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We compare 5 sub-grid models for supernova (SN) feedback in adaptive mesh refinement (AMR) simulations of isolated dwarf and L-star disk galaxies with 20-40 pc resolution. The models are thermal dump, stochastic thermal, 'mechanical' (injecting energy or momentum depending on the resolution), kinetic, and delayed cooling feedback. We focus on the ability of each model to suppress star formation and generate outflows. Our highest-resolution runs marginally resolve the adiabatic phase of the feedback events, which correspond to 40 SN explosions, and the first three models yield nearly identical results, possibly indicating that kinetic and delayed cooling feedback converge to wrong results. At lower resolution all models differ, with thermal dump feedback becoming inefficient. Thermal dump, stochastic, and mechanical feedback generate multiphase outflows with mass loading factors $\beta \ll 1$, which is much lower than observed. For the case of stochastic feedback we compare to published SPH simulations, and find much lower outflow rates. Kinetic feedback yields fast, hot outflows with $\beta\sim 1$, but only if the wind is in effect hydrodynamically decoupled from the disk by using a large bubble radius. Delayed cooling generates cold, dense and slow winds with $\beta> 1$, but large amounts of gas occupy regions of temperature-density space with short cooling times. We conclude that either our resolution is too low to warrant physically motivated models for SN feedback, that feedback mechanisms other than SNe are important, or that other aspects of galaxy evolution, such as star formation, require better treatment., Comment: 22 pages, 15 figures. Accepted for publication in MNRAS with minor revisions

The Initial Star formation and Lifetimes of Andromeda Satellites (ISLAndS) project uses Hubble Space Telescope imaging to study a representative sample of six Andromeda dSph satellite companion galaxies. The main goal of the program is to determine whether the star formation histories (SFHs) of the Andromeda dSph satellites demonstrate significant statistical differences from those of the Milky Way, which may be attributable to the different properties of their local environments. Our observations reach the oldest main sequence turn-offs, allowing a time resolution at the oldest ages of ~ 1 Gyr, which is comparable to the best achievable resolution in the MW satellites. We find that the six dSphs present a variety of SFHs that are not strictly correlated with luminosity or present distance from M31. Specifically, we find a significant range in quenching times (lookback times from 9 to 6 Gyr), but with all quenching times more than ~ 6 Gyr ago. In agreement with observations of Milky Way companions of similar mass, there is no evidence of complete quenching of star formation by the cosmic UV background responsible for reionization, but the possibility of a degree of quenching at reionization cannot be ruled out. We do not find significant differences between the SFHs of the three members of the vast, thin plane of satellites and the three off-plane dSphs. The primary difference between the SFHs of the ISLAndS dSphs and Milky Way dSph companions of similar luminosities and host distances is the absence of very late quenching (< 5 Gyr ago) dSphs in the ISLAndS sample. Thus, models that can reproduce satellite populations with and without late quenching satellites will be of extreme interest., 24 pages, 11 figures, 3 tables, submitted to the ApJ

We investigate the simultaneous triggering of active galactic nuclei (AGN) in merging galaxies, using a large suite of high-resolution hydrodynamical simulations. We compute dual-AGN observability time-scales using bolometric, X-ray, and Eddington-ratio thresholds, confirming that dual activity from supermassive black holes (BHs) is generally higher at late pericentric passages, before a merger remnant has formed, especially at high luminosities. For typical minor and major mergers, dual activity lasts ~20-70 and ~100-160 Myr, respectively. We also explore the effects of X-ray obscuration from gas, finding that the dual-AGN time decreases at most by a factor of ~2, and of contamination from star formation. Using projected separations and velocity differences rather than three-dimensional quantities can decrease the dual-AGN time-scales by up to ~4, and we apply filters which mimic current observational-resolution limitations. In agreement with observations, we find that, for a sample of major and minor mergers hosting at least one AGN, the fraction harbouring dual AGN is ~20-30 and ~1-10 per cent, respectively. We quantify the effects of merger mass ratio (0.1 to 1), geometry (coplanar, prograde, retrograde, and inclined), disc gas fraction, and BH properties, finding that the mass ratio is the most important factor, with the difference between minor and major mergers varying between factors of a few to orders of magnitude, depending on the luminosity and filter used. We also find that a shallow imaging survey will require very high angular resolution, whereas a deep imaging survey will be less resolution-dependent., Accepted for publication in MNRAS; added online-only material

The Guryul Ravine section (Kashmir, India) exposes one the world's most continuous carbonate rock successions throughout the Permian-Triassic boundary and beyond. Due to political instability in this region, the biostratigraphy of this section has not been updated for nearly three decades. Following new high-resolution sampling, we reassess here the conodont biochronology and isotopic records of the fifteen lowermost stratigraphical metres (Member E) of the Khunamuh Formation at Guryul Ravine section. This interval includes both the Permian-Triassic and the Griesbachian-Dienerian (lower-upper Induan) boundaries. The First Occurrence of Hindeodus parvus, the index for the base of the Triassic, is confirmed in the middle of sub-member E2 (Unit 56 in Matsuda, 1981 [Journal of Geosciences, Osaka City University 24, 75–108]; our bed GUR09). We characterize 11 Unitary Association Zones based on the conodont record from China and from Guryul Ravine. UAZ1–2 are Late Permian and identified only in South China, UAZ3–11 are identified both in China and Guryul Ravine. The Griesbachian-Dienerian boundary is included within the interval of separation between UAZ8 and UAZ9. At Guryul Ravine, this boundary is precisely constrained between beds GUR310 and GUR311, and corresponds to the replacement of segminiplanate (here Clarkina and Neoclarkina) by segminate (Sweetospathodus and Neospathodus) conodonts. This faunal turnover was possibly linked to a climate change at the Griesbachian-Dienerian transition, from a cool and dry to a hot and humid climate. This transition could be the trigger of the migration of neogondolellids towards high latitudes and of the radiation of neospathodids during the Dienerian.

The test of the Einstein Equivalence Principle (EEP) is of crucial importance as a deviation from it could hint to quantum effects in gravity or to unification with the other fundamental forces. One aspect of EEP is the local position invariance (LPI), which can be tested by measuring the gravitational red-shift. As an example of a possible space mission which could test the EEP, we will discuss a recently proposed satellite experiment, Einstein Gravitational RedShift Probe (E-GRIP), with the aim to test LPI using an hydrogen maser atomic clock on a highly elliptic orbit around Earth and compare the on-board clock to clocks located on Earth via a microwave link.

