Luminosity function

A universal initial mass function (IMF) is not intuitive, but so far no convincing evidence for a variable IMF exists. The detection of systematic variations of the IMF with star-forming conditions would be the Rosetta Stone for star formation.

We simulate the growth of galaxies and their central supermassive black holes by implementing a suite of semi-analytic models on the output of the Millennium Run, a very large simulation of the concordance LCDM cosmogony. Our procedures follow the detailed assembly history of each object and are able to track the evolution of all galaxies more massive than the Small Magellanic Cloud throughout a volume comparable to that of large modern redshift surveys. In this first paper we supplement previous treatments of the growth and activity of central black holes with a new model for `radio' feedback from those AGN that lie at the centre of a quasistatic X-ray emitting atmosphere in a galaxy group or cluster. We show that for energetically and observationally plausible parameters such a model can simultaneously explain: (i) the low observed mass drop-out rate in cooling flows; (ii) the exponential cut-off at the bright end of the galaxy luminosity function; and (iii) the fact that the most massive galaxies tend to be bulge-dominated systems in clusters and to contain systematically older stars than lower mass galaxies. This success occurs because static hot atmospheres form only in the most massive structures, and radio feedback (in contrast, for example, to supernova or starburst feedback) can suppress further cooling and star formation without itself requiring star formation. We discuss possible physical models which might explain the accretion rate scalings required for our phenomenological `radio mode' model to be successful.

We present an evolutionary model for starbursts, quasars, and spheroidal galaxies in which mergers between gas-rich galaxies drive nuclear inflows of gas, producing starbursts and feeding the buried growth of supermassive black holes (BHs) until feedback expels gas and renders a briefly visible optical quasar. The quasar lifetime and obscuring column density depend on both the instantaneous and peak quasar

We use a large sample of galaxies from the Two Micron All Sky Survey (2MASS) and the Sloan Digital Sky Survey (SDSS) to calculate galaxy luminosity and stellar mass functions in the local Universe. We estimate corrections for passband shifting and galaxy evolution, as well as present-day stellar mass-to-light (M/L) ratios, by fitting the optical-near-infrared galaxy data with simple models. Accounting for the 8% galaxy overdensity in the SDSS early data release region, the optical and near-infrared luminosity functions we construct for this sample agree with most recent literature optical and near-infrared determinations within the uncertainties. We argue that 2MASS is biased against low surface brightness galaxies, and use SDSS plus our knowledge of stellar populations to estimate the 'true' K-band luminosity function. This has a steeper faint end slope and a slightly higher overall luminosity density than the direct estimate. Furthermore, assuming a universally-applicable stellar initial mass function (IMF), we find good agreement between the stellar mass function we derive from the 2MASS/SDSS data and that derived by Cole et al. (2001; MNRAS, 326, 255). The faint end slope slope for the stellar mass function is steeper than −1.1, reflecting the low stellar M/L ratios characteristic of low-mass galaxies. We estimate an upper limit to the stellar mass density in the local Universe Ω * h = 2.0 ± 0.6 × 10 −3 by assuming an IMF as rich in low-mass stars as allowed by observations of galaxy dynamics in the local Universe. The stellar mass density may be lower than this value if a different IMF with fewer low-mass stars is assumed. Finally, we examine typedependence in the optical and near-infrared luminosity functions and the stellar mass function. In agreement with previous work, we find that the characteristic luminosity or mass of early-type galaxies is larger than for later types, and the faint end slope is steeper for later types than for earlier types. Accounting for typing uncertainties, we estimate that at least half, and perhaps as much as 3/4, of the stellar mass in the Universe is in early-type galaxies. As an aid to workers in the field, we present in an appendix the relationship between model stellar M/L ratios and colors in SDSS/2MASS passbands, an updated discussion of near-infrared stellar M/L ratio estimates, and the volume-corrected distribution of g and K-band stellar M/L ratios as a function of stellar mass.

We present a large set of theoretical isochrones, whose distinctive features mostly reside on the greatly improved treatment of the thermally pulsing asymptotic giant branch (TP-AGB) phase. Essentially, we have coupled the TP-AGB tracks described in Paper I, at their stages of pre-flash quiescent H-shell burning, with the evolutionary tracks for the previous evolutionary phases from . Theoretical isochrones for any intermediate value of age and metallicity are then derived by interpolation in the grids. We take care that the isochrones keep, to a good level of detail, the several peculiarities present in these TP-AGB tracks -e.g. the cool tails of C-type stars owing to the use of proper molecular opacities as convective dredge up occurs along the TP-AGB, the bell-shaped sequences in the Hertzsprung-Russell (HR) diagram for stars with hotbottom burning, the changes of pulsation mode between fundamental and first overtone, the sudden changes of mean mass-loss rates as the surface chemistry changes from M-to C-type, etc. Theoretical isochrones are then converted to about 20 different photometric systems -including traditional ground-based systems, and those of recent major wide-field surveys such as SDSS, OGLE, DENIS, 2MASS, UKIDSS, etc., -by means of synthetic photometry applied to an updated library of stellar spectra, suitably extended to include C-type stars. Finally, we correct the predicted photometry by the effect of circumstellar dust during the mass-losing stages of the AGB evolution, which allows us to improve the results for the optical-to-infrared systems, and to simulate mid-and far-IR systems such as those of Spitzer and AKARI. We illustrate the most striking properties of these isochrones by means of basic comparisons with observational data for the Milky Way disk and the Magellanic Clouds. Access to the data is provided both via a web repository of static tables (http://stev.oapd.inaf.it/dustyAGB07 and CDS), and via an interactive web interface (http://stev.oapd.inaf.it/cmd) that provides tables for any intermediate value of age and metallicity, for several photometric systems, and for different choices of dust properties.

