1901.00900
High-precision dark halo viral masses from globular cluster numbers: implications for globular cluster formation and galaxy assembly
Burkert, Forbes
Confirm that the number of globular clusters (GC) N_GC is an excellent tracer of their host's dark halo viral mass M_vir. The simple linear relation M_vir=5e9Msun x N_GC fits the data perfectly from M_vir=1e10 Msun to M_vir=2e15 Msun. This result is independent of galaxy morphology and even extends statistically into the dwarf galaxy regime with M_vir=1e8-1e10 Msun. As this correlation does not depend on GC mass, it is ideally suited for high-precision determinations of M_vir. The linearity is most simply explained as a result of hierarchical cosmological merging of a high-z halo seed population that hosted on average one GC per 5e9 Msun x (1-eta_smooth) of DM mass. Here eta_smooth ~ 0.9 denotes the fraction of the present-day dark halo mass that was accumulated by smooth accretion. Strong secular evolution of the GC system requires significant fine-tuning as processes like GC disruption generate non-linear correlations that are not observed. The cosmological merging scenario also implies a strong decline of the scatter in N_GC with increasing viral mass (delta N_GC)/N_GC ~ M_vir^{-1/2} in contrast with the observations that show a roughly constant scatter, independent of viral mass. This discrepancy can be explained if errors in determining viral masses from kinematical tracers and gravitational lensing are of the order of a factor of 2. Gas in dwarf satellite galaxies pose a serious problem for high-z GC formation scenarios. The dark halo masses of dwarf galaxies hosting GCs therefore might have been one order of magnitude larger than currently estimated.
1901.01410
Making the heaviest elements in the Universe: a review of the rapid neutron capture process
Cowan, et al
The production of about half the heavy elements beyond Fe and Ni is assigned the rapid neutron capture process (r process). The full understanding faces two open questions. (a) The nucleosynthesis path runs close to the neutron-drip line, where presently only limited experimental information is available, and one has to rely on theoretical predictions. (b) While for many years the occurrence of the r process has been associated with supernovae recent studies have cast substantial doubts on this environment. Possibly only a weak r process, not producing the third r-process peak, can be accounted for, while much more neutron-rich conditions are likely responsible for the majority of the heavy r-process elements. Possible scenarios are the mergers of neutron stars (recently observed, GW170817) but include als rare classes of SNe/hypernovae with polar jet ejecta (and possibly also accretion disk outflows in case of BH formation) related to the collapse of fast rotating massive stars with high B fields. The composition of the ejecta from each event determines the temporal evolution of the r-process abundances during the "chemical" evolution of the Galaxy. Stellar r-process abundance observations, have provided insights into, and constraints on the frequency of and conditions in the responsible stellar production sites. These observations, increasingly more precise due to improved experimental atomic data and high resolution observations, have been particularly important in defining the heavy element abundance patterns of the old halo stars, and the nature of the earliest nucleosynthesis in the Galaxy. Combining new results and important breakthroughs in the related nuclear, atomic and astronomical fields of science, the review attempts to provide an answer to the question "How Were the Elements from Fe to U made?"
1901.01540
First measurement of the Hubble constant from a dark standard siren using the Dark Energy Survey galaxies and the LIGO/Virgo binary-black-hole merger GW170814
The DES Collaboration, the LIGO Scientific Collaboration, the Virgo Collaboration, et al
Present a multi-messenger measurement the Hubble constant H0 using the binary BH merger GW170814 as a standard siren, combined with a photometric redshift catalog from the DES. The luminosity distance is obtained from the gravitational wave signal detected by the LIGO/VIRGO Collaboration (LVC) on 2017 August 14, and the z information is provided by the DES Y3 data. BH mergers such as GW170814 are expected to lack bright EM emission to uniquely identify their host galaxies and build an object-by-object Hubble diagram. However, they are suitable for a statistical measurement, provided that a galaxy catalog of adequate depth and z completion is available. Here, present the first Hubble parameter measurement using a BH merger. The analysis results in H0 = 75.2+39.5-32.4 km/s/Mpc, which is consistent with both SN Ia and CMB measurements of the Hubble constant. The quoted 68% credible region comprises 60% of the uniform prior range [20,140] km/s/Mpc. This result shows that even a single dark siren can provide a constraint on the Hubble constant, albeit a weak one. Future combinations of many sirens will lead to improved constraints. A multifold increase in the LVC event detection rate is expected in the coming years, and this bodes will since future combinations of many additional sirens will lead to improved constraints.
1901.01581
Unraveling the Universe with DESI
Vargas-Magana, et al
DESI is a stage IV ground-based DE experiment planned to begin operations in 2020. In this article, provide a short review of DESI presented during the conference Recontres de Moriond 2018. DESI will use 4 different tracers for mapping the universe: from z=0.05 up to 1.7 with galaxies and from 2.1 to 3.5 using quasars. DESI will measure a total of 35M spectra covering regions of universe never explored before, providing a map of large scale structure that will enable major advances in the investigation of cosmic acceleration. The key science goals for DESI are to constrain DE and potential deviations of GR using 2 complementary observables: the BAO and RSD. Additional science goals, such as constraining the sum of neutrino masses and inflation, are expected with the baseline project. DESI installation started on Feb 2018 and the current construction of the instrument is on track. The imaging surveys that will serve to determine the targets are currently in the final stages, having achieved 80% completion, and are expected to be finalized by the end of 2018. The DESI collaboration is actively preparing for survey operations and science analysis, to be ready for the fist light in Jan 2020.
1901.01818
The peculiar velocity field up to $z /sim 0.05$ by forward-modeling Cosmicflows-3 data
Graziani, et al
A hierarchical Bayesian model is applied to the Cosmicflows-3 catalog of galaxy distances in order to derive the peculiar velocity field and distribution of matter within z~0.054. The model assumes the LCDM model within the linear regime and includes the fit of the galaxy distances together with the underlying density field. By forward modeling the data, the method is able to mitigate biases inherent to peculiar velocity analyses, such as the Homogeneous Malmquist bias or the log-normal distribution of peculiar velocities. The statistical uncertainty on the recovered velocity field is about 150 km/s depending on the location. Study systematics coming from the selection function and calibration of distance indicators. The resulting velocity field and related density fields recover the cosmography of the Local Universe which is presented in an unprecedented volume of universe 10x larger than previously reached. This methodology open the doors to reconstruction of initial conditions for larger and more accurate constrained cosmo simulations. This work is also preparatory to larger peculiar velocity datasets coming from Wallaby, TAIPAN or LSST.
1901.01899
Determining the fraction of cosmic-ray protons at ultra-high energies with cosmogenic neutrinos
van Vliet, et al
Cosmogenic neutrinos are produced when UHECRs interact with cosmological photon fields. Limits on the diffuse flux of these neutrinos can be used to constrain the fraction of protons arriving at Earth with energies E_p>~30 EeV, thereby providing constraints on the composition of UHECRs without fully relying on hadronic interaction models. Show to which extent current neutrino telescopes already constrain this fraction of protons and discuss the prospects for next-generation detectors to further constrain it. Additionally, discuss the implications of these limits for several popular candidates for UHECR source classes.
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