Simple Closed Box Model Research Articles

The SAMI Galaxy Survey: the drivers of gas and stellar metallicity differences in galaxies

ABSTRACT The combination of gas-phase oxygen abundances and stellar metallicities can provide us with unique insights into the metal enrichment histories of galaxies. In this work, we compare the stellar and gas-phase metallicities measured within a 1Re aperture for a representative sample of 472 star-forming galaxies extracted from the SAMI Galaxy Survey. We confirm that the stellar and interstellar medium (ISM) metallicities are strongly correlated, with scatter ∼3 times smaller than that found in previous works, and that integrated stellar populations are generally more metal-poor than the ISM, especially in low-mass galaxies. The ratio between the two metallicities strongly correlates with several integrated galaxy properties including stellar mass, specific star formation rate, and a gravitational potential proxy. However, we show that these trends are primarily a consequence of: (a) the different star formation and metal enrichment histories of the galaxies, and (b) the fact that while stellar metallicities trace primarily iron enrichment, gas-phase metallicity indicators are calibrated to the enrichment of oxygen in the ISM. Indeed, once both metallicities are converted to the same ‘element base’ all of our trends become significantly weaker. Interestingly, the ratio of gas to stellar metallicity is always below the value expected for a simple closed-box model, which requires that outflows and inflows play an important role in the enrichment history across our entire stellar mass range. This work highlights the complex interplay between stellar and gas-phase metallicities and shows how care must be taken in comparing them to constrain models of galaxy formation and evolution.

The M dwarf problem: Fe and Ti abundances in a volume-limited sample of M dwarf stars

ABSTRACT We report iron and titanium abundance measurements from high-resolution spectra in a volume-limited sample of 106 M0 and M0.5 dwarf stars. The sample includes stars north of the celestial equator and closer than 29 parsecs. The results imply that there is an M dwarf problem similar to the previously known G dwarf problem, in that the fraction of low-metallicity M dwarfs is not large enough to fit simple closed-box models of Galactic chemical evolution. This volume-limited sample avoids many of the statistical uncertainties present in a previous study using a brightness-limited sample of M dwarf stars.

The interstellar medium in Andromeda's dwarf spheroidal galaxies – II. Multiphase gas content and ISM conditions

We make an inventory of the interstellar medium material in three low-metallicity dwarf spheroidal galaxies of the Local Group (NGC147, NGC185 and NGC205). Ancillary HI, CO, Spitzer IRS spectra, H{\alpha} and X-ray observations are combined to trace the atomic, cold and warm molecular, ionised and hot gas phases. We present new Nobeyama CO(1-0) observations and Herschel SPIRE FTS [CI] observations of NGC205 to revise its molecular gas content. We derive total gas masses of M_gas = 1.9-5.5x10^5 Msun for NGC185 and M_gas = 8.6-25.0x10^5 Msun for NGC205. Non-detections combine to an upper limit on the gas mass of M_gas =< 0.3-2.2x10^5 Msun for NGC147. The observed gas reservoirs are significantly lower compared to the expected gas masses based on a simple closed-box model that accounts for the gas mass returned by planetary nebulae and supernovae. The gas-to-dust mass ratios GDR~37-107 and GDR~48-139 are also considerably lower compared to the expected GDR~370 and GDR~520 for the low metal abundances in NGC 185 (0.36 Zsun) and NGC205 (0.25 Zsun), respectively. To simultaneously account for the gas deficiency and low gas-to-dust ratios, we require an efficient removal of a large gas fraction and a longer dust survival time (~1.6 Gyr). We believe that efficient galactic winds (combined with heating of gas to sufficiently high temperatures in order for it to escape from the galaxy) and/or environmental interactions with neighbouring galaxies are responsible for the gas removal from NGC147, NGC185 and NGC205.

