Fermi Large Area Telescope observations of Local Group galaxies: Detection of M 31 and search for M 33

A. A. Abdo; M. Ackermann; M. Ajello; A. Allafort; W. B. Atwood; L. Baldini; J. Ballet; G. Barbiellini; D. Bastieri; K. Bechtol; R. Bellazzini; B. Berenji; R. D. Blandford; E. D. Bloom; E. Bonamente; A. W. Borgland; A. Bouvier; T. J. Brandt; J. Bregeon; M. Brigida; P. Bruel; R. Buehler; T. H. Burnett; S. Buson; G. A. Caliandro; R. A. Cameron; A. Cannon; P. A. Caraveo; J. M. Casandjian; C. Cecchi; Ö Çelik; E. Charles; A. Chekhtman; J. Chiang; S. Ciprini; R. Claus; J. Cohen-Tanugi; J. Conrad; C. D. Dermer; A. De Angelis; F. De Palma; S. W. Digel; E. Do Couto E Silva; P. S. Drell; A. Drlica-Wagner; R. Dubois; C. Favuzzi; S. J. Fegan; P. Fortin; M. Frailis; Y. Fukazawa; S. Funk; P. Fusco; F. Gargano; S. Germani; N. Giglietto; F. Giordano; M. Giroletti; T. Glanzman; G. Godfrey; I. A. Grenier; M. H. Grondin; S. Guiriec; M. Gustafsson; D. Hadasch; A. K. Harding; K. Hayashi; M. Hayashida; E. Hays; S. E. Healey; P. Jean; G. Jóhannesson; A. S. Johnson; R. P. Johnson; T. J. Johnson; T. Kamae; H. Katagiri; J. Kataoka; M. Kerr; J. Knödlseder; M. Kuss; J. Lande; L. Latronico; S. H. Lee; M. Lemoine-Goumard; F. Longo; F. Loparco; B. Lott; M. N. Lovellette; P. Lubrano; G. M. Madejski; A. Makeev; P. Martin; M. N. Mazziotta; J. Mehault; P. F. Michelson; W. Mitthumsiri; T. Mizuno; A. A. Moiseev; C. Monte; M. E. Monzani; A. Morselli; I. V. Moskalenko; S. Murgia; M. Naumann-Godo; P. L. Nolan; J. P. Norris; E. Nuss; T. Ohsugi; A. Okumura; N. Omodei; E. Orlando; J. F. Ormes; M. Ozaki; D. Paneque; J. H. Panetta; D. Parent; M. Pepe; M. Persic; M. Pesce-Rollins; F. Piron; T. A. Porter; S. Rainò; R. Rando; M. Razzano; A. Reimer; O. Reimer; S. Ritz; R. W. Romani; H. F.W. Sadrozinski; P. M. Saz Parkinson; C. Sgrò; E. J. Siskind; D. A. Smith; P. D. Smith; G. Spandre; P. Spinelli; M. S. Strickman; L. Strigari; A. W. Strong; D. J. Suson; H. Takahashi; T. Takahashi; T. Tanaka; J. B. Thayer; D. J. Thompson; L. Tibaldo; D. F. Torres; G. Tosti; A. Tramacere; Y. Uchiyama; T. L. Usher; J. Vandenbroucke; G. Vianello; N. Vilchez; V. Vitale; A. P. Waite; P. Wang; B. L. Winer; K. S. Wood; Z. Yang; M. Ziegler

doi:10.1051/0004-6361/201015759

Fermi Large Area Telescope observations of Local Group galaxies: Detection of M 31 and search for M 33

