Intergalactic H II regions discovered in SINGG

A number of very small isolated H II regions have been discovered at projected distances up to 30 kpc from their nearest galaxy. These H II regions appear as tiny emission-line objects in narrowband images obtained by the NOAO Survey for Ionization in Neutral Gas Galaxies (SINGG). We present spectroscopic confirmation of four isolated H II regions in two systems; both systems have tidal H I features. The results are consistent with stars forming in interactive debris as a result of cloud-cloud collisions. The Halpha luminosities of the isolated H II regions are equivalent to the ionizing flux of only a few O stars each. They are most likely ionized by stars formed in situ and represent atypical star formation in the low-density environment of the outer parts of galaxies. A small but finite intergalactic star formation rate will enrich and ionize the surrounding medium. In one system, NGC 1533, we calculate a star formation rate of 1.5 x 10(-3) M-. yr(-1), resulting in a metal enrichment of similar to 1 x 10(-3) solar for the continuous formation of stars. Such systems may have been more common in the past and a similar enrichment level is measured for the metallicity floor'' in damped Lyalpha absorption systems.

Ab initio quantum chemical studies on neutral-radical reactions of ethynyl (C2H) and cyano (CN) with unsaturated hydrocarbons

An Ab Initio/RRKM study of the reaction mechanism and product branching ratios of neutral-radical ethynyl (C2H) and cyano (CN) radical species with unsaturated hydrocarbons is performed. The reactions studied apply to cold conditions such as planetary atmospheres including Titan, the Interstellar Medium (ISM), icy bodies and molecular clouds. The reactions of C2H and CN additions to gaseous unsaturated hydrocarbons are an active area of study. NASA's Cassini/Huygens mission found a high concentration of C2H and CN from photolysis of ethyne (C2H2) and hydrogen cyanide (HCN), respectively, in the organic haze layers of the atmosphere of Titan. The reactions involved in the atmospheric chemistry of Titan lead to a vast array of larger, more complex intermediates and products and may also serve as a chemical model of Earth's primordial atmospheric conditions. The C2H and CN additions are rapid and exothermic, and often occur barrierlessly to various carbon sites of unsaturated hydrocarbons. The reaction mechanism is proposed on the basis of the resulting potential energy surface (PES) that includes all the possible intermediates and transition states that can occur, and all the products that lie on the surface. The B3LYP/6-311g(d,p) level of theory is employed to determine optimized electronic structures, moments of inertia, vibrational frequencies, and zero-point energy. They are followed by single point higher-level CCSD(T)/cc-vtz calculations, including extrapolations to complete basis sets (CBS) of the reactants and products. A microcanonical RRKM study predicts single-collision (zero-pressure limit) rate constants of all reaction paths on the potential energy surface, which is then used to compute the branching ratios of the products that result. These theoretical calculations are conducted either jointly or in parallel to experimental work to elucidate the chemical composition of Titan's atmosphere, the ISM, and cold celestial bodies.<.

