Integral field observations of the blue compact galaxy Haro14. Star formation and feedback in dwarf galaxies

(Abridged) Low-luminosity, gas-rich blue compact galaxies (BCG) are ideal laboratories to investigate many aspects of the star formation in galaxies. We study the morphology, stellar content, kinematics, and the nebular excitation and ionization mechanism in the BCG Haro 14 by means of integral field observations with VIMOS in the VLT. From these data we build maps in continuum and in the brighter emission lines, produce line-ratio maps, and obtain the velocity and velocity dispersion fields. We also generate the integrated spectrum of the major HII regions and young stellar clusters identified in the maps to determine reliable physical parameters and oxygen abundances. We find as follows: i) the current star formation in Haro 14 is spatially extended with the major HII regions placed along a linear structure, elongated in the north-south direction, and in a horseshoe-like curvilinear feature that extends about 760 pc eastward; the continuum emission is more concentrated and peaks close to the galaxy center; ii) two different episodes of star formation are present: the recent starburst, with ages $\leq$ 6 Myrs and the intermediate-age clusters, with ages between 10 and 30 Myrs; these stellar components rest on a several Gyr old underlying host galaxy; iii) the H$\alpha$/H$\beta$ pattern is inhomogeneous, with excess color values varying from E(B-V)=0.04 up to E(B-V)=1.09; iv) shocks play a significant role in the galaxy; and v) the velocity field displays a complicated pattern with regions of material moving toward us in the east and north galaxy areas. The morphology of Haro 14, its irregular velocity field, and the presence of shocks speak in favor of a scenario of triggered star formation. Ages of the knots are consistent with the ongoing burst being triggered by the collective action of stellar winds and supernovae originated in the central clusters.Comment: 18 pages, 17 figures. Accepted for publication in A&

Probing star formation and feedback in dwarf galaxies. Integral field view of the blue compact galaxy Tololo 1937-423

(Abridged) Blue compact galaxies (BCG) are gas-rich, low-mass, small systems that form stars at unusually high rates. This makes them excellent laboratories for investigating the process of star-formation (SF) at galactic scales and the effects of massive stellar feedback on the interstellar (and intergalactic) medium. We analyzed the BCG Tololo 1937-423 using optical integral field spectroscopy with VIMOS at the Very Large Telescope to probe its morphology, stellar content, nebular excitation and ionization properties, and the kinematics of its warm ionized gas. We found that Tololo 1937-423 is currently undergoing an extended starburst, with nine major $H\alpha$ clumps. The galaxy presents a single continuum peak that is not cospatial with any knot in emission lines, indicating at least two relatively recent episodes of SF. The inhomogeneous dust distribution reaches its maximum roughly at the position of the continuum peak. We found shocked regions in the galaxy outer regions and at the edges of the SF knots. The oxygen abundance is similar in all the SF regions, suggesting a chemically homogeneous ionized interstellar medium over spatial scales of several kpc. The ionized gas kinematics displays an overall regular rotation around a northwest-southeast axis. The morphology of the galaxy and the two different episodes of SF suggest a scenario of triggered (induced by supernova shock waves) SF acting in Tololo 1937-423. The inferred ages for the different SF episodes (~13-80 Myr for the central post-starburst and 5-7 Myr for the ongoing SF) are consistent with triggered SF, with the most recent SF episode caused by the collective effect of stellar winds and supernova explosions from the central post-starburst. The velocity dispersion pattern, with higher velocity dispersions found at the edges of the SF regions, and shocked regions in the galaxy, also favor this scenario.Comment: 16 pages, 18 figures. Accepted for publication in A&

Study of TeV variability of Mrk 421 from 3 years of monitoring with the Milagro Observatory

The Milagro experiment was a TeV gamma-ray observatory designed to continuously monitor the overhead sky in the 0.1-100 TeV energy range. It operated from 2000 and 2008 and was characterized by a large field of view ($\sim$ 2 sr) and a high duty cycle ($\geq$ 90$\%$). Here we report on the long-term monitoring of the blazar Mrk 421 with Milagro over the period from September 21, 2005 to March 15, 2008. We present a study of the TeV variability of the source and provide upper limits for the measured flux for different time scales, ranging from one week up to one year.Comment: 3 pages, 2 figures. Paper to appear in the Proceedings of the Thirteen Marcel Grossmann Meeting, held in Stockholm, Sweden, on July 2012, World Scientific, Singapore, in pres

The group of strong Galois objects associated to a cocommutative Hopf quasigroup

Let H be a cocommutative faithfully flat Hopf quasigroup in a strict symmetric monoidal category with equalizers. In this paper we introduce the notion of (strong) Galois H-object and we prove that the set of isomorphism classes of (strong) Galois H-objects is a (group) monoid which coincides, in the Hopf algebra setting, with the Galois group of H-Galois objects introduced by Chase and Sweedler