Metallicity Gradients In Galaxies Research Articles

How well do local relations predict gas-phase metallicity gradients? Results from SDSS-IV MaNGA

ABSTRACT Gas-phase metallicity gradients in galaxies provide important clues to those galaxies’ formation histories. Using SDSS-IV MaNGA data, we previously demonstrated that gas metallicity gradients vary systematically and significantly across the galaxy mass–size plane: at stellar masses beyond approximately $10^{10}\, \mathrm{M_\odot }$, more extended galaxies display steeper gradients (in units of dex/Re) at a given stellar mass. Here, we set out to develop a physical interpretation of these findings by examining the ability of local ∼kpc-scale relations to predict the gradient behaviour along the mass–size plane. We find that local stellar mass surface density, when combined with total stellar mass, is sufficient to reproduce the overall mass–size trend in a qualitative sense. We further find that we can improve the predictions by correcting for residual trends relating to the recent star formation histories of star-forming regions. However, we find as well that the most extended galaxies display steeper average gradients than predicted, even after correcting for residual metallicity trends with other local parameters. From these results, we argue that gas-phase metallicity gradients can largely be understood in terms of known local relations, but we also discuss some possible physical causes of discrepant gradients.

The Fornax3D project: The environmental impact on gas metallicity gradients in Fornax cluster galaxies

The role played by environment in galaxy evolution is a topic of ongoing debate among astronomers. There has been little success in elucidating the degree to which environment can alter, re-shape, or drive galaxy evolution, that is, using either observations or simulations. However, our knowledge of the effect of environment on gas metallicity gradients remains limited. Here we present our analysis of the gas metallicity gradients for a sample of ten Fornax cluster galaxies observed with MUSE as part of the Fornax3D project. We used detailed maps of emission lines to determine precise values of gas metallicity and metallicity gradients. The integrated gas metallicity of our Fornax cluster galaxies shows slightly higher metallicities (∼0.045 dex) in comparison to a control sample. In addition, we find signs of a mass and metallicity segregation from the center to the outskirts of the cluster. By comparing our Fornax cluster metallicity gradients with a control sample we find a general median offset of ∼0.04 dex/Re, with eight of our galaxies showing flatter or more positive gradients. The intermediate infallers in our Fornax sample show more positive gradients with respect to the control sample. We find no systematic difference between the gradients of recent and intermediate infallers when considering the projected distance of each galaxy to the cluster center. To identify the origin of the observed offset in the metallicity gradients, we performed a similar analysis with data from the TNG50 simulation. We identify 12 subhalos in Fornax-like clusters and compared their metallicity gradients with a control sample of field subhalos. This exercise also shows a flattening in the metallicity gradients for galaxies in Fornax-like halos, with a median offset of ∼0.05 dex/Re. We also analyzed the merger history, Mach numbers (ℳ), and ram pressure stripping of our TNG50 sample. We conclude that the observed flattening in metallicity gradients is likely due to a combination of galaxies traveling at supersonic velocities (ℳ > 1), which are experiencing high ram pressure stripping and flybys.

The physics of gas phase metallicity gradients in galaxies

ABSTRACT We present a new model for the evolution of gas phase metallicity gradients in galaxies from first principles. We show that metallicity gradients depend on four ratios that collectively describe the metal equilibration time-scale, production, transport, consumption, and loss. Our model finds that most galaxy metallicity gradients are in equilibrium at all redshifts. When normalized by metal diffusion, metallicity gradients are governed by the competition between radial advection, metal production, and accretion of metal-poor gas from the cosmic web. The model naturally explains the varying gradients measured in local spirals, local dwarfs, and high-redshift star-forming galaxies. We use the model to study the cosmic evolution of gradients across redshift, showing that the gradient in Milky Way-like galaxies has steepened over time, in good agreement with both observations and simulations. We also predict the evolution of metallicity gradients with redshift in galaxy samples constructed using both matched stellar masses and matched abundances. Our model shows that massive galaxies transition from the advection-dominated to the accretion-dominated regime from high to low redshifts, which mirrors the transition from gravity-driven to star formation feedback-driven turbulence. Lastly, we show that gradients in local ultraluminous infrared galaxies (major mergers) and inverted gradients seen both in the local and high-redshift galaxies may not be in equilibrium. In subsequent papers in this series, we show that the model also explains the observed relationship between galaxy mass and metallicity gradients, and between metallicity gradients and galaxy kinematics.

