Found 3 talks width keyword grains

Tuesday April 18, 2023
University of Oxford



Nowadays, it is widely accepted that most galaxies undergo an active phase in their evolution. The impact of the energy released by active galactic nuclei (AGN) in the interstellar medium (ISM) of the host galaxy has been proposed as a key mechanism responsible for regulating star formation (SF). The mid-infrared (IR) is the ideal spectral range to investigate the nuclear/circumnuclear regions of AGN since dust extinction is significantly lower compared to the visible range. Furthermore, it provides unique tracers to study the AGN-SF connection such as H2 rotational lines, fine structure lines and Polycyclic Aromatic Hydrocarbons (PAHs). PAHs are also a powerful tool to characterize the ISM in different environments.

Recently, we presented new JWST/MIRI MRS spectroscopy of three Seyfert AGN in which we compare their nuclear PAH emission with that of star-forming regions. This study represents the first of its kind to use sub-arcsecond angular resolution data of local luminous Seyferts (Lbol > 10^44.5 erg/s) with a wide wavelength coverage (4.9-28.1 μm). Our results showed that a suite of PAH features is present in the innermost parts of these Seyfert galaxies. We found that the nuclear regions of AGN lie at different positions of the PAH diagnostic diagrams, whereas the SF regions are concentrated around the average values of SF galaxies. Furthermore, we find that the nuclear PAH emission mainly originates in neutral PAHs while, in contrast, PAH emission originating in the star forming regions favours small ionised PAH grains. Therefore, our results provide evidence that the AGN have a significant impact on the ionization state and size of the PAH grains on scales of ~142-245 pc. This is fundamental since PAH bands are routinely used to measure star-formation activity in near and far SF and active galaxies.

Finally, I will summarise our ongoing JWST work within the GATOS (Galactic Activity, Torus and Outflow Survey) collaboration. In particular, I will focus on our recent study about the survival of PAH molecules in AGN-driven outflows.

Thursday July 25, 2019
University College London


Until the advent in the late 1990’s of sensitive submillimetre arrays such as SCUBA, it was generally thought that the main sources for the interstellar dust found in galaxies were the dusty outflows from evolved AGB stars and M supergiants, although a dust contribution from supernovae had long been predicted on theoretical grounds. The detection at submillimetre wavelengths of very large dust masses in some high redshift galaxies emitting less than a billion years after the Big Bang led to a more serious consideration of core-collapse supernovae (CCSNe) from massive stars as major dust contributors. KAO and Spitzer mid-infrared observations confirmed that CCSN ejecta could form dust but it was not until the Herschel mission and subsequent ALMA observations that direct evidence has been obtained for the presence of significantly large masses of cold dust in young CCSN remnants. As well as using infrared spectral energy distributions to measure the amounts of dust forming in CCSN ejecta, dust masses can also be quantified from the analysis of red-blue asymmetries in their late-time optical emission line profiles. I will describe current results from these methods for estimating ejecta dust masses, and their implications.

Friday March 26, 2010
Instituto de Ciencias del Espacio, Spain


Short-lived nuclides (SLNs) were incorporated to the solar nebula at the time of condensation of the first minerals from the vapor phase. The study of the isotopic ratios preserved in primitive meteorites provides clues on the stellar sources that produced these SLN, being supernovae and Asymptotic Giant Branch stars (AGBs) candidates. On the other hand, stellar grains were also preserved in primitive meteorites and Interplanetary Dust Particles (IDPs). Their survival demonstrates that the solar nebula was not so hot as first researchers proposed in the 60s. Interestingly, the available stellar grain abundances in primitive meteorites (chondrites) depend of the physico-chemical processes suffered by their parent bodies: metamorphism, aqueous alteration, etc. An evaluation of the primordial presolar grain abundances in the protoplanetary disk at the time these materials formed would allow a comparison with the derived from theoretical models. For gaining insight on these processes we should study the most primitive meteorites (the chondrites), but also even more pristine materials arrived from comets, particularly these captured in the stratosphere as IDPs, or collected from 81P/Wild 2 comet by Stardust (NASA) spacecraft.

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