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Register a new userStellar feedback from HMXBs in cosmological hydrodynamical simulations
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Maria Celeste Artale
Publication date
2015
fields
Physics
and research's language is
English
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We explored the role of X-ray binaries composed by a black hole and a massive stellar companion (BHXs) as sources of kinetic feedback by using hydrodynamical cosmological simulations. Following previous results, our BHX model selects low metal-poor stars ($Z = [0,10^{-4}]$) as possible progenitors. The model that better reproduces observations assumes that a $sim 20%$ fraction of low-metallicity black holes are in binary systems which produce BHXs. These sources are estimated to deposit $sim 10^{52}$ erg of kinetic energy per event. With these parameters and in the simulated volume, we find that the energy injected by BHXs represents $sim 30%$ of the total energy released by SNII and BHX events at redshift $zsim7$ and then decreases rapidly as baryons get chemically enriched. Haloes with virial masses smaller than $sim 10^{10} ,M_{odot}$ (or $T_{rm vir} lesssim 10^5 $ K) are the most directly affected ones by BHX feedback. These haloes host galaxies with stellar masses in the range $10^7 - 10^8$ M$_odot$. Our results show that BHX feedback is able to keep the interstellar medium warm, without removing a significant gas fraction, in agreement with previous analytical calculations. Consequently, the stellar-to-dark matter mass ratio is better reproduced at high redshift. Our model also predicts a stronger evolution of the number of galaxies as a function of the stellar mass with redshift when BHX feedback is considered. These findings support previous claims that the BHXs could be an effective source of feedback in early stages of galaxy evolution.
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We study the Intra-Halo Stellar Component (IHSC) of Milky Way-mass systems up to galaxy clusters in the Horizon-AGN cosmological hydrodynamical simulation. We identify the IHSC using an improved phase-space galaxy finder algorithm which provides an adaptive, physically motivated and shape-independent definition of this stellar component, that can be applied to halos of arbitrary masses. We explore the IHSC mass fraction-total halos stellar mass, $f_{M*,IHSC}-M*$, relation and the physical drivers of its scatter. We find that on average the $f_{M*,IHSC}$ increases with $M_{*,tot}$, with the scatter decreasing strongly with mass from 2 dex at $M_{*,tot}sim10^{11}M_odot$ to 0.3 dex at group masses. At high masses, $M_{*,tot}>10^{11.5}M_odot$, $f_{M*,IHSC}$ increases with the number of substructures, and with the mass ratio between the central galaxy and largest satellite, at fixed $M_{*,tot}$. From mid-size groups and systems below $M_{*,tot}<10^{12}M_odot$, we find that the central galaxys stellar rotation-to-dispersion velocity ratio, V/{sigma}, displays the strongest (anti)-correlation with $f_{M*,IHSC}$ at fixed $M_{*,tot}$ of all the galaxy and halo properties explored, transitioning from $f_{M*,IHSC}$<0.1% for high V/{sigma}, to $f_{M*,IHSC}sim5$% for low V/{sigma} galaxies. By studying the $f_{M*,IHSC}$ temporal evolution, we find that, in the former, mergers not always take place, but if they did, they happened early (z>1), while the high $f_{M*,IHSC}$ population displays a much more active merger history. In the case of massive groups and galaxy clusters, $M_{*,tot}>10^{12}M_odot$, a fraction $f_{M*,IHSC}sim$10-20% is reached at $zsim1$ and then they evolve across lines of constant $f_{M*,IHSC}$ modulo some small perturbations. Because of the limited simulations volume, the latter is only tentative and requires a larger sample of simulated galaxy clusters to confirm.
We study the properties of two bars formed in fully cosmological hydrodynamical simulations of the formation of Milky Way-mass galaxies. In one case, the bar formed in a system with disc, bulge and halo components and is relatively strong and long, as could be expected for a system where the spheroid strongly influences the evolution. The second bar is less strong, shorter, and formed in a galaxy with no significant bulge component. We study the strength and length of the bars, the stellar density profiles along and across the bars and the velocity fields in the bar region. We compare them with the results of dynamical (idealised) simulations and with observations, and find, in general, a good agreement, although we detect some important differences as well. Our results show that more or less realistic bars can form naturally in a $Lambda$CDM cosmology, and open up the possibility to study the bar formation process in a more consistent way than previously done, since the host galaxies grow, accrete matter and significantly evolve during the formation and evolution of the bar.
We present a study of hydrodynamic drag forces in smoothed particle simulations. In particular, the deceleration of a resolution-limited cold clump of gas moving through a hot medium is examined. It is found that the drag for subsonic velocities exceeds that predicted by simple physical approximations. This is shown to be a result of the hydrodynamical method which encourages the accretion of particles from the hot medium onto a shell around the cold clump, effectively increasing the radius of the clump. For sonic and supersonic velocities, the drag is shown to be dependent on the effective cross section of the clump. The consequences for cosmological simulations are discussed.
In this work we present a new hybrid method to simulate the thermal effects of the reionization in cosmological hydrodynamical simulations. The method improves upon the standard approach used in simulations of the intergalactic medium (IGM) and galaxy formation without a significant increase of the computational cost allowing for efficient exploration of the parameter space. The method uses a small set of phenomenological input parameters and combines a semi-numerical reionization model to solve for the topology of reionization and an approximate model of how reionization heats the IGM, with the massively parallel texttt{Nyx} hydrodynamics code, specifically designed to solve for the structure of diffuse IGM gas. We have produced several large-scale high resolution cosmological hydrodynamical simulations ($2048^3$, $L_{rm box} = 40$ Mpc/h) with different instantaneous and inhomogeneous HI reionization models that use this new methodology. We study the IGM thermal properties of these models and find that large scale temperature fluctuations extend well beyond the end of reionization. Analyzing the 1D flux power spectrum of these models, we find up to $sim 50%$ differences in the large scale properties (low modes, $klesssim0.01$ s/km) of the post-reionization power spectrum due to the thermal fluctuations. We show that these differences could allow one to distinguish between different reionization scenarios already with existing Ly$alpha$ forest measurements. Finally, we explore the differences in the small-scale cutoff of the power spectrum and we find that, for the same heat input, models show very good agreement provided that the reionization redshift of the instantaneous reionization model happens at the midpoint of the inhomogeneous model.
State-of-the-art cosmological hydrodynamical simulations of galaxy formation have reached the point at which their outcomes result in galaxies with ever more realism. Still, the employed sub-grid models include several free parameters such as the density threshold, $n$, to localize the star-forming gas. In this work, we investigate the possibilities to utilize the observed clustered nature of star formation (SF) in order to refine SF prescriptions and constrain the density threshold parameter. To this end, we measure the clustering strength, correlation length and power-law index of the two-point correlation function of young ($tau<50$ Myr) stellar particles and compare our results to observations from the HST Legacy Extragalactic UV Survey (LEGUS). Our simulations reveal a clear trend of larger clustering signal and power-law index and lower correlation length as the SF threshold increases with only mild dependence on galaxy properties such as stellar mass or specific star formation rate. In conclusion, we find that the observed clustering of SF is inconsistent with a low threshold for SF ($n<1$ cm$^{-3}$) and strongly favours a high value for the density threshold of SF ($n>10$ cm$^{-3}$), as for example employed in the NIHAO project.
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