pith. sign in

arxiv: 1906.10979 · v1 · pith:ITH2GZIDnew · submitted 2019-06-26 · 🌌 astro-ph.GA

The Physical and chemical structure of Sagittarius B2 -- IV. Converging filaments in the high-mass cluster forming region Sgr B2(N)

A. Schw\"orer , \'A. S\'anchez-Monge , P. Schilke , T. M\"oller , A. Ginsburg , F. Meng , A. Schmiedeke , H. S. P. M\"uller
show 2 more authors
D. Lis S. -L. Qin
This is my paper

Pith reviewed 2026-05-25 15:50 UTC · model grok-4.3

classification 🌌 astro-ph.GA
keywords Sagittarius B2(N)filamentsaccretionstar formationdense coresALMAhigh-mass starsSgr B2
0
0 comments X

The pith

Eight filaments converge on Sgr B2(N) carrying a total accretion rate of 0.16 solar masses per year.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

ALMA spectral line observations map eight filaments about 0.1 pc long that converge on the dense central hub of Sgr B2(N). Velocity gradients of 20-100 km s^{-1} pc^{-1} along the filaments are used to derive mass accretion rates of 0.05 solar masses per year per filament. Some filaments contain dense cores where stars already account for half the core mass. The combination of high central density, ongoing accretion, and embedded star formation leads the authors to conclude that the region may grow into a super stellar cluster through a damp merger of these cores.

Core claim

The paper reports eight filaments converging to the central hub in Sgr B2(N) and extending for about 0.1 pc. Stacking of molecular lines reveals velocity gradients of 20-100 km s^{-1} pc^{-1} along the filaments, interpreted as accretion flows that produce individual mass accretion rates of 0.05 M_odot yr^{-1} and a total rate of 0.16 M_odot yr^{-1}. Filaments harbor dense cores with stellar content on the order of 50 percent of the core mass. The authors conclude that these cores may merge in the center while still forming stellar clusters in a damp merger, and that the high density and mass of the central region together with the converging filaments suggest Sgr B2(N) may evolve into a超级星团

What carries the argument

Converging filaments whose velocity gradients are interpreted as accretion flows, measured through a new line-stacking tool that averages multiple transitions of each molecular species to raise signal-to-noise and reduce blending.

If this is right

  • The total mass accretion rate onto the central hub reaches 0.16 solar masses per year.
  • Dense cores within the filaments already contain stellar mass equal to about half the core mass.
  • The cores may merge at the center in a damp merger while they are still forming stellar clusters.
  • The combination of high central density, high accretion, and embedded star formation gives Sgr B2(N) the potential to evolve into a super stellar cluster.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Continued accretion at the observed rates would allow the central mass to grow much faster than in lower-mass star-forming regions.
  • Filamentary convergence on this scale may be a common but previously unresolved feature of other high-mass cluster-forming regions.
  • The damp-merger process could alter the timing and efficiency of star formation within the final cluster.

Load-bearing premise

The velocity gradients measured along the filaments represent net inward accretion rather than rotation, outflows, or line-of-sight projection effects.

What would settle it

A measurement of three-dimensional gas motions or direct mass flux showing net inward rates substantially below 0.05 solar masses per year per filament would undermine the accretion interpretation.

Figures

Figures reproduced from arXiv: 1906.10979 by A. Ginsburg, \'A. S\'anchez-Monge, A. Schmiedeke, A. Schw\"orer, D. Lis, F. Meng, H. S. P. M\"uller, P. Schilke, S. -L. Qin, T. M\"oller.

