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In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Astronomical and Space Sciences | Cosmology and Extragalactic Astronomy
Expanding Knowledge in the Physical Sciences | Expanding Knowledge in the Information and Computing Sciences |
Publisher: Oxford University Press (OUP)
Date: 30-01-2017
DOI: 10.1093/MNRAS/STX243
Publisher: Oxford University Press (OUP)
Date: 25-01-2017
DOI: 10.1093/MNRAS/STX201
Publisher: Oxford University Press (OUP)
Date: 09-09-2017
Publisher: Oxford University Press (OUP)
Date: 24-06-2016
Publisher: Oxford University Press (OUP)
Date: 2012
Publisher: Oxford University Press (OUP)
Date: 11-10-2008
Publisher: Oxford University Press (OUP)
Date: 24-10-2018
Publisher: Springer Science and Business Media LLC
Date: 10-2018
DOI: 10.1038/S41586-018-0564-6
Abstract: Galaxies are surrounded by large reservoirs of gas, mostly hydrogen, that are fed by inflows from the intergalactic medium and by outflows from galactic winds. Absorption-line measurements along the lines of sight to bright and rare background quasars indicate that this circumgalactic medium extends far beyond the starlight seen in galaxies, but very little is known about its spatial distribution. The Lyman-α transition of atomic hydrogen at a wavelength of 121.6 nanometres is an important tracer of warm (about 10
Publisher: Oxford University Press (OUP)
Date: 2020
Abstract: We study the effect of the gas accretion rate ($\\dot{M}_{\\rm accr}$) on the radial gas metallicity profile (RMP) of galaxies using the eagle cosmological hydrodynamic simulations, focusing on central galaxies of stellar mass M⋆ ≳ 109 M⊙ at z ≤ 1. We find clear relations between $\\dot{M}_{\\rm accr}$ and the slope of the RMP (measured within an effective radius), where higher $\\dot{M}_{\\rm accr}$ are associated with more negative slopes. The slope of the RMPs depends more strongly on $\\dot{M}_{\\rm accr}$ than on stellar mass, star formation rate (SFR), or gas fraction, suggesting $\\dot{M}_{\\rm accr}$ to be a more fundamental driver of the RMP slope of galaxies. We find that eliminating the dependence on stellar mass is essential for pinning down the properties that shape the slope of the RMP. Although $\\dot{M}_{\\rm accr}$ is the main property modulating the slope of the RMP, we find that it causes other correlations that are more easily testable observationally: At fixed stellar mass, galaxies with more negative RMP slopes tend to have higher gas fractions and SFRs, while galaxies with lower gas fractions and SFRs tend to have flatter metallicity profiles within an effective radius.
Publisher: Oxford University Press (OUP)
Date: 06-02-2020
Abstract: We address the issue of numerical convergence in cosmological smoothed particle hydrodynamics simulations using a suite of runs drawn from the eagle project. Our simulations adopt subgrid models that produce realistic galaxy populations at a fiducial mass and force resolution, but systematically vary the latter in order to study their impact on galaxy properties. We provide several analytic criteria that help guide the selection of gravitational softening for hydrodynamical simulations, and present results from runs that both adhere to and deviate from them. Unlike dark matter-only simulations, hydrodynamical simulations exhibit a strong sensitivity to gravitational softening, and care must be taken when selecting numerical parameters. Our results – which focus mainly on star formation histories, galaxy stellar mass functions and sizes – illuminate three main considerations. First, softening imposes a minimum resolved escape speed, vϵ, due to the binding energy between gas particles. Runs that adopt such small softening lengths that $v_\\epsilon \\gtrsim 10\\, {\\rm km\\, s^{-1}}$ (the sound speed in ionized ${\\sim }10^4\\, {\\rm K}$ gas) suffer from reduced effects of photoheating. Secondly, feedback from stars or active galactic nuclei may suffer from numerical overcooling if the gravitational softening length is chosen below a critical value, ϵeFB. Thirdly, we note that small softening lengths exacerbate the segregation of stars and dark matter particles in halo centres, often leading to the counterintuitive result that galaxy sizes increase as softening is reduced. The structure of dark matter haloes in hydrodynamical runs respond to softening in a way that reflects the sensitivity of their galaxy populations to numerical parameters.
Publisher: Oxford University Press (OUP)
Date: 30-07-2018
Publisher: Oxford University Press (OUP)
Date: 04-2016
DOI: 10.1093/MNRAS/STW717
Publisher: EDP Sciences
Date: 11-2018
DOI: 10.1051/0004-6361/201833136
Abstract: Star-forming galaxies have been found to follow a relatively tight relation between stellar mass ( M * ) and star formation rate (SFR), dubbed the “star formation sequence”. A turnover in the sequence has been observed, where galaxies with M * 10 10 M ⊙ follow a steeper relation than their higher mass counterparts, suggesting that the low-mass slope is (nearly) linear. In this paper, we characterise the properties of the low-mass end of the star formation sequence between 7 ≤ log M * [ M ⊙ ] ≤ 10.5 at redshift 0.11 z 0.91. We use the deepest MUSE observations of the Hubble Ultra Deep Field and the Hubble Deep Field South to construct a s le of 179 star-forming galaxies with high signal-to-noise emission lines. Dust-corrected SFRs are determined from H β λ 4861 and H α λ 6563. We model the star formation sequence with a Gaussian distribution around a hyperplane between log M * , logSFR, and log(1 + z ), to simultaneously constrain the slope, redshift evolution, and intrinsic scatter. We find a sub-linear slope for the low-mass regime where log SFR [ M ⊙ yr −1 ] = 0.83 +0.07 −0.06 log M * [ M ⊙ ]+1.74 +0.66 −0.68 log(1 + z ), increasing with redshift. We recover an intrinsic scatter in the relation of σ intr = 0.44 +0.05 −0.04 , dex, larger than typically found at higher masses. As both hydrodynamical simulations and (semi-)analytical models typically favour a steeper slope in the low-mass regime, our results provide new constraints on the feedback processes which operate preferentially in low-mass halos.
