The "Lambda Cold Dark Matter" (ΛCDM) model of cosmic structure formation is eminently falsifiable... more The "Lambda Cold Dark Matter" (ΛCDM) model of cosmic structure formation is eminently falsifiable: once its parameters are fixed on large scales, it becomes testable in the nearby Universe. Observations within our Local Group of galaxies, including the satellite populations of the Milky Way and Andromeda, appear to contradict ΛCDM predictions: there are far fewer satellite galaxies than dark matter halos (the "missing satellites" problem (1, 2)), galaxies seem to avoid the largest substructures (the "too big to fail" problem (3, 4)), and the brightest satellites appear to orbit their host galaxies on a thin plane (the "planes of satellites" problem (5)). We present results from the first hydrodynamic simulations of the Local Group that match the observed abundance of galaxies. We find that when baryonic and dark matter are followed simultaneously in the context of a realistic galaxy formation model, all three "problems" are resolved within the ΛCDM paradigm.
Galaxy formation and evolution simulations are essential tools to probe poorly known astrophysics... more Galaxy formation and evolution simulations are essential tools to probe poorly known astrophysics processes, but particular care is needed to compare simulations with galaxy observations, as observed data need to be modelled as well. We present a method to generate mock galaxies from the hydro-dynamical IllustrisTNG simulations which are suited to compare with integral field spectroscopic observation of galaxies from the SDSS-IV/Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. First, we include the same instrumental effects and procedures as adopted in the acquisition and analysis of real data. Furthermore, we generate the galaxy spectra from the simulations using new stellar population models based on the MaNGA stellar library (MaStar). In this way, our mock data cubes have the same spatial sampling, cover the same wavelength range (3600–10 300 Å), and share the same spectral resolution (R ≈ 1800) and flux calibration of real MaNGA galaxy spectra. In this first p...
We have created a show about the Solar System, freely available for both planetariums and home vi... more We have created a show about the Solar System, freely available for both planetariums and home viewing, where objects in space are represented with sound as well as with visuals. For example, the audience listens to the stars appear above the European Southern Observatory’s Very Large Telescope and they hear the planets orbit around their heads. The aim of this show is that it can be enjoyed and understood, irrespective of level of vision. Here we describe how we used our new computer code, STRAUSS, to convert data into sound for the show. We also discuss the lessons learnt during the design of the show, including how it was imperative to obtain a range of diverse perspectives from scientists, a composer and representatives of the blind and vision impaired community.
Chris Harrison, James Trayford, Leigh Harrison and Nicolas Bonne have developed a sensory odyssey... more Chris Harrison, James Trayford, Leigh Harrison and Nicolas Bonne have developed a sensory odyssey to demonstrate how the Universe can be made more accessible.
Monthly Notices of the Royal Astronomical Society, 2022
Using the First Light And Reionisation Epoch Simulations (flares), we explore the dust-driven pro... more Using the First Light And Reionisation Epoch Simulations (flares), we explore the dust-driven properties of massive high-redshift galaxies at z ∈ [5, 10]. By post-processing, the galaxy sample using the radiative transfer code skirt we obtain the full spectral energy distribution. We explore the resultant luminosity functions, IRX–β relations as well as the luminosity-weighted dust temperatures in the Epoch of Reionisation (EoR). We find that most of our results are in agreement with the current set of observations, but underpredict the number densities of bright IR galaxies, which are extremely biased towards the most overdense regions. We see that the flares IRX–β relation (for 5 ≤ z ≤ 8) pre-dominantly follows the local starburst relation. The IRX shows an increase with stellar mass, plateauing at the high-mass end (∼1010 M⊙) and shows no evolution in the median normalisation with redshift. We also look at the dependence of the peak dust temperature (Tpeak) on various galaxy prop...
Proceedings of the International Astronomical Union, 2019
Starburst galaxies are often found to be the result of galaxy mergers. As a result, galaxy merger... more Starburst galaxies are often found to be the result of galaxy mergers. As a result, galaxy mergers are often believed to lie above the galaxy main sequence: the tight correlation between stellar mass and star formation rate. Here, we aim to test this claim.Deep learning techniques are applied to images from the Sloan Digital Sky Survey to provide visual-like classifications for over 340 000 objects between redshifts of 0.005 and 0.1. The aim of this classification is to split the galaxy population into merger and non-merger systems and we are currently achieving an accuracy of 92.5%. Stellar masses and star formation rates are also estimated using panchromatic data for the entire galaxy population. With these preliminary data, the mergers are placed onto the full galaxy main sequence, where we find that merging systems lie across the entire star formation rate - stellar mass plane.
Monthly Notices of the Royal Astronomical Society, 2021
We use mock images of z = 0.1 galaxies in the 100 Mpc EAGLE simulation to establish the differenc... more We use mock images of z = 0.1 galaxies in the 100 Mpc EAGLE simulation to establish the differences between the sizes and morphologies inferred from the stellar mass distributions and the optical light distributions. The optical, r-band images used were constructed with a radiative transfer method to account for the effects of dust, and we measure galaxy structural parameters by fitting Sérsic models to the images with galfit. We find that the derived half-light radii differ systematically from the stellar half-mass radii, as the r-band sizes are typically 0.1 dex larger, and can deviate by as much as ${\approx}0.5\,$ dex, depending on the dust attenuation and star formation activity, as well as the measurement method used. Consequently, we demonstrate that the r-band sizes significantly improve the agreement between the simulated and observed stellar mass–size relation: star-forming and quiescent galaxies in EAGLE are typically only slightly larger than observed (by 0.1 dex), and t...
