Search

MACS J0717 is the most massive and extended of the Hubble Frontier Field clusters. It is one of the more difficult clusters to model, and we argue that this is, in part, due to the line-of-sight structure (LoS) at redshifts beyond 2. We show that the grale mass reconstruction based on sources at 3 < $$z$$ s < 4.1 has at least 1013 M⊙ more mass than that based on nearby sources, $$z$$ s < 2.6, and attribute the excess mass to a putative LoS, which is at least 75 arcsec from the cluster centre. Furthermore, the lens-model fitted $$z$$ s 's of the recent Kawamata et al. reconstruction are biased systematically low compared to photometric $$z$$ s 's, and the bias is a function of images' distance from the cluster centre. We argue that these mimic the effect of LoS. We conclude that even in the presence of 100–200 images, lens-model adjusted source redshifts can conceal the presence of LoS, demonstrating the existence of degeneracies between $$z$$ s and (sub)structure. Also, a very good fit to image positions is not a sufficient condition for having a high-fidelity mass map: Kawamata et al. obtain an rms of 0.52 arcsec for 173 images of 60 sources; our Grale reconstruction of the exact same data yields a somewhat different map, but similarly low rms, 0.62 arcsec. In contrast, a grale model that uses reasonable, but fixed $$z$$ s gives a worse rms of 1.28 arcsec for 44 sources with 126 images. Unaccounted for LoS can bias the mass map, affecting the magnification and luminosity function estimates of high redshift sources. [ABSTRACT FROM AUTHOR]

We measure the evolution of sizes for star-forming galaxies as seen in 1.4 GHz continuum radio for z  = 0–3. The measurements are based on combined VLA+MERLIN data of the Hubble Deep Field, and using a uv -stacking algorithm combined with model fitting to estimate the average sizes of galaxies. A sample of ∼1000 star-forming galaxies is selected from optical and near-infrared catalogues, with stellar masses M⊙ ≈ 1010–1011 M⊙ and photometric redshifts 0–3. The median sizes are parametrized for stellar mass M * = 5 × 1010 M⊙ as |$R_{\rm e} = A\times {}(H(z)/H(1.5))^{\alpha _z}$|⁠. We find that the median radio sizes evolve towards larger sizes at later times with α z  = −1.1 ± 0.6, and A (the median size at z ≈ 1.5) is found to be |$0. \!\!^{\prime\prime} 26\pm {}0. \!\!^{\prime\prime} 07$| or 2.3±0.6 kpc. The measured radio sizes are typically a factor of 2 smaller than those measure in the optical, and are also smaller than the typical H α sizes in the literature. This indicates that star formation, as traced by the radio continuum, is typically concentrated towards the centre of galaxies, for the sampled redshift range. Furthermore, the discrepancy of measured sizes from different tracers of star formation, indicates the need for models of size evolution to adopt a multiwavelength approach in the measurement of the sizes star-forming regions. [ABSTRACT FROM AUTHOR]

We perform spatially resolved, pixel-by-pixel Spectral Energy Distribution (SED) fitting on galaxies up to z ~ 2.5 in the Hubble eXtreme Deep Field (XDF). Comparing stellar mass estimates from spatially resolved and spatially unresolved photometry we find that unresolved masses can be systematically underestimated by factors of up to 5. The ratio of the unresolved to resolved mass measurement depends on the galaxy's specific star formation rate (sSFR): at low sSFRs the bias is small, but above sSFR ~ 10-9.5 yr-1 the discrepancy increases rapidly such that galaxies with sSFRs ~ 10-8 yr-1 have unresolved mass estimates of only one-half to one-fifth of the resolved value. This result indicates that stellar masses estimated from spatially unresolved data sets need to be systematically corrected, in some cases by large amounts, and we provide an analytic prescription for applying this correction. We show that correcting stellar mass measurements for this bias changes the normalization and slope of the star-forming main sequence and reduces its intrinsic width; most dramatically, correcting for the mass bias increases the stellar mass density of the Universe at high redshift and can resolve the long-standing discrepancy between the directly measured cosmic SFR density at z ≳ 1 and that inferred from stellar mass densities ('the missing mass problem'). [ABSTRACT FROM AUTHOR]

