The Eocene unconformity of the Briançonnais domain in the French—Italian Alps, revisited (Marguareis massif, Cuneo); a hint for a Late Cretaceous—Middle Eocene frontal bulge setting

The tectonic significance of the Eocene unconformity in the Brianconnais domain, classically regarded as recording a compressional event, is re-evaluated, based on field studies in the Marguareis m..

Vitesses de réaction de dissolution et précipitation au voisinage de l'interface oxydo-réducteur dans un lac méromictique : le lac Pavin (Puy de Dôme, France)

Une étude à l'échelle centimétrique de l'interface redox situé à la limite entre mixolimnion et monimolimnion d'un lac méromictique (le lac Pavin) a permis d'observer très finement l'évolution de la concentration d'un certain nombre d'éléments chimiques. Nous avons choisi de présenter ici des résultats concernant 5 éléments qui présentent des comportements très contrastés : le rubidium, le fer, le baryum, le vanadium et le manganèse. La comparaison avec un élément conservatif, le sodium, montre que Rb est conservatif, que Fe, Ba et V sont précipités et que Mn est dissous dans cette zone.Une modélisation de ces concentrations en vue de préciser à quelle profondeur et avec quelle vitesse se produisent les réactions concernant ces éléments nécessite la détermination des paramètres de transport au voisinage de cet interface.Une représentation analytique des concentrations de sodium permet de calculer le coefficient de diffusion turbulente Kz en fonction de la profondeur. Au voisinage de l'interface redox, ce coefficient est très petit (0,0017m2/jour) et inférieur au coefficient de diffusion thermique moléculaire.Les concentrations des éléments étudiés ont pu être représentés avec précisions par des polynômes en fonction de la concentration en sodium.Cela permet d'estimer les vitesses des réactions de précipitation dissolution en fonction de la profondeur. Le rubidium n'est affecté par aucune réaction. Le fer précipite entre 63 et 65 m, le baryum entre 68 et 72 m tandis que le vanadium précipite à la fois dans ces 2 zones. Le manganèse réagit dans une zone très étroite : il est précipité entre 61,5 et 62 m et dissous entre 62,8 et 63,1 m.Une étude similaire de tous les éléments majeurs (y compris pH et COD) pourrait permettre d'élucider les processus qui conduisent à ces comportements complexes.Lake Pavin, French Massif Central, is the main meromictic lake in France and has been extensively studied from more than 50 years. The upper part (mixolimnion) at a depth of less than about 60 m behaves as an oligotrophic lake and is oxic during the major part of the year. The lower layer (monimolimnion) has a higher salinity and is permanently anoxic. Unlike the top of the mixolimnion, element concentrations in the monimolimnion can be considered at steady state. The boundary between mixolimnion and monimolimnion is a redox interface. At this interface, an important number of both chemical and biochemical reactions occur. This boundary, where element concentrations vary greatly, was studied at the centimeter scale between 58 and 64 m depth. The present paper is focused on five elements showing very different behaviour: rubidium, iron, manganese, vanadium and barium. Sodium was used as a reference element. Sodium and rubidium concentrations had similar patterns: a progressive increase began at 61 m depth and the maximal gradient was located at 63 m. They continue to increase towards the bottom of the lake. Iron concentrations were low (< 1 µmol/L) at a depth less than 62.8 m and increased very sharply below this depth. Manganese concentrations were very low in the mixolimnion(<0.01 µmol/L), exhibited a peak between 62.4 and 63.5 m depth (up to 60 µmol/L at 63 m) and reached a value of about 30 µmol/L at 85 m. Barium concentrations began to increase only at depths greater than 65-67 m. Vanadium concentrations in the mixolimnion were about 14 nmol/L, decreased to a minimum below the detection limit at 62.2 m and then increase drastically (150 nmol/L at 85 m).In order to derive the accurate location of the chemical reactions and an estimation of their rates from the concentration profiles, knowledge of the transport parameters was needed. As advection can be considered to be negligible, the major parameter of interest is the vertical eddy diffusion coefficient Kz. Na is assumed to be unreactive in the studied layer. Its concentrations can be represented by an analytical function      Cmax - Cmin                 Cmax + CminC = ___________ * th [P(z)] + ___________             2                                    2with P(z)=0.0016 * (z-zo)3 - 0.0493 * (z-zo)2 + 0.5735 * (z-zo) - 0.4811This allows the determination of the coefficient Kz.Kz = λ ch2 [P(z)]/ [P'(z)]λ is determined from the value of Kz at 85 m depth previously obtained from an hydrodynamic study of the lake (Aeshbach-Hertig et al., 1999). This coefficient is about 0.1 m2/day at the bottom of the monimolimnion. It is very low at the redox interface (0.0017 m2/day), far below the molecular thermal diffusion coefficient. It increases very sharply at the bottom of the mixolimnion. The Kz profile is in fair agreement with the results obtained from the earlier hydrodynamic study. A quantitative study of the dissolution-precipitation reactions at the center of the lake at depths between 55 and 85 m can then be undertaken. The 55 m limit corresponds to a depth where inputs of fresh water can occur. The 85 m limit is about 7 m above the bottom of the lake. Below this depth important inputs from the pore waters occur which are not taken into account by the present modeling. Concentrations of Rb, Fe, Ba and V can be accurately represented by polynomial functions of the Na concentration. The parameter u=th[P(z)] represents the concentrations of these 4 elements by polynomials :          NX(u) = Σ an * un          0The rate of dissolution-precipitation for each element as a function of depth can be derived.                                       NR = - λ [P'(z)] * ch-2[P(z)] Σ ann(n-1) * thn-2[P(z)]                                        0Rb concentrations are a linear function of the Na ones and therefore rubidium is not reactive. Fe concentrations can be related to sodium concentrations by a parabolic relationship. From this relationship, it can be derived that strong iron precipitation occurs in the 63 - 65 m depth layer. V concentrations are related to sodium ones by a 4th degree polynomial. It can be derived that V deposition occurs at depths of 63-65 m and at 70 m.Ba precipitates around 70 m depth. Mn concentrations are represented by [Mn]=a0 +a1 u + b1 exp[-(z-z°)2/z*2] and the derivation shows that Mn is strongly dissolved between 62.8 and 63 m and precipitated just above. These results are in good agreement with a previous study of particles fluxes derived from sediment trap analysis (Viollier et al, 1997).This study shows the complexity of this interface and more comprehensive studies including all major elements, dissolved organic carbon (DOC) and pH are needed

