Found 10 talks width keyword ISM

Tuesday June 22, 2021
Dr. Christophe Morisset
Universidad Autónoma Nacional de México


Artificial intelligence techniques are increasingly used in our daily lives. They also play an important role in science, including astrophysics. I am particularly interested in the use of machine learning regressors. I will present an overview of the current situation and some recent uses of these methods in the study of planetary nebulae or HII regions.

Thursday December 5, 2019
Prof. Raffaella Morganti
ASTRON, Netherlands


Our view of the gas and its physical conditions in the central region of AGN has been enriched by the discover of fast and massive outflows of HI and molecular gas. These outflows can be driven by radiation/winds but also by the interaction of the radio plasma with the ISM. Understanding the origin and quantifying their impact requires to trace their location and derive their physical conditions (density of the gas, mass, mass outflow rate and kinetic energy of the outflow etc.). Particularly interesting has been the finding that in the first phase of their life, jet in radio galaxies can be particularly effective in driving such outflows. This crucial phase is at the heart of the idea of feedback, therefore particularly relevant for studying feedback in action.


In this talk, I will present some of the results we have obtained to trace jet-driven HI and molecular gas outflows down to scales ranging from hundred to tens of pc. The impact of low-power radio jets will be discussed and the comparison with the predictions from numerical simulations will also be presented.

Outflows of up to few hundred Msun/yr have been found in molecular gas using ALMA while the HI observed with VLBI is showing that the outflowing gas is clumpy as also predicted from numerical simulations. I will describe the kinematics of the gas and its conditions and the relevance they may have for feedback.    

Thursday July 25, 2019
Prof. Mike Barlow
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.

Thursday November 5, 2015
Dr. Juan Usón
Profesor visitante Jaume Serra


ALMA, the Atacama Large Millimeter Array, was formally dedicated on March 13, 2013. After an overview of the highlights of ALMA: Science drivers, characteristic parameters and observing modes, I will discuss some of the of the tools available to obtain images and spectra from the observations  --those you might propose and those already in the data archive. I will present a real-time demonstration of a quite generic reduction of an actual ALMA dataset obtained from the public archive, starting from the (ASDM) raw data to produce good quality, publishable images with a dynamic range that reaches ~1800 (on the strongest calibrator); although still limited by systematic effects.

Tuesday June 9, 2015
Dr. Fatemeh Tabatabaei


Stars, the most fundamental building blocks of galaxies, are born within the clouds of gas and dust and and during their lives they enrich the gas and the interstellar medium (ISM) with heavy elements, magnetic fields, and cosmic rays all of which strongly affects the subsequent formation of stars and their host galaxy. To understand the evolution and appearance of galaxies it is therefore crucial to study the interplay between stars and the ISM. Putting together the infrared, submm, and radio observations of nearby galaxies, we have studied the physical properties of the dusty and magnetized ISM in nearby galaxies to address the pressing questions: How the ISM components are inter-connected and how their physical properties change in different galactic environments e.g. star forming regions, spiral arms, nucleus and outer disks? In what extent the star formation influences the physical properties and structure of the ISM in a galaxy? I will show the effect of star formation on the dust emission properties, interstellar magnetic fields, cosmic ray electron energy index and further discuss the important factors in the energy balance of the ISM at different scales in M33, M31, NGC6946, and other nearby galaxies.

Thursday June 7, 2012
Dr. Juan Uson
observatoire de Paris - LERMA


Superthin galaxies are bulgeless, late-type spiral galaxies seen edge-on.  HI synthesis observations probe the kinematic structure of their interstellar medium.  Observations of these isolated, quiescent galaxies have reached column densities as low as few x 1018  atoms . cm-2 .  The simple structure of the superthins makes them ideal cosmological laboratories (Uson and Matthews 2003). The strength of the cosmic UV background has a strong influence on the formation of structure in the Universe, from the inhibition of the collapse of small haloes to the ionizing escape fraction in galaxies to the global star formation history.  We have used the VIRUS-P integral-field spectrometer on the University of Texas McDonald Observatory 2.7m telescope to observe the edge of the superthin galaxies UGC7321 and UGC1281 in the Hα emission line, limiting the strength of the local UV background below theoretical expectations (Adams et al., 2011).  New,  observations (March 2011) have improved the sensitivity significantly.  The Hα layer shows a peak brightness of  Σ = 1.0 x 10-19 erg s-1 cm-2 arcsec-2 Å-1 (~7σ)  for spectra smoothed with a 15″ spatial kernel.  This leads to a measurement of the cosmic UV background induced HI photoionization rate Γ = 2.0 x 10-14 s-1 (~7σ, preliminary absolute calibration, Uson et al, BAAS 44, 312-01, 2012).  Contrary to past observational attempts, our measurements covered a large, two-dimensional on-sky area. We reach flux limits that are ~50 times fainter than the sky background with significant smoothing over spatial elements and a sky background model that accounts for variations in the spectral resolution of our instrument.

