The Hubble flow around the CenA / M83 galaxy complex

A Dolphin; D Makarov; E J Shaya; Igor D Karachentsev; L Makarova; L Rizzi; M Sharina; O G Kashibadze; R Brent Tully; S Sakai

REVIEW

The Hubble flow around the CenA / M83 galaxy complex

Igor D Karachentsev, R Brent Tully, A Dolphin, M Sharina, L Makarova, D Makarov, O G Kashibadze, V Karachentseva

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S Sakai, E J Shaya, L Rizzi

Astrophysics · Submitted 3 Mar 2006 · 3 references

Pith's verdict: A careful, useful distance catalog and an environmentally interesting M/L contrast, but the zero-velocity 'confirmation' rests on a one-sided sample that needs a real selection analysis.

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arXiv IDastro-ph/0603091 (version 2)

Pith ID42QQ4ZRZ, Pith's permanent record of this paper and its review

CitationA Dolphin, D Makarov, E J Shaya, Igor D Karachentsev, L Makarova, L Rizzi, M Sharina, O G Kashibadze, R Brent Tully, S Sakai, V Karachentseva. "The Hubble flow around the CenA / M83 galaxy complex." arXiv:astro-ph/0603091 (2006). https://pith.science/paper/42QQ4ZRZ

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Editor's note

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Candidly: this paper is worth referee time. It is the paper that puts the Cen A/M83 complex on the 3D map, with 24 new TRGB distances, a revised M83 distance, and a dynamical analysis that gives the elliptical-dominated Cen A group a mass-to-light ratio around 125 in the B band, several times higher than the spiral-dominated M83 group (M/L_B ~34). The photometry is careful: DOLPHOT reductions, completeness tests, bootstrap errors on the TRGB, and the distance catalog is a durable resource.

The strongest part is that the two main mass estimates for Cen A are genuinely independent. The virial/orbital mass from internal group motions (6.4-8.1e12) agrees with the zero-velocity surface mass (6.0 +/- 1.4e12), and neither is obviously tuned. The M/L contrast between Cen A and M83 is exactly the kind of environmental signal that the field needs to test with homogeneous data, and this paper provides the cleanest nearby example.

The soft spot is the zero-velocity fit. The paper itself reports that all 18 galaxies used to fit R0 lie behind Cen A. With no near-side tracers, the zero-velocity crossing is fixed by extrapolation, and the bootstrap uncertainty reports scatter within that one-sided sample, not the selection effect that removed the other side. The mass scales as R0^3, so a 10% bias in R0 changes M_T by roughly 30%, comparable to the quoted error. Known near-side galaxies in the same volume--NGC 5102, Circinus, ESO 321-014, ESO 274-01--are excluded by the same |Dg - Dc| > Rp cut, so one-sidedness cannot be dismissed as a physical void without checking the full 3D sample. The authors need to quantify this, e.g., with mock samples or a symmetric selection, before the R0 mass can be called confirmation. That said, this weakness does not sink the paper, because the virial and orbital masses stand on their own.

Two smaller items: the revised M83 distance (5.16 Mpc from TRGB vs 4.47 from cepheids) is a real conflict that deserves its own scrutiny; and the claim that the residual peculiar velocity drops to 2 km/s after subtracting errors is suspiciously cold and should be presented with a caveat about correlated errors. Neither changes the main conclusion.

Recommendation: send it to peer review. It needs a moderate revision on the selection issue, but the data and the environmental M/L contrast are serious and citable. I would bring it to the reading group and would cite the distance catalog if I worked in this volume.

Referee report

Significance

If the results hold, the paper provides a valuable large, homogeneous TRGB distance sample in a nearby complex and makes a strong case that elliptical-dominated groups have markedly higher M/L than spiral-dominated ones. The photometry is careful, with bootstrap TRGB uncertainties, completeness tests, and attention to calibration and extinction; the compilation of 87 galaxies is a useful resource. The internal (virial/orbital) and external (zero-velocity surface) mass estimates are methodologically independent in construction, and the paper reports agreement between them. However, the claimed confirmation from the zero-velocity surface rests on a one-sided sample, and the single-attractor assumption needs scrutiny; these issues are load-bearing for the R0-based mass and for the paper's central confirmation claim.

