161 research outputs found
The properties of the star-forming interstellar medium at z = 0.84-2.23 from HiZELS : mapping the internal dynamics and metallicity gradients in high-redshift disc galaxies.
We present adaptive optics assisted, spatially resolved spectroscopy of a sample of nine HÎą-selected galaxies at z = 0.84-2.23 drawn from the HiZELS narrow-band survey. These galaxies have star formation rates of 1-27 Mâ yr-1 and are therefore representative of the typical high-redshift star-forming population. Our Ëkpc-scale resolution observations show that approximately half of the sample have dynamics suggesting that the ionized gas is in large, rotating discs. We model their velocity fields to infer the inclination-corrected, asymptotic rotational velocities. We use the absolute B-band magnitudes and stellar masses to investigate the evolution of the B-band and stellar-mass Tully-Fisher relationships. By combining our sample with a number of similar measurements from the literature, we show that, at fixed circular velocity, the stellar mass of star-forming galaxies has increased by a factor of 2.5 between z = 2 and 0, whilst the rest-frame B-band luminosity has decreased by a factor of Ë 6 over the same period. Together, these demonstrate a change in mass-to-light ratio in the B band of Î(M/LB)/(M/LB)z=0 Ë 3.5 between z = 1.5 and 0, with most of the evolution occurring below z = 1. We also use the spatial variation of [N II]/HÎą to show that the metallicity of the ionized gas in these galaxies declines monotonically with galactocentric radius, with an average Î log(O/H)/ÎR = -0.027 Âą 0.005 dex kpc-1. This gradient is consistent with predictions for high-redshift disc galaxies from cosmologically based hydrodynamic simulations
Global structure and kinematics of stellar haloes in cosmological hydrodynamic simulations
We use the GalaxiesâIntergalactic Medium Interaction Calculation (GIMIC) suite of cosmological hydrodynamical simulations to study the global structure and kinematics of stellar spheroids of Milky Way mass disc galaxies. Font et al. have recently demonstrated that these simulations are able to successfully reproduce the satellite luminosity functions and the metallicity and surface brightness profiles of the spheroids of the Milky Way and M31. A key to the success of the simulations is a significant contribution to the spheroid from stars that formed in situ. While the outer halo is dominated by accreted stars, stars formed in the main progenitor of the galaxy dominate at rⲠ30âkpc. In the present study, we show that this component was primarily formed in a protodisc at high redshift and was subsequently liberated from the disc by dynamical heating associated with mass accretion. As a consequence of its origin, the in situ component of the spheroid has different kinematics (namely net prograde rotation with respect to the disc) than that of the spheroid component built from the disruption of satellites. In addition, the in situ component has a flattened distribution, which is due in part to its rotation. We make comparisons with measurements of the shape and kinematics of local galaxies, including the Milky Way and M31, and stacked observations of more distant galaxies. We find that the simulated disc galaxies have spheroids of the correct shape (oblate with a median axial ratio of âź0.6 at radii of â˛30âkpc, but note there is significant system-to-system scatter in this quantity) and that the kinematics show evidence for two components (due to in situ versus accreted), as observed. Our findings therefore add considerable weight to the importance of dissipative processes in the formation of stellar haloes and to the notion of a âdual stellar haloâ
The effect of baryons on redshift space distortions and cosmic density and velocity fields in the EAGLE simulation
We use the Evolution and Assembly of GaLaxies and their Environments (EAGLE) galaxy formation simulation to study the effects of baryons on the power spectrum of the total matter and dark matter distributions and on the velocity fields of dark matter and galaxies. On scales k âł 4âhâMpcâ1 the effect of baryons on the amplitude of the total matter power spectrum is greater than 1âperâcent. The back-reaction of baryons affects the density field of the dark matter at the level of âź3âperâcent on scales of 1 ⤠k/(âhâMpcâ1) ⤠5. The dark matter velocity divergence power spectrum at k Ⲡ0.5âhâMpcâ1 is changed by less than 1âperâcent. The 2D redshift space power spectrum is affected at the level of âź6âperâcent at |k|âł1hMpcâ1|k|âł1hMpcâ1 (for Îź > 0.5), but for |k|â¤0.4hMpcâ1|k|â¤0.4hMpcâ1 it differs by less than 1âperâcent. We report vanishingly small baryonic velocity bias for haloes: the peculiar velocities of haloes with M200 > 3 Ă 1011âMâ (hosting galaxies with M* > 