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Register a new userLong-term FRII jet evolution: Clues from three-dimensional simulations
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Manel Perucho
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We present a long-term numerical three-dimensional simulation of a relativistic outflow designed to be compared with previous results from axisymmetric, two-dimensional simulations, with existing analytical models and state-of-art observations. We follow the jet evolution from 1~kpc to 200~kpc, using a relativistic gas equation of state and a galactic profile for the ambient medium. We also show results from smaller scale simulations aimed to test convergence and different three-dimensional effects. We conclude that jet propagation can be faster than expected from axisymmetric simulations, covering tens of kiloparsecs in a few million years, until the dentist drill effect produced by the growth of helical instabilities slows down the propagation speed of the jet head. A comparison of key physical parameters of the jet structure as obtained from the simulations with values derived from observations of FRII sources reveals good agreement. Our simulations show that shock heating can play a significant role in the feedback from active galaxies, confirming previous 2D results. A proper description of galactic jets as a relativistic scenario, both dynamical and thermodynamical, reveals an extremely fast and efficient feedback process reheating the ICM, and therefore, with dramatic consequences on the galactic evolution. Our results point towards FRII jets as the source of the energetic electrons observed in radio relics.
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We present a comprehensive investigation of main-sequence (MS) binaries in the DRAGON simulations, which are the first one-million particles direct $N$-body simulations of globular clusters. We analyse the orbital parameters of the binary samples in two of the DRAGON simulations, D1-R7- IMF93 and D2-R7-IMF01, focusing on their secular evolution and correlations up to 12 Gyr. These two models have different initial stellar mass functions: Kroupa 1993 (D1-R7-IMF93) and Kroupa 2001 (D2-R7-IMF01); and different initial mass ratio distributions: random paring (D1-R7-IMF93) and a power-law (D1-R7-IMF93). In general, the mass ratio of a population of binaries increases over time due to stellar evolution, which is less significant in D2-R7-IMF01. In D1-R7-IMF93, primordial binaries with mass ratio $q approx$ 0.2 are most common, and the frequency linearly declines with increasing $q$ at all times. Dynamical binaries of both models have higher eccentricities and larger semi-major axes than primordial binaries. They are preferentially located in the inner part of the star cluster. Secular evolution of binary orbital parameters does not depend on the initial mass-ratio distribution, but is sensitive to the initial binary distribution of the system. At t = 12 Gyr, the binary fraction decreases radially outwards, and mass segregation is present. A color difference of 0.1 mag in $F330W-F814W$ and 0.2 mag in $NUV-y$ between the core and the outskirts of both clusters is seen, which is a reflection of the binary radial distribution and the mass segregation in the cluster. The complete set of data for primordial and dynamical binary systems at all snapshot intervals is made publicly available.
About 10% of stars more massive than ${approx},1.5,mathrm{M}_odot$ have strong, large-scale surface magnetic fields and are being discussed as progenitors of highly-magnetic white dwarfs and magnetars. The origin of these fields remains uncertain. Recent 3D magnetohydrodynamical simulations have shown that strong magnetic fields can be generated in the merger of two massive stars. Here, we follow the long-term evolution of such a 3D merger product in a 1D stellar evolution code. During a thermal relaxation phase after the coalescence, the merger product reaches critical surface rotation, sheds mass and then spins down primarily because of internal mass readjustments. The spin of the merger product after thermal relaxation is mainly set by the co-evolution of the star-torus structure left after coalescence. This evolution is still uncertain, so we also consider magnetic braking and other angular-momentum-gain and -loss mechanisms that may influence the final spin of the merged star. Because of core compression and mixing of carbon and nitrogen in the merger, enhanced nuclear burning drives a transient convective core that greatly contributes to the rejuvenation of the star. Once the merger product relaxed back to the main sequence, it continues its evolution similar to that of a genuine single star of comparable mass. It is a slow rotator that matches the magnetic blue straggler $tau$ Sco. Our results show that merging is a promising mechanism to explain some magnetic massive stars and it may also be key to understand the origin of the strong magnetic fields of highly-magnetic white dwarfs and magnetars.
