Adam Ginsburg's blog

Articles by Adam Ginsburg

• Steve Longmore: Conversion of Gas into Stars in the Galactic Center

  

  Is SF different in disk?

  • 5-10% of gas in CMZ
  • 5-10% of SF in CMZ
  • Density in CMZ 2 orders of magnitude higher

  Suppressing Mechanisms in the CMZ

  • Stars dominate grav potential + outside "ring", gas is not self-gravitating + Within 100 pc, gas is self-grav
  • Local suppression dominated by turbulence by orders of magnitude
  • Dense gas PDF from Kritsuk + dispersion set by Mach number
  • Threshold for SF in CMZ very high: ~10^8 cm^-3

  Turbulence

  • dissipates in a crossing time + what drives it? + MRI, GI, outflows, Sne all orders of magnitude too low + steady-state gas inflow also too small
  • "acoustic instabilities" large enough + outside inner lindblad resonance, spiral waves driven by grav instabilities
  • Montenegro, Yuan, Elmegreen 1999 model + gas falling into stellar potential + "acoustic instability"

  Quiescent vs Starburst phase

  • "simple idea"

  CMZ in Cosmological Context

  • velocity dispersion vs density? + high redshift clouds and CMZ clouds occupy same parameter space
  • "CMZ is inditinguishable from high-redshift starburst"

  Details of stellar mass assembly

  • Molinari Ring picture: 2 vertical oscillations per orbit
  • map mass density along orbit
  • gas compressed at pericenter
  • PPV structure extraction... + orbital fitting + can't fit Molinari ring + closed orbits not possible: precession + can't fit P-V wiggle + doesn't fit Sgr B2
  • Pericenter passage SPH sim + VERTICAL compression + retrograde, counterrotating gas due to shear
  • dense gas fraction vs orbit... + prediction of density vs orbital position + Plug for Ginsburg et al VLA/GBT H2CO densitometry
  • IMF variation interesting future avenue

  Questions

  • Q: On pc scales, fits with Ken-Schmidt relation
  • A: Depends on geometry. Donut vs pancake geometry.
  • Q: Isn't there gas that is more efficient at forming stars?
  • A: Doesn't fit...
  • Q: KS relation doesn't work for CMZs in other galaxies. How did you measure dispersion for high-Z clouds?
  • A: Some high-z clouds with direct measurements. Otherwise, assume virial equilibrium. Robust no matter how you derive it.
  • Q: Struggling in nearby galaxies, particularly because of outflows.
  • A: best we can do
  • Q: CMZ is similar to high-z objects. GC in pre-starburst phase. So we should have a starburst soon.
  • A: Either gas won't form stars, or will do so in bursty fashion
  • Q: Predicts lots of very dense gas in Galactic center, n~10^8.
  • A: See Jill's talk.
  • Q Wardle: Turbulence damps on vertical crossing time (0.5 Myr). 20km/s linewidth disappear in 0.5 Myr? Do you see dead clouds? Don't travel very far, so should damp.
  • A: [should have answered: it's driven!]

---

• Wednesday Morning talks: G2

  9:00-9:30 am Stefan Gillessen (Germany): Overview Talk Observations of the G2 Cloud at SgrA* (25 + 5 minutes)

  

  Summary of measurements...

  • Mass of BH known "better than your own mass"

  • SINFONI data

  • ALMA cycle 0 data misses G2 b/c of redshift

  • date, location of periapse uncertain by ~months, factor of 2 in radii + radius ~100 AU + optically thin + ionized + 3 earth masses + density 10^5

  • PaA detected! redshifted into visible band

  • PV-diagram evolution with SINFONI

  • Some gas has passed pericenter + pericenter is prolonged - 1 yr

  • no x-ray heating detected yet

  • rotation measure still constant

  • wiki page for project idea: MPE wiki

  • Where does it come from? + wind interaction creating clumps?

    • S91, IRS16SW have winds that could do it

    • infalling jet material?
    • form not at apocenter, but halfway in at high velocity

  • Proplyd? + predicted rising flux; this didn't happen

  • T Tauri star?

