Mpc Diameter Research Articles

Easing cosmic tensions with an open and hotter universe

Despite the great observational success of the standard cosmological model some discrepancies in the inferred parameter constraints have manifested among a number of cosmological data sets. These include a tension between the expansion rate of our Cosmos as inferred from the cosmic microwave background (CMB) and as found from local measurements, the preference for an enhanced amplitude of CMB lensing, a somewhat low quadrupole moment of the CMB fluctuations as well as a preference for a lower amplitude of matter fluctuations in large-scale structure surveys than inferred from the CMB. We analyse these observational tensions under the addition of spatial curvature and a free CMB background temperature that may deviate from its locally measured value. With inclusion of these parameters, we observe a trend in the parameter constraints from CMB and baryon acoustic oscillation data towards an open and hotter universe with larger current expansion rate, standard CMB lensing amplitudes, lower amplitude of matter fluctuations, and marginally lower CMB quadrupole moment, consistently reducing the individual tensions among the cosmological data sets. Combining this data with local distance measurements, we find a preference for an open and hotter universe beyond the 99.7% confidence level. Finally, we briefly discuss a local void as a possible source for a deviation of the locally measured CMB temperature from its background value and as mimic of negative spatial curvature for CMB photons. This interpretation implies a $\sim$20% underdensity in our local neighbourhood of $\sim$10-100 Mpc in diameter, which is well within cosmic variance.

Saraswati: An Extremely Massive ∼200 Megaparsec Scale Supercluster

Abstract Here we report the discovery of an extremely massive and large supercluster (called Saraswati5) found in the Stripe 82 region of SDSS. This supercluster is a major concentration of galaxies and galaxy clusters, forming a wall-like structure spanning at least 200 Mpc across at redshift . This enormous structure is surrounded by a network of galaxy filaments, clusters, and large, ∼40–170 Mpc diameter, voids. The mean density contrast δ (relative to the background matter density of the universe) of Saraswati is ≳1.62 and the main body of the supercluster comprises at least 43 massive galaxy clusters (mean z = 0.28) with a total mass of . The spherical collapse model suggests that the central region of radius ∼20 Mpc and mass at least may be collapsing. This places it among the few largest and most massive superclusters known, comparable to the most massive “Shapley Concentration” ( ) in the nearby universe. The Saraswati supercluster and its environs reveal that some extreme large-scale, prominent matter density enhancements formed ∼4 Gyr in the past when dark energy had just started to dominate structure formation. This galactic concentration sheds light on the role of dark energy and cosmological initial conditions in supercluster formation, and tests the competing cosmological models.

The APOSTLE simulations: Rotation curves derived from synthetic 21-cm observations

AbstractThe apostle cosmological hydrodynamical simulation suite is a collection of twelve regions ~5 Mpc in diameter, selected to resemble the Local Group of galaxies in terms of kinematics and environment, and re-simulated at high resolution (minimum gas particle mass of 104 M⊙) using the galaxy formation model and calibration developed for the eagle project. I select a sample of dwarf galaxies (60 < Vmax/km s−1 < 120) from these simulations and construct synthetic spatially- and spectrally-resolved observations of their 21-cm emission. Using the 3Dbarolo tilted-ring modelling tool, I extract rotation curves from the synthetic data cubes. In many cases, non-circular motions present in the gas disc hinder the recovery of a rotation curve which accurately traces the underlying mass distribution; a large central deficit of dark matter, relative to the predictions of cold dark matter N-body simulations, may then be erroneously inferred.

The Local Group: the ultimate deep field

Abstract 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 (∼2 Mpc diameter) imposes insurmountable sample-variance 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 × 109 M⊙. 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.

