We perform a consistent end-to-end validation of estimates of the growth rate of structure, described by the parameter combination $f\sigma_8$, in modified gravity cosmologies. We consider an analysis pipeline based on the redshift-space distortion modelling of the clustering wedges statistic of the galaxy correlation function and apply it to mock catalogues of $\Lambda{\rm CDM}$ and the normal branch of DGP cosmologies. We employ a halo occupation distribution approach to construct our mocks, which we ensure resemble the CMASS sample from BOSS in terms of the total galaxy number density and large scale amplitude of the power spectrum monopole. We show that the clustering wedges model successfully recovers the true growth rate difference between DGP and $\Lambda{\rm CDM}$, even for cases with over 40% enhancement in $f\sigma_8$ compared to $\Lambda{\rm CDM}$. The unbiased performance of the clustering wedges model allows us to use the growth rate values estimated from the BOSS LOWZ and CMASS samples to constrain the cross-over scale $r_c$ of DGP gravity to $\left[r_cH_0\right]^{-1} < 1.2$ ($2\sigma$) or $r_c > 2500\ {\rm Mpc}/h$.
While galaxies at $6 \lesssim z \lesssim 10$ are believed to dominate the epoch of cosmic reionization, the escape fraction of ionizing flux $f_\mathrm{esc}$ and the photon production rate $\dot n_\gamma$ from these galaxies must vary with redshift to simultaneously match CMB and low-redshift observations. We constrain $f_\mathrm{esc}(z)$ and $\dot n_\gamma(z)$ with Planck 2015 measurements of the Thomson optical depth $\tau$, recent low multipole E-mode polarization measurements from Planck 2016, SDSS BAO data, and $3 \lesssim z \lesssim 10$ galaxy observations. We compare different galaxy luminosity functions that are calibrated to HST observations, using both parametric and non-parametric statistical methods that marginalize over the effective clumping factor $C_\mathrm{HII}$, the LyC production efficiency $\xi_\mathrm{ion}$, and the time-evolution of the UV limiting magnitude $dM_\mathrm{SF}/dz$. Using a power-law model, we find $f_\mathrm{esc} \lesssim 0.5$ at $z=8$ with slope $\beta \gtrsim 2.0$ at $68\%$ confidence with little dependence on the galaxy luminosity function or data, although there is non-negligible probability for no redshift evolution $\beta \sim 0$ or small escape fraction $f_\mathrm{esc} \sim 10^{-2}$. A non-parametric form for $f_\mathrm{esc}(z)$ evolves significantly with redshift, yielding $f_\mathrm{esc} \sim 0.2, 0.3, 0.6$ at $z=6,9,12$, respectively. However, a model-independent reconstruction of $\dot n_\gamma(z)$ predicts a suppressed escaped photon production rate at $z=9$ for the latest Planck data compared to the other models, implying a quicker period of reionization. We find evidence for redshift evolution in the limiting magnitude of the galaxy luminosity function for empirical models of the galaxy luminosity function.
Galaxies and their dark matter halos populate a complicated filamentary network around large, nearly empty regions known as cosmic voids. Cosmic voids are usually identified in spectroscopic galaxy surveys, where 3D information about the large-scale structure of the Universe is available. Although an increasing amount of photometric data is being produced, its potential for void studies is limited since photometric redshifts induce line-of-sight position errors of $\sim50$ Mpc/$h$ or more that can render many voids undetectable. In this paper we present a new void finder designed for photometric surveys, validate it using simulations, and apply it to the high-quality photo-$z$ redMaGiC galaxy sample of the Dark Energy Survey Science Verification (DES-SV) data. The algorithm works by projecting galaxies into 2D slices and finding voids in the smoothed 2D galaxy density field of the slice. Fixing the line-of-sight size of the slices to be at least twice the photo-$z$ scatter, the number of voids found in these projected slices of simulated spectroscopic and photometric galaxy catalogs is within 20% for all transverse void sizes, and indistinguishable for the largest voids of radius $\sim 70$ Mpc/$h$ and larger. The positions, radii, and projected galaxy profiles of photometric voids also accurately match the spectroscopic void sample. Applying the algorithm to the DES-SV data in the redshift range $0.2<z<0.8$, we identify 87 voids with comoving radii spanning the range 18-120 Mpc/$h$, and carry out a stacked weak lensing measurement. With a significance of $4.4\sigma$, the lensing measurement confirms the voids are truly underdense in the matter field and hence not a product of Poisson noise, tracer density effects or systematics in the data. It also demonstrates, for the first time in real data, the viability of void lensing studies in photometric surveys.
LIGO's discovery of a gravitational wave from two merging black holes (BHs) of similar masses rekindled suggestions that primordial BHs (PBHs) make up the dark matter (DM). If so, PBHs would add a Poissonian isocurvature density fluctuation component to the inflation-produced adiabatic density fluctuations. For LIGO's BH parameters, this extra component would dominate the small-scale power responsible for collapse of early DM halos at z>10, where first luminous sources formed. We quantify the resultant increase in high-z abundances of collapsed halos that are suitable for producing the first generation of stars and luminous sources. The significantly increased abundance of the early halos would naturally explain the observed source-subtracted near-IR cosmic infrared background (CIB) fluctuations, which cannot be accounted for by known galaxy populations. For LIGO's BH parameters this increase is such that the observed CIB fluctuation levels at 2 to 5 micron can be produced if only a tiny fraction of baryons in the collapsed DM halos forms luminous sources. Gas accretion onto these PBHs in collapsed halos, where first stars should also form, would straightforwardly account for the observed high coherence between the CIB and unresolved cosmic X-ray background in soft X-rays. We discuss modifications possibly required in the processes of first star formation if LIGO-type BHs indeed make up the bulk or all of DM. The arguments are valid only if the PBHs make up all, or at least most, of DM, but at the same time the mechanism appears inevitable if DM is made of PBHs.
We investigate phenomenological interactions between dark matter and dark energy and constrain these models by employing the most recent cosmological data including the cosmic microwave background radiation anisotropies from Planck 2015, Type Ia supernovae, baryon acoustic oscillations, the Hubble constant and redshift-space distortions. We find that the interaction in the dark sector parameterized as an energy transfer from dark matter to dark energy is strongly suppressed by the whole updated cosmological data. On the other hand, an interaction between dark sectors with the energy flow from dark energy to dark matter is proved in better agreement with the available cosmological observations. This coupling between dark sectors is needed to alleviate the coincidence problem.
We use cosmological hydrodynamical simulations to assess the feasibility of constraining the thermal history of the intergalactic medium during reionisation with the Ly$\alpha$ forest at $z \simeq 5$. Pressure smoothing has a measurable impact on the transmitted flux power spectrum that can be isolated from Doppler broadening at this redshift. We parameterise the effect of pressure smoothing on the power spectrum using the cumulative energy per proton, $u_0$, deposited into a gas parcel at the mean background density, a quantity that is tightly linked with the integrated thermal history and the gas density power spectrum in the simulations. We construct mock observations of the line of sight Ly$\alpha$ forest power spectrum and use a Markov Chain Monte Carlo approach to recover $u_{0}$ at redshifts $5 \leq z \leq 12$. A statistical uncertainty of $\sim 20$ per cent is expected (at 68 per cent confidence) at $z\simeq 5$ using high resolution spectra with a total redshift path length of $\Delta z=4$ and a typical signal-to-noise ratio of $\rm S/N=15$ per pixel. Estimates for the expected systematic uncertainties are comparable, such that existing data should enable a measurement of $u_{0}$ to within $\sim 30$ per cent. This translates to distinguishing between reionisation scenarios with similar instantaneous temperatures at $z\simeq 5$, but with an energy deposited per proton that differs by $2$--$3\, \rm eV$ over the redshift interval $5\leq z \leq 12$. For an initial temperature of $T\sim 10^{4}\rm\,K$ following reionisation, this corresponds to the difference between early ($z_{\rm re}=12$) and late ($z_{\rm re}=7$) reionisation in our models.
This brief contribution is devoted to phenomenological consequences of deviations from Lorentz invariance in gravity and dark matter. We will discuss main effects on cosmological observables and current constraints derived from astrophysical and cosmological data.
The Milky Way presents the too-big-to-fail (TBTF) problem that there are two observed satellite galaxies with maximum circular velocity larger than 55km/s, and others have velocity less than 25km/s, but the cold dark matter model predicts there should be more than 10 subhaloes with velocity larger than 25km/s. Those massive subhaloes with $25km/s<V_{max}<55km/s$ should not have failed to form stars. The TBTF problem severely challenges the CDM model. Most efforts are seeking the effects of baryonic feedback, decreasing the mass of the Milky Way, changing the properties of dark matter, so as to assign the observed low-velocity satellites into the massive subhaloes found in simulations. However, the TBTF problem can be avoided if the MW have not accreted subhaloes with velocity between $25km/s<V_{max}<55km/s$ although the probability of such a gap is lower as $\sim 1\%$ and can not be tested against observations. In this work we study the gap in stellar mass of satellite galaxies using the SDSS group catalogue and a semi-analytical model. We find that there are 1-2\% of galaxy groups with a large gap in the stellar mass of their satellites. These 'big gap' groups have accreted less massive subhaloes in their formation history and naturally display a gap between their satellite galaxies. If extrapolating our results to the Milky Way is appropriate, we conclude that it is very likely that our Milky Way has not accreted enough massive subhaloes to host those low-velocity satellites, and the TBTF problem is naturally avoided.
We present a measurement of the abundance of carbon monoxide in the early Universe, utilizing the final results from the CO Power Spectrum Survey (COPSS). Between 2013 and 2015, we performed observations with the Sunyaev-Zel'dovich Array (SZA) to measure the aggregate CO emission from $z\sim3$ galaxies with the intensity mapping technique. Data were collected on 19 fields, covering an area of 0.7 square degrees, over a frequency range of 27 to 35 GHz. With these data, along with data analyzed in COPSS I, we are able to observe the CO(1-0) transition in the redshift range of $z=2.3-3.3$ for spatial frequencies between $k=0.5-10\ h\,\textrm{Mpc}^{-1}$, spanning a comoving volume of $4.9\times10^{6}\ h^{-3}\,\textrm{Mpc}^{3}$. We present estimates of contributions from continuum sources and ground illumination within our measurement. We constrain the amplitude of the CO power spectrum to be $P_{\textrm{CO}}=3.0_{-1.3}^{+1.3}\times10^{3}\ \mu\textrm{K}^{2} (h^{-1}\,\textrm{Mpc})^{3}$, or $\Delta^{2}_{\textrm{CO}}(k\!=\!1\ h\,\textrm{Mpc}^{-1})=1.5^{+0.7}_{-0.7} \times10^{3}\ \mu\textrm{K}^{2}$, at 68% confidence, and $P_{\textrm{CO}}>0$ at 98.9% confidence. These results are a factor of 10 improvement in sensitivity compared to the previous limits set in COPSS I. We use this measurement to place constraints on the CO(1-0) galaxy luminosity function at $z\sim3$. We constrain the ratio of CO(1-0) luminosity to host halo mass to $A_{\textrm{CO}}=6.3_{-2.1}^{+1.4}\times10^{-7}\ L_{\odot}\ M_{\odot}^{-1}$, and estimate a mass fraction of molecular gas of $f_{\textrm{H}_{2}}=5.5^{+3.4}_{-2.2}\times10^{-2}$ for halos with masses of order $10^{12}M_{\odot}$. Using simple theoretical estimates for the scaling of molecular gas mass fraction and halo mass, we estimate the global density of molecular gas to be $\rho_{z\sim3}(\textrm{H}_{2})=1.1_{-0.4}^{+0.7}\times10^{8}\ M_{\odot}\ \textrm{Mpc}^{-3}$.
