2017-07_ICRC_MbmPegasus.ppt Study of the ISM and CRs in the MBM 53-55 Clouds and the Pegasus Loop Jul. 19 th , 2017@ICRC2017 in Busan, South Korea T. Mizuno (Hiroshima Univ.) on behalf of the Fermi-LAT Collaboration Mizuno+16, ApJ 833, 278 (T. Mizuno, S. Abdollahi, Y. Fukui, K. Hayashi, A. Okumura, H. Tajima, 1 and H. Yamamoto) /11 T. Mizuno et al.
Motivation: ISM as a Tracer of CRs(1) ISM: Interstellar medium CR: cosmic ray -ray spectrum shows a low-energy Deconvolved -ray image and Spitzer 4.5 m contours (tracer of cutoff (signature of pi 0 -decay) shocked H 2 ) W44 2-10 GeV Abdo+10, Science 327, 1103 Ackermann+13, Science 339, 807 (CA: Tajima, Tanaka, Uchiyama) (CA: Funk, Tanaka, Uchiyama) 2 /11 T. Mizuno et al.
Motivation: ISM as a Tracer of CRs(2) -ray spectrum shows a low-energy cutoff (signature of pi 0 -decay) Parameters of the source 5x10 51 erg W SN 4x10 49 (n/100cm -3 ) -1 erg W CR An accurate estimate of the ISM densities is crucial to study Galactic CRs, since � � ∝ � � ��� � �� Ackermann+13, Science 339, 807 (CA: Funk, Tanaka, Uchiyama) 3 /11 T. Mizuno et al.
Uncertainty of ISM: Dark Gas(1) Residual rays in Chamaeleon molecular ( ) clouds (fitted by N(HI)+W CO ) • Fermi revealed a component of ISM not measurable by standard tracers (HI 21 cm, CO 2.6 mm), confirming an earlier claim by EGRET (Grenier+05) Residual gas inferred from dust emission (fitted by N(HI)+W CO ) (mag) Ackermann+12, ApJ 725, 22 (CA: Hayashi, TM) 4 /11 T. Mizuno et al.
Uncertainty of ISM: Dark Gas(2) Residual rays in Chamaeleon molecular ( ) clouds (fitted by N(HI)+W CO ) • Fermi revealed a component of ISM not measurable by standard tracers (HI 21 cm, CO 2.6 mm), confirming an earlier claim by EGRET (Grenier+05) • Mass of “dark gas” is comparable to or greater than that of H 2 traced by W CO Molecular cloud H 2 mass traced by “dark gas” mass M DG /M H2,CO W CO (M solar ) (M solar ) ~4 Chamaeleon ~5x10 3 ~2.0x10 4 R CrA ~10 3 ~10 3 ~1 Cepheus & Polaris ~3.3x10 4 ~1.3x10 4 ~0.4 Orion A ~0.5 ~5.5x10 4 ~2.8x10 4 Ackermann+12, ApJ 755, 22 (CA: Hayashi, TM); Ackermann+12, ApJ 756, 4 (CA: Okumura, Kamae) See also Planck Collaboration 2015, A&A 582, 31 (CA: Grenier) 5 /11 T. Mizuno et al.
Study of ISM and CRs using Fermi-LAT • Study of ISM and CRs in high-latitude clouds using Fermi-LAT data has advanced significantly – We can assume that CR flux is uniform – We now have Planck dust thermal emission model to trace total gas column density (N(H tot )) distribution in a fine resolution – Yet, a procedure to convert dust distribution into N(H tot ) has not been established • Here we will present the study of MBM53-55 and Pegasus loop (10 20 cm -2 ) MBM 53-55 Pegasus loop MBM 53,54,55 and Pegasus loop MBM: Magnanim, Britz, & Mundy 1985 6 /11 T. Mizuno et al.
W HI -Dust Relation (1) • Dust is mixed with gas and has been used as a tracer of N(H tot ) – But what kind of quantity should we use? • We examined correlations btw. W HI and two dust tracers (radiance (R) and opacity at 353 GHz ( 353 )) (see also Fukui+14,15, Planck Collab. 2014) – Two tracers show different, dust-temperature (T d ) dependent correlations lines show best-fit linear relations in T d >21.5K to convert R (or 353 ) into N(H tot ) for all T d (initial analysis) 7 /11 (Areas with W co >1.1 K km/s are masked) T. Mizuno et al.
W HI -Dust Relation (2) • We examined correlations btw. W HI and two dust tracers (radiance (R) and opacity at 353 GHz ( 353 )) (see also Fukui+14,15, Planck Collab. 2014) – Two tracers show different and T d -dependent correlations – Two template maps ( ∝ R or 353 ) not well correlate with -ray data; both I ,gas /R and I ,gas / 353 depend on T d . (likely due to dust properties) => use -ray data to compensate for the dependence �� � ∝ � � ��� � �� � N(H tot ) template ( ∝ R) (10 20 cm -2 ) N(H tot ) template ( ∝ 353 ) (10 20 cm -2 ) 8 /11 T. Mizuno et al.
T d -Corrected Modeling We can correct dust-based N(H tot ) map to match with -ray data (robust • tracer of N(H tot )) – start with R-based template and increase N(H tot ) in low T d area • T bk =20.5 K and C=2 (10% increase in N(H tot ) by 1K) provides highest fit likelihood. It gives M DG /M H2,CO <= 5. N(H tot ) inferred from -ray data (10 20 cm -2 ) 9 /11 T. Mizuno et al.