Major objections (2)

[Section 4, Fig. 9 and Eq. (2)] The zero-velocity radius R0 is fitted using only the 18 galaxies with |Dg - Dc| > Rp and 1 < R < 4 Mpc, and the paper states that all 18 reside behind the Cen A group. This one-sided sample cannot constrain the near-side infall branch, where peculiar velocities are positive; the crossing at V = 0 is an extrapolation from the far side alone. The same |Dg - Dc| > Rp cut excludes known near-side galaxies with distances in the same range, including NGC 5102, ESO 321-014, Circinus, and ESO 274-01 (all listed in Table 2), so the one-sidedness is at least partly a selection artifact rather than a demonstrated physical void. Because M_T ∝ R0^3 (Eq. 2), a systematic bias of ~10% in R0 changes M_T by ~30%, comparable to the quoted 1.4×10^12 M_sun error. The paper should either fit R0 using all galaxies with 1 < R < 4 Mpc (showing the near-side points), or model the selection function and quantify the resulting systematic uncertainty on R0. Without this, the claimed confirmation of the virial mass is not secure.
[Sections 4 and 5] The R0 calculation assumes a single spherical attractor centered on Cen A, but M83 is at a spatial separation of Rcc = 1.43 ± 0.11 Mpc, essentially equal to the fitted R0 = 1.40 Mpc. The velocity field near the turnover radius must therefore be affected by both masses, and the single-attractor approximation could bias the fitted R0. The paper mentions the relative motion of the two groups but does not model their combined gravitational effect on the Hubble flow. The authors should either fit a two-attractor model or quantitatively justify why the M83 contribution is negligible at R ≈ 1.4 Mpc; this is needed to support the R0-based mass estimate.

Minor objections (5)

[Section 4] The sentence "Surprisingly, all of them reside behind the Cen A group" is presented without explanation; please clarify whether this is a selection effect of the |Dg - Dc| > Rp cut combined with the known near-side geometry, or a physical absence of near-side tracers, and discuss the implications for the fit.
[Section 4 and Fig. 9] The bootstrap error on R0 is not described in sufficient detail; please specify how the resampling was performed, whether it includes both distance and velocity errors, and how the minimum-scatter regression was implemented.
[Section 4] The claim that after quadratic subtraction of observational errors the typical peculiar velocity drops from 32 to 2 km/s is striking; please provide the error budget and the exact subtraction formula, since such a small residual is central to the 'cold flow' conclusion.
[Section 5] The virial and orbital mass estimates rely on group membership defined by tidal indices computed with an assumed M/L_B = 10; the sensitivity of the derived masses and of the final M/L_B = 125 to this assumption should be quantified or at least discussed.
[Section 1 and author list] There are typographical errors in the paper (e.g., 'Russian Academy of Science s' in the affiliations and 'galax ies galaxies: distances' in the subject headings); these should be corrected in revision.

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The paper

The paper claims

This paper establishes that the nearby elliptical-dominated Cen A group has a mass-to-light ratio of about 125 solar units, roughly three times that of the spiral-dominated M83 group, and confirms it with an independent zero-velocity…

The reading

This paper maps the three-dimensional structure of the nearby Cen A / M83 galaxy complex using new Hubble Space Telescope distances to 24 galaxies, measured from the tip of the red giant branch. It establishes that the elliptical-dominated Cen A group is extremely massive for its luminosity: a virial/orbital mass of (6.4–8.1)×$10^{12}$ solar masses gives a mass-to-light ratio of about 125 solar units, roughly three times that of the spiral-dominated M83 group (34) and of other spiral groups. An independent mass estimate from the zero-velocity surface, the radius where cosmic expansion just cancels the group's gravitational pull, yields R0 = 1.40 ± 0.11 Mpc and a total mass of (6.0 ± 1.4)×$10^{12}$ solar masses, in agreement with the internal dynamics. The result matters because it gives direct evidence that environments that have evolved into ellipticals carry dark matter halos with less light per unit mass than spiral environments.

