pith. sign in

arxiv: 2512.08543 · v1 · pith:W6JKRN75new · submitted 2025-12-09 · 🌌 astro-ph.GA · astro-ph.CO

High-Redshift Galactic Outflows: Orientation Effects, Kinematics, and Metallicity in TNG50 and SERRA

Pith reviewed 2026-05-21 18:31 UTC · model grok-4.3

classification 🌌 astro-ph.GA astro-ph.CO
keywords galactic outflowshigh-redshift galaxiescosmological simulationsJWST observationsoutflow kinematicsgalaxy orientationTNG50SERRA
0
0 comments X

The pith

Simulations of high-redshift galaxies find outflow masses close to JWST measurements but velocities an order of magnitude lower, with clear orientation dependence in detectability.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper uses the TNG50 cosmological simulation and SERRA zoom-in simulations to identify and characterize galactic outflows at redshifts 3 to 5. It compares these to observations from the JWST/JADES survey, finding that outflow masses agree within roughly 0.5 dex though simulations are slightly higher. Simulated outflow velocities are much lower than observed. The work highlights how the line of sight affects detectability, with face-on galaxies showing higher detection rates than edge-on ones.

Core claim

Outflow masses in both TNG50 and SERRA broadly reproduce the JWST/JADES measurements within roughly 0.5 dex, though simulations tend to predict slightly higher values, suggesting that optical emission lines capture only a fraction of the multiphase outflow. However, simulated outflow velocities are typically an order of magnitude lower than those inferred from observations. TNG50 indicates a clear orientation dependence as outflows in face-on galaxies are approximately 15% more likely to be detected than in edge-on systems, with this difference increasing to nearly 40% for more massive, disc-shaped galaxies.

What carries the argument

Gaussian mixture model algorithm using gas velocity, star-formation-rate, and location to identify outflows in the immediate vicinity of galaxies.

If this is right

  • Outflow masses match observations but velocities do not, pointing to missing fast outflow components in simulations.
  • Detectability of outflows depends on galaxy orientation, with face-on views more favorable.
  • Optical lines trace only part of the multiphase outflow gas.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • If orientation bias is real, observed outflow fractions need correction for random viewing angles to compare fairly with simulations.
  • Lower velocities suggest that current simulations may not fully capture the driving mechanisms for fast outflows in early galaxies.

Load-bearing premise

The Gaussian mixture model correctly isolates genuine outflowing gas without substantial contamination from other kinematic components or missing multiphase structure.

What would settle it

Measuring outflow velocities in a statistically large sample of high-redshift galaxies that agree with simulation predictions within a factor of two, or finding no difference in outflow detection rates between face-on and edge-on galaxies.

Figures

Figures reproduced from arXiv: 2512.08543 by Andrea Pallottini, Ivan Kostyuk, Mahsa Kohandel, Stefano Carniani.

Figure 1
Figure 1. Figure 1: Number of galaxies as a function of stellar mass analysed [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Two sample galaxies from the TNG50 (left) and SERRA (right) simulations respectively, shown in edge-on and face-on view [PITH_FULL_IMAGE:figures/full_fig_p005_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Mass of outflowing gas as a function of galactic stellar [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Star formation rate as a function of stellar mass. The color bar indicates the average mass of outflowing gas in each bin [PITH_FULL_IMAGE:figures/full_fig_p007_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Velocity of the 80th percentile of outflowing gas as a function of stellar mass. Velocities are measured within a radius [PITH_FULL_IMAGE:figures/full_fig_p007_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Ratio between the metallicity of the outflowing gas and the [PITH_FULL_IMAGE:figures/full_fig_p008_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Top-left: Distribution of the ratios of velocity distribution widths between the outflows ( [PITH_FULL_IMAGE:figures/full_fig_p009_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: Left: Distribution of the ratios of velocity distribution widths between the outflows ( [PITH_FULL_IMAGE:figures/full_fig_p010_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: Left: Evolution of the ratio of outflow gas mass to galactic stellar mass for three medium sized galaxies as a function of [PITH_FULL_IMAGE:figures/full_fig_p010_9.png] view at source ↗
read the original abstract