The observed massive end of the galaxy stellar mass function is steeper than its predicted dark matter halo counterpart in the standard $Lambda $CDM paradigm. In this paper, we investigate the impact of active galactic nuclei (AGN) feedback on star formation in massive galaxies. We isolate the impact of AGNs by comparing two simulations from the HORIZON suite, which are identical except that one also includes super massive black holes (SMBH), and related feedback models. This allows us to cross-identify individual galaxies between simulations and quantify the effect of AGN feedback on their properties, including stellar mass and gas outflows. We find that massive galaxies ($ rm M_{*} geq 10^{11} M_odot $) are quenched by AGN feedback to the extent that their stellar masses decrease by up to 80% at $z=0$. SMBHs affect their host halo through a combination of outflows that reduce their baryonic mass, particularly for galaxies in the mass range $ rm 10^9 M_odot leq M_{*} leq 10^{11} M_odot $, and a disruption of central gas inflows, which limits in-situ star formation. As a result, net gas inflows onto massive galaxies, $ rm M_{*} geq 10^{11} M_odot $, drop by up to 70%. We measure a redshift evolution in the stellar mass ratio of twin galaxies with and without AGN feedback, with galaxies of a given stellar mass showing stronger signs of quenching earlier on. This evolution is driven by a progressive flattening of the $rm M_{rm SMBH}-M_* $ relation with redshift, particularly for galaxies with $rm M_{*} leq 10^{10} M_odot $. $rm M_{rm SMBH}/M_*$ ratios decrease over time, as falling average gas densities in galaxies curb SMBH growth.
We present 3D, adaptive mesh refinement simulations of G2, a cloud of gas moving in a highly eccentric orbit towards the galactic center. We assume that G2 originates from a stellar wind interacting with the environment of the Sgr A* black hole. The stellar wind forms a cometary bubble which becomes increasingly elongated as the star approaches periastron. A few months after periastron passage, streams of material begin to accrete on the central black hole with accretion rates $dot{M} sim 10^{-8}$ M$_odot$ yr$^{-1}$. Predicted Br$gamma$ emission maps and position-velocity diagrams show an elongated emission resembling recent observations of G2. A large increase in luminosity is predicted by the emission coming from the shocked wind region during periastron passage. The observations, showing a constant Br$gamma$ luminosity, remain puzzling, and are explained here assuming that the emission is dominated by the free-wind region. The observed Br$gamma$ luminosity ($sim 8 times 10^{30}$ erg s$^{-1}$) is reproduced by a model with a $v_w=50$ km s$^{-1}$ wind velocity and a $10^{-7}$ M$_odot$ yr$^{-1}$ mass loss rate if the emission comes from the shocked wind. A faster and less dense wind reproduces the Br$gamma$ luminosity if the emission comes from the inner, free wind region. The extended cometary wind bubble, largely destroyed by the tidal interaction with the black hole, reforms a few years after periastron passage. As a result, the Br$gamma$ emission is more compact after periastron passage.
Supernova (SN) 2015bh (or SNhunt275) was discovered in NGC 2770 on 2015 February with an absolute magnitude of Mr ~ -13.4 mag, and was initially classified as a SN impostor. Here we present the photometric and spectroscopic evolution of SN 2015bh from discovery to late phases (~ 1 yr after). In addition, we inspect archival images of the host galaxy up to ~ 21 yr before discovery, finding a burst ~ 1 yr before discovery, and further signatures of stellar instability until late 2014. Later on, the luminosity of the transient slowly increases, and a broad light curve peak is reached after about three months. We propose that the transient discovered in early 2015 could be a core-collapse SN explosion. The pre-SN luminosity variability history, the long-lasting rise and faintness first light curve peak suggests that the progenitor was a very massive, unstable and blue star, which exploded as a faint SN because of severe fallback of material. Later on, the object experiences a sudden brightening of 3 mag, which results from the interaction of the SN ejecta with circumstellar material formed through repeated past mass-loss events. Spectroscopic signatures of interaction are however visible at all epochs. A similar chain of events was previously proposed for the similar interacting SN 2009ip.
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