We present a new method for interferometric imaging that is ideal for the large fields of view and compact arrays common in 21~cm cosmology. We first demonstrate the method with simulations for two very different low frequency interferometers, the Murchison Widefield Array (MWA) and the MIT Epoch of Reionization (MITEoR) Experiment. We then apply the method to the MITEoR data set collected in July 2013 to obtain the first northern sky map from 128 MHz to 175 MHz at about 2 degree resolution, and find an overall spectral index of -2.73+/-0.11. The success of this imaging method bodes well for upcoming compact redundant low-frequency arrays such as HERA. Both the MITEoR interferometric data and the 150 MHz sky map are publicly available at this http URL
Low-mass (sub-eV) spin-0 dark matter particles, which form a coherently oscillating classical field $\phi = \phi_0 \cos(m_\phi t)$, can induce oscillating variations in the fundamental constants through their interactions with the Standard Model sector. We calculate the effects of such possible interactions, which may include the linear interaction of $\phi$ with the Higgs boson, on atomic and molecular transitions. Using recent atomic clock spectroscopy measurements, we derive new limits on the linear interaction of $\phi$ with the Higgs boson, as well as its quadratic interactions with the photon and light quarks. For the linear interaction of $\phi$ with the Higgs boson, our derived limits improve on existing constraints by up to $2-3$ orders of magnitude.
In this work, we propose different models of extended theories of gravity, which are minimally coupled to the SM fields, to explain the possibility of a dark matter (DM) candidate, without ad-hoc additions to the Standard Model (SM). We modify the gravity sector by allowing quantum corrections motivated from local $f(R)$ gravity, and non-minimally coupled gravity with SM sector and dilaton field. Using an effective field theory (EFT) framework, we constrain the scale of the EFT and DM mass. We consider two cases-Light DM (LDM) and Heavy DM (HDM), and deduce upper bounds on the DM annihilation cross section to SM particles.
We conducted an extensive CCD search for faint, unresolved dwarf galaxies of very low surface brightness in the whole Centaurus group region encompassing the Cen A and M 83 subgroups lying at a distance of roughly 4 and 5 Mpc, respectively. The aim is to significantly increase the sample of known Centaurus group members down to a fainter level of completeness, serving as a basis for future studies of the 3D structure of the group. Following our previous survey of 60 square degrees covering the M 83 subgroup, we extended and completed our survey of the Centaurus group region by imaging another 500 square degrees area in the g and r bands with the wide-field Dark Energy Survey Camera at the 4m Blanco telescope at CTIO. The limiting central surface brightness reached for suspected Centaurus members is $\mu_r \approx 29$ mag arcsec$^{-2}$, corresponding to an absolute magnitude $M_r \approx -9.5$. The images were enhanced using different filtering techniques. We found 41 new dwarf galaxy candidates, which together with the previously discovered 16 dwarf candidates in the M 83 subgroup amounts to almost a doubling of the number of known galaxies in the Centaurus complex, if the candidates are confirmed. We carried out surface photometry in g and r, and report the photometric parameters derived therefrom, for all new candidates as well as previously known members in the surveyed area. The photometric properties of the candidates, when compared to those of LG dwarfs and previously known Centaurus dwarfs, suggest membership in the Centaurus group. The sky distribution of the new objects is generally following a common envelope around the Cen A and M 83 subgroups. How the new dwarfs are connected to the intriguing double-planar feature recently reported by Tully et al. (2015) must await distance information for the candidates.
We explicitly prove that a class of finite quantum gravitational theories (in odd as well as in even dimension) is actually a range of anomaly-free conformally invariant theories in the spontaneously broken phase of the conformal Weyl symmetry. At classical level we show how the Weyl conformal invariance is likely able to tame the spacetime singularities that plague not only Einstein gravity, but also local and weakly non-local higher derivative theories. This latter statement is rigorously proved by a singularity theorem that applies to a large class of weakly non-local theories. Following the seminal paper by Narlikar and Kembhavi, we provide an explicit construction of singularity-free black hole exact solutions conformally equivalent to the Schwarzschild metric. Furthermore, we show that the FRW cosmological solutions and the Belinski, Khalatnikov, Lifshitz (BKL) spacetimes, which exactly solve the classical equations of motion, are conformally equivalent to regular spacetimes. Finally, we prove that the Oppenheimer-Volkov gravitational collapse is a an exact (singularity-free) solution of the non-local conformally invariant theory compatible with the bounce paradigm.
We explore the question of the rapid buildup of black hole mass in the early universe employing a growing black hole mass-based determination of both jet and disk powers predicted in recent theoretical work on black hole accretion and jet formation. Despite simplified, even artificial assumptions about accretion and mergers, we identify an interesting low probability channel for the growth of one billion solar mass black holes within hundreds of millions of years of the Big Bang without appealing to super Eddington accretion. This result is made more compelling by the recognition of a connection between this channel and an end product involving active galaxies with FRI radio morphology but weaker jet powers in mildly sub-Eddington accretion regimes. While FRI quasars have already been shown to occupy a small region of the available parameter space for black hole feedback in the paradigm, we further suggest that the observational dearth of FRI quasars is also related to their connection to the most massive black hole growth due to both these FRIs high redshifts and relative weakness. Our results also allow us to construct the AGN luminosity function at high redshift, that agree with recent studies. In short, we produce a connection between the unexplained paucity of a given family of active galactic nuclei and the rapid growth of supermassive black holes, two heretofore seemingly unrelated aspects of the physics of active galactic nuclei.
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We perform numerical simulations of the merging galaxy cluster 1E 0657-56 (the Bullet Cluster), including the effects of elastic dark matter scattering. In a similar manner to the stripping of gas by ram pressure, dark matter self-interactions would transfer momentum between the two galaxy cluster dark matter haloes, causing them to lag behind the collisionless galaxies. The absence of an observed separation between the dark matter and stellar components in the Bullet Cluster has been used to place upper limits on the cross-section for dark matter scattering. We emphasise the importance of analysing simulations in an observationally-motivated manner, finding that the way in which the positions of the various components are measured can have a larger impact on derived constraints on dark matter's self-interaction cross-section than reasonable changes to the initial conditions for the merger. In particular, we find that the methods used in previous studies to place some of the tightest constraints on this cross-section do not reflect what is done observationally, and overstate the Bullet Cluster's ability to constrain the particle properties of dark matter. We introduce the first simulations of the Bullet Cluster including both self-interacting dark matter and gas. We find that as the gas is stripped it introduces radially-dependent asymmetries into the stellar and dark matter distributions. As the techniques used to determine the positions of the dark matter and galaxies are sensitive to different radial scales, these asymmetries can lead to erroneously measured offsets between dark matter and galaxies even when they are spatially coincident.
In this paper we study the triaxial properties of dark matter haloes of a wide range of masses extracted from a set of cosmological N-body simulations. We measure the shape at different distances from the halo center (characterised by different overdensity thresholds), both in three and in two dimensions, discussing how halo triaxiality increases with (i) mass, (ii) redshift and (iii) overdensity. We also examine how the orientation of the different ellipsoidal shells are aligned with each other and what is the gradient in internal shapes for halos with different virial configurations. Our findings highlight that the internal part of the halo retains memory of the violent formation process keeping the major axis oriented toward the preferential direction of the infalling material while the outer part becomes rounder due to continuous isotropic merging events; this effect is clearly evident in high mass haloes - which formed recently - while it is more blurred in low mass haloes. We present simple distributions that may be used as priors for various mass reconstruction algorithms, operating in different wavelengths, in order to recover a more complex and realistic dark matter distribution of isolated and relaxed systems.
The most recent measurements of the temperature and low-multipole polarization anisotropies of the Cosmic Microwave Background (CMB) from the Planck satellite, when combined with galaxy clustering data from the Baryon Oscillation Spectroscopic Survey (BOSS) in the form of the full shape of the power spectrum, and with Baryon Acoustic Oscillation measurements, provide a $95\%$ confidence level (CL) upper bound on the sum of the three active neutrinos $\sum m _\nu< 0.183$ eV, among the tightest neutrino mass bounds in the literature, to date, when the same datasets are taken into account. This very same data combination is able to set, at $\sim70\%$ CL, an upper limit on $\sum m _\nu$ of $0.0968$ eV, a value that approximately corresponds to the minimal mass expected in the inverted neutrino mass hierarchy scenario. If high-multipole polarization data from Planck is also considered, the $95\%$ CL upper bound is tightened to $\sum m _\nu< 0.176$ eV. Further improvements are obtained by considering recent measurements of the Hubble parameter. These limits are obtained assuming a specific non-degenerate neutrino mass spectrum; they slightly worsen when considering other degenerate neutrino mass schemes. Current cosmological data, therefore, start to be mildly sensitive to the neutrino mass ordering. Low-redshift quantities, such as the Hubble constant or the reionization optical depth, play a very important role when setting the neutrino mass constraints. We also comment on the eventual shifts in the cosmological bounds on $\sum m_\nu$ when possible variations in the former two quantities are addressed.
In a previous paper, we proposed a heterotic dark energy model, called $\Lambda$HDE, in which dark energy is composed of two components: cosmological constant (CC) and holographic dark energy (HDE). The aim of present work is to give a more comprehensive and systematic investigation on the cosmological implications of the $\Lambda$HDE model. Firstly, we make use of the current observations to constrain the $\Lambda$HDE model, and compare its cosmology-fit results with the results of the $\Lambda$CDM and the HDE model. Then, by combining a qualitative theoretical analysis with a quantitative numerical study, we discuss the impact of considering curvature on the cosmic evolutions of fractional HDE density $\Omega_{hde}$ and fractional CC density $\Omega_{\Lambda}$, as well as on the ultimate cosmic fate. Finally, we explore the effects of adopting different types of observational data. We find that: (1) the current observational data cannot distinguish the $\Lambda$HDE model from the $\Lambda$CDM and the HDE model; this indicates that DE may contain multiple components; (2) the asymptotic solution of $\Omega_{hde}$ and the corresponding cosmic fate in a flat universe can be extended to the case of a non-flat universe; however, considering curvature yields a new possibility: $\Omega_{\Lambda}$ may eventually approach a negative value at $2\sigma$ confidence level (CL); (3) compared with SNLS3 dataset, using JLA dataset yields a new possibility: our universe may be dominated by the CC at $1\sigma$ CL; in contrast, using other types of observational data have no significant impact on the ultimate cosmic fate.
