Adam Ginsburg's blog

Articles by Adam Ginsburg

• Ann-Marie Madigan: On the Origin of Young Stars in the Galactic Center

  

  Central pc cluster

  • orbital parameters
  • disk of O/WR stars + distinct from S stars: circular-ish orbits
  • binary disruption formation of S-stars + hypervelocity ejected star + other star has eccentricity > 0.98
  • further stars? + "memory" of initial eccentricity "stored" at large radii + relaxation times increase + can't measure eccentricity directly because of long orbital timescales
  • Simulations of young stars orbiting + initial high eccentricity (disruption formation) + initial low eccentricity (disk formation)
  • Depending on the stellar mass, both origins are possible. + lower masses better fit for disruption mechanism
  • IMF in disk + different formation mechanism would imply they should not be included in IMF measurements
  • start in eccentric, relax into circular + depends on density profile + can infer density profile
  • "h-statistic" + angular momentum vector = ±1 if circular orbit, 0 on plunging "orbit" + degeneracy between inclination and eccentricity
  • "special purpose" n-body code + high-mass stars consistent with disk + low-mass stars more like binary disruption
  • implies top-heavier IMF

  Questions

  • Q Cuadra: What tells you about the cuspiness? Precession?
  • A: Yes. Orbits closer to black hole have long precession scales. Leads to more rapid change in eccentricity (and less precession).
  • Q: What is timescale for thermalization to eccentricity?
  • A: Depends on radius. S-stars, already relaxed. >0.02 pc, takes Myrs
  • Q Farhad: Radial profile of the S-cluster B-stars?
  • A: Haven't looked at that; similar to O and WR stars.
  • A: R^-2? Poisson limited. R^-1.5?

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• Hui Dong (USA): Unveiling the massive stars beyond the three young massive star clusters

  

  HST/NICMOS PaA GC survey

  • Color-based stellar classification + WN,WC stars
  • Isolated WN stars + ejected from clusters
  • spectroscopy of 8 "isolated" stars + LOS velocity to determine memberships...
  • new Of I star

  Questions

  • Q: Mass segregation? Do you expect such a large number of stars kicked out?
  • A: Yes. High density of massive stars in cores, 3-body interaction common there
  • Q: NIII and HeII lines? Stellar wind effects move the centroid
  • Q: Radial velocities are isolated stars on one side of Arches cluster. Is that expected?
  • A: I don't know if we expect that.
  • Q: What stellar masses of escaped stars?
  • A: Not measured yet.
  • A Cornelia: many are radio-continuum detected. Consistent with stellar wind predictions
  • Q Farhad: Star formation rate from runaways?
  • A: Half of the stars come from clusters. Double the SFR from the clusters. 0.05 Msun/yr
  • Q Mark Pound (?): Orbital histories. Are any of the orbits more likely than the others?
  • A: Some could have been members.

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• Anja Feldmeier: The Milky Way Nuclear Star Cluster Beyond 1 pc

  

  Observing the cluster

  • slit-scanning the central cluster with ISAAC
  • foreground removal based on colors
  • included Q-branch H2 lines, stellar CO absorption lines
  • CO -> stellar velocity dispersions
  • flat velocity dispersion profile + fitting profile -> underestimate of BH mass + may affect other galaxies

  Questions

  • Q Fred Lo: Method vs external galaxies. Couldn't understand.
  • Q: What is the error on the anisotropy?
  • A: can fit with different anisotropy
  • Q Lu(?): What happens if you include IR7?
  • A: v disp drops towards center. Problem.
  • Q Soo(?): Does model allow stellar rotation?
  • A: ???

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• Overview Talk Jessica Lu: Young Stars in the Galactic Center

  

  Why care about cmz young stars?

  • lots of them, compared to elsewhere
  • fate of clusters?
  • IMF, stars affected by environment?
  • interaction with SMBH?

  Nuclear cluster

  • HST image covers CND

  • spectroscopic census of stars with IFUs

  • mass limit ~8-10 msun

  • astrometry great + pm 1 km/s

  • Models of formation + in situ? inward migration? + circular orbits? eccentric?

