Day 887

Thursday.  Friday.  Monday.


1505.03142
The bulk composition of exo-planets
Gaensicke et al

Priorities in exo-lanet research are rapidly moving from finding planets to characterizing their physical properties.  Of key importance is their chemical composition, which feeds back into the understanding of planet formation.  For the foreseeable future, far-UV spectroscopy of WD's accreting planetary debris remains the only way to directly and accurately measure the bulk abundances of exo-planetary bodies.  The exploitation of this method is limited by the sensitivity of HST, and significant progress will require a large-aperture space telescope with a high-throughput UV spectrograph.


1505.03143
Strangulation as the primary mechanism for shutting down star formation in galaxies
Peng, Maiolino, Cochrane

Local galaxies are broadly divided into two main classes, SF (gas-rich) and quiescent (passive and gas-poor).  The primary mechanism responsible for quenching SF in galaxies and transforming them into quiescent and passive systems is still unclear.  Sudden removal of gas through outflows or stripping is one of the mechanisms often proposed.  An alternative mechanism is so-called "strangulation", in which the supply of cold gas to the galaxy is halted.  Report that the difference between quiescent and SF galaxies in terms of stellar metallicity (i.e., the fraction of metals heavier than He in stellar atmospheres) can be used to discriminate efficiently between the two mechanisms.  The analysis of the stellar metallicity in local galaxies, from 26,000 spectra, clearly reveals that strangulation is the primary mechanism responsible for quenching star formation, with a typical timescale of 4 billion years, at least for local galaxies with a stellar mass less than 1e11 Msun.   This result is further supported independently by the stellar age difference between quiescent and SF galaxies, which indicates that quiescent galaxies of less than 1e11 Msun are on average observed 4 billion years after quenching due to strangulation.


1505.03407
Confirmation of hostless  type Ia supernovae using Hubble Space Telescope Imaging
Graham, Sand, Zaritsky, Pritchet

As the title says.  Results do not preclude the use of SNe Ia as bright tracers of intracluster light at higher redshifts, but that it will be necessary to first refine the constraints on their rate in dwarfs and GCs with deep imaging for a larger sample of low-z, apparently hostless SNe Ia.


1505.03515
Cosmology through arc statistics I: sensitivity to $\Omega_m$ and $\sigma_8$
Boldrin, Giocoli, Meneghetti, Moscradini, Tormen, Biviano

The next generation of large sky photometric surveys will be able to use arc statistics as a cosmological probe.  Study how arc counts are sensitive to the variation of two cosmological parameters:  Omega_m and sigma_8.  Both these parameters influence the abundances of collapsed structures and their internal structure.  Compute the expected number of gravitational arcs with various length-to-width ratios in mock light cones, by varying these cosmo parameters in the ranges 0.1<Omega_m<0.5 and 0.6<sigma_8<1.  Find that the arc counts' dependence on Omega_m and sigma_8 are similar, but not identical, to that of the halo counts.  Investigate how the precision of the constraints on the cosmo parameters based on arc counts depends on the survey area.  Find that the constraining power of arc statistics degrade critically only for surveys covering an area smaller than 10% of the whole sky.  Finally, consider the case in which the search for arcs is done only in frames where galaxy clusters have been previously identified.  Adopting the selection function for galaxy clusters expected to be detected from photometric data in future wide surveys, find that less than 10% of the arcs will be missed, with only a small degradation of the corresponding cosmological constraints.


1505.03639
The brighter-fatter and other sensor effects in CCD simulations for precision astronomy
Walter

Upcoming and current large astronomical survey experiments often seek to constrain cosmo parameters via measurements of subtle effects such as WL, which can only be measured statistically.  In these cases, instrumental effects in the image plane CCDs need to be accounted and/or corrected for in measurement algorithms.  Otherwise, the systematic errors induced in the measurements might overwhelm the size of the desired effects.  Lateral electric fields in the bulk of the CCDs caused by field shaping potentials or space charge build up as the electron in the image are acquired can cause lateral deflation of the electrons drifting in the CCD bulk.  Here, report on the LSST effort to model these effects on a photon-by-photon basis by the use of a Monte Carlo technique.  The eventual goal of this work is to produce a CCD model validated by laboratory data which can then be used to evaluate its effects on weak lensing science.


1505.03655
A weak lensing comparability study of galaxy mergers that host AGNs
Harvey, Courbin

Compare the total mass density profiles of 3 different types of galaxies using WL: (i) 29 galaxies that host quasars at z~0.32 that are in a post starburst (PSQ) phase with high SF indicating recent merger activity, (ii) 22 large elliptical galaxies from the SLACS sample that do not host a quasar at z~0.23, and (iii) 17 galaxies that host moderately luminous quasars at z~0.36 powered by disk instabilities, but with no intense SF.  On an initial test, found no evidence for a connection between the merger state of a galaxy and the profile of the halo, with the PSQ profile comparable to that of the other 2 samples and consistent with the Leauthaud et al. 2014 study of moderately luminous squares in COSMOS.  Given the compatibility of the two quasar samples, combined these and found no evidence for any connection between black hole activity and the dark matter halo.  All three mass profiles remained compatible with isothermality given the present data.


1505.03786
Quasar quartet embedded in giant nebula reveals rare massive structure in distant universe
Hennawi, Prochaska, Cantalupo, Battaia

All galaxies once passed through a hyper luminous quasar phase powered by accretion onto a SMBH.  But because these episodes are brief, quasars are rare objects typically separated by cosmological distances.  In a survey for Lyman-alpha emission at z~2, discovered a physical association of four quasars embedded in a giant nebula.  Located within a substantial overdensity of galaxies, this system is probably the progenitor of a massive galaxy cluster.  The chance probability of finding ta quadruple quasar is estimated to be ~1e-7, implying a physical connection between Lya nebulae and the locations of rare protoclusters.  The findings imply that the most massive structures in the distant universe have tremendous supply (~1e11 Msun) of cool dense (~1 cm^-3) gas, which is in conflict with current cosmo sims.


1505.03865
Galaxy and mass assembly (GAMA): redshift space distortions from the Clipped galaxy field
Simpson, Blake, Peacock, Baldry, Bland-Hawthorn, Heavens, Heymans, Loveday, Norberg

Present the first cosmo measurement derived from a galaxy density field subject to a 'clipping' transformation.  By enforcing an upper bound on the galaxy number density field in GAMA, contributions from the NL processes of virialisation and galaxy bias are greatly reduced.  This leads to a galaxy PS which is easier to model, without calibration from numerical sims.  Develop a theoretical model for the PS of a clipped field in z space, which is exact for the case of anisotropic Gaussian fields.  Clipping is found to extend the applicability of the conventional Kaiser prescription by more than a factor of three in wavenumber, or a factor of thirty in terms of the number of Fourier modes.  By modeling the galaxy PS on scales k<0.3 h/Mpc and density fluctuations delta_g<4, measure the normalized growth rate f*sigma_8(z=0.18) = 0.29±0.10.