A unified multiwavelength model of galaxy formation Lacey, Cedric G; Baugh, Carlton M; Frenk, Carlos S ...
Monthly Notices of the Royal Astronomical Society,
11/2016, Letnik:
462, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We present a new version of the galform semi-analytical model of galaxy formation. This brings together several previous developments of galform into a single unified model, including a different ...initial mass function (IMF) in quiescent star formation and in starbursts, feedback from active galactic nuclei suppressing gas cooling in massive haloes, and a new empirical star formation law in galaxy discs based on their molecular gas content. In addition, we have updated the cosmology, introduced a more accurate treatment of dynamical friction acting on satellite galaxies, and updated the stellar population model. The new model is able to simultaneously explain both the observed evolution of the K-band luminosity function and stellar mass function, and the number counts and redshift distribution of sub-mm galaxies selected at 850 μm. This was not previously achieved by a single physical model within the Λcold dark matter framework, but requires having an IMF in starbursts that is somewhat top-heavy. The new model is tested against a wide variety of observational data covering wavelengths from the far-UV to sub-mm, and redshifts from z = 0 to 6, and is found to be generally successful. These observations include the optical and near-infrared (IR) luminosity functions, H i mass function, fraction of early type galaxies, Tully–Fisher, metallicity–luminosity and size–luminosity relations at z = 0, as well as far-IR number counts, and far-UV luminosity functions at z ∼ 3–6. Discrepancies are, however, found in galaxy sizes and metallicities at low luminosities, and in the abundance of low-mass galaxies at high-z, suggesting the need for a more sophisticated model of supernova feedback.
Abstract
It is now possible for hydrodynamical simulations to reproduce a representative galaxy population. Accordingly, it is timely to assess critically some of the assumptions of traditional ...semi-analytic galaxy formation models. We use the eagle simulations to assess assumptions built into the galform semi-analytic model, focusing on those relating to baryon cycling, angular momentum and feedback. We show that the assumption in galform that newly formed stars have the same specific angular momentum as the total disc leads to a significant overestimate of the total stellar specific angular momentum of disc galaxies. In eagle, stars form preferentially out of low-specific angular momentum gas in the interstellar medium due to the assumed gas density threshold for stars to form, leading to more realistic galaxy sizes. We find that stellar mass assembly is similar between galform and eagle but that the evolution of gas properties is different, with various indications that the rate of baryon cycling in eagle is slower than is assumed in galform. Finally, by matching individual galaxies between eagle and galform, we find that an artificial dependence of active galactic nucleus feedback and gas infall rates on halo mass-doubling events in galform drives most of the scatter in stellar mass between individual objects. Put together our results suggest that the galform semi-analytic model can be significantly improved in light of recent advances.
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.
ABSTRACT
We present recalibrations of the galform semi-analytical model of galaxy formation in a new N-body simulation with the Planck cosmology. The Planck Millennium simulation uses more than 128 ...billion particles to resolve the matter distribution in a cube of 800 Mpc on a side, which contains more than 77 million dark matter haloes with mass greater than 2.12 × 109 h−1 M⊙ at this day. Only minor changes to a very small number of model parameters are required in the recalibration. We present predictions for the atomic hydrogen content (H i) of dark matter haloes, which is a key input into the calculation of the H i intensity mapping signal expected from the large-scale structure of the Universe. We find that the H i mass–halo mass relation displays a clear break at the halo mass above which AGN heating suppresses gas cooling, ≈3 × 1011h−1 M⊙. Below this halo mass, the H i content of haloes is dominated by the central galaxy; above this mass it is the combined H i content of satellites that prevails. We find that the H i mass–halo mass relation changes little with redshift up to $z$ = 3. The bias of H i sources shows a scale dependence that gets more pronounced with increasing redshift.
We report the study of the far-infrared (IR) sizes of submillimeter galaxies (SMGs) in relation to their dust-obscured star formation rate (SFR) and active galactic nuclei (AGN) presence, determined ...using mid-IR photometry. We determined the millimeter-wave ( m) sizes of 69 Atacama Large Millimeter/submillimeter Array (ALMA)-identified SMGs, selected with confidence on ALMA images ( -7.4 mJy). We found that all of the SMGs are located above an avoidance region in the size-flux plane, as expected by the Eddington limit for star formation. In order to understand what drives the different millimeter-wave sizes in SMGs, we investigated the relation between millimeter-wave size and AGN fraction for 25 of our SMGs at z = 1-3. We found that the SMGs for which the mid-IR emission is dominated by star formation or AGN have extended millimeter-sizes, with respective median and kpc. Instead, the SMGs for which the mid-IR emission corresponds to star-forming/AGN composites have more compact millimeter-wave sizes, with median kpc. The relation between millimeter-wave size and AGN fraction suggests that this size may be related to the evolutionary stage of the SMG. The very compact sizes for composite star-forming/AGN systems could be explained by supermassive black holes growing rapidly during the SMG coalescing, star-formation phase.
