Siegel der Universität

Universität zu Köln
Mathematisch-Naturwissenschaftliche Fakultät
Fachgruppe Physik

I. Physikalisches Institut

Cosmic Ray interactions with ice mantles

The chemistry program Saptarsy has recently been improved to provide a realistic description of grain mantles.  One important physical aspect that is missing is a realistic interaction of cosmic rays with the mantle.  In this thesis, the idea is to include these mechanisms, based on laboratory experiments from the literature.

Polarization in NGC 6334

Polarization measurements in the NGC6334 star forming cloud have been conducted using the POLKA instrument on APEX  This will allow to trace the magnetic field direction.  In the thesis, the magnetic field shall be compared to mass flows traced by molecular observations of the cloud.

Shocks in hot cores

The program Saptarsy can be used to model spectra of astrophysical sources based on evolutionary chemical models.  This shall be done here for a parameter space, taking into account shocks that will provide an instantaneous release of the ice mantle at a random time.

Extragalaktische Entdeckung von Argonium mit ALMA

Argonium, ArH+, wurde mit dem Atacama Large Millimeter Array (ALMA) erstmalig in einer Galaxie außerhalb der Michstraße entdeckt. Es handelt sich dabei um die Vordergrundgalaxie mit Rotverschiebung 0,89 in Richtung des Quasars PKS 1830–211. Bei dieser Rotverschiebung blicken wir etwa 7,5 Milliarden Jahre zurück. Der Quasar dient als "Lichtquelle" für Absorptionsspektroskopie an der Vordergrundgalaxie, die das Licht des Quasars bündelt und mehrere Abbilder schafft. In den beiden hellsten Abbildern im Submillimeterbereich wurden beide interstellar wichtigen Isotopologe 36ArH+ und 38ArH+ entdeckt, und zwar in einem Verhältnis von 3,46 ± 0,16 in dem stärkeren und 4,53 ± 0,33 in dem schwächeren Abbild. Diese Verhältnisse unterscheiden sich vom Verhältnis 5,50 ± 0,01 in der Umgebung der Sonne und deuten darauf hin, dass sehr massereiche Supernovae im frühen Universum eine größere Rolle bei der Erzeugung von Elementen schwerer als Helium ("Metalle" bei den Astronomen) gespielt haben als heute, was man erwartet. Das Isotopolog 40ArH+ wurde nicht entdeckt, da 40Ar interstellar im Vergleich zu den beiden anderen Isotopen fast vernachlässigbar ist. Auf der Erde ist allerdings 40Ar das häufigste Argonisotop. Es entstand (und entsteht) durch den radioaktiven Zerfall von 40K.

Argonium wurde erst kürzlich als weit verbreitetes Molekül in der Milchstraße entdeckt. Es wurde als das Molekül bezeichnet, das Molekülwolken meidet, weil es nur im sehr diffusen interstellaren Medium vorkommt, für dieses ist es aber ein sehr guter Indikator.

H. S. P. Müller, S. Muller, P. Schilke, et al., Detection of Extragalactic Argonium, ArH+, toward PKS 1830–211, Astron. Astrophys. 582 (2015) Art.-Nr. L4.

Extragalactic Detection of Argonium with ALMA

Argonium, ArH+, was detected for the first time outside of Milkyway using the Atacama Large Millimeter Array (ALMA). The source is a foreground galaxy with redshift 0.89 toward the quasar PKS 1830–211. The look-back time at this redshift is about 7.5 billion years. The quasar illuminates the foreground galaxy for absorption spectroscopic studies. The foreground galaxy lenses the radiation of the quasar creating several images of the quasar. The two interstellar important isotopologs 36ArH+ and 38ArH+ were detected in the two most intense images in the submillimeter region. The isotopic ratio was 3.46 ± 0.16 in the stronger and 4.53 ± 0.33 in the weaker image. The ratios differ from 5.50 ± 0.01 in the Solar neighborhood, indicating that high-mass supernovae played a more pronounced role in generating elements heavier than helium (called "metals" by astronomers) in the early Universe compared to today, as may be expected. The isotopolog 40ArH+ was not detected, because 40Ar is almost negligible in comparison to the other two isotopes. On Earth, however, 40Ar is the most abundant argon isotope. It is a product of the radioactive decay of 40K.

Argonium was only recently detected as a ubiquitous molecule in our Galaxy. It was called the molecule which avoids molecular clous because it occurs only in the very diffuse interstellar medium, for which it is an excellent tracer.

H. S. P. Müller, S. Muller, P. Schilke, et al., Detection of Extragalactic Argonium, ArH+, toward PKS 1830–211, Astron. Astrophys. 582 (2015) Art. No. L4.

(hspm, 2015-10-07)

Ubiquitous argonium (ArH+) in the diffuse ISM (P. Schilke et al.)

A molecular tracer of almost pure atomic gas

In section 6. Interstellar and circumstellar matter

by P. Schilke, D. A. Neufeld, H. S. P. Müller, et al., A&A 566, A29

It is not entirely unexpected to find that a molecular ion is a tracer for diffuse atomic ISM clouds. It has been known for some time that ions such as HCO+ observed in absorption against the background of point-like radio sources trace low-density, mainly atomic material. More recently, ions such as H2O+ have been detected with Herschel. Nevertheless, it is a surprise to find that argonium (ArH+) can be detected not only in the Crab nebula but also (as shown in the article by Schilke et al.) in clouds along the line of sight to various strong submm sources in the Galactic plane. It is also surprising to find that, based on the diffuse cloud chemistry models, ArH+ likes to live in clouds with a molecular fraction 2n(H2)/n(HI) of approximately 10–3. All molecules are not alike !

The article was marked as Highlight of the week by Astron. Astrophys.

High Mass Star Formation/Astrochemistry

There currently is no funding for PhD positions, if you come with your own funding, feel free to contact me and a suitable topic in my research interests can be found.