Day 346

Wednesday.

1212.0538
FitSKIRT: genetic algorithms to automatically fit dusty galaxies with a Monte Carlo radiative transfer code
De Geyter, Baes, Fritz, Camps

A method to efficiently fit radiative transfer models to UV/optical images of dusty galaxies.  These images have the advantage that they have better spatial resolution compared to FIR/submm data.  Can recover all 11 parameters from a simulated edge-on spiral galaxy.  Apply code to NGC 4013, gives reasonable agreement with previous results by others, considering degeneracy, etc.

1212.0540
Misalignment of magnetic fields and outflows in protostellar cores
Hull, ... Bower, ... et al

Theoretical models of SF generally assume that bipolar outflows are parallel to the mean B-field direction in protostellar cores.  Present results from 16 nearby-low-mass protostars, mapped with 2.5" resolution at CARMA.  The results show that B-fields in protostellar cores on scales of ~1000 AU are not tightly aligned with outflows from the protostars.  If one assumes that outflows emerge along the rotation axes of circumstellar disks, then these results imply that these disks are not aligned with the fields in the cores from which they formed.

1212.0541
Hot X-ray coronae around massive spiral galaxies: a unique probe of structure formation models
Bogdan et al

Explore the luminous X-ray gas coronae in DM haloes of massive spiral galaxies that are a fundamental prediction of structure formation models.  Detect and characterize extended hot X-ray coronae beyond the optical disks for two normal massive spiral galaxies NGC1961 and 6753.  Hot gaseous emission extending out to ~60 kpc around both galaxies - well beyond their optical radii.  The hot gas, whose best-fit temperature of kT~0.6 keV and abundance is ~0.1 Solar, appears to have a fairly uniform distribution, hinting that the quasi-static gas resides in hydrostatic equilibrium in the potential well of the galaxies.  The bolometric luminosity of the hot gas in the 0.05-0.15 r_200 region, where r_200 is the viriral radius, is ~6e40 erg/s for both galaxies.  Derive the baryon mass fractions of these galaxies and obtain f_b~0.1 [how did they derive this? --- a sum of the X-ray derived hot gas mass, the stellar mass, the cold gas mass derived elsewhere, and the total stellar mass of the group members [why?--because both galaxies are located in poor groups, the baryon mass of these galaxies should also be included in the baryon budget.  The baryon mass of the group members is dominated by their stellar mass, which is estimated from their K-band luminosity, with a fixed M*/L_K=0.8 ratio [Why???]]], whose values fall short of the cosmic baryon fraction.  The detected X-ray coronae around these galaxies offer an excellent basis to probe structure formation simulations; the observations are confronted with the recently developed moving mesh code AREPO and the SPH code GADGET.  The implemented subresolution physics and the gravity solver are identical in the 2 code, but they use different methods to solve the hydrodynamical equations.  Conclude that, while neither model gives a perfect description, the observed luminosities, gas masses, and abundances favor the AREPO code.  Moreover, the shape of the observed density profiles are also well reproduced by AREPO within ~0.4 r_200.  However, neither model incorporates efficient feedback from SMBH or SNe, which could alter the simulated properties of the X-ray coronae.  

1212.0543
What sets temperature gradients in galaxy clusters?  Implications for non-thermal pressure support and mass-observable scaling relations
McCourt, Quataert, Parrish

Present spherically symmetric model for the origin and evolution of the temperature profiles in the hot plasma filling galaxy groups and clusters.  Find: gas in clusters is generically not isothermal, and that the temperature declines with radius at large distances from the cluster center, outside the core- and scale radii.  This temperature profile is determined by the accretion history of the halo, and is not quantitatively well-described by a polytropic model.  Explain quantitatively how the large-scale temperature gradient persists in spite of thermal conduction and convection.  These results are a consequence of the cosmological assembly of clusters and cannot be reproduced with non-cosmological simulations of isolated halos.  Show taht the variation in halo assembly histories produces a ~10% scatter in temperature at fixed mass.  On top of this scatter, conduction decreases the temperature of the gas near the scale radius in massive clusters, which may bias hydrostatic mass estimates inferred from X-ray and SZ observations.  An example application of our model profiles, use mixing-length theory to estimate the turbulent pressure support created by the magnetothermal instability (MTI): in agreement with earlier MHD simulations, find that the convection produced by the MTI can provide ~5% non-thermal pressure support near r_500.  The magnitude of this turbulent pressure support is likely to be non-monotonic in halo mass, peaking in 1e14.5Msun halos.

