1805.02427
Star-galaxy classification in the Dark Energy Survey Y1 dataset
Sevilla-Noarbe, et al
Perform a comparison of different approaches to star-galaxy classification using the broad-band photometric data from Year 1 of DES. This is done by performing a wide range of tests with and without external 'tough' information, which can be ported to other similar datasets. Make a broad evaluation of the performance of the classifiers in two science cases with DES data that are most affected by this systematic effect: LSS and MW studies. In general, even though the default morphological classifiers used for DES Y1 cosmology studies are sufficient to maintain a low level of systematic contamination from stellar mis-classification, contamination can be reduced to the O(1%) level by using multi-epoch and infrared information from external datasets. For MW studies the stellar sample can be augmented by ~20% for a given flux limit. Reference catalogs used in this work will be made available upon publication.
1805.02662
Detecting strongly lensed supernovae at z~5-7 with LSST
Rydberg, et al
Find that LSST main survey could detect ~1-2 lensed Pop III SN but 130-1400 Pop I/II SNe. An alternative deep survey with a one-year cadence could find ~10 Pop III SNe with an 84h exposure and ~50 SNe with a 420h exposure.
1805.01448
The missing satellites of the Magellanic Clouds? Gaia proper motions of the recently discovered ultra-faint galaxies
Kallivayalil, et al
According to LCDM theory, hierarchical evolution should occur on all mass scales, implying that satellites of the MW also once had companions. The recent discovery of several ultra-faint dwarf galaxy candidates in close proximity to the MCs provides a unique opportunity to test this theory. Specifically, proper motions provide a stringent test, because material that is associated with the LMC prior to infall should retain its direction of orbital angular momentum. Present proper motion measurements for the 13 of the 32 newly discovered dwarf galaxy candidates using Gaia DR2. All 13 also have radial velocity measurements. Compare the measured 3d velocities of these dwarfs to those expected at the corresponding distance and location for the debris of an LMC analog in a numerical simulation. Conclude that 4 of these galaxies (Hor1, Car2, Car3 and Hyd1) have come in with the MC system, consituting the first confirmation of the type of satellite infall predicted by LCDM. Ret2, Tuc2 and Gru1 have some velocity components that are not consistent within 3 sigma of the predictions and are therefore less favorable. Hyd2 and Dra2 could be associated with the LCMD and merit further attention. Rule out TUc3, Cra2, Tri2 and Aqu2 as potential members. Of the dwarfs without measured PMs, 6 of them are deemed unlikely on the bases of their positions and distances alone which put them too far from the orbital plane expected for LMC debris (Eri2, Ind2, Cet2, Tri2, Cet3 and Vir1). For the remaining sample use the simulation to predict proper motions and radial velocities, finding that Phx2 has an overdensity of stars in DR2 consistent with this PM prediction. If this radial velocity is confirmed at ~-15 km/s, it is also likely a member.
1805.01421
Concerns about modeling of foregrounds and the 21-cm signal in EDGES data
Hills, et al
Re-analyzed the data in which Bowman+2018 identified a feature that could be due to cosmological 21-cm line absorption in the IGM at z~17. If using exactly their procedures, then find almost identical results, but the fits imply either non-physical properties for the ionosphere or unexpected structure in the spectrum of foreground emission (or both). Furthermore, find that making reasonable changes to the analysis process, e.g., altering the description of the foregrounds or changing the range of frequencies included in the analysis, gives markedly different results for the properties of the absorption profile. Can in fact get what appears to be a satisfactory fit to the data without any absorption feature if there is a periodic feature with an amplitude of ~0.05K present in the data. Believe that this calls into question the interpretation of these data as an unambiguous detection of the cosmo 21-cm absorption signature.
1805.01897
Solar colorna heating by the axion quark nugget dark matter
Raza, van Waerbeke, Zhitnitsky
Astrophysics faces two 80 yr old mysteries: the nature of DM, and the high temperature of the million degree solar corona, radiating an extreme UV (EUV) excess of 1e27 erg/s. The current paradigm is that the corona is heated by hypothetical nano-flares of unknown origin. Recently, in Zhitnitsky 2017 it was suggested that the nano flares can be identified wit the nuggets from the Axion Quark Nugget (AQN) DM model. This model was invented as an explanation of the observed ratio Omega_dark ~ Omega_visible, and has no free parameter other than the Axion mass. It is proposed that the AQN particles moving through the coronal plasma (and annihilating) can both explain the EUV excess and drastic changes of the temperature in the Transition Region. To test this proposal, performed detailed numerical simulations with a realistic AQN particle distribution and physical environment. Remarkably, the calculations predict the correct energy budget for the solar corona, and an energy injection altitude in agreement with the temperature and mass density profile of the solar atmosphere. Therefore, propose that the two 80 yr old mysteries could be two sides of the same coin. Make several predictions based on this proposal that can be tested by the upcoming NASA mission the Parker Solar Probe.
1805.02649
Time evolution of intrinsic alignments of galaxies
Schmitz, Hirata, Blazer, Krause
IA, correlations between the intrinsic shapes and orientations of galaxies on the sky, are both a significant systematic in WL and a probe of the effect of LSS on galactic structure and angular momentum. In the era of precision cosmology, it is thus especially important to model IA with high accuracy. Efforts to use cosmological perturbation theory to model the dependence of IA on the LSS have thus far been relatively successful; however, extant models do not consistently account for time evolution. In particular, advection of galaxies due to peculiar velocities alters the impact of IA, because galaxy positions when observed are generally different from their positions at the epoch when IA is believed to be set. In this work, evolve the galaxy IA from the time of galaxy formation to the time at which they are observed, including the effects of this advection, and show how this process naturally leads to a dependence of IA on the velocity shear. Calculate the galaxy-galaxy-IA bispectrum to tree level (in the linear matter density) in terms of the evolved IA coefficients. Then discuss the implications for WL systematics as well as for studies of galaxy formation and evolution. Find that considering advection introduces non locality into the bispectrum, and that the degree of non-locality represents the memory of a galaxy's path from the time of its formation to the time of observations. Discuss how this result can be used to constraint the redshift at which IA is determined and provide Fisher estimation for the relevant measurements using the example of SDSS-BOSS.
1805.03394
Unidentified quasars among stationary objects from Gaia DR2
Heintz, et al
Apply a novel technique selecting quasar candidates purely as sources with zero proper motions in the Gaia data release 2 (DR2). Demonstrate that this approach is highly efficient toward high Galactic latitudes with <25% contamination from stellar sources. Such a selection technique offers a very pure sample completeness, since all cosmological point sources are selected regardless of their intrinsic spectral properties within the limiting magnitude of Gaia. Carry out a pilot study by defining a sample compiled by including all Gaia-DR2 sources within one degree of the NGP selected to have proper motions consistent with zero within 2-sigma uncertainty. By cross-matching the sample to the optical SDSS and the mid-infrared AllWISE photometric catalogues, investigative the colors of each of the sources. Together with already spectroscopically confirmed quasars, able to determine the efficiency of the selection. The majority of the zero proper motion sources have optical to mid-infrared colors consistent with known quasars. The remaining population may be contaminating stellar sources, but some may also be quasars with colors similar to stars. Spectroscopic follow-up of the zero proper motion sources is needed to unveil such a hitherto hidden quasar population. This approach has the potential to allow substantial progress on many important questions concerning quasars such as determining the fraction of dust-obscured quasars, the fraction or broad absorption line (BAL) quasars, and the metallicity distribution of damped Lyman-alpha absorbers. The technique could also potentially reveal new types of quasars or even new classes of cosmological point sources.
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