Astrophysicist

Category: Publications (Page 3 of 5)

Ehlert et al. (2019)

The Sunyaev-Zel’dovich Effect of Simulated Jet-inflated Bubbles in Clusters

by
Ehlert, Kristian; Pfrommer, Christoph; Weinberger, Rainer; Pakmor, Rüdiger; Springel, Volker

abstract
Feedback by active galactic nuclei (AGNs) is essential for regulating the fast radiative cooling of low-entropy gas at the centers of galaxy clusters and for reducing star formation rates of central ellipticals. The details of self-regulation depend critically on the unknown contents of AGN-inflated bubbles. Observations of the Sunyaev-Zeldovich (SZ) signal of AGN bubbles provide us with the ability to directly measure the lobe electron pressure given a bubble morphology. Here we compute the SZ signal of jet-inflated bubbles in three-dimensional magnetohydrodynamical simulations of the galaxy cluster MS0735.6+7421 with the Arepo code, and compare our synthetic SZ results to inferences obtained with popular modeling approaches. We find that cutting out ellipsoidal bubbles from a double-beta pressure profile only matches the inner bubble edges in the simulations and fails to account for the emission of the shock-enhanced pressure cocoon outside the bubbles. This additional contribution significantly worsens the accuracy of the cut-out method for jets with small inclinations with respect to the line of sight. Also, the kinetic SZ effect of the bubbles, a previously neglected contribution, becomes relevant at these smaller inclinations due to entrainment and mixing of the intracluster medium with low-density jet material. Fortunately, the different signs of the kinetic SZ signal in opposite lobes allow this effect to be modeled. We present an approximate method to determine the jet inclination, which combines jet power and lifetime estimates, the stand-off distance between jet head and bow shock, and the kinetic SZ effect, thereby helping to correctly infer the bubble contents.

published in
The Astrophysical Journal Letters, Volume 872, Issue 1, article id. L8, 6 pp. (February 2019)

link to paper
[ADS][arXiv]

Genel et al. (2019)

A Quantification of the Butterfly Effect in Cosmological Simulations and Implications for Galaxy Scaling Relations

by
Genel, Shy; Bryan, Greg L.; Springel, Volker; Hernquist, Lars; Nelson, Dylan; Pillepich, Annalisa; Weinberger, Rainer; Pakmor, Rüdiger; Marinacci, Federico; Vogelsberger, Mark

abstract
We study the chaotic-like behavior of cosmological simulations by quantifying how minute perturbations grow over time and manifest as macroscopic differences in galaxy properties. When we run pairs of “shadow” simulations that are identical except for random minute initial displacements to particle positions (e.g., of order {10}-7 {pc}), the results diverge from each other at the individual galaxy level (while the statistical properties of the ensemble of galaxies are unchanged). After cosmological times, the global properties of pairs of “shadow” galaxies that are matched between the simulations differ from each other, generally at a level of ̃2-25%, depending on the considered physical quantity. We perform these experiments using cosmological volumes of {(25{–}50{Mpc}/h)}3evolved either purely with dark matter, or with baryons and star formation but no feedback, or else using the full feedback model of the IllustrisTNG project. The runs cover four resolution levels spanning a factor of 512 in mass. We find that, without feedback, the differences between shadow galaxies generally become smaller as the resolution increases—but with the IllustrisTNG model, the results mostly converge toward a “floor.” This hints at the role of feedback in setting the chaotic properties of galaxy formation. Importantly, we compare the macroscopic differences between shadow galaxies to the overall scatter in various galaxy scaling relations, and conclude that, for the star formation-mass and the Tully-Fisher relations, the butterfly effect in our simulations contributes significantly to the overall scatter. We find that our results are robust to whether random numbers are used in the subgrid models or not. We discuss the implications for galaxy formation theory in general and for cosmological simulations in particular.

 published in
The Astrophysical Journal, Volume 871, Issue 1, article id. 21, 27 pp. (January 2019)

links to paper
[ADS][arXiv]

Ehlert et al. (2018)

Simulations of the dynamics of magnetized jets and cosmic rays in galaxy clusters

by
Ehlert, K.; Weinberger, R.; Pfrommer, C.; Pakmor, R.; Springel, V.

