The supply of molecular gas and the efficiency with which it is converted into stars are among the principal determinants of galaxy evolution. Nonetheless, extragalactic surveys of molecular gas conspicuously lag behind optical surveys in terms of unbiased sampling of the galaxy population. The CARMA EDGE survey will provide a measurement of the distribution of molecular gas in a statistically significant sample of over one hundred galaxies. The survey targets the J = 1-0 transition of CO and its 13CO isotopologue, which trace the bulk of the cold, star-forming gas. Paired with matched IFU mapping of the entire optical spectrum, this survey enables studies of resolved star formation efficiencies and histories, gas and stellar kinematics, nebular extinctions, and ionized gas properties across the Hubble sequence. The EDGE survey is designed to move the field of millimeter-wave interferometry from the piecemeal collection of case studies into the realm of large samples.

The EDGE survey targets 170+ galaxies from the CALIFA IFU survey (the Calar Alto Integral Field Area survey), a representative sample of a volume-limited distribution of galaxies (D 20-120 Mpc). EDGE observed 177 sources from CALIFA in 1-hour snapshots in its E-array (8" resolution), following up the 125 brightest CO sources with 5-hour observations in D-array (typical final synthesized beam yields 4.5" resolution). This resolution corresponds to size scales of 0.5-2 kpc at the distances of the sample. All observations used 7-pointing mosaics to achieve uniform sensitivity over the approximate optical angular diameter of the galaxies: CALIFA galaxies are selected to have angular diameters of 45"-80". EDGE has a 1-sigma sensitivity of 40-50 mK, corresponding to a molecular column density N(H
2)=1019 cm-2, or a surface density sensitivity of approximately 10 solar masses per square parsec.

EDGE measures kpc-scale gas distributions, isotopic ratios, and velocity fields, vastly increasing the number of galaxies with CO imaging. These data allow us to investigate a number of key questions:

What governs the total H2 supply? accretion, star formation, or both? The combination of CARMA and CALIFA data, probing the mass, metallicity, and kinematics of both stars and gas, along with the mass of the HI reservoir, will provide fundamental constraints on galaxy evolution models.

How universal is the SFR-H2 relation? By sampling the full range of galaxy properties, we will put the spatially resolved star formation law on a more secure footing. The inclusion of metallicity data is also crucial since metallicity appears to act as a third parameter in the star formation law via its effect on the
2 conversion factor.

What are the roles of feedback and environment? The statistically significant and well-defined sample of galaxies in EDGE will enable a direct study of the effects of AGN and stellar feedback as well as environment (field, groups, clusters) on the morphological transformation of galaxies and the evolution and distribution of the molecular gas.


CARMA CO images for 126 CALIFA galaxies, D+E array


SDSS images in g-band


CO velocity fields


Peak temperature CO maps


SDSS i-g-u composites