The conditions for the formation of close-binary black-hole systems merging over the Hubble time due to gravitational-wave radiation are considered in the framework of current ideas about the evolution of massive close-binary systems. The original systems whose mergers were detected by LIGO consisted of main-sequence stars with masses of 30-100 M . The preservation of the compactness of a binary black hole during the evolution of its components requires either the formation of a common envelope, probably also with a low initial abundance of metals, or the presence of a 'kick'-a velocity obtained during a supernova explosion accompanied by the formation of a black hole. In principle, such a kick can explain the relatively low frequency of mergers of the components of close-binary stellar black holes, if the characteristic speed of the kick exceeds the orbital velocities of the system components during the supernova explosion. Another opportunity for the components of close-binary systems to approach each other is related to their possible motion in a dense molecular cloud. [ABSTRACT FROM AUTHOR]

We report the identification of extended Lyα nebulae at z ≃ 3.3 in the Hubble Ultra Deep Field (HUDF, ≃40 kpc x 80 kpc) and behind the Hubble Frontier Field galaxy cluster MACSJ0416 (≃40 kpc), spatially associated with groups of star-forming galaxies. VLT/MUSE integral field spectroscopy reveals a complex structure with a spatially varying double-peaked Lyα emission. Overall, the spectral profiles of the two Lyα nebulae are remarkably similar, both showing a prominent blue emission, more intense and slightly broader than the red peak. From the first nebula, located in the HUDF, no X-ray emission has been detected, disfavouring the possible presence of active galactic nuclei. Spectroscopic redshifts have been derived for 11 galaxies within 2 arcsec from the nebula and spanning the redshift range 1.037 < z < 5.97. The second nebula, behind MACSJ0416, shows three aligned star-forming galaxies plausibly associated with the emitting gas. In both systems, the associated galaxies reveal possible intense rest-frame-optical nebular emissions lines [O iii] λλ4959, 5007+Hβ with equivalent widths as high as 1500 Å rest frame and star formation rates ranging from a few to tens of solar masses per year. A possible scenario is that of a group of young, star-forming galaxies emitting ionizing radiation that induces Lyα fluorescence, therefore revealing the kinematics of the surrounding gas. Also Lyα powered by star formation and/or cooling radiation may resemble the double-peaked spectral properties and the morphology observed here. If the intense blue emission is associated with inflowing gas, then we may be witnessing an early phase of galaxy or a proto-cluster (or group) formation. [ABSTRACT FROM AUTHOR]

We observed Hubble Deep Field South with the new panoramic integral-field spectrograph MUSE that we built and have just commissioned at the VLT. The data cube resulting from 27 h of integration covers one arcmin2 field of view at an unprecedented depth with a 1σ emission-line surface brightness limit of 1 × 10-19 erg s-1 cm-2 arcsec-2, and contains ~90?000 spectra. We present the combined and calibrated data cube, and we performed a first-pass analysis of the sources detected in the Hubble Deep Field South imaging. We measured the redshifts of 189 sources up to a magnitude I814?=?29.5, increasing the number of known spectroscopic redshifts in this field by more than an order of magnitude. We also discovered 26 Lyα emitting galaxies that are not detected in the HST WFPC2 deep broad-band images. The intermediate spectral resolution of 2.3 Å allows us to separate resolved asymmetric Lyα emitters, [O?ii]3727 emitters, and C?iii]1908 emitters, and the broad instantaneous wavelength range of 4500 Å helps to identify single emission lines, such as [O?iii]5007, Hβ, and Hα, over a very wide redshift range. We also show how the three-dimensional information of MUSE helps to resolve sources that are confused at ground-based image quality. Overall, secure identifications are provided for 83% of the 227 emission line sources detected in the MUSE data cube and for 32% of the 586 sources identified in the HST catalogue. The overall redshift distribution is fairly flat to z = 6.3, with a reduction between z = 1.5 to 2.9, in the well-known redshift desert. The field of view of MUSE also allowed us to detect 17 groups within the field. We checked that the number counts of [O?ii]3727 and Lyα emitters are roughly consistent with predictions from the literature. Using two examples, we demonstrate that MUSE is able to provide exquisite spatially resolved spectroscopic information on the intermediate-redshift galaxies present in the field. This unique data set can be used for a wide range of follow-up studies. We release the data cube, the associated products, and the source catalogue with redshifts, spectra, and emission-line fluxes. [ABSTRACT FROM AUTHOR]