Caratteristiche di emissione delle regioni HII

Le regioni HII sono nubi di idrogeno ionizzato da stelle di recente formazione, massicce e calde. Tali stelle, spesso raggruppate in ammassi, emettono copiosamente fotoni di lunghezza d’onda λ ≤ 912 Å, capaci di ionizzare quasi totalmente il gas che le circonda, composto prevalentemente da idrogeno, ma in cui sono presenti anche elementi ionizzati più pesanti, come He, O, N, C e Ne. Le dimensioni tipiche di queste regioni vanno da 10 a 100 pc, con densità dell’ordine di 10 cm−3. Queste caratteristiche le collocano all’interno del WIM (Warm Ionized Medium), che, insieme con HIM (Hot Ionized Medium), WNM (Warm Neutral Medium) ed CNM (Cold Neutral Medium), costituisce la varietà di fasi in cui si presenta il mezzo interstellare (ISM, InterStellar Medium). Il tema che ci prestiamo ad affrontare è molto vasto e per comprendere a fondo i processi che determinano le caratteristiche delle regioni HII sarebbero necessarie molte altre pagine; lo scopo che questo testo si propone di raggiungere, senza alcuna pretesa di completezza, è dunque quello di presentare l’argomento, approfondendone ed evidenziandone alcuni particolari tratti. Prima di tutto descriveremo le regioni HII in generale, con brevi indicazioni in merito alla loro formazione e struttura. A seguire ci concentreremo sulla descrizione dei processi che determinano gli spettri osservati: inizialmente mostreremo quali siano i processi fisici che generano l’emissione nel continuo, concentrandoci poi su quello più importante, la Bremmstrahlung. Affronteremo poi una breve digressione riguardo al processo di ricombinazione ione-elettrone nei plasmi astrofisici ed alle regole di selezione nelle transizioni elettroniche, concetti necessari per comprendere ciò che segue, cioè la presenza di righe in emissione negli spettri delle regioni foto-ionizzate. Infine ci soffermeremo sulle regioni HII Ultra-Compatte (UC HII Region), oggetto di numerosi recenti studi.

DEVELOPMENT OF A CONDENSED PHASE VELOCITY MAP IMAGING APPARATUS: DISSOCIATION PHOTODYNAMICS OF NITROGEN DIOXIDE AT 355 NM

The photochemistry of the polar regions of Earth, as well as the interstellar medium, is driven by the effect of ultraviolet radiation on ice surfaces and on the materials trapped within them. While the area of ice photochemistry is vast and much research has been completed, it has only recently been possible to study the dynamics of these processes on a microscopic level. One of the leading techniques for studying photoreaction dynamics is Velocity Map Imaging (VMI). This technique has been used extensively to study several types of reaction dynamics processes. Although the majority of these studies have utilized molecular beams as the main medium for reactants, new studies showed the versatility of the technique when applied to molecular dynamics of molecules adsorbed on metal surfaces. Herein the development of a velocity map imaging apparatus capable of studying the photochemistry of condensed phase materials is described. The apparatus is used to study of the photo-reactivity of NO2 condensed within argon matrices to illustrate its capabilities. A doped ice surface is formed by condensing Ar and NO2 gas onto a sapphire rod which is cooled using a helium compressor to 20 K. The matrix is irradiated using an Nd:YAG laser at 355 nm, and the resulting NO fragment is state-selectively ionized using an excimer-pumped dye laser. In all, we are able to detect transient photochemically generated species and can collect information on their quantum state and kinetic energy distribution. It is found that the REMPI spectra changes as different sections of the dissociating cloud are probed. The rotational and translational energy populations are found to be bimodal with a low temperature component roughly at the temperature of the matrix, and a second component with much higher temperature, the rotational temperature showing a possible population inversion, and the translational temperature of 100-200 K. The low temperature translational component is found to dominate at long delay times between dissociation and ionization, while at short time delays the high temperature component plays a larger role. The velocity map imaging technique allows for the detection of both the axial and radial components of the translational energy. The distribution of excess energy over the rotational, electronic and translational states of the NO photofragments provides evidence for collisional quenching of the fragments in the Ar-matrix prior to their desorption.

The large- and small-scale Ca IIK structure of the Milky Way from observations of Galactic and Magellanic sightlines

Aims. The large and small-scale (pc) structure of the Galactic interstellar medium can be investigated by utilising spectra of early-type stellar probes of known distances in the same region of the sky. This paper determines the variation in line strength of Ca ii at 3933.661 Å as a function of probe separation for a large sample of stars, including a number of sightlines in the Magellanic Clouds. 

Methods. FLAMES-GIRAFFE data taken with the Very Large Telescope towards early-type stars in 3 Galactic and 4 Magellanic open clusters in Ca ii are used to obtain the velocity, equivalent width, column density, and line width of interstellar Galactic calcium for a total of 657 stars, of which 443 are Magellanic Cloud sightlines. In each cluster there are between 43 and 111 stars observed. Additionally, FEROS and UVES Ca ii K and Na i D spectra of 21 Galactic and 154 Magellanic early-type stars are presented and combined with data from the literature to study the calcium column density - parallax relationship. 

