Galaxies, Gas and Radio Telescopes:Eric Wilcots

prepared by Ruth HowesMarquette University

with support from theWisconsin Space Grant Consortium

Proton spin

Electron spin

Parallel SpinsHigh Energy

Antiparallel SpinsLow 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”)

Location Atomic or molecular density

Air at sea level on Earth 1019 particles/cm3

A good vacuum on Earth 1012 particles/cm3

Dense cloud in star-forming region 106 particles/cm3

Average Density of interstellar medium

1 particle/cm3

The Doppler Shift

Source moves towards the telescopeλ increases

Source at rest

Source moves towardsThe 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 gasintensity of emission & absorption

2) The motion of hydrogen gas Doppler shift of emission or absorption

3) The temperature of hydrogen gasDoppler 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 fromdistant object are parallel

Radio mirror bends themto form and image at thepoint where the receiver is

Radiomirror

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 ArrayImage courtesy of NRAO/AUI and Earth image courtesy of the SeaWiFS Project NASA/GSFC and ORBIMAGE

Image fromfrom http://www.salt.ac.za/

TheSouthern African LargeTelescope andThe 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 SpiralDownloaded from http://www.astro.wisc.edu/~ewilcots/research/sbm/

Wilcots’ Most Important Questions for Future Astronomy

What is dark energy? (the mysterious accelerator ofthe 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