We describe the algorithm that selects the main sample of galaxies for spectroscopy in the Sloan Digital Sky Survey (SDSS) from the photometric data obtained by the imaging survey. Galaxy photometric properties are measured using the Petrosian magnitude system, which measures flux in apertures determined by the shape of the surface brightness profile. The metric aperture used is essentially independent of cosmological surface brightness dimming, foreground extinction, sky brightness, and the galaxy central surface brightness. The main galaxy sample consists of galaxies with r-band Petrosian magnitudes r 17.77 and r-band Petrosian half-light surface brightnesses l 50 24.5 mag arcsec À2 . These cuts select about 90 galaxy targets per square degree, with a median redshift of 0.104. We carry out a number of tests to show that (1) our star-galaxy separation criterion is effective at eliminating nearly all stellar contamination while removing almost no genuine galaxies, (2) the fraction of galaxies eliminated by our surface brightness cut is very small ($0.1%), (3) the completeness of the sample is high, exceeding 99%, and (4) the reproducibility of target selection based on repeated imaging scans is consistent with the expected random photometric errors. The main cause of incompleteness is blending with saturated stars, which becomes more significant for brighter, larger galaxies. The SDSS spectra are of high enough signal-to-noise ratio (S/N > 4 per pixel) that essentially all targeted galaxies (99.9%) yield a reliable redshift (i.e., with statistical error less than 30 km s À1 ). About 6% of galaxies that satisfy the selection criteria are not observed because they have a companion closer than the 55 00 minimum separation of spectroscopic fibers, but these galaxies can be accounted for in statistical analyses of clustering or galaxy properties. The uniformity and completeness of the galaxy sample make it ideal for studies of large-scale structure and the characteristics of the galaxy population in the local universe.

In preparing the script to plot the Tully-Fisher relation in of our paper "The many lives of active galactic nuclei: cooling flows, black holes and the luminosities and colours of galaxies" (Croton et al. 2006, MNRAS, 365, 11) we inadvertently loaded the incorrect column from our database with the result that the proxy Vc is not the virial velocity of the parent dark matter halo, Vvir, as labeled, but is instead the maximum circular velocity of the dark matter halo, Vmax. The maximum halo circular velocity is a much better estimate of the disk Vc than is Vvir. This confusion influenced the discussion of the Tully-Fisher relation in our paper. In fact, demonstrates that it is possible to simultaneously reproduce both the local Tully-Fisher relation and luminosity function using semi-analytic techniques applied to the standard ΛCDM cosmology, thus contradicting previous studies of this issue and our own discussion in Section 3.6. We will explore this promising aspect of our galaxy formation model in a future paper.

We simulate the assembly of a massive rich cluster and the formation of its constituent galaxies in a flat, low-density universe. Our most accurate model follows the collapse, the star formation history and the orbital motion of all galaxies more luminous than the Fornax dwarf spheroidal, while dark halo structure is tracked consistently throughout the cluster for all galaxies more luminous than the SMC. Within its virial radius this model contains about dark matter particles and almost 5000 distinct dynamically resolved galaxies. Simulations of this same cluster at a variety of resolutions allow us to check explicitly for numerical convergence both of the dark matter structures produced by our new parallel N-body and substructure identification codes, and of the galaxy populations produced by the phenomenological models we use to follow cooling, star formation, feedback and stellar aging. This baryonic modelling is tuned so that our simulations reproduce the observed properties of isolated spirals outside clusters. Without further parameter adjustment our simulations then produce a luminosity function, a mass-to-light ratio, luminosity, number and velocity dispersion profiles, and a morphology–radius relation which are similar to those observed in real clusters. In particular, since our simulations follow galaxy merging explicitly, we can demonstrate that it accounts quantitatively for the observed cluster population of bulges and elliptical galaxies.

The mid-infrared local luminosity function is evolved with redshift to fit the spectrum of the cosmic infrared background (CIRB) at λ > 5 µm and the galaxy counts from various surveys at mid-infrared, far-infrared and submillimeter wavelengths. A variety of evolutionary models provide satisfactory fits to the CIRB and the number counts. The degeneracy in the range of models cannot be broken by current observations. However, the different evolutionary models yield approximately the same comoving number density of infrared luminous galaxies as a function of redshift. Since the spectrum of the cosmic background at λ > 200 µm is quite sensitive to the evolution at high redshift, i.e. z > 1, all models that fit the counts require a flattening at z ∼ 0.8 to avoid overproducing the CIRB. About 80% of the 140 µm CIRB is produced at 0 < z < 1.5 while only about 30% of the 850 µm background is produced within the same redshift range. The nature of the evolution is then translated into a measure of the dust enshrouded star formation rate density as a function of redshift and compared with estimates from rest-frame optical/ultraviolet surveys. The dust obscured -2star formation rate density appears to peak at z = 0.8 ± 0.1, much sooner than previously thought, with a value of 0.25 +0.12 −0.1 M ⊙ yr −1 Mpc −3 , in excellent agreement with a value derived from extinction correction to NICMOS observations, and remains almost constant up to z ∼ 2. At least 70% of this star formation takes place in infrared luminous galaxies with L IR > 10 11 L ⊙ . The long wavelength observations that constrain our evolutionary models do not strongly trace the evolution at z > 2 and a drop off in the dust enshrouded star formation rate density is consistent with both the CIRB spectrum and the number counts. However, a comparison with the infrared luminosity function derived from extinction corrected rest-frame optical/ultraviolet observations of the Lyman-break galaxy (LBG) population at z ∼ 3 suggests that the almost flat comoving star formation rate density seen between redshifts 0.8 and 2, extends up to a redshift of z ∼ 4.

The DEEP2 and COMBO-17 surveys are used to study the evolution of the luminosity function of red and blue galaxies to z ∼ 1. Schechter function fits show that, since z = 1, M * B dims by ∼ 1.3 mag per unit redshift for both color classes, φ * of blue galaxies shows little change, while φ * for red galaxies has formally nearly quadrupled. At face value, the number density of blue galaxies has remained roughly constant since z = 1, whereas that of red galaxies has been rising. Luminosity densities support both conclusions, but we note that most red-galaxy evolution occurs between our data and local surveys and in our highest redshift bin, where the data are weakest. We discuss the implications of having most red galaxies emerge after z = 1 from precursors among the blue population, taking into account the properties of local and distant E/S0s. We suggest a "mixed" scenario in which some blue galaxies have their star-formation quenched in gas-rich mergers, migrate to the red sequence with a variety of masses, and merge further on the red sequence in one or more purely stellar mergers. E/S0s of a given mass today will have formed via different routes, in a manner that may help to explain the fundamental plane and other local scaling laws.

Using semi-analytic models of galaxy formation, we investigate galaxy properties such as the Tully-Fisher relation, the B and K-band luminosity functions, cold gas contents, sizes, metallicities, and colours, and compare our results with observations of local galaxies. We investigate several different recipes for star formation and supernova feedback, including choices that are similar to the treatment in Kauffmann, and as well as some new recipes. We obtain good agreement with all of the key local observations mentioned above. In particular, in our best models, we simultaneously produce good agreement with both the observed B and K-band luminosity functions and the I-band Tully-Fisher relation. Improved cooling and supernova feedback modelling, inclusion of dust extinction, and an improved Press-Schechter model all contribute to this success. We present results for several variants of the CDM family of cosmologies, and find that models with values of Ω 0 ≃ 0.3-0.5 give the best agreement with observations.

