Research

A Salpeter IMF and an NFW halo: disentangling the dark and stellar mass of an elliptical galaxy through precise lens modelling of a double-source-plane system

arXiv

Figure 1 from the IMF and NFW halo paper — Figure 1

Figure 2 from the IMF and NFW halo paper — Figure 2

Abstract

We use the double-source-plane lens J0946+1006 to separate stellar and dark matter components with a flexible two-component mass model. The stellar light is described with a multi-Gaussian expansion, a free global $M/L$, and an allowed radial $M/L$ gradient, while the halo is modeled as an elliptical generalized NFW profile. The extra leverage from the double-source-plane geometry helps suppress the mass-sheet transformation and tighten constraints on the radial mass profile.

Even with this freedom, the preferred solution remains close to the canonical picture of a massive elliptical galaxy: an almost constant stellar $M/L$ with Salpeter-like IMF normalization and a halo consistent with NFW. The inferred parameters are $M_{\star}=4.4^{+0.25}_{-0.39}\times10^{11}\,M_{\odot}$, $\gamma_{\rm in}^{\rm halo}=1.04^{+0.10}_{-0.14}$, and $M_{200}^{\rm halo}=1.11^{+0.37}_{-0.32}\times10^{13}\,M_{\odot}$, suggesting a practical template for future Euclid double-source-plane lens analyses.

Figure 5 from the IMF and NFW halo paper — Figure 5

Cosmology from large populations of galaxy-galaxy strong gravitational lenses

arXiv

Abstract

Future wide-area surveys should discover more than $10^4$ galaxy-galaxy strong lenses, opening the door to cosmological inference from whole lens populations rather than only a few exceptional systems. This paper develops a hierarchical model that jointly fits lens-population parameters and cosmology by combining Einstein-radius measurements with stellar-dynamical mass estimates for every lens.

After marginalizing over lens density profiles and stellar orbital anisotropy, the forecast precision reaches about $\sigma(w)\simeq0.11$ with 10,000 systems, potentially stronger than current single-probe constraints. Applying the method to 161 existing lenses gives $w=-0.96\pm0.46$, and the work also shows how to reduce the impact of possible redshift evolution in the mean density profile of the lens population.

Figure 7 from the large-population strong-lensing cosmology paper — Figure 7

Euclid Quick Data Release (Q1). The Strong Lensing Discovery Engine D -- Double-source-plane lens candidates

arXiv

Figure 1 from the Euclid double-source-plane lens paper — Figure 1

Abstract

Galaxy-scale double-source-plane lenses are rare but especially valuable because the ratio of their Einstein radii depends on the cosmological scaling factor $\beta$, while the systems also probe lens density profiles and dark-matter substructure. In Euclid Q1, four new double-source-plane lens candidates were identified through a combination of machine-learning lens finders and subsequent visual inspection by citizens and experts.

Using the widely used LensPop forecast model, the paper predicts roughly $1700$ double-source-plane lenses over the full Euclid survey, corresponding to about $6\pm3$ systems in the $63\,\mathrm{deg}^2$ Q1 area, consistent with the current detections. Initial lens models and $\beta$ estimates are presented for each candidate, demonstrating Euclid's ability to build statistically useful samples of these rare systems.

Correcting for selection biases in the determination of the Hubble constant from time-delay cosmography

arXiv

Abstract

Time-delay cosmography measures $H_0$ from the delays between multiple images of lensed quasars, but the dominant systematic comes from the mass-sheet transform, which leaves lensing observables unchanged while shifting the inferred Hubble constant. This work tests whether galaxy-galaxy lenses and galaxy-quasar lenses really share the same density-profile family by modeling the parent deflector population with separate stellar and dark-matter components and by explicitly modeling the selection functions for both lens samples.

A power-law profile plus an internal mass sheet remains a good approximation near the Einstein radius, but galaxy-galaxy lenses are found to prefer systematically larger mass-sheet contributions than galaxy-quasar lenses. Propagating that difference through the TDCOSMO framework lowers the inferred Hubble constant by a further $\sim3\%$, yielding $H_0 = 66\pm4\ \mathrm{(stat)} \pm 1\ \mathrm{(model\ sys)} \pm 2\ \mathrm{(measurement\ sys)}\ \mathrm{km}\ \mathrm{s}^{-1}\ \mathrm{Mpc}^{-1}$ for the combined TDCOSMO plus SLACS data set.

Figure 3 from the time-delay cosmography selection-bias paper — Figure 3

Intra-day variability of BL Lacertae from 2016 to 2018

arXiv

Abstract

BL Lacertae was monitored in the $B$, $V$, $R$, and $I$ bands on 14 nights during 2016-2018, and significant intra-day variability was detected on 12 of those nights. The colour-magnitude analysis shows a clear bluer-when-brighter trend, with at least part of that chromatic behaviour driven by larger variability amplitudes at shorter wavelengths.

The variability patterns in different optical bands are tightly correlated, and the analysis finds no measurable inter-band time lag. Together, the data indicate rapid but coherent optical variability across the monitored bands.