Observational hints of radial migration in disc galaxies from CALIFA

Context: According to numerical simulations, stars are not always kept at their birth galactocentric distances but migrate. The importance of this radial migration in shaping galactic light distributions is still unclear. However, if it is indeed important, galaxies with different surface brightness (SB) profiles must display differences in their stellar population properties. Aims: We investigate the role of radial migration on the light distribution and the radial stellar content by comparing the inner colour, age and metallicity gradients for galaxies with different SB profiles. We define these inner parts avoiding the bulge and bar regions and up to around three disc scale-lengths (type I, pure exponential) or the break radius (type II, downbending; type III, upbending). Methods: We analyse 214 spiral galaxies from the CALIFA survey covering different SB profiles. We make use of GASP2D and SDSS data to characterise their light distribution and obtain colour profiles. The stellar age and metallicity profiles are computed using a methodology based on full-spectrum fitting techniques (pPXF, GANDALF, and STECKMAP) to the IFS CALIFA data. Results: The distributions of the colour, stellar age and stellar metallicity gradients in the inner parts for galaxies displaying different SB profiles are unalike as suggested by Kolmogorov-Smirnov and Anderson-Darling tests. We find a trend in which type II galaxies show the steepest profiles of all and type III the shallowest, with type I galaxies displaying an intermediate behaviour. Conclusions: These results are consistent with a scenario in which radial migration is more efficient for type III galaxies than for type I systems with type II galaxies presenting the lowest radial migration efficiency. In such scenario, radial migration mixes the stellar content flattening the radial stellar properties and... [abriged]

Dust and Metallicity across local Galaxies

AbstractThe gas-phase metallicity is one of the key insights we have into measuring the chemical feedback of stars in galaxies, yet remains difficult to correctly determine. However, there is a close relation between gas-phase metals and dust in the ISM, which can give us insight into the correct metallicity in galaxies. Here I will present recent work on metallicity gradients in galaxies, and how we can measure the global metallicity and the radial gradients in nearby galaxies using dust, through the dust-to-gas ratio.

THEORETICAL EVOLUTION OF OPTICAL STRONG LINES ACROSS COSMIC TIME

We use the chemical evolution predictions of cosmological hydrodynamic simulations with our latest theoretical stellar population synthesis, photoionization and shock models to predict the strong line evolution of ensembles of galaxies from z=3 to the present day. In this paper, we focus on the brightest optical emission-line ratios, [NII]/H-alpha and [OIII]/H-beta. We use the optical diagnostic Baldwin-Phillips-Terlevich (BPT) diagram as a tool for investigating the spectral properties of ensembles of active galaxies. We use four redshift windows chosen to exploit new near-infrared multi-object spectrographs. We predict how the BPT diagram will appear in these four redshift windows given different sets of assumptions. We show that the position of star-forming galaxies on the BPT diagram traces the ISM conditions and radiation field in galaxies at a given redshift. Galaxies containing AGN form a mixing sequence with purely star-forming galaxies. This mixing sequence may change dramatically with cosmic time, due to the metallicity sensitivity of the optical emission-lines. Furthermore, the position of the mixing sequence may probe metallicity gradients in galaxies as a function of redshift, depending on the size of the AGN narrow line region. We apply our latest slow shock models for gas shocked by galactic-scale winds. We show that at high redshift, galactic wind shocks are clearly separated from AGN in line ratio space. Instead, shocks from galactic winds mimic high metallicity starburst galaxies. We discuss our models in the context of future large near-infrared spectroscopic surveys.