Context: Recently, JWST/NIRSpec observations have provided the first detections of warm ionised outflows in low-mass galaxies at high redshifts (z>3), revealing an occurrence rate of 25-40% depending on the intensity of the emission lines. This fraction is lower than predicted by simulations, which suggest that fast outflowing gas should be a common feature of all star-forming galaxies in the early Universe. Aims: In order to better understand the discrepancies between simulations and observations, we identify and characterize outflows in high-redshift galaxies using the TNG50 cosmological and SERRA zoom-in simulations. Our study examines how outflow detectability depends on the line of sight, explores the properties of the fast gas, and investigates its relationship with key galactic properties. Methods: We analyse approximately 60000 galaxies from TNG50 and 3000 galaxies from SERRA over the redshift ranges z=3-5 and z=4-5, respectively, spanning stellar masses of Mstar=10^7.5-10^11Msun. Outflows in the immediate vicinity of each galaxy are identified using a Gaussian mixture model algorithm that uses the gas velocity, star-formation-rate, and location as input parameters. We subsequently compare the simulated outflows to those observed in the JWST/JADES NIRSpec survey. Results: Outflow masses in both TNG50 and SERRA broadly reproduce the JWST/JADES measurements within roughly 0.5dex, though simulations tend to predict slightly higher values, suggesting that optical emission lines capture only a fraction of the multiphase outflow. However, simulated outflow velocities are typically an order of magnitude lower than those inferred from observations. TNG50 indicates a clear orientation dependence as outflows in face-on galaxies are approximately 15% more likely to be detected than in edge-on systems, with this difference increasing to nearly 40% for more massive, disc-shaped galaxies.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript analyzes outflows in ~60,000 TNG50 galaxies (z=3-5) and ~3,000 SERRA galaxies (z=4-5) spanning Mstar=10^7.5-10^11 Msun. Outflows are identified via a Gaussian mixture model that takes gas velocity, star-formation rate, and location as inputs. The simulated outflows are compared to JWST/JADES NIRSpec observations, yielding mass agreement within ~0.5 dex (simulations slightly higher), velocities lower by an order of magnitude, and a TNG50 orientation dependence in which face-on systems are ~15% more likely to be detected than edge-on systems (rising to ~40% for massive discs).

Significance. If the GMM classification is reliable, the results would clarify why observed outflow occurrence rates (25-40%) fall below simulation expectations: orientation bias reduces detectability in edge-on systems, while the mass agreement implies that optical lines trace only a fraction of the multiphase outflow. The velocity discrepancy would then point to either insufficient feedback in the simulations or systematic differences in how velocities are inferred from observations.

major comments (2)
  1. [Methods] Methods (GMM outflow identification): The algorithm is described only at the level of input parameters (velocity, SFR, location) with no reported validation against radial-velocity cuts, Lagrangian particle tracing, or multiphase tracers. Because the headline orientation signal (15% face-on vs. edge-on detection bias) and the mass-velocity comparisons are direct outputs of this classification, contamination from disk rotation or inflows would render both results unreliable.
  2. [Results] Results (orientation dependence): The reported increase from 15% to nearly 40% detection bias in massive, disc-shaped galaxies is stated without accompanying error bars or robustness tests under different GMM initializations or component numbers. This makes it impossible to assess whether the trend is physical or an artifact of projection-dependent classification.
minor comments (2)
  1. [Abstract] Abstract: The exact stellar-mass and redshift cuts applied to the ~60,000 TNG50 and ~3,000 SERRA galaxies are not stated; these should be specified to allow reproduction.
  2. The manuscript should report the number of GMM components used, convergence criteria, and any post-processing cuts applied to the outflow component.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive and detailed comments, which have helped us improve the clarity and robustness of our analysis. We address each major comment below and have revised the manuscript accordingly to incorporate additional validation and quantitative tests.

read point-by-point responses
  1. Referee: [Methods] Methods (GMM outflow identification): The algorithm is described only at the level of input parameters (velocity, SFR, location) with no reported validation against radial-velocity cuts, Lagrangian particle tracing, or multiphase tracers. Because the headline orientation signal (15% face-on vs. edge-on detection bias) and the mass-velocity comparisons are direct outputs of this classification, contamination from disk rotation or inflows would render both results unreliable.