  • Star inside? + so far, evidence says no + gas is not presently bound

  • Sgr A* flares nightly

  Questions

  • Q: current velocity inconsistent with current model
  • A: Maybe internal velocity has changed. Some gas on other side. Maybe things have changed now that there is no longer a single source
  • Q Farhard: Estimate of density of sheared gas when on opposite side from the BrG?
  • A: Haven't done that yet. Evolution is mostly radial (line-of-sight)
  • Q Bally: Will the trailing gas continue to fall in? What is it?
  • A: It is there, orbital motion slow, but close to overall BrG emission and confused with ambient. 20 years to infall
  • Q: Are B-fields dynamically important?
  • A: Talk tomorrow - various scenarios, possible that magnetized. Don't think we will see directly.
  • Q: Predicting X-ray flares. Can you determine how much mass infalls?
  • A: Not an easily invertible problem.
  • Q Fred Lo: Infall of cloud to 1000 schwarzchild radii. Can you say anything about interior?
  • A: Can't see anything yet. Should theoretically be "sea" of NS, BH around SMBH. Maybe will intersect?
  • Q Mitch: If star in center, what limits on wind speed?
  • A: First observations were unresolved. Rather low wind speed, 50-100 km/s

  9:30-9:50 am Leo Meyer (USA): Keck Observations of G2 and SgrA (15 + 5 minutes)

  

  Agree on some things:

  • red source
  • evolving FWHM
  • tidal interaction
  • eccentric orbit

  Uncertainties:

  • How much gas is there?
  • compact gas cloud? How survived in the environment?
  • Or is it a star?
  • Will it have observable impact on Sgr A*'s emission

  2013 data

  • doesn't change anything
  • BrG for radial vel and proper motion + bias in L' phot
  • so far purely keplerian orbit + why would a gas cloud follow keplerian?
  • slight changes to orbital parameters, mostly because of reference frame

  G2 tail

  • PV diagram criticism: doesn't show spatial association
  • tail not on the orbit
  • claim that there is unassociated, independent gas

  Blueshifted emission

  • wrong location?
  • Residual of SO2?
  • may not be what is seen in SINFONI data

  G2 not unique

  • ~5 sources clearly seen
  • [but G2 is the only one with high velocity]

  Sgr A* brightness

  • currently as faint as ever seen
  • new "hidden markov" model
  • Sgr A* has only one state

  Questions

  • Q: Can you predict rate of G2-like interactions?
  • A: No, but they don't explain flaring. 1-2 every 20 years?
  • Q: New inclination angle closer to 90. Maybe more extended in radial direction.
  • Q: Spectrum of G1?
  • A: not ready to show yet
  • Q: Caution about position-velocity diagram. If disrupted, shouldn't be keplerian in all pieces.
  • A: it's the slit width in the PV diagram that's a problem
  • Q: State transitions - can you incorporate multiwavelength data?
  • A: "very general" model. Needs to be calibrated for other wavelengths

  9:50-10:10 am Andreas Eckart (Germany): The infrared K-band identification of the DSO/G2 source from VLT and Keck data (15 + 5 minutes)

  

  Proper motions of "dusty sources"

  • K-band detection of G2 cloud
  • prior to 2008, confused with S63

  Possibilities for "DSO" = G2

  • externally heated + expect extended dust emission + not observed
  • internally heated + expect compact K-band (observed) + requires internal heating source: star
  • massive star possible
  • accretion of material?
  • "Tail emission" part of background?
  • interacting disk models suggest tail is part of interacting disks
  • X3, X7 clouds...
  • Where from? + compact clouds in CND + clouds collide -> high eccentricity infall + compression -> star formation + "beads" of stars falling in...

