Old age and supersolar metallicity in a massive z ∼ 1.4 early-type galaxy from VLT/X-Shooter spectroscopy

Journal
Date Issued
2015
Author(s)
Lonoce, I.
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•
Maraston, C.
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Thomas, D.
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Mancini, C.
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Cimatti, A.
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Ciocca, F.
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Citro, A.
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Daddi, E.
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di Serego Alighieri, S.
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•
Maiolino, R.
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•
Moresco, M.
•
•
Quai, S.
•
DOI
Description
We are grateful to the anonymous referee for helpful comments on our manuscript. We kindly thank Francesco La Barbera for his precious help in the data reduction and Kyle Westfall for helpful discussions. IL acknowledges the institute of Cosmology and Gravitation of the University of Portsmouth for a brilliant research visit during which a larger part of this project was worked out. IL, ML, AG and PS acknowledge the support from grant Prin-INAF 2012-2013 1.05.09.01.05. AC, LP, MM acknowledge the support from grant PRIN MIUR 2010-2011. CM and DT acknowledge The Science, Technology and Facilities Council for support through the Survey Cosmology and Astrophysics consolidated grant, ST/I001204/1.
Abstract
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 zform >5 within a short time-scale ∼0.1 Gyr, as testified by the strong [α/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.
Volume
454
Issue
4
Start page
3912
Uri
Url
Issn Identifier
0035-8711
Ads BibCode
2015MNRAS.454.3912L
Rights
open.access
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