1808.07464
Massive neutrinos leave fingerprints on cosmic voids
Kreisch, ..., Spergel, Wandelt, et al
Massive neutrinos uniquely affect cosmic voids. Explore their impact on void clustering using both the DEMNUni and MassiveNuS simulations. For voids, neutrino effects depend on the observed void tracers. As the neutrino mass increases, the number of small voids traced by cold dark matter particles increases and the number of large voids decreases. Surprisingly, when massive, highly biased haloes are used as tracers, find the opposite effect. How neutrinos impact the scale at which voids cluster and the void correlation is similarly sensitive to the tracers. This scale dependent trend is not due to simulation volume or halo density. The interplay of these signatures in the void abundance and clustering leaves a distinct fingerprint that could be detected with observations and potentially help break degeneracies between different cosmological parameters. This paper paves the way to exploit cosmic voids in future surveys to constrain the mass of neutrinos.
1808.07491
Weak lensing shear estimation beyond the shape-noise limit: a machine learning approach
Springer, Ofek, Weiss, Merten
Weak lensing shear estimation typically results in per galaxy statistical errors significantly larger than the gravitational signal of only a few percent. These statistical errors are mostly a result of shape-noise -- an estimation error due to the diverse (and a-priori unknown) morphology of individual background galaxies. These errors are inversely proportional to the limiting angular resolution at which localized objects, such as galaxy clusters, can be probed with weak lensing shear. In this work, report on the initial attempt to reduce statistical errors in weak lensing shear estimation using a machine learning approach -- training a multi-layered convolutional neural network to directly estimate the shear, given an observed background galaxy image. Train, calibrate and evaluate the performance and stability of the estimator using simulated galaxy images designed to mimic the distribution of HST observations of lensed background sources in the CLASH galaxy cluster survey. Using the trained estimator, produce weak lensing shear maps of the cores of 20 galaxy clusters in the CLASH survey, demonstrating an RMS scatter reduced by approximately 26% when compared to maps produced with a commonly used shape estimator. This is equivalent to a survey speed enhancement of approximately 60%. However, given the non-transparent nature of the machine learning approach, this results requires further testing and validation. Provide python code to train and test this estimator on both simulated and real galaxy cluster observations. Also provide updated weak lensing catalogues for the 20 CLASH galaxy clusters studied.
1808.07551
The Dark Universe - Exercises and proceedings form the German-Italian WE Heraeus Summer School held in 2017 in Heidelberg
Brems, et al
The Heroes Summer School series "Astronomy from four perspectives", funded by the WE Heraeus Foundation, draws together teachers and teacher students, astronomers, physicists and astronomy students from Germany and Italy. For each summer school, participants gather at one of the four participating nodes: Heidelberg, Padua, Jena, and Florence. The main goal of the series is to bring astronomy into schools, which is achieved by educating and training the teachers and teacher students. In this e-print, present the exercises, tutorials, and high-school classroom materials developed during the fifth summer school of the series, which took place at House der Astronomie in Heidelberg Aug. 26 -- Sep. 2, 2017. The tutorials were prepared beforehand for the participants of the Summer schools, and are suitable for use in teacher training. Classroom material were developed mainly during the summer school itself, and are suitable for high-school level teaching. They include question sheets for pupils, and some pointers on where to use the material in the German high school curriculum. Both sets of materials address the summer school's four main topics: Supernova cosmology, the viral theorem, rotation curves of galaxies, and the temperature of the cosmic microwave background (CMB).
