Adam Ginsburg's blog

• General Discussion (Day 1)

  Large-scale:

  • Q: incomprehensible.

  • A Kim: turbulent nuclear rings are found... if angular momentum large... ring

    can be very close to center

  • Q: Best guess for age of molecular torus in Herschel data?
  • A Kim: Simulations for external galaxies, didn't run for our Galaxy.
  • Q Morris: Asymmetry in distribution of molecular gas. No asymmetry in stellar distribution. Implies m=1 mode / asymmetry in CMZ. Has the asymmetry been worked into models?
  • A Kim: ????

  [ I can barely understand this discussion ]

  • Q: X1/X2; Kim sees mainly X2, but dust may be X1. Does the ring form at transition?
  • A: No, rarely forms at transition radius.
  • Q: Weak bar case, lindlbad resonance is where x1/x2 change. But with strong bar, that approximation doesn't work.
  • A: Don't know if X2 orbits exist outside of inner lindblad resonance
  • Q: Dust lane on x1, ring on x2
  • Q: What is the filling factor of molecular gas in the inner region?
  • A Bally: 10%-30% very dense, with "soup" of low-density molecular gas. H3+ indicates ionized molecular gas present.
  • Q Which phase dominates?
  • A Bally: Megakelvin plasma must fill the volume (X-ray measurements), thermal free-free emission, plenty of ionized gas. 30-60% ionized gas filling factor
  • A Farhad: controversial what filling factor of mol gas is. Oka, Geballe: 1%
  • A Geballe: 1% along one line of sight, towards Sgr A*
  • A John: Area filling factor is 1, volume filling factor is open question
  • Q Farhad: Twisted ring. Problem with this idea. Where is Sgr B2 w.r.t. X2 orbits?

  • A Bally: Sgr B2 is in the x2 orbit. Not at apocenter yet, Sgr B2 not at

    tangent point, still moving out.

  • Q Crocker: Radius for ring?
  • A Bally: 140, 150 pc? At least a degree
  • A Longmore: I'll show tomorrow inner ~100 pc

  Smaller Scale

  • Q Longmore: What is the connection between the 100pc and 1pc ring?
  • A Ott: 20 km/s cloud is connected to the CND. May be where molecular gas is exchanged
  • A Requen-Torres: John showed work from Rodriguez-Fernandez
  • A Bally: Streamers connected to CND. Why's it called a disk? It's a ring!
  • Q: What's the origin of the cirmnuclear disk?
  • A Bally: Matter that's losing angular momentum. Dynamic friction, magnetic stresses, etc.
  • A Lacy: Suggestion of why gas drives into center....
  • A Kim: Collision between molecular clouds, B-fields too
  • A Morris: Room for controversy. Transient feature because shear timescale is short, but the CND seems to be in some sort of dynamical equilibrium. Is it long-lived, in which stabilities create clumps that are sheared out, or if this is just an infalling cloud that has recently circularized.
  • Requen-Torres: Inclination, two different areas (disks?) inclined to each other
  • Q Any evidence for ring evaporation?

  [ most interesting point of the conference so far ]

  • Q: Gas dynamics in Galactic center complicated... creates bias related to BH mass. How worried should we be about BH mass measurements using gas?
  • A Lacy: If we see gas preferentially at apocenter, we will underestimate BH mass

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• Thibault Paumard: Regularized OSIRIS 3D spectroscopy at the Circumnuclear Disk ionization front

  

  CND

  • clumpy, but how clumpy?
  • self-gravitating, n~10^8?
  • examine small-scale structures in CND + clump-size power spectrum

  Method description

  • noisy image: difficult to fit
  • smoothing bad: spectral resolution varies across OSIRIS field + really, really ugly spectral resolution map
  • Smoothing "during fitting"
  • GOAL: maps of velocity, width, density + similar to deconvolution
  • decomposed into linewidth, centroid, and amplitude + High, narrow peaks

  Result

  • HII / H2 decorrelated + BrG traces low-H2 regions
  • thin filaments with narrow line widths

  Questions

  • Q Farhad: Any asymmetric velocity profiles towards positions, i.e. outflow signatures?
  • A: No asymmetry noted.
  • Q: How unique is the solution?
  • A: If S/N good, fairly unique

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• Friday Talks

  Doug Finkbeiner - the Fermi Bubbles

  Discovered bubbles

  • many explanations... e- e+, protons, agn, sf
  • "evidence for" but not "discovery of" a jet

