Redshift Unity Research Articles

Intracluster light is already abundant at redshift beyond unity.

Intracluster light (ICL) is diffuse light from stars that are gravitationally bound not to individual member galaxies, but to the halo of galaxyclusters. Leading theories1,2 predict that the ICL fraction, defined by the ratio of the ICL to the total light, rapidly decreases with increasing redshift, to the level of a few per cent at z > 1. However, observational studies have remained inconclusive about the fraction beyond redshift unity because, to date, only two clusters in this redshift regime have been investigated. One shows a much lower fraction than the mean value at low redshift3, whereas the other possesses a fraction similar to the low-redshift value4. Here we report an ICL study of ten galaxy clusters at 1 ≲ z ≲ 2 based on deep infrared imaging data. Contrary to the leading theories, our study finds that ICL is already abundant at z ≳ 1, with a mean ICL fraction of approximately 17%. Moreover, no significant correlation between cluster mass and ICL fraction or between ICL colour and cluster-centric radius is observed. Our findings suggest that gradual stripping can no longer be the dominant mechanism of ICL formation. Instead, our study supports the scenario wherein the dominant ICL production occurs in tandem with the formation and growth of the brightest cluster galaxies and/or through the accretion of preprocessed stray stars.

Dark energy density predicted and explained

It has recently been shown that the observed Hubble function for cosmological expansion can be fitted accurately back to redshift unity (7.33 Gyr ago) with only one free constant, while neglecting cosmic curvature and mass density, using the modified Friedmann equation implied by subjecting the Higgs scalar field model to conformal Weyl scaling symmetry. It is shown here that the implied dark energy parameter is produced by dressing the bare scalar field by the neutral gauge boson field induced by weak cosmological time dependence of the conformal Higgs model. Predicted persistent cosmic acceleration is consistent with the nonclassical acceleration parameter inferred by conformal theory from observed excessive galactic rotation velocities and dark galactic halos, all without dark matter.

ThePlanckSZ Cluster Catalog: expected X-ray properties

Surveys based on the Sunyaev-Zel'dovich (SZ) effect provide a fresh view of the galaxy cluster population, one that is complementary to X-ray surveys. To better understand the relation between these two kinds of survey, we construct an empirical cluster model using scaling relations constrained by current X-ray and SZ data. We apply our model to predict the X-ray properties of the Planck SZ Cluster Catalog (PCC) and compare them to existing X-ray cluster catalogs. We find that Planck should significantly extend the depth of the previous all-sky cluster survey, performed in the early 1990s by the ROSAT satellite, and should be particularly effective at finding hot, massive clusters (T > 6 keV) out to redshift unity. These are rare objects, and our findings suggest that Planck could increase the observational sample at z > 0.6 by an order of magnitude. This would open the way for detailed studies of massive clusters out to these higher redshifts. Specifically, we find that the majority of newly-detected Planck clusters should have X-ray fluxes 10^{-13} ergs/s/cm^2 < f_X[0.5-2 keV] < 10^{-12} ergs/s/cm^2, i.e., distributed over the decade in flux just below the ROSAT All Sky Survey limit. This is sufficiently bright for extensive X-ray follow-up campaigns. Once Planck finds these objects, XMM-Newton and \textit{Chandra} could measure temperatures to 10% for a sample of ~ 100 clusters in the range 0.5 < z < 1, a valuable increase in the number of massive clusters studied over this range.

Looking at the distant universe with the MeerKAT Array (LADUMA)

AbstractThe MeerKAT (64 x 13.5m dish radio interferometer) is South Africa's precursor instrument for the Square Kilometre Array (SKA), exploring dish design, instrumentation, and the characteristics of a Karoo desert site and is projected to be on sky in 2016. One of two top-priority, Key Projects is a single deep field, integrating for 5000 hours total with the aim to detect neutral atomic hydrogen through its 21 cm line emission out to redshift unity and beyond. This first truly deep HI survey will help constrain fueling models for galaxy assembly and evolution. It will measure the evolution of the cosmic neutral gas density and its distribution over galaxies over cosmic time, explore evolution of the gas in galaxies, measure the Tully-Fisher relation, measure OH maser counts, and address many more topics. Here we present the observing strategy and envisaged science case for this unique deep field, which encompasses the Chandra Deep Field-South (and the footprints of GOODS, GEMS and several other surveys) to produce a singular legacy multi-wavelength data-set.

