The velocity field of the Lyra complex

D. Eckert; F. Gastaldello; M. Girardi; M. Longhetti; M. Nonino; M. Rossetti; S. Clavico; S. De Grandi; S. Ghizzardi; W. Boschin

REVIEW 3 major objections 6 minor 1 cited by

The velocity field of the Lyra complex

T0 review · 3 major / 6 minor · reviewed 2026-08-14 · deepseek-v4-flash

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Pith's one-line read This paper establishes that the two clusters in the Lyra complex are likely gravitationally bound and pre-merger, with CIZAJ1824 in front and falling toward RXCJ1825.

desk verdict First kinematic map of the Lyra complex with solid velocity dispersions and masses; the pre-merger claim is plausible but hinges on a projection-angle prior that deserves explicit sensitivity testing. read the letter →

arxiv 1908.02277 v2 pith:UBOZPY2C submitted 2019-08-06 astro-ph.GA astro-ph.CO

M. Girardi , W. Boschin , S. De Grandi , M. Longhetti , S. Clavico , D. Eckert , F. Gastaldello , S. Ghizzardi

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M. Nonino M. Rossetti

This is my paper · ORCID

classification astro-ph.GAastro-ph.CO

keywords galaxyclustersclustermergerskinematicsvelocitydispersiondynamicalmassesLyracomplexRXCJ1825.3+3026CIZAJ1824.1+3029

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

This paper presents the first kinematic study of the Lyra complex, a pair of galaxy clusters (RXCJ1825 and CIZAJ1824) separated on the sky by about 16 arcminutes. From spectroscopy of 285 galaxies it selects 198 members and asks whether the two clusters are physically interacting. It concludes that they are likely gravitationally bound and in a pre-merger phase: with the redshift difference read as relative motion, the projected separation is $D=1.272$ Mpc, the line-of-sight velocity difference is $V=1757$ km s$^{-1}$, and a two-body binding analysis admits bound, incoming orbits with CIZAJ1824 in front of RXCJ1825 and moving toward it. The future merged cluster is predicted to have $M_{200}=2.6\pm0.6\times10^{15}\,M_\odot$, making the Lyra complex a very massive assembly caught before core passage. A reader should care because pre-first-crossing cluster mergers are rare observational windows into how the largest structures in the Universe assemble.

What carries the argument

The argument is carried by the two-body Newtonian binding criterion for a pair of clumps on radial orbits, together with the paper's analytical two-body model. The criterion is $V^2 D < 2 G M_{\rm sys}\sin^2\alpha\cos\alpha$, with $V=1757$ km s$^{-1}$, $D=1.272$ Mpc, system mass $M_{\rm sys}=1.5$–$3\times10^{15}\,M_\odot$, and $\alpha$ the angle between the plane of the sky and the line joining the two cluster centers; it decides for which projection angles the pair is bound. The same machinery, through bound-ingoing solutions of the two-body model, gives the geometry of the encounter, placing CIZAJ1824 in front of RXCJ1825 and moving toward it. To feed this test, the paper uses adaptive-kernel density reconstruction to identify the two clusters, local mean-velocity deviation statistics to show the system is unrelaxed at high significance, and a hierarchical binding-energy grouping to assign each galaxy to one of the two clusters and obtain clean velocity dispersions.

What would settle it

Measure independent, redshift-free distances to both clusters, for example from joint X-ray and Sunyaev-Zeldovich analyses of each cluster's gas, and check whether they lie at the same distance; a separation of roughly 30 Mpc would make the redshift difference cosmological and the pre-merger conclusion wrong. A second check is to map the region between the clusters for a radio relic or X-ray shock front, since detecting a shock from a past core crossing would invalidate the pre-first-crossing assumption and change the inferred bound-orbit solution.

Watch

Extended reading notes

Core claim

On the paper's own terms, the discovery is that the Lyra complex is not a chance projection of two unrelated clusters. Using the internal kinematics of 198 member galaxies, the paper separates the two systems: RXCJ1825 has $z=0.0645$, $\sigma_v=995^{+131}_{-125}$ km s$^{-1}$, and $M_{200}=1.1\pm0.4\times10^{15}\,M_\odot$; CIZAJ1824 has $z=0.0708$, $\sigma_v=700\pm50$ km s$^{-1}$, and $M_{200}\simeq0.4\times10^{15}\,M_\odot$. Interpreting the redshift difference as Doppler rather than cosmological, the pair has projected separation $D=1.272$ Mpc and rest-frame velocity difference $V=1757$ km s$^{-1}$. The two-body dynamical analysis, with system mass $M_{\rm sys}=1.5$–$3\times10^{15}\,M_\odot$, finds the bound-incoming solution acceptable for projection angles $\alpha\simeq30^\circ$–$70^\circ$; at $\alpha=50^\circ$ the real separation is about 2 Mpc, so the two clusters' $R_{500}$ regions are just touching and the cores have not yet crossed. Alongside this, the velocity field shows a high-velocity South-West region that the paper attributes to the disrupted group around the galaxy SG, so the Lyra complex hosts a multi-component assembly, not a simple binary collision.

