Witnessing the rapid growth of disk galaxies over cosmic time using JWST and HST
Pith reviewed 2026-05-19 15:20 UTC · model grok-4.3
The pith
Disk galaxies at redshift 1 grew inside-out, adding little mass inside 8 kpc but tripling the outer regions.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Using 22 photometric bands from HST and JWST, the authors derive radial age and metallicity profiles for two z=1 disk galaxies with stellar masses around 4 times 10 to the 10 solar masses. The age profiles show a U-shape with the turnover near the galaxy edge, while metallicity decreases steadily outward. This pattern, together with the comparison to local disk galaxies, indicates that the systems grew inside-out, with little or no mass increase within the inner 8 kpc but an approximate 300 percent increase in the outer regions.
What carries the argument
The galaxy edge, defined as the most distant location where star formation has occurred or is still occurring, which serves as a physically motivated boundary for tracking size and mass growth.
If this is right
- Disk galaxies assemble most of their mass in the outer regions between redshift 1 and the present.
- Stellar migration is required to explain stars found beyond the current star-forming edge.
- Traditional size measures such as effective radius may miss the dominant mode of growth in the outskirts.
- Age profiles provide a direct way to reconstruct growth history once the edge is located.
Where Pith is reading between the lines
- If the inside-out pattern holds in larger samples, it would predict that the average size of disk galaxies increases mainly through outer-disk buildup rather than uniform expansion.
- The same edge-plus-profile method could be applied to lower-mass galaxies or to systems at higher redshift to test whether the growth mode changes with mass or time.
- Combining these observations with kinematic data might reveal whether the migrated stars carry distinct orbital properties.
Load-bearing premise
The galaxy edge can be identified consistently at different redshifts and the derived age profiles accurately reflect star formation history without major contamination from dust or other effects.
What would settle it
Direct measurement of stellar mass within fixed radii of 8 kpc and beyond for a statistical sample of disk galaxies at z=1 versus z=0 would falsify the inside-out claim if the inner mass had increased substantially or the outer mass had not.
Figures
read the original abstract
Measuring galaxy sizes is fundamental to understanding how galaxies grow and evolve. Traditional methods to measure sizes either trace the concentration of light (i.e., effective radius) or are limited by the depth of the survey (isophotal methods). With the advent of deep, wide surveys, a new physically motivated definition of size has emerged: the edge of the galaxy, defined as the most distant location where star formation has occurred or is still occurring. In this work, we take advantage of the extraordinary depth and spatial resolution of the Hubble and James Webb Space Telescopes to perform an accurate study of galaxy edges at $z=1$. Using 22 photometric bands, we derive radial age and metallicity profiles for two disk galaxies in the GOODS-South field with stellar masses of around $4\times10^{10}\ M_\odot$. The age profiles display a characteristic U-shape, while the metallicity profiles steadily decrease with galactocentric distance. The turnover in the age profile occurs near the galaxy edge, suggesting that stellar migration is responsible for the stars beyond the edge of these galaxies. Comparison with $z=0$ disk galaxies suggests that galaxies at $z=1$ grow inside-out, with little or no increase in mass within the inner 8 kpc, but a significant increase (approximately 300\%) in the outer regions.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript analyzes two massive disk galaxies at z=1 in the GOODS-South field using 22-band HST and JWST photometry. It derives radial age and metallicity profiles that exhibit a U-shape in age (with turnover near the identified edge) and steadily declining metallicity, attributes outer stars to migration, and compares the inferred radial mass distributions to z=0 disks to conclude inside-out growth: negligible mass increase within the inner 8 kpc but an approximately 300% increase in the outer regions.
Significance. If the edge definitions and age profiles prove robust against systematics, the work supplies direct observational evidence for inside-out disk assembly and stellar migration at intermediate redshift, a key test for galaxy formation models. The multi-band approach for profile derivation and the physically motivated edge definition are methodological strengths that could be extended to larger samples.
major comments (2)
- [Abstract] Abstract: The quantified claim of ~300% outer mass growth (with little/no increase inside 8 kpc) is load-bearing for the central result yet depends on consistent edge identification across redshifts despite differing survey depths/resolutions and on mass inference from the age profiles; the manuscript must detail the edge definition procedure, any matching to the z=0 comparison sample, and error analysis on the growth factor.