We combine the 2MASS extended source catalogue and the 2dF galaxy redshift survey to produce an infrared-selected galaxy catalogue with 17,173 measured redshifts. We use this extensive dataset to estimate the galaxy luminosity functions in the Jand K S -bands. The luminosity functions are fairly well fit by Schechter functions with parameters M ⋆ J − 5 log h = −22.36 ± 0.02, α J = −0.93 ± 0.04, Φ ⋆ J = 0.0104 ± 0.0016h 3 Mpc −3 in the J-band and M ⋆ KS − 5 log h = −23.44 ± 0.03, α KS = −0.96 ± 0.05, Φ ⋆ KS = 0.0108 ± 0.0016h 3 Mpc −3 in the K S -band (2MASS Kron magnitudes). These parameters are derived assuming a cosmological model with Ω 0 = 0.3 and Λ 0 = 0.7. With datasets of this size, systematic rather than random errors are the dominant source of uncertainty in the determination of the luminosity function. We carry out a careful investigation of possible systematic effects in our data. The surface brightness distribution of the sample shows no evidence that significant numbers of low surface brightness or compact galaxies are missed by the survey. We estimate the present-day distributions of b J −K S and J−K S colours as a function of absolute magnitude and use models of the galaxy stellar populations, constrained by the observed optical and infrared colours, to infer the galaxy stellar mass function. Integrated over all galaxy masses, this yields a total mass fraction in stars (in units of the critical mass density) of Ω stars h = (1.6 ± 0.24) × 10 −3 for a Kennicutt IMF and Ω stars h = (2.9 ± 0.43) × 10 −3 for a Salpeter IMF. These values are consistent with those inferred from observational estimates of the total star formation history of the universe provided that dust extinction corrections are modest.

We refine a technique to measure the absorption corrected ultraviolet (UV) luminosity of starburst galaxies using rest frame UV quantities alone, and apply it to Lyman-limit U-dropouts at z ≈ 3 found in the Hubble Deep field (HDF). The method is based on an observed correlation between the ratio of far infrared (FIR) to UV fluxes with spectral slope β (a UV color). A simple fit to this relation allows the UV flux absorbed by dust and reprocessed to the FIR to be calculated, and hence the dust-free UV luminosity to be determined. International Ultraviolet Explorer spectra and InfraRed Astronomical Satellite fluxes of local starbursts are used to calibrate the F FIR /F 1600 versus β relation in terms of A 1600 (the dust absorption at 1600Å), and the transformation from broad band photometric color to β. Both calibrations are almost completely independent of theoretical stellar population models. We show that the recent marginal and non-detections of HDF U-dropouts at radio and sub-mm wavelengths are consistent with their assumed starburst nature, and our calculated A 1600. This is also true of recent observations of the ratio of optical emission line flux to UV flux density in the brightest U-dropouts. This latter ratio turns out not to be a good indicator of dust extinction. In U-dropouts, absolute magnitude M 1600,0 correlates with β: brighter galaxies are redder, as is observed to be the case for local starburst galaxies. This suggests that a mass-metallicity relationship is already in place at z ≈ 3. The absorption-corrected UV luminosity function of U-dropouts extends up to M 1600,0 ≈ −24 ABmag corresponding to a star formation rate ∼ 200 M ⊙ yr −1 (H 0 = 50 km s −1 Mpc −1 , q 0 = 0.5 assumed throughout). The absorption-corrected UV luminosity density at z ≈ 3 is ρ 1600,0 ≥ 1.4 × 10 27 erg s −1 Hz −1 Mpc −3. It is still a lower limit since completeness corrections have not been done and because only galaxies with A 1600 ∼ < 3.6 mag are blue enough in the UV to be selected as U-dropouts. The luminosity weighted mean dust absorption factor of our sample is 5.4 ± 0.9 at 1600Å.

We present models of photometric evolution of galaxies in which the effects of a dusty interstellar medium have been included with particular care. A chemical evolution code follows the star formation rate, the gas fraction and the metallicity, basic ingredients for the stellar population synthesis. The latter is performed with a grid of integrated spectra of simple stellar populations (SSP) of different ages and metallicities, in which the effects of dusty envelopes around asymptotic giant branch (AGB) stars are included. The residual fraction of gas in the galaxy is divided into two phases: the star forming molecular clouds and the diffuse medium. The relative amount is a model parameter. The molecular gas is sub-divided into clouds of given mass and radius: it is supposed that each SSP is born within the cloud and progressively escapes it. The emitted spectrum of the star forming molecular clouds is computed with a radiative transfer code. The diffuse dust emission (cirrus) is derived by describing the galaxy as an axially symmetric system, in which the local dust emissivity is consistently calculated as a function of the local field intensity due to the stellar component. Effects of very small grains, subject to temperature fluctuations, as well as polycyclic aromatic hydrocarbons (PAH) are included.

We investigate the accretion-driven growth of supermassive black holes in the low-redshift universe using 23,000 narrow-emission-line (''type 2'') active galactic nuclei (AGNs) and the complete sample of 123,000 galaxies in the Sloan Digital Sky Survey from which they were drawn. We use the stellar velocity dispersions of the early-type galaxies and AGN hosts to estimate their black hole masses, and we use the AGN [O iii] k5007 emission line luminosities to estimate black hole accretion rates. We find that most present-day accretion occurs onto black holes with masses less than 10 8 M that reside in moderately massive galaxies (M Ã % 10 10 -10 11.5 M ) with high stellar surface mass densities ( Ã % 10 8:5 -10 9.5 M kpc À2 ) and young stellar populations. The volumeaveraged accretion rates of low-mass black holes (<3 ; 10 7 M ) imply that this population is growing on a timescale that is comparable to the age of the universe. Around half this growth takes place in AGNs that are radiating within a factor of 5 of the Eddington luminosity. Such systems are rare, making up only 0.2% of the lowmass black hole population at the present day. The rest of the growth occurs in lower luminosity AGNs. The growth timescale is more than 2 orders of magnitude longer for the population of the most massive black holes in our sample. The volume-averaged ratio of star formation to black hole accretion in bulge-dominated galaxies is $1000, in remarkable agreement with the observed ratio of stellar mass to black hole mass in nearby galaxy bulges. We conclude that (1) bulge formation and black hole formation are tightly coupled, even in present-day galaxies, and (2) the evolution of the AGN luminosity function documented in recent optical and X-ray surveys is driven by a decrease in the characteristic mass scale of actively accreting black holes.