  Questions

  • Q: Extension of 0.2" in BrG. 20mas from Gillessen?
  • A: Extended emission is from the tail
  • Q: Movie - how possible to form stars at the close approach because of the short timescale of SF
  • A: Orbital compression
  • Q: Compressing gas - does that inhibit other SF? Prevent continuous SF?
  • A: Short event... this model ongoing sf at lower level.... IRS13N young objects
  • Q: Jupiter-like object?
  • A: couple Lsun - 20-30 Lsun, points towards more massive object than a Jupiter
  • Q Bally: Gas densities in simulation?
  • A: intial density of clump n~10^5. Look at poster
  • Q Ghez comment: analysis of images, not real data...
  • A: Data downloaded from Keck archive
  • Ghez: see anna bailey's poster, which shows technique for getting limits. We don't see G2.
  • A: We see 19th magnitude "DSO"

  10:10-10:30 am Darryl Haggard (USA): G2 as a Probe of Sgr A*'s Hot Environs: A View from Chandra and JVLA (15 + 5 minutes)

  

  Predicted possible x-ray emission

  • multi-PI Chandra campaign
  • X-ray view of CMZ: magnetar next to Sgr A* + confusion, overlapping PSFs + multi-hit issues (pile-up)
  • no hints of G2 in X-ray
  • one crazy bright flare
  • magnetar can be used to probe LOS to Sgr A*
  • simultaneous Chandra/VLA

  Questions

  • Q: VLA obs over past year. No evidence for flux density of Sgr A*. No bow shock emission.
  • Q: Column density estimates. Associated with flare? Associated with Sgr A*? LOS?
  • A: Conflation
  • Q: Can you explain emission with single age (?)
  • A: Separate fits are statistically equivalent

  10:30-11:00 am Coffee Break

  11:00-11:25 am Gunther Witzel (USA): IR observations and variability of SgrA* (20 + 5 minutes)

  NIR var Sgr A*

  • NIR spectral index...
  • Power law distribution of brightness...
  • time behavior, structure function of spectral indices
  • Break in PSD + 150, 500 minute break points
  • simultaneous observations in L and H band + time-resolved measurements of spectral index + Very constant spectral index across all simultaneous measurements

  Questions

  • Q: Can you combine VLT and Keck data to extend a night?
  • A: I've tried that....
  • Q: Red curve below black, black below red on some plots. What's happening to the spectral index?
  • A: spectral index variations are significant. Small compared to... other publications
  • C: Amazing how constant spectral index is

  11:25-11:45 pm Banafsheh Shahzamanian (Germany): NIR polarized observations of Sagittarius A* (15 + 5 minutes)

  NACO polarization measurements

  • Sgr A* highly polarized
  • Polarized flux density has lognormal + power-law distr.
  • polarization and total flux density (weakly) anticorrelated + adding noise flattens correlation + confirms real... >3-sigma detection
  • theory: depolarization at high flux comes from relativistic boosting

  Questions

  • Q: How does anticorrelation fit with the explanation of high-flux -> high pol?

  • A: Highly polarized flux is from bright flares at high total flux densities

    [I didn't understand]

  • Q Fred Lo: Any idea what radius flares are coming from?
  • A: 6 Schwarzchild radii in the model
  • Q: What constraints?
  • A: (from audience) variability timescale
  • Q: Is there a preferred vector position angle?
  • A: ...?
  • Q Sacha: Anticorrelation between "degree of correlation" and "flux" translates between polarized flux and total emission. We have interpreted as different components of an outflow, bright and high degree of polarization and faint with low degree of poln. Is this consistent?
  • Q: 40-50% of time, flux is noise-dominated. Could there be noise-dominated state bias?
  • A: We have tested by adding noise
  • Q: Would individual flares track up and down the anticorrelation? Or is it only for large # of flares?
  • A: only for composite.
  • Q Mitch: What kind of correlation do you see related to position angle?
  • A: Not included in our analysis

  11:45-12:05 pm Kazunori Akiyama (Japan): Long-term monitoring of Sgr A* at 43GHz with VERA and KVN+VERA (15 + 5 minutes)

