arXiv subjects

Luca Cortese

Publications and source records attributed to Luca Cortese.

At least 109 records · Page 6Linked to original sources

arXiv2019

The SAMI Galaxy Survey: comparing 3D spectroscopic observations with galaxies from cosmological hydrodynamical simulations

Cosmological hydrodynamical simulations are rich tools to understand the build-up of stellar mass and angular momentum in galaxies, but require some level of calibration to observations. We compare predictions at $z\sim0$ from the Eagle, Hydrangea, Horizon-AGN, and Magneticum simulations with integral field spectroscopic (IFS) data from the SAMI Galaxy Survey, ATLAS3D, CALIFA and MASSIVE surveys. The main goal of this work is to simultaneously compare structural, dynamical, and stellar population measurements in order to identify key areas of success and tension. We have taken great care to ensure that our simulated measurement methods match the observational methods as closely as possible. We find that the Eagle and Hydrangea simulations reproduce many galaxy relations but with some offsets at high stellar masses. There are moderate mismatches in $R_e$ (+), $ε$ (-), $σ_e$ (-), and mean stellar age (+), where a plus sign indicates that quantities are too high on average, and minus sign too low. The Horizon-AGN simulations qualitatively reproduce several galaxy relations, but there are a number of properties where we find a quantitative offset to observations. Massive galaxies are better matched to observations than galaxies at low and intermediate masses. Overall, we find mismatches in $R_e$ (+), $ε$ (-), $σ_e$ (-) and $(V/σ)_e$ (-). Magneticum matches observations well: this is the only simulation where we find ellipticities typical for disk galaxies, but there are moderate differences in $σ_e$ (-), $(V/σ)_e$ (-) and mean stellar age (+). Our comparison between simulations and observational data has highlighted several areas for improvement, such as the need for improved modelling resulting in a better vertical disk structure, yet our results demonstrate the vast improvement of cosmological simulations in recent years.

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arXiv2019

ALMA unveils widespread molecular gas clumps in the ram pressure stripped tail of the Norma jellyfish galaxy

We present the first high-resolution map of the cold molecular gas distribution, as traced by CO(2-1) emission with ALMA, in a prominent ram pressure stripped tail. The Norma cluster galaxy ESO 137-001 is undergoing a strong interaction with the surrounding intra-cluster medium and is one of the nearest jellyfish galaxies with a long multi-phase tail. We have mapped the full extent of the tail at 1" (350 pc) angular resolution and found a rich distribution of mostly compact CO regions extending to nearly 60 kpc in length and 25 kpc in width. In total about 10^9 M_sun of molecular gas was detected. The CO features are found predominantly at the heads of numerous small-scale (~ 1.5 kpc) fireballs (i.e., star-forming clouds with linear streams of young stars extending toward the galaxy) but also of large-scale (~ 8 kpc) super-fireballs, and double-sided fireballs that have additional diffuse ionized gas tails extending in the direction opposite to the stellar tails. The new data help to shed light on the origin of the molecular tail - CO filaments oriented in the direction of the tail with only diffuse associated Halpha emission are likely young molecular features formed in situ, whereas other large CO features tilted with respect to the tail may have originated from the densest gas complexes that were pushed gradually away from the disk. The ALMA observations of ESO 137-001, together with observations from HST, Chandra and VLT/MUSE, offer the most complete view of a spectacular ram pressure stripped tail to date.

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arXiv2019

The SAMI Galaxy Survey: mass-kinematics scaling relations

We use data from the Sydney-AAO Multi-object Integral-field spectroscopy (SAMI) Galaxy Survey to study the dynamical scaling relation between galaxy stellar mass $M_*$ and the general kinematic parameter $S_K = \sqrt{K V_{rot}^2 + σ^2}$ that combines rotation velocity $V_{rot}$ and velocity dispersion $σ$. We show that the $\log M_* - \log S_K$ relation: (1)~is linear above limits set by properties of the samples and observations; (2)~has slightly different slope when derived from stellar or gas kinematic measurements; (3)~applies to both early-type and late-type galaxies and has smaller scatter than either the Tully-Fisher relation ($\log M_* - \log V_{rot}$) for late types or the Faber-Jackson relation ($\log M_* - \logσ$) for early types; and (4)~has scatter that is only weakly sensitive to the value of $K$, with minimum scatter for $K$ in the range 0.4 and 0.7. We compare $S_K$ to the aperture second moment (the `aperture velocity dispersion') measured from the integrated spectrum within a 3-arcsecond radius aperture ($σ_{3^{\prime\prime}}$). We find that while $S_{K}$ and $σ_{3^{\prime\prime}}$ are in general tightly correlated, the $\log M_* - \log S_K$ relation has less scatter than the $\log M_* - \log σ_{3^{\prime\prime}}$ relation.