  • messier now + sharp radial fall-off favors in-situ models + eccentricity rejects in-situ models + "wild dump" of molecular material

  • IMF variation? + claimed very top-heavy mass function

    • rejected by UCLA group

    • fit luminosity function with bayesian model approach
    • modeling required including multiplicity
      • stars brighter than brightest possible unless multiples included
    • salpeter ruled out at 4-sigma significance
      • slope ~1.7

  • Future? + pre-main-sequence should be doable in photometry + astrometry, spectra getting better + can start to measure multiplicity

  Arches cluster

  • membership determined via proper motion measurements + Stolte 2008, Clarkson 2012

  • PMS stars in Arches + disk fraction ~6% + disk evaporation

  • velocity dispersion measurement ~5 km/s + dynamical mass 10^4 msun + compare to photometric mass to get IMF + IMF can't be normal.

    • could be top-heavy or bottom-light

  • Both arches and quintuplet are moving away from Sgr A* in approximately the same direction & amplitude + track orbits backward + Could have common origin (arches & quintuplet)

    • may be in outer x2 orbit, maybe x1/x2 intersection

  • Future: + HST: measure tidal radius + HST: Measure IMF to 1 msun in outer parts

  Ages

  • all seen are young + where are the old? + nonexistent? Or dispersed? + triggering 2-6 Myr ago?

  SMBH interaction

  • most uncertain component

  Young stars around nuclei of other galaxies

  • M31 core cluster + but no gas

  Questions

  I wasn't allowed to ask this question. Apparently I'm invisible to the chair. QUESTION: Can you infer which stars are likely binaries via the IMF modeling? Do spectra velocities agree?

  • Q Evidence for distorted IMF. But you see PDMF. Could it be dynamical?
  • A: in YNC, solid, but not 100%. How do ejection mechanisms scale with mass? Unknown. YNC is the best case. Arches, remains a real concern. Assumption is cluster in equilibrium, may not be true
  • Q Fred Lo: What's the SFR?
  • A: Sgr B2 is forming a massive star cluster today. Continuous as can be. No major evidence for stochasticity.
  • A from the crowd: 3 orders of magnitude scatter.
  • A Gallagher: 0.1-0.01
  • Q Gallagher: How does this compare to M82F? Velocity dispersion too small for luminosity. 40-60 Myr old. Bottom-light IMF
  • A: super star cluster similar
  • Q: When you consider binaries or multiples, are the evolutionary tracks for binaries? Maybe all clusters same age.
  • A: Didn't have them yet, so singles.
  • Q: Correlation between stars and molecular gas?
  • A: no.
  • Q J Ostriker: Given age of clusters, expect 1000x more of them in the galaxy. IF you take number of clusters divided by age, do you get too much mass? If current rate is typical, was there 1000x more in the past?
  • A: IF you add them up, no...? Is SFR now consistent with past? not constant SFR Lower and higher.

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• General Discussion (day 2)

  Farhad discussion points:

  • Fraction of dense molecular gas in CMZ?
  • Volume filling factor of dense gas?
  • Abundances in CMZ?
  • Lada 2012 plot: SFR vs Molecular Gas Mass. Density is crucial
    • Steve: Not volume, column density. Assumptions about 3rd dimension. All gas above Lada's column density threshold.
    • Gallagher: exgal community correlates surface density with SFR. Variations on local scales
  • Aalto: HCN as dense gas tracer in ULIRGs - problem.
  • Steve: comparison to centers of other galaxies... rings have low volume filling factor, not pancakes but rings
    • unlikely that column density uniformly distributed along line of sight; likely to be clumped
  • Bally: comment on face-on views. Mostly filaments. Filaments tend to be end-on on positive side, face-on on negative side. Could Brick be an end-on filament? + Gallagher: +1
  • Mills: ALMA data can answer that with excitation. NH3 thought of as high-density tracer, but not in CMZ. + plug by me
  • Juergen Ott: Interferometer and single-dish, 10% filling factor
  • Gallagher: Density limit on SF from star clusters. 10^6-ish, high SFE. Star clusters may imply upper bound
  • Farhad: Mass of molecular clouds from dust emission. Mass of low and high density gas + Rathborne: Opacity, chemistry very tough
  • Aalto: "Medusa merger" large-scale, very high efficiency. Timescales are a problem: no high-density gas tracers seen, but plenty of star formation is seen
  • Mills: How do you trace this highest density gas, then? + Aalto: H2CO, Ao et al. Weak chemical variation. + Rathborne: "Million dollar question". H2CS follows continuum better than other tracers
  • Dust normally considered better tracer of mass. Do we really know dust to gas ratio? Factor of 2 at best
  • Farhad: Question raised yesterday... asymmetry of SFR/mass How do we explain distribution
    • Steve: How measure SFR?
    • Farhad: YSOs counting
    • Bally: You sure they're YSOs?
    • Farhad: Yes, best we can do, age ~few 10^5 yrs. Maybe YSOs obscured? If not, interesting issues
    • Steve: Could YSOs have moved after they formed? Dynamical time...
  • What's the extinciton at 24um? Selection effect? + Farhad: Could be selection. Sgr B2 makes things worst. + Not clear 24um sources come from same volume
  • Dust is the best measure for mass. Only free parameter is temperature. KS not very fundamental.

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• Rei Enokiya: Large scale and high sensitivity multi line CO surveys toward the Galactic Center

  

  NANTEN2 CO survey

  • 12CO 1-0, 3' beam, 0.43 K
  • high latitude clouds with vlsr -200 to +150 km/s + 24um filaments traced by CO
  • Double Helix nebula (Morris, Uchida, Do 2006) + Torional alfven wave? + polarized lobe from radio arc? + CO detected
  • Other molecular columns tie back to Sgr A*
  • "Magnetic Tower" model + accretion around BH + CND creates B-field, spins it up vertically + 25 km/s outflow speed

  Questions

  • Q McClure-Griffiths: can you distinguish between magnetic and stellar wind models?
  • A: No,not really
  • Q Bally: Do you worry that the LSR velocities are close to local gas and spiral arms? Could foreground confuse? Linewidths consistent with CMZ?
  • A: Star-counting extinction distance estimate gives 8±2 kpc.
  • Q: What evidence for jet?
  • A: no direct evidence.
  • Q Farhad: Could it be infalling rather than outflowing? Maybe hard to tell.
  • A: ...

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• Denise Riquelme Vasquez: Disk/Halo Interactions: Molecular Clouds in the Galactic Center

  

  CMZ mol clds

  • SiO emission, large linewidth, ...
  • Giant molecular loops + magnetic buoyancy + Parker instability
  • NANTEN 4m large-scale survey
  • X1 & X2 velocities...
  • NH3 measurements of "connection points" of loops
  • attempt to measure heating mechanisms + turbulence decay + CR
  • High isotopic ratios towards halo
  • High temperatures at interaction points

  Questions

  • Q Farhad: Shocked gas seen everywhere in loop?
  • A: need to observe complete loop to get gradient temperature

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• Kazushi Sakamoto: The Kinematics and Dynamics of Molecular Gas in Galactic Centers

  

  Driving gas into Galactic centers

  • opposing torques at corotation point drives gas inward
  • observational evidence from nearby galaxies
  • barred galaxies have greater concentration (Sheth et al 2005)
  • observations of CO gas kinematics in M83, NGC 1097 + FCRAO Quarry obs
  • ALMA concentration to M83 core... + high velocity gas near core + southern nucleus has spatially distinct outflow lobes

  Questions

  • Q Fred Lo: Can you distinguish between streamline convergence and cloud collisions? Can you determine what happens when clouds collide?
  • A: Yes, with ALMA.
  • Q Farhad: Physical conditions in NGC 253. Temperature distribution? All warm?
  • A: Our obs don't measure temperature. CO gives 50K on 10's of pc scales, so at least that temperature.
  • Q: Big bubbles in NGC 253. Are there clusters near them?
  • A: Didn't find any in original data.