OPTICAL–NEAR-INFRARED PHOTOMETRIC CALIBRATION OF M DWARF METALLICITY AND ITS APPLICATION

Based on a carefully constructed sample of dwarf stars, a new optical-near infrared photometric calibration to estimate the metallicity of late-type K and early-to-mid-type M dwarfs is presented. The calibration sample has two parts; the first part includes 18 M dwarfs with metallicities determined by high-resolution spectroscopy and the second part contains 49 dwarfs with metallicities obtained through moderate-resolution spectra. By applying this calibration to a large sample of around 1.3 million M dwarfs from the Sloan Digital Sky Survey and the Two-Micron All Sky Survey, the metallicity distribution of this sample is determined and compared with those of previous studies. Using photometric parallaxes, the Galactic heights of M dwarfs in the large sample are also estimated. Our results show that stars farther from the Galactic plane, on average, have lower metallicity, which can be attributed to the age-metallicity relation. A scarcity of metal-poor dwarf stars in the metallicity distribution relative to the Simple Closed Box Model indicates the existence of the "M dwarf problem," similar to the previously known G and K dwarf problems. Several more complicated Galactic chemical evolution models which have been proposed to resolve the G and K dwarf problems are tested and it is shown that these models could, to some extent, mitigate the M dwarf problem as well.

The M dwarf problem in the Galaxy

We present evidence that there is an M dwarf problem similar to the previously identified G dwarf and K dwarf problems: the number of low-metallicity M dwarfs is not sufficient to match simple closed-box models of local Galactic chemical evolution. We estimated the metallicity of 4141 M dwarf stars with spectra from the Sloan Digital Sky Survey (SDSS) using a molecular band strength versus metallicity calibration developed using high resolution spectra of nearby M dwarfs. Using a sample of M dwarfs with measured magnitudes, parallaxes, and metallicities, we derived a relation that describes the absolute magnitude variation as a function of metallicity. When we examined the metallicity distribution of SDSS stars, after correcting for the different volumes sampled by the magnitude-limited survey, we found that there is an M dwarf problem, with the number of M dwarfs at [Fe/H] ~ -0.5 less than 1% the number at [Fe/H] = 0, where a simple model of Galactic chemical evolution predicts a more gradual drop in star numbers with decreasing metallicity.

A simple multistage closed-(box+reservoir) model of chemical evolution

Simple closed-box (CB) models of chemical evolution are extended on two respects, namely (i) simple closed-(box+reservoir) (CBR) models allowing gas outflow from the box into the reservoir (Hartwick 1976) or gas inflow into the box from the reservoir (Caimmi 2007) with rate proportional to the star formation rate, and (ii) simple multistage closed-(box+reservoir) (MCBR) models allowing different stages of evolution characterized by different inflow or outflow rates. The theoretical differential oxygen abundance distribution (TDOD) predicted by the model maintains close to a continuous broken straight line. An application is made where a fictitious sample is built up from two distinct samples of halo stars and taken as representative of the inner Galactic halo. The related empirical differential oxygen abundance distribution (EDOD) is represented, to an acceptable extent, as a continuous broken line for two viable [O/H]-[Fe/H] empirical relations. The slopes and the intercepts of the regression lines are determined, and then used as input parameters to MCBR models. Within the errors (-+?), regression line slopes correspond to a large inflow during the earlier stage of evolution and to low or moderate outflow during the subsequent stages. A possible inner halo - outer (metal-poor) bulge connection is also briefly discussed. Quantitative results cannot be considered for applications to the inner Galactic halo, unless selection effects and disk contamination are removed from halo samples, and discrepancies between different oxygen abundance determination methods are explained.

Accreted versusin situMilky Way globular clusters

Here we examine the Milky Way's GC system to estimate the fraction of accreted versus in situ formed GCs. We first assemble a high quality database of ages and metallicities for 93 Milky Way GCs from literature deep colour-magnitude data. The age-metallicity relation for the Milky Way's GCs reveals two distinct tracks -- one with near constant old age of ~12.8 Gyr and the other branches to younger ages. We find that the latter young track is dominated by globular clusters associated with the Sagittarius and Canis Major dwarf galaxies. Despite being overly simplistic, its age-metallicity relation can be well represented by a simple closed box model with continuous star formation. The inferred chemical enrichment history is similar to that of the Large Magellanic Cloud, but is more enriched, at a given age, compared to the Small Magellanic Cloud. After excluding Sagittarius and Canis Major GCs, several young track GCs remain. Their horizontal branch morphologies are often red and hence classified as Young Halo objects, however they do not tend to reveal extended horizontal branches (a possible signature of an accreted remnant nucleus). Retrograde orbit GCs (a key signature of accretion) are commonly found in the young track. We also examine GCs that lie close to the Fornax-Leo-Sculptor great circle defined by several satellite galaxies. We find that several GCs are consistent with the young track and we speculate that they may have been accreted along with their host dwarf galaxy, whose nucleus may survive as a GC. Finally, we suggest that 27-47 GCs (about 1/4 of the entire system), from 6-8 dwarf galaxies, were accreted to build the Milky Way GC system we seen today.