  9:30-9:50 am Mateusz Ruszkowski (USA): The Fermi Bubbles: Gamma-ray, Microwave, and Polarization Signatures of Leptonic AGN Jets (15 + 5 minutes)

  Using simulation to fit to the fermi bubble

  • "double jet" much better fit than single

  9:50-10:10 am Brian Lacki (USA): Sturm und Drang: The Turbulent, Magnetic Tempest in the Galactic Center (15 + 5 minutes)

  Pressure balance

  • equipartition in MW
  • 100x in CMZ
  • 1000x in M82, 1e6x in Arp 220 + yet still equipartition
  • turbulence dissipates in a flow-crossing time + turbulent plasma drives b-field toward equipart
  • Q Steve: What is your outer scale? Most of molecular gas at radii of 100pc...
  • A: radii go outward... thickness of disk in 3D turbulence sets your upper scale.

  11:15-11:40 am Timothy Linden (USA): Dark Matter in the Galactic Center (20 + 5 minutes)

  Dark matter cross-section

  • significant only as a nonthermal energy source
  • dark matter is the source of electrons in the nonthermal filaments (Linden 2011)
  • Q Gillessen: Does NFW fit Fermi?
  • A: Yes, but requires adiabatic contraction and almost doesn't fit
  • Q: Baganoff: What is the dark matter energy injection?
  • A: 10^36 erg/s over 1 degree in 1-10 GeV electrons
  • Q: Wardle: predict sharp spectral cutoff below 100 GHz.
  • A: MHD makes filament, dark matter feeds electrons into it. Need to find sharp turnover
  • Q Farhad: Only a few nonthermal filaments have X-ray counterparts. Maybe a result of interaction.
  • A: Filaments will be hardest where they are dimmest

  11:40-12:00 pm Chris Gordon (UK): Dark Matter and Pulsar Model Constraints from Galactic Center Fermi-LAT Gamma Ray Observations (15 + 5 minutes)

  12:20-12:40 pm Miwa Goto (Germany): The cosmic-ray ionization rate in the Central parsec of the Galaxy - how we could deal with 10^4 discrepancy? (15 + 5 minutes)

  CR rate 1.6e-15 near Sgr A*

  • disk CR rate: ~1x10-17
  • Uncertainties in extrapolated CR spectrum
  • Chemistry may be way off

  2:00-2:20 pm Andrew Lehmann (Australia): The Galactic Centre molecular cloud G0.13-0.13: a laboratory for understanding cosmic-ray electron acceleration and

  Clouds fluoresce in 6.4 keV Fe K-alpha line

  • electrons from either SN or arc
  • electron losses very fast at low energies + only high energies can penetrate the cloud + Arc electrons higher energy, penetrate further
  • Q: how do electrons escape? field line diffusion? wandering?
  • A: Unknown
  • Q: B-field?
  • A: Turbulent, so diffusion holds

  2:20-2:40 pm Chuck Hailey (USA): First Results from the NuSTAR "Mini-Survey" of the Galactic Center Region (15 + 5 minutes)

  • cannonball: not detected, swamped
  • x-ray filament
  • "GeV results for the PWN in the CMZ"
  • Sgr A-E a magnetic flux tube? + Where do you get 50 TeV electrons?
  • HESS TeV source: everything >40 keV is from a pwn + INTEGRAL source was an artifact

  3:30-3:55 pm Shep Doeleman (USA): Science with the Event Horizon Telescope (20 + 5 minutes)

  • pierce the scattering screen
  • intrinsic size larger than scattering

  3:55-4:15 pm Geoff Bower (USA): The Galactic Center Pulsar, SGR 1745-29 (15 + 5 minutes)

  • Limit of 20% on pointlike contribution to Sgr A* emission

  Diffuse X-rays in the CMZ / NIR comparison

  "GCDX"

  • 7x10^7 K gas.
  • gas can freely escape
  • extinction-corrected stellar number density map
  • awesome extinction-polarization maps + Hatano et al2013

  Discussion

  Farhad: Morphology in inner 1.5" "Missing Pulsar" problem. Dispersion Measure problem: hard to see pulsars

  5:00-5:25 pm Mitch Begelman (USA): Symposium Summary (25 minutes)