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arXiv2019

The Detailed Science Case for the Maunakea Spectroscopic Explorer, 2019 edition

(Abridged) The Maunakea Spectroscopic Explorer (MSE) is an end-to-end science platform for the design, execution and scientific exploitation of spectroscopic surveys. It will unveil the composition and dynamics of the faint Universe and impact nearly every field of astrophysics across all spatial scales, from individual stars to the largest scale structures in the Universe. Major pillars in the science program for MSE include (i) the ultimate Gaia follow-up facility for understanding the chemistry and dynamics of the distant Milky Way, including the outer disk and faint stellar halo at high spectral resolution (ii) galaxy formation and evolution at cosmic noon, via the type of revolutionary surveys that have occurred in the nearby Universe, but now conducted at the peak of the star formation history of the Universe (iii) derivation of the mass of the neutrino and insights into inflationary physics through a cosmological redshift survey that probes a large volume of the Universe with a high galaxy density. MSE is positioned to become a critical hub in the emerging international network of front-line astronomical facilities, with scientific capabilities that naturally complement and extend the scientific power of Gaia, the Large Synoptic Survey Telescope, the Square Kilometer Array, Euclid, WFIRST, the 30m telescopes and many more.

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arXiv2019

The SAMI Galaxy Survey: Quenching of star formation in clusters I. Transition galaxies

We use integral field spectroscopy from the SAMI Galaxy Survey to identify galaxies that show evidence for recent quenching of star formation. The galaxies exhibit strong Balmer absorption in the absence of ongoing star formation in more than 10% of their spectra within the SAMI field of view. These $\rm{H}δ$-strong galaxies (HDSGs) are rare, making up only $\sim 2$% (25/1220) of galaxies with stellar mass ${\rm log(}M_*/M_{\odot})>10$. The HDSGs make up a significant fraction of non-passive cluster galaxies (15%; 17/115) and a smaller fraction (2.0%; 8/387) of the non-passive population in low-density environments. The majority (9/17) of cluster HDSGs show evidence for star formation at their centers, with the HDS regions found in the outer parts of the galaxy. Conversely, the $\rm{H}δ$-strong signal is more evenly spread across the galaxy for the majority (6/8) of HDSGs in low-density environments, and is often associated with emission lines that are not due to star formation. We investigate the location of the HDSGs in the clusters, finding that they are exclusively within 0.6$R_{200}$ of the cluster centre, and have a significantly higher velocity dispersion relative to the cluster population. Comparing their distribution in projected-phase-space to those derived from cosmological simulations indicates that the cluster HDSGs are consistent with an infalling population that have entered the central 0.5$r_{200, 3D}$ cluster region within the last $\sim 1\,$Gyr. In the 8/9 cluster HDSGs with central star formation, the extent of star formation is consistent with that expected of outside-in quenching by ram-pressure stripping. Our results indicate that the cluster HDSGs are currently being quenched by ram-pressure stripping on their first passage through the cluster.

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arXiv2019

SDSS-IV MaNGA: The Roles of AGNs and Dynamical Processes in Star Formation Quenching in Nearby Disk Galaxies

We study how star formation (SF) is quenched in low-redshift disk galaxies with integral-field spectroscopy. We select 131 face-on spiral galaxies with stellar mass greater than $\rm 3\times10^{10}M_\odot$, and with spatially resolved spectrum from MaNGA DR13. We subdivide the sample into four groups based on the offset of their global specific star formation rate (SFR) from the star-forming main sequence and stack the radial profiles of stellar mass and SFR. By comparing the stacked profiles of quiescent and star-forming disk galaxies, we find that the decrease of the global SFR is caused by the suppression of SF at all radii, but with a more significant drop from the center to the outer regions following an inside-out pattern. As the global specific SFR decreases, the central stellar mass, the fraction of disk galaxies hosting stellar bars, and active galactic nuclei (AGNs; including both LINERs and Seyferts) all increase, indicating dynamical processes and AGN feedback are possible contributors to the inside-out quenching of SF in the local universe. However, if we include only Seyferts, or AGNs with ${\rm EW(Hα)>3Å}$, the increasing trend of AGN fraction with decreasing global sSFR disappears. Therefore, if AGN feedback is contributing to quenching, we suspect that it operates in the low-luminosity AGN mode, as indicated by the increasing large bulge mass of the more passive disk galaxies.

