On the Galactic disc age-metallicity relation (original) (raw)
Related papers
The Galactic Disc Age-Metallicity Relation
Cosmic Chemical Evolution, 2002
New ages are computed for stars in the Solar Neighbourhood from the Edvardsson et al. (1993) data set. Distances derived from the Hipparcos parallaxes were adopted to obtain reliable ages (uncertainty less than 12%) for a subset of stars. There is no apparent age-metallicity relation for stars with an age less than 10 Gyr. Only if we consider older stars a slope of ∼ 0.07 dex/Gyr appears. This relation is compared with those obtained from other methods, i.e. galactic open clusters, stellar population synthesis (star counts), and chemical evolution models.
Dynamical evidence of the age--metallicity relation in the Milky Way disk
Astronomy & Astrophysics, 2006
We studied the relationship between the average stellar abundance of several elements and the orbital evolution of stars in the neighbourhood of the Sun, using both observational data for 325 late-type dwarfs in a volume-complete sample and simulations of the orbital diffusion. Metallicities, ages, and initial position and velocities for the simulated stars are sampled from empirical distributions of these quantities in the Milky Way. We found that that there is a relationship between the average stellar abundance of Fe, Na, Si, Ca, Ni, and Ba and the mean orbital radius of stars currently passing through the solar neighbourhood. The greater the difference between the mean orbital radius and the solar Galactocentric distance, the more deficient the star is, on average, in these chemical species. The stars that take a longer time to come from their birthplaces to arrive in the present solar neighbourhood are more likely to be more metal-poor than those that were born here. This resul...
The age structure of stellar populations in the solar vicinity
Astronomy & Astrophysics, 2013
We analyze a sample of solar neighborhood stars which have high-quality abundance determinations and show that there are two distinct regimes of [α/Fe] versus age which we identify as the epochs of the thick and thin disk formation. A tight correlation between metallicity and [α/Fe] versus age is clearly identifiable for thick disk stars, implying that this population formed from a well mixed interstellar medium, probably initially in starburst and then more quiescently, over a time scale of 4-5 Gyr. Thick disk stars have vertical velocity dispersions which correlate with age, with the youngest objects of this population having small scale heights similar to that of thin disk stars. A natural consequence of these two results is that a vertical metallicity gradient is expected in this population. We suggest that the youngest thick disk set the initial conditions from which the inner thin disk started to form about 8 Gyr ago, at [Fe/H] in the range of (-0.1,+0.1) dex and [α/Fe]∼0.1 dex. This also provides an explanation of the apparent coincidence between the existence of a step in metallicity at 7-10 kpc in the thin disk and the confinement of the thick disk within R<10 kpc. We suggest that the outer thin disk developed outside the influence of the thick disk, giving rise to a separate structure, but also that the high alphaenrichment of those regions may originate from a primordial pollution of the outer regions by the gas expelled from the forming thick disk. Metal-poor thin disk stars ([Fe/H]<-0.4 dex) in the solar vicinity, whose properties are best explained by them originating in the outer disk, are shown to be as old as the youngest thick disk (9-10 Gyr). This implies that the outer thin disk started to form while the thick disk was still forming stars in the inner parts of the Galaxy. Hence, while the overall inner (thick+thin) disks is comprised of two structures with different scale lengths and whose combination may give the impression of an inside-out formation process, the local thin disk itself probably formed its first stars in its outskirts. Moreover, we point out that, given the tight age-metallicity and age-[α/Fe] relations that exist in the thick disk, an inside-out process would give rise to a radial gradient in metallicity and α-elements in this population which is not observed. Finally, we argue that our results leave little room for radial migration (in the sense of churning) either to have contaminated the solar vicinity, or, on a larger scale, to have redistributed stars in significant proportion across the solar annulus.
The Relationship between Age, Metallicity, and Abundances for Disk Stars in a Simulated Milky Way
The Astrophysical Journal
Observations of the Milky Way’s low-α disk show that several element abundances correlate with age at fixed metallicity, with unique slopes and small scatters around the age–[X/Fe] relations. In this study, we turn to simulations to explore the age–[X/Fe] relations for the elements C, N, O, Mg, Si, S, and Ca that are traced in a FIRE-2 cosmological zoom-in simulation of a Milky Way–like galaxy, m12i, and understand what physical conditions give rise to the observed age–[X/Fe] trends. We first explore the distributions of mono-age populations in their birth and current locations, [Fe/H], and [X/Fe], and find evidence for inside-out radial growth for stars with ages <7 Gyr. We then examine the age–[X/Fe] relations across m12i’s disk and find that the direction of the trends agrees with observations, apart from C, O, and Ca, with remarkably small intrinsic scatters, σ int (0.01 − 0.04 dex). This σ int measured in the simulations is also metallicity dependent, with σ int ≈ 0.025 dex ...
Astronomy & Astrophysics, 2014
We study the relationship between age, metallicity, and α-enhancement of FGK stars in the Galactic disk. The results are based upon the analysis of high-resolution UVES spectra from the Gaia-ESO large stellar survey. We explore the limitations of the observed dataset, i.e. the accuracy of stellar parameters and the selection effects that are caused by the photometric target preselection. We find that the colour and magnitude cuts in the survey suppress old metal-rich stars and young metal-poor stars. This suppression may be as high as 97% in some regions of the age-metallicity relationship. The dataset consists of 144 stars with a wide range of ages from 0.5 Gyr to 13.5 Gyr, Galactocentric distances from 6 kpc to 9.5 kpc, and vertical distances from the plane 0 < |Z| < 1.5 kpc. On this basis, we find that i) the observed age-metallicity relation is nearly flat in the range of ages between 0 Gyr and 8 Gyr; ii) at ages older than 9 Gyr, we see a decrease in [Fe/H] and a clear absence of metal-rich stars; this cannot be explained by the survey selection functions; iii) there is a significant scatter of [Fe/H] at any age; and iv) [Mg/Fe] increases with age, but the dispersion of [Mg/Fe] at ages >9 Gyr is not as small as advocated by some other studies. In agreement with earlier work, we find that radial abundance gradients change as a function of vertical distance from the plane. The [Mg/Fe] gradient steepens and becomes negative. In addition, we show that the inner disk is not only more α-rich compared to the outer disk, but also older, as traced independently by the ages and Mg abundances of stars.