Load-bearing premise

The conclusion depends on the observed 1757 km s$^{-1}$ difference in redshift being relative motion between two clusters at the same distance, not a cosmological distance difference of about 30 Mpc.

Editorial extensions

If this is right

The Lyra complex becomes a benchmark system for cluster-merger physics in the pre-first-core-passage state, a phase not yet marked by X-ray shocks or a bullet-like morphology.
The merged descendant will be a very massive cluster, with $M_{200}\sim2.6\times10^{15}\,M_\odot$, among the most massive systems known at $z\sim0.067$.
RXCJ1825 itself shows signs of an earlier merger, with two dominant galaxies aligned along the East-West major axis plus a North-East substructure, so the complex records assembly on at least two episodes and axes.
The high-velocity South-West region, centered on the luminous galaxy SG, indicates a third component, likely a disrupted group falling into the system, making the assembly more complex than a binary merger.
The optical dynamical masses agree with the X-ray masses within uncertainties, supporting the use of galaxy velocity dispersions as mass estimators in pre-merger cluster pairs.

Reading between the lines

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

A natural next step, not pursued in the paper, is to apply the same two-body diagnostic to other close cluster pairs in X-ray and Sunyaev-Zeldovich surveys, turning this single system into a statistical sample of pre-merger pairs.
If the pre-merger interpretation holds, one concrete prediction beyond the paper is that the next interaction signatures, such as gas compression or a weak shock on the CIZAJ1824 side and a radio-halo extension along the RXCJ1825-CIZAJ1824 axis, should appear before any core crossing.
The South-West high-velocity stream could be a kinematic signature of a group in the act of disruption; deeper spectroscopy around SG, which the paper does not have, would distinguish a tidal stream from a chance velocity tail.
A redshift-independent distance to CIZAJ1824, for instance from its X-ray and Sunyaev-Zeldovich properties, would settle the weakest assumption; the paper argues statistically that a chance alignment is unlikely but does not measure that distance.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

Bottom line: this is a solid, honest piece of observing science. Girardi et al. deliver the first kinematic sample for the Lyra complex — 285 new redshifts, 198 members — and the first velocity dispersions and dynamical masses for RXCJ1825 and CIZAJ1824. The measurement work is careful: errors are propagated, member selection is checked with photometric CMR, and the velocity-dispersion estimates are cross-checked against X-ray temperatures and masses from Clavico et al. The agreement with X-ray masses is genuinely reassuring. The SW high-velocity field, tied to the possible infalling group around SG, is a nice observational detail and fits the radio/X-ray picture.

The soft spots are concentrated in the dynamical conclusion. The two-body analysis gives bound probabilities of 31–34% for Msys = 1.5e15 and 53–58% for 3e15. Those numbers alone do not justify "likely bound." The jump to 78% comes from excluding alpha < 15°, because such geometries would imply relative velocities above ~6500 km/s. That prior is plausible — observed cluster mergers don't show such extreme infall velocities — but it is an empirical prior, not a direct measurement for this pair. The authors present it transparently, but a referee should ask for a sensitivity test or a more explicit Bayesian treatment. The same caveat applies to the radial-orbit, first-infall assumptions of the Beers et al. model, which the authors acknowledge but do not test.

Two smaller things. CIZAJ1824's velocity dispersion rests on only 17–19 galaxies from the Serna-Gerbal hierarchical method; the systematic uncertainty may be larger than the quoted 50 km/s. And the abstract and summary list M200 = 4 ± 0.1 × 10^14 Msun for CIZAJ1824, while the body says 3.7 ± 1.1 (or 4 ± 1) × 10^14 — the uncertainty is clearly a typo and should be fixed.

