Day 402

Wednesday.


1304.0443
A study of AGN and supernova feedback in simulations of isolated and merging disc galaxies
Newton, Kay

High-res N-body+SPH simulations of isolated MW-like galaxies and major mergers between them: investigate the effect of feedback from both an AGN and SNe on the galaxy's evolution.  Several AGN methods from the literature are used independently and in conjunction with SNe feedback to isolate the most important factors of these feedback processes.  Find that in isolated galaxies, SNe dominate the suppression of SF but the SFR is unaffected by the presence of AGN.  In mergers the converse is true when models with strong AGN feedback are considered, shutting off SF before a starburst can occur.  AGN and SNe simulated together suppress SF only slightly more than if they acted independently.  This low-level interaction between the feedback processes is due to AGN feedback maintaining the temperature of a hot halo of gas formed by SNe.  For each of the feedback processes the heating temperature is the dominant parameter rather than the overall energy budget or timing of heating events.  [yup.]   Find that the BH mass is highly resolution dependent, with more massive BHs found in lower resolution simulations.

1304.0446
HerMES: the contribution to the cosmic infrared background from galaxies selected by mass and redshift
Viero, ... Cooray, et al

Quantify the fraction of CIB that originates from galaxies identified in the UV/optical/NIR by stacking 81k K-selected sources, split according to their rest-frame U-V vs. V-J colors into 72k SF and 9k quiescent galaxies, on maps from Spitzer, Herschel, and AzTEC.  The fraction of the CIB resolved by the catalog is ~50-80% at various wavelengths.  Of that total, about 95% originates from SF galaxies, while the remaining 5% is from apparently quiescent galaxies.  The CIB at lambda < 200 um appears to be sourced predominantly from galaxies at z<1, while at lambda > 200 um the bulk originates from 1<z<2.  Galaxies with stellar masses log(M/Msun=9.5-11 are responsible for the majority of the CIB, with those in the log(M/Msun)=9.5-10 contributing mostly at lambda < 250um, and those in the log(M/Msun)=10.5-11 jointly dominating at lambda>350um.  The contribution from galaxies in the log(M/Msun)=9-9.5 (highest) and log(M/Msun)=11-12 (lowest) stellar mass bins contribute the least, both of order 5%.  The luminosities of the galaxies responsible for the CIB shifts from a combination of "normal" and LIRGs at lambda < 160 um, to being dominated by LIRGs at longer wavelengths.  Stacking analyses were performed using SIMSTACK, a novel algorithm designed to account for possible biases in the stacked flux density due to clustering.  It is made available to the public.

1304.0451
Calcium H & K induced by galaxy haloes
Zhu, Menard

Measurement of the mean density profile of Ca Ii gas around galaxies out to ~200 kpc, traced by Fraunhofer's H & K absorption lines.  The measurement is based on cross-correlating the positions of about one million foreground galaxies at z~0.1 and the flux decrements induced in the spectra of about 1e5 BG quasars from SDSS.  This technique allows tracing of the total amount of Ca II absorption induced by the circumgalactic medium, including absorbers too weak to be detected in individual spectra.  Can statistically measure Ca II rest EWs down to several mA, corresponding to column densities of about 5e1e10/cm2.  Find Ca II column density distribution follows N ~ rp^-1.4 and the mean Ca II mass in the halo within 200 kpc is 5e3 Msun, averaged over the FG galaxy sample with median mass ~1e10.3 Msun.  This is about an order-of-magnitude larger than the Ca II mass in the ISM of MW, suggesting more than 90% of Ca II in the universe is in the circum-and inter-galactic environments.  Measurements indicate that the amount of Ca II in haloes is larger for galaxies with higher stellar mass and higher SFR.  For edge-on galaxies, find Ca II to be more concentrated along the minor axis, i.e., in the polar direction.  This suggests that bipolar outflows induced by SF must have played a significant role in producing Ca II in galaxy haloes.

1304.0455
A highly elongated prominent lens at z=0.87: first strong lensing analysis of El Gordo
Zitrin, Menanteau, Hughes, Coe, Barrientos, Infante, Mandelbaum

SL in cluster El Gordo (z=0.87) in ACS images.  El Gordo is the most massive, hot, X-ray luminous, and bright SZ cluster at z>0.6, and the only 'bullet'-like merging cluster known at these redshifts.  The lens consists of two merging massive clumps, where for a source redshift of z_s~2 each clump exhibits only a small, separate critical area, with a total area of 0.69pm0.11 arcmin^2 over the two clumps.  For a higher source redshift, z_s~4, the critical curves of the two clumps merge together into one bigger and very elongated lens (axis ratio~5.5), enclosing an effective area of 1.44 arcmin^2.  The critical curves continue expanding with increasing redshift so that for high-z sources (z_s>9), they enclose an area of 1.91 arcminsq, and a mass of 6.25e14 Msun.  According to the model, the area of high magnification (mu>10) for such high redshift sources is 0.95 sq arcmin, and the area with mu>5 is 1.92 arcmin sq, making El Gordo a compelling target from the SL regime alone, suggesting a total mass of, roughly, M_200~2.3e15Msun.  The presented mass model could be improved with future HST imaging.