Lagrangian theory of structure formation in relativistic cosmology. II. Average properties of a generic evolution model

Kinematical and dynamical properties of a generic inhomogeneous cosmological model, spatially averaged with respect to free-falling (generalized fundamental) observers, are investigated for the matter model irrotational dust. Paraphrasing a previous Newtonian investigation, we present a relativistic generalization of a backreaction model based on volume-averaging the Relativistic Zeldovich Approximation. In this model we investigate the effect of kinematical backreaction on the evolution of cosmological parameters as they are defined in an averaged inhomogeneous cosmology, and we show that the backreaction model interpolates between orthogonal symmetry properties by covering subcases of the plane-symmetric solution, the Lemaitre-Tolman-Bondi solution and the Szekeres solution. We so obtain a powerful model that lays the foundations for quantitatively addressing curvature inhomogeneities as they would be interpreted as Dark Energy or Dark Matter in a quasi-Newtonian cosmology. The present model, having a limited architecture due to an assumed FLRW background, is nevertheless capable of replacing 1/4 of the needed amount for Dark Energy on domains of 200 Mpc in diameter for typical (one-sigma) fluctuations in a CDM initial power spectrum. However, the model is far from explaining Dark Energy on larger scales (spatially), where a 6% effect on 400 Mpc domains is identified that can be traced back to an on average negative intrinsic curvature today. One drawback of the quantitative results presented is the fact that the epoch when backreaction is effective on large scales and leads to volume acceleration lies in the future. We discuss this issue in relation to the initial spectrum, the Dark Matter problem, the coincidence problem, and the fact that large-scale Dark Energy is an effect on the past light cone (not spatial), and we pinpoint key elements of future research.

IDCS J1426.5+3508: DISCOVERY OF A MASSIVE, INFRARED-SELECTED GALAXY CLUSTER ATz= 1.75

We report the discovery of an IR-selected massive galaxy cluster in the IRAC Distant Cluster Survey (IDCS). We present new data from the Hubble Space Telescope and the W. M. Keck Observatory that spectroscopically confirm IDCS J1426+3508 at z=1.75. Moreover, the cluster is detected in archival Chandra data as an extended X-ray source, comprising 54 counts after the removal of point sources. We calculate an X-ray luminosity of L{0.5-2 keV} = (5.5 +/- 1.2) X 1e44 ergs/s within r = 60 arcsec (~1 Mpc diameter), which implies M_{200,L_x} = (5.6 +/- 1.6) X 1e14 Msun. IDCS J1426+3508 appears to be an exceptionally massive cluster for its redshift.

SIMULATED VOID GALAXIES IN THE STANDARD COLD DARK MATTER MODEL

We analyze a (120 h−1 Mpc)3 adaptive mesh refinement hydrodynamic simulation that contains a higher resolution 31 × 31 × 35 h−3 Mpc subvolume centered on a ∼30 Mpc diameter void. Our detailed ∼1 kpc resolution allows us to identify 1300 galaxies within this void to a limiting halo mass of ∼1010 M☉. Nearly 1000 galaxies are found to be in underdense regions, with 300 galaxies residing in regions less than half the mean density of the simulation volume. We construct mock observations of the stellar and gas properties of these systems and reproduce the range of colors and luminosities observed in the Sloan Digital Sky Survey for nearby (z < 0.03) galaxies. We find no trends with density for the most luminous (Mr < −18) galaxies, however our dwarf void galaxies (Mr > −16), though they are less reliably resolved, typically appear bluer, with higher rates of star formation and specific star formation and lower mean stellar ages than galaxies in average density environments. We find a significant population of low-luminosity (Mr ∼ −14) dwarf galaxies that is preferentially located in low-density regions and specifically in the void center. This population may help to reduce, but not remove, the discrepancy between the predicted and observed number of void galaxies.

Galaxy environments in the UKIDSS Ultra Deep Survey

We present a study of galaxy environments to z~2, based on a sample of over 33,000 K-band selected galaxies detected in the UKIDSS Ultra Deep Survey (UDS). The combination of infrared depth and area in the UDS allows us to extend previous studies of galaxy environment to z>1 without the strong biases associated with optical galaxy selection. We study the environments of galaxies divided by rest frame (U-B) colours, in addition to `passive' and `star-forming' subsets based on template fitting. We find that galaxy colour is strongly correlated with galaxy overdensity on small scales (<1Mpc diameter), with red/passive galaxies residing in significantly denser environments than blue/star-forming galaxies to z~1.5. On smaller scales (<0.5Mpc diameter) we also find a relationship between galaxy luminosity and environment, with the most luminous blue galaxies at z~1 inhabiting environments comparable to red, passive systems at the same redshift. Monte Carlo simulations demonstrate that these conclusions are robust to the uncertainties introduced by photometric redshift errors.

