Several scenarios have been suggested to explain the phase-space distribution of the Milky Way (MW) satellite galaxies in a disc of satellites (DoS). To quantitatively compare these different possibilities, a new method analysing angular momentum directions in modelled data is presented. It determines how likely it is to find sets of angular momenta as concentrated and as close to a polar orientation as is observed for the MW satellite orbital poles. The method can be easily applied to orbital pole data from different models. The observed distribution of satellite orbital poles is compared to published angular momentum directions of subhalos derived from six cosmological state-of-the-art simulations in the Aquarius project. This tests the possibility that filamentary accretion might be able to naturally explain the satellite orbits within the DoS. For the most likely alignment of main halo and MW disc spin, the probability to reproduce the MW satellite orbital pole properties turns out to be less than 0.5 per cent in Aquarius models. Even an isotropic distribution of angular momenta has a higher likelihood to produce the observed distribution. The two Via Lactea cosmological simulations give results similar to the Aquarius simulations. Comparing instead with numerical models of galaxy-interactions gives a probability of up to 90 per cent for some models to draw the observed distribution of orbital poles from the angular momenta of tidal debris. This indicates that the formation as tidal dwarf galaxies in a single encounter is a viable, if not the only, process to explain the phase-space distribution of the MW satellite galaxies.
We use distance measurements in the nearby universe to carry out new tests of gravity, surpassing other astrophysical tests by over two orders of magnitude for chameleon theories. The three nearby distance indicators -- cepheids, tip of the red giant branch (TRGB) stars, and water masers -- operate in gravitational fields of widely different strengths. This enables tests of scalar-tensor gravity theories because they are screened from enhanced forces to different extents. Inferred distances from cepheids and TRGB stars are altered in opposite directions over a range of chameleon gravity theory parameters, well below the sensitivity of cosmological probes. Using published data we have compared cepheid and TRGB distances in a sample of unscreened dwarf galaxies within 10 Mpc. As a control sample we use a comparable set of screened galaxies. We find no evidence for the order unity force enhancements expected in these theories. Using a two-parameter description of the models (the coupling strength and background field value) we obtain constraints on chameleon theories as well as symmetron and dilaton screening scenarios. In particular we show that f(R) models with background field values fR0 above 5e-7 are ruled out at the 95% confidence level. We also compare TRGB and maser distances to the galaxy NGC 4258 as a second test for larger field values. While there are several approximations and caveats in our study, our analysis demonstrates the power of gravity tests in the local universe. We discuss the prospects for additional, improved tests with future observations.
Astrophysical tests of modified modified gravity theories in the nearby universe have been emphasized recently by Hui, Nicolis and Stubbs (2009) and Jain and VanderPlas (2011). A key element of such tests is the screening mechanism whereby general relativity is restored in massive halos or high density environments like the Milky Way. In chameleon theories of gravity, including all f(R) models, field dwarf galaxies may be unscreened and therefore feel an extra force, as opposed to screened galaxies. The first step to study differences between screened and unscreened galaxies is to create a 3D screening map. We use N-body simulations to test and calibrate simple approximations to determine the level of screening in galaxy catalogs. Sources of systematic errors in the screening map due to observational inaccuracies are modeled and their contamination is estimated. We then apply our methods to create a map out to 200 Mpc in the Sloan Digital Sky Survey footprint using data from the Sloan survey and other sources. In two companion papers this map will be used to carry out new tests of gravity using distance indicators and the disks of dwarf galaxies. We also make our screening map publicly available.
Broad absorption lines (BALs) in quasar spectra identify high velocity outflows that likely exist in all quasars and could play a major role in feedback to galaxy evolution. Studying the variability in these BALs can help us understand the structure, evolution, and basic physical properties of these outflows. We are conducting a BAL monitoring program, which so far includes 163 spectra of 24 luminous quasars, covering time-scales from \sim 1 week to 8 years in the quasar rest-frame. We investigate changes in both the CIV {\lambda}1550 and SiIV {\lambda}1400 BALs, and we report here on some of the results from this program.
Upcoming high spectral resolution telescopes, particularly Astro-H, are expected to finally deliver firm quantitative constraints on turbulence in the intra-cluster medium (ICM). We develop a new spectral analysis technique which exploits not just the line width but the entire line shape, and show how the excellent spectral resolution of Astro-H can overcome its relatively poor spatial resolution in making detailed infer- ences about the velocity field. The spectrum is decomposed into distinct components, which can be quantitatively analyzed using Gaussian mixture models. For instance, bulk flows and sloshing produce components with offset means, while partial volume- filling turbulence from AGN or galaxy stirring leads to components with different widths. The offset between components allows us to measure gas bulk motions and separate them from small-scale turbulence, while component fractions and widths con- strain the emission weighted volume and turbulent energy density in each component. We apply mixture modeling to a series of analytic toy models as well as numerical simu- lations of clusters with cold fronts and AGN feedback respectively. From Markov Chain Monte Carlo and Fisher matrix estimates which include line blending and continuum contamination, we show that the mixture parameters can be accurately constrained with Astro-H spectra: at a \sim 10% level when components differ significantly in width, and a \sim 1% level when they differ significantly in mean value. We also study error scalings and use information criteria to determine when a mixture model is preferred. Mixture modeling of spectra is a powerful technique which is potentially applicable to other astrophysical scenarios.
The inflationary scenario has become the paradigm of early universe cosmology, and - in conjuction with ideas from superstring theory - has led to speculations about an "inflationary multiverse". From a point of view of phenomenology, the inflationary universe scenario has been very successful. However, the scenario suffers from some conceptual problems, and thus it does not (yet) have the status of a solid theory. There are alternative ideas for the evolution of the very early universe which do not involve inflation but which agree with most current cosmological observations as well as inflation does. In this lecture I will outline the conceptual problems of inflation and introduce two alternative pictures - the "matter bounce" and "string gas cosmology", the latter being a realization of the "emergent universe" scenario based on some key principles of superstring theory. I will demonstrate that these two alternative pictures lead to the same predictions for the power spectrum of the observed large-scale structure and for the angular power spectrum of cosmic microwave background anisotropies as the inflationary scenario, and I will mention predictions for future observations with which the three scenarios can be observationally teased apart.
We examine scatter and bias in weak lensing selected clusters, employing both analytic models of dark matter haloes and numerical mock data of weak lensing cluster surveys. We pay special attention to effects of the diversity of dark matter distributions within clusters. We examine the dependence of the halo shape on the peak heights, and find that the root-mean-square scatter caused by the halo diversity scales linearly with the peak heights with the proportionality factor of 0.1-0.2. The noise originates from the halo shape is found to be comparable to the source galaxy shape noise and the cosmic shear noise. We find the significant halo orientation bias, i.e., weak lensing selected clusters on average have their major axes aligned with the line-of-sight direction, and that the orientation bias is stronger for higher signal-to-noise ratio peaks. We compute the orientation bias using an analytic triaxial halo model and obtain results quite consistent with the ray-tracing results. We develop a prescription to analytically compute the number count of weak lensing peaks taking into account all the main sources of scatters in peak heights. We find that the improved analytic predictions agree well with the simulation results for high peaks of SN>5. We also compare the expected number count with our weak lensing analysis results for 4 sq deg of Subaru/Suprime-cam observations and find a good agreement.
In this paper we investigate the possible direct, non-gravitational interaction between holographic dark energy (HDE) and dark matter. Firstly, we start with two simple models with the interaction terms $Q \propto \rho_{dm}$ and $Q \propto \rho_{de}$, and then we move on to the general form $Q \propto \rho_m^\alpha\rho_{de}^\beta$. The cosmological constraints of the models are obtained from the joint analysis of the present Union2.1+BAO+CMB+$H_0$ data. We find that the data slightly favor an energy flow from dark matter to dark energy, although the original HDE model still lies in the 95.4% confidence level (CL) region. For all models we find $c<1$ at the 95.4% CL. We show that compared with the cosmic expansion, the effect of interaction on the evolution of $\rho_{dm}$ and $\rho_{de}$ is smaller, and the relative increment (decrement) amount of the energy in the dark matter component is constrained to be less than 9% (15%) at the 95.4% CL. By introducing the interaction, we find that even when $c<1$ the big rip still can be avoided due to the existence of a de Sitter solution at $z\rightarrow-1$. We show that this solution can not be accomplished in the two simple models, while for the general model such a solution can be achieved with a large $\beta$, and the big rip may be avoided at the 95.4% CL.
A new upper limit on the amplitude of primordial magnetic field (PMF) is derived by a comparison between a calculation of elemental abundances in big bang nucleosynthesis (BBN) model and the latest observational constraints on the abundances. Updated nuclear reaction rates are adopted in the calculation. Effects of PMF on the abundances are consistently taken into account in the numerical calculation with the precise formulation of changes in physical variables. We find that abundances of 3He and 6Li increase while that of 7Li decreases when the PMF amplitude increases, in the case of the baryon-to-photon ratio determined from the measurement of cosmic microwave background radiation. We derive a constraint on the present amplitude of PMF, i.e., B(0)<2.2 micro G [corresponding to the amplitude less than 3.0x10^{11} G at BBN temperature of T=10^9 K] based on the rigorous calculation.
We show that the parameter space of axion-like particles can be severly constrained using high-precision measurements of quasar polarisations. Robust limits are derived from the measured bounds on optical circular polarisation and from the distribution of linear polarisations of quasars. As an outlook, this technique can be improved by the observation of objects located behind clusters of galaxies, using upcoming space-borne X-ray polarimeters.
We present a study of the cavity system in the galaxy cluster RBS 797 based on Chandra and VLA data. RBS 797 (z = 0.35), is one of the most distant galaxy clusters in which two pronounced X-ray cavities have been discovered. The Chandra data confirm the presence of a cool core and indicate an higher metallicity along the cavity directions. This is likely due to the AGN outburst, which lifts cool metal-rich gas from the center along the cavities, as seen in other systems. We find indications that the cavities are hotter than the surrounding gas. Moreover, the new Chandra images show bright rims contrasting with the deep, X-ray deficient cavities. The likely cause is that the expanding 1.4 GHz radio lobes have displaced the gas, compressing it into a shell that appears as bright cool arms. Finally we show that the large-scale radio emission detected with our VLA observations may be classified as a radio mini-halo, powered by the cooling flow (CF), as it nicely follows the trend P_radio vs. P_CF predicted by the re-acceleration model.
We present a catalog of 37842 quasars in the Sloan Digital Sky Survey (SDSS) Data Release 7, which have counterparts within 6$"$ in the Wide-field Infrared Survey Explorer (WISE) Preliminary Data Release. The overall WISE detection rate of the SDSS quasars is 86.7%, and it decreases to less than 50.0% when the quasar magnitude is fainter than $i=20.5$. We derive the median color-redshift relations based on this SDSS-WISE quasar sample and apply them to estimate the photometric redshifts of the SDSS-WISE quasars. We find that by adding the WISE W1 and W2-band data to the SDSS photometry we can increase the photometric redshift reliability, defined as the percentage of sources with the photometric and spectroscopic redshift difference less than 0.2, from 70.3% to 77.2%. We also obtain the samples of WISE detected normal and late-type stars with SDSS spectroscopy, and present a criterion in the $z-W1$ vs. $g-z$ color-color diagram, $z-W1>0.66(g-z)+2.01$, to separate quasars from stars. With this criterion we can recover 98.6% of 3089 radio-detected SDSS-WISE quasars with redshifts less than 4 and overcome the difficulty in selecting quasars with redshifts between 2.2 and 3 from the SDSS photometric data alone. We also suggest another criterion involving the WISE color only, $W1-W2>0.57$, to efficiently separate quasars with redshifts less than 3.2 from stars. In addition, we compile a catalog of 5614 SDSS quasars detected by both WISE and UKIDSS surveys and present their color-redshift relations in the optical and infrared bands. By using the SDSS $ugriz$, UKIDSS YJHK and WISE W1 and W2 band photometric data, we can efficiently select quasar candidates and increase the photometric redshift reliability up to 87.0%. We discuss the implications of our results on the future quasar surveys.
This is the third paper of a series devoted to study the properties of bars from long slit spectroscopy to understand their formation, evolution and their influence on the evolution of disk galaxies. In this work we aim to determine the gas metallicity distribution of a sample of 20 barred early-type galaxies. We compare the nebular and stellar metallicity distributions to conclude about the origin of the warm gas. We compare the results of nebular emission metallicities using different semi-empirical methods. We carry out AGN diagnostic diagrams along the radius to determine the radius of influence of the AGN and the nuclei nature of the studied galaxies. We then derive the gas metallicities along the bars and compare the results to the distribution of stellar metallicities in the same regions. Most of the gas emission is centrally concentrated, although 15 galaxies also show emission along the bar. In the central regions, gas oxygen abundances are in the range 12+$\log$(O/H)= 8.4-9.1. The nebular metallicity gradients are very shallow in the bulge and bar regions. For three galaxies (one of them a LINER), the gas metallicities lie well below the stellar ones in the bulge region. These results do not depend on the choice of the semi-empirical calibration used to calculate the abundances. We see that the galaxies with the lowest abundances are those with the largest rotational velocities. The presence of gas of significantly lower metallicity than the stellar abundances in three of our galaxies, points to an external origin as the source of the gas that fuels the present star formation in the centre of some early-type barred galaxies. The fact that the bar/disk nebular metallicities are higher than the central ones might be indicating that the gas could be accreted via cooling flows instead of radial accretion from gas sitting in the outer parts of the disk.
We extend the ModeCode software of Mortonson, Peiris and Easther to enable numerical computation of perturbations in K-inflation models, where the scalar field no longer has a canonical kinetic term. Focussing on models where the kinetic and potential terms can be separated into a sum, we compute slow-roll predictions for various models and use these to verify the numerical code. A Markov chain Monte Carlo analysis is then used to impose constraints from WMAP7 data on the addition of a term quadratic in the kinetic energy to the Lagrangian of simple chaotic inflation models. For a quadratic potential, the data do not discriminate against addition of such a term, while for a quartic (\lambda \phi^4) potential inclusion of such a term is actually favoured. Overall, constraints on such a term from present data are found to be extremely weak.
