Carl Roberts | Searcharxiv

arXiv2017

Tests of $Λ$CDM and Conformal Gravity using GRB and Quasars as Standard Candles out to $z \sim 8$

We compare the cosmology of conformal gravity (CG), (Mannheim 2006), to $Λ$CDM. CG cosmology has repulsive matter and radiation on cosmological scales, while retaining attractive gravity at local scales. Mannheim (2003) finds that CG agrees with $Λ$CDM for supernova data at redshifts $z<1$. We use GRBs and quasars as standard candles to contrast these models in the redshift range $0<z<8$. We find CG deviates significantly from $Λ$CDM at high redshift and that $Λ$CDM is favoured by the data with $Δχ^2=48$. Mannheim's model has a bounded dark energy contribution, but we identify a $λ$ fine-tuning problem and a cosmic coincidence problem.

astro-ph.CO↗

arXiv2015

Observations of radio-quiet quasars at 10mas resolution by use of gravitational lensing

We present VLA detections of radio emission in four four-image gravitational lens systems with quasar sources: HS0810+2554, RXJ0911+0511, HE0435$-$1223 and SDSSJ0924+0219, and e-MERLIN observations of two of the systems. The first three are detected at a high level of significance, and SDSS J0924+0219 is detected. HS0810+2554 is resolved, allowing us for the first time to achieve 10-mas resolution of the source frame in the structure of a radio quiet quasar. The others are unresolved or marginally resolved. All four objects are among the faintest radio sources yet detected, with intrinsic flux densities in the range 1-5$μ$Jy; such radio objects, if unlensed, will only be observable routinely with the Square Kilometre Array. The observations of HS0810+2554, which is also detected with e-MERLIN, strongly suggest the presence of a mini-AGN, with a radio core and milliarcsecond scale jet. The flux densities of the lensed images in all but HE0435-1223 are consistent with smooth galaxy lens models without the requirement for smaller-scale substructure in the model, although some interesting anomalies are seen between optical and radio flux densities. These are probably due to microlensing effects in the optical.

astro-ph.GA↗