A Comprehensive Examination of the Optical Morphologies of 719 Isolated Galaxies in the AMIGA Sample

Ancor Damas-Segovia; Javier Blasco; J. Sulentic; Julian Garrido; Lourdes Verdes-Montenegro; Michael Jones; Mirian Fern\'andez-Lorenzo; Pablo Ramirez-Moreta; Ronald J. Buta; Susana Sanchez

arxiv: 1906.11677 · v1 · pith:4XR4WV3Xnew · submitted 2019-06-27 · 🌌 astro-ph.GA

A Comprehensive Examination of the Optical Morphologies of 719 Isolated Galaxies in the AMIGA Sample

Ronald J. Buta , Lourdes Verdes-Montenegro , Ancor Damas-Segovia , Michael Jones , Javier Blasco , Mirian Fern\'andez-Lorenzo , Susana Sanchez , Julian Garrido

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Pablo Ramirez-Moreta J. Sulentic

This is my paper

Pith reviewed 2026-05-25 14:36 UTC · model grok-4.3

classification 🌌 astro-ph.GA

keywords isolated galaxiesgalaxy morphologyHubble sequencebar fractionspiral armsAMIGA sampleCVRHS classificationgrand design spirals

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The pith

Isolated galaxies span the full revised Hubble sequence, with Sb-Sc spirals most common and over half showing grand-design arms.

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

The paper re-examines optical images of 719 galaxies from the AMIGA sample of the most isolated systems using the Comprehensive de Vaucouleurs revised Hubble-Sandage classification system on Sloan Digital Sky Survey data. It establishes that these galaxies occupy every position along the revised Hubble sequence, though intermediate to late-type spirals (Sb-Sc) appear more frequently than other types. More than 50 percent of the spirals are grand design, the overall bar fraction reaches about 50 percent with only 16 percent strongly barred, and the most common categories are non-barred SA galaxies with pure spiral inner structure and no outer rings. A sympathetic reader would care because the results test whether extreme isolation restricts the morphological outcomes that galaxies can reach through internal processes alone.

Core claim

Isolated galaxies from the AMIGA sample are found across the complete revised Hubble sequence, with intermediate to late-type (Sb-Sc) spirals being relatively more common. The visual bar fraction is approximately 50 percent, though only 16 percent qualify as strongly barred (SB). More than 50 percent of the 514 spirals receive Elmegreen arm classifications of grand design (AC 8, 9, or 12). The dominant family is SA, the dominant inner variety is (s), and the dominant outer variety shows no ring, pseudoring, or lens. Kolmogorov-Smirnov tests find no significant biases linking rings, bars, or arm classes to local environment or far-infrared excess, while stellar mass shows a connection to some

What carries the argument

The Comprehensive de Vaucouleurs revised Hubble-Sandage (CVRHS) morphological classification system, used to assign family, variety, and arm class to SDSS images of the AMIGA isolated galaxies.

If this is right

The AMIGA isolation criteria do not exclude galaxies of any Hubble type or bar strength.
Grand-design spiral structure arises and persists in more than half the sample without requiring external tidal triggers.
The dominant non-barred, pure-spiral morphology indicates that internal secular evolution can produce the observed variety even in low-density environments.
Absence of strong correlations between morphological features and far-infrared excess or local density implies that these features are not primarily driven by environment within the sample limits.

Where Pith is reading between the lines

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

Simulations of galaxy evolution must reproduce grand-design arms and moderate bar fractions through purely internal mechanisms if they aim to match isolated systems.
The higher frequency of Sb-Sc types suggests that environmental processes may play a larger role in producing early-type morphologies than in maintaining late-type ones.
These classifications supply a reference distribution that can be compared directly against mock observations drawn from cosmological simulations filtered for isolation.

Load-bearing premise

The authors' visual morphological classifications are objective enough that knowledge of each galaxy's isolation status does not introduce systematic bias into the reported type, bar, or arm distributions.

What would settle it

Independent reclassification of the same 719 SDSS images by multiple astronomers who do not know the isolation criteria, yielding bar fractions or Hubble-type distributions that differ at high statistical significance from the reported values.

