Unravelling the mass spectrum of destroyed dwarf galaxies with the metallicity distribution function (original) (raw)
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Monthly Notices of the Royal Astronomical Society, 2020
We use magneto-hydrodynamical simulations of Milky Way-mass haloes from the Auriga project to investigate the properties of surviving and destroyed dwarf galaxies that are accreted by these haloes over cosmic time. We show that the combined luminosity function of surviving and destroyed dwarfs at infall is similar in the various Auriga haloes, and is dominated by the destroyed dwarfs. There is, however, a strong dependence on infall time: destroyed dwarfs typically have early infall times of less than 6 Gyr (since the Big Bang), whereas the majority of dwarfs accreted after 10 Gyr have survived to the present day. Because of their late infall, the surviving satellites have higher metallicities at infall than their destroyed counterparts of similar mass at infall; the difference is even more pronounced for the present-day metallicities of satellites, many of which continue to form stars after infall, in particular for M star > 10 7 M. In agreement with previous work, we find that a small number of relatively massive destroyed dwarf galaxies dominate the mass of stellar haloes. However, there is a significant radial dependence: while 90 percent of the mass in the inner regions (< 20 kpc) is contributed, on average, by only 3 massive progenitors, the outer regions (> 100 kpc) typically have ∼ 8 main progenitors of relatively lower mass. Finally, we show that a few massive progenitors dominate the metallicity distribution of accreted stars, even at the metal-poor end. Contrary to common assumptions in the literature, stars from dwarf galaxies of mass M star < 10 7 M make up less than 10 percent of the accreted, metal poor stars ([Fe/H] < −3) in the inner 50 kpc.
Stellar masses and star formation histories for 105 galaxies from the Sloan Digital Sky Survey
Monthly Notices of …, 2003
We develop a new method to constrain the star formation histories, dust attenuation and stellar masses of galaxies. It is based on two stellar absorption line indices, the 4000Å break strength and the Balmer absorption line index Hδ A . Together, these indices allow us to constrain the mean stellar ages of galaxies and the fractional stellar mass formed in bursts over the past few Gyr. A comparison with broad band photometry then yields estimates of dust attenuation and of stellar mass. We generate a large library of Monte Carlo realizations of different star formation histories, including starbursts of varying strength and a range of metallicities. We use this library to generate median likelihood estimates of burst mass fractions, dust attenuation strengths, stellar masses and stellar mass-to-light ratios for a sample of 122,808 galaxies drawn from the Sloan Digital Sky Survey. The typical 95% confidence range in our estimated stellar masses is ± 40 %. We study how the stellar mass-to-light ratios of galaxies vary as a function of absolute magnitude, concentration index and photometric pass-band and how dust attenuation varies as a function of absolute magnitude and 4000Å break strength. We also calculate how the total stellar mass of the present Universe is distributed over galaxies as a function of their mass, size, concentration, colour, burst mass fraction and surface mass density. We find that most of the stellar mass in the local Universe resides in galaxies that have, to within a factor of about 2, stellar masses ∼ 5×10 10 M ⊙ , half-light radii ∼ 3 kpc, and half-light surface mass densities ∼ 10 9 M ⊙ kpc −2 . The distribution of D n (4000) is strongly bimodal, showing a clear division between galaxies dominated by old stellar populations and galaxies with more recent star formation.
Monthly Notices of the Royal Astronomical Society
We study the internal gradients of stellar population properties within 1.5 R e for a representative sample of 721 galaxies with stellar masses ranging between 10 9 M to 10 11.5 M from the SDSS-IV MaNGA IFU survey. Through the use of our full spectral fitting code FIREFLY, we derive light and mass-weighted stellar population properties and their radial gradients, as well as full star formation and metal enrichment histories. We also quanfify the impact that different stellar population models and full spectral fitting routines have on the derived stellar population properties, and the radial gradient measurements. In our analysis, we find that age gradients tend to be shallow for both early-type and late-type galaxies. Massweighted age gradients of early-types are positive (∼ 0.09 dex/R e) pointing to "outside-in" progression of star formation, while late-type galaxies have negative light-weighted age gradients (∼ −0.11 dex/R e), suggesting an "inside-out" formation of discs. We detect negative metallicity gradients in both early and late-type galaxies, but these are significantly steeper in late-types, suggesting that radial dependence of chemical enrichment processes and the effect of gas inflow and metal transport are far more pronounced in discs. Metallicity gradients of both morphological classes correlate with galaxy mass, with negative metallicity gradients becoming steeper with increasing galaxy mass. The correlation with mass is stronger for late-type galaxies, with a slope of d(∇[Z/H])/d(log M) ∼ −0.2 ± 0.05 , compared to d(∇[Z/H])/d(log M) ∼ −0.05 ± 0.05 for early-types. This result suggests that the merger history plays a relatively small role in shaping metallicity gradients of galaxies.
