Notes from the ISM-PP conference

The thickness distribution of interstellar filaments: Evangelia Ntormousi

Filament decomposition

  • RAMSES MHD with/without ambipolar diffusion (AD) + effect of ambipolar diffusion is smoothing + AD builds very slight secondary peak
  • Q Crutcher: How strong B-fields? AD driven by turbulence (or what drives it)?
  • A: Yes, turbulence drives it. B-fields ???
  • Q MacLow: Alfven waves suppressed by AD, but magnetosonic go through & drive small flows. Oishi & MacLow: no break in power-spectrum at small scales. Consistent with small difference.
  • A: Yes, maybe smaller scale motions.
  • Q Keto: Keep B-fields coherent. But don't need to keep them coherent. How does B-field keep filaments coherent? Argues that they only last a crossing time.
  • A: magnetic tension, resists shear. Filaments would reexpand without B-fields. We don't see observed reexpansion.

Anomalous extinction: The degeneracy between dust composition and geometry 15': Peter Scicluna (ESO)

Forward scattering by dust

  • direct forward scattering favored
  • flatter extinction curve when optically thick
  • Q Keto: Wavelength dependence of scattering? Mostly absorption -> IR reemission?
  • A: absorption is treated. Heating.
  • Q Star outside scattering into LOS?
  • A: Yes, but probably not as significant

Latest GREAT results from SOFIA 15': Hans Zinnecker

SOFIA summary... 1000 hrs/year
  • Germany DLR 20% + US
GREAT results
  • M17sw C+, CO 13-12 + CII more distributed
  • G5.89 CO 11-10 outflow
  • Inverse P-Cygni at NH3 1810 GHz in G34.26+0.15
  • OH ground state absorption towards W49 + Wiesemeyer 2012 AA 542 L7
  • OD detected towards IRAS1629A
  • CND in dust with SOFIA: Requenna-Torres
  • Southern targets: NGC 3603, LMC
  • CO & C+ maps of NGC3603 (cool!)

Q Vazquez-Semadeni: What happens when plane hits turbulence? A: Counterweight keeps telescope pointed in the right place

Molecular cloud properties 40': Alvaro Hacar

Skipped

The structure of molecular clouds from 1000 AU to Orion 15': Joao Alves

Extinction Mapping (in Orion)

  • Stars at 2um are colorless

  • Bias: not sensitive to densest part of cloud + NICEST accounts for background population

  • PIPE: high temperatures in the low-column stuff

  • Barnard 68 is a bonnor ebert - 2001 result.. + TP role of B68!

  • Most BE cores are stable (Lada 2008) + pressure confined

  • CMF claim... + "same thing seen by Andre 2011"

  • Burkert Alves 2009: merging cores

  • Hacar 2013: multiple LOS velocity components along a single filament + friends-of-friends velocity components: subsonic + broad line consists of spaghetti + most filaments have no cores

  • summary of Lada, Lombardi led papers

  • Corona Australis cloud (Avles et al submitted) + PDF very lognormal with a tiny power-law excess + Kainulainen did the PDF work...

    • sometimes loglog gives insight...
    • mentioned my poster as rejecting lognormal (oops - that result changed since I wrote the abstract...)

  • NICEST future? + GNICER + do it to other galaxies?

    • nice extinction mapping in CNR of M83

  • Bally CMZ... + M83 analogy?

  • Q Herschel maps: larger dynamic range

  • A: VLT + Spitzer -> A_V ~ 100

  • Q: Features in PDF are clearly associated with individual objects. PDFs extremely useful...

  • A: Still throwing away second dimension. Justin Bieber has same PDF as Pipe Nebula. Hat tip to Chris Beaumont

  • Q Falgarone: Search for thinning of filaments? Change of spinning?

  • A: 1km/s/pc still...

  • Q Vazquez-Semadeni: Is B68 inside an HII region or not?

  • A: No. Herschel data shows tail of warm dust being blown away. Some external agent removed filament B68 was born in. External pressure is higher outside B68 than in, e.g., Taurus.