Discussion (HI emissivity or I CR ) • We compare HI emissivity spectrum with model curves based on the local interstellar spectrum (LIS) and results by relevant LAT studies (employing a conventional template-fitting method) Our spectrum agrees with the model for LIS with m (nuclear • enhancement factor)~1.5, while previous LAT studies favor m ~1.8 ( ∝ � �� � Most of difference comes from different N(H tot ) in low T d area (where our method has more flexibility to adjust N(H tot )) Systematic study of high-lat. regions is necessary to better understand the ISM and CRs 10 /11 T. Mizuno et al.
Summary • An accurate estimate of ISM densities is crucial to study CRs • Diffuse GeV rays are a powerful probe to study the ISM and CRs • We present a joint Planck & Fermi-LAT study of MBM 53-55 clouds and the Pegasus loop for the first time – We propose to use rays as a robust tracer of N(H tot ), and obtained the ISM and CR properties • M DG /M H2,CO <=5, • HI emissivity consistent with LIS & m ~1.5 favored – Systematic study of high-latitude regions is necessary to better understand the ISM and CRs Thank you for your Attention 11 /11 T. Mizuno et al.
References (Fermi-LAT Studies of Diffuse Emission in MW) • Abdo+09, ApJ 703, 1249 (CA: TM) • Abdo+09, PRL 103, 251101 (CA: Johanneson, Porter, Strong) • Abdo+10, ApJ 710, 133 (CA: Grenier, Tibaldo) • Abdo+10, PRL 104, 101101 (CA: Ackermann, Porter, Sellerholm) • Ackermann+11, ApJ 726, 81 (CA: Grenier, TM, Tibaldo) • Ackermann+12, ApJ 750, 3 (CA: Johanneson, Porter, Strong) • Ackermann+12, ApJ 755, 22 (CA: Hayashi, TM) • Ackermann+12, ApJ 756, 4 (CA: Kamae, Okumura) • Ackermann+12, A&A 538, 71 (CA: Grenier, Tibaldo) • Ackermann+14, ApJ 793, 64 (CA: Franckowiak, Malyshev, Petrosian) • Casandjian 2015, ApJ 806, 240 • Ackermann+15, ApJ 799, 86 (CA: Ackermann, Bechtol) • Tibaldo+15, ApJ 807, 161 (CA: Digel, Tibaldo) • Planck Collaboration 2015, A&A 582, 31 (CA: Grenier) • Ajello+16, ApJ 819, 44 (CA: Porter, Murgia) • Acero+16, ApJS 223, 26 (CA: Casandjian, Grenier) • Mizuno+16, ApJ 833, 278 • Remy+17, A&A 601, 78 (CA: Grenier, Remy) 12 /11 T. Mizuno et al.
References (others) • Atwood+09, ApJ 697, 1071 • Bolatto+03, ARAA 51, 207 • Bell+06, MNRAS 371, 1865 • Clemens 85, ApJ 295, 422 • Dame+01, ApJ 547, 792 • Fukui+14, ApJ 796, 59 • Fukui+15, ApJ 798, 6 • Grenier+05, Science 307, 1292 • Grenier+15, ARAA 53, 199 • Kalberla+05, A&A 440, 775 • Kiss+04, A&A 418, 131 • Magnami, Britz & Mundy 1985, ApJ 295, 402 • Planck Collaboration XI 2014, A&A 571, 11 • Strong & Moskalenko 98, ApJ 509, 212 • Welty+89, ApJ 346, 232 • Yamamoto+03, ApJ 592, 217 • Yamamoto+06, ApJ 642, 307 • Ysard+15, A&A 577, 110 13 /11 T. Mizuno et al.
Backup Slides 14 /11 T. Mizuno et al.
Uncertainty of ISM: X CO (1) • Usually CO 2.6 mm line observations have been used to estimate H 2 gas mass (and CR density). A canonical value of � �� ≡ � � � /� �� �� ~� � �� �� �� �� � �� � �� �� • • Uncertainty is uncomfortably large (factor of >=3) Bolatto+03, ARAA 51, 207 15 /11 T. Mizuno et al.
Uncertainty of ISM: X CO (2) A canonical value of � �� ≡ � � � /� �� �� ~� � �� �� �� �� � �� � �� �� • rays are a useful probe to study X CO • – CRs penetrate to the core of H 2 clouds – CR density can be estimated from nearby HI clouds – X CO, does not depend on assumptions on the dynamical state of the gas • Even in nearby clouds, uncertainty is by a factor of >=2 Fermi-LAT radiative transfer of 12 CO and 13 CO dust-derived values Grenier+15, ARAA 53, 199 nearby clouds 2 4 6 8 10 12 14 16 kpc 16 /11 T. Mizuno et al.
X CO in Small and Large Scales • The study confirms (sometimes overlooked) discrepancy of X CO, between measurements at nearby clouds and large Galactic scales • This may be due to determination biases induced by difficulty at large distance to separate HI clouds and dark gas envelopes from CO-bright H 2 cloud X CO =1.5-2.5 (1.5-2.0 by EGRET and Fermi) X CO =0.6-2.1 (0.6-1.4 by EGRET and Fermi) 17 /11 T. Mizuno et al. Remy+17, submitted to A&A
All-Sky Map in Rays • Interstellar Medium (ISM) plays an important role in physical processes in the Milky Way Diffuse GeV rays are a powerful probe to study the ISM gas • [tracer of the total gas column density, N(H tot )] Geminga Vela Galactic plane Crab 3C 454.3 Fermi-LAT 4 year all-sky map = point sources + diffuse rays ~80% of rays 18 /11 T. Mizuno et al.
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