We provide fits to the distribution of galaxy luminosity, size, velocity dispersion and stellar mass as a function of concentration index C r and morphological type in the Sloan Digital Sky Survey (SDSS). (Our size estimate, a simple analogue of the SDSS cmodel magnitude, is new: it is computed using a combination of seeing-corrected quantities in the SDSS data base, and is in substantially better agreement with results from more detailed bulge/disc decompositions.) We also quantify how estimates of the fraction of 'early'-or 'late'-type galaxies depend on whether the samples were cut in colour, concentration or light profile shape, and compare with similar estimates based on morphology. Our fits show that ellipticals account for about 20 per cent of the r-band luminosity density, ρ L r , and 25 per cent of the stellar mass density, ρ * ; including S0s and Sas increases these numbers to 33 per cent and 40 per cent, and 50 per cent and 60 per cent, respectively. The values of ρ L r and ρ * , and the mean sizes, of E, E+S0 and E+S0+Sa samples are within 10 per cent of those in the Hyde & Bernardi, C r ≥ 2.86 and C r ≥ 2.6 samples, respectively. Summed over all galaxy types, we find ρ * ∼ 3 × 10 8 M Mpc −3 at z ∼ 0. This is in good agreement with expectations based on integrating the star formation history. However, compared to most previous work, we find an excess of objects at large masses, up to a factor of ∼10 at M * ∼ 5 × 10 11 M . The stellar mass density further increases at large masses if we assume different initial mass functions for elliptical and spiral galaxies, as suggested by some recent chemical evolution models, and results in a better agreement with the dynamical mass function.We also show that the trend for ellipticity to decrease with luminosity is primarily because the E/S0 ratio increases at large L. However, the most massive galaxies, M * ≥ 5 × 10 11 M , are less concentrated and not as round as expected if one extrapolates from lower L, and they are not well fit by pure deVaucouleur laws. This suggests formation histories with recent radial mergers. Finally, we show that the age-size relation is flat for ellipticals of fixed dynamical mass, but, at fixed M dyn , S0s and Sas with large sizes tend to be younger. Hence, samples selected on the basis of colour or C r will yield different scalings. Explaining this difference between E and S0 formation is a new challenge for models of early-type galaxy formation.
With the Sixth Data Release of the Sloan Digital Sky Survey, the imaging of the Northern Galactic Cap is now complete. The survey contains images and parameters of roughly 287 million objects over 9583 deg^2, and 1.27 million spectra of stars, galaxies, quasars and blank sky (for sky subtraction) selected over 7425 deg^2. This release includes much more extensive stellar spectroscopy than previously, and also includes detailed estimates of stellar temperatures, gravities, and metallicities. The results of improved photometric calibration are now available, with uncertainties of roughly 1% in g, r, i, and z, and 2% in u, substantially better than the uncertainties in previous data releases. The spectra in this data release have improved wavelength and flux calibration, especially in the extreme blue and extreme red, leading to the qualitatively better determination of stellar types and radial velocities. The spectrophotometric fluxes are now tied to point spread function magnitudes of stars rather than fiber magnitudes, giving a 0.35 mag change in the spectrophotometric flux scale. Systematic errors in the velocity dispersions of galaxies have been fixed, and the results of two independent codes for determining spectral classifications and redshifts are made available. (Abridged)Comment: 21 pages with 8 color figures. ApJS, in press. Minor modifications from previous versio
The size-luminosity relation of early-type Brightest Cluster Galaxies (BCGs), R e ∝ L 0.88 , is steeper than that for the bulk of the early-type galaxy population, for which R e ∝ L 0.68 . This is true if quantities derived from either deVaucouleur or Sersic fits to the surface brightness profiles are used. Contamination from an intra-cluster light component centered on the BCG, with similar parameters to what has been seen in some recent studies, is not able to account for this difference. In addition, although BCGs are hardly offset from the Fundamental Plane defined by the bulk of the early-type population, they show considerably smaller scatter. The larger than expected sizes of BCGs, and the increased homogeneity, are qualitatively consistent with models which seek to explain the colors of the most massive galaxies by invoking dry dissipationless mergers, since dissipation tends to reduce the sizes of galaxies, and wet mergers which result in star formation would tend to increase the scatter in luminosity at fixed size and velocity dispersion. Furthermore, BCGs define the same g − r color-magnitude relation as the bulk of the early-type population. If BCGs formed from dry mergers, then BCG progenitors must have been red for their magnitudes, suggesting that they hosted older stellar populations than typical for their luminosities. Our findings have two other consequences. First, the R e − L relation of the early-type galaxy population as a whole (i.e., normal plus BCG) exhibits some curvature: the most luminous galaxies tend to have larger sizes than expected from the R e ∝ L 0.68 scaling-some of this curvature must be a consequence of the fact that an increasing fraction of the most luminous galaxies are BCGs. The second consequence is suggested by the fact that, despite following a steeper size-luminosity relation, BCGs tend to define a tight relation between dynamical mass R e σ 2 /G and luminosity. Although this relation is slightly different than that defined by the bulk of the population, the fact that their sizes are large for their luminosities suggests that their velocity dispersions are small. We find that, indeed, BCGs define a shallower σ − L relation than the bulk of the early-type galaxy population. This shallower relation suggests there may be curvature in the correlation between black hole mass and velocity dispersion; simple extrapolation of a single power law M • − σ relation to large σ will underestimate M • .
We select a sample of about 50,000 early-type galaxies from the Sloan Digital Sky Survey (SDSS), calibrate fitting formulae which correct for known problems with photometric reductions of extended objects, apply these corrections, and then measure a number of pairwise scaling relations in the corrected sample. We show that, because they are not seeing corrected, the use of Petrosian-based quantities in magnitude limited surveys leads to biases, and suggest that this is one reason why Petrosian-based analyses of BCGs have failed to find significant differences from the bulk of the early-type population. These biases are not present when seeing-corrected parameters derived from deVaucouleur fits are used. Most of the scaling relations we study show evidence for curvature: the most luminous galaxies have smaller velocity dispersions, larger sizes, and fainter surface brightnesses than expected if there were no curva-ture. These statements remain true if we replace luminosities with stellar masses; they suggest that dissipation is less important at the massive end. There is curvature in the dynamical to stellar mass relation as well: the ratio of dynamical to stellar mass increases as stellar mass increases, but it curves upwards from this scaling both at small and large stellar masses. In all cases, the curvature at low masses becomes apparent when the sample becomes dominated by objects with stellar masses smaller than 3 x 10^10 M_Sun. We quantify all these trends using second order polynomials; these generally provide significantly better description of the data than linear fits, except at the least luminous end.Comment: 15 pages, 17 figures, Accepted by MNRA
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