arXiv subjects

Jarle Brinchmann

Publications and source records attributed to Jarle Brinchmann.

At least 145 records · Page 8Linked to original sources

arXiv2008

New insights into the stellar content and physical conditions of star-forming galaxies at z = 2-3 from spectral modelling

We have used extensive libraries of model and empirical galaxy spectra (assembled respectively from the population synthesis code of Bruzual and Charlot and the fourth data release of the Sloan Digital Sky Survey) to interpret some puzzling features seen in the spectra of high redshift star-forming galaxies. We show that a stellar He II 1640 emission line, produced in the expanding atmospheres of Of and Wolf-Rayet stars, should be detectable with an equivalent width of 0.5-1.5AA in the integrated spectra of star-forming galaxies, provided the metallicity is greater than about half solar. Our models reproduce the strength of the He II 1640 line measured in the spectra of Lyman break galaxies for established values of their metallicities. With better empirical calibrations in local galaxies, this spectral feature has the potential of becoming a useful diagnostic of massive star winds at high, as well as low, redshifts. We also uncover a relationship in SDSS galaxies between their location in the [O III]/Hb vs. [N II]/Ha diagnostic diagram (the BPT diagram) and their excess specific star formation rate relative to galaxies of similar mass. We infer that an elevated ionisation parameter U is at the root of this effect, and propose that this is also the cause of the offset of high redshift star-forming galaxies in the BPT diagram compared to local ones. We further speculate that higher electron densities and escape fractions of hydrogen ionising photons may be the factors responsible for the systematically higher values of U in the H II regions of high redshift galaxies. The impact of such differences on abundance determinations from strong nebular lines are considered and found to be relatively minor.

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arXiv2008

A census of metals and baryons in stars in the local Universe

We combine stellar metallicity and stellar mass estimates for a large sample of galaxies drawn from the SDSS DR2 spanning wide ranges in physical properties, in order to derive an inventory of the total mass of metals and baryons locked up in stars today. Physical parameter estimates are derived from galaxy spectra with high S/N (>20). Coadded spectra of galaxies with similar velocity dispersions, absolute r-band magnitudes and 4000Å-break values are used for those regions of parameter space where individual spectra have lower S/N. We estimate the total density of metals and of baryons in stars and, from these two quantities, we obtain a mass- and volume-averaged stellar metallicity of =1.04+-0.14 Z_sun, i.e. consistent with solar. We also study how metals are distributed in galaxies according to their mass, morphology and age, and we then compare these distributions with the corresponding distributions of stellar mass. We find that the bulk of metals locked up in stars in the local Universe reside in massive, bulge-dominated galaxies, with red colours and high 4000Å-break values corresponding to old stellar populations. Bulge-dominated and disc-dominated galaxies contribute similar amounts to the total stellar mass density, but have different fractional contributions to the mass density of metals in stars, in agreement with the mass-metallicity relation. Bulge-dominated galaxies contain roughly 40% of the total amount of metals in stars, while disc-dominated galaxies less than 25%. Finally, at a given galaxy stellar mass, we define two characteristic ages as the median of the distributions of mass and metals as a function of age. These characteristic ages decrease progressively from high-mass to low-mass galaxies, consistent with the high formation epochs of stars in massive galaxies.

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arXiv2007

The Lopsidedness of Present-Day Galaxies: Results from the Sloan Digital Sky Survey

Large-scale asymmetries in the stellar mass distribution in galaxies are believed to trace non-equilibrium situations in the luminous and/or dark matter component. These may arise in the aftermath of events like mergers, accretion, and tidal interactions. These events are key in the evolution of galaxies. In this paper we quantify the large-scale lopsidedness of light distributions in 25155 galaxies at z < 0.06 from the Sloan Digital Sky Survey Data Release 4 using the m = 1 azimuthal Fourier mode. We show that the lopsided distribution of light is primarily due to a corresponding lopsidedness in the stellar mass distribution. Observational effects, such as seeing, Poisson noise, and inclination, introduce only small errors in lopsidedness for the majority of this sample. We find that lopsidedness correlates strongly with other basic galaxy structural parameters: galaxies with low concentration, stellar mass, and stellar surface mass density tend to be lopsided, while galaxies with high concentration, mass, and density are not. We find that the strongest and most fundamental relationship between lopsidedness and the other structural parameters is with the surface mass density. We also find, in agreement with previous studies, that lopsidedness tends to increase with radius. Both these results may be understood as a consequence of several factors. The outer regions of galaxies and low-density galaxies are more susceptible to tidal perturbations, and they also have longer dynamical times (so lopsidedness will last longer). They are also more likely to be affected by any underlying asymmetries in the dark matter halo.