We determine the number counts and z=0-5 luminosity function for a well-defined, homogeneous sample of quasars from the Sloan Digital Sky Survey (SDSS). We conservatively define the most uniform statistical sample possible, consisting of 15,343 quasars within an effective area of 1622 deg2 that was derived from a parent sample of 46,420 spectroscopically confirmed broad-line quasars in the 5282 deg2 of imaging data from SDSS Data Release 3. The sample extends from i=15 to 19.1 at z<~3 and to i=20.2 for z>~3. The number counts and luminosity function agree well with the results of the Two Degree Field QSO Redshift Survey (2QZ) at redshifts and luminosities at which the SDSS and 2QZ quasar samples overlap, but the SDSS data probe to much higher redshifts than does the 2QZ sample. The number density of luminous quasars peaks between redshifts 2 and 3, although uncertainties in the selection function in this range do not allow us to determine the peak redshift more precisely. Our best-fit model has a flatter bright-end slope at high redshift than at low redshift. For z<2.4 the data are best fit by a redshift-independent slope of β=-3.1 [Φ(L)~Lβ]. Above z=2.4 the slope flattens with redshift to β>~-2.37 at z=5. This slope change, which is significant at the >~5 σ level, must be accounted for in models of the evolution of accretion onto supermassive black holes.

We present a physically motivated model for the early co-evolution of massive spheroidal galaxies and active nuclei at their centers. Within dark matter halos, forming at the rate predicted by the canonical hierarchical clustering scenario, the gas evolution is controlled by gravity, radiative cooling, and heating by feedback from supernovae and from the growing active nucleus. Supernova heating is increasingly effective with decreasing binding energy in slowing down the star formation and in driving gas outflows. The more massive proto-galaxies virializing at earlier times are thus the sites of the faster star-formation. The correspondingly higher radiation drag fastens the angular momentum loss by the gas, resulting in a larger accretion rate onto the central black-hole. In turn, the kinetic energy carried by outflows driven by active nuclei can unbind the residual gas, thus halting both the star formation and the black-hole growth, in a time again shorter for larger halos. For the most massive galaxies the gas unbinding time is short enough for the bulk of the star-formation to be completed before type Ia supernovae can substantially increase the F e abundance of the interstellar medium, thus accounting for the α-enhancement seen in the largest galaxies. The feedback from supernovae and from the active nucleus also determines the relationship between the black-hole mass and the mass, or the velocity dispersion, of the host galaxy, as well as the black-hole mass function. In both cases the model predictions are in excellent agreement with the observational data. Coupling the model with GRASIL (Silva et al. 1998), the code computing in a self-consistent way the chemical and spectrophotometric evolution of galaxies over a very wide wavelength interval, we have obtained predictions in excellent agreement with observations for a number of observables which proved to be extremely challenging for all the current semi-analytic models, including the sub-mm counts and the corresponding redshift distributions, and the epoch-dependent K-band luminosity function of spheroidal galaxies.

This is the third paper in a series which combines N-body simulations and semi-analytic modelling to provide a fully spatially resolved simulation of the galaxy formation and clustering processes. Here we extract mock redshift surveys from our simulations: a Cold Dark Matter model with either Omega_0=1 (tauCDM) or Omega_0=0.3 and Lambda=0.7 (LambdaCDM). We compare the mock catalogues with the northern region (CfA2N) of the Center for Astrophysics (CfA) Redshift Surveys. We study the properties of galaxy groups and clusters identified using standard observational techniques and we study the relation of these groups to real virialised systems. Most features of CfA2N groups are reproduced quite well by both models with no obvious dependence on Omega_0. Redshift space correlations and pairwise velocities are also similar in the two cosmologies. The luminosity functions predicted by our galaxy formation models depend sensitively on the treatment of star formation and feedback. For the particular choices of Paper I they agree poorly with the CfA survey. To isolate the effect of this discrepancy on our mock redshift surveys, we modify galaxy luminosities in our simulations to reproduce the CfA luminosity function exactly. This adjustment improves agreement with the observed abundance of groups, which depends primarily on the galaxy luminosity density, but other statistics, connected more closely with the underlying mass distribution, remain unaffected. Regardless of the luminosity function adopted, modest differences with observation remain. These can be attributed to the presence of the ``Great Wall'' in the CfA2N. It is unclear whether the greater coherence of the real structure is a result of cosmic variance, given the relatively small region studied, or reflects a physical deficiency of the models.

We report subarcsecond resolution IRAM PdBI millimeter CO interferometry of four z $ 2 submillimeter galaxies (SMGs), and sensitive CO(3Y2) flux limits toward three z $ 2 UV/optically selected star-forming galaxies. The new data reveal for the first time spatially resolved CO gas kinematics in the observed SMGs. Two of the SMGs show double or multiple morphologies, with complex, disturbed gas motions. The other two SMGs exhibit CO velocity gradients of $500 km s À1 across 0.2 00 (1.6 kpc) diameter regions, suggesting that the star-forming gas is in compact, rotating disks. Our data provide compelling evidence that these SMGs represent extreme, short-lived ''maximum'' star-forming events in highly dissipative mergers of gas-rich galaxies. The resulting high-mass surface and volume densities of SMGs are similar to those of compact quiescent galaxies in the same redshift range and much higher than those in local spheroids. From the ratio of the comoving volume densities of SMGs and quiescent galaxies in the same mass and redshift ranges, and from the comparison of gas exhaustion timescales and stellar ages, we estimate that the SMG phase duration is about 100 Myr. Our analysis of SMGs and optically/ UV selected high-redshift starforming galaxies supports a ''universal'' Chabrier IMF as being valid over the star-forming history of these galaxies. We find that the 12 CO luminosity to total gas mass conversion factors at z $ 2Y3 are probably similar to those assumed at z $ 0. The implied gas fractions in our sample galaxies range from 20% to 50%.

