On the galaxy stellar mass function, the mass-metallicity relation, and the implied baryonic mass function

Baldry, Glazebrook & Driver 2008, published in MNRAS, Vol. 388, pp. 945-959 (link: ADS).

Abstract

A comparison between published field galaxy stellar mass functions (GSMFs) shows that the cosmic stellar mass density is in the range 4--8 per cent of the baryon density (assuming Omega_b = 0.045). There remain significant sources of uncertainty for the dust correction and underlying stellar mass-to-light ratio even assuming a reasonable universal stellar initial mass function. We determine the z < 0.05 GSMF using the New York University - Value-Added Galaxy Catalog sample of 49968 galaxies derived from the Sloan Digital Sky Survey and various estimates of stellar mass. The GSMF shows clear evidence for a low-mass upturn and is fitted with a double Schechter function that has alpha_2 =~ -1.6. At masses below ~ 10^8.5 Msun, the GSMF may be significantly incomplete because of missing low surface-brightness galaxies. One interpretation of the stellar mass-metallicity relation is that it is primarily caused by a lower fraction of available baryons converted to stars in low-mass galaxies. Using this principal, we determine a simple relationship between baryonic mass and stellar mass and present an `implied baryonic mass function'. This function has a faint-end slope, alpha_2 =~ -1.9. Thus, we find evidence that the slope of the low-mass end of the galaxy mass function could plausibly be as steep as the halo mass function. We illustrate the relationship between halo baryonic mass function --> galaxy baryonic mass function --> GSMF. This demonstrates the requirement for peak galaxy formation efficiency at baryonic masses ~ 10^11 Msun corresponding to a minimum in feedback effects. The baryonic-infall efficiency may have levelled off at lower masses.

Data:

  • Field galaxy stellar mass function as per Figure 6: binned function data.
  • Notes:
    1. IMFs of Kroupa (2001) or Chabrier (2003) were assumed.
    2. H0 = 70 km/s/Mpc was assumed.
    3. The SDSS NYU-VAGC low-z DR4 sample was used.
    4. The max number densites were multiplied by 1.13, which represents a correction from the z < 0.05 volume to the z < 0.1 volume based on number densities of bright galaxies.
    5. The log stellar mass < 8.5 data points should be regarded as lower limits because of surface-brightness incompleteness (certainly for log mass < 8).
    6. The stellar mass estimates used were by A. Gallazzi [1, 2], K. Glazebrook, G. Kauffmann [1, 3], B. Panter [4] (and their collaborators).
    7. The stellar M/L were applied to Petrosian magnitudes, some correction could be used to correct to total magnitudes (~ factor 1.05 to 1.1 on average). For individual galaxies, Petrosian magnitudes recover 0.8 to 0.99 of the total flux.
    8. How well can population synthesis correct for dust attenuation? Driver et al. [5, 6] advocate a larger correction than likely accounted for by the above M/L estimates, some correction could be used to account for completely obscured stellar populations (upto ~ factor 1.2).
galaxy stellar mass function
  • Gas-to-stellar mass ratios as per Figure 11: compilation data.

    Ivan Baldry, written 2008 April 20.

    Links: - to my home page; to my research page; list of publications.