Gravitational lensing is a powerful astrophysical and cosmological probe and is particularly valuable at submillimeter wavelengths for the study of the statistical and individual properties of dusty starforming galaxies. However the identification of gravitational lenses is often time-intensive, involving the sifting of large volumes of imaging or spectroscopic data to find few candidates. We used early data from the Herschel Astrophysical Terahertz Large Area Survey to demonstrate that wide-area submillimeter surveys can simply and easily detect strong gravitational lensing events, with close to 100% efficiency.
We perform high resolution N-body simulations for f(R) gravity based on a self-adaptive particle- mesh code MLAPM. The Chameleon mechanism that recovers General Relativity on small scales is fully taken into account by self-consistently solving the non-linear equation for the scalar field. We independently confirm the previous simulation results, including the matter power spectrum, halo mass function and density profiles, obtained by Oyaizu et al. (Phys.Rev.D 78, 123524, 2008) and Schmidt et al. (Phys.Rev.D 79, 083518, 2009), and extend the resolution up to k~20 h/Mpc for the measurement of the matter power spectrum. Based on our simulation results, we discuss how the Chameleon mechanism affects the clustering of dark matter and halos on full non-linear scales.
We report that the reported sub-Eddington boundary in the quasar mass-luminosity plane (a departure from the Eddington luminosity limit for the highest quasar black hole masses at a given redshift) is an artifact due to biases in black hole mass measurements. The sub-Eddington boundary was initially found by Steinhardt & Elvis (2010a) using the FWHM-based black hole mass catalogue of Shen et al. (2008). However, the significance of the boundary is reduced when the FWHM-based mass-scaling relationship is recalibrated following Wang et al. (2009) and using the most updated reverberation mapping estimates of black hole masses. Furthermore, this boundary is not seen using mass estimates based on the line dispersion of the same quasars' MgII emission lines. Thus, the initial report of the sub-Eddington boundary was due to biases in estimating masses using the FWHM of a fit of one or two Gaussians to quasar MgII emission lines. We provide evidence that using the line dispersion of the MgII line produces less biased black hole mass estimates.
Rest-frame UV spectral lines of star-forming galaxies are systematically offset from the galaxies’ systemic redshifts, probably because of large-scale outflows. We calibrate galaxy redshifts measured from rest-frame UV lines by utilizing the fact that the mean HI Ly-alpha absorption profiles around the galaxies, as seen in spectra of background objects, must be symmetric with respect to the true galaxy redshifts if the galaxies are oriented randomly with respect to the lines of sight to the background objects. We use 15 QSOs at z~2.5-3 and more than 600 foreground galaxies with spectroscopic redshifts at z~1.9-2.5. All galaxies are within 2 Mpc proper from the lines of sight to the background QSOs. We find that LyA emission and ISM absorption redshifts require systematic shifts of v_LyA=-295(+35)(-35) km/s and v_ISM=145(+70)(-35) km/s. Assuming a Gaussian distribution, we put 1-sigma upper limits on possible random redshift offsets of <220 km/s for LyA and <420 km/s for ISM redshifts. For the small subset (<10%) of galaxies for which near-IR spectra have been obtained, we can compare our results to direct measurements based on nebular emission lines which we confirm to mark the systemic redshifts. While our v_ISM agrees with the direct measurements, our v_LyA is significantly smaller. However, when we apply our method to the near-IR subsample which is characterized by slightly different selection effects, the best-fit velocity offset comes into agreement with the direct measurement. This confirms the validity of our approach, and implies that no single number appropriately describes the whole population of galaxies, in line with the observation that the line offset depends on galaxy spectral morphology. This method provides accurate redshift calibrations and will enable studies of circumgalactic matter around galaxies for which rest-frame optical observations are not available.
Two distinct scenarios for the origin of the ~ 4 \times 10^8 M\odot of dust observed in the high-redshift (z = 6.4) quasar J1148+5251 have been proposed. The first assumes that this galaxy is much younger than the age of the universe at that epoch so that only supernovae (SNe) could have produced this dust. The second scenario assumes a significantly older galactic age, so that the dust could have formed in lower-mass asymptotic giant branch (AGB) stars. Presenting new integral solutions for the chemical evolution of metals and dust in galaxies, we offer a critical evaluation of these two scenarios, and observational consequences that can discriminate between the two. We show that AGB stars can produce the inferred mass of dust in this object, however, the final mass of surviving dust depends on the galaxy's star formation history (SFH). In general supernovae cannot produce the observed amount of dust unless the average SN event creates over ~ 1 M\odot of dust in its ejecta. However, special SFHs can be constructed in which SNe can produce the inferred dust mass with a reasonable average dust yield of ~ 0.15 M\odot. The two scenarios propose different origins for the galaxy's spectral energy distribution, different star formation efficiencies and stellar masses, and consequently different comoving number densities of J1148+5251-type hyperluminous infrared (IR) objects. The detection of diagnostic mid-IR fine structure lines, and more complete surveys determining the comoving number density of these objects can discriminate between the two scenarios.
The Multi-Epoch Nearby Cluster Survey (MENeaCS) has discovered twenty-two cluster Type Ia supernovae (SNe) in the 58 X-ray selected galaxy clusters (0.05 < z < 0.15) surveyed. Four of our SN Ia events have no host galaxy on close inspection, and are likely intracluster SNe. Deep image stacks at the location of the candidate intracluster SNe put upper limits on the luminosities of faint hosts, with $M_{r} > -13.0$ mag and $M_{g} > -12.5$ mag in all cases. For such limits, the fraction of the cluster luminosity in faint dwarfs below our detection limit is $\lesssim0.1%$, assuming a standard cluster luminosity function. All four events occurred within $\sim$600 kpc of the cluster center (projected), as defined by the position of the brightest cluster galaxy, and are more centrally concentrated than the cluster SN Ia population as a whole. After accounting for several observational biases that make intracluster SNe easier to discover and spectroscopically confirm, we calculate an intracluster stellar mass fraction of $0.17^{+0.14}_{-0.09}$ (68% confidence limit) for all objects within $R_{200}$. If we assume that the intracluster stellar population is exclusively old, and the cluster galaxies themselves have a mix of stellar ages, we derive an upper limit on the intracluster stellar mass fraction of $<0.47$ (84% one-sided confidence limit). When combined with the intragroup SNe results of McGee & Balogh, we confirm the declining intracluster stellar mass fraction as a function of halo mass reported by Gonzalez and collaborators. (Abridged)
We suggest an empirical calibration for determination of oxygen and nitrogen abundances and electron temperature in HII regions where the [OII]3727+3729 line (R_2) is not available. The calibration is based on the strong emission lines of OIII, NII, and SII (NS calibration) and derived using the spectra of HII regions with measured electron temperatures as calibration datapoints. The NS calibration makes it possible to derive abundances for HII regions in nearby galaxies from the SDSS spectra where R_2 line is out of the measured wavelength range, but can also be used for the oxygen and nitrogen abundances determinations in any HII region independently whether the nebular oxygen line [OII]3727+3729 is available or not. The NS calibration provides reliable oxygen and nitrogen abundances for HII regions over the whole range of metallicities.
A new cosmic shear analysis pipeline SUNGLASS (Simulated UNiverses for Gravitational Lensing Analysis and Shear Surveys) is introduced. SUNGLASS is a pipeline that rapidly generates simulated universes for weak lensing and cosmic shear analysis. The pipeline forms suites of cosmological N-body simulations and performs tomographic cosmic shear analysis using line-of-sight integration through these simulations while saving the particle lightcone information. Galaxy shear and convergence catalogues with realistic 3D galaxy redshift distributions are produced for the purposes of testing weak lensing analysis techniques and generating covariance matrices for data analysis and cosmological parameter estimation. We present a suite of fast medium resolution simulations with shear and convergence maps for a generic 100 square degree survey out to a redshift of z = 1.5, with angular power spectra agreeing with the theory to better than a few percent accuracy up to l = 10^3 for all source redshifts up to z = 1.5 and wavenumbers up to l = 2000 for the source redshifts z > 1.1. At higher wavenumbers, there is a failure of the theoretical lensing power spectrum reflecting the known discrepancy of the Smith et al. (2003) fitting formula at high physical wavenumbers. A two-parameter Gaussian likelihood analysis of sigma_8 and Omega_m is also performed on the suite of simulations, demonstrating that the cosmological parameters are recovered from the simulations and the covariance matrices are stable for data analysis. We find no significant bias in the parameter estimation at the level of ~ 0.02. The SUNGLASS pipeline should be an invaluable tool in weak lensing analysis.
We have obtained UBVRI images with the Kitt Peak and Cerro Tololo 4-m telescopes and Mosaic cameras of seven dwarfs in (or near) the Local Group, all of which have known evidence of recent star formation: IC10, NGC 6822, WLM, Sextans B, Sextans A, Pegasus,and Phoenix. We construct color-magnitude diagrams (CMDs) of these systems, as well as neighboring regions that can be used to evaluate the degree of foreground contamination by stars in the Milky Way. Inter-comparison of these CMDs with those of M31, M33, the LMC, and the SMC permits us to determine improved reddening values for a typical OB star found within these galaxies. All of the CMDs reveal a strong or modest number of blue supergiants. All but Pegasus and Phoenix also show the clear presence of red supergiants in the CMD, although IC10 appears to be deficient in these objects given its large WR population. The bright stars of intermediate color in the CMD are badly contaminated by foreground stars (30-100%), and considerable spectroscopy is needed before statistics on the yellow supergiants in these systems will be known. This study is intended to serve both as the impetus and "finding charts" for further space-based imaging, and for many spectroscopic programs at large aperture.
We investigate thermal inflation in double-screen entropic cosmology. We find that its realization is general, resulting from the system evolution from non-equilibrium to equilibrium. Furthermore, going beyond the background evolution, we study the primordial curvature perturbations arising from the universe interior, as well as from the thermal fluctuations generated on the holographic screens. We show that the power spectrum is nearly scale-invariant with a red tilt, while the tensor-to-scalar ratio is in agreement with observations. Finally, we examine the non-Gaussianities of primordial curvature perturbations, and we find that a sizable value of the non-linearity parameter is possible due to holographic statistics on the outer screen.
The small subset of hyper-luminous X-ray sources with luminosities in excess of ~1E41 erg/s are hard to explain without the presence of an intermediate mass black hole, as significantly super-Eddington accretion and/or very small beaming angles are required. The recent discovery of HLX-1, the most luminous object in this class with a record breaking luminosity of ~1E42 erg/s in the galaxy ESO 243-49, therefore currently provides some of the strongest evidence for the existence of intermediate mass black holes. HLX-1 is almost an order of magnitude brighter than the other hyper-luminous sources, and appears to exhibit X-ray spectral and flux variability similar to Galactic stellar mass black hole X-ray binaries. In this paper we review the current state of knowledge on this intriguing source and outline the results of multi-wavelength studies from radio to ultra-violet wavelengths, including imaging and spectroscopy of the recently identified optical counterpart obtained with the Very Large Telescope. These results continue to support an intermediate mass black hole in excess of 500 Msun
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We have employed emission-line diagnostics derived from DEIMOS and NIRSPEC spectroscopy to determine the origin of the [OII] emission line observed in six AGN hosts at z~0.9. These galaxies are a subsample of AGN hosts detected in the Cl1604 supercluster that exhibit strong Balmer absorption lines in their spectra and appear to be in a post-starburst or post-quenched phase, if not for their [OII] emission. Examining the flux ratio of the [NII] to Halpha lines, we find that in five of the six hosts the dominant source of ionizing flux is AGN continuum emission. Furthermore, we find that four of the six galaxies have over twice the [OII] line luminosity that could be generated by star formation processes alone given their Halpha line luminosities. This strongly suggests that AGN-excited narrow-line emission is contaminating the [OII] line flux. A comparison of star formation rates calculated from extinction-corrected [OII] and Halpha line luminosities indicates that the former yields a five-fold overestimate of current activity in these galaxies. Our findings reveal the [OII] line to be a poor indicator of star formation activity in a majority of these moderate-luminosity Seyferts. This result bolsters our previous findings that an increased fraction of AGN at high redshifts are hosted by galaxies in a post-starburst phase. The relatively high fraction of AGN hosts in the Cl1604 supercluster that show signs of recently truncated star formation activity suggest AGN feedback may play an increasingly important role in suppressing ongoing activity in large-scale structures at high redshift.
We consider the relationship between molecular-gas and star-formation surface densities in 19 morphologically defined E/S0s with stellar mass <~ 4x10^10 M_sun, paying particular attention to those found on the blue sequence in color vs. stellar mass parameter space, where spiral galaxies typically reside. While some blue-sequence E/S0s must be young major-merger remnants, many low-mass blue-sequence E/S0s appear much less disturbed, and may be experiencing the milder starbursts associated with inner-disk building as spirals (re)grow. For a sample of eight E/S0s (four blue-, two mid-, and two red-sequence) whose CARMA CO(1-0), Spitzer MIPS 24um, and GALEX FUV emission distributions are spatially resolved on a 750pc scale, we find roughly linear relationships between molecular-gas and star-formation surface densities within all galaxies, with power law indices N = 0.6-1.9 (median 1.2). Adding 11 more blue-sequence E/S0s whose CO(1-0) emission is not as well resolved, we find that most of our E/S0s have global 1-8 kpc aperture-averaged molecular-gas surface densities overlapping the range spanned by the disks and centers of spiral galaxies. While many of our E/S0s fall on the same Schmidt-Kennicutt relation as local spirals, ~80% (predominantly on the blue sequence) are offset towards apparently higher molecular-gas star formation efficiency (i.e., shorter molecular gas depletion time). Possible interpretations of the elevated efficiencies include bursty star formation similar to that in local dwarf galaxies, H2 depletion in advanced starbursts, or simply a failure of the CO(1-0) emission to trace all of the molecular gas.
We present a new proxy for the overdensity peak height for which the large-scale clustering of haloes of a given mass does not vary significantly with the assembly history. The peak height, usually taken to be well represented by the virial mass, can instead be approximated by the mass inside spheres of different radii, which in some cases can be larger than the virial radius and therefore include mass outside the individual host halo. The sphere radii are defined as r = $a$ delta_t + $b$ log_10(M_vir/M_nl), where delta_t is the age relative to the typical age of galaxies hosted by haloes with virial mass M_vir, M_nl is the non-linear mass, and $a$=0.2 and $b$=-0.02 are the free parameters adjusted to trace the assembly bias effect. Note that $r$ depends on both halo mass and age. In this new approach, some of the objects which were initially considered low-mass peaks belong to regions with higher overdensities. At large scales, i.e. in the two-halo regime, this model properly recovers the simple prescription where the bias responds to the height of the mass peak alone, in contrast to the usual definition (virial mass) that shows a strong dependence on additional halo properties such as formation time. The dependence on the age in the one-halo term is also remarkably reduced. The population of galaxies whose "peak height" changes with this new definition consists mainly of old stellar populations and are preferentially hosted by low-mass haloes located near more massive objects. The latter is in agreement with recent results which indicate that old, low-mass haloes would suffer truncation of mass accretion by nearby larger haloes or simply due to the high density of their surroundings, thus showing an assembly bias effect. The change in mass is small enough that the Sheth et al. (2001) mass function is still a good fit to the resulting distribution of new masses.
