Study of the ISM and CRs of MBM 53,54,55 Clouds and the Pegasus Loop Sep. 14th, 2016@ASJ meeting in Ehime Tsunefumi Mizuno (Hiroshima Univ.) S. Abdollahi, Y. Fukui, K. Hayashi, A. Okumura, H. Tajima, and H. Yamamoto on behalf of the Fermi-LAT Collaboration 高銀緯分子雲領域のガンマ線観測を紹介 星間ガス特に”dark gas”について議論

Fermi衛星LAT検出器によるMBM 53,54,55およびPegasus Loop領域の観測 2016年9月14日@日本天文学会秋季年会(愛媛大学) 水野恒史 (広島大学宇宙科学センター) S. Abdollahi, 福井康雄, 林克洋、奥村曉、田島宏康、山本宏昭 on behalf of the Fermi-LAT Collaboration （日本語のタイトル）

All-Sky Map in g Rays Interstellar Medium (ISM) plays an important role in physical processes in the Milky Way Diffuse GeV g rays are a powerful probe to study the ISM [tracer of the total gas column density, N(Htot)] Vela Geminga Galactic plane 星間ガス：星の材料。重要。 広がったガンマ線は全星間ガスの優れたトレーサー： 　宇宙線強度が一定ならN(Htot)∝Igamma 全天ガンマ線マップ 銀河座標 銀河面が水平の帯 明るいガンマ線源： 　銀河面のパルサー、パルサー星雲 　系外の活動銀河核 広がったガンマ線放射が主成分。昔から星間ガスの研究に使われてきた Crab MBM 53,54,55 3C 454.3 Fermi-LAT 4 year all-sky map = point sources + diffuse g rays ~80% of g rays

Dark Gas Usually ISM gas has been traced by radio surveys (HI by 21 cm, H2 by 2.6 mm CO) Grenier+05 claimed considerable amount of “dark gas” surrounding nearby CO clouds cold HI or CO-dark H2? MDG? it is inferred from the distribution of dust, but what kind of dust property should we use? Grenier+05 通常はHI by 21cm、H2 by 2.6mm (CO) 電波サーベイでトレースしきれない”dark gas”の存在(dust, ガンマ線) Grenier+05の紹介 原子 or 分子？総量？=>我々が解くべき課題 通常はdustを用いるが「dustのどの物理量を用いるべきか」が不定性の要因 center@l=70deg E(B-V)excess (residual gas inferred by dust) and Wco “dark gas” inferred by g rays (EGRET)

MBM 53,54,55 & Pegasus Loop Nearby, high-latitude clouds suitable to study the ISM and cosmic rays (CRs) in the solar neighborhood (Welty+89, Kiss+04, Yamamoto+03,06) d ~ 150 and 100 pc for MBM 53-55 and Pegasus Loop, respectively most of HI in the region of interest (ROI) is local Planck dust temperature (Td) map Planck radiance (R) map converted in N(Htot) template map MBM53-55 & Pegasus Loopの詳細解析 高銀緯、近傍(HIの速度分布からも近傍と言える) Tdマップ Planck衛星のradiance(全放射強度)から適当に全柱密度を予想したマップ 低Td=高N(Htot)=MBM53-55&Pegasus Loop MBM 53-55 Pegasus Loop

WHI-Dust Relation (1) Dust is mixed with gas and has been used as a tracer of N(Htot) but what kind of quantity should we use? We examined correlations btw. WHI and two dust tracers [radiance (R) and opacity at 353 GHz (t353)] (see also Fukui+14,15, Planck Collab. 2014) two tracers show different, Td-dependent correlation with WHI (areas with Wco>1.1 K km/s masked) ここで「dustのどの物理量を用いるべきか？」を考える WHIとdustのトレーサー(radiance, t353)の比較 両者は温度依存性が大きく異なる radianceがN(Htot)のトレーサーになっていれば概ねWHIに比例(optically thin HI)。 T353がN(Htot)のトレーサーになっていればdark gasの寄与大 lines show best-fit linear relations in Td>21.5K

WHI-Dust Relation (2) Dust is mixed with gas and has been used as a tracer of N(Htot) but what kind of quantity should we use? We examined correlations btw. WHI and two dust tracers [radiance (R) and opacity at 353 GHz (t353)] (see also Fukui+14,15, Planck Collab. 2014) two tracers show different, Td-dependent correlation with WHI we tested two tracers against g-ray data. we also examined Td dependence and found that N(Htot,g)/R (or t353) depends on Td. => use g-ray data to compensate for the dependence N(Htot) template (∝ R) (1020 cm-2) N(Htot) template (∝ t353) (1020 cm-2) N(Htot)のテンプレート(∝R or t353)を作成しガンマ線との相関を見た 　t353の方がコントラストが大きく、ガンマ線との相関から区別できる 細かい話は省略 ガンマ線から示唆されるN(Htot)はR, t353のどちらにも比例せず、gas-dust比はTd依存性を持つ ガンマ線をN(Htot)のロバストなトレーサーとして用い、温度依存性を補正 (two tracers show different contrast in N(Htot) template maps)

