Estimates for the luminosity function of galaxies and its evolution

A new method is presented to obtain a non-parametric maximum likelihood estimate of the luminosity function and the selection function of a flux-limited redshift survey. The method parametrizes the selection function as a series of stepwise power laws and allows possible evolution of the luminosity function. We also propose a new technique to estimate the rate of evolution of the luminosity function. This is based on a minimization of the observed large-scale power with respect to the evolutionary model. We use an ensemble of mock surveys extracted from an N -body simulation to verify the power of this method. We apply our estimators to the 1.2-Jy survey of IRAS galaxies. We find a far-infrared luminosity function in good agreement with previously published results and evidence for rather strong evolution. If the comoving number density of IRAS galaxies is assumed to scale ∝ (1 +  z ) ^P , we estimate P  = 4.3 ± 1.4.     

Possible formation scenarios for the giant H i envelope around the NGC 4490/4485 system

We present observations of H i in the nearby interacting galaxies NGC 4490 and 4485 made with the VLA in both C and D arrays. The galaxies are embedded in an extensive envelope of neutral hydrogen which is elongated in a direction approximately perpendicular to the plane of NGC 4490, with an extent of about 56 kpc. We argue that this distribution of neutral hydrogen can best be explained by a galactic-scale bipolar outflow of H  i driven by supernovae in NGC 4490. The flow from the disc appears to be reasonably well collimated and has probably persisted for approximately 6 × 10⁸ yr. The implications for galaxy evolution when such mass loss occurs are briefly discussed.     

Galaxy formation and evolution – I. The Padua tree-sph code (pd-sph)

In this paper we report on pd-sph , the new tree-sph code developed in Padua. The main features of the code are described and the results of a new and independent series of 1D and 3D tests are shown. The paper is mainly dedicated to the presentation of the code and to the critical discussion of its performance. In particular, great attention is devoted to the convergency analysis. The code is highly adaptive in space and time by means of individual smoothing lengths and individual time-steps. At present it contains both dark and baryonic matter, this latter in the form of gas and stars, cooling, thermal conduction, star formation, feedback from Type I and II supernovae, stellar winds, and ultraviolet flux from massive stars, and finally chemical enrichment. New cooling rates that depend on the metal abundance of the interstellar medium are employed, and the differences with respect to the standard ones are outlined. Finally, we show the simulation of the dynamical and chemical evolution of a disc-like galaxy with and without feedback. The code is suitably designed to study in a global fashion the problem of formation and evolution of elliptical galaxies, and in particular to feed a spectrophotometric code from which the integrated spectra, magnitudes and colours (together with their spatial gradients) can be derived.     

Determination of the IMF on the basis of a recently derived SFR history in the solar neighbourhood

The initial mass function (IMF) in the solar neighbourhood is determined on the basis of a recently derived history of the star formation rate (SFR) which shows the presence of a star formation burst about 8 Gyr ago. The observed present-day mass function (PDMF) is considered, and the average past distribution of stars of a given mass is estimated. Two cases are considered, namely (i) constant SFR, and (ii) variable SFR as derived from the new metallicity distribution of G dwarfs. The resulting IMF is compared with previous determinations by Scalo and Kroupa et al., and the variation with stellar mass of the slope of the IMF is compared with reference determinations in the literature.     

Spatial and temporal variations of subsidence of the East Pacific Rise (0–23°S)

