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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