Results. For the four Magellanic clusters studied with FLAMES, the strength of the Galactic interstellar Ca ii K equivalent width on transverse scales from ∼0.05-9 pc is found to vary by factors of ∼1.8-3.0, corresponding to column density variations of ∼0.3-0.5 dex in the optically-thin approximation. Using FLAMES, FEROS, and UVES archive spectra, the minimum and maximum reduced equivalent widths for Milky Way gas are found to lie in the range ∼35-125 mÅ and ∼30-160 mÅ for Ca ii K and Na i D, respectively. The range is consistent with a previously published simple model of the interstellar medium consisting of spherical cloudlets of filling factor ∼0.3, although other geometries are not ruled out. Finally, the derived functional form for parallax (π) and Ca ii column density (N_CaII) is found to be π(mas) = 1 / (2.39 × 10^-13 × N_CaII (cm^-2) + 0.11). Our derived parallax is ∼25 per cent lower than predicted by Megier et al. (2009, A&A, 507, 833) at a distance of ∼100 pc and ∼15 percent lower at a distance of ∼200 pc, reflecting inhomogeneity in the Ca ii distribution in the different sightlines studied.

Resolved Stars' Insights into Galaxy Physics

Thesis (Ph.D.)--University of Washington, 2016-08

State-Selective Attachment of Helium to Molecular Ions in a New Cryogenic Ion Trap

Light is the main information about the interstellar medium accessible on Earth. Based on this information one can conclude on the composition of the region where the light originates from, as well as on its history. The requirement for this is that it is possible to identify the different absorption and emission features in the spectrum and assign them to certain molecules, atoms or ions. To enable the identification of the different species, precise spectroscopic investigations of the species in the laboratory are necessary. In this work a new spectroscopic method is presented, which can be used to record pure rotational spectra of mass selected, cold, stored molecular ions. It is based on the idea of state specific attachment of helium atoms to the stored molecular ions. The new technique has been made possible through the development and recent completion of two new 22-pole ion trap instruments in the work group of Laboratory Astrophysics at the University of Cologne. These new instruments have the advantage to reach temperatures as low as 4K compared to the 10K of the predecessor instrument. These low temperatures enable the ternary attachment of helium atoms to the stored molecular ions and by this make it possible to develop this new method for pure rotational spectroscopy. According to this, this work is divided into two parts. The first part deals with the new FELion experiment that was build and characterized in the first part of the thesis. FELion is a cryogenic 22-pole ion trap apparatus, allowing to generate, mass select, store and cool down, and analyze molecular ions. The different components of the instrument, e.g. the Storage Ion Source for generating the ions or the first quadrupole mass filter, are described and characterized in this part. Besides this also the newly developed control and data acquisitions system is introduced. With this instrument the measurements presented in the second part of the work were performed. The second part deals with the new action spectroscopic method of state-selective helium attachment to the stored molecular ions. For a deeper analysis of the new technique the systems of CD+ and helium and HCO+ and helium are investigated in detail. Analytical and numerical models of the process are presented and compared to experimental results. The results of these investigations point to a seemingly very general applicability of the new method to a wide class of molecular ions. In the final part of the thesis measurements of the rotational spectrum of l-C3H+ are presented. These measurements have to be high-lighted, since it was possible for the first time in the laboratory to unambiguously measure four low-lying rotational transitions of l-C3H+. These measurements (Brünken et al. ApJL 783, L4 (2014)) enabled the reliable identification of so far unidentified emision lines observed in several regions of the interstellar medium (Pety et al. Astron. Astrophys. 548, A68 (2012), McGuire et al. The Astrophysical Journal 774, 56 (2013) and McGuire et al. The Astrophysical Journal 783, 36 (2014)).

