{"id":"e90ffdc5-ff4a-447b-9b77-6f3d2acfce5b","arxiv_id":"1908.03225","paper_version":1,"verdict":"CONDITIONAL","confidence":"HIGH","novelty_score":4.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":5,"one_line_summary":"Protostellar jet simulations show jets drive local subsonic turbulence and enhance it with higher Mach number, rotation, toroidal magnetic fields, clumpy environments, and interacting jets, but they cannot sustain large-scale supersonic turbulence.","lead":"This paper uses 2D and 3D computer simulations to test whether jets from young stars stir up turbulence in the gas around them. It finds that jets create local, mostly slow (subsonic) motion, but they are not strong enough to drive the large-scale, fast (supersonic) turbulence seen in molecular clouds.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The velocity PDF conflates the coherent jet beam with turbulent fluctuations, so the paper's quantitative efficiency rankings and its central turbulence claim are not established without a beam-masked or Reynolds-decomposed analysis.","rationale":"I identify the velocity-PDF diagnostic as the most load-bearing weakness because the central claim is explicitly about turbulence, yet the only quantitative turbulence measure conflates the jet's ordered supersonic flow with random fluctuations. This is an internal-validity problem that affects every efficiency comparison in the paper, whereas the reader's scale concern, while valid, is an external-validity limitation that the authors themselves acknowledge in Section 3: 'our analysis is constrained to the box size which is about 10^4 AUs and is smaller.' I agree that the small box undermines the large-scale extrapolation, but even within the simulated volume the 'turbulence' is not cleanly identified. The transient-run result (HD10t) strengthens my concern: the disappearance of supersonic PDF features when the jet is switched off suggests the supersonic component is the injected beam, not self-sustained turbulence. I recommend CONDITIONAL rather than REJECT because the paper is explicitly a case study, the qualitative morphology (density maps, instabilities) does show some local mixing, and the negative large-scale claim agrees with earlier literature. However, the paper should be accepted only after reanalysis with a turbulence diagnostic that separates mean flow from fluctuations, or at least after masking the jet beam. If that reanalysis changes the efficiency rankings or the supersonic fractions, the paper's headline conclusions would need substantial revision.","tokens_in":13820,"tokens_out":6569,"duration_ms":66274,"concrete_test":"Recompute the velocity PDF and the supersonic fraction for runs HD10, HD25, HD10Vphi, and HD3D at t=500 and t=1000 after excluding all cells with cylindrical radius r < 2 r_j (the jet beam) or, more rigorously, after subtracting the local mean velocity field and computing the PDF of the fluctuating velocity component. If the masked supersonic fraction drops below roughly 1% and the ordering of runs changes, then the reported efficiency conclusions are an artifact of including the jet's coherent bulk flow rather than a measure of turbulence.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The paper's quantitative measure of 'turbulence' is the velocity PDF defined by Eq. 5, built from vp = sqrt(vr^2+vz^2) over all cells with nonzero velocity. This mixes the coherent, continuously injected jet beam with genuine turbulent fluctuations. Because the jets are supersonic (Mach 10-25), cells inside the beam have vp > c_s by construction; therefore the 'supersonic fraction' shown in Figs. 7, 15, 20, and 24 is contaminated by the beam's ordered kinetic energy, not necessarily by turbulent eddies. The transient run HD10t (Section 3, Fig. 6) is diagnostic: after the jet is switched off, the supersonic PDF vanishes within a few sound-crossing times. That is the expected signature of the injected beam disappearing, not of a decaying turbulent cascade. As a result, the claimed efficiency rankings (higher Mach number, rotation, toroidal magnetic field, clumpy environment, interacting jets, and 3D geometry) are rankings of the total velocity distribution, not of turbulence. The central claim that jets 'can transfer the turbulence' is therefore not quantitatively supported by the presented diagnostic, and the negative claim about supersonic turbulence relies on a measure that may be dominated by the bulk jet flow.","agreement_with_reader":"disagree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports a parameter study of two-dimensional axisymmetric and one three-dimensional hydrodynamic/magnetohydrodynamic simulations of protostellar jets interacting with a uniform or clumpy ambient medium, using the PLUTO 4.2 code. The models vary the jet Mach number (1, 3, 10, 25), the jet velocity field (radial and rotational components), the background magnetic field geometry, the presence of dense clumps, and the number of interacting jets. The principal diagnostic is the probability density function of the poloidal velocity magnitude (Eq. 5), from which the