A. A. Abdo^*, M. Ackermann, M. Ajello, A. Allafort, W. B. Atwood, L. Baldini, J. Ballet, G. Barbiellini, D. Bastieri, K. Bechtol, R. Bellazzini, B. Berenji, R. D. Blandford, E. D. Bloom, E. Bonamente, A. W. Borgland, A. Bouvier, T. J. Brandt, J. Bregeon, M. BrigidaP. Bruel, R. Buehler, T. H. Burnett, S. Buson, G. A. Caliandro, R. A. Cameron, A. Cannon, P. A. Caraveo, J. M. Casandjian, C. Cecchi, Ö Çelik, E. Charles, A. Chekhtman, J. Chiang, S. Ciprini, R. Claus, J. Cohen-Tanugi, J. Conrad, C. D. Dermer, A. De Angelis, F. De Palma, S. W. Digel, E. Do Couto E Silva, P. S. Drell, A. Drlica-Wagner, R. Dubois, C. Favuzzi, S. J. Fegan, P. Fortin, M. Frailis, Y. Fukazawa, S. Funk, P. Fusco, F. Gargano, S. Germani, N. Giglietto, F. Giordano, M. Giroletti, T. Glanzman, G. Godfrey, I. A. Grenier, M. H. Grondin, S. Guiriec, M. Gustafsson, D. Hadasch, A. K. Harding, K. Hayashi, M. Hayashida, E. Hays, S. E. Healey, P. Jean, G. Jóhannesson, A. S. Johnson, R. P. Johnson, T. J. Johnson, T. Kamae, H. Katagiri, J. Kataoka, M. Kerr, J. Knödlseder, M. Kuss, J. Lande, L. Latronico, S. H. Lee, M. Lemoine-Goumard, F. Longo, F. Loparco, B. Lott, M. N. Lovellette, P. Lubrano, G. M. Madejski, A. Makeev, P. Martin, M. N. Mazziotta, J. Mehault, P. F. Michelson, W. Mitthumsiri, T. Mizuno, A. A. Moiseev, C. Monte, M. E. Monzani, A. Morselli, I. V. Moskalenko, S. Murgia, M. Naumann-Godo, P. L. Nolan, J. P. Norris, E. Nuss, T. Ohsugi, A. Okumura, N. Omodei, E. Orlando, J. F. Ormes, M. Ozaki, D. Paneque, J. H. Panetta, D. Parent, M. Pepe, M. Persic, M. Pesce-Rollins, F. Piron, T. A. Porter, S. Rainò, R. Rando, M. Razzano, A. Reimer, O. Reimer, S. Ritz, R. W. Romani, H. F.W. Sadrozinski, P. M. Saz Parkinson, C. Sgrò, E. J. Siskind, D. A. Smith, P. D. Smith, G. Spandre, P. Spinelli, M. S. Strickman, L. Strigari, A. W. Strong, D. J. Suson, H. Takahashi, T. Takahashi, T. Tanaka, J. B. Thayer, D. J. Thompson, L. Tibaldo, D. F. Torres, G. Tosti, A. Tramacere, Y. Uchiyama, T. L. Usher, J. Vandenbroucke, G. Vianello, N. Vilchez, V. Vitale, A. P. Waite, P. Wang, B. L. Winer, K. S. Wood, Z. Yang, M. Ziegler

^*Corresponding author for this work

School of Advanced Science and Engineering

Research output: Contribution to journal › Article › peer-review

115 Citations (Scopus)

Abstract

Context. Cosmic rays (CRs) can be studied through the galaxy-wide gamma-ray emission that they generate when propagating in the interstellar medium. The comparison of the diffuse signals from different systems may inform us about the key parameters in CR acceleration and transport. Aims. We aim to determine and compare the properties of the cosmic-ray-induced gamma-ray emission of several Local Group galaxies. Methods. We use 2 years of nearly continuous sky-survey observations obtained with the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope to search for gamma-ray emission from M 31 and M 33. We compare the results with those for the Large Magellanic Cloud, the Small Magellanic Cloud, the Milky Way, and the starburst galaxies M 82 and NGC 253. Results. We detect a gamma-ray signal at 5σ significance in the energy range 200 MeV-20 GeV that is consistent with originating from M 31. The integral photon flux above 100 MeV amounts to (9.1 ± 1.9_stat ± 1.0) × 10^-9 ph cm^-2. We find no evidence for emission from M 33 and derive an upper limit on the photon flux >100 MeV of 5.1 × 10^-9 ph cm^-2-1 (2σ). Comparing these results to the properties of other Local Group galaxies, we find indications of a correlation between star formation rate and gamma-ray luminosity that also holds for the starburst galaxies. Conclusions. The gamma-ray luminosity of M 31 is about half that of the Milky Way, which implies that the ratio between the average CR densities in M 31 and the Milky Way amounts to ξ = 0.35 ± 0.25. The observed correlation between gamma-ray luminosity and star formation rate suggests that the flux of M 33 is not far below the current upper limit from the LAT observations.