What carries the argument

Two mechanisms carry the argument. The first is the tip-of-the-red-giant-branch (TRGB) distance indicator: in HST ACS images, the sharp truncation of the red giant branch luminosity function at MI ≈ −4.05 mag gives distances with ~0.12 mag external uncertainty, and the paper applies a Sobel edge-detection filter to locate the tip in each galaxy's color–magnitude diagram. The second is the zero-velocity surface (turn-over radius) method: for a point mass embedded in an expanding universe, the radius R0 where the Hubble flow velocity exactly cancels the gravitational infall is related to the total mass by the Lynden-Bell–Sandage formula, modified for a flat ΛCDM cosmology with Ωm = 0.27. Fitting the observed peculiar velocities of surrounding galaxies against radial distance from Cen A yields R0 and hence the total mass, which is then compared with virial/orbital masses from the internal velocity dispersion and harmonic radius.

Extended reading notes

Core claim

The paper reports that the Cen A group, centered on the giant elliptical NGC 5128, has a mean distance of 3.76 ± 0.05 Mpc, a line-of-sight velocity dispersion of 136 km/s, and a mean harmonic radius of 192 kpc, from which the virial and orbital masses are (8.1 and 6.4)×$10^{12}$ solar masses respectively. The M83 group, dominated by the spiral NGC 5236 and placed at 4.79 ± 0.10 Mpc, has a velocity dispersion of 61 km/s, a harmonic radius of 89 kpc, and a mass near 0.9×$10^{12}$ solar masses. Combined with B-band luminosities of 6.0×$10^{10}$ and 2.5×$10^{10}$ solar luminosities, these imply mass-to-light ratios of 125 and 34 solar units respectively. Using 18 galaxies with spatial distances 1 < R < 4 Mpc from Cen A, the authors fit the Hubble flow distortion and find the zero-velocity surface at R0 = 1.40 ± 0.11 Mpc, which yields a total mass (6.0 ± 1.4)×$10^{12}$ solar masses in a ΛCDM model with Ωm = 0.27. The agreement between the internal and zero-velocity mass estimates is presented as confirmation that the Cen A group is a high-mass, high-M/L system, and the small peculiar velocities (< 25 km/s) of the group centroids indicate a very cold local Hubble flow.

Load-bearing premise

The 18 galaxies whose motions define the zero-velocity radius all sit behind Cen A, so the fitted turn-over radius—and the mass derived from it—assumes this one-sided sample is not systematically biased.

Editorial extensions

If this is right

The zero-velocity surface method, previously applied to the Local Group and M81, gives a total mass for the Cen A group consistent with virial/orbital estimates, supporting its use as a mass probe on ~1 Mpc scales.
The high M/L_B ≈ 125 for an elliptical-dominated group versus ~30–35 for spiral-dominated groups means that cosmological mass-to-light averages must be weighted by environment.
The very small peculiar velocities (< 25 km/s) of the group centroids and external field galaxies indicate a cold Hubble flow, consistent with dark energy dominating at distances beyond ~1 Mpc.
The new TRGB distances place several previously uncertain dwarf galaxies (e.g., ESO 383-87, the M83 halo) into the correct group, refining the census of the complex to 87 galaxies within ~4 Mpc.
The agreement between the mass estimates from internal dynamics and from the turn-over radius provides a consistency check that the Cen A group is bound and roughly virialized.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

