The stellar mass function and star formation rate-stellar mass relation of galaxies at z ~ 4 - 7

We investigate the evolution of the star formation rate-stellar mass relation (SFR-M*) and Galaxy Stellar Mass Function (GSMF) of z ~ 4-7 galaxies, using cosmological simulations run with the smoothed particle hydrodynamics code P-GADGET3(XXL). We explore the effects of different feedback prescriptions (supernova driven galactic winds and AGN feedback), initial stellar mass functions and metal cooling. We show that our fiducial model, with strong energy-driven winds and early AGN feedback, is able to reproduce the observed stellar mass function obtained from Lyman-break selected samples of star forming galaxies at redshift 6 < z < 7. At z ~ 4, observed estimates of the GSMF vary according to how the sample was selected. Our simulations are more consistent with recent results from K-selected samples, which provide a better proxy of stellar masses and are more complete at the high mass end of the distribution. We find that in some cases simulated and observed SFR-M* relations are in tension, and this can lead to numerical predictions for the GSMF in excess of the GSMF observed. By combining the simulated SFR(M*) relationship with the observed star formation rate function at a given redshift, we argue that this disagreement may be the result of the uncertainty in the SFR-M* (Luv-M*) conversion. Our simulations predict a population of faint galaxies not seen by current observations.Comment: 23 Pages, 13 figures, modified to match accepted version to MNRA