For early-type galaxies, the correlations between stellar mass and size, velocity dispersion, surface brightness, color, axis ratio and color-gradient all indicate that two mass scales, M* = 3 x 10^10 Msun and M* = 2 x 10^11 Msun, are special. The smaller scale could mark the transition between wet and dry mergers, or it could be related to the interplay between SN and AGN feedback, although quantitative measures of this transition may be affected by morphological contamination. At the more massive scale, mean axis ratios and color gradients are maximal, and above it, the colors are redder, the sizes larger and the velocity dispersions smaller than expected based on the scaling at lower M*. In contrast, the color-sigma relation, and indeed, most scaling relations with sigma, are not curved: they are well-described by a single power law, or in some cases, are almost completely flat. When major dry mergers change masses, sizes, axis ratios and color gradients, they are expected to change the colors or velocity dispersions much less. Therefore, the fact that scaling relations at sigma > 150 km/s show no features, whereas the size-M*, b/a-M*, color-M* and color gradient-M* relations do, suggests that M* = 2 x 10^11 Msun is the scale above which major dry mergers dominate the assembly histories of early-type galaxies.
We consider the signatures of a domain wall produced in the spontaneous symmetry breaking involving a dilaton-like scalar field coupled to electromagnetism. Domains on either side of the wall exhibit slight differences in their respective values of the fine-structure constant, alpha. If such a wall is present within our Hubble volume, absorption spectra at large redshifts may or may not provide a variation in alpha relative to the terrestrial value, depending on our relative position with respect to the wall. This wall could resolve the ``contradiction'' between claims of a variation of alpha based on Keck/Hires data and of the constancy of alpha based on VLT data. We derive the properties of the wall and the parameters of the underlying microscopic model required to reproduce the possible spatial variation of alpha. We discuss the constraints on the existence of the low-energy domain wall and describe its observational implications concerning the variation of the fundamental constants.
We present deep and high-resolution HST/NIC2 F160W imaging at 1.6micron of six z~2 star-forming galaxies with existing near-IR integral field spectroscopy from SINFONI at the VLT. The unique combination of rest-frame optical imaging and nebular emission-line maps provides simultaneous insight into morphologies and dynamical properties. The overall rest-frame optical emission of the galaxies is characterized by shallow profiles in general (Sersic index n<1), with median effective radii of ~5kpc. The morphologies are significantly clumpy and irregular, which we quantify through a non-parametric morphological approach, estimating the Gini (G), Multiplicity (Psi), and M_20 coefficients. The strength of the rest-frame optical emission lines in the F160W bandpass indicates that the observed structure is not dominated by the morphology of line-emitting gas, and must reflect the underlying stellar mass distribution of the galaxies. The sizes and structural parameters in the rest-frame optical continuum and Halpha emission reveal no significant differences, suggesting similar global distributions of the on-going star formation and more evolved stellar population. While no strong correlations are observed between stellar population parameters and morphology within the NIC2/SINFONI sample itself, a consideration of the sample in the context of a broader range of z~2 galaxy types indicates that these galaxies probe the high specific star formation rate and low stellar mass surface density part of the massive z~2 galaxy population, with correspondingly large effective radii, low Sersic indices, low G, and high Psi and M_20. The combined NIC2 and SINFONI dataset yields insights of unprecedented detail into the nature of mass accretion at high redshift. [Abridged]
The bispectrum vanishes for linear Gaussian fields and is thus a sensitive probe of non-linearities and non-Gaussianities in the cosmic density field. Hence, a detection of the bispectrum in the halo density field would enable tight constraints on non-Gaussian processes in the early Universe and allow inference of the dynamics driving inflation. We present a tree level derivation of the halo bispectrum arising from non-linear clustering, non-linear biasing and primordial non-Gaussianity. A diagrammatic description is developed to provide an intuitive understanding of the contributing terms and their dependence on scale, shape and the non-Gaussianity parameter fNL. We compute the terms based on a multivariate bias expansion and the peak-background split method and show that non-Gaussian modifications to the bias parameters lead to amplifications of the tree level bispectrum that were ignored in previous studies. Our results are in a good agreement with published simulation measurements of the halo bispectrum. Finally, we estimate the expected signal to noise on fNL and show that the constraint obtainable from the bispectrum analysis significantly exceeds the one obtainable from the power spectrum analysis.
Subject of this paper is a careful and detailed analysis of the PINOCCHIO algorithm for studying the relative velocity statistics of merging haloes in Lagrangian perturbation theory. Given a cosmological background model, a power spectrum of fluctuations as well as a Gaussian linear density contrast field $\delta_{\rm l}$ is generated on a cubic grid, which is then smoothed repeatedly with Gaussian filters. For each Lagrangian particle at position $\bmath{q}$ and each smoothing radius $R$, the collapse time, the velocities and ellipsoidal truncation are computed using Lagrangian Perturbation Theory. The collapsed medium is then fragmented into isolated objects by an algorithm designed to mimic the accretion and merger events of hierarchical collapse. Directly after the fragmentation process the mass function, merger histories of haloes and the statistics of the relative velocities at merging are evaluated. We reimplemented the algorithm in C++ and optimised the construction of halo merging histories. Comparing our results with the output of the Millennium simulation suggests that PINOCCHIO is well suited for studying relative velocities of merging haloes and is able to reproduce the pairwise velocity distribution.
It is still an unresolved problem how much AGB stars can contribute to the overall gas and dust enrichment processes in the interstellar medium within galaxies. We start tackling this problem, by using our test case observational data from the Large Magellanic Cloud (LMC), from which we obtain the global gas and dust budget. The photometric data from the LMC is obtained with the Spitzer Space Telescope. We established an infrared colour classification scheme to select AGB stars, which are based on spectroscopically identified AGB stars. We further confirm a correlation between the Spitzer colour and mass-loss rate, which leads to a measurement of the total mass-loss rate from the entire AGB population in the LMC. Indeed, AGB stars are an important gas and dust source.
We present the results of spectroscopy of 71 objects with steep and ultra-steep spectra ($\alpha<-0.9$, $S\propto\nu^\alpha$) from the "Big Trio" (RATAN-600-VLA-BTA) project, performed with the "Scorpio" spectrograph on the 6-m telescope of the Special Astrophysical Observatory (Russian Academy of Sciences). Redshifts were determined for these objects. We also present several other parameters of the sources, such as their R-magnitudes, maximum radio sizes in seconds of arc, flux densities at 500, 1425, and 3940 MHz, radio luminosities at 500 and 3940 MHz, and morphology. Of the total number of radio galaxies studied, four have redshifts 1<z<2, three have 2<z<3, one has 3<z<4, and one has z=4.51. Thirteen sources have redshifts 0.7<z<1 and 15 have 0.2<z<0.7. Of all the quasars studied, five have redshifts 0.7<z<1, seven have 1<z<2, four have 2<z<3, and one has z=3.57. We did not detect any spectral lines for 17 objects.
A complex of Halpha emitting blobs with strong FUV excess is associated to the dIrr galaxy VCC1217 / IC3418 (Hester et al. 2010), and extends up to 17 Kpc in the South-East direction. These outstanding features can be morphologically divided into diffuse filaments and compact knots, where most of the star formation activity traced by Halpha takes place. We investigate the properties of the galaxy and the blobs using a multiwavelength approach in order to constrain their origin. We collect publicly available data in UV and Halpha and observe the scene in the optical U,g,r,i bands with LBT. The photometric data allows to evaluate the star formation rate and to perform a SED fitting separately of the galaxy and the blobs in order to constrain their stellar population age. Moreover we analyze the color and luminosity profile of the galaxy and its spectrum to investigate its recent interaction with the Virgo cluster. Our analysis confirms that the most plausible mechanism for the formation of the blobs is ram pressure stripping by the Virgo cluster IGM. The galaxy colors, luminosity profile and SED are consistent with a sudden gas depletion in the last few hundred Myr. The SED fitting of the blobs constrains their ages in < 400 Myr.
The quantum theory of optical coherence is applied to the scrutiny of the statistical properties of the relic inflaton quanta. After adapting the description of the quantized scalar and tensor modes of the geometry to the analysis of intensity correlations, the normalized degrees of first-order and second-order coherence are computed in the concordance paradigm and are shown to encode faithfully the statistical properties of the initial quantum state. The strongly bunched curvature phonons are not only super-Poissonian but also super-chaotic. Testable inequalities are derived in the limit of large angular scales and can be physically interpreted in the light of the tenets of Hanbury Brown-Twiss interferometry. The quantum mechanical results are compared and contrasted with different situations including the one where intensity correlations are the result of a classical stochastic process. The survival of second-order correlations (not necessarily related to the purity of the initial quantum state) is addressed by defining a generalized ensemble where super-Poissonian statistics is an intrinsic property of the density matrix and turns out to be associated with finite volume effects which are expected to vanish in the thermodynamic limit.
We study the bias and scatter in mass measurements of galaxy clusters resulting from fitting spherically-symmetric Navarro, Frenk & White (NFW) model to the reduced tangential shear profile measured in weak lensing observations. The reduced shear profiles are generated for ~10^4 cluster-sized halos formed in LCDM cosmology using a cosmological N-body simulation of a 1 Gpc/h box. In agreement with previous studies, we find that the scatter in the weak lensing masses derived using such fitting method has irreducible contributions from the triaxial shapes of cluster-sized halos and uncorrelated large-scale matter projections along the line-of-sight. Additionally, we find that correlated large-scale structure within several virial radii of clusters contributes a smaller, but nevertheless significant, amount to the scatter. The intrinsic scatter due to these physical sources is ~25-30% depending on the cluster mass and redshift. For current, ground-based observations, however, the total scatter should be dominated by shape noise from the finite number of background galaxies used to measure the shear. Importantly, we find that weak lensing mass measurements can have a small, ~5-10%, but non-negligible amount of bias. Given that weak lensing measurements of cluster masses are a powerful way to calibrate cluster mass-observable relations for precision cosmological constraints in the near future, we strongly emphasize that a robust calibration of the mean amount of bias requires detailed simulations which include more observational effects than we consider here. Such a calibration exercise needs to be carried out for each specific weak lensing mass estimation method, as the details of the method determine in part the expected scatter and bias.
Theoretical models of galaxy formation predict that galaxies acquire most of their baryons via cold mode accretion. Observations of high-redshift galaxies, while finding strong evidence for ubiquitous outflows, have so far not shown convincing traces of the predicted cold streams, which has been interpreted as a challenge for the current models. Using high-resolution, zoom-in smooth particle hydrodynamics simulations of a Milky Way progenitor (corresponding to a modest Lyman break galaxy [LBG] at z~2-3) and of an average-mass LBG, combined with ionizing radiative transfer, we quantify the covering factor of the cold streams at z=2-4. We focus specifically on Lyman limit systems and damped Lya absorbers (DLAs), which can be probed by absorption spectroscopy directly along the line of sight to the galaxy, or using a background galaxy or quasar sightline. We show that the covering factor of these systems is small and decreases rapidly with time. At z=2, the covering factor of DLAs within the virial radius of the simulated galaxies is ~2%, and only ~1% within twice this projected distance. Because of their small covering factor compared to the order unity covering fraction expected for galactic winds, the cold streams are naturally overwhelmed by outflows in absorption spectra. We conclude that the existing observations are consistent with the predictions of cold mode accretion, and outline promising kinematic and chemical diagnostics to separate out the signatures of galactic accretion and feedback.
We study characters of recent type Ia supernova (SNIa) data using evolving dark energy models with changing equation of state parameter w. We consider sudden-jump approximation of w for some chosen redshift spans with double transitions, and constrain these models based on Markov Chain Monte Carlo (MCMC) method using the SNIa data (Constitution, Union, Union2) together with baryon acoustic oscillation A parameter and cosmic microwave background shift parameter in a flat background. In the double-transition model the Constitution data shows deviation outside 1\sigma from LCDM at low redshift whereas no such deviations are noticeable in the Union and Union2 data. By analyzing the Union members in the Constitution set we show that the difference is due to different calibration of the same Union sample in the Constitution set, and is not due to new data added in the Constitution set. All detected deviations are within 2\sigma from the LCDM world model. From the LCDM mock data analysis, we quantify biases in the dark energy equation of state parameters induced by not sufficient data with inhomogeneous distribution of data points in the redshift space and distance modulus errors. We demonstrate that location of peak in the distribution of arithmetic means (computed from the MCMC chain for each mock data) behaves as an unbiased estimator for the average bias, which is valid even for non-symmetric likelihood distributions.
We systematically analyzed the high-quality Suzaku data of 88 Seyfert galaxies. We obtained a clear relation between the absorption column density and the equivalent width of the 6.4 keV line above 10$^{23}$ cm$^{-2}$, suggesting a wide-ranging column density of $10^{23-24.5}$ cm$^{-2}$ with a similar solid and a Fe abundance of 0.7--1.3 solar for Seyfert 2 galaxies. The EW of the 6.4 keV line for Seyfert 1 galaxies are typically 40--120 eV, suggesting the existence of Compton-thick matter like the torus with a column density of $>10^{23}$ cm$^{-2}$ and a solid angle of $(0.15-0.4)*4pi$, and no difference of neutral matter is visible between Seyfert 1 and 2 galaxies. An absorber with a lower column density of $10^{21-23}$ cm$^{-2}$ for Compton-thin Seyfert 2 galaxies is suggested to be not a torus but an interstellar medium. These constraints can be understood by the fact that the 6.4 keV line intensity ratio against the 10--50 keV flux is almost identical within a range of 2--3 in many Seyfert galaxies. Interestingly, objects exist with a low EW, 10--30 eV, of the 6.4 keV line, suggesting that those torus subtends only a small solid angle of $<0.2*4pi$. Ionized Fe-K$\alpha$ emission or absorption lines are detected from several percents of AGNs. Considering the ionization state and equivalent width, emitters and absorbers of ionized Fe-K lines can be explained by the same origin, and highly ionized matter is located at the broad line region. The rapid increase in EW of the ionized Fe-K emission lines at $N_{H}>10^{23}$ cm$^{-2}$ is found, like that of the cold material. It is found that these features seem to change for brighter objects with more than several $10^{44}$ erg/s such that the Fe-K line features become weak. We discuss this feature, together with the torus structure.
