Day 520

Tuesday.

1309.7352
Evolution of star clusters in a cosmological tidal field
Rieder, Ishiyama, Langelaan, Makino, McMillan, Zwart

Present a method to couple N-body star cluster simulations to cosmological tidal field: AMSE.  Embed star cluster in the CosmoGrid DM only LCDM simulation; star clusters born at z=10 by selecting a DM particle and initializing a star cluster with 32,000 stars on its location.  Then follow the dynamical evolution of the star cluster within the cosmological environment.  Compare the evolution of star clusters in two MW-sized haloes with a different accretion history.  Mass loss of the star clusters is continuous irrespective of the tidal history of the host halo, but major merger events tend to increase the rate of mass loss.  Between the two, the halo that experienced the larger number of mergers tends to drive a smaller mass loss rate from the embedded star clusters, even though the final masses of both haloes are similar.  Identify two families of star clusters: native (clusters which became part of the main halo before its final major merger event) and immigrant (accreted after this event).  Native clusters tend to evaporate more quickly than immigrant clusters.  Accounting for the evolution of the DM halo causes immigrant star clusters to retain more mass than when the z=0 tidal field is taken as a static potential---due to the weaker tidal field experienced by immigrant star clusters before merging with the larger DM halo.

1309.7353
A tale of two feedbacks: star-formation in the host galaxies of radio-AGN
Karouzos, ... Goto, ...  et al

The nature of the correlation between AGN and SF is under debate.  Radio jets have long been argued to be an ideal mechanism that allows AGN to interact with their host galaxy and regulate SF.  In this context, use a sample of radio sources in the North Ecliptic Pole field to study the nature of the putative link between AGN activity and SF.  This is done by means of SED fitting.  Use the AKARI IR spectral coverage together with ancillary data available in the NEP to build SEDs extending from UV to FIR.  Through SED fitting, constrain both the AGN and host galaxy components.  Find a significant AGN component in the sample of relatively faint radio-sources (<mJy), that increases in power with increasing radio-luminosity.  At the highest radio-luminosities, the presence of powerful jets dominates the radio emission of these sources.  A positive correlation is found between the luminosity of the AGN component and that of SF in the host galaxy, independent of the radio luminosity.  By contrast, for a given redshift and AGN luminosity, find that increasing radio-luminosity leads to a decrease in the sSFR.  The most radio-loud AGN are found to lie on the MS of SF for their respective redshifts.  For the first time, such a two-sided feedback process is seen in the same sample.  Conclude that radio jets do suppress SF in their host galaxies but appear not to totally quench it.  Results therefore support the maintenance nature of "radio-mode" feedback from radio-AGN jets.

1309.7389
Dust properties of Lyman break galaxies in cosmological simulations
Yajima, Nagamine, Thompson, Choi

Dust properties of high-z galaxies still unknown; present theoretical constraints on dust properties in LBGs at z=3 by post-processing a cosmological smoothed particle hydrodynamics simulation with radiative transfer calculations.  Calculate the dust extinction in 2800 DM haloes using the metallicity information of individual gas particles in simulation.  Use only bright galaxies with rest-frame UV magnitude M_1700 < -20 mag, and study the dust size, dust-to-metal mass ratio, and dust composition.  From the comparison of calculated color excess between B and V-band (i.e., E(B-V)) and the observations, constrain the typical dust size, and show that the best-fitting dust grain size is ~0.05 um, which is consistent with the results of the theoretical dust models for SN II.  Simulation with the dust extinction effect can naturally reproduce the observed rest-frame UV LF of LBGs at z=3 w/o assuming an ad hoc constant extinction value.  In addition, in order to reproduce the observed mean E(B-V), find that the dust-to-metal mass ratio needs to be similar to that of the local galaxies, and that the graphite dust is dominant or at least occupy half of dust mass.

1309.7571
Planetary influence on the young Sun's evolution: the solar neutrino probe
Lopes, Silk

Observations of solar twin stars with planetary systems like the Sun have uncovered that these present a peculiar surface chemical composition.  This is believed to be related to the formation of earth-like planets.  This suggests that twin stars have a radiative interior that is richer in heavy elements than their envelopes.  The current standard solar model does not fully agree with the helioseismology data and solar neutrino flux measurements.  In this work, find that this agreement can improve if the Sun has mass loss during the pre-MS [and what about metallicity?], as was previously shown by other groups.  Despite this better agreement, the internal composition of the Sun is still uncertain, especially for elements heavier than He.  With the goal of inferring the chemical abundance of the solar interior, test several chemical compositions.  Found that heavy element abundances influence the sound speed and solar neutrinos equally.  Nevertheless, the CNO (13N, 15O and 17F) neutrino fluxes are the most affected; this is due to the fact that contrarily to proton-proton (pp, pep, 8B and 7Be) neutrino fluxes, the CNO neutrino fluxes are less dependent on the total luminosity of the star.  Furthermore, if the central solar metallicity increase by 30%, as hinted by the solar twin stars observations, this new solar model predicts that 13N, 15O and 17F neutrino fluxes increase by 25%-80% relative to the standard solar model [does this bring to closer agreement with observation??].  Finally, highlight that the next generation of solar neutrino experiments will not only put constraints on the abundances of C, O and N, but will also give some information about their radial distribution.
1309.7588
Using the CMB angular power spectrum to study Dark Matter-photon interactions
Wilkinson, Lesgourgues, Boehm

Interaction scales as the temperature squared, forthcoming data from CMB polarization experiments and Planck could help to constrain and characterize the physics of the dark sector.  This essentially initiates a new type of DM search that is independent of whether DM is annihilating, decaying or asymmetric.  Thus, any CMB experiment with the ability to measure the temperature and/or polarization PS at high l should be able to investigate the potential interactions of DM and contribute to the fundamental understanding of its nature.

