ALBERT

Description: We use new near-infrared spectroscopic observations to investigate the nature and evolution of the most luminous Hα emitters at z ~ 0.8–2.23, which evolve strongly in number density over this period, and compare them to more typical Hα emitters. We study 59 luminous Hα emitters with L Hα 〉  $L_{\rm H\alpha }^{\ast }$ , roughly equally split per redshift slice at z ~ 0.8, 1.47 and 2.23 from the HiZELS and CF-HiZELS surveys. We find that, overall, 30 ± 8 per cent are active galactic nuclei [AGNs; 80 ± 30 per cent of these AGNs are broad-line AGNs, BL-AGNs], and we find little to no evolution in the AGN fraction with redshift, within the errors. However, the AGN fraction increases strongly with Hα luminosity and correlates best with L Hα / $L_{\rm H\alpha }^{\ast }(z)$ . While L Hα  ≤  $L_{\rm H\alpha }^{\ast }(z)$ Hα emitters are largely dominated by star-forming galaxies (〉80 per cent), the most luminous Hα emitters ( $L_{\rm H\alpha } 〉 10L_{\rm H\alpha }^{\ast }(z)$ ) at any cosmic time are essentially all BL-AGN. Using our AGN-decontaminated sample of luminous star-forming galaxies, and integrating down to a fixed Hα luminosity, we find a factor of ~1300 evolution in the star formation rate density from z  = 0 to 2.23. This is much stronger than the evolution from typical Hα star-forming galaxies and in line with the evolution seen for constant luminosity cuts used to select ‘ultraluminous’ infrared galaxies and/or sub-millimetre galaxies. By taking into account the evolution in the typical Hα luminosity, we show that the most strongly star-forming Hα-selected galaxies at any epoch ( $L_{\rm H\alpha } 〉 L^{\ast }_{\rm H\alpha }(z)$ ) contribute the same fractional amount of 15 per cent to the total star formation rate density, at least up to z  = 2.23.

Description: We exploit Atacama Large Millimeter Array (ALMA) 870 μm observations of sub-millimetre sources in the Extended Chandra Deep Field South to investigate the far-infrared properties of high-redshift sub-millimetre galaxies (SMGs). Using the precisely located 870 μm ALMA positions of 99 SMGs, together with 24μm and radio imaging, we deblend the Herschel /SPIRE imaging to extract their far-infrared fluxes and colours. The median redshifts for ALMA LESS (ALESS) SMGs which are detected in at least two SPIRE bands increases with wavelength of the peak in their spectral energy distributions (SEDs), with z  = 2.3 ± 0.2, 2.5 ± 0.3 and 3.5 ± 0.5 for the 250, 350 and 500 μm peakers, respectively. 34 ALESS SMGs do not have a 〉3 counterpart at 250, 350 or 500 μm. These galaxies have a median photometric redshift derived from the rest-frame UV–mid-infrared SEDs of z  = 3.3 ± 0.5, which is higher than the full ALESS SMG sample; z  = 2.5 ± 0.2. We estimate the far-infrared luminosities and characteristic dust temperature of each SMG, deriving L IR  = (3.0 ± 0.3) 10 12 L (SFR = 300 ± 30 M yr –1 ) and T d  = 32 ± 1 K. The characteristic dust temperature of these high-redshift SMGs is T d  = 3–5 K lower than comparably luminous galaxies at z  = 0, reflecting the more extended star formation in these systems. We show that the contribution of S 870 μm ≥ 1 mJy SMGs to the cosmic star formation budget is 20 per cent of the total over the redshift range z ~ 1–4. Adopting an appropriate gas-to-dust ratio, we estimate a typical molecular mass of the ALESS SMGs of $M_{\rm H_2}$  = (4.2 ± 0.4) 10 10 M . Finally, we show that SMGs with S 870 μm 〉 1 mJy ( L IR  10 12 L ) contain ~ 10 per cent of the z ~ 2 volume-averaged H 2 mass density.