Td-Corrected Modeling We started with R-based N(Htot) map and employed an empirical function as below [modeling the increase of N(Htot) in areas with low Td] Then we scanned coefficient C which best represents g-ray data idea is to use g-ray data as a robust tracer of N(Htot) Tbk=20.5 K and C=2 [10% required increase in N(Htot) by 1K] gives best lnL ガンマ線をN(Htot)のロバストなトレーサーとして用い、温度依存性を補正 経験的な表式を用いる。RadianceベースのN(Htot)を出発点とし低温ほど柱密度を増やす 係数を変えてlikelihoodを評価 1Kで10%の増加がガンマ線に最もよくあう Preliminary

Discussion (ISM) Preliminary Preliminary Left: the correlation between WHI and the “corrected” N(Htot) map scatter due to dark gas (DG). Ts<100 K is inferred in optically thick HI scenario Right: Integral of gas column density (∝ Mgas) as a function of Td for N(Htot), N(HIthin), N(Htot)-N(HIthin)(~N(H) for dark gas) and 2N(H2,CO) MDG is ~25% of MHI,thin and <= 5 x MH2,CO (the factor of 5 is larger compared to those in other regions) MDG differs by a factor of >=4 if we use only R (or t353); the correction based on g ray data is crucial 左：最終的に得られた(NHtot)とWHIの関係 P6と比較。低温でN(Htot)が大きくなる。 Optically-thick HIのモデルカーブを重ね書き。Ts<100Kが示唆 右：Tdごとのガス密度の分布 N(Htot)黒実線, N(Hthin)黒点線, 両者の差(~dark gas)赤点線,H2 traced by CO青点線 M(DG)はM(H2,CO)の5倍程度。他領域に比べdark gas rich Rベースまたはt353ベースの予想にくらべM(DG)は4倍以上異なる=>ガンマ線による補正が本質 1022 cm-2 deg2 corresponds to ~740 Msun for d=150 pc Preliminary Preliminary

Thank you for your Attention Summary Diffuse GeV g rays are a powerful probe to study the ISM (and CRs) We present a joint Planck & Fermi-LAT study of MBM 53,54,55 clouds and the Pegasus Loop for the first time we found neither R nor t353 inferred from Planck observations were good representations of N(Htot) We propose to use g rays as a robust tracer of N(Htot), and obtained the ISM (and CR) properties moderate scatter in WHI-N(Htot) relation. Ts<100 K is inferred in optically-thick HI scenario MDG is ~25% of MHI,thin and <= 5 x MH2,CO [in terms of N(HDG)/N(H2,CO), the region is dark-gas-rich] (more details on ISM and CRs in the paper submitted) まとめ ガンマ線はISMの良いトレーサー MBM53-55 & Pegasus Loopの詳細解析 　N(Htot)/DがTdに依存 ガンマ線による補正 　TsやMDGの議論 　論文投稿中。出版された暁には読んでフィードバックいただけると嬉しい Thank you for your Attention

References Abdo+09, ApJ 703, 1249 Atwood+09, ApJ 697, 1071 Casandjian+15, ApJ 806, 240 Fukui+14, ApJ 796, 59 Fukui+15, ApJ 798, 6 Grenier+05, Science 307, 1292 Kiss+04, A&A 418, 131 Planck Collaboration XI 2014, A&A 571, 11 Welty+89, ApJ 346, 232 Yamamoto+03, ApJ 592, 217 Yamamoto+06, ApJ 642, 307

Backup Slides

All-Sky Map in g Rays GeV g-ray sky = Point sources + Diffuse g rays Cosmi Rays (CRs) x ISM Cepheus & Polaris Taurus Orion R CrA 全天ガンマ線マップ 銀河座標 銀河面が水平の帯 明るいガンマ線源： 　かに星雲、パルサー 　銀河面のパルサー 　系外の活動銀河核 「実は」広がったガンマ線放射が主成分。これはなんだろうか。 Chamaeleon MBM 53,54,55 Fermi-LAT 4 year all-sky map

All-Sky Map in Microwave Planck microwave map (30-857 GHz) = dust thermal emission = ISM Cepheus & Polaris Taurus Orion R CrA Planckによる全天マイクロ波マップ =「星間ガスのマップ」 銀河面の星間ガス、近傍の星間ガス Chamaeleon MBM 53,54,55 nearby gas in high latitude

