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         title="Permalink to Notes from the ISM-PP conference">Notes from the ISM-PP conference</a></h2>
 
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    <abbr class="published" title="2013-10-21T00:00:00-06:00">
      2013/10/21
    </abbr>
    <address class="vcard author">
      By <a class="url fn" href="https://keflavich.github.io/blog/author/adam-ginsburg.html">Adam Ginsburg</a>
    </address>
  </footer><!-- /.post-info -->
  <div class="entry-content">
    <div class="section" id="the-thickness-distribution-of-interstellar-filaments-evangelia-ntormousi">
<h2>The thickness distribution of interstellar filaments: Evangelia Ntormousi</h2>
<p>Filament decomposition</p>
<blockquote>
<ul class="simple">
<li>RAMSES MHD with/without ambipolar diffusion (AD)
+ effect of ambipolar diffusion is smoothing
+ AD builds <em>very slight</em> secondary peak</li>
<li>Q Crutcher:  How strong B-fields?  AD driven by turbulence (or what drives it)?</li>
<li>A: Yes, turbulence drives it.  B-fields ???</li>
<li>Q MacLow: Alfven waves suppressed by AD, but magnetosonic go through &amp; drive small flows.
Oishi &amp; MacLow: no break in power-spectrum at small scales. Consistent with
small difference.</li>
<li>A: Yes, maybe smaller scale motions.</li>
<li>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.</li>
<li>A: magnetic tension, resists shear.  Filaments would reexpand without
B-fields.  We don't see observed reexpansion.</li>
</ul>
</blockquote>
</div>
<div class="section" id="anomalous-extinction-the-degeneracy-between-dust-composition-and-geometry-15-peter-scicluna-eso">
<h2>Anomalous extinction: The degeneracy between dust composition and geometry 15': Peter Scicluna (ESO)</h2>
<p>Forward scattering by dust</p>
<blockquote>
<ul class="simple">
<li>direct forward scattering favored</li>
<li>flatter extinction curve when optically thick</li>
<li>Q Keto: Wavelength dependence of scattering?  Mostly absorption -&gt; IR reemission?</li>
<li>A: absorption is treated.  Heating.</li>
<li>Q Star outside scattering into LOS?</li>
<li>A: Yes, but probably not <em>as</em> significant</li>
</ul>
</blockquote>
</div>
<div class="section" id="latest-great-results-from-sofia-15-hans-zinnecker">
<h2>Latest GREAT results from SOFIA 15': Hans Zinnecker</h2>
<dl class="docutils">
<dt>SOFIA summary... 1000 hrs/year</dt>
<dd><ul class="first last simple">
<li>Germany DLR 20% + US</li>
</ul>
</dd>
<dt>GREAT results</dt>
<dd><ul class="first simple">
<li>M17sw C+, CO 13-12
+ CII more distributed</li>
<li>G5.89 CO 11-10 outflow</li>
<li>Inverse P-Cygni at NH3 1810 GHz in G34.26+0.15</li>
<li>OH ground state absorption towards W49
+ Wiesemeyer 2012 AA 542 L7</li>
<li>OD detected towards IRAS1629A</li>
<li>CND in dust with SOFIA: Requenna-Torres</li>
<li>Southern targets: NGC 3603, LMC</li>
<li>CO &amp; C+ maps of NGC3603 (cool!)</li>
</ul>
<p class="last">Q Vazquez-Semadeni: What happens when plane hits turbulence?