We analyse the output of the hi-res cosmological zoom-in simulation ErisBH to study self-consistently the formation of a strong stellar bar in a Milky Way-type galaxy and its effect on the galactic structure, on the central gas distribution and on star formation. The simulation includes radiative cooling, star formation, SN feedback and a central massive black hole which is undergoing gas accretion and is heating the surroundings via thermal AGN feedback. A large central region in the ErisBH disk becomes bar-unstable after z~1.4, but a clear bar-like structure starts to grow significantly only after z~0.4, possibly triggered by the interaction with a massive satellite. At z~0.1 the bar reaches its maximum radial extent of l~2.2 kpc. As the bar grows, it becomes prone to buckling instability, which we quantify based on the anisotropy of the stellar velocity dispersion. The actual buckling event is observable at z~0.1, resulting in the formation of a boxy-peanut bulge clearly discernible in the edge-on view of the galaxy at z=0. The bar in ErisBH does not dissolve during the formation of the bulge but remains strongly non-axisymmetric down to the resolution limit of ~100 pc at z=0. During its early growth, the bar exerts a strong torque on the gas within its extent and drives gas inflows that enhance the nuclear star formation on sub-kpc scales. Later on the infalling gas is nearly all consumed into stars and, to a lesser extent, accreted onto the central black hole, leaving behind a gas-depleted region within the central ~2 kpc. Observations would more likely identify a prominent, large-scale bar at the stage when the galactic central region has already been quenched. Bar-driven quenching may play an important role in disk-dominated galaxies at all redshift. [Abridged], Comment: 13 pages, 12 figures, MNRAS submitted

Giant planets are thought to have cores in their deep interiors, and the division into a heavy-element core and hydrogen-helium envelope is applied in both formation and structure models. We show that the primordial internal structure depends on the planetary growth rate, in particular, the ratio of heavy elements accretion to gas accretion. For a wide range of likely conditions, this ratio is in one-to-one correspondence with the resulting post-accretion profile of heavy elements within the planet. This flux ratio depends sensitively on the assumed solid surface density in the surrounding nebula. We suggest that giant planets' cores might not be distinct from the envelope and includes some hydrogen and helium, and the deep interior can have a gradual heavy-element structure. Accordingly, Jupiter's core may not be well-defined. Accurate measurements of Jupiter's gravitational field by Juno could put constraints on Jupiter's core mass. However, as we suggest here, the definition of Jupiter's core is complex, and the core's physical properties (mass, density) depend on the actual definition of the core and on its growth history., Comment: accepted for publication in ApJL

Today, with the large number of detected exoplanets and improved measurements, we can reach the next step of planetary characterization. Classifying different populations of planets is not only important for our understanding of the demographics of various planetary types in the galaxy, but also for our understanding of planet formation. We explore the nature of two regimes in the planetary mass-radius (M-R) relation. We suggest that the transition between the two regimes of "small" and "large" planets, occurs at a mass of 124 \pm 7, M_Earth and a radius of 12.1 \pm 0.5, R_Earth. Furthermore, the M-R relation is R \propto M^{0.55\pm 0.02} and R \propto M^{0.01\pm0.02} for small and large planets, respectively. We suggest that the location of the breakpoint is linked to the onset of electron degeneracy in hydrogen, and therefore, to the planetary bulk composition. Specifically, it is the characteristic minimal mass of a planet which consists of mostly hydrogen and helium, and therefore its M-R relation is determined by the equation of state of these materials. We compare the M-R relation from observational data with the one derived by population synthesis calculations and show that there is a good qualitative agreement between the two samples., accepted for publication in A&A

Magnetic fields are widely observed in the Universe in virtually all astrophysical objects, from individual stars to entire galaxies, even in the intergalactic medium, but their specific generation has long been debated. Due to the development of more realistic models of galaxy formation, viable scenarios are emerging to explain cosmic magnetism, thanks to both deeper observations and more efficient and accurate computer simulations. We present here a new cosmological high-resolution zoom-in magnetohydrodynamic (MHD) simulation, using the adaptive mesh refinement (AMR) technique, of a dwarf galaxy with an initially weak and uniform magnetic seed field that is amplified by a small-scale dynamo driven by supernova-induced turbulence. As first structures form from the gravitational collapse of small density fluctuations, the frozen-in magnetic field separates from the cosmic expansion and grows through compression. In a second step, star formation sets in and establishes a strong galactic fountain, self-regulated by supernova explosions. Inside the galaxy, the interstellar medium becomes highly turbulent, dominated by strong supersonic shocks, as demonstrated by the spectral analysis of the gas kinetic energy. In this turbulent environment, the magnetic field is quickly amplified via a small-scale dynamo process and is finally carried out into the circumgalactic medium by a galactic wind. This realistic cosmological simulation explains how initially weak magnetic seed fields can be amplified quickly in early, feedback-dominated galaxies, and predicts, as a consequence of the small scale dynamo process, that high-redshift magnetic fields are likely to be dominated by their small scale components., Comment: 6 pages, 6 figures, submitted to MNRAS

On 2017 August 17 the merger of two compact objects with masses consistent with two neutron stars was discovered through gravitational-wave (GW170817), gamma-ray (GRB 170817A), and optical (SSS17a/AT 2017gfo) observations. The optical source was associated with the early-type galaxy NGC 4993 at a distance of just ~40 Mpc, consistent with the gravitational-wave measurement, and the merger was localized to be at a projected distance of ~2 kpc away from the galaxy's center. We use this minimal set of facts and the mass posteriors of the two neutron stars to derive the first constraints on the progenitor of GW170817 at the time of the second supernova (SN). We generate simulated progenitor populations and follow the three-dimensional kinematic evolution from binary neutron star (BNS) birth to the merger time, accounting for pre-SN galactic motion, for considerably different input distributions of the progenitor mass, pre-SN semimajor axis, and SN-kick velocity. Though not considerably tight, we find these constraints to be comparable to those for Galactic BNS progenitors. The derived constraints are very strongly influenced by the requirement of keeping the binary bound after the second SN and having the merger occur relatively close to the center of the galaxy. These constraints are insensitive to the galaxy's star formation history, provided the stellar populations are older than 1 Gyr.

The Weddell Sea sector of the Antarctic Ice Sheet is hypothesized to have made a significant contribution to sea-level rise since the Last Glacial Maximum. Using a numerical flowline model we investigate the controls on grounding line motion across the eastern Weddell Sea and compare our results with field data relating to past ice extent. Specifically, we investigate the influence of changes in ice temperature, accumulation, sea level, ice shelf basal melt, and ice shelf buttressing on the dynamics of the Foundation Ice Stream. We find that ice shelf basal melt plays an important role in controlling grounding line advance, while a reduction in ice shelf buttressing is found to be necessary for grounding line retreat. There are two stable positions for the grounding line under glacial conditions: at the northern margin of Berkner Island and at the continental shelf break. Global mean sea-level contributions associated with these two scenarios are ~50 mm and ~130 mm, respectively. Comparing model results with field evidence from the Pensacola Mountains and the Shackleton Range, we find it unlikely that ice was grounded at the continental shelf break for a prolonged period during the last glacial cycle. However, we cannot rule out a brief advance to this position or a scenario in which the grounding line retreated behind present during deglaciation and has since re-advanced. Better constraints on past ice sheet and ice shelf geometry, ocean temperature, and ocean circulation are needed to reconstruct more robustly past behavior of the Foundation Ice Stream.

