We present a set of 144 galactic chemical evolution models applied to a Milky Way analogue, computed using four sets of low and intermediate star nucleosynthetic yields, six massive star yield compilations, and six functional forms for the initial mass function. The integrated or true yields for each combination are derived. A comparison is made between a grid of multiphase chemical evolution models computed with these yield combinations and empirical data drawn from the Milky Way's disc, including the solar neighbourhood. By means of a chi2 methodology, applied to the results of these multiphase models, the best combination of stellar yields and initial mass function capable of reproducing these observations is identified.
I discuss three different topics in Galactic chemical evolution:the "puzzling" absence of any observational signature of secondary elements ; the building of the Galactic halo in the framework of hierarchical galaxy formation, as evidenced from its metallicity distribution ; and the potentially important role that radial migration may play in the evolution of galactic disks, according to recent studies.
Galactic chemical evolution is a topic that involves nuclear physics, stellar evolution, galaxy evolution, observation, and cosmology. Continuous communication and feedback between these fields is a key component in improving our understanding of how galaxies form and how elements are created and recycled in galaxies and intergalactic space. In this proceedings, we present the current state of the JINA-NuGrid chemical evolution pipeline. It is designed to probe the impact of nuclear astrophysics uncertainties on galactic chemical evolution, to improve our knowledges regarding the origin of the…
The majority of galactic chemical evolution models assumes the instantaneous mixing approximation (IMA). This assumption is probably not realistic as indicated by the existence of chemical inhomogeneities, although current chemical evolution models of the Milky Way can reproduce the majority of the observational constraints under the IMA. The aim of this paper is to test whether relaxing this approximation in a detailed chemical evolution model can improve or worsen the agreement with observations. To do that, we investigated two possible causes for relaxing of the instantaneous mixing: i) the…
In this review I outline some ideas in chemical evolution, necessary for understanding the evolution of galaxies from measured elemental abundance ratios. I then discuss abundance results from studies of Local Group dwarf galaxies and the globular cluster Omega Cen. I present a qualitative scenario of prolonged chemical enrichment in a leaky box that can explain the observed abundance ratios in these systems. Space limitations prevent a comprehensive review of this vast field, so I have restricted the discussion to dwarf systems.
The dynamics of galactic nuclei can be affected by several mechanisms. Among these are stellar evolution, stellar collisions, mass segregation, and tidal disruptions of stars due to the central black hole. In this presentation I will address how each of these affects the stellar cusp and the resulting observational signatures. Using a set of dynamically evolving Fokker-Planck simulations I present the dynamical evolution a nuclear stellar cluster and the growth of the central massive black hole within the Galactic Nucleus. In addition to the Galactic Center I explore a wide variety of galactic…
The dense concentration of stars and high velocity dispersions in the Galactic centre imply that stellar collisions frequently occur. Stellar collisions could therefore result in significant mass loss rates. We calculate the amount of stellar mass lost due to indirect and direct stellar collisions and find its dependence on the present-day mass function of stars. We find that the total mass loss rate in the Galactic centre due to stellar collisions is sensitive to the present-day mass function adopted. We use the observed x-ray luminosity in the Galactic centre to preclude any present-day mass…
Modeling the evolution of the elements in the Milky Way is a multidisciplinary and challenging task. In addition to simulating the 13 billion years evolution of our Galaxy, chemical evolution simulations must keep track of the elements synthesized and ejected from every astrophysical site of interest (e.g., supernova, compact binary merger). The elemental abundances of such ejecta, which are a fundamental input for chemical evolution codes, are usually taken from theoretical nucleosynthesis calculations performed by the nuclear astrophysics community. Therefore, almost all chemical evolution p…
Galactic disc chemical evolution models generally ignore azimuthal surface density variation that can introduce chemical abundance azimuthal gradients. Recent observations, however, have revealed chemical abundance changes with azimuth in the gas and stellar components of both the Milky Way and external galaxies. To quantify the effects of spiral arm density fluctuations on the azimuthal variations of the oxygen and iron abundances in disc galaxies. We develop a new 2D galactic disc chemical evolution model, capable of following not just radial but also azimuthal inhomogeneities. The density f…
The manner the galaxy accretes matter along with the star formation rates at different epochs, influence the evolution of the stable isotopic inventories of the galaxy. A detailed analysis is presented here to study the dependence of the galactic chemical evolution on the accretion scenario of the galaxy along with the star formation rate during the early accretionary phase of the galactic thick disk and thin disk. Our results indicate that a rapid early accretion of the galaxy during the formation of the galactic thick disk along with an enhanced star formation rate in the early stages of the…
Until recently our knowledge of the Galactic Bulge stellar populations was based on the study of a few low extinction windows. Large photometric and spectroscopic surveys are now underway to map large areas of the bulge. They probe several complex structures which are still to be fully characterized as well as their links with the inner disc, the thick disc and the inner halo. I will review our current, rapidly increasing, knowledge of the bulge stellar populations and the new insight expected towards the Gaia era to disentangle the formation history of the Galactic inner regions.