Monthly Notices of the Royal Astronomical Society, 2020
We present infrared luminosity functions and dust mass functions for the EAGLE cosmological simul... more We present infrared luminosity functions and dust mass functions for the EAGLE cosmological simulation, based on synthetic multiwavelength observations generated with the SKIRT radiative transfer code. In the local Universe, we reproduce the observed infrared luminosity and dust mass functions very well. Some minor discrepancies are encountered, mainly in the high luminosity regime, where the EAGLE-SKIRT luminosity functions mildly but systematically underestimate the observed ones. The agreement between the EAGLE-SKIRT infrared luminosity functions and the observed ones gradually worsens with increasing lookback time. Fitting modified Schechter functions to the EAGLE-SKIRT luminosity and dust mass functions at different redshifts up to z = 1, we find that the evolution is compatible with pure luminosity/mass evolution. The evolution is relatively mild: within this redshift range, we find an evolution of L⋆,250 ∝ (1 + z)1.68, L⋆,TIR ∝ (1 + z)2.51 and M⋆,dust ∝ (1 + z)0.83 for the ch...
Monthly Notices of the Royal Astronomical Society, 2020
ABSTRACTWe compare the spectral energy distributions (SEDs) and inferred physical properties for ... more ABSTRACTWe compare the spectral energy distributions (SEDs) and inferred physical properties for simulated and observed galaxies at low redshift. We exploit UV-submillimetre mock fluxes of ∼7000 z = 0 galaxies from the EAGLE suite of cosmological simulations, derived using the radiative transfer code skirt. We compare these to ∼800 observed galaxies in the UV-submillimetre range, from the DustPedia sample of nearby galaxies. To derive global properties, we apply the SED fitting code cigale consistently to both data sets, using the same set of ∼80 million models. The results of this comparison reveal overall agreement between the simulations and observations, both in the SEDs and in the derived physical properties, with a number of discrepancies. The optical and far-infrared regimes, and the scaling relations based upon the global emission, diffuse dust, and stellar mass, show high levels of agreement. However, the mid-infrared fluxes of the EAGLE galaxies are overestimated while the...
The scatter (σ sSFR) of the specific star formation rates (sSFRs) of galaxies is a measure of the... more The scatter (σ sSFR) of the specific star formation rates (sSFRs) of galaxies is a measure of the diversity in their star formation histories (SFHs) at a given mass. In this paper we employ the EAGLE simulations to study the dependence of the σ sSFR of galaxies on stellar mass (M ⋆) through the σ sSFR-M ⋆ relation in z ∼ 0 − 4. We find that the relation evolves with time, with the dispersion depending on both stellar mass and redshift. The models point to an evolving U-shape form for the σ sSFR-M ⋆ relation with the scatter being minimal at a characteristic mass M ⋆ of 10 9.5 M ⊙ and increasing both at lower and higher masses. This implication is that the diversity of SFHs increases towards both at the low-and high-mass ends. We find that active galactic nuclei feedback is important for increasing the σ sSFR for high mass objects. On the other hand, we suggest that SNe feedback increases the σ sSFR of galaxies at the low-mass end. We also find that excluding galaxies that have experienced recent mergers does not significantly affect the σ sSFR-M ⋆ relation. Furthermore, we employ the combination of the EAGLE simulations with the radiative transfer code SKIRT to evaluate the effect of SFR/stellar mass diagnostics in the σ sSFR-M ⋆ relation and find that the SFR/M ⋆ methodologies (e.g. SED fitting, UV+IR, UV+IRX-β) widely used in the literature to obtain intrinsic properties of galaxies have a large effect on the derived shape and normalization of the σ sSFR-M ⋆ relation.
Monthly Notices of the Royal Astronomical Society, 2019
We use the EAGLE simulations to study the connection between the quenching timescale , τ Q , and ... more We use the EAGLE simulations to study the connection between the quenching timescale , τ Q , and the physical mechanisms that transform star-forming galaxies into passive galaxies. By quantifying τ Q in two complementary ways-as the time over which (i) galaxies traverse the green valley on the colour-mass diagram, or (ii) leave the main sequence of star formation and subsequently arrive on the passive cloud in specific star formation rate (SSFR)-mass space-we find that the τ Q distribution of high-mass centrals, low-mass centrals, and satellites are divergent. In the low stellar mass regime where M < 10 9.6 M , centrals exhibit systematically longer quenching timescales than satellites (≈4 Gyr compared to ≈2 Gyr). Satellites with low stellar mass relative to their halo mass cause this disparity, with ram pressure stripping quenching these galaxies rapidly. Low-mass centrals are quenched as a result of stellar feedback, associated with long τ Q 3 Gyr. At intermediate stellar masses where 10 9.7 < M < 10 10.3 M , τ Q are the longest for both centrals and satellites, particularly for galaxies with higher gas fractions. At M 10 10.3 M , galaxy merger counts and black hole activity increase steeply for all galaxies. Quenching timescales for centrals and satellites decrease with stellar mass in this regime to τ Q 2 Gyr. In anticipation of new intermediate redshift observational galaxy surveys, we analyse the passive and star-forming fractions of galaxies across redshift, and find that the τ Q peak at intermediate stellar masses is responsible for a peak (inflection point) in the fraction of green valley central (satellite) galaxies at z ≈ 0.5-0.7.
Monthly Notices of the Royal Astronomical Society, 2019
We explore scaling relations between the physical properties of spatially resolved regions within... more We explore scaling relations between the physical properties of spatially resolved regions within the galaxies that emerge in the Evolution and Assembly of GaLaxies and their Environments (EAGLE) hydrodynamical, cosmological simulations. Using 1 kpc-scale spaxels, we compute the relationships between the star formation rate and stellar mass surface densities, i.e. the spatially resolved star-forming main sequence (rSFMS), and between the gas metallicity and the stellar mass surface density, i.e. the spatially resolved mass-metallicity relation (rMZR). We compare these with observed relations derived from integral field unit surveys and galaxy imaging. EAGLE reproduces the slope of the local (z ≈ 0.1) rSFMS well, but with a ≈− 0.15 dex offset, close to that found for the galaxy-integrated relation. The shape of the rMZR agrees reasonably well with observations, replicating the characteristic turnover at high surface density, which we show is due to AGN feedback. The residuals of the rSFMS and rMZR are negatively (positively) correlated at low (high) surface density. The rSFMS becomes shallower as the simulation evolves from z = 2 to 0.1, a manifestation of inside-out galaxy formation. The shape of the rMZR also exhibits dramatic evolution, from a convex profile at z = 2 to the observed concave profile at z = 0.1, such that the gas in regions of high stellar density is more enriched at higher redshift. The redshift independence of the relationship between the galaxy-wide gas fraction and metallicity in EAGLE galaxies is not preserved on 1 kpc scales, implying that chemical evolution is non-local due to the transport of gas and metals within galaxies.
