Day 872

Wednesday.


1504.05183
Comparison of weak lensing by NFW and Einasto halos and systematic errors
Sereno, Fedeli, Moscardini

Recent N-body sims have shown that Einasto radial profiles provide the most accurate description of DM haloes.  Predictions based on the traditional NFW functional form may fail to describe the structural properties of cosmic objects at the % level required by precision cosmology.  Compute the systematic errors expected for WL analyses of clusters of galaxies if one wrongly models the lens properties.  Even though the NFW fits of observed tangential shear profiles can be excellent, virial masses and concentrations of very massive halos (>~1e15 Msun/h) can be over- and underestimated by ~10%, respectively.  Misfitting effects also steepen the observed mass-concentration relation, in a way similar to that seen in multi wavelength observations of galaxy groups and clusters.  Einasto lenses can be distinguished from NFW haloes either with deep observations of very massive structures (>~1e15 Msun/h) or by stacking the shear profiles of thousands of group-sized lenses (~1e14 Msun/h).


1504.05186
Early structure formation from primordial density fluctuations with a blue-tilted power spectrum
Hirano, Zhu, Yoshida, Spergel, Yorke

CMB provides strong constraints on the amplitude of primordial PS (PPS) on scales larger than 10Mc, the amplitude of the PS on sub-galactic length scales is much more poorly constrained.  Study early structure formation in a cosmo model with a blue-tilted PPS.  Assume that the standard scale-invariant PPS is modified at small length scales as P(k)~k^m_s with m_s>1.  Run a series of cosmo hydro is to examine the dependence of the formation epoch and the characteristic mass of primordial stars on the tilt of the PPS.  In models with m_s>1, SF gas clouds are formed at z>100, when formation of H2 molecules is inefficient because the intense CMB radiation destroys chemical intermediates.  Without efficient coolant, the gas clouds gravitationally contract while  keeping a high temperature.  The protostars formed in such "hot" clouds grow very rapidly by accretion to become extremely massive stars that may leave massive BHs with a few hundred Msun at z>100.  The shape of the PPS critically affects the properties and the formation epoch of the fist generation of stars.  Future experiments of the CMB polarization and the spectrum distortion may provide important information on the nature of the first stars and their formation epoch, and hence on the shape of the small-scale PS.


1504.05209
Stellar and quasar feedback in concert: effects on AGN accretion, obscuration, and outflows
Hopkins, Torrey, Faucher-Giguere, Quataert, Murray

Use hydro sims to study the interaction of AGN feedback mechanisms (accretion-disk winds & Compton heating) with a multi-phase ISM.  The ISM model includes radiative cooling and explicit stellar feedback from multiple processes.  Simulate radii ~0.1-100 pc around around an isolated (non-merging) BH.  These are the scales where the accretion rate onto the BH is determined and where AGN-powered winds and radiation couple to the ISM.  The primary results include: (1) The BH accretion rate on these scales is determined by exchange of angular momentum between gas and stars in gravitational instabilities.  This produces accretion rates of ~0.03-1 Msunyr, sufficient to power a luminous AGN.  (2) the gas disk in the galactic nucleus undergoes an initial burst of SF followed by several Myrs where stellar feedback suppresses the SFR per dynamical time.  (3) AGN winds injected at small radii with momentum fluxes ~L/c couple efficiently to the ISM and have a dramatic effect on the ISM properties in the central ~100 pc.  AGN winds suppress the nuclear SFR by a factor of ~10-30 and the BH accretion rate by a factor of ~3-30.  They increase the total outflow rate from the galactic nucleus by a factor of ~10. The latter is broadly consistent with observational evidence for galaxy-scale atomic and molecular outflows driven by AGN rather than SF.  (4) In simulations that include AGN feedback, the predicted column density distribution towards the BH is reasonably consistent with observations, whereas absent AGN feedback, the BH is isotropically obscured and there are not enough optically-thin sight lines to explain observed Type I AGN.  A 'torus-like' geometry arises self-consistently because AGN feedback evacuates the gas in the polar regions.