abstract
Feedback processes by active galactic nuclei in the centres of galaxy clusters appear to prevent large-scale cooling flows and impede star formation. However, the detailed heating mechanism remains uncertain. One promising heating scenario invokes the dissipation of Alfvén waves that are generated by streaming cosmic rays (CRs). In order to study this idea, we use three-dimensional magnetohydrodynamical simulations with the AREPO code that follow the evolution of jet-inflated bubbles that are filled with CRs in a turbulent cluster atmosphere. We find that a single injection event produces the CR distribution and heating rate required for a successful CR heating model. As a bubble rises buoyantly, cluster magnetic fields drape around the leading interface and are amplified to strengths that balance the ram pressure. Together with helical magnetic fields in the bubble, this initially confines the CRs and suppresses the formation of interface instabilities. But as the bubble continues to rise, bubble-scale eddies significantly amplify radial magnetic filaments in its wake and enable CR transport from the bubble to the cooling intracluster medium. By varying the jet parameters, we obtain a rich and diverse set of jet and bubble morphologies ranging from Fanaroff-Riley type I-like (FRI) to FRII-like jets. We identify jet energy as the leading order parameter (keeping the ambient density profiles fixed), whereas jet luminosity is primarily responsible for setting the Mach numbers of shocks around FRII-like sources. Our simulations also produce FRI-like jets that inflate bubbles without detectable shocks and show morphologies consistent with cluster observations.

published in
Monthly Notices of the Royal Astronomical Society, Volume 481, Issue 3, p.2878-2900, December 2018

links to paper
[ADS][arXiv]

Lovell et al. (2018)

The fraction of dark matter within galaxies from the IllustrisTNG simulations

by
Lovell, Mark R.; Pillepich, Annalisa; Genel, Shy; Nelson, Dylan; Springel, Volker; Pakmor, Rüdiger; Marinacci, Federico; Weinberger, Rainer; Torrey, Paul; Vogelsberger, Mark; Alabi, Adebusola; Hernquist, Lars

abstract
We use the IllustrisTNG (TNG) cosmological simulations to provide theoretical expectations for the dark matter mass fractions (DMFs) and circular velocity profiles of galaxies. TNG predicts flat circular velocity curves for z = 0 Milky Way (MW)-like galaxies beyond a few kpc from the galaxy centre, in better agreement with observational constraints than its predecessor, Illustris. TNG also predicts an enhancement of the dark matter mass within the 3D stellar half-mass radius (r_half; M_200c = 10^{10}-10^{13} M_{☉ }, z ≤ 2) compared to its dark matter only and Illustris counterparts. This enhancement leads TNG present-day galaxies to be dominated by dark matter within their inner regions, with f_DM(< r_half)≳ 0.5 at all masses and with a minimum for MW-mass galaxies. The 1σ scatter is ≲10 per cent at all apertures, which is smaller than that inferred by some observational data sets, e.g. 40 per cent from the SLUGGS survey. TNG agrees with the majority of the observationally inferred values for elliptical galaxies once a consistent initial mass function is adopted (Chabrier) and the DMFs are measured within the same apertures. The DMFs measured within r_half increase towards lower redshifts: this evolution is dominated by the increase in galaxy size with time. At z ̃ 2, the DMF in disc-like TNG galaxies decreases with increasing galaxy mass, with f_DM(< r_half) ̃ 0.10-0.65 for 1010 ≲ Mstars/M ≲ 1012, and are two times higher than if TNG galaxies resided in Navarro-Frenk-White dark matter haloes unaffected by baryonic physics. It remains to be properly assessed whether recent observational estimates of the DMFs at z ̃ 2 rule out the contraction of the dark matter haloes predicted by the TNG model.

published in
Monthly Notices of the Royal Astronomical Society, Volume 481, Issue 2, p.1950-1975, December 2018

links to paper
[ADS][arXiv]

Barnes et al. (2018)

