Found 21 talks archived in ISM and nebulae
Planetary nebulae (PNe) are excellent tracers to study the chemistry, kinematics, and stellar populations of galaxies. They can be used to
constrain the properties of galactic substructures and peer into the past tidal interactions. In this talk, I present our successful GTC observations of PNe in the Northern Spur and the Giant Stream, two
most prominent substructures of M31. The deep spectroscopy enabled detection of the weak [O III] 4363 temperature-diagnostic line in all target PNe and as a consequence, reliable determination of elemental abundances. Our PN sample have homogeneous oxygen abundances, although
slight difference between the two substructures are marginally noticed. The study of abundances and the spatial and kinematical properties of our sample leads to the tempting conclusions: 1) their progenitors might
belong to the same stellar population, and 2) the Northern Spur and the Giant Stream may have the same origin and may be explained by the stellar orbit proposed by Merrett et al.
The dwarf satellite M32 might be responsible for the two substructures. Deep spectroscopy of PNe in M32 will help to assess this hypothesis.
From the structure of PHL 293B and the physical properties of its ionizing cluster and based on results of hydrodynamic models, we point at the various events required to explain in detail the emission and absorption components seen in its optical spectrum. We ascribe the narrow and well centered emission lines, showing the low metallicity of the galaxy, to an HII region that spans through the main body of the galaxy. The broad emission line components are due to two off-centered supernova remnants evolving within the ionizing cluster volume and the absorption line profiles are due to a stationary cluster wind able to recombine at a close distance from the cluster surface as originally suggested by Silich et al. 2004. Our numerical models and analytical estimates confirm the ionized and neutral column density values and the inferred X-ray emission derived from the observations.
There is an increasing multiplicity of proposed methodologies to derive chemical abundances in HII regions from the measurement of the relative fluxes of their optical emission lines. Particularly there is a known discrepancy between the prediction of some widely used grids of photoionization models and the results of the direct analysis of the spectra from their integrated physical properties (i.e. density, temperature). In this seminar, I will introduce HII-CHI-mistry, a Chi square approximation to compare observations with results of a large grid of models calculated using CLOUDY and varying the oxygen abundance, the nitrogen-to-oxygen ratio and the ionization parameter, covereing all possible conditions observed so far in massive complexes of star-formation. Including N/O as an additional variable allows the correct interpretation of the [NII] 6584 emission lines, widely used to derive abundances both in the Local and the Early Universe in the infra-red part of the spectrum.
The use of this method leads to a derivation of both Z and N/O totally consistent with the results from the direct method when emission line ratios sensitive to the temperature are available (e.g. [OIII] 50007/4363). On the contrary, when these ratios are not available, what is the most common situation in metal-rich/distant objects, it is necessary to assume empirical constraints to the space of parameters covered by the model-grid to arrive to solutions in the whole range of metallicity. Among the applications of this methods it is a consistent study of the metallicity in a wide range of potential variations (e.g. gradients of Z in disc galaxies, mass-metallicity relation, etc ...)
Evolved stars are factories of cosmic dust. This dust is made of tiny grains that are injected into the interstellar medium and plays a key role in the evolution of astronomical objects from galaxies to the embryos of planets. However, the processes involved in dust formation and evolution are still a mystery. The increased angular resolution of the new generation of telescopes will provide for the first time a detailed view of the conditions in the dust formation zone of evolved stars, as shown by our first observations with ALMA. The aim of the NANOCOSMOS project is to take advantage of these new observational capabilities to change our view on the origin and evolution of dust. We will combine astronomical observations, modelling, and top-level experiments to produce stardust analogues in the laboratory and identify the key species and steps that govern the formation of these nanoparticles. We will build two innovative setups: the Stardust chamber to simulate dust formation in the atmosphere of evolved stars, and the gas evolution chamber to identify novel molecules in the dust formation zone. We will also improve existing laboratory setups and combine different techniques to achieve original studies on individual nanoparticles, their processing to produce complex polycyclic aromatic hydrocarbons, the chemical evolution of their precursors and their reactivity with abundant astronomical molecules. Our simulation chambers will be equipped with state-of-the-art in situ and ex situ diagnostics. Our astrophysical models, improved by the interplay between observations and laboratory studies, will provide powerful tools for the analysis of the wealth of data provided by the new generation of telescopes.