Monthly Notices of the Royal Astronomical Society, 2019
The cosmic spectral energy distribution (CSED) is the total emissivity as a function of wavelengt... more The cosmic spectral energy distribution (CSED) is the total emissivity as a function of wavelength of galaxies in a given cosmic volume. We compare the observed CSED from the UV to the submm to that computed from the EAGLE (Evolution and Assembly of GaLaxies and their Environments) cosmological hydrodynamical simulation, post-processed with stellar population synthesis models and including dust radiative transfer using the SKIRT code. The agreement with the data is better than 0.15 dex over the entire wavelength range at redshift z = 0, except at UV wavelengths where the EAGLE model overestimates the observed CSED by up to a factor of 2. Global properties of the CSED as inferred from CIGALE fits, such as the stellar mass density, mean star formation density, and mean dust-to-stellar-mass ratio, agree to within better than 20 per cent. At higher redshift, EAGLE increasingly underestimates the CSED at optical-NIR wavelengths with the FIR/submm emissivity underestimated by more than a factor of 5 by redshift z = 1. We believe that these differences are due to a combination of incompleteness of the EAGLE-SKIRT data base, the small simulation volume and the consequent lack of luminous galaxies, and our lack of knowledge on the evolution of the characteristics of the interstellar dust in galaxies. The impressive agreement between the simulated and observed CSED at lower z confirms that the combination of EAGLE and SKIRT dust processing yields a fairly realistic representation of the local Universe.
Monthly Notices of the Royal Astronomical Society, 2018
We study the formation and evolution of ring galaxies in the Evolution and Assembly of GaLaxies a... more We study the formation and evolution of ring galaxies in the Evolution and Assembly of GaLaxies and their Environments (EAGLE) simulations. We use the largest reference model Ref-L100N1504, a cubic cosmological volume of 100 cMpc on a side, to identify and characterize these systems through cosmic time. The number density of ring galaxies in EAGLE is in broad agreement with the observations. The vast majority of ring galaxies identified in EAGLE (83 per cent) have an interaction origin, i.e. form when one or more companion galaxies drop-through a disc galaxy. The remainder (17 per cent) have very long-lived ring morphologies (>2 Gyr) and host strong bars. Ring galaxies are HI-rich galaxies, yet display inefficient star formation activity and tend to reside in the green valley particularly at z 0.5. This inefficiency is mainly due to the low pressure and metallicity of their interstellar medium (ISM) compared with the ISM of similar star-forming galaxies. We find that the interaction(s) is responsible for decreasing the ISM pressure by causing the ISM gas to flow from the inner regions to the outer disc, where the ring feature forms. At a fixed radius, the star formation efficiency of ring galaxies is indistinguishable from their star-forming counterparts, and thus the main reason for their integrated lower efficiency is the different gas surface density profiles. Since galaxy morphologies are not used to tune the parameters in hydrodynamical simulations, the experiment performed here demonstrates the success of the current numerical models in EAGLE.
We present dust-attenuated and dust emission fluxes for sufficiently resolved galaxies in the EAG... more We present dust-attenuated and dust emission fluxes for sufficiently resolved galaxies in the EAGLE suite of cosmological hydrodynamical simulations, calculated with the SKIRT radiative transfer code. The post-processing procedure includes specific components for star formation regions, stellar sources, and diffuse dust, and takes into account stochastic heating of dust grains to obtain realistic broad-band fluxes in the wavelength range from ultraviolet to sub-millimeter. The mock survey includes nearly half a million simulated galaxies with stellar masses above 10 8.5 M across six EAGLE models. About two thirds of these galaxies, residing in 23 redshift bins up to z = 6, have a sufficiently resolved metallic gas distribution to derive meaningful dust attenuation and emission, with the important caveat that the same dust properties were used at all redshifts. These newly released data complement the already publicly available information about the EAGLE galaxies, which includes intrinsic properties derived by aggregating the properties of the smoothed particles representing matter in the simulation. We further provide an open source framework of Python procedures for post-processing simulated galaxies with the radiative transfer code SKIRT. The framework allows any third party to calculate synthetic images, SEDs, and broadband fluxes for EAGLE galaxies, taking into account the effects of dust attenuation and emission.
Monthly Notices of the Royal Astronomical Society, 2017
We present new observations acquired with the Multi Unit Spectroscopic Explorer instrument on the... more We present new observations acquired with the Multi Unit Spectroscopic Explorer instrument on the Very Large Telescope in a quasar field that hosts a high column density damped Lyα absorber (DLA) at z ≈ 3.25. We detect Lyα emission from a nebula at the redshift of the DLA with line luminosity (27 ± 1) × 10 41 erg s −1 , which extends over 37 ± 1 kpc above a surface brightness limit of 6 × 10 −19 erg s −1 cm −2 arcsec −2 at a projected distance of 30.5 ± 0.5 kpc from the quasar sightline. Two clumps lie inside this nebula, both with Lyα rest-frame equivalent width >50 Å and with relative line-of-sight velocities aligned with two main absorption components seen in the DLA spectrum. In addition, we identify a compact galaxy at a projected distance of 19.1 ± 0.5 kpc from the quasar sightline. The galaxy spectrum is noisy but consistent with that of a star-forming galaxy at the DLA redshift. We argue that the Lyα nebula is ionized by radiation from star formation inside the two clumps, or by radiation from the compact galaxy. In either case, these data imply the presence of a structure with size 50 kpc inside which galaxies are assembling, a picture consistent with galaxy formation in groups and filaments as predicted by cosmological simulations such as the EAGLE simulations.