The cosmic evolution of the field galaxy population has been studied out to a redshift of z ∼ 1 using a sample of 730 I-band selected galaxies, of which 591 have secure redshifts with median < z >∼ 0.56. The tri-variate luminosity function φ(M, color, z) shows unambiguously that the population evolves and that this evolution is strongly differential with color and, less strongly, with luminosity. The luminosity function of red galaxies shows very little change in either number density or luminosity over the entire redshift range 0 < z < 1. In contrast, the luminosity function of blue galaxies shows substantial evolution at redshifts z > 0.5. By 0.5 < z < 0.75 the blue luminosity function appears to have uniformly brightened by approximately 1 magnitude. At higher redshifts, the evolution appears to saturate at the brightest magnitudes but continues at fainter levels leading to a steepening of the luminosity function. A significant excess of galaxies relative to the Loveday et al. (1992) local luminosity function is seen at low redshifts z < 0.2 around M AB (B) ∼ −18 and these galaxies may possibly represent the descendants of the evolving blue population seen at higher redshifts. The changes seen in the luminosity function are also apparent in color-magnitude diagrams constructed at different epochs and in the V /V max statistic computed as a function of spectral type. Finally, it is argued that the picture of galaxy evolution presented here is consistent with the very much smaller samples of field galaxies that have been selected in other wavebands, and with the results of studies of galaxies selected on the basis of Mg II 2799 absorption 1 Visiting Astronomer, Canada-France-Hawaii Telescope, which is operated by the National

Based on data obtained at the European Southern Observatory on Paranal, Chile, and at the W.M. Keck Observatory on Mauna Kea, Hawaii. The W.M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W.M. Keck Foundation.

Using semi-analytic models of galaxy formation set within the Cold Dark Matter (CDM) merging hierarchy, we investigate several scenarios for the nature of the highredshift (z ∼ > 2) Lyman-break galaxies (LBGs). We consider a "collisional starburst" model in which bursts of star formation are triggered by galaxy-galaxy mergers, and find that a significant fraction of LBGs are predicted to be starbursts. This model reproduces the observed comoving number density of bright LBGs as a function of redshift and the observed luminosity function at z ∼ 3 and z ∼ 4, with a reasonable amount of dust extinction. Model galaxies at z ∼ 3 have star formation rates, half-light radii, I−K colours, and internal velocity dispersions that are in good agreement with the data. Global quantities such as the star formation rate density and cold gas and metal content of the Universe as a function of redshift also agree well. Two "quiescent" models without starbursts are also investigated. In one, the star formation efficiency in galaxies remains constant with redshift, while in the other, it scales inversely with disc dynamical time, and thus increases rapidly with redshift. The first quiescent model is strongly ruled out as it does not produce enough high redshift galaxies once realistic dust extinction is accounted for. The second quiescent model fits marginally, but underproduces cold gas and very bright galaxies at high redshift. A general conclusion is that star formation at high redshift must be more efficient than locally. The collisional starburst model appears to accomplish this naturally without violating other observational constraints.

The spectral sensitivities of middle-(M-) and long-(L-) wavelength-sensitive cones have been measured in dichromats of known genotype: M-cone sensitivities in nine protanopes, and L-cone sensitivities in 20 deuteranopes. We have used these dichromat cone spectral sensitivities, along with new luminous efficiency determinations, and existing spectral sensitivity and color matching data from normal trichromats, to derive estimates of the human M-and L-cone spectral sensitivities for 2 and 10°dia. central targets, and an estimate of the photopic luminosity function [V(u)] for 2°dia. targets, which we refer to as V 2 *(u). These new estimates are consistent with dichromatic and trichromatic spectral sensitivities and color matches.

The radio counterparts to the IRAS Redshift Survey galaxies are identified in the NRAO VLA Sky Survey (NVSS) catalog. Our new catalog of the infrared flux-limited (S 60µm ≥ 2 Jy) complete sample of 1809 galaxies lists accurate radio positions, redshifts, and 1.4 GHz radio and IRAS fluxes. This sample is six times larger in size and five times deeper in redshift coverage (to z ≈ 0.15) compared with those used in earlier studies of the radio and far-infrared (FIR) properties of galaxies in the local volume. The well known radio-FIR correlation is obeyed by the overwhelming majority (≥ 98%) of the infrared-selected galaxies, and the radio AGNs identified by their excess radio emission constitute only about 1% of the sample, independent of the IR luminosity. These FIR-selected galaxies can account for the entire population of late-type field galaxies in the local volume, and their radio continuum may be used directly to infer the extinction-free star formation rate in most cases. Both the 1.4 GHz radio and 60 µm infrared luminosity functions are reasonably well described by linear sums of two Schechter functions, one representing normal, late-type field galaxies and the second representing starbursts and other luminous infrared galaxies. The integrated FIR luminosity density for the local volume is (4.8 ± 0.5) × 10 7 L ⊙ Mpc −3 , less than 10% of which is contributed by the luminous infrared galaxies with L F IR ≥ 10 11 L ⊙ . The inferred extinction-free star formation density for the local volume is 0.015 ± 0.005 M ⊙ yr −1 Mpc −3 .

In the course of its commissioning observations, the Sloan Digital Sky Survey (SDSS) has produced one of the largest redshift samples of galaxies selected from CCD images. Using 11,275 galaxies complete to r * = 17.6 over 140 square degrees, we compute the luminosity function of galaxies in the r * band over a range −23 < M r * < −16 (for h = 1). The result is well-described by a Schechter function with parameters φ * = (1.46±0.12)×10 −2 h 3 Mpc −3 , M * = −20.83±0.03, and α = −1.20 ± 0.03. The implied luminosity density in r * is j ≈ (2.6 ± 0.3) × 10 8 hL Mpc −3 . We find that the surface brightness selection threshold has a negligible impact for M r * < −18. Using subsets of the data, we measure the luminosity function in the u * , g * , i * , and z * bands as well; the slope at low luminosities ranges from α = −1.35 to α = −1.2. We measure the bivariate distribution of r * luminosity with half-light surface brightness, intrinsic g * − r * color, and morphology. In agreement with previous studies, we find that high surface brightness, red, highly concentrated galaxies are on average more luminous than low surface brightness, blue, less concentrated galaxies. An important feature of the SDSS luminosity function is the use of Petrosian magnitudes, which measure a constant fraction of a galaxy's total light regardless of the amplitude of its surface brightness profile. If we synthesize results for R GKC -band or b j -band using these Petrosian magnitudes, we obtain luminosity densities 2 times that found by the Las Campanas Redshift Survey in R GKC and 1.4 times that found by the Two-degree Field Galaxy Redshift Survey in b j . However, we are able to reproduce the luminosity functions obtained by these surveys if we also mimic their isophotal limits for defining galaxy magnitudes, which are shallower and more redshift dependent than the Petrosian magnitudes used by the SDSS.

Masami Ouchi 2,3,4,5, Kazuhiro Shimasaku 6, Masayuki Akiyama 7, Chris Simpson 8, Tomoki Saito 9, Yoshihiro Ueda 10, Hisanori Furusawa 7, Kazuhiro Sekiguchi 11, Toru Yamada 12, Tadayuki Kodama 11, Nobunari Kashikawa 11, Sadanori Okamura 6, Masanori Iye 11, Tadafumi ...

