as the target of hadronic gamma rays Yasuo Fukui Nagoya University Southern Observatories CTA meeting April 1617 2015 Adelaide 1 ISM I nterstellar medium ISM between stars ID: 482886
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Slide1
Accurate measurement of interstellar hydrogen
as
the target of
hadronic gamma rays
Yasuo FukuiNagoya UniversitySouthern Observatories CTA meetingApril 16-17, 2015, Adelaide
1Slide2
ISM
I
nterstellar
medium ISM between starsISM consists of gas and dust
Mgas/Mdust is 100, dust grains include most of the heavy elements; H:He:CNO = 1:10-1:10
-
4
Gas consists of neutral and ionized components Neutral is dominant, related to star formationNeutral consists of molecular and atomic gas 1951 discovery of 21cm HI 1970 discovery of 2.6mm CO [H2 has no suitable transition]
2Slide3
HI is assumed to be optically thin in text booksSlide4
Molecular vs. atomic
HI
gas: average density 1 cm-3,
Tk=125K “assumption, 21cm line optically thin”
--NHI=1.8e18 WHIDark gas: gamma rays (pp reaction p0 2g), dust extinction “cannot be seen in HI or CO”
--CO-free H2?
H2 gas: density 1000 cm-3,
Tk=10K “CO 2.6mm line via Xco factor”--NH2=Xco Wco (factor of 2 uncertainty)
4Slide5
Kalberla+ 2005
Courtesy of Legacy Archive for Microwave Background Data Analysis
The Leiden/Argentine/Bonn Galactic HI Survey
HI LAB
5Slide6
GeV Gamma raysSlide7
Planck Collaboration, arXiv:
1101.2029
CO surveys : CfA + NANTENSlide8
Isabelle
Grenier
et al. Science 2005Column density of dark gas ~ 1020.5
-1021.5 /cm28Slide9
Nearby cloud without background source
[Fukui+ 2014]Slide10
MBM 53, 54, 55
tau353-WHI
相関プロット
HI dust correlation is badPlanck sub-mm data 10Slide11
MBM 53, 54, 55
tau353-WHI
相関プロット
HI dust correlation is badPlanck sub-mm data 11
Td highestHI is thinWith Td decreaseHI becomes thickFukui+ 2014; 2015Slide12
Fig. 3
Ts=10, 20, 30, …, 100 KSlide13Slide14
All sky Planck tau353:
Fukui+2015
masked in gray [double HI profiles/H
a/CO/Plane]Slide15Slide16Slide17
Excess NHI
=“Dark gas” Slide18
Planck Collaboration, arXiv:1101.2029Slide19
Planck Collaboration, arXiv:1101.2029Slide20
HI becomes dark at higher density
Goldsmith et al. 2007
20Slide21
Step 1
We estimate the W(HI) range
Step 2
Estimating a conversion factor
form W(HI) to
N
H using linier
fittingStep 3We apply the correction
Tau 353 vs. W(HI)Slide22
(left) Image: Total
interstellar
proton column density, contours: TeV
γ-rays (Aharonian+07)(Right) Azimuthal plotsFukui, Sano+15 in prep.
Vela Jr. total ISM protons & TeV γ-raysSlide23
Vela Jr. total ISM protons &
TeV
γ-rays(optically thick HI corrected)
(left) Image: Total interstellar proton column density, contours: TeV γ-rays (Aharonian+07)(Right) Azimuthal plotsFukui, Sano+15 in prep.Slide24
RX
J1713.7-3946:
Interstellar proton vs.
TeV gamma raysFukui et al. 2012
HI + 2H224Slide25
Dark HI SE Cloud (Self-Absorption)
25Slide26
26
HI self absorptionSlide27
Very accurate measurement of both atomic/molecular
hydrogen has become possible by “truly optically thin HI”
HI
gas: average density 1 cm-3, Tk
=125K “assumption, 21cm line optically thin”--NHI=1.8e18 x WHI but HI is optically thickDark gas: gamma rays (pp
reaction
p
0 2g), dust extinction. CTA will play a major roleH2 gas: density 1000 cm-3, Tk=10K “CO 2.6mm line via Xco factor”--NH2=
Xco
x
Wco
(factor of 2 uncertainty)
27