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http://inaoe.repositorioinstitucional.mx/jspui/handle/1009/998| Thermal emission from H II galaxies: discovering the youngest systems | |
| DANIEL ROSA GONZALEZ ELENA KIRILOVSKY TERLEVICH ROBERTO GIOVANNI TERLEVICH AFONSO | |
| Acceso Abierto | |
| Atribución-NoComercial-SinDerivadas | |
| We studied the radio properties of very young massive regions of star formation in HII galaxies, with the aim of detecting episodes of recent star formation in an early phase of evolution where the first supernovae start to appear. Our sample consists of 31 HII galaxies, characterized by strong Hydrogen emission lines, for which low resolution VLA 3.5 cm and 6 cm observations were obtained. We complemented these observations with archival data at 20 cm. We found that the radio spectral energy distribution (SED) has a range of behaviours; 1) there are galaxies where the SED is characterized by a synchrotron-type slope, 2) galaxies with a thermal slope, and, 3) galaxies with possible free-free absorption at long wavelengths. The latter SEDs were found in a few galaxies (e.g. UM533, Tololo 1223-388) and represent a signature of heavily embedded massive star clusters closely related to the early stages of massive star formation. Based on the comparison of the star formation rates (SFR) determined from the recombination lines and those determined from the radio emission we find that SFR(Hα) is on average five times higher than SFR(1.4 GHz). We confirm this tendency by comparing the ratio between the observed flux at 20 cm and the expected one, calculated based on the Hα star formation rates, both for the galaxies in our sample and for normal ones. This analysis shows that this ratio is a factor of 2 smaller in our galaxies than in normal ones, indicating that they fall below the FIR/radio correlation. This result is further confirmed by the detection of high q-parameter values (the ratio of infrared to radio fluxes) in a few sources. These results suggest that the emission of these galaxies is dominated by a recent and massive star formation event in which the first supernovae (SN) just started to explode. This indicates that the radio emission is most likely dominated by free-free continuum, and that the emission at low frequencies may be optically thick, in agreement with the observed SEDs. We combined the VLA data with age indicators based on optical observations (e.g. equivalent width of Hβ) together with the ratio between the far infrared and the radio continuum fluxes and proposed an evolutionary scenario to explain the observed trends. | |
| The astrophysical journal | |
| 2007 | |
| Artículo | |
| Inglés | |
| Estudiantes Investigadores Público en general | |
| Rosa González, D., et al., (2007). Thermal emission from H II galaxies: discovering the youngest systems, The astrophysical journal, Vol. 654(1): 226-239 | |
| ASTRONOMÍA Y ASTROFÍSICA | |
| Versión aceptada | |
| acceptedVersion - Versión aceptada | |
| Aparece en las colecciones: | Artículos de Astrofísica |
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