On the cosmological-alternative question: if the redshift difference is distance, the clusters are ~30 Mpc apart, and the authors argue the chance of an unrelated cluster as massive as CIZAJ1824 in that volume is <7e-4. That is a reasonable order-of-magnitude argument. It doesn't constrain the inclination of a genuine physical pair, but it does make the projection prior the more important issue.

Who this is for: anyone working on cluster mergers or using the Lyra complex as a target; radio and X-ray groups will want the kinematic anchor. It is not a methodological breakthrough. But it is a well-executed, honestly reported dataset, and the central claim is worth taking seriously rather than dismissing. I would send it to a competent referee, not desk-reject, with a request for a clearer treatment of the two-body systematics and the mass typo.

Referee Report

3 major / 6 minor

Summary. This paper presents the first spectroscopic survey of the Lyra complex (RXCJ1825 plus CIZAJ1824), using 285 new TNG redshifts and Pan-STARRS photometry. After a DEDICA-based member selection (198 members) and rejection of galaxy ID225 as a foreground spiral, the authors identify the two clusters plus minor substructures, measure velocity dispersions of 995 and 700 km/s for RXCJ1825 and CIZAJ1824, derive dynamical masses M200 = 1.1e15 and 4e14 Msun with the Munari et al. scaling relation, and compare these with independent X-ray masses. They detect a significant velocity gradient and a peculiar high-velocity SW region associated with the galaxy SG. Adopting a kinematic interpretation of the redshift difference (Delta_v = 1757 km/s at projected separation 1.272 Mpc), they apply a two-body Newtonian/bimodal model and conclude that the two clusters are likely bound and in a pre-merger phase, with CIZAJ1824 in front of RXCJ1825 and approaching it, and that the future merged system will have M200 = 2.6 +/- 0.6e15 Msun.

Significance. If correct, the main result is astrophysically valuable: the Lyra complex would be a rare example of a massive bimodal cluster pair caught before core passage, complementing the X-ray and radio studies of Clavico et al. and Botteon et al. The paper is careful in presenting the data: member selection is checked against photometric CMR members, substructure and velocity-gradient significances are assessed by Monte Carlo reshuffling, and the dynamical masses are cross-checked against independent X-ray estimates. The main weakness is statistical: the claimed 'likely bound' conclusion rests on a prior for the projection angle that is not derived from the data or from a quantitative cosmological model. This should be fixable with an explicit Monte Carlo or simulation-based calculation, and the underlying dataset remains valuable even if the two-body conclusion is softened.

major comments (3)

[Section 7 (Eq. 3, Fig. 16)] The bound probabilities reported in Sect. 7 are 31-34% for M_sys = 1.5e15 Msun and 53-58% for M_sys = 3e15 Msun; the jump to 'likely bound' is obtained by excluding alpha < 15 deg because cluster-cluster peculiar velocities are generally below 2000 km/s. This prior is not turned into a posterior for the present pair, which was selected with D = 1.272 Mpc and Delta_v = 1757 km/s. The text itself states that the probabilities are 'estimated from the solid angles without regard to other constraints'. Please either derive P(alpha < 15 deg | D, Delta_v, selection) from simulations or an empirical cluster-pair catalog, or present the conclusions as 'possibly bound' rather than 'likely bound'. As written, the headline claim is stronger than the calculation supports.
[Section 5 and Table 5] The adopted sigma_v for CIZAJ1824 is an average value of 700 +/- 50 km/s over Serna-Gerbal solutions that span 678-743 km/s for M/L = 100-200 and use only 17-19 member galaxies; the quoted uncertainty is smaller than the spread across the adopted mass-to-light ratios and does not include the uncertainty in the group assignment. Because the total mass of the pair enters the bound criterion (Eq. 3) and the bimodal model, the mass uncertainty of CIZAJ1824 should be propagated into the merger probabilities. Similarly, RXCJ1825 has sigma_v = 995 km/s for red galaxies and 1244 km/s for all galaxies within 0.4 Mpc, which changes M200 by about 30%; the dynamical analysis should report how the merged-system conclusion depends on this choice.
[Section 8.1] The rejection of the cosmological interpretation of the redshift difference uses the expectation of fewer than 7e-4 clusters as massive as CIZAJ1824 in the sampled volume. This estimate is based on the mean abundance of clusters and does not account for the fact that the search volume is the line of sight to a known massive cluster, where correlated large-scale structure substantially increases the probability of finding a second massive system within about 16 arcmin and Delta_v about 1750 km/s. A quantitative estimate of that conditional probability, or an explicit acknowledgment that it is only an order-of-magnitude prior, is needed before the kinematic interpretation can be treated as established.