Understanding the formation and evolution of the first stars and galaxies represents one of the most exciting frontiers in astronomy. Since the universe was filled with hydrogen atoms at early times, the most promising probe of the epoch of the first stars is the prominent 21-cm spectral line of hydrogen. Current observational efforts are focused on the cosmic reionization era, but observations of the pre-reionization cosmic dawn are also promising. While observationally unexplored, theoretical studies predict a rich variety of observational signatures from cosmic dawn. As the first stars formed, their radiation (plus that from stellar remnants) produced significant cosmic events including Lyman-alpha coupling at z~25, and early X-ray heating. Much focus has gone to studying the angle-averaged power spectrum of 21-cm fluctuations. Additional probes include the global (sky-averaged) 21-cm spectrum, and the line-of-sight anisotropy of the 21-cm power spectrum. A particularly striking signature may result from the recently recognized effect of a supersonic relative velocity between the dark matter and gas. Work in this field, focused on understanding the whole era of reionization and cosmic dawn with analytical models and numerical simulations, is likely to grow in intensity and importance, as the theoretical predictions are finally expected to confront 21-cm observations in the coming years. [Abridged]
I will discuss to what degree the cosmic microwave background (CMB) can be used to constrain primordial non-Gaussianity involving one tensor and two scalar fluctuations, focusing on the correlation of one $B$-mode polarization fluctuation with two temperature fluctuations (BTT). In the simplest models of inflation, the tensor-scalar-scalar primordial bispectrum is non-vanishing and is of the same order in slow-roll parameters as the scalar-scalar-scalar bispectrum. I will show that constraints from an experiment like CMB-Stage IV using this observable are more than an order of magnitude better than those on the same primordial coupling obtained from temperature measurements alone. I will argue that $B$-mode non-Gaussianity opens up an as-yet-unexplored window into the early Universe, demonstrating that significant information on primordial physics remains to be harvested from CMB anisotropies. BTT presents a measure of both primordial tensors and primordial non-Gaussianity, two of the most sought after signatures of the inflationary paradigm.
We develop an automated technique for detecting damped Lyman-$\alpha$ absorbers (DLAs) along spectroscopic sightlines to quasi-stellar objects (QSOs or quasars). The detection of DLAs in large-scale spectroscopic surveys such as SDSS-III sheds light on galaxy formation at high redshift, showing the nucleation of galaxies from diffuse gas. We use nearly 50 000 QSO spectra to learn a novel tailored Gaussian process model for quasar emission spectra, which we apply to the DLA detection problem via Bayesian model selection. We propose models for identifying an arbitrary number of DLAs along a given line of sight. We demonstrate our method's effectiveness using a large-scale validation experiment, with excellent performance. We also provide a catalog of our results applied to 162 861 spectra from SDSS-III data release 12.
We revisit the constraints on the small scale density perturbations ($10^4\,\mathrm{Mpc}^{-1}\lesssim k \lesssim10^5\,\mathrm{Mpc}^{-1}$) from the modification of the freeze-out value of the neutron-proton ratio at big-bang nucleosynthesis era. Around the freeze-out temperature $T\sim 0.5\,\mathrm{MeV}$, the universe can be divided into several local patches which have different temperatures since any perturbation which enters the horizon after the neutrino decoupling has not diffused yet. Taking account of this situation, we calculate the freeze-out value in detail. We find that the small scale perturbations decrease the n-p ratio in contrast to previous works. With use of the latest observed $^4$He abundance, we obtain the constraint on the power spectrum of the curvature perturbations as $\Delta^2_\mathcal{R}\lesssim 0.018$ on $10^4\,\mathrm{Mpc}^{-1}\lesssim k \lesssim 10^5\,\mathrm{Mpc}^{-1}$.
The phantom brane has several important distinctive features: (i) Its equation of state is phantom-like, but there is no future `big rip' singularity, (ii) the effective cosmological constant on the brane is dynamically screened, because of which the expansion rate is smaller than that in $\Lambda$CDM at high redshifts. In this paper, we constrain the Phantom braneworld using distance measures such as Type Ia supernovae (SNeIa), Baryon Acoustic Oscillations (BAO), and the compressed Cosmic Microwave Background (CMB) data. We find that the simplest braneworld models provide a good fit to the data. For instance, BAO +SNeIa data can be accommodated by the braneworld for a large region in parameter space $0 \leq \Omega_l \leq 0.6$ at $1\sigma$. Inclusion of CMB data provides tighter constraints $\Omega_l \leq 0.1$. (Here $\Omega_l$ encodes the ratio of the five and four dimensional Planck mass.) Interestingly, we find that the universe is allowed be marginally closed or open, with $-0.1 \leq \Omega_{\kappa} \leq 0.2$, even on including the compressed CMB data. There appears to be some tension in the low and high $z$ BAO data, future data with better consistency would improve these results.
Using the liminality N-body simulations, we present the first predictions for galaxy clustering in $f(R)$ gravity using subhalo abundance matching. We find that, for a given galaxy density, even for an $f(R)$ model with $f_{R0}=-10^{-6}$, for which the cold dark matter clustering is essentially indistinguishable from $\Lambda$CDM, the predicted clustering of galaxies in the $f(R)$ model is much weaker than in $\Lambda$CDM. The deviation can be as large as $40\%$ for samples with mean densities $<n_g>\sim0.01[{\rm Mpc}/h]^{-3}$ and $<n_g>\sim0.02[{\rm Mpc}/h]^{-3}$ . This large deviation is testable given the accuracy that future large-scale galaxy surveys aim to achieve. Our result demonstrates that galaxy surveys can yield a stringent test of the theory of General Relativity on cosmological scales, which is comparable to the tests from local astrophysical observations.
We present the latest version of Pinocchio, a code that generates catalogues
of DM haloes in an approximate but fast way with respect to an N-body
simulation. This code version extends the computation of particle and halo
displacements up to 3rd-order Lagrangian Perturbation Theory (LPT), in contrast
with previous versions that used Zeldovich approximation (ZA).
We run Pinocchio on the same initial configuration of a reference N-body
simulation, so that the comparison extends to the object-by-object level. We
consider haloes at redshifts 0 and 1, using different LPT orders either for
halo construction - where displacements are needed to decide particle accretion
onto a halo or halo merging - or to compute halo final positions.
We compare the clustering properties of Pinocchio haloes with those from the
simulation by computing the power spectrum and 2-point correlation function
(2PCF) in real and redshift space (monopole and quadrupole), the bispectrum and
the phase difference of halo distributions. We find that 2LPT and 3LPT give
noticeable improvement. 3LPT provides the best agreement with N-body when it is
used to displace haloes, while 2LPT gives better results for constructing
haloes. At the highest orders, linear bias is typically recovered at a few per
cent level.
In Fourier space and using 3LPT for halo displacements, the halo power
spectrum is recovered to within 10 per cent up to $k_{max}\sim0.5\ h/$Mpc. The
results presented in this paper have interesting implications for the
generation of large ensemble of mock surveys aimed at accurately compute
covariance matrices for clustering statistics.
The standard $\Lambda$CDM model can be mimicked at the background and perturbative levels (linear and non-linear) by a class of gravitationally induced particle production cosmology dubbed CCDM cosmology. However, the radiation component in the CCDM model follows a slightly different temperature-redshift $T(z)$-law which depends on an extra parameter, $\nu_r$, describing the subdominant photon production rate. Here we perform a statistical analysis based on a compilation of 36 recent measurements of $T(z)$ at low and intermediate redshifts. The likelihood of the production rate in CCDM cosmologies is constrained by $\nu_r = 0.023 \pm 0.027$ ($1\sigma$ confidence level, thereby showing that $\Lambda$CDM ($\nu_r=0$) is still compatible with the adopted data sample. Although being hardly differentiated in the dynamic sector (cosmic history and matter fluctuations), the so-called thermal sector (temperature law, abundances of thermal relics and CMB power spectrum) offers a clear possibility for crucial tests confronting $\Lambda$CDM and CCDM cosmologies.
We revisit the problem of measuring the number of e-folding during inflation. It has become standard practice to take the logarithmic growth of the scale factor as a measure of the amount of inflation. However, this is only an approximation for the true amount of inflation required to solve the horizon and flatness problems. The aim of this work is to quantify the error in this approximation, and show how it can be avoided. We present an alternative framework for inflation model building using the inverse Hubble radius, aH, as the key parameter. We show that in this formalism, the correct number of e-folding arises naturally as a measure of inflation. As an application, we present an interesting model in which the entire inflationary dynamics can be solved analytically and exactly, and, in special cases, reduces to the familiar class of power-law models.
In the search for an explanation for the current acceleration of the Universe, scalar fields are the most simple and useful tools to build models of dark energy. This field, however, must in principle couple with the rest of the world and not necessarily in the same way to different particles or fluids. We provide the most complete dynamical system analysis to date, consisting of a canonical scalar field conformally and disformally coupled to both dust and radiation. We perform a detailed study of the existence and stability conditions of the systems and comment on constraints imposed on the disformal coupling from Big-Bang Nucleosynthesis and given current limits on the variation of the fine-structure constant.
We present the results of a new search for galaxy-scale strong lensing systems in CFHTLS Wide. Our lens-finding technique involves a preselection of potential lens galaxies, applying simple cuts in size and magnitude. We then perform a Principal Component Analysis of the galaxy images, ensuring a clean removal of the light profile. Lensed features are searched for in the residual images using the clustering topometric algorithm DBSCAN. We find 1098 lens candidates that we inspect visually, leading to a cleaned sample of 109 new lens candidates. Using realistic image simulations we estimate the completeness of our sample and show that it is independent of source surface brightness, Einstein ring size (image separation) or lens redshift. We compare the properties of our sample to previous lens searches in CFHTLS. Including the present search, the total number of lenses found in CFHTLS amounts to 678, which corresponds to ~4 lenses per square degree down to i=24.8. This is equivalent to ~ 60.000 lenses in total in a survey as wide as Euclid, but at the CFHTLS resolution and depth.
Recently we have proposed a novel method to probe primordial gravitational waves from upper bounds on the abundance of primordial black holes (PBHs). When the amplitude of primordial tensor perturbations generated in the early universe is very large, they induce large scalar perturbations due to their second-order effects. If the amplitude of resultant scalar perturbations is too large at the moment of their horizon reenty, then PBHs are overproduced to a level that is inconsistent with a variety of existing observations constraining the abundance of PBHs. This consideration leads to upper bounds on the amplitude of primordial tensor perturbations on super-horizon scales. In contrast to our recent paper in which we only present simple estimations of the upper bounds from PBHs, in this paper, we present detailed derivations, by solving the Einstein equations for scalar perturbations induced at second order in tensor perturbations. We also derive an approximate formula for the probability density function of induced density perturbations, necessary to relate the abundance of PBHs to the primordial tensor power spectrum, assuming primordial tensor perturbations follow Gaussian distributions. Comparison is presented of the upper bounds from PBHs with other existing bounds obtained from Big Bang Nucleosynthesis, Cosmic Microwave Background, LIGO/Virgo and pulsar timing arrays.
In this work, we consider the cosmological constant model $\Lambda\propto\alpha^{-6}$, which is well motivated from three independent approaches. As is well known, the evidence of varying fine structure constant $\alpha$ was found in 1998. If $\Lambda\propto\alpha^{-6}$ is right, it means that the cosmological constant $\Lambda$ should be also varying. In this work, we try to develop a suitable framework to model this varying cosmological constant $\Lambda\propto\alpha^{-6}$, in which we view it from an interacting vacuum energy perspective. We propose two types of models to describe the evolutions of $\Lambda$ and $\alpha$. Then, we consider the observational constraints on these models, by using the 293 $\Delta\alpha/\alpha$ data from the absorption systems in the spectra of distant quasars, and the data of type Ia supernovae (SNIa), cosmic microwave background (CMB), baryon acoustic oscillation (BAO). We find that the model parameters can be tightly constrained to the narrow ranges of ${\cal O}(10^{-5})$ typically. In particular, 3 of 4 models considered in this work favor the varying $\Lambda$ and $\alpha$, while $\Lambda$CDM model and $\alpha=const.$ deviate from the best fit beyond $2\sigma$ or at least $1\sigma$. On the other hand, we can also view the varying cosmological constant model $\Lambda\propto\alpha^{-6}$ from another perspective, namely it can be equivalent to a model containing "dark energy" (whose equation-of-state parameter (EoS) $w_{de}\not=-1$) and "warm dark matter" (whose EoS $w_{dm}\not=0$), but there is no interaction between them. We derive the effective EoS of "warm dark matter" and "dark energy", and find that they are fully consistent with the observational constraints on warm dark matter. We consider that the varying cosmological constant model $\Lambda\propto\alpha^{-6}$ is viable and deserves further studies.