Description: The Human Induced Pluripotent Stem Cell Initiative (HipSci) isf establishing a large catalogue of human iPSC lines, arguably the most well characterized collection to date. The HipSci portal enables researchers to choose the right cell line for their experiment, and makes HipSci's rich catalogue of assay data easy to discover and reuse. Each cell line has genomic, transcriptomic, proteomic and cellular phenotyping data. Data are deposited in the appropriate EMBL-EBI archives, including the European Nucleotide Archive (ENA), European Genome-phenome Archive (EGA), ArrayExpress and PRoteomics IDEntifications (PRIDE) databases. The project will make 500 cell lines from healthy individuals, and from 150 patients with rare genetic diseases; these will be available through the European Collection of Authenticated Cell Cultures (ECACC). As of August 2016, 238 cell lines are available for purchase. Project data is presented through the HipSci data portal ( http://www.hipsci.org/lines ) and is downloadable from the associated FTP site ( ftp://ftp.hipsci.ebi.ac.uk/vol1/ftp ). The data portal presents a summary matrix of the HipSci cell lines, showing available data types. Each line has its own page containing descriptive metadata, quality information, and links to archived assay data. Analysis results are also available in a Track Hub, allowing visualization in the context of public genomic annotations ( http://www.hipsci.org/data/trackhubs ).

Description: We present the results of 325 MHz Giant Metrewave Radio Telescope observations of a supercluster field, known to contain five Abell clusters at redshift z  ~ 0.2. We achieve a nominal sensitivity of 34 μJy beam –1 towards the phase centre. We compile a catalogue of 3257 sources with flux densities in the range $183\,\mu \rm {Jy}{\rm -}1.5\,\rm {Jy}$ within the entire ~6.5 deg 2 field of view. Subsequently, we use available survey data at other frequencies to derive the spectral index distribution for a sub-sample of these sources, recovering two distinct populations – a dominant population which exhibit spectral index trends typical of steep-spectrum synchrotron emission, and a smaller population of sources with typically flat or rising spectra. We identify a number of sources with ultrasteep spectra or rising spectra for further analysis, finding two candidate high-redshift radio galaxies and three gigahertz-peaked-spectrum radio sources. Finally, we derive the Euclidean-normalized differential source counts using the catalogue compiled in this work, for sources with flux densities in excess of 223 μJy. Our differential source counts are consistent with both previous observations at this frequency and models of the low-frequency source population. These represent the deepest source counts yet derived at 325 MHz. Our source counts exhibit the well-known flattening at mJy flux densities, consistent with an emerging population of star-forming galaxies; we also find marginal evidence of a downturn at flux densities below 308 μJy, a feature so far only seen at 1.4 GHz.

Description: We construct forecasts for cosmological parameter constraints from weak gravitational lensing surveys involving the Square Kilometre Array (SKA). Considering matter content, dark energy and modified gravity parameters, we show that the first phase of the SKA (SKA1) can be competitive with other Stage III experiments such as the Dark Energy Survey and that the full SKA (SKA2) can potentially form tighter constraints than Stage IV optical weak lensing experiments, such as those that will be conducted with LSST, WFIRST-AFTA or Euclid -like facilities. Using weak lensing alone, going from SKA1 to SKA2 represents improvements by factors of ~10 in matter, ~10 in dark energy and ~5 in modified gravity parameters. We also show, for the first time, the powerful result that comparably tight constraints (within ~5 per cent) for both Stage III and Stage IV experiments, can be gained from cross-correlating shear maps between the optical and radio wavebands, a process which can also eliminate a number of potential sources of systematic errors which can otherwise limit the utility of weak lensing cosmology.

Description: We investigate the correlations in galaxy shapes between optical and radio wavelengths using archival observations of the Cosmic Evolution Survey (COSMOS) field. Cross-correlation studies between different wavebands will become increasingly important for precision cosmology as future large surveys may be dominated by systematic rather than statistical errors. In the case of weak lensing, galaxy shapes must be measured to extraordinary accuracy (shear systematics of 〈0.01 per cent) in order to achieve good constraints on dark energy parameters. By using shape information from overlapping surveys in optical and radio bands, robustness to systematics may be significantly improved without loss of constraining power. Here we use HST -ACS ( Hubble Space Telescope -Advanced Camera for Surveys) optical data, Very Large Array (VLA) radio data and extensive simulations to investigate both our ability to make precision measurements of source shapes from realistic radio data and to constrain the intrinsic astrophysical scatter between the shapes of galaxies as measured in the optical and radio wavebands. By producing a new image from the VLA-COSMOS L -band radio visibility data that are well suited to galaxy shape measurements, we are able to extract precise measurements of galaxy position angles. Comparing to corresponding measurements from the HST optical image, we set a lower limit on the intrinsic astrophysical scatter in position angles, between the optical and radio bands, of α 〉 0.212 rad (or 38 $_{.}^{\circ}$ 2) at a 95 per cent confidence level.