Parallel analysis of the large-scale morphology and local environment of matched active and control galaxy samples plays an important role in studies of the fueling of active galactic nuclei. We carry out a detailed morphological characterization of a sample of 35 Seyfert galaxies and a matched sample of inactive galaxies in order to compare the evidence of non-axisymmetric perturbation of the potential and, in the second part of this paper, to be able to perform a multicomponent photometric decomposition of the Seyfert galaxies. We constructed contour maps, BVRcIc profiles of the surface brightness, ellipticity, and position angle, as well as colour index profiles. We further used colour index images, residual images, and structure maps, which helped clarify the morphology of the galaxies. We studied the presence of close companions using literature data. By straightening out the morphological status of some of the objects, we derived an improved morphological classification and built a solid basis for a further multicomponent decomposition of the Seyfert sample. We report hitherto undetected (to our knowledge) structural components in some Seyfert galaxies - a bar (Ark 479), an oval/lens (Mrk 595), rings (Ark 120, Mrk 376), a nuclear bar and ring (Mrk 352), and nuclear dust lanes (Mrk 590). We compared the large-scale morphology and local environment of the Seyfert sample to those of the control one and found that (1) the two samples show similar incidences of bars, rings, asymmetries, and close companions; (2) the Seyfert bars are generally weaker than the bars of the control galaxies; (3) the bulk of the two samples shows morphological evidence of non-axisymmetric perturbations of the potential or close companions; (4) the fueling of Seyfert nuclei is not directly related to the large-scale morphology and local environment of their host galaxies.
An unexpected distribution of temperatures in the Cosmic Microwave Background (CMB) could be a sign of new physics. In particular, the existence of cosmic defects could be indicated by temperature discontinuities via the Kaiser-Stebbins effect. In this letter, it is shown how performing finite differences on a CMB map, with the noise regularized in harmonic space, may expose such discontinuities, and report the results of this process on the 7-year WMAP data.
Cosmological models where the standard Big Bang is replaced by a bounce have been studied for decades. The situation has however dramatically changed in the last years for two reasons. First, because new ways to probe the early Universe have emerged, in particular thanks to the Cosmic Microwave Background (CMB). Second, because some well grounded theories -- especially Loop Quantum Cosmology -- unambiguously predict a bounce, at least for homogeneous models. In this article, we investigate into the details the phenomenological parameters that could be constrained or measured by next-generation B-mode CMB experiments. We point out that an important observational window could be opened. We then show that those constraints can be converted into very meaningful limits on the fundamental Loop Quantum Cosmology (LQC) parameters. This establishes the early universe as an invaluable quantum gravity laboratory.
We report evidence for a fully established galaxy cluster at z=2.07, consisting in a ~20sigma overdensity of red, compact spheroidal galaxies which spatially coincides with an extended X-ray emission detected with XMM-Newton. We use VLT VIMOS and FORS2 spectra and deep Subaru, VLT and Spitzer imaging to estimate the redshift of the structure from a prominent z=2.07 spectroscopic redshift spike of emission-line galaxies, concordant with the accurate 12-band photometric redshifts of the red galaxies. Using NICMOS and Keck AO observations, we find that the red galaxies have elliptical morphologies and compact cores. While they do not form a tight red sequence, their colours are consistent with that of a >1.3 Gyr population observed at z~2.1. From an X-ray luminosity of 7.2*10^43 erg s^-1 and the stellar mass content of the red galaxy population, we estimate a halo mass of 5.3-8*10^13 Msun, comparable to the nearby Virgo cluster. These properties imply that this structure could be the most distant, mature cluster known to date and that X-ray luminous, elliptical-dominated clusters are already forming at substantially earlier epochs than what previously known.
The origin of ultracompact dwarf (UCD) galaxies, compact extragalactic stellar systems, is still a puzzle for present galaxy formation models. We present the comprehensive analysis of high resolution multi-object spectroscopic data for a sample of 24 Fornax cluster UCDs obtained with VLT FLAMES. It comprises previously published data for 19 objects (Mieske et al. 2008) which we re-analysed, including 13 with available HST photometric data. Using Virtual Observatory technologies we found archival HST images for two more UCDs and then determined their structural properties. For all objects we derived internal velocity dispersions, stellar population parameters, and stellar mass-to-light ratios (M/L)* by fitting individual simple stellar population (SSP) synthetic spectra convolved with a Gaussian against the observed spectra using the NBursts full spectral fitting technique. For 14 objects we estimated dynamical masses suggesting no dark matter (DM) in 12 of them and no more than 40 per cent DM mass fraction in the remaining two, in contrast to findings for several UCDs in the Virgo cluster. Some Fornax UCDs even have too high values of (M/L)* estimated using the Kroupa stellar initial mass function (IMF) resulting in negative formally computed DM mass fractions. The objects with too high (M/L)* ratios compared to the dynamical ones have relatively short dynamical relaxation timescales, close to the Hubble time or below. We therefore suggest that their lower dynamical ratios (M/L)dyn are caused by low-mass star depletion due to dynamical evolution. Overall, the observed UCD characteristics suggest at least two formation channels: tidal threshing of nucleated dwarf galaxies for massive UCDs (~10^8 M_sun), and a classical scenario of red globular cluster formation for lower-mass UCDs (< 10^7 M_sun).
The Genetic Algorithm is a heuristic that can be used to produce model independent solutions to an optimization problem, thus making it ideal for use in cosmology and more specifically in the analysis of type Ia supernovae data. In this work we use the Genetic Algorithms (GA) in order to derive a null test on the spatially flat cosmological constant model $\Lambda$CDM. This is done in two steps: first, we apply the GA to the Constitution SNIa data in order to acquire a model independent reconstruction of the expansion history of the Universe $H(z)$ and second, we use the reconstructed $H(z)$ in conjunction with the Om statistic, which is constant only for the $\Lambda$CDM model, to derive our constraints. We find that while $\Lambda$CDM is consistent with the data at the $2\sigma$ level, some deviations from $\Lambda$CDM model at low redshifts can be accommodated.
In the first part of this manuscript, I present the results on the properties
of the interstellar medium and the stellar content of galaxies at z=0.6, from a
representative sample of distant galaxies observed with the long slit
spectrograph VLT/FORS2. This study has been realized in the framework of the
ESO large program IMAGES "Intermediate MAss Galaxy Evolution Sequences", which
aims to investigate the evolution of the main global properties of galaxies up
to z~0.9. I discuss the implications of the observed chemical enrichment of the
gas on the scenarios of galaxy formation. I also propose a new method to
estimate reliable stellar masses in starburst galaxies using broadband
photometry and their total star-formation rate.
In a second part, I present a new method to extract, with high accuracy, the
sky in spectra acquired with a fiber-fed instrument. I have developed this code
in the Framework of the phase A of an instrument proposed for the E-ELT:
OPTIMOS-EVE. This is a multi-fiber spectrograph able to observe at optical and
infrared wavelengths simultaneously.
In the third part, I show preliminary results from the CENTRA GEPI- survey at
Calar Alto Observatory to study nearby galaxies, hosts of type Ia supernovae,
using integral field spectroscopy. I present the first 2D maps of the gas and
stellar populations of SNe Ia hosts. The results allow us to directly access
the host properties in the immediate vicinity of the SNe Ia. This is a crucial
step to investigate eventual correlations between galaxy properties and SNe Ia
events and evolution, leading to systematic effects on the derivation of the
cosmological parameters.
Recent results from the CoGeNT collaboration (as well as the annual modulation reported by DAMA/LIBRA) point toward dark matter with a light (5-10 GeV) mass and a relatively large elastic scattering cross section with nucleons (\sigma ~ 10^{-40} cm^2). In order to possess this cross section, the dark matter must communicate with the Standard Model through mediating particles with small masses and/or large couplings. In this Letter, we explore with a model independent approach the particle physics scenarios that could potentially accommodate these signals. We also discuss how such models could produce the gamma rays from the Galactic Center observed in the data of the Fermi Gamma Ray Space Telescope. We find multiple particle physics scenarios in which each of these signals can be accounted for, and in which the dark matter can be produced thermally in the early Universe with an abundance equal to the measured cosmological density.
The inflationary paradigm has enjoyed phenomenological success, however, a compelling particle physics realization is still lacking. The key obstruction is that the requirement of a suitably flat scalar potential is sensitive to Ultra-Violet (UV) physics. Axions are among the best-motivated inflaton candidates, since the flatness of their potential is naturally protected by a shift symmetry. We re-consider the cosmological perturbations in axion inflation, consistently accounting for the coupling to gauge fields \phi F \tilde{F}, which is generically present in these models. This coupling leads to production of gauge quanta, which provide a new source of inflaton fluctuations, \delta\phi. For an axion decay constant < 10^{-2} M_p, this effect typically dominates over the standard fluctuations from the vacuum and dramatically modifies phenomenological predictions. For concrete realizations that admit a UV completion (such as N-flation and axion monodromy), this can be probed in the near future. We show that: (1) a large tensor-to-scalar ratio is not generic in large field inflation, and, (2) large nongaussianity is easily obtained in very minimal and natural realizations of inflation.
A method is developed for dealing with ultraviolet divergences in calculations of cosmological correlations, which does not depend on dimensional regularization. An extended version of the WKB approximation is used to analyze the divergences in these calculations, and these divergences are controlled by the introduction of Pauli--Villars regulator fields. This approach is illustrated in the theory of a scalar field with arbitrary self-interactions in a fixed flat-space Robertson--Walker metric with arbitrary scale factor $a(t)$. Explicit formulas are given for the counterterms needed to cancel all dependence on the regulator properties, and an explicit prescription is given for calculating finite regulator-independent correlation functions. The possibility of infrared divergences in this theory is briefly considered.
Recent observations in X-rays and gamma-rays of nearby FRI radio galaxies have raised the question of the origin of the emission detected in the termination structures of their jets. The study of these structures can give information on the conditions for particle acceleration and radiation at the front shocks. In addition, an evolutionary scenario can help to disentangle the origin of the detected X-ray emission in young FRI sources, like some Gigahertz Peaked Spectrum AGNs. This work focuses on the nature and detectability of the radiation seen from the termination regions of evolving FRI jets. We use the results of a relativistic, two-dimensional numerical simulation of the propagation of an FRI jet, coupled with a radiation model, to make predictions for the spectra and lightcurves of the thermal and non-thermal emission at different stages of the FRI evolution. Our results show that under moderate magnetic fields, the synchrotron radiation would be the dominant non-thermal channel, appearing extended in radio and more compact in X-rays, with relatively small flux variations with time. The shocked jet synchrotron emission would dominate the X-ray band, although the shocked ISM/ICM thermal component alone may be significant in old sources. Inverse Compton scattering of CMB photons could yield significant fluxes in the GeV and TeV bands, with a non-negligible X-ray contribution. The IC radiation would present a bigger angular size in X-rays and GeV than in TeV, with fluxes increasing with time. We conclude that the thermal and non-thermal broadband emission from the termination regions of FRI jets could be detectable for sources located up to distances of a few 100 Mpc.
Encoded in the time- and wavelength dependent properties of pulsating AGB stars are the underlying fundamental parameters of mass, composition and evolutionary state. However, the standard technique of placing stars on a HR diagram, even with the aid of pulsation periods, can not be done easily for extended AGB stars, because of the difficulty of defining a radius or temperature. The atmospheres of Mira variables are so extended that the optical depth unity radius can vary by a factor of ~3 over the energetically important region of the spectrum. Many important constituents in the radiative transfer are far from local thermodynamic equilibrium, and for the coolest stars, the process of dust formation and destruction requires a time-dependent model of grain growth. I will describe the challenges and some of the solutions to modeling these atmospheres, and describe the utility of different kinds of observations in helping understand both fundamental parameters and chaotic processes in complex AGB atmospheres.
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The existence of hot, X-ray luminous gaseous coronae surrounding present day L* galaxies is a generic prediction of galaxy formation theory in the cold dark matter cosmogony. While extended X-ray emission has been known to exist around elliptical galaxies for a long time, diffuse extra-planar emission has only recently been detected around disc galaxies. We compile samples of elliptical and disc galaxies that have Chandra and XMM-Newton measurements, and compare the scaling of the coronal X-ray luminosity (L_X) with both the K-band luminosity (L_K) and the coronal X-ray temperature (T_X). The X-ray flux measurements are corrected for non-thermal point source contamination by spatial excision and spectral subtraction for resolved and unresolved sources respectively. We find that the properties of the extended X-ray emission from galaxies of different morphological types are similar: for both elliptical and disc galaxies, the L_X - L_K and L_X - T_X relations have similar slope, normalisation and scatter. The observed universality of coronal X-ray properties suggests that the bulk of this emission originates from gas that has been accreted, shock-heated and compressed during the assembly of the galaxy and that outflows triggered by stellar processes make only a minor contribution to the X-ray emission. This reservoir of cooling gas is a potential source of morphological transformation; it provides a fresh supply of material for discs to grow around galaxies of all morphological types.
The transformation of atomic hydrogen to molecular hydrogen through three-body reactions is a crucial stage in the collapse of primordial, metal-free halos, where the first generation of stars (Population III stars) in the Universe are formed. However, in the published literature, the rate coefficient for this reaction is uncertain by nearly an order of magnitude. We report on the results of both adaptive mesh refinement (AMR) and smoothed particle hydrodynamics (SPH) simulations of the collapse of metal-free halos as a function of the value of this rate coefficient. For each simulation method, we have simulated a single halo three times, using three different values of the rate coefficient. We find that while variation between halo realizations may be greater than that caused by the three-body rate coefficient being used, both the accretion physics onto Population III protostars as well as the long-term stability of the disk and any potential fragmentation may depend strongly on this rate coefficient.
We present the results on the star formation history and extinction in the disk of M82 over spatial scales of 10" (~180 pc). Multi-band photometric data covering from the far ultraviolet to the near infrared bands were fitted to a grid of synthetic spectral energy distributions. We obtained distribution functions of age and extinction for each of the 117 apertures analyzed, taking into account observational errors through Monte-Carlo simulations. These distribution functions were fitted with gaussian functions to obtain the mean ages and extinctions along with errors on them. The analyzed zones include the high surface brightness complexes defined by O'Connell & Mangano (1978). We found that these complexes share the same star formation history and extinction as the field stellar populations in the disk. There is an indication that the stellar populations are marginally older at the outer disk (450 Myr at ~3 kpc) as compared to the inner disk (100 Myr at 0.5 kpc). For the nuclear regions (radius less than 500 pc), we obtained an age of less than 10 Myr. The results obtained in this work are consistent with the idea that the 0.5-3 kpc part of the disk of M82 formed around 90% of the stellar mass in a star-forming episode that started around 450 Myr ago lasting for about 350 Myr. We found that field stars are the major contributors to the flux over the spatial scales analyzed in this study, with stellar cluster contribution being 7% in the nucleus and 0.7% in the disk.
