[en] The leakage of Lyman continuum (LyC) photons from star-forming galaxies is an elusive parameter. When observed, it provides a wealth of information on star formation in galaxies and on the geometry of the interstellar medium, and puts constraints on the role of star-forming galaxies in the reionization of the universe. Hα-selected galaxies at $z\sim <!--\; ???\; -->2$ trace the highest star formation population at the peak of cosmic star formation history, providing a base for directly measuring LyC escape. Here we present this method and highlight its benefits as well as caveats. We also use the method on 10 Hα emitters in the Chandra Deep Field South at $z=2.2,$ also imaged with the Hubble Space Telescope in the ultraviolet. We find no individual LyC detections, and our stack puts a 5σ upper limit on the average absolute escape fraction of <24%, consistent with similar studies. With future planned observations, the sample sizes should rapidly increase and the method presented here should provide very robust constraints on the escape fraction.

[en] The spatial variations in polycyclic aromatic hydrocarbon (PAH) band intensities are normally attributed to the physical conditions of the emitting PAHs, however in recent years it has been suggested that such variations are caused mainly by extinction. To resolve this question, we have obtained near-infrared (NIR), mid-infrared (MIR), and radio observations of the compact H II region IRAS 12063–6259. We use these data to construct multiple independent extinction maps and also to measure the main PAH features (6.2, 7.7, 8.6, and 11.2 μm) in the MIR. Three extinction maps are derived: the first using the NIR hydrogen lines and case B recombination theory; the second combining the NIR data with radio data; and the third making use of the Spitzer/IRS MIR observations to measure the 9.8 μm silicate absorption feature using the Spoon method and PAHFIT (as the depth of this feature can be related to overall extinction). The silicate absorption over the bright, southern component of IRAS 12063–6259 is almost absent while the other methods find significant extinction. While such breakdowns of the relationship between the NIR extinction and the 9.8 μm absorption have been observed in molecular clouds, they have never been observed for H II regions. We then compare the PAH intensity variations in the Spitzer/IRS data after dereddening to those found in the original data. It was found that in most cases, the PAH band intensity variations persist even after dereddening, implying that extinction is not the main cause of the PAH band intensity variations.

[en] We used the near-IR imager/spectrograph LUCIFER mounted on the Large Binocular Telescope to image, with subarcsecond seeing, the local dwarf starburst NGC 1569 in the JHK bands and He I 1.08 μm, [Fe II] 1.64 μm, and Brγ narrowband filters. We obtained high-quality spatial maps of He I 1.08 μm, [Fe II] 1.64 μm, and Brγ emission across the galaxy, and used them together with Hubble Space Telescope/Advanced Camera for Surveys images of NGC 1569 in the Hα filter to derive the two-dimensional spatial map of the dust extinction and surface star formation rate (SFR) density. We show that dust extinction (as derived from the Hα/Brγ flux ratio) is rather patchy and, on average, higher in the northwest (NW) portion of the galaxy (E_g(B - V) ≅ 0.71 mag) than in the southeast (E_g(B - V) ≅ 0.57 mag). Similarly, the surface density of SFR (computed from either the dereddened Hα or dereddened Brγ image) peaks in the NW region of NGC 1569, reaching a value of about 4 x 10^-6 M_sun yr^-1 pc^-2. The total SFR as estimated from the integrated, dereddened Hα (or, alternatively, Brγ) luminosity is about 0.4 M_sun yr^-1, and the total supernova rate from the integrated, dereddened [Fe II] 1.64 μm luminosity is about 0.005 yr^-1 (assuming a distance of 3.36 Mpc). The azimuthally averaged [Fe II] 1.64 μm/Brγ flux ratio is larger at the edges of the central, gas-deficient cavities (encompassing the superstar clusters A and B) and in the galaxy outskirts. If we interpret this line ratio as the ratio between the average past star formation (as traced by supernovae) and ongoing activity (represented by OB stars able to ionize the interstellar medium), it would then indicate that star formation has been quenched within the central cavities and lately triggered in a ring around them. The number of ionizing hydrogen and helium photons as computed from the integrated, dereddened Hα and He I 1.08 μm luminosities suggests that the latest burst of star formation occurred about 4 Myr ago and produced new stars with a total mass of ≅1.8 x 10⁶ M_sun.

[en] We present near-infrared multi-object spectroscopy and JHK_s imaging of the massive stellar content of the Galactic star-forming region W3 Main, obtained with LUCI at the Large Binocular Telescope. We confirm 15 OB stars in W3 Main and derive spectral types between O5V and B4V from their absorption line spectra. Three massive young stellar objects are identified by their emission line spectra and near-infrared excess. The color-color diagram of the detected sources allows a detailed investigation of the slope of the near-infrared extinction law toward W3 Main. Analysis of the Hertzsprung-Russell diagram suggests that the Nishiyama extinction law fits the stellar population of W3 Main best (E(J – H)/E(H – K_s) = 1.76 and R_Ks = 1.44). From our spectrophotometric analysis of the massive stars and the nature of their surrounding H II regions, we derive the evolutionary sequence of W3 Main and we find evidence of an age spread of at least 2-3 Myr. While the most massive star (IRS2) is already evolved, indications for high-mass pre-main-sequence evolution are found for another star (IRS N1), deeply embedded in an ultracompact H II (UCH II) region, in line with the different evolutionary phases observed in the corresponding H II regions. We derive a stellar mass of W3 Main of (4 ± 1) × 10³ M_☉ by extrapolating from the number of OB stars using a Kroupa initial mass function and correcting for our spectroscopic incompleteness. We have detected the photospheres of OB stars from the more evolved diffuse H II region to the much younger UCH II regions, suggesting that these stars have finished their formation and cleared away their circumstellar disks very fast. Only in the hyper-compact H II region (IRS5) do the early-type stars seem to be still surrounded by circumstellar material.

[en] In this paper, we present VLT/SINFONI integral field spectroscopy of RCW 34 along with Spitzer/IRAC photometry of the surroundings. RCW 34 consists of three different regions. A large bubble has been detected in the IRAC images in which a cluster of intermediate- and low-mass class II objects is found. At the northern edge of this bubble, an H II region is located, ionized by 3 OB stars, of which the most massive star has spectral type O8.5V. Intermediate-mass stars (2-3 M_sun) are detected of G- and K-spectral type. These stars are still in the pre-main-sequence (PMS) phase. North of the H II region, a photon-dominated region is present, marking the edge of a dense molecular cloud traced by H₂ emission. Several class 0/I objects are associated with this cloud, indicating that star formation is still taking place. The distance to RCW 34 is revised to 2.5 ± 0.2 kpc and an age estimate of 2 ± 1 Myr is derived from the properties of the PMS stars inside the H II region. Between the class II sources in the bubble and the PMS stars in the H II region, no age difference could be detected with the present data. The presence of the class 0/I sources in the molecular cloud, however, suggests that the objects inside the molecular cloud are significantly younger. The most likely scenario for the formation of the three regions is that star formation propagated from south to north. First the bubble is formed, produced by intermediate- and low-mass stars only, after that, the H II region is formed from a dense core at the edge of the molecular cloud, resulting in the expansion similar to a champagne flow. More recently, star formation occurred in the rest of the molecular cloud. Two different formation scenarios are possible. (1) The bubble with the cluster of low- and intermediate-mass stars triggered the formation of the O star at the edge of the molecular cloud, which in its turn induces the current star formation in the molecular cloud. (2) An external triggering is responsible for the star formation propagating from south to north.