Monthly Notices of the Royal Astronomical Society, 2017
We study present-day galaxy clustering in the EAGLE cosmological hydrodynamical simulation. EAGLE... more We study present-day galaxy clustering in the EAGLE cosmological hydrodynamical simulation. EAGLE's galaxy formation parameters were calibrated to reproduce the redshift z = 0.1 galaxy stellar mass function, and the simulation also reproduces galaxy colours well. The simulation volume is too small to correctly sample large-scale fluctuations and we therefore concentrate on scales smaller than a few mega parsecs. We find very good agreement with observed clustering measurements from the Galaxy And Mass Assembly (GAMA) survey, when galaxies are binned by stellar mass, colour or luminosity. However, low-mass red galaxies are clustered too strongly, which is at least partly due to limited numerical resolution. Apart from this limitation, we conclude that EAGLE galaxies inhabit similar dark matter haloes as observed GAMA galaxies, and that the radial distribution of satellite galaxies, as a function of stellar mass and colour, is similar to that observed as well.
Monthly Notices of the Royal Astronomical Society, 2017
We present a MUSE (Multi-Unit Spectroscopic Explorer) and KMOS (K-band Multi-Object Spectrograph)... more We present a MUSE (Multi-Unit Spectroscopic Explorer) and KMOS (K-band Multi-Object Spectrograph) dynamical study 405 star-forming galaxies at redshift z = 0.28-1.65 (median redshiftz = 0.84). Our sample is representative of the star-forming 'main sequence', with star formation rates of SFR = 0.1-30 M yr −1 and stellar masses M = 10 8-10 11 M. For 49 ± 4 per cent of our sample, the dynamics suggest rotational support, 24 ± 3 per cent are unresolved systems and 5 ± 2 per cent appear to be early-stage major mergers with components on 8-30 kpc scales. The remaining 22 ± 5 per cent appear to be dynamically complex, irregular (or face-on systems). For galaxies whose dynamics suggest rotational support, we derive inclination-corrected rotational velocities and show that these systems lie on a similar scaling between stellar mass and specific angular momentum as local spirals with j = J/M ∝ M 2/3 but with a redshift evolution that scales as j ∝ M 2/3 (1 + z) −1. We also identify a correlation between specific angular momentum and disc stability such that galaxies with the highest specific angular momentum (log(j /M 2/3) > 2.5) are the most stable, with Toomre Q = 1.10 ± 0.18, compared to Q = 0.53 ± 0.22 for galaxies with log(j /M 2/3) < 2.5. At a fixed mass, the Hubble Space Telescope morphologies of galaxies with the highest specific angular momentum resemble spiral galaxies, whilst those with low specific angular momentum are morphologically complex and dominated by several bright star-forming regions. This suggests that angular momentum plays a major role in defining the stability of gas discs: at z ∼ 1, massive galaxies that have discs with low specific angular momentum are globally unstable, clumpy and turbulent systems. In contrast, galaxies with high specific angular momentum have evolved into stable discs with spiral structure where star formation is a local (rather than global) process.
Monthly Notices of the Royal Astronomical Society, 2016
We explore the co-evolution of the specific angular momentum of dark matter haloes and the cold b... more We explore the co-evolution of the specific angular momentum of dark matter haloes and the cold baryons that comprise the galaxies within. We study over 2000 galaxies within the reference cosmological hydrodynamical simulation of the 'Evolution and Assembly of GaLaxies and their Environments' (EAGLE) project. We employ a methodology within which the evolutionary history of a system is specified by the time-evolving properties of the Lagrangian particles that define it at z = 0. We find a strong correlation between the evolution of the specific angular momentum of today's stars (cold gas) and that of the inner (whole) dark matter halo they are associated with. This link is particularly strong for the stars formed before the epoch of maximum expansion and subsequent collapse of the central dark matter halo (turnaround). Spheroids are assembled primarily from stars formed prior to turnaround, and suffer a net loss of angular momentum associated with the strong merging activity during the assembly of the inner dark matter halo. Stellar discs retain their specific angular momentum since they are comprised of stars formed mainly after turnaround, from gas that mostly preserves the high specific angular momentum it acquired by tidal torques during the linear growth of the halo. Since the specific angular momentum loss of the stars is tied to the galaxy's morphology today, it may be possible to use our results to predict, statistically, the maximum loss of specific angular momentum of the inner part of a halo given the morphology of the galaxy it hosts.
Monthly Notices of the Royal Astronomical Society, 2016
We examine the evolution of intrinsic u−r colours of galaxies in the EAGLE cosmological hydrodyna... more We examine the evolution of intrinsic u−r colours of galaxies in the EAGLE cosmological hydrodynamical simulations, which has been shown to reproduce the observed redshift z = 0.1 colour-magnitude distribution well, with a focus on z < 2. The median u−r of star-forming ('blue cloud') galaxies reddens by 1 mag from z = 2 to 0 at fixed stellar mass, as their specific star formation rates decrease with time. A red sequence starts to build-up around z = 1, due to the quenching of low-mass satellite galaxies at the faint end, and due to the quenching of more massive central galaxies by their active galactic nuclei (AGN) at the bright end. This leaves a dearth of intermediate-mass red sequence galaxies at z = 1, which is mostly filled in by z = 0. We quantify the timescales of colour transition finding that most galaxies spend less than 2 Gyr in the 'green valley'. We find the timescale of transition to be independent of quenching mechanism, i.e. whether a galaxy is a satellite or hosting an AGN. On examining the trajectories of galaxies in a colour-stellar mass diagram, we identify three characteristic tracks that galaxies follow (quiescently star-forming, quenching and rejuvenating galaxies) and quantify the fraction of galaxies that follow each track.
