thirteen of the eighteen galaxies are experiencing ongoing bursts and five galaxies show fossil bursts. From our reconstructed SFHs, it is evident that the elevated SFRs of a burst are sustained for hundreds of Myr with variations on small timescales. A long >100 Myr temporal baseline is thus fundamental to any starburst definition or identification method. The longer lived bursts rule out rapid "self-quenching" of starbursts on global scales. The bursting galaxies' gas consumption timescales are shorter than the Hubble time for all but one galaxy confirming the short-lived nature of starbursts based on fuel limitations. Additionally, we find the strength of the H{\alpha} emission usually correlates with the CMD based SFR during the last 4-10 Myr. However, in four cases, the H{\alpha} emission is significantly less than what is expected for models of starbursts; the discrepancy is due to the SFR changing on timescales of a few Myr. The inherently short timescale of the H{\alpha} emission limits identifying galaxies as starbursts based on the current characteristics which may or may not be representative of the recent SFH of a galaxy.
In this paper we study the evolution of cosmological perturbations in the presence of dynamical dark energy, and revisit the issue of dark energy perturbations. For a generally parameterized equation of state (EoS) such as w_D(z) = w_0+w_1\frac{z}{1+z}, (for a single fluid or a single scalar field ) the dark energy perturbation diverges when its EoS crosses the cosmological constant boundary w_D=-1. In this paper we present a method of treating the dark energy perturbations during the crossing of the $w_D=-1$ surface by imposing matching conditions which require the induced 3-metric on the hypersurface of w_D=-1 and its extrinsic curvature to be continuous. These matching conditions have been used widely in the literature to study perturbations in various models of early universe physics, such as Inflation, the Pre-Big-Bang and Ekpyrotic scenarios, and bouncing cosmologies. In all of these cases the EoS undergoes a sudden change. Through a detailed analysis of the matching conditions, we show that \delta_D and \theta_D are continuous on the matching hypersurface. This justifies the method used[1-4] in the numerical calculation and data fitting for the determination of cosmological parameters. We discuss the conditions under which our analysis is applicable.
We give an account, at non-expert and quantitative level, of physics behind the CMB temperature anisotropy and polarization and their peculiar features. We discuss, in particular, how cosmological parameters are determined from the CMB measurements and their combinations with other observations. We emphasize that CMB is the major source of information on the primordial density perturbations and, possibly, gravitational waves, and discuss the implication for our understanding of the extremely early Universe.
We present an efficient separable approach to the estimation and reconstruction of the bispectrum and the trispectrum from observational (or simulated) large scale structure data. This is developed from general CMB (poly-)spectra methods which exploit the fact that the bispectrum and trispectrum in the literature can be represented by a separable mode expansion which converges rapidly (with $n_\textrm{max}={\cal{O}}(30)$ terms). With an effective grid resolution $l_\textrm{max}$ (number of particles/grid points $N=l_\textrm{max}^3$), we present a bispectrum estimator which requires only ${\cal O}(n_\textrm{max} \times l_\textrm{max}^3)$ operations, along with a corresponding method for direct bispectrum reconstruction. This method is extended to the trispectrum revealing an estimator which requires only ${\cal O}(n_\textrm{max}^{4/3} \times l_\textrm{max}^3)$ operations. The complexity in calculating the trispectrum in this method is now involved in the original decomposition and orthogonalisation process which need only be performed once for each model. However, for non-diagonal trispectra these processes present little extra difficulty and may be performed in ${\cal O}(l_\textrm{max}^4)$ operations. A discussion of how the methodology may be applied to the quadspectrum is also given. An efficient algorithm for the generation of arbitrary nonGaussian initial conditions for use in N-body codes using this separable approach is described. This prescription allows for the production of nonGaussian initial conditions for arbitrary bispectra and trispectra. A brief outline of the key issues involved in parameter estimation, particularly in the non-linear regime, is also given.
We present the first results from a new, deep (200ks) Chandra observation of the X-ray luminous galaxy cluster surrounding the powerful (L ~10^47 erg/s), high-redshift (z=1.067), compact-steep-spectrum radio-loud quasar 3C186. The diffuse X-ray emission from the cluster has a roughly ellipsoidal shape and extends out to radii of at least ~60 arcsec (~500 kpc). The centroid of the diffuse X-ray emission is offset by 0.68(+/-0.11) arcsec (5.5+/-0.9 kpc) from the position of the quasar. We measure a cluster mass within the radius at which the mean enclosed density is 2500 times the critical density, r_2500=283(+18/-13)kpc, of 1.02 (+0.21/-0.14)x10^14 M_sun. The gas mass fraction within this radius is f_gas=0.129(+0.015/-0.016). This value is consistent with measurements at lower redshifts and implies minimal evolution in the f_gas(z) relation for hot, massive clusters at 0<z<1.1. The measured metal abundance of 0.42(+0.08/-0.07) Solar is consistent with the abundance observed in other massive, high redshift clusters. The spatially-resolved temperature profile for the cluster shows a drop in temperature, from kT~8 keV to kT~3 keV, in its central regions that is characteristic of cooling core clusters. This is the first spectroscopic identification of a cooling core cluster at z>1. We measure cooling times for the X-ray emitting gas at radii of 50 kpc and 25 kpc of 1.7(+/-0.2)x10^9 years and 7.5(+/-2.6)x 10^8 years, as well as a nominal cooling rate (in the absence of cooling) of 400(+/-190)M_sun/year within the central 100 kpc. In principle, the cooling gas can supply enough fuel to support the growth of the supermassive black hole and to power the luminous quasar. The radiative power of the quasar exceeds by a factor of 10 the kinematic power of the central radio source, suggesting that radiative heating may be important at intermittent intervals in cluster cores.
