A. Trejo,1,2 L. F. Rodríguez2 and J. Martí3
1 Escuela de Ciencias Físico-matemáticas, Universidad Michoacana de San Nicolás de Hidalgo, Edificio "B", Ciudad Universitaria, Morelia, Michoacán, 58040, México.
2 Centro de Radioastronomía y Astrofísica, UNAM, Apartado Postal 3-72, (Xangari), 58089 Morelia, Michoacán, México. (a.trejo;@astrosmo.unam.mx, l.rodriguez@astrosmo.unam.mx).
3 Departamento de Física (EPS), Universidad de Jaén, Virgen de la Cabeza 2, E-23071 Jaén, Spain. (jmarti@ujaen.es).
Received 2004 July 14 ]]> Accepted 2004 September 7.
ABSTRACT
We present an analysis of radio continuum observations of the nucleus of the spiral galaxy M33, taken from the Very Large Array archives. Most of these observations were made with high angular resolution (≤1") at different epochs and we have used them to search for radio emission associated with the ultraluminous X-ray (ULX) source at the center of M33. At 20 cm, with an angular resolution of 1."3, we detect a source with flux density of 0.20±0.02 mJy that coincides within 0."2 with the position of the center of M33 as reported by 2MASS. In addition, at 3.6 cm (with an angular resolution of 0."3), we detect two faint sources, one of them with a flux density of 0.04±0.01 mJy that is coincident with the 20 cm source (and thus with the center of M33). The second 3.6 cm source, with a flux density of 0.05 ± 0.01 mJy, is ≈ 0."6 north of the first source. Within error, the Chandra position for the ULX overlaps with both 3.6 cm sources.
Key Words: Galaxy: Center — Galaxy: Individual (M33) — Radio Continuum: Galaxies.
RESUMEN
Presentamos un análisis de observaciones de radiocontinuo del núcleo de la galaxia espiral M33, obtenidas del archivo del Very Large Array. La mayoría de estas observaciones fueron hechas con alta resolución angular (≤1") en varias épocas y las hemos utilizado para buscar emisión de radio asociada con la fuente ultraluminosa de rayos X en el centro de M33. A 20 cm, con una resolución angular de 1."3, detectamos una fuente con densidad de flujo de 0.20±002 mJ y que coincide dentro de 0."2 con la posición del centro de M33 reportada por 2MASS. Adicionalmente, a 3.6 cm (con una resolución angular de 0."3), detectamos dos fuentes débiles, una de ellas con densidad de flujo de 004±001 mJy y que coincide con la fuente a 20cm (y por lo tanto con el centro de M33). La segunda fuente detectada a 3.6cm, con densidad de flujo de 005± 001 mJy, está ≈0."6 al norte de la primera fuente. La posición para la fuente ultraluminosa de rayos X del satélite Chandra traslapa dentro del error con ambas fuentes de 3.6 cm.
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]]>ACKNOWLEDGEMENTS
We thank G. Dubus for his valuable comments on the positions of counterparts. AT is supported by a CONACyT scholarship. LFR acknowledges the support of DGAPA, UNAM, and of CONACyT (México). JM acknowledges partial support by DGI of the Ministerio de Ciencia y Tecnología (Spain) under grant AYA2001-3092 and is also supported by the Junta de Andalucía (Spain) under project FQM322. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France.
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