Correlations among global photometric properties of disk galaxies

Using a two-dimensional galaxy image decomposition technique, we extract global bulge and disk parameters for a complete sample of early type disk galaxies in the near infrared K band. We find significant correlation of the bulge parameter n with the central bulge surface brightness $\mu_b(0)$ and with effective radius r_e. Using bivar iate analysis techniques, we find that $\log n$, $\log r_e$ and $\mu_b(0)$ are distributed in a plane with small scatter. We do not find a strong correlation of n with bulge-to-disk luminosity ratio, contrary to earlier reports. r_e and the disk scale length r_d are well correlated for these early type disk galaxies, but with large scatter. We examine the implications of our results to various bulge formation scenarios in disk galaxies.Comment: 14 pages, LaTeX including 14 figures. To appear in the Astrophysical Journa

Quantitative Morphology of Galaxies in the Hubble Deep Field

We measure quantitative structural parameters of galaxies in the Hubble Deep Field (HDF) on the drizzled F814W images. Our structural parameters are based on a two-component surface brightness made up of a S\'ersic profile and an exponential profile. We compare our results to the visual classification of van den Bergh et al. (1996) and the $C-A$ classification of Abraham et al. (1996a). Our morphological analysis of the galaxies in the HDF indicates that the spheroidal galaxies, defined here as galaxies with a dominant bulge profile, make up for only a small fraction, namely 8% of the galaxy population down to m$_{F814W}(AB)$ = 26.0. We show that the larger fraction of early-type systems in the van den Bergh sample is primarily due to the difference in classification of 40% of small round galaxies with half-light radii < 0\arcsecpoint 31. Although these objects are visually classified as elliptical galaxies, we find that they are disk-dominated with bulge fractions < 0.5. Given the existing large dataset of HDF galaxies with measured spectroscopic redshifts, we are able to determine that the majority of distant galaxies ($z>2$) from this sample are disk-dominated. Our analysis reveals a subset of HDF galaxies which have profiles flatter than a pure exponential profile.Comment: 35 pages, LaTeX, 18 Postscript Figures, Tables available at http://astro.berkeley.edu/~marleau/. Accepted for Publication in The Astrophysical Journa

Evidence for tidal interaction and merger as the origin of galaxy morphology evolution in compact groups

We present the results of a morphological study based on NIR images of 25 galaxies, with different levels of nuclear activity, in 8 Compact Groups of Galaxies (CGs). We perform independently two different analysis: a isophotal study and a study of morphological asymmetries. The results yielded by the two analysis are highly consistent. For the first time, it is possible to show that deviations from pure ellipses are produced by inhomogeneous stellar mass distributions related to galaxy interactions and mergers. We find evidence of mass asymmetries in 74% of the galaxies in our sample. In 59% of these cases, the asymmetries come in pairs, and are consistent with tidal effects produced by the proximity of companion galaxies. The symmetric galaxies are generally small in size or mass, inactive, and have an early-type morphology. In 20% of the galaxies we find evidence for cannibalism. In 36% of the early-type galaxies the color gradient is positive (blue nucleus) or flat. Summing up these results, as much as 52% of the galaxies in our sample could show evidence of an on going or past mergers. Our observations suggest that galaxies in CGs merge more frequently under ``dry'' conditions. The high frequency of interacting and merging galaxies observed in our study is consistent with the bias of our sample towards CGs of type B, which represents the most active phase in the evolution of the groups. In these groups we also find a strong correlation between asymmetries and nuclear activity in early-type galaxies. This correlation allows us to identify tidal interactions and mergers as the cause of galaxy morphology transformation in CGs.[abridge]Comment: 64 pages, 35 figures. Accepted for publication in Ap