We present direct constraints on the CO luminosity function at high redshift and the resulting cosmic evolution of the molecular gas density, (z), based on a blind molecular line scan in the Hubble Deep Field North (HDF-N) using the IRAM Plateau de Bure Interferometer. Our line scan of the entire 3 mm window (79-115 GHz) covers a cosmic volume of ∼7000 Mpc3, and redshift ranges z < 0.45, 1.01 < z < 1.89 and z > 2. We use the rich multiwavelength and spectroscopic database of the HDF-N to derive some of the best constraints on CO luminosities in high redshift galaxies to date. We combine the blind CO detections in our molecular line scan (presented in a companion paper) with stacked CO limits from galaxies with available spectroscopic redshifts (slit or mask spectroscopy from Keck and grism spectroscopy from the Hubble Space Telescope) to give first blind constraints on high-z CO luminosity functions and the cosmic evolution of the H2 mass density (z) out to redshifts z ∼ 3. A comparison to empirical predictions of (z) shows that the securely detected sources in our molecular line scan already provide significant contributions to the predicted (z) in the redshift bins 〈 z〉 ∼ 1.5 and 〈 z〉 ∼ 2.7. Accounting for galaxies with CO luminosities that are not probed by our observations results in cosmic molecular gas densities (z) that are higher than current predictions. We note, however, that the current uncertainties (in particular the luminosity limits, number of detections, as well as cosmic volume probed) are significant, a situation that is about to change with the emerging ALMA observatory. [ABSTRACT FROM AUTHOR]

We present a molecular line scan in the Hubble Deep Field North (HDF-N) that covers the entire 3 mm window (79-115 GHz) using the IRAM Plateau de Bure Interferometer. Our CO redshift coverage spans z ≲ 0.45, 1 ≲ z ≲ 1.9 and all z ≳ 2. We reach a CO detection limit that is deep enough to detect essentially all z > 1 CO lines reported in the literature so far. We have developed and applied different line-searching algorithms, resulting in the discovery of 17 line candidates. We estimate that the rate of false positive line detections is ∼2/17. We identify optical/NIR counterparts from the deep ancillary database of the HDF-N for seven of these candidates and investigate their available spectral energy distributions. Two secure CO detections in our scan are identified with star-forming galaxies at z = 1.784 and at z = 2.047. These galaxies have colors consistent with the “BzK” color selection and they show relatively bright CO emission compared with galaxies of similar dust continuum luminosity. We also detect two spectral lines in the submillimeter galaxy HDF 850.1 at z = 5.183. We consider an additional nine line candidates as high quality. Our observations also provide a deep 3 mm continuum map (1σ noise level = 8.6 μJy beam–1). Via a stacking approach, we find that optical/MIR bright galaxies contribute only to <50% of the star formation rate density at 1 < z < 3, unless high dust temperatures are invoked. The present study represents a first, fundamental step toward an unbiased census of molecular gas in “normal” galaxies at high-z, a crucial goal of extragalactic astronomy in the ALMA era. [ABSTRACT FROM AUTHOR]

The Spitzer Extended Deep Survey (SEDS) is a very deep infrared survey within five well-known extragalactic science fields: the UKIDSS Ultra-Deep Survey, the Extended Chandra Deep Field South, COSMOS, the Hubble Deep Field North, and the Extended Groth Strip. SEDS covers a total area of 1.46 deg2 to a depth of 26 AB mag (3σ) in both of the warm Infrared Array Camera (IRAC) bands at 3.6 and 4.5μm. Because of its uniform depth of coverage in so many widely-separated fields, SEDS is subject to roughly 25% smaller errors due to cosmic variance than a single-field survey of the same size. SEDS was designed to detect and characterize galaxies from intermediate to high redshifts (z = 2–7) with a built-in means of assessing the impact of cosmic variance on the individual fields. Because the full SEDS depth was accumulated in at least three separate visits to each field, typically with six-month intervals between visits, SEDS also furnishes an opportunity to assess the infrared variability of faint objects. This paper describes the SEDS survey design, processing, and publicly-available data products. Deep IRAC counts for the more than 300,000 galaxies detected by SEDS are consistent with models based on known galaxy populations. Discrete IRAC sources contribute 5.6 ± 1.0 and 4.4 ± 0.8 nW m−2 sr−1 at 3.6 and 4.5μm to the diffuse cosmic infrared background (CIB). IRAC sources cannot contribute more than half of the total CIB flux estimated from DIRBE data. Barring an unexpected error in the DIRBE flux estimates, half the CIB flux must therefore come from a diffuse component. [ABSTRACT FROM AUTHOR]