The "Lambda Cold Dark Matter" (ΛCDM) model of cosmic structure formation is eminently falsifiable... more The "Lambda Cold Dark Matter" (ΛCDM) model of cosmic structure formation is eminently falsifiable: once its parameters are fixed on large scales, it becomes testable in the nearby Universe. Observations within our Local Group of galaxies, including the satellite populations of the Milky Way and Andromeda, appear to contradict ΛCDM predictions: there are far fewer satellite galaxies than dark matter halos (the "missing satellites" problem (1, 2)), galaxies seem to avoid the largest substructures (the "too big to fail" problem (3, 4)), and the brightest satellites appear to orbit their host galaxies on a thin plane (the "planes of satellites" problem (5)). We present results from the first hydrodynamic simulations of the Local Group that match the observed abundance of galaxies. We find that when baryonic and dark matter are followed simultaneously in the context of a realistic galaxy formation model, all three "problems" are resolved within the ΛCDM paradigm.
Galaxy formation and evolution simulations are essential tools to probe poorly known astrophysics... more Galaxy formation and evolution simulations are essential tools to probe poorly known astrophysics processes, but particular care is needed to compare simulations with galaxy observations, as observed data need to be modelled as well. We present a method to generate mock galaxies from the hydro-dynamical IllustrisTNG simulations which are suited to compare with integral field spectroscopic observation of galaxies from the SDSS-IV/Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. First, we include the same instrumental effects and procedures as adopted in the acquisition and analysis of real data. Furthermore, we generate the galaxy spectra from the simulations using new stellar population models based on the MaNGA stellar library (MaStar). In this way, our mock data cubes have the same spatial sampling, cover the same wavelength range (3600–10 300 Å), and share the same spectral resolution (R ≈ 1800) and flux calibration of real MaNGA galaxy spectra. In this first p...
We have created a show about the Solar System, freely available for both planetariums and home vi... more We have created a show about the Solar System, freely available for both planetariums and home viewing, where objects in space are represented with sound as well as with visuals. For example, the audience listens to the stars appear above the European Southern Observatory’s Very Large Telescope and they hear the planets orbit around their heads. The aim of this show is that it can be enjoyed and understood, irrespective of level of vision. Here we describe how we used our new computer code, STRAUSS, to convert data into sound for the show. We also discuss the lessons learnt during the design of the show, including how it was imperative to obtain a range of diverse perspectives from scientists, a composer and representatives of the blind and vision impaired community.
Chris Harrison, James Trayford, Leigh Harrison and Nicolas Bonne have developed a sensory odyssey... more Chris Harrison, James Trayford, Leigh Harrison and Nicolas Bonne have developed a sensory odyssey to demonstrate how the Universe can be made more accessible.
Monthly Notices of the Royal Astronomical Society, 2022
Using the First Light And Reionisation Epoch Simulations (flares), we explore the dust-driven pro... more Using the First Light And Reionisation Epoch Simulations (flares), we explore the dust-driven properties of massive high-redshift galaxies at z ∈ [5, 10]. By post-processing, the galaxy sample using the radiative transfer code skirt we obtain the full spectral energy distribution. We explore the resultant luminosity functions, IRX–β relations as well as the luminosity-weighted dust temperatures in the Epoch of Reionisation (EoR). We find that most of our results are in agreement with the current set of observations, but underpredict the number densities of bright IR galaxies, which are extremely biased towards the most overdense regions. We see that the flares IRX–β relation (for 5 ≤ z ≤ 8) pre-dominantly follows the local starburst relation. The IRX shows an increase with stellar mass, plateauing at the high-mass end (∼1010 M⊙) and shows no evolution in the median normalisation with redshift. We also look at the dependence of the peak dust temperature (Tpeak) on various galaxy prop...
Proceedings of the International Astronomical Union, 2019
Starburst galaxies are often found to be the result of galaxy mergers. As a result, galaxy merger... more Starburst galaxies are often found to be the result of galaxy mergers. As a result, galaxy mergers are often believed to lie above the galaxy main sequence: the tight correlation between stellar mass and star formation rate. Here, we aim to test this claim.Deep learning techniques are applied to images from the Sloan Digital Sky Survey to provide visual-like classifications for over 340 000 objects between redshifts of 0.005 and 0.1. The aim of this classification is to split the galaxy population into merger and non-merger systems and we are currently achieving an accuracy of 92.5%. Stellar masses and star formation rates are also estimated using panchromatic data for the entire galaxy population. With these preliminary data, the mergers are placed onto the full galaxy main sequence, where we find that merging systems lie across the entire star formation rate - stellar mass plane.
Monthly Notices of the Royal Astronomical Society, 2021
We use mock images of z = 0.1 galaxies in the 100 Mpc EAGLE simulation to establish the differenc... more We use mock images of z = 0.1 galaxies in the 100 Mpc EAGLE simulation to establish the differences between the sizes and morphologies inferred from the stellar mass distributions and the optical light distributions. The optical, r-band images used were constructed with a radiative transfer method to account for the effects of dust, and we measure galaxy structural parameters by fitting Sérsic models to the images with galfit. We find that the derived half-light radii differ systematically from the stellar half-mass radii, as the r-band sizes are typically 0.1 dex larger, and can deviate by as much as ${\approx}0.5\,$ dex, depending on the dust attenuation and star formation activity, as well as the measurement method used. Consequently, we demonstrate that the r-band sizes significantly improve the agreement between the simulated and observed stellar mass–size relation: star-forming and quiescent galaxies in EAGLE are typically only slightly larger than observed (by 0.1 dex), and t...
