Departamento de Fisica y Astronomia

Using echelle spectroscopy, obtained at Las Campanas Observatory, we present a detailed study of the internal kinematics of the nebular material in multiple knots of the blue compact dwarf galaxy Haro 15. A detailed analysis of the complex emission-line profiles shows the presence of an underlying broad component in almost all knots, and the brightest star-forming region shows unmistakable signs for the presence of two distinct narrow kinematical components. We also study the information that our analysis provides regarding the motion of the individual knots in the Haro 15 galaxy potential, confirming that they follow galactic rotation. Finally, we examine the relation between their velocity dispersion and luminosity, finding that almost all knots follow the relation for virialized systems. This holds for the strong narrow components identified in complex fits and for single profile fits, although the latter show a flatter slope. In agreement with previous findings, in this paper we show that the existence of multiple kinematical components among massive starbursts cannot be overlooked, as it has a noticeable effect on any subsequent analysis that relies on basic parameters.

We present new results from our search for giant H II regions in galaxies visible from the Southern hemisphere. In this work we study two galaxies: NGC 7479 and NGC 6070. Using high-resolution spectra, obtained with different instruments at Las Campanas Observatory, we are able to resolve the emission-line profile widths and determine the intrinsic velocity dispersion of the ionized gas. We detect profile widths corresponding to supersonic velocity dispersions in the six observed H II regions. We find that all of them show at least two distinct kinematical components: a relatively narrow feature (between 11 and 22 km s −1) and a broader (between 31 and 77 km s −1) component. Two of the regions show a complex narrow profile in all ion lines, which can be further split into two components with different radial velocities. Whereas the wing broadening of the overall profile can be fitted with a low-intensity broad component for almost all profiles, in one region it was better reproduced by two separate shell-like wings. We have analysed the impact that the presence of multiple components has on the location of the H II regions in the log(L)– log(σ) plane. Although the overall distribution confirms the presence of a regression, the precise location of the regions in the plane is strongly dependent on the components derived from the profile fitting.

We present a detailed study of the physical properties of the nebular material in four star-forming knots of the blue compact dwarf galaxy Haro 15. Using long-slit and echelle spec-troscopy obtained at Las Campanas Observatory, we study the physical conditions (electron density and temperatures), ionic and total chemical abundances of several atoms, reddening and ionization structure, for the global flux and for the different kinematical components. The latter was derived by comparing the oxygen and sulphur ionic ratios to their corresponding observed emission-line ratios (the η and η plots) in different regions of the galaxy. Applying the direct method or empirical relationships for abundance determination, we perform a comparative analysis between these regions. The similarities found in the ionization structure of the different kinematical components imply that the effective temperatures of the ionizing radiation fields are very similar in spite of some small differences in the ionization state of the different elements. Therefore, the different gaseous kinematical components identified in each star-forming knot are probably ionized by the same star cluster. However, the difference in the ionizing structure of the two knots with knot A showing a lower effective temperature than knot B suggests a different evolutionary stage for them consistent with the presence of an older and more evolved stellar population in the first.

Aims. We are presenting here a study of the cold dust in the close environs of the ring nebula Gum 31. We aim at deriving the physical properties of the molecular gas and dust associated with the nebula, and investigating its correlation with the star formation in the region, that was probably triggered by the expansion of the ionization front against its environment. Methods. We make use of 870 µm emission data obtained with the Large APEX Bolometer Camera (LABOCA) to map the dust emission. The 870 µm emission provides an excellent probe of mass and density of dense molecular clouds. The obtained LABOCA image was compared to archival infrared, radio continuum, and optical images. Results. The 870 µm emission follows the 8 µm (Spitzer), 250 µm, and 500 µm (Herschel) emission distributions showing the classical morphology of a two dimensional projection of a spherical shell. We use the 870 µm and 250 µm images to identify 60 dust clumps in the collected layers of molecular gas using the Gaussclumps algorithm. The clumps have effective deconvolved radii between 0.16 pc and 1.35 pc, masses between 70 M ⊙ and 2800 M ⊙ , and volume densities between 1.1 × 10 3 cm −3 and ∼ 2.04 × 10 5 cm −3. The total mass of the clumps is ∼ 37600 M ⊙. The dust temperature of the clumps is in the range from 21 K to 32 K, while inside the Hii region reaches ∼ 40 K. The clump mass distribution for the sample is well-fitted by a power law dN/dlog(M/M ⊙) ∝ M −α , with α = 0.93 ± 0.28. The slope differs from those obtained for the stellar IMF in the solar neighborhood, suggesting that the clumps are not direct progenitors of single stars/protostars. The mass-radius relationship for the 41 clumps detected in the 870 µm emission shows that only 37% of them lie in or above the high-mass star formation threshold, most of them having candidate YSOs projected inside their limits. A comparison of the dynamical age of the Hii region with the fragmentation time, allowed us to conclude that the collect and collapse mechanism may be important for the star formation at the edge of Gum 31, although other processes may also be acting. The position of the identified young stellar objects in the region is also a strong indicator that the collect and collapse process is acting.