We demonstrate estimating the total infrared luminosity, L(TIR), and star formation rates (SFRs) of star-forming galaxies at redshift 0 < z < 2.8 from single-band 24σm observations, using local spectral energy distribution (SED) templates without introducing additional free parameters. Our method is based on characterizing the SEDs of galaxies as a function of their L(TIR) surface density, which is motivated by the indications that the majority of IR luminous star-forming galaxies at 1 < z < 3 have extended star-forming regions, in contrast to the strongly nuclear concentrated, merger-induced starbursts in local luminous and ultraluminous IR galaxies. We validate our procedure for estimating L(TIR) by comparing the resulting L(TIR) with those measured from far-IR observations, such as those from Herschel in the Extended Chandra Deep Field South (ECDFS) and Hubble Deep Field North (HDFN), as well as L(TIR) measured from stacked far-IR observations at redshift 0 < z < 2.8. Active galactic nuclei were excluded using X-ray and 3.6-8.0σm observations, which are generally available in deep cosmological survey fields. The Gaussian fits to the distribution of the discrepancies between the L(TIR) measurements from single-band 24σm and Herschel observations in the ECDFS and HDFN samples have σ < 0.1 dex, with ~10% of objects disagreeing by more than 0.2 dex. Since the 24σm estimates are based on SEDs for extended galaxies, this agreement suggests that ~90% of IR galaxies at high z are indeed much more physically extended than local counterparts of similar L(TIR), consistent with recent independent studies of the fractions of galaxies forming stars in the main-sequence and starburst modes, respectively. Because we have not introduced empirical corrections to enhance these estimates, in principle, our method should be applicable to lower luminosity galaxies. This will enable use of the 21σm band of the Mid-Infrared Instrument on board the James Webb Space Telescope to provide an extremely sensitive tracer of obscured SFR in individual star-forming galaxies across the peak of the cosmic star formation history. [ABSTRACT FROM AUTHOR]

The Hubble Deep Field provides one of the deepest multiwavelength views of the distant Universe and has led to the detection of thousands of galaxies seen throughout cosmic time. An early map of the Hubble Deep Field at a wavelength of 850?micrometres, which is sensitive to dust emission powered by star formation, revealed the brightest source in the field, dubbed HDF?850.1 (ref. 2). For more than a decade, and despite significant efforts, no counterpart was found at shorter wavelengths, and it was not possible to determine its redshift, size or mass. Here we report a redshift of z = 5.183 for HDF?850.1, from a millimetre-wave molecular line scan. This places HDF?850.1 in a galaxy overdensity at z???5.2, corresponding to a cosmic age of only 1.1?billion years after the Big Bang. This redshift is significantly higher than earlier estimates and higher than those of most of the hundreds of submillimetre-bright galaxies identified so far. The source has a star-formation rate of 850 solar masses per year and is spatially resolved on scales of 5 kiloparsecs, with an implied dynamical mass of about 1.3?×?1011 solar masses, a significant fraction of which is present in the form of molecular gas. Despite our accurate determination of redshift and position, a counterpart emitting starlight remains elusive. [ABSTRACT FROM AUTHOR]

