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The use of Gaussian Process Regression (GPR) for foregrounds mitigation in data collected by the LOw-Frequency ARray (LOFAR) to measure the high-redshift 21-cm signal power spectrum has been shown to have issues of signal loss when the 21-cm signal covariance is misestimated. To address this problem, we have recently introduced covariance kernels obtained by using a Machine Learning based Variational Auto-Encoder (VAE) algorithm in combination with simulations of the 21-cm signal. In this work, we apply this framework to 141 h (⁠|${\approx} 10$| nights) of LOFAR data at |$z \approx 9.1$|⁠ , and report revised upper limits of the 21-cm signal power spectrum. Overall, we agree with past results reporting a 2- |$\sigma$| upper limit of |$\Delta ^2_{21} \ \lt\ (80)^2~\rm mK^2$| at |$k = 0.075~h~\rm Mpc^{-1}$|⁠. Further, the VAE-based kernel has a smaller correlation with the systematic excess noise, and the overall GPR-based approach is shown to be a good model for the data. Assuming an accurate bias correction for the excess noise, we report a 2- |$\sigma$| upper limit of |$\Delta ^2_{21} \ \lt\ (25)^2~\rm mK^2$| at |$k = 0.075~h~\rm Mpc^{-1}$|⁠. However, we still caution to take the more conservative approach to jointly report the upper limits of the excess noise and the 21-cm signal components. [ABSTRACT FROM AUTHOR]

Recent quasar absorption line observations suggest that reionization may end as late as |$z \approx 5.3$|⁠. As a means to search for large neutral hydrogen islands at |$z\ \lt\ 6$|⁠ , we revisit long dark gaps in the Ly  |$\beta$| forest in Very Large Telescope/X-Shooter and Keck/Echellette Spectrograph and Imager quasar spectra. We stack the Ly  |$\alpha$| forest corresponding to both edges of these Ly  |$\beta$| dark gaps and identify a damping wing-like extended absorption profile. The average redshift of the stacked forest is |$z=5.8$|⁠. By comparing these observations with reionization simulations, we infer that such a damping wing-like feature can be naturally explained if these gaps are at least partially created by neutral islands. Conversely, simulated dark gaps lacking neutral hydrogen struggle to replicate the observed damping wing features. Furthermore, this damping wing-like profile implies that the volume-averaged neutral hydrogen fraction must be |$\langle x_{\rm H\,{\small {I}}} \rangle \ge 6.1 \pm 3.9~{{\ \rm per\ cent}}$| at |$z = 5.8$|⁠. Our results offer robust evidence that reionization extends below |$z=6$|⁠. [ABSTRACT FROM AUTHOR]

We measure the two-point correlation function (CF) of 1357 galaxy clusters with a mass of log10 M 200 ≥ 13.6 h −1 M⊙ and at a redshift of z ≤ 0.125. This work differs from previous analyses in that it utilizes a spectroscopic cluster catalogue, |$\tt {SDSS-GalWCat}$|⁠ , to measure the CF and detect the baryon acoustic oscillation (BAO) signal. Unlike previous studies which use statistical techniques, we compute covariance errors directly by generating a set of 1086 galaxy cluster light-cones from the GLAM N -body simulation. Fitting the CF with a power-law model of the form ξ(s) = (s / s 0)−γ, we determine the best-fitting correlation length and power-law index at three mass thresholds. We find that the correlation length increases with increasing the mass threshold while the power-law index is almost constant. For log10 M 200 ≥ 13.6 h −1 M⊙, we find s 0 = 14.54 ± 0.87 h −1 Mpc and γ = 1.97 ± 0.11. We detect the BAO signal at s  = 100 h −1 Mpc with a significance of 1.60σ. Fitting the CF with a Lambda cold dark matter model, we find |$D_\mathrm{V}(z = 0.089)\mathit{r}^{\mathrm{ fid}}_\mathrm{ d}/\mathit{r}_\mathrm{ d} = 267.62 \pm 26$|   h −1 Mpc, consistent with Planck 2015 cosmology. We present a set of 108 high-fidelity simulated galaxy cluster light-cones from the high-resolution Uchuu N -body simulation, employed for methodological validation. We find D V(z  = 0.089)/ r d = 2.666 ± 0.129, indicating that our method does not introduce any bias in the parameter estimation for this small sample of galaxy clusters. [ABSTRACT FROM AUTHOR]

We measure the impact of source galaxy clustering on higher order summary statistics of weak gravitational lensing data. By comparing simulated data with galaxies that either trace or do not trace the underlying density field, we show that this effect can exceed measurement uncertainties for common higher order statistics for certain analysis choices. We evaluate the impact on different weak lensing observables, finding that third moments and wavelet phase harmonics are more affected than peak count statistics. Using Dark Energy Survey (DES) Year 3 (Y3) data, we construct null tests for the source-clustering-free case, finding a p -value of p  = 4 × 10−3 (2.6σ) using third-order map moments and p  = 3 × 10−11 (6.5σ) using wavelet phase harmonics. The impact of source clustering on cosmological inference can be either included in the model or minimized through ad hoc procedures (e.g. scale cuts). We verify that the procedures adopted in existing DES Y3 cosmological analyses were sufficient to render this effect negligible. Failing to account for source clustering can significantly impact cosmological inference from higher order gravitational lensing statistics, e.g. higher order N -point functions, wavelet-moment observables, and deep learning or field-level summary statistics of weak lensing maps. [ABSTRACT FROM AUTHOR]

The spectral index n s of scalar perturbation is the significant initial condition set by inflation theory for our observable Universe. According to Planck results, current constraint is n s = 0.965 ± 0.004, while an exact scale-invariant Harrison–Zeldovich spectrum, i.e. n s = 1, has been ruled out at 8.4σ significance level. However, it is well-known that the standard Lambda cold dark matter model is suffering from the Hubble tension, which is at ∼5σ significance level. This inconsistency likely indicates that the comoving sound horizon at last scattering surface is actually lower than expected, which so seems to be calling for the return of n s = 1. Here, in light of recent observations we find strong evidence for a n s = 1 universe. And we show that if so, it would be confirmed conclusively by CMB-S4 experiment. [ABSTRACT FROM AUTHOR]

We investigate the clustering properties of 3 < z < 5 candidate passive galaxies from the Merlin et al. (2019) sample residing in the GOODS-North (35 sources) and GOODS-South (33 sources) fields. Within the large uncertainties due to the paucity of sources we do not detect clustering signal in GOODS-North, while this is present in GOODS-South, highlighting the importance of the effects of cosmic variance. The estimated correlation length in GOODS-South is |$r_0=12^{+4}_{-5}$|  Mpc, while the estimated minimum mass for a halo capable to host one of such high-redshift quenched galaxies is log10(M min/M⊙) = 13.0 ± 0.3, once also the constraints from their space density are taken into account. Both values are compatible with the results from GOODS-North. Putting the above findings in a cosmological context, these suggest no evolution of the dark matter content of the hosts of passive galaxies during the past 12.5 Gyr, i.e. during more than 90 per cent of the age of the Universe. We discuss possible scenarios for the observed trend. [ABSTRACT FROM AUTHOR]

