GLADE+ All-Sky Galaxy Catalog

• GLADE+ is an all-sky galaxy catalog that integrates six major astronomical databases for enhanced multimessenger astrophysics.
• It employs advanced cross-matching and Bayesian statistical methods for redshift correction and peculiar velocity modeling.
• The catalog provides completeness metrics, stellar mass estimates, and merger rate predictions vital for gravitational-wave and cosmological research.

The GLADE+ All-Sky Galaxy Catalog is an extended and integrated multi-catalog astronomical database designed for use in multimessenger astrophysical searches, with a particular emphasis on identifying host galaxies for gravitational-wave events detected by advanced interferometric detectors. The catalog combines heterogeneous data sets, applies sophisticated statistical treatments for galaxy properties and velocities, and aims to maximize completeness and parameter reliability out to cosmologically relevant distances. The technical development and application of GLADE+ have significant implications for both real-time and archival GW–EM follow-up, cosmological inference using standard sirens, and studies of the local universe.

1. Data Integration and Catalog Compilation

GLADE+ merges and cross-matches six major astronomical databases: GWGC, 2MPZ, 2MASS XSC, HyperLEDA, WISExSCOSPZ, and SDSS-DR16Q (Dálya et al., 2021). This integration is enabled by positional matching using a 2 arcsecond radius, reflecting the native resolution of the WISExSCOSPZ input. For galaxies lacking a WISE counterpart, WISE band magnitudes are derived either by direct crossmatch with AllWISE or by using empirically calibrated relationships between the W1 and Ks bands, factoring in redshift. Each contributing catalog supplies complementary parameters—GWGC and HyperLEDA provide accurate nearby distances, 2MPZ and WISExSCOSPZ contribute deep photometric redshifts, SDSS-DR16Q adds quasar populations, and 2MASS XSC and WISE supply near- and mid-infrared photometry.

The cross-matching methodology is critical for duplicate rejection and consistency. The positional approach is supplemented by ancillary information where available (e.g., brightness, redshift) to ensure robust catalog entries.

2. Redshift Correction and Peculiar Velocity Modelling

To transform observed redshifts into cosmologically relevant measurements, GLADE+ accounts for peculiar velocities—non-Hubble motions in the local universe—which are significant out to z ≲ 0.05 (Dálya et al., 2021). The corrections utilize the "Bayesian Origin Reconstruction from Galaxies" formalism, which reconstructs the cosmic large-scale structure and infers the velocity field, combining linear flow and non-linear virial contributions.

Virial velocity dispersion is calculated as:

$$\sigma_{\text{vir}} = 476\,g_v\,[\Delta_{nl}(z) E(z)^2]^{1/6} \left(\frac{M_h}{10^{15} M_\odot h^{-1}}\right)^{1/3}$$

where $g_v=0.9$, $\Delta_{nl}(z) = 18\pi^2 + 60x - 32x^2$ with $x = \Omega_m(1+z)^3/E(z)^2 - 1$, $E(z)$ is the expansion function, and $M_h$ (halo mass) is estimated via an empirical luminosity–mass relation.

The redshift correction propagates uncertainties from both velocity field reconstruction and virial motions, yielding a redshift posterior for each galaxy. Heliocentric redshifts are shifted to the CMB frame using FIRAS data.

3. Catalog Completeness and Luminosity Criteria

Completeness is quantified both via cumulative B-band luminosity and luminosity function fitting. Using an average B-band luminosity density $$(1.98 \pm 0.16) \times 10^{-2} L_{10} \text{ Mpc}^{-3}$$ ($L_{10}=10^{10}\,L_{B,\odot}$), GLADE+ is considered complete up to $d_L=47^{+4}_{-2}$ Mpc in B-band light (Dálya et al., 2021). For the brightest galaxies, completeness extends to 90% of the total B and $K_s$-band luminosity up to $d_L\simeq130$ Mpc; this criterion is highly relevant for host association in gravitational-wave follow-up.

A Schechter luminosity function,

$$\phi^*L_B^*\int_{x_1}^\infty x^{\alpha+1} e^{-x}dx = \phi^*L_B^*\Gamma(\alpha+2,x_1)$$

is used for cross-checking observed luminosity distributions. Here, $\phi^*$ is the normalization constant, $L_B^*$ the characteristic luminosity, and $\alpha$ the faint-end slope. The boundary $x_1$ is chosen so that the brightest galaxies together contribute 90% of cumulative luminosity.

