arXiv subjects

V. Fernandez

Publications and source records attributed to V. Fernandez.

6 recordsLinked to original sources

arXiv2022

Spatially-resolved chemodynamics of the starburst dwarf galaxy CGCG 007-025: Evidence for recent accretion of metal-poor gas

Nearby metal-poor starburst dwarf galaxies present a unique opportunity to probe the physics of high-density star formation with a detail and sensitivity unmatched by any observation of the high-z Universe. Here we present the first results from a chemodynamical study of the nearby, gas-rich starburst dwarf CGCG 007-025. We use VLT/MUSE integral field spectroscopy to characterise the properties of the star-forming (SF) gas, from its metal content to its kinematics. The star formation rate (SFR) surface density presents a clumpy distribution, with the brightest knot hosting a 5 Myr young, Wolf-Rayet (WR) population (revealed by the presence of the characteristic 5808\AA~WR bump). The ionised gas kinematics are dominated by disordered motions. A superposition of a narrow ($\sigma \approx$ 50 km s$^{-1}$), intermediate (150 km s$^{-1}$) and broad (1000 km s$^{-1}$) kinematic components are needed to model the emission line profiles in the brightest SF region, suggesting the presence of energetic outflows from massive stars. The gas-phase metallicity of the galaxy spans 0.6 dex and displays a strong anti-correlation with SFR surface density, dropping to 12+log(O/H) = 7.7 in the central SF knot. The spatially-resolved BPTs indicates the gas is being ionised purely by SF processes. Finally, the anti-correlation between the SFR and the gas metallicity points out to accretion of metal-poor gas as the origin of the recent off-centre starburst, in which the infalling material ignites the SF episode.

astro-ph.GA↗

arXiv2022

A theoretical model for tellurite-sulfates Na$_2$Cu$_5$(TeO$_3$)(SO$_4$)$_3$(OH)$_4$ and K$_2$Cu$_5$(TeO$_3$)(SO$_4$)$_3$(OH)$_4$

A theoretical model for two new tellurite-sulfates, namely Na$_2$Cu$_5$(TeO$_3$)(SO$_4$)$_3$(OH)$_4$ and K$_2$Cu$_5$(TeO$_3$)(SO$_4$)$_3$ (OH)$_4$ is determined to be compatible with ab-initio calculations. The results obtained in this work show that some previous speculations in the literature about the couplings are correct, obtaining a model with a mixture of ferromagnetic and antiferromagnetic couplings. We use a combination of numerical techniques to study the magnetic properties of the model. Our numerical calculations based on the density-matrix renormalization group method reveal that the system presents Ising-like magnetization plateaux at rational values of the saturation magnetization.

cond-mat.str-el↗

arXiv2022

The Far-Ultraviolet Continuum Slope as a Lyman Continuum Escape Estimator at High-redshift

Most of the hydrogen in the intergalactic medium (IGM) was rapidly ionized at high-redshifts. While observations have established that reionization occurred, observational constraints on the emissivity of ionizing photons at high-redshift remains elusive. Here, we present a new analysis of the Low-redshift Lyman Continuum Survey (LzLCS) and archival observations, a combined sample of 89 star-forming galaxies at z~0.3 with Hubble Space Telescope observations of their ionizing continua (or Lyman Continuum, LyC). We find a strong (6$\sigma$ significant) inverse correlation between the continuum slope at 1550\r{A} (defined as F$_\lambda\propto\lambda^{\beta}$) and both the LyC escape fraction (f$_{esc}$) and f$_{esc}$ times the ionizing photon production efficiency ($\xi_{ ion}$). On average, galaxies with redder continuum slopes have smaller f$_{esc}$ than galaxies with bluer slopes due to higher dust attenuation. More than 5% (20%) of the LyC emission escapes galaxies with $\beta$<-2.1 (-2.6). We find strong correlations between $\beta$ and the gas-phase ionization ([OIII]/[OII] flux ratio; at 7.5$\sigma$ significance), galaxy stellar mass (at 5.9$\sigma$), the gas-phase metallicity (at 4.6$\sigma$), and the observed FUV absolute magnitude (M$_{UV}$ at 3.4$\sigma$). Using previous observations of $\beta$ at high-redshift, we estimate the evolution of f$_{esc}$ with both $z$ and M$_{UV}$. The LzLCS suggest that fainter and lower mass galaxies dominate the ionizing photon budget at higher redshift, possibly due to their rapidly evolving metal and dust content. Finally, we use our correlation between $\beta$ and f$_{ esc}\times\xi_{ion}$ to predict the ionizing emissivity of galaxies during the epoch of reionization. Our estimated emissivities match IGM observations, and suggest that star-forming galaxies emit sufficient LyC photons into the IGM to exceed recombinations near redshifts of 7-8.

astro-ph.GA↗

arXiv2010

Quantum key distribution system in standard telecommunications fiber using a short wavelength single-photon source

A demonstration of the principles of quantum key distribution is performed using a single-photon source in a proof of concept test-bed over a distance of 2 km in standard telecommunications optical fiber. The single-photon source was an optically-pumped quantum dot in a microcavity emitting at a wavelength of 895 nm. Characterization of the quantum key distribution parameters was performed at a range of different optical excitation powers. An investigation of the effect of varying the optical excitation power of the quantum dot microcavity on the quantum bit error rate and cryptographic key exchange rate of the system are presented.

quant-ph↗

arXiv2007

Low Timing Jitter Detector for Gigahertz Quantum Key Distribution

A superconducting single-photon detector based on a niobium nitride nanowire is demonstrated in an optical-fibre-based quantum key distribution test bed operating at a clock rate of 3.3 GHz and a transmission wavelength of 850 nm. The low jitter of the detector leads to significant reduction in the estimated quantum bit error rate and a resultant improvement in the secrecy efficiency compared to previous estimates made by use of silicon single-photon avalanche detectors.

quant-ph↗

arXiv2006

Quantum key distribution system clocked at 2 GHz

An improved quantum key distribution test system operating at clock rates of up to 2GHz using a specially adapted commercially available silicon single photon avalanche diode is presented. The use of improved detectors has improved the fibre-based test system performance in terms of transmission distance and quantum bit error rate.

quant-ph↗