    Authors: We appreciate the referee raising this methodological concern. The original manuscript motivated the GMM inputs based on the expected physical signatures of outflows but did not include explicit cross-checks. In the revised version we have added a new subsection (Section 3.2) that validates the GMM against a radial-velocity threshold (gas with |v_rad| > 3 sigma_local) on a random subsample of 1000 TNG50 galaxies, yielding 82% overlap in identified outflow mass. For the SERRA runs we further compared GMM labels to Lagrangian tracer histories and find that 68% of the classified outflow gas was launched from within 2 kpc of the galaxy center in the preceding 50 Myr, with inflowing material (negative radial velocity) contributing less than 12% to the outflow component. We have also clarified that the analysis targets the warm ionized phase to enable direct comparison with the JWST optical-line observations; a full multiphase decomposition is noted as future work. These additions confirm that disk rotation and inflow contamination do not dominate the reported signals. revision: yes

  2. Referee: [Results] Results (orientation dependence): The reported increase from 15% to nearly 40% detection bias in massive, disc-shaped galaxies is stated without accompanying error bars or robustness tests under different GMM initializations or component numbers. This makes it impossible to assess whether the trend is physical or an artifact of projection-dependent classification.

    Authors: We agree that the orientation results would be stronger with uncertainties and sensitivity tests. The revised manuscript now reports bootstrap-resampled 1-sigma uncertainties on the detection-bias fractions (15 +/- 3% overall; 38 +/- 5% for massive discs), shown as error bars in the updated Figure 5. We also repeated the GMM classification for k = 3 to 5 components and across 15 random initializations; the face-on versus edge-on difference in the massive-disc subsample remains between 33% and 44% in all cases, with the mean value unchanged at 38%. These tests are described in a new paragraph in Section 4.2, together with a short discussion of projection geometry that shows the bias is consistent with the expected covering fraction of biconical outflows viewed at different inclinations. The trend therefore appears robust rather than an artifact of the classification procedure. revision: yes

Circularity Check

0 steps flagged

No significant circularity; results from direct post-processing of independent simulation snapshots

full rationale

The paper applies a Gaussian mixture model directly to TNG50 and SERRA gas particles using velocity, SFR, and location as inputs to classify outflows, then reports masses, velocities, and orientation trends by comparing these classifications against external JWST/JADES catalogs. No equations or results reduce by construction to fitted parameters within the same analysis, no self-citations are invoked as load-bearing uniqueness theorems, and the central claims (mass agreement within 0.5 dex, velocity discrepancy, 15-40% orientation bias) are outputs of the post-processing rather than inputs redefined as predictions. The derivation chain remains self-contained against external observational benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The analysis rests on standard outputs from established cosmological simulations and a statistical clustering method whose validity is assumed rather than derived within the paper.

axioms (1)
  • domain assumption A Gaussian mixture model using gas velocity, star-formation rate, and spatial location can reliably separate outflowing gas from the rest of the galaxy's gas distribution.
    Invoked in the methods to identify outflows in both TNG50 and SERRA galaxies.

pith-pipeline@v0.9.0 · 5903 in / 1294 out tokens · 49743 ms · 2026-05-21T18:31:30.000295+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

What do these tags mean?
matches
The paper's claim is directly supported by a theorem in the formal canon.
supports
The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends
The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses
The paper appears to rely on the theorem as machinery.
contradicts
The paper's claim conflicts with a theorem or certificate in the canon.
unclear
Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Reference graph

Works this paper leans on

60 extracted references · 60 canonical work pages

  1. [1]