We investigate strong lensing by non-singular finite isothermal ellipsoids taking into account the influence of the matter along the line of sight and in the close lens vicinity. We compare three descriptions of light propagation: the full approach taking into account all matter inhomogeneities along the rays, the single plane approach, where we take into account the influence of the strong lens neighbours but neglect the foreground and background objects, and the single lens approach. In each case we simulate many strong lensing configurations placing a point source at the same redshift but in different locations inside the region surrounded by caustics. We further analyze configurations of four or five images. For every simulated strong lensing configuration we attempt to fit a simplified lens model using a single isothermal ellipsoid or a single isothermal ellipsoid with external shear. The single lens fits to configurations obtained in the full approach are rejected in majority of cases with 95% significance. For configurations obtained in the single plane approach the rejection rate is substantially lower. Also the inclusion of external shear in simplified modeling improves the chances of obtaining acceptable fits, but the problem is not solved completely. The quantitative estimates of the rates of rejection of simplified models depend on the required accuracy of the models, and we present few illustrative examples, which show that both matter close to the lens and matter along the rays do have important influence on lens modeling. We also estimate the typical value of the external shear and compare the fitted parameters of the simplified models with the parameters of the lenses used in the simulations.
We compare cluster scaling relations published for three different samples selected via X-ray and Sunyaev-Zel'dovich (SZ) signatures. We find tensions driven mainly by two factors: i) systematic differences in the X-ray cluster observables used to derive the scaling relations, and; ii) uncertainty in the modeling of how the gas mass of galaxy clusters scales with total mass. All scaling relations are in agreement after accounting for these two effects. We describe a multivariate scaling model that enables a fully self-consistent treatment of multiple observational catalogs in the presence of property covariance, and apply this formalism when interpreting published results. The corrections due to scatter and observable covariance can be significant. For instance, our predicted YSZ-LX scaling relation differs from that derived using the naive "plug in" method by \approx 25%. Finally, we test the mass normalization for each of the X-ray data sets we consider by applying a space density consistency test: we compare the observed REFLEX luminosity function to expectations from published LX-M relations convolved with the mass function for a WMAP7 flat {\Lambda}CDM model. Not all of the LX-M scaling relations we consider satisfy this consistency test.
We examine systematic differences in the derived X-ray properties of galaxy clusters as reported by three different groups: Vikhlinin et al. (2009a), Mantz et al. (2010b), and Planck Collaboration (2011b). The sample overlap between any two pairs of works ranges between 16 to 28 galaxy clusters in common. We find systematic differences in most reported properties, including the total cluster mass, M500. The most extreme case is an average 45% \pm 5% difference in cluster mass between the Planck Collaboration (2011b) and Mantz et al. (2010b), for clusters at z > 0.13 (averaged over 16 clusters). These mass differences induce differences in cluster observables defined within an R500 aperture. After accounting for aperture differences, we find very good agreement in gas mass estimates between the different groups. However, the soft-band X-ray luminosity, LX, core-excised spectroscopic temperature, TX, and gas thermal energy, YX = MgasTX display mean differences at the 5%-15% level. We also find that the low (z \leq 0.13) and high (z \geq 0.13) galaxy cluster samples in Planck Collaboration (2011b) appear to be systematically different: the YSZ/YX ratio for these two sub- samples is ln(YSZ/YX) = -0.06 \pm 0.04 and ln(YSZ/YX) = 0.08 \pm 0.04 for the low and high redshift sub-samples respectively.
We demonstrate that optical data from SDSS, X-ray data from ROSAT and Chandra, and SZ data from Planck, can be modeled in a fully self-consistent manner. After accounting for systematic errors and allowing for property covariance, we find that scaling relations derived from optical and X-ray selected cluster samples are consistent with one another. Moreover, these clusters scaling relations satisfy several non-trivial spatial abundance constraints and closure relations. Given the good agreement between optical and X-ray samples, we combine the two and derive a joint set of LX-M and YSZ-M relations. Our best fit YSZ-M relation is in good agreement with the observed amplitude of the thermal SZ power spectrum for a WMAP7 cosmology, and is consistent with the masses for the two CLASH galaxy clusters published thus far. We predict the halo masses of the remaining z \leq 0.4 CLASH clusters, and use our scaling relations to compare our results with a variety of X-ray and weak lensing cluster masses from the literature.
We present a multi-wavelength photometric study of ~15,000 resolved stars in the nearby spiral galaxy M83 (NGC5236, D=4.61Mpc) based on Hubble Space Telescope Wide Field Camera 3 observations using four filters: F336W, F438W, F555W, and F814W. We select 50 regions (an average size of 260 pc by 280 pc) in the spiral arm and inter-arm areas of M83, and determine the age distribution of the luminous stellar populations in each region. This is accomplished by correcting for extinction towards each individual star by comparing its colors with predictions from stellar isochrones. We compare the resulting luminosity weighted mean ages of the luminous stars in the 50 regions with those determined from several independent methods, including the number ratio of red-to-blue supergiants, morphological appearance of the regions, surface brightness fluctuations, and the ages of clusters in the regions. We find reasonably good agreement between these methods. We also find that young stars are much more likely to be found in concentrated aggregates along spiral arms, while older stars are more dispersed. These results are consistent with the scenario that star formation is associated with the spiral arms, and stars form primarily in star clusters and then disperse on short timescales to form the field population. The locations of Wolf-Rayet stars are found to correlate with the positions of many of the youngest regions, providing additional support for our ability to accurately estimate ages. We address the effects of spatial resolution on the measured colors, magnitudes, and age estimates. While individual stars can occasionally show measurable differences in the colors and magnitudes, the age estimates for entire regions are only slightly affected.
We briefly review f(R) theories, both in the metric and Palatini formulations, their scalar-tensor representations and the chameleon mechanism that could explain the absence of perceptible consequences in the Solar System. We also review f(T) theories, a different approach to modified gravity consisting in a deformation of the teleparallel equivalent of General Relativity. We show some applications to cosmology and cosmic strings. As f(R)'s, f(T) theories are not exempted from additional degrees of freedom; we also discuss this still open issue.
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The first systematic study of the warm gas (T=10^4-5 K) distribution across a galaxy cluster is presented using multiple background QSOs to the Virgo Cluster. We detect 25 Lya absorbers (N_HI = 10^13.1-15.4 cm^-2) in the Virgo velocity range toward 9 of 12 QSO sightlines observed with COS, with a cluster impact parameter range of 0.25-1.15 Mpc (0.23-1.05Rvir). Including 18 previously STIS or GHRS detected Lya absorbers toward 7 of 11 background QSOs in and around the Virgo Cluster, we establish a sample of 43 absorbers towards a total of 23 background probes for studying the incidence of Lya absorbers in and around the Virgo Cluster. With these absorbers, we find: 1) Warm gas is predominantly in the outskirts of the cluster and avoids the X-ray detected hot ICM. Also, Lya absorption strength increases with a cluster impact parameter. 2) Lya absorbing warm gas traces cold HI emitting gas in the substructures of the Virgo Cluster. 3) Including the absorbers associated with the surrounding substructures, the warm gas covering fraction (100% for N_HI > 10^13.1 cm^-2) is in an agreement with cosmological simulations. We speculate that the observed warm gas is part of large-scale gas flows feeding the cluster both the ICM and galaxies.
Quasi-single field inflation predicts a peculiar momentum dependence in the squeezed limit of the primordial bispectrum which smoothly interpolates between the local and equilateral models. This dependence is directly related to the mass of the isocurvatons in the theory which is determined by the supersymmetry. Therefore, in the event of detection of a non-zero primordial bispectrum, additional constraints on the parameter controlling the momentum-dependence in the squeezed limit becomes an important question. We explore the effects of these non-Gaussian initial conditions on large-scale structure and the cosmic microwave background, with particular attention to the galaxy power spectrum at large scales and scale-dependence corrections to galaxy bias. We determine the simultaneous constraints on the two parameters describing the QSF bispectrum that we can expect from upcoming large-scale structure and cosmic microwave background observations. We find that for relatively large values of the non-Gaussian amplitude parameters, but still well within current uncertainties, galaxy power spectrum measurements will be able to distinguish the QSF scenario from the predictions of the local model. A CMB likelihood analysis, as well as Fisher matrix analysis, shows that there is also a range of parameter values for which Planck data may be able distinguish between QSF models and the related local and equilateral shapes. Given the different observational weightings of the CMB and LSS results, degeneracies can be significantly reduced in a joint analysis.
We present a comparative study of recent works on merger-timescales with dynamical friction and find a strong contrast between idealized/isolated mergers (Boylan-Kolchin et al. 2008) and mergers from a cosmological volume (Jiang et al. 2008). Our study measures the duration of mergers in a cosmological N-body simulation of dark matter, with emphasis on higher redshifts (z < 10) and a lower mass range. In our analysis we consider and compare two merger definitions; tidal disruption and coalescence. We find that the merger-time formula proposed by Jiang et al. (2008) describes our results well and conclude that cosmologically motivated merger-time formulae provide a more versatile and statistically robust approximation for practical applications such as semi-analytic/hybrid models.
We consider whether the non-Gaussian scale-dependent halo bias can be used not only to constrain the local form of non-Gaussianity but also to distinguish among different shapes. In particular, we ask whether it can constrain the behavior of the primordial three-point function in the squeezed limit where one of the momenta is much smaller than the other two. This is potentially interesting since the observation of a three-point function with a squeezed limit that does not go like the local nor equilateral templates would be a signal of non-trivial dynamics during inflation. To this end we use the quasi-single field inflation model of Chen and Wang as a representative two-parameter model, where one parameter governs the amplitude of non-Gaussianity and the other the shape. We also perform a model-independent analysis by parametrizing the scale-dependent bias as a power-law on large scales, where the power is to be constrained from observations. We find that proposed large-scale structure surveys (with characteristics similar to the dark energy task force stage IV surveys) have the potential to distinguish among the squeezed limit behavior of different bispectrum shapes for a wide range of fiducial model parameters. Thus the halo bias can help discriminate between different models of inflation.
We examine cyclic phantom models for the universe, in which the universe is dominated sequentially by radiation, matter, and a phantom dark energy field, followed by a standard inflationary phase. Since this cycle repeats endlessly, the Universe spends a substantial portion of its lifetime in a state for which the matter and dark energy densities have comparable magnitudes, thus ameliorating the coincidence problem. We calculate the fraction of time that the universe spends in such a coincidental state and find that it is nearly the same as in the case of a phantom model with a future big rip. In the limit where the dark energy equation of state parameter, w, is close to -1, we show that the fraction of time, f, for which the ratio of the dark energy density to the matter density lies between r_1 and r_2, is f = -(1+w) ln [(\sqrt{r_2} + \sqrt{1+r_2})/(\sqrt{r_1} + \sqrt{1+r_1})].
Hubble constant can be determined by the time delay of gravitational lensing systems. As data on time delay observation accumulates, it is time to revisit this approach. As in other dynamical phenomena in scales of galaxy and cluster of galaxies, gravitational lensing in these scales is also plagued by the problem of excess acceleration or gravity (a.k.a. missing mass problem). There are always some accelerations unaccounted for by luminous matter. Usually dark matter is introduced to interpret the discrepancy. However, MOdified Newtonian Dynamics (MOND) is more successful in explaining the excess accelerations in galaxy scale. We adopt TeVeS as the relativistic version of MOND to study gravitational lensing phenomena, and we can evaluate the Hubble constant from the derived time-delay formula. To apply our method, we rely on the CASTLE quasar lensing survey and the Sloan Digital Sky Survey (SDSS). Four samples are suitable for our study. Using only the luminous part of the lensing galaxies, the average of the derived Hubble constant is 68.5 km s^-1Mpc^-1
We report X-ray observations of two galaxy clusters Abell 1555 and Abell 1558 with Suzaku, which are included in a large scale filamentary structure and a supercluster, to search for non-thermal emission driven by shocks produced in structure formation. These two clusters are detected by Suzaku/XIS for the first time in the X-ray band of 0.5-7 keV. No significant flux is detected by HXD in the energy band of 13-40 keV, and upper limits are reported. From the analysis of the XIS data, we find that the spectrum of A1555 is fit by a thermal plus power-law model, significantly better than a single-temperature pure thermal spectrum. If this power-law component is due to inverse-Compton scattering, the fraction of total baryon energy imparted to non-thermal electrons is consistent with the typical value inferred from the observation of other clusters. However, other scenarios (e.g., under lying AGNs, multi-temperature thermal models) cannot be excluded and further investigation of this system is desired. Basic physical properties of A1555 (e.g., total mass) are also reported.
We compute analytically the dominant contribution to the tree-level bispectrum in the Starobinsky model of inflation. In this model, the potential is vacuum energy dominated but contains a subdominant linear term which changes the slope abruptly at a point. We show that on large scales compared with the transition scale $k_0$ and in the equilateral limit the analogue of the non-linearity parameter scales as $(k/k_0)^2$, that is its amplitude decays for larger and larger scales until it becomes subdominant with respect to the usual slow-roll suppressed corrections. On small scales we show that the non-linearity parameter oscillates with angular frequency given by $3/k_0$ and its amplitude grows linearly towards smaller scales and can be large depending on the model parameters. We also compare our results with previous results in the literature.
An accurate theoretical description of structure formation at least in the mildly non-linear regime is essential for comparison with data from next generation galaxy surveys. In a recent approach one follows the time evolution of correlators directly and finds a hierarchy of evolution equations with increasing order (Pietroni 2008). So far, in this so called time renormalisation group method the trispectrum was neglected in order to obtain a closed set of equations. In this work we study the influence of the trispectrum on the evolution of the power spectrum. In order to keep the numerical cost at a manageable level we use the tree-level trispectrum from Eulerian perturbation theory. In comparison to numerical simulations we find improvement in the mildly non-linear regime up to k = 0.25 h/Mpc. Beyond k = 0.25 h/Mpc the perturbative description of the trispectrum fails and the method performs worse than without the trispectrum included. Our results reinforce the conceptual advantage of the time renormalisation group method with respect to perturbation theory.
The gravitational properties of torus have been investigated. It is shown that the torus can be formed from the test particles orbiting in the gravitational field of the central mass. In this case the toroidal distribution is achieved due to significant spread of inclinations and eccentricities of their orbits. To investigate a self-gravity of the torus we considered the N-body problem for the torus located in the gravitational field of the central mass. It is shown that in the equilibrium state the cross-section of the torus has an oval shape with Gaussian density distribution. The dependence of obscuring efficiency as a function of torus inclination is found.
In this paper we describe the first data release of the UltraVISTA near-infrared imaging survey of the COSMOS field. We summarise the key goals and design of the survey and provide a detailed description of our data reduction techniques . We provide stacked, sky-subtracted images in $YJHK_{\rm s}$ and narrow-band filters constructed from data collected during the first year of UltraVISTA observations. Our stacked images reach $5\sigma$ $AB$ depths in an aperture of $2\arcsec$ diameter of $\sim 25$ in $Y$ and $\sim 24$ in $JHK_{\rm s}$ bands and all have sub-arcsecond seeing. To this $5\sigma$ limit, our $K_{\rm s}$ catalogue contains 216,268 sources. We carry out a series of quality assessment tests on our images and catalogues, comparing our stacks with existing catalogues. The $1\sigma$ astrometric RMS in both directions for stars selected with $17.0<K_{\rm s}\rm {(AB)} <19.5$ is $\sim 0.08\arcsec$ in comparison to the publicly-available COSMOS ACS catalogues. Our images are resampled to the same pixel scale and tangent point as the publicly available COSMOS data and so may be easily used to generate multi-colour catalogues using this data. All images and catalogues presented in this paper are publicly available through ESO's "phase 3" archiving and distribution system and from the UltraVISTA web site.
