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2014-07_NobeyamaWS.ppt Synergy of Gamma-ray and (mm-) Radio Observations in Studying Molecular Clouds July 23, 2014@Nobeyama T. Mizuno (Hiroshima Astrophysical Science Center) /13 1 T. Mizuno et al. 2014-07_NobeyamaWS.ppt

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

July 23, 2014@Nobeyama

  • T. 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@Nobeyama

  • T. 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

-rays = CRs x ISM (or ISRF)

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

Fermi-LAT (GeV, FOV of ~2.4 sr)

  • r

IACT (TeV, FOV of a few deg.) Cosmic-rays Interstellar Medium

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Fermi-LAT Performance

  • Large FOV (~2.4 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 Orion Taurus

nearby molecular clouds in high latitude

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All-Sky Map in -Rays

  • GeV -ray sky

~ Diffuse -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 -ray Data

  • Under the assumption of a uniform CR density, -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 WCO qHI 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 -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 -rays when fitted by N(HI)+WCO

Chamaeleon Molecular Cloud

-rays w/ CO contour

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

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Dark Gas Seen in GeV -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

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

(“dark-gas“ no longer dark in -rays) Residual -rays when fitted by N(HI)+WCO

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Amount of Dark Gas

  • Fermi revealed a component
  • f ISM not measurable by

those standard tracers

  • Amount of “dark gas” is

comparable to or greater than gas mass traced by WCO

Residual -rays when fitted by N(HI)+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

  • -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
  • f 1.5, within systematic uncertainty (mostly due to

the assumption of Ts)

All-sky average individual regions

E2 x Emissivity (∝ ICR)

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Summary

  • -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 launch 2008.08 Sci. Operation

1873 sources Nolan+ 2012, ApJS 199, 31

Cape Canaveral, Florida

(GC-emphasized observation started in 2013 Dec.)

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-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 ~2.4 sr

GeV -rays (<100 GeV) by Fermi-LAT TeV -rays (>100 GeV) by IACTs

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Processes to Produce -rays (2)

-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, ~2.1 Bremsstrahlung, ~3.2 0 decay, ~2.7 Pro: optically-thin, “direct” tracer of all gas phases Con: low-statistics, contamination (isotropic, IC), depend on CR density

-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 -rays (CGRO EGRET) Confirmation and detailed study by current telescopes are important center@l=70deg

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Dark Gas Seen in TeV -rays

  • Fukui+12 claimed there exist considerable amount of

“dark HI” in RX J1713.7-3946 by comparing HI, CO and -rays

Np(H2) Corrected Np(HI) Np(Htot) TeV -ray (H.E.S.S.)

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XCO and XDG by -rays

  • No apparent spectral change in qCO/qHI and

qDG/qHI, indicating CR penetration to dense H2 (CO) and dark gas

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