Monday, December 14, 2015

The ATLAS3D project - XVIII. CARMA CO imaging survey of early-type galaxies

Early-type and late-type galaxies from the Hubble tuning fork

It is time to change gears from AGN outflows and the different ways that they impact galaxy evolution to the important question of why do “red and dead” galaxies stay dead? In the first blog entry of this series, we talked about the fact that NGC 1266 was found as part of the Atlas3D survey, but now it is time to zoom out and look at the galaxies inside the Atlas3D survey at all 261 galaxies. This blog post takes a lot of the intro from my thesis: “Molecular gas in early-type galaxies” with advisor Carl Heiles.

It starts back with work done by Edwin Hubble, looking at the difference between galaxies, splitting them into early-type and late-type galaxies. Galaxies were also found to be bimodal in color, with blue galaxies and red galaxies. Most red galaxies are also early-type galaxies, and most blue galaxies are late-type galaxies. The Atlas3D project was designed to look at early-type (morphological classification) galaxies in-depth, acting as galactic archaeologists. In that, the team looked in-depth at 261 early-type galaxies, determining the motion of their stars, and taking a more careful, unbiased look at early-type galaxies as a population than had ever been done before. The conclusions most pertinent to the work I did was that over 20% of these objects had a reservoir of molecular gas, and many also had neutral gas (H I), so these dead galaxies often still had the remnants of star forming fuel. These objects never seemed to have large reservoirs of gas (compared to their mass of stars), but gas they had.

Molecular gas (shown in yellow) is overlaid on top of the starlight of the 30 CARMA Atlas3D galaxies
Understanding how dead galaxies could still have gas required deeper observations of the molecular gas, focusing on imaging rather than just detecting. At first, the Atlas3d team was getting a couple galaxies here and there, but by turning to a partnership with Berkeley, were able to command the magnificent power of CARMA. Instead of getting a handful of early-type galaxies each semester, CARMA created a longer-term survey, imaging 30 early-type galaxies, more than doubling the amount of these early-type galaxies that had been imaged up until this point. Our job was to take these images, investigate the extraordinary cases (like NGC 1266), and create download-quality data from the survey so others could use it. That task fell to me.

This paper was used to detail the data acquisition and reduction that took place, with a few little results. For instance, the molecular gas with signs of being morphologically disrupted tended to be bluer in general, suggesting that the gas in these systems was probably acquired from a minor merger, which then underwent a small burst of star formation. I then went on to take the molecular gas we thought was from these minor mergers and compared that to the predicted minor merger rate, finding that our minor mergers were consistent. But for the most part, the point of this paper was showcasing the exquisite data from CARMA. 
Mean velocity maps of the CARMA early-type galaxies.
The official published version can be found on NASA ADS.
To get a PDF version made by me, you can download it here

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