Institute of Cosmology and Gravitation, University of Portsmouth

About: Institute of Cosmology and Gravitation, University of Portsmouth is a based out in . It is known for research contribution in the topics: Galaxy & Redshift. The organization has 297 authors who have published 1207 publications receiving 76919 citations.

Cosmic CARNage I: on the calibration of galaxy formation models

Abstract: We present a comparison of nine galaxy formation models, eight semi-analytical, and one halo occupation distribution model, run on the same underlying cold dark matter simulation (cosmological box of comoving width 125h−1 Mpc, with a dark-matter particle mass of 1.24 × 109h−1M⊙) and the same merger trees. While their free parameters have been calibrated to the same observational data sets using two approaches, they nevertheless retain some ‘memory’ of any previous calibration that served as the starting point (especially for the manually tuned models). For the first calibration, models reproduce the observed z = 0 galaxy stellar mass function (SMF) within 3σ. The second calibration extended the observational data to include the z = 2 SMF alongside the z ∼ 0 star formation rate function, cold gas mass, and the black hole–bulge mass relation. Encapsulating the observed evolution of the SMF from z = 2 to 0 is found to be very hard within the context of the physics currently included in the models. We finally use our calibrated models to study the evolution of the stellar-to-halo mass (SHM) ratio. For all models, we find that the peak value of the SHM relation decreases with redshift. However, the trends seen for the evolution of the peak position as well as the mean scatter in the SHM relation are rather weak and strongly model dependent. Both the calibration data sets and model results are publicly available.

Ultra steep spectrum radio sources in the lockman hole: servs identifications and redshift distribution at the faintest radio fluxes

Abstract: Ultra Steep Spectrum (USS) radio sources have been successfully used to select powerful radio sources at high redshifts (z > 2). Typically restricted to large-sky surveys and relatively bright radio flux densities, it has gradually become possible to extend the USS search to sub-mJy levels, thanks to the recent appearance of sensitive low-frequency radio facilities. Here we present a first detailed analysis of the nature of the faintest USS sources. By using GMRT and VLA radio observations of the Lockman Hole (LH) at 610 MHz and 1.4 GHz, a sample of 58 micro-Jansky USS sources is assembled. Deep infrared data at 3.6 and 4.5 μm from the Spitzer Extragalactic Representative Volume Survey (SERVS) is used to reliably identify counterparts for 48 (83%) of these sources, showing an average magnitude of [3. 6] = 19. 7 mag(AB). Spectroscopic redshifts for 14 USS sources, together with photometric redshift estimates, improved by the use of the deep SERVS data, for a further 19 objects, show redshifts ranging from z = 0. 1 to z = 2. 8, peaking at z ∼ 0. 6 and tailing off at high redshifts.

Eight New Quasar Lenses from the Sloan Digital Sky Survey Quasar Lens Search

Abstract: We report the discovery and confirmation of eight new two-image lensed quasars by the Sloan Digital Sky Survey (SDSS) Quasar Lens Search. The lenses are SDSSJ0904+1512 (image separation \theta=1"13, source redshift z_s=1.826), SDSSJ1054+2733 (\theta=1"27, z_s=1.452), SDSSJ1055+4628 (\theta=1"15, z_s=1.249), SDSSJ1131+1915 (\theta=1"46, z_s=2.915), SDSSJ1304+2001 (\theta=1"87, z_s=2.175), SDSSJ1349+1227 (\theta=3"00, z_s=1.722), SDSSJ1455+1447 (\theta=1"73, z_s=1.424), and SDSSJ1620+1203 (\theta=2"77, z_s=1.158). Three of them, SDSSJ1055+4628, SDSSJ1455+1447, and SDSSJ1620+1203, satisfy the criteria for constructing our statistical sample for studying the cosmological model. Based on galactic absorption lines of the lens galaxies, we also derive lens redshifts of z_l=0.398 and z_l=0.513 for SDSSJ1620+1203 and the previously discovered lens SDSSJ0746+4403, respectively.

SDSS-IV MaStar: A Large and Comprehensive Empirical Stellar Spectral Library—First Release

Abstract: Author(s): Yan, R; Chen, Y; Lazarz, D; Bizyaev, D; Maraston, C; Stringfellow, GS; Mccarthy, K; Meneses-Goytia, S; Law, DR; Thomas, D; Barroso, JF; Sanchez-Gallego, JR; Schlafly, E; Zheng, Z; Argudo-Fernandez, M; Beaton, RL; Beers, TC; Bershady, M; Blanton, MR; Brownstein, J; Bundy, K; Chambers, KC; Cherinka, B; Lee, ND; Drory, N; Galbany, L; Holtzman, J; Imig, J; Kaiser, N; Kinemuchi, K; Liu, C; Luo, AL; Magnier, E; Majewski, S; Nair, P; Oravetz, A; Oravetz, D; Pan, K; Sobeck, J; Stassun, K; Talbot, M; Tremonti, C; Waters, C; Weijmans, AM; Wilhelm, R; Zasowski, G; Zhao, G; Zhao, YH | Abstract: We present the first release of the MaNGA Stellar Library (MaStar), which is a large, well-calibrated, high-quality empirical library covering the wavelength range 3622-10354 A at a resolving power of R ∼ 1800. The spectra were obtained using the same instrument as used by the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) project, by piggybacking on the Sloan Digital Sky Survey (SDSS-IV)/Apache Point Observatory Galaxy Evolution Experiment 2-N (APOGEE-2N) observations. Compared to previous empirical libraries, the MaStar library will have a higher number of stars and a more comprehensive stellar-parameter coverage, especially of cool dwarfs, low-metallicity stars, and stars with different [α/Fe], achieved by a sophisticated target-selection strategy that takes advantage of stellar-parameter catalogs from the literature. This empirical library will provide a new basis for stellar-population synthesis and is particularly well suited for stellar-population analysis of MaNGA galaxies. The first version of the library contains 8646 high-quality per-visit spectra for 3321 unique stars. Compared to photometry, the relative flux calibration of the library is accurate to 3.9% in g-r, 2.7% in r-i, and 2.2% in i-z. The data are released as part of SDSS Data Release 15. We expect the final release of the library to contain more than 10,000 stars.

Observational signatures of the theories beyond Horndeski

Abstract: In the approach of the effective field theory of modified gravity, we derive the equations of motion for linear perturbations in the presence of a barotropic perfect fluid on the flat isotropic cosmological background. In a simple version of Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories, which is the minimum extension of Horndeski theories, we show that a slight deviation of the tensor propagation speed squared $c_{\rm t}^2$ from 1 generally leads to the large modification to the propagation speed squared $c_{\rm s}^2$ of a scalar degree of freedom $\phi$. This problem persists whenever the kinetic energy $\rho_X$ of the field $\phi$ is much smaller than the background energy density $\rho_m$, which is the case for most of dark energy models in the asymptotic past. Since the scaling solution characterized by the constant ratio $\rho_X/\rho_m$ is one way out for avoiding such a problem, we study the evolution of perturbations for a scaling dark energy model in the framework of GLPV theories in the Jordan frame. Provided the oscillating mode of scalar perturbations is fine-tuned so that it is initially suppressed, the anisotropic parameter $\eta=-\Phi/\Psi$ between the two gravitational potentials $\Psi$ and $\Phi$ significantly deviates from 1 for $c_{\rm t}^2$ away from 1. For other general initial conditions, the deviation of $c_{\rm t}^2$ from 1 gives rise to the large oscillation of $\Psi$ with the frequency related to $c_{\rm s}^2$. In both cases, the model can leave distinct imprints for the observations of CMB and weak lensing.