Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 2609.34955

Far-Ultraviolet diffuse emission as a tracer of Galactic extinction at the North Galactic Pole

Swagat Bordoloi·P. Shalima·Rupjyoti Gogoi·Jayant Murthy·Oleg Malkov
View original source ↗Read source document ↗Export metadata ↓

Abstract

Interstellar extinction at high Galactic latitude is often traced by thermal dust emission, but the conversion from infrared surface brightness to reddening is sensitive to grain properties and temperature. We test dust-scattered far-ultraviolet (FUV) and near-ultraviolet (NUV) diffuse emission as a high-resolution extinction tracer towards the North Galactic Pole (NGP), where E(B-V) < 0.1 mag. Using the GALEX diffuse maps of Murthy (2014), we build FUV and NUV intensity maps at 6' resolution over the region b > 70 deg and compare them with the Planck E(B-V) map at matched resolution. A direct pixel-to-pixel regression gives only moderate correlations (rho = 0.536 for FUV, 0.243 for NUV) owing to high per-pixel scatter from H2 fluorescence, line emission, and photon-counting noise; we therefore construct per-pixel GALEX uncertainty maps and apply a centroid-fitting method that fits the mean intensity in bins of E(B-V) after rejection of outliers via iterative sigma-clipping, recovering tight relations (rho = 0.993 for FUV, 0.976 for NUV). We find the best-fit relations for the FUV and NUV intensity per 6'x6' pixel: FUV = 2285.3 E(B-V) + 278.6 and NUV = 1517.6 E(B-V) + 547.2 (photons/cm^2/s/sr/A), inverted to produce a 601x601 GALEX reddening map. GALEX E(B-V) correlates strongly with HI column density from the all-sky HI4PI survey (rho = 0.991). We validate the maps using SDSS quasars as extragalactic extinction calibrators: quasar extinctions from the GALEX and Planck maps agree with a correlation of 0.99 and a slope of 0.986. Comparison with the Pan-STARRS1 stellar reddening map of Schlafly et al. (2014) shows the GALEX-based values have a smaller mean difference (0.039 mag) than the Planck-based values (0.064 mag). These results establish dust-scattered FUV diffuse emission as a viable alternative to thermal-dust extinction maps at high Galactic latitude.

Explore related subjects

astro-ph.GA

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Swagat Bordoloi, P. Shalima, Rupjyoti Gogoi, Jayant Murthy, Oleg Malkov. 2026-09-28. Far-Ultraviolet diffuse emission as a tracer of Galactic extinction at the North Galactic Pole. https://arxiv.org/abs/2609.34955

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

KEEP EXPLORING

Related papers

arXiv2026

LMC-induced Perturbations in the Milky Way Halo:I. HaloDance Simulation Suite and Observational Forecasts

The gravitational interaction between the Milky Way (MW) and the Large Magellanic Cloud (LMC) perturbs the MW halo's density and kinematics, encoding information about both galaxies' masses and structures. We present a suite of 2,848 high-resolution ($10^7$ particles) N-body simulations that systematically vary the mass and shape of both galaxies' haloes. We model how the mean velocities and velocity dispersions of halo stars (30--120 kpc) depend on system parameters, and forecast constraints achievable with current and future observations. Assuming Gaia DR3-level astrometry, 20 km/s radial velocity precision, 10% distance precision, and a sample of $\sim$4,000 RR Lyrae stars, we achieve 1$σ$ uncertainties of $0.11 \times 10^{12} M_\odot$ in MW mass, $2.33 \times 10^{10} M_\odot$ in LMC mass, 2.38 in halo concentration ($c$), and 0.06 in halo flattening ($q$). These correspond to fractional uncertainties of 11%, 16%, 25%, and 6% respectively, relative to fiducial values. Improved Gaia proper motions (DR5) yield modest gains (up to 14%), while adding radial velocities improves constraints by up to 60% relative to using Gaia astrometry alone. Doubling the sample size to $\sim$8,000 stars yields an additional 30% improvement, whereas reducing distance uncertainties has minimal impact ($\le$10%). Mean velocities trace LMC-induced perturbations, while velocity dispersions constrain MW halo properties, jointly breaking degeneracies. Our results demonstrate that combining Gaia astrometry with large spectroscopic surveys will enable precise characterization of the MW-LMC system. This methodology paper establishes the framework for interpreting observations; future work will apply these tools to existing spectroscopic datasets. The full simulation suite, HaloDance, will be made publicly available at: https://github.com/Yanjun-Sheng/HaloDance.

