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The Kennicutt-Schmidt (KS) relation between the gas mass and star formation rate (SFR) describes the star formation regulation in disk galaxies. It is a function of gas metallicity, but the low metallicity regime of the KS diagram is poorly sampled. We have analyzed data for a representative set of extremely metal-poor galaxies (XMPs), as well as auxiliary data, and compared these to empirical and theoretical predictions. The majority of the XMPs possess high specific SFRs, similar to high redshift star-forming galaxies. On the KS plot, the XMP HI data occupy the same region as dwarfs, and extend the relation for low surface brightness galaxies. Considering the HI gas alone, a considerable fraction of the XMPs already fall off the KS law. Significant quantities of dark H$_2$ mass (i.e., not traced by CO) would imply that XMPs possess low star formation efficiencies (SFE$_{rm gas}$). Low SFE$_{rm gas}$ in XMPs may be the result of the metal-poor nature of the HI gas. Alternatively, the HI reservoir may be largely inert, the star formation being dominated by cosmological accretion. Time lags between gas accretion and star formation may also reduce the apparent SFE$_{rm gas}$, as may galaxy winds, which can expel most of the gas into the intergalactic medium. Hence, on global scales, XMPs could be HI-dominated, high specific SFR ($gtrsim $ 10$^{-10}$ yr$^{-1}$), low SFE$_{rm gas}$ ($lesssim$ 10$^{-9}$ yr$^{-1}$) systems, in which the total HI mass is likely not a good predictor of the total H$_2$ mass nor of the SFR.
The surface densities of molecular gas, $Sigma_{rm H_2}$, and the star formation rate (SFR), $dotSigma_star$, correlate almost linearly on kiloparsec scales in observed star-forming (non-starburst) galaxies. We explore the origin of the linear slope
The first galaxies contain stars born out of gas with little or no metals. The lack of metals is expected to inhibit efficient gas cooling and star formation but this effect has yet to be observed in galaxies with oxygen abundance relative to hydroge
Using N-body/gasdynamic simulations of a Milky Way-like galaxy we analyse a Kennicutt-Schmidt relation, $Sigma_{SFR} propto Sigma_{gas}^N$, at different spatial scales. We simulate synthetic observations in CO lines and UV band. We adopt the star for
We report on the result of an ongoing campaign to determine chemical abundances in extremely metal poor (EMP) turn-off (TO) stars selected from the Sloan Digital Sky Survey (SDSS) low resolution spectra. This contribution focuses principally on the l
Results from the UV satellite GALEX revealed large extensions of disks in some nearby spiral galaxies, extending out to 3 to 4 times the isophotal radius, r25. M63 is a remarkable example of a spiral galaxy with one of the most extended UV disks, so