Molecular Gas Scale height ~70 pc. Site star formation Usually traced by CO lines in radio not an “all-sky” map, uncertainty of XCO=N(H2)/WCO typically XCO~2x1020 cm-2/(K km/s) Galactic plane 分子ガス(CO map) scale height、全天マップ、不定性 CO 2.6 mm map (Dame+01)

Atomic Gas Scale height ~200 pc. Main component of ISM Usually traced by 21 cm line uncertainty due to the assumption of the spin temperature (Ts) Galactic plane 原子ガス(21cmマップ) scale height, Tsの不定性 HI 21 cm (LAB survey)

Atomic Gas Scale height ~200 pc. Main component of ISM Usually traced by 21 cm line uncertainty due to the assumption of the spin temperature (Ts) (opt-thin) Galactic plane 原子ガス(21cmマップ) scale height, Tsの不定性 HI 21 cm (LAB survey)

ISM Maps of the Region Studied N(HIthin) in 1020 cm-2 Wco in K km/s Td in K

Initial Modeling with a Single N(Htot) Map We assumed N(Htot)∝R (or t353) and constructed N(Htot) maps coefficients were determined by assuming that HI is optically thin and well represents N(Htot) in Td>21.5 K (dotted lines in slide #6) We used 7 years P8R2 data and modeled g-ray intensity as below qg is the emissivity model adopted. subscript i is for separating N(Htot) we found R-based N(Htot) better represents g-ray data in terms of lnL N(Htot) template (∝ R) (1020 cm-2) N(Htot) template (∝ t353) (1020 cm-2)

Td-Sorted Modeling Preliminary Even though R-based N(Htot) is preferred by g-ray data, true N(Htot) could be appreciably different Therefore we split N(Htot) template map into four based on Td and fit g-ray data with scaling factors freely varying individually scaling factors should not depend on Td if N(Htot)∝D (R or t353) Fit improves significantly and shows clear Td dependence of scaling factors the trend is robust against various tests of systematic uncertainty Preliminary

Possible Explanation of Td Dependence (1) We found, from g-ray data analysis, neither the radiance nor t353 are good tracers of N(Htot) Even though the interstellar radiation field (ISRF) is uniform in the vicinity of the solar system, the radiance (per H) could decrease as the gas (and dust) density increases, because the ISRF is more strongly absorbed by dust. This will cause a correlated decrease in the Td and the radiance (per H). Ysard+15, Fig.2 (radiance per H vs. Td for several choices of ISRF hardness. Both radiance and Td decrease as the ISRF is abosrbed)

Possible Explanation of Td Dependence (2) We found, from g-ray data analysis, neither the radiance nor t353 are good tracers of N(Htot) In the optically-thin limit, In = tn Bn(Td) = sn N(Htot) Bn(Td), where tn and sn are the optical depth and the dust opacity (cross section) per H, respectively. sn depends on the frequency and is often describes as a power law, giving In = tn0 (n/n0)b Bn(Td) (modified blackbody, b~1.5-2). Therefore, IF the dust cross section is uniform, tn ∝ N(Htot) and we can measure the total gas column density by measuring the dust optical depth at any frequency (e.g., t353). Relation btw. Tdust and b in MBM & Pegasus However, dust opacity is not uniform but rather anti-correlates with Td as reported by Planck Collaboration (2014).

Td-Corrected Modeling (2) We started with R-based N(Htot) map and employed an empirical function as below [modeling the increase of N(Htot) in areas with low Td] Tbk=20.5 K and C=2 [10% required increase in N(Htot) by 1K] gives best lnL, and obtained N(Htot,mod) and the spectrum are shown below N(Htot) inferred by g-ray data (1020 cm-2) Preliminary Preliminary

Td-Corrected Modeling (3) Obtained data count map (left) and model count map (right) Preliminary Preliminary

Discussion (HI emissivity) HI emissivity spectrum is compared with model curves based on the local interstellar spectrum (LIS) and results by relevant LAT studies Our spectrum agrees with the model for LIS with em (nuclear enhancement factor)=1.45, while previous LAT studies favor em=1.84 Most of difference can be understood due to the different N(Htot) inferred in low Td area where our method has more flexibility to adjust N(Htot) Preliminary

Intermediate Velocity Clouds We are studying high-latitude region, therefore most of gas is in local. Still, there are some clouds with different velocities [intermediate velocity clouds (IVCs)] (left) WHI of local clouds. (right) WHI of IVCs contribution of IVCs is at the ~5% level -30 < Vlsr (km/s) < 20 -80 < Vlsr(km/s) -30 (K km/s) (K km/s) local clouds IVCs