A new measurement of the expansion history of the Universe at z=1.26 with cosmic chronometers in VANDELS

Understand

We derive a new constraint on the expansion history of the Universe by applying the cosmic chronometers method, studying the age evolution of high-redshift galaxies with a full-spectral-fitting approach.

• We select a sample of 39 massive ($log(M/M_\odot)>10.8$) and passive ($log(sSFR/yr^{-1})<-11$) galaxies from the data release 4 of the VANDELS survey at $1<z<1.5$, combining different selection criteria to minimize the potential contamination by star-forming outliers.
• We perform full-spectral-fitting jointly on spectra and photometry of our sources with the code BAGPIPES, without any cosmological assumption on the age of the population.
• The derived physical properties of the selected galaxies are characteristic of a passive population, with short star formation timescales ($<\tau>=0.28\pm0.02$ Gyr), low dust extinction ($<A_{V,dust}>=0.43\pm0.02$ mag), and sub-solar metallicities ($<Z/Z_{\odot}>=0.44\pm0.01$).