109âMâ) are affected at the level of at most 1âkmâsâ1, which is negligible for 1âperâcent-precision cosmology. We caution that since EAGLE overestimates cluster gas fractions it may also underestimate the impact of baryons, particularly for the total matter power spectrum. Nevertheless, our findings suggest that for theoretical modelling of redshift space distortions and galaxy velocity-based statistics, baryons and their back-reaction can be safely ignored at the current level of observational accuracy. However, we confirm that the modelling of the total matter power spectrum in weak lensing studies needs to include realistic galaxy formation physics in order to achieve the accuracy required in the precision cosmology era
The link between galaxy and black hole growth in the eagle simulation
We investigate the connection between the star formation rate (SFR) of galaxies and their central black hole accretion rate (BHAR) using the EAGLE cosmological hydrodynamical simulation. We find, in striking concurrence with recent observational studies, that the ăSFRăâBHAR relation for an active galactic nucleus (AGN)-selected sample produces a relatively flat trend, whilst the ăBHARăâSFR relation for an SFR-selected sample yields an approximately linear trend. These trends remain consistent with their instantaneous equivalents even when both SFR and BHAR are time averaged over a period of 100 Myr. There is no universal relationship between the two growth rates. Instead, SFR and BHAR evolve through distinct paths that depend strongly on the mass of the host dark matter halo. The galaxies hosted by haloes of mass M200 Ⲡ1011.5âMâ grow steadily, yet black holes (BHs) in these systems hardly grow, yielding a lack of correlation between SFR and BHAR. As haloes grow through the mass range 1011.5 ⲠM200 Ⲡ1012.5 Mâ BHs undergo a rapid phase of non-linear growth. These systems yield a highly non-linear correlation between the SFR and BHAR, which are non-causally connected via the mass of the host halo. In massive haloes (M200 âł 1012.5 Mâ), both SFR and BHAR decline on average with a roughly constant scaling of SFR/BHAR âź 103. Given the complexity of the full SFRâBHAR plane built from multiple behaviours, and from the large dynamic range of BHARs, we find the primary driver of the different observed trends in the ăSFRăâBHAR and ăBHARăâSFR relationships are due to sampling considerably different regions of this plane
The quenching and morphological evolution of central galaxies is facilitated by the feedback-driven expulsion of circumgalactic gas
Large scale structure and cosmolog
Music from the heavens - gravitational waves from supermassive black hole mergers in the EAGLE simulations
We estimate the expected event rate of gravitational wave signals from mergers of supermassive black holes that could be resolved by a space-based interferometer, such as the Evolved Laser Interferometer Space Antenna (eLISA), utilizing the reference cosmological hydrodynamical simulation from the EAGLE suite. These simulations assume a Lambda cold dark matter cosmogony with state-of-the-art subgrid models for radiative cooling, star formation, stellar mass loss, and feedback from stars and accreting black holes. They have been shown to reproduce the observed galaxy population with unprecedented fidelity. We combine the merger rates of supermassive black holes in EAGLE with the latest phenomenological waveform models to calculate the gravitational waves signals from the intrinsic parameters of the merging black holes. The EAGLE models predict âź2 detections per year by a gravitational wave detector such as eLISA. We find that these signals are largely dominated by mergers between seed mass black holes merging at redshifts between z âź 2 and z âź 1. In order to investigate the dependence on the assumed black hole seed mass, we introduce an additional model with a black hole seed mass an order of magnitude smaller than in our reference model. We also consider a variation of the reference model where a prescription for the expected delays in the black hole merger time-scale has been included after their host galaxies merge. We find that the merger rate is similar in all models, but that the initial black hole seed mass could be distinguished through their detected gravitational waveforms. Hence, the characteristic gravitational wave signals detected by eLISA will provide profound insight into the origin of supermassive black holes and the initial mass distribution of black hole seeds
Alignments between galaxies, satellite systems and haloes
