[en] The extraordinary brightness of supernova 1987A in the Large Magellanic Cloud (LMC) allowed the authors to obtain high-resolution spectra with high signal-to-noise ratios, sampling the galactic disk and halo, interstellar gas in the LMC, and the intervening medium. Thirty-five distinct components have been clearly identified, probably located between the Galaxy and the LMC, and showing low dust content. (author)

[en] The supernova 1987A offers a unique opportunity to probe the visible interstellar absorption spectrum towards the Large Magellanic Cloud at high resolution and high signal-to-noise ratio. The authors report the first results of these observations. A Ca II 'forest' is detected through all the velocity range between the Galaxy and the Large Magellanic Cloud and in particular, a component is seen at a velocity of approx. 215 km s^-1 which may correspond to cooler gas in a halo. A preliminary abundance study is also presented. (author)

[en] We present a coherent database of spectroscopic observations of far-IR fine-structure lines from the Herschel/Photoconductor Array Camera and Spectrometer archive for a sample of 170 local active galactic nuclei (AGNs), plus a comparison sample of 20 starburst galaxies and 43 dwarf galaxies. Published Spitzer/IRS and Herschel/SPIRE line fluxes are included to extend our database to the full 10–600 μm spectral range. The observations are compared to a set of Cloudy photoionization models to estimate the above physical quantities through different diagnostic diagrams. We confirm the presence of a stratification of gas density in the emission regions of the galaxies, which increases with the ionization potential of the emission lines. The new [O iv]${}_{25.9\mathrm{\mu <!--\; ??\; -->}\mathrm{m}}$/[O iii]${}_{88\mathrm{\mu <!--\; ??\; -->}\mathrm{m}}$ versus [Ne iii]${}_{15.6\mathrm{\mu <!--\; ??\; -->}\mathrm{m}}$/[Ne ii]${}_{12.8\mathrm{\mu <!--\; ??\; -->}\mathrm{m}}$ diagram is proposed as the best diagnostic to separate (1) AGN activity from any kind of star formation and (2) low-metallicity dwarf galaxies from starburst galaxies. Current stellar atmosphere models fail to reproduce the observed [O iv]${}_{25.9\mathrm{\mu <!--\; ??\; -->}\mathrm{m}}$/[O iii]${}_{88\mathrm{\mu <!--\; ??\; -->}\mathrm{m}}$ ratios, which are much higher when compared to the predicted values. Finally, the ([Ne iii]${}_{15.6\mathrm{\mu <!--\; ??\; -->}\mathrm{m}}$+ [Ne ii]${}_{12.8\mathrm{\mu <!--\; ??\; -->}\mathrm{m}}$)/([S iv]${}_{10.5\mathrm{\mu <!--\; ??\; -->}\mathrm{m}}$+[S iii]${}_{18.7\mathrm{\mu <!--\; ??\; -->}\mathrm{m}}$) ratio is proposed as a promising metallicity tracer to be used in obscured objects, where optical lines fail to accurately measure the metallicity. The diagnostic power of mid- to far-infrared spectroscopy shown here for local galaxies will be of crucial importance to study galaxy evolution during the dust-obscured phase at the peak of the star formation and black hole accretion activity ($1<<!--\; <\; -->z<<!--\; <\; -->4$). This study will be addressed by future deep spectroscopic surveys with present and forthcoming facilities such as the James Webb Space Telescope, the Atacama Large Millimeter/submillimeter Array, and the Space Infrared telescope for Cosmology and Astrophysics.

[en] We compare multi-wavelength star formation rate (SFR) indicators out to z ∼ 3 in the GOODS-South field. Our analysis uniquely combines U to 8 μm photometry from FIREWORKS, MIPS 24 μm and PACS 70, 100, and 160 μm photometry from the PEP, and Hα spectroscopy from the SINS survey. We describe a set of conversions that lead to a continuity across SFR indicators. A luminosity-independent conversion from 24 μm to total infrared luminosity yields estimates of L_IR that are in the median consistent with the L_IR derived from PACS photometry, albeit with significant scatter. Dust correction methods perform well at low-to-intermediate levels of star formation. They fail to recover the total amount of star formation in systems with large SFR_IR/SFR_UV ratios, typically occuring at the highest SFRs (SFR_UV+IR ∼> 100 M_sun yr^-1) and redshifts (z ∼> 2.5) probed. Finally, we confirm that Hα-based SFRs at 1.5 < z < 2.6 are consistent with SFR_SED and SFR_UV+IR provided extra attenuation toward H II regions is taken into account (A_V,neb = A_V,continuum/0.44). With the cross-calibrated SFR indicators in hand, we perform a consistency check on the star formation histories inferred from spectral energy distribution (SED) modeling. We compare the observed SFR-M relations and mass functions at a range of redshifts to equivalents that are computed by evolving lower redshift galaxies backward in time. We find evidence for underestimated stellar ages when no stringent constraints on formation epoch are applied in SED modeling. We demonstrate how resolved SED modeling, or alternatively deep UV data, may help to overcome this bias. The age bias is most severe for galaxies with young stellar populations and reduces toward older systems. Finally, our analysis suggests that SFHs typically vary on timescales that are long (at least several 100 Myr) compared to the galaxies' dynamical time.