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arXiv2007

Bursty stellar populations and obscured AGN in galaxy bulges

[Abridged] We investigate trends between the recent star formation history and black hole growth in galaxy bulges in the Sloan Digital Sky Survey (SDSS). The galaxies lie at 0.01<z<0.07 where the fibre aperture covers only the central 0.6-4.0kpc diameter of the galaxy. We find strong trends between black hole growth, as measured by dust-attenuation-corrected OIII luminosity, and the recent star formation history of the bulges. We conclude that our results support the popular hypothesis for black hole growth occurring through gas inflow into the central regions of galaxies, followed by a starburst and triggering of the AGN. However, while this is a significant pathway for the growth of black holes, it is not the dominant one in the present-day Universe. More unspectacular processes are apparently responsible for the majority of this growth. In order to arrive at these conclusions we have developed a set of new high signal-to-noise ratio (SNR) optical spectral indicators, designed to allow a detailed study of stellar populations which have undergone recent enhanced star formation. Working in the rest-frame wavelength range 3750-4150AA, ideally suited to many recent and ongoing spectroscopic surveys at low and high redshift, the first two indices are equivalent to the previously well studied 4000AA break strength and Hdelta equivalent width. The primary advantage of this new method is a greatly improved SNR for the latter index, allowing the present study to use spectra with SNR-per-pixel as low as 8.

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arXiv2007

UV Star Formation Rates in the Local Universe

We measure star formation rates of ~50,000 optically-selected galaxies in the local universe (z~0.1), spanning a range from gas-rich dwarfs to massive ellipticals. We obtain dust-corrected SFRs by fitting the GALEX (UV) and SDSS (optical) photometry to a library of population synthesis models that include dust attenuation. For star-forming galaxies, our UV-based SFRs compare remarkably well with those derived from SDSS H alpha. Deviations from perfect agreement between these two methods are due to differences in the dust attenuation estimates. In contrast to H alpha, UV provides reliable SFRs for galaxies with weak or no H alpha emission, and where H alpha is contaminated with an emission from an AGN. We use full-SED SFRs to calibrate a simple prescription that uses GALEX UV magnitudes to produce good SFRs for normal star-forming galaxies. The specific SFR is considered as a function of stellar mass for (1) star-forming galaxies with no AGN, (2) those hosting an AGN, and for (3) galaxies without H alpha emission. We find that the three have distinct star formation histories, with AGN lying intermediate between the star-forming and the quiescent galaxies. Normal star forming galaxies (without an AGN) lie on a relatively narrow linear sequence. Remarkably, galaxies hosting a strong AGN appear to represent the massive continuation of this sequence. Weak AGN, while also massive, have lower SFR, sometimes extending to the realm of quiescent galaxies. We propose an evolutionary sequence for massive galaxies that smoothly connects normal star-forming galaxies to quiescent (red sequence) galaxies via strong and weak AGN. We confirm that some galaxies with no H alpha emission show signs of SF in the UV. We derive a UV-based cosmic SFR density at z=0.1 with smaller total error than previous measurements (abridged).

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arXiv2005

Spectrophotometric properties of galaxies at intermediate redshifts (z ~ 0.2--1.0) I. Sample description, photometric properties and spectral measurements