THE VOID PHENOMENON EXPLAINED

We use high-resolution N-body simulations, combined with a halo occupation model of galaxy bias, to investigate voids in the galaxy distribution. Our goal is to address the phenomenon of Peebles, which presents the observed dearth of faint galaxies in voids as a challenge to current cosmology. In our model, galaxy luminosity is determined only as a function of dark matter halo mass. With this simple assumption, we demonstrate that large, empty voids of ~15 h –1 Mpc in diameter are expected even for galaxies seven magnitudes fainter than L *. The predictions of our model are in excellent agreement with several statistical measures: (i) the luminosity function of galaxies in underdense regions, (ii) nearest-neighbor statistics of dwarf galaxies, and (iii) the void probability function of faint galaxies. In the transition between filaments and voids in the dark matter, the halo mass function changes abruptly, causing the maximum galaxy luminosity to decrease by ~5 magnitudes over a range of ~ 1 h –1 Mpc. Thus, the boundary between filaments and voids in the galaxy distribution is nearly as sharp for dwarfs as for ~L * objects. These results support a picture in which galaxy formation is driven predominantly by the mass of the host dark matter halo, and is nearly independent of the larger-scale halo environment. Further, they demonstrate that ΛCDM, combined with a straightforward bias model, naturally predicts the existence of the void phenomenon.

An Increase in the Faint Red Galaxy Population in Massive Clusters sincez∼ 0.5

We compare the luminosity functions for red galaxies lying on the restframe (U-V) color-magnitude sequence in a homogeneous sample of ten X-ray luminous clusters from the MACS survey at z~0.5 to a similarly selected X-ray cluster sample at z~0.1. We exploit deep Hubble Space Telescope ACS imaging in the F555W and F814W passbands of the central 1.2Mpc diameter regions of the distant clusters to measure precise colors for the galaxies in these regions and statistically correct for contamination by field galaxies using observations of blank fields. We apply an identical analysis to ground-based photometry of the z~0.1 sample. This comparison demonstrates that the number of faint, Mv~ -19, red galaxies relative to the bright population seen in the central regions of massive clusters has roughly doubled over the 4 Gyrs between z~0.5 and z~0.1. We quantify this difference by measuring the dwarf to giant ratio on the red sequence which increases by a factor of at least 2.2+/- 0.4 since z~0.5. This is consistent with the idea that many faint, blue star-forming galaxies in high density environments are transforming onto the red sequence in the last half of the Hubble time.

A View of the M81 Galaxy Group via the Hα Window

We present images for 36 galaxies of the M81 Group obtained in the Hα line. Estimates of the Hα flux and star formation rate (SFR) are now available for all the known members of the group with absolute magnitudes down to MB = -10 mag. The character of distribution of the galaxies over three parameters, MB, SFR, and total hydrogen mass, permits us to draw the following conclusions as to the evolutionary status of the group population: (1) Spiral and irregular-type galaxies have time to generate their luminosity (baryon mass) during the cosmological time T0 = 13.7 Gyr, but dwarf spheroidal objects are capable of reproducing only ~5% of their observed luminosity. (2) S and Im/blue compact dwarf (BCD) galaxies possess a supply of gas sufficient to maintain their observed SFRs only during the next T0 yr, while dIrr and dSph populations have a mean gas depletion time of about 3T0. (3) There is indirect evidence that the star formation in Im/BCD and dIrr galaxies proceeds in a mode of vigorous burst activity rather than in the form of a sluggish process. We note that the dwarf tidal system near NGC 3077, the Garland, has the highest SFR per unit luminosity among 150 galaxies of the Local Volume with known SFRs. Being averaged over the local cell of homogeneity of 4 Mpc in diameter around M81, the rate of star formation of the group, SFR = 0.165 M⊙ yr-1 Mpc-3, proves to be 5-8 times higher than the average global rate at z = 0.