The ages and metallicities of galaxies in the local universe
Monthly Notices of …, 2005
We derive stellar metallicities, light-weighted ages and stellar masses for a magnitudelimited sample of 175,128 galaxies drawn from the Sloan Digital Sky Survey Data Release Two (SDSS DR2). We compute median-likelihood estimates of these parameters using a large library of model spectra at medium-high resolution, covering a comprehensive range of star formation histories. The constraints we derive are set by the simultaneous fit of five spectral absorption features, which are well reproduced by our population synthesis models. By design, these constraints depend only weakly on the α/Fe element abundance ratio. Our sample includes galaxies of all types spanning the full range in star formation activity, from dormant early-type to actively starforming galaxies. By analysing a subsample of 44,254 high-quality spectra, we show that, in the mean, galaxies follow a sequence of increasing stellar metallicity, age and stellar mass at increasing 4000Å-break strength. For galaxies of intermediate mass, stronger Balmer absorption at fixed 4000Å-break strength is associated with higher metallicity and younger age. We investigate how stellar metallicity and age depend on total galaxy stellar mass. Low-mass galaxies are typically young and metal-poor, massive galaxies old and metal-rich, with a rapid transition between these regimes over the stellar mass range 3 × 10 9 M * 3 × 10 10 M ⊙ . Both high-and low-concentration galaxies follow these relations, but there is a large dispersion in stellar metallicity at fixed stellar mass, especially for low-concentration galaxies of intermediate mass.
2000
The age-metallicity relation of the solar neighbourhood is studied using a sample of 552 late-type dwarfs. This sample was built from the intersection of photometric catalogues with chromospheric activity surveys of the Mount Wilson group. For these stars, metallicities were estimated from uvby data, and ages were calculated from their chromospheric emission levels using a new metallicity-dependent chromospheric activity-age relation developed by Rocha-Pinto & Maciel (1998). A careful estimate of the errors in the chromospheric age is made. The errors in the chromospheric indices are shown to include partially the effects of the stellar magnetic cycles, although a detailed treatment of this error is still beyond our knowledge. It is shown that the results are not affected by the presence of unresolved binaries in the sample. We derive an age-metallicity relation which confirms the mean trend found by previous workers. The mean metallicity shows a slow, steady increase with time, amo...
Revised ages for stars in the solar neighbourhood
Astronomy & Astrophysics - ASTRON ASTROPHYS, 1998
New ages are computed for the stars from the Edvardsson et al. (1993) data set. The revised values are systematically larger toward older ages (t>4 Gyr), while they are slightly lower for t<4 Gyr. A similar, but considerably smaller trend is present when the ages are computed with the distances based on Hipparcos parallaxes. The resulting age-metallicity relation has a small, but distinct slope of ~ em0.07 dex/Gyr. Tables 3\to8 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or WWW at URL http://cdsweb.u-strasbg.fr/Abstract.html
Astronomy & Astrophysics, 2020
Context. In the era of large spectroscopic surveys, massive databases of high-quality spectra coupled with the products of the Gaia satellite provide tools to outline a new picture of our Galaxy. In this framework, an important piece of information is provided by our ability to infer stellar ages, and consequently to sketch a Galactic timeline. Aims. We aim to provide empirical relations between stellar ages and abundance ratios for a sample of stars with very similar stellar parameters to those of the Sun, namely the so-called solar-like stars. We investigate the dependence on metallicity, and we apply our relations to independent samples, that is, the Gaia-ESO samples of open clusters and of field stars. Methods. We analyse high-resolution and high-signal-to-noise-ratio HARPS spectra of a sample of solar-like stars to obtain precise determinations of their atmospheric parameters and abundances for 25 elements and/or ions belonging to the main nucleosynthesis channels through diffe...
Metallicities and ages of stellar populations at a high Galactic latitude field
Monthly Notices of the Royal Astronomical Society, 2009
We present an analysis of U BV RI data from the Selected Area SA 141. By applying recalibrated methods of measuring ultraviolet excess (UVX), we approximate abundances and absolute magnitudes for 368 stars over 1.3 square degrees out to distances over 10 kpc. With the density distribution constrained from our previous photometric parallax investigations and with sufficient accounting for the metallicity bias in the UVX method, we are able to compare the vertical abundance distribution to those measured in previous studies. We find that the abundance distribution has an underlying uniform component consistent with previous spectroscopic results that posit a monometallic thick disk and halo with abundances of [F e/H] = −0.8 and −1.4, respectively. However, there are a number of outlying data points that may indicate contamination by more metal-rich halo streams. The absence of vertical abundance gradients in the Galactic stellar populations and the possible presence of interloping halo streams would be consistent with expectations from merger models of Galaxy formation. We find that our UVX method has limited sensitivity in exploring the metallicity distribution of the distant Galactic halo, owing to the poor constraint on the U BV properties of very metal-poor stars. The derivation of metallicities from broadband U BV photometry remains fundamentally sound for the exploration of the halo but is in need of both improved calibration and superior data.