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