1212.0544
A census of broad-line active galactic nuclei in nearby galaxies: coeval star formation and rapid black hole growth
Trump, Hsu, Fang, Faber, Koo, Kocevski

Quantified, statistical map of BL-AGN frequency with host galaxy color and stellar mass in 0.01<z<0.11 galaxies.  Disentangle AGN and galaxy emission using aperture photometry and z-band concentration measurements from SDSS; results in uncontaminated galaxy rest-frame color, luminosity, and stellar mass.  BL-AGNs are distributed throughout the blue cloud and green valley at a given stellar mass, and are much rare in quiescent (red sequence) galaxies. This is in contrast to the published host galaxy properties of weaker narrow-line AGNs, indicating that BL-AGNs occur during a different phase in galaxy evolution.  More luminous BL-AGNs have bluer host galaxies, even at fixed mass, suggesting that the same processes that fuel nuclear activity also efficiently form stars.  THe data favor processes that simultaneously fuel both SF activity and rapid SMBH accretion.  If AGNs cause feedback on their host galaxies in the nearby universe, the evidence of galaxy-wide quenching must be delayed until after the BL-AGN phase.

1212.0548
Extremely metal-poor gas at a redshift of 7
Simcoe, ... Burgasser et al

Typical abundance of heavy elements: 0.001 to 2x solar; lower abundances seen in a few MW halo stars and in two quasar absorption systems at z=3.  These are widely interpreted as relics from the early universe, when all gas possessed a primordial chemistry.  Previously no direct abundance measurement from the first Gyr after BB, when the earliest stars began synthesizing elements; report observations of heavy element absorption in a quasar spectrum at z=7.04, when the universe was 772 Myr old (5.6% of present age), detecting a large column of HI but no corresponding heavy elements, limiting the chemical abundance to <1/10,000 solar level, if the gas is in a gravitationally bound protogalaxy, or less than 1/1,000 solar if it is diffuse and unbound.  If the absorption is truly intergalactic, it implies that the universe was neither ionized by starlight nor chemically enriched in this neighborhood at z~7. If it is gravitationally bound, the inferred abundance is too low to promote efficient cooling, and the system would be a viable site to form the predicted by as-yet unobserved massive population III stars in the early universe.

1212.0671
Density profile of cool core of galaxy clusters
Ota, Onzuka, Masai

For a cluster of galaxies initially in virial equilibrium and undergoes radiative cooling, investigate the density profile of its cool core of intracluster gas.  DM potential assumed to have NFW or King model, and gas is hydrostatic within it, with a polytropic profile.  Contribution from masses of gas and galaxies to the potential is ignored compared to the DM in the calculation.  The temperature and density profiles of gas in its quasi-hydrostatic cooling phase, which is expected to last for ~Gyr, is then calculated for different initial gas profiles.  Find: in the quasi-hydrostatic cooling phase, the temperature decreases to be about 1/3, the density increases by a factor of 4-6 at the cluster center compared to the initial polytropic values, though the profile over the core depend on the DM potential.  Hence the core radius in the quasi hydrostatic cooling gas appears smaller than the initial polytropic one.  Compare the density profile of the cool core with observations: find that while the initial density is around the upper bounds of large-core (>100 kpc) clusters (likely most relaxed but cooling is not yet significant), the central density under quasi-hydrostatic cooling falls between the mid- and high-values of small-core (<100kpc) or cool-core clusters.  Found: for the quasi-hydrostatic cooling gas that the entropy profile roughly agrees with the best-fit model for the ACCEPT cluster sample with a low central entropy, and the pressure gradient in the inner core is close to that of the REXCESS sample.  X-ray surface brightness calculated for the quasi-hydrostatic cooling gas is well represented by the conventional double beta-model, giving a physical basis of applying the double beta-model to cool core clusters.

1212.0776
The stacked ISW signal of rare superstructures in \Lambda CDM
Flender, Hotchkiss, Nadathur

Stacked ISW signal in CMB of superstructures from SDSS LRG catalog reported at high significance, with claims of 3 std. dev. larger than LCDM expectation.  However, this calculation was made in linear approximation, and relied on assumptions that may potentially have caused the LCDM expectation to be underestimated.  Update the theoretical model calculation and compare it with an analysis of ISW maps obtained from N-body sims of LCDM universe.  The differences between model predictions and the map analysis are found to be small and cannot explain the discrepancy with observation, which remains at >3 s.d. significance.  Discuss the cosmological significance of this anomaly and speculate on the potential of alternative models to explain it.