1304.0456
Effects of superstructure environment on galaxy groups
Luparello, Lares, Yaryura, Paz, Padilla, Lambas

Find: group galaxy cross correlations depend only on group properties regardless the groups reside in superstructures.  This indicates that the total galaxy density profile around groups is independent of the global environment.  At a given global luminosity, a proxy to group total mass, groups have a larger stellar mass content by a factor 1.3, a relative excess independent of the group luminosity.  Groups in superstructures have 40 per cent higher velocity dispersions and systematically larger minimal enclosing radii.  Also find that the stellar population of galaxies in groups in superstructures is systematically older as inferred from the spectra Dn4000 parameter.  Although the galaxy number density profile of groups is independent of environment, the SFR and stellar mass profile of the groups residing in superstructures differs from groups elsewhere.  For groups residing in superstructures, the combination of a larger stellar mass content and SFR produces a larger time scale for SF regardless the distance to the group center.  Results provide evidence that groups in superstructures formed earlier than elsewhere, as expected in the assembly bias scenario.

1304.0460
A plateau in the planet population below twice the size of earth
Petigura, Marcy, Howard

Compute the occurrence of planets as a function of planet radius and period, correcting for the detection completeness.  Distribution of planet sizes exhibits a power law rise in occurence from 5.7 Earth-radii down to 2 Earth-radii, as found in Howard et al.  That rise clearly ends at 2 Earth-radii.  The occurrence of planets is consistent with constant from 2 Earth-radii toward 1 Earth-radius.  This unexpected plateau in planet occurrence at 2 Earth-radii suggests distinct planet formation processes for planets above and below 2 Earth-radii.  Find 15% of solar-type stars has a 1-2 Earth-radii planet with P=5-50 days.

1304.0526
On the nature of the local spiral arm of the Milky Way
Xu et al

Parallax measurements of 9 water masers, combined with 21 other from literature, suggest that the Local arm does not have the large pitch angle characteristic of a short spur.  Instead its active star formation, overall length (>5kpc) and shallow pitch angle (~10 degrees) suggest that it is more like the adjacent Perseus and Sagittarius arms.  Find Local arm to be closer to Perseus (contrary to previous studies), suggesting that a branching from the former may be more likely.  An average peculiar motion of near-zero toward both the Galactic center and north Galactic pole, and counter rotation of ~5 km/s were observed, indicating that the Local arm has similar kinematic properties as found for other major spiral arms.

1304.0560
How large is the contribution of cosmic web to $\Omega_\Lambda$ ? A preliminary study on a novel inhomogeneous model
Viaggiu, Montouri

Recent proposal: a generalization (LambdaFB model) of the Fractal Bubble model, which accounts for LSS in GR.  The LFB model is an evolution of the FB model, and includes in a consistent way a description of inhomogeneous matter distribution and a Lambda term.  Analyse the LFB model focusing on the relation between cosmological parameters.  The main results is the consistency of LCDM model values for Omega_Lambda0 (~0.7) and Omega_k0 (|Omega_k0|<0.01) with a large fraction of voids.  This allows to quantify to which extent the inhomogeneous structure could account for Lambda constant consistently with standard values of the other cosmological parameters.

1304.0577
Dimensionless constants and cosmological measurements
Rich

Generally admitted that only dimensionless combinations of constants have physical significance; time dependence of these constants needs to be separated from the effects of cosmological parameters; latter can be eliminated by using pairs of redundant measurements; use BAO and SNe.  Distances between co-moving points expand following the same function of time that governs the redshift of photon wavelengths--yielding information only on dimensionless combinations of constants.

1304.0585
Structure finding in cosmological simulations: the state of affairs
Knebe et al

Finding objects ("halo finders") in cosmic structure formation simulations.  Comparison of many methods, brief summary.  Investigate the (possible) origin of any deviations across finders.  Different codes find different numbers of objects leading to a scatter of up to 20% in the halo mass and Vmax function, but also the particulars of those objects that are identified by all finders differ.  Discuss relevance and implications of the scatter across different codes for other fields such as SAM, gravitational lensing, and observables in general.  IN summary, conclude that while the majority of codes give results with a scatter below 1% (at least for the most basic halo properties) once a particular definition has been specified, the residual differences for more complex quantities such as spin parameter are more sensitive to the particular implementation of the initial particle collection.  Caution any user of halo finders and their catalogues to not use the data blindly but to consider the mode of operation and definitions used during its generation.

1304.0686
Strong lensing mass of a galaxy cluster discovered by the Planck satellite
Sifon et al

As the title says: massive z=0.5 cluster (SZ detected, X-ray verified), with prominent z=1.6 lens galaxy.

1304.0689
The crab nebula and the class of Type IIn-P supernovae caused by sub-energetic electron capture explosions
Smith

Several properties of Crab best suited to Type IIn-P explosions (probably arise from relatively low-energy, 1e50 erg, explosions with low 56Ni yield resulting from electron-capture SNe, but their high luminosity and Type IIn spectra dominated by shock interaction with CSM [?]).  After about 120 days, nearly all of the mass in the CSM and ejecta ends up in a slow dense shell.  In the proposed scenario, this thin shell for SN 1054 is accelerated by the growing pulsar wind nebula, producing the complex network of filaments seen today.There is no need to invoke the invisible fast SN envelope hypothesized to reside outside the Crab.  SNeIIn-P explain several observed features of the Crab: (1) No blast wave or rapidly expanding SN envelope outside the filaments, (2) a total mass of 5 Msun swept up in a thin shell, (3) a high peak luminosity despite the low kinetic energy, and (4) chemical abundances consistent with an 8-10 Msun star and low 56Ni yield.  A number of other implications are discussed, concerning other plerionic remnants, dust in the Crab filaments, diversity in the initial masses of SNe IIn, and an association between ecSNe and SN impostors.  This model predicts that if light echoes from SN1054 are discovered, they will be consistent with a Type IIn-P spectrum.