We construct $F(T,\left(\nabla{T}\right)^2,\Box {T})$ gravitational modifications, which are novel classes of modified theories arising from higher-derivative torsional terms in the action, and are different than their curvature analogue. Applying them in a cosmological framework we obtain an effective dark energy sector that comprises of the novel torsional contributions. We perform a detailed dynamical analysis for two specific examples, extracting the stable late-time solutions and calculating the corresponding observables. We show that the universe can result in a dark-energy dominated, accelerating universe, where the dark-energy equation-of-state parameter lies in the quintessence regime, with the scale factor behaving asymptotically as a power law, in agreement with observations.
We statistically study the physical properties of a sample of narrow absorption line (NAL) systems looking for empirical evidences to distinguish between intrinsic and intervening NALs without taking into account any a priori definition or velocity cut-off. We analyze the spectra of 100 quasars with 3.5 < z$\rm_{em}$ < 4.5, observed with X-shooter/VLT in the context of the XQ-100 Legacy Survey. We detect a $\sim$ 8 $\sigma$ excess in the number density of absorbers within 10,000 km/s of the quasar emission redshift with respect to the random occurrence of NALs. This excess does not show a dependence on the quasar bolometric luminosity and it is not due to the redshift evolution of NALs. It extends far beyond the standard 5000 km/s cut-off traditionally defined for associated absorption lines. We propose to modify this definition, extending the threshold to 10,000 km/s when also weak absorbers (equivalent width < 0.2 \AA) are considered. We infer NV is the ion that better traces the effects of the quasar ionization field, offering the best statistical tool to identify intrinsic systems. Following this criterion we estimate that the fraction of quasars in our sample hosting an intrinsic NAL system is 33 percent. Lastly, we compare the properties of the material along the quasar line of sight, derived from our sample, with results based on close quasar pairs investigating the transverse direction. We find a deficiency of cool gas (traced by CII) along the line of sight associated with the quasar host galaxy, in contrast with what is observed in the transverse direction.
We consider Parker particle production in the Ekpyrotic scenario (in particular in the New Ekpyrotic model) and show that the density of particles produced by the end of the phase of Ekpyrotic contraction is sufficient to lead to a hot state of matter after the bounce. Hence, no separate reheating mechanism is necessary.
We present Q-U-I JOint TEnerife (QUIJOTE) intensity and polarisation maps at 10-20 GHz covering a region along the Galactic plane 24<l<45 deg, |b|<8 deg. These maps result from 210 h of data, have a sensitivity in polarisation of ~40 muK/beam and an angular resolution of ~1 deg. Our intensity data are crucial to confirm the presence of anomalous microwave emission (AME) towards the two molecular complexes W43 (22-sigma) and W47 (8-sigma). We also detect at high significance (6-sigma) AME associated with W44, the first clear detection of this emission towards a SNR. The new QUIJOTE polarisation data, in combination with WMAP, are essential to: i) Determine the spectral index of the synchrotron emission in W44, beta_sync=-0.62+/-0.03 in good agreement with the value inferred from the intensity spectrum once a free-free component is included in the fit. ii) Trace the change in the polarisation angle associated with Faraday rotation in the direction of W44 with rotation measure -404+/-49 rad/m2. And iii) set upper limits on the polarisation of W43 of Pi_AME <0.39% (95 per cent C.L.) from QUIJOTE 17 GHz, and <0.22% from WMAP 41 GHz data, which are the most stringent constraints ever obtained on the polarisation fraction of the AME. For typical physical conditions (grain temperature and magnetic field strengths), and in the case of perfect alignment between the grains and the magnetic field, the models of electric or magnetic dipole emissions predict higher polarisation fractions.
We exploit the widely-separated images of the lensed quasar SDSS J1029+2623 ($z_{em}$=2.197, $\theta =22^{\prime\prime}\!\!.5$) to observe its outflowing wind through two different sightlines. We present an analysis of three observations, including two with the Subaru telescope in 2010 February (Misawa et al. 2013) and 2014 April (Misawa et al. 2014), separated by 4 years, and one with the Very Large Telescope, separated from the second Subaru observation by $\sim$2 months. We detect 66 narrow absorption lines (NALs), of which 24 are classified as intrinsic NALs that are physically associated with the quasar based on partial coverage analysis. The velocities of intrinsic NALs appear to cluster around values of $v_{ej}$ $\sim$ 59,000, 43,000, and 29,000 km/s, which is reminiscent of filamentary structures obtained by numerical simulations. There are no common intrinsic NALs at the same redshift along the two sightlines, implying that the transverse size of the NAL absorbers should be smaller than the sightline distance between two lensed images. In addition to the NALs with large ejection velocities of $v_{ej}$ > 1,000 km/s, we also detect broader proximity absorption lines (PALs) at $z_{abs}$ $\sim$ $z_{em}$. The PALs are likely to arise in outflowing gas at a distance of r $\leq$ 620 pc from the central black hole with an electron density of $n_e$ $\geq$ 8.7$\times$10$^{3}$ cm$^{-3}$. These limits are based on the assumption that the variability of the lines is due to recombination. We discuss the implications of these results on the three-dimensional structure of the outflow.
Abdus Salam was a true master of 20th Century Theoretical Physics. Not only was he a pioneer of the Standard Model (for which he shared the Nobel Prize with S. Glashow and S.Weinberg), but he also (co)authored many other outstanding contributions to the field of Fundamental Interactions and their unification. In particular, he was a major contributor to the development of supersymmetric theories, where he also coined the word "Supersymmetry" (replacing the earlier "Supergauges" drawn from String Theory). He also introduced the basic concept of "Superspace" and the notion of "Goldstone Fermion"(Goldstino). These concepts proved instrumental for the exploration of the ultraviolet properties and for the study of spontaneously broken phases of super Yang-Mills theories and Supergravity. They continue to play a key role in current developments in Early-Universe Cosmology. In this contribution we review models of inflation based on Supergravity with spontaneously broken local supersymmetry, with emphasis on the role of nilpotent superfields to describe a de Sitter phase of our Universe.
We probe the feasibility of describing the structure of a multi-component axisymmetric galaxy with a dynamical model based on the Jeans equations while taking into account a third integral of motion. We demonstrate that using the third integral in the form derived by G. Kuzmin, it is possible to calculate the stellar kinematics of a galaxy from the Jeans equations by integrating the equations along certain characteristic curves. In cases where the third integral of motion does not describe the system exactly, the derived kinematics would describe the galaxy only approximately. We apply our method to the Andromeda galaxy, for which the mass distribution is relatively firmly known. We are able to reproduce the observed stellar kinematics of the galaxy rather well. The calculated model suggests that the velocity dispersion ratios ${\sigma}_z^2/{\sigma}_R^2$ of M31 decrease with increasing R. Moving away from the galactic plane, ${\sigma}_z^2/{\sigma}_R^2$ remains the same. The velocity dispersions ${\sigma}_{\theta}^2$ and ${\sigma}_R^2$ are roughly equal in the galactic plane.
We analyse a sample of 85 luminous L3um > 10^45.5 erg/s quasars with restframe ~2-11um spectroscopy from AKARI and Spitzer. Their high luminosity allows a direct determination of the near-infrared quasar spectrum free from host galaxy emission. A semi-empirical model consisting of a single template for the accretion disk and two blackbodies for the dust emission successfully reproduces the 0.1-10um spectral energy distributions (SEDs). Excess emission at 1-2um over the best-fitting model suggests that hotter dust is necessary in addition to the ~1200K blackbody and the disk to reproduce the entire near-infrared spectrum. Variation in the extinction affecting the disk and in the relative strength of the disk and dust components accounts for the diversity of individual SEDs. Quasars with higher dust-to-disk luminosity ratios show slightly redder infrared continua and less prominent silicate emission. We find no luminosity dependence in the shape of the average infrared quasar spectrum. The equivalent width of Paschen alpha in our composite spectrum is a factor ~10 higher compared to lower luminosity quasars in the literature, implying that Paschen alpha emission is boosted in high luminosity quasars relative to the continuum emission from both the disk and the dust. We generate a new quasar template that covers the restframe range 0.1-11um, and templates for the disk and dust components. Comparison with other infrared quasar composites suggests that previous ones are less reliable in the 2-4um range. Our template is the first one to provide a detailed view of the infrared emission on both sides of the 4um bump.
QUBIC is a ground-based experiment, currently under construction, that uses the novel bolometric interferometry technology. It is dedicated to measure the primordial B-modes of CMB. As a bolometric interferometer, QUBIC has high sensitivity and good systematics control. Dust contamination is controlled by operating with two bands -- 150 and 220 GHz. There are two possible sites for QUBIC: either Concordia station in Antarctic or in the Argentinian Puna desert. It is planned to see the first light in 2018-2019.
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Although dark matter is a central element of modern cosmology, the history of how it became accepted as part of the dominant paradigm is often ignored or condensed into a brief anecdotical account focused around the work of a few pioneering scientists. The aim of this review is to provide the reader with a broader historical perspective on the observational discoveries and the theoretical arguments that led the scientific community to adopt dark matter as an essential part of the standard cosmological model.
Strong gravitational lensing provides a geometric probe of cosmology in a unique manner through distance ratios involving the source and lens. This is well known for the time delay distance derived from measured delays between lightcurves of the images of variable sources such as quasars. Recently, double source plane lens systems involving two constant sources lensed by the same foreground lens have been proposed as another probe, involving a different ratio of distances measured from the image positions and fairly insensitive to the lens modeling. Here we demonstrate that these two different sets of strong lensing distance ratios have strong complementarity in cosmological leverage. Unlike other probes, the double source distance ratio is actually more sensitive to the dark energy equation of state parameters $w_0$ and $w_a$ than to the matter density $\Omega_m$, for low redshift lenses. Adding double source distance ratio measurements can improve the dark energy figure of merit by 40% for a sample of fewer than 100 low redshift systems, or even better for the optimal redshift distribution we derive.
We present an improved Global Sky Model (GSM) of diffuse galactic radio emission from 10 MHz to 5 THz, whose uses include foreground modeling for CMB and 21 cm cosmology. Our model improves on past work both algorithmically and by adding new data sets such as the Planck maps and the enhanced Haslam map. Our method generalizes the Principal Component Analysis approach to handle non-overlapping regions, enabling the inclusion of 29 sky maps with no region of the sky common to all. We also perform a blind separation of our GSM into physical components with a method that makes no assumptions about physical emission mechanisms (synchrotron, free-free, dust, etc). Remarkably, this blind method automatically finds five components that have previously only been found "by hand", which we identify with synchrotron, free-free, cold dust, warm dust, and the CMB anisotropy, with maps and spectra agreeing with previous work but in many cases with smaller error bars. The improved GSM is available online at github.com/jeffzhen/gsm2016.
