The Distribution of [CII] 158um emission in the Milky Way revealed by Herschel HIFI

Jorge L. PinedaGOTC+ team: William D. Langer, Paul Goldsmith,

Thangasamy Velusamy, Di Li, Karen Willacy, and Harold Yorke

Jet Propulsion LaboratorySeptember 2011

2

[CII] Tracks Interstellar Cloud Evolution

got C+?

CO H2

HI H0

Bill Langer (JPL), MW2011, September 20, 2011

C+HI + H2

• Diffuse, atomic gas: H, C+

• Transition clouds: H->H2, C+-> C0->CO

• Photon Dominated Regions (PDRs) H2, C+, C0,CO,13CO, etc

• [CII] traces the physical conditions of the gas in all these cloud evolution stages.

• [CII] is the brightest far-infrared line.

3

COBE & BICE to Herschel HIFI

BICE and IRAS

Herschel HIFI has the spectral (<0.5 km/s) and spatial resolution (12”) to study individual clouds.

3kpc armMolecular Ring?

PDR/HII?

Local ISMNearby arms

HIFI

• CII - strongest Galactic far-IR line • COBE 7o beam & ΔV ~ 103 km/s • BICE 15’ beam & ΔV ~ 175 km/s• COBE - widespread distribution of CII in

the Galactic plane • BICE - inner Galaxy distribution.

350o < l < 30o & |b| < 3o

CII

far-IR dust

Galactic Observation ofTerahertz C+ (GOT C+)

11 LOS11 LOS

6 LOS

7 LOS

11 LOS10 LOS

7 LOS

6 LOS

Galactic Plane Survey - systematic volume weighted sample of 500 l.o.s. in the disk– l (0o – 360o) at b = 0o, +/- 0.5o & 1o

Galactic Central Region: CII strip maps at 360 positions in on the fly (OTF) mapping mode.

Observations completed

Galactic Observation of Terahertz C+ (GOT C+)

1.0

0.5

0.0

-0.5

-1.0

Galactic Longitude (l)

• Sampling every degree in galactic longitude in the inner galaxy

• Sampling every 2 degrees in galactic longitude in the outer galaxy

Gal

actic

Lati

tude

(b)

HI

Data from:SGPS, VGPS, and CGPS

HIHI+CO

Data from:Mopra and CSO

HIHI+COCII+HI

CII+HI+CO

Diffuse

Warm DenseCold Dense

-180°

-200 km/s

200 km/s

longitude

LSR Velocity

180°

b=0.0° HI

HI

-180°

-200 km/s

200 km/s

longitude

LSR Velocity

180°

b=0.0° HI

HI

-180°

-200 km/s

200 km/s

longitude

LSR Velocity

180°

b=0.0° HI+CO

HIHI+CO

-180°

-200 km/s

200 km/s

longitude

LSR Velocity

180°

b=0.0° HI+CO

HIHI+CO

-180°

-200 km/s

200 km/s

longitude

LSR Velocity

180°

b=0.0° HI+CO+CII

HIHI+COHI+CIICII+CO+HI

-180°

-200 km/s

200 km/s

longitude

LSR Velocity

180°

b=0.0° HI+CO+CII

HIHI+COHI+CIICII+CO+HI

CO

CO+13COCO

CO+13COCO

CII+COCII+CO+13CO

CII

Cold Dense

Low-Column Density

High-Column Density/PDRs

Diffuse

-180°

-200 km/s

200 km/s

longitude

LSR Velocity

180°

COb=0.0°

CO

-180°

-200 km/s

200 km/s

longitude

LSR Velocity

180°

COb=0.0°

CO

-180°

-200 km/s

200 km/s

longitude

LSR Velocity

180°

CO+13COb=0.0°

COCO+13CO

-180°

-200 km/s

200 km/s

longitude

LSR Velocity

180°

CO+13COb=0.0°

COCO+13CO

-180°

-200 km/s

200 km/s

longitude

LSR Velocity

180°

b=0.0° CO+13CO+CII

COCO+13COCIICO+CIICO+13CO+CII

-180°

-200 km/s

200 km/s

longitude

LSR Velocity

180°

b=0.0° CO+13CO+CII

COCO+13COCIICO+CIICO+13CO+CII

-180°

-200 km/s

200 km/s

longitude

LSR Velocity

180°

b=0.0° CO+13CO+CII

COCO+13COCIICO+CIICO+13CO+CII

CII+HILanger et al. 2010,2011, Bill Langer’s talk tomorrow

HI+CII+COVelusamy et al. 2010, Velusamy’s poster #31

CII+CO+13COPineda et al. 2010

Application:

Disentangling the WNM and CNM in the Galaxy

Disentangling the WNM and CNM in the Galaxy

• The neutral interstellar medium gas is the dominant component of the ISM in galaxies.