Ly-alpha emitters (LAEs) are seen everywhere in the redshift domain from local to z~7. Far-infrared (FIR) counterparts of LAEs at different epochs could provide direct clues on dust content, extinction, and spectral energy distribution (SED) for these galaxies. We search for FIR counterparts of LAEs that are optically detected in the GOODS-North field at redshift z~2.2 using data from the Herschel Space Telescope with the Photodetector Array Camera and Spectrometer (PACS). The LAE candidates were isolated via color-magnitude diagram using the medium-band photometry from the ALHAMBRA Survey, ancillary data on GOODS-North, and stellar population models. According to the fitting of these spectral synthesis models and FIR/optical diagnostics, most of them seem to be obscured galaxies whose spectra are AGN-dominated. From the analysis of the optical data, we have observed a fraction of AGN or composite over source total number of ~0.75 in the LAE population at z~2.2, which is marginally consistent with the fraction previously observed at z=2.25 and even at low redshift (0.2<z<0.45), but significantly different from the one observed at redshift ~3, which could be compatible either with a scenario of rapid change in the AGN fraction between the epochs involved or with a non detection of obscured AGN in other z=2-3 LAE samples due to lack of deep FIR observations. We found three robust FIR (PACS) counterparts at z~2.2 in GOODS-North. This demonstrates the possibility of finding dust emission in LAEs even at higher redshifts.
Mirror dark matter offers a framework to explain the existing dark matter direct detection experiments. Here we confront this theory with the most recent experimental data, paying attention to the various known systematic uncertainties, in quenching factor, detector resolution, galactic rotational velocity and velocity dispersion. We perform a detailed analysis of the DAMA and CoGeNT experiments assuming a negligible channeling fraction and find that the data can be fully explained within the mirror dark matter framework. We also show that the mirror dark matter candidate can explain recent data from the CDMS/Ge, EdelweissII and CRESSTII experiments and we point out ways in which the theory can be further tested in the near future.
Inspired by the decaying dark matter (DM) which can explain cosmic ray anomalies naturally, we consider the supersymmetric Standard Model with three right-handed neutrinos (RHNs) and R-parity, and introduce a TeV-scale DM sector with two fields \phi_{1,2} and a $Z_3$ discrete symmetry. The DM sector only interacts with the RHNs via a very heavy field exchange and then we can explain the cosmic ray anomalies. With the second right-handed neutrino N_2 dominant seesaw mechanism at the low scale around 10^4 GeV, we show that \phi_{1,2} can obtain the vacuum expectation values around the TeV scale, and then the lightest state from \phi_{1,2} is the decay DM with lifetime around \sim 10^{26}s. In particular, the DM very long lifetime is related to the tiny neutrino masses, and the dominant DM decay channels to \mu and \tau are related to the approximate \mu-\tau symmetry. Furthermore, the correct DM relic density can be obtained via the freeze-in mechanism, the small-scale problem for power spectrum can be solved due to the decays of the R-parity odd meta-stable states in the DM sector, and the baryon asymmetry can be generated via the soft leptogensis.
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The Durham GALFORM semi-analytical galaxy formation model has been shown to reproduce the observed rest-frame 1500\AA\ luminosity function of galaxies well over the whole redshift range z=5-10. We show that in this model, this galaxy population also emits enough ionizing photons to reionize the Universe by redshift z=10, assuming a modest escape fraction of 20 per cent. The bulk of the ionizing photons is produced in faint galaxies during starbursts triggered by galaxy mergers. The bursts introduce a dispersion up to ~ 5 dex in galaxy ionizing luminosity at a given halo mass. Almost 90 per cent of the ionizing photons emitted at z=10 are from galaxies below the current observational detection limit at that redshift. Photo-ionization suppression of star formation in these galaxies is unlikely to affect this conclusion significantly, because the gas that fuels the starbursts has already cooled out of their host halos. The galaxies that dominate the ionizing emissivity at z=10 are faint, with M_{1500, AB} ~ -16, have low star formation rates, \dot{M_{*}} ~ 0.06 h^{-1} M_sun yr^{-1}, and reside in halos of mass M ~ 10^9 h^{-1} M_sun.
We describe a new, free and open source semi-analytic model of galaxy formation, Galacticus. The Galacticus model was designed to be highly modular to facilitate expansion and the exploration of alternative descriptions of key physical ingredients. We detail the Galacticus engine for evolving galaxies through a merging hierarchy of dark matter halos and give details of the specific implementations of physics currently available in Galacticus. Finally, we show results from an example model that is in reasonably good agreement with several observational datasets. We use this model to explore numerical convergence and to demonstrate the types of information which can be extracted from Galacticus.