Publisher: Oxford University Press (OUP)
Date: 09-11-2012
DOI: 10.1093/MNRAS/STS156
Publisher: Oxford University Press (OUP)
Date: 25-09-2021
Abstract: We present a study of metal-enriched halo gas traced by Mg ii and C iv absorption at z & 2 in the MUSE Analysis of Gas around Galaxies survey and the Quasar Sightline and Galaxy Evolution survey. Using these large and complete galaxy surveys in quasar fields, we study the dependence of the metal distribution on galaxy properties and overdensities, out to physical projected separations of 750 kpc. We find that the cool, low-ionization gas is significantly affected by the environment across the full redshift range probed, with ≈2–3 times more prevalent and stronger Mg ii absorption in higher overdensity group environments and in regions with greater overall stellar mass and star formation rates. Complementary to these results, we have further investigated the more highly ionized gas as traced by C iv absorption, and found that it is likely to be more extended than the Mg ii gas, with ≈2 times higher covering fraction at a given distance. We find that the strength and covering fraction of C iv absorption show less significant dependence on galaxy properties and environment than the Mg ii absorption, but more massive and star-forming galaxies nevertheless also show ≈2 times higher incidence of C iv absorption. The incidence of Mg ii and C iv absorption within the virial radius shows a tentative increase with redshift, being higher by a factor of ≈1.5 and ≈4, respectively, at z & 1. It is clear from our results that environmental processes have a significant impact on the distribution of metals around galaxies and need to be fully accounted for when analysing correlations between gaseous haloes and galaxy properties.
Publisher: Oxford University Press (OUP)
Date: 26-09-2023
Publisher: Oxford University Press (OUP)
Date: 21-12-2018
Publisher: Oxford University Press (OUP)
Date: 08-2016
Publisher: Oxford University Press (OUP)
Date: 03-2010
Publisher: Oxford University Press (OUP)
Date: 08-10-2016
Publisher: Oxford University Press (OUP)
Date: 23-12-2016
Publisher: EDP Sciences
Date: 10-2021
DOI: 10.1051/0004-6361/202140876
Abstract: Rest-frame ultraviolet (UV) emission lines probe electron densities, gas-phase abundances, metallicities, and ionization parameters of the emitting star-forming galaxies and their environments. The strongest main UV emission line, Ly α , has been instrumental in advancing the general knowledge of galaxy formation in the early universe. However, observing Ly α emission becomes increasingly challenging at z ≳ 6 when the neutral hydrogen fraction of the circumgalactic and intergalactic media increases. Secondary weaker UV emission lines provide important alternative methods for studying galaxy properties at high redshift. We present a large s le of rest-frame UV emission line sources at intermediate redshift for calibrating and exploring the connection between secondary UV lines and the emitting galaxies’ physical properties and their Ly α emission. The s le of 2052 emission line sources with 1.5 z 6.4 was collected from integral field data from the MUSE-Wide and MUSE-Deep surveys taken as part of Guaranteed Time Observations. The objects were selected through untargeted source detection (i.e., no preselection of sources as in dedicated spectroscopic c aigns) in the three-dimensional MUSE data cubes. We searched optimally extracted one-dimensional spectra of the full s le for UV emission features via emission line template matching, resulting in a s le of more than 100 rest-frame UV emission line detections. We show that the detection efficiency of (non-Ly α ) UV emission lines increases with survey depth, and that the emission line strength of He II λ 1640 Å, [O III ] λ 1661 + O III ] λ 1666, and [Si III ] λ 1883 + Si III ] λ 1892 correlate with the strength of [C III ] λ 1907 + C III ] λ 1909. The rest-frame equivalent width (EW 0 ) of [C III ] λ 1907 + C III ] λ 1909 is found to be roughly 0.22 ± 0.18 of EW 0 (Ly α ). We measured the velocity offsets of resonant emission lines with respect to systemic tracers. For C IV λ 1548 + C IV λ 1551 we find that Δ v C IV ≲ 250 km s −1 , whereas Δ v Ly α falls in the range of 250−500 km s −1 which is in agreement with previous results from the literature. The electron density n e measured from [Si III ] λ 1883 + Si III ] λ 1892 and [C III ] λ 1907 + C III ] λ 1909 line flux ratios is generally 10 5 cm −3 and the gas-phase abundance is below solar at 12 + log 10 (O/H)≈8. Lastly, we used “PhotoIonization Model Probability Density Functions” to infer physical parameters of the full s le and in idual systems based on photoionization model parameter grids and observational constraints from our UV emission line searches. This reveals that the UV line emitters generally have ionization parameter log 10 (U) ≈ −2.5 and metal mass fractions that scatter around Z ≈ 10 −2 , that is Z ≈ 0.66 Z ⊙ . Value-added catalogs of the full s le of MUSE objects studied in this work and a collection of UV line emitters from the literature are provided with this paper.