Description: We construct a pipeline for simulating weak lensing cosmology surveys with the Square Kilometre Array (SKA), taking as inputs telescope sensitivity curves; correlated source flux, size and redshift distributions; a simple ionospheric model; source redshift and ellipticity measurement errors. We then use this simulation pipeline to optimize a 2-yr weak lensing survey performed with the first deployment of the SKA (SKA1). Our assessments are based on the total signal to noise of the recovered shear power spectra, a metric that we find to correlate very well with a standard dark energy figure of merit. We first consider the choice of frequency band, trading off increases in number counts at lower frequencies against poorer resolution; our analysis strongly prefers the higher frequency Band 2 (950–1760 MHz) channel of the SKA-MID telescope to the lower frequency Band 1 (350–1050 MHz). Best results would be obtained by allowing the centre of Band 2 to shift towards lower frequency, around 1.1 GHz. We then move on to consider survey size, finding that an area of 5000 deg 2 is optimal for most SKA1 instrumental configurations. Finally, we forecast the performance of a weak lensing survey with the second deployment of the SKA. The increased survey size (3 steradian) and sensitivity improves both the signal to noise and the dark energy metrics by two orders of magnitude.

Description: In this third paper of a series on radio weak lensing for cosmology with the Square Kilometre Array, we scrutinize synergies between cosmic shear measurements in the radio and optical/near-infrared (IR) bands for mitigating systematic effects. We focus on three main classes of systematics: (i) experimental systematic errors in the observed shear; (ii) signal contamination by intrinsic alignments and (iii) systematic effects due to an incorrect modelling of non-linear scales. First, we show that a comprehensive, multiwavelength analysis provides a self-calibration method for experimental systematic effects, only implying 〈50 per cent increment on the errors on cosmological parameters. We also illustrate how the cross-correlation between radio and optical/near-IR surveys alone is able to remove residual systematics with variance as large as 10 –5 , i.e. the same order of magnitude of the cosmological signal. This also opens the possibility of using such a cross-correlation as a means to detect unknown experimental systematics. Secondly, we demonstrate that, thanks to polarization information, radio weak lensing surveys will be able to mitigate contamination by intrinsic alignments, in a way similar but fully complementary to available self-calibration methods based on position–shear correlations. Lastly, we illustrate how radio weak lensing experiments, reaching higher redshifts than those accessible to optical surveys, will probe dark energy and the growth of cosmic structures in regimes less contaminated by non-linearities in the matter perturbations. For instance, the higher redshift bins of radio catalogues peak at z ~= 0.8–1, whereas their optical/near-IR counterparts are limited to z 0.5–0.7. This translates into having a cosmological signal 2–5 times less contaminated by non-linear perturbations.

Description: We present a simulated cosmology analysis using the second and third moments of the weak lensing mass (convergence) maps. The second moment, or variances, of the convergence as a function of smoothing scale contains information similar to standard shear two-point statistics. The third moment, or the skewness, contains additional non-Gaussian information. The analysis is geared towards the third year (Y3) data from the Dark Energy Survey (DES), but the methodology can be applied to other weak lensing data sets. We present the formalism for obtaining the convergence maps from the measured shear and for obtaining the second and third moments of these maps given partial sky coverage. We estimate the covariance matrix from a large suite of numerical simulations. We test our pipeline through a simulated likelihood analyses varying 5 cosmological parameters and 10 nuisance parameters and identify the scales where systematic or modelling uncertainties are not expected to affect the cosmological analysis. Our simulated likelihood analysis shows that the combination of second and third moments provides a 1.5 per cent constraint on S8 ≡ σ8(Ωm/0.3)0.5 for DES Year 3 data. This is 20 per cent better than an analysis using a simulated DES Y3 shear two-point statistics, owing to the non-Gaussian information captured by the inclusion of higher order statistics. This paper validates our methodology for constraining cosmology with DES Year 3 data, which will be presented in a subsequent paper.