The so-called impossibly early galaxy problem, first identified via the Hubble Space Telescope 's observation of galaxies at redshifts z > 10, appears to have been exacerbated by the more recent JWST discovery of galaxy candidates at even higher redshifts (z ∼ 17) which, however, are yet to be confirmed spectroscopically. These candidates would have emerged only ∼230 Myr after the big bang in the context of Lambda cold dark matter (ΛCDM), requiring a more rapid star formation in the earliest galaxies than appears to be permitted by simulations adopting the concordance model parameters. This time-compression problem would therefore be inconsistent with the age–redshift relation predicted by ΛCDM. Instead, the sequence of star formation and galaxy assembly would confirm the timeline predicted by the R h = ct universe, a theoretically advanced version of ΛCDM that incorporates the 'zero active mass' condition from general relativity. This model has accounted for many cosmological data better than ΛCDM, and eliminates all of its inconsistencies, including the horizon and initial entropy problems. The latest JWST discoveries at z ≳ 14, if confirmed, would add further support to the idea that the R h = ct universe is favoured by the observations over the current standard model. [ABSTRACT FROM AUTHOR]

In a previous paper, we demonstrated a single-rung method for measuring cosmological distances in active galactic nuclei (AGNs) that can be used from low redshift (z < 0.1) to high redshift (z > 3). This method relies on the assumption that the variability seen in AGNs is constrained by the speed of light during a flare event and can therefore be used to estimate the size of an emitting region. A limitation of this method is that previously, the Doppler factor was required to be known. In this paper, we derive an extension of the 'standard speed-gun' method for measuring cosmological distances that depends on the maximum intrinsic brightness temperature that a source can reach, rather than the Doppler factor. If the precise value of the intrinsic brightness temperature does not evolve with redshift, and flares are statistically independent, we can in principle improve the errors on measurements of the matter content of the Universe (in a flat Lambda cold dark matter model) statistically. We then explored how well a future observing programme would constrain cosmological parameters. We found that recovering the input cosmology depends critically on the uncertainty of the intrinsic brightness temperature and the number of flares observed. [ABSTRACT FROM AUTHOR]

When Type Ia supernovae are used to infer cosmological parameters, their luminosities are compared to those from a homogeneous cosmology. In this note, we propose a test to examine to what degree SN Ia have been observed on lines of sight where the average matter density is not representative of the homogeneous background. We apply our test to the Pantheon SN Ia compilation, and find two redshift bins which indicate a moderate bias to over-density at ∼2σ. We modify the Tripp estimator to explicitly de-lens SN Ia magnitudes, and show that this reduces scatter of Hubble diagram residuals. Using our revised Tripp estimator, the effect on cosmological parameters from Pantheon in ΛCDM is however small with a change in mean value from Ωm = 0.317 ± 0.027 (baseline) to Ωm = 0.312 ± 0.025 (de-lensed). For the Flat w CDM case, it is Ωm = 0.332 ± 0.049 and w  = −1.16 ± 0.16 (baseline) versus Ωm = 0.316 ± 0.048 and w  = −1.12 ± 0.15 (de-lensed). We note that the effect of lensing on cosmological parameters may be larger for future high-z surveys. [ABSTRACT FROM AUTHOR]

While the cosmic microwave background (CMB) dipole is largely assumed to be entirely kinematic, there is evidence that part of it is primordial. Such a possibility arises in models implying a tilt, interpreted as a dark flow, across the observable Universe. The kinematic nature of the entire CMB dipole can be probed using the dipole of cosmic backgrounds from galaxies after the last scattering. The near-infrared (near-IR) cosmic infrared background (CIB) spectral energy distribution leads to an amplified dipole compared with the CMB. The CIB dipole is affected by galaxy clustering, decreasing with fainter, more distant galaxies, and by Solar System emissions and Galactic dust, which dominate the net CIB cosmological dipole in the optical/near-IR. We propose a technique that enables an accurate measurement of the kinematic near-IR CIB dipole. The CIB, effectively the integrated galaxy light (IGL), would be reconstructed from resolved galaxies in forthcoming space-borne wide surveys covering four bands, 0.9–2.5 μm. The galaxies will be subselected from the identified magnitude range where the dipole component from galaxy clustering is below the expected kinematic dipole. Using this technique, the dipole can be measured in each of the bands at the statistical signal-to-noise ratio S / N ≳50–100 with the forthcoming Euclid and Roman surveys, isolating the CMB dipole's kinematic nature. [ABSTRACT FROM AUTHOR]

The light-cone effect breaks the periodicity and statistical homogeneity (ergodicity) along the line-of-sight direction of cosmological emission/absorption line surveys. The spherically averaged power spectrum (SAPS), which by definition assumes ergodicity and periodicity in all directions, can only quantify some of the second-order statistical information in the 3D light-cone signals, and therefore, gives a biased estimate of the true statistics. The multifrequency angular power spectrum (MAPS), by extracting more information from the data, does not rely on these assumptions. It is therefore better aligned with the properties of the signal. We have compared the performance of the MAPS and SAPS metrics for parameter estimation of a mock 3D light-cone observation of the 21-cm signal from the Epoch of Reionization. Our investigation is based on a simplified 3-parameter 21cmFAST model. We find that the MAPS produces parameter constraints, which are a factor of ∼2 more stringent than when the SAPS is used. The significance of this result does not change much even in the presence of instrumental noise expected for 128 h of SKA-Low observations. Our results therefore suggest that a parameter estimation framework based on the MAPS metric would yield superior results over one using the SAPS metric. [ABSTRACT FROM AUTHOR]

We derive constraints on a coupled quintessence model with pure momentum exchange from the public ∼1000 deg2 cosmic shear measurements from the Kilo-Degree Survey and the Planck 2018 cosmic microwave background data. We compare this model with Lambda cold dark matter and find similar χ2 and log-evidence values. We accelerate parameter estimation by sourcing cosmological power spectra from the neural network emulator CosmoPower. We highlight the necessity of such emulator-based approaches to reduce the computational runtime of future similar analyses, particularly from Stage IV surveys. As an example, we present Markov Chain Monte Carlo forecasts on the same coupled quintessence model for a Euclid -like survey, revealing degeneracies between the coupled quintessence parameters and the baryonic feedback and intrinsic alignment parameters, but also highlighting the large increase in constraining power Stage IV surveys will achieve. The contours are obtained in a few hours with CosmoPower , as opposed to the few months required with a Boltzmann code. [ABSTRACT FROM AUTHOR]

Near-field cosmology - using detailed observations of the Local Group and its environs to study wide-ranging questions in galaxy formation and dark matter physics - has become a mature and rich field over the past decade. There are lingering concerns, however, that the relatively small size of the present-day Local Group (~2Mpc diameter) imposes insurmountable samplevariance uncertainties, limiting its broader utility.We consider the region spanned by the Local Group's progenitors at earlier times and show that it reaches 3 arcmin ≈ 7 comoving Mpc in linear size (a volume of ≈350 Mpc3) at z = 7. This size at early cosmic epochs is large enough to be representative in terms of the matter density and counts of dark matter haloes with Mvir(z = 7) ≲ 2 × 109M⊙. The Local Group's stellar fossil record traces the cosmic evolution of galaxies with 103 ≲ M*(z = 0)/M⊙ ≲ 109 (reaching M1500 > -9 at z ~ 7) over a region that is comparable to or larger than the Hubble Ultra-Deep Field (HUDF) for the entire history of the Universe. In the JWST era, resolved stellar populations will probe regions larger than the HUDF and any deep JWST fields, further enhancing the value of near-field cosmology.