We present the spectrophotometric properties of a sample of 141 emission-line galaxies at redshifts in the range $0.2<z<1.0$ with a peak around $z\in[0.2,0.4]$. The analysis is based on medium resolution ($R\_{\mathrm{s}}=500-600$), optical spectra obtained at VLT and Keck. The targets are mostly {} "Canada-France Redshift Survey" emission-line galaxies, with the addition of field galaxies randomly selected behind lensing clusters. We complement this sample with galaxy spectra from the {} "Gemini Deep Deep Survey" public data release. We have computed absolute magnitudes of the galaxies and measured the line fluxes and equivalent widths of the main emission/absorption lines. The last two have been measured after careful subtraction of the fitted stellar continuum using the \texttt{platefit} software originally developed for the SDSS and adapted to our data. We present a careful comparison of this software with the results of manual measurements. The pipeline has also been tested on lower resolution spectra, typical of the {} "VIMOS/VLT Deep Survey" ($R\_{\mathrm{s}}=250$), by resampling our medium resolution spectra. We show that we can successfully deblend the most important strong emission lines. These data are primarily used to perform a spectral classification of the galaxies in order to distinguish star-forming galaxies from AGNs. Among the initial sample of 141 emission-line galaxies, we find 7 Seyfert 2 (narrow-line AGN), 115 star-forming galaxies and 16 {} "candidate" star-forming galaxies. Scientific analysis of these data, in terms of chemical abundances, stellar populations, etc, will be presented in subsequent papers of this serie.

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arXiv2005

Spectrophotometric properties of galaxies at intermediate redshifts (z ~ 0.2--1.0) II. The Luminosity -- Metallicity relation

We present the gas-phase oxygen abundance (O/H) for a sample of 131 star-forming galaxies at intermediate redshifts ($0.2<z<1.0$). The sample selection, the spectroscopic observations (mainly with VLT/FORS) and associated data reduction, the photometric properties, the emission-line measurements, and the spectral classification are fully described in a companion paper (Paper I). We use two methods to estimate the O/H abundance ratio: the {} "standard" $R\_{\mathrm{23}}$ method which is based on empirical calibrations, and the CL01 method which is based on grids of photo-ionization models and on the fitting of emission lines. For most galaxies, we have been able to solve the problem of the metallicity degeneracy between the high- and low-metallicity branches of the O/H vs. $R\_{\mathrm{23}}$ relationship using various secondary indicators. The luminosity -- metallicity ($L-Z$) relation has been derived in the $B$- and $R$-bands, with metallicities derived with the two methods ($R\_{\mathrm{23}}$ and CL01). In the analysis, we first consider our sample alone and then a larger one which includes other samples of intermediate-redshift galaxies drawn from the literature. The derived $L-Z$ relations at intermediate redshifts are very similar (same slope) to the $L-Z$ relation obtained for the local universe. Our sample alone only shows a small evolution of the $L-Z$ relation with redshift up to $z\sim1.0$. We only find statistical variations consistent with the uncertainty in the derived parameters. Including other samples of intermediate-redshift galaxies, we find however that galaxies at $z\sim1$ appear to be metal-deficient by a factor of $\sim3$ compared with galaxies in the local universe. For a given luminosity, they contain on average about one third of the metals locked in local galaxies.

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arXiv2005

Extracting Star Formation Histories from Medium-resolution Galaxy Spectra

We adapt an existing data compression algorithm, MOPED, to the extraction of median-likelihood star formation (SF) histories from medium-resolution galaxy spectra. By focusing on the high-pass components of galaxy spectra, we minimize potential uncertainties arising from the spectro-photometric calibration and intrinsic attenuation by dust. We validate our approach using model high-pass spectra of galaxies with different SF histories covering the wavelength range 3650-8500 A at a resolving power of about 2000. We show that the method can recover the full SF histories of these models, without prior knowledge of the metallicity, to within an accuracy that depends sensitively on signal-to-noise ratio. The investigation of the sensitivity of the flux at each wavelength to the mass fraction of stars of different ages allows us to identify new age-sensitive features in galaxy spectra. We also highlight a fundamental limitation in the recovery of the SF histories of galaxies for which the optical signatures of intermediate-age stars are masked by those of younger and older stars. We apply this method to derive average SF histories from the highest-quality spectra of morphologically identified early- and late-type galaxies in the SDSS EDR [...]. We also investigate the constraints set by the high-pass signal in the stacked spectra of a magnitude-limited sample of SDSS-EDR galaxies on the global SF history of the Universe. We confirm that the stellar populations in the most massive galaxies today appear to have formed on average earlier than those in the least massive ones. Our results do not support the recent suggestion of a statistically significant peak in the SF activity of the Universe at redshifts below unity, although such a peak is not ruled out [abridged].