Distribution and evolution of high-z galaxies in the Subaru/XMM-Newton Deep Survey Field (SXDF)

AbstractWe present results from our on-going study of the distribution and evolution of high-z galaxies. We exploited the large area coverage (~1.3 deg2) of the Subaru / XMM-Newton Deep Survey field (SXDF) to search for Lyman-break galaxies (LBGs) and Lyα Emitters (LAEs) at 3 &lt;z&lt; 7. We have found filamentary large scale structures, which are made of LAEs, with ~10 to 40 Mpc (in commoving units) scale voids as early as at z = 5.7. Galaxies at this redshift show clustering of ~1 Mpc in diameter (in physical unit). The inferred star formation rate density of these clustering is ~130 times the mean of the whole area, indicates burst of star formation activities. Combined with the UKIDSS/UDS photometry, the optical+near-IR SED fitting provides the estimate of masses for some of these high-z galaxies. Preliminary results indicate a number of galaxies at z &gt;5 have already grown up to ~1011 solar mass.

A Wide‐FieldHubble Space TelescopeSurvey of the Cluster Cl 0024+16 atz= 0.4. III. Spectroscopic Signatures of Environmental Evolution in Early‐Type Galaxies

We report results from a panoramic spectroscopic survey of 955 objects in the field of the rich cluster Cl 0024+1654 (z~0.4), complementing the HST imaging presented in the first paper in this series. Our new spectroscopic sample includes over 200 high quality spectra of cluster members, spread across an area 10 Mpc in diameter. We examine the properties of a large sample of 104 cluster early-types as a function of cluster radius and local density, using them as sensitive tracers of the various physical processes that may be responsible for galaxy evolution. By constructing the Fundamental Plane of Cl 0024, we infer an evolution in the mean mass to light ratio of early-types equal to \Delta = -0.14 +- 0.02. In the cluster center, we detect a significantly increased scatter in the relationship compared to that seen in local clusters. Moreover, we observe a clear radial trend in the mass to light ratios of individual early types, with the oldest galaxies located in the cluster core. Galaxies are apparently younger at larger radius, with E+S0s in the periphery having M/L_V ratios that nearly match values seen in the field at a similar redshift. Independent spectral indicators used in combination reveal an abrupt interaction with the cluster environment which occurs near the virial radius of Cl 0024, revealed by small bursts of star formation in a population of dim early-types, as well as by enhanced Balmer absorption for a set of larger E+S0s closer to the cluster core. We construct a simple infall model used to compare the timescales and strengths of the observed interactions in this cluster. We examine the possibility that bursts of star formation are triggered when galaxies suffer shocks as they encounter the intra-cluster medium, or by the onset of galaxy harassment.

The NGC 5846 Group: Dynamics and the Luminosity Function toMR = -12

We conduct a photometric and spectroscopic survey of a 10 deg2 region surrounding the nearby NGC 5846 group of galaxies, using the Canada-France-Hawaii and Keck I telescopes to study the population of dwarf galaxies as faint as MR = -10. Candidates are identified on the basis of quantitative surface brightness and qualitative morphological criteria. Spectroscopic follow up and a spatial correlation analysis provide the basis for affirming group memberships. Altogether, 324 candidates are identified, and 83 have spectroscopic membership confirmation. We argue on statistical grounds that a total of 251 ? 10 galaxies in our sample are group members. The observations, together with archival Sloan Digital Sky Survey, ROSAT, XMM-Newton, and ASCA data, suggest that the giant ellipticals NGC 5846 and NGC 5813 are the dominant components of subgroups separated by 600?kpc in projection and embedded in a 1.6?Mpc diameter dynamically evolved halo. The galaxy population is overwhelmingly early type. The group velocity dispersion is 322?km s-1, its virial mass is 8.4 ? 1013 M?, and M/LR = 320 M? L. The ratio of dwarfs to giants is large compared with other environments in the Local Supercluster studied, and, correspondingly, the luminosity function is relatively steep, with a faint-end Schechter function slope of ?d = -1.3 ? 0.1 (statistical) ?0.1 (systematic) at our completeness limit of MR = -12.

