We quantitatively investigate the dependence of central galaxy HI mass($M_{\rm HI}$) on the stellar mass ($M_\ast$), halo mass ($M_{\rm h}$), starformation rate (SFR), and central stellar surface density within 1 kpc($\Sigma_1$), taking advantage of the HI spectra stacking technique using boththe Arecibo Fast Legacy ALFA Survey and the Sloan Digital Sky Survey. We findthat the shapes of $M_{\rm HI}$-$M_{\rm h}$ and $M_{\rm HI}$-$M_\ast$ relationsare remarkably similar for both star-forming and quenched galaxies, withmassive quenched galaxies having constantly lower HI masses of around 0.6 dex.This similarity strongly suggests that neither halo mass nor stellar mass isthe direct cause of quenching, but rather the depletion of HI reservoir. Whilethe HI reservoir for low-mass galaxies of $M_\ast<10^{10.5}M_\odot$ stronglyincreases with $M_{\rm h}$, more massive galaxies show no significantdependence of $M_{\rm HI}$ on $M_{\rm h}$, indicating the effect of halo todetermine the smooth cold gas accretion. We find that the star formation andquenching of central galaxies are directly regulated by the available HIreservoir, with an average relation of ${\rm SFR}\propto M_{\rmHI}^{2.75}/M_\ast^{0.40}$, implying a quasi-steady state of star formation. Wefurther confirm that galaxies are depleted of their HI reservoir once they dropoff the star-formation main sequence and there is a very tight and consistentcorrelation between $M_{\rm HI}$ and $\Sigma_1$ in this phase, with $M_{\rmHI}\propto\Sigma_1^{-2}$. This result is in consistent with thecompaction-triggered quenching scenario, with galaxies going through threeevolutionary phases of cold gas accretion, compaction and post-compaction, andquenching.

We present a observational study of the dark matter fraction in 225 rotationsupported star-forming galaxies at $z\approx 0.9$ having stellar mass range: $9.0 \leq log(M_* \ \mathrm{M_\odot}) \leq 11.0$ and star formation rate: $0.49\leq log \left(SFR \ \mathrm{[M_{\odot}\ yr^{-1}]} \right) \leq 1.77$. This isa sub sample of KMOS redshift one spectroscopic survey (KROSS) previouslystudied by \citet{GS20}. The stellar masses ($M_*$) of these objects werepreviously estimated using mass-to-light ratios derived from fitting thespectral energy distribution of the galaxies. Star formation rates were derivedfrom the H$_\alpha$ luminosities. The total gas masses ($M_{gas}$) aredetermined by scaling relations of molecular and atomic gas\citep[][respectively] {Tacconi2018, Lagos2011}. The dynamical masses($M_{dyn}$) are directly derived from the rotation curves (RCs) at differentscale lengths (effective radius: $R_e$, $\sim 2 \ R_e$ and $\sim 3 \ R_e$) andthen the dark matter fractions ($f_{ DM }=1-M_{bar}/M_{dyn}$) at these radiiare calculated. We report that at $z\sim 1$ only a small fraction ($\sim 5\%$)of our sample has a low ($< 20\%$) DM fraction within $\sim$ 2-3 $R_e$. Themajority ($> 72\%$) of SFGs in our sample have dark matter dominated outerdisks ($\sim 5-10$ kpc) in agreement with local SFGs. Moreover, we find a largescatter in the fraction of dark matter at a given stellar mass (or circularvelocity) with respect to local SFGs, suggesting that galaxies at $z \sim 1$,a) span a wide range of stages in the formation of stellar disks, b) havediverse DM halo properties coupled with baryons.

We present a new set of index-based measurements of [$\alpha$/Fe] for asample of 2093 galaxies in the SAMI Galaxy Survey. Following earlier work, wefit a global relation between [$\alpha$/Fe] and the galaxy velocity dispersion$\sigma$ for red sequence galaxies,[$\alpha$/Fe]=(0.378$\pm$0.009)log($\sigma$/100)+(0.155$\pm$0.003). We observea correlation between the residuals and the local environmental surfacedensity, whereas no such relation exists for blue cloud galaxies. Returning tothe full sample, we find that galaxies in high-density environments are$\alpha$-enhanced by up to 0.06 dex at galaxy velocity dispersions $\sigma$<100km/s, compared to their counterparts in low-density environments. This$\alpha$-enhancement includes a dependence on morphology, with an offset of0.057$\pm$0.014 dex for ellipticals, and decreasing along the Hubble sequencetowards spirals, with an offset of 0.019$\pm$0.014 dex. Conversely, forgalaxies with $\sigma$>100 km/s in low-density environments, the[$\alpha$/Fe]-$\sigma$ relation is consistent across all morphological typesearlier than Sc. At low galaxy velocity dispersion and controlling formorphology, we therefore estimate that star formation in galaxies inhigh-density environments is truncated $\sim$1 Gyr earlier, compared to thosein low-density environments. At the highest velocity dispersions, $\sigma$>200km/s, we find no difference in the [$\alpha$/Fe] ratio of galaxies earlier thanSc. Hence, we infer that the integrated star-formation timescales cannot differsubstantially between high-$\sigma$ galaxies across varied environments,supporting the relative dominance of mass-based quenching mechanisms at thehighest mass scales.