Inversion of stellar statistics equation for the Galactic Bulge

A method based on Lucy (1974, AJ 79, 745) iterative algorithm is developed to invert the equation of stellar statistics for the Galactic bulge and is then applied to the K-band star counts from the Two-Micron Galactic Survey in a number of off-plane regions (10 deg.>|b|>2 deg., |l|<15 deg.). The top end of the K-band luminosity function is derived and the morphology of the stellar density function is fitted to triaxial ellipsoids, assuming a non-variable luminosity function within the bulge. The results, which have already been outlined by Lopez-Corredoira et al.(1997, MNRAS 292, L15), are shown in this paper with a full explanation of the steps of the inversion: the luminosity function shows a sharp decrease brighter than M_K=-8.0 mag when compared with the disc population; the bulge fits triaxial ellipsoids with the major axis in the Galactic plane at an angle with the line of sight to the Galactic centre of 12 deg. in the first quadrant; the axial ratios are 1:0.54:0.33, and the distance of the Sun from the centre of the triaxial ellipsoid is 7860 pc. The major-minor axial ratio of the ellipsoids is found not to be constant. However, the interpretation of this is controversial. An eccentricity of the true density-ellipsoid gradient and a population gradient are two possible explanations. The best fit for the stellar density, for 1300 pc<t<3000 pc, are calculated for both cases, assuming an ellipsoidal distribution with constant axial ratios, and when K_z is allowed to vary. From these, the total number of bulge stars is ~ 3 10^{10} or ~ 4 10^{10}, respectively.Comment: 19 pages, 23 figures, accepted in MNRA

Astrophysical inputs on the SUSY dark matter annihilation detectability

If dark matter (DM), which is considered to constitute most of the mass of galaxies, is made of supersymmetric (SUSY) particles, the centers of galaxies should emit gamma-rays produced by their self-annihilation. We present accurate estimates of continuum gamma-ray fluxes due to neutralino annihilation in the central regions of the Milky Way. We use detailed models of our Galaxy, which satisfy available observational data, and include some important physical processes, which were previously neglected. Our models predict that spatially extended annihilation signal should be detected at high confidence levels by incoming experiments assuming that neutralinos make up most of the DM in the Universe and that they annihilate according to current SUSY models.Comment: 4 pages, submitted to Physical Review Letter

How far do they go? The outer structure of dark matter halos

We study the density profiles of collapsed galaxy-size dark matter halos with masses 1e11-5e12 Msun focusing mostly on the halo outer regions from the formal virial radius Rvir up to 5-7Rvir. We find that isolated halos in this mass range extend well beyond Rvir exhibiting all properties of virialized objects up to 2-3Rvir: relatively smooth density profiles and no systematic infall velocities. The dark matter halos in this mass range do not grow as one naively may expect through a steady accretion of satellites, i.e., on average there is no mass infall. This is strikingly different from more massive halos, which have large infall velocities outside of the virial radius. We provide accurate fit for the density profile of these galaxy-size halos. For a wide range (0.01-2)Rvir of radii the halo density profiles are fit with the approximation rho=rho_s exp(-2n[x^{1/n}-1])+rho_m, where x=r/r_s, rho_m is the mean matter density of the Universe, and the index n is in the range n=6-7.5. These profiles do not show a sudden change of behavior beyond the virial radius. For larger radii we combine the statistics of the initial fluctuations with the spherical collapse model to obtain predictions for the mean and most probable density profiles for halos of several masses. The model give excellent results beyond 2-3 formal virial radii.Comment: 15 pages, 10 figures, submitted to Ap

What does the functional-structural plant model HydroShoot tell us about the reasons for photosynthesis depression in grapevine (​Vitis vinifera​ L.)photosynthesis depression?

Grapevine is a species that get along with water deficit. Yet, it cannot always stand thirst when accompanied by high temperatures, reducing noticeably its gas-exchange rates. Elucidating the origins of this reduction is a challenge, regarded the complex hydraulic, biochemical and energy processes lying behind gas-exchanges. In this work we analyze data collected from an experiment conducted at he whole plant scale on Syrah vines with the aid of the functional-structural plant model HydroShoot. During our experiment, we submitted grapevines to a severe water stress and observed a steep drop in whole plant photosynthetic rates at midday, that was not due to stomatal closure, suggesting that both processes were decoupled at this moment. Using HydroShoot, we explore whether this decoupling results from a direct water limitation on biochemical processes. HydroShoot links xylem hydraulic transport to gas and energy exchanges processes at the organ level. It simulates the effect of water deficit on xylem and stomatal conductances. The biochemical reactions of photosynthesis are affected by water deficit both indirectly through diffusional limitation and directly, through a reduced electron transport rate. Temperature affects photosynthetic rates through Arrhenius functions. Using HydroShoot, we show that photosynthetic, midday depression could not be explained by simple hydraulic limitations. Bulk leaf water potential dropped to -1.6 MPa but this drop only affected J max when temperatures exceeded 34 °C. Neither the Arrhenius response, nor the water limitation considered independently were sufficient to predict the observed drops. Only when responses to water and temperature were combined were we able to reproduce these observations, suggesting that photoinhibition may have occurred under these conditions. Apart from an evidence of photoinhibition, our simulations indicate that xylem cavitation could not explain the observed drop in bulk leaf water potential. By contrast, a decrease in soil water potential has dramatic effects, much stronger than changes in xylem conductivity. The hydraulic architecture did not seem to play a major role in triggering stomatal closure. We conclude that an adequate prediction of grapevines water use efficiency under water deficit conditions relies strongly on soil hydraulic properties and photoinhibition predictions

Past Holocene detritism quantification and modeling from lacustrine archives in order to deconvoluate human-climate interactions on natural ecosystem over long time-scale

International audienceWater budget is one of the main challenges to paleoclimate researchers in relation to present-day global warming and its consequences for human societies

French Alpine Foreland Holocene Paleoseismicity Revealed by Coeval Mass Wasting Deposits in Glacial Lakes

International audienceThe French alpine foreland area has been struck by several earthquakes with magnitudes above 5 on Richter scale in recent history. In this paper we document the regional impact of historical and Holocene earthquakes based on the identification of mass wasting deposits in glacial lakes at different settings. Lake Le Bourget and Lake Paladru are situated at low elevations (respectively 231 m–492 m) and Lake Blanc Huez is located at 2500 m altitude. Through the integration of high-resolution acoustic profiles and accurately dated sediment samples from cores, recent coeval mass wasting deposits in each lake were correlated with nearby historical earthquakes, whereas coeval mass wasting deposits around 5200 cal BP and 9550 cal BP in these three lakes were correlated to regional earthquakes events