Search

En esta contribución se presenta el comportamiento de las emisiones en la región espectral del infrarrojo cercano y medio (NIR-MIR) de los Hidrocarburos Aromáticos Policíclicos (PAHs), provenientes de distintos tipos de objetos extragalácticos: Núcleos Activos de galaxias (AGNs), galaxias infrarrojas y galaxias starburst. Para este trabajo, se seleccionó una muestra de galaxias con tipologías Seyfert 1, Seyfert 2, Starbursts, LIRGs, ULIRGs (LINERS-HII) y Quasars (PG-3CR). Usamos el ancho equivalente (EQW) y el flujo como indicadores de la intensidad de actividad estelar y la actividad del AGN, para discriminar las diferentes fuentes a través del uso de diagramas de diagnóstico del cociente de la luminosidad del continuo en 12 um y 60 um, y los PAHs en 6.2 um, 8.6 um y 11.3 um.

Deep SCUBA surveys have uncovered a large population of massive submm galaxies (SMGs) at z>~1. Although it is generally believed that these galaxies host intense star-formation activity, there is growing evidence that a substantial fraction also harbor an AGN. We present here possibly the strongest evidence for this viewpoint to date: the combination of ultra-deep X-ray observations (the 2 Ms CDF-N) and deep Keck spectroscopic data. We find that the majority (~75%) of the spectroscopically identified SMGs host AGN activity; the other ~25% have X-ray properties consistent with star formation (X-ray derived SFRs of ~1300-2700 solars/yr). The AGNs have properties generally consistent with those of nearby luminous AGNs (L_X~1E43-3E44) and the majority (~80%) are heavily obscured. We construct composite rest-frame 2-20 keV spectra for three different obscuration classes. An ~1 keV equivalent width FeK-alpha emission line is seen in the composite X-ray spectrum of the most heavily obscured AGNs (N_H>5x10^{23}), suggesting Compton-thick or near Compton-thick absorption. Even taking into account the effects of absorption, we find that the average X-ray-FIR ratio of the AGN-classified SMGs is approximately one order of magnitude below that found for typical quasars. This result suggests that intense star-formation activity dominates the bolometric output; however, we also explore whether the X-ray-FIR ratio is intrinsically less than that found for typical quasars and postulate that some SMGs may be AGN dominated. We investigate the growth of massive black holes, discuss prospects for deeper observations, and explore the potential of the next generation of X-ray observatories. (ABRIDGED)., 16 pages, 9 figures, ApJ in press

We present a sample of 17 type 2 Seyfert galaxies which have an X-ray column density lower than 1022 cm-2. The Compton thin nature of these sources is strongly suggested by isotropic indicators. We estimate the fraction of these sources to be in the range of 10%-30% of the population of type 2 Seyfert galaxies. Furthermore, this fraction appears to increase progressively at lower luminosities. The simple formulation of the Unified Model for Seyfert galaxies is not applicable in such sources since the pc-scale molecular torus is not likely to be responsible for the low column density observed; instead the absorption observed is likely to originate at larger scales. According to this hypothesis, in these objects the broad line regions are covered by some dusty obscuring material. In particular, this could occur in objects with dust lanes, patches or HII regions. However, we cannot rule out that in the lowest luminosity sources the BLR is weak, absent or has faded away. This last scenario is consistent with the predictions of some recent theoretical models for low luminosity AGNs