Chemical and physical evolution of the intergalactic medium

2008/2009The aim of this thesis work is to explore coherently different aspects related to the properties of the Intergalactic Medium (IGM) and to its chemical and physical evolution from high to low redshift, especially regarding metal enrichment and the impact of different feedback processes. In the last years, high resolution spectroscopic observations have shown that the neutral hydrogen (HI) in the IGM at redshift around three, traced by the Lyman-alpha forest lines in absorption, is subjected to metal pollution down to very low column density (10^13 atoms cm^-2) with a metallicity of about 10^-3 in solar units. Since metals are produced only by stars inside galaxies, the diffuse metals in the IGM retain an important trace of the star formation and of the feedback processes from the galaxies to the IGM. The purpose of the thesis is to identify the mechanisms responsible of the enrichment, propose some physically motivated theoretical models and compare the prediction of the models with the latest observational data. In particular we focussed on two different type of enrichment: galactic (energy and momentum driven) winds produced by "starburst" galaxies at redshift z=1.5-4 and AGN feedback associated to the energy released by gas accretion onto super-massive black holes. We analysed in detail the following aspects: dynamic and energetic of wind and AGN feedbacks, IGM contamination efficiency as a function of different astrophysical and cosmological parameters, temperature and chemical composition of the metal systems, nature of the ultraviolet ionizing background (UVB). In the first part of the thesis we investigated the properties of a particular class of cosmological objects, the so called Damped Lyman-alpha systems (DLAs). These are defined as quasar (QSO) absorption systems with neutral hydrogen column density N_HI > 2 x 10^20 atoms cm^-2 (Wolfe et al. 1986). DLAs are considered as an important reservoir and/or sink of gas for the galaxy formation process in the high redshift Universe and their HI content dominate the total neutral hydrogen budget over a large fraction of the cosmic history. The interplay between DLAs and galaxies is thereby fundamental and should be addressed by any galaxy formation model. Using parallel national and internationals supercomputers, we ran high-resolution and large box-size cosmological hydrodynamical simulations of a LambdaCDM model. The numerical code used is a modified version of the Tree Particle-Mesh Smoothed Particle Hydrodynamics code GADGET-2 (Springel 2005). The main modification consists in an accurate modelling of the chemical evolution which allow us to follow the metal release from Type II and Type Ia supernovae (SNII, SNIa), along with low and intermediate mass stars (LIMS) (see Tornatore et al. 2007). We explored the numerical convergence of some relevant physical quantities and we vary the parameters describing: the properties of galactic winds, the initial stellar mass function, the linear dark matter power spectrum and the metal enrichment pattern of the IGM around DLAs. We focussed on the properties of dark matter haloes that are likely to be the hosts of DLAs systems: we predict relatively low star formation rates (0.01-0.1 M_sun/year) and metallicities around 0.1 Z_sun, at least for the bulk of our haloes of masses between 10^9 and 10^10 h^-1 M_sun hosting DLAs. For more massive haloes metallicities and star formation rates depend on the specific wind model. We found that strong galactic winds with speed of about 600 km/s, in an energy-driven wind scenario, are needed in order to match the observed column density distribution function for DLAs and the evolution of the neutral hydrogen content with redshift. The momentum-driven implementation of the galactic wind model, that relates the speed and mass load in the wind to the properties of the dark matter haloes, shows a behaviour which is intermediate between the energy-driven galactic winds of small (100 km/s) and large (600 km/s) velocities. At z=3 the contribution of haloes of masses between 10^9 and 10^10 h^-1 M_sun, for DLAs below 10^20.8 atoms cm^-2, to the column density distribution function, is significant. By interpolating physical quantities along line-of-sights through massive haloes we qualitatively showed how different galactic wind models impact on the IGM around DLAs. Furthermore, we analysed statistics related to the velocity widths of SiII associated to DLAs: while the expanding shells of gaseous matter associated to the wind can account for the observed velocities, the metallicity in the wind seems to be rather clumpy and this produces an underestimation of the observed velocity widths. We outlined possible solutions to this problem. These results are published in the paper Tescari et al. (2009, MNRAS, 397, 411). In the second part of the thesis we turned our attention to the cosmic evolution of the CIV, i.e. triply ionized carbon. Most studies of the high redshift IGM have focussed on CIV absorption, because it is strong and lies redward of the Lyman-alpha forest. Moreover the absorption line is actually a doublet with rest frame wavelengths 1548.204 and 1550.781 Angstrom, so its identification in the observational spectra is easier because of the fixed ratio between the wavelengths of the two components. The cosmological mass density of CIV, Omega_CIV, observed as a function of redshift is a fundamental quantity closely related to the metal enrichment of the IGM. Its apparent lack of evolution in the redshift interval z=[1.5,5] (Songaila 2001; Pettini et al. 2003; Boksenberg et al. 2003) is puzzling since both the physical conditions of the IGM and the properties of the ionizing background are thought to evolve between these epochs. The most recent measurements of CIV absorptions in spectra of QSOs at z=6 seem to indicate a downturn in the CIV mass density at z>5 (Becker et al. 2009; Ryan-Weber et al. 2009). At z<1, recent results based on HST UV data (Cooksey et al. 2009) give Omega_CIV=(6 +- 1) x 10^-8 corresponding to a 2.8 +- 0.5 increase over the 1.5<z<5 values. Our work was the theoretical counterpart of the D'Odorico et al. (2009) paper in which the authors present a new measurement of Omega_CIV in the redshift range [1.5,4] based on a sample of 25 high resolution, high signal-to-noise QSO spectra plus an additional sample of 8 QSO spectra from the literature. The main result is that Omega_CIV is no longer approximately constant in the considered redshift range, but shows a steady increase from z=3-5 to z=1.5-2. Using the same high-resolution and large box-size cosmological simulations of the first part, and adding some new runs with improved feedback parameters prescriptions (for example we run a simulation with the combined effect of wind and AGN feedbacks) we reproduced the Omega_CIV evolution, at least in the range z=1.5-3, by extracting mock but realistic QSO spectra inside the cosmological box and subsequently fit the CIV lines with the public available software package VPFIT. Statistically, with the momentum-driven wind run we fitted, even if with some discrepancies, the observed CIV column density distribution function, the CIV Doppler parameter (b_CIV) probability distribution function and the relation b_CIV-N_CIV, at redshifts z=1.5, 2.25 and 3. A paper containing the results of this work will be soon submitted to MNRAS (Tescari et al. 2010, in preparation).Lo scopo di questa tesi di dottorato è l'esplorazione coerente di diversi aspetti concernenti le proprietà del Mezzo Intergalattico (IGM) e la sua evoluzione chimica e fisica da alto a basso redshift, specialmente considerando l'arricchimento metallico e l'impatto di differenti processi di feedback. Negli ultimi anni, osservazioni spettroscopiche ad alta risoluzione hanno mostrato che l'idrogeno neutro (HI) nell'IGM a redshift circa tre, tracciato dalle linee di