The spatial distribution of the satellite populations of the Milky Way and Andromeda are puzzling in that they are nearly perpendicular to the discs of their central galaxies. To understand the origin of such configurations we study the alignment of the central galaxy, satellite system and dark matter halo in the largest of the âEvolution and Assembly of GaLaxies and their Environmentsâ (EAGLE) simulation. We find that centrals and their satellite systems tend to be well aligned with their haloes, with a median misalignment angle of 33° in both cases. While the centrals are better aligned with the inner 10âkpc halo, the satellite systems are better aligned with the entire halo indicating that satellites preferentially trace the outer halo. The centralâsatellite alignment is weak (median misalignment angle of 52°) and we find that around 20âperâcent of systems have a misalignment angle larger than 78°, which is the value for the Milky Way. The centralâsatellite alignment is a consequence of the tendency of both components to align with the dark matter halo. As a consequence, when the central is parallel to the satellite system, it also tends to be parallel to the halo. In contrast, if the central is perpendicular to the satellite system, as in the case of the Milky Way and Andromeda, then the centralâhalo alignment is much weaker. Dispersion-dominated (spheroidal) centrals have a stronger alignment with both their halo and their satellites than rotation-dominated (disc) centrals. We also found that the halo, the central galaxy and the satellite system tend to be aligned with the surrounding large-scale distribution of matter, with the halo being the better aligned of the three
The Fundamental Plane of star formation in galaxies revealed by the EAGLE hydrodynamical simulations
We investigate correlations between different physical properties of star-forming galaxies in the âEvolution and Assembly of GaLaxies and their Environmentsâ (EAGLE) cosmological hydrodynamical simulation suite over the redshift range 0 ⤠z ⤠4.5. A principal component analysis reveals that neutral gas fraction (fgas,neutral), stellar mass (Mstellar) and star formation rate (SFR) account for most of the variance seen in the population, with galaxies tracing a two-dimensional, nearly flat, surface in the three-dimensional space of fgas, neutralâMstellarâSFR with little scatter. The location of this plane varies little with redshift, whereas galaxies themselves move along the plane as their fgas, neutral and SFR drop with redshift. The positions of galaxies along the plane are highly correlated with gas metallicity. The metallicity can therefore be robustly predicted from fgas, neutral, or from the Mstellar and SFR. We argue that the appearance of this âFundamental Plane of star formationâ is a consequence of self-regulation, with the plane's curvature set by the dependence of the SFR on gas density and metallicity. We analyse a large compilation of observations spanning the redshift range 0 Ⲡz Ⲡ3, and find that such a plane is also present in the data. The properties of the observed Fundamental Plane of star formation are in good agreement with EAGLE's predictions
The link between the assembly of the inner dark matter halo and the angular momentum evolution of galaxies in the EAGLE simulation
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 âEvolution and Assembly of GaLaxies and their Environmentsâ (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 host
The ARTEMIS simulations: stellar haloes of Milky Way-mass galaxies
We introduce the Assembly of high-ResoluTion Eagle-simulations of MIlky Way-type galaxieS (ARTEMIS) simulations, a new set of 42 zoomed-in, high-resolution (baryon particle mass of â2Ă104Mâhâ1â ), hydrodynamical simulations of galaxies residing in haloes of Milky Way mass, simulated with the EAGLE galaxy formation code with re-calibrated stellar feedback. In this study, we analyse the structure of stellar haloes, specifically the mass density, surface brightness, metallicity, colour, and age radial profiles, finding generally very good agreement with recent observations of local galaxies. The stellar density profiles are well fitted by broken power laws, with inner slopes of ââ3, outer slopes of ââ4, and break radii that are typically â20â40 kpc. The break radii generally mark the transition between in situ formation and accretion-driven formation of the halo. The metallicity, colour, and age profiles show mild large-scale gradients, particularly when spherically averaged or viewed along the major axes. Along the minor axes, however, the profiles are nearly flat, in agreement with observations. Overall, the structural properties can be understood by two factors: that in situ stars dominate the inner regions and that they reside in a spatially flattened distribution that is aligned with the disc. Observations targeting both the major and minor axes of galaxies are thus required to obtain a complete picture of stellar haloes
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