Publisher: Oxford University Press (OUP)
Date: 04-2010
Publisher: Oxford University Press (OUP)
Date: 19-12-2015
Publisher: Oxford University Press (OUP)
Date: 03-10-2013
Publisher: Oxford University Press (OUP)
Date: 11-02-2005
Publisher: Oxford University Press (OUP)
Date: 26-10-2018
Publisher: American Astronomical Society
Date: 11-09-2019
Publisher: Oxford University Press (OUP)
Date: 31-08-2023
Publisher: Oxford University Press (OUP)
Date: 09-03-2017
DOI: 10.1093/MNRAS/STX578
Publisher: Oxford University Press (OUP)
Date: 06-04-2018
DOI: 10.1093/MNRAS/STY871
Publisher: Oxford University Press (OUP)
Date: 31-12-2016
Publisher: Oxford University Press (OUP)
Date: 15-07-2017
Publisher: American Astronomical Society
Date: 07-2023
Abstract: We study the relation between the metallicities of ionized and atomic gas in star-forming galaxies at z = 0–3 using the Evolution and Assembly of GaLaxies and their Environments (EAGLE) cosmological, hydrodynamical simulations. This is done by constructing a dense grid of sight lines through the simulated galaxies and obtaining the star formation rate- and H i column density-weighted metallicities, Z SFR and Z H I , for each sightline as proxies for the metallicities of ionized and atomic gas, respectively. We find Z SFR ≳ Z H I for almost all sight lines, with their difference generally increasing with decreasing metallicity. The stellar masses of galaxies do not have a significant effect on this trend, but the positions of the sight lines with respect to the galaxy centers play an important role: the difference between the two metallicities decreases when moving toward the galaxy centers, and saturates to a minimum value in the central regions of galaxies, irrespective of redshift and stellar mass. This implies that the mixing of the two gas phases is most efficient in the central regions of galaxies where sight lines generally have high column densities of H i . However, a high H i column density alone does not guarantee a small difference between the two metallicities. In galaxy outskirts, the inefficiency of the mixing of star-forming gas with H i seems to dominate over the dilution of heavy elements in H i through mixing with the pristine gas. We find good agreement between the available observational data and the Z SFR – Z H I relation predicted by the EAGLE simulations. Though, observed regions with a nuclear starburst mode of star formation appear not to follow the same relation.
Publisher: Oxford University Press (OUP)
Date: 09-09-2017
Abstract: This work presents a study of galactic outflows driven by stellar feedback. We extract main-sequence 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 σ (∼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 & 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 & K (ii) high-σ tail ⇔ galactic winds ⇔ gas with T ≥105 K.
Publisher: Oxford University Press (OUP)
Date: 14-11-2019
Abstract: Galaxy cluster outskirts mark the transition region from the mildly non-linear cosmic web to the highly non-linear, virialised, cluster interior. It is in this transition region that the intra-cluster medium (ICM) begins to influence the properties of accreting galaxies and groups, as ram pressure impacts a galaxy’s cold gas content and subsequent star formation rate. Conversely, the thermodynamical properties of the ICM in this transition region should also feel the influence of accreting substructure (i.e. galaxies and groups), whose passage can drive shocks. In this paper, we use a suite of cosmological hydrodynamical zoom simulations of a single galaxy cluster, drawn from the nIFTy comparison project, to study how the dynamics of substructure accreted from the cosmic web influences the thermodynamical properties of the ICM in the cluster’s outskirts. We demonstrate how features evident in radial profiles of the ICM (e.g. gas density and temperature) can be linked to strong shocks, transient and short-lived in nature, driven by the passage of substructure. The range of astrophysical codes and galaxy formation models in our comparison are broadly consistent in their predictions (e.g. agreeing when and where shocks occur, but differing in how strong shocks will be) this is as we would expect of a process driven by large-scale gravitational dynamics and strong, inefficently radiating, shocks. This suggests that mapping such shock structures in the ICM in a cluster’s outskirts (via e.g. radio synchrotron emission) could provide a complementary measure of its recent merger and accretion history.
Publisher: EDP Sciences
Date: 04-2022
DOI: 10.1051/0004-6361/202142302
Abstract: Hydrogen Ly α haloes (LAHs) are commonly used as a tracer of the circumgalactic medium (CGM) at high redshifts. In this work, we aim to explore the existence of Ly α haloes around in idual UV-selected galaxies, rather than around Ly α emitters (LAEs), at high redshifts. Our s le was continuum-selected with F 775 W ≤ 27.5, and spectroscopic redshifts were assigned or constrained for all the sources thanks to the deepest (100- to 140-h) existing Very Large Telescope (VLT)/Multi-Unit Spectroscopic Explorer (MUSE) data with adaptive optics. The final s le includes 21 galaxies that are purely F 775 W -magnitude selected within the redshift range z ≈ 2.9 − 4.4 and within a UV magnitude range −20 ≤ M 1500 ≤ −18, thus avoiding any bias toward LAEs. We tested whether galaxy’s Ly α emission is significantly more extended than the MUSE PSF-convolved continuum component. We find 17 LAHs and four non-LAHs. We report the first in idual detections of extended Ly α emission around non-LAEs. The Ly α halo fraction is thus as high as 81.0 −11.2 +10.3 %, which is close to that for LAEs at z = 3 − 6 in the literature. This implies that UV-selected galaxies generally have a large amount of hydrogen in their CGM. We derived the mean surface brightness (SB) profile for our LAHs with cosmic dimming corrections and find that Ly α emission extends to 5.4 arcsec (≃40 physical kpc at the midpoint redshift z = 3.6) above the typical 1 σ SB limit. The incidence rate of surrounding gas detected in Ly α per one-dimensional line of sight per unit redshift, d n /d z , is estimated to be 0.76 −0.09 +0.09 for galaxies with M 1500 ≤ −18 mag at z ≃ 3.7. Assuming that Ly α emission and absorption arise in the same gas, this suggests, based on abundance matching, that LAHs trace the same gas as d ed Ly α systems (DLAs) and sub-DLAs.