The ages and metallicities of galaxies in the local universe
Monthly Notices of …, 2005
We derive stellar metallicities, light-weighted ages and stellar masses for a magnitudelimited sample of 175,128 galaxies drawn from the Sloan Digital Sky Survey Data Release Two (SDSS DR2). We compute median-likelihood estimates of these parameters using a large library of model spectra at medium-high resolution, covering a comprehensive range of star formation histories. The constraints we derive are set by the simultaneous fit of five spectral absorption features, which are well reproduced by our population synthesis models. By design, these constraints depend only weakly on the α/Fe element abundance ratio. Our sample includes galaxies of all types spanning the full range in star formation activity, from dormant early-type to actively starforming galaxies. By analysing a subsample of 44,254 high-quality spectra, we show that, in the mean, galaxies follow a sequence of increasing stellar metallicity, age and stellar mass at increasing 4000Å-break strength. For galaxies of intermediate mass, stronger Balmer absorption at fixed 4000Å-break strength is associated with higher metallicity and younger age. We investigate how stellar metallicity and age depend on total galaxy stellar mass. Low-mass galaxies are typically young and metal-poor, massive galaxies old and metal-rich, with a rapid transition between these regimes over the stellar mass range 3 × 10 9 M * 3 × 10 10 M ⊙ . Both high-and low-concentration galaxies follow these relations, but there is a large dispersion in stellar metallicity at fixed stellar mass, especially for low-concentration galaxies of intermediate mass.
Elemental abundances in Milky Way-like galaxies from a hierarchical galaxy formation model
We develop a new method to account for the finite lifetimes of stars and trace individual abundances within a semi-analytic model of galaxy formation. At variance with previous methods, based on the storage of the (binned) past star formation history of model galaxies, our method projects the information about the metals produced by each simple stellar population (SSP) in the future. Using this approach, an accurate accounting of the timings and properties of the individual SSPs composing model galaxies is possible. We analyse the dependence of our chemical model on various ingredients, and apply it to six simulated haloes of roughly Milky Way mass and with no massive close neighbour at z=0. For all models considered, the [Fe/H] distributions of the stars in the disc component are in good agreement with Milky Way data, while for the spheroid component (whose formation we model only through mergers) these are offset low with respect to observational measurements for the Milky Way bulge. This is a consequence of narrow star formation histories, with relatively low rates of star formation. The slow recycling of gas and energy from supernovae in our chemical model has important consequences on the predicted star formation rates, which are systematically lower than the corresponding rates in the same physical model but with an instantaneous recycling approximation. The halo that resembles most our Galaxy in terms of its global properties also reproduces the observed relation between the average metallicity and luminosity of the Milky Way satellites, albeit with a slightly steeper slope.
The Astrophysical Journal Supplement Series
Building on the relatively accurate star formation histories (SFHs) and metallicity evolution of 40 Local Group (LG) dwarf galaxies derived from resolved color-magnitude diagram modeling, we carried out a comprehensive study of the influence of SFHs, metallicity evolution, and dust extinction on the UV-to-near-IR color-mass-to-light ratio (color- ¡ log (λ)) distributions and M å estimation of local universe galaxies. We find that (1) the LG galaxies follow color- ¡ log (λ) relations that fall in between the ones calibrated by previous studies; (2) optical color- ¡ log (λ) relations at higher [M/H] are generally broader and steeper; (3) the SFH "concentration" does not significantly affect the color- ¡ log (λ) relations; (4) light-weighted ages á ñ l age and metallicities á ñ l [ ] M H together constrain ¡ log (λ) with uncertainties ranging from 0.1 dex for the near-IR up to 0.2 dex for the optical passbands; (5) metallicity evolution induces significant uncertainties to the optical but not near-IR ¡ (λ) at a given á ñ l age and á ñ l [ ] M H ; (6) the V band is the ideal luminance passband for estimating ¡ (λ) from single colors, because the combinations of ¡ (V) and optical colors such as B − V and g − r exhibit the weakest systematic dependences on SFHs, metallicities, and dust extinction; and (7) without any prior assumption on SFHs, M å is constrained with biases 0.3 dex by the optical-to-near-IR SED fitting. Optical passbands alone constrain M å with biases 0.4 dex (or 0.6 dex) when dust extinction is fixed (or variable) in SED fitting. SED fitting with monometallic SFH models tends to underestimate M å of real galaxies. M å tends to be overestimated (or underestimated) at the youngest (or oldest) á ñ age mass .
