Author Topic: Saturday the fifth of July  (Read 2450 times)

Rick Nowell

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Saturday the fifth of July
« on: July 05, 2014, 03:42:40 am »
Green Pea Galaxies & The Early Universe.

Recently, a paper was published in ArXiv by Anne Jaskot and Sally Oey from the University of Michigan.
Entitled: "Linking Ly-alpha and Low-Ionization Transitions at Low Optical Depth", it delivered the first hints
of just how important some Green Pea galaxies will be in the studies of the early universe. Below is an image
of GP-J1219, which combines a newly-available Near Ultraviolet picture (on the left) from the Cosmic Origins
Spectrograph on board the Hubble Space Telescope with a familiar SDSS picture on the right. The scale bar in each
picture shows 1 arcsec, which corresponds to ~10,750 light years at the distance of 2.69 billion light years for
this particular Pea.

We are some of the first to see this HST COS NUV image of GP J1219!
SDSS J121903.98+152608.5
http://skyserver.sdss3.org/dr9/en/tools/explore/obj.asp?id=1237661070336852109 (DR9)

Credit: Anne Jaskot, Sally Oey, HST COS and Rick Nowell.

Not only that, the author Anne Jaskot kindly emailed me a few words about their latest studies:

"Our latest results not only support the idea that some GPs are LyC [Lyman Continuum] leakers, but they show
that the GPs are immensely important for our understanding of high-redshift Ly-alpha Emitters (LAEs). Ly-alpha
emitting galaxies are one of the main galaxy populations we detect at high redshift (z>2), but because of their
great distance, it's difficult to study many of their physical properties. With the Ultraviolet spectra of the GPs,
we've already solved one longstanding puzzle regarding LAE spectra: why certain low-ionization emission lines
appear to correlate with strong Ly-alpha emission. We show that the neutral gas geometry can explain the observed
emission. Galaxies with strong Ly-alpha emission, low-ionization emission lines, and no low-ionization absorption lines
may be LyC leakers, with most of their neutral gas located to the side of the starburst, instead of in front of it.
What's striking is how compact and featureless this galaxy appears, even with HST. The compact starburst region
completely dominates the light of the galaxy.

We have imaging observations in both continuum and emission lines scheduled for the four GPs discussed
in our recent Letter. Some of the data are in hand, and we're waiting on the rest. Stay tuned for a future
analysis of the images." (July 2014)

Determining the population of objects that reionized the Universe (the epoch of reionization) remains a
outstanding and pressing question in cosmology. The process of re-ionization is theorised to have taken
place between 150 million and one billion years after the Big Bang. Finding suitable candidates in the local
universe has proved difficult, as astronomers are looking for galaxies that emit Lyman Continuum photons (LyC).
Lyman continuum photons (LyC) are a kind of photon emitted from stars. Hydrogen is ionized by the
absorption of LyC photons, so finding galaxies that do this is very important to the study of the early
universe. This seems straightforward, but so far only two have been found in the local Universe
(Haro 11 and Tol 1247-232). With the recent finds from Hubble, a few GPs are about to be added to
those.

That would be a major achievement! An achievement that started here on this very forum...

SDSS Spectrum of GP-J1219 (SDSS DR9). LyC photons are way to the left, below 912 Angstroms in the ultraviolet
(not redshifted) or ~2000 Angstroms in the spectrum below.


'Linking Ly-alpha and Low-Ionization Transitions at Low Optical Depth' 
A. E. Jaskot, M. S. Oey   http://arxiv.org/abs/1406.4413
http://en.wikipedia.org/wiki/Cosmic_Origins_Spectrograph
http://en.wikipedia.org/wiki/Pea_galaxy
http://en.wikipedia.org/wiki/Lyc_photon
http://en.wikipedia.org/wiki/Reionization

Hanny

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Re: Saturday the fifth of July
« Reply #1 on: July 05, 2014, 07:06:31 am »
Nice one :)

AlexandredOr

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Re: Saturday the fifth of July
« Reply #2 on: July 05, 2014, 07:10:42 am »
Both informative and fascinating. Thank you Rick !

Baby star opening its eyes on the Universe.

djj

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Re: Saturday the fifth of July
« Reply #3 on: July 05, 2014, 12:40:52 pm »
Thankyou, Rick 8).

mitch

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Re: Saturday the fifth of July
« Reply #4 on: July 06, 2014, 05:00:12 am »
Excellent OOTD Rick.  8) 8) 8)

Rick Nowell

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Re: Saturday the fifth of July
« Reply #5 on: July 07, 2014, 09:44:11 am »
Ooops, forgot the year! Thanks for the pleasant comments. Anne Jaskot took time out from
working on her dissertation, which is due to be defended this week, to reply to my email.

Galaxy Hunters Inc

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Re: Saturday the fifth of July
« Reply #6 on: July 07, 2014, 02:49:27 pm »
I love the pea stories.
Good work Rick.
 :)