1309.7599
Magnetic field dispersion in the neighbourhood of Bok Globules
Rodrigues et al

F in 20 sky regions containing Bok globules (dust-obscured young stellar objects only seen in IR).  The interstellar B-field direction is mapped using optical polarimetry.  These maps are used to estimate the dispersion of the interstellar B-field direction in each region from a Gaussian fit, sigma_B.  In addition to the Gaussian dispersion, a new parameter eta measures the B-field alignment (does not rely on any function fitting).  Statistical tests show that the dispersion of the B-field direction is different in SF globules relative to quiescent globules: the less organized B-fields occur in regions having young stellar objects.

1309.7651
One of the most massive stars in the Galaxy may have formed in isolation
Oskinova, et al

As the title says.  It's the Peony nebular star.

1309.7660
The large-scale distribution of cool gas around luminous red galaxies
Zhu, Ménard, ... Ho, More, et al

Measurement of the correlation function between luminous red galaxies and cool gas traced by Mg II (2796, 2803) absorption, on scales ranging from 30 kpc to 20 Mpc; based on cross-correlating the positions of about one million red galaxies at z~0.5 and the flux decrements induced  in the spectra of about 1e5 BG quasars from the SDSS.  Find that: (i) this galaxy-gas correlation reveals a change of slope on scales of about 1 Mpc, consistent with the expected transition from DM halo dominated environment to a regime where clustering is dominated by halo-halo correlations.  Assuming that, on average, the distribution of Mg II gas follows that of DM up to a gas-to-mass ratio, find the standard halo model to provide an accurate description of the gas distribution over 3 orders of magnitude in scale.  Within this framework, estimate the average host halo mass of luminous red galaxies to be about 1e13.5 M_sun, in agreement with other methods.  Also find the Mg II gas-to-mass ratio around LRGs to be consistent with the cosmic value estimated on Mpc scales.  Combining galaxy-gas correlation and the galaxy-mass correlation function from gg lensing analyses, directly measure the Mg II gas-to-mass ratio as a function of scale and reach the same conclusion.  (ii) From line-width estimates, show that the velocity dispersion of the gas clouds also shows the expected 1- and 2-halo behaviors.  On large scales the gas distribution follows the Hubble flow, whereas on small scales, observe the velocity dispersion of the Mg II gas clouds to be lower than that of collisionless DM particles within the host halo.  This is in line with the fact that cool clouds are subject to the pressure of the virialized hot gas.

1309.7844
Probability distributions of ellipticity
Viola, Kitching, Joachimi

Derive an exact full expression for the 2d probability distribution of the ellipticity of an object measured from data, only assuming Gaussian noise in pixel values.  This is a generalisation of the probability distribution for the ratio of single random variables, that is well-known, to the multivariate case.  This expression is derived within the context of the meausrement of WL from noisy galaxy images.  Find that the third flattening, or epsilon-ellipticity, has a biased maximum likelihood but an unbiased mean; and that the third eccentricity, or normalized polarization chi, has both a biased maximum likelihood and a biased mean.  The very fact that the bias in the ellipticity is itself a function of the ellpiticity requires an accurate knowledge of the intrinsic ellipticity distribution of the galaxies in order to properly calibrate shear measurements.  Use this expression to explore strategies for calibration of biases caused by measurement processes in weak gravitational lensing.  Find that upcoming WL surveys like KiDS or DES require calibration fields of order of several degrees and 1.2 magnitudes deeper than the wide survey in order to correct for the noise bias.  Future surveys like Euclid will require calibration fields of order 40 sq. deg. and several magnitude deeper than the wide survey.  Also investigate the use of the Stokes parameters to estimate the shear as an alternative to the ellipticity.  Find that they can provide unbiased shear estimates at the cost of a very large variance in the measurement.  The python code used to compute the distributions presented in the paper and to perform the numerical calculations are available on request.

1309.7586
A novel SETI strategy targeting the solar focal regions of the most nearby stars
Gillon

One explanation the Fermi paradox: self-replicating probes could have explored the whole Galaxy, and that they are still to be detected.  In this scenario, proposed that probes from neighboring stellar systems could use the stars they orbit as gravitational lenses to communicate efficiently with each other.  Under this hypothesis, a novel SETI approach would be to monitor the solar focal regions of the most nearby stars to search for communication devices.  The envisioned devices are probably not detectable by imagery or stellar occultation, but an intensive multi-spectral monitoring campaign could possibly detect some communication leakages.  Another and more direct option would be to message the focal regions of nearby stars in an attempt to initiate a reaction.