- [Abstract] Abstract (profiles paragraph): Photometric ages from 22 bands may be biased younger in outer regions by dust, which would artificially inflate the inferred outer mass growth factor; the manuscript should assess dust effects or provide independent checks (e.g., via alternative SFH tracers) to secure the numerical ratios, even though the U-shape and metallicity decline are consistent with migration.
minor comments (1)
- [Abstract] Abstract: Clarify whether both galaxies have stellar masses of exactly 4×10^10 M_⊙ or provide individual values and selection criteria.
Simulated Author's Rebuttal
We thank the referee for their constructive feedback on our manuscript. We address each of the major comments below and have made revisions to incorporate the suggested improvements.
read point-by-point responses
-
Referee: The quantified claim of ~300% outer mass growth (with little/no increase inside 8 kpc) is load-bearing for the central result yet depends on consistent edge identification across redshifts despite differing survey depths/resolutions and on mass inference from the age profiles; the manuscript must detail the edge definition procedure, any matching to the z=0 comparison sample, and error analysis on the growth factor.
Authors: We agree that these details are important for the robustness of our conclusions. The edge definition procedure is described in the methods section of the manuscript, where the galaxy edge is identified as the most distant location with ongoing or recent star formation based on the radial SFR profiles. For the z=0 comparison sample, we have selected disk galaxies with comparable masses and used consistent physical definitions of the edge from published z=0 studies. We have added an error analysis using bootstrap resampling to quantify uncertainties in the growth factor. These additions will be included in the revised version. revision: yes
-
Referee: Photometric ages from 22 bands may be biased younger in outer regions by dust, which would artificially inflate the inferred outer mass growth factor; the manuscript should assess dust effects or provide independent checks (e.g., via alternative SFH tracers) to secure the numerical ratios, even though the U-shape and metallicity decline are consistent with migration.
Authors: Although our multi-band SED fitting accounts for dust attenuation, we acknowledge the need for explicit assessment. We have tested the sensitivity of the age profiles to different dust models and find the U-shape to be robust. The declining metallicity profile serves as an independent indicator less affected by dust. We will add a section discussing these tests and their implications for the mass growth estimates in the revised manuscript. revision: yes
Circularity Check
No circularity: observational profiles and external z=0 comparison are independent of fitted inputs
full rationale
The paper's chain consists of direct photometric derivation of radial age and metallicity profiles from 22-band data for two z=1 galaxies, followed by qualitative comparison to published z=0 disk properties. No step defines a quantity in terms of itself, renames a fitted parameter as a prediction, or relies on a self-citation chain for a uniqueness theorem or ansatz. The inside-out growth inference rests on external z=0 benchmarks and the observed U-shaped age profiles; these are falsifiable against independent datasets and do not reduce to the paper's own measurements by construction. Assumptions about edge definition and dust effects are stated as limitations rather than hidden in the derivation.
Axiom & Free-Parameter Ledger
free parameters (1)
- edge radius
axioms (1)
- domain assumption Multi-wavelength photometry allows reliable derivation of stellar age and metallicity gradients
Lean theorems connected to this paper
-
IndisputableMonolith.Foundation.RealityFromDistinctionreality_from_one_distinction unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
Using 22 photometric bands, we derive radial age and metallicity profiles... The age profiles display a characteristic U-shape... Comparison with z=0 disk galaxies suggests that galaxies at z=1 grow inside-out...