Rest-frame UV emission lines offer the exciting possibility to directly image the gas around high-redshift galaxies with upcoming optical instruments. We use a suite of large, hydrodynamical simulations to predict the nature and detectability of emission lines from the intergalactic medium at 2<z<5. The brightest emission comes from H I Ly-alpha and the strongest metal line, C III, is about an order of magnitude fainter. The highest surface brightness regions for C IV, Si III, Si IV and O VI are fainter than the brightest C III by factors of a few. The N V and Ne VIII lines, as well as He II H-alpha, are substantially weaker but their maximum surface brightnesses still exceed 10^2 photon/s/cm^2/sr at z=2. Lower ionisation lines typically arise in denser and colder gas that produces clumpier emission. The brightest H I Ly-alpha emission arises exclusively in highly overdense gas (rho>10^3 rho_mean), but the highest surface brightness emission from high-ionisation metal lines traces a much wider range of overdensities. Bright metal-line emission traces gas with temperatures close to the peak of the corresponding emissivity curve. While H I Ly-alpha, He II H-alpha, C III, Si III, and Si IV are excellent probes of cold accretion flows and the colder parts of outflows, C IV, N V, O VI, and Ne VIII are powerful tracers of the diffuse warm-hot intergalactic medium and galactic winds. A comparison of results from simulations with varying physical prescriptions demonstrates that the predictions for the brighter emission are robust to within factors of a few. The Cosmic Web Imager, operating on Palomar, may be able to detect the emission from C III, C IV, Si III, Si IV and O VI lines at 2<z<3 and H I Ly-alpha emission up to z=5. Emission from higher redshifts and other lines should be within reach of the VLT Multi Unit Spectroscopic Explorer, and of the Keck Cosmic Web Imager. (Abridged)
We present an analysis of the properties of HI holes detected in 20 galaxies that are part of "The HI Nearby Galaxy Survey" (THINGS). We detected more than 1000 holes in total in the sampled galaxies. Where they can be measured, their sizes range from about 100 pc (our resolution limit) to about 2 kpc, their expansion velocities range from 4 to 36 km/s, and their ages are estimated to range between 3 and 150 Myr. The holes are found throughout the disks of the galaxies, out to the edge of the HI; 23% of the holes fall outside R25. We find that shear limits the age of holes in spirals (shear is less important in dwarf galaxies) which explains why HI holes in dwarfs are rounder, on average than in spirals. Shear, which is particularly strong in the inner part of spiral galaxies, also explains why we find that holes outside R25 are larger and older. We derive the scale height of the HI disk as a function of galactocentric radius and find that the disk flares up in all galaxies. We proceed to derive the surface and volume porosity (Q2D and Q3D) and find that this correlates with the type of the host galaxy: later Hubble types tend to be more porous. The size distribution of the holes in our sample follows a power law with a slope of a ~ -2.9. Assuming that the holes are the result of massive star formation, we derive values for the supernova rate (SNR) and star formation rate (SFR) which scales with the SFR derived based on other tracers. If we extrapolate the observed number of holes to include those that fall below our resolution limit, down to holes created by a single supernova, we find that our results are compatible with the hypothesis that HI holes result from star formation.
We constrain the chameleonic Sunyaev--Zel'dovich (CSZ) effect in the Coma cluster from measurements of the Coma radial profile presented in the WMAP 7-year results. The CSZ effect arises from the interaction of a scalar (or pseudoscalar) particle with the cosmic microwave background in the magnetic field of galaxy clusters. We combine this radial profile data with SZ measurements towards the centre of the Coma cluster in different frequency bands, to find Delta T_{SZ,RJ}(0)=-400+/-40 microKelvin and Delta T_{CSZ}^{204 GHz}(0)=-20+/-15 microKelvin (68% CL) for the thermal SZ and CSZ effects in the cluster respectively. The central value leads to an estimate of the photon to scalar (or pseudoscalar) coupling strength of g = (5.2 - 23.8) x 10^{-10} GeV^{-1}, while the 95% confidence bound is estimated to be g < (8.7 - 39.4) x 10^{-10} GeV^{-1}.
The Wide Field X-ray Telescope (WFXT) will provide tens of millions of AGN, with more than 4x10^5 expected at z>3. Here we review the issues present in the identification of (large) samples of faint and high-redshift X-ray sources, and describe a statistical, powerful tool that can be applied to WFXT catalogs. The depth of associated optical and near infrared catalogs, needed for a reliable and as much complete as possible identification, are also discussed, along with the combined synergies with existing or planned facilities
The universe, with large-scale homogeneity, is locally inhomogeneous, clustering into stars, galaxies and larger structures. Such property is described by the smoothness parameter $\alpha$ which is defined as the proportion of matter in the form of intergalactic medium. If we take consideration of the inhomogeneities in small scale, there should be modifications of the cosmological distances compared to a homogenous model. Dyer and Roeder developed a second-order ordinary differential equation (D-R equation) that describes the angular diameter distance-redshift relation for inhomogeneous cosmological models. Furthermore, we may obtain the D-R equation for observational $H(z)$ data (OHD). The density-parameter $\Omega_{\rm M}$, the state of dark energy $\omega$, and the smoothness-parameter $\alpha$ are constrained by a set of OHD in a spatially flat $\Lambda$CDM universe as well as a spatially flat XCDM universe. By using of $\chi^2$ minimization method we get $\alpha=0.81^{+0.19}_{-0.20}$ and $\Omega_{\rm M}=0.32^{+0.12}_{-0.06}$ at $1\sigma$ confidence level. If we assume a Gaussian prior of $\Omega_{\rm M}=0.26\pm0.1$, we get $\alpha=0.93^{+0.07}_{-0.19}$ and $\Omega_{\rm M}=0.31^{+0.06}_{-0.05}$. For XCDM model, $\alpha$ is constrained to $\alpha\geq0.80$ but $\omega$ is weakly constrained around -1, where $\omega$ describes the equation of the state of the dark energy ($p_{\rm X}=\omega\rho_{\rm X}$). We conclude that OHD constrains the smoothness parameter more effectively than the data of SNe Ia and compact radio sources.