We propose a new dynamical picture of galactic stellar and gas spirals, based on hydrodynamic simulations in a `live' stellar disk. We focus especially on spiral structures excited in a isolated galactic disk without a stellar bar. Using high-resolution, 3-dimensional N-body/SPH simulations, we found that the spiral features of the gas in galactic disks are formed by essentially different mechanisms from the galactic shock in stellar density waves. The stellar spiral arms and the interstellar matter on average corotate in a galactic potential at any radii. Unlike the stream motions in the gala…
We investigate how a single generation galactic mass function (SGMF) depends on the existence of variations in the initial stellar mass functions (IMF) of stellar clusters. We show that cluster-to-cluster variations of the IMF lead to a multicomponent SGMF where each component in a given mass range can be described by a distinct power-law function. We also show that a dispersion of $\approx 0.3$ M$_{\odot}$ in the characteristic mass of the IMF, as observed for young Galactic clusters, leads to a low mass slope of the SGMF that matches the observed Galactic stellar mass function even when the …
In this lecture I will introduce the concept of galactic chemical evolution, namely the study of how and where the chemical elements formed and how they were distributed in the stars and gas in galaxies. The main ingredients to build models of galactic chemical evolution will be described. They include: initial conditions, star formation history, stellar nucleosynthesis and gas flows in and out of galaxies. Then some simple analytical models and their solutions will be discussed together with the main criticisms associated to them. The yield per stellar generation will be defined and the hypot…
The elemental abundance structure of the Galactic disc has been extensively studied in the solar neighbourhood using long-lived stars such as F and G dwarfs or K and M giants. These are stars whose atmospheres preserve the chemical composition of their natal gas clouds, and are hence excellent tracers of the chemical evolution of the Galaxy. As far as we are aware, there are no such studies of the inner Galactic disc, which hampers our ability to constrain and trace the origin and evolution of the Milky Way. Therefore, we aim in this study to establish the elemental abundance trend(s) of the d…
The Galactic habitable zone is defined as the region with highly enough metallicity to form planetary systems in which Earth-like planets could be born and might be capable of sustaining life surviving to the destructive effects of nearby supernova explosion events. Galactic chemical evolution models can be useful tools for studying the galactic habitable zones in different systems. Our aim here is to find the Galactic habitable zone using chemical evolution models for the Milky Way disc, adopting the most recent prescriptions for the evolution of dust and for the probability of finding planet…
We adopt a scenario in which the Galactic thick disk was formed by minor merging between the first generation of the Galactic thin disk (FGTD) and a dwarf galaxy about 9 Gyr ago and thereby investigate chemical and dynamical properties of the Galactic thick disk. In this scenario, the dynamical properties of the thick disk have long been influenced both by the mass growth of the second generation of the Galactic thin disk (i.e., the present thin disk) and by its non-axisymmetric structures. On the other hand, the early star formation history and chemical evolution of the thin disk was influenc…
Galactic bulges are central to understanding galaxy formation and evolution. Here we report on recent studies using micro-lensing events to obtain spectra of high resolution and moderately high signal-to-noise ratios of dwarf stars in the Galactic bulge. Normally this is not feasible for the faint turn-off stars in the Galactic bulge, but micro-lensing offers this possibility. Elemental abundance trends in the Galactic bulge as traced by dwarf stars are very similar to those seen for dwarf stars in the solar neighbourhood. We discuss the implications of the ages and metallicity distribution fu…
In view of their nature, planetary nebulae have very short lifetimes, and the chemical abundances derived so far have a natural bias favoring younger objects. In this work, we report physical parameters and abundances for a sample of old PNe located in the galactic bulge, based on low dispersion spectroscopy secured at the SOAR telescope using the Goodman Spectrograph. The new data allow us to extend our database including older, weaker objects that are at the faint end of the planetary nebula luminosity function (PNLF). The results show that the abundances of our sample are lower than those f…
