Data On Galaxies

Are active galactic nuclei (AGNs) exceptions to the Tully-Fischer rule or are they just hard to measure?

Active galactic nuclei have sometimes been excluded from Tully-Fischer fits because the underlying data points have high uncertainties, due to their low inclinations relative to solar system based observers leading, in turn, to "large scatter" although the magnitude of the scatter really isn't all that high for fairly imprecise astronomy measurements of distant galaxies.

The small data set in a new paper doesn't really bely that but these may also be galaxies which are out of equilibrium or have non-gravitational forces (e.g., the massive nuclear forces involved in star formation) that are relevant and significant in their dynamics. The authors of a new paper note that:

While the samples used to calibrate the canonical TF relations did not explicitly flag AGNs for removal (Tully& Pierce 2000; Tully et al. 2008; Tully&Courtois 2012; Kourkchi et al. 2020a), the selection criteria generally exclude active galaxies. Primarily, all works above select spirals with inclinations greater than 45◦. As Type 1 AGNs have been observed to be preferentially hosted by face-on (<45◦) galaxies (Keel 1980; Maiolino & Rieke 1995; McLeod & Rieke 1995; Simcoe et al. 1997; Gkini et al. 2021), this criterion naturally excludes a significant amount of Seyfert 1 hosts. The nuclear flux from unobscured Type 1 AGNs represents the primary expected source of photometric scatter in TF relations, whereas the high levels of nuclear obscuration inherent in Type 2 systems are expected to largely mitigate such contamination.

Visually, their data set does show high AGN scatter but also shows big error bars largely consistent with the baryonic Tully-Fischer relation.

We present an investigation of the Tully-Fisher (TF) relation solely for galaxies hosting an active galactic nucleus (AGN). Using 22 galaxies with primary, z-independent distances, we find that active galaxies exhibit significantly larger scatter about all TF relations compared to each respective calibration for (largely) inactive galaxies. 

The larger scatter persists despite removal of the AGN contamination from the photometry of the Type 1 AGNs via 1) careful surface brightness decompositions or 2) employing SEDs to constrain the light contribution of the AGN. These results suggest that the influence of an AGN on its host galaxy's surface brightness may extend beyond the nucleus. 

We also calculate the percentage difference between TF and primary distances, and find that TF-based distances are biased towards overestimation of the primary distances to active galaxies by anywhere from 5-10 percent for the optical/near-infrared and approximately 15 percent for distances predicted from inverting the Baryonic TF (BTF) relation. As TF-based distances (especially the I-band) are relied on heavily for analysis and modeling of the local peculiar velocity (Vpec) field, we suggest that active galaxies be removed from future Vpec modeling samples.

Justin H. Robinson, et al., "On the Tully-Fisher Relation for Active Galaxies -- I: Evidence of Larger Scatter" arXiv:2606.22575 (June 21, 2026) (Accepted for publication in ApJ).

In one context, a new paper (which also has a small sample size) finds that inferred spherical dark matter halos aren't ruled out, although slightly flattened halos are still preferred.

Wide-field surveys like Euclid mark a new era of extragalactic stellar stream studies. With a large number of streams, it is now possible to constrain the dark matter halos of galaxies in a cosmological volume and draw comparisons to theoretical expectations for the geometry of dark matter halos. 

This study combines Euclid imaging with visual detection and segmentation annotations to analyse streams. We use projected stream morphologies to constrain the shape and centre-of-mass position (CoM) of each host galaxy's potential, jointly probing baryonic and dark matter distributions. These inferences complement weak lensing methods, with sensitivity to halo profile and geometry on sub-virial scales. The method enables both stacked, population-level constraints on halo flattening and CoM position, and constraints on these quantities for individual halos. 

We also present a novel method for transforming segmentation maps of stellar streams into smooth, curvature-preserving tracks optimised for fast and robust dynamical inference. This approach enables rapid modelling of stream morphology, supports a statistically rigorous combination of constraints across multiple streams within a single galaxy, and enables joint inference across galactic hosts. 

From our study of 13 galaxies with prominent tidal streams, we find agreement with spherical halos, albeit a mild preference for flattening with q=0.95+0.05−0.10 at 68% confidence. This is promising early agreement with ΛCDM predictions. 

With thousands more discovered streams expected across Euclid's mission, our programme will enable precise measurements of halo shapes and CoM positions across large samples and redshifts, offering constraints on the geometry of dark matter halos.

Euclid Collaboration, "Euclid Quick Data Release (Q1): The geometry of dark matter halos from extragalactic streams" arXiv:2606.21774 (June 19, 2026) (Submitted to A&A).

