Old age and super-solar metallicity in a massive z~1.4 early-type galaxy from VLT/X-Shooter spectroscopy

Ilaria Lonoce, Marcella Longhetti, Claudia Maraston, Daniel Thomas, Chiara Mancini, Andrea Cimatti, Federica Ciocca, Annalisa Citro, Emanuele Daddi, Sperello di Serego Alighieri, Adriana Gargiulo, Roberto Maiolino, Filippo Mannucci, Michele Moresco, Lucia Pozzetti, Salvatore Quai, Paolo Saracco

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We present the first estimate of age, stellar metallicity and chemical abundance ratios, for an individual early-type galaxy at high-redshift (z = 1.426) in the COSMOS field. Our analysis is based on observations obtained with the X-Shooter instrument at the VLT, which cover the visual and near infrared spectrum at high (R >5000) spectral resolution. We measure the values of several spectral absorptions tracing chemical species, in particular Magnesium and Iron, besides determining the age-sensitive D4000 break. We compare the measured indices to stellar population models, finding good agreement. We find that our target is an old (t > 3 Gyr), high-metallicity ([Z/H] > 0.5) galaxy which formed its stars at z_{form} > 5 within a short time scale ~0.1 Gyr, as testified by the strong [\alpha/Fe] ratio ( > 0.4), and has passively evolved in the first > 3-4 Gyr of its life. We have verified that this result is robust against the choice and number of fitted spectral features, and stellar population model. The result of an old age and high-metallicity has important implications for galaxy formation and evolution confirming an early and rapid formation of the most massive galaxies in the Universe.
Original languageEnglish
Pages (from-to)3912-3919
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - 21 Dec 2015


  • astro-ph.GA
  • ST/I001204/1
  • RCUK
  • STFC
  • galaxies: elliptical and lenticular, cD
  • galaxies: high-redshift
  • galaxies: stellar content


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