Day 394

Monday.

1303.5443
Toward a comprehensive model for feedback by active galactic nuclei: new insights from M87 observations by LOFAR, Fermi and H.E.S.S.
Pfrommer

AGN appears to be critical in balancing radiative cooling of the low-entropy gas at the centers of galaxy clusters and in mitigating the SF of elliptical galaxies.  New observations of M87 enable a comprehensive model for the physical heating mechanism.  Low-frequency radio observations by LOFAR revealed the absence of fossil CR electrons [what the heck is that?] in the radio halo surrounding M87.  This can be resolved by accounting for the CR release from the radio cocoons and the subsequent mixing of CRs with the dense ambient IC gas, which thermalizes the electrons on a timescale similar to the radio halo age of 40 Myrs.  Hadronic interactions of similarly injected CR protons with the ambient gas should produce an observable gamma-ray signal in accordance with the steady emission of the low state [low state?] of M87 detected by Fermi and HESS.  Hence, normalize the CR population to the gamma-ray emission, which shows the same spectral slope as the CR injection spectrum probed by LOFAR, thereby supporting a common origin.  Show that CRs, which stream at the Alfven velocity wrt the plasma rest frame, heat the surrounding thermal plasma at a rate that balances that of radiative cooling on average at each radius, thereby setting the thermal pressure profile equal to that of the streaming CRs.  However, the resulting global thermal equilibrium is locally unstable and allows for the formation of the observed cooling multi-phase medium through thermal instability.  Provided CR heating balances cooling during the emerging "cooling flow", the collapse of the majority of the gas is halted at 1 keV, which is in accordance with x-ray data.  Show that both the existence of a temperature floor and the similar radial scaling of the heating and cooling rates are generic predictions of the CR heating model.


1303.5445
Describing galaxy weak lensing measurements from tenths to tens of Mpc and up to z~0.6 with a single model
Cacciato, van Uitert, Hoekstra

The clustering of galaxies and the matter distribution around them can be described using the halo model complemented with a realistic description of the way galaxies populate dark matter haloes.  This has been used successfully to describe statistical properties of samples of galaxies at z<0.2.  Without adjusting any model parameters, compare the predicted WL signal induced by LRGs to measurements from SDSS DR7 on much larger scales (up to ~90 Mpc/h, h=0.7) and at higher redshift (z~0.4).  Find excellent agreement, suggesting that the model captures the main properties of the galaxy-DM connection.  To extend the comparison to lenses at even higher redshifts, complement the SDSS data with shape measurements from the deeper RCS2, resulting in precise lensing measurements for lenses up to z~0.6.  These measurements are also well described using the same model.  Considering solely these WL meausrements, robustly assess that, up to z~0.6, the number of central galaxies as a function of halo mass is well described by a log-normal distribution with scatter sigma_log(L_c) = 0.146 pm 0.011, in agreement with previous independent studies at lower z. Results demonstrate the value of complementing the information about the properties of the lens galaxies provided by SDSS with deeper, high-quality imaging data.

1303.5490
The supermassive black hole mass - spheriod stellar mass relation for S\'ersic and Core-S\'ersic galaxies
Scott, Graham, Schombert

For core-Sersic galaxies (typically massive and luminous, with M_BH>2e8Msun), find M_BH propto M*_sph^0.97, consistent with other literature relations.  However, for the Sersic galaxies (typically lower masses, M*_sph < 3e10 Msun), find M_BH propto M*_sph^2.22, a dramatically steeper slope that differs by more than 2 std devs.  For Sersic galaxies, M_BH is not a constant fraction of M*_sph.  Sersic galaxies can grow via the accretion of gas which fuels both SF and the central BH, as well as through merging.  Their BH grows significantly more rapidly than their host spheroid, prior to growth by dry merging events that produce core-Sersic galaxies, where the BH and spheroid grow in lock step.  Additional compare Sersic relation with the corresponding relation for nuclear star clusters, confirming that the two classes of central massive object follow significantly different scaling relations.

1303.5528
What determines the grain size distribution in galaxies?
Asano et al

Dust production by SNeII and AGB stars, additional 3 other processes: (i) dust destruction by SN shocks, (i) metal accretion onto the surface of preexisting grains in the cold neutral medium (CNM) -- "grain growth", and (iii) grain-grain collisions (shattering and coagulation) in the warm neutral medium (WNM) and CNM.  Find: grain size distribution in galaxies controlled by stellar sources in early stage of galaxy evolution, and that afterwards the main processes that govern the size distribution changes to those in the ISM.  Since shattering produces a large abundance of small grains (surface-to-vlue ratio of grains increases), it enhances the efficiency of grain growth, contributing to the increase in total dust mass.  Grain growth creates a large bump in the grain size distribution around ~0.01 um.  Coagulation occurs effectively after the number of small grains is enhanced by shattering, and the grain size distribution is deformed to have bump at a ~0.03-0.05 um at t~10 Gyr.  Conclude that the evolutions of the total dust mass and the grain size distribution in galaxies are closely related to each other, and the grain size distribution changes considerably through the galaxy evolution because the dominant dust processes which regulate the grain size distribution change.

1303.5577
Recent variability of the solar spectral irradiance and its impact on climate modelling
Ermolli, etal

More variability in UV spectral range; changes in the visible and NIR bands in anti-phase with the solar cycle.  Chemistry-climent model (CCM) sims show that this might have significant implications on the Earth's atmosphere.  Motivated by these results, summarize current knowledge of SSI (solar spectral irradiance) variability and its impact on Earth's climent.  SSI changes influence the Earth's atmosphere, both directly (due to changes in shortwave heating, and hence temperature and ozone distributions in the stratosphere), and indirectly (dynamical feedbacks).  Investigate these effects with CCM sims with measured and modeled SSI changes.  Discuss the reliability of the available data and propose adidtional coordinated work.

1303.5586
Star formation and metallicity gradients in semi-analytic models of disk galaxy formation
Fu, Kaufmann, Huang, Yates, Moran, Heckman, Dave, Guo

Update radially-resolved SAMs to track the radial distribution of stars, metals, atomic and molecular gas in galactic disks.  MS and MSII sims, modify to (1) simpler SF law, (2) inject heavy elements by SNe directly into the halo (no prior mixing with disk cold gas), (3) include radial gas inflows in disks using a model of the form v_inflow=alpha r.  The sigma_H2 profiles in L* strongly constraints the inflow velocities to (7 km/s at r=10 kpc).  Metallicity gradients affected more strongly by the fraction of metals that are directly injected into the halo gas.  Metals ejected out of the galaxy at early epochs result in late infall of pre-enriched gas and flatter present-day gas metallicity gradients.  Prescription in which 80% of the metals produced by stars are injected into the halo gas provides the best fit to the relative flat observed metallicity gradients of galaxies with stellar masses >1e10 Msun.  Also results in a good fit to the relation between gas metallicity and sSFR in the outer parts of disks.  Examine the correlation between gas metallicity gradient and some global galaxy properties, finding that it is most strongly correlated with the B/T ratio of the galaxy.  This is because gas is consumed when the bulge forms during the galaxy merger, and the gas metallicity gradient is then set by newly-accreted gas.  THese model predictions appear to be in good agreement with observations.