astro-ph.GA↗
arXiv2026

Gravitational Waves from Cosmic Dawn: Tracing Cosmic Black Hole Binaries with ET, LGWA, and LISA

Next-generation detectors, such as LISA, LGWA, and ET, will for the first time probe the high redshift Universe, offering unique insight into the birth, growth, and dynamics of the first black holes (BHs) during their earliest stages of formation. We aim to predict merger rates and gravitational wave (GW) signatures of "cosmic" binary BHs forming as a result of galaxy mergers at $z\geq 4$. We investigate how BH seeding, accretion physics, and dynamical delays affect their properties and detectability across cosmic epochs. We used the semi-analytic model Cosmic Archaeology Tool (CAT) to trace the evolution and delayed mergers, driven by dynamical friction, of BH binaries formed from light, medium-weight, and heavy seeds under Eddington-limited (EL) and super-Eddington (SE) accretion prescriptions. We employed the GWFish package to evaluate their GW signals and detectability by LISA, LGWA, and ET. Our results show the impact of BH accretion and seeding prescriptions on the properties and distribution of detectable sources. In the EL model, the detected populations are dominated by nearly equal-mass binaries ($\tilde{q} = 0.7$). In contrast, SE growth leads to lower mass ratios for LISA detections ($\tilde{q} \sim 0.2$) and medium ratios for ET and LGWA ($\tilde{q} \sim 0.4$ and $0.3$, respectively). We present the total detection rates predicted under the two accretion scenarios. The SE model allows BHs to grow faster, transferring a significant fraction of detectable systems from the ET band to the LISA band, compared to the EL model. As a result, the predicted LISA detection rate increases from ~ 32 yr$^{-1}$ in the EL case to ~ 64 yr$^{-1}$ in the SE scenario, and the ET detection rate reduces from ~ 64 yr$^{-1}$ in the EL model to only ~ 4 yr$^{-1}$ in the SE scenario. In both scenarios, LGWA yields comparable detection rates (~ 21 yr$^{-1}$ in EL and ~ 12 yr$^{-1}$ in SE).

astro-ph.GA↗
arXiv2026

The Radio-FIR Correlation in the Context of Deep Radio Source Counts

Increasingly deep, confusion-limited radio surveys have pushed direct radio source-count measurements down to tens of $μ$Jy at 1.4 GHz. Confusion-noise P(D) analyses extend the statistical counts to below $1\,\mathrm{μJy}$. Radio source counts have allowed for constraints on the radio-derived star formation rate density (SFRD) history through models of the backwards evolution of the local radio luminosity function, using the radio-FIR correlation, $q \propto \log(L_{\mathrm{FIR}}/L_{1.4})$, to convert radio luminosities to FIR luminosities and hence star-formation rates. Recent deep radio source counts from MeerKAT suggest a potential tension in the SFRD history between radio and UV/IR measurements at $1\lesssim z\lesssim 2$. This corresponds to a $\gtrsim 3σ$ discrepancy between the predicted and measured source counts near the star forming galaxy source count $S^2n(S)$ peak of ${\sim}30\,\mathrm{μJy}$ under both a pure luminosity (PLE) and combined luminosity and density evolution (LADE). We consider what the requirement of agreement between radio source counts and the observed UV/IR SFRD indicates about the redshift evolution of the radio-FIR correlation and its intrinsic scatter out to $z=3$. We introduce a radio-luminosity based parameterization to $q_{\mathrm{FIR}}(z)$ based on changing thermal radio fractions alone that agrees with the observed stellar-mass dependent $q_{\mathrm{FIR}}(z)$ better than a non-evolving or decreasing $q_{\mathrm{FIR}}(z)$. Despite this, we find that a decreasing $q_{\mathrm{FIR}}(z)$ at fixed radio luminosity provides better agreement between source counts and the observed SFRD, while a $q_{\mathrm{FIR}}(z)$ that breaks down due to cosmic ray losses requires an intrinsic scatter up to $σ_q\approx 0.3\,\mathrm{dex}$.

astro-ph.GA↗