Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 2401.17281

Discovery of a >13 Mpc long X-ray filament between two galaxy clusters beyond three times their virial radii

J. Dietl·F. Pacaud·T. H. Reiprich·A. Veronica·K. Migkas·C. Spinelli·K. Dolag·B. Seidel
View original source ↗Read source document ↗Export metadata ↓

Abstract

The new Spectrum Roentgen Gamma (SRG) eROSITA X-ray telescope has a superior response to extended soft X-rays, which makes it ideal for studying low X-ray surface brightness emission of cosmic filaments. We search for extended X-ray emission between the two nearby galaxy clusters Abell~3667 and Abell~3651, which are separated by a projected transverse distance of ${\sim}13\,\mathrm{Mpc}$, using data from the SRG/eROSITA All-Sky Survey. We performed a detailed X-ray image analysis of the region between the two galaxy clusters and conducted a redshift analysis of the sources between them. We carried out a thorough surface brightness and spectral analysis between the clusters. The analysis was complemented with an X-ray pointed observation from XMM-Newton, infrared 2MASS data, and redshift information from NED. We discover an emission filament beyond the known radio relic northwest of A3667 and even beyond three times its virial radius. It is smoothly connected to A3651. The X-ray emission in the direction of the filament shows an enhancement of $30\pm3\,\%$ with a significance of $11\,σ$. The 2MASS map and redshift analysis show an alignment of galaxies along the filament and make a projection effect unlikely. Taking the redshift progression of galaxies within the filament into account, we estimate its three-dimensional length to be in the range of $25\,\mathrm{Mpc} - 32\,\mathrm{Mpc}$. The surface brightness analysis in combination with the temperature $T=({0.91}_{-0.11}^{+0.07})\,\mathrm{keV}$ and metallicity $Z=({0.10}_{-0.08}^{+0.05})\,\mathrm{Z_{\odot}}$ from the spectral analysis leads to estimates of a total flux, gas mass, and central baryon overdensity of $F_\mathrm{X}= (7.4\pm1.2)\times 10^{-12}\,\mathrm{erg\,s^{-1}\,cm^{-2}}$, $M_\mathrm{g}=(2.7^{+1.4}_{-0.8})\times 10^{14}\,\mathrm{M_\odot}$ and $δ_0=215^{+86}_{-50}$.

Explore related subjects

astro-ph.COastro-ph.GA

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

J. Dietl, F. Pacaud, T. H. Reiprich, A. Veronica, K. Migkas, C. Spinelli, K. Dolag, B. Seidel. 2024-11-05. Discovery of a >13 Mpc long X-ray filament between two galaxy clusters beyond three times their virial radii. https://doi.org/10.1051/0004-6361%2F202449354

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

From quantum fluctuations to galaxy power spectrum multipoles

These notes trace large-scale structure from primordial curvature perturbations generated by inflationary quantum fluctuations to galaxy power-spectrum multipoles. Three core lectures develop the linear matter power spectrum, spherical and anisotropic collapse, galaxy bias, redshift-space distortions, the Kaiser model, and multipole estimators with Gaussian covariance. The extension develops nonlinear bias and the one-loop effective field theory model used in full-shape analyses. Derivations are explicit; appendices collect longer calculations and solutions. The core lectures assume undergraduate-level cosmology; the extension assumes familiarity with perturbation theory.

astro-ph.CO↗
arXiv2026

A universal connection between lens density profiles and low-frequency wave optics in gravitational-wave lensing

We investigate the low-frequency behavior of the amplification factor in gravitational lensing and explore how it encodes information about the density profile of the lensing object. We derive the low-frequency expansion of the amplification factor under the Born approximation for a broad class of projected density profiles. For spherically symmetric profiles that decay faster than any power law at large distances, we derive a systematic expansion of the amplification factor in powers of frequency, with the logarithmic dependence appearing only in the leading term, and show that each expansion coefficient is determined by a finite set of moments of the density profile. We then extend the analysis to profiles with power-law tails and demonstrate that such profiles induce additional non-analytic frequency dependences, including fractional powers and logarithmic terms, which directly reflect the asymptotic behavior of the density distribution. Furthermore, we investigate the effects of non-sphericity and show that contributions from the quadrupole moment appear only as higher-order corrections relative to the spherically symmetric component in the low-frequency regime. Finally, we investigate the validity of the Born approximation in the low-frequency expansion. We derive a criterion for the maximum order of the low-frequency expansion up to which the Born approximation remains dominant over the post-Born corrections.

astro-ph.CO↗
arXiv2026

Initial clustering of primordial black holes: A general formulation for arbitrary local non-Gaussianity

Initial spatial clustering of primordial black holes (PBHs) induced by local-type non-Gaussianity (LNG) can substantially modify cosmological constraints on PBH abundance. Several inflationary scenarios that enhance curvature perturbations at small scales relevant to PBH formation predict LNG that is not necessarily perturbative. Therefore, it is crucial to establish a theoretical framework capable of investigating the initial clustering induced by arbitrary LNG. Here, we present a general analytical formulation for the PBH two-point correlation function applicable to arbitrary LNGs in the alternative approach. Under the assumptions that PBHs form only at the large peaks of perturbations, and that large-scale modes weakly modulate the local variance of small-scale perturbations, we derive an analytic expression for the PBH bias parameter, directly connecting initial clustering to the primordial trispectrum in the collapsed limit. We demonstrate the versatility of our formula by computing the bias parameters in the ultra-slow-roll inflation, curvaton, and modulated reheating scenarios. We also formally generalize the framework to broad power spectra to account for correlations across different PBH mass scales. Because our formulation does not rely on weak or perturbative non-Gaussianity assumptions, our result provides a universal theoretical basis for evaluating initial clustering impact on PBH observables.

astro-ph.CO↗