Monthly Notices of the Royal Astronomical Society, 2020
We present infrared luminosity functions and dust mass functions for the EAGLE cosmological simul... more We present infrared luminosity functions and dust mass functions for the EAGLE cosmological simulation, based on synthetic multiwavelength observations generated with the SKIRT radiative transfer code. In the local Universe, we reproduce the observed infrared luminosity and dust mass functions very well. Some minor discrepancies are encountered, mainly in the high luminosity regime, where the EAGLE-SKIRT luminosity functions mildly but systematically underestimate the observed ones. The agreement between the EAGLE-SKIRT infrared luminosity functions and the observed ones gradually worsens with increasing lookback time. Fitting modified Schechter functions to the EAGLE-SKIRT luminosity and dust mass functions at different redshifts up to z = 1, we find that the evolution is compatible with pure luminosity/mass evolution. The evolution is relatively mild: within this redshift range, we find an evolution of L⋆,250 ∝ (1 + z)1.68, L⋆,TIR ∝ (1 + z)2.51 and M⋆,dust ∝ (1 + z)0.83 for the ch...
Monthly Notices of the Royal Astronomical Society, 2020
ABSTRACTWe compare the spectral energy distributions (SEDs) and inferred physical properties for ... more ABSTRACTWe compare the spectral energy distributions (SEDs) and inferred physical properties for simulated and observed galaxies at low redshift. We exploit UV-submillimetre mock fluxes of ∼7000 z = 0 galaxies from the EAGLE suite of cosmological simulations, derived using the radiative transfer code skirt. We compare these to ∼800 observed galaxies in the UV-submillimetre range, from the DustPedia sample of nearby galaxies. To derive global properties, we apply the SED fitting code cigale consistently to both data sets, using the same set of ∼80 million models. The results of this comparison reveal overall agreement between the simulations and observations, both in the SEDs and in the derived physical properties, with a number of discrepancies. The optical and far-infrared regimes, and the scaling relations based upon the global emission, diffuse dust, and stellar mass, show high levels of agreement. However, the mid-infrared fluxes of the EAGLE galaxies are overestimated while the...
The scatter (σ sSFR) of the specific star formation rates (sSFRs) of galaxies is a measure of the... more The scatter (σ sSFR) of the specific star formation rates (sSFRs) of galaxies is a measure of the diversity in their star formation histories (SFHs) at a given mass. In this paper we employ the EAGLE simulations to study the dependence of the σ sSFR of galaxies on stellar mass (M ⋆) through the σ sSFR-M ⋆ relation in z ∼ 0 − 4. We find that the relation evolves with time, with the dispersion depending on both stellar mass and redshift. The models point to an evolving U-shape form for the σ sSFR-M ⋆ relation with the scatter being minimal at a characteristic mass M ⋆ of 10 9.5 M ⊙ and increasing both at lower and higher masses. This implication is that the diversity of SFHs increases towards both at the low-and high-mass ends. We find that active galactic nuclei feedback is important for increasing the σ sSFR for high mass objects. On the other hand, we suggest that SNe feedback increases the σ sSFR of galaxies at the low-mass end. We also find that excluding galaxies that have experienced recent mergers does not significantly affect the σ sSFR-M ⋆ relation. Furthermore, we employ the combination of the EAGLE simulations with the radiative transfer code SKIRT to evaluate the effect of SFR/stellar mass diagnostics in the σ sSFR-M ⋆ relation and find that the SFR/M ⋆ methodologies (e.g. SED fitting, UV+IR, UV+IRX-β) widely used in the literature to obtain intrinsic properties of galaxies have a large effect on the derived shape and normalization of the σ sSFR-M ⋆ relation.
Monthly Notices of the Royal Astronomical Society, 2019
We use the EAGLE simulations to study the connection between the quenching timescale , τ Q , and ... more We use the EAGLE simulations to study the connection between the quenching timescale , τ Q , and the physical mechanisms that transform star-forming galaxies into passive galaxies. By quantifying τ Q in two complementary ways-as the time over which (i) galaxies traverse the green valley on the colour-mass diagram, or (ii) leave the main sequence of star formation and subsequently arrive on the passive cloud in specific star formation rate (SSFR)-mass space-we find that the τ Q distribution of high-mass centrals, low-mass centrals, and satellites are divergent. In the low stellar mass regime where M < 10 9.6 M , centrals exhibit systematically longer quenching timescales than satellites (≈4 Gyr compared to ≈2 Gyr). Satellites with low stellar mass relative to their halo mass cause this disparity, with ram pressure stripping quenching these galaxies rapidly. Low-mass centrals are quenched as a result of stellar feedback, associated with long τ Q 3 Gyr. At intermediate stellar masses where 10 9.7 < M < 10 10.3 M , τ Q are the longest for both centrals and satellites, particularly for galaxies with higher gas fractions. At M 10 10.3 M , galaxy merger counts and black hole activity increase steeply for all galaxies. Quenching timescales for centrals and satellites decrease with stellar mass in this regime to τ Q 2 Gyr. In anticipation of new intermediate redshift observational galaxy surveys, we analyse the passive and star-forming fractions of galaxies across redshift, and find that the τ Q peak at intermediate stellar masses is responsible for a peak (inflection point) in the fraction of green valley central (satellite) galaxies at z ≈ 0.5-0.7.
Monthly Notices of the Royal Astronomical Society, 2019
We explore scaling relations between the physical properties of spatially resolved regions within... more We explore scaling relations between the physical properties of spatially resolved regions within the galaxies that emerge in the Evolution and Assembly of GaLaxies and their Environments (EAGLE) hydrodynamical, cosmological simulations. Using 1 kpc-scale spaxels, we compute the relationships between the star formation rate and stellar mass surface densities, i.e. the spatially resolved star-forming main sequence (rSFMS), and between the gas metallicity and the stellar mass surface density, i.e. the spatially resolved mass-metallicity relation (rMZR). We compare these with observed relations derived from integral field unit surveys and galaxy imaging. EAGLE reproduces the slope of the local (z ≈ 0.1) rSFMS well, but with a ≈− 0.15 dex offset, close to that found for the galaxy-integrated relation. The shape of the rMZR agrees reasonably well with observations, replicating the characteristic turnover at high surface density, which we show is due to AGN feedback. The residuals of the rSFMS and rMZR are negatively (positively) correlated at low (high) surface density. The rSFMS becomes shallower as the simulation evolves from z = 2 to 0.1, a manifestation of inside-out galaxy formation. The shape of the rMZR also exhibits dramatic evolution, from a convex profile at z = 2 to the observed concave profile at z = 0.1, such that the gas in regions of high stellar density is more enriched at higher redshift. The redshift independence of the relationship between the galaxy-wide gas fraction and metallicity in EAGLE galaxies is not preserved on 1 kpc scales, implying that chemical evolution is non-local due to the transport of gas and metals within galaxies.