The synergy in NANOCOSMOS between astronomers, vacuum and microwave engineers, molecular and plasma physicists, surface scientists, including both experimentalists and theoreticians is the key to provide a cutting-edge view of cosmic dust.
Following the observational and theoretical evidence that points at core collapse supernovae as major producers of dust, we calculate the hydrodynamics of the matter reinserted within young and massive super stellar clusters under the assumption of gas and dust radiative cooling. The large supernova rate expected in massive clusters allows for a continuous replenishment of dust immersed in the high temperature thermalized reinserted matter and warrants a stationary presence of dust within the cluster volume during the type II supernova era (~ 3 Myr - 40 Myr). Such a balance determines the range of dust to gas mass ratio and this the dust cooling law. We then search for the critical line in the cluster mechanical luminosity (or cluster mass) vs cluster size, that separates quasi- adiabatic and strongly radiative cluster wind solutions from the bimodal cases. In the latter, strong radiative cooling reduces considerably the cluster wind mechanical energy output and affects particularly the cluster central regions, leading to frequent thermal instabilities that diminish the pressure and inhibit the exit of the reinserted matter. Instead matter accumulates there and is expected to eventually lead to gravitational instabilities and to further stellar formation with the matter reinserted by former massive stars. The main outcome of the calculations is that the critical line is almost two orders of magnitude or more, depending on the assumed value of V\infty, lower than when only gas radiative cooling is applied. And thus, massive clusters (M_sc > 10^5 Msun) are predicted to enter the bimodal regime.
I will present an extensive analysis of the 850 microns (353 GHz) polarization maps of the SCUBA Polarimeter Legacy (SCUPOL) Catalogue produced by Matthews et al., focusing on the molecular clouds and star-forming regions. The first half of the presentation will concern the several methods used in order to analyze and characterize the observed polarization maps and a statistical analysis of the results will be presented. The second half of the talk will focus on a method used for describing the turbulent regimes of the four well sampled regions, S106, OMC-2/3, W49, and DR21, based on comparisons with three-dimensional magnetohydrodynamics (MHD) numerical simulations scaled to the observed polarization maps. It will be shown how this method can be used for constraining the values of the inclination angle of the mean magnetic field with respect to the line of sight. Consistency of the results obtained from the comparison of the information extracted from the analysis of the observed and simulated maps with results obtained from independent observation data analysis by other authors will be discussed. Conclusions regarding how simple, ideal, isothermal, and non-self-gravitating MHD simulations may be sufficient in order to describe the large-scale observed physical properties of some molecular cloud envelopes will be given.
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.
A serious limitation in the study of the Galactic inner halo and bulge globular clusters has been the existence of large and differential extinction by foreground dust. We have mapped the differential extinction and removed its effects, using a new dereddening technique, in a sample of 25 clusters in the direction of the inner Galaxy, observed in the optical using the Magellan 6.5m telescope and the Hubble Space Telescope. We have also observed a sample of 33 inner Galactic globular clusters in the framework of the VVV survey that is currently being conducted with the new Vista 4m telescope, in infrared bands where the extinction is highly reduced. Using these observations we have produced high quality color-magnitude diagrams of these poorly studied clusters that allow us to determine these clusters relative ages, distances and chemistry more accurately and to address important questions about the formation and the evolution of the inner Galaxy.
The anomalous microwave emission (AME) is an additional diffuse foreground component, originated by an emission mechanism in the ISM different from the well-known synchrotron, free-free and thermal dust emissions. It was first discovered at the end of the nineties as a correlated signal between microwave CMB maps and infrared maps tracing the dust emission. Ever since several detections have been found in individual clouds in our Galaxy. This emission is an important contaminant for current and future CMB experiments, and therefore its characterization (both in temperature and in polarization) and understanding is mandatory. So far different theoretical models have been proposed to explain the physical mechanism that give rise to this emission. In this talk we will review these models and will present the current observational status of the AME, with particular emphasis on some recent studies that have been performed by our group in the IAC in the Perseus molecular complex and in the Pleiades reflection nebula.
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.
- The Pristine survey: An efficient search for extremely metal-poor starsDr. Kris YouakimTuesday January 23, 2018 - 12:30
- Kinematics and dynamics of molecular gas in galaxiesDr. Alessandro LupiThursday February 8, 2018 - 10:30