Publisher: Oxford University Press (OUP)
Date: 10-01-2023
Abstract: We use a suite of idealized N-body simulations to study the impact of spurious heating of star particles by dark matter (DM) particles on the kinematics and morphology of simulated galactic discs. We find that spurious collisional heating leads to a systematic increase of the azimuthal velocity dispersion (σϕ) of stellar particles and a corresponding decrease in their mean azimuthal velocities ($\\overline{v}_\\phi$). The rate of heating is dictated primarily by the number of DM halo particles (or equivalently, by the DM particle mass at fixed halo mass) and by radial gradients in the local DM density along the disc it is largely insensitive to the stellar particle mass. Galaxies within haloes resolved with fewer than ≈106 DM particles are particularly susceptible to spurious morphological evolution, irrespective of the total halo mass (with even more particles required to prevent heating of the galactic centre). Collisional heating transforms galactic discs from flattened structures into rounder spheroidal systems, causing them to lose rotational support in the process. It also affects the locations of galaxies in standard scaling relations that link their various properties: at fixed stellar mass, it increases the sizes of galaxies, and reduces their mean stellar rotation velocities and specific angular momenta. Our results urge caution when extrapolating simulated galaxy scaling relations to low masses where spurious collisional effects can bias their normalization, slope, and scatter.
Publisher: EDP Sciences
Date: 03-2021
DOI: 10.1051/0004-6361/202039887
Abstract: We report the discovery of diffuse extended Ly α emission from redshift 3.1 to 4.5, tracing cosmic web filaments on scales of 2.5−4 cMpc. These structures have been observed in overdensities of Ly α emitters in the MUSE Extremely Deep Field, a 140 h deep MUSE observation located in the Hubble Ultra-Deep Field. Among the 22 overdense regions identified, five are likely to harbor very extended Ly α emission at high significance with an average surface brightness of 5 × 10 −20 erg s −1 cm −2 arcsec −2 . Remarkably, 70% of the total Ly α luminosity from these filaments comes from beyond the circumgalactic medium of any identified Ly α emitter. Fluorescent Ly α emission powered by the cosmic UV background can only account for less than 34% of this emission at z ≈ 3 and for not more than 10% at higher redshift. We find that the bulk of this diffuse emission can be reproduced by the unresolved Ly α emission of a large population of ultra low-luminosity Ly α emitters ( 10 40 erg s −1 ), provided that the faint end of the Ly α luminosity function is steep ( α ⪅ −1.8), it extends down to luminosities lower than 10 38 − 10 37 erg s −1 , and the clustering of these Ly α emitters is significant (filling factor 1/6). If these Ly α emitters are powered by star formation, then this implies their luminosity function needs to extend down to star formation rates 10 −4 M ⊙ yr −1 . These observations provide the first detection of the cosmic web in Ly α emission in typical filamentary environments and the first observational clue indicating the existence of a large population of ultra low-luminosity Ly α emitters at high redshift.
Publisher: American Astronomical Society
Date: 10-2023
Publisher: SPIE
Date: 14-06-2006
DOI: 10.1117/12.669772
Publisher: Oxford University Press (OUP)
Date: 20-08-2012
Publisher: Oxford University Press (OUP)
Date: 07-10-2020
Abstract: We investigate the dependence of the local galaxy stellar-to-halo mass relation (SHMR) on galaxy morphology. We use data from the Sloan Digital Sky Survey (SDSS) data release 7 with morphological classifications from Galaxy Zoo, and compare with the EAGLE cosmological simulation. At fixed halo mass in the mass range $10^{11.7}\\!-\\!10^{12.9}\\, {\\rm M_{\\odot }}$, the median stellar masses of SDSS disc galaxies are up to a factor of 1.4 higher than the median masses of their elliptical counterparts. However, when we switch from the stellar masses from Kauffmann et al. to those calculated by Chang et al. or Brinchmann et al., the median SHMR from discs and ellipticals coincides in this mass range. For halo masses larger than $10^{13}\\, {\\rm M_{\\odot }}$, discs are less massive than ellipticals in same-mass haloes, regardless of whose stellar mass estimates we use. However, we find that for these high halo masses the results for discs may be affected by central/satellite misclassifications. The EAGLE simulation predicts that discs are up to a factor of 1.5 more massive than elliptical galaxies residing in same-mass haloes less massive than $10^{13}\\, {\\rm M_{\\odot }}$, in agreement with the Kauffmann et al. data. Haloes with masses between 1011.5 and $10^{12}\\, {\\rm M_{\\odot }}$, which host disc galaxies, were assembled earlier than those hosting ellipticals. This suggests that the discs are more massive because they had more time for gas accretion and star formation. In $10^{12}\\!-\\!10^{12.5}\\, {\\rm M_{\\odot }}$ haloes, the central black holes in elliptical galaxies grew faster and became more massive than their counterparts in disc galaxies. This suggests that in this halo mass range the ellipticals are less massive because active galactic nucleus feedback ejected more of the halo’s gas reservoir, reducing star formation, and suppressing the (re)growth of stellar discs.
