Day 521

Wednesday.  Thursday, Tag der Deutchen Einheit.

1310.0006
The cosmic evolution of Fermi BL Lacertae objects
Ajello et al

211 BL Lac objects (blazars) from Fermi; determine LF and its evolution; Find: the evolution is positive with a space density peaking at z~1.2; the low-luminosity, high-synchrotron peaked (HSP) BL Lacs are an exception, showing a strong negative evolution, with number density increasing for z<~0.5.  This rise corresponds to a drop-off in the density of flat-spectrum radio quasars, possible to interpret these HSPs represent an accretion-starved end-state of an earlier merger-driven gas-rich phase.  Additionally find that the known BL Lac correlation between luminosity and photon spectral index persists after correction for the substantial observational selection effects with implications for the 'blazar sequence' [?].  Estimating the beaming corrections to the LF, find that BL Lacs have an average Lorentz factor of gamma=6.1pm1.0, and that most are seen within 10 deg of the jet axis.

1310.0007
The significant contribution of minor mergers to the cosmic star formation budget
Kaviraj

Estimate the empirical lower limit for the fraction of cosmic SF that is triggered by minor mergers in the local Universe.  Find ETGs host ~14% of the budget, while Sb/Sc galaxies host the bulk (~53%) of the activity.  Indication of SF in nearby ETGs driven by minor mergers, implying that at least ~14% of local SF is triggered by this process.  Infall satellite onto later-type trigger a larger starburst, both due to higher availability of gas in the accreting galaxy, and because a bigger bulge better stabilizes the disk against SF.  Use the SF in ETGs to estimate a lower limit for the fraction of SF in LTGs that is minor-merger-driven.  Use a subsample of ETGs that is mass and environment-matched to the LTGs (implying a similar infalling satellite population), estimate this limit to be ~24%.  Thus, a lower limit for the fraction of cosmic SF that is induced by minor mergers is ~35% (14% EGTs + 0.24*86% LTGs).  The observed positive correlation between BH and galaxy mass further implies that similar fraction of BH accretion may also be triggered by minor mergers.  Detailed studies of minor-merger remnants are therefore essential, to quantify the role of this important process in driving stellar mass and BH growth in the local Universe.

1310.0021
Strong lensing in RX J1347.5-1145 revisited
Köhlinger, Schmidt

Revisit SF mass reconstruction of this cluster at z=0.451 with previous studies and incorporating CLASH, identify 4 systems of multiply lensed images in 1.75<z<4.19.  One system has 8 multiply lensed image of the same source.  The parametric mass model suggests high image multiplicity is due to the source (z_phot=4.19) being located on a so-called "swallowtail" caustic.  Also employ a non-parametric approach; reconstruct the projected mass of the cluster using the same SL data input.  Both reconstructed mass models agree in revealing several mass components and a highly elliptic shape of the mass distribution.  The projected mass inside, a radius R~35"~200 kpc of the cluster for a source at z=1.75 differ by 13% between the two estimates; could be related to the fundamental degeneracy involved when constraining DM substructures with gravitaionally lensed arcs.

1310.0022
Tracing mass and light in the universe: where is the dark matter?
Bahcall, Kulier

Examine distribution of mass (from WL) and starlight around >1e5 SDSS MaxBCG groups and clusters as a function of environment and scale, from deep inside clusters to large cosmic scales of 22 Mpc/h.  The observed cumulative M/L(<r) rises on small scales, reflecting the increasing M/L of the central bright galaxy of the cluster, then flattens to a nearly constant ratio on scales above ~300 kpc/h, where light follows mass on all scales and in all environments.  A trend of slightly decreasing M/L(r) with scale is shown to be consistent with the varying stellar population following the morphology-density relation.  This suggests that stars trace mass remarkably well even though they represent only a few % of the total mass.  Determine the stellar mass fraction and find it to be nearly constant on all scales above ~300 kpc/h, with M*/M_tot = 1.0 pm 0.4%.  Further suggest that most of the DM in the universe is located in the large haloes of individual galaxies (~300 kpc for L* galaxies) and show that the entire M/L(r) profile -- from groups and clusters to large-scale structure -- can be accounted for by the aggregate masses of the individual galaxies, plus gas.  Use the observed M/L ratio on large scales to determine the mass density of the universe: Omega_m=0.24 pm 0.02*b^2_M/L = 0.26 pm 0.02.

1310.0049
Analytical representations of unified equations of state for neutron-star matter
Potekhin et al

A unified EoS should describe the crust and the core of a NS using the same physical model.    Recent derivations of a family of such EoSs based on nuclear energy-density functional theory with generalized Skyrme effective forces [?], fitted to the available mass data, have been derived.  These forces were constrained to reproduce microscopic calculations of homogeneous neutron matter based on realistic 2 and 3-nucleon forces.  Aim: to represent basic physical characteristics of the latest Brussels-Montreal EoS models by analytical expressions to facilitate their inclusion in astrophysical simulations.  Consider 3 models differing my stiffness; for each construct two versions of the EoS parameterization.  The first version: pressure P and gravitational mass density rho are given as functions of the baryon number density n_b.  Second: P, rho, and n_b are given as functions of pseudo-enthalpy, which is useful for 2-d calculations of stationary rotating configurations of NSs.  In addition to the EoS, derive analytical expressions for several related quantities that are required in NS simulations: number fractions of electrons and muons in the stellar core, nucleon numbers per nucleus in the inner crust, and equivalent radii and shape parameters of the nuclei in the inner crust.  Obtain analytical representations for the basic characteristics of the models of cold dense matter, which are most important for studies of NSs.  Demonstrate the usability of these results by applying them to calculations of NS mass-radius relations, maximum and minimum masses, thresholds of direct Urca processes, and the electron conductivity in the NS crust.

