1

Angular Momentum in Galaxies: Does Environment Matter?

Insights from observations & simulations

Amidou Sorgho

& AMIGA team

Instituto de Astrofísica de Andalucía (IAA-CSIC) — Spain

2026 AfAS Conference

Kasane, Botswana

24 March 2026

Grant PID2021-123930OB-C21 is funded by

2

Galaxy evolution & Angular momentum

Angular momentum:

• Controls morphology (disc vs spheroid)
• Linked to star formation
• Encodes galaxy assembly history

Galaxy evolution governed by internal & external mechanisms: nature vs nurture

3

Angular momentum vs. external processes

Lagos+ 2018

Numerical simulations:

• internal j of galaxies changes after mergers
• transfer of j between disk and DM halo

Tumlinson+ 2018

4

Angular momentum: Fall relation

Fall relation:

Fall 1983

5

Angular momentum: isolated galaxies

AMIGA: Analysis of Interstellar Medium of Isolated GAlaxies (Verdes-Montenegro+ 2005)

• Drawn from CIG catalogue (1051 gals, Karachentseva 1973)
• Highly isolated galaxies, minimal environmental effects (Verley+ 2007)
• A multi-𝛌 dataset collected and analysed: radio continuum (Leon+ 2008), HI (Espada+ 2011, Jones+ 2018), CO (Lisenfeld+ 2011), FIR (Lisenfeld+ 2007), NIR (Sabater+ 2012), MIR (Bok+ 2020), optical (Sulentic+ 2006)
• Morphologies: 70% Sb-Sc, 10% S0-S0a, 5% Ellipticals (Sulentic+ 2006)
• AMIGA sample shows extremely low values for parameters that are usually enhanced by interaction

tidal strength —>

local number density —>

6

Angular momentum: AMIGA

AMIGA vs Virgo

• HI scaling relations of the AMIGA sample define an up-to-date metric of the HI content of almost nurture free galaxies
• allow to predict the expected HI mass of an individual galaxy within 0.25 dex

AMIGA vs HI pairs

• Isolated galaxies show lower scatters than pairs, & galaxies in more densely populated environments adopt a more stochastic behaviour across a broad range of quantities

Bok+ 2020

7

Angular momentum: measurement

Total baryons: stars and HI gas (H₂ neglected)

8

Angular momentum: isolated vs non-isolated

j_AMIGA

>

other galaxies

Sorgho et al. 2024

9

Angular momentum: isolated vs non-isolated

Sorgho et al. 2024

9

Angular momentum: gas & stars

Dependence of j on fatm

Outliers

most likely

gas rich

galaxies

Sorgho et al. 2024

10

Angular momentum: obs. vs CDM

• Most AMIGA galaxies lie within the range predicted by CDM model
• no correlation between the j_bar and isolation parameters η_k and Q
• there may be a threshold density beyond which the effects of interactions become important in removing j

Sorgho et al. 2024

11

Angular momentum: obs. vs simulations

Expand sample to larger AMIGA:

• consistent j_star for 36 galaxies
• subsample representative of AMIGA

Sorgho et al., in prep.

12

Angular momentum: TNG100

Large sample of TNG100 star-forming galaxies:

• 3722 galaxies, including 510 isolated discs

Sorgho et al., in prep.

13

Angular momentum: obs. vs simulations

AMIGA vs TNG100: isolation

– Variation of j_star with gas fraction

– No differences between isolated & non-isolated

– TNG’s turnover region (‘dip’) not reproduced by observation

No variation of j_star with density!

Sorgho et al., in prep.

14

Angular momentum: TNG100 simulations

TNG100: j_star vs gas content & SF

• j_star variation with gas fraction

​

• Weak correlation with sSFR

(low-mass galaxies more actively form stars)

​

• No correlation with deviation from SFR MS

Sorgho et al., in prep.

15

Summary

• At fixed Mbar, j_bar of isolated galaxies > j_bar of non-isolated galaxies: direct evidence of the role of the environment in removing J from galaxies
• No clear correlation between j_bar and degree of isolation: possible existence of a threshold density beyond which the effects of interactions become important in removing j_bar
• From TNG:
• j_star is NOT correlated with galaxy density
• j_star is tightly correlated with gas fraction

Acknowledgement:

espSRC service and support, funded by the MICIU, by the Junta de Andalucía, by the ERDF and by the NextGenerationEU/PRTR

Grant PID2021-123930OB-C21 is funded by