The Discovery of Primeval Large-Scale Structures with Forming Clusters at Redshift 6

We report the discovery of primeval large-scale structures (LSSs) including two protoclusters in a forming phase at z = 5.7. We carried out extensive deep narrowband imaging in the 1 deg2 sky of the Subaru/XMM-Newton Deep Field and obtained a cosmic map of 515 Lyα emitters (LAEs) in a volume with a transverse dimension of 180 Mpc × 180 Mpc and a depth of ~40 Mpc in comoving units. This cosmic map shows filamentary LSSs, including clusters and surrounding 10-40 Mpc scale voids, similar to the present-day LSSs. Our spectroscopic follow-up observations identify overdense regions in which two dense clumps of LAEs with a sphere of 1 Mpc diameter in physical units are included. These clumps show about 130 times higher star formation rate density, mainly due to a large overdensity, ~80, of LAEs. These clumps would be clusters in a formation phase involving a burst of galaxy formation.

Cosmological black holes as seeds of voids in the galaxy distribution

Deep surveys indicate a bubbly structure on cosmological large scales which should be the result of evolution of primordial density perturbations. Several models have been proposed to explain the origin and dynamics of such features but, till now, no exhaustive and fully consistent theory has been found. We discuss a model where cosmological black holes, deriving from primordial perturbations, are the seeds for large-scale-structure voids. We give details of the dynamics and accretion of the system voids-cosmological black holes from the epoch z � 10 3 till now, finding that a void of 40 h −1 Mpc diameter and under-density of −0.9 fits the observations without conflicting with the homogeneity and isotropy of the cosmic microwave background radiation.

Two world systems revisited: a comparison of plasma cosmology and the big bang

Despite its great popularity, the Big Bang framework for cosmology faces growing contradictions with observation. The Big Bang theory requires three hypothetical entities-the inflation field, nonbaryonic (dark) matter, and the dark energy field-to overcome gross contradictions of theory and observation. Yet, no evidence has ever confirmed the existence of any of these three hypothetical entities. The predictions of the theory for the abundance of /sup 4/He, /sup 7/Li, and D are more than 7/spl sigma/ from the data for any assumed density of baryons and the probability of the theory fitting the data is less than 10/sup -14/. Observations of voids in the distribution of galaxies that are in excess of 100 Mpc in diameter, combined with observed low streaming velocities of galaxies, imply an age for these structure that is at least triple and more likely six times the hypothesized time since the Big Bang. Big Bang predictions for the anisotropy of the microwave background, which now involve seven or more free parameters, still are excluded by the data at the 2/spl sigma/ level. The observed preferred direction in the background anisotropy completely contradicts Big Bang assumptions. In contrast, the predictions of plasma cosmology have been strengthened by new observations, including evidence for the stellar origin of the light elements, the plasma origin of large-scale structures, and the origin of the cosmic microwave background in a radio fog of dense plasma filaments. This review of the evidence shows that the time has come, and indeed has long since come, to abandon the Big Bang as the primary model of cosmology.

The structure of voids

Using high-resolution N-body simulations, we address the problem of the emptiness of giant ∼20 h−1 Mpc diameter voids found in the distribution of bright galaxies. Are the voids filled by dwarf galaxies? Do cosmological models predict too many small dark matter haloes inside the voids? Can the problems of cosmological models on small scales be addressed by studying the abundance of dwarf galaxies inside voids? We find that voids in the distribution of 1012h−1 M⊙ haloes (expected galactic magnitudes ∼M*) are almost the same as the voids in 1011h−1 M⊙ haloes. Yet, much smaller haloes with masses 109h−1 M⊙ and circular velocities vcirc∼ 20 km s−1 readily fill the voids: there should be almost 1000 of these haloes in a 20 h−1 Mpc diameter void. A typical void of diameter 20 h−1 Mpc contains about 50 haloes with vcirc > 50 km s−1. The haloes are arranged in a pattern, which looks like a miniature universe: it has the same structural elements as the large-scale structure of the galactic distribution of the Universe. There are filaments and voids; larger haloes are at the intersections of filaments. The only difference is that all masses are four orders of magnitude smaller. There is severe (anti)bias in the distribution of haloes, which depends on halo mass and on the distance from the centre of the void. Large haloes are more antibiased and have a tendency to form close to void boundaries. The mass function of haloes in voids is different from the ‘normal’ mass function. It is much steeper for high masses, resulting in very few M33-type galaxies (vcirc≈ 100 km s−1). We present an analytical approximation for the mass function of haloes in voids.