We investigate the effect of modified gravity on the specific angular momentum of galactic halos by analyzing the halo catalogs at z=0 from high-resolution N- body simulations for a f(R)-gravity model that meets the solar-system constraint. It is shown that the galactic halos in the $f(R)$ gravity model tend to acquire significantly higher specific angular momentum than those in the standard LCDM model. The largest difference in the specific angular momentum distribution between these two models occurs for the case of the isolated galactic halos with mass less than 10^{11}Msun/h, which are likely least shielded by the chameleon screening mechanism. As the specific angular momentum of galactic halos is rather insensitive to the other cosmological parameters, it can in principle be an independent discriminator of modified gravity. We speculate a possibility of using the relative abundance of the low surface brightness galaxies (LSBGs) as a test of GR given that the formation of the LSBGs befalls in the fast spinning dark halos.
Nearly massless axion-like particles are of interest for astrophysical observations, and some constraints on their parameter space do exist in the literature. Here, we propose to put new constraints on these particles using polarisation and, in particular, the polarisation differences observed between different quasar classes.
If the waterfall field of hybrid inflation couples to a U(1) gauge field, the waterfall can generate a statistically anisotropic contribution to the curvature perturbation. We investigate this possibility, generalising in several directions the seminal work of Yokoyama and Soda. The statistical anisotropy of the bispectrum could be detectable by PLANCK even if the statistical anisotropy of the spectrum is too small to detect.
We show how scaling arguments may be used to generate templates for the tidal stresses around saddles for a vast class of MONDian theories {\it detached from their obligations as dark matter alternatives}. Such theories are to be seen simply as alternative theories of gravity with a preferred acceleration scale, and could be tested in the solar system by extending the LISA Pathfinder mission. The constraints thus obtained may then be combined, if one wishes, with requirements arising from astrophysical and cosmological applications, but a clear separation of the issues is achieved. The central technical content of this paper is the derivation of a scaling prescription allowing complex numerical work to be bypassed in the generation of templates.
We present a detailed analytical calculation of CMB temperature anisotropies
\alpha_k and polarization \beta_k generated by scalar metric perturbations in
synchronous gauge, parallel to our previous work with RGW as a generating
source. This is realized primarily by an analytic time-integration of
Boltzmann's equation, yielding the closed forms of \alpha_k and \beta_k.
Approximations, such as the tight-coupling approximation for photons a prior to
the recombination and the long wavelength limit for scalar perturbations are
used. The residual gauge modes in scalar perturbations are analyzed and a
proper joining condition of scalar perturbations at the radiation-matter
equality is chosen, ensuring the continuity of energy perturbation.
The resulting analytic expressions of the multipole moments of polarization
a^E_l, and of temperature anisotropies a^T_l are explicit functions of the
scalar perturbations, recombination time, recombination width, photon free
streaming damping factor, baryon fraction, initial amplitude, primordial scalar
spectral index, and the running index. These results show that a longer
recombination width yields higher amplitudes of polarization on large scales
and more damping on small scales, and that a late recombination time shifts the
peaks of C^{XX'}_l to larger angular scales.
The analytic spectra C^{XX'}_l agree with the numerical ones and with those
observed by WMAP on large scales (l \lesssim 500), but deviate considerably
from the numerical results on smaller scales, showing the limitations of our
approximate analytic calculations. Several possible improvements are pointed
out for further studies.
We present an investigation into the impact of feedback from outflowing UV and X-ray absorbers in nearby z < 0.04 AGN. From studies of the kinematics, physical conditions, and variability of the absorbers in the literature, we calculate the possible ranges in total mass outflow rate and kinetic luminosity for each AGN, summed over all of its absorbers. These calculations make use of values (or limits) for the radial locations of the absorbers determined from variability, excited-state absorption, and other considerations. From a sample of 10 Seyfert 1 galaxies with detailed photoionization models for their absorbers, we find that 7 have sufficient constraints on the absorber locations to determine feedback parameters. For the low-luminosity AGN NGC 4395, these values are low, although we do not have sufficient constraints on the X-ray absorbers to make definitive conclusions. At least 5 of the 6 Seyfert 1s with moderate bolometric luminosities have mass outflow rates that are 10 - 1000 times the mass accretion rates needed to generate their observed luminosities, indicating that most of the mass outflow originates from outside the inner accretion disk. Three of these (NGC 4051, NGC 3516, and NGC 3783) have kinetic luminosities in the range 0.5 to 5% bolometric, which is the range typically required by feedback models for efficient self-regulation of black-hole and galactic bulge growth. At least 2 of the other 3 (NGC 5548, NGC 4151, and NGC 7469) have kinetic luminosities > 0.1% bolometric, although these values may increase if radial locations can be determined for more of the absorbers. We conclude that the outflowing UV and X-ray absorbers in moderate-luminosity AGN have the potential to deliver significant feedback to their environments.
We explore the prospects for constraining cosmology using gravitational wave (GW) observations of neutron star binaries by the proposed Einstein Telescope (ET), exploiting the narrowness of the neutron star mass function. Double neutron star (DNS) binaries are expected to be one of the first sources detected after "first-light" of Advanced LIGO and are expected to be detected at a rate of a few tens per year in the advanced era. However the proposed Einstein Telescope (ET) could catalogue tens of thousands per year. Combining the measured source redshift distributions with GW-network distance determinations will permit not only the precision measurement of background cosmological parameters, but will provide an insight into the astrophysical properties of these DNS systems. Of particular interest will be to probe the distribution of delay times between DNS-binary creation and subsequent merger, as well as the evolution of the star-formation rate density within ET's detection horizon. Keeping H_0, Omega_{m,0} and Omega_{\Lambda,0} fixed and investigating the precision with which the dark energy equation-of-state parameters could be recovered, we found that with 10^5 detected DNS binaries we could constrain these parameters to an accuracy similar to forecasted constraints from future CMB+BAO+SNIa measurements. Furthermore, modeling the merger delay-time distribution as a power-law, and the star-formation rate (SFR) density as a parametrised version of the Porciani and Madau SF2 model, we find that the associated astrophysical parameters are constrained to within ~ 10%. All parameter precisions scaled as 1/sqrt(N), where N is the number of catalogued detections. We also investigated how precisions varied with the intrinsic underlying properties of the Universe and with the distance reach of the network (which may be affected by the lower frequency cutoff of the detector).
We identify a novel physical mechanism that may be responsible for energy release in $\gamma$-ray bursts. Radial perturbations in the neutron core, induced by its collision with collapsing outer layers during the early stages of supernova explosions, can trigger a gravitational shock, which can readily eject a small but significant fraction of the collapsing material at ultra-relativistic speeds. The development of such shocks is a strong-field effect arising in near-critical collapse in General Relativity and has been observed in numerical simulations in various contexts, including in particular radially perturbed neutron star collapse, albeit for a tiny range of initial conditions. Therefore, this effect can be easily missed in numerical simulations if the relevant parameter space is not exhaustively investigated. In the proposed picture, the observed rarity of $\gamma$-ray bursts would be explained if the relevant conditions for this mechanism appear in only about one in every $10^4-10^5$ core collapse supernovae. We also mention the possibility that near-critical collapse could play a role in powering the central engines of Active Galactic Nuclei.
We develop and demonstrate a classification system constituted by several Support Vector Machines (SVM) classifiers, which can be applied to select quasar candidates from large sky survey projects, such as SDSS, UKIDSS, GALEX. How to construct this SVM classification system is presented in detail. When the SVM classification system works on the test set to predict quasar candidates, it acquires the efficiency of 93.21% and the completeness of 97.49%. In order to further prove the reliability and feasibility of this system, two chunks are randomly chosen to compare its performance with that of the XDQSO method used for SDSS-III's BOSS. The experimental results show that the high faction of overlap exists between the quasar candidates selected by this system and those extracted by the XDQSO technique in the dereddened i-band magnitude range between 17.75 and 22.45, especially in the interval of dereddened i-band magnitude < 20.0. In the two test areas, 57.38% and 87.15% of the quasar candidates predicted by the system are also targeted by the XDQSO method. Similarly, the prediction of subcategories of quasars according to redshift achieves a high level of overlap with these two approaches. Depending on the effectiveness of this system, the SVM classification system can be used to create the input catalog of quasars for the GuoShouJing Telescope (LAMOST) or other spectroscopic sky survey projects. In order to get higher confidence of quasar candidates, cross-result from the candidates selected by this SVM system with that by XDQSO method is applicable.
We investigate cosmological scenarios in the theory of gravity with the scalar field possessing a non-minimal kinetic coupling to the curvature. It is shown that the kinetic coupling provides an essentially new inflationary mechanism. Namely, at early cosmological times the domination of coupling terms in the field equations guarantees the quasi-De Sitter behavior of the scale factor: $a(t)\propto e^{H_{\kappa} t}$ with $H_\kappa=1/\sqrt{9\kappa}$, where $\kappa\simeq 10^{-74}$ sec$^2$ is the coupling parameter. The primary inflationary epoch driven by non-minimal kinetic coupling comes to the end at $t_f \simeq 10^{-35}$ sec. Later on, the matter terms are dominating, and the universe enters into the matter-dominated epoch which lasts approximately $0.5H_0^{-1}\sim 0.5\times10^{18}$ sec. Then, the cosmological term comes into play, and the universe enters into the secondary inflationary epoch with $a(t)\propto e^{H_{\Lambda} t}$, where $H_\Lambda=\sqrt{\Lambda/3}$. Note that the present value of the acceleration parameter $q=\ddot a a/\dot a^2$ is estimated as $q_0\simeq0.25$, that is the universe is at the beginning of the epoch of accelerated expansion. Thus, the cosmological model non-minimal kinetic coupling represents the realistic cosmological scenario which successfully describes basic cosmological epochs and provide the natural mechanism of epoch change without any fine-tuned potential.
Very high energy (VHE) gamma-rays from extragalactic sources, interacting by gamma-gamma collisions with diffuse intergalactic radiation fields, provide an alternative way to constrain the diffuse background light, completely independent of direct measurements. The limits depend however on our knowledge of the physics of the gamma-ray sources. After clarifying the interplay between background light and VHE spectra, I summarize the extent and validity of the obtainable limits, and where future improvements can be expected.
We review some perturbative results obtained in quantum gravity in an accelerating cosmological background. We then describe a class of non-local, purely gravitational models which have the correct structure to reproduce the leading infrared logarithms of quantum gravitational back-reaction during the inflationary regime. These models end inflation in a distinctive phase of oscillations with slight and short violations of the weak energy condition and should, when coupled to matter, lead to rapid reheating. By elaborating this class of models we exhibit one that has the same behaviour during inflation, goes quiescent until the onset of matter domination, and induces a small, positive cosmological constant of about the right size thereafter. We also briefly comment on the primordial density perturbations that this class of models predict.
We revisit the recently studied supersymmetric gauged inverse seesaw model \cite{An:2011uq} to incorporate astrophysical constraints on lightest supersymmetric particle (LSP) lifetime such that LSP constitutes the dark matter of the Universe. The authors in \cite{An:2011uq} considered light sneutrino LSP that can play the role of inelastic dark matter (iDM) such that desired iDM mass splitting and tiny Majorana masses of neutrinos can have a common origin. Here we point out that due to spontaneous R-parity $(R_p = (-1)^{3(B-L)+2s})$ breaking in such generic supersymmetric gauged inverse seesaw models, LSP can not be perfectly stable but decays to standard model particles after non-renormalizable operators allowed by the gauge symmetry are introduced. We show that strong astrophysical constraints on LSP lifetime makes sneutrino dark matter more natural than standard neutralino dark matter. We also show that long-livedness of sneutrino dark matter constrains the left right symmetry breaking scale $M_R < 10^4 \; \text{GeV}$.
For an arbitrary strong, spherically symmetric super-horizon curvature perturbation, we present analytical solutions of the Einstein equations in terms of asymptotic expansion over the ratio of the Hubble radius to the length-scale of the curvature perturbation under consideration. To obtain this solution we develop a recursive method of quasi-linearization which reduces the problem to a system of coupled ordinary differential equations for the $N$-th order terms in the asymptotic expansion with sources consisting of a non-linear combination of the lower order terms. We use this solution for setting initial conditions for subsequent numerical computations. For an arbitrary precision requirement predetermined by the intended accuracy and stability of the computer code, our analytical solution yields optimal truncated asymptotic expansion which can be used to find the upper limit on the moment of time when the initial conditions expressed in terms of such truncated expansion should be set. Examples of how these truncated (up to eighth order) solutions provide initial conditions with given accuracy for different radial profiles of curvature perturbations are presented.
Vacuum energy density and stresses are investigated for a scalar field in de Sitter spacetime with an arbitrary number of toroidally compactified spatial dimensions and in anti-de Sitter spacetime with two parallel branes. On the branes the field obeys the Robin boundary conditions. The behavior of the vacuum expectation values is discussed in various asymptotic regions of the parameters. Applications are given to Randall-Sundrum type braneworlds.
In this work, we have explored the advantages and drawbacks of using GPUs instead of CPUs in the calculation of a standard 2-point correlation function algorithm, which is useful for the analysis of Large Scale Structure of galaxies. Taking into account the huge volume of data foreseen in upcoming surveys, our main goal has been to accelerate significantly the analysis codes. We find that GPUs offer a 100-fold increase in speed with respect to a single CPU without a significant deviation in the results. For comparison's sake, an MPI version was developed as well. Some issues, like code implementation, which arise from using this option are discussed.