The dynamics of expansion and large scale structure formation in the multicomponent Universe with dark energy modeled by the minimally coupled scalar field with generalized linear barotropic equation of state (EoS) are analyzed. It is shown that the past dynamics of expansion and future of the Universe -- eternal accelerated expansion or turnaround and collapse -- are completely defined by the current energy density of a scalar field and relation between its current and early EoS parameters. The clustering properties of such models of dark energy and their imprints in the power spectrum of matter density perturbations depend on the same relation and, additionally, on the "effective sound speed" of a scalar field, defined by its Lagrangian. It is concluded that barotropic scalar fields with different values of these parameters are distinquishible in principle. This gives the possibility to constrain them by confronting the theoretical predictions with the corresponding observational data. For that we have used the 7-year WMAP data on CMB anisotropies, the Union2 dataset on Supernovae Ia and SDSS DR7 data on lumious red galaxies (LRG) space distribution. Using the Markov Chain Monte Carlo technique the marginalised posterior and mean likelihood distributions are computed for the scalar fields with two different Lagrangians: Klein-Gordon and Dirac-Born-Infeld ones. The properties of such scalar field models of dark energy with best fitting parameters and uncertainties of their determination are also analyzed in the paper.
Certain covariant theories of the modified Newtonian dynamics paradigm seem to require an additional hot dark matter (HDM) component - either in form of heavy ordinary neutrinos or more recently light sterile neutrinos (SNs) with a mass around 11eV - to be relieved of problems ranging from cosmological scales down to intermediate ones relevant for galaxy clusters. Here we suggest using gravitational lensing by galaxy clusters to test such a "marriage" of neutrino HDM and modified gravity, adopting the framework of tensor-vector-scalar theory (TeVeS). Unlike conventional cold dark matter (CDM), such HDM is subject to strong phase-space constraints, which allows to check cluster lens models inferred within the modified framework for consistency. Since the considered HDM particles cannot collapse into arbitrarily dense clumps and only form structures well above the galactic scale, systems which indicate the need for dark substructure are of particular interest. As a first example, we study the cluster lens Abell 2390 and its impressive straight arc with help of numerical simulations. Based on our results, we outline a general and systematic approach to model cluster lenses in TeVeS which significantly reduces the calculation complexity. We further consider a simple bimodal lens configuration, capable of producing the straight arc, to demonstrate our approach. We find that such a model is marginally consistent with the hypothesis of 11eV SNs. Future work including more detailed and realistic lens models may further constrain the necessary SN distribution and help to conclusively assess this point. Cluster lenses could therefore provide an interesting discriminator between CDM and such modified gravity scenarios supplemented by SNs or other choices of HDM.
Particles with TeV mass and strong self-interactions generically have the right annihilation cross section to explain an observed excess of cosmic electrons and positrons if the end-product of the annihilation is charged leptons. We present an explicit model of strongly-coupled TeV-scale dark matter whose relic abundance related to the matter-antimatter asymmetry of the observed universe. The B - L asymmetry of the standard model is transfered to the dark sector by an operator carrying standard model lepton number. Lepton number violation naturally induces dark matter particle-antiparticle oscillations at late times, allowing dark matter-antimatter annihilations today. The dark matter annihilates into lighter strongly-interacting particles in the dark sector that decay to leptons via the transfer operator. The strong dynamics in the dark sector is at the weak scale due to supersymmetry breaking. The correct dark matter abundance is automatically obtained for natural values of dimensionless parameters, analogous to the situation for conventional WIMPs.
We numerically solve the mass-less test scalar field equation on the space-time background of boson stars and black holes. In order to do so, we use a numerical domain that contains future null infinity. We achieve this construction using a scri-fixing conformal compactification technique based on hyperboloidal constant mean curvature foliations of the space-time and solve the conformally invariant wave equation. We present two results: the scalar field shows oscillations of the quasi- normal-mode type found for black holes only for boson star configurations that are compact, and no signs of tail decay is found in the parameter space we explored. Even though our results do not correspond to the master equation of perturbations of boson star solutions, they indicate that the parameter space of boson stars as black hole mimickers is restricted to compact configurations.
We explore dark matter mechanisms that can simultaneously explain the galactic 511 keV gamma rays observed by INTEGRAL/SPI, the DAMA/LIBRA annual modulation, and the excess of low-recoil dark matter candidates observed by CoGeNT. It requires three nearly degenerate states of dark matter in the 4-7 GeV mass range, with splittings respectively of order an MeV and a few keV. The top two states have the small mass gap and transitions between them, either exothermic or endothermic, can account for direct detections. Decays from one of the top states to the ground state produce low-energy positrons in the galaxy whose associated 511 keV gamma rays are seen by INTEGRAL. This decay can happen spontaneously, if the excited state is metastable (longer-lived than the age of the universe), or it can be triggered by inelastic scattering of the metastable states into the shorter-lived ones. We focus on a simple model where the DM is a triplet of an SU(2) hidden sector gauge symmetry, broken at the scale of a few GeV, giving masses of order \lsim 1 GeV to the dark gauge bosons, which mix kinetically with the standard model hypercharge. The purely decaying scenario can give the observed angular dependence of the 511 keV signal with no positron diffusion, while the inelastic scattering mechanism requires transport of the positrons over distances \sim 1 kpc before annihilating. We note that an x-ray line of several keV in energy, due to single-photon decays involving the top DM states, could provide an additional component to the diffuse x-ray background. The model is testable by proposed low-energy fixed target experiments.