Mini-Neptunes seem to be common planets. In this work we investigate the possible formation histories and predicted occurrence rates of mini-Neptunes assuming the planets form beyond the iceline. We consider pebble and planetesimal accretion accounting for envelope enrichment and two different opacity conditions. We find that the formation of mini-Neptunes is a relatively frequent output when envelope enrichment by volatiles is included, and that there is a "sweet spot" for mini-Neptune formation with a relatively low solid accretion rate of ~10^{-6} Earth masses per year. This rate is typical for low/intermediate-mass protoplanetary disks and/or disks with low metallicities. With pebble accretion, envelope enrichment and high opacity favor the formation of mini-Neptunes, with more efficient formation at large semi-major axes (~30 AU) and low disk viscosity. For planetesimal accretion, such planets can form also without enrichment, with the opacity being a key aspect in the growth history and favorable formation location. Finally, we show that the formation of Neptune-like planets remains a challenge for planet formation theories., Comment: Accepted for publication in ApJ

Magnetic fields in galaxies are believed to be the result of dynamo amplification of initially weak seed fields, reaching equipartition strength inside the interstellar medium. The small-scale dynamo appears to be a viable mechanism to explain observations of strong magnetic fields in present-day and high-redshift galaxies, considering the extreme weakness of seed fields predicted by battery mechanisms or primordial fields. Performing high-resolution adaptive mesh magneto-hydrodynamic simulations of a small mass, isolated cooling halo with an initial magnetic seed field strength well below equipartition, we follow the small-scale dynamo amplification from supernova-induced turbulence up to saturation of the field. We find that saturation occurs when the average magnetic pressure reaches only 3 % to 5 % of the turbulent pressure. The magnetic energy growth transitions from exponential to linear, and finally comes to halt. The saturation level increases slightly with grid resolution. These results are in good agreement with theoretical predictions for magnetic Prandtl numbers of order $\mathrm{Pr_M} \sim 1$ and turbulent Mach numbers of order $\mathrm{M} \sim 10$. When we suppress supernova feedback after our simulation has reached saturation, we find that turbulence decays and that the gas falls back onto a thin disk with the magnetic field in local equipartition. We propose a scenario in which galactic magnetic fields are amplified from weak seed fields in the early stages of the Universe to sub-equipartition fields, owing to the turbulent environment of feedback-dominated galaxies at high redshift, and are evolved further in a later stage up to equipartition, as galaxies transformed into more quiescent, large spiral disks., Comment: 14 pages, 14 figures, submitted to MNRAS. Part I (The kinematic phase) can be found at https://doi.org/10.1093/mnras/stv2985 (journal article) or at arXiv:1506.00849

We present a suite of cosmological zoom-in simulations at z>5 from the Feedback In Realistic Environments project, spanning a halo mass range M_halo~10^8-10^12 M_sun at z=5. We predict the stellar mass-halo mass relation, stellar mass function, and luminosity function in several bands from z=5-12. The median stellar mass-halo mass relation does not evolve strongly at z=5-12. The faint-end slope of the luminosity function steepens with increasing redshift, as inherited from the halo mass function at these redshifts. Below z~6, the stellar mass function and ultraviolet (UV) luminosity function slightly flatten below M_star~10^4.5 M_sun (fainter than M_1500~-12), owing to the fact that star formation in low-mass halos is suppressed by the ionizing background by the end of reionization. Such flattening does not appear at higher redshifts. We provide redshift-dependent fitting functions for the SFR-M_halo, SFR-M_star, and broad-band magnitude-stellar mass relations. We derive the star formation rate density and stellar mass density at z=5-12 and show that the contribution from very faint galaxies becomes more important at z>8. Furthermore, we find that the decline in the z~6 UV luminosity function brighter than M_1500~-20 is largely due to dust attenuation. Approximately 37% (54%) of the UV luminosity from galaxies brighter than M_1500=-13 (-17) is obscured by dust at z~6. Our results broadly agree with current data and can be tested by future observations., 23 pages, 17 figures, resubmitted to MNRAS after minor revision. The predicted stellar mass functions and luminosity functions are made publicly available (see Appendix C for details)

Massive gas-rich galaxy discs at $z \sim 1-3$ host massive star-forming clumps with typical baryonic masses in the range $10^7-10^8$~M$_{\odot}$ which can affect the orbital decay and concurrent growth of supermassive black hole (BH) pairs. Using a set of high-resolution simulations of isolated clumpy galaxies hosting a pair of unequal-mass BHs, we study the interaction between massive clumps and a BH pair at kpc scales, during the early phase of the orbital decay. We find that both the interaction with massive clumps and the heating of the cold gas layer of the disc by BH feedback tend to delay significantly the orbital decay of the secondary, which in many cases is ejected and then hovers for a whole Gyr around a separation of 1--2 kpc. In the envelope, dynamical friction is weak and there is no contribution of disc torques: these lead to the fastest decay once the orbit of the secondary BH has circularised in the disc midplane. In runs with larger eccentricities the delay is stronger, although there are some exceptions. We also show that, even in discs with very sporadic transient clump formation, a strong spiral pattern affects the decay time-scale for BHs on eccentric orbits. We conclude that, contrary to previous belief, a gas-rich background is not necessarily conducive to a fast BH decay and binary formation, which prompts more extensive investigations aimed at calibrating event-rate forecasts for ongoing and future gravitational-wave searches, such as with Pulsar Timing Arrays and the future evolved Laser Interferometer Space Antenna., Accepted by MNRAS

The Advanced LIGO and Advanced Virgo observatories recently discovered gravitational waves from a binary neutron star inspiral. A short gamma-ray burst (GRB) that followed the merger of this binary was also recorded by the Fermi Gamma-ray Burst Monitor (Fermi-GBM), and the Anti-Coincidence Shield for the Spectrometer for the International Gamma-Ray Astrophysics Laboratory (INTEGRAL), indicating particle acceleration by the source. The precise location of the event was determined by optical detections of emission following the merger. We searched for high-energy neutrinos from the merger in the GeV–EeV energy range using the Antares, IceCube, and Pierre Auger Observatories. No neutrinos directionally coincident with the source were detected within ±500 s around the merger time. Additionally, no MeV neutrino burst signal was detected coincident with the merger. We further carried out an extended search in the direction of the source for high-energy neutrinos within the 14 day period following the merger, but found no evidence of emission. We used these results to probe dissipation mechanisms in relativistic outflows driven by the binary neutron star merger. The non-detection is consistent with model predictions of short GRBs observed at a large off-axis angle.

Observations show a prevalence of high redshift galaxies with large stellar masses and predominantly passive stellar populations. A variety of processes have been suggested that could reduce the star formation in such galaxies to observed levels, including quasar mode feedback, virial shock heating, or galactic winds driven by stellar feedback. However, the main quenching mechanisms have yet to be identified. Here we study the origin of star formation quenching using Argo, a cosmological, hydrodynamical zoom-in simulation that follows the evolution of a massive galaxy at $z\geq{}2$. This simulation adopts the same sub-grid recipes of the Eris simulations, which have been shown to form realistic disk galaxies, and, in one version, adopts also a mass and spatial resolution identical to Eris. The resulting galaxy has properties consistent with those of observed, massive (M_* ~ 1e11 M_sun) galaxies at z~2 and with abundance matching predictions. Our models do not include AGN feedback indicating that supermassive black holes likely play a subordinate role in determining masses and sizes of massive galaxies at high z. The specific star formation rate (sSFR) of the simulated galaxy matches the observed M_* - sSFR relation at early times. This period of smooth stellar mass growth comes to a sudden halt at z=3.5 when the sSFR drops by almost an order of magnitude within a few hundred Myr. The suppression is initiated by a leveling off and a subsequent reduction of the cool gas accretion rate onto the galaxy, and not by feedback processes. This "cosmological starvation" occurs as the parent dark matter halo switches from a fast collapsing mode to a slow accretion mode. Additional mechanisms, such as perhaps radio mode feedback from an AGN, are needed to quench any residual star formation of the galaxy and to maintain a low sSFR until the present time., 20 pages, 12 figures, 2 tables, accepted for publication in MNRAS