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arXiv2018

Atomic gas fractions in active galactic nucleus host galaxies

The feedback from an active galactic nucleus (AGN) is frequently invoked as a mechanism through which gas can be heated or removed from a galaxy. However, gas fraction measurements in AGN hosts have yielded mixed support for this scenario. Here, we re-visit the assessment of fgas (=MHI/M*) in z<0.05 AGN hosts in the Sloan Digital Sky Survey (SDSS) using two complementary techniques. First, we investigate fgas for 75 AGN host galaxies in the extended GALEX Arecibo SDSS Survey (xGASS), whose atomic gas fractions are complete to a few percent. Second, we construct HI spectral stacks of 1562 AGN from the Arecibo Legacy Fast ALFA (ALFALFA) survey, which enables us to extend the AGN sample to lower stellar masses. Both techniques find that, at fixed M*, AGN hosts with log M*>10.2 are HI rich by a factor of ~2. However, this gas fraction excess disappears when the control sample is additionally matched in star formation rate (SFR), indicating that these AGN hosts are actually HI normal. At lower stellar mass, the stacking analysis reveals that AGN hosts are HI poor at fixed stellar mass. In the lowest M* regime probed by our sample, 9<log M*<9.6, the HI deficit in AGN hosts is a factor of ~4, and remains at a factor of ~2 even when the control sample is additionally matched in SFR. Our results help reconcile previously conflicting results, by showing that matching control samples by more than just stellar mass is critical for a rigourous comparison.

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arXiv2018

YZiCS: Preprocessing of dark halos in the hydrodynamic zoom-in simulation of clusters

To understand the galaxy population in clusters today, we should also consider the impact of previous environments prior to cluster infall, namely preprocessing. We use YZiCS, a hydrodynamic high-resolution zoom-in simulation of 15 clusters, and focus on the tidal stripping suffered by the dark matter halos of cluster members due to preprocessing. We find ~48% of today's cluster members were once satellites of other hosts. This is slightly higher than previous estimates, in part, because we consider not just group-mass hosts, but hosts of all masses also. Thus, we find the preprocessed fraction is poorly correlated with cluster mass and is instead related to each cluster's recent mass growth rate. Hosts less massive than groups are significant contributors, providing more than one-third of the total preprocessed fraction. We find that halo mass loss is a clear function of the time spent in hosts. However, two factors can increase the mass loss rate considerably; the mass ratio of a satellite to its host, and the cosmological epoch when the satellite was hosted. The latter means we may have previously underestimated the role of high redshift groups. From a sample of heavily tidally stripped members in clusters today, nearly three quarters were previously in a host. Thus, visibly disturbed cluster members are more likely to have experienced preprocessing. Being hosted before cluster infall enables cluster members to experience tidal stripping for extended durations compared to direct cluster infall and at earlier epochs when hosts were more destructive.

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arXiv2018

The SAMI Galaxy Survey: Data Release Two with absorption-line physics value-added products

We present the second major release of data from the SAMI Galaxy Survey. Data Release Two includes data for 1559 galaxies, about 50% of the full survey. Galaxies included have a redshift range 0.004 < z < 0.113 and a large stellar mass range 7.5 < log (M_star/M_sun) < 11.6. The core data for each galaxy consist of two primary spectral cubes covering the blue and red optical wavelength ranges. For each primary cube we also provide three spatially binned spectral cubes and a set of standardised aperture spectra. For each core data product we provide a set of value-added data products. This includes all emission line value-added products from Data Release One, expanded to the larger sample. In addition we include stellar kinematic and stellar population value-added products derived from absorption line measurements. The data are provided online through Australian Astronomical Optics' Data Central. We illustrate the potential of this release by presenting the distribution of ~350,000 stellar velocity dispersion measurements from individual spaxels as a function of R/R_e, divided in four galaxy mass bins. In the highest stellar mass bin (log (M_star/M_sun)>11), the velocity dispersion strongly increases towards the centre, whereas below log (M_star/M_sun)<10 we find no evidence for a clear increase in the central velocity dispersion. This suggests a transition mass around log (M_star/M_sun) ~10 for galaxies with or without a dispersion-dominated bulge.