A discrepancy has emerged between the cosmic lithium abundance inferred by
the WMAP satellite measurement coupled with the prediction of the standard
big-bang nucleosynthesis theory, and the constant Li abundance measured in
metal-poor halo dwarf stars (the so-called Spite plateau). Several models are
being proposed to explain this discrepancy, involving either new physics, in
situ depletion, or the efficient depletion of Li in the pristine Galaxy by a
generation of massive first stars. The realm of possibilities may be narrowed
considerably by observing stellar populations in different galaxies, which have
experienced different evolutionary histories.
The WCen stellar system is commonly considered as the remnant of a dwarf
galaxy accreted by the Milky Way (MW). We investigate the Li content of a
conspicuous sample of unevolved stars in this object.
We obtained moderate resolution (R=17000) spectra for 91 main-sequence/early
sub-giant branch (MS/SGB) WCen stars using the FLAMES-GIRAFFE/VLT spectrograph.
Li abundances were derived by matching the equivalent width of the LiI
resonance doublet at 6708A, to the prediction of synthetic spectra computed
with different Li abundances. Synthetic spectra were computed using the SYNTHE
code along with ATLAS9 model atmospheres. The stars effective temperatures are
derived by fitting the wings of the Ha line with synthetic profiles.
We obtain a mean content of A(Li)=2.19+-0.14~dex for WCen MS/SGB stars. This
is comparable to what is observed in Galactic halo field stars of similar
metallicities and temperatures.
The Spite plateau seems to be an ubiquitous feature of old, warm metal-poor
stars. It exists also in external galaxies, if we accept the current view about
the origin of WCen. This implies that the mechanism(s) that causes the
"cosmological lithium problem" may be the same in the MW and other galaxies.
The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept for an 8-meter to 16-meter UVOIR space observatory for launch in the 2025-2030 era. ATLAST will allow astronomers to answer fundamental questions at the forefront of modern astronphysics, including "Is there life elsewhere in the Galaxy?" We present a range of science drivers that define the main performance requirements for ATLAST (8 to 16 milliarcsec angular resolution, diffraction limited imaging at 0.5 {\mu}m wavelength, minimum collecting area of 45 square meters, high sensitivity to light wavelengths from 0.1 {\mu}m to 2.4 {\mu}m, high stability in wavefront sensing and control). We will also discuss the synergy between ATLAST and other anticipated future facilities (e.g., TMT, EELT, ALMA) and the priorities for technology development that will enable the construction for a cost that is comparable to current generation observatory-class space missions.
We study the bounds on tensor wave in a class of twisted inflation models where $D(4+2k)$-branes are wrapped on cycles in the compact manifold and wrap the KK-direction in the corresponding effective field theory. While the lower bound is found to be analogous to that in Type IIB models of brane inflation, the upper bound turns out to be significantly different. This is argued for a range of values for the parameter $g_s M$ satisfying the self-consistency relation and the WMAP data. Further, we observe that the wrapped $D8$-brane appears to be the most attractive from a cosmological perspective.
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Using a generalized self-similar secondary infall model, which accounts for tidal torques acting on the halo, we analyze the velocity profiles of halos in order to gain intuition for N-body simulation results. We analytically calculate the asymptotic behavior of the internal radial and tangential kinetic energy profiles in different radial regimes. We then numerically compute the velocity anisotropy and pseudo-phase-space density profiles and compare them to recent N-body simulations. For cosmological initial conditions, we find both numerically and analytically that the anisotropy profile asymptotes at small radii to a constant set by model parameters. It rises on intermediate scales as the velocity dispersion becomes more radially dominated and then drops off at radii larger than the virial radius where the radial velocity dispersion vanishes in our model. The pseudo-phase-space density is universal on intermediate and large scales. However, its asymptotic slope on small scales depends on the halo mass and on how mass shells are torqued after turnaround. The results largely confirm N-body simulations but show some differences that are likely due to our assumption of a one-dimensional phase space manifold.
The observation of a broad excess of sub-TeV cosmic rays compatible with the direction of the heliospheric tail (Nagashima et al. 1998) and the discovery of two significant localized excess regions of multi-TeV cosmic rays by the MILAGRO collaboration (Abdo et al. 2008), also from the same region of the sky, have raised questions on their origin. In particular, the coincidence of the most significant localized region with the direction of the heliospheric tail and the small angular scale of the observed anisotropy (~ 10deg) is suggestive a local origin and of a possible connection to the low energy broad excess. Cosmic ray acceleration from magnetic reconnection in the magnetotail is proposed as a possible source of the energetic particles.
The power of a relativistic jet depends on the number of leptons and protons carried by the jet itself. We have reasons to believe that powerful gamma-ray flat spectrum radio sources emit most of their radiation where radiative cooling is severe. This helps to find the minimum number of emitting leptons needed to explain the radiation we see. The number of protons is more uncertain. If there is one proton per electron, they dominate the jet power, but they could be unimportant if the emission is due to electron-positron pairs. In this case the total jet power could be much smaller. However, if the gamma-ray flux is due to inverse Compton scattering with seed photons produced outside the jet, the radiation is anisotropic also in the comoving frame, making the jet to recoil. This Compton rocket effect is strong for light, electron-positron jets, and negligible for heavy, proton dominated jets. No significant deceleration, required by fast superluminal motion, requires a minimum number of protons per lepton, and thus a minimum jet power. We apply these ideas to the blazar 3C 454.3, to find a robust lower limit to its total jet power: if the viewing angle theta_v ~ 1/Gamma the jet power is larger than the accretion luminosity L_d for any bulk Lorentz factor Gamma. For theta_v =0, instead, the minimum jet power can be smaller than L_d for Gamma<25. No more than ~10 pairs per proton are allowed.