  • Q Zinnecker: B68. Structure more complex? Niel Boch? Not isothermal?

  • A: BE are isothermal; fit cores well a lot. BE still decent representation.

  • Q Klessen: Degeneracy distribution highly degenerate. Possible to reproduce from turbulence without contained sphere.

  • A: No change in B68. Long, subsonic things.

  • "Danger is applying one model to everything." -Klessen

  • "Shouldn't apply turbulence to everything." -Alves

  • Keto: Non-isothermal = factor of 2? Numerical models say doesn't strongly affect dynamics, still acts BE-like.

  • Vasquez-Semadeni: We are taking turbulence too far! But these are not stable either.

Herschel view of mol cld structure & SF: Nicola Schneider

Unscheduled talk.
  • massive stars at junctinos of filaments
  • DR21, Taurus + "striations" correlated with B-fields
  • Herschel PDF goes to higher density
  • ChamII: subtract sources, get lognormal (kinda) + "weak" slope difference in power law tails
  • compressed shells -> double-peak, broadened PDF
  • Q Joao: 2 power laws. Coincide with OB stars. Could it be unaccounted for temperature increase?
  • A:
  • Q Kainulainen Cham II: Subtracted bound cores.
  • A: A_V > 10 is core collapse
  • Q: in PDFs, are the pixels all independent, or does the PDF from a single bright source contribute to many bins?
  • A: Too many pixels

Properties of interstellar filaments observed with Herschel and 3D magnetic field structure derived from the polarization parameters observed with Planck 15': Doris Arzoumanian

Constant filament width
  • 0.1 pc
B-fields in filaments
  • geometry of field can lead to depolarization
  • Q Crutcher: Polarization fraction is much higher than observed in cores. Very minor effect.
  • A: Cores would be lower.

Magnetic Fields in Bok globules 15': Gesa Bertrang

Supercritical: B-fields play no role
  • comparison of NIR and submm poln
  • VLT/ISAAC poln
  • Q Zinnecker: IR poln vector vs B-field. Radiative acceleration vs B-field alignment?
  • Q Keto: How do you know surrounding gas is associated with core?
  • A: We don't see anything else in the images. The globules are very isolated

"Bok Globules" sounds very like "Buckyballs"

Effect of turbulence on the density statistics of molecular clouds: an observational view: J Kainulainen

Density structure dominated by turbulent motions
  • Yields a lognormal function
  • powerlaw tail from gravity
  • assume that 2D pdf can be used to yield 3D pdf
  • Can't use background stars at N kpc... + high dynamic range: 3-120x10^21 cm^-2 + 2" res
  • avoid LOS contamination by using a column cutoff
  • use 8 clouds to determine b
  • "First direct observation determination of b"
  • Dense gas mass fraction + lognormal PDF -> exponential DGMF + IRDCs have greater "fraction" of high density gas
  • COMMENT: You CAN estimate the volume density.
  • Yes, I agree, I can do it too.
  • Q: Vazquez-Semadeni. Low b suggests more solenoidal than compressive.
  • A: B-field squishes PDF.
  • A: b-parameter drives SF. B-field close second.
  • Q: How do you handle projection effects?
  • A: Not observationally, but simulations seem to show we're doing OK
  • Q Hennebelle: Equation of state. Higher adiabatic index leads to different PDF.
  • A: Should repeat experiment...
  • Q Nicola Schneider: How do you get Mach number? I get much lower Mach number. Why is there no clearly defined power-law tail?
  • A: Mach #: line width, assume temperature, -> 3D vel dispersion.
  • A: We need quantitative comparison between Herschel & extinction map. Depends on scale. We could fit with power-laws. But, looks like lognormal..
  • A: MAYBE powerlaw tails due to gravity. Maybe not! Maybe young IRDCs not dominated by gravity.

