OMEG Series: Multi-Domain Research

• OMEG Series is a multi-disciplinary framework integrating extragalactic surveys, chemo-dynamical mapping of ω Centauri, RMF-based neutron star models, and Ω⁻ baryon spectroscopy.
• The OMEGA survey employs IFU mapping to study ram-pressure stripping in galaxies, while oMEGACat offers detailed stellar kinematics and chemical dynamics in a complex globular cluster.
• RMF EoS models and Ω⁻ baryon studies provide insights into neutron star structure and strangeness dynamics, enhancing our understanding of microphysical and macrophysical processes.

The term "OMEG Series" encompasses several distinct but prominent research domains in contemporary astrophysics, nuclear physics, and hadron spectroscopy. It principally refers to (1) the OMEGA (OSIRIS Mapping of Emission-line Galaxies in A901/2) survey series, a multi-epoch extragalactic IFU survey targeting cluster environmental effects and ram-pressure-stripping phenomena such as jellyfish galaxies; (2) the oMEGACat (Ω Centauri MEGA-field Catalog) series, a coordinated chemo-dynamical survey of ω Centauri; and (3) the OMEG nuclear equation-of-state (EoS) family, a systematic set of RMF-based EoSs for neutron star structure calculations. This entry synthesizes these major axes, elucidating their foundational frameworks, methodologies, empirical results, and astrophysical implications.

1. OMEGA (OSIRIS Mapping of Emission-line Galaxies in A901/2): Survey Design and Objectives

The OMEGA program is a targeted emission-line mapping campaign designed to dissect how environmental mechanisms—chiefly, cluster ICM-driven ram-pressure stripping and tidal effects—quench or transiently enhance star formation and AGN activity in massive galaxy clusters. OMEGA targets Abell 901/2, a multi-cluster system at $z\approx0.167$ with extensive ancillary coverage (STAGES/HST, COMBO-17, GALEX, Spitzer, XMM). The survey leverages the OSIRIS tunable-filter on the 10.4 m Gran Telescopio Canarias to achieve contiguous, spatially-resolved mapping of Hα and [N II] emission over a 0.5 × 0.5 deg² field (Roman-Oliveira et al., 2018, Chies-Santos et al., 2015).

Key survey parameters:

Aspect	Value/Method	Reference
Redshift range	$0.1594\leq z\leq0.1718$	(Chies-Santos et al., 2015)
Spectral resolution	FWHM=14 Å, 7 Å step between tunings	(Chies-Santos et al., 2015)
SFR sensitivity	Hα flux limit $3\times10^{-17}$ erg s⁻¹ cm⁻² (SFR ≳ 0.05 M⊙ yr⁻¹ at $z=0.165$)	(Roman-Oliveira et al., 2018)
Classification	WHAN diagram (Cid Fernandes et al. 2011)	(Roman-Oliveira et al., 2018, Chies-Santos et al., 2015)
Coverage	20 fields, OSIRIS 7.8′ diameter, overlap ensures calibration and spatial completeness	(Chies-Santos et al., 2015)

The Hα–[N II] diagnostic captures both current star-formation and low-luminosity AGN activity with robust S/N, sampling galaxies from $M_*\sim10^9$ to $10^{11.5}\ M_\odot$ (Chies-Santos et al., 2015).

2. Data Processing, Emission-Line Analysis, and Source Classification

Raw data undergo bias and flat-field correction, wavelength calibration including field-angle passband shifts, and telluric correction. Spectral extraction proceeds on a per-object basis using optimal PSF matching. Gaussian decomposition is applied to the $λ$6563 (Hα) and blended $λ$6548, $6583$ ([N II]) lines. The WHAN diagnostic partitions sources in terms of log([N II]/Hα) and Hα equivalent width into star-forming, strong/weak AGN, and retired/passive systems (Roman-Oliveira et al., 2018, Chies-Santos et al., 2015).

Star formation rates follow the dust-corrected Kennicutt relation:

$$\mathrm{SFR\ (M}_\odot\,\mathrm{yr}^{-1})=4.6\times10^{-4} L(\mathrm{H}\alpha)/(10^{39}\ \mathrm{erg\ s}^{-1})$$

Specific star formation rate is $sSFR=SFR/M_*$, enabling direct comparison to the field galaxy main sequence.

3. Systematic Census of Jellyfish Galaxies and Environmental Diagnostics

OMEGA V compiles the largest single-system catalog of visually-identified "jellyfish" galaxies—systems showing unambiguous signatures of ram-pressure gas stripping, from unilateral disk compression to downstream star-forming tails and debris (Roman-Oliveira et al., 2018). Visual screening yielded 70 bona fide jellyfish (JClass ≥ 3): overwhelmingly late-type, blue-cloud systems, with only 7% secure AGN hosts.

Demographic and environmental signatures include:

• Enhanced sSFR: 55% are above the field main sequence; 27% meet $sSFR\geq2{\times}sSFR_\mathrm{MS}$ "starburst" criteria. JClass correlates with starburst fraction, e.g., 8/11 J5 galaxies are starbursts.
• Spatial distribution: Jellyfish lack a unidirectional infall preference but the most extreme cases (J5) concentrate toward massive sub-cluster cores.
• AGN incidence: Minimal overlap with AGN hosts, suggesting RPS is not a major AGN trigger (Roman-Oliveira et al., 2018).
• Hα emission morphology: Asymmetric and extended, aligned with optical tails, confirming in-situ star formation in stripped wakes.

The prevalence ($\sim$16% of Hα emitters) in A901/2 compared to single/dynamically relaxed clusters points to a direct enhancement of RPS phenomena by cluster mergers and disturbed ICM kinematics (Roman-Oliveira et al., 2018).