We present an application of the da Cunha, Charlot & Elbaz (2008) model of the spectral energy distribution (SEDs) of galaxies from the ultraviolet to far-infrared to a small pilot sample of purely star-forming Ultra-Luminous Infrared Galaxies (ULIRGs). We interpret the observed SEDs of 16 ULIRGs using this physically-motivated model which accounts for the emission of stellar populations from the ultraviolet to the near-infrared and for the attenuation by dust in two components: an optically-thick starburst component and the diffuse ISM. The infrared emission is computed by assuming that all the energy absorbed by dust in these components is re-radiated at mid- and far-infrared wavelengths. This model allows us to derive statistically physical properties including star formation rates, stellar masses, as well as temperatures and masses of different dust components and plausible star formation histories. We find that, although the ultraviolet to near-infrared emission represents only a small fraction of the total power radiated by ULIRGs, observations in this wavelength range are important to understand the properties of the stellar populations and dust attenuation in the diffuse ISM of these galaxies. Furthermore, our analysis indicates that the use of mid-infrared spectroscopy from the Infrared Spectrograph on the Spitzer Space Telescope is crucial to obtain realistic estimates of the extinction to the central energy source, mainly via the depth of the 9.7-micron silicate feature, and thus accurately constrain the total energy balance. Our findings are consistent with the notion that, in the local Universe, the physical properties of ULIRGs are fundamentally different from those of galaxies with lower infrared luminosities and that local ULIRGs are the result of merger-induced starbursts. [abridged]
What do advanced Josephson junction technologies, SQUIDs, coupled Josephson qubits and related superconducting devices used in nanotechnology have in common with the problem of dark matter in the early universe? A lot more than might seem obvious at first sight, as will be shown in this letter. One of the major candidates for dark matter in the universe is the axion. The equation of motion of the axion misalignment angle and that of the phase difference in a Josephson junction are identical if the symbols in the mathematical equations are properly re-interpreted. This allows for analogue simulation of early-universe physics using superconducting electronic devices such as SQUIDs and Josephson junctions. It also allows for new experimental setups that test axionic interaction strengths in a Josephson junction environment, similar in nature to recent experiments that test for quantum entanglement of two coupled Josephson qubits. The parameter values relevant for early-universe axion cosmology are accessible with present day's achievements in nanotechnology.
Studying molecular gas properties in merging galaxies gives important clues
to the onset and evolution of interaction-triggered starbursts. The CO/13CO 1-0
line intensity ratio can be used as a tracer of how dynamics and star formation
processes impact the gas properties. The Medusa (NGC~4194) merger is
particularly interesting to study since its LFIR/LCO ratio rivals that of
ultraluminous galaxies (ULIRGs), despite the comparatively modest luminosity,
indicating an exceptionally high star formation efficiency (SFE) in the Medusa
merger.
Interferometric OVRO observations of CO and 13CO 1-0 in the Medusa show the
CO/13CO intensity ratio increases from normal, quiescent values (7-10) in the
outer parts (r>2 kpc) of the galaxy to high (16 to >40) values in the central
(r<1 kpc) starburst region. In the centre there is an east-west gradient where
the line ratio changes by more than a factor of three over 5" (945 pc). The
integrated 13CO emission peaks in the north-western starburst region while the
central CO emission is strongly associated with the prominent crossing
dust-lane. We discuss the central east-west gradient in the context of gas
properties in the starburst and the central dust lane. We suggest that the
central gradient is mainly caused by diffuse gas in the dust lane. In this
scenario, the actual molecular mass distribution is better traced by the 13CO
1-0 emission than the CO. The possibilities of temperature and abundance
gradients are also discussed. We compare the central gas properties of the
Medusa to those of other minor mergers and suggest that the extreme and
transient phase of the Medusa star formation activity has similar traits to
those of high-redshift galaxies.
The "Extreme starbursts in the local universe" workshop was held at the Insituto de Astrofisica de Andalucia in Granada, Spain on 21-25 June 2010. Bearing in mind the advent of a new generation of facilities such as JWST, Herschel, ALMA, eVLA and eMerlin, the aim of the workshop was to bring together observers and theorists to review the latest results. The purpose of the workshop was to address the following issues: what are the main modes of triggering extreme starbursts in the local Universe? How efficiently are stars formed in extreme starbursts? What are the star formation histories of local starburst galaxies? How well do the theoretical simulations model the observations? What can we learn about starbursts in the distant Universe through studies of their local counterparts? How important is the role of extreme starbursts in the hierarchical assembly of galaxies? How are extreme starbursts related to the triggering of AGN in the nuclei of galaxies? Overall, 41 talks and 4 posters with their corresponding 10 minutes short talks were presented during the workshop. In addition, the workshop was designed with emphasis on discussions, and therefore, there were 6 discussion sessions of up to one hour during the workshop. Here is presented a summary of the purposes of the workshop as well as a compilation of the abstracts corresponding to each of the presentations. The summary and conclusions of the workshop along with a description of the future prospects by Sylvain Veilleux can be found in the last section of this document. A photo of the assistants is included.