A: Counterweight keeps telescope pointed in the right place</p>
</dd>
</dl>
</div>
<div class="section" id="molecular-cloud-properties-40-alvaro-hacar">
<h2>Molecular cloud properties 40': Alvaro Hacar</h2>
<p>Skipped</p>
</div>
<div class="section" id="the-structure-of-molecular-clouds-from-1000-au-to-orion-15-joao-alves">
<h2>The structure of molecular clouds from 1000 AU to Orion 15': Joao Alves</h2>
<dl class="docutils">
<dt>Extinction Mapping (in Orion)</dt>
<dd><ul class="first last">
<li><p class="first">Stars at 2um are colorless</p>
</li>
<li><p class="first">Bias: not sensitive to densest part of cloud
+ NICEST accounts for background population</p>
</li>
<li><p class="first">PIPE: high temperatures in the low-column stuff</p>
</li>
<li><p class="first">Barnard 68 is a bonnor ebert - 2001 result..
+ TP role of B68!</p>
</li>
<li><p class="first">Most BE cores are stable (Lada 2008)
+ pressure confined</p>
</li>
<li><p class="first">CMF claim...
+ &quot;same thing seen by Andre 2011&quot;</p>
</li>
<li><p class="first">Burkert Alves 2009: merging cores</p>
</li>
<li><p class="first">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</p>
</li>
<li><p class="first">summary of Lada, Lombardi led papers</p>
</li>
<li><p class="first">Corona Australis cloud (Avles et al submitted)
+ PDF very lognormal with a tiny power-law excess
+ Kainulainen did the PDF work...</p>
<blockquote>
<ul class="simple">
<li>sometimes loglog gives insight...</li>
</ul>
</blockquote>
<ul class="simple">
<li>mentioned my poster as rejecting lognormal (oops - that result changed since I wrote the abstract...)</li>
</ul>
</li>
<li><p class="first">NICEST future?
+ GNICER
+ do it to other galaxies?</p>
<blockquote>
<ul class="simple">
<li>nice extinction mapping in CNR of M83</li>
</ul>
</blockquote>
</li>
<li><p class="first">Bally CMZ...
+ M83 analogy?</p>
</li>
<li><p class="first">Q Herschel maps: larger dynamic range</p>
</li>
<li><p class="first">A: VLT + Spitzer -&gt; A_V ~ 100</p>
</li>
<li><p class="first">Q: Features in PDF are clearly associated with individual objects.  PDFs extremely useful...</p>
</li>
<li><p class="first">A: Still throwing away second dimension.  Justin Bieber has same PDF as Pipe Nebula.  Hat tip to Chris Beaumont</p>
</li>
<li><p class="first">Q Falgarone: Search for thinning of filaments?  Change of spinning?</p>
</li>
<li><p class="first">A: 1km/s/pc still...</p>
</li>
<li><p class="first">Q Vazquez-Semadeni: Is B68 inside an HII region or not?</p>
</li>
<li><p class="first">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.</p>
</li>
<li><p class="first">Q Zinnecker: B68.  Structure more complex?  Niel Boch?  Not isothermal?</p>
</li>
<li><p class="first">A: BE are isothermal; fit cores well a lot.  BE still decent representation.</p>
</li>
<li><p class="first">Q Klessen: Degeneracy distribution highly degenerate.  Possible to reproduce
from turbulence without contained sphere.</p>
</li>
<li><p class="first">A: No change in B68.  Long, subsonic things.</p>
</li>
<li><p class="first">&quot;Danger is applying one model to everything.&quot; -Klessen</p>
</li>
<li><p class="first">&quot;Shouldn't apply turbulence to everything.&quot; -Alves</p>
</li>
<li><p class="first">Keto: Non-isothermal = factor of 2?  Numerical models say doesn't strongly
affect dynamics, still acts BE-like.</p>
</li>
<li><p class="first">Vasquez-Semadeni: We are taking turbulence too far!  But these are not
stable either.</p>
</li>
</ul>
</dd>
</dl>
</div>
<div class="section" id="herschel-view-of-mol-cld-structure-sf-nicola-schneider">
<h2>Herschel view of mol cld structure &amp; SF: Nicola Schneider</h2>
<dl class="docutils">
<dt>Unscheduled talk.</dt>
<dd><ul class="first last simple">
<li>massive stars at junctinos of filaments</li>
<li>DR21, Taurus