We employ high-resolution dissipationless simulations of the concordance LCDM cosmology to model the observed luminosity dependence and evolution of galaxy clustering through most of the age of the universe, from z~5 to z~0. We use a simple, non-parametric model which monotonically relates galaxy luminosities to the maximum circular velocity of dark matter halos (V_max) by preserving the observed galaxy luminosity function in order to match the halos in simulations with observed galaxies. The novel feature of the model is the use of the maximum circular velocity at the time of accretion, V_max,acc, for subhalos, the halos located within virial regions of larger halos. We argue that for subhalos in dissipationless simulations, V_max,acc reflects the luminosity and stellar mass of the associated galaxies better than the circular velocity at the epoch of observation, V_max,now. The simulations and our model L-V_max relation predict the shape, amplitude, and luminosity dependence of the two-point correlation function in excellent agreement with the observed galaxy clustering in the SDSS data at z~0 and in the DEEP2 samples at z~1 over the entire probed range of projected separations, 0.1<r_p/(Mpc/h)<10.0. In particular, the small-scale upturn of the correlation function from the power-law form in the SDSS and DEEP2 luminosity-selected samples is reproduced very well. At z~3-5, our predictions also match the observed shape and amplitude of the angular two-point correlation function of Lyman-break galaxies (LBGs) on both large and small scales, including the small-scale upturn.

We use the Aquarius simulations to show that the most massive subhalos in galaxymass dark matter halos in ΛCDM are grossly inconsistent with the dynamics of the brightest Milky Way dwarf spheroidal galaxies. While the best-fitting hosts of the dwarf spheroidals all have 12 V max 25 km s −1 , ΛCDM simulations predict at least ten subhalos with V max > 25 km s −1 . These subhalos are also among the most massive at earlier times, and significantly exceed the UV suppression mass back to z ∼ 10.

We present a 90 per cent flux-complete sample of the 201 X-ray brightest clusters of galaxies in the northern hemisphere (δ ≥ 0 • ), at high Galactic latitudes (|b| ≥ 20 • ), with measured redshifts z ≤ 0.3 and fluxes higher than 4.4×10 −12 erg cm −2 s −1 in the 0.1-2.4 keV band. The sample, called the ROSAT Brightest Cluster Sample (BCS), is selected from ROSAT All-Sky Survey data and is the largest X-ray selected cluster sample compiled to date. In addition to Abell clusters, which form the bulk of the sample, the BCS also contains the X-ray brightest Zwicky clusters and other clusters selected from their X-ray properties alone. Effort has been made to ensure the highest possible completeness of the sample and the smallest possible contamination by non-cluster X-ray sources. X-ray fluxes are computed using an algorithm tailored for the detection and characterization of X-ray emission from galaxy clusters. These fluxes are accurate to better than 15 per cent (mean 1σ error).

Hubble Space Telescope ultraviolet (UV) images of nine starburst galaxies reveal them to be highly irregular, even after excluding compact sources (clusters and resolved stars). Most (7/9) are found to have a similar intrinsic effective surface brightnesses, suggesting that a negative feedback mechanism is setting an upper limit to the star formation rate per unit area. All starbursts in our sample contain UV bright star clusters indicating that cluster formation is an important mode of star formation in starbursts. On average about 20% of the UV luminosity comes from these clusters. The brightest clusters, or super star clusters (SSC), are preferentially found at the very heart of starbursts. The size of the nearest SSCs are consistent with those of Galactic globular clusters. The luminosity function of SSCs is well represented by a power law with a slope alpha ~ -2. There is a strong correlation between the far infrared excess and the UV spectral slope. The correlation is well modeled by a geometry where much of their dust is in a foreground screen near to the starburst, but not by a geometry of well mixed stars and dust.

We present the final catalogue of the 2dF QSO Redshift Survey (2QZ), based on Anglo-Australian Telescope 2dF spectroscopic observations of 44576 colour-selected (u b_J r) objects with 18.25<b_J<20.85 selected from APM scans of UK Schmidt Telescope (UKST) photographic plates. The 2QZ comprises 23338 QSOs, 12292 galactic stars (including 2071 white dwarfs) and 4558 compact narrow-emission-line galaxies. We obtained a reliable spectroscopic identification for 86 per cent of objects observed with 2dF. We also report on the 6dF QSO Redshift Survey (6QZ), based on UKST 6dF observations of 1564 brighter 16<b_J<18.25 sources selected from the same photographic input catalogue. In total, we identified 322 QSOs spectroscopically in the 6QZ. The completed 2QZ is, by more than a factor 50, the largest homogeneous QSO catalogue ever constructed at these faint limits (b_J<20.85) and high QSO surface densities (35 QSOs deg^-2). As such it represents an important resource in the study of the Universe at moderate-to-high redshifts. As an example of the results possible with the 2QZ, we also present our most recent analysis of the optical QSO luminosity function and its cosmological evolution with redshift. For a flat, Omega_m=0.3 and Omega_lam=0.7, Universe, we find that a double power law with luminosity evolution that is exponential in look-back time, t, of the form L*(z) exp(6.15t), equivalent to an e-folding time of 2Gyr, provides an acceptable fit to the redshift dependence of the QSO luminosity function over the range 0.4 < z < 2.1 and M_bJ<-22.5. Evolution described by a quadratic in redshift is also an acceptable fit, with L*(z)~10^(1.39z-0.29z^2).

Using a complete sample of ~300 star-forming galaxies within 11 Mpc of the Milky Way, we evaluate the consistency between star formation rates (SFRs) inferred from the far ultraviolet (FUV) non-ionizing continuum and Halpha nebular emission, assuming standard conversion recipes in which the SFR scales linearly with luminosity at a given wavelength. Our analysis probes SFRs over 5 orders of magnitude, down to ultra-low activities on the order of ~10-4 M sun yr-1. The data are drawn from the 11 Mpc Halpha and Ultraviolet Galaxy Survey (11HUGS), which has obtained Halpha fluxes from ground-based narrowband imaging, and UV fluxes from imaging with GALEX. For normal spiral galaxies (SFR ~ 1 M sun yr-1), our results are consistent with previous work which has shown that FUV SFRs tend to be lower than Halpha SFRs before accounting for internal dust attenuation, but that there is relative consistency between the two tracers after proper corrections are applied. However, a puzzle is encounte...