A census of cool-core galaxy clusters in IllustrisTNG

by
Barnes, David J.; Vogelsberger, Mark; Kannan, Rahul; Marinacci, Federico; Weinberger, Rainer; Springel, Volker; Torrey, Paul; Pillepich, Annalisa; Nelson, Dylan; Pakmor, Rüdiger; Naiman, Jill; Hernquist, Lars; McDonald, Michael

abstract
The thermodynamic structure of hot gas in galaxy clusters is sensitive to astrophysical processes and typically difficult to model with galaxy formation simulations. We explore the fraction of cool-core (CC) clusters in a large sample of 370 clusters from IllustrisTNG, examining six common CC definitions. IllustrisTNG produces continuous CC criteria distributions, the extremes of which are classified as CC and non-cool core (NCC), and the criteria are increasingly correlated for more massive clusters. At z = 0, the CC fractions for two criteria are in reasonable agreement with the observed fractions but the other four CC fractions are lower than observed. This result is partly driven by systematic differences between the simulated and observed gas fraction profiles. The simulated CC fractions with redshift show tentative agreement with the observed fractions, but linear fits demonstrate that the simulated evolution is steeper than observed. The conversion of CCs to NCCs appears to begin later and act more rapidly in the simulations. Examining the fraction of CCs and NCCs defined as relaxed we find no evidence that CCs are more relaxed, suggesting that mergers are not solely responsible for disrupting CCs. A comparison of the median thermodynamic profiles defined by different CC criteria shows that the extent to which they evolve in the cluster core is dependent on the CC criteria. We conclude that the thermodynamic structure of galaxy clusters in IllustrisTNG shares many similarities with observations, but achieving better agreement most likely requires modifications of the underlying galaxy formation model.

published in
Monthly Notices of the Royal Astronomical Society, Volume 481, Issue 2, p.1809-183, December 2018

links to paper
[ADS][arXiv]

Marinacci et al. (2018)

First results from the IllustrisTNG simulations: radio haloes and magnetic fields

by
Marinacci, Federico; Vogelsberger, Mark; Pakmor, Rüdiger; Torrey, Paul; Springel, Volker; Hernquist, Lars; Nelson, Dylan; Weinberger, Rainer; Pillepich, Annalisa; Naiman, Jill; Genel, Shy

abstract
We introduce the IllustrisTNG project, a new suite of cosmological magnetohydrodynamical simulations performed with the moving-mesh code AREPO employing an updated Illustris galaxy formation model. Here we focus on the general properties of magnetic fields and the diffuse radio emission in galaxy clusters. Magnetic fields are prevalent in galaxies, and their build-up is closely linked to structure formation. We find that structure formation amplifies the initial seed fields (10-14comoving Gauss) to the values observed in low-redshift galaxies (1-10 {μ G}). The magnetic field topology is closely connected to galaxy morphology such that irregular fields are hosted by early-type galaxies, while large-scale, ordered fields are present in disc galaxies. Using two simple models for the energy distribution of relativistic electrons we predict the diffuse radio emission of 280 clusters with a baryonic mass resolution of 1.1× 107 {M_{☉}}, and generate mock observations for Very Large Array (VLA), Low-Frequency Array (LOFAR), Australian Square Kilometre Array Pathfinder (ASKAP), and Square Kilometre Array (SKA). Our simulated clusters show extended radio emission, whose detectability correlates with their virial mass. We reproduce the observed scaling relations between total radio power and X-ray emission, M500, and the Sunyaev-Zel’dovich Y500 parameter. The radio emission surface brightness profiles of our most massive clusters are in reasonable agreement with VLA measurements of Coma and Perseus. Finally, we discuss the fraction of detected extended radio haloes as a function of virial mass and source count functions for different instruments. Overall our results agree encouragingly well with observations, but a refined analysis requires a more sophisticated treatment of relativistic particles in large-scale galaxy formation simulations.

published in
Monthly Notices of the Royal Astronomical Society, Volume 480, Issue 4, p.5113-5139, November 2018

links to paper
[ADS][arXiv]

Villaescusa-Navarro et al. (2018)

