Search

The most luminous quasars at high-redshift harbour the fastest growing and most massive black holes in the early Universe. They are exceedingly rare and hard to find. Here, we present our search for the most luminous quasars in the redshift range from z = 4.5 to 5 using data from SkyMapper, Gaia , and WISE. We use colours to select likely high-redshift quasars and reduce the stellar contamination of the candidate set with parallax and proper motion data. In ∼12 500 deg2 of Southern sky, we find 92 candidates brighter than Rp = 18.2. Spectroscopic follow-up has revealed 21 quasars at z ≥ 4 (16 of which are within z = [4.5, 5]), as well as several red quasars, Broad-Absorption-Line (BAL) quasars and objects with unusual spectra, which we tentatively label OFeLoBALQSOs at redshifts of z ≈ 1 to 2. This work lifts the number of known bright z ≥ 4.5 quasars in the Southern hemisphere from 10 to 26 and brings the total number of quasars known at Rp < 18.2 and z ≥ 4.5 to 42. [ABSTRACT FROM AUTHOR]

Presently, a>3σ tension exists between values of the Hubble constant H0 derived from analysis of fluctuations in the cosmic microwave background by Planck, and local measurements of the expansion using calibrators of Type Ia supernovae (SNe Ia). We perform a blinded reanalysis of Riess et al. (2011) to measure H0 from low-redshift SNe Ia, calibrated by Cepheid variables and geometric distances including to NGC 4258. This paper is a demonstration of techniques to be applied to the Riess et al. (2016) data. Our end-to-end analysis starts from available Harvard -Smithsonian Center for Astrophysics (CfA3) and Lick Observatory Supernova Search (LOSS) photometries, providing an independent validation of Riess et al. (2011). We obscure the value of H0 throughout our analysis and the first stage of the referee process, because calibration of SNe Ia requires a series of often subtle choices, and the potential for results to be affected by human bias is significant. Our analysis departs from that of Riess et al. (2011) by incorporating the covariance matrix method adopted in Supernova Legacy Survey and Joint Lightcurve Analysis to quantify SN Ia systematics, and by including a simultaneous fit of all SN Ia and Cepheid data. We find H0 = 72.5 ± 3.1(stat) ± 0.77(sys) km s-1 Mpc-1 with a three-galaxy (NGC 4258+LMC+MW) anchor. The relative uncertainties are 4.3 per cent statistical, 1.1 per cent systematic, and 4.4 per cent total, larger than in Riess et al. (2011) (3.3 per cent total) and the Efstathiou (2014) re-analysis (3.4 per cent total). Our error budget for H0 is dominated by statistical errors due to the small size of the SN sample, whilst the systematic contribution is dominated by variation in the Cepheid fits, and for the SNe Ia, uncertainties in the host galaxy mass dependence and Malmquist bias. [ABSTRACT FROM AUTHOR]

We used observations from the Giant Metrewave Radio Telescope to measure the atomic hydrogen gas content of 324 galaxies around the galaxy cluster Abell 370 at a redshift of (a look-back time of ∼4 billion years). The H i 21 cm emission from these galaxies was measured by co-adding their signals using precise optical redshifts obtained with the Anglo-Australian Telescope. The average H i mass measured for all 324 galaxies is , while the average H i mass measured for the 105 optically blue galaxies is . The significant quantities of gas found around Abell 370 suggest that there has been substantial evolution in the gas content of galaxy clusters since redshift . The total amount of atomic hydrogen gas found around Abell 370 is up to approximately eight times more than that seen around the Coma cluster, a nearby galaxy cluster of similar size. Despite this higher gas content, Abell 370 shows the same trend as nearby clusters that galaxies close to the cluster core have lower H i gas content than galaxies further away where the galaxy density is lower. The optically blue galaxies contain the majority of the H i gas surrounding the cluster. However, there is evidence that the optically red galaxies contain appreciable quantities of H i gas within their central regions. The Abell 370 galaxies have H i mass-to-optical-light ratios similar to local galaxy samples and have the same correlation between their star formation rate and H i mass as found in the nearby galaxies. The average star formation rate derived from [O ii] emission and from deredshifted 1.4 GHz radio continuum for the Abell 370 galaxies also follows the correlation found in the local Universe. The large amounts of H i gas found around the cluster can easily be consumed entirely by the observed star formation rate in the galaxies over ∼4 billion years (from ) to the present day. Abell 370 appears set to evolve into a gas-poor system similar to galaxy clusters observed in the local Universe. [ABSTRACT FROM AUTHOR]

We use published spectroscopic and photometric data for eight Type Ia supernovae (SNe Ia) to construct a dispersion spectrum for this class of object, showing their diversity over the wavelength range 3700–7100 Å. We find that the B and V bands are the spectral regions with the least dispersion, while the U band below 4100 Å is more diverse. Some spectral features such as the Si line at 6150 Å are also highly diverse. We then construct two objective measures of ‘peculiarity’ by (i) using the deviation of individual objects from the average SN Ia spectrum compared to the typical dispersion and (ii) applying principal component analysis. We demonstrate these methods on several SNe Ia that have previously been classified as peculiar. [ABSTRACT FROM AUTHOR]