Original language	English
Article number	L2
Journal	Astronomy and Astrophysics
Volume	523
Issue number	1
DOIs	https://doi.org/10.1051/0004-6361/201015759
Publication status	Published - 2010 Nov 10

Keywords

Local Group
cosmic rays
gamma rays: galaxies

ASJC Scopus subject areas

Astronomy and Astrophysics
Space and Planetary Science

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10.1051/0004-6361/201015759

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Abdo, A. A., Ackermann, M., Ajello, M., Allafort, A., Atwood, W. B., 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., Bouvier, A., Brandt, T. J., Bregeon, J., ... Ziegler, M. (2010). Fermi Large Area Telescope observations of Local Group galaxies: Detection of M 31 and search for M 33. Astronomy and Astrophysics, 523(1), Article L2. https://doi.org/10.1051/0004-6361/201015759

Abdo, AA, Ackermann, M, Ajello, M, Allafort, A, Atwood, WB, Baldini, L, Ballet, J, Barbiellini, G, Bastieri, D, Bechtol, K, Bellazzini, R, Berenji, B, Blandford, RD, Bloom, ED, Bonamente, E, Borgland, AW, Bouvier, A, Brandt, TJ, Bregeon, J, Brigida, M, Bruel, P, Buehler, R, Burnett, TH, Buson, S, Caliandro, GA, Cameron, RA, Cannon, A, Caraveo, PA, Casandjian, JM, Cecchi, C, Çelik, Ö, Charles, E, Chekhtman, A, Chiang, J, Ciprini, S, Claus, R, Cohen-Tanugi, J, Conrad, J, Dermer, CD, De Angelis, A, De Palma, F, Digel, SW, Do Couto E Silva, E, Drell, PS, Drlica-Wagner, A, Dubois, R, Favuzzi, C, Fegan, SJ, Fortin, P, Frailis, M, Fukazawa, Y, Funk, S, Fusco, P, Gargano, F, Germani, S, Giglietto, N, Giordano, F, Giroletti, M, Glanzman, T, Godfrey, G, Grenier, IA, Grondin, MH, Guiriec, S, Gustafsson, M, Hadasch, D, Harding, AK, Hayashi, K, Hayashida, M, Hays, E, Healey, SE, Jean, P, Jóhannesson, G, Johnson, AS, Johnson, RP, Johnson, TJ, Kamae, T, Katagiri, H, Kataoka, J, Kerr, M, Knödlseder, J, Kuss, M, Lande, J, Latronico, L, Lee, SH, Lemoine-Goumard, M, Longo, F, Loparco, F, Lott, B, Lovellette, MN, Lubrano, P, Madejski, GM, Makeev, A, Martin, P, Mazziotta, MN, Mehault, J, Michelson, PF, Mitthumsiri, W, Mizuno, T, Moiseev, AA, Monte, C, Monzani, ME, Morselli, A, Moskalenko, IV, Murgia, S, Naumann-Godo, M, Nolan, PL, Norris, JP, Nuss, E, Ohsugi, T, Okumura, A, Omodei, N, Orlando, E, Ormes, JF, Ozaki, M, Paneque, D, Panetta, JH, Parent, D, Pepe, M, Persic, M, Pesce-Rollins, M, Piron, F, Porter, TA, Rainò, S, Rando, R, Razzano, M, Reimer, A, Reimer, O, Ritz, S, Romani, RW, Sadrozinski, HFW, Saz Parkinson, PM, Sgrò, C, Siskind, EJ, Smith, DA, Smith, PD, Spandre, G, Spinelli, P, Strickman, MS, Strigari, L, Strong, AW, Suson, DJ, Takahashi, H, Takahashi, T, Tanaka, T, Thayer, JB, Thompson, DJ, Tibaldo, L, Torres, DF, Tosti, G, Tramacere, A, Uchiyama, Y, Usher, TL, Vandenbroucke, J, Vianello, G, Vilchez, N, Vitale, V, Waite, AP, Wang, P, Winer, BL, Wood, KS, Yang, Z & Ziegler, M 2010, 'Fermi Large Area Telescope observations of Local Group galaxies: Detection of M 31 and search for M 33', Astronomy and Astrophysics, vol. 523, no. 1, L2. https://doi.org/10.1051/0004-6361/201015759

