Fundamental physics with ESPRESSO: Precise limit on variations in the fine-structure constant towards the bright quasar HE 0515$-$4414
Creators: name: Murphy, Michael T.
name: Molaro, Paolo
name: Leite, Ana C. O.
name: Cupani, Guido
name: Cristiani, Stefano
name: D'Odorico, Valentina
name: Santos, Ricardo Génova
name: Martins, Carlos J. A. P.
name: Milaković, Dinko
name: Nunes, Nelson J.
name: Schmidt, Tobias M.
name: Pepe, Francesco A.
name: Rebolo, Rafael
name: Santos, Nuno C.
name: Sousa, Sérgio G.
name: Osorio, Maria-Rosa Zapatero
name: Amate, Manuel
name: Adibekyan, Vardan
name: Alibert, Yann
name: Prieto, Carlos Allende
name: Baldini, Veronica
name: Benz, Willy
name: Bouchy, François
name: Cabral, Alexandre
name: Dekker, Hans
name: Di Marcantonio, Paolo
name: Ehrenreich, David
name: Figueira, Pedro
name: Hernández, Jonay I. González
name: Landoni, Marco
name: Lovis, Christophe
name: Curto, Gaspare Lo
name: Manescau, Antonio
name: Mégevand, Denis
name: Mehner, Andrea
name: Micela, Giuseppina
name: Pasquini, Luca
name: Poretti, Ennio
name: Riva, Marco
name: Sozzetti, Alessandro
name: Mascareño, Alejandro Suárez
name: Udry, Stéphane
name: Zerbi, Filippo
Publisher: name: arXiv
Year: 2021
Subjects: subject: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: The strong intervening absorption system at redshift 1.15 towards the very bright quasar HE 0515$-$4414 is the most studied absorber for measuring possible cosmological variations in the fine-structure constant, $α$. We observed HE 0515$-$4414 for 16.1$\,$h with the Very Large Telescope and present here the first constraint on relative variations in $α$ with parts-per-million (ppm) precision from the new ESPRESSO spectrograph: $Δα/α= 1.3 \pm 1.3_{\rm stat} \pm 0.4_{\rm sys}\,{\rm ppm}$. The statistical uncertainty (1$σ$) is similar to the ensemble precision of previous large samples of absorbers, and derives from the high S/N achieved ($\approx$105 per 0.4$\,$km$\,$s$^{-1}$ pixel). ESPRESSO's design, and calibration of our observations with its laser frequency comb, effectively removed wavelength calibration errors from our measurement. The high resolving power of our ESPRESSO spectrum ($R=145000$) enabled the identification of very narrow components within the absorption profile, allowing a more robust analysis of $Δα/α$. The evidence for the narrow components is corroborated by their correspondence with previously detected molecular hydrogen and neutral carbon. The main remaining systematic errors arise from ambiguities in the absorption profile modelling, effects from redispersing the individual quasar exposures, and convergence of the parameter estimation algorithm. All analyses of the spectrum, including systematic error estimates, were initially blinded to avoid human biases. We make our reduced ESPRESSO spectrum of HE 0515$-$4414 publicly available for further analysis. Combining our ESPRESSO result with 28 measurements, from other spectrographs, in which wavelength calibration errors have been mitigated, yields a weighted mean $Δα/α= -0.5 \pm 0.5_{\rm stat} \pm 0.4_{\rm sys}\,$ppm at redshifts 0.6-2.4.
description: Accepted by A&amp;A. The ESPRESSO quasar spectrum, reduced contributing exposures, and absorption profile fits are available at https://github.com/MTMurphy77/ESPRESSO_HE0515-4414