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arXiv2018

The SAMI Galaxy Survey: Spatially Resolved Metallicity and Ionization Mapping

We present gas-phase metallicity and ionization parameter maps of 25 star-forming face-on spiral galaxies from the SAMI Galaxy Survey Data Release 1. Self-consistent metallicity and ionization parameter maps are calculated simultaneously through an iterative process to account for the interdependence of the strong emission line diagnostics involving ([OII]+[OIII])/H$β$ (R23) and [OIII]/[OII] (O32). The maps are created on a spaxel-by-spaxel basis because HII regions are not resolved at the SAMI spatial resolution. We combine the SAMI data with stellar mass, star formation rate (SFR), effective radius (R$_e$), ellipticity, and position angles (PA) from the GAMA survey to analyze their relation to the metallicity and ionization parameter. We find a weak trend of steepening metallicity gradient with galaxy stellar mass, with values ranging from -0.03 to -0.20 dex/R$_e$. Only two galaxies show radial gradients in ionization parameter. We find that the ionization parameter has no significant correlation with either SFR, sSFR (specific star formation rate), or metallicity. For several individual galaxies we find structure in the ionization parameter maps suggestive of spiral arm features. We find a typical ionization parameter range of $7.0 < \log(q) < 7.8$ for our galaxy sample with no significant overall structure. An ionization parameter range of this magnitude is large enough to caution the use of metallicity diagnostics which have not considered the effects of a varying ionization parameter distribution.

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arXiv2018

Enhanced atomic gas fractions in recently merged galaxies: quenching is not a result of post-merger gas exhaustion

We present a detailed assessment of the global atomic hydrogen gas fraction in a sample of post-merger galaxies identified in the Sloan Digital Sky Survey (SDSS). Archival HI measurements of 47 targets are combined with new Arecibo observations of a further 51 galaxies. The stellar mass range of the post-merger sample, our observing strategy, detection thresholds and data analysis procedures replicate those of the extended GALEX Arecibo SDSS Survey (xGASS) which can therefore be used as a control sample. Our principal results are: 1) The post-merger sample shows a ~50 per cent higher HI detection fraction compared with xGASS; 2) Accounting for non-detections, the median atomic gas fraction of the post-merger sample is larger than the control sample by 0.3 -- 0.6 dex; 3) The median atomic gas fraction enhancement (delta fgas), computed on a galaxy-by-galaxy basis at fixed stellar mass, is 0.51 dex. Our results demonstrate that recently merged galaxies are typically a factor of ~3 more HI rich than control galaxies of the same M*. If the control sample is additionally matched in star formation rate, the median HI excess is reduced to delta fgas = 0.2 dex, showing that the enhanced atomic gas fractions in post-mergers are not purely a reflection of changes in star formation activity. We conclude that merger-induced starbursts and outflows do not lead to prompt quenching via exhaustion/expulsion of the galactic gas reservoirs. Instead, we propose that if star formation ceases after a merger, it is more likely due to an enhanced turbulence which renders the galaxy unable to effectively form new stars.

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arXiv2018

A relation between characteristic stellar age of galaxies and their intrinsic shape

Stellar population and stellar kinematic studies provide unique but complementary insights into how galaxies build-up their stellar mass and angular momentum. A galaxy's mean stellar age reveals when stars were formed, but provides little constraint on how the galaxy's mass was assembled. Resolved stellar dynamics trace the change in angular momentum and orbital distribution of stars due to mergers, but major mergers tend to obscure the effect of earlier interactions. With the rise of large multi-object integral field spectroscopic (IFS) surveys, such as SAMI and MaNGA, and single-object IFS surveys (e.g., ATLAS$^{\rm{3D}}$, CALIFA, MASSIVE), it is now feasible to connect a galaxy's star formation and merger history on the same resolved physical scales, over a large range in galaxy mass, and across the full range of optical morphology and environment. Using the SAMI Galaxy Survey, here we present the first study of spatially-resolved stellar kinematics and global stellar populations in a large IFS galaxy survey. We find a strong correlation of stellar population age with location in the ($V / σ$, $ε_{\rm{e}}$) diagram that links the ratio of ordered rotation to random motions in a galaxy to its observed ellipticity. For the large majority of galaxies that are oblate rotating spheroids, we find that characteristic stellar age follows the intrinsic ellipticity of galaxies remarkably well. This trend is still observed when galaxies are separated into early-type and late-type samples.