Figures

Figures reproduced from arXiv: 1906.11677 by Ancor Damas-Segovia, Javier Blasco, J. Sulentic, Julian Garrido, Lourdes Verdes-Montenegro, Michael Jones, Mirian Fern\'andez-Lorenzo, Pablo Ramirez-Moreta, Ronald J. Buta, Susana Sanchez.

**Figure 1.** Figure 1: Distribution of radial velocities for the full CIG sample and our subset of 719 galaxies. This shows that both samples cover about the same redshift range (0.005 to 0.080), meaning that our capacity to separate details in the morphology of the galaxies will be roughly equivalent [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗

**Figure 3.** Figure 3: Comparison of Phase 1 and 2 classifications ( [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗

**Figure 4.** Figure 4 [PITH_FULL_IMAGE:figures/full_fig_p006_4.png] view at source ↗

**Figure 6.** Figure 6: Histograms of morphological classifications from Table 6 for the full sample (light solid histogram) and a subsample restricted to inclinations i less than or equal to 60o (heavy solid histogram). The numbers of objects N in each sample are indicated. Over the full type range of S0/a to Sm, a more significant difference emerges: f2bar = 50%±3% for AMIGA galaxies versus f1bar = 66%±2% for S4G galaxies. M… view at source ↗

**Figure 8.** Figure 8: Graphs of the inner ring/pseudoring/lens fraction fIV versus the mean phase 1 and 2 stage along the CVRHS Hubble sequence: (a) for the full sample unrestricted by inclination, and (b) for the restricted subset of galaxies having i less than or equal to 60o . The number of objects n at each stage is indicated. with outer pseudoring-lenses, R′L, these features are found in 56%±4% of the restricted AMIGA subs… view at source ↗

**Figure 9.** Figure 9: shows six of the grand design cases. One case, CIG 86, has a strong bar that could drive its grand-design pattern (Kormendy and Norman 1979). The other five, however, are mostly nonbarred, and in fact 50% of the 276 AC 8, 9, and 12 galaxies in the full sample are nonbarred. While all six of the galaxies in [PITH_FULL_IMAGE:figures/full_fig_p011_9.png] view at source ↗

**Figure 10.** Figure 10: Graphs of the mean log stellar mass of subsets of our AMIGA sample versus morphological structure. Filled circles are for the full (unrestricted by inclination) samples, while open circles are for the subsets restricted to inclination i≤60o . The total numbers of objects in each subset are indicated in each frame. The error bars are 1σ standard deviations about the means. The horizontal dashed lines ind… view at source ↗

**Figure 11.** Figure 11: Comparison between the relative frequency of stages, families, inner varieties, and outer varieties in [PITH_FULL_IMAGE:figures/full_fig_p013_11.png] view at source ↗

**Figure 13.** Figure 13: Relative frequencies of stages, families, and inner and outer varieties versus local density parameter ηk [PITH_FULL_IMAGE:figures/full_fig_p014_13.png] view at source ↗

**Figure 14.** Figure 14: Relative frequencies of stages, families, and inner and outer varieties versus tidal strength parameter QKar,p. corresponding to LFIR versus LB. This fit gives the reference for isolated galaxies, although there is some dispersion within the AMIGA sample itself which is likely due to different degrees of isolation and different formation histories. It is therefore worth checking if there is any correlat… view at source ↗