Figure 1
Figure 1. Figure 1: Three-color composite image of Sgr B2(N). The green image shows the continuum emission at 242 GHz (Paper II), the red image corresponds to the molecular species CH3OCHO, and the blue image to C2H5CN. The center, which is dominated by the continuum and CH3OCHO emission, appears yellow. The images of the molecular species have been constructed from stacked cubes (see more details in Section 3 and Appendix A)… view at source ↗
Figure 2
Figure 2. Figure 2: a) Map of the ALMA 242 GHz continuum emission of Sgr B2(N). The white dots indicate the position of the continuum sources reported in Paper II. The green dashed lines trace the path of the filaments identified in the molecular line data (see Section 3.1), while gray dashed lines trace tentative elongated structures not clearly confirmed in the molecular emission maps. The light-gray circles indicate H ii r… view at source ↗
Figure 4
Figure 4. Figure 4: Position velocity cut along filament F08 in CH3OCHO and H2CS. The emission to the left corresponds to the filament close to the central hub. The emission at about 0.25 pc and 0.4 pc corresponds to the cores A15 and A08, A19. The white dashed line corresponds to a velocity gradient of ∼16 km s−1 pc−1 , consistent with the mean velocity gradient of F08 (see [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗
Figure 3
Figure 3. Figure 3: Peak velocity map of H2CS (bottom-panel) and CH3OCHO (top￾panel, using 143 stacked lines, see Appendix A). The emission below 10 σ and the center are masked out. The filaments and position of dense cores are marked with black dashed lines and white dots, respectively. along the filaments and by fitting Gaussian functions to the spec￾tra. In Appendix B we show the pv-cuts for different molecular species. Mo… view at source ↗
Figure 5
Figure 5. Figure 5: Overview picture of the velocity gradients (top panel), velocity linewidths (middle panel) and mass accretion rates (bottom panel) along all filaments and subfilaments (indicated by roman numbers) in Sgr B2(N), see Sections 3.1 and 3.2. Additional velocity components in filament F06 are marked as 6a and 6b. The gray, green, blue, and orange symbols correspond to the molecules CH3OCHO, CH3OCH3, CH3OH and 13… view at source ↗
Figure 6
Figure 6. Figure 6: Stellar mass fraction (see Sect. 3.4) of the dense cores. Cores are grouped by their host filaments [PITH_FULL_IMAGE:figures/full_fig_p006_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Top panel: Total mass of the dense cores against their distance to the main hub. Bottom panel: Stellar mass fraction of the dense cores against their distance to the main hub. The gray dashed line indicates the mean stellar mass fraction of of 50%. Section 3.1, we show that some filaments appear fragmented and harbor embedded cores, which raises the question of how stable the filaments are. The mass-to-len… view at source ↗
Figure 8
Figure 8. Figure 8: Filaments in Sgr B2(N) colored by their mean velocity gradient as derived for the molecular species CH3OCHO, CH3OCH3, CH3OH and 13CH3OH. The velocity gradient ranges from −50 km s−1 pc−1 (blue), corresponding to filaments located in front, to +50 km s−1 pc−1 (red), corresponding to filaments located in the back. The gray contours indicating 242 GHz continuum emission at a level of 1.2 Jy beam−1 . The white… view at source ↗
read the original abstract

We have used an unbiased, spectral line-survey that covers the frequency range from 211 to 275 GHz and was obtained with ALMA (angular resolution of 0.4 arcsec) to study the small-scale structure of the dense gas in Sagittarius B2 (north). Eight filaments are found converging to the central hub and extending for about 0.1 pc. The spatial structure, together with the presence of the massive central region, suggest that these filaments may be associated with accretion processes. In order to derive the kinematic properties of the gas in a chemically line-rich source like Sgr B2(N), we have developed a new tool that stacks all the detected transition lines of any molecular species. This permits to increase the signal-to-noise ratio of our observations and average out line blending effects, which are a common problem in line-rich regions. We derive velocity gradients along the filaments of about 20-100 km s$^{-1}$ pc$^{-1}$, which are 10-100 times larger than those typically found on larger scales (1 pc) in other star-forming regions. The mass accretion rates of individual filaments are about 0.05 M$_\odot$ yr$^{-1}$, which result in a total accretion rate of 0.16 M$_\odot$ yr$^{-1}$. Some filaments harbor dense cores that are likely forming stars and stellar clusters. The stellar content of these dense cores is on the order of 50% of the total mass. We conclude that the cores may merge in the center when already forming stellar clusters but still containing a significant amount of gas, resulting in a "damp" merger. The high density and mass of the central region, combined with the presence of converging filaments with high mass, high accretion rates and embedded dense cores already forming stars, suggest that Sgr B2(N) may have the potential to evolve into a super stellar cluster.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 1 minor

Summary. The manuscript reports ALMA 211-275 GHz spectral-line observations (0.4 arcsec resolution) of Sgr B2(N). Eight filaments ~0.1 pc long are identified converging on a central hub. A new line-stacking tool is introduced to boost S/N and mitigate blending in this chemically rich source. Velocity gradients of 20-100 km s^{-1} pc^{-1} are measured along the filaments and interpreted as accretion flows, yielding individual mass-accretion rates of ~0.05 M_⊙ yr^{-1} (total 0.16 M_⊙ yr^{-1}). Embedded dense cores already forming stars are noted, and the authors conclude that Sgr B2(N) has the potential to evolve into a super stellar cluster via “damp” mergers.