Galactic winds from star-forming galaxies are crucial to the process of galaxy formation and evolution, regulating star formation, shaping the stellar mass function and the mass-metallicity relation, and enriching the intergalactic medium with metals. Galactic winds associated with stellar feedback may be driven by overlapping supernova explosions, radiation pressure of starlight on dust grains, and cosmic rays. Galactic winds are multiphase, the growing observations of emission and absorption of cold molecular, cool atomic, ionized warm and hot outflowing gas in a large number of galaxies hav…
Stellar migration is an important dynamical process in Galactic disk. Here we model the radial stellar migration in the Galactic disk with an analytical method, then add it to detailed Galactic chemical evolution model to study the influence of radial stellar migration on the chemical evolution of the Milky Way, especially for the abundance gradients. We found that the radial stellar migration in the Galactic disk can make the profile of the G-dwarf metallicity distribution of the solar neighborhood taller and narrower, thus it becomes another solution to the "G-dwarf problem". It can also sca…
The origin of the Galactic Anticenter Stellar Structure (GASS) or "Monoceros ring" --- a low latitude overdensity at the edge of the Galactic disk spanning at least the second and third Galactic quadrants --- remains controversial. Models for the origin of GASS fall generally into scenarios where it is either a part (e.g., warp) of the Galactic disk or it represents tidal debris from the disruption of a Milky Way (MW) satellite galaxy. To further constrain models for the origin of GASS, we derive chemical abundance patterns from high resolution spectra for 21 M giants spatially and kinematical…
The formation processes that led to the current Galactic stellar halo are still under debate. Previous studies have provided evidence for different stellar populations in terms of elemental abundances and kinematics, pointing to different chemical and star-formation histories. In the present work we explore, over a broader range in metallicity (-2.2 < [Fe/H] < -0.5), the two stellar populations detected in the first paper of this series from metal-poor stars in DR13 of the Apache Point Observatory Galactic Evolution Experiment (APOGEE). We aim to infer signatures of the initial mass function (…
The predictions of the multiple burst accretion model of chemical evolution are compared to the observations of the stellar masses and metallicities of star-forming galaxies. With the addition of one parameter, the model can account for the observations of the star-forming galaxies if the observations of the galaxies are identified with the star bursting behaviour of the model. This consistency with the model holds only if galaxy downsizing is assumed to occur.
Galactic winds in dwarf galaxies are driven by the energy released by supernova explosions and stellar winds following an intense episode of star formation, which create an over-pressured cavity of hot gas. Although the luminosity of the star formation episode and the mass of the galaxy play a key role in determining the occurrence of the galactic winds and the fate of the freshly produced metals, other parameters play an equally important role. In this contribution we address the following questions (i) What is the late evolution of superbubbles and what is the final fate of the superbubble c…
The galactic habitable zone is defined as the region with sufficient abundance of heavy elements to form planetary systems in which Earth-like planets could be born and might be capable of sustaining life, after surviving to close supernova explosion events. Galactic chemical evolution models can be useful for studying the galactic habitable zones in different systems. We apply detailed chemical evolution models including radial gas flows to study the galactic habitable zones in our Galaxy and M31. We compare the results to the relative galactic habitable zones found with "classical" (independ…
Recent work has produced a wealth of data concerning the chemical evolution of the galactic bulge, both for stars and nebulae. Present theoretical models generally adopt a limited range of such constraints, frequently using a single chemical element (usually iron), which is not enough to describe it unambiguously. In this work, we take into account constraints involving as many chemical elements as possible, basically obtained from bulge nebulae and stars. Our main goal is to show that different scenarios can describe, at least partially, the abundance distribution and several distance-indepen…
Resonant torques couple stellar bars to dark matter halos. Here we use high-resolution numerical simulations to demonstrate long-term angular momentum transfer between stellar bars and dark matter orbits of varying orientation. We show that bar-driven reversals of dark matter orbit orientations can play a surprisingly large role in the evolution of the bar pattern speed. In predominantly prograde (co-rotating) halos, dark matter orbits become trapped in the stellar bar forming a parallel dark matter bar. This dark matter bar reaches more than double the vertical height of the stellar bar. In h…