Galaxy evolution by color-log(n) type since redshift unity in the Hubble Ultra Deep Field

Aims. We explore the use of the color-log(n) (where n is the global Sérsic index) plane as a tool for subdividing the galaxy population in a physically-motivated manner out to redshift unity. We thereby aim to quantify surface brightness evolution by color-log(n) type, accounting separately for the specific selection and measurement biases against each.

Do Newton’sGand Milgrom’sa0vary with cosmological epoch?

In the scalar-tensor gravitational theories Newton's constant ${G}_{N}$ evolves in the expanding universe. Likewise, it has been speculated that the acceleration scale ${\mathfrak{a}}_{0}$ in Milgrom's modified Newtonian dynamics is tied to the scale of the cosmos, and must thus evolve. With the advent of relativistic implementations of the modified dynamics, one can address the issue of variability of the two gravitational ``constants'' with some confidence. Using TeVeS, the tensor-vector-scalar gravitational theory, as an implementation of Milgrom's modified Newtonian dynamics, we calculate the dependence of ${G}_{N}$ and ${\mathfrak{a}}_{0}$ on the TeVeS parameters and the coeval cosmological value of its scalar field, ${\ensuremath{\phi}}_{c}$. We find that ${G}_{N}$, when expressed in atomic units, is strictly nonevolving, a result fully consistent with recent empirical limits on the variation of ${G}_{N}$. By contrast, we find that ${\mathfrak{a}}_{0}$ depends on ${\ensuremath{\phi}}_{c}$ and may thus vary with cosmological epoch. However, for the brand of TeVeS which seems most promising, ${\mathfrak{a}}_{0}$ variation occurs on a time scale much longer than Hubble's, and should be imperceptible back to redshift unity or even beyond it. This is consistent with emergent data on the rotation curves of disk galaxies at significant redshifts.

Non-linear structure formation in cosmologies with early dark energy

We argue that a few per cent of Dark can be detected by the statistics of nonlinear structures. The presence of Dark Energy during linear structure formation is natural in models where the current low Dark-Energy density is related to the age of the Universe rather than a new fundamental small parameter. Generalisation of the spherical collapse model shows that the linear collapse parameter δ c is lowered. The corresponding relative enhancement of weak gravitational lensing on arc-minute scales lowers the value of σ 8 inferred from a given lensing amplitude, as compared to ACDM. In the presence of Early Dark Energy, structures grow slower, such that for a given σ 8 , the number of galaxies and galaxy clusters is substantially increased at moderate and high redshift. For realistic models, the number of clusters detectable through their thermal Sunyaev-Zel'dovich effect at redshift unity and above, e.g. with the Planck satellite, can be an order of magnitude larger than for ACDM.

Testing a New Analytic Model for Gravitational Lensing Probabilities

We study gravitational lensing with a multiple lens plane approach, proposing a simple analytical model for the probability distribution function (PDF) of the dark matter convergence, kappa, for the different lens planes in a given cosmology as a function of redshift and smoothing angle, theta. The model is fixed solely by the variance of kappa, which in turn is fixed by the amplitude of the power spectrum, sigma_8. We test the PDF against a high resolution Tree-Particle-Mesh simulation and find that it is far superior to the Gaussian or the lognormal, especially for small values of theta << 1 arcmin and at large values of kappa relevant to strong lensing. With this model, we predict the probabilities of strong lensing by a single plane or by multiple planes. We find that for theta ~ 10 arcsec, a single plane accounts for almost all (~ 98%) of the strong lensing cases for source redshift unity. However, for a more typical source redshift of 4, about 12% of the strong lensing cases will result from the contribution of a secondary clump of matter along the line of sight, introducing a systematic error in the determination of the surface density of clusters, typically overestimating it by about 2-5%. We also find that matter inhomogenieties introduce a dispersion in the value of the angular diameter distance about its cosmological mean. The probable error relative to the mean increases with redshift to a value of about 8% for z ~ 6 and theta ~ 10 arcsec.