The Gemini Deep Deep Survey. VII. The Redshift Evolution of the Mass‐Metallicity Relation

We have investigated the mass-metallicity (M-Z) relation using galaxies at 0.4 < z < 1.0 from the Gemini Deep Deep Survey (GDDS) and Canada-France Redshift Survey (CFRS). Deep K- and z'-band photometry allowed us to measure stellar masses for 69 galaxies. From a subsample of 56 galaxies, for which metallicity of the interstellar medium is also measured, we identified a strong correlation between mass and metallicity for the first time in the distant universe. This was possible because of the larger baseline spanned by the sample in terms of metallicity (a factor of 7) and mass (a factor of 400) than in previous works. This correlation is much stronger and tighter than the luminosity-metallicity relation, confirming that stellar mass is a more meaningful physical parameter than luminosity. We find clear evidence for temporal evolution in the M-Z relation in the sense that at a given mass, a galaxy at z ~ 0.7 tends to have lower metallicity than a local galaxy of similar mass. We use the z ~ 0.1 Sloan Digital Sky Survey M-Z relation and a small sample of z ~ 2.3 Lyman break galaxies with known mass and metallicity to propose an empirical redshift-dependent M-Z relation. According to this relation the stellar mass and metallicity in small galaxies evolve for a longer time than they do in massive galaxies. This relation predicts that the generally metal-poor damped Lyα galaxies have stellar masses of the order of 108.8 M☉ (with a dispersion of 0.7 dex) all the way from z ~ 0.2 to 4. The observed redshift evolution of the M-Z relation can be reproduced remarkably well by a simple closed-box model in which the key assumption is an e-folding time for star formation that is higher or, in other words, a period of star formation that lasts longer in less massive galaxies than in more massive galaxies. Such a picture supports the downsizing scenario for galaxy formation.

Complexity on Small Scales: The Metallicity Distribution of the Carina Dwarf Spheroidal Galaxy

The Carina dwarf spheroidal galaxy is the only galaxy of this type that shows clearly episodic star formation separated by long pauses. Here we present metallicities for 437 radial velocity members of this Galactic satellite. The metallicities and radial velocities were measured as part of a Large Programme with the Very Large Telescope at the European Southern Observatory, Chile. We obtained medium-resolution spectroscopy with the multiobject spectrograph FLAMES. Our target red giants cover the entire projected surface area of Carina. Our spectra are centered at the near-infrared Ca II triplet, which is a well-established metallicity indicator for old and intermediate-age red giants. The resulting data sample provides the largest collection of spectroscopically derived metallicities for a Local Group dwarf spheroidal galaxy to date. Four of our likely radial velocity members of Carina lie outside this galaxy's nominal tidal radius, supporting earlier claims of the possible existence of such stars beyond the main body of Carina. We find a mean metallicity of [Fe/H] ~ -1.7 dex on the 1997 metallicity scale of Carretta and Gratton for Carina. The formal FWHM of the metallicity distribution function is 0.92 dex, while the full range of metallicities is found to span approximately -3.0 dex < [Fe/H] < 0.0 dex. The metallicity distribution function might be indicative of several subpopulations distinct in metallicity. There appears to be a mild radial gradient such that more metal-rich populations are more centrally concentrated, matching a similar trend for an increasing fraction of intermediate-age stars (see the 2001 work of Harbeck and coworkers). This, as well as the photometric colors of the more metal-rich red giants, suggests that Carina exhibits an age-metallicity relation. Indeed, the age-metallicity degeneracy seems to conspire to form a narrow red giant branch despite the considerable spread in metallicity and wide range of ages. The metallicity distribution function is not well matched by a simple closed-box model of chemical evolution. Qualitatively better matches are obtained by chemical models that also take into account infall and outflows. A G dwarf problem remains for all these models.

