synergy of gamma-ray and (mm-) radio o bservations in studying m olecular clouds

2014-07_NobeyamaWS.ppt

T. Mizuno et al. /13

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Synergy of Gamma-ray and (mm-) Radio Observations in Studying Molecular Clouds

July 23, 2014@NobeyamaT. Mizuno

(Hiroshima Astrophysical Science Center)



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分子雲研究におけるガンマ線観測と ( ミリ波 ) 電波観測の連携

July 23, 2014@NobeyamaT. Mizuno

(Hiroshima Astrophysical Science Center)



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Introduction: Gamma-Ray Astrophysics

A powerful probe to study CRs and ISM in distant locations=> Molecular Clouds

g-rays = CRs x ISM (or ISRF)

• known ISM distribution => CRs• those “measured” CRs => ISM

Fermi-LAT (GeV, FOV of ~2.4p sr) or IACT (TeV, FOV of a few deg.)

Cosmic-rays

Interstellar Medium



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Fermi-LAT Performance

• Large FOV (~2.4p sr)• Large effective area (>=0.7 m2 in >= 1 GeV• Moderate PSF (~0.8 deg@1 GeV, ~0.2 deg@10 GeV)

Effective Area (P7rep) PSF

http://www.slac.stanford.edu/exp/glast/groups/canda/lat_Performance.htm

Ackermann+12, ApJS 203, 70 (CA: Baldini, Charles, Rando)Bregeon+13, arXiv:1304.5456



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All-Sky Map in Microwave

• Planck microwave map (30-857 GHz)= dust thermal emission = ISM

Cepheus & Polaris

MBM53,54,55

R CrA

Chamaeleon

OrionTaurus

nearby molecular clouds in high latitude



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All-Sky Map in g-Rays

• GeV g-ray sky~ Diffuse g-rays ~ Cosmic Rays (CRs) x ISM

Fermi-LAT 1 year all-sky map Cepheus & Polaris

R CrA

Chamaeleon

Orion

detailed study of individual clouds (+ISM in galactic plane) published

MBM53,54,55

Taurus



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Modeling of g-ray Data

• Under the assumption of a uniform CR density, g-rays can be represented by a linear combination of template maps

= +

+ Dark Neutral Gas (gas not properly traced by HI and WCO)+ point sources

Inverse Compton

qCO x WCOqHI x N(HI)

Isotropic++

Fermi-LAT data

∝ICR ∝(ICR x XCO)

(HI is usually assumed to be opt-thin; Ts>=120K)(WCO is not a all-sky map)

(e.g., galprop)

(21 cm) (2.6 mm)



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Dark Gas Seen in GeV g-rays (1)

• ISM has been mapped by radio surveys (HI by 21 cm, H2 by 2.6 mm CO)

• Fermi revealed a component of ISM not measurable by those standard tracers

Residual g-rays when fitted by N(HI)+WCO

Chamaeleon Molecular Cloudg-rays w/ CO contour

Ackermann+12, ApJ 755, 22(CA: Hayashi, TM)



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Dark Gas Seen in GeV g-rays (2)

• ISM has been mapped by radio surveys (HI by 21 cm, H2 by 2.6 mm CO)

• Fermi revealed a component of ISM not measurable by those standard tracers, confirming an earlier claim based on EGRET study (Grenier+05)Residual gas inferred by dust


(“dark-gas“ no longer dark in g-rays)




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Amount of Dark Gas

• Fermi revealed a component of ISM not measurable by those standard tracers

• Amount of “dark gas” is comparable to or greater than gas mass traced by WCO


Molecular cloud Gas mass traced by CO (Msolar)

“dark gas” (Msolar)

Chamaeleon ~5x103 ~2.0x104

R CrA ~103 ~103

Cepheus & Polaris ~3.3x104 ~1.3x104

See also Abdo+10 (ApJ 710, 133), Ackermann+11 (ApJ 726, 81)and Ackermann+12 (ApJ 756, 4)

(Both MCO and MDG ∝ ICR ∝ N(HI))