Filamentary Structures in the ISM 15: Rowan Smith

Arepo!
  • time dependent chemistry
  • molecular cloud factory
  • filamentary structures generated
  • filaments examined with DiSPERSE + can generate filaments with shallow profiles with or without B-fields
  • How do 2D filaments match 3D filaments?
  • DiSPERSE connects maxima: Cores are forced onto filaments!
  • Question for the audience: How do you fit a filament with a gaussian?
  • 3D reasonably consistent with 2D? + but major degeneracy between R-flat and p
  • Q Hennebelle: Why do you need B-fields for a shallow profile?
  • A: You don't need B-fields for shallow profiles.
  • (more conversation that was probably important but I missed it)
  • Q: filaments embedded in hot medium, not same as mol cloud filaments
  • Q: Xu - We found a filamentary wisp just like what you saw
  • Q: Adam Leroy: Why did you pick a particular number for the CO?
  • A: If my sensitivity to CO is a certain value, how much gas do I miss? Cumulative plots help avoid "threshold"
  • Q Adam: Would you make this back up by filling beam with faint CO?
  • A: Haven't looked at beam sizes yet.
  • Q Zinnecker: How do you get H2 at such low CO values? Such low extinction, shouldn't H2 go away?
  • A: Very well self-shielding

Turbulence in the ISM 30': Fabian Heitsch

Turbulent mixing -> serious resolution issues?
  • Fragmentation rather than support
  • lognormals are easy to generate
How is turbulence driven? (how does it arise?)
  • Hydrodynamic eqns -> dispersive and curly components 1. Gradients in the velocity field (shear) 2. Angular momentum conservation term: vorticity increases when gas compressed. Make something smaller -> spin up 3. Pressure / density misaligned -> turbulence. Thermal instability.
  • "Turbulence in the ISM is a consequence"
Turbulence decays
  • On a dynamical timescale? + lifetime can be extended somehow...
  • Drivers? + Expansion of shells + Global graviational instability
  • Vazquez-Semadeni simulation: gravitational collapse drives turbulence in a "core"
How is turbulence driven in the models?
  • Local: Driven / fourier forcing + Choose amplitude in fourier space (Kolmogorov or Burgers) + Uniform random phase in fourier space + transform to real + apply forcing at every timestep (at constant luminosity)
  • Large scales feed smaller scales
  • Problems: + phases should be coherent (HII region shells are coherent) + driving is volume-filling! (bow shocks!) + only makes sense if accretion timescale longer than crossing time (this is OK) + periodic box: uncertain jeans mass, virial parameter.
  • Alternative: cloud formation by colliding flows.
Support vs Fragmentation
  • assume turbulence is an extra support parameter + if true, one core should form 1 star instead of 100 (? this doesn't make sense to me) + Energy from out->in. How does this yield support? + Turbulence isotropic on small scales? Not true. Most energy on largest scales. + mildly supersonic turbulence CAN support cores... M=10 doesn't
Turbulence doesn't work, so...?
  • turbulent support is line splitting... no hair splitting
  • turbulence REALLY leads to fragmentation
  • Q Jouni Kainulainen: Should we (observers) stop measuring CO line widths and calling it turbulent energy?
  • A: Don't stop measuring. Turbulence support can't come from gravity-driven turbulence.
  • Q: Assumed anisotropic turbulence. In B-fields, turbulence could be 2D.
  • A: Yes, but need dynamically dominant B-fields
  • Q Phillip Girichidis: Detailed description of how to model turbulence in simulations. Matters whether acceleration or force.
  • A: We know what the difference is...
  • A Vazquez-Semadeni: Force -> acceleration depends on density. Only get a lognormal when you have acceleration, not force. Force -> dense regions accelerated less -> powerlaw.

Molecular cloud formation in converging flows 30': Patrick Hennebelle (SAp/CEA Saclay)

Converging flows
  • convert WNM -> CNM in "converging flows" (not shocks?)
  • alternative: bistable medium..
  • polytropic EOS -> powerlaw + 2-phase is strongly non-lognormal + but they consist of two separated lognormals
  • molecular clouds are 2-phase: HI and H2 spatially coincident
  • Mass spectrum "Higher order statistics"
  • mass-size-velocity dispersion relations "consistent with larson relation" + scatter still huge
  • Accretion of HI is adequate in early stages + maybe feedback is needed in later stages?
  • Magnetization is mass-dependent?