fraction of supersonic gas and its time evolution are measured. The central conclusion is that stellar jets can transfer turbulent motions to their immediate surroundings, with higher efficiency for higher jet Mach number, jet rotation, toroidal background magnetic fields, clumpy environments, jet-jet interactions, and three-dimensional geometry, but that jets are not sufficient drivers of large-scale supersonic turbulence in molecular clouds.","tokens_in":14134,"tokens_out":6549,"duration_ms":67139,"significance":"The question addressed is important for star-formation feedback, and the manuscript usefully expands the parameter space covered by earlier studies such as Banerjee et al. (2007). Its strengths include a systematic set of models in a well-tested code, a transient-jet experiment designed to measure the decay of the induced motions, and explicit admissions of the limitations imposed by the box size and by the lower resolution of the 3D run. If the central result is accepted, it strengthens the emerging picture that protostellar outflows are local turbulence drivers rather than cloud-scale supersonic drivers. However, because the velocity PDF used as the turbulence measure includes the coherent jet beam and no decomposition into mean and fluctuating components is made, the quantitative efficiency rankings are not yet established by the presented analysis; the paper's significance therefore depends on a re-analysis described below.","major_comments":[{"comment":"Equation (5) defines the velocity PDF using vp = sqrt(vr^2+vz^2) over all cells with nonzero velocity, so it counts the ordered, continuously injected jet beam together with any turbulent fluctuations. For the supersonic runs (M=10 and 25), cells inside the jet beam have vp > c_s by construction, so the 'supersonic fraction' plotted in Figures 7, 15, 20, and 24 is contaminated by the beam's coherent kinetic energy. The transient run HD10t (Figure 6) illustrates this: once the jet is switched off, the supersonic component disappears within a few hundred code units, which is exactly what one expects when the beam is removed, not necessarily evidence about the decay of a turbulent cascade. The efficiency rankings listed in the abstract and Section 4 are therefore rankings of the total velocity distribution, not of turbulence. I request a Reynolds decomposition or a masking of the jet-beam region (for example, cells with r < r_j and/or cells connected to the injection boundary) and the PDF of the fluctuating component, together with a velocity power spectrum, before the central claim of 'transferring turbulence' can be assessed quantitatively.","section":"2.4, 3, Figs. 6, 7, 15, 20, 24"},{"comment":"The term 'turbulence' is used for what the velocity PDF and visual inspection of maps show, but a one-point PDF of the total velocity does not establish a turbulent cascade or distinguish random motions from coherent shear, and it cannot provide a scale-dependent measure of driving efficiency. No velocity power spectrum, structure function, or vorticity map is presented anywhere in the paper. The qualitative statements about 'more fluctuations and random motions' in Sections 3.1-3.5 are therefore not backed by a quantitative turbulence metric. I recommend adding at least one scale-resolved statistic (for example, a kinetic-energy power spectrum, a longitudinal structure function, or a vorticity map) to justify the term 'turbulence' and the efficiency rankings.","section":"3, 3.1-3.5"},{"comment":"No resolution or convergence study is reported for the axisymmetric runs, and the single 3D run uses a lower resolution than the 2D reference run (Section 3.5). The authors themselves note that the lower resolution implies higher numerical diffusivity and numerical heating that increase the entropy and the amount of fluctuations in HD3D. Since the paper's quantitative conclusions depend on PDF tails, supersonic fractions, and their decay times, a convergence check is load-bearing; without it, one cannot separate physical turbulence driving from numerical diffusion, and the 3D-versus-2D comparison is ambiguous. I ask for at least one higher-resolution 3D run (or two resolutions of the reference run with the same solver and domain) and a brief comparison of the PDF and supersonic fraction as a function of resolution.","section":"2.2, 3.5"},{"comment":"The concluding statement that jets are 'not sufficient drivers of the large-scale supersonic turbulence in molecular clouds' goes beyond the simulated domain, which is 60 x 100 r_j (about 10^4 AU) and which the authors themselves describe as smaller than the scale of interest, with the ambient gas still affected by jet propagation at the end of the runs (Section 3). The simulations contain no cloud-scale driving or large-scale velocity structure, so they can only constrain turbulence within a small star-forming core environment, not the maintenance of cloud-scale supersonic turbulence. The abstract and Section 4 should be reframed to state the negative result for the box scale, or supplemented with a quantitative argument connecting the box-size