2012ApJ...756....4A

Query : 2012ApJ...756....4A

2012ApJ...756....4A - Astrophys. J., 756, 4 (2012/September-1)

Gamma-ray observations of the Orion molecular clouds with the Fermi large area telescope.

ACKERMANN M., AJELLO M., ALLAFORT A., ANTOLINI E., BALDINI L., BALLET J., BARBIELLINI G., BASTIERI D., BECHTOL K., BELLAZZINI R., BERENJI B., BLANDFORD R.D., BLOOM E.D., BONAMENTE E., BORGLAND A.W., BOTTACINI E., BRANDT T.J., BREGEON J., BRIGIDA M., BRUEL P., BUEHLER R., BUSON S., CALIANDRO G.A., CAMERON R.A., CARAVEO P.A., CECCHI C., CHEKHTMAN A., CHIANG J., CIPRINI S., CLAUS R., COHEN-TANUGI J., CONRAD J., D'AMMANDO F., DE ANGELIS A., DE PALMA F., DERMER C.D., DO COUTO E SILVA E., DRELL P.S., DRLICA-WAGNER A., ENOTO T., FALLETTI L., FAVUZZI C., FEGAN S.J., FERRARA E.C., FOCKE W.B., FUKAZAWA Y., FUKUI Y., FUSCO P., GARGANO F., GASPARRINI D., GERMANI S., GIGLIETTO N., GIORDANO F., GIROLETTI M., GLANZMAN T., GODFREY G., GUIRIEC S., HADASCH D., HANABATA Y., HARDING A.K., HAYASHIDA M., HAYASHI K., HORAN D., HOU X., HUGHES R.E., JACKSON M.S., JOHANNESSON G., JOHNSON A.S., KAMAE T., KATAGIRI H., KATAOKA J., KERR M., KNODLSEDER J., KUSS M., LANDE J., LARSSON S., LEE S.-H., LONGO F., LOPARCO F., LOVELLETTE M.N., LUBRANO P., MAKISHIMA K., MAZZIOTTA M.N., MEHAULT J., MITTHUMSIRI W., MOISEEV A.A., MONTE C., MONZANI M.E., MORSELLI A., MOSKALENKO I.V., MURGIA S., NAKAMORI T., NAUMANN-GODO M., NISHINO S., NORRIS J.P., NUSS E., OHNO M., OHSUGI T., OKUMURA A., ORIENTI M., ORLANDO E., ORMES J.F., OZAKI M., PANEQUE D., PANETTA J.H., PARENT D., PELASSA V., PESCE-ROLLINS M., PIERBATTISTA M., PIRON F., PIVATO G., PORTER T.A., RAINO S., RAZZANO M., REIMER A., REIMER O., ROTH M., SADROZINSKI H.F.-W., SGRO C., SISKIND E.J., SPANDRE G., SPINELLI P., STRONG A.W., TAKAHASHI H., TAKAHASHI T., TANAKA T., THAYER J.G., THAYER J.B., TIBOLLA O., TINIVELLA M., TORRES D.F., TRAMACERE A., TROJA E., UCHIYAMA Y., USHER T.L., VANDENBROUCKE J., VASILEIOU V., VIANELLO G., VITALE V., WAITE A.P., WANG P., WINER B.L., WOOD K.S., YANG Z. and ZIMMER S.

Abstract (from CDS):

We report on the gamma-ray observations of giant molecular clouds Orion A and B with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. The gamma-ray emission in the energy band between ∼100 MeV and ∼100 GeV is predicted to trace the gas mass distribution in the clouds through nuclear interactions between the Galactic cosmic rays (CRs) and interstellar gas. The gamma-ray production cross-section for the nuclear interaction is known to ∼10% precision which makes the LAT a powerful tool to measure the gas mass column density distribution of molecular clouds for a known CR intensity. We present here such distributions for Orion A and B, and correlate them with those of the velocity-integrated CO intensity (WCO) at a 1°x1° pixel level. The correlation is found to be linear over a WCO range of ∼10-fold when divided in three regions, suggesting penetration of nuclear CRs to most of the cloud volumes. The WCO-to-mass conversion factor, XCO, is found to be ∼2.3x1020/cm2(K km/s)–1 for the high-longitude part of Orion A (l > 212°), ∼1.7 times higher than ∼1.3x1020 found for the rest of Orion A and B. We interpret the apparent high XCO in the high-longitude region of Orion A in the light of recent works proposing a nonlinear relation between H2 and CO densities in the diffuse molecular gas. WCOdecreases faster than the H2 column density in the region making the gas "darker" to WCO.

Abstract Copyright: ∼

Journal keyword(s): gamma rays: ISM - ISM: clouds - ISM: general - ISM: individual: Orion A and Orion B

Simbad objects: 14

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Number of rows : 14
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024 		#notes
1 NAME Per Arm PoG 03 30 +45.0           ~ 1513 0
2 1FGL J0534.7-0531c gam 05 34 45 -05 31.3           ~ 6 0
3 M 42 HII 05 35 17 -05 23.4           ~ 4076 0
4 NAME Ori Region reg 05 35 17.30 -05 23 28.0           ~ 579 0
5 1FGL J0536.2-0607c gam 05 36 15 -06 07.7           ~ 6 0
6 NAME Ori A MoC 05 38 -07.1           ~ 3012 0
7 1FGL J0540.4-0737c gam 05 40 29 -07 37.6           ~ 6 0
8 3C 147.1 HII 05 41 42.6 -01 54 16           ~ 31 0
9 NAME Ori B MoC 05 41 43.0 -01 54 44           ~ 1377 0
10 1FGL J0547.0+0020c gam 05 47 04.95 +00 21 44.8           ~ 15 0
11 NGC 2149 RNe 06 03 28.1 -09 43 57           ~ 33 0
12 NAME Mon R2 HII 06 07 47.58 -06 22 42.6           ~ 742 2
13 NAME Galactic Center reg 17 45 39.60213 -29 00 22.0000           ~ 14416 0
14 NAME Gould Belt PoG ~ ~           ~ 874 1

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