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arXiv2005

The Colours of Elliptical galaxies

We have compiled a sample of 2728 nearby ($z<0.08$) elliptical galaxies with photometry in the $g,r,i,z$ bands from the Sloan Digital Sky Survey (SDSS) and $J,H,K$ photometry from the Two Micron All Sky Survey (2MASS). Stellar masses, stellar velocity dispersions and structural parameters such as sizes and surface mass densities are also available for these objects. In order to correct the aperture mismatch between SDSS and 2MASS, we correct the SDSS magnitudes to the isophotal circular radius where the 2MASS magnitudes are measured. We compare the correlations between optical, optical-infrared and infrared colours and galaxy luminosity, stellar mass, velocity dispersion and surface mass density. We find that all galaxy colours correlate more strongly with stellar mass and velocity dispersion than with any other structural parameter. The dispersion about these two relations is also smaller. We also study the correlations between a variety of stellar absorption line indices and the same set of galaxy parameters and we reach very similar conclusions. Finally, we analyze correlations between absorption line indices and colour. Our results suggest that the optical colours of elliptical galaxies are sensitive to a combination of age, metallicity and $α$-enhancement, while the optical-infrared colours are sensitive to metallicity and to $α$-enhancement, but are somewhat less sensitive to age.

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arXiv2005

Gas Infall and Stochastic Star Formation in Galaxies in the Local Universe

We study the recent star formation histories of local galaxies by analyzing the scatter in their colours and spectral properties. We present evidence that the distribution of star formation histories changes qualitatively above a characteristic stellar surface mass density of 3x10^8 M_sol kpc^-2, corresponding to the transition between disk-dominated and bulge-dominated galaxies. When we average over subpopulations of galaxies with densities below this value, we find that subpopulations of all masses form their stars at the same average rate per unit stellar mass. However, the scatter in galaxy colours and emission line strengths is larger for more compact galaxies of a given mass. This suggests that star formation occurs in shorter, higher amplitude events in galaxies with smaller sizes. Above the characteristic density, galaxy growth through star formation shuts down. We propose that star formation events are triggered when cold gas is accreted onto a galaxy. We have used the new high resolution Millennium Simulation of structure formation in a concordance LCDM Universe to quantify the incidence of these accretion events and we show that the observational data are well fit by a model in which the consumption time of accreted gas decreases with the surface density of the galaxy as t_cons \propto mu*^-1. The dark matter halos hosting massive galaxies with high densities are also expected to grow through accretion, but the observations indicate that star formation in bulge- dominated galaxies is no longer coupled to the hierarchical build-up of their surrounding dark matter halos.

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arXiv2005

The ages and metallicities of galaxies in the local universe

We derive stellar metallicities, light-weighted ages and stellar masses for a magnitude-limited sample of 175,128 galaxies drawn from the Sloan Digital Sky Survey Data Release Two (SDSS DR2). We compute median-likelihood estimates of these parameters using a large library of model spectra at medium-high resolution, covering a comprehensive range of star formation histories. The constraints we derive are set by the simultaneous fit of five spectral absorption features, which are well reproduced by our population synthesis models. By design, these constraints depend only weakly on the alpha/Fe element abundance ratio. Our sample includes galaxies of all types spanning the full range in star formation activity, from dormant early-type to actively star-forming galaxies. We show that, in the mean, galaxies follow a sequence of increasing stellar metallicity, age and stellar mass at increasing 4000AA-break strength (D4000). For galaxies of intermediate mass, stronger Balmer absorption at fixed D4000 is associated with higher metallicity and younger age. We investigate how stellar metallicity and age depend on total galaxy stellar mass. Low-mass galaxies are typically young and metal-poor, massive galaxies old and metal-rich, with a rapid transition between these regimes over the stellar mass range 3x10^9<M/Msun<3x10^10. Both high- and low-concentration galaxies follow these relations, but there is a large dispersion in stellar metallicity at fixed stellar mass, especially for low-concentration galaxies of intermediate mass. Despite the large scatter, the relation between stellar metallicity and stellar mass is similar to the correlation between gas-phase oxygen abundance and stellar mass for star-forming galaxies. [abriged]

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arXiv2004

Stellar masses, star formation rates, metallicities and AGN properties for 200,000 galaxies in the SDSS Data Release Two (DR2)