@article{3d68954b46e84e80bf0e12a0dbbb28e3,

title = "Fermi Large Area Telescope observations of Local Group galaxies: Detection of M 31 and search for M 33",

abstract = "Context. Cosmic rays (CRs) can be studied through the galaxy-wide gamma-ray emission that they generate when propagating in the interstellar medium. The comparison of the diffuse signals from different systems may inform us about the key parameters in CR acceleration and transport. Aims. We aim to determine and compare the properties of the cosmic-ray-induced gamma-ray emission of several Local Group galaxies. Methods. We use 2 years of nearly continuous sky-survey observations obtained with the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope to search for gamma-ray emission from M 31 and M 33. We compare the results with those for the Large Magellanic Cloud, the Small Magellanic Cloud, the Milky Way, and the starburst galaxies M 82 and NGC 253. Results. We detect a gamma-ray signal at 5σ significance in the energy range 200 MeV-20 GeV that is consistent with originating from M 31. The integral photon flux above 100 MeV amounts to (9.1 ± 1.9stat ± 1.0) × 10-9 ph cm-2. We find no evidence for emission from M 33 and derive an upper limit on the photon flux >100 MeV of 5.1 × 10-9 ph cm-2-1 (2σ). Comparing these results to the properties of other Local Group galaxies, we find indications of a correlation between star formation rate and gamma-ray luminosity that also holds for the starburst galaxies. Conclusions. The gamma-ray luminosity of M 31 is about half that of the Milky Way, which implies that the ratio between the average CR densities in M 31 and the Milky Way amounts to ξ = 0.35 ± 0.25. The observed correlation between gamma-ray luminosity and star formation rate suggests that the flux of M 33 is not far below the current upper limit from the LAT observations.",