The Distribution of Metallicity in the Intergalactic Medium atz ∼ 2.5: Oviand CivAbsorption in the Spectra of Seven QSOs

We present a direct measurement of the metallicity distribution function for the high-redshift intergalactic medium (IGM). We determine the shape of this function using survival statistics, which incorporate both detections and nondetections of O VI and C IV absorption, associated with H I lines in high-resolution quasar spectra. The O VI sample (taken from seven QSOs at zabs ~ 2.5) contains lines with N ≥ 1013.6, encompassing ~50% of all baryons at z ~ 2.5. Our survey accounts for ≈98.8% of the C IV mass and ≈90% of the O VI mass in the universe at this epoch. We find a median intergalactic abundance of [O,C/H] = -2.82; the differential abundance distribution is approximately lognormal with mean ≈ -2.85 and σ = 0.75 dex. We discuss the sensitivity of these results to the assumed form of the ionizing UV radiation field. Some ~60%-70% of lines in the Lyα forest are enriched to observable levels of [O,C/H] -3.5, while the remaining ~30% of the lines have even lower abundances. Thus we have not detected a universal metallicity floor, as has been suggested for some Population III enrichment scenarios. In fact, we argue that the bulk of the intergalactic metals formed later than the first stars that are thought to have triggered reionization. We do not observe a strong trend of decreasing metallicity toward the lower density IGM, at least within regions that would be characterized as filaments in numerical simulations. However, an [O/H] enhancement may be present at somewhat high densities. We estimate that roughly half of all baryons at these redshifts have been enriched to [O,C/H] -3.5. Using a simple closed box model for the metallicity evolution of the IGM, we estimate the chemical yield of galaxies formed prior to z ~ 2.5, finding that the typical galaxy recycled 0.1%-0.4% of its mass back into the IGM as heavy elements in the first 3 Gyr after the big bang.

Interstellar Medium Abundances in Sculptor Group Dwarf Irregular Galaxies

Using the Cerro Tololo Inter-American Observatory 4 m telescope, we have obtained optical spectra of H II regions in five Sculptor group dwarf irregular galaxies. We derive oxygen, nitrogen, and sulfur abundances from the H II region spectra. Oxygen abundances are derived via three different methods (the direct method, the empirical method guided by photoionization modeling of McGaugh [published in 1991], and the purely empirical method of Pilyugin, published in 2000) and are compared. Significant systematic differences are found between the three methods, and we suggest that a recalibration of the empirical abundance scale is required. Until differences between these three methods are better understood, the issue of the degree of uniformity of the interstellar medium abundances in a dwarf galaxy cannot be properly addressed. The N/O ratio for the metal-poor dI ESO 473-G24 of log (N/O) = -1.43 ± 0.03 lies well above the plateau of log (N/O) = -1.60 ± 0.02 found by Izotov & Thuan for a collection of metal-poor, blue compact galaxies. This shows that not all galaxies with 12 + log (O/H) ≤ 7.6 have identical elemental abundance ratios, and this implies that the Izotov & Thuan scenario for low-metallicity galaxies is not universal. Measurements of the H II regions in NGC 625 yield log (N/O) ≈ -1.25. Assuming N production by intermediate-mass stars, this relatively high N/O ratio may be indicative of a long quiescent period prior to the recent active burst of star formation. The oxygen abundances in the Sculptor group dI's are in good agreement with the relationship between metallicity and luminosity observed in the Local Group dI's. Taken together, the observations show a better relationship between metallicity and luminosity than between metallicity and galaxy central surface brightness. The Sculptor group dI's, in general, lie closer to the simple closed-box model evolutionary path than the Local Group dI's. The higher gas contents, lower average star formation rates, and closer resemblance to closed-box evolution could all be indicative of evolution in a relatively low density environment.

