The massive end of the luminosity and stellar mass functions: Dependence on the fit to the light profile

Abstract: In addition to the large systematic differences arising from assumptions about the stellar mass-to-light ratio, the massive end of the stellar mass function is rather sensitive to how one fits the light profiles of the most luminous galaxies. We quantify this by comparing the luminosity and stellar mass functions based on SDSS cmodel magnitudes, and PyMorph single-Sersic and Sersic-Exponential fits to the surface brightness profiles of galaxies in the SDSS. The PyMorph fits return more light, so that the predicted masses are larger than when cmodel magnitudes are used. As a result, the total stellar mass density at z~0.1 is about 1.2x larger than in our previous analysis of the SDSS. The differences are most pronounced at the massive end, where the measured number density of objects having M* > 6 x 10^{11} Msun is ~5x larger. Alternatively, at number densities of 10^{-6} Mpc^{-3}, the limiting stellar mass is 2x larger. The differences with respect to fits by other authors, typically based on Petrosian-like magnitudes, are even more dramatic, although some of these differences are due to sky-subtraction problems, and are sometimes masked by large differences in the assumed $M_*/L$ (even after scaling to the same IMF). Our results impact studies of the growth and assembly of stellar mass in galaxies, and of the relation between stellar and halo mass, so we provide simple analytic fits to these new luminosity and stellar mass functions and quantify how they depend on morphology, as well as the binned counts in electronic format.

• The paper demonstrates that using PyMorph fits significantly increases stellar mass estimates for massive galaxies compared to SDSS cmodel magnitudes.
• The authors compare methods and reveal up to a fivefold difference in galaxy number densities for stellar masses above 6×10^11 solar masses.
• Findings impact galaxy evolution and halo models by showing that accurate light profile fitting yields higher stellar mass densities at z≈0.1.

Analyzing the Massive End of the Luminosity and Stellar Mass Functions

The paper "The massive end of the luminosity and stellar mass functions: Dependence on the fit to the light profile" by Bernardi et al. provides a detailed examination of how different methods of fitting light profiles impact the estimates of galaxy luminosity and stellar mass functions, particularly at the massive end. The authors utilize data from the Sloan Digital Sky Survey (SDSS) and explore the sensitivity of these functions to the modeling approach used to fit the surface brightness profiles of the most luminous galaxies.

Methodological Comparisons

The authors compare several fitting methods for estimating galaxy luminosities:

• SDSS cmodel magnitudes
• PyMorph single-Sersic fits
• PyMorph Sersic-Exponential fits

Results indicate that PyMorph fits capture more light than SDSS cmodel magnitudes, assigning larger stellar masses to galaxies as a result. This discrepancy is particularly pronounced at the high-mass end, showing differences of up to five times in the number density of galaxies with stellar masses of $M_* \ge 6 \times 10^{11} M_\odot$ when PyMorph fits are used compared to cmodel magnitudes.

Implications for Stellar Mass Density

The study finds that the total stellar mass density at redshift $z\sim 0.1$ is approximately 1.2 times larger with PyMorph fitting compared to previous analyses using SDSS data. The differences are mainly observed at the bright end, underscoring the importance of precise modeling and method selection in determining galaxy properties.

Theoretical and Practical Implications

These findings have significant implications for several areas of astrophysical research:

• Galaxy Evolution Models: The revised stellar mass functions suggest that massive galaxies are more numerous than previously estimated. This affects models of galaxy evolution which rely on stellar mass distributions to understand merger histories and formation processes.
• Halo Model Analyses: Since stellar mass functions are critical for connecting galaxies to their dark matter halos, these results suggest that previous models may need adjustment. The relationship between stellar and halo mass will be especially impacted, necessitating recalibration of abundance matching techniques.
• Baryon Accretion Studies: Higher estimates of stellar mass density in massive galaxies could inform studies on baryon fractions and feedback mechanisms in galaxy formation.

Methodological Refinements

The paper emphasizes the need for careful treatment of sky subtraction and model fitting to mitigate biases in estimates of galaxies’ total light. The authors caution about neglecting these refinements, particularly at the high-mass end where intracluster light may contribute substantially to the observed profiles.

Future Directions

Future research should refine the conversion from luminosity to stellar mass, with a focus on standardizing the assumptions for stellar mass-to-light ratios (M*/L) across studies. As spectroscopic and imaging surveys extend to higher redshifts, the principles highlighted in this paper will become increasingly vital for constructing accurate models of galaxy formation and evolution.

In summary, this paper underscores the variability introduced by different light profile fitting methods and the significant implications this has on understanding the massive end of galaxy luminosity and stellar mass functions. As such, it provides crucial insights for both theoretical frameworks and observational methodologies in astrophysics.