We have used high resolution (~2.3") observations of the local (D = 46 Mpc) luminous infrared galaxy Arp 299 to map out the physical properties of the molecular gas which provides the fuel for its extreme star formation activity. The 12CO J=3-2, 12CO J=2-1 and 13CO J=2-1 lines were observed with the Submillimeter Array and the short spacings of the 12CO J=2-1 and J=3-2 observations have been recovered using James Clerk Maxwell Telescope single dish observations. We use the radiative transfer code RADEX to estimate the physical properties (density, column density and temperature) of the different regions in this system. The RADEX solutions of the two galaxy nuclei, IC 694 and NGC 3690, are consistent with a wide range of gas components, from warm moderately dense gas with T_{kin} > 30 K and n(H_{2}) ~ 0.3 - 3 x 10^{3} cm^{-3} to cold dense gas with T_{kin} ~ 10-30 K and n(H_{2}) > 3 x 10^{3} cm^{-3}. The overlap region is shown to have a better constrained solution with T_{\rm{kin}}$ ~ 10-50 K and n(H_{2}) ~ 1-30 x 10^{3} cm^{-3}. We estimate the gas masses and star formation rates of each region in order to derive molecular gas depletion times. The depletion times of all regions (20-60 Myr) are found to be about 2 orders of magnitude lower than those of normal spiral galaxies. This rapid depletion time can probably be explained by a high fraction of dense gas on kiloparsec scales in Arp 299. We estimate the CO-to-H_{2} factor, \alpha_{co} to be 0.4 \pm 0.3 (3 x 10^{-4}/ x_{CO}) M_{sol} (K km s^{-1} pc^{2})^{-1} for the overlap region. This value agrees well with values determined previously for more advanced merger systems.
We present a new computational scheme aimed at reducing the complexity of the chemical networks in astrophysical models, one which is shown to markedly improve their computational efficiency. It contains a flux-reduction scheme that permits to deal with both large and small systems. This procedure is shown to yield a large speed-up of the corresponding numerical codes and provides good accord with the full network results. We analyse and discuss two examples involving chemistry networks of the interstellar medium and show that the results from the present reduction technique reproduce very well the results from fuller calculations.
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We present 7 spectroscopically confirmed Type II cluster supernovae (SNeII) discovered in the Multi-Epoch Nearby Cluster Survey, a supernova survey targeting 57 low redshift 0.05 < z < 0.15 galaxy clusters with the Canada-France-Hawaii Telescope. We find the rate of Type II supernovae within the virial radius of these galaxy clusters to be 0.026 (+0.085 -0.018 stat; +0.003 -0.001 sys) SNe per century per 1e10 solar masses. Surprisingly, one SNII is in a red sequence host galaxy that shows no clear evidence of recent star formation. This is unambiguous evidence in support of ongoing, low-level star formation in at least some cluster elliptical galaxies, and illustrates that galaxies that appear to be quiescent cannot be assumed to host only Type Ia SNe. Based on this single SNII we make the first measurement of the SNII rate in red sequence galaxies, and find it to be 0.007 (+0.014 -0.007 stat; +0.009 -0.001 sys) SNe per century per 1e10 solar masses. We also make the first derivation of cluster specific star formation rates (sSFR) from cluster SNII rates. We find that for all galaxy types, sSFR is 5.1 (+15.8 -3.1 stat; +0.9 -0.9 sys) solar masses per year per 1e12 solar masses, and for red sequence galaxies only, it is 2.0 (+4.2 -0.9 stat; +0.4 -0.4 sys) solar masses per year per 1e12 solar masses. These values agree with SFRs measured from infrared and ultraviolet photometry, and H-alpha emission from optical spectroscopy. Additionally, we use the SFR derived from our SNII rate to show that although a small fraction of cluster Type Ia SNe may originate in the young stellar population and experience a short delay time, these results do not preclude the use of cluster SNIa rates to derive the late-time delay time distribution for SNeIa.
We present first results from a narrowband imaging program for intermediate redshift emission-line galaxies using the newly commissioned FourStar infrared camera at the 6.5m Magellan telescope. To enable prompt identification of H\alpha\ emitters, a pair of custom 1% filters, which sample low-airglow atmospheric windows at 1.19 \mu m and 2.10 \mu m, is used to detect both H\alpha\ and [OII]\lambda 3727 emission from the same redshift volume at z=2.2. Initial observations are taken over a 130 arcmin^2 area in the CANDELS-COSMOS field. The exquisite image quality resulting from the combination of the instrument, telescope, and standard site conditions (~0.55" FWHM) allows the 1.19 \mu m and 2.10 \mu m data to probe 3\sigma\ emission-line depths down to 1.0e-17 erg/s/cm^2 and 1.2e-17 erg/s/cm^2 respectively, in less than 10 hours of integration time in each narrowband. For H\alpha\ at z=0.8 and z=2.2, these fluxes correspond to observed star formation rates of ~0.3 and ~4 Msun/yr respectively. We find 122 sources with a 1.19 \mu m excess, and 136 with a 2.10 \mu m excess, 41 of which show an excess in both bands. The dual narrowband technique, as implemented here, is estimated to identify about >80% of z=2.2 H\alpha\ emitters in the narrowband excess population. With the most secure such sample obtained to-date, we compute constraints on the faint-end slope of the z=2.2 H\alpha\ luminosity function. These "narrow-deep" FourStar observations have been obtained as part of the larger NewH\alpha\ Survey, which will combine the data with "wide-shallow" imaging through a similar narrowband filter pair with NEWFIRM at the KPNO/CTIO 4m telescopes, to enable study of both luminous (but rare) and faint emission-line galaxies in the intermediate redshift universe. [Abridged]
We investigate the optical spectral properties of the blazar PKS 1222+216 during a period of 3 years. While the continuum is highly variable the broad line emission is practically constant. This supports a scenario in which the broad line region is not affected by jet continuum variations. We thus infer the thermal component of the continuum from the line luminosity and we show that it is comparable with the continuum level observed during the phases of minimum optical activity. The mass of the black hole is estimated through the virial method from the FWHM of MgII, Hbeta, and Halpha broad lines and from the thermal continuum luminosity. This yields a consistent black hole mass value of 6x10^8 solar masses.
We use transport techniques to calculate the trispectrum produced in multiple-field inflationary models with canonical kinetic terms. Our method allows the time evolution of the local trispectrum parameters, tauNL and gNL, to be tracked throughout the inflationary phase. We illustrate our approach using examples. We give a simplified method to calculate the superhorizon part of the relation between field fluctuations on spatially flat hypersurfaces and the curvature perturbation on uniform density slices, and obtain its third-order part for the first time. We clarify how the 'backwards' formalism of Yokoyama et al. relates to our analysis and other recent work. We supply explicit formulae which enable each inflationary observable to be computed in any canonical model of interest, using a suitable first-order ODE solver.
We present high-resolution mid-infrared (MIR) imaging, nuclear spectral energy distributions (SEDs) and archival Spitzer spectra for 22 low-luminosity active galactic nuclei (LLAGN; Lbol \lesssim 10^42 erg/sec). Infrared (IR) observations may advance our understanding of the accretion flows in LLAGN, the fate of the obscuring torus at low accretion rates, and, perhaps, the star formation histories of these objects. However, while comprehensively studied in higher-luminosity Seyferts and quasars, the nuclear IR properties of LLAGN have not yet been well-determined. We separate the present LLAGN sample into three categories depending on their Eddington ratio and radio emission, finding different IR characteristics for each class. (I) At the low-luminosity, low-Eddington ratio (log Lbol/LEdd < -4.6) end of the sample, we identify "host-dominated" galaxies with strong polycyclic aromatic hydrocarbon bands that may indicate active (circum-)nuclear star formation. (II) Some very radio-loud objects are also present at these low Eddington ratios. The IR emission in these nuclei is dominated by synchrotron radiation, and some are likely to be unobscured type 2 AGN that genuinely lack a broad line region. (III) At higher Eddington ratios, strong, compact nuclear sources are visible in the MIR images. The nuclear SEDs of these galaxies are diverse; some resemble typical Seyfert nuclei, while others lack a well-defined MIR "dust bump". Strong silicate emission is present in many of these objects. We speculate that this, together with high ratios of silicate strength to hydrogen column density, could suggest optically thin dust and low dust-to-gas ratios, in accordance with model predictions that LLAGN do not host a Seyfert-like obscuring torus.
We present 90, 140, and 268GHz sub-arcminute resolution imaging of the Sunyaev-Zel'dovich effect (SZE) in MACSJ0717.5+3745. Our 90GHz SZE data result in a sensitive, 34uJy/bm map at 13" resolution using MUSTANG. Our 140 and 268GHz SZE imaging, with resolutions of 58" and 31" and sensitivities of 1.8 and 3.3mJy/beam respectively, was obtained using Bolocam. We compare these maps to a 2-dimensional pressure map derived from Chandra X-ray observations. Our MUSTANG data confirm previous indications from Chandra of a pressure enhancement due to shock-heated, >20keV gas immediately adjacent to extended radio emission seen in low-frequency radio maps. The MUSTANG data also detect pressure substructure that is not well-constrained by the X-ray data in the remnant core of a merging subcluster. We find that the small-scale pressure enhancements in the MUSTANG data amount to ~2% of the total pressure measured in the 140GHz Bolocam observations. The X-ray template also fails on larger scales to accurately describe the Bolocam data, particularly at the location of a subcluster known to have a high line of sight optical velocity (~3200km/s). Our Bolocam data are adequately described when we add an additional component - not described by a thermal SZE spectrum - coincident with this subcluster. Using flux densities extracted from our model fits, and marginalizing over the temperature constraints for the region, we fit a thermal+kinetic SZE spectrum to our data and find the subcluster has a best-fit line of sight proper velocity of 3600+3440/-2160km/s. This agrees with the optical velocity estimates for the subcluster. The probability of velocity<0 given our measurements is 2.1%. Repeating this analysis using flux densities measured non-parametrically results in a 3.4% probability of a velocity<=0. We note that this tantalizing result for the kinetic SZE is on resolved, subcluster scales.
We have revisited the extended excursion set theory in modified gravity models, taking the chameleon model as an example. Instead of specifying their Lagrangian size, here we define the environments by the Eulerian size, chosen to be of the same order of the Compton length of the scalar field by physical arguments. We find that the Eulerian and Lagrangian environments have very different environmental density contrast probability distributions, the former more likely to have high matter density, which in turn suppressing the effect of the fifth force in matter clustering and halo formation. The use of Eulerian environments also evades the unphysical restriction of having an upper mass limit in the case of Lagrangian environments. Two methods of computing the unconditional mass functions, numerical integration and Monte Carlo simulation, are discussed and found to give consistent predictions.
We show how correlated steps introduces significant contributions to the modification of the halo mass function in modified gravity models, taking the chameleon models as an example, in the framework of the excursion set approach. This correction applies to both Lagrangian and Eulerian environments discussed in previous studies. Correlated steps also enhances the modifications due to the fifth force in the conditional mass function as well as the halo bias. We found that abundance and clustering measurements from different environments can provide strong constraints on the chameleon models.
Emission-line spectra extracted at multiple locations across 39 ultraluminous infrared galaxies have been compiled into a spectrophotometric atlas. Line profiles of H alpha, [N II], [S II], [O I], H beta, and [O III] are resolved and fit jointly with common velocity components. Diagnostic ratios of these line fluxes are presented in a series of plots, showing how the Doppler shift, line width, gas excitation, and surface brightness change with velocity at fixed position and also with distance from the nucleus. One general characteristic of these spectra is the presence of shocked gas extending many kiloparsecs from the nucleus. In some systems, the shocked gas appears as part of a galactic gas disk based on its rotation curve. These gas disks appear primarily during the early stages of the merger. The general characteristics of the integrated spectra are also presented.
Using a spectral decomposition technique (Soto & Martin 2012, hereafter Paper I), we investigate the physical origin of the high-velocity emission line gas in a sample of 39 gas-rich, ultraluminous infrared galaxy (ULIRG) mergers. Regions with shock-like excitation were identified in two kinematically distinct regimes, characterized by broad ($\sigma >$ 150 \kms) and narrow linewidths. Here we investigate the physical origin of the high-velocity (broad) emission with shock-like line ratios. Considering the large amount of extinction in these galaxies, the blueshift of the broad emission suggests an origin on the near side of the galaxy and therefore an interpretation as a galactic outflow. The large spatial extent of the broad, shocked emission component is generally inconsistent with an origin in the narrow-line region of a AGN, so we conclude that energy and momentum supplied by the starburst drives these outflows. The new data are used to examine the fraction of the supernova energy radiated by shocks and the mass loss rate in the warm-ionized phase of the wind. We show that the shocks produced by galactic outflows can be recognized in moderately high-resolution, integrated spectra of these nearby, ultraluminous starbursts. The spectral fitting technique introduced in Paper I may therefore be used to improve the accuracy of the physical properties measured for high-redshift galaxies from their (observed frame) infrared spectra.
We study effects of the fully ionized initial state, or pre-ionization, on the subsequent thermal evolution of low-metallicity clouds under various intensities of the external far-ultraviolet(FUV) and cosmic-ray(CR) fields. The pre-ionization significantly affects the thermal and dynamical evolution of metal-free clouds without FUV/CRs by way of efficient HD formation. On the other hand, the pre-ionization effect on the thermal evolution is limited in very low-density regime for more metal-enriched clouds ([Z/H] >~ -4) or those under modest FUV (>10^{-3}) or CR field (>0.1 of the present-day Galactic disk levels). In any case, for >10^8 cm^{-3}, neither the initial ionization state nor the irradiating FUV strength affect the thermal evolution. The dust cooling is an important mechanism for making sub-solar mass fragments in low-metallicity gas. Since this fragmentation occurs at the temperature minimum by the dust cooling at >10^{10} cm^{-3}, this process is not vulnerable either to initial ionization state or external radiation.
We present analysis of the UV-spectrum of the low-z AGN IRAS-F22456-5125 obtained with the Cosmic Origins Spectrograph on board the Hubble Space Telescope. The spectrum reveals six main kinematic components, spanning a range of velocities of up to 800 km s-1, which for the first time are observed in troughs associated with CII, CIV, NV, SiII, SiIII, SiIV and SIV. We also obtain data on the OVI troughs, which we compare to those available from an earlier FUSE epoch. Column densities measured from these ions allow us to derive a well-constrained photoionization solution for each outflow component. Two of these kinematic components show troughs associated with transitions from excited states of SiII\ and CII. The number density inferred from these troughs, in combination with the deduced ioinization parameter, allows us to determine the distance to these outflow components from the central source. We find these components to be at a distance of ~ 10 kpc. The distances and the number densities derived are consistent with the outflow being part of a galactic wind.
We present VLT/VIMOS-IFU emission-line spectroscopy of a volume limited
sample of 18 southern ULIRGs selected with z<0.09 and dec<10. By covering a
wide range of ULIRG types, this dataset provides an important set of templates
for comparison with high-redshift galaxies. We employed an automated Gaussian
line fitting program to decompose the emission line profiles of Halpha, [NII],
[SII], and [OI] into individual components, and chart the Halpha kinematics,
and the ionized gas excitations and densities. 11/18 of our galaxies show
evidence for outflowing warm ionized gas with speeds between 500 and a few 1000
km/s, with the fastest outflows associated with systems that contain an AGN.