+ &quot;striations&quot; correlated with B-fields</li>
<li>Herschel PDF goes to higher density</li>
<li>ChamII: subtract sources, get lognormal (kinda)
+ &quot;weak&quot; slope difference in power law tails</li>
<li>compressed shells -&gt; double-peak, broadened PDF</li>
<li>Q Joao: 2 power laws.  Coincide with OB stars.  Could it be unaccounted for temperature increase?</li>
<li>A:</li>
<li>Q Kainulainen Cham II: Subtracted bound cores.</li>
<li>A: A_V &gt; 10 is core collapse</li>
<li>Q: in PDFs, are the pixels all independent, or does the PDF from a single bright source contribute to many bins?</li>
<li>A: Too many pixels</li>
</ul>
</dd>
</dl>
</div>
<div class="section" id="properties-of-interstellar-filaments-observed-with-herschel-and-3d-magnetic-field-structure-derived-from-the-polarization-parameters-observed-with-planck-15-doris-arzoumanian">
<h2>Properties of interstellar filaments observed with Herschel and 3D magnetic field structure derived from the polarization parameters observed with Planck 15': Doris Arzoumanian</h2>
<dl class="docutils">
<dt>Constant filament width</dt>
<dd><ul class="first last simple">
<li>0.1 pc</li>
</ul>
</dd>
<dt>B-fields in filaments</dt>
<dd><ul class="first last simple">
<li>geometry of field can lead to depolarization</li>
<li>Q Crutcher: Polarization fraction is much higher than observed in cores.  Very minor effect.</li>
<li>A: Cores would be lower.</li>
</ul>
</dd>
</dl>
</div>
<div class="section" id="magnetic-fields-in-bok-globules-15-gesa-bertrang">
<h2>Magnetic Fields in Bok globules 15': Gesa Bertrang</h2>
<dl class="docutils">
<dt>Supercritical: B-fields play no role</dt>
<dd><ul class="first last simple">
<li>comparison of NIR and submm poln</li>
<li>VLT/ISAAC poln</li>
<li>Q Zinnecker: IR poln vector vs B-field.  Radiative acceleration vs B-field alignment?</li>
<li>Q Keto: How do you know surrounding gas is associated with core?</li>
<li>A: We don't see anything else in the images.  The globules are very isolated</li>
</ul>
</dd>
</dl>
<p>&quot;Bok Globules&quot; sounds very like &quot;Buckyballs&quot;</p>
</div>
<div class="section" id="effect-of-turbulence-on-the-density-statistics-of-molecular-clouds-an-observational-view-j-kainulainen">
<h2>Effect of turbulence on the density statistics of molecular clouds: an observational view: J Kainulainen</h2>
<dl class="docutils">
<dt>Density structure dominated by turbulent motions</dt>
<dd><ul class="first last simple">
<li>Yields a lognormal function</li>
<li>powerlaw tail from gravity</li>
<li>assume that 2D pdf can be used to yield 3D pdf</li>
<li>Can't use background stars at N kpc...
+ high dynamic range: 3-120x10^21 cm^-2
+ 2&quot; res</li>
<li>avoid LOS contamination by using a column cutoff</li>
<li>use 8 clouds to determine b</li>
<li>&quot;First direct observation determination of b&quot;</li>
<li>Dense gas mass fraction
+ lognormal PDF -&gt; exponential DGMF
+ IRDCs have greater &quot;fraction&quot; of high density gas</li>
<li>COMMENT: You CAN estimate the volume density.</li>
<li>Yes, I agree, I can do it too.</li>
<li>Q: Vazquez-Semadeni.  Low b suggests more solenoidal than compressive.</li>
<li>A: B-field squishes PDF.</li>
<li>A: b-parameter drives SF.  B-field close second.</li>
<li>Q: How do you handle projection effects?</li>
<li>A: Not observationally, but simulations seem to show we're doing OK</li>
<li>Q Hennebelle: Equation of state.  Higher adiabatic index leads to different PDF.</li>
<li>A: Should repeat experiment...</li>
<li>Q Nicola Schneider: How do you get Mach number?  I get much lower Mach
number.  Why is there no clearly defined power-law tail?</li>
<li>A: Mach #: line width, assume temperature, -&gt; 3D vel dispersion.</li>
<li>A: We need quantitative comparison between Herschel &amp; extinction map.