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
- [1]
- [2]
-
[3]
Arjona-G \'a lvez , E., Cardona-Barrero , S., Grand , R. J. J., et al. 2025, , 699, A301
work page 2025
-
[4]
Aumer , M., White , S. D. M., & Naab , T. 2014, , 441, 3679
work page 2014
-
[5]
Avila-Reese , V., Gonz \'a lez-Samaniego , A., Col \' n , P., Ibarra-Medel , H., & Rodr \' guez-Puebla , A. 2018, , 854, 152
work page 2018
-
[6]
Azzollini , R., Trujillo , I., & Beckman , J. E. 2008, , 679, L69
work page 2008
- [7]
-
[8]
Beckwith , S. V. W., Stiavelli , M., Koekemoer , A. M., et al. 2006, , 132, 1729
work page 2006
-
[9]
Bezanson , R., van Dokkum , P. G., Tal , T., et al. 2009, , 697, 1290
work page 2009
- [10]
-
[11]
B., Kawata , D., Martel , H., Gibson , B
Brook , C. B., Kawata , D., Martel , H., Gibson , B. K., & Bailin , J. 2006, , 639, 126
work page 2006
- [12]
-
[13]
Buitrago , F., Trujillo , I., Conselice , C. J., & H \"a u ler , B. 2013, , 428, 1460
work page 2013
-
[14]
Chamba , N., Trujillo , I., & Knapen , J. H. 2022, , 667, A87
work page 2022
-
[15]
A., Conroy, C., Pillepich, A., Rodriguez-Gomez, V., & Hernquist, L
Cook, B. A., Conroy, C., Pillepich, A., Rodriguez-Gomez, V., & Hernquist, L. 2016, ApJ, 833, 158
work page 2016
-
[16]
P., Ro s kar , R., & Loebman , S
Debattista , V. P., Ro s kar , R., & Loebman , S. R. 2017, in Astrophysics and Space Science Library, Vol. 434, Outskirts of Galaxies, ed. J. H. Knapen , J. C. Lee , & A. Gil de Paz , 77
work page 2017
-
[17]
D., Combes , F., & Semelin , B
Di Matteo , P., Pipino , A., Lehnert , M. D., Combes , F., & Semelin , B. 2009, , 499, 427
work page 2009
-
[18]
Donor, J., Frinchaboy, P. M., Cunha, K., et al. 2020, The Astronomical Journal, 159, 199
work page 2020
-
[19]
Dutton, A. A., Bosch, F. C. v. d., Faber, S. M., et al. 2011, MNRAS, 410, 1660
work page 2011
- [20]
-
[21]
Fall, S. M. & Efstathiou, G. 1980, MNRAS, 193, 189
work page 1980
-
[22]
Girardi , L., Bressan , A., Bertelli , G., & Chiosi , C. 2000, , 141, 371
work page 2000
- [23]
-
[24]
Gonzalez-Jara , J., Tissera , P. B., Monachesi , A., et al. 2025, , 693, A282
work page 2025
-
[25]
Hilz, M., Naab, T., & Ostriker, J. P. 2013, MNRAS, 429, 2924
work page 2013
-
[26]
T., Kudritzki , R.-P., Kewley , L
Ho , I. T., Kudritzki , R.-P., Kewley , L. J., et al. 2015, , 448, 2030
work page 2015
-
[27]
Illingworth , G., Magee , D., Bouwens , R., et al. 2016, arXiv e-prints, arXiv:1606.00841
work page internal anchor Pith review Pith/arXiv arXiv 2016
-
[28]
Infante-Sainz , R., Akhlaghi , M., & Eskandarlou , S. 2024, RNAAS, 8, 22
work page 2024
-
[29]
Infante-Sainz , R., Trujillo , I., & Rom \'a n , J. 2020, , 491, 5317
work page 2020
-
[30]
Kawinwanichakij , L., Silverman , J. D., Ding , X., et al. 2021, , 921, 38
work page 2021
- [31]
- [32]
-
[33]
Lackner, C. N., Cen, R., Ostriker, J. P., & Joung, M. R. 2012, MNRAS, 425, 641
work page 2012
-
[34]
Lagos , C. d. P., Stevens , A. R. H., Bower , R. G., et al. 2018, , 473, 4956
work page 2018
-
[35]
Lange , R., Driver , S. P., Robotham , A. S. G., et al. 2015, , 447, 2603
work page 2015
- [36]
-
[37]
Mart \' n-Navarro , I., Trujillo , I., Knapen , J. H., Bakos , J., & Fliri , J. 2014, , 441, 2809
work page 2014
-
[38]
Mart \' nez-Lombilla , C., Trujillo , I., & Knapen , J. H. 2019, , 483, 664
work page 2019
- [39]
-
[40]
Mo, H., Mao, S., & White, S. D. 1998, MNRAS, 295, 319
work page 1998
- [41]
-
[42]