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arXiv2018

The SAMI Galaxy Survey: gravitational potential and surface density drive stellar populations -- I. early-type galaxies

The well-established correlations between the mass of a galaxy and the properties of its stars are considered evidence for mass driving the evolution of the stellar population. However, for early-type galaxies (ETGs), we find that $g-i$ color and stellar metallicity [Z/H] correlate more strongly with gravitational potential $Φ$ than with mass $M$, whereas stellar population age correlates best with surface density $Σ$. Specifically, for our sample of 625 ETGs with integral-field spectroscopy from the SAMI Galaxy Survey, compared to correlations with mass, the color--$Φ$, [Z/H]--$Φ$, and age--$Σ$ relations show both smaller scatter and less residual trend with galaxy size. For the star formation duration proxy [$α$/Fe], we find comparable results for trends with $Φ$ and $Σ$, with both being significantly stronger than the [$α$/Fe]-$M$ relation. In determining the strength of a trend, we analyze both the overall scatter, and the observational uncertainty on the parameters, in order to compare the intrinsic scatter in each correlation. These results lead us to the following inferences and interpretations: (1) the color--$Φ$ diagram is a more precise tool for determining the developmental stage of the stellar population than the conventional color--mass diagram; and (2) gravitational potential is the primary regulator of global stellar metallicity, via its relation to the gas escape velocity. Furthermore, we propose the following two mechanisms for the age and [$α$/Fe] relations with $Σ$: (a) the age--$Σ$ and [$α$/Fe]--$Σ$ correlations arise as results of compactness driven quenching mechanisms; and/or (b) as fossil records of the $Σ_{SFR}\proptoΣ_{gas}$ relation in their disk-dominated progenitors.

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arXiv2018

xGASS: Total cold gas scaling relations and molecular-to-atomic gas ratios of galaxies in the local Universe

We present the extended GALEX Arecibo SDSS Survey (xGASS), a gas fraction-limited census of the atomic (HI) gas content of 1179 galaxies selected only by stellar mass ($M_\star =10^{9}-10^{11.5} M_\odot$) and redshift ($0.01<z<0.05$). This includes new Arecibo observations of 208 galaxies, for which we release catalogs and HI spectra. In addition to extending the GASS HI scaling relations by one decade in stellar mass, we quantify total (atomic+molecular) cold gas fractions and molecular-to-atomic gas mass ratios, $R_{mol}$, for the subset of 477 galaxies observed with the IRAM 30 m telescope. We find that atomic gas fractions keep increasing with decreasing stellar mass, with no sign of a plateau down to $\log M_\star/M_\odot = 9$. Total gas reservoirs remain HI-dominated across our full stellar mass range, hence total gas fraction scaling relations closely resemble atomic ones, but with a scatter that strongly correlates with $R_{mol}$, especially at fixed specific star formation rate. On average, $R_{mol}$ weakly increases with stellar mass and stellar surface density $μ_\star$, but individual values vary by almost two orders of magnitude at fixed $M_\star$ or $μ_\star$. We show that, for galaxies on the star-forming sequence, variations of $R_{mol}$ are mostly driven by changes of the HI reservoirs, with a clear dependence on $μ_\star$. Establishing if galaxy mass or structure plays the most important role in regulating the cold gas content of galaxies requires an accurate separation of bulge and disk components for the study of gas scaling relations.

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arXiv2018

Lurking systematics in predicting galaxy cold gas masses using dust luminosities and star formation rates

We use galaxies from the Herschel Reference Survey to evaluate commonly used indirect predictors of cold gas masses. We calibrate predictions for cold neutral atomic and molecular gas using infrared dust emission and gas depletion time methods which are self-consistent and have ~20% accuracy (with the highest accuracy in the prediction of total cold gas mass). However, modest systematic residual dependences are found in all calibrations which depend on the partition between molecular and atomic gas, and can over/under-predict gas masses by up to 0.3dex. As expected, dust-based estimates are best at predicting the total gas mass while depletion time-based estimates are only able to predict the (star-forming) molecular gas mass. Additionally, we advise caution when applying these predictions to high-z galaxies, as significant (0.5dex or more) errors can arise when incorrect assumptions are made about the dominant gas phase. Any scaling relations derived using predicted gas masses may be more closely related to the calibrations used than to the actual galaxies observed.

