arXiv subjects

Fernando Valenciano

Publications and source records attributed to Fernando Valenciano.

3 recordsLinked to original sources

arXiv2026

Decisive evidence for a global cosmic-ray feature in gamma-ray data

We analyze 17 years of Fermi-LAT data to study the diffuse $\gamma$-ray emission along the Galactic plane and its connection to cosmic-ray (CR) propagation. Accounting for correlated instrumental systematics, we find decisive evidence for a spectral break at $\sim20-30$ GeV, present across the inner Galactic disk, with a preference of $\Delta\chi^2=39.78$ ($4.44 \sigma$ global). The energy and amplitude of this feature are in striking agreement with the spectral feature observed in local CR nuclei, indicating that it is a global property of the Galactic disk rather than a local phenomenon. The measured slope change, $\Delta\gamma \simeq 0.20$, is consistent with local CR data and with expectations from a transition in the CR diffusion regime from Kolmogorov to Kraichnan turbulence. Our results provide strong evidence that diffuse $\gamma$-ray emission along the Galactic disk is dominated by $\pi^0-$decay emission up to a hundred GeV. These findings provide key insights into the origin of the CR spectral hardening and the propagation of CRs throughout the Galaxy, and illustrate how this multimessenger approach can be used to probe the origin of features in the CR spectra, such as the long-studied CR Knee.

astro-ph.HE↗

arXiv2026

The Impact of Star Formation Histories on the Inner Dark Matter Density Slopes of Galaxies

Aims. We aim to investigate the connection between star formation histories (SFHs) and the inner dark matter density profiles of simulated galaxies. In particular, we test whether the burstiness and temporal distribution of star formation influence the formation of cored versus cuspy dark matter profiles. Methods. We homogeneously analysed simulated galaxies from the NIHAO and FIRE-2 projects. For each galaxy, we derived dark matter density profiles and measured the logarithmic slope in the inner region of the dark matter halo (1-2% of R$_{\rm vir}$). To characterise star formation burstiness, we introduced a criterion based on comparing the star formation rate (SFR) averaged over two distinct timescales. We further quantified the temporal concentration of SFHs by computing $M_{\star, \rm post}$ / $M_{\star, \rm pre}$, the ratio of stellar mass formed after versus before the epoch of reionisation at redshift z $\sim$ 6.5. Results. Homogeneous analysis reveals that inner slope versus stellar-to-halo mass ratio trends for NIHAO and FIRE-2 galaxies are in much better agreement than reported in previous works. The burstiness and post-to-pre reionisation stellar mass ratio of the SFH explain the scatter in the inner slope versus stellar-to-halo mass ratio relation, revealing that galaxies with above average burstiness and more extended SFHs are more efficient at developing cored dark matter profiles. In contrast, galaxies with smoother SFHs and earlier stellar mass assembly tend to maintain cuspier dark matter profiles. We present an analytic expression that improves predictions for the inner slope using the parameter $M_{\star \rm,post}$ / $M_{\star \rm,pre}$, which reduces the mean squared error in both simulation suites relative to previous formulations based solely on the stellar-to-halo mass ratio.

astro-ph.GA↗

arXiv2025

Cored galaxies in cuspy dark matter halos

We investigate constraints on the inner stellar density profile from photometric data of dwarf spheroidal and ultra-faint dwarf galaxies. Our aim is to clarify under what conditions cored stellar profiles require dark matter halos that are also cored, deviating from the cuspy profiles expected for cold dark matter halos. We consider a variety of spherically symmetric stellar profiles, which we classify as "strong" or "weak" cores and cusps according to the behavior of the slope ($b_0$) and logarithmic slope ($\gamma_0$) at their centers. We explore which profiles lead to unphysical negative distribution functions when embedded in a cuspy halo, treating isotropic and anisotropic kinematics separately. We find that weakly-cored stellar profiles in 3D (i.e., $b_0 \neq 0$, $\gamma_0=0$) can be consistent with cuspy dark matter profiles, but strong 3D cores ($b_0=\gamma_0=0$) are not. However, both weak and strong 3D cores yield nearly indistinguishable inner profiles in projection, which implies that ruling out a dark matter cusp from photometric data alone is highly challenging. As an example, we study the profiles of ultra-faint dwarf galaxies and find that they are consistent with both weak and strong 3D cores. This is not just a result of the limited numbers of stars in these systems, since we reach the same conclusion even for Fornax, one of the most luminous and best-studied dwarf spheroidal companions of the Milky Way. We conclude that, based on current data and analysis techniques, cored surface density profiles in nearby dwarf galaxies cannot be taken as strong evidence against the presence of cuspy dark matter halos.

astro-ph.GA↗