A new numerical technique to identify the cosmic web is proposed. It is based on locating multi-stream flows, i.e. the places where the velocity field is multi-valued. The method is local in Eulerian space, simple and computaionally efficient. This technique uses the velocities of particles and thus takes into account the dynamical information. This is in contrast with the majority of standard methods that use the coordinates of particles only. Two quantities are computed in every mesh cell: the mean and variance of the velocity field. In the cells where the velocity is single-valued the variance must be equal to zero exactly, therefore the cells with non-zero variance are identified as multi-stream flows. The technique has been tested in a N-body simulation of the \L CDM model. The preliminary analysis has shown that numerical noise does not pose a significant problem. The web identified by the new method has been compared withthe web identified by the standard technique using only the particle coordinates. The comparison has shown overall similarity of two webs as expected, however they by no means are identical. For example, the isocontours of the corresponding fields have significantly different shapes and some density peaks of similar heights exhibit significant differences in the velocity variance and vice versa. This suggest that the density and velocity variance have a significant degree of independence. The shape of the two-dimensional pdf of density and velocity variance confirms this proposition. Thus, we conclude that the dynamical information probed by this technique introduces an additional dimension into analysis of the web.
(Abridged) Ultracompact Minihaloes (UCMHs), which formed by dark matter accretion onto primordial black holes (PBHs) or initial dark matter overdensity produced by the primordial density perturbation, provide a new type of dark matter annihilation source to ionize and heat the IGM after matter-radiation equality z_eq, which is much earlier than the formation of the first cosmological dark halo structure and later first star radiation. We show that dark matter annihilation density contributed by UCMHs can totally dominated over that by the homogenous dark matter background, and provide a new gamma-ray background in the early Universe. The main constraint of UCMH abundance is given by the CMB optical depth measurement, under which UCMH annihilation can increase the gas reionization fraction by one order of magnitude higher, and the IGM temperature from adiabatic cooling T_m ~ (1+z)^{2} to T_m ~ (1+z). A small fraction of UCMHs are seeded by PBHs. The X-ray emission from accreting baryonic gas into PBHs may totally dominated over dark matter annihilation within the host UCMHs, but the constraints of gas accretion rate and X-ray absorption by the accumulated baryons within the UCMHs show the PBH radiation can only be a promising source much later than UCMH annihilation at z<z_m<<1000, where z_m depends on M_{PBH}, the initial minihalo mass and dark matter particle mass. The effects of pure UCMH annihilation on the structure evolution are obvious for the gas chemical quantities, but quite small for the temperature and structure formation. PBH host UCMHs, on the other hand, can significantly suppress the first baryonic structure formation, as they provide a much hotter IGM background before the structure formation.
Quasars that allow the study of IGM He II are very rare, since they must be at high redshift along sightlines free of substantial hydrogen absorption, but recent work has dramatically expanded the number of such quasars known. We analyze two dozen higher-redshift (z=3.1-3.9) low-resolution He II quasar spectra from HST and find that their He II Gunn-Peterson troughs suggest exclusion of very early and very late reionization models, favoring a reionization redshift of z~3. Although the data quality is not sufficient to reveal details such as the expected redshift evolution of helium opacity, we obtain the first ensemble measure of helium opacity at high redshift averaged over many sightlines: tau=4.90 at z~3.3. We also find that it would be very difficult to observe the IGM red wing of absorption from the beginning of He II reionization, but depending on the redshift of reionization and the size of ionization zones, it might be possible to do so in some objects with the current generation of UV spectrographs.
We present galaxy spectroscopic data on a pencil beam of $10.75' \times7.5'$ centered on the X-ray cluster RXJ0054.0-2823 at $z = 0.29$. We study the spectral evolution of galaxies from $z=1$ down to the cluster redshift in a magnitude-limited sample at $\rm R\leq23$, for which the statistical properties of the sample are well understood. We divide emission-line galaxies in star-forming galaxies, LINERs, and Seyferts by using emission-line ratios of [OII], $\rm H\beta$, and [OIII], and derive stellar fractions from population synthesis models. We focus our analysis on absorption and low-ionization galaxies. For absorption-line galaxies we recover the well known result that these galaxies have had no detectable evolution since $z\sim0.6-0.7$, but we also find that in the range $z=0.65-1$ at least 50% of the stars in bright absorption systems are younger than 2.5Gyr. Faint absorption-line galaxies in the cluster at $z = 0.29$ also had significant star formation during the previous 2-3Gyr, while their brighter counterparts seem to be composed only of old stars. At $z\sim0.8$, our dynamically young cluster had a truncated red-sequence. This result seems to be consistent with a scenario where the final assembly of E/S0 took place at $z<1$. In the volume-limited range $0.35\leq z\leq0.65$ we find that 23% of the early-type galaxies have LINER-like spectra with $\rm H\beta$ in absorption and a significant component of A stars. The vast majority of LINERs in our sample have significant populations of young and intermediate-aged stars and are thus not related to AGN, but to the population of `retired galaxies' recently identified by Cid-Fernandes et al. (2010) in the SDSS. Early-type LINERs with various fractions of A stars, and E+A galaxies appear to play an important role in the formation of the red sequence.
We study the star/galaxy classification efficiency of 13 different decision tree algorithms applied to photometric objects in the Sloan Digital Sky Survey Data Release Seven (SDSS DR7). Each algorithm is defined by a set of parameters which, when varied, produce different final classification trees. We extensively explore the parameter space of each algorithm, using the set of $884,126$ SDSS objects with spectroscopic data as the training set. The efficiency of star-galaxy separation is measured using the completeness function. We find that the Functional Tree algorithm (FT) yields the best results as measured by the mean completeness in two magnitude intervals: $14\le r\le21$ ($85.2%$) and $r\ge19$ ($82.1%$). We compare the performance of the tree generated with the optimal FT configuration to the classifications provided by the SDSS parametric classifier, 2DPHOT and Ball et al. (2006). We find that our FT classifier is comparable or better in completeness over the full magnitude range $15\le r\le21$, with much lower contamination than all but the Ball et al. classifier. At the faintest magnitudes ($r>19$), our classifier is the only one able to maintain high completeness ($>$80%) while still achieving low contamination ($\sim2.5%$). Finally, we apply our FT classifier to separate stars from galaxies in the full set of $69,545,326$ SDSS photometric objects in the magnitude range $14\le r\le21$.
Spatial inhomogeneities in the spectral shape of the ultra-violet background (UVB) at the tail-end of HeII reionisation are thought to be the primary cause of the large fluctuations observed in the HeII to HI Ly-a forest optical depth ratio, tau_HeII/tau_HI, at z~2-3. These spectral hardness fluctuations will also influence the ionisation balance of intergalactic metals; we extract realistic quasar absorption spectra from a large hydrodynamical simulation to examine their impact on intergalactic SiIV and CIV absorbers. Using a variety of toy UVB models, we find that while the predicted spatial inhomogeneities in spectral hardness have a significant impact on tau_HeII/tau_HI, the longer mean free path for photons with frequencies above and below the HeII ionisation edge means these fluctuations have less effect on the SiIV and CIV ionisation balance. Furthermore, UVB models which produce the largest fluctuations in specific intensity at the HeII ionisation edge also have the softest ionising spectra, and thus result in photo-ionisation rates which are too low to produce significant fluctuations in the observed tau_SiIV/tau_CIV. Instead, we find spatial variations in the IGM metallicity will dominate any scatter in tau_SiIV/tau_CIV. Our results suggest that observational evidence for homogeneity in the observed tau_SiIV/tau_CIV distribution does not rule out the possibility of significant fluctuations in the UVB spectral shape at z~2-3. On the other hand, the scatter in metallicity inferred from observations of intergalactic CIV and SiIV absorption using spatially uniform ionisation corrections is likely intrinsic, and therefore provides a valuable constraint on intergalactic metal enrichment scenarios at high redshift.
Using deep Subaru/FOCAS spectra of 34 HII regions in both the inner and outer parts of the extended ultraviolet (XUV) disc galaxy NGC 4625 we have measured an abundance gradient out to almost 2.5 times the optical isophotal radius. We applied several strong line abundance calibrations to determine the HII region abundances, including R23, [NII]/[OII], [NII]/Ha as well as the [OIII]4363 auroral line, which we detected in three of the HII regions. We find that at the transition between the inner and outer disc the abundance gradient becomes flatter. In addition, there appears to be an abundance discontinuity in proximity of this transition. Several of our target HII regions appear to deviate from the ionisation sequence defined in the [NII]/Ha vs. [OIII]/Hb diagnostic diagram by bright extragalactic HII regions. Using theoretical models we conclude that the most likely explanations for these deviations are either related to the time evolution of the HII regions, or stochastic variations in the ionising stellar populations of these low mass HII regions, although we are unable to distinguish between these two effects. Such effects can also impact on the reliability of the strong line abundance determinations.
Studies of 22GHz H2O maser emission from the merging galaxy NGC 6240 with double nuclei are presented. Two epochs of Very Large Array (VLA) observations in the A-configuration in spectral-line mode were carried out at 0.1 arcsec resolution by covering the redshifted velocity range of ~ 300 km/s with respect to the systemic velocity of the galaxy. The purpose of these new observations is twofold: to detect an H2O maser that an earlier VLA observation pinpointed in the southern nucleus in the northern nucleus as well to clarify the kinematics of the double nuclei, and to understand the origin of the maser in the galaxy. In the second epoch, one velocity feature peaking at Vlsr=7491.1 km/s, redshifted by ~200 km/s relative to the systemic velocity, was detected only toward the southern nucleus. The detection of an H2O maser feature at or near this velocity had never been reported in earlier observations. However, including the known velocity features at redshifted velocities, no other velocity features were observed toward either nuclei throughout these epochs. The maser remains unresolved at an angular resolution of ~ 0".1, corresponding to a linear size of less than about 45 pc. The two epochs of VLA observations show that the maser intensity is variable on timescales of at least three months, while the correlation between the maser intensity and the radio continuum intensity is not certain from our data. It is plausible that the maser in NGC 6240 is associated with the activity of an active galactic nucleus in the southern nucleus. Alternatively, the maser can be explained by starforming activity at the site of massive starformation in the galaxy.
We study cosmological consequences of a kinetic braiding model, which is proposed as an alternative to the dark energy model. The kinetic braiding model we study is characterised by a parameter n, which corresponds to the original Galileon cosmological model for n=1. We find that the background expansion of the universe of the kinetic braiding model is the same as the Dvali-Turner's model. Then, we focus our study on the evolution of the linear density perturbation as well as the spherical collapse in the nonlinear regime of the density perturbations, which are important in order to distinguish between the kinetic braiding model and the Lambda cold dark matter (CDM) model. The theoretical prediction for the large scale structure is confronted with the multipole power spectrum of the luminous red galaxy sample of the Sloan Digital Sky survey. We also discuss future prospects of constraining the kinetic braiding model using a future redshift survey like the WFMOS/SUMIRE as well as the cluster redshift distribution in the South Pole Telescope survey.
The evolution of an inhomogeneous universe composed entirely of matter is followed from an early, nearly uniform state until the time when the inhomogeneities have begun to grow large. The particular distribution of matter studied in this article is chosen to have a periodic variation in only one of the directions, which is simple enough to allow the behavior of the metric to be solved analytically, well beyond a linear approximation based on the initial smallness of the fluctuation. This example provides an illustration of a universe where the inhomogeneities can affect its average expansion rate; and its simplicity allows a condition to be derived that tells when their presence should begin to become important. Since the averages of the non-uniform parts of the metric and the matter density grow faster than their uniform parts, the average expansion rate accelerates with the advent of the era governed by the inhomogeneities.
We develop a new method which measures the projected density distribution w_p(r_p)n of photometric galaxies surrounding a set of spectroscopically-identified galaxies, and simultaneously the projected cross-correlation function w_p(r_p) between the two populations. In this method we are able to divide the photometric galaxies into luminosity intervals even when redshift information is unavailable, enabling us to measure w_p(r_p)n and w_p(r_p) as a function of not only the luminosity of the spectroscopic galaxy, but also that of the photometric galaxy. We have applied our method to data from the Sloan Digital Sky Survey (SDSS) including a sample of 10^5 luminous red galaxies (LRGs) at z~0.4 and a sample of about half a million galaxies at z~0.1, both of which are cross-correlated with a deep photometric sample drawn from the SDSS. On large scales, the relative bias factor measured from w_p(r_p) for LRGs at z~0.4 depends on luminosity in a manner similar to what is found for galaxies at z~0.1, which are usually probed by autocorrelations of spectroscopic samples in previous studies. On scales smaller than a few Mpc and at both z~0.4 and z~0.1, the w_p(r_p)n and w_p(r_p) for central galaxies with fixed luminosity show quite similar slopes to each other, regardless which types of satellite galaxies we consider. This provides direct support for the assumption commonly-adopted in halo occupation distribution (HOD) models that satellite galaxies of different luminosities are distributed in a similar way, following the dark matter distribution within their host halos.
In this paper we discuss the results of a programme of spectral synthesis modelling of a sample of starburst radio galaxies in the context of scenarios for the triggering of the activity and the evolution of the host galaxies. The starburst radio galaxies -- comprising ~15 - 25% of all powerful extragalactic radio sources -- frequently show disturbed morphologies at optical wavelengths, and unusual radio structures, although their stellar masses are typical of radio galaxies as a class. In terms of the characteristic ages of their young stellar populations (YSP), the objects can be divided into two groups: those with YSP ages t_ysp < 0.1 Gyr, in which the radio source has been triggered quasi-simultaneously with the main starburst episode, and those with older YSP in which the radio source has been triggered or re-triggered a significant period after the starburst episode. Combining the information on the YSP with that on the optical morphologies of the host galaxies, we deduce that the majority of the starburst radio galaxies have been triggered in galaxy mergers in which at least one of the galaxies is gas rich. However, the triggering (or re-triggering) of the radio jets can occur immediately before, around, or a significant period after the final coalescence of the merging nuclei, reflecting the complex gas infall histories of the merger events. Overall, our results provide further evidence that powerful radio jet activity can be triggered via a variety of mechanisms, including different evolutionary stages of major galaxy mergers; clearly radio-loud AGN activity is not solely associated with a particular stage of a unique type of gas accretion event.
We explore the complementarity of weak lensing and galaxy peculiar velocity measurements to better constrain modifications to General Relativity. We find no evidence for deviations from GR on cosmological scales from a combination of peculiar velocity measurements (for Luminous Red Galaxies in the Sloan Digital Sky Survey) with weak lensing measurements (from the CFHT Legacy Survey). We provide a Fisher error forecast for a Euclid-like space-based survey including both lensing and peculiar velocity measurements, and show that the expected constraints on modified gravity will be at least an order of magnitude better than with present data, i.e. we will obtain 5% errors on the modified gravity parametrization described here. We also present a model--independent method for constraining modified gravity parameters using tomographic peculiar velocity information, and apply this methodology to the present dataset.
