Update: Peas are a Mess!

Hi all,

About two weeks ago, a group of astronomers led by Ricardo Amorin posted a new paper on the peas to astro-ph. They used the giant Gran Telescopio Canarias (GranTeCan or GTC) to take really high-quality spectra of some of the peas. What they find is amazing, but not entirely unexpected. We already knew from Carie Cardamone’s paper that the peas are extremely intense starbursts, that is, they form more stars relative to their mass than any other kind of galaxy in the nearby universe. Now, Amorin et al. show that they are a real mess:

A GTC spectrum of a pea from Amorin et al. (arXiv:1207.0509) zoomed in on the Halpha emission line. The Halpha line comes from gas ionised by the powerful radiation from very young stars. The high-resolution spectrum clearly shows that the single Halpha line is actually due to several different components.

The Halpha emission lines of the peas, once studies at high resolution and signal-to-noise, show that they are actually composed of several different lines. The Halpha line is generated by the powerful ionising radiation from young, massive stars hitting the surrounding gas. The multiple lines mean that the peas have several chunks of gas and stars moving at large velocities relative to each other.

This makes sense from what we know from the few peas that have nice Hubble images.

Hubble image of a pea galaxy (Amorin et al. (arXiv:1207.0509)) showing that it actually consists of multiple components; it’s a real mess!

The multiple Halpha lines are almost certainly from these multiple components and suggest that the gas (and stars) in the peas are effectively a turbulent mess. Some of those clumps whiz past each other at over 500 km/sec. Yes, km/sec. Some of the Halpha lines are also broadened suggesting that really energetic events are occurring inside those star-forming clumps, such as multiple supernova remnants or powerful Wolf-Rayet stars.

You can get the full paper as PDF or other formats here on arxiv.