assorbimento della foresta Lyman-alpha, è soggetto ad arricchimento metallico fino a densità di colonna estremamente basse (10^13 atomi cm^-2) con metallicità attorno a 10^-3 in unità solari. Poiché i metalli sono prodotti solo dalle stelle all'interno delle galassie, i metalli diffusi nell'IGM conservano la traccia dei processi di formazione stellare e dei processi di feedback dalle galassie al mezzo intergalattico. Il fine di questa tesi è di identificare i meccanismi responsabili dell'arricchimento, proporre alcuni modelli teorici fisicamente plausibili e confrontare le predizioni dei modelli con i più aggiornati dati osservativi disponibili. In particolare ci siamo concentrati su due tipi distinti di arricchimento: feedback da venti galattici (sia a conservazione di energia che a conservazione di momento), prodotti da galassie "starburst" a redshift z=1.5-4, e feedback da AGN, associato all'energia rilasciata dall'accrescimento del gas su buchi neri supermassivi. Abbiamo analizzato in dettaglio i seguenti aspetti: dinamica ed energetica dei due precedenti tipi di feedback, efficienza di contaminazione dell'IGM in funzione di differenti parametri astrofisici e cosmologici, temperatura e composizione chimica dei sistemi metallici, natura del background ionizzante ultravioletto (UVB). Nella prima parte della tesi abbiamo investigato le proprietà di una particolare classe di oggetti cosmologici, i sistemi Damped Lyman-alpha (DLAs): definiti come sistemi di assorbimento con densità di colonna in idrogeno neutro N_HI > 2 x 10^20 atomi cm^-2 (Wolfe et al. 1986). I DLAs sono considerati come un importante bacino e/o riserva di gas per i processi di formazione delle galassie ad alto redshift e contengono la maggior parte dell'idrogeno neutro dell'Universo per una larga frazione della storia cosmica. La reciproca interazione tra galassie e DLAs è quindi di fondamentale importanza e ogni modello di formazione galattica dovrebbe essere in grado di spiegarla all'interno di un contesto fisicamente plausibile. Usando supercomputer in Italia e all'estero, abbiamo eseguito simulazioni cosmologiche idrodinamiche, ad alta risoluzione e per box di grandi dimensioni, di un modello di universo LambdaCDM. Il codice utilizzato è una versione modificata del codice TreePM-SPH GADGET-2 (Springel 2005). La modifica principale consiste in un'accurata modellizzazione dell'arricchimento chimico dovuto a supernovae di tipo Ia e di tipo II (SNIa, SNII), e a stelle di massa intermedia (LIMS) (Tornatore et al. 2007). Abbiamo analizzato la convergenza numerica di alcune quantità fisiche rilevanti e variato i parametri che descrivono: le proprietà dei venti galattici, la funzione di massa stellare iniziale (IMF), lo spettro di potenza iniziale della materia oscura e il modello di arricchimento metallico dell'IGM attorno ai DLAs. Ci siamo concentrati sulle proprietà degli aloni di materia oscura che, statisticamente, ospitano sistemi DLAs, trovando tassi di formazione stellare relativamente bassi (0.01-0.1 M_sun/anno) e metallicità attorno a 0.1 Z_sun, almeno per il grosso degli aloni con masse tra 10^9 e 10^10 h^-1 M_sun contenenti DLAs. Per aloni più massivi le metallicità e i tassi di formazione stellare dipendono dallo specifico modello di vento. Venti galattici "forti" con velocità di 600 km/s, nello scenario a conservazione di energia, riproducono la funzione di distribuzione della densità di colonna osservata per i DLAs e l'evoluzione col redshift del contenuto totale di idrogeno neutro nella box. L'implementazione dei venti galattici a conservazione del momento, che mette in stretta relazione la velocità e l'efficienza del vento con le proprietà degli aloni di materia oscura, mostra un andamento intermedio tra i venti galattici "deboli" (100 km/s) e "forti" (600 km/s) nello scenario a conservazione dell'energia. A z=3 il contributo degli aloni di massa tra 10^9 and 10^10 h^-1 M_sun alla funzione di distribuzione della densità di colonna, per DLAs con densità di colonna minori di 10^20.8 atomi cm^-2, è significativo. Interpolando quantitià fisiche di interesse lungo linee di vista attraverso gli aloni più massivi delle simulazioni abbiamo mostrato qualitativamente come i diversi modelli di vento galattico influiscono sull'IGM attorno ai DLAs. Inoltre, abbiamo analizzato statistiche relazionate alla "velocity width" del SiII associato ai DLAs: anche se le velocità delle bolle di gas espulse dai venti galattici riproducono le velocità osservate, l'arricchimento prodotto dal vento sembra essere costituito da piccoli agglomerati metallici isolati e non un arricchimento uniforme. Questo produce una sottostima delle velocity widths osservate. Possibili soluzioni a questo problema sono brevemente discusse. I risultati di questo lavoro sono stati pubblicati nell'articolo Tescari et al. (2009, MNRAS, 397, 411). Nella seconda parte della tesi ci siamo focalizzati sull'evoluzione cosmica del CIV, cioè il carbonio tre volte ionizzato. Molti studi dell'IGM ad alto redshift si basano sull'analisi delle righe di assorbimento del CIV, perché sono ben definite e marcate e si situano a lunghezza d'onda superiore rispetto alla foresta Lyman-alpha, non essendone pertanto contaminate. Inoltre, la linea di assorbimento è in realtà un doppietto con lunghezze d'onda a riposo di 1548.204 e 1550.781 Angstrom, per cui la sua identificazione nello spettro è più facile per via della distanza fissata tra le lunghezze d'onda delle due componenti. La densità di massa cosmologica in CIV, Omega_CIV, osservata in funzione del redshift è una quantità fondamentale strettamente correlata all'arricchimento chimico dell'IGM. La sua apparente mancanza di evoluzione nell'intervallo di redshift z=[1.5,5] (Songaila 2001; Pettini et al. 2003; Boksenberg et al. 2003) è interessante poiché sia le condizioni fisiche dell'IGM che le proprietà del background ionizzante ultravioletto evolvono tra queste due epoche. Le più recenti osservazioni delle righe di assorbimento del CIV in spettri di quasars (QSOs) a z=6, sembrano indicare una flessione nella densità di massa in CIV a z>5 (Becker et al. 2009; Ryan-Weber et al. 2009). A z<1, risultati recenti basati su dati HST in banda UV (Cooksey et al. 2009) danno come risultato Omega_CIV=(6 +- 1) x 10^-8 corrispondente a un incremento di 2.8 +- 0.5 rispetto ai valori a 1.5<z<5. Il nostro lavoro è in sostanza la controparte teorica dell'articolo di D'Odorico et al. (2009), in cui gli autori presentano una nuova misura di Omega_CIV nell'intervallo di redshift [1.5,4], basata su un campione di 25 spettri di QSO ad alta risoluzione e alto rapporto segnale/rumore, più un campione addizionale di 8 spettri di QSO presi dalla letteratura. Il risultato principale è che Omega_CIV non è più approssimativamente costante nell'intervallo di redshift considerato, ma mostra un progressivo incremento da z=3-5 a z=1.5-2. Usando le stesse simulazioni cosmologiche ad alta risoluzione e con box di grandi dimensioni della prima parte, e con l'aggiunta di alcune nuove simulazioni con una diversa descrizione dei parametri di feedback (per esempio abbiamo eseguito una simulazione con l'effetto combinato del feedback da venti galattici e da AGN), abbiamo riprodotto l'evoluzione di Omega_CIV, nell'intervallo di redshift z=1.5-4, estraendo spettri sintetici di QSO all'interno delle box cosmologiche e successivamente modellando le linee di assorbimento del CIV con il software pubblico VPFIT. Statisticamente, la simulazione con venti galattici a conservazione del momento riproduce, seppure con qualche discrepanza, la funzione di distribuzione della densità di colonna osservata per il CIV, la funzione di distribuzione di probabilità per il parametro Doppler del CIV (b_CIV) e la relazione b_CIV-N_CIV, ai redshifts z=1.5, 2.25 e 3. Un articolo contenente i risultati di questo lavoro sarà sottomesso a breve nella rivista scientifica MNRAS (Tescari et al. 2010, in preparazione).XXII Ciclo198