Methane Clathrates in the Solar System

We review the reservoirs of methane clathrates that may exist in the different bodies of the Solar System. Methane was formed in the interstellar medium prior to having been embedded in the protosolar nebula gas phase. This molecule was subsequently trapped in clathrates that formed from crystalline water ice during the cooling of the disk and incorporated in this form into the building blocks of comets, icy bodies, and giant planets. Methane clathrates may play an important role in the evolution of planetary atmospheres. On Earth, the production of methane in clathrates is essentially biological, and these compounds are mostly found in permafrost regions or in the sediments of continental shelves. On Mars, methane would more likely derive from hydrothermal reactions with olivine-rich material. If they do exist, martian methane clathrates would be stable only at depth in the cryosphere and sporadically release some methane into the atmosphere via mechanisms that remain to be determined. In the case of Titan, most of its methane probably originates from the protosolar nebula, where it would have been trapped in the clathrates agglomerated by the satellite's building blocks. Methane clathrates are still believed to play an important role in the present state of Titan. Their presence is invoked in the satellite's subsurface as a means of replenishing its atmosphere with methane via outgassing episodes. The internal oceans of Enceladus and Europa also provide appropriate thermodynamic conditions that allow formation of methane clathrates. In turn, these clathrates might influence the composition of these liquid reservoirs. Finally, comets and Kuiper Belt Objects might have formed from the agglomeration of clathrates and pure ices in the nebula. The methane observed in comets would then result from the destabilization of clathrate layers in the nuclei concurrent with their approach to perihelion. Thermodynamic equilibrium calculations show that methane-rich clathrate layers may exist on Pluto as well. Key Words: Methane clathrate-Protosolar nebula-Terrestrial planets-Outer Solar System.

Ab Initio Quantum Chemical Studies on Neutral-Radical Reactions of Ethynyl (C2H) and Cyano (CN) with Unsaturated Hydrocarbons

An Ab Initio/RRKM study of the reaction mechanism and product branching ratios of neutral-radical ethynyl (C2H) and cyano (CN) radical species with unsaturated hydrocarbons is performed. The reactions studied apply to cold conditions such as planetary atmospheres including Titan, the Interstellar Medium (ISM), icy bodies and molecular clouds. The reactions of C2H and CN additions to gaseous unsaturated hydrocarbons are an active area of study. NASA’s Cassini/Huygens mission found a high concentration of C2H and CN from photolysis of ethyne (C2H2) and hydrogen cyanide (HCN), respectively, in the organic haze layers of the atmosphere of Titan. The reactions involved in the atmospheric chemistry of Titan lead to a vast array of larger, more complex intermediates and products and may also serve as a chemical model of Earth’s primordial atmospheric conditions. The C2H and CN additions are rapid and exothermic, and often occur barrierlessly to various carbon sites of unsaturated hydrocarbons. The reaction mechanism is proposed on the basis of the resulting potential energy surface (PES) that includes all the possible intermediates and transition states that can occur, and all the products that lie on the surface. The B3LYP/6-311g(d,p) level of theory is employed to determine optimized electronic structures, moments of inertia, vibrational frequencies, and zero-point energy. They are followed by single point higher-level CCSD(T)/cc-vtz calculations, including extrapolations to complete basis sets (CBS) of the reactants and products. A microcanonical RRKM study predicts single-collision (zero-pressure limit) rate constants of all reaction paths on the potential energy surface, which is then used to compute the branching ratios of the products that result. These theoretical calculations are conducted either jointly or in parallel to experimental work to elucidate the chemical composition of Titan’s atmosphere, the ISM, and cold celestial bodies.

