Day 1601

Monday.  Tuesday.  Wednesday.

1907.11245

Key challenges for AAS Journals in the next decade

Levesque, et al

The American Astronomical Society (AAS) Journals are a vital asset of our professional society. With the push towards open access, page charges are a viable and sustainable option for continuing to effectively fund and publish the AAS Journals. However, the existing page charge model, which requires individual authors to pay page charges out of their grants or even out of pocket, is already challenging to some researchers and could be exacerbated in the Open Access (OA) era if charges increase. A discussion of alternative models for funding page charges and publishing costs should be part of the Astro2020 decadal survey if we wish to continue supporting the sustainable and accessible publication of US research in AAS journals in the rapidly-shifting publication landscape. The AAS Publications Committee recommends that the National Academy of Sciences form a task force to develop solutions and recommendations with respect to the urgent concerns and considerations highlighted in this White Paper.

1907.12285

Testing for gravitational preferred directions with galaxy and lensing surveys

Resco, Maroto

We analyze the sensitivity of galaxy and weak-lensing surveys to detect preferred directions in the gravitational interaction. We consider general theories of gravity involving additional vector degrees of freedom with non-vanishing spatial components in the background. We use a model-independent parametrization of the perturbations equations in terms of four effective parameters, namely, the standard effective Newton constant $G_{eff}$ and slip parameter $\gamma$ for scalar modes and two new parameters $\mu_Q$ and $\mu_h$ for vector and tensor modes respectively, which are required when preferred directions are present. We obtain the expressions for the multipole galaxy power spectrum in redshift space and for the weak-lensing shear, convergence and rotation spectra in the presence of preferred directions. By performing a Fisher matrix forecast analysis, we estimate the sensitivity of a future Euclid-like survey to detect this kind of modification of gravity. We finally compare with the effects induced by violations of statistical isotropy in the primordial power spectrum and identify the observables which could discriminate between them.

1907.12402

Observational evidence for a local under density in the Universe and its effect on the measurement of the Hubble Constant

Boehringer, Chor, Collins

For precision cosmological studies it is important to know the local properties of our reference point from which we observe the Universe. In particular for the determination of the Hubble constant with low redshift distance indicators, the values observed will depend on the local average matter density. In this work we used the spatial distribution of galaxy clusters to map the matter density distribution in the local Universe. The study is based on our CLASSIX galaxy cluster survey, where galaxy clusters are detected by their X-ray emission. In total 1653 galaxy clusters are involved in this study. We find a local underdensity in the cluster distribution of about 30 - 60% which extends about 85 Mpc to the north and about 170 Mpc to the South. For three regions for which the galaxy density distribution was studied previously, we find good agreement between the density distribution of clusters and galaxies. Correcting for the bias in the cluster distribution we infer an underdensity in the matter distribution of about -30 +- 15% (-20 +- 10%) in a region with a radius of about 100 (140) Mpc. Calculating the probability of finding such an underdensity through structure formation theory in a LambdaCDM universe with concordance cosmological parameters, we find a probability characterised by sigma-values of 1.3 - 3.7. This indicates low probabilities, but with values around 10% at the lower uncertainty limit, this finding is not so unlikely. Inside this underdensity, the observed Hubble parameter will be larger by about 5.5 (+2.1 -2.8)%, which explains part of the discrepancy between the locally measured value of H_0 compared to the value of the Hubble parameter inferred from the Planck observations of cosmic microwave background anisotropies.

1907.12576

Photosynthesis on exoplanets and exomoons from reflected light

Lingam, Loeb

Photosynthesis offers a convenient means of sustaining biospheres. We quantify the constraints for photosynthesis to be functional on the permanent nightside of tidally locked rocky exoplanets via reflected light from their exomoons. We show that the exomoons must be at least half the size of Earth's moon in order for photosynthesis to operate. This scenario of photosynthesis is unlikely for exoplanets around late-type M-dwarfs due to the low likelihood of large exomoons and their orbital instability over long timescales. We also investigate the prospects for photosynthesis on habitable exomoons via reflected light from the giant planets that they orbit. Our analysis indicates that such photosynthetic biospheres are potentially sustainable on these moons except those around late-type M-dwarfs.

1907.12867

Testing the near-infrared optical assembly of the space telescope Euclid

Bodendorf, et al

Euclid is a space telescope currently developed in the framework of the ESA Cosmic Vision 2015-2025 Program. It addresses fundamental cosmological questions related to dark matter and dark energy. The lens system of one of the two scientific key instruments [a combined near-infrared spectrometer and photometer (NISP)] was designed, built-up and tested at the Max Planck Institute for Extraterrestrial Physics (MPE). We present the final imaging quality of this diffraction-limited optical assembly with two complementary approaches, namely a point-spread function and a Shack-Hartmann sensor-based wavefront measurement. The tests are performed under space operating conditions within a cryostat. The large field of view of Euclid's wide-angle objective is sampled with a pivot arm, carrying a measurement telescope and the sensors. A sequence of highly accurate movements to several field positions is carried out by a large computer controlled hexapod. Both measurement approaches are compared among one another and with the corresponding simulations. They demonstrate in good agreement a solely diffraction limited optical performance over the entire field of view.


1907.12995

Effects of primitive photosynthesis on Earth's early climate system

Ozaki, et al

The evolution of different forms of photosynthetic life has profoundly altered the activity level of the biosphere, radically reshaping the composition of Earth's oceans and atmosphere over time. However, the mechanistic impacts of a primitive photosynthetic biosphere on Earth's early atmospheric chemistry and climate are poorly understood. Here, we use a global redox balance model to explore the biogeochemical and climatological effects of different forms of primitive photosynthesis. We find that a hybrid ecosystem of H2-based and Fe-based anoxygenic photoautotrophs - organisms that perform photosynthesis without producing oxygen - gives rise to a strong nonlinear amplification of Earth's methane (CH4) cycle, and would thus have represented a critical component of Earth's early climate system before the advent of oxygenic photosynthesis. Using a Monte Carlo approach, we find that a hybrid photosynthetic biosphere widens the range of geochemical conditions that allow for warm climate states well beyond either of these metabolic processes acting in isolation. Our results imply that Earth's early climate was governed by a novel and poorly explored set of regulatory feedbacks linking the anoxic biosphere and the coupled H, C and Fe cycles. We suggest that similar processes should be considered when assessing the potential for sustained habitability on Earth-like planets with reducing atmospheres.


1907.13001

Anoxygenic photosynthesis and the delayed oxygenation of Earth's atmosphere

Ozaki, et al

The emergence of oxygenic photosynthesis created a new niche with dramatic potential to transform energy flow through Earth's biosphere. However, more primitive forms of photosynthesis that fix CO2 into biomass using electrons from reduced species like Fe(II) and H2 instead of water would have competed with Earth's early oxygenic biosphere for essential nutrients. Here, we combine experimental microbiology, genomic analyses, and Earth system modeling to demonstrate that competition for light and nutrients in the surface ocean between oxygenic phototrophs and Fe(II)-oxidizing, anoxygenic photosynthesizers (photoferrotrophs) translates into diminished global photosynthetic O2 release when the ocean interior is Fe(II)-rich. These results provide a simple ecophysiological mechanism for inhibiting atmospheric oxygenation during Earth's early history. We also find a novel positive feedback within the coupled C-P-O-Fe cycles that can lead to runaway planetary oxygenation as rising atmospheric pO2 sweeps the deep ocean of the ferrous iron substrate for photoferrotrophy.