Our spatially resolved spectroscopy has allowed us to map the outflows, and in
some cases determine for the first time to which nucleus the wind is
associated. In three of our targets we find line components with widths >2000
km/s over spatially extended regions in both the recombination and forbidden
lines; in two of these three, they are associated with a known Sy2 nucleus.
Eight galaxies have clear rotating gaseous disks, and for these we measure
rotation velocities, virial masses, and calculate Toomre Q parameters. We find
radial gradients in the emission line ratios in a significant number of systems
in our study. We attribute these gradients to changes in ionizing radiation
field strength, most likely due to an increasing contribution of shocks with
radius. We conclude with a detailed discussion of the results for each
individual system, with reference to the existing literature.
Our observations demonstrate that the complexity of the kinematics and gas
properties in ULIRGs can only be disentangled with high sensitivity, spatially
resolved IFU observations. Many of our targets are ideal candidates for future
high spatial resolution follow-up observations.
We study the extension of Minimal Supersymmetric Standard Model by adding one singlet and one hypercharge zero SU(2) triplet chiral superfield. The triplet sector gives an additional contributions to the scalar masses and we find that the lightest CP-even Higgs boson can have a mass of 125 Gev even at the tree level, while keeping the scalar couplings in the perturbative regime. In this model no significant contributions from stop loops is needed to get the required Higgs mass which alleviates the fine tuning problem of fixing the stop mass to a high precision at the GUT scale. In addition this model gives a neutralino dark matter of mass around 100 Gev which is a mixture of Higgsino and Triplino with a dark matter density consistent with WMAP observations. The spin-independent scattering cross-section with nucleons is $10^{-43} cm^2$, which makes it consistent with the bounds from direct detection experiments like XENON100 and others.
We present EzGal, a flexible python program designed to easily generate observable parameters (magnitudes, colors, mass-to-light ratios) for any stellar population synthesis (SPS) model. As has been demonstrated by various authors, the choice of input SPS models can be a significant source of systematic uncertainty. A key strength of EzGal is that it enables simple, direct comparison of different models sets. EzGal is also capable of generating composite stellar population models (CSPs) and can interpolate between metallicities for a given model set. We have created a web interface to run EzGal and generate observables for a variety of star formation histories and model sets. We make many commonly used SPS models available from this interface; the BC03 models, an updated version of these models, the Maraston models, the BaSTI models, and finally the FSPS models. We use EzGal to compare magnitude predictions for the model sets as a function of wavelength, age, metallicity, and star formation history. We recover the well-known result that the models agree best in the optical for old, solar metallicity models, with differences at the ~0.1 magnitude level. The most problematic regime for SPS modeling is for young ages (<2 Gyrs) and long wavelengths (lambda >7500 Angstroms) where scatter between models can vary from 0.3 mags (Sloan i') to 0.7 mags (Ks). We find that these differences are best understood as general uncertainties in SPS modeling. Finally we explore a more physically motivated example by generating CSPs with a star formation history matching the global star formation history of the universe. We demonstrate that the wavelength and age dependence of SPS model uncertainty translates into a redshift dependent model uncertainty, highlighting the importance of a quantitative understanding of model differences when comparing observations to models as a function of redshift.
(Abridged) We analyzed the {\it Chandra} and {\it XMM-Newton} archival observations for 72 type 2 quasars at $z<1$. These objects were was selected based on the [O III]$\lambda$5007 optical emission line which we assume to be an approximate indicator of the intrinsic AGN luminosity. We find that the means of the column density and photon index of our sample are $\log N_{\rm H}=23.0$ cm$^{-2}$ and $\Gamma=1.87$ respectively, which are consistent with results from deep X-ray surveys. The observed ratios of hard X-ray and [O III] line luminosities imply that the majority of our sample suffer significant amounts of obscuration in the hard X-ray band. A more physically realistic model which accounts for both Compton scattering and a potential partial covering of the central X-ray source was used to estimate the true absorbing column density. We find that the absorbing column density estimates based on simple power-law models significantly underestimate the actual absorption in approximately half of the sources. Eleven sources show a prominent Fe K$\alpha$ emission line, and we detect this line in the other sources through a joint fit (spectral stacking). The correlation between the Fe K$\alpha$ and [O III] fluxes and the inverse correlation of the equivalent width of Fe K$\alpha$ line with the ratio of hard X-ray and [O III] fluxes is consistent with previous results for lower luminosity Seyfert 2 galaxies. We conclude that obscuration is the cause of the weak hard X-ray emission rather than intrinsically low X-ray luminosities. We find that about half of the population of optically-selected type 2 quasars are likely to be Compton-thick. We also find no evidence that the amount of X-ray obscuration depends on the AGN luminosity (over a range of more than three orders-of-magnitude in luminosity).
We present a {\it Chandra} observation of IRAS 19254--7245, a nearby ULIRG also known as {\it the Superantennae}. The high spatial resolution of {\it Chandra} allows us to disentangle for the first time the diffuse starburst emission from the embedded Compton-thick AGN. The 2-10 keV spectrum of the AGN emission is fitted by a flat power-law $\Gamma=1.3$) and a He-like Fe K$\alpha$ line with EW$\sim$1.5 keV, consistent with previous observations. The Fe K$\alpha$ line profile could be resolved as a blend of a neutral 6.4 keV line and an ionized 6.7 keV (He-like) or 6.9 keV (H-like) line. Variability is detected compared with the previous {\it XMM-Newton} and {\it suzaku} observations, demonstrating the compact size of the iron line emission. We fit the spectrum of the galaxy-scale extended emission excluding the AGN and other bright point sources with a soft thermal component with kT~0.8 keV. The luminosity of the extended emission is about one order of magnitude lower than that of the AGN. The basic physical and structural properties of the extended emission are fully consistent with a galactic wind being driven by the starburst (no contribution to the feedback by the AGN is required). A candidate ultra-luminous X-ray source is detected 8\arcsec\ south of the southern nucleus. The 0.3-10 keV luminosity of this off-nuclear point source is ~$6\times 10^{40}$ erg s$^{-1}$ if the emission is isotropic and the source is associated with the Superantennae.
The VERITAS array of 12-m atmospheric-Cherenkov telescopes in southern Arizona is one of the world's most-sensitive detectors of very-high-energy (VHE, E>100 GeV) gamma rays. More than 50 extragalactic sources are known to emit VHE photons; these include blazars, radio galaxies, and starburst galaxies. Blazar observations are one of the VERITAS Collaboration's Key Science Projects. More than 400 hours per year are devoted to this program and ~100 blazars have already been observed with the array, in most cases with the deepest ever VHE exposure. These observations have resulted in 21 detections, including 10 VHE discoveries, all of them with supporting multiwavelength observations. Recent highlights from VERITAS extragalactic observation program and the collaboration's long-term blazar observation strategy are presented.
We show how constraints on the time integrated event rate from a given dark matter (DM) direct detection experiment can be used to set a stringent constraint on the amplitude of the annual modulation signal in another experiment. The method requires only very mild assumptions about the properties of the local DM distribution: that it is temporally stable on the scale of months and spatially homogeneous on the ecliptic. We apply the method to the annual modulation signal in DAMA/LIBRA, which we compare to the bounds derived from the constraints on the time-averaged rates from XENON10, XENON100, CDMS and SIMPLE. Assuming a DM mass of 10 GeV, we show that a DM interpretation of the DAMA/LIBRA signal is excluded at 6.3sigma (4.6sigma) for isospin conserving (violating) spin-independent interactions, and at 4.9sigma for spin-dependent interactions on protons.
We study the effect of massive isocurvaton on density perturbations in quasi-single field inflation models, when the mass of the isocurvaton M becomes larger than the order of the Hubble parameter H. We analytically compute the correction to the power spectrum, leading order in coupling but exact for all values of mass. This verifies the previous numerical results for the range 0<M<3H/2 and shows that, in the large mass limit, the correction is of order H^2/M^2.
We revisit a two-component inflaton model with a turning trajectory in the field space, where the field slowly rolls down along the trajectory. We consider the case when the effective mass in the direction perpendicular to the trajectory, namely the isocurvature direction, is either of the same order as or much larger than the Hubble parameter. Assuming that the turning angular velocity is small, we compute analytically the corrections to the power spectrum of curvature perturbation caused by the mediation of the heavy isocurvature perturbation, and compare our analytic results with the numerical ones. Especially, when M_\mathrm{eff}^2>>H^2, we find that it is proportional to M_\mathrm{eff}^{-2}. This result is consistent with the one obtained previously by an effective field theory approach.
Using high resolution Chandra data, we report the presence of a weak X-ray point source coincident with the nucleus of NGC 4178, a late-type bulgeless disk galaxy known to have high ionization mid-infrared (mid-IR) lines typically associated with active galactic nuclei (AGNs). Although the faintness of this source precludes a direct spectral analysis, we are able to infer its basic spectral properties using hardness ratios. X-ray modeling, combined with the nuclear mid-IR characteristics, suggests that NGC 4178 may host a highly absorbed AGN accreting at a high rate with a bolometric luminosity on order of 10^43 ergs/s. The black hole mass estimate, based on our Chandra data and archival VLA data using the most recent fundamental plane relations is \sim 10^4 - 10^5 M\odot, possibly the lowest mass nuclear black hole currently known. There are also three off-nuclear sources, two with a similar brightness to the nuclear source at 36" and 32" from the center. As with the nuclear source, hardness ratios are used to estimate spectra for these two sources, and both are consistent with a simple power- law model with absorption. These two sources have X-ray luminosities of the order of \sim 10^38 ergs/s, which place them at the threshold between X-ray binaries and ultra-luminous X-ray sources (ULXs). The third off-nuclear source, located 49" from the center, is the brightest source detected, with an X-ray luminosity of \sim 10^40 ergs/s. Its spectrum is well-fit with an absorbed power law model, suggesting that it is a ULX. We also fit its spectrum with the Bulk Motion Comptonization (BMC) model and suggest that this source is consistent with an intermediate-mass black hole (IMBH) of mass (6\times2)\times10^3 M\odot.
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We report a bimodality in the azimuthal angle distribution of gas around galaxies as traced by MgII absorption: Halo gas prefers to exist near the projected galaxy major and minor axes. The bimodality is demonstrated by computing the mean azimuthal angle probability distribution function using 88 spectroscopically confirmed MgII absorption-selected galaxies [W_r(2796)> 0.1A] and 35 spectroscopically confirmed non-absorbing galaxies [W_r(2796)<0.1A] imaged with HST and SDSS. The azimuthal angle distribution for non-absorbers is flat, indicating no azimuthal preference for gas characterized by W_r(2796)<0.1A. We find that blue star-forming galaxies clearly drive the bimodality. We compute an azimuthal angle dependent MgII absorption covering fraction and find that it is enhanced by as much as 20-30% along the major and minor axes. The equivalent width distribution for gas along the major axis is likely skewed toward weaker MgII absorption than for gas along the projected minor axis. These combined results are highly suggestive that the bimodality is driven by gas accreted along the galaxy major axis and outflowing along the galaxy minor axis. The opening angle of outflows is 2.5 times larger than for accreting gas. We find the probably of detecting outflows is 60%, implying that winds are more commonly observed. This scenario is consistent with ideas of galaxy evolution were star-forming galaxies accrete new gas reservoirs, forming new stars and producing winds, while red early-type galaxies exist passively due to a lack of new gas reservoirs to form new stars.
The flare of radiation from the tidal disruption and accretion of a star can be used as a marker for supermassive black holes that otherwise lie dormant and undetected in the centres of distant galaxies. Previous candidate flares have had declining light curves in good agreement with expectations, but with poor constraints on the time of disruption and the type of star disrupted, because the rising emission was not observed. Recently, two `relativistic' candidate tidal disruption events were discovered, each of whose extreme X-ray luminosity and synchrotron radio emission were interpreted as the onset of emission from a relativistic jet. Here we report the discovery of a luminous ultraviolet-optical flare from the nuclear region of an inactive galaxy at a redshift of 0.1696. The observed continuum is cooler than expected for a simple accreting debris disk, but the well-sampled rise and decline of its light curve follows the predicted mass accretion rate, and can be modelled to determine the time of disruption to an accuracy of two days. The black hole has a mass of about 2 million solar masses, modulo a factor dependent on the mass and radius of the star disrupted. On the basis of the spectroscopic signature of ionized helium from the unbound debris, we determine that the disrupted star was a helium-rich stellar core.
In the standard picture of disc galaxy formation, baryons and dark matter receive the same tidal torques, and therefore approximately the same initial specific angular momentum. However, observations indicate that disc galaxies typically have only about half as much specific angular momentum as their dark matter haloes. We argue this does not necessarily imply that baryons lose this much specific angular momentum as they form galaxies. It may instead indicate that galaxies are most directly related to the inner regions of their host haloes, as may be expected in a scenario where baryons in the inner parts of haloes collapse first. A limiting case is examined under the idealised assumption of perfect angular momentum conservation. Namely, we determine the density contrast Delta, with respect to the critical density of the Universe, by which dark matter haloes need to be defined in order to have the same average specific angular momentum as the galaxies they host. Under the assumption that galaxies are related to haloes via their characteristic rotation velocities, the necessary Delta is ~600. This Delta corresponds to an average halo radius and mass which are ~60% and ~75%, respectively, of the virial values (i.e., for Delta = 200). We refer to this radius as the radius of baryonic collapse R_BC, since if specific angular momentum is conserved perfectly, baryons would come from within it. It is not likely a simple step function due to the complex gastrophysics involved, therefore we regard it as an effective radius. In summary, the difference between the predicted initial and the observed final specific angular momentum of galaxies, which is conventionally attributed solely to angular momentum loss, can more naturally be explained by a preference for collapse of baryons within R_BC, with possibly some later angular momentum transfer.
Recent hydrostatic X-ray studies of the hot interstellar medium (ISM) in early-type galaxies underestimate the gravitating mass as compared to stellar dynamics, implying modest, but significant deviations from exact hydrostatic equilibrium. We present a method for combining X-ray measurements and stellar dynamical constraints in the context of Bayesian statistics that allows the radial distribution of the implied nonthermal pressure or bulk motions in the hot ISM to be constrained. We demonstrate the accuracy of the method with hydrodynamical simulations tailored to produce a realistic galaxy model. Applying the method to the nearby elliptical galaxy NGC4649, and assuming negligible systematic errors in the stellar dynamics, we find a significant but subdominant nonthermal pressure fraction (0.27+/-0.06) in the central (<5 kpc) part of the galaxy, similar to the level of deviations from hydrostatic equilibrium expected in galaxy clusters. This would imply >360 km/s random turbulence or a magnetic field B=(39+/-6)(n_e/0.1 cm^{-3})^{0.59+/-0.09} muG, whereas gas rotation alone is unlikely to explain the detailed nonthermal profile. Future observations with Astro-H will allow turbulence or gas rotation at this level to be detected.