Depends on scale.  We could fit with power-laws.  But, looks like lognormal..</li>
<li>A: MAYBE powerlaw tails due to gravity.  Maybe not!  Maybe young IRDCs not
dominated by gravity.</li>
</ul>
</dd>
</dl>
</div>
<div class="section" id="filamentary-structures-in-the-ism-15-rowan-smith">
<h2>Filamentary Structures in the ISM 15: Rowan Smith</h2>
<dl class="docutils">
<dt>Arepo!</dt>
<dd><ul class="first last simple">
<li>time dependent chemistry</li>
<li>molecular cloud factory</li>
<li>filamentary structures generated</li>
<li>filaments examined with DiSPERSE
+ can generate filaments with shallow profiles with or without B-fields</li>
<li>How do 2D filaments match 3D filaments?</li>
<li>DiSPERSE connects maxima: Cores are forced onto filaments!</li>
<li>Question for the audience: How do you fit a filament with a gaussian?</li>
<li>3D reasonably consistent with 2D?
+ but major degeneracy between R-flat and p</li>
<li>Q Hennebelle: Why do you need B-fields for a shallow profile?</li>
<li>A: You <em>don't</em> need B-fields for shallow profiles.</li>
<li>(more conversation that was probably important but I missed it)</li>
<li>Q: filaments embedded in hot medium, not same as mol cloud filaments</li>
<li>Q: Xu - We found a filamentary wisp just like what you saw</li>
<li>Q: Adam Leroy: Why did you pick a particular number for the CO?</li>
<li>A: <em>If</em> my sensitivity to CO is a certain value, how much gas do I miss?
Cumulative plots help avoid &quot;threshold&quot;</li>
<li>Q Adam: Would you make this back up by filling beam with faint CO?</li>
<li>A: Haven't looked at beam sizes yet.</li>
<li>Q Zinnecker: How do you get H2 at such low CO values?  Such low extinction, shouldn't H2 go away?</li>
<li>A: Very well self-shielding</li>
</ul>
</dd>
</dl>
</div>
<div class="section" id="turbulence-in-the-ism-30-fabian-heitsch">
<h2>Turbulence in the ISM 30': Fabian Heitsch</h2>
<dl class="docutils">
<dt>Turbulent mixing -&gt; serious resolution issues?</dt>
<dd><ul class="first last simple">
<li>Fragmentation rather than support</li>
<li>lognormals are easy to generate</li>
</ul>
</dd>
<dt>How is turbulence driven? (how does it arise?)</dt>
<dd><ul class="first last simple">
<li>Hydrodynamic eqns -&gt; dispersive and curly components
1. Gradients in the velocity field (shear)
2. Angular momentum conservation term: vorticity increases when gas compressed.  Make something smaller -&gt; spin up
3. Pressure / density misaligned -&gt; turbulence.  Thermal instability.</li>
<li>&quot;Turbulence in the ISM is a <em>consequence</em>&quot;</li>
</ul>
</dd>
<dt>Turbulence decays</dt>
<dd><ul class="first last simple">
<li>On a dynamical timescale?
+ lifetime can be extended somehow...</li>
<li>Drivers?