The failure of magmatic foams has been implicated as a fundamental process in eruptions occurring at open-conduit, basaltic volcanoes. In order to investigate the failure of magmatic foams we applied the fiber bundle model using global load sharing. The strengths of the fibers for the model were taken from bubble wall widths measured in four computer-simulated foams of low-porosity and from one very low-porosity and two high-porosity foams produced in the laboratory by heating hydrated basaltic glasses to 1200 °C. The relative strength of an individual fiber in the model was calculated from the square of a bubble wall's average width and absolute strengths of the foams were calculated based upon the correlation of the strength of one modeled foam with experimental data. The fiber bundle model is shown to successfully reproduce measured tensile strengths of porous volcanic rocks studied by other researchers and confirms previous findings of the primary importance of foam porosity, as well as the secondary importance of structural details that affect the number and size of bubble walls and permeability. Because of the success of the fiber bundle model in reproducing experimental foam failure, its results are compared to infrasonic measurements associated with bubbles at Stromboli (Italy) and demonstrate that within uncertainty the power-law exponents of the infrasonic energies and of the fiber bundle model energies are in agreement; both show a crossover from an exponent of 5/2 associated with the bursting of small bubbles in the infrasonic measurements to an exponent of 3/2 for normal Strombolian eruptions associated with infrasonic signals from meter-scale bubbles. The infrasonic signals for major explosions and a paroxysmal eruption at Stromboli fall near the extrapolation of the power law defined by the low-amplitude, bubble bursting events and are interpreted to reflect the bursting of multitudes of small bubbles, rather than a few large bubbles. The measurement of small-amplitude infrasonic events at Stromboli appears useful in predicting the recurrence interval of paroxysmal eruptions at this volcano and may also provide a tool that uses common, small-amplitude infrasonic events to constrain the frequency of larger eruptions at other volcanoes.

We present a study of the substructure finder dependence of subhalo clustering in the Aquarius Simulation. We run 11 different subhalo finders on the haloes of the Aquarius Simulation and we study their differences in the density profile, mass fraction and 2-point correlation function of subhaloes in haloes. We also study the mass and vmax dependence of subhalo clustering. As the Aquarius Simulation has been run at different resolutions, we study the convergence with higher resolutions. We find that the agreement between finders is at around the 10% level inside R200 and at intermediate resolutions when a mass threshold is applied, and better than 5% when vmax is restricted instead of mass. However, some discrepancies appear in the highest resolution, underlined by an observed resolution dependence of subhalo clustering. This dependence is stronger for the smallest subhaloes, which are more clustered in the highest resolution, due to the detection of subhaloes within subhaloes (the sub-subhalo term). This effect modifies the mass dependence of clustering in the highest resolutions. We discuss implications of our results for models of subhalo clustering and their relation with galaxy clustering., Comment: 19 pages, 15 figures

Solar radiation is the primary source of energy for the Earth's climate system. Although the incoming and outgoing solar fluxes at the top of atmosphere can be quantified with high accuracy, large uncertainties still exist in the partitioning of solar absorption between surface and atmosphere. To compute best estimates of absorbed solar radiation at the surface and within the atmosphere representative for Europe during 2000–2010, we combine temporally homogeneous and spatially representative ground-based observations of surface downwelling solar radiation with collocated satellite-retrieved surface albedo and top-of-atmosphere net irradiance. We find best estimates of Europe land annual mean surface and atmospheric absorption of 117.3 ± 6 W m−2 (41.6 ± 2% of top-of-atmosphere incident irradiance) and 65.0 ± 3 W m−2 (23.0 ± 1%). The fractional atmospheric absorption of 23% represents a robust estimate largely unaffected by variations in latitude and season, thus, making it a potentially useful quantity for first-order validation of regional climate models. Uncertainties of the individual absorption estimates arise mostly from the measurements themselves. In this context, the surface albedo and the ground-based solar radiation data are the most critical variables. Other sources of uncertainty, like the multiplicative combination of spatially averaged surface solar radiation and surface albedo estimates, and the spatial representativeness of the point observations, are either negligibly small or can be corrected for.

We study the effect of baryonic processes on the halo mass function in the galaxy cluster mass range using a catalogue of 153 high resolution cosmological hydrodynamical simulations performed with the AMR code ramses. We use the results of our simulations within a simple analytical model to gauge the effects of baryon physics on the halo mass function. Neglect of AGN feedback leads to a significant boost in the cluster mass function similar to that reported by other authors. However, including AGN feedback not only gives rise to systems that are similar to observed galaxy clusters, but they also reverse the global baryonic effects on the clusters. The resulting mass function is closer to the unmodified dark matter halo mass function but still contains a mass dependent bias at the 5-10% level. These effects bias measurements of the cosmological parameters, such as $\sigma_8$ and $\Omega_m$. For current cluster surveys baryonic effects are within the noise for current survey volumes, but forthcoming and planned large SZ, X-ray and multi-wavelength surveys will be biased at the percent level by these processes. The predictions for the halo mass function including baryonic effects need to be carefully studied with larger and improved simulations. However, simulations of full cosmological boxes with the resolution we achieve and including AGN feedback are still computationally challenging., Comment: 12 pages, 3 tables, 6 figures, accepted for publication in MNRAS

We develop a model for the matter power spectrum as the sum of Zeldovich approximation and even powers of $k$, i.e., $A_0 - A_2k^2 + A_4k^4 - ...$, compensated at low $k$. With terms up to $k^4$ the model can predict the true power spectrum to a few percent accuracy up to $k\sim 0.7 h \rm{Mpc}^{-1}$, over a wide range of redshifts and models. The $A_n$ coefficients contain information about cosmology, in particular amplitude of fluctuations. We write a simple form of the covariance matrix as a sum of Gaussian part and $A_0$ variance, which reproduces the simulations remarkably well. In contrast, we show that one needs an N-body simulation volume of more than 1000 $({\rm Gpc}/h)^3$ to converge to 1\% accuracy on covariance matrix. We investigate the super-sample variance effect and show it can be modeled as an additional parameter that can be determined from the data. This allows a determination of $\sigma_8$ amplitude to about 0.2\% for a survey volume of 1$({\rm Gpc}/h)^3$, compared to 0.4\% otherwise. We explore the sensitivity of these coefficients to baryonic effects using hydrodynamic simulations of van Daalen (2011). We find that because of baryons redistributing matter inside halos all the coefficients $A_{2n}$ for $n>0$ are strongly affected by baryonic effects, while $A_0$ remains almost unchanged, a consequence of halo mass conservation. Our results suggest that observations such as weak lensing power spectrum can be effectively marginalized over the baryonic effects, while still preserving the bulk of the cosmological information contained in $A_0$ and Zeldovich terms., Comment: 21 pages,11 figures, 1 table; Accepted for publication in MNRAS

The giant impact hypothesis for Moon formation successfully explains the dynamic properties of the Earth-Moon system but remains challenged by the similarity of isotopic fingerprints of the terrestrial and lunar mantles. Moreover, recent geochemical evidence suggests that the Earth's mantle preserves ancient (or "primordial") heterogeneity that predates the Moon-forming giant impact. Using a new hydrodynamical method, we here show that Moon-forming giant impacts lead to a stratified starting condition for the evolution of the terrestrial mantle. The upper layer of the Earth is compositionally similar to the disk, out of which the Moon evolves, whereas the lower layer preserves proto-Earth characteristics. As long as this predicted compositional stratification can at least partially be preserved over the subsequent billions of years of Earth mantle convection, the compositional similarity between the Moon and the accessible Earth's mantle is a natural outcome of realistic and high-probability Moon-forming impact scenarios. The preservation of primordial heterogeneity in the modern Earth not only reconciles geochemical constraints but is also consistent with recent geophysical observations. Furthermore, for significant preservation of a proto-Earth reservoir, the bulk composition of the Earth-Moon system may be systematically shifted towards chondritic values., Comments are welcome