minor comments (6)

[Table 5] The second table footnote is labeled 'a' but should be labeled 'b'.
[Fig. 9 caption] The caption contains the typo 'CIZAJ1924' for 'CIZAJ1824'.
[Abstract] The abstract gives the CIZAJ1824 mass as 4e14 Msun without an uncertainty, while Table 5 gives 0.4 +/- 0.1e15 Msun; please make the abstract consistent.
[Section 4.4] The NFW Monte Carlo simulation shown in Fig. 10 is described qualitatively; please state the fraction of simulations that reproduce the observed high-velocity SW region.
[Section 7 and Table 7] Table 7 lists V = 1757 +/- 96 km/s but D = 1.272 Mpc without an uncertainty; the small uncertainty in the adopted cosmology should be propagated or explicitly stated as negligible.
[Section 7, after Eq. (3)] The angles alpha_V and alpha_R are introduced in the text but never defined; please define them explicitly.

Circularity Check

1 steps flagged · score 2.0 of 10

No significant circularity: the central two-body claim rests on observed velocities plus an externally calibrated mass scaling; only a minor self-consistency loop appears in the caustic check.

self definitional [Section 6 (mass estimates), discussion of caustics around Fig. 12]
"We used the recipe of den Hartog & Katgert (1996) with the assumption of a NFW mass density profile (Navarro et al. 1997; Dolag et al. 2004) to derive from our mass estimate the 'caustics', that is the curves delimiting the region where the rest-frame velocity v rf is smaller than the escape velocity. The inspection of Fig. 12 (top panel, solid blue curves) suggests that our mass estimate is adequate to describe the position of the RXCJ1825 galaxies in the phase-space."

The caustic envelope is a deterministic function of the same M200 that it is used to check: M200 is first obtained from sigma_v through the Munari et al. scaling (Eq. 1), and the NFW escape-velocity caustics are then derived from that M200. Verifying that member galaxies fall inside the caustics therefore tests only that the assumed mass is consistent with the galaxies being bound under that same assumed mass, not whether the mass is independently correct. This is a self-consistency loop rather than an external validation. It is not load-bearing for the central two-body claim because the M200 values are separately compared with independent X-ray masses, and the caustic check does not enter the bimodal model.

full rationale

The central derivation chain is self-contained and uses independently calibrated inputs. The velocity dispersions come from new TNG spectroscopy (Sect. 5), the dynamical masses use the externally calibrated Munari et al. (2013) scaling (Eq. 1), and the resulting M200 values agree with independent X-ray masses from Clavico et al. (2019). The two-body analysis (Sect. 7) uses the observed line-of-sight velocity difference V and projected separation D together with a system mass range that follows from those individual velocity dispersions; the bound/ingoing solution is selected by comparing the model's required mass with that range, so the conclusion is not hard-wired by construction. The 'likely bound' wording does depend on an explicit prior excluding alpha < 15 deg, but that prior is drawn from external cluster-velocity and merger-velocity statistics, not from the target conclusion. The only genuine circularity is a minor consistency check: the caustic curves in Figs. 12-13 are computed from the same M200 they are then said to validate. Because the mass estimates are independently benchmarked against X-ray data and the caustic check does not feed back into the mass values, this does not rise above a minor internal self-consistency loop.

Assumptions & free parameters 6 free parameters · 7 assumptions · 0 invented entities

The masses and dynamics depend on several external calibrations and modeling choices; none of them is fitted to force the pre-merger conclusion, but the conclusion inherits their uncertainties.

free parameters (6)

CMR intercept and slope for r-i red sequence = r-i = 0.950 - 0.032 r
Fitted to 132 spectroscopic members in Sect. 4.1 and used to select photometric members with a 0.07 mag threshold.
CMR for g-r used to define red galaxies = g-r = 1.334 - 0.032 r
Fitted to 116 galaxies in Sect. 4.3; the 0.15 mag blue cutoff defines the red-galaxy sample used for the RXCJ1825 sigma_v estimate.
Mass-to-light ratio M/L_r for Serna-Gerbal method = adopted 150 Msun/Lsun; also 100 and 200
Used in Sect. 5 to define HT1 and HT2 groups; CIZAJ1824 membership and sigma_v vary mildly with this choice.
Radius cutoff for uncontaminated RXCJ1825 galaxies = 0.4 Mpc
Chosen from the mean velocity profile in Sect. 5 where contamination from CIZAJ1824 appears; directly sets sigma_v = 995 km/s for the adopted estimate.
Velocity dispersion to mass scaling parameters = A1D = 1090 km/s, 1/alpha = 3
External calibration from Munari et al. (2013), Eq. (1), used for all M200 estimates.
System mass range for two-body model = 1.5-3.0 × 10^15 Msun
Assumed in Sect. 7 as the sum of cluster masses doubled to account for mass outside R200; the bound probability is sensitive to this range.

