1810.06686
Science with the ngVLA: H$_2$O Megamaser Cosmology
Braatz, et al
In combination with observations of the CMB, a measurement of the Hubble Constant provides a direct test of the standard LCDM cosmo model and a powerful constraint on the equation of state of DE. Observations of circumnuclear water vapor megamasers at 22 GHz in nearby active galaxies can be used to measure their distances, geometrically, and thereby provide a direct, one step measurement of the Hubble Constant. The measurement is independent of distance ladders and standard candles. With present-day instrumentation, the Megamaser Cosmology Project is expected to reach a ~4% measurement using the megamaser technique, based on distances to fewer than 10 megamaser systems. A goal of the observational cosmology community is to reach a percent-level measurement of H0 from several independent astrophysical measurements to minimize the systematics. The ngVLA will provide the sensitivity at 22 GHz required to discover and measure the additional megamaser disks that will enable an H0 measurement at the ~1% level.
1810.06561
Measurement of the primordial helium abundance from the intergalactic medium
Cooke, Fumagalli
Almost every helium atom in the Universe was created just a few minutes after the BB through a process commonly referred to as BBN. The amount of He that was made during BBN is determined by the combination of particle physics and cosmology. The current leading measures of the primordial He abundance (Y_P) are based on the relative strengths of H I and He I emission lines emanating from SF regions in local metal-poor galaxies. As the statistical errors on these measurements improve, it is essential to test for systematics by developing independent techniques. Here, report the first determination of the primordial He abundance based on a near-pristine intergalactic gas cloud that is seen in absorption against the light of a background quasar. This gas cloud, observed when the Universe was just 1/3 of its present age (z_abs=1.724), has a metal content ~100 times less than the Sun and ~30% less metals than the most metal-poor H II region currently known where a determination of the primordial He abundance is afforded, conclude that the He abundance of this intergalactic gas cloud is Y=0.250+0.033-0.025, which agrees with the Standard Model primordial value, Y_P=0.24672±0.00017. The determination of the primordial He abundance is not yet as precise as that derived using metal-poor galaxies, but the method has the potential to offer a competitive test of physics beyond the Standard Model during BBN.
1810.07200
Testing MOG theory in the Milky Way
Negrelli, et al
Perform a test of John Moffat's Modified Gravity theory (MOG) within the MW, adopting the well known "Rotation Curve" method. Use the dynamics of observed tracers within the disk to determine the gravitational potential as a function of galactocentric distance, and compare that with the potential that is expected to be generated by the visible component only (stars and gas) under different "flavors" of the MOG theory, making use of a state-of-the-art setup for both the observed tracers and baryonic morphology. The analysis shows that in both the original and the modified version (considering a self-consistent evaluation of the MW mass), the theory fails to reproduce the observed rotation curve. Conclude that in none of its present formulation, the MOG theory s able to explain the observed Rotation Curve of the MW.
1810.07628
$H_0$ tension: response to Riess et al arXiv:1810.03526
Shanks, Hogarth, Metcalfe
Riess+2018 have claimed there exist seven problems in the analyses presented by Shanks+2018 where it is argued that there is enough uncertainty in Cepheid distances and local peculiar velocity fields to explain the current tension in H0. Here, take each of the Riess+2018 points in turn and suggest that either they do no apply or that the necessary caveats are already made by Shanks+2018. Conclude that the main point to be inferred from the analyses still stands which is that previous claims by Riess+ that Gaia parallaxes confirm their Cepheid scale are, at best, premature in advance of fur their improvements in the Gaia astrometric solution.
1810.07265
Gravitational lenses at high-resolution telescopes
Barnacka
The inner regions of active galaxies host the most extreme and energetic phenomena in the universe including, relativistic jets, SMBH binaries, and recoiling SMBHs. However, many of these sources cannot be resolved with direct observations. Review how strong gravitational lensing can be used to elucidate the structures of these sources from radio frequencies up to very high energy gamma rays. The deep gravitational potentials surrounding galaxies act as natural gravitational lenses. These gravitational lenses split background sources into multiple images, each with a gravitationally-induced time delay. These time delays and positions of lensed images depend on the source location, and thus, can be used to infer the spatial origins of the emission. For example, using gravitationally-induced time delays improves angular resolution of modern gamma-ray instruments by six orders of magnitude, and provides evidence that gamma-ray outbursts can be produced at even thousands of light years from a SMBH, and that the compact radio emission does not always trace the position of the SMBH. These findings provide unique physical information about the central structure of active galaxies, force us to revise the models of operating particle acceleration mechanisms, and challenge the assumptions about the origin of compact radio emission. Future surveys, including LSST, SKA and Euclid, will provide observations for hundreds of thousands of gravitationally lensed sources, which will allow us to apply strong gravitational lensing to study the multi-wavelength structure for large ensembles of sources. This large ensemble of gravitationally lensed active galaxies will allow elucidation of the physical origins of multi-wavelength emissions, their connections to SMBHs, and their cosmic evolution.
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