keywords = "Local Group, cosmic rays, gamma rays: galaxies",

author = "Abdo, {A. A.} and M. Ackermann and M. Ajello and A. Allafort and Atwood, {W. B.} and L. Baldini and J. Ballet and G. Barbiellini and D. Bastieri and K. Bechtol and R. Bellazzini and B. Berenji and Blandford, {R. D.} and Bloom, {E. D.} and E. Bonamente and Borgland, {A. W.} and A. Bouvier and Brandt, {T. J.} and J. Bregeon and M. Brigida and P. Bruel and R. Buehler and Burnett, {T. H.} and S. Buson and Caliandro, {G. A.} and Cameron, {R. A.} and A. Cannon and Caraveo, {P. A.} and Casandjian, {J. M.} and C. Cecchi and {\"O} {\c C}elik and E. Charles and A. Chekhtman and J. Chiang and S. Ciprini and R. Claus and J. Cohen-Tanugi and J. Conrad and Dermer, {C. D.} and {De Angelis}, A. and {De Palma}, F. and Digel, {S. W.} and {Do Couto E Silva}, E. and Drell, {P. S.} and A. Drlica-Wagner and R. Dubois and C. Favuzzi and Fegan, {S. J.} and P. Fortin and M. Frailis and Y. Fukazawa and S. Funk and P. Fusco and F. Gargano and S. Germani and N. Giglietto and F. Giordano and M. Giroletti and T. Glanzman and G. Godfrey and Grenier, {I. A.} and Grondin, {M. H.} and S. Guiriec and M. Gustafsson and D. Hadasch and Harding, {A. K.} and K. Hayashi and M. Hayashida and E. Hays and Healey, {S. E.} and P. Jean and G. J{\'o}hannesson and Johnson, {A. S.} and Johnson, {R. P.} and Johnson, {T. J.} and T. Kamae and H. Katagiri and J. Kataoka and M. Kerr and J. Kn{\"o}dlseder and M. Kuss and J. Lande and L. Latronico and Lee, {S. H.} and M. Lemoine-Goumard and F. Longo and F. Loparco and B. Lott and Lovellette, {M. N.} and P. Lubrano and Madejski, {G. M.} and A. Makeev and P. Martin and Mazziotta, {M. N.} and J. Mehault and Michelson, {P. F.} and W. Mitthumsiri and T. Mizuno and Moiseev, {A. A.} and C. Monte and Monzani, {M. E.} and A. Morselli and Moskalenko, {I. V.} and S. Murgia and M. Naumann-Godo and Nolan, {P. L.} and Norris, {J. P.} and E. Nuss and T. Ohsugi and A. Okumura and N. Omodei and E. Orlando and Ormes, {J. F.} and M. Ozaki and D. Paneque and Panetta, {J. H.} and D. Parent and M. Pepe and M. Persic and M. Pesce-Rollins and F. Piron and Porter, {T. A.} and S. Rain{\`o} and R. Rando and M. Razzano and A. Reimer and O. Reimer and S. Ritz and Romani, {R. W.} and Sadrozinski, {H. F.W.} and {Saz Parkinson}, {P. M.} and C. Sgr{\`o} and Siskind, {E. J.} and Smith, {D. A.} and Smith, {P. D.} and G. Spandre and P. Spinelli and Strickman, {M. S.} and L. Strigari and Strong, {A. W.} and Suson, {D. J.} and H. Takahashi and T. Takahashi and T. Tanaka and Thayer, {J. B.} and Thompson, {D. J.} and L. Tibaldo and Torres, {D. F.} and G. Tosti and A. Tramacere and Y. Uchiyama and Usher, {T. L.} and J. Vandenbroucke and G. Vianello and N. Vilchez and V. Vitale and Waite, {A. P.} and P. Wang and Winer, {B. L.} and Wood, {K. S.} and Z. Yang and M. Ziegler",

year = "2010",

month = nov,

day = "10",

doi = "10.1051/0004-6361/201015759",

language = "English",

volume = "523",

journal = "Astronomy and Astrophysics",

issn = "0004-6361",

publisher = "EDP Sciences",

number = "1",

}

TY - JOUR

T1 - Fermi Large Area Telescope observations of Local Group galaxies

T2 - Detection of M 31 and search for M 33

AU - Abdo, A. A.

AU - Ackermann, M.

AU - Ajello, M.

AU - Allafort, A.

AU - Atwood, W. B.

AU - Baldini, L.

AU - Ballet, J.

AU - Barbiellini, G.

AU - Bastieri, D.

AU - Bechtol, K.

AU - Bellazzini, R.

AU - Berenji, B.

AU - Blandford, R. D.

AU - Bloom, E. D.

AU - Bonamente, E.

AU - Borgland, A. W.

AU - Bouvier, A.

AU - Brandt, T. J.

AU - Bregeon, J.

AU - Brigida, M.

AU - Bruel, P.

AU - Buehler, R.

AU - Burnett, T. H.

AU - Buson, S.

AU - Caliandro, G. A.

AU - Cameron, R. A.