PRISM (Polarized Radiation Imaging and Spectroscopy Mission): an extended white paper

PRISM (Polarized Radiation Imaging and Spectroscopy Mission) was proposed to ESA in May 2013 as a large-class mission for investigating within the framework of the ESA Cosmic Vision program a set of important scientific questions that require high res- olution, high sensitivity, full-sky observations of the sky emission at wavelengths ranging from millimeter-wave to the far-infrared. PRISM’s main objective is to explore the distant universe, probing cosmic history from very early times until now as well as the structures, distribution of matter, and velocity flows throughout our Hubble volume. PRISM will survey the full sky in a large number of frequency bands in both intensity and polarization and will measure the absolute spectrum of sky emission more than three orders of magnitude bet- ter than COBE FIRAS. The data obtained will allow us to precisely measure the absolute sky brightness and polarization of all the components of the sky emission in the observed frequency range, separating the primordial and extragalactic components cleanly from the galactic and zodiacal light emissions. The aim of this Extended White Paper is to provide a more detailed overview of the highlights of the new science that will be made possible by PRISM, which include: (1) the ultimate galaxy cluster survey using the Sunyaev-Zeldovich (SZ) e↵ect, detecting approximately 106 clusters extending to large redshift, including a char- acterization of the gas temperature of the brightest ones (through the relativistic corrections to the classic SZ template) as well as a peculiar velocity survey using the kinetic SZ e↵ect that comprises our entire Hubble volume; (2) a detailed characterization of the properties and evolution of dusty galaxies, where the most of the star formation in the universe took place, the faintest population of which constitute the di↵use CIB (Cosmic Infrared Background); (3) a characterization of the B modes from primordial gravity waves generated during inflation and from gravitational lensing, as well as the ultimate search for primordial non-Gaussianity using CMB polarization, which is less contaminated by foregrounds on small scales than thetemperature anisotropies; (4) a search for distortions from a perfect blackbody spectrum, which include some nearly certain signals and others that are more speculative but more informative; and (5) a study of the role of the magnetic field in star formation and its inter- action with other components of the interstellar medium of our Galaxy. These are but a few of the highlights presented here along with a description of the proposed instrument.

ISM simulations: an overview of models

Until recently the dynamical evolution of the interstellar medium (ISM) was simu- lated using collisional ionization equilibrium (CIE) conditions. However, the ISM is a dynamical system, in which the plasma is naturally driven out of equilibrium due to atomic and dynamic processes operating on different timescales. A step forward in the field comprises a multi-fluid approach taking into account the joint thermal and dynamical evolutions of the ISM gas.

Rotational and ro-vibrational spectroscopy of small nitrogen-containing species and their astrophysical applications

This thesis presents the study of small nitrogen-bearing molecules, from diatomic radicals to complex organic molecules, by means of rotational and ro-vibrational spectroscopy. Besides their theoretical relevance, which spans from anharmonic force field analyses to energetic and structural properties, I have chosen this family of species because of their astrochemical importance. After some basic knowledge of molecular spectroscopy and astrochemistry is introduced, the instrumentation used during the course of my PhD school is described. Then, the most relevant studies I conducted during the last three years are presented. Generally speaking, a number of molecules of astrophysical relevance have been characterized by means of rotational and ro-vibrational spectroscopy. The sample of studied species is constituted by small radicals (imidogen, amidogen, and titanium nitride), cyanopolyynes (cyanoacetylene) and pre-biotic molecules (aminoacetonitrile): these studies are presented in great detail. Among the results, the first astronomical detection of two deuterated radicals (NHD and ND2) is presented in this thesis.Thanks to our studies, it was possible to clearly identify molecular absorptions of these species towards the pre-stellar core IRAS16293-2422, as recorded by the Herschel Space Observatory mission. These observations confirm the strong deuterium enhancement generally observed in this cloud but they reveal that models underestimate the abundances of NHD and ND2. I also report the detection of vibrationally excited aminoacetonitrile (NH2CH2CN) in Sagittarius B2, as observed in the ReMoCa survey. This is the second detection of aminoacetonitrile in the interstellar medium and the first astronomical observation of its vibrationally hot lines. This represents a small step toward the comprehension on how complex organic molecules are formed and which processes can lead to the formation of glycine. Finally, few general remarks are discussed and the importance of future laboratory studies is pointed out, along with possible perspectives.

