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FR0 jets and recollimation-induced instabilities
Astronomy & Astrophysics ( IF 6.5 ) Pub Date : 2024-02-26 , DOI: 10.1051/0004-6361/202348954 A. Costa , G. Bodo , F. Tavecchio , P. Rossi , A. Capetti , S. Massaglia , A. Sciaccaluga , R.D. Baldi , G. Giovannini
Astronomy & Astrophysics ( IF 6.5 ) Pub Date : 2024-02-26 , DOI: 10.1051/0004-6361/202348954 A. Costa , G. Bodo , F. Tavecchio , P. Rossi , A. Capetti , S. Massaglia , A. Sciaccaluga , R.D. Baldi , G. Giovannini
Context. The recently discovered population of faint Fanaroff-Riley type 0 (FR0) radio galaxies has been interpreted as the extension to low power of the classical FRI sources. Their radio emission appears to be concentrated in very compact parsec scale cores, any extended emission is very weak or absent, and very-long-baseline interferometry (VLBI) observations show that jets are already mildly or sub-relativistic at parsec scales. Based on these observational properties, we propose here that the jets of FR0s are strongly decelerated and disturbed at the parsec scale by hydrodynamical instabilities.Aims. With the above scenario in mind, we studied the dynamics of a low-power relativistic jet propagating into a confining external medium, focusing on the effects of entrainment and mixing promoted by the instabilities developing at the jet-environment interface downstream of a recollimation shock.Methods. We performed a 3D relativistic hydrodynamical simulation of a recollimated jet by means of the state-of-the-art code PLUTO. The jet was initially conical, relativistic (with an initial Lorentz factor Γ = 5), cold, and light with respect to the confining medium, whose pressure is assumed to slowly decline with distance. The magnetic field is assumed to be dynamically unimportant.Results. The 3D simulation shows that, after the first recollimation and reflection shock system, a rapidly growing instability develops, as a result of the interplay between recollimation-induced instabilities and Richtmyer-Meshkov modes. In turn, the instabilities promote strong mixing and entrainment that rapidly lead to the deceleration of the jet and spread its momentum to slowly moving, highly turbulent external gas. We argue that this mechanism could account for the peculiarities of the low-power FR0 jets. For outflows with a higher power, Lorentz factor, or magnetic field, we expect that the destabilizing effects are less effective, allowing the survival of the jet up to the kiloparsec scale, as observed in FRIs.
中文翻译：
FR0 射流和重准引起的不稳定性
语境。最近发现的微弱 Fanaroff-Riley 0 型 (FR0) 射电星系群被解释为经典 FRI 源低功率的延伸。它们的无线电发射似乎集中在非常紧凑的秒差距尺度核心中，任何扩展的发射都非常微弱或不存在，并且超长基线干涉测量（VLBI）观测表明，喷流在秒差距尺度上已经具有轻微或亚相对论性。基于这些观测特性，我们在此提出，FR0 的射流在秒差距尺度上受到流体动力学不稳定性的强烈减速和干扰。目标。考虑到上述情况，我们研究了低功率相对论性射流传播到受限外部介质中的动力学，重点关注重准直激波下游射流-环境界面处发展的不稳定性所促进的夹带和混合的影响。方法。我们利用最先进的代码 PLUTO 对重新准直射流进行了 3D 相对论流体动力学模拟。射流最初是圆锥形的，相对论性的（初始洛伦兹因子 γ = 5），相对于限制介质而言是冷且轻的，假设其压力随着距离的增加而缓慢下降。假设磁场在动态上不重要。结果。3D 模拟表明，在第一次重准直和反射激波系统之后，由于重准直引起的不稳定性和 Richtmyer-Meshkov 模式之间的相互作用，不稳定性迅速增长。反过来，不稳定性会促进强烈的混合和夹带，从而迅速导致射流减速并将其动量传播到缓慢移动、高度湍流的外部气体。我们认为这种机制可以解释低功率 FR0 喷气机的特殊性。对于具有较高功率、洛伦兹因子或磁场的流出，我们预计不稳定效应不太有效，从而使射流能够存活到千秒差距尺度，如在 FRI 中观察到的那样。
更新日期：2024-02-26
中文翻译：
FR0 射流和重准引起的不稳定性
语境。最近发现的微弱 Fanaroff-Riley 0 型 (FR0) 射电星系群被解释为经典 FRI 源低功率的延伸。它们的无线电发射似乎集中在非常紧凑的秒差距尺度核心中，任何扩展的发射都非常微弱或不存在，并且超长基线干涉测量（VLBI）观测表明，喷流在秒差距尺度上已经具有轻微或亚相对论性。基于这些观测特性，我们在此提出，FR0 的射流在秒差距尺度上受到流体动力学不稳定性的强烈减速和干扰。目标。考虑到上述情况，我们研究了低功率相对论性射流传播到受限外部介质中的动力学，重点关注重准直激波下游射流-环境界面处发展的不稳定性所促进的夹带和混合的影响。方法。我们利用最先进的代码 PLUTO 对重新准直射流进行了 3D 相对论流体动力学模拟。射流最初是圆锥形的，相对论性的（初始洛伦兹因子 γ = 5），相对于限制介质而言是冷且轻的，假设其压力随着距离的增加而缓慢下降。假设磁场在动态上不重要。结果。3D 模拟表明，在第一次重准直和反射激波系统之后，由于重准直引起的不稳定性和 Richtmyer-Meshkov 模式之间的相互作用，不稳定性迅速增长。反过来，不稳定性会促进强烈的混合和夹带，从而迅速导致射流减速并将其动量传播到缓慢移动、高度湍流的外部气体。我们认为这种机制可以解释低功率 FR0 喷气机的特殊性。对于具有较高功率、洛伦兹因子或磁场的流出，我们预计不稳定效应不太有效，从而使射流能够存活到千秒差距尺度，如在 FRI 中观察到的那样。
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