Publisher: Oxford University Press (OUP)
Date: 10-04-2018
DOI: 10.1093/MNRAS/STY879
Publisher: Oxford University Press (OUP)
Date: 02-06-2021
Abstract: The dispersion measure (DM) of fast radio bursts (FRBs) provides a unique way to probe ionized baryons in the intergalactic medium (IGM). Cosmological models with different parameters lead to different DM–redshift (DM–z) relations. Additionally, the over/underdense regions in the IGM and the circumgalactic medium of intervening galaxies lead to scatter around the mean DM–z relations. We have used the Evolution and Assembly of GaLaxies and their Environments (EAGLE) simulations to measure the mean DM–z relation and the scatter around it using over 1 billion lines of sight at redshifts 0 & z & 3. We investigated two techniques to estimate line-of-sight DM: pixel scrambling and box transformations. We find that using box transformations (a technique from the literature) causes strong correlations due to repeated replication of structure. Comparing a linear and a non-linear model, we find that the non-linear model with a dependence on cosmological parameters provides a better fit to the DM–z relation. The differences between these models are the most significant at low redshifts (z & 0.5). The scatter around the DM–z relation is highly asymmetric, especially at low redshift (z & 0.5), and becomes more Gaussiana as redshift approaches z = 3, the limit of this study. The increase in Gaussianity with redshift is indicative of the large-scale structure that is better s led with longer lines of sight. The DM–z relation measured in EAGLE is available with an easy-to-use python interface in the open-source FRB redshift estimation package fruitbat.
Publisher: Oxford University Press (OUP)
Date: 25-04-2015
DOI: 10.1093/MNRAS/STV689
Publisher: Oxford University Press (OUP)
Date: 18-05-2018
Publisher: Oxford University Press (OUP)
Date: 02-10-2021
Abstract: We use idealized N-body simulations of equilibrium stellar discs embedded within course-grained dark matter (DM) haloes to study the effects of spurious collisional heating on disc structure and kinematics. Collisional heating artificially increases the vertical and radial velocity dispersions of disc stars, as well as the thickness and size of discs the effects are felt at all galacto-centric radii. The integrated effects of collisional heating are determined by the mass of DM halo particles (or equivalently, by the number of particles at fixed halo mass), their local density and characteristic velocity dispersion, but are largely insensitive to the stellar particle mass. The effects can therefore be reduced by increasing the mass resolution of DM in cosmological simulations, with limited benefits from increasing the baryonic (or stellar) mass resolution. We provide a simple empirical model that accurately captures the effects of spurious collisional heating on the structure and kinematics of simulated discs, and use it to assess the importance of disc heating for simulations of galaxy formation. We find that the majority of state-of-the-art zoom simulations, and a few of the highest-resolution, smallest-volume cosmological runs, are in principle able to resolve thin stellar discs in Milky Way-mass haloes, but most large-volume cosmological simulations cannot. For ex le, DM haloes resolved with fewer than ≈106 particles will collisionally heat stars near the stellar half-mass radius such that their vertical velocity dispersion increases by ≳ 10 per cent of the halo’s virial velocity in approximately one Hubble time.
Publisher: American Astronomical Society
Date: 24-03-2017
Publisher: EDP Sciences
Date: 07-2019
DOI: 10.1051/0004-6361/201935227
Abstract: We present the first measurements of the Lyman-continuum photon production efficiency ξ ion, 0 at z ∼ 4–5 for galaxies fainter than 0.2 L * (−19 mag). ξ ion, 0 quantifies the production rate of ionizing photons with respect to the UV luminosity density assuming a fiducial escape fraction of zero. Extending previous measurements of ξ ion, 0 to the faint population is important, as ultra-faint galaxies are expected to contribute the bulk of the ionizing emissivity. We probe ξ ion, 0 to such faint magnitudes by taking advantage of 200-h depth Spitzer /IRAC observations from the GREATS program and ≈300 3 z 6 galaxies with spectroscopic redshifts from the MUSE GTO Deep + Wide programs. Stacked IRAC [3.6]−[4.5] colors are derived and used to infer the H α rest-frame equivalent widths, which range from 403 Å to 2818 Å. The derived ξ ion, 0 is log 10 ( ξ ion,0 /Hz erg −1 ) = 25.36 ± 0.08 over −20.5 M UV −17.5, similar to those derived for brighter galaxy s les at the same redshift and therefore suggesting that ξ ion shows no strong dependence on M UV . The ξ ion, 0 values found in our s le imply that the Lyman-continuum escape fraction for M UV ≈ −19 star-forming galaxies cannot exceed ≈8–20% in the reionization era.