  • "Maybe the solar system is in the Galactic center..."
  • Galactic "Center": dynamical
  • CMZ: Characterized by physical conditions - amount of molecular gas and extreme conditions
  • CMZ vs starbursts: 10-100x lower pressure, 10^-4 gamma rays
  • CMZ disagrees with "sacred" KS law (or Krumholz-McKee law)
  • Supsersonic turbulence accepted in the CMZ... not in Mitch's circles
  • intermittent SF: turbulent, cloud-cloud collisions
  • turbulent clouds are transient
  • starbursts = global conditions, local: cloud collisions
  • pressure gradient in the CMZ -> wind
  • could wind-strength be the trigger? + put threshold at 10x tidal limit + wind luminosity required = L_w = 10 (c_s^2 sigma^3 / G) T_100 sigma_150^3 erg/s + bimodal: feedback drives further SF
  • CND - CMZ connection...
  • Central nuclear cluster: formed from binaries? + tidal limit on SF + tidal compression -> tiny jeans mass
  • G2 + Mitch thinks it contains a star + high eccentricity means hard to form close-in + plausible star with 50km/s 10^-7 msun/yr

---

• IAU 303 Thursday notes

  Many good talks today, but I was too tired to take complete notes.

  Roman Shcherbakov and Alessandro Ballone

  Models of the G2 cloud, particularly using CLOUDY.

  Thaisa Storchi-Bergmann (Brasil): Feeding versus Feedback in Nearby AGNs

  IFU views of central 100-ish pc in a number of normal spiral galaxies, e.g. NGC 1068. Outflow rates exceed infall rates: indicates mass-loading in the outflow.

  Mark Morris

  Impressive images of the central few pc at 6cm. "Smoke Rings" indicating Sgr A*'s outflow.

  Jorge Cuadra

  Formation of G2-like clumps via WR wind collisions. Most form far out, though?

  Jerry Ostriker

  Bondi solution inadequate: angular momentum

  • boundary conditions are a problem
  • self-similarity fails because bondi radius >> centrifugal radius
  • at low accretion rates, 1/250 of mass hits SMBH, most gets outflow'd
  • vast majority of time spent at tiny fraction of eddington...
  • Equatorial outflow of angular momentum
  • C Thaisa: observations include equatorial outflow
  • Q Fred Lo: Compare to what we see in CMZ?
  • A: Mark Morris's outflows fit the picture. Equatorial outflow may not be generic.
  • Jets unimportant for galaxies, only important for IGM

  Dan Marrone (USA): The Millimeter-Wavelength Polarization of Sgr A*

  Accretion flow causes polarization rotation of Sgr A* backlight

  • JCMT polarimeter first detection of linear poln
  • there is circular poln in Sgr A*

  Joey Neilsen

  "fundamental plane" is correlation between BH mass, X-ray, and radio luminosity

  • Sgr A* fits it only in flare mode

---

• Miquel Requena-Torres: Opening again the debate: the transient nature of the circumnuclear disk

  

  Data from many sources

  • IRAM, APEX, Herschel
  • SOFIA now: FORCAST & GREAT

  CO SED

  • Measure up to CO 21-20
  • Model with LVG
  • Needs multiple components
    • but no high-density components

  HNC/HCO+

  • Mills et al, 2013... on arxiv tomorrow
  • Vibrationally excited H3CN
  • RADEX -> n~10^5.3-6.5
  • most of CND not tidally stable
  • High temperatures (120-150K) required to excite vibrationally excited gas

  Many works indicate CND not stable

  • [Lacy indicated: doesn't need to be gravitationally stable; is formed by shear]
  • Betsy proposing HCN ladder with ALMA

  Questions

  • Q: If densities below Roche densities, maybe clumps are not virialized but they contain virialized cores.
  • A: In very close...
  • Q: Model - black hole compresses clumps when they get closer to BH

---

• Nanase Harada: Molecules in CND (Theory)

  

  Line survey in the southwest lobe of the CND

  • IRAM + APEX
  • RADEX LVG analysis

  • Assumed source size

    • density 10^5
    • grav unstable

  • column densities in many molecules

  Physics affecting the chemistry

  • cosmic ray ionization rate
  • X-ray ionization + Less penetrating
  • UV photons + highly dependent on extinction + 10^4-10^5 G_0
  • Shocks + shock chemical models + gas & dust phase shock chem

  Concl

  • High CR rates favored (zeta = 10^-14/s) + lower acceptable if UV included (zeta = 10^-15/s)

