SECCO1 is an extremely dark, low-mass (M_star=10^5 M_sun), star-formingstellar system lying in the Low Velocity Cloud (LVC) substructure of the Virgocluster of galaxies, and hosting several HII regions. Here we review ourknowledge of this remarkable system, and present the results of (a) additionalanalysis of our panoramic spectroscopic observations with MUSE, (b) thecombined analysis of Hubble Space Telescope and MUSE data, and (c) newnarrow-band observations obtained with OSIRIS@GTC to search for additional HIIregions in the surroundings of the system. We provide new evidence supportingan age as young as 4 Myr for the stars that are currently ionising the gas inSECCO1. We identify only one new promising candidate HII region possiblyassociated with SECCO1, thus confirming the extreme isolation of the system. Wealso identify three additional candidate pressure-supported dark clouds inVirgo among the targets of the SECCO survey. Various possible hypotheses forthe nature and origin of SECCO1 are considered and discussed, also with thehelp of dedicated hydrodynamical simulations showing that a hydrogen cloud withthe characteristics of SECCO1 can likely survive for >1 Gyr while travelingwithin the LVC Intra Cluster Medium.

By analysing a sample of galaxies selected from the HI Parkes All Sky Survey(HIPASS) to contain more than 2.5 times their expected HI content based ontheir optical properties, we investigate what drives these HI eXtreme (HIX)galaxies to be so HI-rich. We model the HI kinematics with the Tilted RingFitting Code TiRiFiC and compare the observed HIX galaxies to a control sampleof galaxies from HIPASS as well as simulated galaxies built with thesemi-analytic model Dark Sage. We find that (1) HI discs in HIX galaxies aremore likely to be warped and more likely to host HI arms and tails than in thecontrol galaxies, (2) the average HI and average stellar column density of HIXgalaxies is comparable to the control sample, (3) HIX galaxies have higher HIand baryonic specific angular momenta than control galaxies, (4) most HIXgalaxies live in higher-spin haloes than most control galaxies. These resultssuggest that HIX galaxies are HI-rich because they can support more HI againstgravitational instability due to their high specific angular momentum. Themajority of the HIX galaxies inherits their high specific angular momentum fromtheir halo. The HI content of HIX galaxies might be further increased bygas-rich minor mergers. This paper is based on data obtained with the AustraliaTelescope Compact Array (ATCA) through the large program C 2705.

The traditional picture of post-starburst galaxies as dust- and gas-poormerger remnants, rapidly transitioning to quiescence, has been recentlychallenged. Unexpected detections of a significant ISM in many post-starburstsraise important questions. Are they truly quiescent and, if so, what mechanismsinhibit further star formation? What processes dominate their ISM energetics?We present an infrared spectroscopic and photometric survey of 33 SDSS-selectedE+A post-starbursts, aimed at resolving these questions. We find compact, warmdust reservoirs with high PAH abundances, and total gas and dust massessignificantly higher than expected from stellar recycling alone. Both PAH/TIRand dust-to-burst stellar mass ratios are seen to decrease with post-burst age,indicative of the accumulating effects of dust destruction and an incipienttransition to hot, early-type ISM properties. Their infrared spectralproperties are unique, with dominant PAH emission, very weak nebular lines,unusually strong H$_{2}$ rotational emission, and deep ${\rm [C\, II]}$deficits. There is substantial scatter among SFR indicators, and both PAH andTIR luminosities provide overestimates. Even as potential upper limits, alltracers show that the SFR has typically experienced a more than twoorder-of-magnitude decline since the starburst, and that the SFR isconsiderably lower than expected given both their stellar masses and moleculargas densities. These results paint a coherent picture of systems in which starformation was, indeed, rapidly truncated, but in which the ISM was$\textit{not}$ completely expelled, and is instead supported against collapseby latent or continued injection of turbulent or mechanical heating. Theresulting aging burst populations provide a "high-soft" radiation field whichseemingly dominates the E+As' unusual ISM energetics.