Galactic winds and extended Lyα emission from the host galaxies of high column density quasi-stellar object absorption systems

We present three-dimensional (3D) resonant radiative transfer simulations of the spatial and spectral diffusion of the Lyα radiation from a central source in the host galaxies of high column density absorption systems at z∼ 3. The radiative transfer simulations are based on a suite of cosmological galaxy formation simulations which reproduce a wide range of observed properties of damped Lyα absorption systems. The Lyα emission is predicted to be spatially extended up to several arcsec, and the spectral width of the Lyα emission is broadened to several hundred (in some case more than thousand) km s−1. The distribution and the dynamical state of the gas in the simulated galaxies are complex, the latter with significant contributions from rotation and both in- and out-flows. The emerging Lyα radiation extends to gas with column densities of NH I∼ 1018 cm−2 and its spectral shape varies strongly with viewing angle. The strong dependence on the central H i column density and the H i velocity field suggests that the Lyα emission will also vary strongly with time on time-scales of a few dynamical times of the central region. Such variations with time should be especially pronounced at times where the host galaxy undergoes a major merger and/or starburst. Depending on the pre-dominance of in- or out-flow along a given sightline and the central column density, the spectra show prominent blue peaks, red peaks or double-peaked profiles. Both spatial distribution and spectral shape are very sensitive to details of the galactic wind implementation. Stronger galactic winds result in more spatially extended Lyα emission and - somewhat counterintuitively - a narrower spectral distributio