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• Betsy Mills: Hot Gas, Masers, and Cloud Collisions: The extreme properties of molecular gas at the heart of the Milky Way Galaxy

  

  VLA Survey

  • DnC at 24-36 GHz

  • Brick NH3 + very high temperatures in brick: 100's of K + optically thin 4-4,5-5,7-7 + brightest, densest clumps have lowest temperatures + 300K gas, but no SF

    • CR heating?
    • Shock heating?

  • 36 GHz methanol maser + shock excited + dozens of point sources + 75 candidates, 29 T_B > 1000K (masing)

  • why so many masers? + large-scale shocks? + 80 km/s velocity gradient across cloud + methanol & ammonia emission dominated by convergence point of velocities

  • class I methanol masers usually show SF

  SF in the Brick?

  • 7 VLA continuum sources + peaks in a more distributed set of continuum emission
  • 25 GHz continuum + most continuum outside of the molecular gas + external ionization

  Rest of the CMZ

  • Pistol & Quintuplet continuum with streaks from the nonthermal filaments + second LBV seen in radio
  • NH3 near Sgr A* + NH3 traces edges of Sgr A East SNR + some SF in 50km/s cloud and 20km/s cloud
  • CND not in HC3N, weakly in ammonia
  • no NH3 or HC3N at brightest submm clump
  • nonthermal 3-3 line

  Sgr B2

  • CH3OH only non-self-absorbed against hot core + shell structure
  • NH3 2-2 maser

  Questions

  • Q Walsh: NH3 3-3 maser. Expected more of those. Were there others?
  • A: yes, there are at least 2 others
  • Q: Temperatures of ammonia. Is ammonia the only tracer that gives high temperature towards the Brick?
  • A: Yes, only one towards brick. 400-600K from H2 from Rodriguez-Fernandez. 400K in Sgr A from NH3 too.
  • Q: Formation pumping?
  • A: yes, possible. Need to form on short timescales.
  • Q: Need hefty CR for that heating. Can you expand on what VLA is good for?
  • A: CRs 10^-14, 10^-15. May happen. Hard to explain 100's K
  • A: VLA gets NH3 transitions for temperatures. ALMA gives density. VLA gives free-free. No overlap in frequency
  • Q: Is the brick a cloud? Is this really a transient colliding flow?
  • A: I don't claim that it's bound.

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• Jill Rathborne: ALMA’s view of the initial conditions within a massive protocluster

  

  The Brick / Lima Bean

  • deep extinction feature
  • Tdust 20K
  • MALT90 gas gives different T than dust + HNCO usually traces 70K gas at n~10^6 + 0.3 pc resolution

  ALMA 13pt mosaic

  • 1.7", dv=3.5 km/s, 20 microJy/bm
  • column pdf is fairly lognormal + tiny excess on the tail + tail is only location of active SF
  • lognormal is predicted...
  • will form stars (already forming some)

  Gallery of data

  • rgb slice movies
  • cold absorption filaments + huge aspect ratio & line width + only seen in HCO+ + approximately perpendicular to polarization

  Questions

  • Q Mitch: Any qualtitative feel for the bulk velocity field? Rotation, shear, compression?
  • A: Probably shear.
  • Q: Estimate mach number of shocks?
  • A: yes can but haven't yet.
  • A Steve: M~70
  • Q: Column to volume densities. What range?
  • A: 10^6 cm^-3 from the dust, up to 10^7
  • A: Only one transition of each molecule, haven't done local density estimates
  • Q Lang: Is the absorption filament a continuum feature?
  • A: Doesn't line up with anything in particular.
  • A Betsy: There's a parallel filament.
  • Q Farhad: What is happening at the one site of SF?
  • A: 80 blobs throughout the cloud, sizes ~0.3 pc, masses 10-100 msun. 1 water maser with 85 msun. No YSO correspondence

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