Galaxy luminosities, stellar masses, sizes, velocity dispersions as a function of morphological type (0910.1093v2)

Abstract: 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 SDSS. We also quantify how estimates of the fraction of early' orlate' type galaxies depend on whether the samples were cut in color, concentration or light profile shape, and compare with similar estimates based on morphology. Our fits show that Es account for about 20% of the r-band luminosity density, rho_Lr, and 25% of the stellar mass density, rho_; including S0s and Sas increases these numbers to 33% and 40%, and 50% and 60%, respectively. Summed over all galaxy types, we find rho_ ~ 3 * 10^8 M_Sun 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_Sun. The stellar mass density further increases at large masses if we assume different IMFs for Es 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_Sun, 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 Es of fixed dynamical mass, but, at fixed M_dyn, S0s and Sas with large sizes tend to be younger. Explaining this difference between E and S0 formation is a new challenge for models of early-type galaxy formation.

• The paper introduces refined measurements of galaxy properties across morphological types using SDSS data and improved bulge/disk decompositions.
• The analysis finds that elliptical galaxies contribute significantly to r-band luminosity and stellar mass densities, revealing an excess of high-mass systems.
• The study reveals that massive galaxies show lower concentration and roundness, suggesting recent radial mergers that challenge existing galaxy formation models.

Overview of "Galaxy Luminosities, Stellar Masses, Sizes, and Velocity Dispersions as a Function of Morphological Type"

This paper investigates the relationships between various physical properties of galaxies—such as luminosity, stellar mass, size, and velocity dispersion—across different morphological types. Using data from the Sloan Digital Sky Survey (SDSS), the authors analyze how these properties vary as a function of the concentration index ($C_r$) and morphological classification.

Summary of Findings

1. Morphological Classification and Galaxy Properties:
   • The paper provides fits to the distribution of galaxy properties (luminosity, size, velocity dispersion, and stellar mass) for different morphological types. The authors introduce a new size estimate derived from SDSS data, which aligns better with detailed bulge/disk decompositions.
   • The analysis illustrates how different cuts in color, concentration index, and light profile shape affect the classification of galaxies into 'early' and 'late' types. Elliptical galaxies represent approximately 20% of the r-band luminosity density and 25% of the stellar mass density, with these numbers increasing when including lenticular (S0) and Sa-type galaxies.
2. Stellar Mass Density:
   • By summing over all galaxy types, the paper estimates a stellar mass density of about $3 \times 10^8 \, M_\odot$ Mpc$^{-3}$ at $z \approx 0$. The paper finds an excess of high-mass galaxies compared to previous works, suggesting potential corrections for initial mass functions (IMFs) in modeling galaxy evolution.
3. Galaxy Shape and Formation History:
   • For massive galaxies ($M_* \geq 5 \times 10^{11} \, M_\odot$), the findings indicate fewer concentrations and less roundness than expected, hinting at formation histories involving recent radial mergers. The ellipticity decreases with luminosity mainly due to the increasing ratio of elliptical to lenticular galaxies at high luminosities.
   • The paper shows a flat age-size relation for ellipticals at fixed dynamical mass. In contrast, S0s and Sa galaxies with larger sizes tend to be younger, presenting challenges for existing models of early-type galaxy formation.

Implications and Future Developments

The research provides a comprehensive quantitative framework for understanding the distribution of galaxy properties across different morphological types and informs models of galaxy evolution. The paper's insights into the excess of massive galaxies have significant implications for constraining the galaxy mass function and improving our understanding of galaxy formation and evolution theories. By examining galaxy shape and structural parameters alongside stellar populations, the paper contributes to a more nuanced view of galaxy formation history.

Future work could focus on refining the understanding of the IMF differences between galaxy types and further exploring the implications of the deviations observed in massive galaxies. It is anticipated that improvements in observational capabilities and data accumulation, particularly from deep sky surveys, will continue to validate or challenge current findings and theoretical frameworks proposed in this paper.