• This gas consist in two components in rough thermal pressure equilibrium (Wolfire et al. 1995): the cold neutral medium (nh ~40cm-3; T=100K; CNM) and the warm neutral medium (nh ~0.5cm-3; 8000K; WNM).

• HI 21cm observations are only sensitive to the total column density of the gas making it impossible to disentangle the CNM and WNM gas from just from the HI emission in the galaxy.

• The [CII] emission traces the diffuse neutral gas but is sensitive to density and temperature. We can use GOTC+ [CII] observations along with HI to separate the CNM and WNM components in the Galaxy.

Disentangling the WNM and CNM in the Galaxy

• The [CII] intensity is proportional to density and temperature as

CII n∝ h*exp(-91.3K/Tkin)

• For T = 100K , and a typical HI column density of 1021 cm-2, the GOTC+ survey is sensitive to a HI gas with nh > 50 cm-3.

• We use the GOT C+ survey to separate the CNM and WNM components from the HI position velocity map of the Galaxy.

CNM Column Density

WNM ColumnDensity

WNM Velocity Range

CNM Velocity Range

CNM Column Density

WNM ColumnDensity

Disentangling the WNM and CNM in the Galaxy

HI, CNM HI, WNM [CII]b=0.0°

-180° +180°

-200 km/s

200 km/s

longitude

LSR Velocity

Total Column density and Velocity Range vs galactic longitude: b=0.0

Column density

Velocity Range

Total Column Density

WNM Column Density

CNM Column Density

Total Velocity Range

WNM Velocity Range

CNM Velocity Range

Column density Velocity Range

Total Column density and Velocity Range vs galactic longitude: b=+/-0.5

Column density Velocity Range

Total Column density and Velocity Range vs galactic longitude : b=+/-1.0

-180° < l < 180°

b = -1.0 b = -0.5 b = 0.0 b = +0.5 b = -1.0

15 1621

12 9

85 8379

88 91

Mass Fraction

CNM WNM

longitudeb = -1.0 b = -0.5 b = 0.0 b = +0.5 b = -1.0

16 13 1610 12

84 87 8490 88

Area Fraction

CNM WNM

-60° < l < 60°

b = -1.0 b = -0.5 b = 0.0 b = +0.5 b = -1.0

1420

26

1511

8680

74

8589

Mass Fraction

CNM WNM

b = -1.0 b = -0.5 b = 0.0 b = +0.5 b = -1.0

15 1620

13 14

85 8480

87 86

Area Fraction

CNM WNM

-30° < l < 30°

b = -1.0 b = -0.5 b = 0.0 b = +0.5 b = -1.0

2027

33

2015

8073

67

8085

Mass Fraction

CNM WNM

b = -1.0 b = -0.5 b = 0.0 b = +0.5 b = -1.0

19 22 25

17 17

81 78 75

83 83

Area Fraction

CNM WNM

• 20% of HI mass is in the CNM (nh ~40 cm-3; T=100K) and 80% in the WNM (nh ~0.5cm-3; T=8000K)

• The cold neutral medium mass increases up to about 30% in the inner galaxy.

• 16% of the area in the galaxy is populated by cold neutral medium clouds and 84% by warm neutral medium clouds.

Disentangling the WNM and CNM in the Galaxy

Fraction of the Column density and Velocity range in CNM and WNM : b=0.0

Column density

Velocity Range

WNM Column Density Fraction

CNM Column Density Fraction

WNM Velocity Range Fraction

CNM Velocity Range Fraction

Column density Velocity Range

Fraction of the Column density and Velocity range in CNM and WNM : b=+/-0.5

Column density Velocity Range

Fraction of the Column density and Velocity range in CNM and WNM : b=+/-1.0