1310.0052
Towards a unified description of the intergalactic medium ad redshift z~2.5
Prochaska, Madaum O'Maera, Fumagalli

Examine recent measurements of z~2.5 IGM which constrain the HI frequency distribution f(N) and the MFP to ionizing radiation.  Argue that line-blending and the clustering of strong absorption-line systems have led previous authors to systematically overestimate the effective Lyman limit opacity, yielding too small of a MFP for the IGM.  Further show that recently published measurements of f(N) at log NHI ~ 16 lie in strong disagreement, implying underestimated uncertainty from sample variance and/or systematics line line-saturation.  Allowing for a larger uncertainty in the f(N) measurements, provide a new f(N) model which reasonably satisfies all of the observational constraints under the assumption of randomly distributed absorption systems.  Caution that this formalism is invalid in light of absorber clustering and use a toy model to estimate the effects.  Future work must property account for the non-Poissonian nature of the IGM.

1310.0082
Beads on a strong and spurs in galactic disks
Renaud, ... Teyssier et al

Use simulation of MW-like galaxy to explore the formation and dynamical organization of the SF gas in a proto-typical disk.  Along spiral arms forms regularly spaced clouds: "beads on a string" form through gravitational instabilities, while "spurs" originate from Kelvin-Hemholtz instabilities.  Propose that the co-existence of both structures in the same galaxy can be explained by a different role of the disk dynamics, depending on the location within the disk.  Highlight the impact of the pitch angle of the spiral arm in the development of either type of structure.

1310.0156
How empty are disk gaps opened by giant planets?
Fung, Shi, Chiang

Gap clearing by giant planets has been proposed to explain the optically thin cavities observed in many protoplanetary disks.  How much material remains in the gap determines not only how detectable young planets are in their birth environments, but also how strong corotation torques are, which impacts how planets can survive fast orbital migration.  Determine numerically how the average surface density inside the gap, sigma_gap, depends on planet-to-star mass ratio q, Shakura-Sunyaev viscosity parameter alpha, and disk hight-to-radius aspect ratio h/r.  Results are derived from Lagrangian hydro code PEnGUIn, and verified by independent simulations with ZEUS90.  Find sigma_gap for Jupiter-like planets and for near brown dwarf masses.  Surface density contrasts inside and outside gaps can be as large as 1e4, even when the planet does not accrete.  Derive a simple analytic scaling, sigma_gap propto q^2 alpha^1 (h/r)^5, that compares reasonably well to empirical results, especially at low Neptune-like masses, and use discrepancies to highlight areas for progress.

1310.0427
Potential multiple steady-states in the long-term carbon cycle
Tennenbaum et al

Investigate the possibility of multiple climatic steady states.  Find steady states in Abiotic World (lacking any biotic influence), resulting from possible variations in planetary albedo in different temperature, atmospheric CO2 level regimes, with the same weathering forcing balancing a volcanic source to the atmosphere, ocean pool.  In Plant World, modeling relevant to the Phanerozoic, include the additional effects of biotic enhancement of weathering on land, organic carbon burial, oxidation of reduced organic carbon in terrestrial sediments and the variation of biotic productivity with temperature, finding a second stable steady state appearing between twenty and fifty degrees C.  The very warm early Triassic climate may be the prime candidate for an upper temperature steady state.  Given these results, the anthropogenic driven rise of atmospheric CO2 could potentially drive the climate into tipping points to a modestly higher temperature steady state, instead of relaxing back to pre anthropogenic conditions.

1310.0430
Massive Milky Way satellites in cold and warm dark matter: Dependence on cosmology
Polisensky, Ricotti

Inconsistency in high-res dissipationless CDM simulations of MW in its dynamics with observations of its most luminous satellites: attributable to the large values of sigma_8 and n_s adopted in the simulations, producing satellites that form too early and therefore are too dense.  This sensitivity makes satellites a sensitive test of CDM.  Find Via Lactea II halo to be atypical for haloes in a WMAP3 cosmology, a discrepancy attributable to its earlier formation epoch than the man for its mass.  Also explore WDM cosmologies for 1-4 keV thermal relics: in 1 keV, subhaloes have circular velocities at kpc scales ~60% lower than their CDM counterparts, but are reduced by only 10% in 4 keV cosmologies.  Since relic masses <2-3 keV are ruled out by constraints from the number of MW satellites and Lya forest, WDM has a minor effect in reducing the densities of massive satellites.  Given the uncertainties on the mass and formation epoch of the Milky Way, the need for reducing the satellite densities with baryonic effects or WDM is alleviated.  [So what cosmo param set sims best reproduces the observed satellite galaxies?]