4. oMEGACat: Integrated Chemo-Kinematics of ω Centauri

The oMEGACat series is a multi-instrument, multi-epoch project, mapping the spatially-complete chemo-dynamical structure of ω Centauri (NGC 5139), the Milky Way's most massive and complex globular cluster (Nitschai et al., 2023, Häberle et al., 6 Mar 2025). Combining MUSE integral-field spectroscopy ($>300,000$ stars to $r_h$) and HST proper motions ($1.4$M stars), the series provides:

Installment	Data Type	Coverage/Content	Reference
I	MUSE LOS velocities, [M/H]	$156,871$ stars at $r\leq r_h$	(Nitschai et al., 2023)
II	HST PMs/photometry	$1.4$M PMs, $610,846$ quality-cut	(Häberle et al., 6 Mar 2025)
VI	3D kinematics	$24,928$ stars w/ full kinematics	(Häberle et al., 6 Mar 2025)

Principal kinematic results (Häberle et al., 6 Mar 2025):

• Core isotropy, outer radial anisotropy: $\beta\approx0$ at $r<30''$, rising to $\beta\approx0.3$ at $r_h$.
• 2D velocity-dispersion maps trace cluster ellipticity and rotation axes.
• Kinematic distance: $D=5494\pm61$ pc (1.1% uncertainty), derived from LOS-PM dispersion matching.
• Metallicity–kinematics decoupling: No systematic difference in dispersion or rotation as a function of [Fe/H] within $r_h$.
• Energy equipartition: Partial in the center ($\eta\approx0.09$), declining with radius.

Data products enable precision dynamical model constraints and fundamental studies of multi-population cluster evolution.

5. OMEG Series: RMF Equations of State for Neutron Star Structure

The OMEG family constitutes a controlled set of relativistic mean-field (RMF) EoS parameterizations tailored for neutron star applications, sharing identical saturation ($n_0=0.1484$ fm⁻³), effective mass ($M^*/M=0.62$), and incompressibility ($K_0=256$ MeV), with only the symmetry energy slope $L$ varied (Kwon et al., 14 Nov 2025).

Model	$L$ (MeV)	$S_0$ (MeV)	$R_{1.4\,M_\odot}$ (0 Hz)	$R_{1.4\,M_\odot}$ (200 Hz, KEH)
OMEG1	70	35.06	12.77 km	12.85 km
OMEG2	45	33.00	12.41 km	12.48 km
OMEG3	20	30.00	12.27 km	12.34 km

Variation of $L$ governs EoS stiffness, star radii, and rotational deformation. At slow rotation ($\Omega\lesssim200$ Hz), both perturbative Hartle-Thorne (HT) and fully relativistic Komatsu-Eriguchi-Hachisu (KEH) methods agree within 0.5% for radius and ellipticity. At higher rotation rates (e.g., millisecond pulsars), the fully relativistic KEH approach becomes necessary for accurate shape and stability analyses (Kwon et al., 14 Nov 2025).

6. Spectroscopy and Production of Ω⁻ Baryons: The OMEG Baryon Series

Beyond galactic and nuclear structural contexts, the OMEG designation appears in the study of strangeness $S=-3$ baryons ($\Omega^-$), particularly in baryon spectroscopy and heavy-ion production (Menapara et al., 2021, Collaboration et al., 2015). High-statistics measurements of $\Omega^-$ formation and $\Omega/\phi$ yield ratios at RHIC energies (STAR) probe strange quark hadronization and QCD transition dynamics:

• In central collisions at $\sqrt{s_{NN}}\gtrsim19.6$ GeV, the $\Omega/\phi$ ratio and constituent-quark number (NCQ) scaling directly reflect thermal strange-quark distributions with "temperatures" $T\sim0.35$ GeV and amplitude $A$ tracking strange quark phase-space occupancy.
• At $\sqrt{s_{NN}}=7.7,\,11.5$ GeV, both the ratio and $f_s$ amplitude are suppressed, indicating a change from partonic to hadronic-dominant dynamics at lower beam energies (Collaboration et al., 2015).
• Spectroscopically, the $\Omega^-$ spectrum within the hypercentral constituent quark model is linear in Regge $(n, M^2)$ space (slope $\alpha' = 0.427-0.565\;\mathrm{GeV}^2$), and the ground-state magnetic moment is $\mu_{\Omega^-}=-1.68\ \mu_N$ (vs. $-2.02\ \mu_N$ experimental) (Menapara et al., 2021).

7. Synthesis and Scientific Significance

The OMEG Series, in its various incarnations, exemplifies the power of homogeneous, high-precision surveys and parameter studies for unraveling astrophysical and nuclear processes across scales. In extragalactic astronomy, OMEGA has advanced understanding of ram-pressure-induced galaxy evolution, linking environment to transient starburst and quenching phenomena. oMEGACat supplies the definitive dataset for testing dynamical, chemo-evolutionary, and population mixing models in massive globular clusters. The OMEG RMF EoS provides a systematic control of symmetry energy effects on neutron star structure, fully leveraging precision mass/radius/rotation constraints. Finally, in QCD matter studies, OMEG-based analyses clarify strangeness generation and hadronization at the parton–hadron transition. The cross-disciplinary interconnections across the OMEG Series highlight a unifying theme: systematically probing the microphysics–macrophysics link through coordinated observational, experimental, and theoretical campaigns (Roman-Oliveira et al., 2018, Chies-Santos et al., 2015, Nitschai et al., 2023, Häberle et al., 6 Mar 2025, Kwon et al., 14 Nov 2025, Menapara et al., 2021, Collaboration et al., 2015).