Seminar report:
Lyman alpha Spectra

Contents:

• Lyman Spectraby Christian Herenz
• Seminar scheduleSeminar schedule

How to cure a boring day:

Sometimes I can feel that I have very boring days, what to do? At the university where I live in Stockholm you can find a lot of interesting seminars during day time. I decided to make one day free each week to visit these seminars, the seminars I write about here are about astronomy.

With modern technology there is possible to get 2-dimesional spectra in the UV wavelengths. That's what I'm going to listen to today.

Some useful links:

Lyman spectra:

• https://en.wikipedia.org/ wiki/ Lyman series (Lyman series, Wikipedia)
• https://en.wikipedia.org/ wiki/ Hydrogen spectral series (Hydrogen spectral series, Wikipedia)

Deciphering Lyman alpha emitting galaxies with integral field spectroscopy:

By Christian Herenz

You can read his abstract here:
"Lyman alpha emitting high-redshift galaxies offer insights into galaxy formation processes in the young universe. Moreover, they can be used to address cosmological questions regarding the "Epoch of Reionisation" and the nature of dark energy. In my talk I will show how integral field spectroscopy (IFS) is a viable observational technique for such studies. In particular, I will detail how we use IFS data to understand Lyman alpha escape mechanisms in a sample of nearby high-redshift analogues. I will then show how we use the revolutionary IFS instrument MUSE for conducting surveys of Lyman emitting galaxies in the redshift range 3 < z < 6. Here I will provide an overview over the latest results from those campaigns, with a particular focus on luminosity function studies. My talk will conclude with new (preliminary) results from a 17.5 hour MUSE integration of an extremely luminous extended z=3.1 Lyman alpha emitter known as 'Lyman Alpha Blob 1'."

Christian is Post Doc at Stockholm University and that's where the seminar is hold today, 2019.

Christian tells:
The instruments that measure simultaneously spatial - and spectral properties of astronomical targets are called "integral field spectrographs". The "datacubes" from MUSE have typically 300x300 spatial pixels, with one spatial pixel sampling 0.2''x0.2'' (0.04 square arcseconds) on the sky. The spectral range is one octave in the (red) optical from 480 to 930 nanometres, and we sample it at steps of 1.2 Angstrom, i.e. ~3600 pixel in spectral direction.

More about MUSE, Multi-unit spectroscopic explorer at Wikipedia:

• https://en.wikipedia.org/ wiki/ Multi-unit spectroscopic explorer (Multi-unit spectroscopic explorer, Wikipedia)

Christian tells:
High Z (from expanding universe) makes Doppler shift at the spectra to study.

Christian tells:
Lyman alpha is resonant.

Christian tells:
The spectral profile seen in this slide is not a rotating galaxy, quite the contrary. This is how Lyman alpha looks for a static configuration, i.e. homogenous hydrogen gas at a fixed temperature. The splitting of the line is a result of the radiative transfer process, since LyA photons scatter resonantly on hydrogen. The reason for this is the high absorption cross-section of hydrogen for Lyman alpha photons. There are a few atom configurations which have this "resonant" property - another one that is of astrophysical interest is C³⁺, i.e. carbon with three electrons removed.

Christian tells:
This slide actually shows not observations, but a simulation of the extended Lyman alpha emission around a galaxy due to resonant scatterings of LyA photons.

Christian tells:
This is a Lyman alpha reference sample.

Photography of the instruments used to gets these spectras: "Potsdam Multi Aperture" and " Multi Unit Spectroscopic Explorer".

Christian tells:
The left one is called Potsdam Multi Aperture Spectrophotometer - note that this instrument only has 16x16 spatial pixels (1''x1'' each on the sky), but has more versatile settings regarding the spectral range covered. It is also on a 3.6m telescope, compared to MUSE which is on ESOs VLT with 8m diameter.

Christian tells:
Ionised cavities perpendicular to the line-of-sight may promote Lyman alpha and possibly Lyman C radiation. The C in LyC stands for Continuum. We use this abbreviation to indicate radiation with energies > 1 Rydberg (13.6 eV), i.e. those photons that keep the gas in the universe ionised between galaxies.

Summary of LARS-PMAS results.

What is the nature of the most Luminous and extended Lyman alpha emitters at high-z?

LABs are rare, but more frequent in overdensities pro-cluster regions.

LAB 1 powered by photoionisation ?

Mapping of the Lyman alpha characteristics.

Christian list a summary of LAB 1 MUSE observations.

You can read more about Christian Herenz (a personal page comes later) here:

• Christian moving to Chile(Christian Herenz, Stockholm's University)

This was the last seminar before the summer holiday.

These seminars was a good cure to my boring days. Do you have boring days too? Join me next time!

• https://www.nordita.org/ events/ seminars/ schedule/ (Theory seminar schedule, Nordita)

If you not live in Stockholm in Sweden as I do I'm sure that you can find something similar to visit at your place. Or you do as all other do, search the internet, TED Talks is good.

• https://www.ted.com/ (TED Talks)

No more boring days!