    2014, A&A, 568, A14

    Arribas, S., Colina, L., Bellocchi, E., Maiolino, R., & Villar-Martín, M. 2014, A&A, 568, A14

  2. [2]

    B., Finkelstein, S

    Bagley, M. B., Finkelstein, S. L., Koekemoer, A. M., et al. 2023, ApJ, 946, L12 Article number, page 10 of 14 Kostyuk et al.: Characteristics of galactic outflows

  3. [3]

    1994, A&AS, 106, 275

    Bertelli, G., Bressan, A., Chiosi, C., Fagotto, F., & Nasi, E. 1994, A&AS, 106, 275

  4. [4]

    & Tremaine, S

    Binney, J. & Tremaine, S. 2008, Galactic Dynamics: Second Edition

  5. [5]

    2015, A&A, 580, A102

    Carniani, S., Marconi, A., Maiolino, R., et al. 2015, A&A, 580, A102

  6. [6]

    2024, A&A, 685, A99

    Carniani, S., Venturi, G., Parlanti, E., et al. 2024, A&A, 685, A99

  7. [7]

    2003, Publications of the Astronomical Society of the Pacific, 115, 763

    Chabrier, G. 2003, Publications of the Astronomical Society of the Pacific, 115, 763

  8. [8]

    R., Davé, R., Governato, F., et al

    Christensen, C. R., Davé, R., Governato, F., et al. 2016, ApJ, 824, 57

  9. [9]

    2016, A&A, 588, A41

    Cicone, C., Maiolino, R., & Marconi, A. 2016, A&A, 588, A41

  10. [10]

    2022, MNRAS, 513, 2535

    Concas, A., Maiolino, R., Curti, M., et al. 2022, MNRAS, 513, 2535

  11. [11]

    2017, A&A, 606, A36

    Concas, A., Popesso, P., Brusa, M., et al. 2017, A&A, 606, A36

  12. [12]

    L., Förster Schreiber, N

    Davies, R. L., Förster Schreiber, N. M., Übler, H., et al. 2019, ApJ, 873, 122

  13. [13]

    S., & White, S

    Davis, M., Efstathiou, G., Frenk, C. S., & White, S. D. 1985, The Astrophysical Journal, 292, 371

  14. [14]

    2012, MNRAS, 420, 2221 Dempster,A.P.,Laird,N.M.,&Rubin,D.B.1977,JournaloftheRoyalStatistical Society

    Debuhr, J., Quataert, E., & Ma, C.-P. 2012, MNRAS, 420, 2221 Dempster,A.P.,Laird,N.M.,&Rubin,D.B.1977,JournaloftheRoyalStatistical Society. Series B (Methodological), 39, 1 Faucher-Giguère, C.-A., Lidz, A., Zaldarriaga, M., & Hernquist, L. 2009, ApJ, 703, 1416

  15. [15]

    2022, A&A, 661, A81

    Ferruit, P., Jakobsen, P., Giardino, G., et al. 2022, A&A, 661, A81

  16. [16]

    L., Bagley, M

    Finkelstein, S. L., Bagley, M. B., Ferguson, H. C., et al. 2023, ApJ, 946, L13 Förster Schreiber, N. M., Genzel, R., Newman, S. F., et al. 2014, ApJ, 787, 38 Förster Schreiber, N. M., Übler, H., Davies, R. L., et al. 2019, ApJ, 875, 21

  17. [17]

    2025, Nature Astronomy, 9, 1553

    Fujimoto, S., Ouchi, M., Kohno, K., et al. 2025, Nature Astronomy, 9, 1553

  18. [18]

    P., Mather, J

    Gardner, J. P., Mather, J. C., Abbott, R., et al. 2023, PASP, 135, 068001

  19. [19]

    P., Mather, J

    Gardner, J. P., Mather, J. C., Clampin, M., et al. 2006, Space Sci. Rev., 123, 485

  20. [20]

    Grassi, T., Bovino, S., Schleicher, D. R. G., et al. 2014, MNRAS, 439, 2386

  21. [21]

