Day 375

Monday.

1302.5420
A comparative study of AGN feedback algorithms
Wurster, Thacker

5 distinct approaches to modeling AGN feedback within gravito-hydrodynamic simulations of major mergers of MW-sized galaxies, constrain differences to only be between AGN feedback models: use same IC and SF algorithm.  5 key aspects: to BH accretion rate, energy feedback rate and method, particle accretion algorithm, and BH merger algorithm.  All models follow different accretion histories, with accretion rates that differ by up to 3 orders of magnitude at any given time.  Consider models with either thermal or kinetic feedback, with the associated energy deposited locally around the BH.  Each feedback algorithm modifies the gas properties near the BH to different extents.  THe particle accretion algorithms usually (but not always) maintain good agreement between the mass accreted by Mdot/dt and the mass of gas particles removed from the simulation.  The BH advection algorithms dampen inappropriate dragging of the BHs by 2-body interactions.  Advecting the BH a limited distance based upon a local mass distribution has many desirable properties.  The BHs merger when given criteria are met, and find a range of merger times for different criteria.  Using the M_BH-sigma relation as a diagnostic of the remnants yields 3 models that lie within the 1 sigma scatter of the observed relation and two that fall below it.  The wide variation in accretion behaviours of the models reinforces the fact that there remains much to be learnt about the evolution of galactic nuclei.  

1302.5424
The binodal metallicity distribution of the cool circumgalactic medium at z<1
Lehner ... Prochaska et al

Assess the metal content of CGM about galaxies at z<1 using 27 HI-selected LLS, observed in absorption against BG QSOs by HST COS.  The N(HI) selection avoids metallicity biases inherent in many previous studies of low-z CGM.  Compare the column densities of weakly ionized metal species to N(HI) in the strongest HI component of each absorber.  Find taht the metallicity distribution of the LLS (and hence the cool CGM) is bimodal with metal-poor and metal-rich branches peaking at 1.6 and -0.4 (2.5% and 40% solar metallicities).  The cool CGM probed by these LLS is predominantly ionized.  The metal-rich branch of the population likely traces winds, reycled outflows, and tidally stripped gas; the metal-poor branch has properties consistent with cold accretion streams thought to be a major source of fresh gas for SF galaxies.  Both branches have a nearly equal number of absorbers.  Results thus demonstrate that there is a significant mass of previously undiscovered cold, metal-poor gas in the CGM of z<1 galaxies.

1302.5444
Why multi-tracer surveys beat cosmic variance
Abramo, Leonard

Enhancement drives from comparing the relative clustering between different tracers of lSS.  Present simple but fully generic expression for the Fisher information matrix of surveys with any discrete number of tracers, and show that the enhancement of the constraints on bias-sensitive parameters are a straightforward consequence of this multi-tracer Fisher matrix.  The relative clustering amplitudes between tracers are eigenvectors of the multi-tracer Fisher matrix.  The relative clustering amplitudes between tracers are eigenvectors of this multi-tracer Fisher matrix.  The diagnalized matrix clearly shows that while the effective volume is bounded by the physical volume of the survey, the relational information between species is unbounded.  The gain by combining multiple tracers is highest at low z, which can be x3 in z-space distortion parameter, and x5 for local non-Gaussianity parameter.  Radial and angular distance determinations may also benefit from the multi-tracer approach.

1302.5462
Dark matter annihilation energy output and its effects on the high-z IGM
Araya, Padilla

DM self annihilation as energy injection mechanism to the IGM / medium within particular DM halos.  Consider two WIMP candidates (SUSY neutralino, KK excited state of B EW boson).  Compute the energy output (or Luminosity) of DM haloes due to annihilations, and compare the obtained luminosities with the standard AGN feedback process, concluding that DM annihilation does not provide the necessary output as to constitute an important feedback mechanism.  Then compute the energy injection rate per baryon of annihilations on the IGM, in order to calculate the effects that it has on its temperature and ionization fraction.  Find significant deviations in the evolutions of the temperature and ionization fraction of the IGM in scenarios that take into account the clustering of DM at all levels (eg a 1TeV WIMP may, for example, maintain the temperature of the IGM on the ~100K level, or contribute to the ionization fraction to 1e-2.  Conclude: although DM annihilation can have a significant impact on the properties of the IGM, it cannot be regarded as an alternative reionization scenario.  ...

1302.5482
Multipole gravitational lensing and high-order perturbations on the quadrupole lens
Chu, Lin, Li, Kang

Decompose lens into multipole components.  

1302.5655
Stochastic bias of color-selected BAO tracers by joint clustering--weak-lensing analysis
Comparat, Jullo, Kneib, ... Erben, Ilbert, ... Mostek, Schlegel, ... et al

BAO at high z (0.6<z<1.7), determine bias and HOD model parameters.  Also use aperture-mass statistic to extrac the galaxy bias and cross-correlation coefficient and compare to the HOD prediction.  Apply this analysis on data set composed of photometry of the deep co-addition on SDSS stripe 82, CFHT, WISE IR W1.  Selection at z=0.5 is in agreement with previous studies on the tracer; confirm that the brightest galaxy populations selected are strongly biased (b>1.5), but are limited by current data-sets depth to derive precise values of the galaxy bias.  

1302.5663
Magnetic fields in galaxies
Beck, Wielebinski

Ionized matter generates B-field easily, but lack of magnetic monopoles makes it hard to destroy B-fields.  B-fields observed everywhere.  Radio observations in particular increased info on B-fields.  Some B-fields only partly related to objects observed in other wavelengths.  LSS of MW B-field still under debate.  External galaxies well explained by field amplification and ordering via the dynamo mechanism.  The measured B-field strengths, similarity of field patterns and flow patterns of diffuse ionized gas give strong indication that galactic B-fields are dynamically important.  May affect the formation of spiral arms, outflows, and the general evolution of galaxies.  In spite of the increasing knowledge, the questions on origin and evolution of B-fields, or the existence of large-scale intergalactic fields remain unanswered.  Upgrade existing instruments!