Day 385

Monday.  Tuesday already.  Wednesday.

1303.1817
The vast thin plane of M31 co-rotating dwarfs: an additional fossil signature of the M31 merger and of its considerable impact in the whole Local Group
Hammer, Yang, ... Kroupa, et al

Vast thin disk of satellites (VTDS) around M31 and unexpected proximity of Magellanic clouds (MCs) and another vast polar structure (VPOS) which is almost perpendicular to our Galaxy disk---these pose new challenges for the understanding of the LG properties.  Find: VTDS plan coincides with several stellar, tidally-induced streams in the outskirts of M31, and that its velocity distribution is consistent with that of the Gian Stream (GS); suggestive of a common physical mechanism, likely linked to merger tidal interactions; similar argument may apply to the VPOS at the MW location.  The VTDS is pointing towards the MW, being almost perpendicular to the MW disk, as the VPOS is.  Compare these properties to the modeling of M31 as an ancient, gas-rich major merger, which has been successfully used to predict the M31 substructures and the GS origin.  Find that without fine tuning, the induced tidal tails are lying in the VTDS plane, providing a single and common origin for many stellar streams and for the vast stellar structures surrounding both the MW and M31.  The model also reproduces quite accurately positions and velocities of the VTDS dSphs.  Conjecture leads to a novel interpretation of the LG past history, as a gigantic tidal tail due to the M31 ancient merger is expected to send material towards the MW, including the MCs.  Such a link between M31 and the MW is expected to be quite exceptional, though it may be in qualitative agreement with the reported rareness of fMW-MCs systems in nearby galaxies.

1303.1819
The X-ray properties of optically selected clusters of galaxies
Hicks ... Gladders, Bohringer, Yee, Yan, ... et al

Chandra and Suzaku x-ray observations of 9 clusters of 0.16<z<0.42 from RCS.  Fit surface brightness to beta models, determine gas mass, get integrated spectra from R2500, X-ray temperatures and luminosities are inferred.  The Lx-Tx relationship expected from self-similar evolution is tested; find that optically selected clusters are systematically less luminous than X-ray selected clusters of similar X-ray temperature at both moderate and high-z [what could this mean?  More optical luminous, less x-ray luminous?].  Unable to constrain evolution in the Lx-Tx relation, but find consistent with no evolution.  Investigate selection effects, compare the x-ray properties of sample to those of clusters in the representative X-ray selected REXCESS sample, also determined within R2500.  Find that while RCS cluster x-ray properties span the entire range of those of massive clusters selected by other methods, their average X-ray properties are most similar to those of dynamically disturbed X-ray selected clusters.  This similarity suggests that the true cluster distribution might contain a higher fraction of disturbed objects than are typically detected in X-ray selected surveys.

1303.1874
Morphologies of low-redshift AGN host galaxies: what role does AGN luminosity play?
Villforth, ... Koekemoer, ... CANDELS collaboration

Mergers of galaxies suspected to trigger AGN, but AGN host galaxies often show no enhanced signs of interaction.  Possible explanation: mergers only are of importance for triggering AGN but only dominate at the very high luminosity end.  Compare morphologies of AGN hosts to a matched control sample and particularly study the role of AGN luminosity.  Find no enhanced merger rates in AGN hosts and also find no trend for stronger signs of disturbance at higher AGN luminosities.  Can exclude a strong connection between AGN and mergers over a wide range of AGN luminosities.

1303.1937
The large-scale Quasar-Lyman \alpha\ Forest cross-correlation from BOSS
Font-Ribera, ... et al

Measure the large-scale cross-correlation of quasars with Lya forest in z-space, using 60k quasar spectra from DR9.  The cross-correlation is detectd over a wide range of scales, up to comoving separations of 80 Mpc/h.  For r>15 Mpc/h, show that the cross-correlation is well fitted by the linear theory prediction for the mean overdensity around a quasar host halo in the standard LCDM model, with the z distortions indicative of gravitational evolution detected at high confidence.  Using previous determinations of the Lya forest bias factor from autocorrelation, infer the quasar bias factor to be b_q=3.64 pm 0.15 at a mean z = 2.38, in agreement with previous measurements from the quasar auto-correlation.  Also obtain a new estimate of the Lya forest z distortion factor, beta_F=1.1 pm 0.15, slightly larger than but consistent with the previous measurement from the Lya forest autocorrelation.  The simple linear model fails at separations r<15 Mpc/h, and we show that this may reasonably be due to the enhanced ionization due to radiation from the quasars.  Also provide the expected correction that the mass overdensity around the quasar implies for measurement of the ionizing radiation bg from the LoS proximity effect.

1303.1965
Detection of the large scale alignment of massive galaxies at z~0.6
Li, Jing, Faltenbacher, Wang

Detection of the alignment between galaxies and large-scale structure at z~0.6 based on the CMASS galaxy sample from BOSS DR9.  Use 2 statistics:  1) alignment 2-pt correlation function which probes the dependence of galaxy clustering at a given esparation in z s-ace on the projected angle (theta_p) between the orientation of galaxies and the line connecting to other galaxies, and 2) the cos(2theta)-statistic which estimates the average of cos(2theta_p) for all correlated pairs at given separation s.  Find significant alignment signal out to about 70 Mpc/h in the alignment correlation function, while the signal extends up to 120 Mpc/h when probed with the cos(2theta)-statistics.  Applications of the same statistics to DM haloes of mass above 1e12 Msun/h in a large cosmo simulation show similar scale-dependent alignment signals to the observation, but with hgiher amplitudes at all scales probed.  Show that this discrepancy may be partially explained by a misalignment angle between central galaxies and their host haloes, though detailed modeling is needed in order to better understand the link between the orientations of galaxies and host haloes.  In addition, find systematic trends of the alignment statistics with the stellar mass of the CMASS galaxies.  More massive galaxies are more strongly aligned with the large-scale structure and the effect extends to larger scales at higher masses.