Ingredients for 21 cm Intensity Mapping

by
Villaescusa-Navarro, Francisco; Genel, Shy; Castorina, Emanuele; Obuljen, Andrej; Spergel, David N.; Hernquist, Lars; Nelson, Dylan; Carucci, Isabella P.; Pillepich, Annalisa; Marinacci, Federico; Diemer, Benedikt; Vogelsberger, Mark; Weinberger, Rainer; Pakmor, Rüdiger

author
Current and upcoming radio telescopes will map the spatial distribution of cosmic neutral hydrogen (H I) through its 21 cm emission. In order to extract the maximum information from these surveys, accurate theoretical predictions are needed. We study the abundance and clustering properties of H I at redshifts z ≤ 5 using TNG100, a large state-of-the-art magnetohydrodynamic simulation of a 75 h -1Mpc box size, which is part of the IllustrisTNG Project. We show that most of the H I lies within dark matter halos, and we provide fits for the halo H I mass function, i.e., the mean H I mass hosted by a halo of mass M at redshift z. We find that only halos with circular velocities larger than ≃30 km s-1contain H I. While the density profiles of H I exhibit a large halo-to-halo scatter, the mean profiles are universal across mass and redshift. The H I in low-mass halos is mostly located in the central galaxy, while in massive halos the H I is concentrated in the satellites. Our simulation reproduces the bias value of damped Lyα systems from observations. We show that the H I and matter density probability distribution functions differ significantly. Our results point out that for small halos, the H I bulk velocity goes in the same direction and has the same magnitude as the halo peculiar velocity, while in large halos, differences show up. We find that halo H I velocity dispersion follows a power law with halo mass. We find a complicated H I bias, with H I already becoming nonlinear at k = 0.3 h Mpc-1 at z ≳ 3. The clustering of H I can, however, be accurately reproduced by perturbative methods. We find a new secondary bias by showing that the clustering of halos depends not only on mass but also on H I content. We compute the amplitude of the H I shot noise and find that it is small at all redshifts, verifying the robustness of BAO measurements with 21 cm intensity mapping. We study the clustering of H I in redshift space and show that linear theory can explain the ratio between the monopoles in redshift and real space down to 0.3, 0.5, and 1 h Mpc-1 at redshifts 3, 4, and 5, respectively. We find that the amplitude of the Fingers-of-God effect is larger for H I than for matter, since H I is found only in halos above a certain mass. We point out that 21 cm maps can be created from N-body simulations rather than full hydrodynamic simulations. Modeling the one-halo term is crucial for achieving percent accuracy with respect to a full hydrodynamic treatment. Although our results are not converged against resolution, they are, however, very useful as we work at the resolution where the model parameters have been calibrated to reproduce galaxy properties.

published in
The Astrophysical Journal, Volume 866, Issue 2, article id. 135, 41 pp. (October 2018).

links to paper
[ADS][arXiv]

Zhu et al. (2018)

Formation of a Malin 1 analogue in IllustrisTNG by stimulated accretion

by
Zhu, Qirong; Xu, Dandan; Gaspari, Massimo; Rodriguez-Gomez, Vicente; Nelson, Dylan; Vogelsberger, Mark; Torrey, Paul; Pillepich, Annalisa; Zjupa, Jolanta; Weinberger, Rainer; Marinacci, Federico; Pakmor, Rüdiger; Genel, Shy; Li, Yuexing; Springel, Volker; Hernquist, Lars

abstract
The galaxy Malin 1 contains the largest stellar disc known but the formation mechanism of this structure has been elusive. In this paper, we report a Malin 1 analogue in the 100 Mpc IllustrisTNG simulation and describe its formation history. At redshift zero, this massive galaxy, having a maximum circular velocity Vmax of 430 km s-1, contains a 100 kpc gas/stellar disc with morphology similar to Malin 1. The simulated galaxy reproduces well many observed features of Malin 1’s vast disc, including its stellar ages, metallicities, and gas rotation curve. We trace the extended disc back in time and find that a large fraction of the cold gas at redshift zero originated from the cooling of hot halo gas, triggered by the merger of a pair of intruding galaxies. Our finding provides a novel way to form large galaxy discs as extreme as Malin 1 within the current galaxy formation framework.

