Paul van derder Werf

Leiden Observatory

HH22 emission as a diagnostic emission as a diagnostic

of physical processesof physical processesin star forming galaxiesin star forming galaxies

ParisParis

October 1, October 1, 19991999

Molecular hydrogen emission in star forming galaxiesMolecular hydrogen emission in star forming galaxies 2

HH22 emission as a diagnostic emission as a diagnostic

HH22 rotational lines: rotational lines:

HH22 vibrational lines: vibrational lines:

cf. CO J=1cf. CO J=1--0:0:

T: few hundred KT: few hundred Kn > 10n > 1022 cm cm-3-3

T: few thousand KT: few thousand Kn > 10n > 104-54-5 cm cm-3-3

T: few tens of KT: few tens of Kn > 10n > 1022 cm cm-3-3

Molecular hydrogen emission in star forming galaxiesMolecular hydrogen emission in star forming galaxies 3

HH22 emission lines trace excitation emission lines trace excitation

General General problem: problem: what is the what is the excitation excitation mechanism?mechanism? ShocksShocks UV-pumpingUV-pumping X-ray excitationX-ray excitation ……..

HH22 2.12 2.12 m in NGC253 m in NGC253 (Van der Werf & Moorwood, in preparation)(Van der Werf & Moorwood, in preparation)

15” = 180 15” = 180 pcpc

Molecular hydrogen emission in star forming galaxiesMolecular hydrogen emission in star forming galaxies 4

Two case studiesTwo case studies

Rotational HRotational H22 lines in the disk of NGC891: lines in the disk of NGC891:

Vibrational HVibrational H22 lines in the nuclear region of lines in the nuclear region of

NGC6240:NGC6240:

A new view of the warm molecular mediumA new view of the warm molecular medium(Valentijn & Van der Werf 1999, ApJ 522, L29)(Valentijn & Van der Werf 1999, ApJ 522, L29)

A new diagnostic of the nuclei of gas-rich mergersA new diagnostic of the nuclei of gas-rich mergers(Van der Werf, Moorwood & Israel, in preparation)(Van der Werf, Moorwood & Israel, in preparation)

Molecular hydrogen emission in star forming galaxiesMolecular hydrogen emission in star forming galaxies 5

Dust in NGC891Dust in NGC891

SCUBA 850 SCUBA 850 mm Sky surveySky survey

Israel, Van der WerfIsrael, Van der Werf& Tilanus 1999& Tilanus 1999A&A 344, L83A&A 344, L83

Molecular hydrogen emission in star forming galaxiesMolecular hydrogen emission in star forming galaxies 6

HH22 emission in NGC891 emission in NGC891 ISO-SWS survey to 11 ISO-SWS survey to 11

kpc from centrekpc from centre 2828m and 17m and 17m m

detected at all detected at all positionspositions

0th-order analysis:0th-order analysis:High-density limitHigh-density limitIsothermalIsothermalOrtho/para = 3Ortho/para = 3

All three assumptions fail!All three assumptions fail!

Molecular hydrogen emission in star forming galaxiesMolecular hydrogen emission in star forming galaxies 7

Simple analysis of position 8kpc NSimple analysis of position 8kpc N

Solution: abandon high-density Solution: abandon high-density assumptionassumption

0th order analysis 0th order analysis gives:gives:

T=76KT=76KN(HN(H22)=2.7)=2.710102222cmcm-2-2

CO gives:CO gives:

T~20 KT~20 KN(HN(H22)=1.0)=1.0..10102222cmcm-2-2

Molecular hydrogen emission in star forming galaxiesMolecular hydrogen emission in star forming galaxies 8

Low-density solutionLow-density solution

Adopt density from Adopt density from CO:CO:n(Hn(H22)~200 cm)~200 cm-3-3

T~130 KT~130 KN(HN(H22)=3.6)=3.6..10102121cmcm-2-2

HH22 J=3 (and CO J=2) J=3 (and CO J=2) subthermally populatedsubthermally populated

• Low-density PDRs Low-density PDRs cf. [CII] cf. [CII]• Good throughout inner diskGood throughout inner disk• In outer disk: 2 components?In outer disk: 2 components?