ABSTRACT We present new Giant Metre-wave Radio Telescope (GMRT) observations of Hubble Deep Field (HDF) 130, an inverse-Compton (IC) ghost of a giant radio source that is no longer being powered by jets. We compare the properties of HDF 130 with the new and important constraint of the upper limit of the radio flux density at 240 MHz to an analytic model. We learn what values of physical parameters in the model for the dynamics and evolution of the radio luminosity and X-ray luminosity [due to IC scattering of the cosmic microwave background (CMB)] of a Fanaroff-Riley type II (FR II) source are able to describe a source with features (lobe length, axial ratio, X-ray luminosity, photon index and upper limit of radio luminosity) similar to those of the observations. HDF 130 is found to agree with the interpretation that it is an IC ghost of a powerful double-lobed radio source, and we are observing it at least a few Myr after jet activity (which lasted 5-100 Myr) has ceased. The minimum Lorentz factor of injected particles into the lobes from the hotspot is preferred to be γ∼ 103 for the model to describe the observed quantities well, assuming that the magnetic energy density, electron energy density and lobe pressure at time of injection into the lobe are linked by constant factors according to a minimum energy argument, so that the minimum Lorentz factor is constrained by the lobe pressure. We also apply the model to match the features of 6C 0905+3955, a classical double FR II galaxy thought to have a low-energy cut-off of γ∼ 104 in the hotspot due to a lack of hotspot IC X-ray emission. The models suggest that the low-energy cut-off in the hotspots of 6C 0905+3955 is γ≳ 103, just slightly above the particles required for X-ray emission. [ABSTRACT FROM AUTHOR]

We present a search for galaxies at using the latest Hubble Space Telescope/Wide Field Camera 3 (WFC3) near-infrared data, based on the Lyman-break technique. We search for galaxies which have large colours (the '-drops') on account of the Lyman α forest absorption, and with colours inconsistent with being low-redshift contaminants. We identify 24 candidates at redshift (15 are robust and a further nine more marginal but consistent with being high redshift) over an area of arcmin. Previous searches for -drops with WFC3 have focused only on the Hubble Ultra Deep Field, and our larger survey (involving two other nearby deep fields and a wider area survey) has trebled the number of robust -drop candidates. For the first time, we have sufficient galaxies to fit both and of the UV Schechter luminosity function. There is evidence for evolution in this luminosity function from to , in the sense that there are fewer UV-bright galaxies at , consistent with an evolution mainly in . The candidate galaxies we detect have insufficient ionizing flux to reionize the Universe, and it is probable that galaxies below our detection limit provide a significant UV contribution. The faint-end slope, α, is not well constrained. However, adopting a similar faint-end slope to that determined at () and a Salpeter initial mass function (IMF), then the ionizing photon budget still falls short if , even integrating down to . A steeper faint-end slope or a low-metallicity population (or a top-heavy IMF) might still provide sufficient photons for star-forming galaxies to reionize the Universe, but confirmation of this might have to await the James Webb Space Telescope. [ABSTRACT FROM AUTHOR]

Searches for very-high-redshift galaxies over the past decade have yielded a large sample of more than 6,000 galaxies existing just 900-2,000 million years (Myr) after the Big Bang (redshifts 6 > z > 3; ref. 1). The Hubble Ultra Deep Field (HUDF09) data have yielded the first reliable detections of z ≈ 8 galaxies that, together with reports of a γ-ray burst at z ≈ 8.2 (refs 10, 11), constitute the earliest objects reliably reported to date. Observations of z ≈ 7-8 galaxies suggest substantial star formation at z > 9-10 (refs 12, 13). Here we use the full two-year HUDF09 data to conduct an ultra-deep search for z ≈ 10 galaxies in the heart of the reionization epoch, only 500 Myr after the Big Bang. Not only do we find one possible z ≈ 10 galaxy candidate, but we show that, regardless of source detections, the star formation rate density is much smaller (∼10%) at this time than it is just ∼200 Myr later at z ≈ 8. This demonstrates how rapid galaxy build-up was at z ≈ 10, as galaxies increased in both luminosity density and volume density from z ≈ 10 to z ≈ 8. The 100-200 Myr before z ≈ 10 is clearly a crucial phase in the assembly of the earliest galaxies. [ABSTRACT FROM AUTHOR]

We revise and extend the extreme value statistic, introduced in Gupta et al., to study direction dependence in the high-redshift supernova data, arising either from departures, from the cosmological principle or due to direction-dependent statistical systematics in the data. We introduce a likelihood function that analytically marginalizes over the Hubble constant and use it to extend our previous statistic. We also introduce a new statistic that is sensitive to direction dependence arising from living off-centre inside a large void as well as from previously mentioned reasons for anisotropy. We show that for large data sets, this statistic has a limiting form that can be computed analytically. We apply our statistics to the gold data sets from Riess et al., as in our previous work. Our revision and extension of the previous statistic show that the effect of marginalizing over the Hubble constant instead of using its best-fitting value on our results is only marginal. However, correction of errors in our previous work reduces the level of non-Gaussianity in the 2004 gold data that were found in our earlier work. The revised results for the 2007 gold data show that the data are consistent with isotropy and Gaussianity. Our second statistic confirms these results. [ABSTRACT FROM AUTHOR]