Uncovering Additional Clues to Galaxy Evolution. I. Dwarf Irregular Galaxies in the Field

In order to recognize environmental effects on the evolution of dwarf galaxies in clusters of galaxies, it is first necessary to quantify the properties of objects that have evolved in relative isolation. With oxygen abundance as the gauge of metallicity, two key diagnostics of the evolution of dwarf irregular galaxies in the field are reexamined: the metallicity-luminosity relationship and the metallicity–gas fraction relationship. Gas fractions are evaluated from the masses of luminous components only, i.e., constituents of the nucleogenetic pool. Results from new optical spectroscopy obtained for H II regions in five dwarf irregular galaxies in the local volume are incorporated into a new analysis of field dwarfs with [O III] λ4363 detections and good distances. The updated fit to the metallicity-luminosity relationship is consistent with results reported in the literature. The fit to the metallicity–gas fraction relation shows an excellent correlation consistent with expectations of the simple closed box model of chemical evolution. The simplest explanation consistent with the data is that flow rates are zero, although the observations allow for the possibility of modest flows. The derived oxygen yield is one-quarter of the value for the solar neighborhood.

On the effect of discrete numbers of stars in chemical evolution models

We examine the impact of discrete numbers of stars in stellar populations on the results of Chemical Evolution Models. We explore the resulting dispersion in the true yields and their possible relation with the dispersion in observational data based on a Simple Closed-Box model. In this framework we find that the dispersion is larger for the less evolved or low abundance regions. Thus, the age-metallicity relation may be a tracer of the Star Formation History of our Galaxy. This theoretical dispersion is especially high for the relative abundance log(N/O) in regions where the total number of stars created is still low. This may explain part of the scatter in the N/O ratio observed in star forming galaxies. We have also found a first order theoretical estimation for the goodness of a linear fit of the Helium abundance vs. 12 + log (O/H) with values of the regression coefficient between 0.9 and 0.7 (independent of sampling effects). We conclude that it is necessary to include these sampling effects in a more realistic Chemical Evolution Model in order that such a model reproduces, at the same time, the mean value and the dispersion of observed abundances.

A revision of the solar neighbourhood metallicity distribution

We present a revised metallicity distribution of dwarfs in the solar neighbourhood. This distribution is centred on solar metallicity. We show that previous metallicity distributions, selected on the basis of spectral type, are biased against stars with solar metallicity or higher. A selection of G-dwarf stars is inherently biased against metal rich stars and is not representative of the solar neighbourhood metallicity distribution. Using a sample selected on colour, we obtain a distribution where approximately half the stars in the solar neighbourhood has a metallicity higher than [Fe/H]=0. The percentage of mid-metal-poor stars ([Fe/H]$<$-0.5) is approximately 4 per cent, in agreement with present estimates of the thick disc. In order to have a metallicity distribution comparable to chemical evolution model predictions, we convert the star fraction to mass fraction, and show that another bias against metal-rich stars affects dwarf metallicity distributions, due to the colour (or spectral type) limits of the samples. Reconsidering the corrections due to the increasing thickness of the stellar disc with age, we show that the Simple Closed-Box model with no instantaneous recycling approximation gives a reasonable fit to the observed distribution. Comparisons with the age-metallicity relation and abundance ratios suggest that the Simple Closed-Box model may be a viable model of the chemical evolution of the Galaxy at solar radius.

The Metallicity Distribution in the Halo Stars of NGC 5128: Implications for Galaxy Formation

The Hubble Space Telescope has been used to obtain WFPC2 (V,I) photometry for a sample of 10,000 red giant stars the outer halo of the giant elliptical NGC 5128. Comparison with the fiducial RGBs of Milky Way globular clusters and model isochrones demonstrates that this outer-halo population is completely dominated by old stars, with an extremely broad metallicity range extending from the most metal-poor Galactic globulars at [Fe/H] = -2 up to Solar abundance. By interpolation within the fiducial lines we derive the metallicity distribution function (MDF) for the halo, which turns out to have a distinct two-component structure: about 2/3 of the stars belong to a sharply peaked metal-richer component ([Fe/H] = -0.3, sigma = 0.22 dex), while the remaining one-third belong to a more extended metal-poor distribution sloping gradually down to low metallicity. The MDF can be remarkably well matched by a simple closed-box model of chemical enrichment, where the first component starts with an initial abundance Z_0 =0 and the second component with Z_0 = 0.18 Z_Sun. A basic in situ formation picture with two distinct epochs of star formation fits the observations better than other models involving major contributions from accretions or mergers.

