arXiv subjects

Guinevere Kauffmann

Publications and source records attributed to Guinevere Kauffmann.

At least 73 records · Page 4Linked to original sources

arXiv2015

Connection Between the Circumgalactic Medium and the Interstellar Medium of Galaxies: Results from the COS-GASS Survey

We present a study exploring the nature and properties of the Circum-Galactic Medium (CGM) and its connection to the atomic gas content in the interstellar medium (ISM) of galaxies as traced by the HI 21cm line. Our sample includes 45 low-z (0.026-0.049) galaxies from the GALEX Arecibo SDSS Survey. Their CGM was probed via absorption in the spectra of background Quasi-Stellar Objects at impact parameters of 63 to 231kpc. The spectra were obtained with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope. We detected neutral hydrogen (Ly$α$ absorption-lines) in the CGM of 92% of the galaxies. We find the radial profile of the CGM as traced by the Ly$α$ equivalent width can be fit as an exponential with a scale length of roughly the virial radius of the dark matter halo. We found no correlation between the orientation of sightline relative to the galaxy major axis and the Ly$α$ equivalent width. The velocity spread of the circumgalactic gas is consistent with that seen in the atomic gas in the interstellar medium. We find a strong correlation (99.8% confidence) between the gas fraction (M(HI)/M*) and the impact-parameter-corrected Ly$α$ equivalent width. This is stronger than the analogous correlation between corrected Ly$α$ equivalent width and SFR/M* (97.5% confidence). These results imply a physical connection between the HI disk and the CGM, which is on scales an order-of-magnitude larger. This is consistent with the picture in which the HI disk is nourished by accretion of gas from the CGM.

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arXiv2015

Physical origin of the large-scale conformity in the specific star formation rates of galaxies

Two explanations have been put forward to explain the observed conformity between the colours and specific star formation rates (SFR/$M_*$) of galaxies on large scales: 1) the formation times of their surrounding dark matter halos are correlated (commonly referred to as "assembly bias"), 2) gas is heated over large scales at early times, leading to coherent modulation of cooling and star formation between well-separated galaxies (commonly referred to as "pre-heating") . To distinguish between the pre-heating and assembly bias scenarios, we search for relics of energetic feedback events in the neighbourhood of central galaxies with different specific star formation rates. We find a significant excess of very high mass ($\log M_* > 11.3$) galaxies out to a distance of 2.5 Mpc around low SFR/$M_*$ central galaxies compared to control samples of higher SFR/$M_*$ central galaxies with the same stellar mass and redshift. We also find that very massive galaxies in the neighbourhood of low SFR/$M_*$ galaxies have much higher probability of hosting radio loud active galactic nuclei. The radio-loud AGN fraction in neighbours with $\log M_* > 11.3$ is four times higher around passive, non star-forming centrals at projected distances of 1 Mpc and two times higher at projected distances of 4 Mpc. Finally, we carry out an investigation of conformity effects in the recently publicly-released Illustris cosmological hydrodynamical simulation, which includes energetic input both from quasars and from radio mode accretion onto black holes. We do not find conformity effects of comparable amplitude on large scales in the simulations and we propose that gas needs to be pushed out of dark matter halos more efficiently at high redshifts.

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arXiv2015

The variation in molecular gas depletion time among nearby galaxies: II the impact of galaxy internal structures

We use a data set of nearby galaxies drawn from the HERACLES, ATLAS3D, and COLD GASS surveys to study variations in molecular gas depletion time (Tdep) in galaxy structures such as bulges, grand-design spiral arms, bars and rings. Molecular gas is traced by CO line emission and star formation rate (SFR) is derived using the combination of far-ultraviolet and mid-infrared (MIR) data. The contribution of old stars to MIR emission for the ATLAS3D sample is corrected using 2MASS K-band images. We apply a two-dimensional image decomposition algorithm to decompose galaxies into bulges and discs. Spiral arms, bars and rings are identified in the residual maps, and molecular gas depletion times are derived on a square grid of 1 kpc^2 size. In previous work, we showed that Tdep correlates strongly with specific star formation rate (sSFR). We now find that at a given sSFR, the bulge has shorter Tdep than the disc. The shift to shorter depletion times is most pronounced in the inner bulge (R < 0.1Re). Grids from galaxies with bars and rings are similar to those from galactic bulges in that they have reduced Tdep at a given sSFR. In contrast, the Tdep versus sSFR relation in the discs of galaxies with spiral arms is displaced to longer Tdep at fixed sSFR. We then show that the differences in the Tdep-sSFR relation for bulges, discs, arms, bars and rings can be linked to variations in "stellar", rather than gas surface density between different structures. Our best current predictor for Tdep, both globally and for 1 kpc grids, is given by Tdep= -0.36log(Sigma_SFR)-0.5log(Sigma_*)+5.87.