We consider the effects of large structures in the Universe on the Hubble diagram. This problem is treated non-linearly by considering a Swiss Cheese model of the Universe in which underdense voids are represented as negatively curved regions of space–time. Exact expressions for luminosity distances and redshifts are used to investigate the non-linear effects of structure on the magnitudes of astrophysical sources. It is found that the intervening voids we consider, between the observer and source, produce changes in apparent magnitude of less than 0.012. Sources inside voids, however, can be affected considerably at redshifts below . By averaging observable quantities over many randomly generated distributions of voids we find that the presence of these structures has the effect of introducing a dispersion around the mean, which itself can be displaced the background value. Observers in an inhomogeneous universe, who take averages of observables along many different lines of sight, may then introduce systematic biases, and underestimate errors, if these effects are not taken into account. Estimates of the potential size of these effects are made using data from simulated large-scale structure. [ABSTRACT FROM AUTHOR]

The article discusses the 2007 report of the Department of Mathematical Sciences of the University of South Africa. An overview of the issues of their personnel and students are mentioned. It is suggested that Dr Dmitri Wiebe visited the university and was able to apply his chemical codes in the parallel-processing machine of the university. Research on the dust extinction of disc galaxies at intermediate redshifts in the Hubble Deep Field and the IAU Symposium 242 was also included.

A general approach for investigating Bianchi-V cosmological models is introduced in a scalar-tensor theory of gravitation proposed by Saez and Ballester in which the law of variation for Hubble's parameter is taken into account. This variation for Hubble's parameter that yields a constant value of deceleration parameter is then utilized to solve the field equations governing anisotropic Bianchi-V space–time filled with perfect fluid. Two types of exact solutions that correspond to singular and nonsingular models are presented. Finally, we arrive to the conclusion that the universe decelerates for positive value of deceleration parameter whereas it accelerates for negative one. The behaviors of observationally important parameters are discussed in detail. Exact expressions for look-back time, luminosity distance and event horizon versus redshift are derived and their significance are discussed in detail. It has been observed that the solutions are compatible with the results of recent observations. [ABSTRACT FROM AUTHOR]

We present a simplified dynamical model of the ‘Bullet’ system of two colliding clusters. The model constrains the masses of the system by requiring that the orbits of the main and the subcomponents satisfy the cosmological initial conditions of vanishing physical separation a Hubble time ago. This is also known as the timing argument. The model considers a system embedded in an overdense region. We argue that a relative speed of 4500 km s−1 between the two components is consistent with cosmological conditions if the system is of a total mass of and is embedded in a region of a (mild) overdensity of 10 times the cosmological background density. Combining this with the lensing measurements of the projected mass, the model yields a ratio of 3:1 for the mass of the main relative to that of the subcomponent. The effect of the background weakens as the relative speed between the two components is decreased. For relative speeds lower than ∼3700 km s−1, the timing argument yields masses which are too low to be consistent with lensing. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we use observations of the Hubble parameter from the differential ages of passively evolving galaxies and the recent detection of the Baryon Acoustic Oscillations (BAO) at to constrain the Dvali–Gabadadze–Porrati (DGP) Universe. For the case with a curvature term, we set a prior and the best-fit values suggest a spatially closed Universe. For a flat Universe, we set h free and we get consistent results with other recent analyses. [Copyright &y& Elsevier]

An explanation of the anomalous acceleration of the Pioneer spacecraft is presented. The explanation depends upon an analogy between the effects of an increase in the gravitational potential and the effects of the Hubble expansion. The derivation depends upon an ether-based theory of gravity. Though such a gravitational theory appears radical, the equations for an elastic ether differ in relatively minor detail from the equations of Einstein's general theory of relativity. The details of the ether-based gravity theory have been previously described, but the pertinent portions are repeated herein. The explanation of the apparent force fits the anomalous acceleration of the Pioneer 10 and 11 spacecraft very accurately. Several tests of the theory are suggested. First, and most important, evidence is cited that indicates that the newly described mechanism will significantly reduce the annual and diurnal cyclic residuals described in the referenced literature. Second, the placement of a transponder package like that of the Pioneer spacecraft upon one of the planets or moons of the planets could provide a relatively rapid verification of the mechanism. Finally, the launch of a "drag-free" spacecraft would also enable a test of the newly described mechanism. [ABSTRACT FROM AUTHOR]