We present new results on the kinematics, thermal and ionization state, and spatial distribution of metal-enriched gas in the circumgalactic medium (CGM) of massive galaxies at redshift 3, using the "Eris" suite of cosmological "zoom-in" simulations. The reference run adopts a blastwave scheme for supernova feedback that produces galactic outflows, a star formation recipe based on a high gas density threshold, metal-dependent radiative cooling, and a model for the diffusion of metals and thermal energy. Synthetic spectra through the multiphase CGM produce interstellar absorption line strengths of Lya, CII, CIV, SiII, and SiIV as a function of galactocentric impact parameter that are in broad agreement with those observed at high-redshift by Steidel et al. (2010). Only about one third of all the gas within R_vir is outflowing. The fraction of sightlines within one virial radius that intercept optically thick material is 27%, in agreement with recent observations by Rudie et al. (2012). Such optically thick absorption is shown to trace inflowing "cold" streams that penetrate deep inside the virial radius. The streams, enriched to metallicities above 0.01 solar,give origin to strong (log N > 13) CII absorption with a covering factor of 22% (10%) within R_vir (2 R_vir). Galactic outflows do not cause any substantial suppression of the cold accretion mode. The central galaxy is surrounded by a large OVI halo, with a typical column density log N>14 and a near unity covering factor maintained all the way out to 150 kpc. This matches the trends recently observed in star-forming galaxies at low redshift by Tumlinson et al. (2011). Our zoom-in simulations of this single system appear to reproduce quantitatively the complex baryonic processes that determine the exchange of matter, energy, and metals between galaxies and their surroundings. (Abridged)
We present our new deep optical imaging and long-slit spectroscopy for Arp 220 that is the archetypical ULIRG in the local universe. Our sensitive Ha imaging has newly revealed large-scale, Ha absorption, i.e., post-starburst regions in this merger; one is found in the eastern superbubble and the other is in the two tidal tails that are clearly reveled in our deep optical imaging. The size of Ha absorption region in the eastern bubble is 5 kpc x 7.5 kpc and the observed Ha equivalent widths are ~2 A +- 0.2 A. The sizes of the northern and southern Ha-absorption tidal tails are ~5 kpc x 10 kpc and ~6 kpc x 20 kpc, respectively. The observed Ha equivalent widths range from 4 A to 7 A. In order to explain the presence of the two post-starburst tails, we suggest a possible multiple-merger scenario for Arp 220 in which two post-starburst disk-like structures merged into one, and then caused the two tails. This favors that Arp 220 is a multiple merging system composed of four or more galaxies, arising from a compact group of galaxies. Taking our new results into account, we discuss a star formation history in the last 1 Gyr in Arp 220.
The pattern speeds of NGC 3031, NGC 2366, and DDO 154 are measured using a solution of the Tremaine-Weinberg equations derived in a previous paper. Four different data sets of NGC 3031 produce consistent results despite differences in angular resolution, spectral resolution, and sensitivities to structures on different scales. The results for NGC 3031 show that the pattern speed is more similar to the material speed than it is to the speed of a rigidly rotating pattern, and that there are no clear indications of unique corotation or Lindblad resonances. Unlike NGC 3031, the results for NGC 2366 and DDO 154 show clear departures from the material speed. The results for NGC 2366 and DDO 154 also show that the solution method can produce meaningful results that are simple to interpret even if there is not a coherent or well-defined pattern in the data. The angular resolution of a data set has the greatest affect on the results, especially for determining the radial behavior of the pattern speed, and whether there is a single, global pattern speed.
The Milky Way's dwarf spheroidal satellites include the nearest, smallest and least luminous galaxies known. They also exhibit the largest discrepancies between dynamical and luminous masses. This article reviews the development of empirical constraints on the structure and kinematics of dSph stellar populations and discusses how this phenomenology translates into constraints on the amount and distribution of dark matter within dSphs. Some implications for cosmology and the particle nature of dark matter are discussed, and some topics/questions for future study are identified.
Super-Eddington accretion is very efficient in growing the mass of a black hole: in a fraction of the Eddington time its mass can grow to an arbitrary large value if the feedback effect is not taken into account. However, since super-Eddington accretion has a very low radiation efficiency, people have argued against it as a major process for the growth of the black holes in quasars since observations have constrained the average accretion efficiency of the black holes in quasars to be $\ga 0.1$. In this paper we show that the observational constraint does not need to be violated if the black holes in quasars have undergone a two-phase growing process: with a short super-Eddington accretion process they get their masses inflated by a very large factor until the feedback process becomes important, then with a prolonged sub-Eddington accretion process they have their masses increased by a factor $\ga 2$. The overall average efficiency of this two-phase process is then $\ga 0.1$, and the existence of black holes of $10^9 M_\odot$ by redshift 6 is easily explained. Observational test of the existence of the super-Eddington accretion phase is briefly discussed.
We use Genetic Algorithms to extract information from several cosmological probes, such as the type Ia supernovae (SnIa), the Baryon Acoustic Oscillations (BAO) and the growth rate of matter perturbations. This information consists of a model independent and bias-free reconstruction of the various scales and distances that characterize the data, like the luminosity $d_L(z)$ and the angular diameter distance $d_A(z)$ in the SnIa and BAO data, respectively, or the dependence with redshift of the matter density $\om_m(a)$ in the growth rate data, $f\sigma_8(z)$. This information can then be used to reconstruct the expansion history of the Universe, and the resulting Dark Energy (DE) equation of state $w(z)$ in the context of FRW models, or the mass radial function $\om_M(r)$ in LTB models. In this way, the reconstruction is completely independent of our prior bias. Furthermore, we use this method to test the Etherington relation, ie the well-known relation between the luminosity and the angular diameter distance, $\eta \equiv \frac{d_L(z)}{(1+z)^2 d_A(z)}$, which is equal to 1 in metric theories of gravity. We find that the present data seem to suggest a 3-$\sigma$ deviation from one at redshifts $z\sim 0.5$.
The unequivocal, spectroscopic detection of the 2175 bump in extinction curves outside the Local Group is rare. To date, the properties of the bump have been examined in only two GRB afterglows (GRB 070802 and GRB 080607). In this work we analyse in detail the detections of the 2175 extinction bump in the optical spectra of the two further GRB afterglows: GRB 080605 and 080805. We gather all available optical/NIR photometric, spectroscopic and X-ray data to construct multi-epoch SEDs for both GRB afterglows. We fit the SEDs with the Fitzpatrick & Massa (1990) model with a single or broken PL. We also fit a sample of 38 GRB afterglows, known to prefer a SMC-type extinction curve, with the same model. We find that the SEDs of GRB 080605 and GRB 080805 at two epochs are fit well with a single PL with a derived extinction of A_V = 0.52(+0.13 -0.16) and 0.50 (+0.13 -0.10), and 2.1(+0.7-0.6) and 1.5+/-0.2 respectively. While the slope of the extinction curve of GRB 080805 is not well-constrained, the extinction curve of GRB 080605 has an unusual very steep far-UV rise together with the 2175 bump. Such an extinction curve has previously been found in only a small handful of sightlines in the MW. One possible explanation of such an extinction curve may be dust arising from two different regions with two separate grain populations, however we cannot distinguish the origin of the curve. We finally compare the four 2175 bump sightlines to the larger GRB afterglow sample and to Local Group sightlines. We find that while the width and central positions of the bumps are consistent with what is observed in the Local Group, the relative strength of the detected bump (A_bump) for GRB afterglows is weaker for a given A_V than for almost any Local Group sightline. Such dilution of the bump strength may offer tentative support to a dual dust-population scenario.
We investigate the parsec-scale structure of 17 high frequency peaking radio sources from the faint HFP sample. VLBA observations were carried out at two adjacent frequencies, 8.4 and 15.3 GHz, both in the optically-thin part of the spectrum, to obtain the spectral index information. We found that 64% of the sources are resolved into subcomponents, while 36% are unresolved even at the highest frequency. Among the resolved sources, 7 have a morphology and a spectral index distribution typical of young radio sources, while in other 4 sources, all optically associated with quasars, the radio properties resemble those of the blazar population. The equipartition magnetic field of the single components are a few tens milliGauss, similar to the values found in the hotspots of young sources with larger sizes. Such high magnetic fields cause severe radiative losses, precluding the formation of extended lobe structures emitting at centimeter wavelengths. The magnetic fields derived in the various components of individual source are usually very different, indicating a non self-similar source evolution, at least during the very first stages of the source growth.
We present the images and kinematics of circumnuclear molecular gas from 100 pc scale down to 10 pc scale in nearby active galactic nuclei (AGNs) using the Submillimeter Array (SMA) and the Plateau de Bure Interferometer (PdBI). We have observed several nearby galaxies that host AGNs, such as the nearest radio galaxy Centaurus A (NGC 5128), the Seyfert 2 galaxy M51 (NGC 5194), the Seyfert 2 galaxy NGC 1068, the Seyfert 1 galaxy NGC 1097, and the Seyfert 2 / starburst composite galaxy NGC 4945, in CO lines to see whether the molecular gas distribution, kinematics, and physical conditions at 10 - 100 pc scale follows the AGN unified model or not. In 100 pc scale, most of the circumnuclear molecular gas shows smooth velocity gradient, suggesting a regular rotating feature, and also shows abnormal line ratios, suggesting the existence of active sources to make the circumnuclear molecular gas dense and/or warm conditions or abnormal chemical compositions. In 10 pc scale, on the other hand, the molecular gas kinematics shows various characteristics, some shows very disturbed kinematics such as a jet-entrained feature in the galaxies that have jets, but some still shows regular rotation feature in a galaxy that does not have obvious jets. These results indicate that the kinematics and physical/chemical conditions of the circumnuclear molecular gas at the scale less than 100 pc is highly affected by the AGN activities, and at this scale, there is no clear evidence of any unified feature seen in the circumnuclear molecular gas.
The accurate understanding of the ionization history of the Universe plays a fundamental role in modern cosmology. It includes a phase of cosmological reionization after the standard recombination epoch, possibly associated to the early stages of structure and star formation. While the simple "{\tau}-parametrization" of the reionization process and, in particular, of its imprints on the CMB anisotropy likely represents a sufficiently accurate modelling for the interpretation of current CMB data, a great attention has been recently posed on the accurate computation of the reionization signatures in the CMB for a large variety of astrophysical scenarios and physical processes. This work is aimed at a careful characterization of the imprints introduced in the polarization anisotropy, with particular attention to the B-modes. We have implemented a modified version of CAMB, the Cosmological Boltzmann code for computing the angular power spectrum (APS) of the anisotropies of the CMB, to introduce the hydrogen and helium ionization fractions predicted in astrophysical and phenomenological reionization histories, beyond the simple {\tau}-parametrization. We compared the results obtained for these models for all the non-vanishing (in the assumed scenarios) modes of the CMB APS. The amplitude and shape of the B-mode APS depends, in particular, on the tensor-to-scalar ratio, r, and on the reionization history, thus an accurate modeling of the reionization process will have implications for the precise determination of r or to set more precise constraints on it through the joint analysis of E and B-mode polarization data available in the next future and from a mission of next generation. Considering also the limitation from potential residuals of astrophysical foregrounds, we discussed the capability of next data to disentangle between different reionization scenarios in a wide range of r.
Gravitational lensing of the Cosmic Microwave Background (CMB) encodes cosmological information in the observed anisotropies of temperature and polarization. Accurate extraction of this additional information requires precise modeling of the covariance matrix of the power spectra of observed CMB fields. We introduce a new analytical model to describe the non-Gaussian structure of this covariance matrix and display the importance of second-order terms that were previously neglected. When compared with direct numerical simulations our model captures parameter errors to better than a few percent for cases where the non-Gaussianity causes an order unity degradation in errors. We also provide a detailed comparison between the information content of lensed CMB power spectra and ideal reconstruction of the lensing potential. We illustrate the impact of the non-Gaussian terms in the power spectrum covariance by providing Fisher errors on the sum of the masses of the neutrinos, the dark energy equation of state, and the curvature of the Universe.
In this review, recent progress in theoretical models for the broadband (radio through gamma-ray) emission from blazars are summarized. The salient features of both leptonic and hadronic models are reviewed. I present sample modeling results of spectral energy distributions (SEDs) of different types of Fermi-detected blazars along the traditional blazar sequence, using both types of models. In many cases, the SEDs of high-frequency peaked blazars (HBLs) have been found to be well represented by simple synchrotron + synchrotron self-Compton (SSC) models. However, a few HBLs recently discovered as very-high-energy (VHE) gamma-ray emitters by VERITAS are actually better represented by either external-Compton or hadronic models. Often, spectral modeling with time-independent single-zone models alone is not sufficient to constrain models, as both leptonic and lepto-hadronic models are able to provide acceptable fits to the overall SED. This degeneracy can be lifted by considering further constraints from spectral variability. Recent developments of time-dependent and inhomogeneous blazar models will be discussed, including detailed numerical simulations as well as a semi-analytical approach to the time-dependent radiation signatures of shock-in-jet models.
We study the vortex lines that are a feature of many random or disordered three-dimensional systems. These show universal statistical properties on long length scales, and geometrical phase transitions analogous to percolation transitions but in distinct universality classes. The field theories for these problems have not previously been identified, so that while many numerical studies have been performed, a framework for interpreting the results has been lacking. We provide such a framework with mappings to simple supersymmetric models. Our main focus is on vortices in short-range correlated complex fields, which show a geometrical phase transition that we argue is described by the CP^{k|k} model (essentially the CP^{n-1} model in the replica limit n\rightarrow 1). This can be seen by mapping a lattice version of the problem to a lattice gauge theory. A related field theory with a noncompact gauge field, the 'NCCP^{k|k} model', is a supersymmetric extension of the standard dual theory for the XY transition, and we show that XY duality gives another way to understand the appearance of field theories of this type. The supersymmetric descriptions yield results relevant, for example, to vortices in the XY model and in superfluids, to optical vortices, and to certain models of cosmic strings. A distinct but related field theory, the RP^{2l|2l} model (or the RP^{n-1} model in the limit n\rightarrow 1) describes the unoriented vortices which occur for instance in nematic liquid crystals. Finally, we show that in two dimensions, a lattice gauge theory analogous to that discussed in three dimensions gives a simple way to see the known relation between two-dimensional percolation and the CP^{k|k} sigma model with a \theta-term.