Star formation and metallicity gradients in semi-analytic models of disc galaxy formation

We have updated our radially-resolved SAMs of galaxy formation, which track both the atomic and molecular gas phases of the ISM. The models are adapted from those of Guo et al. using similar methodology as in Fu et al. and are run on halo merger trees from the MS and MS II with the following main changes: (1) We adopt a simple star formation law where \Sigma_SFR \propto \Sigma_H2 (2) We inject the heavy elements produced by supernovae directly into the halo hot gas, instead of first mixing them with the cold gas in the disk. (3) We include radial gas inflows in disks using a model of the form v_inflow = \alpha r. The models are used to study the radial profiles of star formation rate and gas-phase metallicity in present-day galaxies. The \Sigma_H2 profiles in L* galaxies place strong constraints on inflow velocities, favouring models where v_inflow~7km/s at a galactocentric radius of 10kpc. Radial gas inflow has little influence on gas-phase and stellar metallicity gradients, which are affected much more strongly by the fraction of metals that are directly injected into the halo gas, rather than mixed with the cold gas. Metals ejected out of the galaxy in early epochs result in late infall of pre-enriched gas and flatter present-day gas-phase metallicity gradients. A prescription in which 80% of the metals are injected into the halo gas results in good fits to the flat observed metallicity gradients in galaxies with stellar masses greater than 10^10 M_sun, as well as the relations between gas-phase metallicity and sSFR in the outer parts of galactic disks. We examine the correlation between gas-phase metallicity gradient and global galaxy properties, finding that it is most strongly correlated with the bulge-to-total ratio of the galaxy. This is because gas is consumed when the bulge forms during galaxy mergers, and the gas-phase metallicity gradient is then set by newly-accreted gas.

The SAURON project - XXI. The spatially resolved UV-line strength relations of early-type galaxies

The unexpected rising flux of early-type galaxies at decreasing ultraviolet (UV) wavelengths is a long-standing mystery. One important observational constraint is the correlation between UV-optical colours and Mg2 line strengths found by Burstein et al. (1988). The simplest interpretation of this phenomenon is that the UV strength is related to the Mg line strength. Under this assumption, we expect galaxies with larger Mg gradients to have larger UV colour gradients. By combining UV imaging from GALEX, optical imaging from MDM and SAURON integral-field spectroscopy, we investigate the spatially-resolved relationships between UV colours and stellar population properties of 34 early-type galaxies from the SAURON survey sample. We find that galaxies with old stellar populations show tight correlations between the FUV colours (FUV-V and FUV-NUV) and the Mgb index, H{\beta} index and metallicity [Z/H]. The equivalent correlations for the Fe5015 index, {\alpha}-enhancement [{\alpha}/Fe] and age are present but weaker. We have also derived logarithmic internal radial colour, measured line strength and derived stellar population gradients for each galaxy and again found a strong dependence of the FUV-V and FUV-NUV colour gradients on both the Mg b line strength and the metallicity gradients for galaxies with old stellar populations. In particular, global gradients of Mg b and [Z/H] with respect to the UV colour across galaxies are consistent with their local gradients within galaxies, suggesting that the global correlations also hold locally. From a simple model based on multi-band colour fits of UV upturn and UV-weak galaxies, we have identified a plausible range of parameters that reproduces the observed radial colour profiles. In these models, the centers of elliptical galaxies, where the UV flux is strong, are enhanced in metals by roughly 60% compared to UV-weak regions.

Dust attenuation in hydrodynamic simulations of spiral galaxies

We study the effects of dust in hydrodynamic simulations of spiral galaxies when different radial metallicity gradients are assumed. SUNRISE, a Monte-Carlo radiative-transfer code, is used to make detailed calculations of the internal extincti on of disk galaxies caused by their dust content. SUNRISE is used on eight different Smooth Particle Hydrodynamics (SPH) simulations of isolated spiral galaxies. These galaxies vary mainly in mass and hence luminosity, spanning a range in luminosities from 16 to 22 magnitudes in the B band. We focus on the attenuation in different wavelength bands as a function of the disk inclination and the luminosity of the models, and compare this to observations. Observations suggest different metallicity gradients for galaxies of different luminosities. These metallicity gradients were explored in our different models, finding that the resulting dust attenuation matches observations for edge-on galaxies, but do not show a linear behaviour in log axis ratio as some observations have suggested. A quadratic law describing the dependence of attenuation on inclination, as proposed by more recent observations, reconciles the attenuation of the simulations at intermediate inclinatio ns with observations. We also compare the total infrared-to-ultraviolet flux ratios for the s imulated galaxies with those of the SINGS sample and find general agreement. Finally we compare o ur results with those from simpler models that do not take into account structure such as spiral arms, finding that the inclusion of sub-structure on the size scale of spiral arms d oes not change conclusions about the attenuation dependence on inclination or wavelength.