Inferring high-fidelity constraints on the spatial curvature parameter, ΩK, under as few assumptions as possible, is of fundamental importance in cosmology. We propose a method to non-parametrically infer ΩK from late-Universe probes alone. Using Gaussian processes (GPs) to reconstruct the expansion history, we combine cosmic chronometers (CCs) and type Ia supernovae (SNe Ia) data to infer constraints on curvature, marginalized over the expansion history, calibration of the CC and SNe Ia data, and the GP hyper-parameters. The obtained constraints on ΩK are free from parametric model assumptions for the expansion history and are insensitive to the overall calibration of both the CC and SNe Ia data (being sensitive only to relative distances and expansion rates). Applying this method to Pantheon SNe Ia and the latest compilation of CCs, we find ΩK = −0.03 ± 0.26, consistent with spatial flatness at the |$\mathcal {O}(10^{-1})$| level, and independent of any early-Universe probes. Applying our methodology to future baryon acoustic oscillations and SNe Ia data from upcoming Stage IV surveys, we forecast the ability to constrain ΩK at the |$\mathcal {O}(10^{-2})$| level. [ABSTRACT FROM AUTHOR]

A string of recent studies has debated the exact form and physical origin of an evolutionary trend between the peak luminosity of Type Ia supernovae (SNe Ia) and the properties of the galaxies that host them. We shed new light on the discussion by presenting an analysis of ∼200 low-redshift SNe Ia in which we measure the separation of Hubble residuals (HR; as probes of luminosity) between two host-galaxy morphological types. We show that this separation can test the predictions made by recently proposed models, using an independently and empirically determined distribution of each morphological type in host-property space. Our results are partially consistent with the new HR–age slope, but we find significant scatter in the predictions from different galaxy catalogues. The inconsistency in age illuminates an issue in the current debate that was not obvious in the long-discussed mass models: HR–host-property models are strongly dependent on the methods employed to determine galaxy properties. While our results demonstrate the difficulty in constructing a universal model for age as a proxy for host environment, our results indeed identify evolutionary trends between mass, age, morphology, and HR values, encouraging (or requiring, if such trends are to be accounted for in cosmological studies) further investigation. [ABSTRACT FROM AUTHOR]

Much of the cosmological utility thus far extracted from Type Ia supernovae (SNe Ia) relies on the assumption that SN Ia peak luminosities do not evolve significantly with the age (local or global) of their stellar environments. Two recent studies have provided conflicting results in evaluating the validity of this assumption, with one finding no correlation between Hubble residuals (HR) and stellar environment age, while the other claims a significant correlation. In this Letter we perform an independent reanalysis that rectifies issues with the statistical methods employed by both of the aforementioned studies. Our analysis follows a principled approach that properly accounts for regression dilution and critically (and unlike both prior studies) utilizes the Bayesian-model-produced SN environment age estimates (posterior samples) instead of point estimates. Moreover, the posterior is used as an informative prior in the regression. We find the Pearson correlation between the HR and local (global) age to be in excess of 4σ (3σ). Assuming there exists a linear relationship between HR and local (global) age, we find a corresponding slope of −0.035 ± 0.007 mag Gyr−1 (−0.036 ± 0.007 mag Gyr−1). We encourage further use of our approach to examine HR and host environment correlations, as well as experiments in correcting for luminosity evolution in SN Ia standardization. [ABSTRACT FROM AUTHOR]

We show an efficient way to compute wide-angle or all-sky statistics of galaxy intrinsic alignment in three-dimensional configuration space. For this purpose, we expand the two-point correlation function using a newly introduced spin-dependent tripolar spherical harmonic basis. Therefore, the angular dependencies on the two line of sight (LOS) directions pointing to each pair of objects, which are degenerate with each other in the conventional analysis under the small-angle or plane-parallel (PP) approximation, are unambiguously decomposed. By means of this, we, for the first time, compute the wide-angle auto and cross correlations between intrinsic ellipticities, number densities, and velocities of galaxies and compare them with the PP-limit results. For the ellipticity−ellipticity and density−ellipticity correlations, we find more than |$10{{\ \rm per\ cent}}$| deviation from the PP-limit results if the opening angle between two LOS directions exceeds 30°−50°. It is also shown that even if the PP-limit result is strictly zero, the non-vanishing correlation is obtained over the various scales, arising purely from the curved-sky effects. Our results indicate the importance of the data analysis not relying on the PP approximation in order to determine the cosmological parameters more precisely and/or find new physics via ongoing and forthcoming wide-angle galaxy surveys. [ABSTRACT FROM AUTHOR]

Recent measurements of the Cosmic Microwave Anisotropies power spectra measured by the Planck satellite show a preference for a closed universe at more than |$99 {{\ \rm per\ cent}}$| confidence level (CL). Such a scenario is however in disagreement with several low redshift observables, including luminosity distances of Type Ia supernovae. Here we show that interacting dark energy (IDE) models can ease the discrepancies between Planck and supernovae Ia data in a closed Universe, leading to a preference for both a coupling and a curvature different from zero above the 99 per cent CL. Therefore IDE cosmologies remain as very appealing scenarios, as they can provide the solution to a number of observational tensions in different fiducial cosmologies. The results presented here strongly favour broader analyses of cosmological data, and suggest that relaxing the usual flatness and vacuum energy assumptions can lead to a much better agreement among theory and observations. [ABSTRACT FROM AUTHOR]

We study constraints on allowed reionization histories by comparing predictions of a physical seminumerical model with secondary temperature and polarization anisotropies of the cosmic microwave background (CMB). Our model has four free parameters characterizing the evolution of ionizing efficiency ζ and the minimum mass M min of haloes that can produce ionizing radiation. Comparing the model predictions with the presently available data of the optical depth τ and kinematic Sunyaev–Zeldovich signal, we find that we can already rule out a significant region of the parameter space. We limit the duration of reionization |$\Delta z= 1.30^{+0.19}_{-0.60}$| (Δ z < 2.9 at |$99{{\ \rm per\ cent}}$| C.L.), one of the tightest constraints on the parameter. The constraints mildly favour M min ≳ 109 M⊙ (at |$68{{\ \rm per\ cent}}$| C.L.) at z ∼ 8, thus indicating the presence of reionization feedback. Our analysis provides an upper bound on the secondary B-mode amplitude |$D_{l=200}^{BB} \lt 18$| nK2 at |$99{{\ \rm per\ cent}}$| C.L. We also study how the constraints can be further tightened with upcoming space- and ground-based CMB missions. Our study, which relies solely on CMB data , has implications not only for upcoming CMB surveys for detecting primordial gravitational waves but also redshifted 21 cm studies. [ABSTRACT FROM AUTHOR]