We present high-resolution echelle spectroscopy of 676 nearby M dwarfs. Our measurements include radial velocities, equivalent widths of important chromospheric emission lines, and rotational velocities for rapidly rotating stars. We identify several distinct groups by their Hα properties, and investigate variations in chromospheric activity amongst early (M0-M2.5) and mid (M3-M6) dwarfs. Using a volume-limited sample together with a relationship between age and chromospheric activity, we show that the rate of star formation in the immediate Solar Neighbourhood has been relatively constant over the last 4 Gyr. In particular our results are inconsistent with recent large bursts of star formation. We use the correlation between Hα activity and age as a function of colour to set constraints on the properties of L and T dwarf secondary components in binary systems. We also identify a number of interesting stars, including rapid rotators, radial velocity variables, and spectroscopic binaries.

The UKIDSS Galactic Plane Survey (GPS) is one of the five near infrared Public Legacy Surveys that are being undertaken by the UKIDSS consortium, using the Wide Field Camera on the United Kingdom Infrared Telescope. It is surveying 1868 deg 2 of the northern and equatorial Galactic plane at Galactic latitudes −5 • < b < 5 • in the J, H and K filters and a ∼ 200 deg 2 area of the Taurus-Auriga-Perseus molecular cloud complex in these three filters and the 2.12 µm (1-0) H 2 filter. It will provide data on ∼ 2 × 10 9 sources. Here we describe the properties of the dataset and provide a user's guide for its exploitation. We also present brief Demonstration Science results from DR2 and from the Science Verification programme. These results illustrate how GPS data will frequently be combined with data taken in other wavebands to produce scientific results. The Demonstration Science comprises six studies. (1) A GPS-Spitzer-GLIMPSE cross match for the star formation region G28.983-0.603 to identify YSOs. This increases the number of YSOs identified by a factor of ten compared to GLIMPSE alone. (2) A wide field study of the M17 nebula, in which an extinction map of the field is presented and the effect of source confusion on luminosity functions in different sub-regions is noted. (3) H 2 emission in the ρ Ophiuchi dark cloud. All the molecular jets are traced back to a single active clump containing only a few protostars, which suggests that the duration of strong jet activity and associated rapid accretion in low mass protostars is brief. (4) X-ray sources in the Nuclear Bulge. The GPS data distinguishes local main sequence counterparts with soft X-ray spectra from Nuclear Bulge giant counterparts with hard X-ray spectra. (5) External galaxies in the Zone of Avoidance. The galaxies are clearly distinguished from stars in fields at longitudes l>90 • . (6) IPHAS-GPS optical-infrared spectrophotometric typing. The (i'-J) vs.(J-H) diagram is used to distinguish A-F type dwarfs, G dwarfs, K dwarfs and red clump giants in a field with high reddening.

The extragalactic background light (EBL) is of fundamental importance both for understanding the entire process of galaxy evolution and for γ-ray astronomy. However, the overall spectrum of the EBL between 0.1 and 1000 µm has never been determined directly neither from observed luminosity functions (LFs), over a wide redshift range, nor from any multiwavelength observation of galaxy spectral energy distributions (SEDs). The evolving, overall spectrum of the EBL is derived here utilizing a novel method based on observations only. The changing fractions of quiescent galaxies, star-forming galaxies, starburst galaxies and active galactic nucleus (AGN) galaxies from redshift 0.2 to 1 are estimated, and two alternative extrapolations of SED types to higher redshifts are considered. This allows calculation of the evolving EBL. The EBL uncertainties in our modelling based directly on the data are quantified, and their consequences for attenuation of very-high-energy γ-rays due to pair production on the EBL are discussed. It is concluded that the EBL seems well constrained from the UV to the mid-IR at an intensity level roughly matching galaxy count data. Independent efforts from IR and γ-ray astronomy are needed in order to reduce the uncertainties in the far-IR.

We present a new census of the stellar and substellar members of the young cluster IC 348. We have obtained images at I and Z for a 42'x28' field encompassing the cluster and have combined these measurements with previous optical and near-infrared photometry. From spectroscopy of candidate cluster members appearing in these data, we have identified 122 new members, 15 of which have spectral types of M6.5-M9, corresponding to masses of 0.08-0.015 M_sun by recent evolutionary models. The latest census for IC 348 now contains a total of 288 members, 23 of which are later than M6 and thus are likely to be brown dwarfs. From an extinction-limited sample of members (A_V<=4) for a 16'x14' field centered on the cluster, we construct an IMF that is unbiased in mass and nearly complete for M/M_sun>=0.03 (<=M8). In logarithmic units where the Salpeter slope is 1.35, the mass function for IC 348 rises from high masses down to a solar mass, rises more slowly down to a maximum at 0.1-0.2 M_sun, and then declines into the substellar regime. In comparison, the similarly-derived IMF for Taurus from Briceno et al. and Luhman et al. rises quickly to a peak near 0.8 M_sun and steadily declines to lower masses. The distinctive shapes of the IMFs in IC 348 and Taurus are reflected in the distributions of spectral types, which peak at M5 and K7, respectively. These data provide compelling, model-independent evidence for a significant variation of the IMF with star-forming conditions.

We describe TRILEGAL, a new populations synthesis code for simulating the stellar photometry of any Galaxy field. The code attempts to improve upon several technical aspects of star count models, by: dealing with very complete input libraries of evolutionary tracks; using a stellar spectral library to simulate the photometry in virtually any broad-band system; being very versatile allowing easy changes in the input libraries and in the description of all of its ingredients-like the star formation rate, age-metallicity relation, initial mass function, and geometry of Galaxy components. In a previous paper (Groenewegen et al. 2002, Paper I), the code was first applied to describe the very deep star counts of the CDFS stellar catalogue. Here, we briefly describe its initial calibration using EIS-deep and DMS star counts, which, as we show, are adequate samples to probe both the halo and the disc components of largest scale heights (oldest ages). We then present the changes in the calibration that were necessary to cope with some improvements in the model input data, and the use of more extensive photometry datasets: Now the code is shown to successfully simulate also the relatively shallower 2MASS catalogue, which probes mostly the disc at intermediate ages, and the immediate solar neighbourhood as sampled by Hipparcos-in particular its absolute magnitude versus colour diagram-, which contains a somewhat larger fraction of younger stars than deeper surveys. Remarkably, the same model calibration can reproduce well the star counts in all the above-mentioned data sets, that span from the very deep magnitudes of CDFS (16 < R < 23) to the very shallow ones of Hipparcos (V < 8). Significant deviations (above 50 percent in number counts) are found just for fields close to the Galactic Center (since no bulge component was included) and Plane, and for a single set of South Galactic Pole data. The TRILEGAL code is ready to use for the variety of wide-angle surveys in the optical/infrared that will become available in the coming years.