The distributions of crustal depths as a function of age have been analysed for the southeast Pacific region, along the East Pacific Rise, between the Equator and the Easter microplate (23°S). Using age data and a new compilation of bathymetric data, subsidence rates (for both eastern and western flanks), asymmetry of subsidence and zero-age depths, are computed within flow-line corridors on the Nazca and Pacific plates. Variations of subsidence rates, axial depths and subsidence asymmetry are examined both in space (within corridors) and time (within several age intervals). The variability in these parameters along the strike of the East Pacific Rise is systematic and serves to define several orders of ridge segmentation. The largest variations of these parameters are correlated with the large-scale segmentation of the ridge axis (i.e. transform faults and very large overlapping spreading centres) and are interpreted as related to variations in mantle heterogeneities mainly dependent upon temperature. Smaller variations of subsidence parameters are correlated with second- (and sometimes third-) order segmentation of the ridge axis, which could be related to variations in axial magmatic supply. Across-strike variations of subsidence suggest the existence of small lateral temperature and density variations in the mantle. When analysing the slope of the distribution of depth versus square root of age within corridors, we have observed the existence of changes in the slope which occur at specific age limits. We have estimated the subsidence over different age ranges in order to determine the temporal evolution of subsidence parameters (rates and asymmetry). Such an analysis may inform on the past axial segmentation and on the persistence of axial discontinuities in time. A linear relationship between subsidence rates and axial depths is determined for each age range and suggests that shallower segments subside faster than deeper segments. Although a similar, statistically defined linear relationship exists for any mid-ocean spreading ridge (both for intermediate or fast–ultrafast spreading), the resultant slopes of this relationship vary from ocean to ocean and show that this relationship is not universal over all oceans.     

Epigenetic gorges in fluvial landscapes

Epigenetic gorges form when channels that have been laterally displaced during episodes of river blockage or aggradation incise down into bedrock spurs or side‐walls of the former valley rather than excavating unconsolidated fills and reinhabiting the buried paleovalley. Valley‐filling events that promote epigenetic gorges can be localized, such as a landslide dam or an alluvial/debris flow fan deposit at a tributary junction, or widespread, such as fluvial aggradation in response to climate change or fluctuating base‐level. The formation of epigenetic gorges depends upon the competition between the resistance to transport, strength and roughness of valley‐filling sediments and a river's ability to sculpt and incise bedrock. The former affects the location and lateral mobility of a channel incising into valley‐filling deposits; the latter determines rates of bedrock incision should the path of the incising channel intersect with bedrock that is not the paleovalley bottom. Epigenetic gorge incision, by definition, post‐dates the incision that originally cut the valley. Strath terraces and sculpted bedrock walls that form in relation to epigenetic gorges should not be used to directly infer river incision induced by tectonic activity or climate variability. Rather, they are indicative of the variability of short‐term bedrock river incision and autogenic dynamics of actively incising fluvial landscapes. The rate of bedrock incision associated with an epigenetic gorge can be very high (>1 cm/yr), typically orders of magnitude higher than both short‐ and long‐term landscape denudation rates. In the context of bedrock river incision and landscape evolution, epigenetic gorges force rivers to incise more bedrock, slowing long‐term incision and delaying the adjustment of rivers to regional tectonic and climatic forcing. Copyright © 2008 John Wiley & Sons, Ltd.     

A Model for Contact Binary Systems

A model for contact binary systems is presented, which incorporates the following special features: a) The energy exchange between the components is based on the understand-ing that the energy exchange is due to the release of potential, kinetic and thermal energies of the exchanged mass. b) A special form of mass and angular momentum loss occurring in contact binaries is losses via the outer Lagrangian point. c) The effects of spin, orbital rota-tion and tidal action on the stellar structure as well as the effect of meridian circulation on the mixing of the chemical elements are considered. d) The model is valid not only for low-mass contact binaries but also for high-mass contact binaries. For illustration, we used the model to trace the evolution of a massive binary system consisting of one 12M and one 5M star. The result shows that the start and end of the contact stage fall within the semi-detached phase during which the primary continually transfers mass to the secondary. The time span of the contact stage is short and the mass transfer rate is very large. Therefore, the contact stage can be regarded as a special part of the semi-detached phase with a large mass transfer rate. Both mass loss through the outer Lagrangian point and oscillation between contact and semi-contact states can occur during the contact phase, and the effective temperatures of the primary and the secondary are almost equal.     

Mass-luminosity relation for massive stars

A catalog of massive (⩾10 M _⊙) stars in binary and multiple systems with well-known masses and luminosities has been compiled. The catalog is analyzed using a theoretical mass-luminosity relation. This relation allows both normal main-sequence stars and stars with peculiarities: with clear manifestations of mass transfer, mass accretion, and axial rotation, to be identified. Least-squares fitting of the observational data in the range of stellar masses 10M _⊙ ⩽ M ≲ 50 M _⊙ yields the relation L ∼ M ^2.76. An erratum to this article is available at .