AU - Cannon, A.

AU - Caraveo, P. A.

AU - Casandjian, J. M.

AU - Cecchi, C.

AU - Çelik, Ö

AU - Charles, E.

AU - Chekhtman, A.

AU - Chiang, J.

AU - Ciprini, S.

AU - Claus, R.

AU - Cohen-Tanugi, J.

AU - Conrad, J.

AU - Dermer, C. D.

AU - De Angelis, A.

AU - De Palma, F.

AU - Digel, S. W.

AU - Do Couto E Silva, E.

AU - Drell, P. S.

AU - Drlica-Wagner, A.

AU - Dubois, R.

AU - Favuzzi, C.

AU - Fegan, S. J.

AU - Fortin, P.

AU - Frailis, M.

AU - Fukazawa, Y.

AU - Funk, S.

AU - Fusco, P.

AU - Gargano, F.

AU - Germani, S.

AU - Giglietto, N.

AU - Giordano, F.

AU - Giroletti, M.

AU - Glanzman, T.

AU - Godfrey, G.

AU - Grenier, I. A.

AU - Grondin, M. H.

AU - Guiriec, S.

AU - Gustafsson, M.

AU - Hadasch, D.

AU - Harding, A. K.

AU - Hayashi, K.

AU - Hayashida, M.

AU - Hays, E.

AU - Healey, S. E.

AU - Jean, P.

AU - Jóhannesson, G.

AU - Johnson, A. S.

AU - Johnson, R. P.

AU - Johnson, T. J.

AU - Kamae, T.

AU - Katagiri, H.

AU - Kataoka, J.

AU - Kerr, M.

AU - Knödlseder, J.

AU - Kuss, M.

AU - Lande, J.

AU - Latronico, L.

AU - Lee, S. H.

AU - Lemoine-Goumard, M.

AU - Longo, F.

AU - Loparco, F.

AU - Lott, B.

AU - Lovellette, M. N.

AU - Lubrano, P.

AU - Madejski, G. M.

AU - Makeev, A.

AU - Martin, P.

AU - Mazziotta, M. N.

AU - Mehault, J.

AU - Michelson, P. F.

AU - Mitthumsiri, W.

AU - Mizuno, T.

AU - Moiseev, A. A.

AU - Monte, C.

AU - Monzani, M. E.

AU - Morselli, A.

AU - Moskalenko, I. V.

AU - Murgia, S.

AU - Naumann-Godo, M.

AU - Nolan, P. L.

AU - Norris, J. P.

AU - Nuss, E.

AU - Ohsugi, T.

AU - Okumura, A.

AU - Omodei, N.

AU - Orlando, E.

AU - Ormes, J. F.

AU - Ozaki, M.

AU - Paneque, D.

AU - Panetta, J. H.

AU - Parent, D.

AU - Pepe, M.

AU - Persic, M.

AU - Pesce-Rollins, M.

AU - Piron, F.

AU - Porter, T. A.

AU - Rainò, S.

AU - Rando, R.

AU - Razzano, M.

AU - Reimer, A.

AU - Reimer, O.

AU - Ritz, S.

AU - Romani, R. W.

AU - Sadrozinski, H. F.W.

AU - Saz Parkinson, P. M.

AU - Sgrò, C.

AU - Siskind, E. J.

AU - Smith, D. A.

AU - Smith, P. D.

AU - Spandre, G.

AU - Spinelli, P.

AU - Strickman, M. S.

AU - Strigari, L.

AU - Strong, A. W.

AU - Suson, D. J.

AU - Takahashi, H.

AU - Takahashi, T.

AU - Tanaka, T.

AU - Thayer, J. B.

AU - Thompson, D. J.

AU - Tibaldo, L.

AU - Torres, D. F.

AU - Tosti, G.

AU - Tramacere, A.

AU - Uchiyama, Y.

AU - Usher, T. L.

AU - Vandenbroucke, J.

AU - Vianello, G.