By providing homogeneous photometric and spectroscopic data of high quality for very large and objectively selected samples of galaxies, the Sloan Digital Sky Survey allows statistical studies of the physical properties of galaxies and AGN to be carried out at an unprecedented level of precision and detail. Here we publicly release catalogues of derived physical properties for 211,894 galaxies, including 33,589 narrow-line AGN. These are complete samples with well understood selection criteria drawn from the normal galaxy spectroscopic sample in the second SDSS public data release (DR2). We list properties obtained from the SDSS spectroscopy and photometry using modelling techniques presented in papers already published by our group. These properties include: stellar masses; stellar mass-to-light ratios; attenuation of the starlight by dust; indicators of recent major starbursts; current total and specific star-formation rates, both for the regions with spectroscopy and for the galaxies as a whole; gas-phase metallicities; AGN classifications based on the standard emission line ratio diagnostic diagrams and AGN [OIII] emission line luminosities. We also list our own measurements of absorption line indices and emission line fluxes from which these quantities were derived, together with a few quantities from the standard SDSS pipelines which play an important role in our work. Many other observed properties of these galaxies can be obtained from the SDSS DR2 catalogues themselves. We will add further physical properties to this release site as the relevant papers are accepted for publication. Catalogies containing these parameters may be accessed at http://www.mpa-garching.mpg.de/SDSS/.

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arXiv2004

Present-Day Growth of Black Holes and Bulges: the SDSS Perspective

We investigate the accretion-driven growth of supermassive black holes in the low-redshift Universe using 23,000 ``Type 2'' AGN and the complete sample of 123,000 galaxies in the SDSS 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 [OIII]5007 emission line luminosities to estimate black hole accretion rates. We find that most present-day accretion occurs onto black holes with masses < 10E8 Msun that reside in moderately massive galaxies (M ~ 10E10 to 10E11.5 Msun) with high stellar densities (~10E8.5 to 10E9.5 Msun/kpc^2) and young stellar populations. The volume-averaged accretion rates of low mass black holes (<10E7.5 Msun) 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 AGN that are radiating within a factor of five of the Eddington luminosity. Such systems are rare, making up only 0.2% of the low mass black hole population at the present day. The rest of the growth occurs in lower luminosity AGN. The growth timescale is more than two 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: a) that bulge formation and black hole formation are tightly coupled, even in present-day galaxies; and b) that 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 accreting black holes.

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arXiv2004

The Environmental Dependence of the Relations between Stellar Mass, Structure, Star Formation and Nuclear Activity in Galaxies

We use a complete sample of galaxies drawn from the SDSS to study how structure, star formation and nuclear activity depend on local density and on stellar mass. Local density is estimated by counting galaxies above a fixed absolute magnitude limit within cylinders 2 Mpc in projected radius and +-500 km/s in depth. The stellar mass distribution of galaxies shifts by nearly a factor of two towards higher masses between low and high density regions. At fixed stellar mass, both star formation and nuclear activity depend strongly on local density, while structural parameters such as size and concentration are almost independent of it. The galaxy property most sensitive to environment is specific star formation rate. For galaxies with stellar masses less than 3 x 10^10 M_sun, the median SFR/M* decreases by more than a factor of 10 from low to high densities. This decrease is less marked for massive galaxies. At fixed stellar mass, twice as many galaxies host AGN with strong [OIII] emission in low density regions as in high. Massive galaxies in low-density environments also contain more dust. We have analyzed correlations between spectroscopic indicators that probe SFH on different timescales (D4000, Hdelta_A and SFR/M*). The correlations do not depend on environment, suggesting that the decrease in star formation has ocurred over long (>1 Gyr) timescales. Since structure does not depend on environment for more massive galaxies, trends in recent SFH, dust and AGN for these systems cannot be driven by processes that alter structure, e.g. mergers. The SFH-density correlation is strongest for small scale (< 1 Mpc) estimates of local density. Finally, we highlight a striking similarity between changes in the galaxy population as a function of density and as a function of redshift and we interpret this using N-body simulations.