The existence of critical points for the peculiar velocity field is a natural feature of the correlated vector field. These points appear in contact zones of the velocity domains with different orientation of the averaged velocity vector. At the same time peculiar velocities are the cause of the scatter of the Hubble expansion rate. We propose that a more precise determination of the Hubble constant can be made by restricting analysis to subsample of observational data containing only the zones around the critical points of the peculiar velocity field, associated with voids and saddle points. On large-scales the critical points where the first derivative of the gravitational potential vanishes can be easily identified using the density field and classified by the behavior of the Hessian of the gravitational potential. We use high- resolution N-body simulations to show that these regions are stable in time and hence are excellent tracers of the initial conditions. Furthermore, we show that the variance of the Hubble flow can be substantially minimized by restricting observations to the subsample of such regions of vanishing velocity instead of aiming at increasing the statistics by averaging indiscriminately using the full data sets as is the common approach. This could help to reconcile the CMB-measured value of the Hubble constant with that obtained from the local measurements.
When comparing constraints on the Weakly Interacting Massive Particle (WIMP) properties from direct and indirect detection experiments it is crucial that the assumptions made about the dark matter (DM) distribution are realistic and consistent. For instance, if the Fermi-LAT Galactic centre GeV gamma-ray excess was due to WIMP annihilation, its morphology would be incompatible with the Standard Halo Model that is usually used to interpret data from direct detection experiments. In this article, we calculate exclusion limits from direct detection experiments using self-consistent velocity distributions, derived from mass models of the Milky Way where the DM halo has a generalized NFW profile. We use two different methods to make the mass model compatible with a DM interpretation of the Galactic centre gamma-ray excess. Firstly, we fix the inner slope of the DM density profile to the value that best fits the morphology of the excess. Secondly, we allow the inner slope to vary and include the morphology of the excess in the data sets used to constrain the gravitational potential of the Milky Way. The resulting direct detection limits differ significantly from those derived using the Standard Halo Model, in particular for light WIMPs, due to the differences in both the local DM density and velocity distribution.
Large-scale structure has been shown as a promising cosmic probe for distinguishing and constraining dark energy models. Using the growth index parametrization, we obtain an analytic formula for the growth rate of structures in a coupled dark energy model in which the exchange of energy-momentum is proportional to the dark energy density. We find that the evolution of $f \sigma_8$ can be determined analytically once we know the coupling, the dark energy equation of state, the present value of the dark energy density parameter and the current mean amplitude of dark matter fluctuations. We use our analytic result to confront the interacting model to observations of redshift-space distortions.
The set-up of the initial conditions in cosmological N-body simulations is usually implemented by rescaling the desired low-redshift linear power spectrum to the required starting redshift consistently with the Newtonian evolution of the simulation. The implementation of this practical solution requires more care in the context of massive neutrino cosmologies, mainly because of the non-trivial scale-dependence of the linear growth that characterises these models. In this work we consider a simple two-fluid, Newtonian approximation for cold dark matter and massive neutrinos perturbations that can reproduce the cold matter linear evolution predicted by Boltzmann codes such as CAMB or CLASS with a 0.1% accuracy or below for all redshift relevant to nonlinear structure formation. We use this description, in the first place, to quantify the systematic errors induced by several approximations often assumed in numerical simulations, including the typical set-up of the initial conditions for massive neutrino cosmologies adopted in previous works. We then take advantage of the flexibility of this approach to rescale the late-time linear power spectra to the simulation initial redshift, in order to be as consistent as possible with the dynamics of the N-body code and the approximations it assumes. We implement our method in a public code providing the initial displacements and velocities for cold dark matter and neutrino particles that will allow accurate, i.e. one-percent level, numerical simulations for this cosmological scenario.
We study the spherical evolution model for voids in $\Lambda$CDM, where the evolution of voids is governed by dark energy at an earlier time than that for the whole universe or in overdensities. We show that the presence of dark energy suppresses the growth of peculiar velocities, causing void shell-crossing to occur at progressively later epochs as $\Omega_{\Lambda}$ increases. We apply the spherical model to evolve the initial conditions of N-body simulated voids and compare the resulting final void profiles. We find that the model is successful in tracking the evolution of voids with radii greater than $30 h^{-1} \rm Mpc$, implying that void profiles could be used to constrain dark energy. We find that the initial peculiar velocities of voids play a significant role in shaping their evolution. Excluding the peculiar velocity in the evolution model delays the time of shell crossing.
The axion monodromy model involves a canonical scalar field that is governed by a linear potential with superimposed modulations. The modulations in the potential are responsible for a resonant behavior which gives rise to persisting oscillations in the scalar and, to a smaller extent, in the tensor power spectra. Interestingly, such spectra have been shown to lead to an improved fit to the cosmological data than the more conventional, nearly scale invariant, primordial power spectra. The scalar bi-spectrum in the model too exhibits continued modulations and the resonance is known to boost the amplitude of the scalar non-Gaussianity parameter to rather large values. An analytical expression for the scalar bi-spectrum had been arrived at earlier which, in fact, has been used to compare the model with the cosmic microwave background anisotropies at the level of three-point functions involving scalars. In this work, with future applications in mind, we arrive at a similar analytical template for the scalar-scalar-tensor cross-correlation. We also analytically establish the consistency relation (in the squeezed limit) for this three-point function. We conclude with a summary of the main results obtained.
If the initial quantum state of the primordial perturbations broke rotational invariance, that would be seen as a statistical anisotropy in the angular correlations of the cosmic microwave background radiation (CMBR) temperature fluctuations. This can be described by a general parameterisation of the initial conditions that takes into account the possible direction-dependence of both the amplitude and the phase of particle creation during inflation. The leading effect in the CMBR two-point function is typically a quadrupole modulation, whose coefficient is analytically constrained here to be $|B| \lesssim 0.06$. The CMBR three-point function then acquires enhanced non-gaussianity, especially for the local configurations. In the large occupation number limit, a distinctive prediction is a modulation of the non-gaussianity around a mean value depending on the angle that short and long wavelength modes make with the preferred direction. The maximal variations with respect to the mean value occur for the configurations which are coplanar with the preferred direction and the amplitude of the non-gaussianity increases (decreases) for the short wavelength modes aligned with (perpendicular to) the preferred direction. For a high scale model of inflation with maximally pumped up isotropic occupation and $\epsilon\simeq 0.01$ the difference between these two configurations is about $0.27$, which could be detectable in the future. For purely anisotropic particle creation, the non-Gaussianity can be larger and its anisotropic feature very sharp. The non-gaussianity can then reach $f_{NL} \sim 30$ in the preferred direction while disappearing from the correlations in the orthogonal plane.
We study direct detection in simplified models of Dark Matter (DM) in which interactions with Standard Model (SM) fermions are mediated by a heavy vector boson. We consider fully general, gauge-invariant couplings between the SM, the mediator and both scalar and fermion DM. We account for the evolution of the couplings between the energy scale of the mediator mass and the nuclear energy scale. This running arises from virtual effects of SM particles and its inclusion is not optional. We compare bounds on the mediator mass from direct detection experiments with and without accounting for the running and find that in some cases these bounds differ by several orders of magnitude. We also highlight the importance of these effects when translating LHC limits on the mediator mass into bounds on the direct detection cross section. For an axial-vector mediator, the running can alter the derived bounds on the spin-dependent DM-nucleon cross section by a factor of two or more. Finally, we provide tools to facilitate the inclusion of these effects in future studies: general approximate expressions for the low energy couplings and a public code runDM to evolve the couplings between arbitrary energy scales.
The substantial decrease in star formation density from z=1 to the present day is curious given the relatively constant neutral gas density over the same epoch. Future radio astronomy facilities, including the SKA and pathfinder telescopes, will provide pioneering measures of both the gas content of galaxies and star formation activity over cosmological timescales. Here we investigate the commensalities between neutral atomic gas (HI) and radio continuum observations, as well as the complementarity of the data products. We start with the proposed HI and continuum surveys to be undertaken with the SKA precursor telescope MeerKAT, and building on this, explore optimal combinations of survey area coverage and depth of proposed HI and continuum surveys to be undertaken with the SKA1-MID instrument. Intelligent adjustment of these observational parameters results in a tiered strategy that minimises observation time while maximising the value of the dataset, both for HI and continuum science goals. We also find great complementarity between the HI and continuum datasets, with the spectral line HI data providing redshift measurements for gas-rich, star-forming galaxies with stellar masses Mstellar~10^9 Msun to z~0.3, a factor of three lower in stellar mass than would be feasible to reach with large optical spectroscopic campaigns.
We revisit the compatibility between the chaotic inflation, which provides a natural solution to the initial condition problem, and the metastable electroweak vacuum, which is suggested by the results of LHC and the current mass measurements of top quark and Higgs boson. It is known that the chaotic inflation poses a threat to the stability of the electroweak vacuum because it easily generates large Higgs fluctuations during inflation or preheating and triggers the catastrophic vacuum decay. In this paper, we propose a simple cosmological solution in which the vacuum is stabilized during chaotic inflation, preheating and after that. This simple solution naturally predicts formation of primordial black holes. We find interesting parameter regions where the present dark matter density is provided by them. Also, the thermal leptogensis can be accommodated in our scenario.
We use the large cosmological hydro-dynamic simulation BlueTides to predict the photometric properties of galaxies during the epoch of reionisation ($z=8-15$). These properties include the rest-frame UV to near-IR broadband spectral energy distributions, the Lyman continuum photon production, the UV star formation rate calibration, and intrinsic UV continuum slope. In particular we focus on exploring the effect of various modelling assumptions, including the assumed choice of stellar population synthesis model, initial mass function, and the escape fraction of Lyman continuum photons, upon these quantities. We find that these modelling assumptions can have a dramatic effect on photometric properties leading to consequences for the accurate determination of physical properties from observations. For example, at $z=8$ we predict that nebular emission can account for up-to $50\%$ of the rest-frame $R$-band luminosity, while the choice of stellar population synthesis model can change the Lyman continuum production rate up to a factor of $\times 2$.
We consider the finite interactions of the generalized Proca theory including the sixth-order Lagrangian and derive the full linear perturbation equations of motion on the flat Friedmann-Lema\^{i}tre-Robertson-Walker background in the presence of a matter perfect fluid. By construction, the propagating degrees of freedom (besides the matter perfect fluid) are two transverse vector perturbations, one longitudinal scalar, and two tensor polarizations. The Lagrangians associated with intrinsic vector modes neither affect the background equations of motion nor the second-order action of tensor perturbations, but they do give rise to non-trivial modifications to the no-ghost condition of vector perturbations and to the propagation speeds of vector and scalar perturbations. We derive the effective gravitational coupling $G_{\rm eff}$ with matter density perturbations under a quasi-static approximation on scales deep inside the sound horizon. We find that the existence of intrinsic vector modes allows a possibility for reducing $G_{\rm eff}$. In fact, within the parameter space, $G_{\rm eff}$ can be even smaller than the Newton gravitational constant $G$ at the late cosmological epoch, with a peculiar phantom dark energy equation of state (without ghosts). The modifications to the slip parameter $\eta$ and the evolution of growth rate $f\sigma_8$ are discussed as well. Thus, dark energy models in the framework of generalized Proca theories can be observationally distinguished from the $\Lambda$CDM model according to both cosmic growth and expansion history. Furthermore, we study the evolution of vector perturbations and show that outside the vector sound horizon the perturbations are nearly frozen and start to decay with oscillations after the horizon entry.