The geometry of the Universe may be probed using the Alcock–Paczyński (AP) effect, in which the observed redshift size of a spherical distribution of sources relative to its angular size varies according to the assumed cosmological model. Past applications of this effect have been limited, however, by a paucity of suitable sources and mitigating astrophysical factors, such as internal redshift-space distortions and poorly known source evolution. In this Letter , we introduce a new test based on the AP effect that avoids the use of spatially bound systems, relying instead on sub-samples of quasars at redshifts z  ≲ 1.5 in the Sloan Digital Sky Survey IV, with a possible extension to higher redshifts and improved precision when this catalogue is expanded by upcoming surveys. We here use this method to probe the redshift-dependent expansion rate in three pertinent Friedmann–Lemaître–Robertson–Walker cosmologies: Λ cold dark matter (ΛCDM), which predicts a transition from deceleration to acceleration at z  ∼ 0.7; Einstein–de Sitter, in which the Universe is always decelerating; and the R h = ct universe, which expands at a constant rate. ΛCDM is consistent with these data, but R h = ct is favoured overall. [ABSTRACT FROM AUTHOR]

We quantify the evidence for cosmic acceleration using simulations of H (z) measurements from SKA- and Euclid-like surveys. We perform a non-parametric reconstruction of the Hubble parameters and its derivative to obtain the deceleration parameter q (z) using the Gaussian Processes method. This is a completely model-independent approach, so we can determine whether the Universe is undergoing accelerated expansion regardless of any assumption of a dark energy model. We find that Euclid-like and SKA-like band 1 surveys can probe cosmic acceleration at over 3 and 5σ confidence level, respectively. By combining them with an SKA-like band 2 survey, which reaches lower redshift ranges, the evidence for a current accelerated phase increases to over 7σ. This is a significant improvement from current H (z) measurements from cosmic chronometers and galaxy redshift surveys, showing that these surveys can underpin cosmic acceleration in a model-independent way. [ABSTRACT FROM AUTHOR]

We study observations in toy models that constitute exact cosmological solutions to the Einstein equation. These models are statistically homogeneous but locally inhomogeneous, without an a priori introduced Friedmann–Lemaître–Roberston–Walker (FLRW) background and with 'structures' evolving fairly slowly. The mean redshift–distance relation and redshift drift along 500 light rays in each of two models are compared with relations based on spatial averages. The relations based on spatial averages give a good reproduction of the mean redshift–distance relation, although most convincingly in the model where the kinematical backreaction and average spatial curvature cancel each other to a subpercentage precision. In both models, the mean redshift drift clearly differs from the drift of the mean redshift. This indicates that redshift drift could be an important tool for testing the backreaction conjecture as redshift drift appears to distinguish between local and global effects. The method presented for computing the redshift drift is straightforward to generalize and can thus be utilized to fairly easily compute this quantity in a general space–time. [ABSTRACT FROM AUTHOR]

The counts-in-cells (CIC) galaxy probability distribution depends on both the dark matter clustering amplitude σ8 and the galaxy bias b. We present a theory for the CIC distribution based on a previous prescription of the underlying dark matter distribution and a linear volume transformation to redshift space. We show that, unlike the power spectrum, the CIC distribution breaks the degeneracy between σ8 and b on scales large enough that both bias and redshift distortions are still linear; thus, we obtain a simultaneous fit for both parameters. We first validate the technique on the Millennium Simulation and then apply it to the Sloan Digital Sky Survey main galaxy sample. We find σ8 = 0.92 ±.08 and |$b = 1.39^{+.11}_{-.09}$| consistent with previous complementary results from redshift distortions and from Planck. [ABSTRACT FROM AUTHOR]

We study an efficient way to enhance the measurability of the galaxy density and/or velocity power spectrum in redshift space. It is based on the angular decomposition with the tripolar spherical harmonic (TripoSH) basis and applicable even to galaxy distributions in wide-angle galaxy surveys. While non-trivial multipole-mode mixings are inevitable in the covariance of the Legendre decomposition coefficient commonly used in the small-angle power spectrum analysis, our analytical computation of the covariance of the TripoSH decomposition coefficient shows that such mixings are absent by virtue of high separability of the TripoSH basis, yielding the minimum variance. Via the simple signal-to-noise ratio assessment, we confirm that the detectability improvement by the TripoSH decomposition approach becomes more significant at higher multipole modes, and the hexadecapole of the density power spectrum has two orders of magnitude improvement. The TripoSH decomposition approach is expected to be applied to not only currently available survey data but also forthcoming wide-angle data, and to bring about something new or much more accurate cosmological information. [ABSTRACT FROM AUTHOR]

Line intensity mapping (LIM) is an emerging observational method to study the large-scale structure of the Universe and its evolution. LIM does not resolve individual sources but probes the fluctuations of integrated line emissions. A serious limitation with LIM is that contributions of different emission lines from sources at different redshifts are all confused at an observed wavelength. We propose a deep learning application to solve this problem. We use conditional generative adversarial networks to extract designated information from LIM. We consider a simple case with two populations of emission-line galaxies; H  |$\rm \alpha$|  emitting galaxies at |$z$|  = 1.3 are confused with [O  iii ] emitters at |$z$|  = 2.0 in a single observed waveband at 1.5 |$\mu{\textrm m}$|⁠. Our networks trained with 30 000 mock observation maps are able to extract the total intensity and the spatial distribution of H  |$\rm \alpha$|  emitting galaxies at |$z$|  = 1.3. The intensity peaks are successfully located with 74 per cent precision. The precision increases to 91 per cent when we combine five networks. The mean intensity and the power spectrum are reconstructed with an accuracy of ∼10 per cent. The extracted galaxy distributions at a wider range of redshift can be used for studies on cosmology and on galaxy formation and evolution. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new approach to determining cosmological distances to active Galactic nuclei (AGNs) via light travel-time arguments, which can be extended from nearby sources to very high redshift sources. The key assumption is that the variability seen in AGNs is constrained by the speed of light and therefore provides an estimate of the linear size of an emitting region. This can then be compared with the angular size measured with very long baseline interferometryer to derive a distance. We demonstrate this approach on a specific well-studied low-redshift (z  = 0.0178) source 3C 84 (NGC 1275), which is the bright radio core of the Perseus Cluster. We derive an angular diameter distance including statistical errors of |$D_{\mathrm{ A}} = 72^{+5}_{-6}$|  Mpc for this source, which is consistent with other distance measurements at this redshift. Possible sources of systematic errors and ways to correct for them are discussed. [ABSTRACT FROM AUTHOR]

Recent observations of the fields surrounding a few Milky Way-like galaxies in the local Universe have become deep enough to enable investigations of the predictions of the standard lambda cold dark matter (ΛCDM) cosmological model down to small scales outside the Local Group (LG). Motivated by an observed correlation between the number of dwarf satellites (N sat) and the bulge-to-total baryonic mass ratios (B / T) of the three main galaxies in the LG, i.e. the Milky Way, Andromeda, and Triangulum (M33), we use published data of three well-studied galaxies outside the LG, namely M81, Centaurus A, and M101, and their confirmed satellites, and we find a strong and significant correlation between N sat and B / T. This presents itself in contradiction with the hitherto published results from cosmological simulations reporting an absence of a correlation between N sat and B / T in the ΛCDM model. We conclude that, based on the current data, the N sat versus B / T correlation is no longer a property confined to only the LG. [ABSTRACT FROM AUTHOR]