  Questions

  • Q: Ionization provides external pressure on clumps.
  • A: Would like to include in model...?
  • Q: Gamma ray ionization could do something. Considered?
  • A: No, but cross-section is low. Need lots of gamma rays.
  • Q Farhad: Age of molecular ring based on chemical model?
  • A: Assumed some age from CR turn-on, not age of CND
  • Q: More extreme CR ionization rate near Arches cluster, etc. What is the best chemical approach for higher CR rate?
  • A: If CR rate too high, can't form molecules / will destroy molecules

---

• John Lacy: Gas Motions in Inner 2 pc of SgrA West

  

  NeII 12um line

  Observationally, little has changed. Interpretation has changed a lot

  • Ne II and 6cm continuum look identical
  • data avilable from Irons et al erratum

  Two models

  • elliptical orbit
  • spiral density wave + both assume same plane as CND
  • northern arm offset in PV diagram, but matched slope + similar in western arm
  • model assumes gas moving along ellipse + reality: probably moving at some angle to the ellipse
  • spiral model same as infalling streamer, something close to circle... + linear spiral + Eastern arm doesn't fit the model

  Is there a physical explanation for a 1-arm spiral density wave?

  • 1-armed spiral is dominant instability in a keplerian disk

  • perturber needed: gas not self-gravitating, so can't be same as disk + B-field perturber?

  • dynamical model + orbits precess with power-law mass distribution + orbit crowding near apocenter -> spiral formation + 2e5 yrs to develop

    • persists for a long time: the precession timescale

    • fitting with Keplerian velocity is wrong
      • gas is seen at the apocenter of its elliptical orbit

  • inflow rate is small

  [Exercise: reproduce his simulation & movie]

  Questions

  • Q: Clumps in CND interacting with each other?
  • A: Spiral density wave fails at 2pc from center. Should not persist outside of 2pc, but accidental spirals should persist because there is no differential precession
  • Q Fred Lo: Trying to explain gas, that is not collisionless.
  • A: People here know how to do HD, MHD.
  • Q: Not a complete explanation. What about western arm?
  • A: Maybe magnetically controlled structure? Not in the same plane.
  • Q: Not a density wave in the Western arm
  • Q: What is the source of ionization?
  • A: Assumed massive stars. But, too bright. Maybe shock ionization?

---

• Jay Gallagher: Lessons from Comparisons between the Nuclear Region of the Milky Way and Those in Nearby Spirals

  

  Investigation to understand assumptions made in extragalactic obs

  • MW single example - what is unique, what general?
  • SNR / CR interaction model works in M82 & NGC 253, not in MW
  • MW SFR? Is it right?
  • lots of nearby SAB moderately-barred spirals moderately analogous to MW
  • Maffei 2 + 5x10^7 msun mol gas in rotating core
  • NGC 253 + 10^8 msun molecular gas
  • MW + 3-4x10^7

  Similar molecular and stellar content

  Major differences

  • MW: SFR 0.01 Msun/yr [my comment: this seems low?]
  • IC 342 & Maffei 2: 1 Msun/yr
  • NGC 253, M82: 3-8 msun/yr + nuclei don't follow CO vs SFR
  • NGC 253: huge wind (almost naked eye) + 10-100x MW CMZ thermal pressure
  • Gamma rays: MW overluminous at low energies?

  Statement: "No correlation. Extragalactic relation totally fails" on a plot with 5 data points...

  • not tied to CO
  • Must be a large range in SF efficiency
  • SFR not correlated with nuclear stellar mass
  • MW in SFR low-state

  Episodic SF

  • Physical state varies + Chemical transition? + driven by chemistry rather than mass?
  • SF bimodal? Need larger sample
  • Unexpected SMBH impacts?

  Advertisement: AJ - interested in improving figure distribution. aj@astro.wisc.edu

  Questions

  • Q: Comment - SF adequate to explain energetics seen
  • Q Longmore: Idea for what's stopping SF in our own galaxy. Rate limiting factor is that gas is not self-gravitating.
  • A: turbulent, yeah.
  • Q Mitch: Positive feedback. SF starts, gets intensified. Squeezed by external pressures.
  • A: Agree
  • Q: SFR density of mol gas.
  • A: Cloud production mechanism is different (rather than SF "relation" breaking down)
  • Q: Large range in star formation. Is wind/outflow to SFR more constant?
  • A: would like to know. Outflows not well-measured.
  • Q: Constant at what value?
  • A: Outflow/SFR constant
  • Q Farhad: Dense gas in other galaxies?
  • A: Not known yet. Need to know dense gas fractions
  • Q Farhad: Need to know fraction of dense gas.
  • A: Bigger debate in N253

