The origin of supermassive black holes (SMBHs) that inhabit the centers of massive galaxies is largely unconstrained 1, 2 . Remnants from supermassive stars (SMSs) with masses around 10,000 solar masses provide the ideal seed candidates, known as direct collapse black holes 3-6 . However, their very existence and formation environment in the early Universe are still under debate, with their supposed rarity further exacerbating the problem of modeling their ab-initio formation 7,8 . SMS models have shown that rapid collapse, with an infall rate above a critical value, in metal-free haloes is a requirement for the formation of a proto-stellar core which will then form an SMS 9, 10 . Using a radiation hydrodynamics simulation of early galaxy formation 11, 12 , we show the natural emergence of metal-free haloes both massive enough, and with sufficiently high infall rates, to form an SMS. We find that haloes that are exposed to both a Lyman-Werner intensity of JLW ∼ 3 J21 * and that undergo at least one period of rapid growth early in their evolution are ideal cradles for SMS formation. This rapid growth induces substantial dynamical heating 13, 14 , amplifying the existing Lyman-Werner suppression originating from a group of young galaxies 20 kiloparsecs away. Our results strongly indicate that structure formation dynamics, rather than a critical Lyman-Werner (LW) flux, may be the main driver of massive black hole formation in the early Universe. We find that massive black hole seeds may be much more common in overdense regions of the early Universe than previously considered with a comoving number density up to 10 −3 Mpc −3 .Standard cold dark matter cosmologies predict large-scale structure forms hierarchically. Smaller objects forming at early times subsequently merge and grow into larger objects. The existence of SMBHs 15, 16 with masses around 10 9 M (M , solar mass) only 800 Myr after the Big Bang indicate that there must have been an early intense convergence of mass in rare locations.We performed a suite of cosmological radiation hydrodynamics simulations (named Renaissance; see Methods) to elucidate the formation of the first generations of stars and galaxies in the Universe 11, 12 with the code ENZO 17 . It includes models for the formation of massive metal-free (Population III; Pop III) stars and subsequent metal-enriched stars not unlike ones found in the Galaxy. We follow the impact of their ionizing radiation 18 and supernova explosions on their environments as * J21is the intensity of background radiation in units of 10 −21 erg cm −2 s −1 Hz −1 sr −1 . galaxies first assemble, both of which play an important role in regulating early galaxy formation.Motivated by possible early SMS formation, we analyze the region from the Renaissance Simulation suite that is centered on the densest cosmological volume of 133.6 comoving Mpc 3 and contains 822 galaxies at its ending redshift of z = 15 (270 Myr after the Big Bang). We identify candidate SMS host haloes by searching the simulation for metal-free atomic coo...

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Context. The momentum, age and momentum injection rate (thrust) of molecular outflows are key parameters in theories of star formation. Systematic biases in these quantities as inferred from CO line observations are introduced through simplified calculations. These biases were quantified for radially expanding flows. However, recent studies suggest that the youngest outflows may be better described by jet-driven bowshocks, where additional biases are expected. Aims. We investigate quantitatively the biases in momentum, age, and thrust estimates in the case of young jet-driven molecular outflows, and propose more accurate methods of determining these quantities. Methods. We use long-duration (1500 yr) high resolution numerical simulations in concert with the standard observational methods of inferring the relevant quantities to quantify the systematic biases in these calculations introduced, in particular, by dissociation, erroneous inclusion of transverse momentum, and hidden material at cloud velocity. Jet/ambient density contrasts of 0.1-1 are considered, leading to bow speeds of 60-135 km s −1 . Results. When mass-weighted velocities are used, lifetimes are overestimated by typically an order of magnitude. The molecular thrust is then underestimated by similar amounts. Using the maximum velocity in CO profiles gives better results, if empirical corrections for inclination are applied. We propose a new method of calculating the lifetime of an outflow which dramatically improves estimates of age and molecular thrust independent of inclination. Our results are applicable to younger flows which have not broken out of their parent cloud. Conclusions. Published correlations between the molecular flow thrust and the source bolometric luminosity obtained with the maximum CO velocity method should remain valid. However, dissociation at the bow head may cause the observable thrust to underestimate the total flow thrust by a factor of up to 2-4, depending on the bow propagation speed and the magnetic field strength. Detailed evaluation of this effect would greatly help to better constrain the efficiency of the ejection mechanism in protostars.

Abstract. We present a model of a pulsar wind nebula evolving inside its associated supernova remnant. The model uses a hydrodynamics code to simulate the evolution of this system when the pulsar has a high velocity. The simulation distinguishes four different stages of pulsar wind nebula evolution: the supersonic expansion stage, the reverse shock interaction stage, the subsonic expansion stage and ultimately the bow shock stage. The simulation bears out that, due to the high velocity of the pulsar, the position of the pulsar is off-centered with respect to its pulsar wind nebula, after the passage of the reverse shock. Subsequently the pulsar wind nebula expands subsonically until the event of the bow shock formation, when the motion of the pulsar becomes supersonic. The bow shock formation event occurs at roughly half the crossing time, when the pulsar is positioned at 0.677 times the radius of the supernova remnant blastwave, in complete agreement with analytical predictions. The crossing time is defined by the age of the supernova remnant when the pulsar overtakes the blastwave bounding the supernova remnant.The results of the model are applied to three supernova remnants: N157B, G327.1-1.1 and W44. We argue that the head of the pulsar wind nebula, containing the active pulsar, inside the first two systems is not bounded by a bow shock. However, in the case of W44 we argue for a scenario in which the pulsar wind nebula is bounded by a bow shock, due to the supersonic motion of the pulsar.

Abstract. We use numerical simulations to examine the mass-velocity and intensity-velocity relations in the CO J = 2−1 and H 2 S(1)1−0 lines for jet-driven molecular outflows. Contrary to previous expectations, we find that the mass-velocity relation for the swept-up gas is a single power-law, with a shallow slope −1.5 and no break to a steeper slope at high velocities. An analytic bowshock model with no post-shock mixing is shown to reproduce this behaviour very well. We show that molecular dissociation and the temperature dependence of the line emissivity are both critical in defining the shape of the line profiles at velocities above ∼20 km s −1 . In particular, the simulated CO J = 2−1 intensity-velocity relation does show a break in slope, even though the underlying mass distribution does not. These predicted CO profiles are found to compare remarkably well with observations of molecular outflows, both in terms of the slopes at low and high velocities and in terms of the range of break velocities at which the change in slope occurs. Shallower slopes are predicted at high velocity in higher excitation lines, such as H 2 S(1)1−0. This work indicates that, in jet-driven outflows, the CO J = 2−1 intensity profile reflects the slope of the underlying massvelocity distribution only at velocities ≤20 km s −1 , and that higher temperature tracers are required to probe the mass distribution at higher speed.