The HST-Hyperion Survey: Companion fraction and overdensity in a z ∼ 2.5 proto-supercluster

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Volume 706 (February 2026)

A&A, 706 (2026) A55

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Table 4.

Companion statistics for our identified systems.

Sample	Value [Units]	r_proj ≤ 30 [kpc]	30 < r_proj ≤ 50 [kpc]	50 < r_proj ≤ 150 [kpc]
	$Δ \tilde{v}$ $\Delta\tilde{v}$ [km/s]	421	258	288
	$\tilde{M_{}}$ $\tilde{M_}$ [log(M_*/M_⊙)]	9.83 ± 0.48	10.14 ± 0.14	9.84 ± 0.13
	$\tilde{z}$ $\tilde{z}$	2.52 ± 0.05	2.47 ± 0.01	2.47 ± 0.01
Hyperion	${\tilde{σ}}_{δ}$ $\tilde{\sigma}_{\mathrm{\delta}}$	3.59 ± 1.04	4.93 ± 0.59	4.45 ± 0.74
	${\tilde{N}}_{bin}$ $\tilde{N}_{\mathrm{bin}}$	2 ± 1.3	5 ± 1.1	17 ± 3.7
	${\tilde{f}}_{bin}$ $\tilde{f}_{\mathrm{bin}}$	7.7 ± 5.2%	20.3 ± 5.1%	72.0 ± 6.5%
	⟨T_merge⟩ [Gyr]	$3 . 54_{- 1.09}^{+ 2.03}$ $3.54_{-1.09}^{+2.03}$	$4 . 06_{- 0.44}^{+ 0.53}$ $4.06_{-0.44}^{+0.53}$	$9 . 32_{- 1.20}^{+ 1.49}$ $9.32_{-1.20}^{+1.49}$

	$Δ \tilde{v}$ $\Delta\tilde{v}$ [km/s]	470	490	494
	$\tilde{M_{}}$ $\tilde{M_}$ [log(M_*/M_⊙)]	9.60 ± 0.06	9.61 ± 0.05	9.54 ± 0.02
	$\tilde{z}$ $\tilde{z}$	2.31 ± 0.11	2.26 ± 0.04	2.27 ± 0.02
Field	${\tilde{σ}}_{δ}$ $\tilde{\sigma}_{\mathrm{\delta}}$	0.56 ± 0.20	0.55 ± 0.17	0.59 ± 0.05
	${\tilde{N}}_{bin}$ $\tilde{N}_{\mathrm{bin}}$	44 ± 6.7	58 ± 7.2	489 ± 23
	${\tilde{f}}_{bin}$ $\tilde{f}_{\mathrm{bin}}$	7.5 ± 1.0%	9.7 ± 1.2%	82.4 ± 1.4%
	⟨T_merge⟩ [Gyr]	$4 . 10_{- 0.28}^{+ 0.32}$ $4.10_{-0.28}^{+0.32}$	$6 . 48_{- 0.40}^{+ 0.44}$ $6.48_{-0.40}^{+0.44}$	$13 . 10_{- 0.31}^{+ 0.33}$ $13.10_{-0.31}^{+0.33}$

Notes. Provided are the median LoS velocity differences ( $Δ \tilde{v}$ $\Delta\tilde{v}$ ), median stellar masses ( ${\tilde{M}}_{*}$ $\tilde{M}_*$ ), and median redshifts ( $\tilde{z}$ $\tilde{z}$ ) for each bin of projected separation for companion systems in Hyperion and the field. Also included are the ⟨T_merge⟩ values and median σ_δ density ( ${\tilde{σ}}_{δ}$ $\tilde{\sigma}_{\delta}$ ) for each bin, as well as the median overall counts ( ${\tilde{N}}_{bin}$ $\tilde{N}_{\mathrm{bin}}$ ) and the median fraction of companion systems ( ${\tilde{f}}_{bin}$ $\tilde{f}_{\mathrm{bin}}$ ) at that projected separation.

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