published in
Monthly Notices of the Royal Astronomical Society: Letters, Volume 480, Issue 1, p.L18-L22, October 2018

links to paper
[ADS][arXiv]

Weinberger et al. (2018)

Supermassive black holes and their feedback effects in the IllustrisTNG simulation

by
Weinberger, Rainer; Springel, Volker; Pakmor, Rüdiger; Nelson, Dylan; Genel, Shy; Pillepich, Annalisa; Vogelsberger, Mark; Marinacci, Federico; Naiman, Jill; Torrey, Paul; Hernquist, Lars

abstract
We study the population of supermassive black holes (SMBHs) and their effects on massive central galaxies in the IllustrisTNG cosmological hydrodynamical simulations of galaxy formation. The employed model for SMBH growth and feedback assumes a two-mode scenario in which the feedback from active galactic nuclei occurs through a kinetic, comparatively efficient mode at low accretion rates relative to the Eddington limit, and in the form of a thermal, less efficient mode at high accretion rates. We show that the quenching of massive central galaxies happens coincidently with kinetic-mode feedback, consistent with the notion that active supermassive black holes cause the low specific star formation rates observed in massive galaxies. However, major galaxy mergers are not responsible for initiating most of the quenching events in our model. Up to black hole masses of about 10^{8.5} M_{☉}, the dominant growth channel for SMBHs is in the thermal mode. Higher mass black holes stay mainly in the kinetic mode and gas accretion is self-regulated via their feedback, which causes their Eddington ratios to drop, with SMBH mergers becoming the main channel for residual mass growth. As a consequence, the quasar luminosity function is dominated by rapidly accreting, moderately massive black holes in the thermal mode. We show that the associated growth history of SMBHs produces a low-redshift quasar luminosity function and a redshift zero black hole mass – stellar bulge mass relation is in good agreement with observations, whereas the simulation tends to overpredict the high-redshift quasar luminosity function.

published in
Monthly Notices of the Royal Astronomical Society, Volume 479, Issue 3, p.4056-4072, September 2018

links to paper
[ADS][arXiv]

Naiman et al. (2018)

First results from the IllustrisTNG simulations: a tale of two elements – chemical evolution of magnesium and europium

by
Naiman, Jill P.; Pillepich, Annalisa; Springel, Volker; Ramirez-Ruiz, Enrico; Torrey, Paul; Vogelsberger, Mark; Pakmor, Rüdiger; Nelson, Dylan; Marinacci, Federico; Hernquist, Lars; Weinberger, Rainer; Genel, Shy

abstract
The distribution of elements in galaxies provides a wealth of information about their production sites and their subsequent mixing into the interstellar medium. Here we investigate the elemental distributions of stars in the IllustrisTNG simulations. We analyse the abundance ratios of magnesium and europium in Milky Way-like galaxies from the TNG100 simulation (stellar masses log (M/M) ̃ 9.7-11.2). Comparison of observed magnesium and europium for individual stars in the Milky Way with the stellar abundances in our more than 850 Milky Way-like galaxies provides stringent constraints on our chemical evolutionary methods. Here, we use the magnesium-to-iron ratio as a proxy for the effects of our SNII (core-collapse supernovae) and SNIa (Type Ia supernovae) metal return prescription and as a comparison to a variety of galactic observations. The europium-to-iron ratio tracks the rare ejecta from neutron star-neutron star mergers, the assumed primary site of europium production in our models, and is a sensitive probe of the effects of metal diffusion within the gas in our simulations. We find that europium abundances in Milky Way-like galaxies show no correlation with assembly history, present-day galactic properties, and average galactic stellar population age. We reproduce the europium-to-iron spread at low metallicities observed in the Milky Way, and find it is sensitive to gas properties during redshifts z ≈ 2-4. We show that while the overall normalization of [Eu/Fe] is susceptible to resolution and post-processing assumptions, the relatively large spread of [Eu/Fe] at low [Fe/H] when compared to that at high [Fe/H] is quite robust.

published in
Monthly Notices of the Royal Astronomical Society, Volume 477, Issue 1, p.1206-1224, June 2018

links to paper
[ADS][arXiv]

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