AU - Vilchez, N.

AU - Vitale, V.

AU - Waite, A. P.

AU - Wang, P.

AU - Winer, B. L.

AU - Wood, K. S.

AU - Yang, Z.

AU - Ziegler, M.

PY - 2010/11/10

Y1 - 2010/11/10

N2 - Context. Cosmic rays (CRs) can be studied through the galaxy-wide gamma-ray emission that they generate when propagating in the interstellar medium. The comparison of the diffuse signals from different systems may inform us about the key parameters in CR acceleration and transport. Aims. We aim to determine and compare the properties of the cosmic-ray-induced gamma-ray emission of several Local Group galaxies. Methods. We use 2 years of nearly continuous sky-survey observations obtained with the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope to search for gamma-ray emission from M 31 and M 33. We compare the results with those for the Large Magellanic Cloud, the Small Magellanic Cloud, the Milky Way, and the starburst galaxies M 82 and NGC 253. Results. We detect a gamma-ray signal at 5σ significance in the energy range 200 MeV-20 GeV that is consistent with originating from M 31. The integral photon flux above 100 MeV amounts to (9.1 ± 1.9stat ± 1.0) × 10-9 ph cm-2. We find no evidence for emission from M 33 and derive an upper limit on the photon flux >100 MeV of 5.1 × 10-9 ph cm-2-1 (2σ). Comparing these results to the properties of other Local Group galaxies, we find indications of a correlation between star formation rate and gamma-ray luminosity that also holds for the starburst galaxies. Conclusions. The gamma-ray luminosity of M 31 is about half that of the Milky Way, which implies that the ratio between the average CR densities in M 31 and the Milky Way amounts to ξ = 0.35 ± 0.25. The observed correlation between gamma-ray luminosity and star formation rate suggests that the flux of M 33 is not far below the current upper limit from the LAT observations.

AB - Context. Cosmic rays (CRs) can be studied through the galaxy-wide gamma-ray emission that they generate when propagating in the interstellar medium. The comparison of the diffuse signals from different systems may inform us about the key parameters in CR acceleration and transport. Aims. We aim to determine and compare the properties of the cosmic-ray-induced gamma-ray emission of several Local Group galaxies. Methods. We use 2 years of nearly continuous sky-survey observations obtained with the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope to search for gamma-ray emission from M 31 and M 33. We compare the results with those for the Large Magellanic Cloud, the Small Magellanic Cloud, the Milky Way, and the starburst galaxies M 82 and NGC 253. Results. We detect a gamma-ray signal at 5σ significance in the energy range 200 MeV-20 GeV that is consistent with originating from M 31. The integral photon flux above 100 MeV amounts to (9.1 ± 1.9stat ± 1.0) × 10-9 ph cm-2. We find no evidence for emission from M 33 and derive an upper limit on the photon flux >100 MeV of 5.1 × 10-9 ph cm-2-1 (2σ). Comparing these results to the properties of other Local Group galaxies, we find indications of a correlation between star formation rate and gamma-ray luminosity that also holds for the starburst galaxies. Conclusions. The gamma-ray luminosity of M 31 is about half that of the Milky Way, which implies that the ratio between the average CR densities in M 31 and the Milky Way amounts to ξ = 0.35 ± 0.25. The observed correlation between gamma-ray luminosity and star formation rate suggests that the flux of M 33 is not far below the current upper limit from the LAT observations.

KW - Local Group

KW - cosmic rays

KW - gamma rays: galaxies

UR - http://www.scopus.com/inward/record.url?scp=78149448307&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=78149448307&partnerID=8YFLogxK

U2 - 10.1051/0004-6361/201015759

DO - 10.1051/0004-6361/201015759

M3 - Article

AN - SCOPUS:78149448307

SN - 0004-6361

VL - 523

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

IS - 1

M1 - L2

ER -

Fermi Large Area Telescope observations of Local Group galaxies: Detection of M 31 and search for M 33

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