The evolution of the Galactic metallicity gradient from high-resolution spectroscopy of open clusters

By Laura Magrini, P. Sestito, S. Randich, D. Galli. 2008

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Context. Open clusters offer a unique possibility to study the time evolution of the radial metallicity gradients of several elements in our Galaxy, because they span large intervals in age and Galactocentric distance, and both quantities can be more accurately derived than for field stars. Aims. We re-address the issue of the Galactic metallicity gradient and its time evolution by comparing the empirical gradients traced by a sample of 45 open clusters with a chemical evolution model of the Galaxy. Methods. At variance with previous similar studies, we have collected from the literature only abundances derived from high-resolution spectra. The clusters have Galactocentric distances $7 \la R_{\rm GC} \la 22$ kpc and ages from ~30 Myr to 11 Gyr. We also consider the α -elements Si, Ca, Ti, and the iron-peak elements Cr and Ni. Cepheids trace instead the present-day Fe gradient in the inner parts of the disk. Results. The data for iron-peak and α -elements indicate a steep metallicity gradient for $R_{\rm GC}\la 12$ kpc and a plateau at larger radii. The time evolution of the metallicity distribution is characterized by a uniform increase of the metallicity at all radii, preserving the shape of the gradient, with marginal evidence for a flattening of the gradient with time in the radial range 7-12 kpc. Our model is able to reproduce the main features of the metallicity gradient and its evolution with an infall law exponentially decreasing with radius and with a collapse time scale of the order of 8 Gyr at the solar radius. This results in a rapid collapse in the inner regions, i.e. $R_{\rm GC}\la 12$ kpc (that we associate with an early phase of disk formation from the collapse of the halo) and in a slow inflow of material per unit area in the outer regions at a constant rate with time (that we associate with accretion from the intergalactic medium). An additional uniform inflow per unit disk area would help to better reproduce the metallicity plateau at large Galactocentric radii, but it is difficult to reconcile with the present-day radial behaviour of the star formation rate. Conclusions. Our results favour a scenario where the Galactic disk is formed inside-out by the rapid collapse of the halo and by a subsequent continuous accretion of intergalactic gas

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/a5a5dac8d5259de3ba9cde30d366b9604b7bd826

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Citations in the corpus

A characteristic oxygen abundance gradient in galaxy disks unveiled with CALIFA (2013, methodology): “In the case of the Milky Way (MW), studies using open clusters (e.g., Bragaglia et al. 2008; Magrini et al. 2009; Yong et al. 2012; Pedicelli et al. 2009), Cepheids (e.g., Andrievsky et al. 2002, 2004; Luck et al. 2003; Lemasle et al. 2008), H ii regions (e.g., Vilchez & Esteban 1996; Esteban et…”
Metallicity distributions of mono-age stellar populations of the Galactic disc from the LAMOST Galactic spectroscopic surveys (2018, background): “…variables (Andrievsky et al. 2002; Luck, Kovtyukh & Andrievsky 2006), H II regions (Balser et al. 2011), open clusters (Chen, Hou & Wang 2003; Magrini et al. 2009), planetary nebulae (Costa, Uchida & Maciel 2004; Henry et al. 2010) , FGK dwarfs (Katz et al. 2011; Cheng et al. 2012; Boeche et…”
Clusters and mirages: cataloguing stellar aggregates in the Milky Way (2019, background): “Article published by EDP Sciences A99, page 1 of 22 gradient (e.g. Janes 1979; Twarog et al. 1997; Yong et al. 2012; Magrini et al. 2009; Cantat-Gaudin et al. 2016; Jacobson et al. 2016; Casamiquela et al. 2017; Donor et al. 2018).”
SDSS IV MaNGA – metallicity and nitrogen abundance gradients in local galaxies (2017, background): “…al. 2015), O/B-type stars (Smartt & Rolleston 1997; Rolleston et al. 2000), Cepheids (Luck et al. 2003; Pedicelli et al. 2009; Lemasle et al. 2013; Genovali et al. 2014), open clusters (Magrini et al. 2009; Yong et al. 2012) and planetary nebulae (Maciel & Quireza 1999; Stanghellini et al. 2006).”
A Gaia DR2 view of the open cluster population in the Milky Way (2018, background): “…2005; Bragaglia & Tosi 2006; Carrera & Pancino 2011; Netopil et al. 2016; Casamiquela et al. 2017) and its evolution through time (e.g. Friel et al. 2002; Magrini et al. 2009; Yong et al. 2012; Frinchaboy et al. 2013; Jacobson et al. 2016), providing insight on the formation of the Galactic disk.”
On the metallicity of open clusters. III. Homogenised sample (2015, background): “Thus, a strict AMR does not exist in the Galactic disc, but there is a tendency that older clusters have on average lower metallicities (Magrini et al. 2009).”
Chemical abundance analysis of the open clusters Cr 110, NGC 2099 (M 37), NGC 2420, NGC 7789, and M 67 (NGC 2682) (2009, background): “…for a –0.16 dex correction to the low resolution abundances, thissample is∼50% larger than any compilation presented before (see e.g., Sestito et al., 2008; De Silva et al., 2009; Magrini et al., 2009) and shows that the community is proceeding fast in fillig up the gaps of our knowledge of OC.”
On the fine structure of the Cepheid metallicity gradient in the Galactic thin disk (2014, result): “This result supports similar findings available in the literature e.g. Carraro et al. (2007b), Bragaglia et al. (2008), Magrini et al. (2009, 2010), Jacobson et al. (2011a,b), Yong et al. (2012).”
FORMATION AND EVOLUTION OF THE DISK SYSTEM OF THE MILKY WAY: [α/Fe] RATIOS AND KINEMATICS OF THE SEGUE G-DWARF SAMPLE (2011, result): “…many previous studies (e.g., Nordström et al. 2004; Holmberg et al. 2007; Andrievsky et al. 2004; Lemasle et al. 2007; Sestito et al. 2008; Magrini et al. 2009) that used open clusters and/or field stars to derive radial metallicity gradients report rather small gradients, on the order…”