Publisher: American Astronomical Society
Date: 26-06-2019
Publisher: Oxford University Press (OUP)
Date: 13-02-2019
DOI: 10.1093/MNRAS/STZ448
Publisher: EDP Sciences
Date: 03-2022
DOI: 10.1051/0004-6361/202141900
Abstract: Context. The hydrogen Lyman α line is often the only measurable feature in optical spectra of high-redshift galaxies. Its shape and strength are influenced by radiative transfer processes and the properties of the underlying stellar population. High equivalent widths of several hundred Å are especially hard to explain by models and could point towards unusual stellar populations, for ex le with low metallicities, young stellar ages, and a top-heavy initial mass function. Other aspects influencing equivalent widths are the morphology of the galaxy and its gas properties. Aims. The aim of this study is to better understand the connection between the Lyman α rest-frame equivalent width (EW 0 ) and spectral properties as well as ultraviolet (UV) continuum morphology by obtaining reliable EW 0 histograms for a statistical s le of galaxies and by assessing the fraction of objects with large equivalent widths. Methods. We used integral field spectroscopy from the Multi Unit Spectroscopic Explorer (MUSE) combined with broad-band data from the Hubble Space Telescope (HST) to measure EW 0 . We analysed the emission lines of 1920 Lyman α emitters (LAEs) detected in the full MUSE-Wide (one hour exposure time) and MUSE-Deep (ten hour exposure time) surveys and found UV continuum counterparts in archival HST data. We fitted the UV continuum photometric images using the Galfit software to gain morphological information on the rest-UV emission and fitted the spectra obtained from MUSE to determine the double peak fraction, asymmetry, full-width at half maximum, and flux of the Lyman α line. Results. The two surveys show different histograms of Lyman α EW 0 . In MUSE-Wide, 20% of objects have EW 0 240 Å, while this fraction is only 11% in MUSE-Deep and ≈16% for the full s le. This includes objects without HST continuum counterparts (one-third of our s le), for which we give lower limits for EW 0 . The object with the highest securely measured EW 0 has EW 0 = 589 ± 193 Å (the highest lower limit being EW 0 = 4464 Å). We investigate the connection between EW 0 and Lyman α spectral or UV continuum morphological properties. Conclusions. The survey depth has to be taken into account when studying EW 0 distributions. We find that in general, high EW 0 objects can have a wide range of spectral and UV morphological properties, which might reflect that the underlying causes for high EW 0 values are equally varied.
Publisher: Oxford University Press (OUP)
Date: 23-05-2016
Publisher: Springer Science and Business Media LLC
Date: 30-10-2018
DOI: 10.1038/S41586-018-0664-3
Abstract: Change history: In this Letter, author M. Akhlaghi should be associated with affiliation (2) rather than (3). This error has been corrected online.
Publisher: Springer Berlin Heidelberg
Date: 2008
Publisher: Oxford University Press (OUP)
Date: 28-01-2019
DOI: 10.1093/MNRAS/STZ295
Abstract: We investigate the evolution in colour and morphology of the progenitors of red-sequence galaxies in the EAGLE cosmological hydrodynamical simulation. We quantify colours with u* − r* intrinsic magnitudes and morphologies with a measure of the stellar kinematics. The time when galaxies moved on to the red sequence depends on their morphology. Disc-type galaxies tend to have become red during the last 3 Gyr, while elliptical-type galaxies joined the red sequence earlier, with half the s le already being red 5 Gyr ago. The time-scale, τGreen, of colour transition through the ‘green valley’ depends weakly on the galaxy’s morphological type. Elliptical-type galaxies cross the green valley slightly faster (τGreen ≈ 1 Gyr) than disc-type galaxies (τGreen ≈ 1.5 Gyr). While τGreen is similar for central and satellite galaxies, for satellites τGreen decreases with increasing stellar mass to host-halo mass ratio. Coupled with our finding that galaxies tend to become green after becoming satellites, this indicates that satellite-specific processes are important for quenching red-sequence galaxies. The last time central, elliptical-type red-sequence galaxies left the blue cloud is strongly correlated with the time the luminosity of the central black hole peaked, but this is not the case for discs. This suggests that active galactic nuclei (AGNs) feedback is important for quenching ellipticals, particularly centrals, but not for discs. We find only a weak connection between transformations in colour and morphology.
Publisher: Oxford University Press (OUP)
Date: 08-03-2019
DOI: 10.1093/MNRAS/STZ691
Publisher: Oxford University Press (OUP)
Date: 04-07-2019
Abstract: We study the impact of numerical parameters on the properties of cold dark matter haloes formed in collisionless cosmological simulations. We quantify convergence in the median spherically averaged circular velocity profiles for haloes of widely varying particle number, as well as in the statistics of their structural scaling relations and mass functions. In agreement with prior work focused on single haloes, our results suggest that cosmological simulations yield robust halo properties for a wide range of gravitational softening parameters, ϵ, provided: (1) ϵ is not larger than a ‘convergence radius’, rconv, which is dictated by two-body relaxation and determined by particle number, and (2) a sufficient number of time-steps are taken to accurately resolve particle orbits with short dynamical times. Provided these conditions are met, median circular velocity profiles converge to within ≈10 per cent for radii beyond which the local two-body relaxation time-scale exceeds the Hubble time by a factor $\\kappa \\equiv t_{\\rm relax}/t_{\\rm H}\\rm{\\,\\, \\buildrel\\gt \\over \\sim \\,\\,}0.177$, with better convergence attained for higher κ. We provide analytic estimates of rconv that build on previous attempts in two ways: first, by highlighting its explicit (but weak) softening-dependence and, second, by providing a simpler criterion in which rconv is determined entirely by the mean inter-particle spacing, l, for ex le better than 10 per cent convergence in circular velocity for $r\\rm{\\,\\, \\buildrel\\gt \\over \\sim \\,\\,}0.05\\, l$. We show how these analytic criteria can be used to assess convergence in structural scaling relations for dark matter haloes as a function of their mass or maximum circular speed.
