A parsec-scale study of the 5/15-GHz spectral indices of the compact radio sources in M82

被引:71
作者
McDonald, AR [1 ]
Muxlow, TWB
Wills, KA
Pedlar, A
Beswick, RJ
机构
[1] Univ Manchester, Jodrell Bank Observ, Macclesfield SK11 9DL, Cheshire, England
[2] Univ Sheffield, Dept Phys, Sheffield S3 7RH, S Yorkshire, England
[3] Onsala Space Observ, S-43992 Onsala, Sweden
关键词
HII regions; galaxies : individual : M82; galaxies : starburst; radio continuum : galaxies;
D O I
10.1046/j.1365-8711.2002.05580.x
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Observations of the starburst galaxy, M82, have been made with the Very Large Array (VLA) in its A configuration at 15 GHz and the Multi-Element Radio-Linked Interferometer Network (MERLIN) at 5 GHz, enabling a spectral analysis of the compact radio structure on a scale of <0.1 arcsec (1.6 pc). Crucial to these observations was the inclusion of the Pie Town Very Long Baseline Array (VLBA) antenna, which increased the resolution of the VLA observations by a factor of similar to2. A number of the weaker sources are shown to have thermal spectra and are identified as H ii regions with emission measures similar to10(7) cm(-6) pc. Some of the sources appear to be optically thick at 5 GHz, implying even higher emission measures of similar to10(8) cm(-6) pc. The number of compact radio sources in M82 whose origin has been determined is now 46, of which 30 are supernova-related and the remaining 16 are Hii regions. An additional 15 sources are noted, but have yet to be identified, meaning that the total number of compact sources in M82 is at least 61. Also, it is shown that the distribution of Hii regions is correlated with the large-scale ionized gas distribution, but is different from the distribution of supernova remnants. In addition, the brightest Hii region at (B1950) 09(h) 51(m) 42(s) .21 + 69degrees54'59'.2 shows a spectral index gradient across its resolved structure which we attribute to the source becoming optically thick towards its centre.
引用
收藏
页码:912 / 924
页数:13
相关论文
共 23 条
[1]   STRUCTURE AND KINEMATICS WITHIN THE STARBURST NUCLEUS OF M82 - SEARCHING FOR A BAR [J].
ACHTERMANN, JM ;
LACY, JH .
ASTROPHYSICAL JOURNAL, 1995, 439 (01) :163-175
[2]  
Allen ML, 1999, ASTR SOC P, V168, P205
[3]   Radio spectra of selected compact sources in the nucleus of M82 [J].
Allen, ML ;
Kronberg, PP .
ASTROPHYSICAL JOURNAL, 1998, 502 (01) :218-228
[4]   STUDY OF VELOCITY FIELD IN M82 + ITS BEARIN ON EXPLOSIVE PHENOMENA IN THAT GALAXY [J].
BURBIDGE, EM ;
RUBIN, VC ;
BURBRIDGE, GR .
ASTROPHYSICAL JOURNAL, 1964, 140 (03) :942-&
[5]   Supernova remnants in the fossil starburst in M82 [J].
de Grijs, R ;
O'Connell, RW ;
Becker, GD ;
Chevalier, RA ;
Gallagher, JS .
ASTRONOMICAL JOURNAL, 2000, 119 (02) :681-687
[6]   A MULTIDIMENSIONAL VERSION OF THE KOLMOGOROV-SMIRNOV TEST [J].
FASANO, G ;
FRANCESCHINI, A .
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 1987, 225 (01) :155-170
[7]   COMPACT RADIO-SOURCES IN THE STARBURST GALAXY M82 AND THE SIGMA-D RELATION FOR SUPERNOVA-REMNANTS [J].
HUANG, ZP ;
THUAN, TX ;
CHEVALIER, RA ;
CONDON, JJ ;
YIN, QF .
ASTROPHYSICAL JOURNAL, 1994, 424 (01) :114-125
[8]   Signatures of the youngest starbursts: Optically thick thermal bremsstrahlung radio sources in Henize 2-10 [J].
Kobulnicky, HA ;
Johnson, KE .
ASTROPHYSICAL JOURNAL, 1999, 527 (01) :154-166
[9]   THE NUCLEUS OF M82 AT RADIO AND X-RAY BANDS - DISCOVERY OF A NEW RADIO POPULATION OF SUPERNOVA CANDIDATES [J].
KRONBERG, PP ;
BIERMANN, P ;
SCHWAB, FR .
ASTROPHYSICAL JOURNAL, 1985, 291 (02) :693-707
[10]   Global very long-baseline interferometry observations of compact radio sources in M82 [J].
McDonald, AR ;
Muxlow, TWB ;
Pedlar, A ;
Garrett, MA ;
Wills, KA ;
Garrington, ST ;
Diamond, PJ ;
Wilkinson, PN .
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 2001, 322 (01) :100-106