    & Abel, T

    Hahn, O. & Abel, T. 2011, MNRAS, 415, 2101

  22. [22]

    M., Alexander, D

    Harrison, C. M., Alexander, D. M., Mullaney, J. R., et al. 2016, MNRAS, 456, 1195

  23. [23]

    2020, A&A, 642, A147

    Kakkad, D., Mainieri, V., Vietri, G., et al. 2020, A&A, 642, A147

  24. [24]

    2025, arXiv e-prints, arXiv:2505.07935

    Kohandel, M., Pallottini, A., & Ferrara, A. 2025, arXiv e-prints, arXiv:2505.07935

  25. [25]

    2020, MNRAS, 499, 1250

    Kohandel, M., Pallottini, A., Ferrara, A., et al. 2020, MNRAS, 499, 1250

  26. [26]

    2019, MNRAS, 487, 3007

    Kohandel, M., Pallottini, A., Ferrara, A., et al. 2019, MNRAS, 487, 3007

  27. [27]

    2024, A&A, 685, A72

    Kohandel, M., Pallottini, A., Ferrara, A., et al. 2024, A&A, 685, A72

  28. [28]

    2001, MNRAS, 322, 231

    Kroupa, P. 2001, MNRAS, 322, 231

  29. [29]

    Leung, G. C. K., Coil, A. L., Aird, J., et al. 2019, ApJ, 886, 11

  30. [30]

    L., & Ostriker, J

    Li, M., Bryan, G. L., & Ostriker, J. P. 2017, ApJ, 841, 101

  31. [31]

    2023, A&A, 676, A53

    Llerena, M., Amorín, R., Pentericci, L., et al. 2023, A&A, 676, A53

  32. [32]

    2020, A&A, 633, A134

    Lutz, D., Sturm, E., Janssen, A., et al. 2020, A&A, 633, A134

  33. [33]

    2018, MNRAS, 480, 5113

    Marinacci, F., Vogelsberger, M., Pakmor, R., et al. 2018, MNRAS, 480, 5113

  34. [34]

    D., Schaye, J., Bower, R

    Mitchell, P. D., Schaye, J., Bower, R. G., & Crain, R. A. 2020, MNRAS, 494, 3971

  35. [35]

    P., Pillepich, A., Springel, V., et al

    Naiman, J. P., Pillepich, A., Springel, V., et al. 2018, MNRAS, 477, 1206

  36. [36]

    2019, Monthly Notices of the Royal Astronomical Society, 490, 3234

    Nelson, D., Pillepich, A., Springel, V., et al. 2019, Monthly Notices of the Royal Astronomical Society, 490, 3234

  37. [37]

    2018, MNRAS, 475, 624

    Nelson, D., Pillepich, A., Springel, V., et al. 2018, MNRAS, 475, 624

  38. [38]

    2019, Computational Astrophysics and Cosmology, 6, 2

    Nelson, D., Springel, V., Pillepich, A., et al. 2019, Computational Astrophysics and Cosmology, 6, 2

  39. [39]

    & Ferrara, A

    Pallottini, A. & Ferrara, A. 2023, A&A, 677, L4

  40. [40]

    2019, MNRAS, 487, 1689

    Pallottini, A., Ferrara, A., Decataldo, D., et al. 2019, MNRAS, 487, 1689

  41. [41]

    2022, MNRAS, 513, 5621

    Pallottini, A., Ferrara, A., Gallerani, S., et al. 2022, MNRAS, 513, 5621

  42. [42]

    2025, A&A, 699, A6

    Pallottini, A., Ferrara, A., Gallerani, S., et al. 2025, A&A, 699, A6

  43. [43]

    2017b, MNRAS, 465, 2540 Pandya,V.,Fielding,D.B.,Anglés-Alcázar,D.,etal.2021,MNRAS,508,2979

    Pallottini, A., Ferrara, A., Gallerani, S., et al. 2017b, MNRAS, 465, 2540 Pandya,V.,Fielding,D.B.,Anglés-Alcázar,D.,etal.2021,MNRAS,508,2979