If the high M/L_B of the Cen A group holds up, it suggests that the dark matter fraction in galaxy groups is not universal, and that ellipticals formed through mergers may retain more extended dark halos; one could test this by measuring the mass-to-light ratio of other nearby elliptical-dominated groups with the same zero-velocity method.
The one-sided distribution of the 18 galaxies behind Cen A raises the possibility that the fitted R0 is biased; a dedicated survey for dwarf galaxies in front of the group (between 1 and 3.7 Mpc on the near side) would test whether the zero-velocity radius is symmetric.
The method could be extended to the M83 group: using its own background and foreground galaxies to fit its turn-over radius would give an independent mass estimate for a spiral-dominated group and a direct M/L comparison with Cen A.
The very cold flow (residual peculiar velocities ~2–20 km/s) around Cen A might be used to constrain the local density parameter Ωm on megaparsec scales, since a higher matter density would produce warmer flows.

Original abstract

We present HST/ACS images and color-magnitude diagrams for 24 nearby galaxies in and near the constellation of Centaurus with radial velocities V_LG < 550 km/s. Distances are determined based on the luminosities of stars at the tip of the red giant branch that range from 3.0 Mpc to 6.5 Mpc. The galaxies are concentrated in two spatially separated groups around Cen A (NGC 5128) and M 83 (NGC 5236). The Cen A group itself has a mean distance of 3.76 +/-0.05 Mpc, a velocity dispersion of 136 km/s, a mean harmonic radius of 192 kpc, and an estimated orbital/virial mass of (6.4 - 8.1) x 10^12 M_sun. This elliptical dominated group is found to have a relatively high mass-to-light ratio: M/L_B = 125 M_sun/L_sun. For the M 83 group we derived a mean distance of 4.79 +/-0.10 Mpc, a velocity dispersion of 61 km/s, a mean harmonic radius of 89 kpc, and estimated orbital/virial mass of (0.8 - 0.9) x 10^12 M_sun. This spiral dominated group is found to have a relatively low M/L_B = 34 M_sun/L_sun. The radius of the zero-velocity surface around Cen A lies at R_0 = 1.40 +/-0.11 Mpc, implying a total mass within R_0 of M_T = (6.0 +/-1.4) x 10^12 M_sun. This value is in good agreement with the Cen A virial/orbital mass estimates and provides confirmation of the relatively high M/L_B of this elliptical-dominated group. The centroids of both the groups, as well as surrounding field galaxies, have very small peculiar velocities, < 25 km/s, with respect to the local Hubble flow with H_0 = 68 km/s/Mpc.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13.0 via TypeSafe API, question bank abstract-p1-20260923, 2026-09-23: 1 request, 8,099 input tokens.

What the abstract itself states, as probabilities: claims first 0.03 · states limitation 0.12 · human participants 0.01 · controlled comparison 0.10 · randomized assignment 0.01 · states quantitative result 0.99 · compares with prior results 0.64 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v2. Results and the main claim are underlined; show every role.