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arXiv2015

A systematic study of the inner rotation curves of galaxies observed as part of the GASS and COLD GASS surveys

We present a systematic analysis of the rotation curves of 187 galaxies with masses greater than 10^10 M_sol, with atomic gas masses from the GALEX Arecibo Sloan Survey (GASS), and with follow-up long-slit spectroscopy from the MMT. Our analysis focuses on stellar rotation curves derived by fitting stellar template spectra to the galaxy spectra binned along the slit. In this way, we are able to obtain accurate rotation velocity measurements for a factor of 2 more galaxies than possible with the Halpha line. Galaxies with high atomic gas mass fractions are the most dark-matter dominated galaxies in our sample and have dark matter halo density profiles that are well fit by Navarro, Frenk & White profiles with an average concentration parameter of 10. The inner slopes and of the rotation curves correlate more strongly with stellar population age than with galaxy mass or structural parameters. At fixed stellar mass, the rotation curves of more actively star-forming galaxies have steeper inner slopes than less actively star-forming galaxies. The ratio between the galaxy specific angular momentum and the total specific angular momentum of its dark matter halo, R_j, correlates strongly with galaxy mass, structure and gas content. Low mass, disk-dominated galaxies with atomic gas mass fractions greater than 20% have median values of R_j of around 1, but massive, bulge-dominated galaxies have R_j=0.2-0.3. We argue that these trends can be understood in a picture where gas inflows triggered by disk instabilities lead to the formation of passive, bulge-dominated galaxies with low specific angular momentum.

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arXiv2015

HI scaling relations of galaxies in the environment of HI-rich and control galaxies observed by the Bluedisk project

Our work is based on the "Bluedisk" project, a program to map the neutral gas in a sample of 25 HI-rich spirals and a similar number of control galaxies with the Westerbork Synthesis Radio Telescope (WSRT). In this paper we focus on the HI properties of the galaxies in the environment of our targeted galaxies. In total, we extract 65 galaxies from the WSRT cubes with stellar masses between $10^8M_{\odot}$ and $10^{11}M_{\odot}$. Most of these galaxies are located on the same HI mass-size relation and "HI-plane" as normal spiral galaxies. We find that companions around HI-rich galaxies tend to be HI-rich as well and to have larger R90,HI/R50,HI. This suggests a scenario of "HI conformity", similar to the colour conformity found by Weinmann et al. (2006): galaxies tend to adopt the HI properties of their neighbours. We visually inspect the outliers from the HI mass-size relation and galaxies which are offset from the HI plane and find that they show morphological and kinematical signatures of recent interactions with their environment. We speculate that these outliers have been disturbed by tidal or ram-pressure stripping processes, or in a few cases, by accretion events.

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arXiv2015

The spatially resolved Kennicutt-Schmidt relation in the HI dominated regions of spiral and dwarf irregular galaxies

We study the Kennicutt-Schmidt relation between average star formation rate and average cold gas surface density in the Hi dominated ISM of nearby spiral and dwarf irregular galaxies. We divide the galaxies into grid cells varying from sub-kpc to tens of kpc in size. Grid-cell measurements of low SFRs using H-alpha emission can be biased and scatter may be introduced because of non-uniform sampling of the IMF or because of stochastically varying star formation. In order to alleviate these issues, we use far-ultraviolet emission to trace SFR, and we sum up the fluxes from different bins with the same gas surface density to calculate the average $Σ_{SFR}$ at a given value of $Σ_{gas}$. We study the resulting Kennicutt-Schmidt relation in 400 pc, 1 kpc and 10 kpc scale grids in nearby massive spirals and in 400 pc scale grids in nearby faint dwarf irregulars. We find a relation with a power law slope of 1.5 in the HI-dominated regions for both kinds of galaxies. The relation is offset towards longer gas consumption timescales compared to the molecular hydrogen dominated centres of spirals, but the offset is an order-of-magnitude less than that quoted by earlier studies. Our results lead to the surprising conclusion that conversion of gas to stars is independent of metallicity in the HI dominated regions of star-forming galaxies. Our observed relations are better fit by a model of star formation based on thermal and hydrostatic equilibrium in the ISM, in which feedback driven turbulence sets the thermal pressure.