Far-Ultraviolet Color Gradients in Early-Type Galaxies

We discuss far-UV (1500 A) surface photometry and FUV-B color profiles for 8 E/S0 galaxies from images taken with the Ultraviolet Imaging Telescope, primarily during the Astro-2 mission. In three cases, the FUV radial profiles are more consistent with an exponential than a de Vaucouleurs function, but there is no other evidence for the presence of a disk or of young, massive stars. In all cases except M32 the FUV-B color becomes redder at larger radii. There is a wide range of internal radial FUV-B color gradients. However, we find no correlation between the FUV-B color gradients and internal metallicity gradients based on Mg absorption features. We conclude that metallicity is not the sole parameter controlling the "UV upturn component" in old populations.Comment: 11 pages; tar.gz file includes LaTeX text file, 3 PostScript figures. Paper to be published in ApJ Letter

Evidence for an outer disk in the Prototype `Compact Elliptical' Galaxy M32

M32 is the prototype for the relatively rare class of galaxies referred to as `compact ellipticals'. It has been suggested that M32 may be a tidally disturbed r^(1/4) elliptical galaxy, or the remnant bulge of a disk-stripped early-type spiral galaxy. This paper reveals that the surface brightness profile, the velocity dispersion measurements, and the estimated supermassive black hole mass in M32 are inconsistent with the galaxy having, and probably ever having had, an r^(1/4) light profile. Instead, the radial surface brightness distribution of M32 resembles an almost perfect (bulge + exponential disk) profile, which is accompanied by a marked increase in the ellipticity profile and an associated change in the position angle profile where the `disk' starts to dominate. Compelling evidence that this bulge/disk interpretation is accurate comes from the best-fitting r^(1/n) bulge model which has a Sersic index n=1.5, in agreement with the recently discovered relation between a bulge's Sersic index and the mass of its supermassive black hole. An index n>4 would also be inconsistent with the stellar velocity dispersion of M32. The bulge-to-disk size ratio r_e /h equals 0.20, and the logarithm of the bulge-to-disk luminosity ratio log(B/D) equals 0.22, typical of lenticular galaxies. The effective radius of the bulge is 27" (~100 pc), while the scale-length of the disk is less well determined: due to possible tidal- stripping of the outer profile beyond 220-250", the scale-length may be as large as 1.3 kpc. M32 is a relatively face-on, nucleated, dwarf galaxy with a low surface brightness disk and a high surface brightness bulge. This finding brings into question the existence of the compact elliptical class of galaxies.Comment: Accepted for publication in ApJ Letter

Central Structural Parameters of Early-Type Galaxies as Viewed with HST/NICMOS

We present surface photometry for the central regions of a sample of 33 early-type (E, S0, and S0/a) galaxies observed at 1.6 microns (H band) using the Hubble Space Telescope (HST). We employ a new technique of two-dimensional fitting to extract quantitative parameters for the bulge light distribution and nuclear point sources, taking into consideration the effects of the point-spread function. Parameterizing the bulge profile with a ``Nuker'' law, we confirm that the central surface-brightness distributions largely fall into two categories, each of which correlates with the global properties of the galaxies. ``Core'' galaxies tend to be luminous ellipticals with boxy or pure elliptical isophotes, whereas ``power-law'' galaxies are preferentially lower luminosity systems with disky isophotes. Unlike most previous studies, however, we do not find a clear gap in the distribution of inner cusp slopes; several objects have inner cusp slopes (0.3 < gamma < 0.5) which straddle the regimes conventionally defined for core and power-law type galaxies. The nature of these intermediate objects is unclear. We draw attention to two objects in the sample which appear to be promising cases of galaxies with isothermal cores that are not the brightest members of a cluster. Unresolved nuclear point sources are found in about 50% of the sample galaxies, roughly independent of profile type, with magnitudes in the range m^{nuc}_H = 12.8 to 17.4 mag, which correspond to M_H^{nuc} = -12.8 to -18.4 mag. (Abridged)Comment: To appear in The Astronomical Journal. Latex, 24 pages and 17 JPEG image