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Compilation of Xco

• g-ray is a useful probe to study Xco– Penetrate the clouds– CR density can be estimated from nearby HI regions– Does not depend on assumptions about the dynamical state

(NB green shaded region was determined using an a priori assumption on CR flux)

Nearby clouds show smaller Xco

Study of other clouds is important

individual clouds



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Compilation of local ICR

• “local” CR densities among regions agree by a factor of 1.5, within systematic uncertainty (mostly due to the assumption of Ts)

All-sky average

individual regions

E2 x E

mis

sivi

ty (

∝I CR

)



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Summary

• g-ray is a powerful probe to CRs and ISM– optically thin, directly traces all gas phases

• Fermi-LAT performed detailed studies of molecular clouds– confirmation of dark neutral gas– measurement of ICR, Xco(MCO), MDG – but limitation exists …

• Desirable data to resolve limitations– accurate determination of N(HI)– (more) complete survey of Wco

Thank you for your Attention

(sorry not a specific suggestion to 45m Telescope. fine resolution maps are certainly important. would be useful if combined with accurate N(HI) and large-scale Wco)



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Reference

• Dame et al. 2001, ApJ 547, 792• Kalberla et al. 2005, A&A 440, 775• Grenier et al. 2005, Science 307, 1292• Atwood et al. 2009, ApJ 687, 1071• Abdo et al. 2009, ApJ 703, 1249• Abdo et al. 2009, PRL 103, 251101• Abdo et al. 2010, ApJ 710, 133• Ackermann et al. 2011, ApJ 726, 81• Fukui et al. 2012, ApJ 746, 82• Ackermann et al. 2012, ApJ 755, 22• Ackermann et al. 2012, ApJ 756, 4



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Backup Slides



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Fermi Gamma-ray Space Telescope

• Fermi = LAT + GBM• LAT = GeV Gamma-ray Space Telescope (20 MeV

~ >300 GeV; All-Sky Survey )

3c454.3

2008.06 launch2008.08 Sci. Operation

1873 sourcesNolan+ 2012, ApJS 199, 31

Cape Canaveral, Florida

(GC-emphasized observation started in 2013 Dec.)



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g-ray Telescopes

Imaging Atmospheric Cherenkov Telescopes (HESS, MAGIC, VERITAS)30 GeV-10 TeV, FOV of a few degree

Fermi-LAT (Satellite)20 MeV-300 GeV, FOV of ~2.4p sr

GeV g-rays (<100 GeV) by Fermi-LATTeV g-rays (>100 GeV) by IACTs



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Processes to Produce g-rays (2)

g-rays = CRs x ISM (or ISRF)

A powerful probe to study CRs and ISM

Abdo+09, PRL 103, 251101(CA: Porter, Strong, Johanneson)

(isotropic)

Inverse Compton,G~2.1

Bremsstrahlung,G~3.2

p0 decay, G~2.7

Pro: optically-thin, “direct” tracer of all gas phasesCon: low-statistics, contamination (isotropic, IC), depend on CR density

g-ray data and model(mid-lat. region)



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Dark Neutral Gas

• Grenier+05 claimed there exist considerable amount of gas not properly traced by radio surveys (HI by 21 cm, H2 by 2.6 mm CO) surrounding nearby CO clouds– cold HI? CO-dark H2?

Grenier+05, Science 307, 1292

E(B-V)excess (residual gas inferred by dust) and Wco

“Dark-gas” inferred by g-rays(CGRO EGRET)

Confirmation and detailed study by current telescopes are important

center@l=70deg



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Dark Gas Seen in TeV g-rays

• Fukui+12 claimed there exist considerable amount of “dark HI” in RX J1713.7-3946 by comparing HI, CO and g-rays

Np(H2) Corrected Np(HI)

Np(Htot) TeV g-ray (H.E.S.S.)



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XCO and XDG by g-rays

• No apparent spectral change in qCO/qHI and qDG/qHI, indicating CR penetration to dense H2 (CO) and dark gas


High E

low E

synergy of gamma-ray and (mm-) radio o bservations in studying m olecular clouds

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