Regionally aggregated, stitched and de‐drifted CMIP‐climate data, processed with netCDF‐SCM v2.0.0

The world's most complex climate models are currently running a range of experiments as part of the Sixth Coupled Model Intercomparison Project (CMIP6). Added to the output from the Fifth Coupled Model Intercomparison Project (CMIP5), the total data volume will be in the order of 20PB. Here, we present a dataset of annual, monthly, global, hemispheric and land/ocean means derived from a selection of experiments of key interest to climate data analysts and reduced complexity climate modellers. The derived dataset is a key part of validating, calibrating and developing reduced complexity climate models against the behaviour of more physically complete models. In addition to its use for reduced complexity climate modellers, we aim to make our data accessible to other research communities. We facilitate this in a number of ways. Firstly, given the focus on annual, monthly, global, hemispheric and land/ocean mean quantities, our dataset is orders of magnitude smaller than the source data and hence does not require specialized ‘big data’ expertise. Secondly, again because of its smaller size, we are able to offer our dataset in a text-based format, greatly reducing the computational expertise required to work with CMIP output. Thirdly, we enable data provenance and integrity control by tracking all source metadata and providing tools which check whether a dataset has been retracted, that is identified as erroneous. The resulting dataset is updated as new CMIP6 results become available and we provide a stable access point to allow automated downloads. Along with our accompanying website (cmip6.science.unimelb.edu.au), we believe this dataset provides a unique community resource, as well as allowing non-specialists to access CMIP data in a new, user-friendly way

Panchromatic spectral energy distributions of simulated galaxies: results at redshift z = 0

We present predictions of spectral energy distributions (SEDs), from the UV to the FIR, of simulated galaxies at z = 0. These were obtained by post-processing the results of an N-body+hydro simulation of a cosmological box of side 25 Mpc, which uses the Multi-Phase Particle Integrator (MUPPI) for star formation and stellar feedback, with the grasil-3d radiative transfer code that includes reprocessing of UV light by dust. Physical properties of our sample of \u2dc500 galaxies resemble observed ones, though with some tension at small and large stellar masses. Comparing predicted SEDs of simulated galaxies with different samples of local galaxies, we find that these resemble observed ones, when normalized at 3.6 \u3bcm. A comparison with the Herschel Reference Survey shows that the average SEDs of galaxies, divided in bins of star formation rate (SFR), are reproduced in shape and absolute normalization to within a factor of \u2dc2, while average SEDs of galaxies divided in bins of stellar mass show tensions that are an effect of the difference of simulated and observed galaxies in the stellar mass-SFR plane. We use our sample to investigate the correlation of IR luminosity in Spitzer and Herschel bands with several galaxy properties. SFR is the quantity that best correlates with IR light up to 160 \u3bcm, while at longer wavelengths better correlations are found with molecular mass and, at 500 \u3bcm, with dust mass. However, using the position of the FIR peak as a proxy for cold dust temperature, we assess that heating of cold dust is mostly determined by SFR, with stellar mass giving only a minor contribution. We finally show how our sample of simulated galaxies can be used as a guide to understand the physical properties and selection biases of observed samples

Galactic Winds and Extended Lya Emission from the Host Galaxies of High Column Density QSO Absorption Systems

We present 3D resonant radiative transfer simulations of the spatial and spectral diffusion of the Lya radiation from a central source in the host galaxies of high column density absorption systems at z ~ 3. The radiative transfer simulations are based on a suite of cosmological galaxy formation simulations that reproduce a wide range of observed properties of damped Lya absorption systems. The Lya emission is predicted to be spatially extended up to several arcsec, and the spectral width of the Lya emission is broadened to several hundred (in some case more than thousand) km/s. The distribution and the dynamical state of the gas in the simulated galaxies is complex, the latter with significant contributions from rotation and both in- and out-flows. The emerging Lya radiation extends to gas with column densities of N_HI ~ 10^{18} cm^{-2} and its spectral shape varies strongly with viewing angle. The strong dependence on the central \hi column density and the HI velocity field suggests that the Lya emission will also vary strongly with time on timescales of a few dynamical times of the central region. Such variations with time should be especially pronounced at times where the host galaxy undergoes a major merger and/or starburst. Depending on the pre-dominance of in- or out-flow along a given sightline and the central column density, the spectra show prominent blue peaks, red peaks or double-peaked profiles. Both spatial distribution and spectral shape are very sensitive to details of the galactic wind implementation. Stronger galactic winds result in more spatially extended Lya emission and - somewhat counterintuitively - a narrower spectral distribution.Comment: 16 pages, 9 figures. Submitted to MNRAS on 20th Dec, 201