Cosmological hydrodynamical simulations are rich tools to understand the build-up of stellar mass and angular momentum in galaxies, but require some level of calibration to observations. We compare ...predictions at |$z$| ∼ 0 from the eagle, hydrangea, horizon-agn, and magneticum simulations with integral field spectroscopic (IFS) data from the SAMI (Sydney-AAO Multi-object Integral field spectrograph) Galaxy Survey, ATLAS^3D, CALIFA (Calar Alto Legacy Integral Field Area), and MASSIVE surveys. The main goal of this work is to simultaneously compare structural, dynamical, and stellar population measurements in order to identify key areas of success and tension. We have taken great care to ensure that our simulated measurement methods match the observational methods as closely as possible, and we construct samples that match the observed stellar mass distribution for the combined IFS sample. We find that the eagle and hydrangea simulations reproduce many galaxy relations but with some offsets at high stellar masses. There are moderate mismatches in R_e (+), ε (−), σ_e (−), and mean stellar age (+), where a plus sign indicates that quantities are too high on average, and minus sign too low. The horizon-agn simulations qualitatively reproduce several galaxy relations, but there are a number of properties where we find a quantitative offset to observations. Massive galaxies are better matched to observations than galaxies at low and intermediate masses. Overall, we find mismatches in R_e (+), ε (−), σ_e (−), and (V/σ)_e (−). magneticum matches observations well: this is the only simulation where we find ellipticities typical for disc galaxies, but there are moderate differences in σ_e (−), (V/σ)_e (−), and mean stellar age (+). Our comparison between simulations and observational data has highlighted several areas for improvement, such as the need for improved modelling resulting in a better vertical disc structure, yet our results demonstrate the vast improvement of cosmological simulations in recent years.
ABSTRACT
We explore the connection between the gravitational wave (GW) merger rates of stellar-mass binary black holes (BBHs) and galaxy properties. We do this by generating populations of stars ...using the binary population synthesis code COMPAS and evolving them in galaxies from the semi-analytic galaxy formation model Shark, to determine the number of mergers occurring in each simulation time-step. We find that metal-rich and massive galaxies with star formation rate (SFR) greater than $1\, {\rm M}_{\odot }\, \rm yr^{-1}$ are 10 times more likely to have GW events compared to younger, less massive, and metal-poor galaxies. Our simulation with the default input parameters predicts a higher local merger rate density compared to the third GW transient catalogue (GWTC-3) prediction from LIGO, VIRGO, and KAGRA, due to short coalescence times, low metallicities, and a high SFR at low redshift in the simulation, which produces more BBHs that merge within the age of the Universe compared to observations. We identify alternate remnant mass models that more accurately reproduce the volumetric rate and provide updated fits to the merger rate as a function of redshift. We then investigate the relative fraction of GW events in our simulation that are in observable host galaxies from upcoming galaxy surveys, determining which of those are ideal for tracing host galaxies with high merger rates. The implications of this work can be utilized for constraining stellar evolution models, better informing follow-up programs, and placing informative priors on host galaxies when measuring cosmological parameters such as the Hubble constant.
Abstract
We consider the effect of including an active galactic nuclei (AGN) component when fitting spectral energy distributions of 109 spectroscopically confirmed
z
≈ 3.5–12.5 galaxies with JWST. ...Remarkably, we find that the resulting cosmic star formation history is ≈0.4 dex lower at
z
≳ 9.5 when an AGN component is included in the fitting. This alleviates previously reported excess star formation at
z
≳ 9.5 compared to models based on typical baryon conversion efficiencies inside dark matter halos. We find that the individual stellar masses and star formation rates can be as much as ≈4 dex lower when fitting with an AGN component. These results highlight the importance of considering both stellar mass assembly and supermassive black hole growth when interpreting the light distributions of among the first galaxies to ever exist.
PDF