We use the Hubble Ultra Deep Field to study the galaxy luminosity–size distribution. With a careful analysis of selection effects due to both detection completeness and measurement reliability, we identify bias-free regions in the plane for a series of volume-limited samples. By comparison to a nearby survey also having well-defined selection limits, namely the Millennium Galaxy Catalogue, we present clear evidence for evolution in surface brightness since . Specifically, we demonstrate that the mean, rest-frame B-band for galaxies in a sample spanning 8 mag in luminosity between and −14 mag increases by ∼1.0 mag arcsec−2 from to 0.7. We also highlight the importance of considering surface brightness-dependent measurement biases in addition to incompleteness biases. In particular, the increasing, systematic underestimation of Kron fluxes towards low surface brightnesses may cause diffuse, yet luminous, systems to be mistaken for faint, compact objects. [ABSTRACT FROM AUTHOR]

Using the 100-m Green Bank Telescope, we have conducted a cm-wavelength search for CO line emission towards the high-redshift, far-infrared (FIR) luminous object HDF850.1 over the redshift interval 3.3 ≲ z≲ 5.4. Despite the wealth of existing multiwavelength observations, and the recent identification of a galaxy counterpart in deep K′-band (2.2 μm) imaging, an unambiguous spectroscopic redshift has not yet been obtained for this object. A FIR-to-radio wavelength photometric redshift technique, however, predicts a ∼90 per cent probability that the redshift is in the range, (equivalent to an observed redshifted CO emission line frequency, ), making HDF850.1 a potential occupant of the ‘high-redshift tail’ of submillimetre (submm)-selected galaxies. We have also conducted a search for CO line emission over the narrower redshift range, . Although we do not detect any CO line emission in this object, our limits to the CO line luminosity are in broad agreement with the median value measured in the current sample of high-redshift, submm-selected objects detected in high- J CO line emission, but not sufficient to fully test the validity of the photometric redshift technique. [ABSTRACT FROM AUTHOR]

We investigate cosmological solutions of Brans-Dicke theory with both the vacuum energy density and the gravitational constant decaying linearly with the Hubble parameter. A particular class of them, with a constant deceleration factor, sheds light on the cosmological constant problems, leading to a presently small vacuum term, and to a constant ratio between the vacuum and matter energy densities. By fixing the only free parameter of these solutions, we obtain cosmological parameters in accordance with observations of both the relative matter density and the universe age. In addition, we have three other solutions, with Brans-Dicke parameter ? = ?1 and negative cosmological term, two of them with a future singularity of big-rip type. Although interesting from the theoretical point of view, two of them are not in agreement with the observed universe. The third one leads, in the limit of large times, to a constant relative matter density, being also a possible solution to the cosmic coincidence problem. [ABSTRACT FROM AUTHOR]

We present a highly simplified model of the dynamical structure of a disc galaxy where only two parameters fully determine the solution, mass and angular momentum. We show through simple physical scalings that once the mass has been fixed, the angular momentum parameter λ is expected to regulate such critical galactic disc properties as colour, thickness of the disc and bulge-to-disc ratio. It is, hence, expected to be the determinant physical ingredient resulting in a given Hubble type. A simple analytic estimate of λ for an observed system is provided. An explicit comparison of the distribution of several galactic parameters against both Hubble type and λ is performed using observed galaxies. Both such distributions exhibit highly similar characteristics for all galactic properties studied, suggesting λ as a physically motivated classification parameter for disc galaxies. [ABSTRACT FROM AUTHOR]

The technique of adjacent pixel brightness variation in log scale was applied to ultra deep field objects captured by the Hubble telescope. The local surface brightness fluctuation has a Gaussian–like distribution implying a random accretion of material, with collisions, as a random-walk motion. The larger fluctuation of log brightness in the mid to outer regions of some galaxies is consistent with the presence of dark matter. The absence of such fluctuation enhancement in two i-drop candidates at z ∼ 3 may mean that some dark matter is the result of nucleosynthesis in the evolution process. Large fluctuation in the B+V bands in contrast to the i+z band near the center in an i-drop candidate at z ∼ 3 was interpreted to be an AGN center. The distribution average shifts towards zero for more spiral galaxies, signifying the use of local surface brightness fluctuation distribution as a morphology parameter. [Copyright &y& Elsevier]