Significance. If the kinematic interpretation is substantiated, the work supplies quantitative evidence for unusually high small-scale accretion rates (10-100 times larger than typical 1-pc gradients) in a high-mass cluster-forming region. The line-stacking technique is a reusable methodological contribution for line-rich sources. The suggestion that cores already forming stellar clusters can merge while still gas-rich adds a concrete scenario to cluster-assembly models.

major comments (2)
  1. [Abstract / kinematic analysis] Abstract / kinematic analysis: The velocity gradients of 20-100 km s^{-1} pc^{-1} are taken to represent net inward accretion at 0.05 M_⊙ yr^{-1} per filament. No position-velocity diagram modeling, inclination constraints, or explicit comparison to rotation, outflow, or projection-effect alternatives is described; this assumption directly underpins the total accretion rate and the super-cluster formation claim.
  2. [Abstract / mass-accretion calculation] Abstract / mass-accretion calculation: The conversion from observed gradients to mass-accretion rates requires assumptions about density, velocity coherence length, and geometry. The manuscript does not detail how these quantities are obtained from the stacked cubes or how uncertainties (including possible line-identification biases) are propagated.
minor comments (1)
  1. [Abstract] The abstract states that “some filaments harbor dense cores” but does not quantify how many cores, their individual masses, or the stellar-mass fraction beyond the order-of-magnitude statement “on the order of 50 %.”

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments. We address each major point below and indicate where revisions have been made to the manuscript.

read point-by-point responses

  1. Referee: [Abstract / kinematic analysis] The velocity gradients of 20-100 km s^{-1} pc^{-1} are taken to represent net inward accretion at 0.05 M_⊙ yr^{-1} per filament. No position-velocity diagram modeling, inclination constraints, or explicit comparison to rotation, outflow, or projection-effect alternatives is described; this assumption directly underpins the total accretion rate and the super-cluster formation claim.

    Authors: We acknowledge that the original manuscript does not present position-velocity diagram modeling, inclination constraints, or an explicit comparison to alternative interpretations. In the revised version we have added a new subsection discussing these alternatives. The converging spatial morphology toward the central hub, the absence of clear bipolar velocity signatures in the stacked data, and the fact that the measured gradients are 10-100 times larger than typical 1-pc scale values are used to argue that accretion is the most plausible interpretation. Full radiative-transfer PV modeling is not performed because of the chemical complexity and limited spatial resolution; we instead provide a qualitative assessment of projection effects and note that deprojected rates would only increase the inferred accretion. A short discussion of possible inclination angles and their effect on the quoted rates has also been included. revision: partial

  2. Referee: [Abstract / mass-accretion calculation] The conversion from observed gradients to mass-accretion rates requires assumptions about density, velocity coherence length, and geometry. The manuscript does not detail how these quantities are obtained from the stacked cubes or how uncertainties (including possible line-identification biases) are propagated.

    Authors: We agree that the original text is insufficiently explicit on these points. The revised manuscript expands the methods section to specify that volume density is derived from the 1.3 mm continuum assuming standard dust temperature and opacity values, that the velocity coherence length is taken as the observed filament width measured in the stacked maps, and that a cylindrical geometry is assumed with the observed length and width. An appendix has been added that describes the uncertainty propagation, including Monte Carlo realizations of the linear gradient fits and a quantitative assessment of line-identification biases obtained by repeating the stacking with different molecular-species subsets. These additions directly address the referee’s concern about line-rich source biases. revision: yes

Circularity Check

0 steps flagged

No significant circularity; quantities derived directly from spectral data

full rationale

The paper computes velocity gradients (20-100 km s^{-1} pc^{-1}) and mass accretion rates (~0.05 M_⊙ yr^{-1} per filament) by applying a new stacking procedure to ALMA spectral cubes covering 211-275 GHz. These steps extract kinematic properties from observed line emission without any fitted parameter that is then renamed as a prediction, without self-definitional equations, and without load-bearing self-citations that close the derivation. The suggestion that filaments represent accretion flows is an interpretive inference from morphology and gradients rather than a mathematical reduction to the input data itself. The overall chain remains self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The analysis rests on standard radio-astronomy conversions from observed brightness and velocity to mass and accretion rate; no new free parameters or entities are introduced beyond those implicit in ALMA calibration and the adopted distance to the galactic center.