assumptions (7)

domain assumption The redshift difference between the two clusters is kinematic, meaning both are at the same cosmological distance.
Invoked in Sect. 7 to convert redshift difference into V = 1757 km/s and D = 1.272 Mpc; the alternative cosmological interpretation is discussed in Sect. 8.1.
domain assumption The Beers et al. (1982) two-body model with radial orbits, zero initial separation, and no clump mass distribution is applicable.
Used in Sect. 7; the authors list limitations, including typical impact parameters near 160 kpc and neglect of mass distribution inside the clumps.
domain assumption Red galaxies trace the cluster core and are less contaminated by interlopers.
Basis for adopting sigma_v = 995 km/s for RXCJ1825 in Sect. 5 instead of the all-galaxy value of 1244 km/s.
domain assumption The Serna-Gerbal constant mass-to-light ratio identifies physical galaxy groups from binding energy hierarchies.
Used in Sect. 5 to derive the CIZAJ1824 velocity dispersion and to separate HT1 and HT2.
ad hoc to paper Galaxy ID225 is a foreground spiral, not a cluster member.
Stateed in Sect. 3 based on morphology and analogy with misclassified BCGs; if wrong, the bright core population of RXCJ1825 changes.
domain assumption The Munari et al. (2013) velocity dispersion to M200 scaling relation is valid for these clusters.
External calibration used in Eq. (1) for all dynamical mass estimates in Sect. 6.
domain assumption NFW density profile and the den Hartog and Katgert (1996) recipe describe the caustic envelope.
Used in Sect. 6 to draw caustics and to argue that galaxies lie within the escape-velocity region.

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Pith. "Pith review of The velocity field of the Lyra complex." pith.science (2026). https://pith.science/paper/UBOZPY2C

@misc{pith2026190802277,
  author       = {Pith},
  title        = {Pith review of: The velocity field of the Lyra complex},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/UBOZPY2C}},
  note         = {Machine review of arXiv:1908.02277}
}

read the original abstract

The formation of cosmic structure culminates with the assembly of galaxy clusters, a process quite different from cluster to cluster. We present the study of the structure and dynamics of the Lyra complex formed of the two clusters RXC J1825.3+3026 and CIZA J1824.1+3029, very recently studied using both X-ray and radio data. This is the first analysis based on kinematics of member galaxies. New spectroscopic data for 285 galaxies were acquired at the Italian Telescopio Nazionale Galileo and used in combination with PanSTARRS photometry. The result of our member selection is a sample of 198 galaxies. For RXCJ1825 and CIZAJ1824 we report the redshifts, z=0.0645 and z=0.0708, the first estimates of velocity dispersion, sigmav=995 and 700 km/s, and dynamical mass, M200=1.1E15 and 4E14 Msun. The past assembly of RXCJ1825 is traced by the two dominant galaxies, both aligned with the major axis of the galaxy distribution along the East-West direction, and by a minor North-East substructure. We also detect a quite peculiar high velocity field in the South-West region of the Lyra complex. This feature is likely related to a high velocity, very luminous galaxy, suggested to be the central galaxy of a group in interaction with RXCJ1825 by very recent studies based on X-ray and radio data. The redshift of the whole Lyra complex is z=0.067. Assuming that the redshift difference between RXCJ1825 and CIZAJ1824 is due to the relative kinematics, the projected distance between the cluster centers is 1.3 Mpc and the los velocity difference is 1750 km/s. A dynamical analysis of the system shows that the two clusters are likely to be gravitationally bound, in a pre-merger phase, with CIZAJ1824 in front of RXCJ1825 and going toward it. Our results corroborate a picture where the Lyra region is the place of a very complex scenario of cluster assembly.

Figures

Figures reproduced from arXiv: 1908.02277 by the authors.