+ Expansion of shells
+ Global graviational instability</li>
<li>Vazquez-Semadeni simulation: gravitational collapse drives turbulence in a &quot;core&quot;</li>
</ul>
</dd>
<dt>How is turbulence driven in the models?</dt>
<dd><ul class="first last simple">
<li>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)</li>
<li>Large scales feed smaller scales</li>
<li>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.</li>
<li>Alternative: cloud formation by colliding flows.</li>
</ul>
</dd>
<dt>Support vs Fragmentation</dt>
<dd><ul class="first last simple">
<li>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-&gt;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</li>
</ul>
</dd>
<dt>Turbulence doesn't work, so...?</dt>
<dd><ul class="first last simple">
<li>turbulent support is line splitting... no hair splitting</li>
<li>turbulence REALLY leads to fragmentation</li>
<li>Q Jouni Kainulainen: Should we (observers) stop measuring CO line widths and
calling it turbulent energy?</li>
<li>A: Don't stop measuring.  Turbulence support can't come from gravity-driven turbulence.</li>
<li>Q: Assumed anisotropic turbulence.    In B-fields, turbulence could be 2D.</li>
<li>A: Yes, but need dynamically dominant B-fields</li>
<li>Q Phillip Girichidis: Detailed description of how to model turbulence in
simulations.  Matters whether <em>acceleration</em> or <em>force</em>.</li>
<li>A: We know what the difference is...</li>
<li>A Vazquez-Semadeni: Force -&gt; acceleration depends on density.  Only get a
lognormal when you have acceleration, <em>not</em> force.  Force -&gt; dense regions
accelerated less -&gt; powerlaw.</li>
</ul>
</dd>
</dl>
</div>
<div class="section" id="molecular-cloud-formation-in-converging-flows-30-patrick-hennebelle-sap-cea-saclay">
<h2>Molecular cloud formation in converging flows 30': Patrick Hennebelle (SAp/CEA Saclay)</h2>
<dl class="docutils">
<dt>Converging flows</dt>
<dd><ul class="first last simple">
<li>convert WNM -&gt; CNM in &quot;converging flows&quot; (not shocks?)</li>
<li>alternative: bistable medium..</li>
<li>polytropic EOS -&gt; powerlaw
+ 2-phase is strongly non-lognormal
+ but they consist of two separated lognormals</li>
<li>molecular clouds are 2-phase: HI and H2 spatially coincident</li>
<li>Mass spectrum &quot;Higher order statistics&quot;</li>
<li>mass-size-velocity dispersion relations &quot;consistent with larson relation&quot;
+ scatter still huge</li>
<li>Accretion of HI is adequate in early stages
+ maybe feedback is needed in later stages?</li>
<li>Magnetization is mass-dependent?</li>
</ul>
</dd>
</dl>
<p>SF in colliding flows?</p>
<dl class="docutils">
<dt>Filaments in MHD turbulence</dt>
<dd><ul class="first last simple">
<li>don't need converging flows to get filaments</li>
<li>filaments from intersection of shocked sheets?
