What question did this study set out to answer?

The study aims to evaluate how varying the initial mass function (IMF) normalization affects the SLACS mass gap.

June 22, 2026Open Access

CDN-333: The IMF Test — Can a heavier initial mass function close the SLACS mass gap?

Key Points

The study aims to evaluate how varying the initial mass function (IMF) normalization affects the SLACS mass gap.
Normalized IMF values range from 1.0 to 3.0 across 20 grade-A strong lenses.
Recomputed g_bar, ν(x), and R_DM at each step of IMF normalization.
Analyzed the impact of Salpeter normalization on R_DM.
Salpeter normalization reduces R_DM from 0.94 to 0.91, a negligible change.
The median critical α where R_DM=0 is found to be 2.58, exceeding normal IMF values.
At α≥2.4, more than 33% of lenses become unphysical, indicating structural issues.

Abstract

CDN-333 sweeps IMF normalisation α from 1. 0 (Chabrier) through 1. 8 (Salpeter) to 3. 0 (super-Salpeter) across all 20 SLACS grade-A strong lenses, self-consistently recomputing gbar, ν (x), and RDM at each step. Salpeter reduces RDM from 0. 94 to 0. 91 — negligible. The median critical α (where RDM=0) is 2. 58, well beyond any observationally motivated IMF. At α≥2. 4, more than a third of lenses become unphysical (f*>1). Verdict: MARGINAL — IMF alone is strained but not excluded. The SLACS mass gap is structural, not a systematic artefact. D13 IMF path closed. CDN-334 pre-registered: adiabatic contraction test. Predecessor: CDN-332 (zenodo. org/records/20775186). Lock: CDN333IMFTESTLOCKED. Art Edition PDF + computation scripts included.

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