Molecular hydrogen emission in star forming galaxiesMolecular hydrogen emission in star forming galaxies 9

Two-component solutionTwo-component solution

Solution: ortho-para ratio ~ 1Solution: ortho-para ratio ~ 1

•Warm HWarm H22 dominates S(1) dominates S(1)

•Cool HCool H22 dominates S(0) dominates S(0)

T > 130 KT > 130 K

T < 90 KT < 90 KN(HN(H22) > 10) > 102323 cm cm-2-2

M(HM(H22) > 10) > 10 . . M(HI)M(HI)

Problem: temperature balance;Problem: temperature balance; [CII] indicates 15[CII] indicates 15 lower mass lower mass

Molecular hydrogen emission in star forming galaxiesMolecular hydrogen emission in star forming galaxies 10

Vibrational HVibrational H22 emission in ULIGs emission in ULIGs

Sub-arcsecond resolution Sub-arcsecond resolution near-IR Hnear-IR H22 imaging shows imaging shows gas components betweengas components betweenthe nuclei of merging galaxies,the nuclei of merging galaxies,e.g., NGC6240e.g., NGC6240

( Van der Werf ( Van der Werf et al. et al. 1993 ApJ 405, 522)1993 ApJ 405, 522)

•Origin: dissipative components merge first ?Origin: dissipative components merge first ?

•Fate: nuclear starburst ? AGN ?Fate: nuclear starburst ? AGN ?

•Properties: MProperties: Mgasgas ~ M ~ Mdyndyn ? ?

•Role of HRole of H22 emission ? emission ?

Arp220 HArp220 H22 1-0 S(1) 1-0 S(1)(Van der Werf & Israel, (Van der Werf & Israel, in preparation)in preparation)

Molecular hydrogen emission in star forming galaxiesMolecular hydrogen emission in star forming galaxies 11

HH22 2.1 2.1 m emission in NGC6240m emission in NGC6240

HH22 emission peaks emission peaks between the nuclei.between the nuclei.

•MorphologyMorphology•SpectraSpectra }}HH22 emission from emission from

cloud-cloud shockscloud-cloud shocks

HH22 emission powered by emission powered by dissipation of dissipation of mechanical energymechanical energy in nuclear medium in nuclear medium

HH22 emission measures emission measures inflow rate of inflow rate of molecular gas to centre of potential wellmolecular gas to centre of potential well

KK

HH22 1-0 S(1) 1-0 S(1)

10” = 5 kpc10” = 5 kpc

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HH22 vibrational spectrum in NGC6240 vibrational spectrum in NGC6240

•Vibrational lines: Vibrational lines: T~1900 KT~1900 K•Rotational lines: Rotational lines: T~400 KT~400 K

Energy radiated by shocks:Energy radiated by shocks: LLradrad ~ 1.6 ~ 1.6 .. 10 1099 L L

Energy dissipated by shocks:Energy dissipated by shocks: LLdisdis ~ ½ M ~ ½ MHH22

vv22..

LLradrad = L = Ldisdis v~280 km sv~280 km s-1-1

MMHH22 ~ 260 M ~ 260 M yr yr-1-1

..

Molecular hydrogen emission in star forming galaxiesMolecular hydrogen emission in star forming galaxies 13

Fate of the infalling gasFate of the infalling gas

•Southern nucleus: Southern nucleus: MMHH22 ~ 50 M ~ 50 M yr yr-1-1

•Northern nucleus: Northern nucleus: MMHH22 ~ 20 M ~ 20 M yr yr-1-1

•Central component: Central component: MMHH22 ~ 190 M ~ 190 M yr yr-1-1

Nuclei: total mass inflow rate Nuclei: total mass inflow rate 70 M70 M yr yr-1-1

total star formation rate total star formation rate 45 M45 M yr yr-1-1

..

....

Central component: Central component: MMHH22

~2.2 ~2.2 . . 10109 9 MM ~ 30% of M~ 30% of Mdyndyn

ttaccacc ~ 10 ~ 1077 yr yr large shear prevents star formationlarge shear prevents star formation explosive nuclear starburst will resultexplosive nuclear starburst will result

KK

HH22 1-0 S(1) 1-0 S(1) NN

Molecular hydrogen emission in star forming galaxiesMolecular hydrogen emission in star forming galaxies 14

A merger sequence?A merger sequence?

(counterrotating disks)(counterrotating disks)

AntennaeAntennae NGC6240 NGC6240 Arp220Arp220 SCUBA 850 SCUBA 850 mm

(Van der Werf & Moorwood, in preparation)(Van der Werf & Moorwood, in preparation)

Molecular hydrogen emission in star forming galaxiesMolecular hydrogen emission in star forming galaxies 15

ConclusionsConclusions

•In disks of late-type galaxies, HIn disks of late-type galaxies, H22 rotational lines trace rotational lines trace extended low-density PDRsextended low-density PDRs

•In mergers, HIn mergers, H22 lines trace dissipation of mechanical energy lines trace dissipation of mechanical energy in the merging gas componentsin the merging gas components

•In both cases, HIn both cases, H22 lines provide lines provide uniqueunique diagnostics once diagnostics once the excitation mechanism is understood the excitation mechanism is understood