results to cloud scales (for example, comparing the turbulent energy injection rate with the dissipation rate on cloud scales).","section":"3, 4"}],"minor_comments":[{"comment":"Section 3.3 refers to runs HD-M10cl and HD-M10pcl, while Table 1 lists the same runs as HD-Qcl and HD-Ecl; please make the run labels consistent throughout the manuscript.","section":"3.3, Table 1"},{"comment":"There are several typographical errors that should be corrected: 'grcm' for 'g cm^-3', 'solenodality' for 'solenoidality', 'magnetite' for 'magnetic' in Section 3.2, and 'peresented' and 'studeid' in Section 4.","section":"2.3, 3.2, 4"},{"comment":"The 'entropy' shown in Figures 3, 13, and 23 is never defined in Section 2; please specify the entropy diagnostic (for example, p/rho^gamma or a normalized version) so that the reader can interpret the maps.","section":"3, Figs. 3, 13, 23"},{"comment":"The actual grid resolution of the 3D run HD3D is not reported in the text or in Table 1; since the authors state that the 3D run uses a lower resolution, the numerical setup is incomplete without the specific number of cells.","section":"3.5"}],"recommendation":"major_revision","confidential_remarks":"The manuscript is a plausible parameter study, but the principal diagnostic issue (beam contamination of the velocity PDF) is central to the quantitative claims. I am not recommending rejection because the requested re-analysis (masked or Reynolds-decomposed PDF, a resolution check, and scale-restricted claims) is feasible from the existing simulations and the qualitative conclusions are consistent with prior work. No concerns about citation practice or novelty beyond the need to engage more directly with Banerjee et al. (2007) on the origin of the quantitative differences."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Plain English: this paper is a numerical case study of protostellar jets driving turbulence. The genuinely useful part is the breadth: Mach number, rotation, magnetic field geometry, clumpy environment, interacting jets, and one 3D run, all with the same code and setup. That is more coverage than Banerjee et al. 2007 or Cunningham et al. 2009. The authors are honest that they are confirming prior conclusions, not overturning them. The runs look like standard PLUTO, the setup is sensible, and the qualitative behavior (bow shock, shear, entrainment, decay after switching off) matches expectation. I believe them when they say jets drive local, mostly subsonic motions and are not large-scale supersonic drivers.\n\nBut I would not trust the efficiency rankings yet. The quantitative measure is the velocity PDF over every cell with nonzero velocity. That includes the continuously injected jet beam, whose vp is supersonic by construction. The transient run is the giveaway: after the jet is switched off, the supersonic part of the PDF disappears within a few sound-crossing times. That is the beam vanishing, not a turbulence cascade decaying. So the claim that higher Mach number, rotation, toroidal fields, clumps, interacting jets, or 3D geometry increase 'turbulence' is really about the total velocity distribution, with beam and shocked gas mixed in. A proper analysis would mask the beam or Reynolds-decompose and look at the velocity dispersion of the ambient gas, or use a structure function or power spectrum. Without that, the efficiency results are suggestive, not established.\n\nThere are lesser issues. No resolution study, so numerical diffusivity could be doing some of the work; the 3D run is actually lower resolution and the authors admit it has higher numerical viscosity, which muddies the 3D comparison. The box is ~10^4 AU, so the claim about 'large-scale' turbulence in molecular clouds is an extrapolation, not something the simulation directly tests. The authors do flag the box-size limitation in Section 3, which is to their credit. The citation pattern looks fine: Banerjee et al. and Cunningham et al. are properly credited, and the paper explicitly frames itself as confirmation. No obvious circularity.\n\nBottom line: the qualitative conclusion is probably correct and consistent with the literature. The quantitative efficiency story is not yet supported. This is a decent candidate for a revised paper, not a desk reject, but it needs a better turbulence diagnostic and at least one convergence run before I would rely on it.","headline":"A competent but incremental parameter scan of jet-driven turbulence; the qualitative conclusion is probably right, but the main diagnostic does not separate the jet beam from actual turbulent fluctuations.","tokens_in":14611,"tokens_out":2132,"would_cite":false,"duration_ms":24355,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Stellar jets can transfer turbulence to neighboring regions but are not sufficient drivers of the large-scale supersonic turbulence in molecular clouds, these simulations conclude.","keywords":["stellar jets","molecular clouds","supersonic turbulence","protostellar outflows","magnetohydrodynamics","numerical simulation","velocity probability density function","star formation"],"falsifier":"A