Publisher: EDP Sciences
Date: 10-2018
DOI: 10.1051/0004-6361/201832866
Abstract: We present a study of the [O III ]/[O II ] ratios of star-forming galaxies drawn from Multi-Unit Spectroscopic Explorer (MUSE) data spanning a redshift range 0.28 z 0.85. Recently discovered Lyman continuum (LyC) emitters have extremely high oxygen line ratios: [O III ] λ 5007/[O II ] λλ 3726, 3729 4. Here we aim to understand the properties and the occurrences of galaxies with such high line ratios. Combining data from several MUSE Guaranteed Time Observing (GTO) programmes, we select a population of star-forming galaxies with bright emission lines, from which we draw 406 galaxies for our analysis based on their position in the z -dependent star formation rate (SFR)–stellar mass ( M ∗ ) plane. Out of this s le 15 are identified as extreme oxygen emitters based on their [O III ]/[O II ] ratios (3.7%) and 104 galaxies have [O III ]/[O II ] 1 (26%). Our analysis shows no significant correlation between M ∗ , SFR, and the distance from the SFR− M ∗ relation with [O III ]/[O II ]. We find a decrease in the fraction of galaxies with [O III ]/[O II ] 1 with increasing M ∗ , however, this is most likely a result of the relationship between [O III ]/[O II ] and metallicity, rather than between [O III ]/[O II ] and M ∗ . We draw a comparison s le of local analogues with ⟨ z ⟩ ≈ 0.03 from the Sloan Digital Sky Survey, and find similar incidence rates for this s le. In order to investigate the evolution in the fraction of high [O III ]/[O II ] emitters with redshift, we bin the s le into three redshift subs les of equal number, but find no evidence for a dependence on redshift. Furthermore, we compare the observed line ratios with those predicted by nebular models with no LyC escape and find that most of the extreme oxygen emitters can be reproduced by low metallicity models. The remaining galaxies are likely LyC emitter candidates.
Publisher: Oxford University Press (OUP)
Date: 15-07-2019
Abstract: The impact of 2-body scattering on the innermost density profiles of dark matter haloes is well established. We use a suite of cosmological simulations and idealized numerical experiments to show that 2-body scattering is exacerbated in situations where there are two species of unequal mass. This is a consequence of mass segregation and reflects a flow of kinetic energy from the more to less massive particles. This has important implications for the interpretation of galaxy sizes in cosmological hydrodynamic simulations, which nearly always model stars with less massive particles than are used for the dark matter. We compare idealized models as well as simulations from the eagle project that differ only in the mass resolution of the dark matter component, but keep subgrid physics, baryonic mass resolution, and gravitational force softening fixed. If the dark matter particle mass exceeds the mass of stellar particles, then galaxy sizes – quantified by their projected half-mass radii, R50 – increase systematically with time until R50 exceeds a small fraction of the redshift-dependent mean interparticle separation, l (${\\rm R_{50}} \\gtrsim 0.05\\times l$). Our conclusions should also apply to simulations that adopt different hydrodynamic solvers, subgrid physics, or adaptive softening, but in that case may need quantitative revision. Any simulation employing a stellar-to-dark matter particle mass ratio greater than unity will escalate spurious energy transfer from dark matter to baryons on small scales.
Publisher: Oxford University Press (OUP)
Date: 09-02-2011
Publisher: Oxford University Press (OUP)
Date: 20-01-2020
Abstract: There is a severe tension between the observed star formation rate (SFR)–stellar mass (M⋆) relations reported by different authors at z = 1–4. In addition, the observations have not been successfully reproduced by state-of-the-art cosmological simulations that tend to predict a factor of 2–4 smaller SFRs at a fixed M⋆. We examine the evolution of the SFR–M⋆ relation of z = 1–4 galaxies using the skirt simulated spectral energy distributions of galaxies s led from the Evolution and Assembly of GaLaxies and their Environments simulations. We derive SFRs and stellar masses by mimicking different observational techniques. We find that the tension between observed and simulated SFR–M⋆ relations is largely alleviated if similar methods are used to infer the galaxy properties. We find that relations relying on infrared wavelengths (e.g. 24 ${\\rm \\, \\mu m}$, MIPS – 24, 70, and 160 ${\\rm \\, \\mu m}$ or SPIRE – 250, 350, and 500 ${\\rm \\, \\mu m}$) have SFRs that exceed the intrinsic relation by 0.5 dex. Relations that rely on the spectral energy distribution fitting technique underpredict the SFRs at a fixed stellar mass by −0.5 dex at z ∼ 4 but overpredict the measurements by 0.3 dex at z ∼ 1. Relations relying on dust-corrected rest-frame ultraviolet luminosities, are flatter since they overpredict/underpredict SFRs for low/high star-forming objects and yield deviations from the intrinsic relation from 0.10 to −0.13 dex at z ∼ 4. We suggest that the severe tension between different observational studies can be broadly explained by the fact that different groups employ different techniques to infer their SFRs.