A Hot Hypothesis For Neptune And Uranus

Normally, I don't write much about planetary astronomy, not because there's anything wrong with the discipline, but because I'm concerned mostly with the quest to determine the fundamental laws of physics, and planetary astronomy is basically unrelated to that. But this paradigm shifting interpretation of the data regarding Uranus and Neptune deserves a mention.

Uranus and Neptune are commonly interpreted as volatile-rich "ice giants", an assumption that underpins most interior models. 

Here we show that their observed radii, bulk densities, gravitational harmonics, normalized moments of inertia, intrinsic luminosities, and key features of their atmospheric compositions are consistent with interiors comprising supercritical, hydrogen-rich magma oceans overlain by H2-rich envelopes. 

Our results, based on three fit parameters for each planet, provide a parsimonious explanation for the structures, thermal states, and atmospheric chemistries of Uranus and Neptune. We find that the Solar System's ice giants are better understood as magma-ocean giants, with origins parallel to those of sub-Neptune gas-dwarf planets. A continuum among gas dwarf planets permits Neptune and Uranus to serve as accessible, data-driven test cases for structure models and material properties used to understand sub-Neptunes.

Edward D. Young, Sarah P. Marcum, Aaron Werlen, Paula N. Wulff, "Ice Giants Revisited: Uranus and Neptune as Magma Ocean Worlds" arXiv:2606.18219 (June 16, 2026).

More Cosmology Limits On Neutrino Mass

In principle, the sum of the three neutrino masses and the number of neutrino types can be determined from astronomy observations in the context of a cosmology model. 

In practice, to a certain extent this determination is model dependent, although the estimates are consistently quite a bit less than 150 meV at the two sigma level. This is far less than the current 1410 meV lower bound (expected to be ultimately reduced to 660 meV) set by direct measurements of lightest of the three neutrino mass eigenstates in the Katrin experiment (currently 450 meV but expected to reach 200 meV once the experiment runs its course). 

Even fairly extreme tweaks to dark energy assumptions and a prior that the sum of the neutrino masses can't be less than the minimum established by neutrino oscillation experiments, in the paper below sets of cap of about 115 meV. So, the results are robust in the general vicinity of absolute neutrino masses, even if their specific limits vary by scores of meVs from each other.

Like other cosmology based absolute neutrino mass estimates, it doesn't absolutely rule out an inverted neutrino mass hierarchy, but it disfavors one in a statistically significant manner with fairly mild assumptions.

The effective number of neutrino types determined from cosmology measurements is more robust and overwhelming a fit to three types (plus an expected adjustment for radiation), ruling out additional sterile neutrinos with masses on the order of 10 eV or less (N(eff) is not sensitive to heavier neutrinos). 

This doesn't rule out seesaw neutrino mass models (which can involve very heavy sterile neutrinos) or sterile neutrino warm dark matter (which characteristically has keV scale masses), but it does seriously limit sterile neutrino explanations of anomalies in neutrino oscillation experiments (which tellingly are frequently inconsistent with each other).

We present a robust assessment of cosmological constraints on the sum of neutrino masses (∑mν) when relaxing the standard assumption of purely adiabatic primordial initial conditions. 

Allowing for a neutrino density isocurvature (NDI) component alongside the adiabatic mode, we analyse the latest CMB-SPA combination (Planck 2018, ACT DR6, and SPT-3G), DESI DR2 baryon acoustic oscillation data, and the DES Year 5 supernova sample. Within the ΛCDM model, the 95% upper limit weakens only marginally from ∑mν < 0.052 eV (purely adiabatic) to < 0.057 eV (including NDI), with the NDI amplitude consistent with zero. In the CPL dynamical dark energy model, the adiabatic limit is < 0.111 eV, shifting to < 0.115 eV with NDI, yet the isocurvature mode remains undetected. 

While these limits are robust against the inclusion of isocurvature perturbations, they are highly sensitive to both the assumed dark energy equation of state and the prior lower bound on ∑mν. Notably, the adiabatic ΛCDM limit of 0.052 eV lies below the minimum sum required by the normal neutrino mass hierarchy (0.05878 eV), indicating that this bound is an artifact of the statistical prior extending to zero. Imposing a physically motivated hierarchy-informed prior raises the limit to <0.092 eV. 

Our results demonstrate that current data show no evidence for NDI modes and that the inferred neutrino mass upper limit is robust against this extension, but a definitive, model-independent bound requires addressing prior dependencies and dark energy uncertainties. This work provides the first joint constraint on ∑mν and NDI using the full CMB-SPA+DESI DR2+DES dataset.

Hongsheng Hou, Sai Wang, Zhi-Chao Zhao, Xin Zhang, ""Constraints on the Sum of Neutrino Masses from ACT DR6 and DESI DR2 Considering Isocurvature Initial Conditions" arXiv:2606.17994 (June 16, 2026).