Based on the star formation histories (SFH) of galaxies in halos of different masses, we develop an empirical model to grow galaxies in dark mattet halos. This model has very few ingredients, any of which can be associated to observational data and thus be efficiently assessed. By applying this model to a very high resolution cosmological $N$-body simulation, we predict a number of galaxy properties that are a very good match to relevant observational data. Namely, for both centrals and satellites, the galaxy stellar mass function (SMF) up to redshift $z\simeq4$ and the conditional stellar mass functions (CSMF) in the local universe are in good agreement with observations. In addition, the 2-point correlation is well predicted in the different stellar mass ranges explored by our model. Furthermore, after applying stellar population synthesis models to our stellar composition as a function of redshift, we find that the luminosity functions in $^{0.1}u$, $^{0.1}g$, $^{0.1}r$, $^{0.1}i$ and $^{0.1}z$ bands agree quite well with the SDSS observational results down to an absolute magnitude at about -17.0. The SDSS conditional luminosity functions (CLF) itself is predicted well. Finally, the cold gas is derived from the star formation rate (SFR) to predict the HI gas mass within each mock galaxy. We find a remarkably good match to observed HI-to-stellar mass ratios. These features ensure that such galaxy/gas catalogs can be used to generate reliable mock redshift surveys.
Following our first detection reported in Izotov et al. (2016), we present the detection of Lyman continuum (LyC) radiation of four other compact star-forming galaxies observed with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope (HST). These galaxies, at redshifts of z~0.3, are characterized by high emission-line flux ratios [OIII]5007/[OII]3727 > 5. The escape fractions of the LyC radiation fesc(LyC) in these galaxies are in the range of ~6%-13%, the highest values found so far in low-redshift star-forming galaxies. Narrow double-peaked Lyalpha emission lines are detected in the spectra of all four galaxies, compatible with predictions for Lyman continuum leakers. We find escape fractions of Lyalpha, fesc(Lyalpha) ~60%-90%, among the highest known for Lyalpha emitters (LAEs). Surface brightness profiles produced from the COS acquisition images reveal bright star-forming regions in the center and exponential discs in the outskirts with disc scale lengths alpha in the range ~0.6-1.4 kpc. Our galaxies are characterized by low metallicity, ~1/8-1/5 solar, low stellar mass ~(0.2 - 4)e9 Msun, high star formation rates SFR~14-36 Msun/yr, and high SFR densities Sigma~2-35 Msun/yr/kpc^2. These properties are comparable to those of high-redshift star-forming galaxies. Finally, our observations, combined with our first detection reported in Izotov et al. (2016), reveal that a selection for compact star-forming galaxies showing high [OIII]5007/[OII]3727 ratios appears to pick up very efficiently sources with escaping Lyman continuum radiation: all five of our selected galaxies are LyC leakers.
The problem of consistency of smoothed particle hydrodynamics (SPH) has demanded considerable attention in the past few years due to the ever increasing number of applications of the method in many areas of science and engineering. A loss of consistency leads to an inevitable loss of approximation accuracy. In this paper, we revisit the issue of SPH kernel and particle consistency and demonstrate that SPH has a limiting second-order convergence rate. Numerical experiments with suitably chosen test functions validate this conclusion. In particular, we find that when using the root mean square error as a model evaluation statistics, well-known corrective SPH schemes, which were thought to converge to second, or even higher order, are actually first-order accurate, or at best close to second order. We also find that observing the joint limit when $N\to\infty$, $h\to 0$, and $n\to\infty$, as was recently proposed by Zhu et al., where $N$ is the total number of particles, $h$ is the smoothing length, and $n$ is the number of neighbor particles, standard SPH restores full $C^{0}$ particle consistency for both the estimates of the function and its derivatives and becomes insensitive to particle disorder.
We present a measurement of the volumetric rate of superluminous supernovae (SLSNe) at z~1, measured using archival data from the first four years of the Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS). We develop a method for the photometric classification of SLSNe to construct our sample. Our sample includes two previously spectroscopically-identified objects, and a further new candidate selected using our classification technique. We use the point-source recovery efficiencies from Perrett et.al. (2010) and a Monte Carlo approach to calculate the rate based on our SLSN sample. We find that the three identified SLSNe from SNLS give a rate of 91 (+76/-36) SNe/Yr/Gpc^3 at a volume-weighted redshift of z=1.13. This is equivalent to 2.2 (+1.8/-0.9) x10^-4 of the volumetric core collapse supernova rate at the same redshift. When combined with other rate measurements from the literature, we show that the rate of SLSNe increases with redshift in a manner consistent with that of the cosmic star formation history. We also estimate the rate of ultra-long gamma ray bursts (ULGRBs) based on the events discovered by the Swift satellite, and show that it is comparable to the rate of SLSNe, providing further evidence of a possible connection between these two classes of events. We also examine the host galaxies of the SLSNe discovered in SNLS, and find them to be consistent with the stellar-mass distribution of other published samples of SLSNe.
A gravitationally collapsed object can bounce-out from its horizon via a tunnelling process that violates the classical equations in a finite region. Since tunnelling is a non-perturbative phenomenon, it cannot be described in terms of quantum fluctuations around a classical solution and a background-free formulation of quantum gravity is needed to analyze it. Here we use Loop Quantum Gravity to compute the amplitude for this process, in a first approximation. The amplitude determines the tunnelling time as a function of the mass. This is the key information to evaluate the astrophysical relevance of this process. The calculation offers a template and a concrete example of how a background-free quantum theory of gravity can be used to compute a realistical observable quantity.
The low-energy dynamics of relativistic continuous media is given by a shift-symmetric effective theory of four scalar fields. These scalars describe the embedding in spacetime of the medium and play the role of Stuckelberg fields for spontaneously broken spatial and time translations. Perfect fluids are selected imposing a stronger symmetry group or reducing the field content to a single scalar. We explore the relation between the field theory description of perfect fluids to thermodynamics. By drawing the correspondence between the allowed operators at leading order in derivatives and the thermodynamic variables, we find that a complete thermodynamic picture requires the four Stuckelberg fields. We show that thermodynamic stability plus the null energy condition imply dynamical stability. We also argue that a consistent thermodynamic interpretation is not possible if any of the shift symmetries is explicitly broken.
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We study the overdensity of point sources in the direction of X-ray-selected galaxy clusters from the Meta-Catalog of X-ray detected Clusters of galaxies (MCXC; $\langle z \rangle = 0.14$) at South Pole Telescope (SPT) and Sydney University Molonglo Sky Survey (SUMSS) frequencies. Flux densities at 95, 150 and 220 GHz are extracted from the 2500 deg$^2$ SPT-SZ survey maps at the locations of SUMSS sources, producing a multi-frequency catalog of radio galaxies. In the direction of massive galaxy clusters, the radio galaxy flux densities at 95 and 150 GHz are biased low by the cluster Sunyaev-Zel'dovich Effect (SZE) signal, which is negative at these frequencies. We employ a cluster SZE model to remove the expected flux bias and then study these corrected source catalogs. We find that the high frequency radio galaxies are centrally concentrated within the clusters and that their luminosity functions (LFs) exhibit amplitudes that are characteristically an order of magnitude lower than the cluster LF at 843 MHz. We use the 150 GHz LF to estimate the impact of cluster radio galaxies on an SPT-SZ like survey. The radio galaxy flux typically produces a small bias on the SZE signal and has negligible impact on the observed scatter in the SZE mass-observable relation. If we assume there is no redshift evolution in the radio galaxy LF then $1.8\pm0.7$ percent of the clusters would be lost from the sample. Allowing for redshift evolution of the form $(1+z)^{2.5}$ increases the incompleteness to $5.6\pm1.0$ percent. Improved constraints on the evolution of the cluster radio galaxy LF require a larger cluster sample extending to higher redshift.
Gravitational time delays, observed in strong lens systems where the variable background source is multiply-imaged by a massive galaxy in the foreground, provide direct measurements of cosmological distance that are very complementary to other cosmographic probes. The success of the technique depends on the availability and size of a suitable sample of lensed quasars or supernovae, precise measurements of the time delays, accurate modeling of the gravitational potential of the main deflector, and our ability to characterize the distribution of mass along the line of sight to the source. We review the progress made during the last 15 years, during which the first competitive cosmological inferences with time delays were made, and look ahead to the potential of significantly larger lens samples in the near future.
We measure the gravitational lensing shear signal around dark matter halos hosting CMASS galaxies using light sources at $z\sim 1$ (background galaxies) and at the surface of last scattering at $z\sim 1100$ (the cosmic microwave background). The galaxy shear measurement uses data from the CFHTLenS survey, and the microwave background shear measurement uses data from the Planck satellite. The ratio of shears from these cross-correlations provides a purely geometric distance measurement across the longest possible cosmological lever arm. This is because the matter distribution around the halos, including uncertainties in galaxy bias and systematic errors such as miscentering, cancels in the ratio exactly. We measure this distance ratio in three different redshift slices of the CMASS sample, and combine them to obtain a $15\%$ measurement of the distance ratio, $r=0.344 \pm 0.052$ at an effective redshift of $z=0.54$. This is consistent with the predicted ratio from the Planck best-fit $\Lambda$CDM cosmology of $r=0.410$.
Cosmic voids found in galaxy surveys are defined based on the galaxy distribution in redshift space. We show that the large scale distribution of voids in redshift space traces the fluctuations in the dark matter density field \delta(k) (in Fourier space with \mu being the line of sight projected k-vector): \delta_v^s(k) = (1 + \beta_v \mu^2) b^s_v \delta(k), with a beta factor that will be in general different than the one describing the distribution of galaxies. Only in case voids could be assumed to be quasi-local transformations of the linear (Gaussian) galaxy redshift space field, one gets equal beta factors \beta_v=\beta_g=f/b_g with f being the growth rate, and b_g, b^s_v being the galaxy and void bias on large scales defined in redshift space. Indeed, in our mock void catalogs we measure void beta factors being in good agreement with the galaxy one. Further work needs to be done to confirm the level of accuracy of the beta factor equality between voids and galaxies, but in general the void beta factor needs to be considered as a free parameter for RSD studies.
We analyzed deep $Chandra$ ACIS-I exposures of the cluster-scale X-ray halo surrounding the radio source 4C+37.11. This remarkable system hosts the closest resolved pair of super-massive black hole and an exceptionally luminous elliptical galaxy, the likely product of a series of past mergers. We characterize the halo with $r_{500} = 0.95$ Mpc, $M_{500} = (2.5 \pm 0.2) \times 10^{14} \ M_{\rm{\odot}}$, $ kT = 4.6\pm 0.2$ keV, and a gas mass of $M_{\rm g,500} = (2.2 \pm 0.1) \times 10^{13} M_\odot$. The gas mass fraction within $r_{500}$ is $f_{\rm g} = 0.09 \pm 0.01$. The entropy profile shows large non-gravitational heating in the central regions. We see several surface brightness jumps, associated with substantial temperature and density changes, but approximate pressure equilibrium, implying that these are sloshing structures driven by a recent merger. A residual intensity image shows core spiral structure closely matching that seen for the Perseus cluster, although at $z=0.055$ the spiral pattern is less distinct. We infer the most recent merger occurred $1-2$ Gyr ago and that the event that brought the two observed super-massive black holes to the system core is even older. Under that interpretation, this black hole binary pair has, unusually, remained at pc-scale separation for more than 2 Gyr.