We present radio, optical and X-ray-detected counterparts to the submillimetre sources found using SCUBA in theHubble Deep FieldNorth region (GOODS-N). A new counterpart identification statistic is developed to identify properties of galaxies detected at other wavelengths that can be used to aid counterpart identification. We discriminate between criteria that can use used to pre-select submillimetre bright objects, and those that identify the counterpart to a known submillimetre object. Optically faint galaxies detected in the deepest 1.4-GHz radio continuum maps are the only effective way of pre-selecting SCUBA galaxies, and radio sources are the best way to identify counterparts to known submillimetre detections. Looking at radio spectral indices, only the steeper sources (indicative of star formation) are detected in the submillimetre range. Although we find several X-ray identifications, we show that deepChandraimages do not contribute to counterpart identifications, as in all cases they are already detected in the more easily obtained VLA radio maps. We also find no evidence for clustering betweenChandraand SCUBA sources in this field. For a known SCUBA position, the reddest source tends to be the correct association, although we can find no cut on colour, magnitude or clustering property that efficiently pre-selects for SCUBA sources. 15-μmISOsources are statistically detected by SCUBA, but the limiting mid-infrared flux is not low enough to provide useful constraints. We present postage stamp strips for each SCUBA detection in separate bands from X-ray to radio bands, providing direct visual evidence that approximately half of the submillimetre sources in this field remain unidentified, despite an abundance of deep multiwavelength data. [ABSTRACT FROM AUTHOR]

Using the known connection between Schrödinger-like equations and Dirac-like equations in the supersymmetric context, we discuss an extension of FRW barotropic cosmologies in which a Dirac mass-like parameter is introduced. New Hubble cosmological parameters HK(η) depending on the Dirac-like parameter are plotted and compared with the standard Hubble case H0(η). The new HK(η) are complex quantities. The imaginary part is a supersymmetric way of introducing dissipation and instabilities in the barotropic FRW hydrodynamics. [ABSTRACT FROM AUTHOR]

We investigate how a different calibration of the Cepheid period–luminosity (PL) relation, taking into account metallicity corrections, affects the absolute magnitude calibration of Type Ia supernovae (SNe Ia) and, in turn, the determination of the Hubble constant . We use SN Ia light curves from the literature and previously unpublished data to establish the relation, and calibrate the zero point by means of nine SNe Ia with Cepheid-measured distances. This relation is then used to establish the Hubble diagram, and in turn to derive . In the attempt to correct for the host-galaxy extinction, we find that the data suggest a value for the total to selective absorption ratio of , which is smaller than the standard value for our own Galaxy of . Depending on the metallicity correction for the Cepheid PL relation, the value of , and SN sample selection criteria, the value of the Hubble constant takes a value in the range 68–74 km s−1 Mpc−1, with associated uncertainties of the order of 10 per cent. Unpublished photometry is also presented for 18 SNe of our sample (1991S, 1991T, 1992A, 1992K, 1993H, 1993L, 1994D, 1994M, 1994ae, 1995D, 1995ac, 1995bd, 1996bo, 1997bp, 1997br, 1999aa, 1999dk, 2000cx). These data are the results of a long-standing effort in supernova monitoring at ESO – La Silla and Asiago observatories. [ABSTRACT FROM AUTHOR]

We consider the brane universe in the bulk background of the topological Reissner–Nordström de Sitter black holes. We show that the thermodynamic quantities (including entropy) of the dual CFT take usual special forms expressed in terms of Hubble parameter and its time derivative at the moment, when the brane crosses the black hole horizon or the cosmological horizon. We obtain the generalized Cardy–Verlinde formula for the CFT with a charge and cosmological constant, for any values of the curvature parameter k in the Friedmann equations. [ABSTRACT FROM AUTHOR]

Presents an analysis of the submillimeter common user bolometer array observation of the Hubble Deep Field. Review of the observing strategy and data acquisition; Discussion of data reduction algorithms; Consideration of source astrometry and flux calibration uncertainties.