A significant fraction of spiral galaxies are red, gas-poor, and have lowstar formation rates (SFRs). We study these unusual objects using theIllustrisTNG100 simulation. Among 1912 well-resolved disk galaxies selectedfrom the last simulation output, we identify 377 red objects and describe theirproperties and origins using a few representative examples. The simulated redspirals turn out to be typically very gas-poor, have very low SFRs, are moremetal-rich, and have larger stellar masses than the remaining disks. Only about13% of red spirals suffered strong mass loss and thus could have resulted fromenvironmental quenching by ram pressure and tidal stripping of the gas, orsimilar processes. The majority of red disks were probably quenched by feedbackfrom the active galactic nucleus (AGN). This conclusion is supported by thehigher black hole masses and lower accretion rates of red disks, as well as thelarger total AGN feedback energies injected into the surrounding gas in thekinetic feedback mode implemented in the IllustrisTNG simulations. Thetimescales of the gas loss correlate with the black hole growth for theAGN-quenched galaxies and with the dark-matter loss for the environmentallyquenched ones. The red spirals are more likely to possess bars, and their barsare stronger than in the remaining disks, which is probably the effect of gasloss rather than the reason for quenching.

Using data from the Arecibo Galaxy Environment Survey, we report thediscovery of five HI clouds in the Leo I group without detected opticalcounterparts. Three of the clouds are found midway between M96 and M95, one isonly 10$^{\prime}$ from the south-east side of the well-known Leo Ring, and thefifth is relatively isolated. HI masses range from 2.6$\times$10$^{6}$ -9.0$\times$10$^{6}$M$_{\odot}$ and velocity widths (W50) from 16 - 42 km/s.Although a tidal origin is the most obvious explanation, this formationmechanism faces several challenges. For the most isolated cloud, thedifficulties are its distance from neighbouring galaxies and the lack of anysigns of disturbance in the HI discs of those systems. Some of the clouds alsoappear to follow the baryonic Tully-Fisher relation between mass and velocitywidth for normal, stable galaxies which is not expected if they are tidal inorigin. Three clouds are found between M96 and M95 which have no opticalcounterparts, but have otherwise similar properties and location to theoptically detected galaxy LeG 13. While overall we favour a tidal debrisscenario to explain the clouds, we cannot rule out a primordial origin. If theclouds were produced in the same event that gave rise to the Leo Ring, they mayprovide important constraints on any model attempting to explain that structure

We analyze Ha or CO rotation curves (RCs) extending out to several galaxyeffective radii for 100 massive, large, star-forming disk galaxies (SFGs)across the peak of cosmic galaxy star formation (z~0.6-2.5), more than doublingthe previous sample presented by Genzel et al. (2020) and Price et al. (2021).The observations were taken with SINFONI and KMOS integral-field spectrographsat ESO-VLT, LUCI at LBT, NOEMA at IRAM, and ALMA. We fit the major axiskinematics with beam-convolved, forward models of turbulent rotating disks withbulges embedded in dark matter (DM) halos, including the effects of pressuresupport. The fraction of dark to total matter within the disk effective radius($R_e ~ 5 kpc$), $f_DM (R_e)=V_{DM}^2 (R_e)/V_{circ}^2 (R_e)$, decreases withredshift: At z~1 (z~2) the median DM fraction is $0.38\pm 0.23$ ($0.27\pm0.18$), and a third (half) of all galaxies are "maximal" disks with $f_{DM}(R_e)<0.28$. Dark matter fractions correlate inversely with the baryonicsurface density, and the low DM fractions require a flattened, or cored, innerDM density distribution. At z~2 there is ~40% less dark matter mass on averagewithin $R_e$ compared to expected values based on cosmological stellar-masshalo-mass relations. The DM deficit is more evident at high star formation rate(SFR) surface densities ($\Sigma_{SFR}>2.5 M_{\odot} yr^{-1} kpc^{-2}$) andgalaxies with massive bulges ($M_{bulge}>10^{10} M_{\odot}$). A combination ofstellar or active galactic nucleus (AGN) feedback, and/or heating due todynamical friction, either from satellite accretion or clump migration, maydrive the DM from cuspy into cored mass distributions. The observationsplausibly indicate an efficient build-up of massive bulges and central blackholes at z~2 SFGs.