1303.2056
Orbital anisotropy in cosmological haloes revisited
Wojtak, Gottloeber, Klypin

Velocity anisotropy of particles inside DM haloes required for the accurate modeling of mass profiles of galaxies and clusters of galaxies.  Typically measured using the ratio of the radial-to-tangential velocity dispersions at a given distance from the halo centre.  This measure is insufficient to describe the dynamics of realistic haloes, which are typically quite elongated.  Studying the velocity distribution in massive DM haloes in cosmological sims, find that in the inner parts of the haloes the local velocity ellipsoids are strongly aligned with the major axis of the halo, the alignment being stronger for more relaxed haloes.  In the outer regions of the haloes, the ligament becomes gradually weaker and the orientation is more random.  The two distinct regions of different degree of the alignment coincide with 2 characteristic regimes of the DM density profile: shallower and steeper than rho r^-2.  This alignment of the local velocity ellipsoids requires reinterpretation of features found in measurements based on the spherically averaged ratio of the radial-to-tangential velocity dispersions.  In particular, show that the velocity distribution in the central halo regions is highly anisotropic.  For cluster-size haloes with mass 1e14-15 Msun/h, the velocity anisotropy along the major axis is nearly independent of radius and is equal to beta=1-sigma^2_perp / sigma^2radial = 0.4, which is significantly larger than the previously estimated spherically averaged velocity anisotropy.  The alignment of density and velocity anisotropies, and the radial trends may also have some implications for the mass modeling based on kinematical data of such objects as galaxy clusters or dwarf spheroidals, where the orbital anisotropy is a key element in an unbiased mass inference.

1303.2081
Constraints on neutrino mass from Sunyaev--Zeldovich cluster surveys
Mak, Pierpaoli

Forecast on the capability of the number count and PS measured from ongoing and future SZ cluster surveys, combined with CMB to constrain total neutrino mass in flat LCDM.  Use self-calibration for the mass-observable scaling relation, and evaluate constraints for the SPT and SPTPol, Planck, ACTPol surveys.  Find that a sample of ~1k clusters obtained from Planck cluster, plus extra info from CMB lensing could tighten the current upper bound on the sum of neutrino masses to sigma_mnu=0.17 eV at 68% CL.  Analysis shows that cluster number counts and PS provide complementary constraints and as a result they help reduce the error bars on mnu by a factor of 4-8 when both probes are combined.  Also show that the main strength of cluster measurements in constraining mnu is when good control of cluster systematics is available.  When applying a weak prior on the mass-observable relations, obtain sigma_mnu=0.48 eV using cluster only, and 0.08 eV with CMB (a S/N~4 detection for mnu>0.3eV) .  

1303.0181
Three classes of Newtonian three-body planar periodic orbits
Suvakov, Dmitrasinovic

Results of numerical search of periodic orbits of 3 equal masses moving in a plane under the influence of Newtonian gravity with zero angular momentum.  Use a topological method to classify periodic 3-body orbits into families, which fall into 4 classes, with all 3 previously known families belonging to one class.  The classes are defined by the orbits geometric and algebraic symmetries.  In each class, present a few orbits initial conditions, 15 in all; 13 of these corresponds to distinct orbits.

1303.2432
The SDSS galaxy angular two-point correlation function
Wang, Brunner, Dolence

SDSS DR7 2pt angular correlation function, by apparent magnitude bins [why?].  Systematics checked: seeing, extinction, survey uniformity.  Use observations with seeing < 1.5", and r_extinction < 0.13 mag, smaller than previous results.  Confirm that photometry is minimally affected by stripe geometry.  THe 2-pt angular correlation function can be described by a power law, with ~theta^-0.72, voer the range 0.005 to 10 degrees.  Similar relation to the 4 magnitude subsamples, in agreement with previous results.  Find systematic signals are well below galaxy angular correlation function for angles less than approximately 5 deg, which limits the modeling of galaxy angular correlations on large scales.  Make available parallelized 2pt correlation code used for analysis.

1302.2463
The shape of dark matter haloes in edge-on galaxies: I. overview of HI observations
Peters, van der Kruit, Allen, Freeman

The shape of the DM halo of galaxies offers clues on the physical nature of DM.  Model the structure and kinematics of the baryons in edge-on galaxies.  The flaring of the HI disk provides a measure of the vertical force field on that disk.  The rotation curve provides a measure of the horizontal force field.  As the galaxies are at rest, the combination of these two provides all the required ingredients for full hydrostatic models.  Use these models to analyze their potential wells as generated by the DM halo and its shape.  In the first paper, explain this project in detail and present the HI observations of 8 sample edge-on galaxies.  Argue that self-absorption of the HI has significant effect in these galaxies.