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arXiv2018

The SAMI Galaxy Survey: Spatially Resolving the Main Sequence of Star Formation

We present the ~800 star formation rate maps for the SAMI Galaxy Survey based on Hα emission maps, corrected for dust attenuation via the Balmer decrement, that are included in the SAMI Public Data Release 1. We mask out spaxels contaminated by non-stellar emission using the [O III]/Hβ, [N II]/Hα, [S II]/Hα, and [O I]/Hα line ratios. Using these maps, we examine the global and resolved star-forming main sequences of SAMI galaxies as a function of morphology, environmental density, and stellar mass. Galaxies further below the star-forming main sequence are more likely to have flatter star formation profiles. Early-type galaxies split into two populations with similar stellar masses and central stellar mass surface densities. The main sequence population has centrally-concentrated star formation similar to late-type galaxies, while galaxies >3σ below the main sequence show significantly reduced star formation most strikingly in the nuclear regions. The split populations support a two-step quenching mechanism, wherein halo mass first cuts off the gas supply and remaining gas continues to form stars until the local stellar mass surface density can stabilize the reduced remaining fuel against further star formation. Across all morphologies, galaxies in denser environments show a decreased specific star formation rate from the outside in, supporting an environmental cause for quenching, such as ram-pressure stripping or galaxy interactions.

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arXiv2017

xCOLD GASS: the complete IRAM-30m legacy survey of molecular gas for galaxy evolution studies

We introduce xCOLD GASS, a legacy survey providing a census of molecular gas in the local Universe. Building upon the original COLD GASS survey, we present here the full sample of 532 galaxies with CO(1-0) measurements from the IRAM-30m telescope. The sample is mass-selected in the redshift interval $0.01 10^9$M$_{\odot}$. The CO(1-0) flux measurements are complemented by observations of the CO(2-1) line with both the IRAM-30m and APEX telescopes, HI observations from Arecibo, and photometry from SDSS, WISE and GALEX. Combining the IRAM and APEX data, we find that the CO(2-1) to CO(1-0) luminosity ratio for integrated measurements is $r_{21}=0.79\pm0.03$, with no systematic variations across the sample. The CO(1-0) luminosity function is constructed and best fit with a Schechter function with parameters {$L_{\mathrm{CO}}^* = (7.77\pm2.11) \times 10^9\,\mathrm{K\,km\,s^{-1}\, pc^{2}}$, $ϕ^{*} = (9.84\pm5.41) \times 10^{-4} \, \mathrm{Mpc^{-3}}$ and $α= -1.19\pm0.05$}. With the sample now complete down to stellar masses of $10^9$M$_{\odot}$, we are able to extend our study of gas scaling relations and confirm that both molecular gas fraction and depletion timescale vary with specific star formation rate (or offset from the star-formation main sequence) much more strongly than they depend on stellar mass. Comparing the xCOLD GASS results with outputs from hydrodynamic and semi-analytic models, we highlight the constraining power of cold gas scaling relations on models of galaxy formation.

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arXiv2017

The role of atomic hydrogen in regulating the scatter of the mass-metallicity relation

In this paper, we stack neutral atomic hydrogen (HI) spectra for 9,720 star forming galaxies along the mass-metallicity relation. The sample is selected according to stellar mass (10$^9 \leq$ M$_{\star}$/M$_{\odot}\leq$10$^{11}$) and redshift ($0.02 \leq z \leq 0.05$) from the overlap of the Sloan Digital Sky Survey and Arecibo Legacy Fast ALFA survey. We confirm and quantify the strong anti-correlation between HI mass and gas-phase metallicity at fixed stellar mass. Furthermore, we show for the first time that the relationship between gas content and metallicity is consistent between different metallicity estimators, contrary to the weaker trends found with star formation which are known to depend on the observational techniques used to derive oxygen abundances and star formation rates. When interpreted in the context of theoretical work, this result supports a scenario where galaxies exist in an evolving equilibrium between gas, metallicity and star formation. The fact that deviations from this equilibrium are most strongly correlated with gas mass suggests that the scatter in the mass-metallicity relation is primarily driven by fluctuations in gas accretion.

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