We assess the possibility to detect the warm-hot intergalactic medium (WHIM) in emission and to characterize its physical conditions and spatial distribution through spatially resolved X-ray spectroscopy, in the framework of the recently proposed DIOS, EDGE, Xenia, and ORIGIN missions, all of which are equipped with microcalorimeter-based detectors. For this purpose we analyze a large set of mock emission spectra, extracted from a cosmological hydrodynamical simulation. These mock X-ray spectra are searched for emission features showing both the OVII K alpha triplet and OVIII Ly alpha line, which constitute a typical signature of the warm hot gas. Our analysis shows that 1 Ms long exposures and energy resolution of 2.5 eV will allow us to detect about 400 such features per deg^2 with a significance >5 sigma and reveals that these emission systems are typically associated with density ~100 above the mean. The temperature can be estimated from the line ratio with a precision of ~20%. The combined effect of contamination from other lines, variation in the level of the continuum, and degradation of the energy resolution reduces these estimates. Yet, with an energy resolution of 7 eV and all these effects taken into account, one still expects about 160 detections per deg^2. These line systems are sufficient to trace the spatial distribution of the line-emitting gas, which constitute an additional information, independent from line statistics, to constrain the poorly known cosmic chemical enrichment history and the stellar feedback processes.
Noncommutative geometry can provide effective description of physics at very short distances taking into account generic effects of quantum gravity. Inflation amplifies tiny quantum fluctuations in the early universe to macroscopic scales and may thus imprint high energy physics signatures in the cosmological perturbations that could be detected in the CMB. It is shown here that this can give rise to parity-violating modulations of the primordial spectrum and odd non-Gaussian signatures. The breaking of rotational invariance of the CMB provides constraints on the scale of noncommutativity that are competitive with the existing noncosmological bounds, and could explain the curious hemispherical asymmetry that has been claimed to be observed in the sky. This introduces also non-Gaussianity with peculiar shape- and scale-dependence, which in principle allows an independent cross-check of the presence of noncommutativity at inflation.
A great deal of our understanding of star formation in the local universe has been built upon an extensive foundation of H-alpha observational studies. However, recent work in the ultraviolet (UV) with GALEX has shown that star formation rates (SFRs) inferred from H-alpha in galactic environments characterized by low stellar and gas densities tend to be less than those based on the UV luminosity. The origin of the discrepancy is actively debated because one possible explanation is that the stellar initial mass function is systematically deficient in high mass stars in such environments. In this contribution, we summarize our work on this topic using a dwarf galaxy dominated sample of ~300 late-type galaxies in the 11 Mpc Local Volume. The sample allows us to examine the discrepancy between H-alpha and UV SFRs using a statistical number of galaxies with activities less than 0.1 Msun/yr. A range of potential causes for such an effect are reviewed. We find that while the IMF hypothesis is not inconsistent with our observations, alternate explanations remain that must be investigated further before a final conclusion can be drawn.
We present new medium resolution kinematic data for a sample of 21 dwarf early-type galaxies (dEs) mainly in the Virgo cluster, obtained with the WHT and INT telescopes at the Roque de los Muchachos Observatory (La Palma, Spain). These data are used to study the origin of the dwarf elliptical galaxy population inhabiting clusters. We confirm that dEs are not dark matter dominated galaxies, at least up to the half-light radius. We also find that the observed galaxies in the outer parts of the cluster are mostly rotationally supported systems with disky morphological shapes. Rotationally supported dEs have rotation curves similar to those of star forming galaxies of similar luminosity and follow the Tully-Fisher relation. This is expected if dE galaxies are the descendant of low luminosity star forming systems which recently entered the cluster environment and lost their gas due to a ram pressure stripping event, quenching their star formation activity and transforming into quiescent systems, but conserving their angular momentum.
Underground searches for dark matter involve a complicated interplay of particle physics, nuclear physics, atomic physics and astrophysics. We attempt to remove the uncertainties associated with astrophysics by developing the means to map the observed signal in one experiment directly into a predicted rate at another. We argue that it is possible to make experimental comparisons that are completely free of astrophysical uncertainties by focusing on {\em integral} quantities, such as $g(v_{min})=\int_{v_{min}} dv\, f(v)/v $ and $\int_{v_{thresh}} dv\, v g(v)$. Direct comparisons are possible when the $v_{min}$ space probed by different experiments overlap. As examples, we consider the possible dark matter signals at CoGeNT, DAMA and CRESST-Oxygen. We find that expected rate from CoGeNT in the XENON10 experiment is higher than observed, unless scintillation light output is low. Moreover, we determine that S2-only analyses are constraining, unless the charge yield $Q_y< 2.4 {\, \rm electrons/keV}$. For DAMA to be consistent with XENON10, we find for $q_{Na}=0.3$ that the modulation rate must be extremely high ($\gsim 70%$ for $m_\chi = 7\, \gev$), while for higher quenching factors, it makes an explicit prediction (0.8 - 0.9 cpd/kg) for the modulation to be observed at CoGeNT. Finally, we find CDMS-Si, even with a 10 keV threshold, as well as XENON10, even with low scintillation, would have seen significant rates if the excess events at CRESST arise from elastic WIMP scattering, making it very unlikely to be the explanation of this anomaly.
This paper discusses the methodology necessary to measure the Hubble constant
Ho to a high degree of accuracy based upon Doppler tracking of spacecraft in
the solar system. Using this methodology with available published data we
determine a model independent value of the Hubble constant for the current
epoch in the solar system to be Ho = 2.59 \pm 0.05 x 10^-18 (s^-1) or as 79.8
\pm 1.7 (km/s/Mpc).
We calculate the direct effect of the Cosmic Redshift on Doppler tracking of
spacecraft in the solar system. It is shown that with current tracking systems,
such as NASA's Deep Space Tracking Network, when the return trip light time of
the Doppler signal exceeds a certain threshold, imposed by the stability of the
frequency standard, the effect of the Cosmic Redshift is coherently conserved
in the returning Doppler signal.
We demonstrate that in an underdetermined orbit, one determined by line of
sight Doppler alone, that if this Cosmic Redshift term is not accounted for,
the orbit determination program (ODP) miscalculates the actual recessional
velocity of the spacecraft from the measured recessional velocity causing a
mismatch between the actual and the predicted trajectory of the spacecraft. One
consequence is that the ODP will generate Doppler residuals, the difference
between the actual trajectory and the predicted trajectory which show an
anomalous force. When this effect is integrated in long arc solutions, it can
grow to considerable magnitude. We show that the ODP residuals uniquely
separate the Cosmic Redshift term from velocity Doppler sources and that the
solution can provide an accurate determination of Ho.
In this Letter, by reconstructing the $Om$ diagnostic and the deceleration parameter $q$ from the latest Union2 Type Ia supernova sample with and without the systematic error along with the baryon acoustic oscillation (BAO) and the cosmic microwave background (CMB), we study the cosmic expanding history, using the Chevallier-Polarski-Linder (CPL) parametrization. We obtain that Union2+BAO favor an expansion with a decreasing of the acceleration at $z<0.3$. However, once the CMB data is added in the analysis, the cosmic acceleration is found to be still increasing, indicating a tension between low redshift data and high redshift. In order to reduce this tension significantly, two different methods are considered and thus two different subsamples of Union2 are selected. We then find that two different subsamples+BAO+CMB give completely different results on the cosmic expanding history when the systematic error is ignored, with one suggesting a decreasing cosmic acceleration, the other just the opposite, although both of them alone with BAO support that the cosmic acceleration is slowing down. However, once the systematic error is considered, two different subsamples of Union2 along with BAO and CMB all favor an increasing of the present cosmic acceleration. Therefore a clear-cut answer on whether the cosmic acceleration is slowing down calls for more consistent data and more reliable methods to analyze them.
The past decade has seen a large progress in the X-ray investigation of early-type galaxies of the local universe, and first attempts have been made to reach redshifts z>0 for these objects, thanks to the high angular resolution and sensitivity of the satellites Chandra and XMM-Newton. Major advances have been obtained in our knowledge of the three separate contributors to the X-ray emission, that are the stellar sources, the hot gas and the galactic nucleus. Here a brief outline of the main results is presented, pointing out the questions that remain open, and finally discussing the prospects to solve them with a wide area X-ray survey mission such as WFXT.
We study the cosmic expansion history by reconstructing the deceleration parameter $q(z)$ from the SDSS-II type Ia supernova sample (SNIa) with two different light curve fits (MLCS2k2 and SALT-II), the baryon acoustic oscillation (BAO) distance ratio, the cosmic microwave background (CMB) shift parameter, and the lookback time-redshift (LT) from the age of old passive galaxies. Three parametrization forms for the equation of state of dark energy (CPL, JBP, and UIS) are considered. Our results show that, for the CPL and the UIS forms, MLCS2k2 SDSS-II SNIa+BAO+CMB and MLCS2k2 SDSS-II SNIa+BAO+CMB+LT favor a currently slowing-down cosmic acceleration, but this does not occur for all other cases, where an increasing cosmic acceleration is still favored. Thus, the reconstructed evolutionary behaviors of dark energy and the course of the cosmic acceleration are highly dependent both on the light curve fitting method for the SNIa and the parametrization form for the equation of state of dark energy.
In this work we provide the fitting formula valid for the simulated photon spectra from WIMP annihilation into light quark-anti quark (qq-) channels in a wide range of WIMP masses. We illustrate our results for the cc- channel.
We present the preliminary results of two Gemini campaigns to constrain the mass of the black hole in an ultraluminous X-ray source (ULX) via optical spectroscopy. Pilot studies of the optical counterparts of a number of ULXs revealed two candidates for further detailed study, based on the presence of a broad He II 4686 Angstrom emission line. A sequence of 10 long-slit spectra were obtained for each object, and the velocity shift of the ULX counterpart measured. Although radial velocity variations are observed, they are not sinusoidal, and no mass function is obtained. However, the broad He II line is highly variable on timescales shorter than a day. If associated with the reprocessing of X-rays in the accretion disc, its breadth implies that the disc must be close to face-on.
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The functional form of the galaxy-wide stellar initial mass function is of fundamental importance for understanding galaxies. So far this stellar initial mass function has been assumed to be identical to the IMF observed directly in star clusters. But because stars form predominantly in embedded groups rather than uniformly distributed over the whole galaxy, the galaxy-wide IMF needs to be calculated by adding all IMFs of all embedded groups. This integrated galactic stellar initial mass function (IGIMF) is steeper than the canonical IMF and steepens with decreasing SFR, leading to fundamental new insights and understanding of star forming properties of galaxies. This contribution reviews the existing applications of the IGIMF theory to galactic astrophysics, while the parallel contribution by Weidner, Pflamm-Altenburg & Kroupa (this volume) introduces the IGIMF theory.
Using a semi-analytical model developed by Choudhury & Ferrara (2005) we study the observational constraints on reionization via a principal component analysis (PCA). Assuming that reionization at z>6 is primarily driven by stellar sources, we decompose the unknown function N_{ion}(z), representing the number of photons in the IGM per baryon in collapsed objects, into its principal components and constrain the latter using the photoionization rate obtained from Ly-alpha forest Gunn-Peterson optical depth, the WMAP7 electron scattering optical depth and the redshift distribution of Lyman-limit systems at z \sim 3.5. The main findings of our analysis are: (i) It is sufficient to model N_{ion}(z) over the redshift range 2<z<14 using 5 parameters to extract the maximum information contained within the data. (ii) All quantities related to reionization can be severely constrained for z<6 because of a large number of data points whereas constraints at z>6 are relatively loose. (iii) The weak constraints on N_{ion}(z) at z>6 do not allow to disentangle different feedback models with present data. There is a clear indication that N_{ion}(z) must increase at z>6, thus ruling out reionization by a single stellar population with non-evolving IMF, and/or star-forming efficiency, and/or photon escape fraction. The data allows for non-monotonic N_{ion}(z) which may contain sharp features around z \sim 7. (iv) The PCA implies that reionization must be 99% completed between 5.8<z<10.3 (95% confidence level) and is expected to be 50% complete at z \approx 9.5-12. With future data sets, like those obtained by Planck, the z>6 constraints will be significantly improved.
We study the scale and redshift dependence of the power spectra for density perturbations and peculiar velocities, and the evolution of a coarse grained phase space density for (WDM) particles that decoupled during the radiation dominated stage. The (WDM) corrections are obtained in a perturbative expansion valid in the range of redshifts at which N-body simulations set up initial conditions, and for a wide range of scales. The redshift dependence is determined by the kurtosis $\beta_2$ of the distribution function at decoupling. At large redshift there is an enhancement of peculiar velocities for $\beta_2 > 1$ that contributes to free streaming and leads to further suppression of the matter power spectrum and an enhancement of the peculiar velocity autocorrelation function at scales smaller than the free streaming scale. Statistical fluctuations of peculiar velocities are also suppressed on these scales by the same effect. In the linearized approximation, the coarse grained phase space density features redshift dependent (WDM) corrections from gravitational perturbations determined by the power spectrum of density perturbations and $\beta_2$. For $\beta_2 > 25/21$ it \emph{grows logarithmically} with the scale factor as a consequence of the suppression of statistical fluctuations. Two specific models for WDM are studied in detail. The (WDM) corrections relax the bounds on the mass.
It has been recently proposed that the interpretation of gravity as an emergent, entropic force might have nontrivial implications to cosmology. Here two approaches are investigated: in one, the Friedman equation receives entropic contributions from the usually neglected surface terms, and in another, the extra terms are derived from quantum corrections to the entropy formula. UV terms may drive inflation, avoiding a recently derived no-go theorem, though in some cases leading to a graceful exit problem. IR terms can generate dark energy, alleviating the cosmological constant problem. The quantum corrections are bounded by their implications to the BBN, and the surface terms are constrained in addition by their effect upon the behavior of matter. Likelihood analyses are performed to constrain the modifications by the SNeIa, BAO and CMB data. It is found that a monomial correction to the area-entropy formula results in late acceleration in very good agreement with observations, which then turn out to be compatible with positive curvature. The evolution of perturbations is deduced by assuming the Jebsen-Birkhoff theorem. Distinct signatures can then be identified in the large scale structure formation. Furthermore, it is shown that the visible universe satisfies the Bekenstein bound.
We analyze our accurate kinematical data for the old clusters in the inner regions of M31. These velocities are based on high S/N Hectospec data (Caldwell et al 2010). The data are well suited for analysis of M31's inner regions because we took particular care to correct for contamination by unresolved field stars from the disk and bulge in the fibers. The metal poor clusters show kinematics which are compatible with a pressure-supported spheroid. The kinematics of metal-rich clusters, however, argue for a disk population. In particular the innermost region (inside 2 kpc) shows the kinematics of the x2 family of bar periodic orbits, arguing for the existence of an inner Lindblad resonance in M31.
