(this paper was led by Tim Davis as first-author. I am second author of this paper.)
We continue our exploration of the molecular gas properties of early-type galaxies, which I have already blogged about here, here, and here. In this case, we look again at a paper that Tim Davis wrote, in particular, about the extent of molecular gas in our ATLAS3D early-type galaxies.
We start by thinking about the "default" galaxies: spiral, late-type, star-forming galaxies are the ones that have been studied most often in molecular gas. This makes sense, because the galaxies that are forming stars are also the ones with the most prevalent molecular gas, and were the ones assumed to have molecular gas. As we've already discussed, early-type galaxies until very recently were assumed to be "red and dead". Some hints that that might not be true existed, but ATLAS3D was the first group to put a quantifiable value on just how many still had cold gas, albeit usually at small molecular gas fractions. This though explains why it is really just now that we are getting around to trying to understand how molecular gas behaves in early-type galaxies, and how that compares to the "default."
|The stars (underlying photo) and molecular gas (blue) in the Whirlpool Galaxy. Image credit: PAWS Team/IRAM/NASA HST/ T. A. Rector, this site.|
In spirals, this is hardly a surprise. The very stars in the spiral are often forming out of that molecular gas, so their connection makes sense. What we set out to do was find out if the same was true for early-type galaxies. The first thing that we noticed though, was that the overall extent (that is, how far out in physical units the gas is found) of the molecular gas in the early-types was smaller than in the late-types of BIMA-SONG. But again, that was in absolute terms. What about when you look at the gas relative to the stars?
|The extent of the molecular gas (traced by CO) compared to the extent of the stars in ATLAS3D galaxies (top, red) and BIMA-SONG spirals (bottom, purple). The extents match fairly well (adapted from Davis et al. 2013)|
|The extent of the molecular gas (traced by CO) in both Virgo and field ATLAS3D early-type galaxies. Here we see the extents are different (adapted from Davis et al. 2013)|
One thing is clear though, it is time to get better observations of galaxies of all types to begin to understand molecular gas: its fate, its relationships, and its origin. Especially in galaxy clusters (like Virgo).