C  ii is one of the brightest emission lines from star-forming galaxies and is an excellent tracer for star formation. Recent work measured the C  ii emission line amplitude for redshifts 2 < z < 3.2 by cross-correlating Planck High Frequency Instrument emission maps with tracers of overdensity from the Baryon Oscillation Spectroscopic Sky Survey, finding |${I}_{{\text C}\,\rm {\small II}}=6.6^{+5.0}_{-4.8}\times {10}^{4}$|  Jy sr−1 at |$95\,{\text{per cent}}$| confidence level. In this paper, we present a refinement of this earlier work by improving the mask weighting in each of the Planck bands and the precision in the covariance matrix. We report a detection of excess emission in the 545 GHz Planck band separate from the cosmic infrared background (CIB) present in the 353–857 GHz Planck bands. This excess is consistent with redshifted C  ii emission, in which case we report |$b_{{\text C} \,\rm {\small II}}I_{{\text C} \,\rm {\small II}} =2.0^{+1.2}_{-1.1}\times 10^5$|  Jy sr−1 at |$95\ {\text {per cent}}$| confidence level, which strongly favours many collisional excitation models of C  ii emission. Our detection shows strong evidence for a model with a non-zero C  ii parameter, though line intensity mapping observations at high spectral resolution will be needed to confirm this result. [ABSTRACT FROM AUTHOR]

Weak lensing will play an important role in future cosmological surveys, including e.g. Euclid and SKA. Sufficiently accurate theoretical predictions are important for correctly interpreting these surveys and hence for extracting correct cosmological parameter estimations. We quantify for the first time in a relativistic setting how many post-Born and lens–lens coupling corrections are required for sub-per cent accuracy of the theoretical weak lensing convergence for |$z$| ≤ 2 (the primary weak lensing range for Euclid and SKA). We do this by ray tracing through a fully relativistic exact solution of the Einstein field equations, which consists of randomly packed mass-compensated underdensities of realistic amplitudes. We find that including lens–lens coupling terms and post-Born corrections up to second and third order respectively is sufficient for sub-per cent accuracy of the convergence along |$94{{\ \rm per\ cent}}$| of the studied light rays. We also find that a significant percentage of the studied rays have post-Born corrections of size over |$10{{\ \rm per\ cent}}$| of the usual gravitational convergence, κ(1), and several rays even have post-Born corrections several times the size of κ(1) at |$z$|  = 2. [ABSTRACT FROM AUTHOR]

We here propose a new model-independent technique to overcome the circularity problem affecting the use of gamma-ray bursts (GRBs) as distance indicators through the use of E p−Eiso correlation. We calibrate the E p −E iso correlation and find the GRB distance moduli that can be used to constrain dark energy models. We use observational Hubble data to approximate the cosmic evolution through Bézier parametric curve obtained through the linear combination of Bernstein basis polynomials. In doing so, we build up a new data set consisting of 193 GRB distance moduli. We combine this sample with the supernova JLA data set to test the standard ΛCDM model and its w CDM extension. We place observational constraints on the cosmological parameters through Markov Chain Monte Carlo numerical technique. Moreover, we compare the theoretical scenarios by performing the Akaike and Deviance Information statistical criteria.the 2σ level, while for the w CDM model we obtain |$\Omega _m=0.34^{+0.13}_{-0.15}$| and |$w=-0.86^{+0.36}_{-0.38}$| at the 2σ level. Our analysis suggests that ΛCDM model is statistically favoured over the w CDM scenario. No evidence for extension of the ΛCDM model is found. [ABSTRACT FROM AUTHOR]

We present the detection of the average H2 absorption signal in the overall population of neutral gas absorption systems at z∼ 3 using composite absorption spectra built from the Sloan Digital Sky Survey-III damped Lyman α catalogue. We present a new technique to directly measure the H2 column density distribution function $f_{\rm H_2}(N)$ from the average H2 absorption signal. Assuming a power-law column density distribution, we obtain a slope $\beta = -1.29 \pm 0.06(\rm stat) \pm 0.10 (\rm sys)$ and an incidence rate of strong H2 absorptions [with N(H2) ≳ 1018 cm−2] to be $4.0 \pm 0.5(\rm stat) \pm 1.0 (\rm sys)\, \hbox{ per cent}$ in H i absorption systems with N(H i) ≥1020 cm−2. Assuming the same inflexion point where $f_{\rm H_2}(N)$ steepens as at z = 0, we estimate that the cosmological density of H2 in the column density range $\log N(\rm H_2) ({\rm cm}^{-2})= 18{\text{--}}22$ is ${\sim } 15\hbox{ per cent}$ of the total. We find one order of magnitude higher H2 incident rate in a sub-sample of extremely strong damped Lyman α absorption systems (DLAs) [ $\log N(\rm{H\,\small {I}}) ({\rm cm}^{-2}) \ge 21.7$ ], which, together with the derived shape of $f_{\rm H_2}(N)$ , suggests that the typical H i–H2 transition column density in DLAs is log N(H)(cm−2) ≳ 22.3 in agreement with theoretical expectations for the average (low) metallicity of DLAs at high-z. [ABSTRACT FROM AUTHOR]

Combining measurements on the expansion history of the Universe and on the growth rate of cosmic structures is key to discriminate between alternative cosmological frameworks and to test gravity. Recently, Linder proposed a new diagram to investigate the joint evolutionary track of these two quantities. In this letter, we collect the most recent cosmic growth and expansion rate data sets to provide the state-of-the-art observational constraints on this diagram. By performing a joint statistical analysis of both probes, we test the standard Λcold dark matter model, confirming a mild tension between cosmic microwave background predictions from Planck mission and cosmic growth measurements at low redshift (z < 2). Then we test alternative models allowing the variation of one single cosmological parameter at a time. In particular, we find a larger growth index than the one predicted by general relativity γ = 0.65-0.04+0.05. However, also a standard model with total neutrino mass of 0.26 ± 0.10 eV provides a similarly accurate description of the current data. By simulating an additional data set consistent with next-generation dark-energy mission forecasts, we show that growth rate constraints at z > 1 will be crucial to discriminate between alternative models. [ABSTRACT FROM AUTHOR]

Star-forming galaxies at high redshifts are the ideal targets to probe the hypothetical variation of the fine-structure (FS) constant α over cosmological time-scales.We propose a modification of the alkali doublets method that allows us to search for variation in α combining far-infrared and submillimetre spectroscopic observations. This variation manifests as velocity offsets between the observed positions of the FS and gross-structure transitions when compared to laboratory wavelengths. Here we describe our method whose sensitivity limit to the fractional changes in α is about 5 × 10-7. We also demonstrate that current spectral observations of hydrogen and [CII] 158 μm lines provide an upper limit on Δα/α ≲ 6 × 10-5 at redshifts z = 3.1 and 4.7. [ABSTRACT FROM AUTHOR]

The peculiar emission properties of the z ~ 6.6 Lyα emitter COSMOS redshift 7 (CR7) have been initially interpreted with the presence of either a direct collapse black hole (DCBH) or a substantial mass of Pop III stars. Instead, updated photometric observations by Bowler et al. seem to suggest that CR7 is a more standard system. Here, we confirm that the original DCBH hypothesis is consistent also with the new data. Using radiation-hydrodynamic simulations, we reproduce the new infrared photometry with two models involving a Compton-thick DCBH of mass ≈7 × 106M☉ accreting (a) metal-free (Z = 0) gas with column density NH = 8 × 1025 cm-2 or (b) low-metallicity gas (Z = 5 × 10-3 Z☉) with NH = 3 × 1024 cm-2. The best-fitting model reproduces the photometric data to within 1σ. Such metals can be produced by weak star-forming activity occurring after the formation of the DCBH. The main contribution to the Spitzer/IRAC 3.6 μm photometric band in both models is due to He I/He II λλ4714, 4687 emission lines, while the contribution of [OIII] λλ4959, 5007 emission lines, if present, is sub-dominant. Spectroscopic observations with JWST will be required to ultimately clarify the nature of CR7. [ABSTRACT FROM AUTHOR]