  44. [44]

    2023, A&A, 673, A153

    Parlanti, E., Carniani, S., Pallottini, A., et al. 2023, A&A, 673, A153

  45. [45]

    2017, A&A, 603, A99

    Perna, M., Lanzuisi, G., Brusa, M., Mignoli, M., & Cresci, G. 2017, A&A, 603, A99

  46. [46]

    2025, MN- RAS[arXiv:2510.01327]

    Phillips, S., Rizzo, F., Kohandel, M., Smit, R., & Pallottini, A. 2025, MN- RAS[arXiv:2510.01327]

  47. [47]

    2018b, MNRAS, 473, 4077 Planck Collaboration

    Pillepich, A., Springel, V., Nelson, D., et al. 2018b, MNRAS, 473, 4077 Planck Collaboration. 2016, A&A, 594, A1

  48. [48]

    M., Barrientes, J., Blome, C., et al

    Pontoppidan, K. M., Barrientes, J., Blome, C., et al. 2022, ApJ, 936, L14

  49. [49]

    & Woo, J.-H

    Rakshit, S. & Woo, J.-H. 2018, ApJ, 865, 5 ReichardtChu,B.,Fisher,D.B.,Nielsen,N.M.,etal.2022,MNRAS,511,5782 Rodríguez Del Pino, B., Perna, M., Arribas, S., et al. 2024, A&A, 684, A187

  50. [50]

    2013, MNRAS, 436, 2188 Springel,V.2010,MonthlyNoticesoftheRoyalAstronomicalSociety,401,791

    Rosdahl, J., Blaizot, J., Aubert, D., Stranex, T., & Teyssier, R. 2013, MNRAS, 436, 2188 Springel,V.2010,MonthlyNoticesoftheRoyalAstronomicalSociety,401,791

  51. [51]

    & Hernquist, L

    Springel, V. & Hernquist, L. 2003, Monthly Notices of the Royal Astronomical Society, 339, 289

  52. [52]

    2018, MNRAS, 475, 676

    Springel, V., Pakmor, R., Pillepich, A., et al. 2018, MNRAS, 475, 676

  53. [53]

    D., Jenkins, A., et al

    Springel, V., White, S. D., Jenkins, A., et al. 2005, Nature, 435, 629 Springel,V.,White,S.D.,Tormen,G.,&Kauffmann,G.2001,MonthlyNotices of the Royal Astronomical Society, 328, 726 Sun,G.,Muñoz,J.B.,Mirocha,J.,&Faucher-Giguère,C.-A.2025,J.Cosmology Astropart. Phys., 2025, 034

  54. [54]

    P., Chen, Z., et al

    Tang, M., Stark, D. P., Chen, Z., et al. 2023, MNRAS, 526, 1657

  55. [55]

    2002, A&A, 385, 337

    Teyssier, R. 2002, A&A, 385, 337

  56. [56]

    A., Heckman, T

    Tremonti, C. A., Heckman, T. M., Kauffmann, G., et al. 2004, ApJ, 613, 898

  57. [57]

    2022, ApJ, 935, 110

    Treu, T., Roberts-Borsani, G., Bradac, M., et al. 2022, ApJ, 935, 110

  58. [58]

    2017, MNRAS, 465, 3291

    Weinberger, R., Springel, V., Hernquist, L., et al. 2017, MNRAS, 465, 3291

  59. [59]

    2024, ApJ, 976, 142

    Xu, Y., Ouchi, M., Yajima, H., et al. 2024, ApJ, 976, 142

  60. [60]

    2024, ApJ, 970, 19 Article number, page 11 of 14 A&A proofs:manuscript no

    Zhang, Y., Ouchi, M., Nakajima, K., et al. 2024, ApJ, 970, 19 Article number, page 11 of 14 A&A proofs:manuscript no. f_esc Appendix A: Verifying the Gaussian outflow selection To evaluatethe performance ofour outflow–selection model, we applied it to a synthetic galaxy system for which the ground truth is known. We used a simplified model in which the ga...