The standard treatment of cooling in Cold Dark Matter halos assumes that all of the gas within a "cooling radius" cools and contracts monolithically to fuel galaxy formation. Here we take into account the expectation that the hot gas in galactic halos is thermally unstable and prone to fragmentation during cooling and show that the implications are more far-reaching than previously expected: allowing multi-phase cooling fundamentally alters expectations about gas infall in galactic halos and naturally gives rise to a characteristic upper-limit on the masses of galaxies, as observed. Specifically, we argue that cooling should proceed via the formation of high-density, ∼ 10 4 K clouds, pressure-confined within a hot gas background. The background medium that emerges has a low density, and can survive as a hydrostatically stable corona with a long cooling time. The fraction of halo baryons contained in the residual hot core component grows with halo mass because the cooling density increases with gas temperature, and this leads to an upper-mass limit in quiescent, non-merged galaxies of ∼ 10 11 M ⊙ .

We report an extensive search for Lyα emitters (LAEs) at z = 6.5 in the Subaru Deep Field. Subsequent spectroscopy with Subaru and Keck identified eight more LAEs, giving a total of 17 spectroscopically confirmed LAEs at z = 6.5. Based on this spectroscopic sample of 17, complemented by a photometric sample of 58 LAEs, we have derived a more accurate Lyα luminosity function of LAEs at z = 6.5, which reveals an apparent deficit at the bright end of ∼ 0.75 mag fainter L * , compared with that observed at z = 5.7. The difference in the LAE luminosity functions between z = 5.7 and 6.5 is significant at the 3 σ level, which is reduced to 2 σ when cosmic variance is taken into account. This result may imply that the reionization of the universe has not been completed at z = 6.5. We found that the spatial distribution of LAEs at z = 6.5 was homogeneous over the field. We discuss the implications of these results for the reionization of the universe.

We measured the K-band luminosity function using a complete sample of 4192 morphologically-typed 2MASS galaxies with µ Ks = 20 mag/arcsec 2 isophotal magnitudes 7 < K 20 < 11.25 mag spread over 2.12 str. Early-type (T ≤ −0.5) and late-type (T > −0.5) galaxies have similarly shaped luminosity functions, α e = −0.92 ± 0.10 and α l = −0.87 ± 0.09. The early-type galaxies are brighter, M * e = −23.53 ± 0.06 mag compared to M * l = −22.98 ± 0.06 mag, but less numerous, n * e = (0.45 ± 0.06) × 10 −2 h 3 Mpc −3 compared to n * l = (1.01 ± 0.13) × 10 −2 h 3 Mpc −3 for H 0 = 100h km s −1 Mpc −1 , such that the late-type galaxies slightly dominate the K-band luminosity density, j late /j early = 1.17 ± 0.12. Our morphological classifications are internally consistent, consistent with previous classifications and lead to luminosity functions unaffected by the estimated uncertainties in the classifications. These luminosity functions accurately predict the K-band number counts and redshift distributions for K < ∼ 18 mag, beyond which the results depend on galaxy evolution and merger histories.

We use the deep ground-based optical photometry of the Lyman Break Galaxy (LBG) Survey to derive robust measurements of the faint-end slope (alpha) of the UV LF at redshifts 1.9<z<3.4. Our sample includes >2000 spectroscopic redshifts and ~31000 LBGs in 31 spatially-independent fields over a total area of 3261 arcmin^2. These data allow us to select galaxies to 0.07L* and 0.10L* at z~2 and z~3, respectively. A maximum likelihood analysis indicates steep values of alpha(z=2)=-1.73+/-0.07 and alpha(z=3)=-1.73+/-0.13. This result is robust to luminosity dependent systematics in the Ly-alpha equivalent width and reddening distributions, is similar to the steep values advocated at z>4, and implies that ~93% of the unobscured UV luminosity density at z~2-3 arises from sub-L* galaxies. With a realistic luminosity dependent reddening distribution, faint to moderately luminous galaxies account for >70% and >25% of the bolometric luminosity density and present-day stellar mass density, respectively, when integrated over 1.9<z<3.4. We find a factor of 8-9 increase in the star formation rate density between z~6 and z~2, due to both a brightening of L* and an increasing dust correction proceeding to lower redshifts. The previously observed discrepancy between the integral of the star formation history and stellar mass density measurements at z~2 may be reconciled by invoking a luminosity dependent reddening correction to the star formation history combined with an accounting for the stellar mass contributed by UV-faint galaxies. The steep and relatively constant alpha of the UV LF at z>2 contrasts with the shallower value inferred locally, suggesting that the evolution in the faint-end slope may be dictated simply by the availability of low mass halos capable of supporting star formation at z<2. [Abridged]

The Universidad Complutense de Madrid (UCM) Survey is a long-term project aiming at finding and analysing star-forming galaxies detected by their Hα emission in Schmidt objective-prism plates. The instrumental set-up limits the volume of the Universe surveyed to a redshift z ∼ < 0.045. So far we have discovered several hundred emission-line galaxies (ELGs) undergoing star formation at a wide range of levels. Analyzing a complete sample of ELGs from the UCM survey we have computed the Hα luminosity function for the star-forming galaxies in the surveyed volume of the Universe. A Schechter function provides a good fit to the Hα luminosity function with the following parameters: α = −1.3 ± 0.2; L * (Hα) = 10 42.15±0.08 erg s −1 and φ * = 10 −3.2±0.2 Mpc −3 for H 0 = 50 km s −1 Mpc −1 . Integrating over the full range of luminosities, we obtain an Hα luminosity density of 10 39.1±0.2 erg s −1 Mpc −3 . Using the Hα emission as a star formation rate (SFR) estimator, this translates into a SFR density for the Local Universe of 0.013 +0.007 −0.005 M ⊙ yr −1 Mpc −3 in star-forming galaxies with EW (Hα+[NII]) > 10Å and z ∼ < 0.045, for a Scalo Initial Mass Function. This is the first observational determination of this quantity, which will provide a direct test of current galaxy formation and evolution models.

We also derive results for the occupation number, luminosity function of cluster galaxies, group luminosity function and multiplicity function. Then, using some additional assumptions, we further derive results for biasing between mass and light and mass and galaxy number, light distribution function and the void probability distribution. Our results for the most part seem to match well with observations and previous expectations. We feel this is a potentially powerful way of modelling this relation, since the main inputs are readily testable against dark matter simulation results and galaxy surveys. (abridged)