Escape of Lyman continuum radiation from local galaxies - Detection of leakage from the young starburst Tol 1247-232

The escape fraction of hydrogen ionizing photons (f_esc) from galaxies has been suggested to be evolving with time, but the picture is far from clear. While evidence for significant escape fractions has been found at high redshifts in several studies, the picture looks different in the more nearby universe. Here, we apply a new background subtraction routine on archival data from the Far Ultraviolet Spectroscopic Explorer (FUSE), in order to study local galaxies in search for possible Lyman Continuum (LyC) leakage. In the process, for the first time a stacked spectrum in the LyC is produced for local galaxies. With this small sample, we also make a more tentative approach to look for possible correlations between f_esc and physical parameters such as internal absorption E(B-V)_i, mass, H I mass, specific star formation rate (SSFR), metallicity, and Ly-alpha emission. Eight star forming galaxies with redshifts z > 0.015 from the FUSE archive were re-examined. Also, a sub-sample of an additional four galaxies with lower redshifts were included, for which the escape fraction was estimated from residual flux in the low ionization interstellar C II(1036{\AA}) line. Out of the eight galaxies, only one was found to have significant LyC leakage, Tol 1247-232 (S/N=5.2). This is the second detection of a leaking galaxy in the local universe. We find an absolute escape fraction for Tol 1247-232 of f_esc = 2.4(+0.9/-0.8) %. The stacked sample show an excess in the LyC with f_esc = 1.4(+0.6/-0.5) %, but we note that there might be important selection biases involved. With the small sample, we suggest a possible trend for higher f_esc with lower mass and with enhanced SSFR. None of the galaxies with high values of E(B-V)_i were found to show any sign of leakage.Comment: Accepted for publication in A&A. 16 pages, 7 picture

Local starburst galaxies and their descendants

Despite strong interest in the starburst (hereafter SB) phenomenon, the concept remains ill-defined. We use a strict definition of SB to examine the statistical properties of local SB and post-starburst (hereafter PB) galaxies. We also seek relationships to active galaxies. Potential SB galaxies are selected from the SDSS DR7 and their stellar content is analysed. We apply an age dependent dust attenuation correction and derive star formation rates (SFR), ages and masses of the young and old populations. The photometric masses nicely agree with dynamical masses derived from the H-alpha emission line width. To select SB galaxies, we use the birthrate parameter b=SFR/, requiring b>=3. The PB sample is selected from the citerion EW(Hdelta_abs)>=6 A. Only 1% of star-forming galaxies are found to be SB galaxies. They contribute 3-6% to the stellar production and are therefore unimportant for the local star formation activity. The median SB age is 70 Myr, roughly independent of mass. The b-parameter strongly depends on burst age. Values close to b=60 are found at ages ~10 Myr, while almost no SBs are found at ages >1 Gyr. The median baryonic burst mass fraction of sub-L* galaxies is 5%, decreasing slowly with mass. The median mass fraction of the recent burst in the PB sample is 5-10%. The age-mass distribution of the progenitors of the PBs is bimodal with a break at log(M)~10.6 above which the ages are doubled. The SB and PB luminosity functions (hereafter LFs) follow each other closely until M_r~-21, when AGNs begin to dominate. The PB LF continues to follow the AGN LF while SB loose significance. This suggests that the number of luminous SBs is underestimated by about one dex at high luminosities, due to large amounts of dust and/or AGN blending. It also indicates that the SB phase preceded the AGN phase. We also discuss the conditions for global gas outflow caused by stellar feedback.Comment: Accepted for publication in Astronomy and Astrophysics. This is an extended, substantially revised and corrected version with partly modified conclusion

The faint outskirts of the blue compact galaxy Haro 11: is there a red excess?

Previous studies of the low surface brightness host of the blue compact galaxy (BCG) Haro 11 have suggested an abnormally red color of V-K=4.2+-0.8 for the host galaxy. This color is inconsistent with any normal stellar population over a wide range of stellar metallicities (Z=0.001-0.02). Similar though less extreme host colors have been measured for other BCGs and may be reconciled with population synthesis models, provided that the stellar metallicity of the host is higher than that of the ionized gas in the central starburst. We present the deepest V and K band observations to date of Haro 11 and derive a new V-K color for the host galaxy. Our new data suggest a far less extreme colour of V-K=2.3+-0.2, which is perfectly consistent with the expectations for an old host galaxy with the same metallicty as that derived from nebular emission lines in the star-forming center.Comment: This paper contains 8 figures and 2 table

Deep multiband surface photometry on star forming galaxies: I. A sample of 24 blue compact galaxies

[Abridged] We present deep optical and near-infrared UBVRIHKs imaging data for 24 blue compact galaxies (BCGs). The sample contains luminous dwarf and intermediate-mass BCGs which are predominantly metal-poor, although a few have near-solar metallicities. We have analyzed isophotal and elliptical integration surface brightness and color profiles, extremely deep (mu_B<29 mag arcsec^{-2}) contour maps and RGB images for each galaxy in the sample. The colors are compared to different spectral evolutionary models. We detect extremely extended low surface brightness (LSB) components dominant beyond the Holmberg radius as well as optical bridges between companion galaxies at the mu_V~28th mag arcsec^{-2} isophotal level. The central surface brightness mu_0 and scale length h_r are derived from two radial ranges typically assumed to be dominated by the underlying host galaxy. We find that mu_0 and h_r of the BCGs host deviate from those of dwarf ellipticals (dE) and dwarf irregulars (dI) solely due to a strong burst contribution to the surface brightness profile almost down to the Holmberg radius. Structural parameters obtained from a fainter region, mu_B=26-28 mag arcsec^{-2}, are consistent with those of true LSB galaxies for the starbursting BCGs in our sample, and with dEs and dIs for the BCGs with less vigorous star formation.Comment: 61 pages, 45 figures, submitte