We report the discovery of a potentially major supercluster that extends across the Galactic plane in the constellation of Vela, at a mean recessional velocity of ∼18 000 km s−1. Recent multiobject spectroscopic observations of this Vela supercluster (VSCL), using AAOmega+2dF and the Southern African Large Telescope, confirm an extended galaxy overdensity in the Zone of Avoidance (ZOA) located where residual bulk flows predict a considerable mass excess. We present a preliminary analysis of ∼4500 new spectroscopic galaxy redshifts obtained in the ZOA centred on the Vela region (l = 272.°5±20°, b=0° ± 10°). The presently sparsely sampled data set traces an overdensity that covers 25° in Galactic longitude on either side of the Galactic plane, suggesting an extent of 25 × 20 deg2, corresponding to ∼ 115 × 90 h70 Mpc at the supercluster redshift. In redshift space, the overdensity appears to consist of two merging wall-like structures, interspersed with clusters and groups. Both the velocity histogram and the morphology of the multibranching wall structure are consistent with a supercluster classification. Ks° galaxy counts show an enhancement of ∼1.2 over the survey area for galaxies brighter than MK* at the VSCL distance, and a galaxy overdensity of δ = 0.50–0.77 within a photometric redshift shell around the VSCL, when compared with various Two Micron All-Sky Survey samples. Taking account of selection effects, the VSCL is estimated to contribute vLG ≳ 50 km s−1 to the motion of the Local Group [ABSTRACT FROM AUTHOR]

We investigate the expected cosmological constraints from a combination of cosmic shear and large-scale galaxy clustering using realistic photometric redshift distributions. Introducing a systematic bias in the lensing distributions (of 0.05 in redshift) produces a >2σ bias in the recovered matter power spectrum amplitude and dark energy equation of state for preliminary Stage III surveys. We demonstrate that cosmological error can be largely removed by marginalizing over biases in the assumed weak-lensing redshift distributions. Furthermore, the cosmological constraining power is retained despite removing much of the information on the lensing redshift biases. This finding relies upon high-quality redshift estimates for the clustering sample, but does not require spectroscopy. All galaxies in this analysis can thus be assumed to come from a single photometric survey. We show that this internal constraint on redshift biases arises from complementary degeneracy directions between cosmic shear and the combination of galaxy clustering and shear–density cross-correlations. Finally we examine a case where the assumed redshift distributions differ from the truth by more than a simple uniform bias. We find that the effectiveness of this self-calibration method will depend on the survey details and the nature of the uncertainties on the estimated redshift distributions. [ABSTRACT FROM AUTHOR]

We present a comparison of major methodologies of fast generating mock halo or galaxy catalogues. The comparison is done for two-point (power spectrum and two-point correlation function in real and redshift space), and the three-point clustering statistics (bispectrum and three-point correlation function). The reference catalogues are drawn from the BigMultiDark N-body simulation. Both friend-of-friends (including distinct haloes only) and spherical overdensity (including distinct haloes and subhalos) catalogues have been used with the typical number density of a large volume galaxy surveys. We demonstrate that a proper biasing model is essential for reproducing the power spectrum at quasi-linear and even smaller scales. With respect to various clustering statistics, a methodology based on perturbation theory and a realistic biasing model leads to very good agreement with N-body simulations. However, for the quadrupole of the correlation function or the power spectrum, only the method based on semi-N-body simulation could reach high accuracy (1 per cent level) at small scales, i.e. r < 25 h-1 Mpc or k > 0.15 h Mpc-1. Full N-body solutions will remain indispensable to produce reference catalogues. Nevertheless, we have demonstrated that the more efficient approximate solvers can reach a few per cent accuracy in terms of clustering statistics at the scales interesting for the large-scale structure analysis. This makes them useful for massive production aimed at covariance studies, to scan large parameter spaces, and to estimate uncertainties in data analysis techniques, such as baryon acoustic oscillation reconstruction, redshift distortion measurements, etc. [ABSTRACT FROM AUTHOR]

We present a catalogue of 348 galaxy clusters and groups with 0.2 < z < 1.2 selected in the 2.78 deg² Advanced Large, Homogeneous Area Medium Band Redshift Astronomical (ALHAMBRA) survey. The high precision of our photometric redshifts, close to 1 per cent, and the wide spread of the seven ALHAMBRA pointings ensure that this catalogue has better mass sensitivity and is less affected by cosmic variance than comparable samples. The detection has been carried out with the Bayesian Cluster Finder, whose performance has been checked in ALHAMBRA-like light-cone mock catalogues. Great care has been taken to ensure that the observable properties of the mocks photometry accurately correspond to those of real catalogues. From our simulations, we expect to detect galaxy clusters and groups with both 70 per cent completeness and purity down to dark matter halo masses of Mh ~ 3 × 1013M⊙ for z < 0.85. Cluster redshifts are expected to be recovered with ~0.6 per cent precision for z <1.We also expect to measure cluster masses with σMh|M*CL ~ 0.25-0.35 dex precision down to ~ 3 × 1013M⊙, masses which are 50 per cent smaller than those reached by similar work. We have compared these detections with previous optical, spectroscopic and X-rays work, finding an excellent agreement with the rates reported from the simulations. We have also explored the overall properties of these detections such as the presence of a colour-magnitude relation, the evolution of the photometric blue fraction and the clustering of these sources in the different ALHAMBRA fields. Despite the small numbers, we observe tentative evidence that, for a fixed stellar mass, the environment is playing a crucial role at lower redshifts (z < 0.5). [ABSTRACT FROM AUTHOR]

Dust-Obscured Galaxies (DOGs) are bright 24 μm-selected sources with extreme obscuration at optical wavelengths. They are typically characterized by a rising power-law continuum of hot dust (TD ∼ 200-1000 K) in the near-IR indicating that their mid-IR luminosity is dominated by an active galactic nucleus (AGN). DOGs with a fainter 24 μm flux display a stellar bump in the near-IR and their mid-IR luminosity appears to be mainly powered by dusty star formation. Alternatively, it may be that the mid-IR emission arising from AGN activity is dominant but the torus is sufficiently opaque to make the near-IR emission from the AGN negligible with respect to the emission from the host component. In an effort to characterize the astrophysical nature of the processes responsible for the IR emission in DOGs, this paper exploits Herschel data (PACS + SPIRE) on a sample of 95 DOGs within the COSMOS field. We derive a wealth of far-IR properties (e.g. total IR luminosities; mid-to-far-IR colours; dust temperatures and masses) based on spectral energy distribution fitting. Of particular interest are the 24 μm-bright DOGs (F24 μm > 1 mJy). They present bluer far-IR/mid-IR colours than the rest of the sample, unveiling the potential presence of an AGN. The AGN contribution to the total 8-1000 μm flux increases as a function of the rest-frame 8 μm-luminosity irrespective of the redshift. This confirms that faint DOGs (L8 μm < 1012 L⊙) are dominated by star formation while brighter DOGs show a larger contribution from an AGN. [ABSTRACT FROM AUTHOR]

