Found 6 talks width keyword ISM molecules

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Thursday May 18, 2023
Manouba Institut Supérieur des Arts Multimédia de la Manouba (Tunisia)

Abstract

More than 200 species have been detected in the interstellar medium (ISM), among them many molecules, radicals and ions, containing the −C≡N functional group. Both linear and branched isomers of propyl cyanide (PrCN; C 3 H 7 CN) are ubiquitous in interstellar space. To date, PrCN is one of the most complex molecules found in the interstellar medium. Furthermore, it is the only one observed species to share the branched atomic backbone of amino acids, some of the building blocks of life. Radical-radical chemical reactions in gas phase and on an ice model are examined in detail using density functional theory M062X/6-311++g(d,p) and ab initio methods CCSD(T)-F12//MP2. The reaction mechanism involves the following radicals association: CH 3 CHCH 3 +CN, CH 3 +CH3CHCN for iso-PrCN and CH 3 CH 2 +CH 2 CN, CH 3 +CH 2 CH 2 CN, CN+CH 3 CH 2 CH 2 for n-PrCN formation. Rate constants (see Figure 1) are also reported for gas phase association reactions. All reaction paths are exoergic and barrier-less in the gas phase and on the ice-model, suggesting that the formation of iso-PrCN and n-PrCN is efficient on the water-ice model adopted.

 Another molecule : acetaldehyde (CH 3 CHO) is ubiquitous in interstellar space and is important for astrochemistry as it can contribute to the formation of amino acids through reaction with nitrogen containing chemical species. Quantum chemical and reaction kinetics studies are reported for acetaldehyde formation from the chemical reaction of C(3 P) with a methanol molecule adsorbed at the eighth position of a cubic water cluster. We present extensive quantum chemical calculations by means of CCSD(T)//wB97XD/6-311++G(2d,p) for total spin S=1 and S=0. The rate limiting step for forming acetaldehyde is the CO bond breaking in CH 3 OCH to form adsorbed
CH 3 and HCO. We find two positions on the reaction path where spin crossing may be possible such that acetaldehyde can form in its singlet spin state.


1. I. BenChouikha, B. Kerkeni, et al. Quantum chemical study of the reaction paths and kinetics of acetaldehyde formation on a methanol-water ice model”, ACS Adv., 12,18994 (2022).
2. B. Kerkeni, V Gámez, G. Ouerfelli, M-L. Senent, and N. Feautrier “Understanding Propyl-cyanide and its isomers Formation: Ab initio Study of the Spectroscopy and Reaction Mechanisms.”, Mon. Not. Roy. Astron. Soc. https://doi.org/10.48550/arXiv.2301.12297 (2023).


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Tuesday April 18, 2023
University of Oxford

Abstract

 

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.


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Thursday May 27, 2021
INAF/Trieste

Abstract

This talk will be dedicated to luminous (LBol~1E47 erg/s),
high-redshift quasars, which are ideal targets to investigate (i) feedback
from SMBHs, and (ii) the early growth phases of giant galaxies. I will
present evidence of  SMBH-driven outflows  at all Cosmic epochs, back to
the early Universe. These outflows involve all gas phases (molecular,
neutral, ionised) and extend on nuclear to galactic and circum-galactic
scales. I will report on the first systematic study of the molecular gas
properties in the host-galaxies of the most luminous quasars, fundamental
to probe the impact of SMBH feedback on the host-galaxy evolution. I will
show that luminous quasars pinpoint high-density sites where giant galaxies
assemble, and I will discuss the major contribution of mergers to the final
galaxy mass. To this aim, I will present a wealth of multi-wavelength (UV
to sub-millimeter) observations from the WISE/SDSS hyper-luminous quasars
survey  at z~2-5 (WISSH), and recent results from the ESO large program
XQR-30, the Ultimate X-SHOOTER Legacy Survey of Quasars at the Reionization
epoch.

 


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Thursday July 25, 2019
University College London

Abstract

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.


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Tuesday June 26, 2012
Centro de Radioastronomía y Astrofísica, Morelia, Mexico

Abstract

A simple model using the balance of photodissociation assuming a one-dimensional plane-parallel model yields total hydrogen volume densities for a column of atomic hydrogen under the influence of a far-ultraviolet radiation field. This can be applied wherever atomic hydrogen can be assumed to be the product of photodissociation, or perhaps where it is being kept in its atomic state because of the local radiation field. I have previously applied this model to the nearby spiral galaxies M33, M81 and M83 in the past, but the application is mostly manual and cumbersome. In order to make this method suitable to apply to larger samples of galaxies, we developed an automated procedure that identifies candidate PDRs, calculates the balance of photodissociation at locations where PDR-produced HI can be expected and provides total hydrogen volume densities. We applied the procedure to M83 as a consistency check. It is also ready to take advantage of the latest integral field spectroscopy data (metallicity), which we did in the case of M74. In principle this procedure is most suitable to probe the diffuse interstellar medium at the edges of HII regions in other galaxies than our own. However, if detailed morphological information is already available, we can improve our understanding of the method by applying it to very specific cases, such as parts of the Taurus molecular cloud. While the results are highly sensitive to the local morphology, they can potentially be used as an independent probe of the molecular gas.


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Thursday June 21, 2012
Observatoire de Paris, LERMA. France

Abstract

I will review some recent results about the molecular content of galaxies and its dynamics, obtained from CO lines, dense tracers (HCN,HCO+), or the dust continuum emission. New data to constrain the conversion factor XCO will be discussed. The molecular surface density is essential to determine the star formation efficiency in galaxies, and the resolved Kennicutt-Schmidt law will be presented as a function of surface density and galaxy type. Large progress has been made on galaxy at moderate and high redshifts, allowing to interprete the star formation history and star formation efficiency as a function of gas content, or galaxy evolution. In massive galaxies, the gas fraction was higher in the past, and galaxy disks were more unstable and more turbulent. ALMA observations will allow the study of more normal galaxies at high z with higher spatial resolution and sensitivity.


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