1808.07772
Easily interpretable bulk flows: continuing tension with the standard cosmological model
Peery, Watkins, Feldman
Present an improved Minimal Variance (MV) method for using a radial peculiar velocity sample to estimate the average of the three-dimensional velocity field over a spherical volume, which leads to an easily interpretable bulk flow measurement. The only assumption required is that the velocity field is irrotational. The resulting bulk flow estimate is particularly insensitive to smaller scale flows. Also introduce a new constraint into the MV method that ensures that bulk flow estimates are independent of the value of the Hubble constant H_0; this is important given the tension between the locally measured H_0 and that obtained from the CMB observations. Apply the method to the Cosmic Flows-3 catalogues and find that, while the bulk flows for shallower spheres are consistent with the standard cosmological model, there is some tension between the bulk flow in a spherical volume with radius 150 hMpc and its expectations; find only a ~2% chance of obtaining a bulk flow as large or larger in the standard cosmological model with Planck parameters.
1808.08235
'Upper-limit lensing': constraining galaxy stellar masses with singly-imaged background sources
Smith, Lucey, Collier
Strong gravitational lensing can provide accurate measurements of the stellar mass-to-light ratio Upsilon in low-z (<~0.05) early-type galaxies, and hence probe for possible variations in the stellar initial mass function (IMF). However, true multiple imaging lens systems are rare, hindering the construction of large nearby lens samples. Here, present a method to derive upper limits on Upsilon in galaxies with single close-projected background sources, where where no counter-image is detected, down to some relative flux limit. Present a proof-of-principle applications to 3 galaxies with integral field observations from different instruments. in the first case study, only a weak constraint on Upsilon is obtained. In the second, the absence of a detectable counter-image excludes stellar masses higher than expected for a Salpeter IMF. In the 3rd system, the current observations do not yield a useful limit, but the analysis indicates that deeper observations should reveal a counter-image if the stellar mass is any larger than expected for a MW IMF. Discuss how this method can help enlarge the current samples of low-z galaxies with lensing constraints, both by adding upper limits on Upsilon and by guiding follow-up to promising single-image systems in search of fainter counter-images.
1808.08800
Discovery of strongly inverted metallicity gradients in dwarf galaxies at $z$$\sim$2
Wang, Jones, Treu, et al
Report the first sub-kiloparsec spatial resolution measurements of strongly inverted gas-phase metallicity gradients in two dwarf galaxies at z~2. The galaxies have stellar masses ~1e9 Msun, sSFR ~20 Gyr^{-1}, and global metallicity 12+log(O/H)~8.1 (1/4 solar). Their metallicity radial gradients are measured to be highly inverted, i.e., 0.122±).008 and 0.111±0.017 dex/kpc, which is hitherto unseen at such small masses in similar redshift ranges. From the HST observations of the source nebular emission and stellar continuum, present the 2-dimensional spatial maps of SFR surface density, stellar population age, and gas fraction, which show that the galaxies are currently undergoing rapid mass assembly via disk inside-out growth. More importantly, using a simple chemical evolution model, find that the gas fractions for different metallicity regions cannot be explained by pure gas accretion. The spatially resolved analysis based on a more advanced gas regulator model results in a spatial map of net gaseous outflows, triggered by active central starbursts, that potentially play a significant role in shaping the spatial distribution of metallicity by effectively transporting stellar nucleosynthesis yields outwards. The relation between wind mass loading factors and stellar surface densities measured in different regions of the galaxies shows that a single type of wind mechanism, driven by either energy or momentum conservation, cannot explain the entire galaxy. These sources present a unique constraint on the effects of gas flows on the early phase of disk growth from the perspective of spatially resolved chemical evolution within individual systems.
1808.08912
On the measurement of the local Hubble constant from the superlimninal motion of the jet launched in GW170817
Dado, Dar
The direction of the axis of the orbital motion of the merging binary neutron stars in the GW170817 event coincided with that of the apparent superluminal jet, which produced the short hard gamma ray burst (SHB) 170817A. It supports the local value of the Hubble constant provided by standard candle Type Ia SNe, H_0=73.24±1.74 km/s/Mpc, which differs by 3 sigma from the cosmic value H_0=67.74±0.46 km/s/Mpc obtained from the CMB radiation by Planck assuming the standard LCDM cosmology. The measured superluminal motion of the jet also allows critical tests of the assumed production mechanism of SHBs in general and of SHB170817A in particular.
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