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[Abridged] Aims. We present a large atmospheric study of 49 gas giantexoplanets using infrared transmission photometry with Spitzer/IRAC at 3.6 and4.5um. Methods. We uniformly analyze 70 photometric light curves of 33transiting planets using our custom pipeline, which implements pixel leveldecorrelation. We use this survey to understand how infrared photometry traceschanges in atmospheric chemical properties as a function of planetarytemperature. We compare our measurements to a grid of 1D radiative-convectiveequilibrium forward atmospheric models which include disequilibrium chemistry.We explore various strengths of vertical mixing (Kzz = 0 - 10^12 cm2/s) as wellas two chemical compositions (1x and 30x solar). Results. We find that, onaverage, Spitzer probes a difference of 0.5 atmospheric scale heights between3.6 and 4.5um, which is measured at 7.5sigma level of significance. We findthat the coolest planets show a lack of methane compared to expectations, whichhas also been reported by previous studies of individual objects. We show thatthe sample of coolest planets rule out 1x solar composition with >3sigmaconfidence while supporting low vertical mixing (Kzz = 10^8 cm2/s). On theother hand, we find that the hot planets are best explained by models with 1xsolar metallicity and high vertical mixing (Kzz = 10^12 cm2/s). We interpretthis as the lofting of CH4 to the upper atmospheric layers. Changing theinterior temperature changes the expectation for equilibrium chemistry in deeplayers, hence the expectation of disequilibrium chemistry higher up. We alsofind a significant scatter in the transmission signatures of the mid-temperateand ultra-hot planets, likely due to increased atmospheric diversity, withoutthe need to invoke higher metallicities. Additionally, we compare Spitzertransmission with emission for the same planets and find no evidence forcorrelation.

astronomy and astrophysics

Evidence for disequilibrium chemistry from vertical mixing in hot  Jupiter atmospheres. A comprehensive survey of transiting close-in gas giant  exoplanets with warm-Spitzer/IRAC