Monthly Notices of the Royal Astronomical Society, 2019
The cosmic spectral energy distribution (CSED) is the total emissivity as a function of wavelengt... more The cosmic spectral energy distribution (CSED) is the total emissivity as a function of wavelength of galaxies in a given cosmic volume. We compare the observed CSED from the UV to the submm to that computed from the EAGLE (Evolution and Assembly of GaLaxies and their Environments) cosmological hydrodynamical simulation, post-processed with stellar population synthesis models and including dust radiative transfer using the SKIRT code. The agreement with the data is better than 0.15 dex over the entire wavelength range at redshift z = 0, except at UV wavelengths where the EAGLE model overestimates the observed CSED by up to a factor of 2. Global properties of the CSED as inferred from CIGALE fits, such as the stellar mass density, mean star formation density, and mean dust-to-stellar-mass ratio, agree to within better than 20 per cent. At higher redshift, EAGLE increasingly underestimates the CSED at optical-NIR wavelengths with the FIR/submm emissivity underestimated by more than a factor of 5 by redshift z = 1. We believe that these differences are due to a combination of incompleteness of the EAGLE-SKIRT data base, the small simulation volume and the consequent lack of luminous galaxies, and our lack of knowledge on the evolution of the characteristics of the interstellar dust in galaxies. The impressive agreement between the simulated and observed CSED at lower z confirms that the combination of EAGLE and SKIRT dust processing yields a fairly realistic representation of the local Universe.
Monthly Notices of the Royal Astronomical Society, 2018
We study the formation and evolution of ring galaxies in the Evolution and Assembly of GaLaxies a... more We study the formation and evolution of ring galaxies in the Evolution and Assembly of GaLaxies and their Environments (EAGLE) simulations. We use the largest reference model Ref-L100N1504, a cubic cosmological volume of 100 cMpc on a side, to identify and characterize these systems through cosmic time. The number density of ring galaxies in EAGLE is in broad agreement with the observations. The vast majority of ring galaxies identified in EAGLE (83 per cent) have an interaction origin, i.e. form when one or more companion galaxies drop-through a disc galaxy. The remainder (17 per cent) have very long-lived ring morphologies (>2 Gyr) and host strong bars. Ring galaxies are HI-rich galaxies, yet display inefficient star formation activity and tend to reside in the green valley particularly at z 0.5. This inefficiency is mainly due to the low pressure and metallicity of their interstellar medium (ISM) compared with the ISM of similar star-forming galaxies. We find that the interaction(s) is responsible for decreasing the ISM pressure by causing the ISM gas to flow from the inner regions to the outer disc, where the ring feature forms. At a fixed radius, the star formation efficiency of ring galaxies is indistinguishable from their star-forming counterparts, and thus the main reason for their integrated lower efficiency is the different gas surface density profiles. Since galaxy morphologies are not used to tune the parameters in hydrodynamical simulations, the experiment performed here demonstrates the success of the current numerical models in EAGLE.
We present dust-attenuated and dust emission fluxes for sufficiently resolved galaxies in the EAG... more We present dust-attenuated and dust emission fluxes for sufficiently resolved galaxies in the EAGLE suite of cosmological hydrodynamical simulations, calculated with the SKIRT radiative transfer code. The post-processing procedure includes specific components for star formation regions, stellar sources, and diffuse dust, and takes into account stochastic heating of dust grains to obtain realistic broad-band fluxes in the wavelength range from ultraviolet to sub-millimeter. The mock survey includes nearly half a million simulated galaxies with stellar masses above 10 8.5 M across six EAGLE models. About two thirds of these galaxies, residing in 23 redshift bins up to z = 6, have a sufficiently resolved metallic gas distribution to derive meaningful dust attenuation and emission, with the important caveat that the same dust properties were used at all redshifts. These newly released data complement the already publicly available information about the EAGLE galaxies, which includes intrinsic properties derived by aggregating the properties of the smoothed particles representing matter in the simulation. We further provide an open source framework of Python procedures for post-processing simulated galaxies with the radiative transfer code SKIRT. The framework allows any third party to calculate synthetic images, SEDs, and broadband fluxes for EAGLE galaxies, taking into account the effects of dust attenuation and emission.
Monthly Notices of the Royal Astronomical Society, 2017
We present new observations acquired with the Multi Unit Spectroscopic Explorer instrument on the... more We present new observations acquired with the Multi Unit Spectroscopic Explorer instrument on the Very Large Telescope in a quasar field that hosts a high column density damped Lyα absorber (DLA) at z ≈ 3.25. We detect Lyα emission from a nebula at the redshift of the DLA with line luminosity (27 ± 1) × 10 41 erg s −1 , which extends over 37 ± 1 kpc above a surface brightness limit of 6 × 10 −19 erg s −1 cm −2 arcsec −2 at a projected distance of 30.5 ± 0.5 kpc from the quasar sightline. Two clumps lie inside this nebula, both with Lyα rest-frame equivalent width >50 Å and with relative line-of-sight velocities aligned with two main absorption components seen in the DLA spectrum. In addition, we identify a compact galaxy at a projected distance of 19.1 ± 0.5 kpc from the quasar sightline. The galaxy spectrum is noisy but consistent with that of a star-forming galaxy at the DLA redshift. We argue that the Lyα nebula is ionized by radiation from star formation inside the two clumps, or by radiation from the compact galaxy. In either case, these data imply the presence of a structure with size 50 kpc inside which galaxies are assembling, a picture consistent with galaxy formation in groups and filaments as predicted by cosmological simulations such as the EAGLE simulations.