Studies of the Galactic Centre suggest that in-situ star formation may have given rise to the observed stellar population near the central supermassive black hole (SMBH). Direct evidence for a recent starburst is provided by the currently observed young stellar disc (2-7 Myr) in the central 0.5 pc of the Galaxy. This result suggests that star formation in galactic nuclei may occur close to the SMBH and produce initially flattened stellar discs. Here we explore the possible build-up and evolution of nuclear stellar clusters near SMBHs through in-situ star formation producing stellar discs simil…
Stellar halo substructures were identified using statistical photometric parallax of blue main sequence turnoff stars from fourteen Sloan Digital Sky Survey stripes in the north Galactic cap. Four structures are consistent with previous measurements of the Sagittarius dwarf tidal stream: the leading tail, the "bifurcated" stream, the trailing tail, and Stream C. The stellar overdensity in Virgo, about 15 kpc from the Sun, could arise from the crossing of the Parallel Stream and a new, candidate stream dubbed the Perpendicular Stream. The data suggests the presence of a wide stream near NGC 546…
The interstellar medium (ISM) is an inseparable part of the Milky Way ecosystem whose evolutionary history remains a challenging question. We trace the evolution of the molecular ISM using a sample of Young Stellar Objects (YSO) association --molecular cloud complex (YSO-MC complex). We derive their three-dimensional (3D) velocities by combining the Gaia astrometric measurements of the YSO associations and the CO observations of the associated molecular clouds. Based on the 3D velocities, we simulate the motions of the YSO-MC complexes in the Galactic potential and forecast the ISM evolution b…
Context. The Galactic chemical evolution of sulphur is still under debate. At low metallicities some studies find no correlation between [S/Fe] and [Fe/H], others find [S/Fe] increasing towards lower metallicities, and still others find a combination of the two. Each scenario has different implications for the Galactic chemical evolution of sulphur. Aims. To contribute to the discussion on the Galactic chemical evolution of sulphur by deriving sulphur abundances from non-LTE insensitive spectral diagnostics in Disk and Halo stars with homogeneously determined stellar parameters. Methods. We de…
Standard chemical evolution models based on long-term infall are affected by a number of problems, evidenced by the analysis of the most recent data. Among these: (1) models rely on the local metallicity distribution, assuming its shape is valid for the entire Galaxy, which it is not; (2) they assume that the solar vicinity abundance patterns resulted from a unique chemical evolution, which it does not; (3) they assume the disk is a single structure with chemical properties that are a smooth function of the distance to the galactic center, which it is not. Moreover, new results point to a thic…
A new method for selecting stars in the Galactic bar based on 2MASS infrared photometry in combination with stellar proper motions from the Kharkiv XPM catalogue has been implemented. In accordance with this method, red clump and red giant branch stars are preselected on the color -- magnitude diagram and their photometric distances are calculated. Since the stellar proper motions are indicators of a larger velocity dispersion toward the bar and the spiral arms compared to the stars with circular orbits, applying the constraints on the proper motions of the preselected stars that take into acc…
The early science results from the new generation of high-resolution stellar spectroscopic surveys, such as GALAH and the Gaia-ESO survey, will represent major milestones in the quest to chemically tag the Galaxy. Yet this technique to reconstruct dispersed coeval stellar groups has remained largely untested until recently. We build on previous work that developed an empirical chemical tagging probability function, which describes the likelihood that two field stars are conatal, that is, they were formed in the same cluster environment. In this work we perform the first ever blind chemical tag…
We have categorized possible transonic solutions of galactic outflows in the gravitational potential of DMH and SMBH using the isothermal, spherically symmetric and steady model. We conclude that the gravitational potential of SMBH generates a new transonic branch while Tsuchiya et al. (2013) concluded that the gravitational potential of DMH forms one transonic solution. Because these two transonic solutions have different mass fluxes and starting points, these solutions will make different influences to the star formation rate, the evolution of galaxies, and the chemical evolution of the inte…