Mock HI observations of Milky Way-like simulated galaxies

L'obiettivo di questo lavoro di tesi consiste nel descrivere sia il processo necessario per la creazione di osservazioni sintetiche di galassie simulate simili alla Via Lattea nella riga di emissione a 21 cm dell'idrogeno neutro (HI), sia il lavoro di analisi fondamentale che serve a confrontare in modo efficace l'output generato con delle osservazioni di galassie reali. Come prima cosa è descritta la teoria quantistica che sta alla base dell'emissione a 21 cm di HI, illustrando l'importanza di tale riga di emissione nell'ambito dell'astronomia e come si possano ottenere informazioni fondamentali sulle sorgenti di questa radiazione a partire dai dati osservativi. Il lavoro poi si focalizza sull'utilizzo del software MARTINI per la creazione di osservazioni sintetiche della linea a 21 cm per una galassia simulata con proprietà simili alla Via Lattea generata utilizzando il modello numerico SMUGGLE. Infine, si passa ad una breve descrizione dell'analisi dei dati sintetici creati, e al loro confronto con dei dati provenienti da osservazioni reali di galassie con proprietà simili, per ottenere una valutazione qualitativa della bontà del modello SMUGGLE impiegato nella simulazione numerica.

Reconnection current sheet structure in a turbulent medium

In the presence of turbulence, magnetic field lines lose their dynamical identity and particles entrained on field lines diffuse through space at a rate determined by the amplitude of the turbulence. In previous work (Lazarian and Vishniac, 1999; Kowal et al., 2009; Eyink et al., 2011) we showed that this leads to reconnection speeds which are independent of resistivity. In particular, in Kowal et al. (2009) we showed that numerical simulations were consistent with the predictions of this model. Here we examine the structure of the current sheet in simulations of turbulent reconnection. Laminar flows consistent with the Sweet-Parker reconnection model produce very thin and well ordered currents sheets. On the other hand, the simulations of Kowal et al. (2009) show a strongly disordered state even for relatively low levels of turbulence. Comparing data cubes with and without reconnection, we find that large scale field reversals are the cumulative effect of many individual eddies, each of which has magnetic properties which are not very different from turbulent eddies in a homogeneous background. This implies that the properties of stationary and homogeneous MHD turbulence are a reasonable guide to understanding turbulence during large scale magnetic reconnection events. In addition, dissipation and high energy particle acceleration during reconnection events take place over a macroscopic volume, rather than being confined to a narrow zone whose properties depend on microscopic transport coefficients.

Short-term Physiological Changes In Roots And Leaves Of Sugarcane Varieties Exposed To H2o2 In Root Medium.

The aim of this study was to evaluate the differential sensitivity of sugarcane genotypes to H2O2 in root medium. As a hypothesis, the drought tolerant genotype would be able to minimize the oxidative damage and maintain the water transport from roots to shoots, reducing the negative effects on photosynthesis. The sugarcane genotypes IACSP94-2094 (drought tolerant) and IACSP94-2101 (drought sensitive) were grown in a growth chamber and exposed to three levels of H2O2 in nutrient solution: control; 3mmolL(-1) and 80mmolL(-1). Leaf gas exchange, photochemical activity, root hydraulic conductance (Lr) and antioxidant metabolism in both roots and leaves were evaluated after 15min of treatment with H2O2. Although, root hydraulic conductance, stomatal aperture, apparent electron transport rate and instantaneous carboxylation efficiency have been reduced by H2O2 in both genotypes, IACSP94-2094 presented higher values of those variables as compared to IACSP94-2101. There was a significant genotypic variation in relation to the physiological responses of sugarcane to increasing H2O2 in root tissues, being root changes associated with modifications in plant shoots. IACSP94-2094 presented a root antioxidant system more effective against H2O2 in root medium, regardless H2O2 concentration. Under low H2O2 concentration, water transport and leaf gas exchange of IACSP94-2094 were less affected as compared to IACSP94-2101. Under high H2O2 concentration, the lower sensitivity of IACSP94-2094 was associated with increases in superoxide dismutase activity in roots and leaves and increases in catalase activity in roots. In conclusion, we propose a general model of sugarcane reaction to H2O2, linking root and shoot physiological responses.