SF in colliding flows?

Filaments in MHD turbulence
  • don't need converging flows to get filaments
  • filaments from intersection of shocked sheets? + HD vs MHD: filaments form in HD, but they live longer in MHD
  • filament identification: inertia matrix -> eigenvectors -> filament direction
  • MHD -> greater elongation + B-field keeps filaments more coherent + B-fields weaken shocks, therefore shocks are not the formation driver of filaments
  • Q:Burkhert Coherence length scale in galaxies
  • Vazquez-Semadeni: Colliding flows are just a representation for any style of converging flow (e.g., grav instability)
  • Jin Koda: 500pc scale cloud formation, would expect GMC to follow flow. But, we find retrograde & prograde.
  • A: Why do you expect spin? Local turbulent motions... at 500 pc, local turbulence comparable to shear.
  • Q Keto: If cloud initially forms as Jeans mass by grav frag process, so converging flows isn't really the explanation.
  • A: converging flows generated by gravitational collapse are still converging flows.
  • Q Klessen: distribution of spins arise naturally (because of curvature?)

On the characteristic mass of stars in stellar clusters 15': Paul Clark

Try to take low density clouds (~100) and collapse them
  • Bate 2008 showed radiation limited fragmentation
  • heating/coolring rate strong function of density + photoelectric heating dominant
  • ISM physics in AREPO
  • vary turbulent driving (b=0.3, 0.5, 1)
  • take into account shielding
  • compressive, weak/strong G0: more small-scale filaments in low-G0 field
  • solenoidal: SF takes longer, more shreddy + solenoidal vs compressive take very different amts of time to create stars
  • difference in mass function at high mass + compressive with high G0 forms more massive stars + compressive case leaves gaps: more internal heating
  • systematically offset from Chabrier IMF: deficit of low-mass stars + not forming enough low-mass stars + Why? sinks prevent binary formation
Q: Is the solenoidal driving less mass to high density? i.e., is the density distribution still the driver of SF?
  • Q Zinnecker:
  • A: isothermal doesn't work (especially at high densities)
  • Q What about binaries?
  • A: Yes, that's it.

Photoionization of the diffuse ionised gas in an MHD supernova-driven turbulent Interstellar Medium Jo Barnes (University of St Andrews)

1st year phd
  • explaining [N II]/Halpha line ratios, etc.
  • scattered light + HII region -> dust -> us + diffuse gas -> dust -> us
  • scattered/total ~ 0.5 at midplane. at super high latitudes, can be 20% again
  • Q: Could low scale height be because SNe are not blown up together?
  • A: We use average SN rate, but arms should be enhanced

The molecular richness of diffuse ISM: a tracer of turbulent dissipation 15': Edith Falgarone

Discussing diffuse medium
  • large range in physical scale of clouds
  • 5 order of magnitude scatter in transfer rate of kinetic energy. + No trends with scale.
  • All forms of Larson relation fail at scales <0.1 pc
  • intermittency... most dissipation occurs in very small volume + dissipation occurs on filamentary structures + resolve pairs of CO-emitting regions corresponding to the dissipative high velocity shears
  • CH+ cation - known for 70 years, but poorly understood + highly endothermic formation + rapidly destroyed by H2, in ~1yr + requires extremely efficient formation rate + detected to be far too abundant
  • M82 LOS: detected in high latitude cloud! + gigantic inverse P-cygni from M82 + infalling HVC tracer?
  • also detected CH+ to another galaxy at high latitude
  • Associated with HI (same line shape)
  • highly non-equilibrium chemistry
  • "TDR" = Turbulence Dissipation Region models

Q: CH+ seen drastically enhanced in diffuse clouds. Should we expect gigantic abundance variations in dense molecular clouds too?

  • Q CH+ + B-fields?
  • Q Frequency of events?
  • A: 1% of gas

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