Data with uncertain, missing, censored, and correlated values are commonplace in many research fields including astronomy. Unfortunately, such data are often treated in an ad hoc way in the astronomical literature potentially resulting in inconsistent parameter estimates. Furthermore, in a realistic setting, the variables of interest or their errors may have non-normal distributions which complicates the modeling. I present a novel approach to compute the likelihood function for such data sets. This approach employs Gaussian copulas to decouple the correlation structure of variables and their marginal distributions resulting in a flexible method to compute likelihood functions of data in the presence of measurement uncertainty, censoring, and missing data. I demonstrate its use by determining the slope and intrinsic scatter of the star forming sequence of nearby galaxies from observational data. The outlined algorithm is implemented as the flexible, easy-to-use, open-source Python package LEO-Py., Comment: 21 pages, 8 figures, 2 tables, to appear in Astronomy and Computing, LEO-Py is available at github.com/rfeldmann/leopy

We present a self-consistent hydrodynamical simulation of a Milky Way-like galaxy at a resolution of 0.05 pc. The model includes star formation and a new implementation of stellar feedback through photoionization, radiative pressure and supernovae. The simulation resolves the structure of the interstellar medium at sub-parsec resolution for a few cloud lifetimes and at 0.05 pc for about a cloud-crossing time. The turbulence cascade and gravitation from kpc scales are de facto included in smaller structures like molecular clouds. We show that the formation of a bar influences the dynamics of the central ˜100 pc by creating resonances. At larger radii, the spiral arms host the formation of regularly spaced clouds: beads on a string and spurs. These instabilities pump turbulent energy into the gas, generally in the supersonic regime. Because of asymmetric drift, the supernovae explode outside their gaseous nursery, which diminishes the effect of feedback on the structure of clouds. The evolution of clouds is thus mostly due to fragmentation and gas consumption, regulated mainly by supersonic turbulence. The transition from turbulence-supported to self-gravitating gas is detected in the gas density probability distribution function at ˜2000 cm-3. The power-spectrum density suggests that gravitation governs the hierarchical organization of structures from the galactic scale down to a few pc.

We analyse the structure and chemical enrichment of a Milky Way-like galaxy with a stellar mass of 2 10^{10} M_sun, formed in a cosmological hydrodynamical simulation. It is disk-dominated with a flat rotation curve, and has a disk scale length similar to the Milky Way's, but a velocity dispersion that is ~50% higher. Examining stars in narrow [Fe/H] and [\alpha/Fe] abundance ranges, we find remarkable qualitative agreement between this simulation and observations: a) The old stars lie in a thickened distribution with a short scale length, while the young stars form a thinner disk, with scale lengths decreasing, as [Fe/H] increases. b) Consequently, there is a distinct outward metallicity gradient. c) Mono-abundance populations exist with a continuous distribution of scale heights (from thin to thick). However, the simulated galaxy has a distinct and substantive very thick disk (h_z~1.5 kpc), not seen in the Milky Way. The broad agreement between simulations and observations allows us to test the validity of observational proxies used in the literature: we find in the simulation that mono-abundance populations are good proxies for single age populations (, Comment: 11 page, 10 figures, submitted. Comments welcome

[1] Discharge from marine-terminating outlet glaciers represents a key component of the Greenland Ice Sheet mass budget and observations suggest that mass loss from northwest Greenland has recently accelerated. Despite this, the factors controlling outlet glacier dynamics within this region have been comparatively poorly studied. Here we use remotely sensed data to investigate the influence of atmospheric, oceanic, and glacier-specific controls on the frontal position of Alison Glacier (AG), northwest Greenland, and nine surrounding outlet glaciers. AG retreated by 9.7 km between 2001 and 2005, following at least 25 years of minimal change. Results suggest that sea ice and air temperatures influence glacier frontal position at seasonal and interannual timescales. However, the response of individual outlet glaciers to forcing was strongly modified by factors specific to each glacier, specifically variations in fjord width and terminus type. Overall, our results underscore the need to consider these factors in order to interpret recent rapid changes and predict the dynamic response of marine-terminating outlet glaciers to atmospheric and oceanic forcing.

In this contribution we analyze and discuss the microanatomy and histology of postcranial osteoderms of a number of "rauisuchians" from different localities of South America (Argentina and Brazil). The studied sample includes osteoderms of Fasolasuchus tenax, Prestosuchus chiniquensis, Saurosuchus galilei and an undetermined rauisuchian from Brazil. The bone microanatomy of the osteoderms is variable: whereas some specimens have a rather compact structure, others show a diploe architecture with a central cancellous core bordered by two compact cortices. Both external and basal cortices are mainly composed of poorly vascularized, fine and coarse parallel-fibred bone and networks of interwoven and mineralized fiber bundles. The internal region of the non-remodeled specimens consists of a well- vascularized core in which the intrinsic fibers exhibit important variations (even in the same specimen), ranging from coarse, parallel-fibred to woven-fibred bone tissues. Lines of arrested growth (LAGs) are well recorded in both basal and external cortices. Differences in the bone microstructure (compact vs. diploe) could be related to the age, sex and reproductive status of the sampled individuals. Hence, age estimation based on the count of LAGs in rauisuchian osteoderms appears to be reliable only in the early stages of ontogeny. The bone microstructure suggests that rauisuchian osteoderms were originated through a mechanism that involves both intramembranous and metaplastic ossifications. Fil: Cerda, Ignacio Alejandro. Universidad Nacional de Rio Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiologia y Geologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Desojo, Julia Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; Argentina Fil: Scheyer,Torsten M. . Universität Zürich. Paläontologisches Institut und Museum; Suiza Fil: Schultze, Cesar Leandro . Universidade Federal do Rio Grande do Sul; Brasil

In a recent study (Martizzi et al. 2012), we used cosmological simulations to show that active galactic nuclei (AGN) feedback on the gas distribution in clusters of galaxies can be important in determining the spatial distribution of stars and dark matter in the central regions of these systems. The hierarchical assembly of dark matter, baryons and black holes obscures the physical mechanism behind the restructuring process. Here we use idealized simulations to follow the response of a massive dark matter halo as we feed the central black hole with a controlled supply of cold gas. This removes most of the complexity taking place in the cosmological simulations that may have biased our previous study. We confirm our previous results: gas heated and expelled from the central regions of the halo by AGN feedback can return after cooling; repeated cycles generate gravitational potential fluctuations responsible for irreversible modifications of the dark matter mass profile. The main result is the expulsion of large amounts of baryons and dark matter from the central regions of the halo. According to the work presented here, outflow induced fluctuations represent the only mechanism able to efficiently create dark matter cores in clusters of galaxies., 9 pages, 5 figures, Published on MNRAS