Monthly Notices of the Royal Astronomical Society, 2017
We study present-day galaxy clustering in the EAGLE cosmological hydrodynamical simulation. EAGLE... more We study present-day galaxy clustering in the EAGLE cosmological hydrodynamical simulation. EAGLE's galaxy formation parameters were calibrated to reproduce the redshift z = 0.1 galaxy stellar mass function, and the simulation also reproduces galaxy colours well. The simulation volume is too small to correctly sample large-scale fluctuations and we therefore concentrate on scales smaller than a few mega parsecs. We find very good agreement with observed clustering measurements from the Galaxy And Mass Assembly (GAMA) survey, when galaxies are binned by stellar mass, colour or luminosity. However, low-mass red galaxies are clustered too strongly, which is at least partly due to limited numerical resolution. Apart from this limitation, we conclude that EAGLE galaxies inhabit similar dark matter haloes as observed GAMA galaxies, and that the radial distribution of satellite galaxies, as a function of stellar mass and colour, is similar to that observed as well.
Monthly Notices of the Royal Astronomical Society, 2017
We present a MUSE (Multi-Unit Spectroscopic Explorer) and KMOS (K-band Multi-Object Spectrograph)... more We present a MUSE (Multi-Unit Spectroscopic Explorer) and KMOS (K-band Multi-Object Spectrograph) dynamical study 405 star-forming galaxies at redshift z = 0.28-1.65 (median redshiftz = 0.84). Our sample is representative of the star-forming 'main sequence', with star formation rates of SFR = 0.1-30 M yr −1 and stellar masses M = 10 8-10 11 M. For 49 ± 4 per cent of our sample, the dynamics suggest rotational support, 24 ± 3 per cent are unresolved systems and 5 ± 2 per cent appear to be early-stage major mergers with components on 8-30 kpc scales. The remaining 22 ± 5 per cent appear to be dynamically complex, irregular (or face-on systems). For galaxies whose dynamics suggest rotational support, we derive inclination-corrected rotational velocities and show that these systems lie on a similar scaling between stellar mass and specific angular momentum as local spirals with j = J/M ∝ M 2/3 but with a redshift evolution that scales as j ∝ M 2/3 (1 + z) −1. We also identify a correlation between specific angular momentum and disc stability such that galaxies with the highest specific angular momentum (log(j /M 2/3) > 2.5) are the most stable, with Toomre Q = 1.10 ± 0.18, compared to Q = 0.53 ± 0.22 for galaxies with log(j /M 2/3) < 2.5. At a fixed mass, the Hubble Space Telescope morphologies of galaxies with the highest specific angular momentum resemble spiral galaxies, whilst those with low specific angular momentum are morphologically complex and dominated by several bright star-forming regions. This suggests that angular momentum plays a major role in defining the stability of gas discs: at z ∼ 1, massive galaxies that have discs with low specific angular momentum are globally unstable, clumpy and turbulent systems. In contrast, galaxies with high specific angular momentum have evolved into stable discs with spiral structure where star formation is a local (rather than global) process.
Monthly Notices of the Royal Astronomical Society, 2016
We explore the co-evolution of the specific angular momentum of dark matter haloes and the cold b... more We explore the co-evolution of the specific angular momentum of dark matter haloes and the cold baryons that comprise the galaxies within. We study over 2000 galaxies within the reference cosmological hydrodynamical simulation of the 'Evolution and Assembly of GaLaxies and their Environments' (EAGLE) project. We employ a methodology within which the evolutionary history of a system is specified by the time-evolving properties of the Lagrangian particles that define it at z = 0. We find a strong correlation between the evolution of the specific angular momentum of today's stars (cold gas) and that of the inner (whole) dark matter halo they are associated with. This link is particularly strong for the stars formed before the epoch of maximum expansion and subsequent collapse of the central dark matter halo (turnaround). Spheroids are assembled primarily from stars formed prior to turnaround, and suffer a net loss of angular momentum associated with the strong merging activity during the assembly of the inner dark matter halo. Stellar discs retain their specific angular momentum since they are comprised of stars formed mainly after turnaround, from gas that mostly preserves the high specific angular momentum it acquired by tidal torques during the linear growth of the halo. Since the specific angular momentum loss of the stars is tied to the galaxy's morphology today, it may be possible to use our results to predict, statistically, the maximum loss of specific angular momentum of the inner part of a halo given the morphology of the galaxy it hosts.
Monthly Notices of the Royal Astronomical Society, 2016
We examine the evolution of intrinsic u−r colours of galaxies in the EAGLE cosmological hydrodyna... more We examine the evolution of intrinsic u−r colours of galaxies in the EAGLE cosmological hydrodynamical simulations, which has been shown to reproduce the observed redshift z = 0.1 colour-magnitude distribution well, with a focus on z < 2. The median u−r of star-forming ('blue cloud') galaxies reddens by 1 mag from z = 2 to 0 at fixed stellar mass, as their specific star formation rates decrease with time. A red sequence starts to build-up around z = 1, due to the quenching of low-mass satellite galaxies at the faint end, and due to the quenching of more massive central galaxies by their active galactic nuclei (AGN) at the bright end. This leaves a dearth of intermediate-mass red sequence galaxies at z = 1, which is mostly filled in by z = 0. We quantify the timescales of colour transition finding that most galaxies spend less than 2 Gyr in the 'green valley'. We find the timescale of transition to be independent of quenching mechanism, i.e. whether a galaxy is a satellite or hosting an AGN. On examining the trajectories of galaxies in a colour-stellar mass diagram, we identify three characteristic tracks that galaxies follow (quiescently star-forming, quenching and rejuvenating galaxies) and quantify the fraction of galaxies that follow each track.
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Papers by James Trayford