1504.05249
SLoWPoKES-II: 100,000 wide binaries identified in SDSS without proper motions
Dhital, West, ... et al

Present catalog of low-mass visual binaries identified from SDSS by matching photometric distances.  The candidate pairs are vetted by comparing the stellar information.  The candidate pairs are vetted by comparing the stellar density at their respective Galactic positions to MC realizations of a simulated MW.  In this way, able to identify large numbers of bona fide wide binaries without need of proper motions.  105k visual binaries with angular separations of ~1-20" were identified, each with a probability of chance alignment of <5%.  This is the largest catalog of bona fide wide binaries to date, and it contains a diversity of systems --- in mass, mass ratios, binary separations, metallicity, and evolutionary states---that should facilitate follow-up studies to characterize the properties of M dwarfs and white dwarfs. There is a subtle but definitive suggesting of multiple populations in the physical separation distribution, supporting earlier findings.  Suggest that wide binaries are comprised of multiple populations, most likely representing different formation modes.  There are 141 M7 or later wide binary candidates, representing  a 7-fold increase in the number currently known.  These binaries are too wide to have been formed via the ejection mechanism.  Finally, found a 6% of spectroscopically confirmed M dwarfs are not included in the SDSS STAR catalog; they are misclassified as extended sources due to the presence of nearby or partially resolved companion.  The SLoWPoKES-II catalog is publicly available to the entire community on the WWW via the Filtergraph data visualization portal.


1504.05456
Galaxy alignments: an overview
Joachimi, Cacciato, Kitching, ... et al

The alignment between galaxies, their underlying matter structures, and the cosmic web constitute vital ingredients for a comprehensive understanding of gravity, the nature of matter, and structure formation in the Universe.  Provide an overview on the state of the art in the study of these alignment processes and their observational signatures, aimed at a non-specialist audience.  The development of the field over the past one hundred years is briefly reviewed.  Also discuss the impact of galaxy alignments on measurements of WL, and discuss avenues for making theoretical and observational progress over the coming decade.


1504.05465
Galaxy alignments: observations and impact on cosmology
Kirk, Brown, Hoekstra, Joachimi, et al

Galaxy shapes are not randomly oriented, rather they are statistically aligned in a way that can depend on formation environment, history and galaxy type.  Studying the alignment of galaxies can therefore deliver important information about the astrophysics of galaxy formation and evolution as well as the growth of structure in the Universe.  In this review paper, summarize key measurements of IA, divided by galaxy type, scale and environment.  Also cover the statistic and formalism necessary to understand the observations in the literature.  With the emergence of WL as a precision probe of cosmo, galaxy alignments took on an added importance because they can mimic cosmic shear, the effect of gravitational lensing by LSS on observed galaxy shapes.  This makes IA an important systematic effect in WL studies.  Quantify the impact of IA on cosmic shear surveys and finish by reviewing practical mitigation techniques which attempt to remove contamination by IA.


1504.05546
Galaxy alignments: theory, modeling and simulations
Kiessling, Cacciato, Joachimi, et al

The shapes of galaxies are not randomly oriented on the sky.  During the galaxy formation and evolution process, environment has a strong influence, as tidal gravitational fields in LSS tend to align the shapes and angular momenta of nearby galaxies.  Additionally, events such as galaxy mergers affect the relative alignments of galaxies throughout their history.  These "intrinsic galaxy alignments" are known to exist, but are still poorly understood.  This review will offer a pedagogical introduction to the current theories that describe IA, including the apparent difference in IA between early- and late-type galaxies and the latest efforts to model them analytically.  It will then describe the ongoing efforts to simulate IA using both N-body and hydrodynamic sims.  Due to the relative youth of this field, there is still much to be done to understand intrinsic galaxy alignments and this review summaries the current state of the field, providing a solid bases for future work.