We present a result of a blind search for [CII] 158 µm emitters at z ~ 4.5 using Atacama Large Millimeter Array (ALMA) Cycle 0 archival data. We collected extragalactic data covering at 330-360 GHz (band 7) from 8 Cycle 0 projects from which initial results have been already published. The total number of fields is 243 and the total on-source exposure time is 19.2 h. We searched for line emitters in continuum-subtracted data cubes with spectral resolutions of ~50, 100, 300 and 500 km s-1.We could not detect any new line emitters above a 6s significance level. This result provides upper limits to the [CII] luminosity function at z ~ 4.5 over L[C II] ~ 108-1010 L⊙ or star formation rate, SFR ~ 10-1000 M⊙yr-1. These limits are at least two orders of magnitude larger than the [CII] luminosity functions expected from the z ~ 4 UV luminosity function or from numerical simulation. However, this study demonstrates that we would be able to better constrain the [C II] luminosity function and to investigate possible contributions from dusty galaxies to the cosmic star formation rate density by collecting Cycle 1+2 archival data as the ALMA Patchy Deep Survey. [ABSTRACT FROM AUTHOR]

Using wide-field narrow-band surveys, we provide a new measurement of the z = 6.6 Lymana emitter (LAE) luminosity function (LF), which constraints the bright end for the first time. We use a combination of archival narrow-band NB921 data in UDS and new NB921 measurements in SA22 and COSMOS/UltraVISTA, all observed with the Subaru telescope, with a total area of ~5 deg². We exclude lower redshift interlopers by using broad-band optical and nearinfrared photometry and also exclude three supernovae with data split over multiple epochs. Combining the UDS and COSMOS samples, we find no evolution of the bright end of the Lya LF between z = 5.7 and 6.6, which is supported by spectroscopic follow-up, and conclude that sources with Himiko-like luminosity are not as rare as previously thought, with number densities of ~1.5 × 10-5 Mpc-3. Combined with our wide-field SA22 measurements, our results indicate a non-Schechter-like bright end of the LF at z = 6.6 and a different evolution of observed faint and bright LAEs, overcoming cosmic variance. This differential evolution is also seen in the spectroscopic follow-up of UV-selected galaxies and is now also confirmed for LAEs, and we argue that it may be an effect of reionization. Using a toy model, we show that such differential evolution of the LF is expected, since brighter sources are able to ionize their surroundings earlier, such that Lya photons are able to escape. Our targets are excellent candidates for detailed follow-up studies and provide the possibility to give a unique view on the earliest stages in the formation of galaxies and reionization process. [ABSTRACT FROM AUTHOR]

The 21-cm line brightness temperature brings rich information about Epoch of Reionizaton (EoR) and high-z universe (Cosmic Dawn and Dark Age). While the power spectrum is a useful tool to investigate the EoR signal statistically, higher order statistics such as bispectrum are also valuable because the EoR signal is expected to be highly non-Gaussian. In this paper, we develop a formalism to calculate the bispectrum contributed from the thermal noise taking array configuration of telescopes into account, by extending a formalism for the power spectrum. We apply our formalism to the ongoing and future telescopes such as expanded Murchison Widefield Array (MWA), LOw Frequency ARray (LOFAR), Hydrogen Epoch of Reionization Array (HERA) and Square Kilometre Array (SKA). We find that expanded MWA does not have enough sensitivity to detect the bispectrum signal. On the other hand, LOFAR has better sensitivity and will be able to detect the peaks of the bispectrum as a function of redshift at large scales with comoving wavenumber k ≲ 0.03 Mpc-1. The SKA has enough sensitivity to detect the bispectrum for much smaller scales k &#8818 0.3Mpc-1 and redshift z ≲ 20. [ABSTRACT FROM AUTHOR]

We address the problem of separating stars from galaxies in future large photometric surveys. We focus our analysis on simulations of the Dark Energy Survey (DES). In the first part of the paper, we derive the science requirements on star/galaxy separation, for measurement of the cosmological parameters with the gravitational weak lensing and large-scale structure probes. These requirements are dictated by the need to control both the statistical and systematic errors on the cosmological parameters, and by point spread function calibration. We formulate the requirements in terms of the completeness and purity provided by a given star/galaxy classifier. In order to achieve these requirements at faint magnitudes, we propose a new method for star/galaxy separation in the second part of the paper. We first use principal component analysis to outline the correlations between the objects parameters and extract from it the most relevant information. We then use the reduced set of parameters as input to an Artificial Neural Network. This multiparameter approach improves upon purely morphometric classifiers (such as the classifier implemented in SExtractor), especially at faint magnitudes: it increases the purity by up to 20 per cent for stars and by up to 12 per cent for galaxies, at i-magnitude fainter than 23. [ABSTRACT FROM AUTHOR]

We use the WISE-2MASS infrared galaxy catalogue matched with Pan-STARRS1 (PS1) galaxies to search for a supervoid in the direction of the cosmic microwave background (CMB) cold spot (CS). Our imaging catalogue has median redshift z - 0.14, and we obtain photometric redshifts from PS1 optical colours to create a tomographic map of the galaxy distribution. The radial profile centred on the CS shows a large low-density region, extending over tens of degrees. Motivated by previous CMB results, we test for underdensities within two angular radii, 5°, and 15°. The counts in photometric redshift bins show significantly low densities at high detection significance, ≪5σ and ≪6σ, respectively, for the two fiducial radii. The line-of-sight position of the deepest region of the void is z ≃0.15-0.25. Our data, combined with an earlier measurement by Granett, Szapudi & Neyrinck, are consistent with a largeR void = (220 ± 50) h-1 Mpc supervoid with δm ∇ - 0.14 ± 0.04 centred at z = 0.22 ± 0.03. Such a supervoid, constituting at least a ~3.3σ fluctuation in a Gaussian distribution of the Μ cold dark matter model, is a plausible cause for the CS. [ABSTRACT FROM AUTHOR]

CIZA J2242.8+5301 ('Sausage') and 1RXS J0603.3+4213 ('Toothbrush') are two low-redshift (z ~ 0.2), massive (~2 x 1015M⊙), post-core passage merging clusters, which host-shock waves traced by diffuse radio emission. To study their star formation properties, we uniformly survey the 'Sausage' and 'Toothbrush' clusters in broad- and narrow-band filters and select a sample of 201 and 463 line emitters, down to a rest-frame equivalent width (13 Å). We robustly separate between Hα and higher redshift emitters using a combination of optical multiband (B, g, V, r, i, z) and spectroscopic data. We build Hα luminosity functions for the entire cluster region, near the shock fronts, and away from the shock fronts and find striking differences between the two clusters. In the dynamically younger, 1 Gyr old 'Sausage' cluster we find numerous (59) Hα emitters above a star formation rate (SFR) of 0.17 M⊙ yr-1 surprisingly located in close proximity to the shock fronts, embedded in very hot intracluster medium plasma. The SFR density for the cluster population is at least at the level of typical galaxies at z ~ 2. Down to the same SFR, the possibly dynamically more evolved 'Toothbrush' cluster has only nine Hα galaxies. The cluster Hα galaxies fall on the SFR-stellar mass relation z ~ 0.2 for the field. However, the 'Sausage' cluster has an Hα emitter density >20 times that of blank fields. If the shock passes through gas-rich cluster galaxies, the compressed gas could collapse into dense clouds and excite star formation for a few 100 Myr. This process ultimately leads to a rapid consumption of the molecular gas, accelerating the transformation of gas-rich field spirals into cluster S0s or ellipticals. [ABSTRACT FROM AUTHOR]