The uncertainty in the redshift distributions of galaxies has a significant potential impact on the cosmological parameter values inferred from multi-band imaging surveys. The accuracy of the photometric redshifts measured in these surveys depends not only on the quality of the flux data, but also on a number of modeling assumptions that enter into both the training set and SED fitting methods of photometric redshift estimation. In this work we focus on the latter, considering two types of modeling uncertainties: uncertainties in the SED template set and uncertainties in the magnitude and type priors used in a Bayesian photometric redshift estimation method. We find that SED template selection effects dominate over magnitude prior errors. We introduce a method for parameterizing the resulting ignorance of the redshift distributions, and for propagating these uncertainties to uncertainties in cosmological parameters.
The "cosmological principle" was set up early without realizing its implications for the horizon problem, and almost entirely without support from observational data. Consistent signals of anisotropy have been found in data on electromagnetic propagation, polarizations of QSOs and $CMB$ temperature maps. The axis of Virgo is found again and again in signals breaking isotropy, from independent observables in independent energy regimes. There are no satisfactory explanations of these effects in conventional astrophysics. Axion-photon mixing and propagation in axion condensates are capable of encompassing the data.
We introduce a probabilistic approach to the problem of counting dwarf satellites around host galaxies in databases with limited redshift information. This technique is used to investigate the occurrence of satellites with luminosities similar to the Magellanic Clouds around hosts with properties similar to the Milky Way in the object catalog of the Sloan Digital Sky Survey. Our analysis uses data from SDSS Data Release 7, selecting candidate Milky-Way-like hosts from the spectroscopic catalog and candidate analogs of the Magellanic Clouds from the photometric catalog. Our principal result is the probability for a Milky-Way-like galaxy to host N_{sat} close satellites with luminosities similar to the Magellanic Clouds. We find that 81 percent of galaxies like the Milky Way are have no such satellites within a radius of 150 kpc, 11 percent have one, and only 3.5 percent of hosts have two. The probabilities are robust to changes in host and satellite selection criteria, background-estimation technique, and survey depth. These results demonstrate that the Milky Way has significantly more satellites than a typical galaxy of its luminosity; this fact is useful for understanding the larger cosmological context of our home galaxy.
We searched for quasars that are ~ 3 mag fainter than the SDSS quasars in the redshift range 3.7 < z < 4.7 in the COSMOS field to constrain the faint end of the quasar luminosity function. Using optical photometric data, we selected 31 quasar candidates with 22 < i' < 24 at z ~ 4. We obtained optical spectra for most of these candidates using FOCAS on the Subaru telescope, and identified 8 low-luminosity quasars at z ~ 4. In order to derive the quasar luminosity function (QLF) based on our spectroscopic follow-up campaign, we estimated the photometric completeness of our quasar survey through detailed Monte Carlo simulations. Our QLF at z ~ 4 has a much shallower faint-end slope beta = -1.67^{+0.11}_{-0.17} than that obtained by other recent surveys in the same redshift. Our result is consistent with the scenario of downsizing evolution of active galactic nuclei inferred by recent optical and X-ray quasar surveys at lower redshifts.
We combine the GALFORM semi-analytical model of galaxy formation, which predicts the star formation and merger histories of galaxies, the GRASIL spectro-photometric code, which calculates the spectral energy distributions (SEDs) of galaxies self-consistently including reprocessing of radiation by dust, and artificial neural networks (ANN), to investigate the clustering properties of galaxies selected by their emission at submillimetre wavelengths (SMGs). We use the Millennium Simulation to predict the spatial and angular distribution of SMGs. At redshift z = 2, we find that these galaxies are strongly clustered, with a comoving correlation length of r0 = 5.6 \pm 0.9 Mpc/h for galaxies with 850{\mu}m flux densities brighter than 5 mJy, in agreement with observations. We predict that at higher redshifts these galaxies trace denser and increasingly rarer regions of the universe. We present the predicted dependence of the clustering on luminosity, submillimetre colour, halo and total stellar masses. Interestingly, we predict tight relations between correlation length and halo and stellar masses, independent of sub-mm luminosity.
The EDELWEISS-II experiment uses cryogenic heat-and-ionization detectors in order to detect the rare interactions from possible WIMP dark matter particles on Germanium nuclei. Recently, new-generation detectors with an interleaved electrode geometry were developped and validated, enabling an outstanding rejection of gamma-rays and surface interactions. We present here preliminary results of a one-year WIMP search carried out with ten of such detectors in the Laboratoire Souterrain de Modane. A sensitivity to the spin-independent WIMP-nucleon cross-section of 5 \times 10-8 pb was achieved using a 322 kg
Measurement of redshifted 21-cm emission from neutral hydrogen promises to be the most effective method for studying the reionisation history of hydrogen and, indirectly, the first galaxies. These studies will be limited not by raw sensitivity to the signal, but rather, by bright foreground radiation from Galactic and extragalactic radio sources and the Galactic continuum. In addition, leakage due to gain errors and non-ideal feeds conspire to further contaminate low-frequency radio obsevations. This leakage leads to a portion of the complex linear polarisation signal finding its way into Stokes I, and inhibits the detection of the non-polarised cosmological signal from the epoch of reionisation. In this work, we show that rotation measure synthesis can be used to recover the signature of cosmic hydrogen reionisation in the presence of contamination by polarised foregrounds. To achieve this, we apply the rotation measure synthesis technique to the Stokes I component of a synthetic data cube containing Galactic foreground emission, the effect of instrumental polarisation leakage, and redshifted 21-cm emission by neutral hydrogen from the epoch of reionisation. This produces an effective Stokes I Faraday dispersion function for each line of sight, from which instrumental polarisation leakage can be fitted and subtracted. Our results show that it is possible to recover the signature of reionisation in its late stages (z ~ 7) by way of the 21-cm power spectrum, as well as through tomographic imaging of ionised cavities in the intergalactic medium.
We consider the Einstein equations within the DBI scenario for a spatially flat Friedmann-Robertson-Walker (FRW) spacetime without a cosmological constant. We derive the inflationary scenario by applying the symmetry transformations which preserve the form of the Friedmann and conservation equations. These form invariance transformations generate a symmetry group parametrized by the Lorentz factor $\ga$. We explicitly obtain an inflationary scenario by the cooperative effect of adding energy density into the Friedmann equation. For the case of a constant Lorentz factor, and under the slow roll assumption, we find the transformation rules for the scalar and tensor power spectra of perturbations as well as their ratio under the action of the form invariance symmetry group. Within this case and due to its relevance for the inflationary paradigm, we find the general solution of the dynamical equations for a DBI field driven by an exponential potential and show a broad set of inflationary solutions. The general solution can be split into three subsets and all these behave asymptotically as a power law solution at early and at late times.
We present a series of colour evolution models for Luminous Red Galaxies (LRGs) in the 7th spectroscopic data release of the Sloan Digital Sky Survey (SDSS), computed using the full-spectrum fitting code VESPA on high signal-to-noise stacked spectra. The colour-evolution models are computed as a function of colour, luminosity and redshift, and we do not a-priori assume that LRGs constitute a uniform population of galaxies in terms of stellar evolution. By computing star-formation histories from the fossil record, the measured stellar evolution of the galaxies is decoupled from the survey's selection function, which also evolves with redshift. We present these evolutionary models computed using three different sets of Stellar Population Synthesis (SPS) codes. We show that the traditional fiducial model of purely passive stellar evolution of LRGs is broadly correct, but it is not sufficient to explain the full spectral signature. We also find that higher-order corrections to this model are dependent on the SPS used, particularly when calculating the amount of recent star formation. The amount of young stars can be non-negligible in some cases, and has important implications for the interpretation of the number density of LRGs within the selection box as a function of redshift. Dust extinction, however, is more robust to the SPS modelling: extinction increases with decreasing luminosity, increasing redshift, and increasing r-i colour. We are making the colour evolution tracks publicly available at this http URL
In this paper I review the recent progress in understanding the physics of the gas outflowing from active galactic nuclei and its impact on the surrounding environment, using the combined information provided by multiwavelength Ultraviolet-X-ray campaigns.
Infrared-faint radio sources (IFRS) are objects that have flux densities of several mJy at 1.4GHz, but that are invisible at 3.6um when using sensitive Spitzer observations with uJy sensitivities. Their nature is unclear and difficult to investigate since they are only visible in the radio. High-resolution radio images and comprehensive spectral coverage can yield constraints on the emission mechanisms of IFRS and can give hints to similarities with known objects. We imaged a sample of 17 IFRS at 4.8GHz and 8.6GHz with the Australia Telescope Compact Array to determine the structures on arcsecond scales. We added radio data from other observing projects and from the literature to obtain broad-band radio spectra. We find that the sources in our sample are either resolved out at the higher frequencies or are compact at resolutions of a few arcsec, which implies that they are smaller than a typical galaxy. The spectra of IFRS are remarkably steep, with a median spectral index of -1.4 and a prominent lack of spectral indices larger than -0.7. We also find that, given the IR non-detections, the ratio of 1.4GHz flux density to 3.6um flux density is very high, and this puts them into the same regime as high-redshift radio galaxies. The evidence that IFRS are predominantly high-redshift sources driven by active galactic nuclei (AGN) is strong, even though not all IFRS may be caused by the same phenomenon. Compared to the rare and painstakingly collected high-redshift radio galaxies, IFRS appear to be much more abundant, but less luminous, AGN-driven galaxies at similar cosmological distances.
Wide-field surveys are a commonly-used method for studying thousands of objects simultaneously, to investigate, e.g., the joint evolution of star-forming galaxies and active galactic nuclei. VLBI observations can yield valuable input to such studies because they are able to identify AGN. However, VLBI observations of large swaths of the sky are impractical using standard methods, because the fields of view of VLBI observations are of the order of 10" or less. We have embarked on a project to carry out Very Long Baseline Array (VLBA) observations of all 96 known radio sources in one of the best-studied areas in the sky, the Chandra Deep Field South (CDFS). The challenge was to develop methods which could significantly reduce the amount of observing (and post-processing) time. We have developed an extension to the DiFX software correlator which allows one to correlate hundreds of positions within the primary beams. This extension enabled us to target many sources, at full resolution and high sensitivity, using only a small amount of observing time. The combination of wide fields-of-view and high sensitivity across the field in this survey is unprecedented. We have observed with the VLBA a single pointing containing the Chandra Deep Field South, in which 96 radio sources were known from previous observations with the ATCA. From our input sample, 20 were detected with the VLBA. The majority of objects have flux densities in agreement with arcsec-scale observations, implying that their radio emission comes from very small regions. One VLBI-detected object had earlier been classified as a star-forming galaxy. Comparing the VLBI detections to sources found in sensitive, co-located X-ray observations we find that X-ray detections are not a good indicator for VLBI detections. Wide-field VLBI survey science is now coming of age.
VLBI observations are a reliable method to identify AGN, since they require high brightness temperatures for a detection to be made. However, because of the tiny fields of view it is unpractical to carry out VLBI observations of many sources using conventional methods. We used an extension of the DiFX software correlator to image with high sensitivity 96 sources in the Chandra Deep Field South, using only 9h of observing time with the VLBA. We detected 20 sources, 8 of which had not been identified as AGN at any other wavelength, despite the comprehensive coverage of this field. The lack of X-ray counterparts to 1/3 of the VLBI-detected sources, despite the sensitivity of co-located X-ray data, demonstrates that X-ray observations cannot be solely relied upon when searching for AGN activity. Surprisingly, we find that sources classified as type 1 QSOs using X-ray data are always detected, in contrast to the 10% radio-loud objects which are found in optically-selected QSOs. We present the continuation of this project with the goal to image 1450 sources in the Lockman Hole/XMM region.
Cosmological observations on the largest scales exhibit a solid record of unexpected anomalies and alignments, apparently pointing towards a large scale violation of statistical isotropy. These include a variety of CMB measurements, as well as alignments of quasar polarisation vectors. In this paper we explore the possibility that several of the aforementioned large scale correlations are in fact not independent, and can be understood in a coherent way within the framework of a parity odd local Universe, and ultimately related to the nature of Dark Energy and its interactions with light.
We have derived colour gradients for a sample of 20 early-type galaxies (ETGs) at 1 < z_spec < 2 selected from the GOODS-South field. The sample includes both normal ETGs (13) having effective radii comparable to the mean radius of local ones and compact ETGs (7) having effective radii from two to six times smaller. Colour gradients have been derived in the F606W-F850LP bands (UV-U rest-frame) taking advantage of the ultradeep HST-ACS observations covering this field and providing a spatial resolution of about 0.8 kpc at the redshift of the galaxies. Despite of the narrow wavelength baseline covered (1000 Angstrom), sampling approximatively the emission dominated by the same stellar population, we detect significant radial colour variations in 50 per cent of our sample. In particular, we find five ETGs with positive colour gradients (cores bluer than the external regions), and five galaxies with negative colour gradients (cores redder than the external regions), as commonly observed in the local Universe. These results show that at 1 < z < 2, when the Universe was only 3-4 Gyr old, ETGs constituted a composite population of galaxies whose different assembly histories have generated different stellar distributions with the bluest stellar population either in the center or in the outskirts as well as throughout the whole galaxy. Moreover, we find that compact galaxies seem to preferentially show a blue cores while moving towards normal galaxies, central stellar populations become progressively redder. Nonetheless, the narrow baseline covered together with the low statistics still prevent us to be conclusive about a possible physical connection between colour gradients and the degree of compactness of high-z ETGs.
We have carried out a narrow-band survey of the Local Group galaxy, M33, in the HeII4686 emission line, to identify HeII nebulae in this galaxy. With spectroscopic follow-up observations, we confirm three of seven candidate objects, including identification of two new HeII nebulae, BCLMP651, HBW673. We also obtain spectra of associated ionizing stars for all the HII regions, identifying two new WN stars. We demonstrate that the ionizing source for the known HeII nebula, MA 1, is consistent with being the early-type WN star MC8 (M33-WR14), by carrying out a combined stellar and nebular analysis of MC8 and MA1. We were unable to identify the helium ionizing sources for HBW 673 and BCLMP 651, which do not appear to be Wolf-Rayet stars. According to the [OIII]5007/Hbeta vs [NII]6584/Halpha diagnostic diagram, excitation mechanisms apart from hot stellar continuum are needed to account for the nebular emission in HBW 673, which appears to have no stellar source at all.
