Source structure from ALMA CO imaging of SPT-selected dusty star-forming galaxies(SPT: The South Pole Telescope)
Chenxing Dong董辰兴2nd year graduate studentAdvisor: Anthony Gonzalez
SUGAR-RUSH Shanghai June 15 2018
The SPT SMG collaboration
• SPT = The South Pole Telescope• SMG = Sub-Millimeter Galaxy
May 2017, Tuscon, Arizona
Dustystar-forminggalaxies (DSFGs)
Starlight absorbed by dust
UV from young, hot starsStellar bump from old stars
Dust re-emits in the FIR
Sub-mm magic
SPTThe South Pole Telescope
Telescope• 10 meter off-axis sub/mm telescope • located at the geographic south pole• 1 deg2 field of view• ~1' beams• optimized for fine scale anisotropy measurements
SPT-SZ Camera (1st Generation):• 2007 − 2011• 960 pixel mm camera, 1 deg2 FOV • 1.4, 2.0, and 3.0 mm• completed 2500 deg2 • 18 μK-arcmin depth, ~1 mJy
SPT-pol Camera (2nd Generation):• 2012 − 2016 • 1600 detector mm camera, 1 deg2 FOV• 2 and 3 mm + polarization• completed 500 deg2 + wide field• 4.5 μK-arcmin depth
SPT-3G Camera (3rd Generation):• 2017 − 2020 • 15k detector mm camera, 2.4 deg2 FOV • 1.4, 2, 3 mm + polarization• planned 2500 deg2 x5 deeper• 2.5 μK-arcmin depth
!17
2500deg2 SPT-SZSurvey
2500 deg2 SPT survey81 strongly lensed SMGs at S870um > 25 mJy
!34
IRAS full sky map and SPT survey region
81 strongly lensed SMGs at S870um > 25 mJy
ALMA: AtacamaLarge(sub-)MillimeterArray— follow-up studies
• 54 12m antennas+ 12 7m antennas• 10bands, 35-950 GHz (0.3-8.6 mm)• ResolutiongreaterthanHubble• Largestandmostsensitiveinstrumentintheworldatmillimeterandsubmillimeterwavelengths
©ESO/Clem&AdriBacri-Normier
Fivestronglylensedgalaxies — ALMA cycle 2
• Selectedtodetectdarkmattersub-halos(Morningstaretal.inprep.)
• Red: more likely tohave a M=108.6M⊙sub-halo at thatposition
Hezaveh etal.2016
Continuum
Visibility-basedGravitationalLens Modelling
• Visibility: Fourier transform of theimage• Considering calibration errors• Fitting unknown phase errors
• MarkovChainMonteCarlo(MCMC)approach
Lens
Source
Image
Model parameters →visibilities →χ2Observed visibilities + errors ↗
Visibility-basedGravitationalLens Modelling
• Parameterized(Hezaveh etal.2013,Spilker etal.2016)• Lensparameters+sourceparameters• Lessparameters• Simpleandfast
• Pixelated(Hezaveh etal.2016)• Lensparameters+pixelvalues• Muchmoreparameters• Muchmoretimeconsuming
Lens
Source
Image
Model parameters →visibilities →χ2Observed visibilities + errors ↗
LensSingularIsothermalEllipsoid(SIE)
5 parametersSometimes + shear (2 parameters)
Source• Parameterized
• Point (3 parameters)• Sersic (7 parameters)• Gaussian (6 parameters)
• Pixelated• X × Y parameters
Image
(x,y)
a
b
φ
Visibility-basedGravitationalLens Modelling
ParameterizedLensModelling
• CO• Singlevelocity channel• Multiplevelocity channels
• 4sourceswithrobustmodels
Continuum
-300km/s
-50km/s
+200km/s
+450km/s
Observation Model Residuals High-resModel
Results: Velocitygradient
(nolinearvelocitygradient)
Position(arcsec)
Velocity(km/s)
Merger(confirmed with CII,Litke etal.inprep.)
Likelyrotation
Crosses:positionsofdifferentvelocitycomponentsEllipses:errors
Results:CO size vs dustsize
• Keyresult:TheCOsizefromCO(8-7) and(6-5) appearslargerthanthedustcontinuum• SimilartrendpreviouslyseenatlowJCO (e.g.Spilker etal.2015,Tadaki etal.2017;Chen etal.2017)• Possibleexplanations
• OpticallythindustemissionandopticallythickCO• Temperaturegradientinthedust• COgashasalargerspatialextentthanthedust
Results:differentialmagnification
• Differentialmagnification:• AcrossCOlineprofile• COvsdust• COdifferenttransitions
• Affectsestimationofphysicalpropertiesoflensedgalaxies• Handledwithourlensmodellingapproaches
LargeVelocityGradient(LVG)modelling Line
Ratio
Black:SourceColor: Image
• Thesourcemid-J/low-Jlineratioiscomparabletotheimagelineratio• Thenumberoflinesuseddominates• It’simportanttoacquireanumberoflinesforLVGmodelling
Tkin (K)logNCO (cm-2) log nH2 (cm-3)
logn H
2(cm
-3)
T kin(K)
LineRatio
Black:SourceColor: Image
Red: Source 2 linesBlue: Image 2 linesGreen: Image >3 lines
LargeVelocityGradient(LVG)modelling
• Thesourcemid-J/low-Jlineratioishigherthantheimagelineratio• DifferentialmagnificationbetweenCO(2-1)andCO(6-5)dominates• Weseediscrepancyifweignorethemagnificationsandconductourstudyintheimageplane
LineRatio
Tkin (K)logNCO (cm-2) log nH2 (cm-3)
logn H
2(cm
-3)
T kin(K)
Black:SourceColor: Image
Red: Source 2 linesBlue: Image 2 linesGreen: Image >3 lines
LargeVelocityGradient(LVG)modelling
Summary
• Stronglylenseddustystar-forminggalaxiesareexcellenttoolsforstudyingtheinternalphysicsofhigh-redshiftgalaxies• Visibilitybased lens modellingiscritical• For individualsystems• We identify dynamical features (velocity gradient, merger…)• CO Jup=6-8 sizesthatareonaveragelargerthanthedustsizes• We constrainthegaspressureandcombinationofgasdensitiesandtemperatures
• Forsourceswithdifferentialmagnification,workinginthesourceplaneisessentialtogetthecorrectanswer