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• Deokkeun An: The Galactic Center: Not an active galactic nucleus

  

  Focus on infrared

  • high gas surface density
  • cloud-cloud collisions

  Spitzer IRS survey of CMZ

  • 107 candidates
  • 35 YSOs discovered
  • half of observing time spent on background
    • 428 total spectra on ISM lines of sight
  • NeII, SII, SiII maps
  • parameter maps:
    • ionization state
    • electron density
    • rad field hardness

  Comparison to IRS observations of other galaxies

  • SINGS comparison + NeIII/NeII ratio vs O/H abundance + Galactic center is moderately inconsistent with AGN
  • Other line ratios (FeII/NeII vs SiII/SIII) - GC offset from AGNagain + Most CMZ points look like "normal" star forming regions + lots of scatter, but trend with longitude
  • photoionization by hot stars & shocks explain colors

  Questions

  • Q: Is there any significance to the idea that high-latitude are most similar to AGN?
  • A: ...didn't understand question... talked about oxygen abundance determinations and statistical significance
  • Q: Is there any physical significance to the high-latitude points having AGN colors? Could it be from AGN being "turned off" years ago?
  • A: you tell me. Could be X-ray binaries, wolf-rayet stars. No clear evidence that Sgr A* excited it.
  • Q: Need bright source. XRBs would have to be very bright.
  • A: Our obs don't show much. Distance unknown. Could be foreground.
  • Q Stocke: - detections of Ne V. Couldn't see. How many had Ne V definitely detected? In infrared or diffuse?
  • A: ~12 out of 400 detected. Mostly Ne V in ISM, not in point sources.
  • Q Farhad: What does # of detected YSOs tell you about SFR? How are they distributed in plane?
  • A: Consistent with Schmidt law. Not far from Farhad's measurement. YSOs selected on IR photometry. 50% of sources from near Sgr B. Asymmetry: YSOs on left

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• Naomi McClure Griffiths: HI Outflows from the Galactic Center (20 + 5 minutes)

  

  Outflows - M82 example

  Our Galaxy

  • 8.3um correlated with radio continuum
  • Fermi bubbles
  • Radio polarization - magnetized bubble
  • ATCA + Parkes HI survey
  • HI data publicly available: http://arxiv.org/abs/1201.2438, http://www.atnf.csiro.au/research/HI/sgps/queryForm.html + 86 high latitude clouds that are completely distinct from the rest + ± 200 km/s + negative velocities at the bottom + size ~15 pc, ~few hundred Msun + 4000K clouds + n~1cm^-3 + not in circular orbits

  Lockman "very dumb simulation"

  • model as outflowing clouds
  • wind velocity, outflow angle
  • min/max velocity plots: look for clouds beyond the min/max vel + wind velocities 150-270 km/s can reproduce population

  Cooper 2008, Melioli 2013

  • simulations predict entrainment of dense gas
  • cold wind is responsible
  • 2 Myr to get clouds to observed height

  Wind dynamics

  • cold clumps entrained in hot outflow total mass ~4x10^4, but completeness loss -> 10^5 msun
  • energy total ~10^52 erg
  • easily supplied by present SFR

  Future

  • can look further in both lat & long + determine lifetime + constrain opening angle

  Questions

  • Q: Where does the mass come from? Is it hard to resupply? Where does it go?
  • Q: Do you see any warm gas (H-alpha)?
  • A: looked at WHAM, but resolution too poor. Not clear yet.

  • Q Mitch: 600 km/s. Injected explosively or must go through a sonic point

    with a grav. potential, which would imply that it's coming from a black hole

  • A: OK, great, someone else give me the theoretical explanation

  • Q Stocke: Warm component has been detected in absorption against AGN; velocities consistent.

    Gas goes up to 12 kpc on either side and does not escape. Hot wind requires Chandra, not yet successful.

  • Q: for Stocke - How much gas in hot wind?
  • A: Not detected
  • Q: Could this be inflow?
  • A: We don't see this around other parts of the galaxy except around superbubbles. No conspiracy accreting towards CMZ
  • Q Farhad: We've looked at RRLs in inner degree. Don't see any high-velocity ionized gas. Must be accelerated away from disk.
  • Q Namir Kassim: High energy emission from cosmic rays impacting these clouds?
  • A: Possibly, we'd like to look at that more

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