A novel modified theory of gravity with the function $F(R) = R\exp(\alpha R)$ instead of Ricci scalar $R$ in the Einstein$-$Hilbert action is suggested and analyzed. The action is converted into Einstein$-$Hilbert action at small value of the parameter $\alpha$. From local tests we obtain a bound on the parameter $\alpha\leq 10^{-6}$ cm$^2$. The Jordan and Einstein frames are considered and the potential of the scalar field in Einstein's frame is found. The static solutions of the model are obtained corresponding to the Schwarzschild$-$de Sitter space. We show that the de Sitter space is unstable but a solution with zero curvature is stable. It was demonstrated that the model passes the matter stability test.
Interactions of cosmic rays with the interstellar gas and radiation fields of the Milky Way provide the majority of the gamma rays observed by the Fermi Gamma Ray Space Telescope. In addition to the gas which is densely concentrated along the Galactic Disk, hydrodynamical simulations and observational evidence favor the presence of a halo of hot (T~10^6 K) ionized hydrogen (H_II), extending with non-negligible densities out to the virial radius of the Milky Way. We show that cosmic ray collisions with this circum-galactic gas should be expected to provide a significant flux of gamma rays, on the order of 10% of the observed isotopic gamma ray background at energies above 1 GeV. In addition, gamma rays originating from the extended H_II halos of other galaxies along a given line-of-sight should contribute to this background at a similar level.
An interesting feature of the Davies-Unruh effect is that an uniformly accelerated observer sees an isotropic thermal spectrum of particles even though there is a preferred direction in this context, determined by the direction of the acceleration g. We investigate the thermal fluctuations in the Unruh bath by studying the Brownian motion of particles in the bath, especially as regards to isotropy. We find that the thermal fluctuations are anisotropic and induce different frictional drag forces on the Brownian particle depending on whether it has a drift velocity along the direction of acceleration g or in a direction transverse to it. Using the fluctuation-dissipation theorem, we argue that this anisotropy arises due to quantum correlations in the fluctuations at large correlation time scales.
A debate has arisen regarding the importance of stationary versus eruptive mass loss for massive star evolution. The reason is that stellar winds have been found to be clumped, which results in the reduction of unclumped empirical mass-loss rates. Most stellar evolution models employ theoretical mass-loss rates which are already reduced by a moderate factor of ~2-3 compared to non-corrected empirical rates. A key question is whether these reduced rates are of the correct order of magnitude, or if they should be reduced even further, which would mean that the alternative of eruptive mass loss becomes necessary. Here we introduce the transition mass-loss rate (dM/dt)_trans between O and Wolf-Rayet (WR) stars. Its novelty is that it is model independent. All that is required is postulating the spectroscopic transition point in a given data-set, and determining the stellar luminosity, which is far less model dependent than the mass-loss rate. The transition mass-loss rate is subsequently used to calibrate stellar wind strength by its application to the Of/WNh stars in the Arches cluster. Good agreement is found with two alternative modelling/theoretical results, suggesting that the rates provided by current theoretical models are of the right order of magnitude in the ~50Msun mass range. Our results do not confirm the specific need for eruptive mass loss as Luminous Blue Variables, and current stellar evolution modelling for Galactic massive stars seems sound. Mass loss through alternative mechanisms might still become necessary at lower masses, and/or metallicities, and the quantification of alternative mass loss is desirable.
We investigate a model of modified gravity recovering the modified Newtonian dynamics (MOND) in the non-relativistic limit, based on the introduction of a preferred time foliation violating Lorentz invariance in the weak-field regime. Lorentz-invariance violation has been studied in the framework of Einstein-aether theory, the generalization of which, known as non-canonical Einstein-aether theory, having been proposed as a relativistic formulation of MOND. Our model can be seen as a minimal specialization to the hypersurface orthogonal case, which allows a different interpretation in terms of the preferred time : it can be either treated as a dynamical scalar field in a 4D formulation, or chosen as the time coordinate in a 3+1 formulation. We discuss the equivalence of the two points of view and the non-relativistic limit of the model.
We present a preliminary analysis of new high resolution radio observations of the nearby TeV blazar Markarian 421 (z=0.031). This study is part of an ambitious multifrequency campaign, with observations in sub-mm (SMA), optical/IR (GASP), UV/X-ray (Swift, RXTE, MAXI), and gamma rays (Fermi-LAT, MAGIC, VERITAS). In this manuscript we consider only data obtained with the Very Long Baseline Array (VLBA) at seven epochs (one observation per month from January to July 2011) at 15 and 23.8 GHz. We investigate the inner jet structure on parsec scales through the study of model-fit components for each epoch. We identified 5-6 components which are consistent with being stationary during the 6-month period reported here. The aim is to try to shed light on questions such as the nature of radiating particles, the connection between radio and gamma-ray emission, the location of emitting regions and the origin of the flux variability.
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We examine the detailed physics of the feedback mechanism by relativistic AGN jets interacting with a two-phase fractal interstellar medium (ISM). The (negative) feedback efficiency, as measured by the amount of cloud-dispersal generated by the jet-ISM interactions, is sensitive to the maximum size of clouds in the fractal cloud distribution; for a given filling factor and density, distributions of smaller clouds lead to higher outflow velocities. Feedback ceases to be efficient for Eddington ratios P_jet/L_edd <~ 10^-4, although systems with large cloud complexes >~ 50 pc require jets of Eddington ratio in excess of 10^-2 to disperse the clouds appreciably. Compared to the ISM density and maximum cloud size, the feedback efficiency depends weakly on volume filling factor. Based on measurements of the bubble expansion rates in our simulations we argue that sub-grid AGN prescriptions resulting in negative feedback in cosmological simulations without a multi-phase treatment of the ISM are good approximations if the volume filling factor of warm phase material is less than 0.1 and the cloud complexes are smaller than ~25 pc. We find that the acceleration of the dense embedded clouds is provided by the ram pressure (rather than the thermal pressure) of the high velocity flow through the porous channels of the warm phase, flow that has fully entrained the shocked hot-phase gas it has swept up, and is additionally mass-loaded by ablated cloud material. This mechanism, reminiscent of a two-stage feedback scenario proposed by Hopkins & Elvis (2010), transfers 10% to 40% of the jet energy to the cold and warm gas, accelerating it to several 100 to several 1000 km s^-1 within a few 10 to 100 Myr. Our predicted velocities match those observed in a range of high and low redshift radio galaxies hosting powerful radio jets.
We study the star formation rate (SFR) - stellar mass (M*) relation in a self-consistent manner from 0 < z < 2.5 with a sample of galaxies selected from the NEWFIRM Medium-Band Survey. We find a significant non-linear slope of the relation, SFR \propto M*^0.7, and a constant observed scatter of 0.34 dex, independent of redshift and M*. However, if we select only blue galaxies we find a linear relation SFR \propto M*, similar to previous results at z = 0 by Peng et al. (2010). This selection excludes red, dusty, star-forming galaxies with higher masses, which brings down the slope. By selecting on L_IR/L_UV (a proxy for dust obscuration) and the rest-frame U-V colors, we show that star-forming galaxies fall in three distinct regions of the log(SFR)-log(M*) plane: 1) actively star-forming galaxies with "normal" dust obscuration and associated colors (53% for log(M*) > 10 at 1 < z < 1.5), 2) red star-forming galaxies with low levels of dust obscuration and low specific SFRs (12%), and 3) dusty, blue star-forming galaxies with high specific SFRs (6%). The remaining 29% comprises quiescent galaxies. Galaxies on the "normal" star formation sequence show strong trends of increasing dust attenuation and decreasing sSFR with stellar mass, with an observed scatter of 0.26 dex (0.19 dex intrinsic scatter). The dusty, blue galaxies reside in the upper envelope of the star formation sequence with remarkably similar spectral shapes at all masses, suggesting that the same physical process is dominating the stellar light. The red, low-dust star-forming galaxies may be in the process of shutting off and migrating to the quiescent population.
Future cluster surveys will observe galaxy clusters numbering in the hundred thousands. We consider this work how these surveys can be used to constrain dark energy parameters: in particular, the equation of state parameter w and the non-adiabatic sound speed c_s^2. We demonstrate that, in combination with Cosmic Microwave Background (CMB) observations from Planck, cluster surveys such as that in the ESA Euclid project will be able to determine a time-independent w with subpercent precision. Likewise, if the dark energy sound horizon falls within the length scales probed by the cluster survey, then c_s^2 can be pinned down to within an order of magnitude. In the course of this work, we also investigate the process of dark energy virialisation in the presence of an arbitrary sound speed. We find that dark energy clustering and virialisation can lead to dark energy contributing to the total cluster mass at approximately the 0.1% level at maximum.
Results from the Wilkinson Microwave Anisotropy Probe (WMAP), Atacama Cosmology Telescope (ACT) and recently from the South Pole Telescope (SPT) have indicated the possible existence of an extra radiation component in addition to the well known three neutrino species predicted by the Standard Model of particle physics. In this paper, we explore the possibility of the apparent extra \textit{dark} radiation being linked directly to the physics of cold dark matter (CDM). In particular, we consider a generic scenario where dark radiation, as a result of an interaction, is produced directly by a fraction of the dark matter density effectively decaying into dark radiation. At an early epoch when the dark matter density is negligible, as an obvious consequence, the density of dark radiation is also very small. As the Universe approaches matter radiation equality, the dark matter density starts to dominate thereby increasing the content of dark radiation and changing the expansion rate of the Universe. As this increase in dark radiation content happens naturally after Big Bang Nucleosynthesis (BBN), it can relax the possible tension with lower values of radiation degrees of freedom measured from light element abundances compared to that of the CMB. We numerically confront this scenario with WMAP+ACT and WMAP+SPT data and derive an upper limit on the allowed fraction of dark matter decaying into dark radiation.
A large sample of spectroscopically confirmed galaxies at 1.4<z<3.7, with complementary imaging in the near- and mid-IR from the ground and from Hubble and Spitzer, is used to infer the average star formation histories (SFHs) of typical galaxies from z~7 to 2. For a subset of 302 galaxies at 1.5<z<2.6, we perform a comparison of star formation rates (SFRs) determined from SED modeling (SFRs[SED]) and those calculated from deep Keck UV and Spitzer/MIPS 24 micron imaging (SFRs[IR+UV]). Exponentially declining SFHs yield SFRs[SED] that are 5-10x lower on average than SFRs[IR+UV], indicating that declining SFHs may not be accurate for typical galaxies at z>2. The SFRs of z~2-3 galaxies are directly proportional to their stellar masses M*, with unity slope---a result that is confirmed with Spitzer/IRAC stacks of 1179 UV-faint (R>25.5) galaxies---for M*>5e8 Msun and SFRs >2 Msun/yr. We interpret this result in the context of several systematic biases that can affect determinations of the SFR-M* relation. The average specific SFRs at z~2-3 are similar within a factor of two to those measured at z>4, implying an average SFH where SFRs increase with time. A consequence of these rising SFHs is that (a) a substantial fraction of UV-bright z~2-3 galaxies had faint sub-L* progenitors at z>4; and (b) gas masses must increase with time from z=7 to 2, over which time the net cold gas accretion rate---as inferred from the specific SFR and the Kennicutt-Schmidt relation---is ~2-3x larger than the SFR . However, if we evolve to higher redshift the SFHs and masses of the halos that are expected to host L* galaxies at z~2, we find that <10% of the baryons accreted onto typical halos at z>4 actually contribute to star formation at those epochs. These results highlight the relative inefficiency of star formation even at early cosmic times when galaxies were first assembling. [Abridged]
We investigate the effect of primordial non-Gaussianity on the cross-correlation between the CMB anisotropies and the 21cm fluctuations from the epoch of reionization. We assume an analytic reionization model and an ionization fraction with f_{NL} induced scale dependent bias. We estimate the angular power spectrum of the cross-correlation of the CMB and 21 cm. In order to evaluate the detectability, the signal-to-noise (S/N) ratio for only a single redshift slice is also calculated for current and future observations, such as CMB observations by Planck satellite and 21cm observations by Omniscope. The obtained S/N ratio is 3.2 (2.8) for f_{NL}=100 (50) in our fiducial reionization model. Our work suggests in the absence of significant foregrounds and systematics, the auto-correlations of 21 cm is a better probe of f_{NL} than the cross-correlations (as expected since it depends on b^2), while the cross-correlations contain only one factor of b. Nevertheless, it is interesting to examine the cross-correlations between 21 cm and CMB, as the signal-to-noise ratio is not negligible and it is more likely we can rid ourselves of systematics and foregrounds that are common to both CMB and 21 cm experiments than completely clean 21 cm of all of the possible foregrounds and systematics in large scales.
Using HST/COS/STIS and HIRES/Keck high-resolution spectra, we have studied a remarkable HI absorbing complex at z=0.672 toward the quasar Q1317+277. The HI absorption has a velocity spread of 1600 km/s, comprises 21 Voigt profile components, and resides at an impact parameter of D=58 kpc from a bright, high mass [log(M_vir/M_sun) ~ 13.7] elliptical galaxy that is deduced to have a 6 Gyr old, solar metallicity stellar population. Ionization models suggest the majority of the structure is cold gas surrounding a shock heated cloud that is kinematically adjacent to a multi-phase group of clouds with detected CIII, CIV and OVI absorption, suggestive of a conductive interface near the shock. The deduced metallicities are consistent with the moderate in situ enrichment relative to the levels observed in the z ~ 3 Ly-alpha forest. We interpret the HI complex as a metal-poor filamentary structure being shock heated as it accretes into the halo of the galaxy. The data support the scenario of an early formation period (z > 4) in which the galaxy was presumably fed by cold-mode gas accretion that was later quenched via virial shocking by the hot halo such that, by intermediate redshift, the cold filamentary accreting gas is continuing to be disrupted by shock heating. Thus, continued filamentary accretion is being mixed into the hot halo, indicating that the star formation of the galaxy will likely remain quenched. To date, the galaxy and the HI absorption complex provide some of the most compelling observational data supporting the theoretical picture in which accretion is virial shocked in the hot coronal halos of high mass galaxies.
We study a cosmological model composed of a matter fluid interacting with a dark fluid in a spatially flat Universe. The matter component represents the baryon and dark matter and it is taken into account, through a bulk viscosity, the irreversible process that the matter fluid undergoes because of the accelerated expansion of the universe. The bulk viscous coefficient is assumed to be proportional to the Hubble parameter. The interaction term between the fluids is not assumed a priori but it is expressed in terms of the barotropic indexes of the fluids, which are considered as a function of the ratio between their energy densities. The radiation component is also taken into account in the model. The model is constrained using the type Ia supernova observations, the shift parameter of the CMB, the acoustic peak of the BAO and the Hubble expansion rate, to constrain the values of the barotropic index of dark energy and the bulk viscous coefficient. It is found that the bulk viscosity is constrained to be negligible (around zero) from the observations and that the barotropic index for the dark energy to be negative and close to zero too, indicating a phantom energy.