Gravitational Lensing in a Concordance ΛCDM Universe: The Importance of Secondary Matter along the Line of Sight

To date, in almost all strong gravitational lensing analyses for modeling giant arc systems and multiple quasar images, it has been assumed that all the deflecting matter is concentrated in one lens plane at a certain distance—the thin lens approximation. However, in a few observed cases, lenses at more than one redshift have been identified as contributing to the image splitting. Here we report on a quantitative investigation of the importance and frequency of significant multiple lensing agents. We use multilens plane simulations to evaluate how frequently the combination of two or more lens planes is essential for multiple imaging, as compared with the cases for which a single lens plane alone provides enough focusing to be supercritical. We find that the fraction of cases for which more than one lens plane contributes significantly to a multiimage lensing situation is a strong function of source redshift. For sources at redshift unity, 95% of lenses involve only a single mass concentration, but for a more typical scenario with, e.g., a source at a redshift of zs = 3.8, as many as 38% of the strongly lensed quasars/arcs occur because of a significant matter contribution from one or more additional lens planes. In the roughly 30% of cases when additional planes make a significant contribution, the surface mass density of the primary lens will be overestimated by about 10%-15%, if the additional contributions are not recognized.

Cluster Ellipticities as a Cosmological Probe

We investigate the dependence of the ellipticities of clusters of galaxies on cosmological parameters using large-scale cosmological simulations. We determine cluster ellipticities out to redshift unity for λCDM models with different mean densities Ωm and amplitudes of mass fluctuation σ8,0. The mean ellipticity increases monotonically with redshift for all models. Larger values of σ8,0, i.e., earlier cluster formation times, produce lower ellipticities. The dependence of ellipticity on Ωm is relatively weak in the range 0.2 ≤ Ωm ≤ 0.5 for high-mass clusters. The mean ellipticity (z) decreases linearly with the amplitude of mass fluctuations at the cluster redshift z, nearly independent of Ωm; on average, older clusters are more relaxed and are thus less elliptical. The distribution of ellipticities about the mean is approximated by a Gaussian, allowing a simple characterization of the evolution of ellipticity with redshift as a function of cosmological parameters. At z = 0, the mean ellipticity of high-mass clusters is approximated by (z = 0) = 0.245 - 0.070σ8,0 + 0.020Ωm,0. This relation opens up the possibility that, when compared with future observations of large cluster samples, the mean cluster ellipticity and its evolution could be used as a new, independent tool to constrain cosmological parameters, especially the amplitude of mass fluctuations, σ8,0.

SpitzerandISOgalaxy counts in the mid-infrared

Galaxy source counts that simultaneously fit the deep mid-infrared surveys at 24 microns and 15 microns made by the Spitzer Space Telescope and the Infrared Space Observatory (ISO), respectively, are presented for two phenomenological models. The models are based on starburst and luminous infrared galaxy dominated populations. Both models produce excellent fits to the counts in both wavebands and provide an explanation for the high-redshift population seen in the longer Spitzer 24-micron band supporting the hypothesis that they are luminous–ultraluminous infrared galaxies at z= 2–3, being the mid-infrared counterparts to the submillimetre galaxy population. The source counts are characterized by strong evolution to redshift unity, followed by less drastic evolution to higher redshift. The number–redshift distributions in both wavebands are well explained by the effect of the many mid-infrared features passing through the observation windows. The sharp upturn at around a millijansky in the 15-μm counts in particular depends critically on the distribution of mid-infrared features around 12 μm, in the assumed spectral energy distribution.