Aims: We study the relations between stellar kinematics and chemical abundances of a large sample of RAVE giants in search for selection criteria needed for disentangling different Galactic stellar populations. Methods: We select a sample of 2167 giant stars with signal-to-noise per spectral measurements above 75 from the RAVE chemical catalogue and follow the analysis performed by Gratton and colleagues on 150 subdwarf stars spectroscopically observed at high-resolution. We then use a larger sample of 9131 giants (with signal-to-noise above 60) to investigate the chemo-kinematical characteris…
Planetary nebulae (PNe) constitute an important tool to study the chemical evolution of the Milky Way and other galaxies, probing the nucleosynthesis processes, abundance gradients and the chemical enrichment of the interstellar medium. In particular, Galactic bulge PNe (GBPNe) have been extensively used in the literature to study the chemical properties of this Galactic structure. However, the presently available GBPNe chemical composition studies are strongly biased, since they were focused on brighter objects, predominantly located in Galactic regions of low interstellar reddening. In this …
We compute the chemical evolution of the Galactic bulge to explain the existence of two main stellar populations recently observed. After comparing model results and observational data we suggest that the old more metal poor stellar population formed very fast (on a timescale of 0.1-0.3 Gyr) by means of an intense burst of star formation and an initial mass function flatter than in the solar vicinity whereas the metal rich population formed on a longer timescale (3 Gyr). We predict differences in the mean abundances of the two populations (-0.52 dex for <[Fe/H]>) which can be interpreted as a …
Results of recent observations of the Galactic bulge demand that we discard a simple picture of its formation, suggesting the presence of two stellar populations represented by two peaks of stellar metallicity distribution (MDF) in the bulge. To assess this issue, we construct Galactic chemical evolution models that have been updated in two respects: First, the delay time distribution (DTD) of type Ia supernovae (SNe Ia) recently revealed by extensive SN Ia surveys is incorporated into the models. Second, the nucleosynthesis clock, the s-processing in asymptotic giant branch (AGB) stars, is ca…
Stars born from the same molecular cloud should be nearly homogeneous in their element abundances. The concept of chemical tagging is to identify members of disrupted clusters by their clustering in element abundance space. Chemical tagging requires large samples of stars with precise abundances for many individual elements. With uncertainties of $σ_{[X/{\rm Fe}]}$ and $σ_{\rm [Fe/H]} \simeq 0.05$ for 10 elements measured for $>10^4$ stars, the APOGEE DR12 spectra may be the first well-suited data set to put this idea into practice. We find that even APOGEE data offer only $\sim 500$ independe…
We use the OMEGA galactic chemical evolution code to investigate how the assumptions used for the treatment of galactic inflows and outflows impact numerical predictions. The goal is to determine how our capacity to reproduce the chemical evolution trends of a galaxy is affected by the choice of implementation used to include those physical processes. In pursuit of this goal, we experiment with three different prescriptions for galactic inflows and outflows and use OMEGA within a Markov Chain Monte Carlo code to recover the set of input parameters that best reproduces the chemical evolution of…
In this paper, we present a holistic view of the detection, characterization, and origin of stellar streams in the disk of a simulated Milky Way-like galaxy. The star-by-star simulation of the Galaxy evolves stars born in clusters in a realistic galactic potential that includes spiral arms, a bar, and giant molecular clouds over $5$ Gyr. We first devise a new hybrid method to detect stellar streams that combines phase space density information along with the action-angle space spanned by stars in our simulation. We find that streams' progenitor star clusters and associations are all preferenti…
We present the first detailed chemical abundances for distant RR Lyrae stars members of the Virgo Stellar Stream (VSS), derived from X-Shooter medium-resolution spectra. Sixteen elements from carbon to barium have been measured in six VSS RR Lyrae stars, sampling all main nucleosynthetic channels. For the first time we will be able to compare in detail the chemical evolution of the VSS progenitor with those of Local Group dwarf spheroidal galaxies (LG dSph) as well as the one of the smooth halo.