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arXiv2015

The Variation in Molecular Gas Depletion Time among Nearby Galaxies: What are the Main Parameter Dependencies?

We re-analyze correlations between global molecular gas depletion time (Tdep) and galaxy parameters including stellar mass, specific star formation rate (sSFR), stellar mass surface density and concentration index. The analysis is based on the COLD GASS survey, which includes galaxies with stellar mass in the range 10^10 - 10^11.5 Msun with molecular gas mass estimates derived from CO(1-0) line measurements. We improve on previous work by Saintonge et al. (2011b) by estimating SFRs using the combination of GALEX FUV and WISE 22 micron data and by deriving Tdep within a fixed aperture set by the IRAM beam size. In our new study we find correlations with much smaller scatter. Dependences of the Tdep on galaxy structural parameters such as stellar mass surface density and concentration index are now weak or absent. Differences with previous work arise because dust extinction correlates strongly with galaxy structural parameters. We further demonstrate that the 'primary' global parameter correlation is between Tdep and sSFR; all other remaining correlations can be shown to be induced by this primary dependence. This implies that galaxies with high current-to-past-averaged star formation activity, will drain their molecular gas reservoir sooner. We then analyze molecular gas depletion times on 1-kpc scales in galactic disks using data from the HERACLES survey. There is remarkably good agreement between the global Tdep versus sSFR relation for the COLD GASS galaxies and that derived for 1 kpc scale grid regions in disks. The strong correlation between Tdep and sSFR extends continuously over a factor of 10 in Tdep from log(SFR/M*) = -11.5 to -9, i.e. from nearly quiescent patches of the disk to disk regions with very strong star formation. This leads to the conclusion that the local molecular gas depletion time in galactic disks is dependent on the local fraction of young-to-old stars.

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arXiv2015

The Outer Stellar Populations and Environments of Unusually HI-rich Galaxies

We investigate the nature of HI-rich galaxies from the ALFALFA and GASS surveys, which are defined as galaxies in the top 10th percentile in atomic gas fraction at a given stellar mass. We analyze outer (R>1.5 Re) stellar populations for a subset of face-on systems using optical g-r versus r-z colour/colour diagrams. The results are compared with those from control samples that are defined without regard to atomic gas content, but are matched in redshift, stellar mass and structural parameters. HI-rich early-type (C>2.6) and late-type (C<2.6) galaxies are studied separately. When compared to the control sample, the outer stellar populations of the majority of HI-rich early-type galaxies are shifted in the colour/colour plane along a locus consistent with younger stellar ages, but similar metallicities. The outer colours of HI-rich late-type galaxies are much bluer in r-z than the HI-rich early types, and we infer that they have outer disks which are both younger and more metal-poor. We then proceed to analyze the galaxy environments of HI-rich galaxies on scales of 500 kpc. HI-rich early-type galaxies with low (log M* < 10.5) stellar masses differ significantly from the control sample in that they are more likely to be central rather than satellite systems. Their satellites are also less massive and have younger stellar populations. Similar, but weaker effects are found for low mass HI-rich late-type galaxies. In addition, we find that the satellites of HI-rich late-types exhibit a greater tendency to align along the major axis of the primary. No environmental differences are found for massive (log M* > 10.5) HI-rich galaxies, regardless of type.

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arXiv2014

The nature of obscuration in AGN: II. insights from clustering properties

Based on large optical and mid-infrared (IR) surveys, we investigate the relation between nuclear activity in local Seyfert 2 galaxies and galaxy interactions using a statistical neighbour counting technique. At the same level of host galaxy star formation (SF), we find that active galactic nuclei (AGNs) with stronger [OIII] emission lines do not show an excess of near neighbours, while AGNs with stronger mid-IR emission do have more near neighbours within a projected distance of 100 kpc. The excess neighbour count increases with decreasing projected radius. These results suggest a phase of torus formation during galaxy interactions.