Gamma Rays from Intergalactic Shocks

Structure formation in the intergalactic medium (IGM) produces large-scale, collisionless shock waves, where electrons can accelerate to highly relativistic energies. Such electrons can Compton scatter cosmic microwave background photons up to gamma-ray energies. We study the radiation emitted in this process using a hydrodynamic cosmological simulation of a LCDM universe. This radiation, extending beyond TeV energies, has roughly constant energy flux per decade in photon energy, in agreement with the predictions of Loeb & Waxman (2000). Assuming that a fraction xi_e=0.05 of the shock thermal energy is transferred to relativistic electrons, as inferred from collisionless non-relativistic shocks in the interstellar medium, we find that the radiation energy flux, e^2(dJ/de)~ 50-160 eV cm^-2 s^-1 sr^-1, constitutes ~10% of the extragalactic gamma-ray background. The associated point-sources are too faint to account for the ~60 unidentified EGRET gamma-ray sources, but GLAST should resolve several sources associated with large-scale IGM structures for xi_e~0.03, and many more sources for larger xi_e. The intergalactic origin of the radiation can be verified through a cross-correlation with, e.g., the galaxy distribution that traces the same structure. Its shock-origin may be tested by a cross-correlation with radio synchrotron radiation, emitted as the same electrons gyrate in post-shock magnetic fields. We predict that GLAST and Cherenkov telescopes such as MAGIC, VERITAS and HESS should resolve gamma-rays from nearby (redshifts z < 0.01) rich galaxy clusters, perhaps in the form of a \~5-10 Mpc diameter ring-like emission tracing the cluster accretion shock, with luminous peaks at its intersections with galaxy filaments detectable even at z~0.025.

Evidence for shock acceleration and intergalactic magnetic fields in a large-scale filament of galaxies ZwCl 2341.1+0000

We report the discovery of large-scale diffuse radio emission from what appears to be a large-scale filamentary network of galaxies in the region of cluster ZwCl 2341.1+0000, and stretching over an area of at least 6 h 50 −1 Mpc in diameter. Multicolour CCD observations yield photometric redshifts indicating that a significant fraction of the optical galaxies in this region is at a redshift of z=0.3. This is supported by spectroscopic measurements of 4 galaxies in the Sloan Digitized Sky Survey (SDSS) survey at a mean z=0.27. We present VLA images at λ=20 cm (NVSS) and 90 cm, showing the detailed radio structure of the filaments. Comparison with the high resolution FIRST radio survey shows that the diffuse emission is not due to known individual point sources. The diffuse radio-emission has a spectral index α≲−0.5, and is most likely synchrotron emission from relativistic charged particles in an inter-galactic magnetic field. Furthermore, this optical/radio structure is detected in X-rays by the ROSAT all-sky survey. It has a 0.1–2.4 keV luminosity of about 10 44 erg s −1 and shows an extended highly non-relaxed morphology. These observations suggest that ZwCl 2341.1+0000 is possibly a proto-cluster of galaxies in which we are witnessing the process of structure formation. We show that the energetics of accretion shocks generated in forming large-scale structures are sufficient to produce enough high energy cosmic-ray (CR) electrons required to explain the observed radio emission, provided a magnetic field of strength B≳0.3 μG is present there. The latter is only a lower limit and the actual magnetic field is likely to be higher depending on the morphology of the emitting region. Finally, we show results from a numerical simulation of large-scale structure formation including acceleration of CR electrons at cosmological shocks and magnetic field evolution. Our results are in accord with the observed radio synchrotron and X-ray thermal bremsstrahlung fluxes. Thus we conclude that the reported radio detection is the first evidence of cosmic-ray particle acceleration taking place at cosmic shocks in a magnetized inter-galactic medium over scales of ≳5 h 50 −1 Mpc.