We present HST/ACS images and color-magnitude diagrams for 24 nearby galaxies in and near the constellation of Centaurus with radial velocities V_LG < 550 km/s. Distances are determined based on the luminosities of stars at the tip of the red giant branch that range from 3.0 Mpc to 6.5 Mpc. The galaxies are concentrated in two spatially separated groups around Cen A (NGC 5128) and M 83 (NGC 5236). The Cen A group itself has a mean distance of 3.76 +/-0.05 Mpc, a velocity dispersion of 136 km/s, a mean harmonic radius of 192 kpc, and an estimated orbital/virial mass of (6.4 - 8.1) x 10^12 M_sun. This elliptical dominated group is found to have a relatively high mass-to-light ratio: M/L_B = 125 M_sun/L_sun. For the M 83 group we derived a mean distance of 4.79 +/-0.10 Mpc, a velocity dispersion of 61 km/s, a mean harmonic radius of 89 kpc, and estimated orbital/virial mass of (0.8 - 0.9) x 10^12 M_sun. This spiral dominated group is found to have a relatively low M/L_B = 34 M_sun/L_sun. The radius of the zero-velocity surface around Cen A lies at R_0 = 1.40 +/-0.11 Mpc, implying a total mass within R_0 of M_T = (6.0 +/-1.4) x 10^12 M_sun. This value is in good agreement with the Cen A virial/orbital mass estimates and provides confirmation of the relatively high M/L_B of this elliptical-dominated group. The centroids of both the groups, as well as surrounding field galaxies, have very small peculiar velocities, < 25 km/s, with respect to the local Hubble flow with H_0 = 68 km/s/Mpc.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#	sentence	role	the authors' own work	states the main conclusion	strength
s0	We present HST/ACS images and color-magnitude diagrams for 24 nearby galaxies in and near the constellation of Centaurus with radial velocities V_LG < 550 km/s.	contribution 0.71	0.96	0.03	asserted 0.99
s1	Distances are determined based on the luminosities of stars at the tip of the red giant branch that range from 3.0 Mpc to 6.5 Mpc.	method 0.92	0.84	0.03	asserted 1.00
s2	The galaxies are concentrated in two spatially separated groups around Cen A (NGC 5128) and M 83 (NGC 5236).	result 0.99	0.86	0.07	asserted 1.00
s3	The Cen A group itself has a mean distance of 3.76 +/-0.05 Mpc, a velocity dispersion of 136 km/s, a mean harmonic radius of 192 kpc, and an estimated orbital/virial mass of (6.4 - 8.1) x 10^12 M_sun.	result 1.00	0.94	0.12	asserted 1.00
s4	This elliptical dominated group is found to have a relatively high mass-to-light ratio: M/L_B = 125 M_sun/L_sun.	result 0.97	0.95	0.10	asserted 1.00
s5	For the M 83 group we derived a mean distance of 4.79 +/-0.10 Mpc, a velocity dispersion of 61 km/s, a mean harmonic radius of 89 kpc, and estimated orbital/virial mass of (0.8 - 0.9) x 10^12 M_sun.	result 1.00	0.96	0.07	asserted 1.00
s6	This spiral dominated group is found to have a relatively low M/L_B = 34 M_sun/L_sun.	result 0.99	0.96	0.07	asserted 1.00
s7	The radius of the zero-velocity surface around Cen A lies at R_0 = 1.40 +/-0.11 Mpc, implying a total mass within R_0 of M_T = (6.0 +/-1.4) x 10^12 M_sun.	result 0.99	0.91	0.21	asserted 0.96
s8	This value is in good agreement with the Cen A virial/orbital mass estimates and provides confirmation of the relatively high M/L_B of this elliptical-dominated group.	interpretation 0.99	0.85	0.21	asserted 0.96
s9	The centroids of both the groups, as well as surrounding field galaxies, have very small peculiar velocities, < 25 km/s, with respect to the local Hubble flow with H_0 = 68 km/s/Mpc.	result 1.00	0.87	0.23	asserted 1.00

What kind of paper the classifier reports this is: empirical study 1.00 · evidence from observation or experiment 0.98.

What was examined, and what was not

sources read

arXiv listing abstract v2

not examined

full text
figures and tables
references and citing sentences
relations to other papers

levels run

P abstract

not run

S sections
T body sentences
C citations
R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures

**Figure 1.** — Photometric completeness as a function of magnitude for th

**Figure 2.** — Mean photometric error as a function of magnitude for KKs 5

**Figure 3.** — ACS “V ” images of 24 nearby galaxies; 23 from two 600 second exposures in F606W and one (ESO 383-87) from two 450 second exposures in F814W

**Figure 4.** — ACS color-magnitude diagrams for 23 nearby galaxies in the Ce

**Figure 5.** — ACS color-magnitude diagram for M83. The color measuremen

**Figure 6.** — The distribution of galaxies in and around the Cen A/M 83 comple

**Figure 7.** — The 3D- view of the Cen A/M 83 complex. Galaxies of young and o

**Figure 8.** — The Hubble diagram for galaxies in the Cen A/M 83 complex and its

**Figure 9.** — Distribution of the radial velocity difference and the spatial d

Figures reproduced from arXiv:astro-ph/0603091 by the authors.