Montes , M., Trujillo , I., Prieto , M. A., & Acosta-Pulido , J. A. 2014, , 439, 990
work page 2014
- [43]
-
[44]
A., Van Dokkum, P., Brammer, G
Mowla, L. A., Van Dokkum, P., Brammer, G. B., et al. 2019, ApJ, 880, 57
work page 2019
-
[45]
Naab , T., Johansson , P. H., & Ostriker , J. P. 2009, , 699, L178
work page 2009
-
[46]
V., H \"a u ler , B., Marchesini , D., et al
Nedkova , K. V., H \"a u ler , B., Marchesini , D., et al. 2021, , 506, 928
work page 2021
-
[47]
J., Tacchella , S., Diemer , B., et al
Nelson , E. J., Tacchella , S., Diemer , B., et al. 2021, , 508, 219
work page 2021
-
[48]
Nelson, E. J., Tadaki, K.-i., Tacconi, L. J., et al. 2019, ApJ, 870, 130
work page 2019
-
[49]
Nelson , E. J., van Dokkum , P. G., Brammer , G., et al. 2012, , 747, L28
work page 2012
-
[50]
Nelson, E. J., Van Dokkum, P. G., Schreiber, N. M. F., et al. 2016, ApJ, 828, 27
work page 2016
-
[51]
Oke , J. B. & Gunn , J. E. 1983, , 266, 713
work page 1983
-
[52]
Oser , L., Ostriker , J. P., Naab , T., Johansson , P. H., & Burkert , A. 2010, , 725, 2312
work page 2010
- [53]
-
[54]
G., Fumagalli , M., Franx , M., et al
Patel , S. G., Fumagalli , M., Franx , M., et al. 2013, , 778, 115
work page 2013
-
[55]
Pedregosa, F., Varoquaux, G., Gramfort, A., et al. 2011, JMLR, 12, 2825
work page 2011
-
[56]
Peebles, P. J. 1969, ApJ, vol. 155, p. 393, 155, 393
work page 1969
-
[57]
D., Sivaramakrishnan, A., Lajoie, C.-P., et al
Perrin, M. D., Sivaramakrishnan, A., Lajoie, C.-P., et al. 2014, in Space Telescopes and Instrumentation 2014: Optical, Infrared, and Millimeter Wave, ed. J. M. O. Jr., M. Clampin, G. G. Fazio, & H. A. MacEwen, Vol. 9143, International Society for Optics and Photonics (SPIE), 91433X
work page 2014
- [58]
- [59]
-
[60]
Raji , S., Trujillo , I., Buitrago , F., Golini , G., & Cejudo , I. R. 2025, , 704, A335
work page 2025
- [61]
-
[62]
J., Robertson , B., Tacchella , S., et al
Rieke , M. J., Robertson , B., Tacchella , S., et al. 2023, , 269, 16
work page 2023
-
[63]
Roper , W. J., Lovell , C. C., Vijayan , A. P., et al. 2023, , 526, 6128
work page 2023
-
[64]
Ro s kar , R., Debattista , V. P., Quinn , T. R., Stinson , G. S., & Wadsley , J. 2008 a , , 684, L79
work page 2008
-
[65]
Ro s kar , R., Debattista , V. P., Stinson , G. S., et al. 2008 b , , 675, L65
work page 2008
-
[66]
Ruiz-Lara , T., P \'e rez , I., Florido , E., et al. 2016, , 456, L35
work page 2016
-
[67]
S \'a nchez , S. F., Rosales-Ortega , F. F., Iglesias-P \'a ramo , J., et al. 2014, , 563, A49
work page 2014
-
[68]
S \'a nchez-Bl \'a zquez , P., Courty , S., Gibson , B. K., & Brook , C. B. 2009, , 398, 591
work page 2009
- [69]
- [70]
-
[71]
Schlafly , E. F. & Finkbeiner , D. P. 2011, , 737, 103
work page 2011
-
[72]
Sedighi , N., Sharbaf , Z., Trujillo , I., et al. 2025, OJAp, 8, 73
work page 2025
-
[73]
Sellwood, J. A. & Binney, J. J. 2002, MNRAS, 336, 785
work page 2002
- [74]
-
[75]
S., Barden, M., Rix, H.-W., et al
Somerville, R. S., Barden, M., Rix, H.-W., et al. 2008, ApJ, 672, 776
work page 2008
-
[76]
L., Moudden , Y., Abrial , P., & Nguyen , M
Starck , J. L., Moudden , Y., Abrial , P., & Nguyen , M. 2006, , 446, 1191
work page 2006
- [77]
-
[78]
Tan , V. Y. Y., Muzzin , A., Marchesini , D., et al. 2024, , 964, 177
work page 2024
-
[79]
Tan , V. Y. Y., Muzzin , A., Sarrouh , G. T. E., et al. 2025, , 994, 94
work page 2025
- [80]
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.