Day 1278

Tuesday.


1706.07814
Halo intrinsic alignment: dependence on mass, formation time and environment
Xia et al

In this paper, use high-resolution cosmo sims to study halo IA and its dependence on mass, formation time and LS environment.  In agreement with previous studies using N-body simulations, it is found that massive halos have stronger alignment.  For a given mass, older halos have stronger alignment than younger ones.  By identifying the cosmic environment of halo using a Hessian matrix, find that for a given mass, halos in cluster regions also have a stronger alignment than those in a filament.  The existing theory has not addressed these dependencies explicitly.  In this work, extend the linear alignment model with inclusion of halo bias and find that the halo alignment with its mass and formation time dependence can be explained by halo bias.  However, the model can not account for the environment dependence, as it is found that halo bias is lower in cluster and higher in filament.  The results suggest that halo bias and environment are independent factors in determining halo alignment.  Also study the halo alignment correlation function and find that haloes are strongly clustered along their major axes and less clustered along the minor axes.  The correlated halo alignment can extend to scale as large as 100 Mpc/h where its feature is mainly driven by the baryon acoustic oscillation effect.


1706.07815
MACS J0416.1-2403: impact of line-of-sight structures on strong gravitational lensing modeling of galaxy clusters
Chirivì, Suyu, et al

Exploiting the powerful tool of SL by galaxy clusters to study the highest-redshift Universe and cluster mass distributions relies on precise lens mass modeling.  In this work, present the first attempt at modeling line-of-sight mass distribution in addition to that of the cluster, extending previous modeling techniques that assume mass distributions to be on a single lens plane.  Focus on the Hubble Frontier Field cluster MACS J0416.1-2403, and the multi-plane model reproduces the observed image positions with a rms offset of ~0.53".  Starting from this best-fitting model, simulate a mock cluster that resembles MACS J0416 in order to explore the effects of LoS structures on cluster mass modeling.  By systematically analysing the mock cluster under different model assumptions, find that neglecting the lensing environment has a significant impact on the reconstruction of image positions (rms~0.3"); accounting for LoS galaxies as if they were at the cluster redshift can partially reduce this offset.  Moreover, FG galaxies are more important to include into the model than the BG ones.  While the magnification factors of the lensed multiple images are recovered within ~10% for ~95% of them, those ~5% that lie near critical curves can be significantly affected by the exclusion of the lensing environment in the models (up to a factor of ~200).  In addition, LoS galaxies cannot explain the apparent discrepancy in the properties of massive sub halos between MACS J0416.1-2403 and N-body simulated clusters.  Since the model of MACS J0416 with LoS galaxies only reduced modestly the rms offset in the image positions, conclude that additional complexities, such as more flexible halo shapes, would be needed in future models of MACS J0416.


1706.07870
Weak lensing of the Lyman-alpha forest
Croft, Romeo, Metcalf

The angular positions of quasars are deflected by the gravitational lensing effect of FG matter.  The Lyman-alpha forest seen in the spectrum of these quasars is therefore also lensed.  Propose that the signature of WL of the forest could be measured using similar techniques that have been applied to the lensed CMB, and which have also been proposed for application to spectral data from 21cm radio telescopes.  As with 21cm data, the forest has the advantage of spectral information, potentially yielding many lensed "slices" at different redshifts.  Perform an illustrative idealized test, generating a high resolution angular grid of quasars (of order arc minute separation), and lensing the Lyman-alpha forest spectra at z=2-3 using a FG density field.  Find that standard quadratic estimators can be used to reconstruct images of the FG mass distribution at z~1.  There currently exists a wealth of Lya forest data from quasar and galaxy spectral surveys, with smaller sightline separations expected in the future.  Lya forest lensing is sensitive to the FG mass distribution at z intermediate between CMB lensing and galaxy shear, and avoids the difficulties of shape measurement associated with the latter.  With further refinement and application of mass reconstruction techniques, WL of the high-z Lya forest may become a useful new cosmological probe.


1706.07871
The impact of assembly bias on the galaxy content of dark matter halos
Zehavi, et al

Study the dependence of the galaxy content of DM haloes on LS environment and halo formation time using semi-analytic galaxy models applied to the Millennium sim.  Analyze subsamples of halos at the extremes of these distributions and measure the occupation functions for the galaxies they host.  Find distinct differences in these occupation functions.  The main effect with environment is that central galaxies (and in one model also the satellite) in denser regions start populating lower-mass halos.  A similar, but significant stronger, trend exists with halo age, where early-forming haloes are more likely to host central galaxies at lower halo mass.  Discuss the origin of these trends and the connection to the stellar mass -- halo mass relation.  Find that, at fixed halo mass, older halos and to some extent also halos in dense environments tend to host more massive galaxies.  Additionally, see a reverse trend for the satellite galaxies occupation where early-forming halos have fewer satellites, likely due to having more time for them to merge with the central galaxy.  Describe these occupancy variations also in terms of the changes in the occupation function parameters, which can aid in constructing realistic mock galaxy catalogs.  Finally, study the corresponding galaxy auto- and cross-correlation functions of the different samples and elucidate the impact of assembly bias on galaxy clustering.  The realists can inform theoretical models of assembly bias and attempts to detect it in the real universe.