**Figure 1.** Pan-STARRs r-band image of the Lyra complex (RXCJ1825+CIZAJ1824 clusters) with, superimposed, the contour levels of the XMM X-ray emission taken from Clavico et al. (2019). Circles and squares indicate cluster members and non-members, respectively (see [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗

**Figure 2.** TNG V-band image of the RXCJ1825 region around the two brightest galaxies (BCG-E and BCG-W). The color scale units are ADU using a logarithmic display function. hereafter BCG-W). The centroid of the XMM X-ray emission lies between these two galaxies, much closer to the BCGW. Hereafter, for the center of RXCJ1825 we adopt the position of the X-ray centroid reported by Clavico et al. (2019), [R.A.=18h25m21 s . 77, … view at source ↗

**Figure 4.** Spatial distribution on the sky and relative isodensity contour map of the 198 spectroscopic members of the Lyra complex, obtained with the 2D-DEDICA method. The peaks from East to West are RXCJ1825NE, RXCJ1825main, MiddlePeak, CIZAJ1824 (see Tab. 2). The X-ray centroid in RXCJ1825 is taken as the center of the whole complex. The position of the prominent galaxies (BCGs of RXCJ1825, BCG of CIZAJ1824, SG, RG) are i… view at source ↗

Figures from the paper (12 more)

**Figure 3.** Figure 3: Redshift galaxy distribution. The solid red line histogram refers to the galaxies assigned to the Lyra complex according to the DEDICA reconstruction method. The distribution of the 198 member galaxies with the redshift of prominent galaxies is shown in the inset plo…

**Figure 6.** Figure 6: shows the contour map for the 450 photometric members having r ≤ 20, that is ∼ 4 mags fainter than M∗ , [PITH_FULL_IMAGE:figures/full_fig_p005_6.png]

**Figure 7.** Figure 7: Spatial distribution of the 198 members of the Lyra complex, each marked by a circle: the larger the circle, the larger is the deviation δV,i of the local mean velocity from the global mean velocity (the socalled bubble plot). Thin/blue and thick/red circles show wher…

**Figure 8.** Figure 8: Upper panel. As [PITH_FULL_IMAGE:figures/full_fig_p006_8.png]

**Figure 9.** Figure 9: Bubble plot for the 58 red galaxies belonging to the West region (CIZAJ1824+SouthWestPeak) where the velocity gradient, pointing from low to high velocities, is indicated by the little arrow. The spatial distribution of all red galaxies is indicated by small black do…

**Figure 11.** Figure 11: Spatial distribution of the 198 galaxies of the Lyra complex, each marked by a circle: the larger the circle, the larger is the velocity. The eight galaxies with velocity equal or larger than SG are pointed out by red circles. The position of prominent galaxies is ind…

**Figure 12.** Figure 12: (middle panel) presents the integral mean velocity profile for all member galaxies and for red galaxies only. It is shown that hvi agrees with vBCG−EW in the central region of RXCJ1825 and that the inclusion of more galaxies at larger clustercentric distances causes…

**Figure 13.** Figure 13: As [PITH_FULL_IMAGE:figures/full_fig_p009_13.png]

**Figure 14.** Figure 14: Dendogram obtained through the Serna & Gerbal algorithm applied to the 194 members with available magnitudes (here the case for M/Lr=150 M⊙/L⊙). The y-axis indicates the binding energy, here in arbitrary units, with the deepest negative energy levels on the bottom. Th…

**Figure 15.** Figure 15: Spatial distribution on the sky of 194 galaxies of the Lyra complex having available magnitudes. Blue triangles, red squares, and cyan circles indicate galaxies of HT1, HT2, and HTSG as obtained from Serna & Gerbal method (see [PITH_FULL_IMAGE:figures/full_fig_p010_…

**Figure 16.** Figure 16: System mass vs. projection angle for bound and unbound solutions (thick solid and thick dashed blue curves, respectively) of the two– body model applied to the two clusters. Labels BIa and BIb indicate the bound and incoming, i.e., collapsing solutions. Label BO and …

**Figure 17.** Figure 17: TNG spectrum of BCG-CC where no emission line is present, in particular Hα expected at λ ∼ 7020 angstrom at the cluster redshift. as an evidence that the two galaxies have already interacted, that is the real/deprojected velocity is small and that we are catching RXCJ…

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Forward citations

Cited by 1 Pith paper

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

Particle acceleration in a nearby galaxy cluster pair: the role of cluster dynamics
astro-ph.CO 2019-08 accept novelty 6.0 of 10

A Mpc-scale radio halo is discovered in the merging cluster RXC J1825.3+3026, while the relaxed companion CIZA J1824.1+3029 shows no diffuse radio emission.

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