Galactic chemical evolution (GCE), solar analogues or twins, and peculiarities of the solar composition with respect to the twins are inextricably related. We examine GCE parameters from the literature and present newly derived values using a quadratic fit that gives zero for a Solar age (i.e., 4.6 Gyr). We show how the GCE parameters may be used not only to "correct" abundances to the solar age, but to predict relative elemental abundances as a function of age. We address the question of whether the solar abundances are depleted in refractories and enhanced in volatiles and find that the answ…
In this paper, we study the formation and chemical evolution of the Milky Way disc with particular focus on the abundance patterns ([$α$/Fe] vs. [Fe/H]) at different Galactocentric distances, the present-time abundance gradients along the disc and the time evolution of abundance gradients. We consider the chemical evolution models for the Galactic disc developed by Grisoni et al. (2017) for the solar neighborhood, both the two-infall and the one-infall ones, and we extend our analysis to the other Galactocentric distances. In particular, we examine the processes which mainly influence the form…
We analyze the evolution of oxygen abundance radial gradients resulting from our chemical evolution models calculated with different prescriptions for the star formation rate (SFR) and for the gas infall rate, in order to assess their respective roles in shaping gradients. We also compare with cosmological simulations and confront all with recent observational datasets, in particular with abundances inferred from planetary nebulae. We demonstrate the critical importance in isolating the specific radial range over which a gradient is measured, in order for their temporal evolution to be useful …
We have computed the Galactic Habitable Zones (GHZs) of the Andromeda galaxy (M31) based on the probability of terrestrial planet formation, which depends on the metallicity (Z) of the interstellar medium, and the number of formed stars per surface unit. The GHZ was therefore obtained from a chemical evolution model built to reproduce a precise metallicity gradient in the galactic disk, [O/H](r) $ = -0.015 \pm 0.003 dex kpc^{-1} x r(kpc) + 0.44 \pm 0.04 dex $. This gradient is the most probable when intrinsic scatter is present in the observational data. The chemical evolution model predicted …
Assuming the dark matter halo of the Milky Way as a non-spherical potential (i.e. triaxial, prolate, oblate), we show how the assembling process of the Milky Way halo, may have left long lasting stellar halo kinematic fossils only due to the shape of the dark matter halo. In contrast with tidal streams, associated with recent satellite accretion events, these stellar kinematic groups will typically show inhomogeneous chemical and stellar population properties. However, they may be dominated by a single accretion event for certain mass assembling histories. If the detection of these peculiar ki…
Owing to their extreme crowding and high and variable extinction, stars in the Galactic Bulge, within +-2 degrees of the Galactic plane, and especially those in the Nuclear Star Cluster, have only rarely been targeted for an analyses of their detailed abundances. There is also some disagreement about the high end of the abundance scale for these stars. It is now possible to obtain high dispersion, high S/N spectra in the infrared K band (2.0-2.4 microns) for these giants; we report our progress at Keck and VLT in using these spectra to infer the composition of this stellar population.
In the last years, stellar migration in galactic discs has been the subject of several investigations. However, its impact on the chemical evolution of the Milky Way still needs to be fully quantified. In this paper, we aim at imposing some constraints on the significance of this phenomenon by considering its influence on the chemical evolution of the Milky Way thin disc. We do not investigate the physical mechanisms underlying the migration of stars. Rather, we introduce a simple, heuristic treatment of stellar migration in a detailed chemical evolution model for the thin disc of the Milky Wa…
Observations of the spatial distribution and kinematics of young stars in the Galactic centre can be interpreted as showing that the stars occupy one, or possibly two, discs of radii ~0.05-0.5 pc. The most prominent (`clockwise') disc exhibits a strong warp: the normals to the mean orbital planes in the inner and outer third of the disc differ by ~60 deg. Using an analytical model based on Laplace-Lagrange theory, we show that such warps arise naturally and inevitably through vector resonant relaxation between the disc and the surrounding old stellar cluster.
We study the chemical evolution of Zr, La, Ce and Eu in the Milky Way discs and bulge by means of chemical evolution models compared with recent spectroscopic data. We consider detailed chemical evolution models for the Galactic thick disc, thin disc and bulge, which have been already tested to reproduce the observed [$α$/Fe] vs [Fe/H] diagrams and metallicity distribution functions for the three different components, and we apply them to follow the evolution of neutron capture elements. In the [Eu/Fe] vs [Fe/H] diagram, we observe and predict three distinct sequences corresponding to the thic…