4. Derivation of Stellar Masses and Merger Rate Estimates

Stellar masses in GLADE+ are computed, wherever possible, from WISE W1-band photometry, which offers robustness to dust and population differences. Passive systems (identified via the cut $W2-W3\leq1.5$) use $M_*/L_{W1}=0.65\pm0.07$, while star forming galaxies follow a log-linear relation $\log_{10}(M_*/L_{W1})=-0.4\pm0.2$ (Dálya et al., 2021). Absolute magnitudes are calculated as

$M = m + 5 - 5\log_{10}(d_L) - K$

where $K=-7.1\log_{10}(1+z)$ is the K-correction.

Binary neutron star (BNS) merger rates per galaxy are estimated using the relation from Artale et al. (2019):

$$\log_{10}(N_{\text{BNS}}/\text{Gyr}) = (1.15 \pm 0.08)\log_{10}(M_*/M_\odot) - (7.22 \pm 0.22),$$

valid for $M_*>10^7 M_\odot$ and $z\leq0.1$. Errors in masses and rates propagate both magnitude and distance uncertainties. Coverage is $>97\%$ for mass estimates over catalog galaxies.

5. Applications in Multimessenger Astrophysics

GLADE+ is specifically tailored for multimessenger search prioritization—most notably in gravitational-wave volumetric follow-up (Collaboration et al., 4 Sep 2025). By providing full-sky, redshift- and luminosity-weighted galaxy lists with stellar mass and BNS merger rate estimates, the catalog enables rapid host galaxy ranking. This reduces the telescope time and pointing required to locate electromagnetic counterparts.

In hierarchical Bayesian inference frameworks, GLADE+ delivers redshift priors for "dark sirens" (GW sources without EM counterparts), enabling measurement of the Hubble constant ($H_0$) via the standard siren method. The catalog information enters likelihood calculations both as a galaxy-weighted redshift distribution and, through completeness models, as a correction for missing faint galaxies. Host weighting typically uses luminosity-based probabilities such as $w_j(\epsilon, M_j) = 10^{-0.4\epsilon(M_j - M_*)}$, with $M_*$ set by the "knee" of the Schechter function.

Recent results using GLADE+ report $H_0=76.6^{+13.0}_{-9.5}$ km s$^{-1}$ Mpc$^{-1}$ combined with GW170817 (Collaboration et al., 4 Sep 2025), and exploit the catalog for constraints on modified GW propagation through parameters such as $\Xi_0$.

6. Comparison to Previous Catalogs and Ongoing Development

Relative to its predecessor GLADE, GLADE+ improves completeness (from $d_L\sim37$ to $d_L=47$ Mpc for bright galaxies), expands ancillary data with stellar mass and merger rate predictions, and applies Bayesian velocity field corrections for local redshift accuracy. Compared to alternative compilations (e.g., HECATE, REGALADE, SuperCOSMOS), GLADE+ focuses on maximal utility for GW follow-up—prioritizing completeness in B- and $K_s$-band luminosity, reliability of mass estimates, and rapid host ranking.

The catalog’s construction from six major datasets, inclusion of quasar populations, and dedicated treatment of duplicate entries position it as a reference database for both transient searches and cosmological parameter inference.

7. Technical Limitations and Future Prospects

GLADE+ is currently most complete within $d_L\sim130$ Mpc for high-luminosity galaxies; fainter systems and higher-redshift objects are less complete due to the flux limits and depth boundaries of the constituent catalogs. Stellar mass and merger rate estimations rely on robust photometry and adopted empirical relations, which inherit uncertainties from population synthesis models and photometric calibration.

A plausible implication is that continued integration with deeper large-area surveys (e.g., LSST, Euclid, and future mid-infrared missions) will further enhance catalog depth and reliability. Synergy with catalogs such as REGALADE, which incorporates deeper imaging and hybrid cleaning techniques, may provide even higher completeness for transient host searches at $z\gtrsim0.05$, particularly for low-mass and low-surface-brightness systems.

GLADE+ remains a critical dataset for real-time GW follow-up, joint EM–GW astrophysics, and robust cosmological inference using standard sirens and modified gravity tests. Its extension and refinement are essential for the evolving landscape of multi-messenger astronomy.