[Paper Review] The galaxy stellar mass function from CCSNe with improved photo-z techniques

Thomas M. Sedgwick, I. K. Baldry+2 more|Liverpool John Moores University|Sep 10, 2019

Galaxies: Formation, Evolution, Phenomena1 references4 citations

TL;DR

This study improves photometric redshift (photo-z) estimation for core-collapse supernova (CCSN) host galaxies using scaled flux matching, enabling more accurate stellar mass measurements and tighter constraints on the star-forming galaxy stellar mass function (GSMF). It finds no truncation in galaxy formation down to 10⁶.² M⊙, with a power-law increase in number density, indicating no evidence for mass-dependent suppression of dwarf galaxy formation.

ABSTRACT

In Sedgwick et al. (2019) we introduced and utilised a method to combat surface brightness and mass biases in galaxy sample selection, using core-collapse supernovae (CCSNe) as pointers towards their host galaxies, in order to: (i) search for low-surface brightness galaxies (LSBGs); (ii) assess the contributions of galaxies at a given mass to the star-formation-rate density (SFRD); and (iii) infer from this, using estimates of specific star-formation (SF) rate, the form of the SF-galaxy stellar mass function (GSMF). A CCSN-selection of SF-galaxies allows a probe of the form of the SFRD and GSMF deep into the dwarf galaxy mass regime. In the present work, we give improved constraints on our estimates of the SFRD and star-forming GSMF, in light of improved photometric redshift estimates required for estimates of galaxy stellar mass. The results are consistent with a power-law increase to SF-galaxy number density down to our low stellar mass limit of $\sim 10^{6.2}$ M$_{\odot}$. No deviation from the high-mass version of the surface brightness - mass relation is found in the dwarf mass regime. These findings imply no truncation to galaxy formation processes at least down to $\sim 10^{6.2}$ M$_{\odot}$.

Motivation & Objective

• To reduce surface brightness and mass biases in galaxy sample selection by using core-collapse supernovae (CCSNe) as tracers of their host galaxies.
• To improve constraints on the star-formation-rate density (SFRD) and star-forming galaxy stellar mass function (GSMF) using enhanced photometric redshift (photo-z) techniques.
• To test whether galaxy formation processes are truncated at low masses by analyzing the GSMF and surface brightness–mass relation in the dwarf regime.
• To assess the impact of improved photo-z methods on stellar mass estimates and their implications for low-mass galaxy number densities.

Proposed method

• Employed scaled flux matching (SFM) as an alternative to zMedIC for photometric redshift estimation, using SDSS ugriz photometry and a training set of spectroscopically confirmed galaxies from Stripe 82.
• Defined a chi-squared statistic to match fluxes of target galaxies to those in the reference sample, minimizing residuals across photometric bands.
• Incorporated flux errors from SExtractor and added fractional errors (0.02–0.05) to account for photometric uncertainties in the chi-squared calculation.
• Used reliability weights based on chi-squared and bin weights to improve photo-z accuracy and reduce systematic errors.
• Calculated galaxy stellar masses using the improved photo-z estimates, applying k-corrections and surface brightness dimming corrections.
• Applied Monte Carlo simulations with 1000 iterations to propagate redshift uncertainties into stellar mass and surface brightness estimates.

Experimental results

Research questions

• RQ1 Does the star-forming galaxy stellar mass function (GSMF) exhibit a turnover or truncation at low masses, suggesting suppressed formation below a certain mass scale?
• RQ2 How do improved photometric redshift techniques affect the accuracy of galaxy stellar mass estimates in low-surface-brightness systems?
• RQ3 Is there a break in the surface brightness–stellar mass relation at low masses, indicating a phase change in galaxy formation or star-formation processes?
• RQ4 To what extent do CCSN-selected galaxies provide a complete census of star-forming dwarfs, especially below 10⁶.² M⊙?

Key findings

• The star-forming GSMF shows a continuous power-law increase in number density down to 10⁶.² M⊙, with no evidence of a turnover or truncation.
• Improved photo-z estimates via scaled flux matching reduce uncertainties in stellar mass and SFRD, leading to tighter constraints on the GSMF.
• No deviation from the high-mass surface brightness–stellar mass relation is observed in the dwarf regime, supporting a continuous formation process.
• The surface brightness–mass relation is linear over the full mass range, with μ_abs,r,50 ≈ -1.35 log(M/10⁹ M⊙) + 22, indicating no phase change in galaxy evolution.
• The study confirms that CCSN-based selection effectively probes the low-mass end of the GSMF, identifying previously missed low-surface-brightness dwarfs.
• Future surveys like LSST are expected to detect ~500 z < 0.2 CCSNe per year in galaxies with log(M/M⊙) < 7.0, enabling deeper exploration of the dwarf GSMF.