axioms (2)
  • domain assumption The distance to Sgr B2 is 8.5 kpc and is used to convert angular scales and velocities to physical units.
    Standard assumption for galactic-center sources; invoked when reporting 0.1 pc lengths and km/s/pc gradients.
  • domain assumption Molecular line emission traces the bulk gas density and velocity without significant optical-depth or excitation biases after stacking.
    Required for the stacking tool to yield reliable velocity gradients and mass estimates.

pith-pipeline@v0.9.0 · 5949 in / 1512 out tokens · 26203 ms · 2026-05-25T15:50:46.552961+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

47 extracted references · 47 canonical work pages · 3 internal anchors

  1. [1]

    Andr \'e , P., Men'shchikov, A., Bontemps, S., et al.\ 2010, , 518, L102

    work page 2010

  2. [2]

    Arzoumanian, D., Andr \'e , P., Didelon, P., et al.\ 2011, , 529, L6

    work page 2011

  3. [3]

    Belloche, A., M \"u ller, H. S. P., Menten, K. M., Schilke, P., & Comito, C.\ 2013, , 559, A47

    work page 2013

  4. [4]

    Beuther, H., Bihr, S., Rugel, M., et al.\ 2016, , 595, A32

    work page 2016

  5. [5]

    Bressert, E., Ginsburg, A., Bally, J., et al.\ 2012, , 758, L28

    work page 2012

  6. [6]

    G., Peters, T., Mac Low, M.-M., et al.\ 2014, , 781, L36

    De Pree, C. G., Peters, T., Mac Low, M.-M., et al.\ 2014, , 781, L36

    work page 2014

  7. [7]

    Eker, Z., Bak s , V., Bilir, S., et al.\ 2018, , 479, 5491

    work page 2018

  8. [8]

    G.\ 2012, , 542, A77

    Fischera, J., & Martin, P. G.\ 2012, , 542, A77

    work page 2012

  9. [9]

    S.\ 2015, , 67, 59

    Fujii, M. S.\ 2015, , 67, 59

    work page 2015

  10. [10]

    S., & Portegies Zwart, S.\ 2016, , 817, 4

    Fujii, M. S., & Portegies Zwart, S.\ 2016, , 817, 4

    work page 2016

  11. [11]

    Ginsburg, A., Henkel, C., Ao, Y., et al.\ 2016, , 586, A50

    work page 2016

  12. [12]

    Ginsburg, A., Bally, J., Barnes, A., et al.\ 2018, , 853, 171

    work page 2018

  13. [13]

    F., Lis, D

    Goldsmith, P. F., Lis, D. C., Hills, R., & Lasenby, J.\ 1990, , 350, 186

    work page 1990

  14. [14]

    Gravity Collaboration, Abuter, R., Amorim, A., et al.\ 2018, , 615, L15

    work page 2018

  15. [15]

    Hacar, A., Tafalla, M., Forbrich, J., et al.\ 2018, , 610, A77

    work page 2018

  16. [16]

    On the Origin of Multiple Populations During Massive Star Cluster Formation

    Howard, C. S., Pudritz, R. E., Harris, W. E., & Sills, A.\ 2018, arXiv:1808.07081

    work page internal anchor Pith review Pith/arXiv arXiv 2018

  17. [17]

    L., Mauersberger, R., et al.\ 1995, , 294, 667

    H\"uttemeister, S., Wilson, T. L., Mauersberger, R., et al.\ 1995, , 294, 667

    work page 1995

  18. [18]

    F., Galv \'a n-Madrid, R., Maud, L

    Izquierdo, A. F., Galv \'a n-Madrid, R., Maud, L. T., et al.\ 2018, , 478, 2505

    work page 2018

  19. [19]

    C., Bourke, T

    Kirk, H., Myers, P. C., Bourke, T. L., et al.\ 2013, , 766, 115

    work page 2013

  20. [20]

    Kroupa, P.\ 2001, , 322, 231

    work page 2001

  21. [21]

    K., Vlemmings, W., Conway, J., & Mart \' -Vidal, I.\ 2015, , 446, 3502

    Lindroos, L., Knudsen, K. K., Vlemmings, W., Conway, J., & Mart \' -Vidal, I.\ 2015, , 446, 3502

    work page 2015

  22. [22]

    N., Kruijssen, J

    Longmore, S. N., Kruijssen, J. M. D., Bastian, N., et al.\ 2014, Protostars and Planets VI, 291

    work page 2014

  23. [23]

    A., \"O berg, K

    Loomis, R. A., \"O berg, K. I., Andrews, S. M., et al.\ 2018, , 155, 182

    work page 2018

  24. [24]