Using a Bayesian framework, we quantify what current observations imply about the history of the epoch of reionisation (EoR). We use a popular, three-parameter EoR model, flexible enough to accommodate a wide range of physically-plausible reionisation histories. We study the impact of various EoR observations: (i) the optical depth to the CMB measured by Planck 2016; (ii) the dark fraction in the Lyman $\alpha$ and $\beta$ forests; (iii) the redshift evolution of galactic Ly$\alpha$ emission (so-called "Ly$\alpha$ fraction"); (iv) the clustering of Ly$\alpha$ emitters; (v) the IGM damping wing imprint in the spectrum of QSO ULASJ1120+0641; (vi) and the patchy kinetic Sunyaev-Zel'dovich signal. Combined, (i) and (ii) already place interesting constraints on the reionisation history, with the epochs corresponding to an average neutral fraction of (75, 50, 25) per cent, constrained at 1$\sigma$ to $z= (9.21\substack{+1.22 \\ -1.15}, 8.14\substack{+1.08 \\ -1.00}, 7.26\substack{+1.13 \\ -0.96})$. Folding-in more model-dependent EoR observations [(iii--vi)], strengthens these constraints by tens of per cent, at the cost of a decrease in the likelihood of the best-fit model, driven mostly by (iii). The tightest constraints come from (v). Unfortunately, no current observational set is sufficient to break degeneracies and constrain the astrophysical EoR parameters. However, model-dependent priors on the EoR parameters themselves can be used to set tight limits by excluding regions of parameter space with strong degeneracies. Motivated by recent observations of $z\sim7$ faint, lensed galaxies, we show how a conservative upper limit on the virial temperature of haloes which host reionising galaxies can constrain the escape fraction of ionising photons to $f_{\rm esc} = 0.14\substack{+0.26 \\ -0.09}$
We explore the accuracy of the clustering-based redshift estimation proposed by M\'enard et al. (2013) when applied to VIPERS and CFHTLS real data. This method enables us to reconstruct redshift distributions from measurement of the angular clus- tering of objects using a set of secure spectroscopic redshifts. We use state of the art spectroscopic measurements with iAB < 22.5 from the VIMOS Public Extragalactic Redshift Survey (VIPERS) as reference population to infer the redshift distribution of galaxies from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) T0007 release. VIPERS provides a nearly representative sample to the flux limit iAB < 22.5 at redshift > 0.5 which allows us to test the accuracy of the clustering-based red- shift distributions. We show that this method enables us to reproduce the true mean color-redshift relation when both populations have the same magnitude limit. We also show that this technique allows the inference of redshift distributions for a population fainter than the one of reference and we give an estimate of the color-redshift mapping in this case. This last point is of great interest for future large redshift surveys which suffer from the need of a complete faint spectroscopic sample.
Cosmological measurements of the radiation density in the early universe can be used as a sensitive probe of physics beyond the standard model. Observations of primordial light element abundances have long been used to place non-trivial constraints on models of new physics and to inform our understanding of the thermal history to the first few minutes of our present phase of expansion. Precision measurements of the angular power spectrum of the cosmic microwave background temperature and polarization will drastically improve our measurement of the cosmic radiation density over the next decade. These improved measurements will either uncover new physics or place much more stringent constraints on physics beyond the standard model, while pushing our understanding of the early universe to much earlier times.
Persisting tensions between the cosmological constraints derived from low-redshift probes and the ones obtained from temperature and polarisation anisotropies of the Cosmic Microwave Background -- although not yet providing compelling evidence against the $\Lambda $CDM model -- seem to consistently indicate a slower growth of density perturbations as compared to the predictions of the standard cosmological scenario. Such behavior is not easily accommodated by the simplest extensions of General Relativity, such as f(R) models, which generically predict an enhanced growth rate. In the present work we present the outcomes of a suite of large N-body simulations carried out in the context of a cosmological model featuring a non-vanishing scattering cross section between the dark matter and the dark energy fields, for two different parameterisations of the dark energy equation of state. Our results indicate that these Dark Scattering models have very mild effects on many observables related to large-scale structures formation and evolution, while providing a significant suppression of the amplitude of linear density perturbations and the abundance of massive clusters. Our simulations therefore confirm that these models offer a promising route to alleviate existing tensions between low-redshift measurements and those of the CMB.
Lensing of the CMB is affected by post-Born lensing, producing corrections to the convergence power spectrum and introducing field rotation. We show numerically that the lensing convergence power spectrum is affected at the $\lesssim 0.2\%$ level on accessible scales, and that this correction and the field rotation are negligible for observations with arcminute beam and noise levels $\gtrsim 1 \mu {\text{K}}\,{\text{arcmin}} $. The field rotation generates $\sim 2.5\%$ of the total lensing B-mode polarization amplitude ($0.2\%$ in power on small scales), but has a blue spectrum on large scales, making it highly subdominant to the convergence B modes on scales where they are a source of confusion for the signal from primordial gravitational waves. Since the post-Born signal is non-linear, it also generates a bispectrum with the convergence. We show that the post-Born contributions to the bispectrum substantially change the shape predicted from large-scale structure non-linearities alone, and hence must be included to estimate the expected total signal and impact of bispectrum biases on CMB lensing reconstruction quadratic estimators and other observables. The field-rotation power spectrum only becomes potentially detectable for noise levels $\ll 1 \mu {\text{K}}\,{\text{arcmin}}$, but its bispectrum with the convergence may be observable at $\sim 3\sigma$ with Stage IV observations. Rotation-induced and convergence-induced B modes are slightly correlated by the bispectrum, and the bispectrum also produces additional contributions to the lensed BB power spectrum.
We present new Hubble Space Telescope/Wide Field Camera 3 imaging of 25 extremely luminous (-23.2 < M_ UV < -21.2) Lyman-break galaxies (LBGs) at z ~ 7. The sample was initially selected from 1.65 deg^2 of ground-based imaging in the UltraVISTA/COSMOS and UDS/SXDS fields, and includes the extreme Lyman-alpha emitters, `Himiko' and `CR7'. A deconfusion analysis of the deep Spitzer photometry available suggests that these galaxies exhibit strong rest-frame optical nebular emission lines (EW_0(H_beta + [OIII]) > 600A). We find that irregular, multiple-component morphologies suggestive of clumpy or merging systems are common (f_multi > 0.4) in bright z ~ 7 galaxies, and ubiquitous at the very bright end (M_UV < -22.5). The galaxies have half-light radii in the range r_1/2 ~ 0.5-3 kpc. The size measurements provide the first robust determination of the size-luminosity relation at z ~ 7 extending to M_UV ~ -23, which we find to be steep with r_1/2 ~ L^1/2. Excluding clumpy, multi-component galaxies however, we find a shallower relation that implies an increased star-formation rate surface density in bright LBGs. Using the new, independent, HST/WFC3 data we confirm that the rest-frame UV luminosity function at z ~ 7 favours a power-law decline at the bright-end, compared to an exponential Schechter function drop-off. Finally, these results have important implications for the Euclid mission, which we predict will detect > 1000 similarly bright galaxies at z ~ 7. Our new HST imaging suggests that the vast majority of these galaxies will be spatially resolved by Euclid, mitigating concerns over dwarf star contamination.
We present a new, detailed analysis of the morphologies and molecular gas fractions for a complete sample of 65 local luminous infrared galaxies (LIRGs) from the Great Observatories All-Sky LIRG Survey (GOALS) using high resolution $I$-band images from The Hubble Space Telescope, the University of Hawaii 2.2m Telescope and the Pan-STARRS1 Survey. Our classification scheme includes single undisturbed galaxies, minor mergers, and major mergers, with the latter divided into five distinct stages from pre-first pericenter passage to final nuclear coalescence. We find that major mergers of molecular gas-rich spirals clearly play a major role for all sources with $L_{\rm IR} > 10^{11.5} L_\odot $; however, below this luminosity threshold, minor mergers and secular processes dominate. Additionally, galaxies do not reach $L_{\rm IR} > 10^{12.0} L_\odot $ until late in the merger process when both disks are near final coalescence. The mean molecular gas fraction (MGF $= M_{\rm H_2} / (M_* + M_{\rm H_2})$) for non-interacting and early-stage major merger LIRGs is 18$\pm 2$%, which increases to 33$\pm 3$%, for intermediate stage major merger LIRGs, consistent with the hypothesis that, during the early-mid stages of major mergers, most of the initial large reservoir of atomic gas (HI) at large galactocentric radii is swept inward where it is converted into molecular gas (H$_2$).
We consider higher-order derivative interactions beyond second-order generalized Proca theories that propagate only the three desired polarizations of a massive vector field besides the two tensor polarizations from gravity. These new interactions follow the similar construction criteria to those arising in the extension of scalar-tensor Horndeski theories to Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories. On the maximally symmetric space-time, we perform the Hessian and Hamiltonian analysis and show the presence of a second-class constraint that removes the would-be ghost associated with the temporal component of the vector field. Furthermore, we study the behavior of linear perturbations on top of the homogeneous and isotropic cosmological background in the presence of a matter perfect fluid and find the same number of propagating degrees of freedom as in generalized Proca theories. Moreover, we obtain the conditions for the avoidance of ghosts and Laplacian instabilities of tensor, vector, and scalar perturbations. We observe key differences in the scalar sound speed, which is mixed with the matter sound speed outside the domain of generalized Proca theories.
We describe a new open source package for calculating properties of galaxy clusters, including NFW halo profiles with and without the effects of cluster miscentering. This pure-Python package, cluster-lensing, provides well-documented and easy-to-use classes and functions for calculating cluster scaling relations, including mass-richness and mass-concentration relations from the literature, as well as the surface mass density $\Sigma(R)$ and differential surface mass density $\Delta\Sigma(R)$ profiles, probed by weak lensing magnification and shear. Galaxy cluster miscentering is especially a concern for stacked weak lensing shear studies of galaxy clusters, where offsets between the assumed and the true underlying matter distribution can lead to a significant bias in the mass estimates if not accounted for. This software has been developed and released in a public GitHub repository, and is licensed under the permissive MIT license. The cluster-lensing package is archived on Zenodo (Ford 2016). Full documentation, source code, and installation instructions are available at this http URL
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Intensity mapping (IM) is sensitive to the cumulative line emission of galaxies. As such it represents a promising technique for statistical studies of galaxies fainter than the limiting magnitude of traditional galaxy surveys. The strong hydrogen Ly-alpha line is the primary target for such an experiment, as its intensity is linked to star formation activity and the physical state of the interstellar (ISM) and intergalactic (IGM) medium. However, to extract the meaningful information one has to solve the confusion problems caused by interloping lines from foreground galaxies. We discuss here the challenges for a Ly-alpha IM experiment targeting z > 4 sources. We find that the Ly-alpha power spectrum can be in principle easily (marginally) obtained with a 40 cm space telescope in a few days of observing time up to z < 8 (z = 10) assuming that the interloping lines (e.g. H-alpha, [O II], [O III] lines) can be efficiently removed. We show that interlopers can be removed by using an ancillary photometric galaxy survey with limiting AB mag 26 in the NIR bands (Y, J, H, or K). This would enable detection of the Ly-alpha signal from 5 < z < 9 faint sources. However, if a [C II] IM experiment is feasible, by cross-correlating the Ly-alpha with the [C II] signal the required depth of the galaxy survey can be decreased to AB mag 24. This would bring the detection at reach of future facilities working in close synergy.