We construct new galaxy angular power spectra based on the extended, updated and final SDSS II Luminous Red Galaxy (LRG) photometric redshift survey: MegaZ DR7. Encapsulating 7746 deg^{2} we utilise 723,556 photometrically determined LRGs between 0.45 < z < 0.65 in a 3.3 (Gpc h^{-1})^3 spherical harmonic analysis of the galaxy distribution. By combining four photometric redshift bins we find preliminary parameter constraints of f_{b} = \Omega_{b}/\Omega_{m} = 0.173 +/- 0.046 and \Omega_{m} = 0.260 +/- 0.035 assuming H_{0} = 75 km s^{-1} Mpc^{-1}, n_{s}=1 and \Omega_{k} = 0. These limits are consistent with the CMB and the previous data release (DR4). The C_{\ell} are sensitive to redshift space distortions and therefore we also recast our constraints into a measurement of \beta ~ \Omega_{m}^{0.55}/b in different redshift shells. The robustness of these power spectra with respect to a number of potential systematics such as extinction, photometric redshift and ANNz training set extrapolation are examined. The latter includes a cosmological comparison of available photometric redshift estimation codes where we find excellent agreement between template and empirical estimation methods. MegaZ DR7 represents a methodological prototype to next generation surveys such as the Dark Energy Survey (DES) and, furthermore, is a photometric precursor to the spectroscopic BOSS survey. Our galaxy catalogue and all power spectra data can be found at this http URL
We show that redshift-space distortions of galaxy correlations have a strong effect on correlation functions with distinct, localized features, like the signature of the Baryon Acoustic Oscillations (BAO). Near the line of sight, the features become sharper as a result of redshift-space distortions. We demonstrate this effect by measuring the correlation function in Gaussian simulations and the Millennium Simulation. We also analyze the SDSS DR7 main-galaxy sample (MGS), splitting the sample into slices 2.5 degrees on the sky in various rotations. Measuring 2D correlation functions in each slice, we do see a sharp bump along the line of sight. Using Mexican-hat wavelets, we localize it to (110 +/- 10) Mpc/h. At a particular wavelet scale and location, employing the variance of the wavelet transform, we estimate its significance at about 4 sigma. We estimate that there is about a 0.2% chance of getting such a signal anywhere in the vicinity of the BAO scale from a power spectrum lacking a BAO feature. However, these estimates of the significances make some use of idealized Gaussian simulations, and thus are likely a bit optimistic.
We report results from a reanalysis of data from the Cryogenic Dark Matter Search (CDMS II) experiment at the Soudan Underground Laboratory. Data taken between October 2006 and September 2008 using eight germanium detectors are reanalyzed with a lowered, 2 keV recoil-energy threshold, to give increased sensitivity to interactions from Weakly Interacting Massive Particles (WIMPs) with masses below ~10 GeV/c^2. This analysis provides stronger constraints than previous CDMS II results for WIMP masses below 9 GeV/c^2 and excludes parameter space associated with possible low-mass WIMP signals from the DAMA/LIBRA and CoGeNT experiments.
This paper presents the first results from a new citizen science project: Galaxy Zoo Supernovae. This proof of concept project uses members of the public to identify supernova candidates from the latest generation of wide-field imaging transient surveys. We describe the Galaxy Zoo Supernovae operations and scoring model, and demonstrate the effectiveness of this novel method using imaging data and transients from the Palomar Transient Factory (PTF). We examine the results collected over the period April-July 2010, during which nearly 14,000 supernova candidates from PTF were classified by more than 2,500 individuals within a few hours of data collection. We compare the transients selected by the citizen scientists to those identified by experienced PTF scanners, and find the agreement to be remarkable - Galaxy Zoo Supernovae performs comparably to the PTF scanners, and identified as transients 93% of the ~130 spectroscopically confirmed SNe that PTF located during the trial period (with no false positive identifications). Further analysis shows that only a small fraction of the lowest signal-to-noise SN detections (r > 19.5) are given low scores: Galaxy Zoo Supernovae correctly identifies all SNe with > 8{\sigma} detections in the PTF imaging data. The Galaxy Zoo Supernovae project has direct applicability to future transient searches such as the Large Synoptic Survey Telescope, by both rapidly identifying candidate transient events, and via the training and improvement of existing machine classifier algorithms.
We present a new measurement of the mass of the Milky Way (MW) based on observed properties of its largest satellite galaxies, the Magellanic Clouds (MCs), and an assumed prior of a {\Lambda}CDM universe. A large, high resolution cosmological simulation of this universe provides a means to statistically sample the dynamical properties of bright satellite galaxies in a large population of dark matter halos. The observed properties of the MCs, including their circular velocity, distance from the center of the MW, and velocity within the MW halo, are used to evaluate the likelihood that a given halo would have each or all of these properties; the posterior PDF for any property of the MW system can thus be constructed. This method provides a constraint on the MW virial mass, 1.2^{+0.7}_{-0.4}x10^12 M0 (68% confidence), which is consistent with recent determinations that involve very different assumptions. In addition, we calculate the posterior PDF for the density profile of the MW and its satellite accretion history. Although typical satellites of 1e12 M_\bigodot halos are accreted over a wide range of epochs over the last 10 Gyr, we find a 72% probability that the Magellanic Clouds were accreted within the last Gyr, and a 50% probability that they were accreted together.
We review the developments in modeling gravitational recoil from merging black-hole binaries and introduce a new set of simulations to test our previously proposed empirical formula for the recoil. The configurations are chosen to represent generic binaries with unequal masses and precessing spins. Results of these simulations indicate that the recoil formula is accurate to within a few km/s in the similar mass-ratio regime for the out-of-plane recoil.
The ultraluminous X-ray source (ULX) Holmberg II X-1 has been observed over 4 months in 2009/2010 by the Swift observatory. The source luminosity varied by a factor of up to 14, reaching a maximum 0.3-10 keV luminosity of ~3.0E40 erg/s. The spectral properties do not vary much over these 4 months, with only a slight monotonic increase of the hardness ratio with the count rate. This means that the erratic flaring activity of the source is not associated with spectral changes, as seen in other ULXs. Conversely, comparison with data obtained by Swift in 2006 shows a completely different picture: while at a luminosity also seen in the 2009/2010 data, the source appears with a hard spectrum. Thus, it appears that, as in Galactic black hole binaries, spectral states in this ULX are not determined only by the X-ray luminosity.
The warm inflation paradigm considers the continuous production of radiation during inflation due to dissipative effects. In its strong dissipation limit, warm inflation gives way to a radiation dominated Universe. High scale inflation then yields a high reheating temperature, which then poses a severe gravitino overproduction problem for the supersymmetric realisations of warm inflation. In this paper we show that in certain class of supersymmetric models the dissipative dynamics of the inflaton is such that the field can avoid its complete decay after inflation. In some cases, the residual energy density stored in the field oscillations may come to dominate over the radiation bath at a later epoch. If the inflaton field finally decays much later than the onset of the matter dominated phase, the entropy produced in its decay may be sufficient to counteract the excess of gravitinos produced during the last stages of warm inflation.
There is a continued debate as to the form of the outer disc of the Milky Way galaxy, which has important implications for its formation. Stars are known to exist at a galacto-centric distance of at least 20 kpc. However, there is much debate as to whether these stars can be explained as being part of the disc or whether another extra galactic structure, the so called Monoceros ring/stream, is required. To examine the outer disc of the Galaxy toward the anti-centre to determine whether the star counts can be explained by the thin and thick discs alone. Using Sloan star counts and extracting the late F and early G dwarfs it is possible to directly determine the density of stars out to a galacto-centric distance of about 25 kpc. These are then compared with a simple flared disc model. A flared disc model is shown to reproduce the counts along the line of sights examined, if the thick disc does not have a sharp cut off. The flare starts at a Galacto-centric radius of 16 kpc and has a scale length of 4.5+/-1.5 kpc. Whilst the interpretation of the counts in terms of a ring/stream cannot be definitely discounted, it does not appear to be necessary, at least along the lines of sight examined towards the anti centre.
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(Abridged) We study the rate at which gas accretes on to galaxies and haloes and investigate whether the accreted gas was shocked to high temperatures before reaching a galaxy. For this purpose we use a suite of large cosmological, hydrodynamical simulations from the OWLS project. We improve on previous work by considering a wider range of halo masses and redshifts, by distinguishing accretion on to haloes and galaxies, by including important feedback processes, and by comparing simulations with different physics. The specific rate of gas accretion on to haloes is, like that for dark matter, only weakly dependent on halo mass. For halo masses Mhalo>>10^11 Msun it is relatively insensitive to feedback processes. In contrast, accretion rates on to galaxies are determined by radiative cooling and by outflows driven by supernovae and active galactic nuclei. Galactic winds increase the halo mass at which the central galaxies grow the fastest by about two orders of magnitude to Mhalo~10^12 Msun. Gas accretion is bimodal, with maximum past temperatures either of order the virial temperature or <~10^5 K. The fraction of gas accreted on to haloes in the hot mode is insensitive to feedback and metal-line cooling. It increases with redshift, but is mostly determined by halo mass, increasing gradually from less than 10% for ~10^11 Msun to greater than 90% at 10^13 Msun. In contrast, for accretion on to galaxies the cold mode is always significant and the relative contributions of the two accretion modes are more sensitive to feedback and metal-line cooling. On average, the majority of stars present in any mass halo at any redshift were formed from gas accreted in the cold mode, although the hot mode contributes typically over 10% for Mhalo>~10^11 Msun. Galaxies, but not their gaseous haloes, are predominantly fed by gas that did not experience an accretion shock when it entered the host halo.
Recent studies emphasize that an empirical relation between the stellar mass of galaxies and the mass of their host dark matter subhaloes can predict the clustering of galaxies and its evolution with cosmic time. In this paper we study the assumptions made by this methodology using a semi-analytical model (SAM). To this end, we randomly swap between the locations of model galaxies within a narrow range of subhalo mass (M_infall). We find that shuffled samples of galaxies have different auto-correlation functions in comparison with the original model galaxies. This difference is significant even if central and satellite galaxies are allowed to follow a different relation between M_infall and stellar mass, and can reach a factor of 2 for massive galaxies at redshift zero. We analyze three features within SAMs that contribute to this effect: a) The relation between stellar mass and subhalo mass evolves with redshift for central galaxies, affecting satellite galaxies at the time of infall. b) The stellar mass of galaxies falling into groups and clusters at high redshift is different from the mass of central galaxies at the same time. c) The stellar mass growth for satellite galaxies after infall can be significant and depends on the infall redshift and the group mass. We show that the above is true for differing SAMs, and that the effect is sensitive to the treatment of dynamical friction and stripping of gas in satellite galaxies. We find that by using the FoF group mass at redshift zero in addition to M_infall, an empirical model is able to accurately reproduce the clustering properties of galaxies. On the other hand, using the infall redshift as a second parameter does not yield as good results because it is less correlated with stellar mass. Our analysis indicates that environmental processes are important for modeling the clustering and abundance of galaxies. (Abridged)
We use two cosmological simulations of structure formation to study the conditions under which dark matter haloes emerge from the linear density field. Our analysis focuses on matching sites of halo collapse to local density maxima, or "peaks", in the initial conditions of the simulations and provides a crucial test of the central ansatz of the peaks formalism. By identifying peaks on a variety of smoothed, linearly extrapolated density fields we demonstrate that as many as ~70% of well-resolved dark matter haloes form preferentially near peaks whose characteristic masses are similar to that of the halo, with more massive haloes showing a stronger tendency to reside near peaks initially. We identify a small but significant fraction of haloes that appear to evolve from peaks of substantially lower mass than that of the halo itself. We refer to these as "peakless haloes" for convenience. By contrasting directly the properties of these objects with the bulk of the proto-halo population we find two clear differences: 1) their initial shapes are significantly flatter and more elongated than the predominantly triaxial majority, and 2) they are, on average, more strongly compressed by tidal forces associated with their surrounding large scale structure. Using the two-point correlation function we show that peakless haloes tend to emerge from highly clustered regions of the initial density field implying that, at fixed mass, the accretion geometry and mass accretion histories of haloes in highly clustered environments differ significantly from those in the field. This may have important implications for understanding the origin of the halo assembly bias, of galaxy properties in dense environments and how environment affects the morphological transformation of galaxies near groups and rich galaxy clusters.
We perform a statistical analysis of the peculiar velocity field around dark matter haloes in numerical simulations. We examine different properties of the infall of material onto haloes and its relation to central halo shapes and the shape of the large scale surrounding regions (LSSR). We find that the amplitude of the infall velocity field along the halo shape minor axis is larger than that along the major axis. This is consistent for general triaxial haloes, and for both prolate and oblate systems. We also report a strong anisotropy of the velocity field along the principal axes of the LSSR. The infall velocity field around dark matter haloes reaches a maximum value along the direction of the minor axis of the LSSR, whereas along the direction of its major axis, it exhibits the smallest velocities. We also analyse the dependence of the matter velocity field on the local environment. The amplitude of the infall velocity at high local density regions is larger than at low local density regions. The velocity field tends to be more laminar along the direction towards the minor axis of the LSSR, where the mean ratio between flow velocity and velocity dispersion is of order unity and nearly constant up to scales of 15 Mpc/h. We also detect anisotropies in the outflowing component of the velocity field, showing a maximum amplitude along the surrounding LSSR major axis.
High-spatial resolution near-infrared (NIR) images of the central 24 x 24 arcsec^2 (~ 2 x 2 kpc^2) of the elliptical galaxy NGC 1052 reveal a total of 25 compact sources randomly distributed in the region. Fifteen of them exhibit Halpha luminosities an order of magnitude above the estimate for an evolved population of extreme horizontal branch stars. Their Halpha equivalent widths and optical-to-NIR spectral energy distributions are consistent with them being young stellar clusters aged < 7 Myr. We consider this to be the first direct observation of spatially resolved star-forming regions in the central kiloparsecs of an elliptical galaxy. The sizes of these regions are ~< 11 pc and their median reddening is E(B - V) ~ 1 mag. According to previous works, NGC 1052 may have experienced a merger event about 1 Gyr ago. On the assumption that these clusters are spreaded with similar density over the whole galaxy, the fraction of galaxy mass (5 x 10^{-5}) and rate of star formation (0.01 Msun/yr) involved, suggest the merger event as the possible cause for the star formation we see today.
Using new photometric and spectroscopic data in the fields of nine strong gravitational lenses that lie in galaxy groups, we analyze the effects of both the local group environment and line-of-sight galaxies on the lens potential. We use Monte Carlo simulations to derive the shear directly from measurements of the complex lens environment, providing the first detailed independent check of the shear obtained from lens modeling. We account for possible tidal stripping of the group galaxies by varying the fraction of total mass apportioned between the group dark matter halo and individual group galaxies. The environment produces an average shear of gamma = 0.08 (ranging from 0.02 to 0.17), significant enough to affect quantities derived from lens observables. However, the direction and magnitude of the shears do not match those obtained from lens modeling in three of the six 4-image systems in our sample (B1422, RXJ1131, and WFI2033). The source of this disagreement is not clear, implying that the assumptions inherent in both the environment and lens model approaches must be reconsidered. If only the local group environment of the lens is included, the average shear is gamma = 0.05 (ranging from 0.01 to 0.14), indicating that line-of-sight contributions to the lens potential are not negligible. We isolate the effects of various theoretical and observational uncertainties on our results. Of those uncertainties, the scatter in the Faber-Jackson relation and error in the group centroid position dominate. Future surveys of lens environments should prioritize spectroscopic sampling of both the local lens environment and objects along the line of sight, particularly those bright (I < 21.5) galaxies projected within 5' of the lens.
