The EDGE-CALIFA Survey: The Resolved Star Formation Efficiency and Local Physical Conditions
Vicente Villanueva, Alberto D. Bolatto, S. N. Vogel, Rebecca C. Levy, S. F. Sánchez, J. K. Barrera-Ballesteros, Tony Wong, Erik Rosolowsky, Dario Colombo, M. Rubio, Yixian Cao, V. Kalinova, Adam K. Leroy, Dyas Utomo, Rodrigo Herrera-Camus, Leo Blitz, Yufeng Luo
Abstract
Abstract We measure the star formation rate (SFR) per unit gas mass and the star formation efficiency (SFE gas for total gas, SFE mol for the molecular gas) in 81 nearby galaxies selected from the EDGE-CALIFA survey, using 12 CO ( J = 1–0) and optical IFU data. For this analysis we stack CO spectra coherently by using the velocities of H α detections to detect fainter CO emission out to galactocentric radii r gal ∼ 1.2 r 25 (∼3 R e ) and include the effects of metallicity and high surface densities in the CO-to-H 2 conversion. We determine the scale lengths for the molecular and stellar components, finding a close to 1:1 relation between them. This result indicates that CO emission and star formation activity are closely related. We examine the radial dependence of SFE gas on physical parameters such as galactocentric radius, stellar surface density Σ ⋆ , dynamical equilibrium pressure P DE , orbital timescale τ orb , and the Toomre Q stability parameter (including star and gas Q star+gas ). We observe a generally smooth, continuous exponential decline in the SFE gas with r gal . The SFE gas dependence on most of the physical quantities appears to be well described by a power law. Our results also show a flattening in the SFE gas – τ orb relation at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">[</mml:mo> <mml:msub> <mml:mrow> <mml:mi>τ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>orb</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">]</mml:mo> <mml:mo>∼</mml:mo> <mml:mn>7.9</mml:mn> <mml:mo>–</mml:mo> <mml:mn>8.1</mml:mn> </mml:math> and a morphological dependence of the SFE gas per orbital time, which may reflect star formation quenching due to the presence of a bulge component. We do not find a clear correlation between SFE gas and Q star+gas .