+ HD vs MHD: filaments form in HD, but they live longer in MHD</li>
<li>filament identification: inertia matrix -&gt; eigenvectors -&gt; filament direction</li>
<li>MHD -&gt; greater elongation
+ B-field keeps filaments more coherent
+ B-fields weaken shocks, therefore shocks are not the formation driver of filaments</li>
<li>Q:Burkhert Coherence length scale in galaxies</li>
<li>Vazquez-Semadeni: Colliding flows are just a representation for any style of converging flow (e.g., grav instability)</li>
<li>Jin Koda: 500pc scale cloud formation, would expect GMC to follow flow.  But, we find retrograde &amp; prograde.</li>
<li>A: Why do you expect spin?  Local turbulent motions...  at 500 pc, local turbulence comparable to shear.</li>
<li>Q Keto: If cloud initially forms as Jeans mass by grav frag process, so converging flows isn't really the explanation.</li>
<li>A: converging flows generated by gravitational collapse are still converging flows.</li>
<li>Q Klessen: distribution of spins arise naturally (because of curvature?)</li>
</ul>
</dd>
</dl>
</div>
<div class="section" id="on-the-characteristic-mass-of-stars-in-stellar-clusters-15-paul-clark">
<h2>On the characteristic mass of stars in stellar clusters 15': Paul Clark</h2>
<dl class="docutils">
<dt>Try to take low density clouds (~100) and collapse them</dt>
<dd><ul class="first last simple">
<li>Bate 2008 showed radiation limited fragmentation</li>
<li>heating/coolring rate strong function of density
+ photoelectric heating dominant</li>
<li>ISM physics in AREPO</li>
<li>vary turbulent driving (b=0.3, 0.5, 1)</li>
<li>take into account shielding</li>
<li>compressive, weak/strong G0: more small-scale filaments in low-G0 field</li>
<li>solenoidal: SF takes longer, more shreddy
+ solenoidal vs compressive take very different amts of time to create stars</li>
<li>difference in mass function at high mass
+ compressive with high G0 forms more massive stars
+ compressive case leaves gaps: more internal heating</li>
<li>systematically offset from Chabrier IMF: deficit of low-mass stars
+ not forming enough low-mass stars
+ Why? sinks prevent binary formation</li>
</ul>
</dd>
<dt>Q: Is the solenoidal driving less mass to high density?  i.e., is the density distribution still the driver of SF?</dt>
<dd><ul class="first last simple">
<li>Q Zinnecker:</li>
<li>A: isothermal doesn't work (especially at high densities)</li>
<li>Q What about binaries?</li>
<li>A: Yes, that's it.</li>
</ul>
</dd>
</dl>
</div>
<div class="section" id="photoionization-of-the-diffuse-ionised-gas-in-an-mhd-supernova-driven-turbulent-interstellar-medium-jo-barnes-university-of-st-andrews">
<h2>Photoionization of the diffuse ionised gas in an MHD supernova-driven turbulent Interstellar Medium Jo Barnes (University of St Andrews)</h2>
<dl class="docutils">
<dt>1st year phd</dt>
<dd><ul class="first last simple">
<li>explaining [N II]/Halpha line ratios, etc.</li>
<li>scattered light
+ HII region -&gt; dust -&gt; us
+ diffuse gas -&gt; dust -&gt; us</li>
<li>scattered/total ~ 0.5 at midplane.  at super high latitudes, can be 20% again</li>
<li>Q: Could low scale height be because SNe are not blown up together?</li>
<li>A: We use average SN rate, but arms should be enhanced</li>
</ul>
</dd>
</dl>
</div>
<div class="section" id="the-molecular-richness-of-diffuse-ism-a-tracer-of-turbulent-dissipation-15-edith-falgarone">
<h2>The molecular richness of diffuse ISM: a tracer of turbulent dissipation 15': Edith Falgarone</h2>
<dl class="docutils">
<dt>Discussing diffuse medium</dt>
<dd><ul class="first last simple">
<li>large range in physical scale of clouds</li>
<li>5 order of magnitude scatter in transfer rate of kinetic energy.
+ No trends with scale.</li>
<li>All forms of Larson relation fail at scales &lt;0.1 pc</li>
<li>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</li>
<li>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</li>
<li>M82 LOS: detected in high latitude cloud!
+ gigantic inverse P-cygni from M82
+ infalling HVC tracer?</li>
<li>also detected CH+ to another galaxy at high latitude</li>
<li>Associated with HI (same line shape)</li>
<li>highly non-equilibrium chemistry</li>
<li>&quot;TDR&quot; = Turbulence Dissipation Region models</li>
</ul>
</dd>
</dl>
<p>Q: CH+ seen drastically enhanced in diffuse clouds.  Should we expect gigantic abundance variations in dense molecular clouds too?</p>
<blockquote>
<ul class="simple">
<li>Q CH+ + B-fields?</li>
<li>Q Frequency of events?</li>
<li>A: 1% of gas</li>
</ul>
</blockquote>
</div>

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