The Formation of the Galactic Bulge

The question is adressed whether the problem of the stellar metallicity distribution and the dynamics of the stellar components in the bulge as found out by refined observations during recent years can be understood within the context of the evolution of the whole Galaxy. A selfconsistent galaxy model has to explain the apparent differences in the effective yields of the enrichment of bulge, disk and halo. Moreover, it has to account for the observed age-metallicity distribution of the stellar components. It appears that chemo-dynamical infall models provide a consistent description of the bulge, in particular the metallicity distribution of the K giants. It should be emphasized that simple closed-box models are not appropriate, because during the bulge formation there is infall of cloudy medium (CM), as well as outflow of hot, ionized gas ejected by supernovae type II (SNII). Therefore dynamical processes have to be taken into account. For details of the chemo-dynamical description we refer to Samland &amp; Hensler (1994) and references therein.

Case study on the interaction of size dependent multiphase chemistry and detailed microphysics

It is widely accepted that clouds and precipitation systems are very important for the transformation and redistribution of chemical species in the atmosphere. Cloud droplets provide an alternate medium to the gas phase in which chemical reactions may proceed. The spectral composition of the droplets, on the one hand, is controlled by the drop formation via the activation of cloud condensation nuclei (CCN), the uptake of trace-gases and aqueous-phase chemical reactions. On the other hand, the chemical composition of the drops affects the dissolution of trace-gases and the rates and equilibria of the aqueous-phase reactions. A simple closed box model including explicitly spectral microphysics and a representative chemical mechanism is used to study the time evolution of the spectrally chemical composition of cloud droplets and to contrast the effects of dilution by condensation, of mixing by coagulation and break-up, of liquid phase reactions, and of interaction between the phases. The presented study suggest that cloud droplets of different sizes have different solute concentrations determined by the activation of size distributed aerosol particles and affected by condensation, coagulation, and break-up. If a chemically homogeneous aerosol distribution is assumed, the droplets of different sizes will have in this manner different dilutions and different pH but equal ratios between the aerosol related compounds. If also gas-liquid interactions and liquid-phase reactions are taken into account, the different pH and mass transfer coefficients in conjunction with microphysical processes will lead to quite different chemical composition over the drop spectrum and to a change of the spectral pH level.

The metallicity distribution of G and K giants in Baade's window

view Abstract Citations (46) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Metallicity Distribution of G and K Giants in Baade's Window Geisler, Doug ; Friel, Eileen D. Abstract Metal abundances accurate to 0.25 dex have been obtained for a large (314) and unbiased sample of G and K giants in Baade's Window from Washington CCD photometry. Good agreement is obtained with the results of Rich based on intermediate resolution spectra of 88 K giants, including the derived metallicities for 15 stars in common. The abundance distribution ranges from about 0.1 to 10 times solar, with a mean Fe/H = +0.17 +/- 0.15, a mean linear abundance of 2.3 +/- 0.5 times solar and a large intrinsic dispersion of about 0.35 dex. A quarter of the sample have Fe/H greater than +0.5, two-thirds exceed the sun's metallicity, and only 8 percent are more metal poor than Fe/H = -0.5. The metallicity distribution function is very well fit by the simple closed box model of Galactic chemical evolution with complete gas consumption. Publication: The Astronomical Journal Pub Date: July 1992 DOI: 10.1086/116225 Bibcode: 1992AJ....104..128G Keywords: Charge Coupled Devices; G Stars; Galactic Bulge; Galactic Evolution; Giant Stars; K Stars; Metallicity; Abundance; Color-Magnitude Diagram; Hydrogen; Iron; Stellar Composition; Stellar Spectrophotometry; Astrophysics; STARS: GIANT; STARS: ABUNDANCES full text sources ADS | data products SIMBAD (4)