read the original abstract

Using images from Sloan Digital Sky Survey Data Release 8, we have re-examined the morphology of 719 galaxies from the Analysis of the interstellar Medium in Isolated GAlaxies (AMIGA) project, a sample consisting of the most isolated galaxies that have yet been identified. The goal is to further improve the classifications of these galaxies by examining them in the context of the Comprehensive de Vaucouleurs revised Hubble-Sandage (CVRHS) system, which includes recognition of features that go beyond the original de Vaucouleurs point of view. Our results confirm previous findings that isolated galaxies are found across the complete revised Hubble sequence, with intermediate to late-type (Sb-Sc) spirals being relatively more common. Elmegreen Arm Classifications are also presented, and show that more than 50% of the 514 spirals in the sample for which an arm class could be judged are grand design (AC 8,9,12). The visual bar fraction for the sample is ~50%, but only 16% are classified as strongly-barred (SB). The dominant family classification is SA (nonbarred), the dominant inner variety classification is (s) (pure spiral), and the dominant outer variety classification is no outer ring, pseudoring, or lens. The Kolmogorov-Smirnov test is used to check for potential biases in the morphological interpretations, and for any possible relation between rings, bars, and arm classes with local environment and far-infrared excess. The connection between morphology and stellar mass is also examined for a subset of the sample.

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.

Desk Editor's Note private letter to a colleague

New CVRHS classifications for the AMIGA sample give useful reference numbers on bars and arms but rest on single-team visual work without blinding or agreement metrics.

read the letter

This paper delivers updated visual morphologies for 719 AMIGA isolated galaxies from SDSS DR8 using the CVRHS system. The headline numbers are that isolated galaxies span the full revised Hubble sequence with Sb-Sc types more common, the visual bar fraction sits near 50% but only 16% are SB, and over half of the 514 spirals are grand design. They also tabulate family, variety, and Elmegreen arm classes and run KS tests against local environment and FIR excess plus a stellar-mass check on a subset. The work is straightforward cataloging on public imaging with a documented scheme, so the statistics are reproducible in principle and the sample is cleanly defined by prior isolation criteria. That makes the numbers a usable reference for studies of morphology in low-density environments. The soft spot is exactly the one the stress-test flags. All the reported fractions come from the authors' own visual assignments on galaxies they already knew were the most isolated. No inter-rater kappa, no multiple independent classifiers, and no blinding to isolation status are described, so any systematic tendency to call or miss weak bars or continuous arms would go undetected. The KS tests only look at correlations after the classifications are fixed. This is a minor but real limitation for a paper whose main product is those classifications. The paper is for people who need the specific AMIGA statistics or want a uniform set of CVRHS types on an isolated sample. It is worth sending to referees because the data are public, the methods are standard, and the results are presented without over-claiming. Referees can decide whether the lack of classification reliability metrics is a problem worth addressing in revision.

Referee Report

1 major / 2 minor

Summary. The paper re-examines the optical morphologies of 719 AMIGA isolated galaxies using SDSS DR8 imaging, classifying them in the CVRHS system. It reports that isolated galaxies span the full revised Hubble sequence (with Sb-Sc spirals relatively common), a visual bar fraction of ~50% (only 16% strongly barred SB), and that >50% of the 514 spirals with assignable arm class are grand design (AC 8,9,12). KS tests examine possible biases or relations of rings/bars/arm classes with local environment and FIR excess; a subset analysis links morphology to stellar mass.

Significance. If the classifications hold, the work supplies a large, well-defined reference sample of isolated-galaxy morphologies that can benchmark environmental effects. Strengths include the use of public SDSS imaging, application of the extended CVRHS system, and standard KS tests on external data; no free parameters or circular derivations are involved.

major comments (1)

[Abstract and classification procedure] The headline statistics (Sb-Sc dominance, ~50% bar fraction with 16% SB, >50% grand-design arms) rest entirely on single-team visual CVRHS assignments. The abstract states that KS tests check for biases in the morphological interpretations, yet these tests are applied only after classification and do not quantify inter-rater agreement, blinding, or reproducibility of the classifications themselves.

minor comments (2)

[Methods] Clarify in the methods whether any galaxies were excluded post-classification and whether the isolation criteria were known to the classifier(s) during the visual inspection.
[Results] The abstract reports 514 spirals with assignable arm class; confirm this number and the exact selection criterion in the main text or a table.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the careful reading of the manuscript, the positive assessment of its significance, and the recommendation for minor revision. We address the single major comment below.

read point-by-point responses

Referee: [Abstract and classification procedure] The headline statistics (Sb-Sc dominance, ~50% bar fraction with 16% SB, >50% grand-design arms) rest entirely on single-team visual CVRHS assignments. The abstract states that KS tests check for biases in the morphological interpretations, yet these tests are applied only after classification and do not quantify inter-rater agreement, blinding, or reproducibility of the classifications themselves.