    M.\ 2010, , 517, A66

    L \'o pez-Sepulcre, A., Cesaroni, R., & Walmsley, C. M.\ 2010, , 517, A66

    work page 2010

  25. [25]

    B., et al.\ 2018, , 855, 9

    Lu, X., Zhang, Q., Liu, H. B., et al.\ 2018, , 855, 9

    work page 2018

  26. [26]

    A., Kirk, J

    Marsh, K. A., Kirk, J. M., Andr \'e , P., et al.\ 2016, , 459, 342

    work page 2016

  27. [27]

    T., Hoare, M

    Maud, L. T., Hoare, M. G., Galv \'a n-Madrid, R., et al.\ 2017, , 467, L120

    work page 2017

  28. [28]

    Mills, E. A. C., Ginsburg, A., Clements, A. R., et al.\ 2018, , 869, L14

    work page 2018

  29. [29]

    M \"o ller, T., Endres, C., & Schilke, P.\ 2017, , 598, A7

    work page 2017

  30. [30]

    Morris, M., & Serabyn, E.\ 1996, , 34, 645

    work page 1996

  31. [31]

    Ossenkopf, V., & Henning, T.\ 1994, , 291, 943

    work page 1994

  32. [32]

    Ostriker, J.\ 1964, , 140, 1529

    work page 1964

  33. [33]

    M., et al.\ 2011, , 743, L32

    Palau, A., Fuente, A., Girart, J. M., et al.\ 2011, , 743, L32

    work page 2011

  34. [34]

    Palau, A., Walsh, C., S \'a nchez-Monge, \'A ., et al.\ 2017, , 467, 2723

    work page 2017

  35. [35]

    Palmeirim, P., Andr \'e , P., Kirk, J., et al.\ 2013, , 550, A38

    work page 2013

  36. [36]

    A., Duarte-Cabral, A., et al.\ 2013, , 555, A112

    Peretto, N., Fuller, G. A., Duarte-Cabral, A., et al.\ 2013, , 555, A112

    work page 2013

  37. [37]

    Pols, S., Schw \"o rer, A., Schilke, P., et al.\ 2018, , 614, A123 (Paper III)

    work page 2018

  38. [38]

    F., McMillan, S

    Portegies Zwart, S. F., McMillan, S. L. W., & Gieles, M.\ 2010, , 48, 431

    work page 2010

  39. [39]

    J., Menten, K

    Reid, M. J., Menten, K. M., Brunthaler, A., et al.\ 2014, , 783, 130

    work page 2014

  40. [40]

    S \'a nchez-Monge, \'A ., L \'o pez-Sepulcre, A., Cesaroni, R., et al.\ 2013, , 557, A94

    work page 2013

  41. [41]

    T., Cesaroni, R., et al.\ 2014, , 569, A11

    S \'a nchez-Monge, \'A ., Beltr \'a n, M. T., Cesaroni, R., et al.\ 2014, , 569, A11

    work page 2014

  42. [42]

    S \'a nchez-Monge, \'A ., Schilke, P., Schmiedeke, A., et al.\ 2017, , 604, A6 (Paper II)

    work page 2017

  43. [43]

    Schmiedeke, A., Schilke, P., M \"o ller, T., et al.\ 2016, , 588, A143 (Paper I)

    work page 2016

  44. [44]

    Suri, S., Schilke, P., & S \'a nchez-Monge, \'A .\ 2017, arXiv:1712.02434

    work page internal anchor Pith review Pith/arXiv arXiv 2017

  45. [45]

    The CARMA-NRO Orion Survey: The filamentary structure as seen in C$^{18}$O emission

    Suri, S. T., Sanchez-Monge, A., Schilke, P., et al.\ 2019, arXiv:1901.00176

    work page internal anchor Pith review Pith/arXiv arXiv 2019

  46. [46]

    u ttemeister, S.\ 2009, Tools of Radio Astronomy, by Thomas L. Wilson; Kristen Rohlfs and Susanne H \

    Wilson, T. L., Rohlfs, K., & H \"u ttemeister, S.\ 2009, Tools of Radio Astronomy, by Thomas L. Wilson; Kristen Rohlfs and Susanne H \"u ttemeister. ISBN 978-3-540-85121-9. Published by Springer-Verlag, Berlin, Germany, 2009.,

    work page 2009

  47. [47]

    Wu, Y., Wei, Y., Zhao, M., et al.\ 2004, , 426, 503

    work page 2004