The Einstein Equivalence Principle (EEP) can be verified by the measurement of the spectral distortions of the Cosmic Microwave Background (CMB). The existence of energy-dependency in the cosmological redshift effect means the EEP violation. Introducing the energy-dependent Friedmann-Robertson-Walker metric motivated by rainbow gravity, we show that the energy-dependent redshift effect causes the CMB spectral distortions. Assuming the simple energy-dependent form of the metric, we evaluate the distortions. From the COBE/FIRAS bound, we find that the deviation degree from the EEP, which is comparable to the difference of the parameterized-post-Newtonian parameter "gamma" in energy, is less than 10^{-9} at the CMB energy scale. Our bound is the first constraint on the EEP at cosmological time scale.
Super-chameleon models where all types of matter belong to three secluded sectors, i.e. the dark, supersymmetry breaking and matter sectors, are shown to be dynamically equivalent to ultra-local models of modified gravity. In the dark sector, comprising both dark matter and dark energy, the interaction range between the dark energy field and dark matter is constrained to be extremely short, i.e. shorter than the inverse gravitino mass set by supersymmetry breaking. This realises an extreme version of chameleon screening of the dark energy interaction. On the other hand, the baryonic matter sector decouples from the dark energy in a Damour-Polyakov way. These two mechanisms preclude the existence of any modification of gravity locally in the Solar System due to the presence of the super-chameleon field. On larger scales, the super-chameleon can have effects on the growth of structure and the number of dark matter halos. It can also affect the dynamics of galaxies where the fifth force interaction that it induces can have the same order of magnitude as Newton's interaction.
Cold dark matter (CDM) is a well established paradigm to describe cosmological structure formation, and works extraordinarily well on large, linear, scales. Progressing further in dark matter physics requires being able to understand structure formation in the non-linear regime, both for CDM and its alternatives. This short note describes a calculation, and accompanying code, WarmAndFuzzy, incorporating the popular models of warm and fuzzy dark matter (WDM and FDM) into the standard halo model to compute the non-linear matter power spectrum. The FDM halo model power spectrum has not been computed before. The FDM implementation models ultralight axions and other scalar fields with $m_a\approx 10^{-22}\text{ eV}$. The WDM implementation models thermal WDM with mass $m_X\approx 1\text{ keV}$. The halo model shows that differences between WDM, FDM, and CDM survive at low redshifts in the quasi-linear and fully non-linear regimes. The code uses analytic transfer functions for the linear power spectrum, modified collapse barriers in the halo mass function, and a modified concentration-mass relationship for the halo density profiles. Modified halo density profiles (for example, cores) are not included, but are under development. Cores are expected to have very minor effects on the power spectrum on observable scales. Applications of this code to the Lyman-$\alpha$ forest flux power spectrum and the cosmic microwave background lensing power spectrum will be discussed in companion papers. \textsc{WarmAndFuzzy} is available online at \url{https://github.com/DoddyPhysics/HMcode}, where collaboration in development is welcomed.
We derive the contribution to relativistic galaxy number count fluctuations from vector and tensor perturbations within linear perturbation theory. Our result is consistent with the the relativistic corrections to number counts due to scalar perturbation, where the Bardeen potentials are replaced with line-of-sight projection of vector and tensor quantities. Since vector and tensor perturbations do not lead to density fluctuations the standard density term in the number counts is absent. We apply our results to vector perturbations which are induced from scalar perturbations at second order and give numerical estimates of their contributions to the power spectrum of relativistic galaxy number counts.
Testing fundamental physics has become a major aim of modern cosmology, with the nature of gravity under very close scrutiny due to its plausible connection to cosmic acceleration. This program requires flexible tools to obtain accurate numerical predictions in a variety of models, which should also be fast to allow for an efficient exploration of their parameter spaces. We present the public version of the hi_class code (www.hiclass-code.net), an implementation into the Boltzmann code CLASS of very general modifications of gravity. hi_class can calculate predictions for models based on Horndeski's theory, which is the most general scalar-tensor theory described by second-order equations of motion and encompasses any perfect-fluid dark energy, quintessence, Brans-Dicke, $f(R)$ and covariant Galileon models. The code internally uses a reformulation of the effective field theory for dark energy, based on the physical properties of the gravitational and scalar degrees of freedom. hi_class has been thoroughly tested and can be readily used to understand the impact of gravity on linear structure formation as well as for MCMC parameter extraction.
The observational data on the anisotropy of the cosmic microwave background constraints the scalar spectral tilt $n_s$ and the tensor to scalar ratio $r$ which depend on the first and second derivatives of the inflaton potential. The information can be used to reconstruct the inflaton potential in the polynomial form up to some orders. However, for some classes of potentials, $n_s$ and $r$ behave as $n_s(N)$ and $r(N)$ universally in terms of the number of e-folds $N$. The universal behaviour of $n_s(N)$ can be used to reconstruct a class of inflaton potentials. By parametrizing one of the parameters $n_s(N)$, $\epsilon(N)$ and $\phi(N)$, and fitting the parameters in the models to the observational data, we obtain the constraints on the parameters and reconstruct the classes of the inflationary models which include the chaotic inflation, T-model, hilltop inflation, s-dual inflation, natural inflation and $R^2$ inflation.
We show that the recent results of \ [Int. J. Mod. Phys. D 25 (2016) 1650051] on the application of Lie/Noether symmetries in scalar field cosmology are well-known in the literature while the problem could have been solved easily under a coordinate transformation. That follows from the property, that the admitted group of invariant transformations of dynamical system is independent on the coordinate system.
We analyze the scenario where the IceCube high energy neutrino events are explained in terms of an extraterrestrial flux due to two different components: a contribution coming from know astrophysical sources for energies up to few hundreds TeV and a top-down contribution originated by the decay of heavy dark matter particles with a mass of few PeV. Contrary to previous approaches, we consider a leptophilic three-body decay that dominates at PeV energies due to the absence of quarks in the final state. We find that the theoretical predictions of such a scenario are in a slightly better agreement with the IceCube data if the astrophysical component has a cut-off at about 100 TeV. This interpretation of IceCube data can be easily tested in the near future since the decaying dark matter scenario predicts a sharp cut-off at PeV energy scale and the observation of an anisotropy towards Galactic Center of our Galaxy in contrast with the isotropic astrophysical flux.
We investigate primordial gravitational waves and curvature perturbations in de Rham-Gabadadze-Tolley (dRGT) bimetric gravity. We evaluate the power-spectra in the leading order in slow roll. Taking into account the decay of massive graviton, we find that the action up to the second order reduces to the Einstein theory with a non-minimally coupled scalar field, which is simplified to a minimally coupled model by conformal transformation. We also find that the tensor to scalar ratio for large field inflation with power law potential is larger than the general relativity counterpart for any choice of parameters in dRGT bimetric gravity. In addition, we confirm that the usual consistency relation holds and we have a steeper spectrum for the gravitational waves.
Arina et al. have proposed the Dirac fermionic dark matter with pseudoscalar-mediated interactions to explain the Galactic Center excess, correct relic density and DAMA signal. They have assumed that contact interactions remain roughly valid in calculating scattering rates at the direct detection even when the mediator mass is the same order as the typical momentum transfer. We show that such a replacement is not suitable. Adopting the full form of interactions, we show that the gamma-ray excess allowed parameters are completely outside of the DAMA iodine 3$\sigma$ region, even for heavy-flavor-universal couplings, for which $m_{DM} \sim 40$ GeV in the gamma-ray excess fit. As for Higgs-like couplings, the two regions overlap for $m_a\lesssim$ 15 MeV, where long-range interactions, instead of contact interactions, occur at the DAMA.
We show from theoretical considerations, that if the graviton is massive, its mass is constrained to be about $10^{-32}~eV/c^2$. This estimate is consistent with those obtained from experiments, including the recent gravitational wave detection in advanced LIGO.
It has been shown by Remmen and Carroll that, for a model universe which contains only a kinetically canonical scalar field minimally coupled to gravity it is possible to choose 'special coordinates' to describe a two-dimensional effective phase space. The special, non-canonical, coordinates are $\phi$,$\dot{\phi}$ and the ability to describe an effective phase space with these coordinates empowers the common usage of $\phi-\dot{\phi}$ as the space to define inflationary initial conditions. This paper extends the result to the full Horndeski action. The existence of a two-dimensional effective phase space is shown for the general case. Subsets of the Horndeski action, relevant to cosmology are considered as particular examples to highlight important aspects of the procedure.
We study radiation emitted during the gravitational collapse from two different types of shells. We assume that one shell is made of dark matter and is completely transparent to the test scalar (for simplicity) field which belongs to the standard model, while the other shell is made of the standard model particles and is totally reflecting to the scalar field. These two shells have exactly the same mass, charge and angular momentum (though we set the charge and angular momentum to zero), and therefore follow the same geodesic trajectory. However, we demonstrate that they radiate away different amount of energy during the collapse. This difference can in principle be used by an asymptotic observer to reconstruct the physical properties of the initial collapsing object other than mass, charge and angular momentum. This result has implications for the information paradox and expands the list of the type of information which can be released from a collapsing object.
We study cosmological dynamics of an extended gravitational theory that gravity is coupled non-minimally with derivatives of a dark energy component and there is also a phenomenological interaction between the dark energy and dark matter. Depending on the direction of energy flow between the dark sectors, the phenomenological interaction gets two different signs. We show that this feature affects the existence of attractor solution, the rate of growth of perturbations and stability of the solutions. By considering an exponential potential as a self-interaction potential of the scalar field, we obtain accelerated scaling solutions that are attractors and have the potential to alleviate the coincidence problem. While in the absence of the nonminimal derivative coupling there is no attractor solution for phantom field when energy transfers from dark matter to dark energy, we show an attractor solution exists if one considers an explicit nonminimal derivative coupling for phantom field in this case of energy transfer. We treat the cosmological perturbations in this setup with details to show that with phenomenological interaction, perturbations can grow faster than the minimal case.\\ {\bf Keywords}: Dynamical Systems; Dark Energy; Dark Matter; Non-Minimal Derivative Coupling, Statefinder Diagnostic, Cosmological Perturbations.
We compute the time variation of the fundamental constants (such as the ratio of the proton mass to the electron mass, the strong coupling constant, the fine structure constant and Newton's constant) within the context of the so-called running vacuum models (RVM's) of the cosmic evolution. Recently, compelling evidence has been provided showing that these models are able to fit the main cosmological data (SNIa+BAO+H(z)+LSS+BBN+CMB) significantly better than the concordance $\Lambda$CDM model. Specifically, the vacuum parameters of the RVM (i.e. those responsible for the dynamics of the vacuum energy) prove to be nonzero at a confidence level of $\gtrsim3\sigma$. Here we use such remarkable status of the RVM's to make definite predictions on the cosmic time variation of the fundamental constants. It turns out that the predicted variations are close to the present observational limits. Furthermore, we find that the time variation of the dark matter particles should be necessarily involved in the total mass variation of our Universe. A positive measurement of this kind of effects could be interpreted as strong support to the "micro and macro connection" (viz. the dynamical feedback between the evolution of the cosmological parameters and the time variation of the fundamental constants of the microscopic world), previously proposed by two of us (HF and JS).
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