We study the formation of a supermassive black hole (SMBH) binary and the shrinking of the separation of the two holes to sub-pc scales starting from a realistic major merger between two gas-rich spiral galaxies with mass comparable to our Milky Way. The simulations, carried out with the Adaptive Mesh Refinement (AMR) code RAMSES, are capable of resolving separations as small as 0.1 pc. The collision of the two galaxies produces a gravo-turbulent rotating nuclear disk with mass (10^9 Msun) and size (60 pc) in excellent agreement with previous SPH simulations with particle splitting that used a similar setup (Mayer et al. 2007) but were limited to separations of a few parsecs. The AMR results confirm that the two black holes sink rapidly as a result of dynamical friction onto the gaseous background, reaching a separation of 1 pc in less than 10^7 yr. We show that the dynamical friction wake is well resolved by our model and we find good agreement with analytical predictions of the drag force as a function of the Mach number. Below 1 pc, black hole pairing slows down significantly, as the relative velocity between the sinking SMBH becomes highly subsonic and the mass contained within their orbit falls below the mass of the binary itself, rendering dynamical friction ineffective. In this final stage, the black holes have not opened a gap as the gaseous background is highly pressurized in the center. Non-axisymmetric gas torques do not arise to restart sinking in absence of efficient dynamical friction, at variance with previous calculations using idealized equilibrium nuclear disk models. (abridged), Comment: Accepted for publication in MNRAS. 10 pages, 6 figures

Geophysical mapping and coring of the central Arctic Ocean seafloor provide evidence for repeated occurrences of ice sheet/ice shelf complexes during previous glacial periods. Several ridges and bathymetric highs shallower than present water depths of ~1000?m show signs of erosion from deep drafting (armadas of) icebergs which originated from thick outlet glaciers and ice shelves. Mapped glacigenic landforms and dates of cored sediments suggest that the largest ice shelf complex was confined to the Amerasian sector of the Arctic Ocean during Marine Isotope Stage (MIS) 6. However the spatial extent of ice shelves can not be well reconstructed from occasional groundings on bathymetric highs. Therefore we apply a statistical approach to provide independent support for an extensive MIS 6 ice shelf complex which previously was inferred only from interpretation of geophysical and geological data. Specifically we assess whether this ice shelf complex comprises a likely source of the deep draft icebergs responsible for the mapped scour marks. The statistical modeling is based on exploiting relations between contemporary Antarctic ice shelves and their local physical environments and the assumption that Arctic Ocean MIS?6 ice shelves scale similarly. Analyzing ice thickness data along the calving front of contemporary ice shelves a peak over threshold method is applied to determine sources of deep drafting icebergs in the Arctic Ocean MIS?6 ice shelf complex. This approach is novel to modeling Arctic paleoglacial configurations. Predicted extreme calving front drafts match observed deep draft iceberg scours if the ice shelf complex is sufficiently large.

Models of the Sagittarius Stream have consistently found that the Milky Way disc is oriented such that its short axis is along the intermediate axis of the triaxial dark matter halo. We attempt to build models of disc galaxies in such an `intermediate-axis orientation'. We do this with three models. In the first two cases we simply rigidly grow a disc in a triaxial halo such that the disc ends up perpendicular to the global intermediate axis. We also attempt to coax a disc to form in an intermediate-axis orientation by producing a gas+dark matter triaxial system with gas angular momentum about the intermediate axis. In all cases we fail to produce systems which remain with stellar angular momentum aligned with the halo's intermediate axis, even when the disc's potential flattens the inner halo such that the disc is everywhere perpendicular to the halo's local minor axis. For one of these unstable simulations we show that the potential is even rounder than the models of the Milky Way potential in the region probed by the Sagittarius Stream. We conclude that the Milky Way's disc is very unlikely to be in an intermediate axis orientation. However we find that a disc can persist off one of the principal planes of the potential. We propose that the disc of the Milky Way must be tilted relative to the principal axes of the dark matter halo. Direct confirmation of this prediction would constitute a critical test of Modified Newtonian Dynamics., 12 pages, 13 figures. Updated to reflect the accepted version which has some further discussion and more references, corrects an error in the literature which modifies figure 7 slightly, includes an additional figure, adds results from further evolution of one of the simulations and other minor changes. None of the conclusions of the paper are changed as a result

Dysregulation of the immune system occurs during spaceflight and may represent a crew health risk during exploration missions because astronauts are challenged by many stressors. Therefore, it is crucial to understand the biology of immune modulation under spaceflight conditions in order to be able to maintain immune homeostasis under such challenges. In the framework of the THESEUS project whose aim was to develop an integrated life sciences research roadmap regarding human space exploration, experts working in the field of space immunology, and related disciplines, established a questionnaire sent to scientists around the world. From the review of collected answers, they deduced a list of key issues and provided several recommendations such as a maximal exploitation of currently available resources on Earth and in space, and to increase increments duration for some ISS crew members to 12 months or longer. These recommendations should contribute to improve our knowledge about spaceflight effects on the immune system and the development of countermeasures that, beyond astronauts, could have a societal impact.

The consistency of planet formation models suffers from the disconnection between the regime of small and large bodies. This is primarily caused by so-called growth barriers: the direct growth of larger bodies is halted at centimetre-sized objects and particular conditions are required for the formation of larger, gravitationally bound planetesimals. We aim to connect models of dust evolution and planetesimal formation to identify regions of protoplanetary discs that are favourable for the formation of kilometre-sized bodies and the first planetary embryos. We combine semi-analytical models of viscous protoplanetary disc evolution, dust growth and drift including backreaction of the dust particles on the gas, and planetesimal formation via the streaming instability into one numerical code. We investigate how planetesimal formation is affected by the mass of the protoplanetary disc, its initial dust content, and the stickiness of dust aggregates. We find that the dust growth and drift leads to a global redistribution of solids. The pile-up of pebbles in the inner disc provides local conditions where the streaming instability is effective. Planetesimals form in an annulus with its inner edge lying between 0.3 AU and 1 AU and its width ranging from 0.3 AU to 3 AU. The resulting surface density of planetesimals follows a radial profile that is much steeper than the initial disc profile. These results support formation of terrestrial planets in the solar system from a narrow annulus of planetesimals, which reproduces their peculiar mass ratios., Comment: 11 pages, 7 figures, 2 tables, accepted for publication in Astronomy & Astrophysics, updated to match the published version

Recent spatially resolved observations of galaxies at z=0.6-3 reveal that high-redshift galaxies show complex kinematics and a broad distribution of gas-phase metallicity gradients. To understand these results, we use a suite of high-resolution cosmological zoom-in simulations from the Feedback in Realistic Environments (FIRE) project, which include physically motivated models of the multi-phase ISM, star formation, and stellar feedback. Our simulations reproduce the observed diversity of kinematic properties and metallicity gradients, broadly consistent with observations at z=0-3. Strong negative metallicity gradients only appear in galaxies with a rotating disk, but not all rotationally supported galaxies have significant gradients. Strongly perturbed galaxies with little rotation always have flat gradients. The kinematic properties and metallicity gradient of a high-redshift galaxy can vary significantly on short time-scales, associated with starburst episodes. Feedback from a starburst can destroy the gas disk, drive strong outflows, and flatten a pre-existing negative metallicity gradient. The time variability of a single galaxy is statistically similar to the entire simulated sample, indicating that the observed metallicity gradients in high-redshift galaxies reflect the instantaneous state of the galaxy rather than the accretion and growth history on cosmological time-scales. We find weak dependence of metallicity gradient on stellar mass and specific star formation rate (sSFR). Low-mass galaxies and galaxies with high sSFR tend to have flat gradients, likely due to the fact that feedback is more efficient in these galaxies. We argue that it is important to resolve feedback on small scales in order to produce the diverse metallicity gradients observed., 17 pages, 10 figures, re-submitted to MNRAS after addressing referee's comments