In this paper we discuss a multi-field model of inflation in which generally all fields are non-minimally coupled to the Ricci scalar and have non-canonical kinetic terms. The background evolution and first-order perturbations for the model are evaluated in both the Jordan and Einstein frames, and the respective curvature perturbations compared. We confirm that they are indeed not the same - unlike in the single-field case - and also that the difference is a direct consequence of the isocurvature perturbations inherent to multi-field models. This result leads us to conclude that the notion of adiabaticity is not invariant under conformal transformations. Using a two-field example we show that even if in one frame the evolution is adiabatic, meaning that the curvature perturbation is conserved on super-horizon scales, in general in the other frame isocurvature perturbations continue to source the curvature perturbation. We also find that it is possible to realise a particular model in which curvature perturbations in both frames are conserved but with each being of different magnitude. These examples highlight that the curvature perturbation itself, despite being gauge-invariant, does not correspond directly to an observable. The non-equivalence of the two curvature perturbations would also be important when considering the addition of Standard Model matter into the system.
The cosmic microwave background (CMB) anisotropies in spherical 3-spaces with a non-trivial topology are studied. This paper discusses the special class of the so-called double action manifolds, which are for the first time analysed with respect to their CMB anisotropies. The CMB anisotropies are computed for all double action manifolds generated by a dihedral and a cyclic group with a group order of up to 180 leading to 33 different topologies. Several spaces are found which show a suppression of the CMB anisotropies on large angular distances as it is found on the real CMB sky. It turns out that these spaces possess fundamental cells defined as Voronoi domains which are close to highly symmetric polyhedra like Platonic or Archimedean ones.
The baryon acoustic oscillation (BAO) feature in the distribution of galaxies provides a fundamental standard ruler which is widely used to constrain cosmological parameters. In most analyses, the comoving length of the ruler is inferred from a combination of CMB observations and theory. However, this inferred length may be biased by various non-standard effects in early universe physics; this can lead to biased inferences of cosmological parameters such as H_0, \Omega_m and w, so it would be valuable to measure the absolute BAO length by combining a galaxy redshift survey and a suitable direct low-z distance measurement. One obstacle is that low-redshift BAO surveys mainly constrain the ratio r_S / D_V(z), where D_V is a dilation scale which is not directly observable by standard candles. Here, we find a new approximation D_V(z) \simeq (3/4) D_L(4z/3) (1+ 4z/3)^{-1} (1 - 0.02455 z^3 + 0.0105 z^4) which connects D_V to the standard luminosity distance D_L at a somewhat higher redshift; this is shown to be very accurate (relative error < 0.2 percent) for all WMAP-compatible Friedmann models at z < 0.4, with very weak dependence on cosmological parameters H_0, \Omega_m, \Omega_k, w. This provides a route to measure the absolute BAO length using only observations at z < 0.3, including type-Ia supernovae, and potentially future H_0-free physical distance indicators such as gravitational lenses or gravitational wave standard sirens. This would provide a zero-parameter check of the standard cosmology at 10^3 < z < 10^5, and can constrain the number of relativistic species N_{eff} with fewer degeneracies than the CMB.
What are the main drivers of activity in the local universe? Observations have been instrumental in identifying the mechanisms responsible for fueling activity in galaxy nuclei. In this context we summarize the main results of the NUclei of GAlaxies (NUGA) survey. The aim of NUGA is to map, at high resolution and high sensitivity, the distribution and dynamics of the molecular gas in the central kiloparsec region of 25 galaxies, and to study the different mechanisms responsible for gas fueling of low-luminosity AGNs (LLAGN). Gas flows in NUGA maps reveal a wide range of instabilities. The derived gravity torque maps show that only about 1/3 of NUGA galaxies show evidence of ongoing fueling. Secular evolution and dynamical decoupling are seen to be key ingredients to understand the AGN fueling cycle. We discuss the future prospects for this research field with the advent of instruments like the Atacama Large Millimeter Array (ALMA).
Ultraviolet observations of the QSO 3C 263 (zem = 0.652) with COS and FUSE reveal O VI absorption systems at z = 0.06342 and 0.14072 . WIYN multi-object spectrograph observations provide information about the galaxies associated with the absorbers. The multi-phase system at z = 0.06342 traces cool photoionized gas and warm collisionally ionized gas associated with a L ~ 0.31L* compact spiral emission line galaxy with an impact parameter of 63 kpc. The cool photoionized gas in the absorber is well modeled with log U ~ -2.6, log N(H) ~17.8, log n(H) ~ -3.3 and [Si/H] = -0.14\pm0.23. The collisionally ionized gas containing C IV and O VI probably arises in cooling shock heated transition temperature gas with log T ~ 5.5. The absorber is likely tracing circumgalactic gas enriched by gas ejected from the spiral emission line galaxy. The simple system at z = 0.14072 only contains O VI and broad and narrow H I. The O VI with b = 33.4\pm11.9 km s-1 is likely associated with the broad H I {\lambda}1215 absorption with b = 86.7\pm15.4 km s-1. The difference in Doppler parameters implies the detection of a very large column of warm gas with log T = 5.61(+0.16, -0.25), log N(H) = 19.54(+0.26, -0.44) and [O/H] = -1.48 (+0.46, -0.26). This absorber is possibly associated with a 1.6L* absorption line galaxy with an impact parameter of 617 kpc although an origin in warm filament gas or in the halo of a fainter galaxy is more likely.
This paper revisits the Inflationary scenario within the framework of scalar field models possessing a non-canonical kinetic term. We obtain closed form solutions for all essential quantities associated with chaotic inflation including slow roll parameters, scalar and tensor power spectra, spectral indices, the tensor-to-scalar ratio, etc. We also examine the Hamilton-Jacobi equation and demonstrate the existence of an inflationary attractor. Our results highlight the fact that non-canonical scalars can significantly improve the viability of inflationary models. They accomplish this by decreasing the tensor-to-scalar ratio while simultaneously increasing the value of the scalar spectral index, thereby redeeming models which are incompatible with the cosmic microwave background (CMB) in their canonical version. For instance, the non-canonical version of the chaotic inflationary potential, $V(\phi) \sim \lambda\phi^4$, is found to agree with observations for values of $\lambda$ as large as unity! The exponential potential can also provide a reasonable fit to CMB observations. Interestingly, non-canonical scalars violate the consistency relation $r = -8n_T$, which emerges as a {\em smoking gun} test for this class of models.
The matter content of extragalactic relativistic jets is still an unsolved issue. There are strong arguments against pure electron-positron pair jets, but pairs could outnumber the electrons associated with protons by a factor 10-20. This impacts on the estimate of the jet kinetic power, by reducing it by the same factor, and on the total energy delivered to leptons by the particle acceleration mechanism. Pairs cannot be created in the same jet-zone responsible for the high energy gamma-ray emission we see in blazars, because the reprocessing of the created pairs would overproduce the X-ray flux. Copious pair creation could occur in the inner zone of the still accelerating jet, where the bulk Lorentz factor is small. It is found that the inner zone can produce a sufficient number of pairs to replenish the zone of the jet where most of the luminosity is emitted, but only if the gamma-ray luminosity of the inner jet is above 1e44 erg/s at ~1 MeV. Since the beaming is modest, this emission can be observed at large viewing angles, and detected in radio-galaxies and lobe dominated quasars at the flux level of 1e-12 - 1e-11 erg/cm2/s for a source at a redshift z=0.1.
We propose a simple model for Warm Dark Matter (WDM) in which two fermions are added to the Standard Model: (quasi-) stable "keVins" (keV inert fermions) which account for WDM and their unstable brothers, the "GeVins" (GeV inert fermions), both of which carry zero electric charge and lepton number, and are (approximately) "inert", in the sense that their only interactions are via suppressed couplings to the Z. We consider scenarios in which stable keVins are thermally produced and their abundance is subsequently diluted by entropy production from the decays of the heavier unstable GeVins. This mechanism could be implemented in a wide variety of models, including E_6 inspired supersymmetric models or models involving sterile neutrinos.
We reinvestigate the emission of Hawking radiation during gravitational collapse to a black hole. Both CGHS collapse of a shock wave in (1+1)-dimensional dilaton gravity and Schwarzschild collapse of a spherically symmetric thin shell in (3+1)-dimensional gravity are considered. Studying the dynamics of in-vacuum polarization, we find that a multi-parametric family of out-vacua exists. Initial conditions for the collapse lead dynamically to different vacua from this family as the final state. Therefore, the form of the out-vacuum encodes memory about the initial quantum state of the system. While most out-vacua feature a non-thermal Hawking flux and are expected to decay quickly, there also exists a thermal vacuum state. Collectively, these observations suggest an interesting possible resolution of the information loss paradox.
Elementary keV sterile Dirac neutrinos can be a natural ingredient of the composite neutrino scenario. For a certain class of composite neutrino theories, these sterile neutrinos naturally have the appropriate mixing angles to be resonantly produced warm dark matter (WDM). Alternatively, we show these sterile neutrinos can be WDM produced by an entropy-diluted thermal freeze-out, with the necessary entropy production arising not from an out-of-equilibrium decay, but rather from the confinement of the composite neutrino sector, provided there is sufficient supercooling.
In globular clusters, dynamical evolution produces luminous X-ray emitting binaries at a rate about 200 times greater than in the field. If globular clusters also produce SNe Ia at a high rate, it would account for much of the SN Ia events in early type galaxies and provide insight into their formation. Here we use archival HST images of nearby galaxies that have hosted SNe Ia to examine the rate at which globular clusters produce these events. The location of the SN Ia is registered on an HST image obtained before the event or after the supernova faded. Of the 36 nearby galaxies examined, 21 had sufficiently good data to search for globular cluster hosts. None of the 21 supernovae have a definite globular cluster counterpart, although there are some ambiguous cases. This places an upper limit to the enhancement rate of SN Ia production in globular clusters of about 42 at the 95% confidence level, which is an order of magnitude lower than the enhancement rate for luminous X-ray binaries. Even if all of the ambiguous cases are considered as having a globular cluster counterpart, the upper bound for the enhancement rate is 82 at the 95% confidence level, excluding an enhancement rate of 200. Barring unforeseen selection effects, we conclude that globular clusters are not responsible for producing a significant fraction of the SN Ia events in early-type galaxies.
As a result of discussions with Bousso and Vilenkin I want to return to the
question of whether the multiverse is past-eternal or if there was a beginning.
Not surprisingly, given three people, there were three answers. However, the
discussions have led to some common ground.
The multiverse being past-eternal, or at least extremely old has content and
potential phenomenological implications. I will discuss how the oldness of the
multiverse is connected with recent speculations of Douglas.
We present a detail analysis on a general class of holographic dark energy models characterized by the length scale $L=\frac1{a^n(t)}\int_0^t dt' a^m(t')$. We show that $n \geq 0$ is required by the recent cosmic accelerated expansion of universe. In the early universe dominated by the constituent with constant equation of state $w_m$, we have $w_{de}\simeq -1-\frac{2n}{3}$ for $n \geq 0$ and $m<0$, and $w_{de}\simeq-\frac23(n-m)+w_m$ for $n > m \geq 0$. The models with $n > m \geq 0$ become single-parameter models like the $\Lambda$CDM model due to the analytic feature $\Omega_{de}\simeq \frac{d^2}4(2m+3w_m+3)^2a^{2(n-m)}$ at radiation- and matter-dominated epoch. Whereas the cases $n=m\geq 0$ should be abandoned as the dark energy cannot dominate the universe forever and there might be too large fraction of dark energy in early universe, and the cases $m> n \geq 0$ are forbidden by the self-consistent requirement $\Omega_{de}\ll1 $ in the early universe. Thus a detailed study on the single-parameter models corresponding to cases $n >m \geq 0$ is carried out by using recent observations. The best-fit analysis indicates that the conformal-age-like models with $n=m+1$, i.e. $L\propto\frac1{Ha}$ in early universe, are more favored and also the models with smaller $n$ for the given $n-m$ are found to fit the observations better. The equation of state of the dark energy in models with $n=m+1 >0$ transits from $w_{de}<-1$ during inflation to $w_{de}>-1$ in radiation- and matter-dominated epoch, and then back to $w_{de}<-1$ eventually. The best-fit result of the case $(n=0, m=-1)$ which is so-called $\eta$HDE model proposed in \cite{Huang:2012xm} is the most favorable model and compatible with the $\Lambda$CDM model.
We put forward a scenario where blazars are classified as flat-spectrum radio quasars, BL Lacs, low synchrotron, or high synchrotron peaked objects according to a varying combination of Doppler boosted radiation from the jet, emission from the accretion disk, the broad line region, and light from the host galaxy. We thoroughly test this new approach, which builds upon unified schemes, using Monte Carlo simulations and show that it can provide simple answers to a number of long-standing open issues. We also demonstrate that selection effects play a very important role in the diversity observed in radio and X-ray samples and in the correlation between luminosity and peak frequency of the synchrotron power (the so-called "blazar sequence"). It turns out that sources so far classified as BL Lacs on the basis of their observed weak, or undetectable, emission lines are of two physically different classes: intrinsically weak-lined objects, more common in X-ray selected samples, and heavily diluted broad-lined sources, more frequent in radio selected samples, which explains some of the confusion in the literature.
We review a construction of holographic geometries dual to N=4 SYM theory on a Friedmann-Robertson-Walker background and in the presence or absence of a gluon condensate and instanton density. We find the most general solution with arbitrary scale factor and show that it is diffeomorphic to topological black holes. We introduce a time-dependent boundary cosmological constant \lambda(t) and show energy-momentum conservation in this background. For constant \lambda, the deconfinement properties of the temporal Wilson loop are analysed. In most cases the Wilson loop confines throughout cosmological evolution. However, there is an exceptional case which shows a transition from deconfinement at early times to confinement at late times. We classify the presence or absence of horizons, with important implications for the Wilson loop.
We discuss and clarify the validity of effective single field theories of inflation obtained by integrating out heavy degrees of freedom in the regime where adiabatic perturbations propagate with a suppressed speed of sound. We show by construction that it is indeed possible to have inflationary backgrounds where the speed of sound remains suppressed and slow-roll persists for long enough. In this class of models, heavy fields influence the evolution of adiabatic modes in a manner that is consistent with decoupling of physical low and high energy degrees of freedom. We emphasize the distinction between the effective masses of the isocurvature modes and the eigenfrequencies of the propagating high energy modes. Crucially, we find that the mass gap that defines the high frequency modes increases with the strength of the turn, even as the naive heavy (isocurvature) and light (curvature) modes become more strongly coupled. Adiabaticity is preserved throughout, and the derived effective field theory remains in the weakly coupled regime, satisfying all current observational constraints on the resulting primordial power spectrum. In addition, these models allow for an observably large equilateral non-Gaussianity, which is computed.
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