Author Topic: Discussion: Green Peas: A Class of Compact Extremely Star-Forming Galaxies  (Read 24012 times)


starry nite

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Comment: Great! But I need to learn some more astronomy.

Question: What is the subscript symbol after capital M of a dot inside a circle?
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zookeeperKevin

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That means "solar mass".

EigenState

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Comment: Great! But I need to learn some more astronomy.

Question: What is the subscript symbol after capital M of a dot inside a circle?

M denotes Solar mass.

starry nite

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Solar Mass defined at wikipedia.

So this sentence from page 8:
"Finally, using the corrected H flux measurements, we measured star-formation rates (Kennicutt 1998) up to ~ 30 M⊙yr−1."

...means approximately 30 million times the mass of our sun? But "yr-1"? What's that?
And how does that compare to the mass of star formation in our Milky Way?


« Last Edit: July 28, 2009, 03:00:08 pm by starry nite »
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zookeeperKevin

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30 M_sun/yr means "thirty solar masses per year", i.e. this object is forming new stars at a rate of thirty solar masses every year.

starry nite

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I'm sure there's some good reason for it, but I find it amusing that "yr-1" is an "abbreviation" for year yet it's the same number of characters.

So "M⊙" means solar mass, not the "⊙" by itself.
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zookeeperKevin

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Sorry, yr^-1 means year to the power minus one, which is the same as 1/year.

NGC3314

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Sorry, yr^-1 means year to the power minus one, which is the same as 1/year.
and the somewhat clumsy symbol is based on a requirement from the journals that essentially all units be in built-up form (i.e. km s-1 instead of km/s). It gets even uglier when the text has been transferred to some pure-text medium along the way. So the units of flux in a plotted SDSS spectrum, messy enough as erg/cm2 s A, become erg cm-2 s-1 A-1.

starry nite

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Okay, so up to thirty solar masses a year...
Are the types of stars being produced on average different in a "Pea" than a "normal" galaxy?
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Rick Nowell

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I am at a loss to decipher one of the first lines of the abstract: 'with an unusually large equivalent width of up to [average] 1000 Angstroms.
Urrrr, equivalent to what, please...
 

zookeeperKevin

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I am at a loss to decipher one of the first lines of the abstract: 'with an unusually large equivalent width of up to [average] 1000 Angstroms.
Urrrr, equivalent to what, please...

"Equivalent width" is a slightly odd but very robust way to measure the amount of luminosity in an emission (or absorption line). You basically compute the amount of luminosity in the line and then look at the continuum next to it and see how far in wavelength (Angstroms) you have to go until you've got the equivalent in luminosity - the equivalent width.

An EW of 1000 A is HUUUUUUUUUUUUUUUGE!

Mark OConnell

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So basically such a huge difference means the galaxy is highly defined or has precise edges?

zookeeperKevin

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So basically such a huge difference means the galaxy is highly defined or has precise edges?

It means that the emission line is very powerful compared to the underlying continuum of starlight.

starry nite

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I'm wondering about the relation between the Green Peas of the paper and various objects we've found with an "OIII-dominant spectrum". (Quotes since I think that's a GZ term, not proper astronomer-speak.)
If Peas
Quote
may be similar to the most luminous members of the Blue Compact Dwarfs category
how do the nearer non-BCD's we've found fit in with this? We've seen strong narrow OIII peaks on fairly flat baselines from some very different objects, such as spirals, odd mergers, and what seem to be lenticulars.
And what about the most distant OIII's, out to z=0.9? Are they just more distant Green Peas or something else?
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