We analyse the star formation rates (SFRs), colours, and dust extinctions of galaxies in massive (10^12.5-10^13.5 Msun) haloes at z~2 in high-resolution, cosmological zoom-in simulations as part of the Feedback in Realistic Environments (FIRE) project. The simulations do not model feedback from active galactic nuclei (AGN) but reproduce well the observed relations between stellar and halo mass and between stellar mass and SFR. About half (a third) of the simulated massive galaxies (massive central galaxies) at z~2 have broad-band colours classifying them as 'quiescent', and the fraction of quiescent centrals is steeply decreasing towards higher redshift, in agreement with observations. The progenitors of z~2 quiescent central galaxies are, on average, more massive, have lower specific SFRs, and reside in more massive haloes than the progenitors of similarly massive star forming centrals. The simulations further predict a morphological mix of galaxies that includes disk-dominated, irregular, and early-type galaxies. However, our simulations do not reproduce the reddest of the quiescent galaxies observed at z~2. We also do not find evidence for a colour bimodality, but are limited by our modest sample size. In our simulations, the star formation activity of central galaxies of moderate mass (Mstar~10^10-10^11 Msun) is affected by a combination of two distinct physical processes. Outflows powered by stellar feedback result in a short-lived (, 24 pages, 17 figures, 4 tables, accepted for publication in MNRAS

We study the orbital decay of a pair of massive black holes (BHs) with masses 5 * 10^5 and 10^7 M_sun, using hydrodynamical simulations of circumnuclear disks (CNDs) with the alternating presence of sub-grid physics such as radiative cooling, star formation, supernova feedback, BH accretion and feedback. In the absence of such processes, the orbit of the secondary BH decays over timescales of ~10 Myr to the center of the CND, where the primary BH resides. When strong dissipation operates in CNDs, fragmentation into massive objects the size of giant molecular clouds and with densities in the range 10^4 - 10^7 amu / cm^3 occurs, causing stochastic torques and hits that can eject the secondary BH from the midplane. Outside the plane, the low-density medium provides only weak drag, and the BH return is governed by inefficient dynamical friction. In rare cases, clump-BH interactions can lead to a faster decay. Feedback processes lead to outflows, but do not change significantly the overall density of the CND midplane. However, with a spherically distributed BH feedback a hot bubble is generated behind the secondary, which almost shuts off dynamical friction, a phenomenon we dub "wake evacuation", leading to delays in the decay of possibly ~0.3 Gyr. We discuss the non-trivial implications on the discovery space of the eLISA telescope. Our results suggest the largest uncertainty in predicting BH merger rates lies in the potentially wide variety of galaxy host systems, with different degrees of gas dissipation and heating, yielding decay timescales from ~10 to ~300 Myr., 20. pages, 14 figures. Accepted for publication in ApJ. Comments are welcome

The largest galaxies acquire their mass early on, when the Universe is still youthful. Cold streams violently feed these young galaxies a vast amount of fresh gas, resulting in very efficient star formation. Using a well resolved hydrodynamical simulation of galaxy formation, we demonstrate that these mammoth galaxies are already in place a couple of billion years after the Big Bang. Contrary to local starforming galaxies, where dust re-emits a large part of the stellar ultraviolet (UV) light at infrared and sub-millimetre wavelengths, our self-consistent modelling of dust extinction predicts that a substantial fraction of UV photons should escape from primordial galaxies. Such a model allows us to compute reliably the number of high redshift objects as a function of luminosity, and yields galaxies whose UV luminosities closely match those measured in the deepest observational surveys available. This agreement is remarkably good considering our admittedly still simple modelling of the interstellar medium (ISM) physics. The luminosity functions (LF) of virtual UV luminous galaxies coincide with the existing data over the whole redshift range from 4 to 7, provided cosmological parameters are set to their currently favoured values. Despite their considerable emission at short wavelengths, we anticipate that the counterparts of the brightest UV galaxies will be detected by future sub-millimetre facilities like ALMA, Comment: 5 pages, 3 figures, submitted to MNRAS-let

We explore cloudy, extended H2-He atmosphere scenarios for the warm super-Earth GJ 1214b using an optimal estimation retrieval technique. This planet, orbiting an M4.5 star only 13 pc from the Earth, is of particular interest because it lies between the Earth and Neptune in size and may be a member of a new class of planet that is neither terrestrial nor gas giant. Its relatively flat transmission spectrum has so far made atmospheric characterisation difficult. The NEMESIS algorithm (Irwin et al. 2008) is used to explore the degenerate model parameter space for a cloudy, H2-He-dominated atmosphere scenario. Optimal estimation is a data-led approach that allows solutions beyond the range permitted by ab initio equilibrium model atmosphere calculations, and as such prevents restriction from prior expectations. We show that optimal estimation retrieval is a powerful tool for this kind of study, and present an exploration of the degenerate atmospheric scenarios for GJ 1214b. Whilst we find a family of solutions that provide a very good fit to the data, the quality and coverage of these data are insufficient for us to more precisely determine the abundances of cloud and trace gases given an H2-He atmosphere, and we also cannot rule out the possibility of a high molecular weight atmosphere. Future ground- and space-based observations will provide the opportunity to confirm or rule out an extended H2-He atmosphere, but more precise constraints will be limited by intrinsic degeneracies in the retrieval problem, such as variations in cloud top pressure and temperature., 15 pages, 13 figures, 10 tables. Accepted for publication in MNRAS

We infer the normalization and the radial and angular distributions of the number density of satellites of massive galaxies ($\log_{10}[M_{h}^*/M\odot]>10.5$) between redshifts 0.1 and 0.8 as a function of host stellar mass, redshift, morphology and satellite luminosity. Exploiting the depth and resolution of the COSMOS HST images, we detect satellites up to eight magnitudes fainter than the host galaxies and as close as 0.3 (1.4) arcseconds (kpc). Describing the number density profile of satellite galaxies to be a projected power law such that $P(R)\propto R^{\rpower}$, we find $\rpower=-1.1\pm 0.3$. We find no dependency of $\rpower$ on host stellar mass, redshift, morphology or satellite luminosity. Satellites of early-type hosts have angular distributions that are more flattened than the host light profile and are aligned with its major axis. No significant average alignment is detected for satellites of late-type hosts. The number of satellites within a fixed magnitude contrast from a host galaxy is dependent on its stellar mass, with more massive galaxies hosting significantly more satellites. Furthermore, high-mass late-type hosts have significantly fewer satellites than early-type galaxies of the same stellar mass, likely a result of environmental differences. No significant evolution in the number of satellites per host is detected. The cumulative luminosity function of satellites is qualitatively in good agreement with that predicted using subhalo abundance matching techniques. However, there are significant residual discrepancies in the absolute normalization, suggesting that properties other than the host galaxy luminosity or stellar mass determine the number of satellites., 23 pages, 12 figures, Accepted for publication in the Astrophysical Journal

The GAUGE (GrAnd Unification and Gravity Explorer) mission proposes to use a drag-free spacecraft platform onto which a number of experiments are attached. They are designed to address a number of key issues at the interface between gravity and unification with the other forces of nature. The equivalence principle is to be probed with both a high-precision test using classical macroscopic test bodies, and, to lower precision, using microscopic test bodies via cold-atom interferometry. These two equivalence principle tests will explore string-dilaton theories and the effect of space-time fluctuations respectively. The macroscopic test bodies will also be used for intermediate-range inverse-square law and an axion-like spin-coupling search. The microscopic test bodies offer the prospect of extending the range of tests to also include short-range inverse-square law and spin-coupling measurements as well as looking for evidence of quantum decoherence due to space-time fluctuations at the Planck scale. © Springer Science + Business Media B.V. 2008.

