Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 454, Issue 4, Pages 3912-3919Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stv2150
Keywords
galaxies: elliptical and lenticular, cD; galaxies: high-redshift; galaxies: stellar content
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Funding
- grant Prin-INAF [1.05.09.01.05]
- grant PRIN MIUR
- Science, Technology and Facilities Council through the Survey Cosmology and Astrophysics consolidated grant [ST/I001204/1]
- STFC [ST/K00090X/1, ST/M001172/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/K00090X/1, ST/M001172/1] Funding Source: researchfish
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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 (Cosmological Evolution Survey) field. Our analysis is based on observations obtained with the X-Shooter instrument at the Very Large Telescope (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 similar to 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.
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