The Origin of the Mass--Metallicity Relation: Insights from 53,000 Star-Forming Galaxies in the SDSS
Arxiv preprint astro-ph/ …, 2004
We utilize Sloan Digital Sky Survey imaging and spectroscopy of ∼53,000 star-forming galaxies at z ∼ 0.1 to study the relation between stellar mass and gas-phase metallicity. We derive gas-phase oxygen abundances and stellar masses using new techniques which make use of the latest stellar evolutionary synthesis and photoionization models. We find a tight (±0.1 dex) correlation between stellar mass and metallicity spanning over 3 orders of magnitude in stellar mass and a factor of 10 in metallicity. The relation is relatively steep from 10 8.5 -10 10.5 M ⊙ h −2 70 , in good accord with known trends between luminosity and metallicity, but flattens above 10 10.5 M ⊙ . We use indirect estimates of the gas mass based on the Hα luminosity to compare our data to predictions from simple closed box chemical evolution models. We show that metal loss is strongly anti-correlated with baryonic mass, with low mass dwarf galaxies being 5 times more metal-depleted than L * galaxies at z ∼ 0.1. Evidence for metal depletion is not confined to dwarf galaxies, but is found in galaxies with masses as high as 10 10 M ⊙ . We interpret this as strong evidence both of the ubiquity of galactic winds and of their effectiveness in removing metals from galaxy potential wells.
The Astrophysical …, 2004
We utilize Sloan Digital Sky Survey imaging and spectroscopy of 53,000star−forminggalaxiesatz53,000 star-forming galaxies at z 53,000star−forminggalaxiesatz 0:1 to study the relation between stellar mass and gas-phase metallicity. We derive gas-phase oxygen abundances and stellar masses using new techniques that make use of the latest stellar evolutionary synthesis and photoionization models. We find a tight (AE0.1 dex) correlation between stellar mass and metallicity spanning over 3 orders of magnitude in stellar mass and a factor of 10 in metallicity. The relation is relatively steep from 10 8.5 to 10 10.5 M h À2 70 , in good accord with known trends between luminosity and metallicity, but flattens above 10 10.5 M . We use indirect estimates of the gas mass based on the H luminosity to compare our data to predictions from simple closed box chemical evolution models. We show that metal loss is strongly anticorrelated with baryonic mass, with lowmass dwarf galaxies being 5 times more metal depleted than L Ã galaxies at z $ 0:1. Evidence for metal depletion is not confined to dwarf galaxies but is found in galaxies with masses as high as 10 10 M . We interpret this as strong evidence of both the ubiquity of galactic winds and their effectiveness in removing metals from galaxy potential wells.
Monthly Notices of the Royal Astronomical Society, 2018
We present a comparison of the observed evolving galaxy stellar mass functions with the predictions of eight semi-analytic models and one halo occupation distribution model. While most models are able to fit the data at low redshift, some of them struggle to simultaneously fit observations at high redshift. We separate the galaxies into 'passive' and 'star-forming' classes and find that several of the models produce too many low-mass star-forming galaxies at high redshift compared to observations, in some cases by nearly a factor of 10 in the redshift range 2.5 < z < 3.0. We also find important differences in the implied mass of the dark matter haloes the galaxies inhabit, by comparing with halo masses inferred from observations. Galaxies at high redshift in the models are in lower mass haloes than suggested by observations, and the star formation efficiency in low-mass haloes is higher than observed. We conclude that many of the models require a physical prescription that acts to dissociate the growth of low-mass galaxies from the growth of their dark matter haloes at high redshift.
The evolution of the mass-metallicity relation in galaxies of different morphological types
Astronomy and Astrophysics, 2009
Aims. By means of chemical evolution models for ellipticals, spirals and irregular galaxies, we aim at investigating the physical meaning and the redshift evolution of the mass-metallicity relation as well as how this relation is connected with galaxy morphology. Methods. Our models distinguish among different morphological types through the use of different infall, outflow, and star formation prescriptions. We assume that galaxy morphologies do not change with cosmic time. We present a method to account for a spread in the epochs of galaxy formation and to refine the galactic mass grid. To do that, we extract the formation times randomly and assume an age dispersion ∆ t . We compare our predictions to observational results obtained for galaxies between redshifts 0.07 and 3.5. Results. We reproduce the mass-metallicity (MZ) relation mainly by means of an increasing efficiency of star formation with mass in galaxies of all morphological types, without any need to invokegalactic outflows favoring the loss of metals in the less massive galaxies. Our predictions can help constraining the slope and the zero point of the observed local MZ relation, both affected by uncertainties related to the use of different metallicity calibrations. We show how, by considering the MZ, the O/H vs star formation rate (SFR), and the SFR vs galactic mass diagrams at various redshifts, it is possible to constrain the morphology of the galaxies producing these relations. Our results indicate that the galaxies observed at z = 3.5 should be mainly proto-ellipticals, whereas at z = 2.2 the observed galaxies consist of a morphological mix of proto-spirals and proto-ellipticals. At lower redshifts, the observed MZ relation is well reproduced by considering both spirals and irregulars. Galaxies with different star formation histories may overlap in the MZ diagram, but measures of abundance ratios such as [O/Fe] can help to break this degeneracy. Predictions for the MZ relations for other elements (C, N, Mg, Si, Fe) are also presented, with largest dispersions predicted for elements produced in considerable amounts by Type Ia SNe, owing to the long lifetimes of their progenitors.