Galaxies, Gas and Radio Telescopes: Eric Wilcots prepared by Ruth Howes Marquette University with support from the Wisconsin Space Grant Consortium

Proton spin Electron spin Parallel Spins High Energy Antiparallel Spins Low Energy Decay after millions of years 21 cm radiation Hydrogen Atoms – 1 proton & 1 electron

Density of gases in different places (data from “Ask an Astronomer”) LocationAtomic or molecular density Air at sea level on Earth particles/cm 3 A good vacuum on Earth particles/cm 3 Dense cloud in star-forming region 10 6 particles/cm 3 Average Density of interstellar medium 1 particle/cm 3

The Doppler Shift Source moves towards the telescope λ increases Source at rest Source moves towards The telescope – λ decreases

Cassiopeia A This image was generated with data from telescopes of the National Radio Astronomy Observatory, a National Science Foundation Facility, managed by Associated Universities. Inc

Galaxies stretch through space and time as far as we can see.

In Galaxies, Radio Astronomers Measure 1) The amount of hydrogen gas intensity of emission & absorption 2) The motion of hydrogen gas Doppler shift of emission or absorption 3) The temperature of hydrogen gas Doppler broadening of emission or absorption lines

Magnetic Fields in M51 Image courtesy of NRAO/AUI

Image from Wikipedia article on Dark Matter A is predicted rotation of a spiral galaxy. B is measured rotation. Dark Matter halo explains the increase at large distances.

Surprising Findings on Hydrogen Gas in Galaxies There is more of it than predicted. Where does it come from? The galaxy? An outside source? The gas is hotter than predicted. What is the heating mechanism? These are still unanswered questions!

Radio waves from distant object are parallel Radio mirror bends them to form and image at the point where the receiver is Radio mirror Receiver National Radio Astronomy Observatory / Associated Universities, Inc. / National Science Foundation

The Very Large Array From National Radio Astronomy Observatory / Associated Universities, Inc. / National Science Foundation

The Very Large Baseline Array Image courtesy of NRAO/AUI and Earth image courtesy of the SeaWiFS Project NASA/GSFC and ORBIMAGE

Image from from The Southern African Large Telescope and The Milky Way

“The southern Milky Way is more spectacular and provides a richer treasure trove of objects than the northern Milky Way. We're now players in the world of large telescopes. We're in an age in which answering the big, fundamental questions requires access to large telescopes in good, dark skies. SALT is just such a telescope.” Eric Wilcots

Tucanae taken by SALT

Eric Wilcots’ Current Research Questions 1) hydrogen gas around galaxies 2) hot diffuse hydrogen within galaxies 3) groups of galaxies 4) barred Magellanic spirals 5) evolution of very massive stars

Wicots’ radio image of NGC 4618, a typical barred Magellanic Spiral Downloaded from

Wilcots’ Most Important Questions for Future Astronomy What is dark energy? (the mysterious accelerator of the expansion of the universe) How do planets form around very young stars? How did the first galaxies evolve after the Big Bang? His Favorite Future Instrument? The Square Kilometer Array