Day 1400

Tuesday.

1804.03888
EDGES result versus CMB and low-redshift constraints on ionization histories
Witte, et al

Examine the results from the Experiment to Direct the Global Epoch of Reionization Signature (EDGES), which has recently claimed the detection of a strong absorption in the 21 cm hyperfine transition line of neutral hydrogen, and z demarcating the early stages of star formation.  More concretely, study the compatibility of the shape of the EDGES absorption profile, centered at a z of z~17.2, with measurements of the reionization optical depth, the Gunn-Peterson optical depth, and Lyman-alpha emission from star-forming galaxies, for a variety of possible reionization models within the standard LCDM framework.  When, conservatively, only the location of the absorption dip is attempted to have accommodated, identify a region in the parameter space of the astrophysical parameters that successfully explains all of the aforementioned observations.  However, one of the most abnormal features of the EES measurement is the absorption amplitude, which is roughly a factor of 2 larger than the maximum allowed value in the LCDM framework.  Point out that the simple considered astrophysical models that produce the largest absorption amplitudes are unable to explain the depth of the dip and of reproducing the observed shape of the absorption profile.


1804.04139
Measured and found wanting: reconciling mass-estimates of ultra-diffuse galaxies
Laporte, Agnello, Navarro

The viral masses of UDGs have been estimated using the kinematics and abundance of their globular cluster populations, leading to disparate results.  Some studies conclude that UDGs reside in massive DM haloes while other, controversially, argue for the existence of UDGs with no DM at all.  Here, show that these results arise because the uncertainties of these mass estimates have been substantially underestimated.  Applying the same procedure to the well-studied Fornax dwarf spheroidal would conclude that it has an "over massive" dark halo or, alternatively, that it lacks DM.  Corroborate the argument with self-consistent mocks of tracers in cosmological haloes, showing that masses from samples with 5<N<10 tracers (assuming no measurement errors) are uncertain by at least an order of magnitude.  Finally, estimate masses of UDGs with HST imaging in Coma and show that their recent mass measurements (with adequate uncertainties) are in agreement with that of other dwarfs, such as Fornax.  Also provide bias and scatter factors for a range of sample sizes and measurement errors, of wider applicability.