We study the expected properties of starbursts in order to provide the point of reference for interpretation of high-z galaxy surveys and of very metal-poor galaxies. We concentrate mainly on the UV characteristics such as the ionizing spectra, the UV continuum, the Ly alpha and HeII 1640 A line and two-photon continuum emission. We use evolutionary synthesis models covering metallicities from Pop III to solar and a wide range of IMFs. We also combine the synthetic SEDs with the CLOUDY photoionization code for more accurate predictions of nebular emission, and to study possible departures from case B assumed in the synthesis models. The ionizing fluxes, UV continuum properties, and predicted Ly alpha and HeII 1640 A line strengths are presented for synthesis models covering a wider range of parameter space than our earlier calculations. Strong departures from case B predictions are obtained for Ly alpha and two-photon continuum at low metallicities. At low nebular densities both are shown to be enhanced proportionally to the mean energy carried by the Lyman continuum photons emitted by the ionizing source. Larger Ly alpha equivalent widths are therefore predicted at low metallicity. The HeII 1640 A line can be weaker than case B predicts (in terms of flux as well as the equivalent width) due to its ionization parameter dependence and to the enhanced underlying two-photon continuum. Our results have implications for the interpretation of star-forming metal-poor and/or high redshift galaxies, for galaxies among the Ly alpha emitters (LAE) and Lyman Break galaxy (LBG) populations, and for searches of Population III stars in the distant Universe.
Observations of H$_2$O masers from circumnuclear disks in active galaxies for the Megamaser Cosmology Project allow accurate measurement of the mass of supermassive black holes (BH) in these galaxies. We present the Very Long Baseline Interferometry (VLBI) images and kinematics of water maser emission in six active galaxies: NGC~1194, NGC~2273, NGC~2960 (Mrk~1419), NGC~4388, NGC~6264 and NGC~6323. We use the Keplerian rotation curves of these six megamaser galaxies, plus a seventh previously published, to determine accurate enclosed masses within the central $\sim0.3$ pc of these galaxies, smaller than the radius of the sphere of influence of the central mass in all cases. We also set lower limits to the central mass densities of between 0.12 and 60 $\times 10^{10} M_{\odot}$~pc$^{-3}$. For six of the seven disks, the high central densities rule out clusters of stars or stellar remnants as the central objects, and this result further supports our assumption that the enclosed mass can be attributed predominantly to a supermassive black hole. The seven BHs have masses ranging between 0.76 and 6.5$\times$10$^7 M_{\odot}$. The BH mass errors are $\approx11$\%, dominated by the uncertainty of the Hubble constant. We compare the megamaser BH mass determination with other BH mass measurement techniques. The BH mass based on virial estimation in four galaxies is consistent with the megamaser BH mass given the latest empirical value of $\langle f \rangle$, but the virial mass uncertainty is much greater. MCP observations continue and we expect to obtain more maser BH masses in the future.
[Abridged] To investigate the evolution in the relation between galaxy stellar and central black hole mass we construct a volume limited complete sample of 85 AGN with host galaxy stellar masses M_{*} > 10^{10.5} M_{sol}, and specific X-ray luminosities L_{X} > 2.35 x 10^{43} erg s^{-1} at 0.4 < z < 3. We calculate the Eddington limiting masses of the supermassive black holes residing at the centre of these galaxies, and observe an increase in the average Eddington limiting black hole mass with redshift. By assuming that there is no evolution in the Eddington ratio (\mu) and then that there is maximum possible evolution to the Eddington limit, we quantify the maximum possible evolution in the M_{*} / M_{BH} ratio as lying in the range 700 < M_{*}/M_{BH} < 10000, compared with the local value of M_{*}/M_{BH} ~ 1000. We furthermore find that the fraction of galaxies which are AGN (with L_{X} > 2.35 x 10^{43} erg s^{-1}) rises with redshift from 1.2 +/- 0.2 % at z = 0.7 to 7.4 +/- 2.0 % at z = 2.5. We use our results to calculate the maximum timescales for which our sample of AGN can continue to accrete at their observed rates before surpassing the local galaxy-black hole mass relation. We use these timescales to calculate the total fraction of massive galaxies which will be active (with L_{X} > 2.35 x 10^{43} erg s^{-1}) since z = 3, finding that at least ~ 40% of all massive galaxies will be Seyfert luminosity AGN or brighter during this epoch. Further, we calculate the energy density due to AGN activity in the Universe as 1.0 (+/- 0.3) x 10^{57} erg Mpc^{-3} Gyr^{-1}, potentially providing a significant source of energy for AGN feedback on star formation. We also use this method to compute the evolution in the X-ray luminosity density of AGN with redshift, finding that massive galaxy Seyfert luminosity AGN are the dominant source of X-ray emission in the Universe at z < 3.
We investigate phantom cosmology in which the scale factor is a power law, and we use cosmological observations from Cosmic Microwave Background (CMB), Baryon Acoustic Oscillations (BAO) and observational Hubble data, in order to impose complete constraints on the model parameters. We find that the power-law exponent is $\beta\approx-6.51^{+0.24}_{-0.25}$, while the Big Rip is realized at $t_s\approx104.5^{+1.9}_{-2.0}$ Gyr, in 1$\sigma$ confidence level. Providing late-time asymptotic expressions, we find that the dark-energy equation-of-state parameter at the Big Rip remains finite and equal to $w_{DE}\approx -1.153$, with the dark-energy density and pressure diverging. Finally, we reconstruct the phantom potential.