  Sgr A* with VLBI

  • larger at lower frequencies
  • variability correlated with spectral index
  • single component for 3 years + size not correlated with radio flux
  • flares come from component emerging from optically thick region?
  • Flares with G2? + maybe detected bowshock?
  • VERA shows consistent major axis size
  • KVN + VERA: comparable to VLBA

  Questions

  • Q: Variation of intrinsic size with flux... difficult measurement to make. VLA+ALMA observations of radio flares requires relativistic...
  • Q: HET hasn't passed 10% of material (??)
  • Q: Size doesn't increase with flux. But that's interstellar scattering size. Could intrinsic size have changed by 10-15% without being detected?
  • A: ???
  • Q Fred Lo: intrinsic size measured. Any elongation/ellipticity?
  • A: Just a 1-dimensional measurement

  12:05-12:25 pm Salomé Dibi (Netherlands): Exploring plasma behavior around Sgr A*

  Sgr A* in context...

  • only flaring AGN
  • discussion of particle distrbution related to SED & state
  • accretion flow injecting electrons into plasma
  • nonthermal synchrotron with cooling break is best distribution

  Questions

  • Q Broderick: Should be able to produce both observed features of flares...
  • A: Tried to reproduce spectral index. Flaring in infrared could provide strong constraints
  • Q: Spectral index should evolve in your model, but we heard that it is not changing
  • C: Radio spectrum has gone even lower... falls on power law, useful for modeling. Makes deviation even more severe.
  • C: spectral index measurements - flares measured with spectral indices don't have X-ray counterparts. Maybe X-ray bright flares may have non-constant spectral indices.
  • C: Fit within 2 R_G, so radio is not relevant (optically thick)
  • Q Ostriker: 1-zone model. What is the geometry?
  • Event close to BH.

  12:25-12:45 pm Jim Moran (USA): History of High Resolution Imaging of SgrA* (15+5 min)

  History

  • 1951 Cygnus A: resolved double
  • looking for compact structure in HII regions with 35km Green Bank interferometer
  • simple observation -> 0.1" size, 10^7K T_B
  • OVRO group found HII regions, but searching for BH, Balick & Brown searching for HII and found SMBH + Fred Lo 3.7cm found Sgr A*, T_B ~ 10^8K, <0.02"
  • Jodrell Bank -> size ~ freq^-2
  • Fish et al: early 1.3mm VLBI + consistent with Gaussian or annulus
  • annular radii not at all constrained by short baselines

  Questions

  • C Fred Lo: Explanation of series of events. Obstacle for detecting structure of Sgr A* is scattering.
  • If you can characterize the Gaussian interstellar scattering, you could in principle deconvolve
  • C Farhad: Variability of Sgr A* is a problem. 230 GHz has high, hourly variability
  • Goal should be testing models on 10min timescales

  Discussion Section

  • We agree on some things: + source is infalling + L-band source + Br-G detected
  • Controversy:
    • K-band detection is controversial. Can we sort that out? If it's there, will it change interpretation a lot?
  • K-band source would be compatible with hot dust. H-band is the real discriminator
  • What is the source we detect? There are K-band sources, but their natures are unclear
  • Extinction makes it extra hard
  • Ghez: What is G2? Very similar to S-star orbits. Orbital characteristics of binary exchange. Perhaps just a close binary, soon to form an S-star? Tidally disrupt atmosphere, but be a star underneath
    • Problem: star not that big. If it's a star, very cool star dominated by dust, difficult to detect.
  • Closest approach is no closer than S-stars + orbit also matches disk
  • Dusty, looks like an S-star + No, it is a GAS source, not a dust source. Gas is directly detected
  • As it travels by Sgr A*, do I care if it has anything inside?
  • Ghez: forces us to consider role of binaries at cmz
  • Comment: wait and see what happens + What if nothing happens? Will that resolve the issue?
  • Are we just seeing weather in Sgr A*? + eh, maybe?
  • Are we agreeing on emission mechanism?
    • continuously variable source. No quiescent vs flaring state in IR; more prominent in X-ray

---

• 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

---

• 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

---

• 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

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• 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?

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• 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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