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arXiv2014

Overview of the SDSS-IV MaNGA Survey: Mapping Nearby Galaxies at Apache Point Observatory

We present an overview of a new integral field spectroscopic survey called MaNGA (Mapping Nearby Galaxies at Apache Point Observatory), one of three core programs in the fourth-generation Sloan Digital Sky Survey (SDSS-IV) that began on 2014 July 1. MaNGA will investigate the internal kinematic structure and composition of gas and stars in an unprecedented sample of 10,000 nearby galaxies. We summarize essential characteristics of the instrument and survey design in the context of MaNGA's key science goals and present prototype observations to demonstrate MaNGA's scientific potential. MaNGA employs dithered observations with 17 fiber-bundle integral field units that vary in diameter from 12" (19 fibers) to 32" (127 fibers). Two dual-channel spectrographs provide simultaneous wavelength coverage over 3600-10300 A at R~2000. With a typical integration time of 3 hr, MaNGA reaches a target r-band signal-to-noise ratio of 4-8 (per A, per 2" fiber) at 23 AB mag per sq. arcsec, which is typical for the outskirts of MaNGA galaxies. Targets are selected with stellar mass greater than 1e9 Msun using SDSS-I redshifts and i-band luminosity to achieve uniform radial coverage in terms of the effective radius, an approximately flat distribution in stellar mass, and a sample spanning a wide range of environments. Analysis of our prototype observations demonstrates MaNGA's ability to probe gas ionization, shed light on recent star formation and quenching, enable dynamical modeling, decompose constituent components, and map the composition of stellar populations. MaNGA's spatially resolved spectra will enable an unprecedented study of the astrophysics of nearby galaxies in the coming 6 yr.

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arXiv2014

Quantitative constraints on starburst cycles in galaxies with stellar masses in the range 108-1010 Msol

We have used 4000 Å break and H$δ_A$ indices in combination with SFR/M* derived from emission line flux measurements, to constrain the recent star formation histories of galaxies with stellar masses in the range 10**8-10**10 Msol. The fraction of the total SFR density in galaxies with ongoing bursts is a strong function of stellar mass, declining from 0.85 at a stellar mass of 10**8 Msol to 0.25 for galaxies with M* = 10**10 Msol. Low mass galaxies are not all young. The distribution of half mass formation times for galaxies with stellar masses less than 10**9 Msol is broad, spanning the range 1-10 Gyr. The peak-to-trough variation in star formation rate among the bursting population ranges lies in the range 10-25. In low mass galaxies, the average duration of the burst is comparable to the dynamical time of the galaxy. Galaxy structure is correlated with estimated burst mass fraction, but in different ways in low and in high mass galaxies. High mass galaxies with large burst mass fractions are more centrally concentrated, indicating that bulge formation is at work. In low mass galaxies, stellar surface mass densities decrease as a function of F_{burst}. These results are in good agreement with the observational predictions of Teyssier et al (2013) and lend further credence to the idea that the cuspy halo problem can be solved by energy input from multiple starbursts over the lifetime of the galaxy. We note that there is no compelling evidence for IMF variations in the population of star-forming galaxies in the local Universe.

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arXiv2014

An observational and theoretical view of the radial distribution of HI gas in galaxies

We analyze the radial distribution of HI gas for 23 disk galaxies with unusually high HI content from the Bluedisk sample, along with a similar-sized sample of "normal" galaxies. We propose an empirical model to fit the radial profile of the HI surface density, an exponential function with a depression near the center. The radial HI surface density profiles are very homogeneous in the outer regions of the galaxy; the exponentially declining part of the profile has a scale-length of $\sim 0.18$ R1, where R1 is the radius where the column density of the HI is 1 M$_{\odot}$ pc$^{-2}$. This holds for all galaxies, independent of their stellar or HI mass. The homogenous outer profiles, combined with the limited range in HI surface density in the non-exponential inner disk, results in the well-known tight relation between HI size and HI mass. By comparing the radial profiles of the HI-rich galaxies with those of the control systems, we deduce that in about half the galaxies, most of the excess gas lies outside the stellar disk, in the exponentially declining outer regions of the HI disk. In the other half, the excess is more centrally peaked. We compare our results with existing smoothed-particle hydrodynamical simulations and semi-analytic models of disk galaxy formation in a $Λ$ Cold Dark Matter universe. Both the hydro simulations and the semi-analytic models reproduce the HI surface density profiles and the HI size-mass relation without further tuning of the simulation and model inputs. In the semi-analytic models, the universal shape of the outer HI radial profiles is a consequence of the {\em assumption} that infalling gas is always distributed exponentially. The conversion of atomic gas to molecular form explains the limited range of HI surface densities in the inner disk. These two factors produce the tight HI mass-size relation.

