ALMaQUEST -- VII: Star Formation Scaling Relations of Green Valley Galaxies

Abstract

We utilize the ALMA-MaNGA QUEnch and STar formation (ALMaQUEST) survey to investigate the kpcscale scaling relations, presented as the resolved star forming main sequence (rSFMS: Σ SFR vs. Σ * ), the resolved Schmidt-Kennicutt relation (rSK: Σ SFR vs. Σ H2 ), and the resolved molecular gas main sequence (rMGMS: Σ H2 vs. Σ * ), for 11478 star-forming and 1414 retired spaxels (oversampled by a factor of ∼ 20) located in 22 green valley (GV) and 12 main sequence (MS) galaxies. For a given galaxy type (MS or GV), the retired spaxels are found to be offset from the sequences formed by the star-forming spaxels on the rSFMS, rSK, and rMGMS planes, toward lower absolute values of sSFR, SFE, and f H2 by ∼ 1.1, 0.6, and 0.5 dex. The scaling relations for GV galaxies are found to be distinct from that of the MS galaxies, even if the analyses are restricted to the star-forming spaxels only. It is found that for star-forming spaxels, sSFR, SFE, and f H2 in GV galaxies are reduced by ∼0.36, 0.14, and 0.21 dex, respectively, compared to those in MS galaxies. Therefore, the suppressed sSFR/SFE/ f gas in GV galaxies is associated with not only an increased proportion of retired regions in GV galaxies but also a depletion of these quantities in star-forming regions. Finally, the reduction of SFE and f H2 in GV galaxies relative to MS galaxies is seen in both bulge and disk regions (albeit with larger uncertainties), suggesting that statistically, quenching in the GV population may persist from the inner to the outer regions.

MASCOT: molecular gas depletion times and metallicity gradients – evidence for feedback in quenching active galaxies

“…Within the ALMaQUEST survey (described in more detail in Section 2.2), starbursts selected to feature at least a 50% elevation of the SFR in the central region were shown to be primarily driven by an increased star-forming efficiency (Ellison et al 2020), which is the ratio of the SFR over the molecular gas mass 𝑀 H 2 . On the other hand, Green Valley galaxies show both suppressed star-forming efficiencies and molecular gas fractions (𝑀 H 2 /𝑀 ★ ) with respect to the MS, both in star-forming as well as 'retired' spaxels (Lin et al 2022). We also refer the reader to Sánchez et al (2021a,b) for a summary of the resolved and integrated relations between molecular gas mass, SFR and stellar mass, and the connection between the different scales.…”