Surface Brightness Fluctuations from Archival ACS Images: A Stellar Population and Distance Study

We derive Surface Brightness Fluctuations (SBF) and integrated magnitudes in the V- and I-bands using Advanced Camera for Surveys (ACS) archival data. The sample includes 14 galaxies covering a wide range of physical properties: morphology, total absolute magnitude, integrated color. We take advantage of the latter characteristic of the sample to check existing empirical calibrations of absolute SBF magnitudes both in the I- and V-passbands. Additionally, by comparing our SBF and color data with the Teramo-SPoT simple stellar population models, and other recent sets of population synthesis models, we discuss the feasibility of stellar population studies based on fluctuation magnitudes analysis. The main result of this study is that multiband optical SBF data and integrated colors can be used to significantly constrain the chemical composition of the dominant stellar system in the galaxy, but not the age in the case of systems older than 3 Gyr. SBF color gradients are also detected and analyzed. These SBF gradient data, together with other available data, point to the existence of mass dependent metallicity gradients in galaxies, with the more massive objects showing a non--negligible SBF versus color gradient. The comparison with models suggests that such gradients imply more metal rich stellar populations in the galaxies' inner regions with respect to the outer ones.

Optical and Near‐Infrared Color Profiles in Nearby Early‐Type Galaxies and the Implied Age and Metallicity Gradients

We present results of an age and metallicity gradient analysis inferred from both optical and near-infrared surface photometry. The analysis is based on a sample of 36 nearby early-type galaxies, obtained from the Early Data Release of the Sloan Digital Sky Survey and the Two Micron All Sky Survey. Surface brightness profiles were derived in each band and used to study the color gradients of the galaxies. Using simple stellar population models with both optical and near-infrared colors, we may interpret the color gradients in terms of age and metallicity gradients of galaxies. Using g(Z) equivalent to d log Z(met)/d log R and g(A) = d log (age)/d log R to represent the metallicity and age gradients, we found a median value of g(Z) = -0.25 +/- 0.03 for the metallicity gradient, with a dispersion sigma(gZ) = 0.19 +/- 0.02. The corresponding values for the age gradients were g(A) = 0.02 +/- 0.04 and sigma(gA) = 0.25 +/- 0.03. These results are in good agreement with recent observational results, as well as with recent simulations that suggest that both monolithic collapse and major mergers have played important roles in the formation of early-type galaxies. Our results demonstrate the potential of using multi-wave band colors obtained from current and future optical and infrared surveys in constraining the age and metallicity gradients of early-type galaxies.

Dust-to-gas ratio in the outer regions of spiral galaxies

view Abstract Citations (13) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dust-to-gas ratio in the outer regions of spiral galaxies Jura, M. Abstract Some spiral galaxies are surrounded by extended clouds of neutral hydrogen; if dust is associated with this gas, the dust should appear as a faint extended reflection nebula illuminated by the light from the entire galaxy. It is suggested that observations of the surface brightness of the outer regions of M83 and M101 could be worthwhile, since these two galaxies are bright and have extended surrounding gas clouds. Such studies would be of interest with regard to the possible presence of faint extended halos of stars around galaxies, the extent of the metallicity gradients in galaxies, and the value of the dust-to-gas ratio in quasar absorption-line systems. Publication: The Astrophysical Journal Pub Date: November 1980 DOI: 10.1086/158410 Bibcode: 1980ApJ...241..965J Keywords: Cosmic Dust; Galactic Structure; Hydrogen Clouds; Interstellar Matter; Spiral Galaxies; Absorption Spectra; Halos; Interstellar Gas; Line Spectra; Optical Thickness; Astrophysics full text sources ADS |