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arXiv2013

Dilution in elliptical galaxies: Implications for the relation between metallicity, stellar mass and star formation rate

We investigate whether gradual dilution of the gas in some elliptical galaxies is the cause of a positive correlation between star formation rate (SFR) and gas-phase metallicity (Zg) at high stellar mass (M*) in the local Universe. To do this, two classes of massive (M* >= 10^10.5 Msun) galaxy are selected from the Sloan Digital Sky Survey (SDSS) and the Munich semi-analytic model of galaxy formation, L-Galaxies. The first class is selected by high specific star formation rates (sSFR) and high Zg, and the second class by low sSFR and low Zg. These criteria roughly distinguish disc-dominant galaxies from metal-poor, elliptical galaxies. In the semi-analytic model, the second class of galaxies obtain low sSFR and low Zg due to gradual dilution of the interstellar medium by accretion of metal-poor gas via infalling clumps and low-mass satellites. This occurs after a merger-induced starburst and the associated supernova feedback have quenched most of the original gas reservoir. A number of signatures of this evolution are present in these model galaxies at z=0, including low gas fractions, large central black holes, elliptical morphologies, old ages, and importantly, low (Zg-Z*) indicating dilution after star formation. Remarkably, all of these properties are also found in low-sSFR, low-Zg, massive galaxies in the SDSS-DR7. This provides strong, indirect evidence that some elliptical galaxies are undergoing gradual dilution after a gas-rich merger in the local Universe. This dilution scenario also explains the positive correlation between SFR and Zg measured in high-M* galaxies, and therefore has consequences for the local fundamental metallicity relation (FMR), which assumes a weak anti-correlation between SFR and Zg above 10^10.5 Msun.

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arXiv2013

The Nature of Obscuration in AGN: I. Insights from Host Galaxies

We analyze a sample of 30,000 nearby obscured AGNs with optical spectra from SDSS and mid-IR photometry from WISE. Our aim is to investigate the AGN host galaxy properties with mid-IR luminosities as AGN activity indicator, and to compare with previous studies based on [OIII] emission lines. First we find that the [3.4] - [4.6] colour has weak dependence on host stellar age, but strong dependence on AGN activity. We then use a "pair-matching" technique to subtract the host 4.6 micron contribution. By combining Seyferts with a sample of SDSS quasars at z < 0.7, we show that the [OIII] and the intrinsic AGN 4.6 micron luminosities correlate roughly linearly over 4 orders of magnitude, but with substantial scatter. We also compare the partition functions of the total integrated 4.6 micron and [OIII] line luminosities from Seyferts and a sub-population of LINERs with significant nuclear 4.6 micron emission, as function of a variety of host galaxy properties, finding that they are identical. We conclude, therefore, that [OIII] as an AGN indicator shows no particular biases as compared to the 4.6 micron luminosity. Our results also demonstrate that some LINERs do fit in with the expectations of the simple Unified Model.