Authors: We acknowledge that the classifications are the result of visual inspection by our team using the CVRHS system on the SDSS DR8 images; no separate inter-rater reliability study, blinding protocol, or quantitative reproducibility metric was performed for this re-examination. The KS tests are applied after classification to search for possible relations (or lack thereof) between the assigned morphological features and local environment or FIR excess, thereby testing for sample biases in those properties rather than validating the classifications themselves. The abstract phrasing 'check for potential biases in the morphological interpretations' is imprecise in this regard and could be read as referring to the classification process. We will revise the abstract and the relevant methods/results text to clarify the scope of the KS tests and to note explicitly that the classifications are single-team visual assignments following the established CVRHS criteria. This is a minor clarification that leaves the scientific results unchanged. revision: partial

Circularity Check

0 steps flagged

No circularity: purely observational classifications and statistics on external imaging data

full rationale

The paper performs visual morphological classifications of 719 AMIGA galaxies on SDSS DR8 images using the CVRHS system, reports bar/arm/ring fractions, and applies Kolmogorov-Smirnov tests to check for environmental correlations. No equations, fitted parameters, derivations, or self-citation chains reduce any claim to the inputs by construction. The classifications and statistics are direct outputs from external data; the KS tests address post-classification relations rather than validating the classifications themselves. This matches the default expectation of a non-circular observational study.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The analysis rests on the validity of the CVRHS classification scheme and the prior definition of the AMIGA isolation criteria; no new free parameters or invented entities are introduced.

axioms (2)

domain assumption The CVRHS morphological classification system provides a reliable and consistent description of galaxy optical structure.
Invoked throughout the re-classification process described in the abstract.
domain assumption The AMIGA sample selection identifies galaxies with minimal external environmental influence.
Central to interpreting the morphologies as representative of isolated evolution.

pith-pipeline@v0.9.0 · 5862 in / 1241 out tokens · 38066 ms · 2026-05-25T14:36:03.450699+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

2 extracted references · 2 canonical work pages · 1 internal anchor

[1]

Abbott T., et al., 2019, arXiv 1801.03181 Aihara H., et al., 2011, ApJS, 193, 29 Aihara H., et al., 2018, PASJ, 70, 84 Andrae R., Jahnke K., Melchoir P.,

work page internal anchor Pith review Pith/arXiv arXiv 2019
[2]

B., Seo M., Ha D

411, 385 Ann H. B., Seo M., Ha D. K., 2015, ApJS, 217, 27 Argudo M., Verley S., Bergond G., Sulentic J., Espada D., Santander-Vela J. D., Ruiz J. E., Sabater J., Verdes- Montonegro L., Mart ´ ınez-Badenes V., 2011, in Highlights o f Spanish Physics, Vol. 6, p. 374 Argudo-Fern´ andez M., Verley S., Bergond G.,Sulentic J.,Sabater J., Fern´ andez-Lorenzo M.,...

work page 2015

[1] [1]

Abbott T., et al., 2019, arXiv 1801.03181 Aihara H., et al., 2011, ApJS, 193, 29 Aihara H., et al., 2018, PASJ, 70, 84 Andrae R., Jahnke K., Melchoir P.,

work page internal anchor Pith review Pith/arXiv arXiv 2019

[2] [2]

B., Seo M., Ha D

411, 385 Ann H. B., Seo M., Ha D. K., 2015, ApJS, 217, 27 Argudo M., Verley S., Bergond G., Sulentic J., Espada D., Santander-Vela J. D., Ruiz J. E., Sabater J., Verdes- Montonegro L., Mart ´ ınez-Badenes V., 2011, in Highlights o f Spanish Physics, Vol. 6, p. 374 Argudo-Fern´ andez M., Verley S., Bergond G.,Sulentic J.,Sabater J., Fern´ andez-Lorenzo M.,...

work page 2015