numerical experiment that switches a jet off at late time and measures the mass fraction of supersonic gas afterward: the paper reports that no supersonic features survive after switch-off, so any run that sustains a significant supersonic fraction for many crossing times after the jet dies would refute the claim. Observationally, mapping a star-forming region where outflows have recently ceased and finding cloud-scale supersonic line widths uncorrelated with outflow power would likewise contradict the insufficiency conclusion.","tokens_in":13622,"feed_emoji":"🌌","tokens_out":8482,"duration_ms":80033,"temperature":0.7,"pith_summary":"This paper asks whether the jets launched by young stars can be the engine of the supersonic turbulence seen in molecular clouds. The authors run a battery of two- and three-dimensional hydrodynamics and magnetohydrodynamics simulations that vary the jet's Mach number, its velocity structure, the background magnetic field, the cloud environment, and the number of interacting jets. They find that jets do inject random, turbulent motions into the surrounding gas, and that the injection is stronger for faster jets, rotating jets, magnetized environments, clumpy environments, and multiple interacting jets. However, most of the entrained gas stays subsonic or transonic, and once the jet stops driving, the supersonic fluctuations decay quickly. The conclusion is that jets are effective local stirring agents but cannot sustain the large-scale supersonic turbulence of molecular clouds, which matters because that turbulence is thought to control how and where stars form.","feed_headline":"Jets stir gas but cannot drive cloud-scale supersonic turbulence","feed_subtitle":"Faster, rotating, magnetized and clumpy jets stir more, but the induced motions stay mostly subsonic and fade fast.","key_machinery":"The central measurement is the velocity probability density function (PDF), defined by binning the poloidal velocity $v_p = \\sqrt{v_r^2 + v_z^2}$ over all cells excited by the jet and normalizing by the total number of cells. Comparing the PDF with the local sound speed allows the authors to split the entrained gas into subsonic and supersonic populations and to track how the high-velocity tail decays after the jet engine is switched off. This PDF sits at the center of a deliberately broad parameter study: hydrodynamic and ideal-magnetohydrodynamic runs on a $60 \\times 100$ jet-radius grid, with Mach numbers 1, 3, 10 and 25; runs with added radial or rotational jet velocity; runs with radial, vertical, toroidal, and poloidal background fields; runs with a quiescent or explosive dense clump in the ambient gas; runs with two or three interacting jets; and one 3D counterpart of the reference run. The comparison set is what lets the paper claim that the efficiency, not just the possibility, of jet-driven turbulence depends on these parameters.","core_discovery":"On the paper's own terms, the central discovery is a confirmation with expanded parameter coverage: protostellar jets transfer turbulence to their immediate neighborhood, but they are not sufficient drivers of large-scale supersonic turbulence in molecular clouds. The evidence is the velocity probability density function of the entrained gas: in every run the bulk of the excited motions lies at subsonic velocities, with only a small fraction supersonic, and that fraction decreases with time. A transient-jet run shows that when the driving stops, the supersonic part disappears almost immediately. The efficiency of the local driving does vary: higher Mach number, jet rotation, a toroidal background magnetic field, a clumpy ambient medium, and interacting jets all raise the amount and longevity of the fluctuations, and a 3D run produces more and faster entrained gas than the axisymmetric runs, though the paper attributes part of that enhancement to the lower resolution and higher numerical diffusivity of the 3D setup.","pith_inferences":["Beyond the paper, if jets are only local drivers, then the global supersonic line widths of molecular clouds have to be sustained by processes the small box cannot see, such as large-scale gravitational contraction, converging flows, or supernova remnants, and jet feedback would set the local velocity dispersion near outflow cavities rather than the cloud's global turbulence.","Beyond the paper, a testable extension would be a resolution-convergence study: the paper's 3D run mixes the physical growth of non-axisymmetric shear modes with numerical diffusivity from a lower resolution, so a matched-resolution 2D versus 3D comparison would isolate how much of the extra 3D fluctuations is real.","Beyond the paper, the interacting-jet simulations suggest a saturation effect: adding more jets raises the transonic gas but suppresses supersonic tails, so one could predict that in a dense cluster the outflow-driven velocity dispersion approaches a ceiling set by jet separation and cooling, a relation observable as a flattening of outflow power versus local line width."],"forward_implications":["In the immediate vicinity of a protostellar