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arXiv2013

Galactic accretion and the outer structure of galaxies in the CDM model

We have combined the semi-analytic galaxy formation model of Guo et al. (2011) with the particle-tagging technique of Cooper et al. (2010) to predict galaxy surface brightness profiles in a representative sample of ~1900 massive dark matter haloes (10^12--10^14 M_sol) from the Millennium II Lambda-CDM N-body simulation. Here we present our method and basic results focusing on the outer regions of galaxies, consisting of stars accreted in mergers. These simulations cover scales from the stellar haloes of Milky Way-like galaxies to the 'cD envelopes' of groups and clusters, and resolve low surface brightness substructure such as tidal streams. We find that the surface density of accreted stellar mass around the central galaxies of dark matter haloes is well described by a Sersic profile, the radial scale and amplitude of which vary systematically with halo mass (M_200). The total stellar mass surface density profile breaks at the radius where accreted stars start to dominate over stars formed in the galaxy itself. This break disappears with increasing M_200 because accreted stars contribute more of the total mass of galaxies, and is less distinct when the same galaxies are averaged in bins of stellar mass, because of scatter in the relation between M_star and M_200. To test our model we have derived average stellar mass surface density profiles for massive galaxies at z~0.08 by stacking SDSS images. Our model agrees well with these stacked profiles and with other data from the literature, and makes predictions that can be more rigorously tested by future surveys that extend the analysis of the outer structure of galaxies to fainter isophotes. We conclude that it is likely that the outer structure of the spheroidal components of galaxies is largely determined by collisionless merging during their hierarchical assembly

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arXiv2013

Star Formation and Metallicity Gradients in Semi-analytic Models of Disk 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 Σ_SFR \propto Σ_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 = αr. The models are used to study the radial profiles of star formation rate and gas-phase metallicity in present-day galaxies. The Σ_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.

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arXiv2013

Spatially resolved star formation histories of nearby galaxies: evidence for episodic star formation in discs

We use long-slit spectroscopy from Moran et al. to study the radial dependence of the recent star formation histories of nearby galaxies with stellar masses greater than 10^10M_sun. We fit stellar population models to the combination of SSFR, D4000 and Hdelta_A and show that many galaxies have Balmer absorption line equivalent widths that require recent short-lived episodes or bursts of star formation. The fraction of galaxies that have experienced episodic rather than continuous star formation is highest for late-type galaxies with low stellar masses. In these systems, bursts occur both in the inner and outer regions of the galaxy. The fraction of stars formed in a single burst episode is typically around 15% of the total stellar mass in the inner regions of the galaxy and around 5% of the mass in the outer regions. When we average over the population, we find that such bursts contribute around a half of the total mass in stars formed in the last 2 Gyr. In massive galaxies, bursts occur predominantly in the outer disk. Around a third of all massive, bulge-dominated galaxies have experienced recent star formation episodes that are fully confined to their outer (R > 0.7R_90) regions. The fraction of stars formed in a single episode is only 2 - 3 % of the underlying stellar mass, but such bursts contribute nearly all the stellar mass formed in the last 2 Gyr. Recent star formation in outer disks is strongly correlated with the global atomic gas fraction of the galaxy, but not its global molecular gas fraction. We suggest that outer episodic star formation is triggered by gas accretion events.

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arXiv2013

Modelling Element Abundances in Semi-analytic Models of Galaxy Formation

We update the treatment of chemical evolution in the Munich semi-analytic model, L-GALAXIES. Our new implementation includes delayed enrichment from stellar winds, supernovae type II (SNe-II) and supernovae type Ia (SNe-Ia), as well as metallicity-dependent yields and a reformulation of the associated supernova feedback. Two different sets of SN-II yields and three different SN-Ia delay-time distributions (DTDs) are considered, and eleven heavy elements (including O, Mg and Fe) are self-consistently tracked. We compare the results of this new implementation with data on a) local, star-forming galaxies, b) Milky Way disc G dwarfs, and c) local, elliptical galaxies. We find that the z=0 gas-phase mass-metallicity relation is very well reproduced for all forms of DTD considered, as is the [Fe/H] distribution in the Milky Way disc. The [O/Fe] distribution in the Milky Way disc is best reproduced when using a DTD with less than or equal to 50 per cent of SNe-Ia exploding within ~400 Myrs. Positive slopes in the mass-[alpha/Fe] relations of local ellipticals are also obtained when using a DTD with such a minor `prompt' component. Alternatively, metal-rich winds that drive light alpha elements directly out into the circumgalactic medium also produce positive slopes for all forms of DTD and SN-II yields considered. Overall, we find that the best model for matching the wide range of observational data considered here should include a power-law SN-Ia DTD, SN-II yields that take account of prior mass loss through stellar winds, and some direct ejection of light alpha elements out of galaxies.

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