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arXiv2003

The Relationship between Stellar and Halo Masses of Disk Galaxies at z = 0.2 - 1.2

We present the results of a study to determine the co-evolution of the virial and stellar masses for a sample of 83 disk galaxies between redshifts z = 0.2 - 1.2. The virial masses of these disks are computed using measured maximum rotational velocities from Keck spectroscopy and scale lengths from Hubble Space Telescope imaging. We compute stellar masses based on stellar population synthesis model fits to spectral energy distributions including K-band magnitudes. We find no apparent evolution with redshift from z = 0.2 - 1.2 in the relationship between stellar masses and maximum rotational velocities through the stellar mass Tully-Fisher relationship. We also find no evolution when comparing disk stellar and virial masses. Massive disk galaxies therefore appear to be already in place, in terms of their virial and stellar masses, out to the highest redshifts where they can be morphologically identified.

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arXiv2003

The dependence on environment of the color-magnitude relation of galaxies

The distribution in color and absolute magnitude is presented for 55,158 galaxies taken from the Sloan Digital Sky Survey in the redshift range $0.08<z<0.12$, as a function of galaxy number overdensity in a line-of-sight cylinder of transverse radius $1 h^{-1} \mathrm{Mpc}$. In all environments, bulge-dominated galaxies (defined to be those with radial profiles best fit with large Sérsic indices) form a narrow, well defined color--magnitude relation. Although the most luminous galaxies reside preferentially in the highest density regions, there is only a barely detectable variation in the color (zero-point) or slope of the color--magnitude relation ($<0.02 \mathrm{mag}$ in $^{0.1}[g-r]$ or $[B-V]$). These results constrain variations with environmental density in the ages or metallicities of typical bulge-dominated galaxies to be under 20 percent.

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arXiv2003

The Host Galaxies of AGN

We examine the properties of the host galaxies of 22,623 narrow-line AGN with 0.02<z<0.3 selected from a complete sample of 122,808 galaxies from the Sloan Digital Sky Survey. We focus on the luminosity of the [OIII]$λ$5007 emission line as a tracer of the strength of activity in the nucleus. We study how AGN host properties compare to those of normal galaxies and how they depend on L[OIII]. We find that AGN of all luminosities reside almost exclusively in massive galaxies and have distributions of sizes, stellar surface mass densities and concentrations that are similar to those of ordinary early-type galaxies in our sample. The host galaxies of low-luminosity AGN have stellar populations similar to normal early-types. The hosts of high- luminosity AGN have much younger mean stellar ages. The young stars are not preferentially located near the nucleus of the galaxy, but are spread out over scales of at least several kiloparsecs. A significant fraction of high- luminosity AGN have strong H$δ$ absorption-line equivalent widths, indicating that they experienced a burst of star formation in the recent past. We have also examined the stellar populations of the host galaxies of a sample of broad-line AGN. We conclude that there is no significant difference in stellar content between type 2 Seyfert hosts and QSOs with the same [OIII] luminosity and redshift. This establishes that a young stellar population is a general property of AGN with high [OIII] luminosities.

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arXiv2002

Stellar Masses and Star Formation Histories for 10^5 Galaxies from the Sloan Digital Sky Survey

We develop a new method to constrain the star formation histories, dust attenuation and stellar masses of galaxies. It is based on two stellar absorption line indices, the 4000 Angstrom break strength and the Balmer absorption line index Hdelta_A. Together, these indices allow us to constrain the mean stellar ages of galaxies and the fractional stellar mass formed in bursts over the past few Gyr. A comparison with broad band photometry then yields estimates of dust attenuation and of stellar mass. We generate a large library of Monte Carlo realizations of different star formation histories, including starbursts of varying strength and a range of metallicities. We use this library to generate median likelihood estimates of burst mass fractions, dust attenuation strengths, stellar masses and stellar mass-to-light ratios for a sample of 122,208 galaxies drawn from the Sloan Digital Sky Survey. The typical 95% confidence range in our estimated stellar masses is +-40%. We study how the stellar mass-to-light ratios of galaxies vary as a function of absolute magnitude, concentration index and photometric pass-band and how dust attenuation varies as a function of absolute magnitude and 4000 Angstrom break strength. We also calculate how the total stellar mass of the present Universe is distributed over galaxies as a function of their mass, size, concentration, colour, burst mass fraction and surface mass density. We find that most of the stellar mass in the local Universe resides in galaxies that have stellar masses \~5\times 10^10 M_sol, half light radii ~3 kpc, and half- light surface mass densities ~10^9 M_sol/kpc^2. The distribution of D(4000) is strongly bimodal, showing a clear division between galaxies dominated by old stellar populations and galaxies with more recent star formation.

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