outflow, jets can keep the gas stirred with subsonic and transonic velocity fluctuations for as long as the jet keeps running.","A single transient protostellar jet cannot maintain supersonic turbulence: once the jet is switched off, the supersonic fraction of the entrained gas drops away, so outflow feedback must be continuous or constantly replenished by new outflows to matter.","The most powerful outflows, with higher Mach numbers, are the ones most likely to leave a lasting turbulent imprint on their surroundings, since their pdfs stay broader and their supersonic fractions survive longer.","Outflow interactions in clustered star formation mainly add transonic and subsonic fluctuations; after jets collide, supersonic motions are suppressed, so cluster-scale multiple outflows do not by themselves solve the cloud-scale supersonic driving problem.","In magnetized clouds, the toroidal field geometry is the one that most increases the entrained gas energy and the supersonic fraction, meaning the orientation of the background field relative to the outflow matters for feedback efficiency."],"supporting_citations":[{"why":"Supplies the earlier conclusion the paper confirms, the velocity-PDF method, and the slower-jet comparison that the present Mach-number study revisits.","marker":"Banerjee et al. 2007"},{"why":"Establishes the review context of turbulence drivers in molecular clouds and defines why supersonic turbulence constrains star formation.","marker":"Mac Low & Klessen 2004"},{"why":"First study that proposed stellar outflows can drive turbulent motions, the starting point the paper tests.","marker":"Mac Low 2000"},{"why":"Shows outflow cavities re-energize turbulent motions only when turbulence already exists, the background for the local-driving claim.","marker":"Cunningham et al. 2009"},{"why":"Supplies the grid-based code that integrates the hydrodynamic and ideal MHD equations for all runs.","marker":"Mignone et al. 2007"},{"why":"Observational evidence that outflows can transfer enough energy to account for cloud turbulent energy, motivating the efficiency question.","marker":"Bally et al. 1996"},{"why":"Another observational estimate of outflow energy input into clouds, used to frame the sufficiency question.","marker":"Quillen et al. 2005"},{"why":"Motivates the clumpy ambient medium by showing interstellar gas is structured, which the clump runs model.","marker":"Krumholz & Tan 2007"},{"why":"Places interacting outflows in the cluster-formation context and supports the multi-jet runs.","marker":"Federrath et al. 2014"}],"fun_headline_variants":["Jets stir gas locally, but can't drive cloud turbulence","Jets churn nearby gas, not cloud-scale turbulence","Stellar jets are local stirrers, not cloud turbulence engines","Jets agitate gas, but large-scale turbulence stays subsonic"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that a simulation box of about $10^4$ AU and simulated times of up to a few thousand time units (roughly $10^5$ to $10^6$ yr) captures the processes that decide whether jets can drive cloud-scale turbulence, even though the cloud itself is orders of magnitude larger and longer-lived.","fun_headline_variants_meta":{"raw":{"variants":["Jets stir gas locally, but can't drive cloud turbulence","Jets churn nearby gas, not cloud-scale turbulence","Stellar jets are local stirrers, not cloud turbulence engines","Jets agitate gas, but large-scale turbulence stays subsonic"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.00053,"raw_usage":{"total_tokens":2602,"prompt_tokens":1039,"completion_tokens":1563,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":655,"completion_tokens_details":{"reasoning_tokens":1490}},"tokens_in":655,"tokens_out":1563,"duration_ms":12544,"temperature":1.0,"reasoning_tokens":1490,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-14T14:20:19.841443+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A numerical experiment that switches a jet off at late time and measures the mass fraction of supersonic gas afterward: the paper reports that no supersonic features survive after switch-off, so any run that sustains a significant supersonic fraction for many crossing times after the jet dies would refute the claim. Observationally, mapping a star-forming region where outflows have recently ceased and finding cloud-scale supersonic line widths uncorrelated with outflow power would likewise contradict the insufficiency conclusion.","supporting_citations":[{"cited_title":"S., & Fendt, C","cited_arxiv_id":null,"evidence_quote":"Supplies the earlier conclusion the paper confirms, the velocity-PDF method, and the slower-jet comparison that the present Mach-number study revisits."},{"cited_title":"2007, ApJS, 170, 228","cited_arxiv_id":null,"evidence_quote":"Supplies the grid-based code that integrates the hydrodynamic and ideal MHD equations for all runs."},{"cited_title":"1996, ApJ, 473, 921","cited_arxiv_id":null,"evidence_quote":"Observational evidence that outflows can transfer enough energy to account for cloud turbulent energy, motivating the efficiency question."}],"review_version":1}