Using high resolution, fully cosmological smoothed particle hydro-dynamical simulations of dwarf galaxies in a Lambda cold dark matter Universe, we show how baryons attain a final angular momentum distribution which allows pure disc galaxies to form. Blowing out substantial amounts of gas through supernovae and stellar winds, which is well supported observationally, is a key ingredient in forming bulgeless discs. We outline why galactic outflows preferentially remove low angular momentum material, and show that this is a natural result when structure forms in a cold dark matter cosmology. The driving factors are a) the mean angular momentum of accreted material increases with time, b) lower potentials at early times, c) the existence of an extended reservoir of high angular momentum gas which is not within star forming regions, meaning that only gas from the inner region (low angular momentum gas) is expelled and d) the tendency for outflows to follow the path of least resistance which is perpendicular to the disc. We also show that outflows are enhanced during mergers, thus expelling much of the gas which has lost its angular momentum during these events, and preventing the formation of "classical", merger driven bulges in low mass systems. Stars formed prior to such mergers form a diffuse, extended stellar halo component., accepted version: MNRAS in press

The correlation between the large-scale distribution of galaxies and their spectroscopic properties at z=1.5 is investigated using the Horizon MareNostrum cosmological run. We have extracted a large sample of 10^5 galaxies from this large hydrodynamical simulation featuring standard galaxy formation physics. Spectral synthesis is applied to these single stellar populations to generate spectra and colours for all galaxies. We use the skeleton as a tracer of the cosmic web and study how our galaxy catalogue depends on the distance to the skeleton. We show that galaxies closer to the skeleton tend to be redder, but that the effect is mostly due to the proximity of large haloes at the nodes of the skeleton, rather than the filaments themselves. This effects translate into a bimodality in the colour distribution of our sample. The origin of this bimodality is investigated and seems to follow from the ram pressure stripping of satellite galaxies within the more massive clusters of the simulation. The virtual catalogues (spectroscopical properties of the MareNostrum galaxies at various redshifts) are available online at http://www.iap.fr/users/pichon/MareNostrum/catalogues, 18 pages, 27 figures, accepted for publication in MNRAS

The morphology of massive star-forming galaxies at high redshift is often dominated by giant clumps of mass ~10^8-10^9 Msun and size ~100-1000 pc. Previous studies have proposed that giant clumps might have an important role in the evolution of their host galaxy, particularly in building the central bulge. However, this depends on whether clumps live long enough to migrate from their original location in the disc or whether they get disrupted by their own stellar feedback before reaching the centre of the galaxy. We use cosmological hydrodynamical simulations from the FIRE (Feedback in Realistic Environments) project that implement explicit treatments of stellar feedback and ISM physics to study the properties of these clumps. We follow the evolution of giant clumps in a massive (stellar mass ~10^10.8 Msun at z=1), discy, gas-rich galaxy from redshift z>2 to z=1. Even though the clumpy phase of this galaxy lasts over a gigayear, individual gas clumps are short-lived, with mean lifetime of massive clumps of ~20 Myr. During that time, they turn between 0.1% and 20% of their gas into stars before being disrupted, similar to local GMCs. Clumps with M>10^7 Msun account for ~20% of the total star formation in the galaxy during the clumpy phase, producing ~10^10 Msun of stars. We do not find evidence for net inward migration of clumps within the galaxy. The number of giant clumps and their mass decrease at lower redshifts, following the decrease in the overall gas fraction and star-formation rate., 20 pages, 19 figures; revised version, accepted for publication in MNRAS

Spatial and temporal patterns of forest background (understory) reflectance are crucial for retrieving biophysical parameters of forest canopies (overstory) and subsequently for ecosystem modeling. In this communication, we retrieved seasonal courses of understory normalized difference vegetation index (NDVI) from multiangular Moderate Resolution Imaging Spectroradiometer bidirectional reflectance distribution function (MODIS BRDF)/albedo data. We compared satellite-based seasonal courses of understory NDVI to understory NDVI values measured in different types of forests distributed along a wide latitudinal gradient (65.12°N-31.35°N). Our results indicated that the retrieval method performs well particularly over open forests of different types. We also demonstrated the limitations of the method for closed canopies, where the understory signal retrieval is much attenuated.

We introduce a series of 20 cosmological hydrodynamical simulations of Lstar (M_200 =10^11.7 - 10^12.3 Msol) and group-sized (M_200 = 10^12.7 - 10^13.3 Msol) haloes run with the model used for the EAGLE project, which additionally includes a non-equilibrium ionization and cooling module that follows 136 ions. The simulations reproduce the observed correlation, revealed by COS-Halos at z~0.2, between O VI column density at impact parameters b < 150 kpc and the specific star formation rate (sSFR=SFR/Mstar) of the central galaxy at z~0.2. We find that the column density of circumgalactic O VI is maximal in the haloes associated with Lstar galaxies, because their virial temperatures are close to the temperature at which the ionization fraction of O VI peaks (T~10^5.5 K). The higher virial temperature of group haloes (> 10^6 K) promotes oxygen to higher ionization states, suppressing the O VI column density. The observed NO VI-sSFR correlation therefore does not imply a causal link, but reflects the changing characteristic ionization state of oxygen as halo mass is increased. In spite of the mass-dependence of the oxygen ionization state, the most abundant circumgalactic oxygen ion in both Lstar and group haloes is O VII; O VI accounts for only 0.1% of the oxygen in group haloes and 0.9-1.3% with Lstar haloes. Nonetheless, the metals traced by O VI absorbers represent a fossil record of the feedback history of galaxies over a Hubble time; their characteristic epoch of ejection corresponds to z > 1 and much of the ejected metal mass resides beyond the virial radius of galaxies. For both Lstar and group galaxies, more of the oxygen produced and released by stars resides in the circumgalactic medium (within twice the virial radius) than in the stars and ISM of the galaxy., 25 pages, 14 figures, 2 tables. Accepted in MNRAS

In quasars which are lensed by galaxies, the point-like images sometimes show sharp and uncorrelated brightness variations (microlensing). These brightness changes are associated with the innermost region of the quasar passing through a complicated pattern of caustics produced by the stars in the lensing galaxy. In this paper, we study whether the universal properties of optical caustics could enable extraction of shape information about the central engine of quasars. We present a toy model with a crescent-shaped source crossing a fold caustic. The silhouette of a black hole over an accretion disk tends to produce roughly crescent sources. When a crescent-shaped source crosses a fold caustic, the resulting light curve is noticeably different from the case of a circular luminosity profile or Gaussian source. With good enough monitoring data, the crescent parameters, apart from one degeneracy, can be recovered.