Thursday October 20, 2011
Dr. Adal Mesa
University of Hawaii, USA


The spectral analysis of HII regions allows one to determine the chemical composition of the ionized gas phase of the interstellar medium (ISM) from the solar neighborhood to the high-redshift galaxies. Therefore, it stands as an essential tool for our knowledge of the chemical evolution of the Universe. However, it turns out that chemical abundances of heavy-element ions determined from the bright collisionally excited lines (CELs) are systematically lower than the abundances derived from the faint recombination lines (RLs) emitted by the same ions. Today, this controversial issue is known as abundance discrepancy problem and it is far from negligible. In the analysis of Galactic and extragalactic HII regions the O2+/H+ ratio calculated from the OII RLs is between 0.10 and 0.35 dex higher than that obtained from the [OIII] CELs. In this talk, we will face this problem in the benchmark object of the solar vicinity, the Orion Nebula. Due to its high surface brightness and proximity, the Orion Nebula is an ideal lab, which allows us to study in detail the possible role of its rich and well-resolved internal structure (such as Herbig-Haro objects, protoplanetary disks or bars) on the abundance discrepancy.

Thursday February 10, 2011
Dr. Christophe Morisset
Instituto de Astronomía, UNAM, Mexico


We revisit the question of the ionization of the diffuse medium in late type galaxies, by studying NGC 891, the prototype of edge-on spiral galaxies. The most important challenge for the models considered so far was the observed increase of [O III]/Hβ, [O II]/Hβ and [N II]/Hα with increasing distance to the galactic plane. We propose a scenario based on the expected population of massive OB stars and hot low-mass evolved stars (HOLMES) in this galaxy to explain this observational fact. In the framework of this scenario we construct a finely meshed grid of photoionization models. For each value of the galactic latitude z we look for the models which simultaneously fit the observed values of the [O III]/Hβ, [O II]/Hβ and [N II]/Hα ratios. For each value of z we find a range of solutions which depends on the value of the oxygen abundance. The models which fit the observations indicate a systematic decrease of the electron density with increasing z. They become dominated by the HOLMES with increasing z only when restricting to solar oxygen abundance models, which argues that the metallicity above the galactic plane should be close to solar. They also indicate that N/O increases with increasing z.

Tuesday January 25, 2011
Mr. José Ramón Sánchez Gallego
Instituto de Astrofísica de Canarias, Spain


In this talk I will present the first complete 12CO J=3-2 map of M81, observed as part of the Nearby Galaxies Legacy Survey. We have detected nine regions of significant CO emission located at different positions within the spiral arms, and confirmed that the global CO emission in the galaxy is low. Using a new Hα map obtained with the Isaac Newton Telescope and archival data I will discuss a series of topics including the correlation between the molecular gas and star forming regions, the CO (3-2)/(1-0) line ratio, and the amount of hydrogen produced in photo-dissociation regions near the locations where CO J=3-2 was detected.

Friday July 11, 2008
Dr. Mauricio Tapia
Instituto de Astronomía, UNAM, Sede Ensenada, Mexico


El jovencísimo cúmulo GM 24, a una distancia de 2 kpc, se encuentra embebido en una caliente nube de CO aislada, en donde se formó hace menos de 105 años. El núcleo del cúmulo se compone de estrellas O tardías y de tipo B principalmente y pareciera carecer actualmente de una población estelar de baja masa. Se presentan nuevas observaciones en el infrarrojo cercano y medio que dan mayor definición a las características de sus principales objetos estelares jóvenes.

« Newer Older »

Upcoming talks

More upcoming talks

Recent Colloquia

Recent Talks