We study the simulated CO emission from elliptical galaxies formed in the mergers of gas-rich disk galaxies. The cold gas not consumed in the merger-driven starburst quickly resettles into a disk-like configuration. By analyzing a variety of arbitrary merger orbits that produce a range of fast to slow-rotating remnants, we find that molecular disk formation is a fairly common consequence of gas-rich galaxy mergers. Hence, if a molecular disk is observed in an early-type merger remnant, it is likely the result of a "wet merger" rather than a "dry merger". We compare the physical properties from our simulated disks (e.g. size and mass) and find reasonably good agreement with recent observations. Finally, we discuss the detectability of these disks as an aid to future observations.
In this study we predict the total distributions of powerful (FR II) active double-lobed radio galaxies and ghost sources, and their observable distribution in the X-ray sky. We develop an analytic model for the evolution of the lobe emission at radio and X-ray energies. During jet activity, a double radio source emits synchrotron radiation in the radio and X-ray emission due to inverse-Compton (IC) upscattering by gamma~10^3 electrons of the cosmic microwave background. After the jets switch off, the radio luminosity (due to higher gamma electrons) falls faster than the X-ray luminosity and for some time the source appears as an IC ghost of a radio galaxy before becoming completely undetectable in the X-ray. With our model, for one set of typical parameters, we predict radio lobes occupy a volume fraction of the universe of 0.01, 0.03, 0.3 at z=2 (during the quasar era) of the filamentary structures in which they are situated, for typical jet lifetimes 5*10^7 yr, 10^8 yr, 5*10^8 yr; however since the inferred abundance of sources depends on how quickly they fall below the radio flux limit the volume filling factor is found to be a strong function of radio galaxy properties such as energy index and minimum gamma factor of injected particles, the latter not well constrained by observations. We test the predicted number density of sources against the Chandra X-ray Deep Field North survey and also find the contribution to the unresolved cosmic X-ray background by the lobes of radio galaxies. 10-30 per cent of observable double-lobed structures in the X-ray are predicted to be IC ghosts. The derived X-ray luminosity function of our synthetic population shows that double-lobed sources have higher space densities than X-ray clusters at redshifts z>2 and X-ray luminosities above 10^44 erg s^-1.
We propose a dark matter model in which the signal in direct detection experiments arises from electromagnetic, not nuclear, energy deposition. This can provide a novel explanation for DAMA while avoiding many direct detection constraints. The dark matter state is taken nearly degenerate with another state. These states are naturally connected by a dipole moment operator, which can give both the dominant scattering and decay modes between the two states. The signal at DAMA then arises from dark matter scattering in the Earth into the excited state and decaying back to the ground state through emission of a single photon in the detector. This model has unique signatures in direct detection experiments. The density and chemical composition of the detector is irrelevant, only the total volume affects the event rate. In addition, the spectrum is a monoenergetic line, which can fit the DAMA signal well. This model is readily testable at experiments such as CDMS and XENON100 if they analyze their low-energy, electronic recoil events.
We study critical black hole separations for the formation of a common apparent horizon in systems of $N$ - black holes in a time symmetric configuration. We study in detail the aligned equal mass cases for $N=2,3,4,5$, and relate them to the unequal mass binary black hole case. We then study the apparent horizon of the time symmetric initial geometry of a ring singularity of different radii. The apparent horizon is used as indicative of the location of the event horizon in an effort to predict a critical ring radius that would generate an event horizon of toroidal topology. We found that a good estimate for this ring critical radius is $20/(3\pi) M$. We briefly discuss the connection of this two cases through a discrete black hole 'necklace' configuration.
We used a sample of 11 nearby relaxed clusters of galaxies observed with the X-ray instruments XMM-Newton (EPIC) pn and MOS, Chandra ACIS-S and ACIS-I and BeppoSAX MECS to examine the cross-calibration of the energy dependence and normalisation of the effective area of these instruments as of December 2009. We also examined the Fe XXV/XXVI line ratio temperature measurement method for the pn and MOS. We performed X-ray spectral analysis on the XMM-Newton and Chandra data for a sample of 11 clusters. We obtained the information for BeppoSAX from DeGrandi & Molendi (2002). We compared the spectroscopic results obtained with different instruments for the same clusters in order to examine possible systematic calibration effects between the instruments. We did not detect any significant systematic differences between the temperatures derived in the 2-7 keV band using the different instruments. Also, the EPIC temperatures derived from the bremsstrahlung continuum agreed with those obtained from the Fe XXV/XXVI emission line ratio, implying that the energy dependence of the hard band effective area of the above instruments is accurately calibrated. On the other hand, the hard band EPIC/ACIS fluxes disagreed by 5-10% (i.e. at 6-25 sigma level) which indicates a similar level of uncertainty in the normalisations of the effective areas of these instruments in the 2--7 keV band. In the soft energy band (0.5-2.0 keV) there are greater cross-calibration differences between EPIC and ACIS. Due to the high statistical weight of the soft band data, the 0.5-7.0 keV band temperature measurements of clusters of galaxies with EPIC or ACIS are uncertain by ~10-15% on average.
We show that modified gravity presents distinctive nonlinear features on the Cosmic Microwave Background (CMB) anisotropies comparing with General Relativity (GR). We calculate the contribution to the CMB non-Gaussianity from nonlinear Sachs-Wolfe effect in $f(R)$ gravity and show that, contrary to GR's contribution which is typically $\lesssim \mathcal{O}(1)$, the contribution in $f(R)$ gravity is sensitive to the nonlinear structure of $f(R)$ and can be large in principle. Optimistically, this gives an alternative origin for the possibly observed large CMB non-Gaussianities besides the primordial ones. On the other hand, such nonlinear features can be employed to provide a new cosmological test of $f(R)$ or other modified theories of gravitation, which is unique and is independent of previously known tests.
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