We investigate the large-scale influence of outflows from AGNs in enriching the IGM with metals in a cosmological context. We combine cosmological simulations of large scale structure formation with a detailed model of metal enrichment, in which outflows expand anisotropically along the direction of least resistance, distributing metals into the IGM. The metals carried by the outflows are generated by two separate stellar populations: stars located near the central AGN, and stars located in the greater galaxy. Using this algorithm, we performed a series of 5 simulations of the propagation of AGN-driven outflows in a cosmological volume of size (128/h Mpc)^3 in a Lambda-CDM universe, and analyze the resulting metal enrichment of the IGM. We found that the metallicity induced in the IGM is greatly dominated by AGNs having bolometric luminosity L > 10^9 L_sun, sources with 10^8 < L / L_sun < 10^9 having a negligible contribution. Our simulations produced an average IGM metallicity of [O/H] = -5 at z = 5.5, which then rises gradually, and remains relatively flat at a value [O/H] = -2.8 between z = 2 and z = 0. The ejection of metals from AGN host galaxies by AGN-driven outflows is found to enrich the IGM to > 10 - 20% of the observed values, the number dependent on redshift. The enriched IGM volume fractions are small at z > 3, then rise rapidly to the following values at z = 0: 6 - 10% of the volume enriched to [O/H] > -2.5, 14 - 24% volume to [O/H] > -3, and 34 - 45% volume to [O/H] > -4. At z > 2, there is a gradient of the induced enrichment, the metallicity decreasing with increasing IGM density, enriching the underdense IGM to higher metallicities, a trend more prominent with increasing anisotropy of the outflows. This can explain observations of metal-enriched low-density IGM at z = 3 - 4.
Cosmological observations indicate that our universe is flat and dark energy (DE) dominated at present. The luminosity distance plays an important role in the investigation of the evolution and structure of the universe. Nevertheless, the evaluation of the luminosity distance d_L is associated computationally heavy numerical quadratures in practice. In this Letter we find a series solution of the luminosity distance in a spatially flat LCDM cosmological model. And it is further shown that the series solution has a relative error of less than 0.36% for any relative parameter \beta (\beta = Omega_m / Omega_L) from zero to four, i.e. 0.2 < Omega_L < 1 and redshift z > 0.1 when the order of the series is n = 100.
We propose a simple model for dark energy useful for comparison with observations.This is based on the idea that dark energy and inflation should be caused by exactly the same physical process. Linde's simple chaotic inflation V=\frac{1}{2}m^{2}\phi^{2} produces values of n_{s}=0.967 and r=0.13 which are consistent with the WMAP 1{\sigma} error bars. We therefore propose V=\frac{1}{2}m_{2}^{2}\phi_{2}^{2}+\frac{1}{2}m_{1}^{2}\phi_{1}^{2} with m_{1}\sim10^{-5} and m_{2}\leq10^{-60}. The fine tuning problem is thus only half as bad as if one wanted dark energy to be produced by a constant V_{0}\sim10^{-120}. For comparison, neutrino masses are of order 10^{-29}. The field \phi_{1} drives inflation and has damped by now (\phi_{1,0}=0), while \phi_{2} in slow roll produces dark energy with values today of \delta w_{0}\equiv w_{0}+1\approx4/(3\phi_{2,0}^{2}+2). Our numerical results are well fit by \delta w(z)\approx\delta w_{0}\left(H_{0}/H(z)\right)^{2}. This should be true in any slow roll inflation. Our potential can be easily realized in N-flation models with many fields. This model is easily falsifiable by upcoming experiments-for example, if Linde's chaotic inflation is ruled out. But if r values consistent with Linde's chaotic inflation are detected then one should take this model seriously indeed.
Context: The baryonic dark matter dominating the structures of galaxies is widely considered as mysterious, but hints for it have been in fact detected in several astronomical observations at optical, infrared, and radio wavelengths. We call attention to the nature of galaxy merging, the observed rapid microlensing of a quasar, the detection of "cometary knots" in planetary nebulae, and the Lyman-alpha clouds as optical phenomena revealing the compact objects. Radio observations of "extreme scattering events" and "parabolic arcs" and microwave observations of "cold dust cirrus" clouds are observed at 15 - 20 K temperatures are till now not considered in a unifying picture. Aims: The theory of gravitational hydrodynamics predicts galactic dark matter arises from Jeans clusters that are made up of almost a trillion micro brown dwarfs (mBDs) of earth weight. It is intended to explain the aforementioned anomalous observations and to make predictions within this framework. Methods: We employ analytical isothermal modeling to estimate various effects. Results: Estimates of their total number show that they comprise enough mass to constitute the missing baryonic matter. Mysterious radio events are explained by mBD pair merging in the Galaxy. The "dust" temperature of cold galaxy halos arises from a thermostat setting due to a slow release of latent heat at the 14 K gas to solid transition at the mBD surface. The proportionality of the central black hole mass of a galaxy and its number of globular clusters is explained. The visibility of an early galaxy at redshift 8.6 is obvious with most hydrogen locked up in mBDs. Conclusions: Numerical simulations of various steps would further test the approach. It looks promising to redo MACHO searches against the Magellanic clouds.
We study non-linear contributions to the power spectrum of the curvature perturbation on super-horizon scales, produced during slow-roll inflation driven by a canonical single scalar field. We find that on large scales the linear power spectrum completely dominates and leading non-linear corrections remain totally negligible, indicating that we can safely rely on linear perturbation theory to study inflationary power spectrum. We also briefly comment on the infrared and ultraviolet behaviour of the non-linear corrections.
Aims. We report on a detailed study of the optical afterglow of GRB 061121 with our original time-series photometric data. In conjunction with X-ray observations, we discuss the origin of its optical and X-ray afterglows. Methods. We observed the optical afterglow of Swift burst GRB 061121 with the Kanata 1.5-m telescope at Higashi-Hiroshima Observatory. Our observation covers a period just after an X-ray plateau phase. We also performed deep imaging with the Subaru telescope in 2010 in order to estimate the contamination of the host galaxy. Results. In the light curve, we find that the optical afterglow also exhibited a break as in the X-ray afterglow. However, our observation suggests a possible hump structure or a flattening period before the optical break in the light curve. There is no sign of such a hump in the X-ray light curve. Conclusions. This implies that the emitting region of optical was distinct from that of X-rays. The hump in the optical light curve was possibly caused by the passage of the typical frequency of synchrotron emission from another forward shock distinct from the early afterglow. The observed decay and spectral indices are inconsistent with the standard synchrotron-shock model. Hence, the observation requires a change in microphysical parameters in the shock region or a prior activity of the central engine. Alternatively, the emission during the shallow decay phase may be a composition of two forward shock emissions, as indicated by the hump structure in the light curve.
Population III stars first form in dark matter halos with masses around 10^6 Msun. By definition, they are metal-free, and their protostellar collapse is driven by molecular hydrogen cooling in the gas-phase, leading to a massive characteristic mass ~100 Msun and suppressed fragmentation. Population II stars with lower characteristic masses form when the star-forming gas reaches a critical metallicity of 10^{-6} - 10^{-3.5} Zsun, depending on whether dust cooling is important. We present adaptive mesh refinement radiation hydrodynamics simulations that follows the transition from Population III to II star formation. We model stellar radiative feedback with adaptive ray tracing. A top-heavy initial mass function for the Population III stars is considered, resulting in a plausible distribution of pair-instability supernovae and associated metal enrichment. We find that the gas fraction recovers from 5 percent to nearly the cosmic fraction in halos with merger histories rich in halos above 10^7 Msun. A single pair-instability supernova is sufficient to enrich the host halo to a metallicity floor of 10^{-3} Zsun and to transition to Population II star formation. This provides a natural explanation for the observed floor on damped Lyman alpha (DLA) systems metallicities reported in the literature, which is of this order. We find that stellar metallicities do not necessarily trace stellar ages, as mergers of halos with established stellar populations can create superpositions of t-Z evolutionary tracks. A bimodal metallicity distribution is created after a starburst occurs when the halo can cool efficiently through atomic line cooling.
In this paper we study the footprint of cosmic string as the topological defects in the very early universe on the cosmic microwave background radiation. We develop the method of level crossing analysis in the context of the well-known Kaiser-Stebbins phenomenon for exploring the signature of cosmic strings. We simulate a Gaussian map by using the best fit parameter given by WMAP-7 and then superimpose cosmic strings effects on it as an incoherent and active fluctuations. In order to investigate the capability of our method to detect the cosmic strings for the various values of tension, $G\mu$, a simulated pure Gaussian map is compared with that of including cosmic strings. Based on the level crossing analysis, the superimposed cosmic string with $G\mu\gtrsim 4\times 10^{-9}$ in the simulated map without instrumental noise and the resolution $R=1'$ could be detected. In the presence of anticipated instrumental noise the lower bound increases just up to $G\mu\gtrsim 5.8\times 10^{-9}$.
In recent years the possibility of measuring the temporal change of radial and transverse position of sources in the sky in real time have become conceivable thanks to the thoroughly improved technique applied to new astrometric and spectroscopic experiments, leading to the research domain we call Real-time cosmology. We review for the first time great part of the work done in this field, analysing both the theoretical framework and some endeavor to foresee the observational strategies and their capability to constrain models. We firstly focus on real time measurements of the overall redshift drift and angular separation shift in distant source, able to trace background cosmic expansion and large scale anisotropy, respectively. We then examine the possibility of employing the same kind of observations to probe peculiar and proper acceleration in clustered systems and therefore the gravitational potential. The last two sections are devoted to the short time future change of the cosmic microwave background, as well as to the temporal shift of the temperature anisotropy power spectrum and maps. We conclude revisiting in this context the effort made to forecast the power of upcoming experiments like CODEX, GAIA and PLANCK in providing these new observational tools.
In this concise, albeit subjective review of structure formation, I shall introduce the cosmological standard model and its theoretical and observational underpinnings. I will focus on recent results and current issues in theoretical cosmology, in particular in cosmological perturbation theory and its applications.
Recent publications claim that there is no convincing evidence for measurements of the baryonic acoustic (BAO) feature in galaxy samples using either monopole or radial information. Different claims seem contradictory: data is either not consistent with the BAO model or data is consistent with both the BAO model and featureless models without BAO. We investigate this point with a set of 216 realistic mock galaxy catalogs extracted from MICE7680, one of the largest volume dark matter simulation run to date, with a volume of 1300 cubical gigaparsecs. Our mocks cover similar volume, densities and bias as the real galaxies and provide 216 realizations of the Lambda or w=-1 Cold Dark Matter (wCDM) BAO model. We find that only 20% of the mocks show a statistically significant (3 sigma) preference for the true (input) wCDM BAO model as compared to a featureless (non-physical) model without BAO. Thus the volume of current galaxy samples is not yet large enough to claim that the BAO feature has been detected. Does this mean that we can not locate the BAO position? Using a simple (non optimal) algorithm we show that in 50% (100%) of the mocks we can find the BAO position within 5% (20%) of the true value. These two findings are not in contradiction: the former is about model selection, the later is about parameter fitting within a model. We conclude that current monopole and radial BAO measurements can be used as standard rulers if we assume wCDM type of models.
Star formation rate and accummulated stellar mass are two fundamental physical quantities that describe the evolutionary state of a forming galaxy. Two recent attempts to determine the relationship between these quantities, by interpreting a sample of star-forming galaxies at redshift of z~4, have led to opposite conclusions. We use a model galaxy population to investigate possible causes for this discrepancy and conclude that minor errors in the conversion from observables to physical quantities can lead to major misrepresentation when applied without awareness of sample selection. We also investigate, in a general way, the physical origin of the correlation between star formation rate and stellar mass within hierarchical galaxy formation theory.
The weak-lensing science of the LSST project drives the need to carefully model and separate the instrumental artifacts from the intrinsic lensing signal. The dominant source of the systematics for all ground based telescopes is the spatial correlation of the PSF modulated by both atmospheric turbulence and optical aberrations. In this paper, we present a full FOV simulation of the LSST images by modeling both the atmosphere and the telescope optics with the most current data for the telescope specifications and the environment. To simulate the effects of atmospheric turbulence, we generated six-layer phase screens with the parameters estimated from the on-site measurements. For the optics, we combined the ray-tracing tool ZEMAX and our simulated focal plane data to introduce realistic aberrations and focal plane height fluctuations. Although this expected flatness deviation for LSST is small compared with that of other existing cameras, the fast f-ratio of the LSST optics makes this focal plane flatness variation and the resulting PSF discontinuities across the CCD boundaries significant challenges in our removal of the systematics. We resolve this complication by performing PCA CCD-by-CCD, and interpolating the basis functions using conventional polynomials. We demonstrate that this PSF correction scheme reduces the residual PSF ellipticity correlation below 10^-7 over the cosmologically interesting scale. From a null test using HST/UDF galaxy images without input shear, we verify that the amplitude of the galaxy ellipticity correlation function, after the PSF correction, is consistent with the shot noise set by the finite number of objects. Therefore, we conclude that the current optical design and specification for the accuracy in the focal plane assembly are sufficient to enable the control of the PSF systematics required for weak-lensing science with the LSST.
In this article we give a brief review of the fundamental physics that can be done with the future space-based gravitational wave detector LISA. This includes detection of gravitational wave bursts coming from cosmic strings, measuring a stochastic gravitational wave background, mapping spacetime around massive compact objects in galactic nuclei with extreme-mass-ratio inspirals and testing the predictions of General Relativity for the strong dynamical fields of inspiralling binaries. We give particular attention to new results which show the capability of LISA to constrain cosmological parameters using observations of coalescing massive Black Hole binaries.
We investigate the star formation history and metallicity of the Local Group irregular dwarf galaxy WLM using wide-field JHK near-infrared imaging, spanning a region of approximately 1 sq. degree, obtained with WFCAM on UKIRT. JHK photometry clearly reveals the tip of the red giant branch, allowing a new estimate of the distance, and allows ready identification of C-type and M-type AGB stars. The C/M ratio was used to produce a surface map of the metallicity distribution which is compared to previous studies. Multi-wavelength spectral energy distributions (SEDs) were constructed for some AGB stars.
A new mechanism for the formation of cometary tails behind dense clouds or globules is discussed. Numerical hydrodynamical models show that when a dense shell of swept-up matter overruns a cloud, material in the shell is focussed behind the cloud to form a tail. This mode of tail formation is completely distinct from other methods, which involve either the removal of material from the cloud, or shadowing from a strong, nearby source of ionization. This mechanism is relevant to the cometary tails seen in planetary nebulae and to the interaction of superbubble shells with dense clouds.
We review the various theories which have been proposed along the years to explain the origin of the stellar initial mass function. We pay particular attention to four models, namely the competitive accretion and the theories based respectively on stopped accretion, MHD shocks and turbulent dispersion. In each case, we derive the main assumptions and calculations that support each theory and stress their respective successes and failures or difficulties.
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