Detection of a possible superluminous supernova in the epoch of reionization

An interesting transient has been detected in one of our three Dark Energy Camera deep fields. Observations of these deep fields take advantage of the high red sensitivity of DECam on the Cerro Tololo Interamerican Observatory Blanco telescope. The survey includes the Y band with rest wavelength 1430{\AA} at z = 6. Survey fields (the Prime field 0555-6130, the 16hr field 1600-75 and the SUDSS New Southern Field) are deeper in Y than other infrared surveys. They are circumpolar, allowing all night to be used efficiently, exploiting the moon tolerance of 1 micron observations to minimize conflict with the Dark Energy Survey. As an i-band dropout (meaning that the flux decrement shortward of Lyman alpha is in the i bandpass), the transient we report here is a supernova candidate with z ~ 6, with a luminosity comparable to the brightest known current epoch superluminous supernova (i.e., ~ 2 x 10^11 solar luminosities).Comment: Reference adde

The SAMI Galaxy Survey: The link between angular momentum and optical morphology

We investigate the relationship between stellar and gas specific angular momentum j, stellar massM* and optical morphology for a sample of 488 galaxies extracted from the Sydney-AAO Multi-object Integral field Galaxy Survey.We find that j, measured within one effective radius, monotonically increases with M* and that, for M* > 109.5 M⊙, the scatter in this relation strongly correlates with optical morphology (i.e. visual classification and Sérsic index). These findings confirm that massive galaxies of all types lie on a plane relating mass, angular momentum and stellar-light distribution, and suggest that the large-scale morphology of a galaxy is regulated by its mass and dynamical state. We show that the significant scatter in the M*-j relation is accounted for by the fact that, at fixed stellar mass, the contribution of ordered motions to the dynamical support of galaxies varies by at least a factor of 3. Indeed, the stellar spin parameter (quantified via λR) correlates strongly with Sérsic and concentration indices. This correlation is particularly strong once slow rotators are removed from the sample, showing that late-type galaxies and early-type fast rotators form a continuous class of objects in terms of their kinematic properties

The SAMI Galaxy Survey: understanding observations of large-scale outflows at low redshift with EAGLE simulations

This work presents a study of galactic outflows driven by stellar feedback. We extract mainsequence disc galaxies with stellar mass 109 ≤ M*/ M⊙ ≤ 5.7 × 1010 at redshift z = 0 from the highest resolution cosmological simulation of the Evolution and Assembly of GaLaxies and their Environments (EAGLE) set. Synthetic gas rotation velocity and velocity dispersion (σ) maps are created and compared to observations of disc galaxies obtained with the Sydney-AAO (Australian Astronomical Observatory) Multi-object Integral field spectrograph (SAMI), where σ-values greater than 150 km s-1 are most naturally explained by bipolar outflows powered by starburst activity. We find that the extension of the simulated edge-on (pixelated) velocity dispersion probability distribution depends on stellar mass and star formation rate surface density (ΣSFR), with low-M*/low-ΣSFR galaxies showing a narrow peak at low s (~30 km s-1) and more active, high-M*/high-ΣSFR galaxies reaching σ > 150 km s-1. Although supernova-driven galactic winds in the EAGLE simulations may not entrain enough gas with T < 105 K compared to observed galaxies, we find that gas temperature is a good proxy for the presence of outflows. There is a direct correlation between the thermal state of the gas and its state of motion as described by the σ-distribution. The following equivalence relations hold in EAGLE: (i) low-σ peak ⇔ disc of the galaxy ⇔ gas with T < 105 K; (ii) high-σ tail ⇔ galactic winds ⇔ gas with T ≥105 K.SMC acknowledges the support of an Australian Research Council Future Fellowship (FT100100457). Support for AMM is provided by NASA through Hubble Fellowship grant #HST-HF2-51377 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5- 2655