The connection between star formation and stellar mass: specific star formation rates to redshift one

Abstract We investigate the contribution of star formation to the growth of stellar mass in galaxies over the redshift range 0.5 &amp;lt; ɀ &amp;lt; 1.1 by studying the redshift evolution of the specific star formation rate (SSFR), defined as the star formation rate per unit stellar mass. We use an I-band-selected sample of 6180 field galaxies from the Munich Near-Infrared Cluster Survey (MUNICS) with spectroscopically calibrated photometric redshifts. The SSFR decreases with stellar mass at all redshifts. The low SSFRs of massive galaxies indicate that star formation does not significantly change their stellar mass over this redshift range: the majority of massive galaxies have assembled the bulk of their mass before redshift unity. Furthermore, these highest mass galaxies contain the oldest stellar populations at all redshifts. The line of maximum SSFR runs parallel to lines of constant star formation rate. With increasing redshift, the maximum SFR is generally increasing for all stellar masses, from SFR ≃ 5 M⊙ yr−1 at ɀ≃ 0.5 to SFR ≃ 10 M⊙ yr−1 at ɀ ≃ 1.1. We also show that the large SSFRs of low-mass galaxies cannot be sustained over extended periods of time. Finally, our results do not require a substantial contribution of merging to the growth of stellar mass in massive galaxies over the redshift range probed. We note that highly obscured galaxies which remain undetected in our sample do not affect these findings for the bulk of the field galaxy population.

Stacking clusters in the ROSAT All-Sky Survey

Ongoing and planned wide-area surveys at optical and infrared wavelengths should detect a few times 10^5 galaxy clusters, roughly 10% of which are expected to be at redshifts >~ 0.8. We investigate what can be learned about the X-ray emission of these clusters from the ROSAT All-Sky Survey. While individual clusters at redshifts >~ 0.5 contribute at most a few photons to the survey, a significant measurement of the mean flux of cluster subsamples can be obtained by stacking cluster fields. We show that the mean X-ray luminosity of clusters with mass M >~ 2 x 10^{14} M_sun/h selected from the Sloan Digital Sky Survey should be measurable out to redshift unity with signal-to-noise >~ 10, even if clusters are binned with Delta z=0.1 and Delta ln M ~ 0.3. For such bins, suitably chosen hardness ratio allows the mean temperature of clusters to be determined out to z ~ 0.7 with a relative accuracy of Delta T/T 10^{14} M_sun/h.

The Evolution of X-Ray Clusters of Galaxies

▪ Abstract Considerable progress has been made over the past decade in the study of the evolutionary trends of the population of galaxy clusters in the Universe. In this review we focus on observations in the X-ray band. X-ray surveys with the ROSAT satellite, supplemented by follow-up studies with ASCA and Beppo-SAX, have allowed an assessment of the evolution of the space density of clusters out to z ≈ 1 and the evolution of the physical properties of the intracluster medium out to z ≈ 0.5. With the advent of Chandra and Newton-XMM and their unprecedented sensitivity and angular resolution, these studies have been extended beyond redshift unity and have revealed the complexity of the thermodynamical structure of clusters. The properties of the intracluster gas are significantly affected by nongravitational processes including star formation and Active Galactic Nuclei (AGN) activity. Convincing evidence has emerged for modest evolution of both the bulk of the X-ray cluster population and their thermodynamical properties since redshift unity. Such an observational scenario is consistent with hierarchical models of structure formation in a flat low-density universe with Ωm ≃ 0.3 and σ8 ≃ 0.7–0.8 for the normalization of the power spectrum. Basic methodologies for construction of X-ray–selected cluster samples are reviewed, and implications of cluster evolution for cosmological models are discussed.