Cluster mergers may play a fundamental role in the formation and evolution of cluster galaxies. Stroe et al. revealed unexpected overdensities of candidate Hα emitters near the ~1-Mpc-wide shock fronts of the massive (~2 x 1015 M⊙) 'Sausage' merging cluster, CIZA J2242.8+5301. We used the Keck/Deep Imaging Multi-Object Spectrograph and the William Herschel Telescope/AutoFib2+WYFFOS to confirm 83 Hα emitters in and around the merging cluster. We find that cluster star-forming galaxies in the hottest X-ray gas and/or in the cluster subcores (away from the shock fronts) show high [S ii]6716/[S ii]6761 and high [S ii] 6716/Hα, implying very low electron densities (<30 x lower than all other star-forming galaxies outside the cluster) and/or significant contribution from supernovae, respectively. All cluster star-forming galaxies near the cluster centre show evidence of significant outflows (blueshifted Na D ~200-300 km s-1), likely driven by supernovae. Strong outflows are also found for the cluster Hα active galactic nucleus (AGN). Hα star-forming galaxies in the merging cluster follow the z ~ 0 mass-metallicity relation, showing systematically higher metallicity (~0.15-0.2 dex) than Hα emitters outside the cluster (projected R > 2.5 Mpc). This suggests that the shock front may have triggered remaining metal-rich gas which galaxies were able to retain into forming stars. Our observations show that the merger of impressively massive (~1015 M⊙) clusters can provide the conditions for significant star formation and AGN activity, but, as we witness strong feedback by star-forming galaxies and AGN (and given how massive the merging cluster is), such sources will likely quench in a few 100 Myr. [ABSTRACT FROM AUTHOR]

We consider some aspects of the perturbation to the luminosity distance d(z) that are of relevance for SN1a cosmology and for future peculiar velocity surveys at non-negligible redshifts. (1) Previous work has shown that the correction to the lowest order perturbation δd/d = -δv/cz has the peculiar characteristic that it appears to depend on the absolute state of motion of sources, rather than on their motion relative to that of the observer. The resolution of this apparent violation of the equivalence principle is that it is necessary to allow for evolution of the velocities with time, and also, when considering perturbations on the scale of the observer-source separation, to include the gravitational redshift effect. We provide an expression for δd/d that provides a physically consistent way to measure peculiar velocities and determine their impact for SN1a cosmology. (2) We then calculate the perturbation to the redshift as a function of source flux density, which has been proposed as an alternative probe of large-scale motions. We show how the inclusion of surface brightness modulation modifies the relation between δz(m) and the peculiar velocity, and that, while the noise properties of this method might appear promising, the velocity signal is swamped by the effect of galaxy clustering for most scales of interest. (3) We show how, in linear theory, peculiar velocity measurements are biased downwards by the effect of smaller scale motions or by measurement errors (such as in photometric redshifts). Our results nicely explain the effects seen in simulations by Koda et al. We critically examine the prospects for extending peculiar velocity studies to larger scales with near-term future surveys. [ABSTRACT FROM AUTHOR]

ABSTRACT The current cosmological dark sector (dark matter plus dark energy) is challenging our comprehension about the physical processes taking place in the Universe. Recently, some authors tried to falsify the basic underlying assumptions of such dark matter-dark energy paradigm. In this Letter, we show that oversimplifications of the measurement process may produce false positives to any consistency test based on the globally homogeneous and isotropic Λ cold dark matter (ΛCDM) model and its expansion history based on distance measurements. In particular, when local inhomogeneity effects due to clumped matter or voids are taken into account, an apparent violation of the basic assumptions ('Copernican Principle') seems to be present. Conversely, the amplitude of the deviations also probes the degree of reliability underlying the phenomenological Dyer-Roeder procedure by confronting its predictions with the accuracy of the weak lensing approach. Finally, a new method is devised to reconstruct the effects of the inhomogeneities in a ΛCDM model, and some suggestions of how to distinguish between clumpiness (or void) effects from different cosmologies are discussed. [ABSTRACT FROM AUTHOR]

Using the published Wilkinson Microwave Anisotropy Probe ( WMAP) 5-yr data, we first show how sensitive the WMAP power spectra are to the form of the WMAP beam. It is well known that the beam profile derived from observations of Jupiter is non-Gaussian and indeed extends, in the W band for example, well beyond its -arcmin FWHM core out to more than 1° in radius. This means that even though the core width corresponds to wavenumber , the form of the beam still significantly affects the WMAP results even at , which is the scale of the first acoustic peak. The difference between the beam convolved and the final is per cent at the scale of the first peak, rising to per cent at the scale of the second. New estimates of the Q-, V- and W-band beam profiles are then presented, based on a stacking analysis of the WMAP5 radio source catalogue and temperature maps. The radio sources show a significantly broader beam profile on scales of 10–30 arcmin than that found by the WMAP team, whose beam analysis is based on measurements of Jupiter. Beyond these scales, the beam profiles from the radio sources are too noisy to give useful information. Furthermore, we find tentative evidence for a non-linear relation between WMAP and ATCA/IRAM 95-GHz source fluxes. We discuss whether the wide beam profiles could be caused either by radio source extension or clustering and find that neither explanation is likely. We also argue against the possibility that Eddington bias is affecting our results. The reasons for the difference between the radio source and the Jupiter beam profiles are therefore still unclear. If the radio source profiles were then used to define the WMAP beam, there could be a significant change in the amplitude and position of even the first acoustic peak. It is therefore important to identify the reasons for the differences between these two beam profile estimates. [ABSTRACT FROM AUTHOR]

Recently, Kashlinsky et al. reported a discovery of a ∼103 km s−1 bulk flow of the Universe out to , through the dark flow induced cosmic microwave background (CMB) dipole in directions of clusters. We point out that, if this dark flow exists, it will also induce observable CMB temperature fluctuations at multipole , through modulation of the inhomogeneous electron distribution on the uniform dark flow. The induced small-scale kinetic Sunyaev–Zel'dovich (SZ) effect will reach at multipole , only a factor of smaller than the conventional kinetic SZ effect. Furthermore, it will be correlated with the large-scale structure (LSS) and its correlation with Two-Micron All-Sky Survey (2MASS) galaxy distribution reaches K at , under a directional dependent optimal weighting scheme. We estimate that, Wilkinson Microwave Anisotropy Probe plus 2MASS should already be able to detect this dark flow induced small-scale kinetic SZ effect with confidence. Deeper galaxy surveys such as the Sloan Digital Sky Survey can further improve the measurement. Planck plus existing galaxy surveys can reach detection. Existing CMB–LSS cross-correlation measurements shall be reanalysed to test the existence of the dark flow and, if it exists, shall be used to eliminate possible bias on the integrated Sachs–Wolfe effect measurement through the CMB–LSS cross-correlation. [ABSTRACT FROM AUTHOR]