Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe time evolution of the Milky Ways oxygen abundance gradient
58
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We study the evolution of oxygen abundance radial gradients as a function of time for the Milky Way Galaxy obtained with our {sc Mulchem} chemical evolution model. We review the recent data of abundances for different objects observed in our Galactic disc. We analyse with our models the role of the growth of the stellar disc, as well as the effect of infall rate and star formation prescriptions, or the pre-enrichment of the infall gas, on the time evolution of the oxygen abundance radial distribution. We compute the radial gradient of abundances within the {sl disk}, and its corresponding evolution, taking into account the disk growth along time. We compare our predictions with the data compilation, showing a good agreement. Our models predict a very smooth evolution when the radial gradient is measured within the optical disc with a slight flattening of the gradient from $sim -0.057$,dex,kpc$^{-1}$ at $z=4$ until values around $sim -0.015$,dex,kpc$^{-1}$ at $z=1$ and basically the same gradient until the present, with small differences between models. Moreover, some models show a steepening at the last times, from $z=1$ until $z=0$ in agreement with data which give a variation of the gradient in a range from $-0.02$ to $-0.04$,de,kpc$^{-1}$ from $t=10$,Gyr until now. The gradient measured as a function of the normalized radius $R/R_{rm eff}$ is in good agreement with findings by CALIFA and MUSE, and its evolution with redshift falls within the error bars of cosmological simulations.
rate research
Read More
We present a semi-empirical, largely model-independent approach for estimating Galactic birth radii, r_birth, for Milky Way disk stars. The technique relies on the justifiable assumption that a negative radial metallicity gradient in the interstellar medium (ISM) existed for most of the disk lifetime. Stars are projected back to their birth positions according to the observationally derived age and [Fe/H] with no kinematical information required. Applying our approach to the AMBRE:HARPS and HARPS-GTO local samples, we show that we can constrain the ISM metallicity evolution with Galactic radius and cosmic time, [Fe/H]_ISM(r, t), by requiring a physically meaningful r_birth distribution. We find that the data are consistent with an ISM radial metallicity gradient that flattens with time from ~-0.15 dex/kpc at the beginning of disk formation, to its measured present-day value (-0.07 dex/kpc). We present several chemo-kinematical relations in terms of mono-r_birth populations. One remarkable result is that the kinematically hottest stars would have been born locally or in the outer disk, consistent with thick disk formation from the nested flares of mono-age populations and predictions from cosmological simulations. This phenomenon can be also seen in the observed age-velocity dispersion relation, in that its upper boundary is dominated by stars born at larger radii. We also find that the flatness of the local age-metallicity relation (AMR) is the result of the superposition of the AMRs of mono-r_birth populations, each with a well-defined negative slope. The solar birth radius is estimated to be 7.3+-0.6 kpc, for a current Galactocentric radius of 8 kpc.
Context. Galactic structure studies can be used as a path to constrain the scenario of formation and evolution of our Galaxy. The dependence with the age of stellar population parameters would be linked with the history of star formation and dynamical evolution. Aims. We aim to investigate the structures of the outer Galaxy, such as the scale length, disc truncation, warp and flare of the thin disc and study their dependence with age by using 2MASS data and a population synthesis model (the so-called Besanc{c}on Galaxy Model). Methods. We have used a genetic algorithm to adjust the parameters on the observed colour-magnitude diagrams at longitudes 80 deg <= l <= 280 deg for |b| <= 5.5 deg. We explored parameter degeneracies and uncertainties. Results. We identify a clear dependence of the thin disc scale length, warp and flare shapes with age. The scale length is found to vary between 3.8 kpc for the youngest to about 2 kpc for the oldest. The warp shows a complex structure, clearly asymmetrical with a node angle changing with age from approximately 165 deg for old stars to 195 deg for young stars. The outer disc is also flaring with a scale height that varies by a factor of two between the solar neighbourhood and a Galactocentric distance of 12 kpc. Conclusions. We conclude that the thin disc scale length is in good agreement with the inside-out formation scenario and that the outer disc is not in dynamical equilibrium. The warp deformation with time may provide some clues to its origin.
A major goal in the field of galaxy formation is to understand the formation of the Milky Ways disk. The first step toward doing this is to empirically describe its present state. We use the new high-dimensional dataset of 19 abundances from 27,135 red clump APOGEE stars to examine the distribution of clusters defined using abundances. We explore different dimensionality reduction techniques and implement a non-parametric agglomerate hierarchical clustering method. We see that groups defined using abundances are spatially separated, as a function of age. Furthermore, the abundance groups represent different distributions in the [Fe/H]-age plane. Ordering our clusters by age reveals patterns suggestive of the sequence of chemical enrichment in the disk over time. Our results indicate that a promising avenue to trace the details of the disks assembly is via a full interpretation of the empirical connections we report.
Using combined asteroseismic and spectroscopic observations of 418 red-giant stars close to the Galactic disc plane (6 kpc $<R_{rm Gal}lesssim13$ kpc, $|Z_{rm Gal}|<0.3$ kpc), we measure the age dependence of the radial metallicity distribution in the Milky Ways thin disc over cosmic time. The slope of the radial iron gradient of the young red-giant population ($-0.058pm0.008$ [stat.] $pm0.003$ [syst.] dex/kpc) is consistent with recent Cepheid measurements. For stellar populations with ages of $1-4$ Gyr the gradient is slightly steeper, at a value of $-0.066pm0.007pm0.002$ dex/kpc, and then flattens again to reach a value of $sim-0.03$ dex/kpc for stars with ages between 6 and 10 Gyr. Our results are in good agreement with a state-of-the-art chemo-dynamical Milky-Way model in which the evolution of the abundance gradient and its scatter can be entirely explained by a non-varying negative metallicity gradient in the interstellar medium, together with stellar radial heating and migration. We also offer an explanation for why intermediate-age open clusters in the Solar Neighbourhood can be more metal-rich, and why their radial metallicity gradient seems to be much steeper than that of the youngest clusters. Already within 2 Gyr, radial mixing can bring metal-rich clusters from the innermost regions of the disc to Galactocentric radii of 5 to 8 kpc. We suggest that these outward-migrating clusters may be less prone to tidal disruption and therefore steepen the local intermediate-age cluster metallicity gradient. Our scenario also explains why the strong steepening of the local iron gradient with age is not seen in field stars. In the near future, asteroseismic data from the K2 mission will allow for improved statistics and a better coverage of the inner-disc regions, thereby providing tighter constraints on the evolution of the central parts of the Milky Way.
We determine the radial abundance gradient of Cl in the Milky Way from HII regions spectra. For the first time, the Cl/H ratios are computed by simply adding ionic abundances and not using an ionization correction factor (ICF). We use a collection of published very deep spectra of Galactic HII regions. We have re-calculated the physical conditions, ionic and total abundances of Cl and O using the same methodology and updated atomic data for all the objects. We find that the slopes of the radial gradients of Cl and O are identical within the uncertainties: -0.043 dex/kpc. This is consistent with a lockstep evolution of both elements. We obtain that the mean value of the Cl/O ratio across the Galactic disc is log(Cl/O) = -3.42 +/- 0.06. We compare our Cl/H ratios with those determined from Cl++ abundances and using some available ICF schemes of the literature. We find that our total Cl abundances are always lower than the values determined using ICFs, indicating that those correction schemes systematically overestimate the contribution of Cl+ and Cl+++ species to the total Cl abundance. Finally, we propose an empirical ICF(Cl++) to estimate the Cl/H ratio in HII regions.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