Publisher: Oxford University Press (OUP)
Date: 09-06-2011
Publisher: EDP Sciences
Date: 09-2020
DOI: 10.1051/0004-6361/202038133
Abstract: We investigated the ultraviolet (UV) spectral properties of faint Lyman- α emitters (LAEs) in the redshift range 2.9 ≤ z ≤ 4.6, and we provide material to prepare future observations of the faint Universe. We used data from the MUSE Hubble Ultra Deep Survey to construct mean rest-frame spectra of continuum-faint (median M UV of −18 and down to M UV of −16), low stellar mass (median value of 10 8.4 M ⊙ and down to 10 7 M ⊙ ) LAEs at redshift z ≳ 3. We computed various averaged spectra of LAEs, subs led on the basis of their observational (e.g., Ly α strength, UV magnitude and spectral slope) and physical (e.g., stellar mass and star-formation rate) properties. We searched for UV spectral features other than Ly α , such as higher ionization nebular emission lines and absorption features. We successfully observed the O III ] λ 1666 and [C III ] λ 1907+C III ] λ 1909 collisionally excited emission lines and the He II λ 1640 recombination feature, as well as the resonant C IV λ λ 1548,1551 doublet either in emission or P-Cygni. We compared the observed spectral properties of the different mean spectra and find the emission lines to vary with the observational and physical properties of the LAEs. In particular, the mean spectra of LAEs with larger Ly α equivalent widths, fainter UV magnitudes, bluer UV spectral slopes, and lower stellar masses show the strongest nebular emission. The line ratios of these lines are similar to those measured in the spectra of local metal-poor galaxies, while their equivalent widths are weaker compared to the handful of extreme values detected in in idual spectra of z 2 galaxies. This suggests that weak UV features are likely ubiquitous in high z , low-mass, and faint LAEs. We publicly released the stacked spectra, as they can serve as empirical templates for the design of future observations, such as those with the James Webb Space Telescope and the Extremely Large Telescope.
Publisher: American Astronomical Society
Date: 14-09-2018
Publisher: Oxford University Press (OUP)
Date: 12-08-2015
Publisher: Oxford University Press (OUP)
Date: 23-08-2017
Abstract: We investigate the relation between kinematic morphology, intrinsic colour and stellar mass of galaxies in the EAGLE cosmological hydrodynamical simulation. We calculate the intrinsic u − r colours and measure the fraction of kinetic energy invested in ordered corotation of 3562 galaxies at z = 0 with stellar masses larger than 1010 M⊙. Inspection of gri-composite images suggests that the kinematic morphology is a useful proxy for visual morphology. EAGLE produces a galaxy population for which morphology is tightly correlated with the location in the colour–mass diagram, with the red sequence mostly populated by elliptical galaxies and the blue cloud by disc galaxies. Satellite galaxies are more likely to be on the red sequence than centrals, and for satellites the red sequence is morphologically more erse. These results show that the connection between mass, intrinsic colour and morphology arises from galaxy-formation models that reproduce the observed galaxy mass function and sizes.
Publisher: Oxford University Press (OUP)
Date: 04-03-2020
Abstract: While low-luminosity galaxies dominate number counts at all redshifts, their contribution to cosmic reionization is poorly understood due to a lack of knowledge of their physical properties. We isolate a s le of 35 z ≈ 4–5 continuum-faint Lyman-α emitters from deep VLT/MUSE spectroscopy and directly measure their H α emission using stacked Spitzer/IRAC Ch. 1 photometry. Based on Hubble Space Telescope imaging, we determine that the average UV continuum magnitude is fainter than −16 (≈ 0.01 L⋆), implying a median Lyman-α equivalent width of 259 Å. By combining the H α measurement with the UV magnitude, we determine the ionizing photon production efficiency, ξion, a first for such faint galaxies. The measurement of log10 (ξion [Hz erg−1]) = 26.28 ($^{+0.28}_{-0.40}$) is in excess of literature measurements of both continuum- and emission line-selected s les, implying a more efficient production of ionizing photons in these lower luminosity, Lyman-α-selected systems. We conclude that this elevated efficiency can be explained by stellar populations with metallicities between 4 × 10−4 and 0.008, with light-weighted ages less than 3 Myr.
Publisher: Oxford University Press (OUP)
Date: 15-07-2015
Publisher: Oxford University Press (OUP)
Date: 06-08-2015
Publisher: Oxford University Press (OUP)
Date: 06-04-2018
DOI: 10.1093/MNRAS/STY846
Publisher: Oxford University Press (OUP)
Date: 23-02-2018
DOI: 10.1093/MNRAS/STY489
Publisher: Oxford University Press (OUP)
Date: 25-04-2015
DOI: 10.1093/MNRAS/STV697
Publisher: Oxford University Press (OUP)
Date: 17-01-2013
DOI: 10.1093/MNRAS/STS587
No related organisations have been discovered for Joop Schaye.
Start Date: 10-2021
End Date: 09-2024
Amount: $645,000.00
Summary: “Beacons in the Night” unveiling how galaxies light up dark matter. How dark matter influences the formation and evolution of galaxies is to this day an outstanding question in astrophysics. To answer it, world-class facilities and a unique combination of observations and theory are required. This DP team, a world-class team of observers and theorists, will tackle this question by leveraging on two multi-million dollar projects: the MAGPI galaxy survey and the hydrodynamical simulations suite EA .... “Beacons in the Night” unveiling how galaxies light up dark matter. How dark matter influences the formation and evolution of galaxies is to this day an outstanding question in astrophysics. To answer it, world-class facilities and a unique combination of observations and theory are required. This DP team, a world-class team of observers and theorists, will tackle this question by leveraging on two multi-million dollar projects: the MAGPI galaxy survey and the hydrodynamical simulations suite EAGLE-XL. MAGPI will deliver exquisite kinematics for hundreds of galaxies in the middle ages of the Universe, providing a view to the effect of dark matter on galaxies at this critical time, while EAGLE-XL represents the technological frontier in simulations and provides the best interpretative framework for MAGPI. Read more Read less
Funder: Australian Research Council
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