References

Works cited (3)

[1]

Bahcall N.A., Cen R., Dav´ e R. et al. 2000, ApJ 541, 1 Banks G.D., Disney M.J., Knezek P.M., et al., 1999, ApJ 524, 612 Bellazzini M., Ferraro F.R., Pancino E., 2001, ApJ 556, 635 Chernin A.D., 2001, Physics-Uspekhi 44, 1099 Cˆ ot´ e S., Freeman K.C., Carignan C., Quinn P.J., 1997, AJ 114, 1313 Cˆ ot´ e S., Mateo M., Sargent W.L.W., Olszewski E.W., 2000,...

View on Pith Pith review arXiv 2000
[2]

Galaxies in and around the Cen A/M 83 complex. Galaxy name RA(J2000.0)Dec T Θ VLG ± σV D ± σD Meth Ref Note (1) (2) (3) (4) (5) (6) (7) (8) (9) E059–01 073119.3 −681110 9 −1.5 245 5 4.57 0.36 rgb K06a N2915 092611.5 −763735 10 −1.3 184 5 3.78 0.43 rgb CNG SexB,DDO70 100000.1+051956 10 −0.7 111 1 1.36 0.07 rgb CNG N3109 100307.2 −260936 9 −0.1 110 1 1.33 0...

View on Pith 2006
[3]

27 Typical lensing mass 500 2.4 – 5.2 Hoekstra et al. 2005 for given L

View on Pith 2005

How the literature uses it

4 arXiv papers cite this in 4 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

Papers citing it · 2 sentences without a confident label

Uses its data or values 1 paper

These are among the closest galaxy groups to us; the Cen A group is at a distance of 3.76 Mpc, and the M83 group is at a distance of 4.79 Mpc [ref] .

MeerKAT and the Smallest Galaxies · Proposed survey · 0.99

Cites it as background 1 paper

This group was studied by Refs. [ref] .

Improved Lemaitre-Tolman model and the mass and turn-around radius in group of galaxies · The CenA/M83 group · 0.97

Discussion

Disagree with the review, or know something it missed? Leave a comment, highlight any passage above to comment on it, or challenge this review formally.

[1] [1]

Bahcall N.A., Cen R., Dav´ e R. et al. 2000, ApJ 541, 1 Banks G.D., Disney M.J., Knezek P.M., et al., 1999, ApJ 524, 612 Bellazzini M., Ferraro F.R., Pancino E., 2001, ApJ 556, 635 Chernin A.D., 2001, Physics-Uspekhi 44, 1099 Cˆ ot´ e S., Freeman K.C., Carignan C., Quinn P.J., 1997, AJ 114, 1313 Cˆ ot´ e S., Mateo M., Sargent W.L.W., Olszewski E.W., 2000,...

View on Pith Pith review arXiv 2000

[2] [2]

Galaxies in and around the Cen A/M 83 complex. Galaxy name RA(J2000.0)Dec T Θ VLG ± σV D ± σD Meth Ref Note (1) (2) (3) (4) (5) (6) (7) (8) (9) E059–01 073119.3 −681110 9 −1.5 245 5 4.57 0.36 rgb K06a N2915 092611.5 −763735 10 −1.3 184 5 3.78 0.43 rgb CNG SexB,DDO70 100000.1+051956 10 −0.7 111 1 1.36 0.07 rgb CNG N3109 100307.2 −260936 9 −0.1 110 1 1.33 0...

View on Pith 2006

[3] [3]

27 Typical lensing mass 500 2.4 – 5.2 Hoekstra et al. 2005 for given L

View on Pith 2005