Aims. We present a multi-wavelength analysis of the infrared dust bubble S 24, and the extended IR sources G341.220-0.213 and G341.217-0.237 located in its environs, with the aim of investigating the characteristics of the molecular gas and the interstellar dust linked to them, and analyzing the evolutionary state of the young stellar objects identified there and its relation to S 24 and the IR sources. Methods. Using the APEX telescope, we mapped the molecular emission in the CO(2-1), 13 CO(2-1), C 18 O(2-1), and 13 CO(3-2) lines in a region of about 5 ′ × 5 ′ in size around the bubble. The cold dust distribution was analyzed using submillimeter continuum images from ATLASGAL and Herschel. Complementary IR and radio data at different wavelengths were used to complete the study of the interstellar medium in the region. Results. The molecular gas distribution shows that gas linked to the S 24 bubble, G341.220-0.213, and G341.217-0.237 has velocities between –48.0 km s −1 and –40.0 km s −1 , compatible with a kinematical distance of 3.7 kpc generally adopted for the region. The gas distribution reveals a shell-like molecular structure of ∼0.8 pc in radius bordering the S 24 bubble. A cold dust counterpart of the shell is detected in the LABOCA and Herschel-SPIRE images. The presence of weak extended emission at 24 µm from warm dust and radio continuum emission projected inside the bubble indicates the existence of exciting sources and that the bubble is a compact Hii region. Part of the molecular gas bordering the S 24 Hii region coincides with the extended infrared dust cloud SDC341.194-0.221. A molecular and cold dust clump is present at the interface between the S 24 Hii region and G341.217-0.237, shaping the eastern border of the IR bubble. As regards G341.220-0.213, the presence of an arc-like molecular structure encircling the northern and eastern sections of this IR source indicates that G341.220-0.213 is interacting with the molecular gas. The analysis of the available IR point source catalogs reveals the existence of young stellar objects (YSO) candidates linked to the IR extended sources, thus confirming its nature as active star-forming regions. Gas and dust masses were estimated for the different features. The total gas mass in the region and the H 2 ambient density amount to 10300 M ⊙ and 5900 cm −3 , indicating that G341.220-0.213, G341.217-0.237, and the S 24 Hii region are evolving in a high density medium. A triggering star formation scenario for the Hii region is investigated. Key words. ISM:molecules – stars:protostars – (ISM:)IR dust bubbles – ISM:individual objects: S 24 – ISM:individual ob-jects:IRAS 16487-4423

Deep, high-resolution spectroscopic observations have been obtained for six compact, strongly star-forming galaxies at redshift z ∼ 0.1–0.3, most of them also known as green peas. Remarkably, these galaxies show complex emission-line profiles in the spectral region including Hα, [N ii] λλ6548, 6584, and [S ii] λλ6717, 6731, consisting of the superposition of different kinematical components on a spatial extent of few kiloparsecs: a very broad line emission underlying more than one narrower component. For at least two of the observed galaxies some of these multiple components are resolved spatially in their two-dimensional spectra, whereas for another one a faint detached Hα blob lacking stellar continuum is detected at the same recessional velocity ∼7 kpc away from the galaxy. The individual narrower Hα components show high intrinsic velocity dispersion (σ ∼ 30–80 km s −1), suggesting together with unsharped masking Hubble Space Telescope images that star formation proceeds in an ensemble of several compact and turbulent clumps, with relative velocities of up to ∼500 km s −1. The broad underlying Hα components indicate in all cases large expansion velocities (full width zero intensity 1000 km s −1) and very high luminosities (up to ∼10 42 erg s −1), probably showing the imprint of energetic outflows from supernovae. These intriguing results underline the importance of green peas for studying the assembly of low-mass galaxies near and far.

X-shooter and WHT-ISIS spectra of the star-forming galaxy PHL 293B also known as A2228-00 and SDSS J223036.79-000636.9 are presented in this paper. We find broad (FWHM = 1000 km s −1) and very broad (FWZI = 4000 km s −1) components in the Balmer lines, narrow absorption components in the Balmer series blueshifted by 800 km s −1 , previously undetected Fe II multiplet (42) absorptions also blueshifted by 800 km s −1 , IR Ca II triplet stellar absorptions consistent with [Fe/H] < −2.0 and no broad components or blueshifted absorptions in the He I lines. Based on historical records, we found no optical variability at the 5σ level of 0.02 mag between 2005 and 2013 and no optical variability at the level of 0.1 mag for the past 24 yr. The lack of variability rules out transient phenomena like luminous blue variables or Type IIn supernovae as the origin of the blueshifted absorptions of H I and Fe II. The evidence points to either a young and dense expanding supershell or a stationary cooling wind, in both cases driven by the young cluster wind.

We analyse high signal-to-noise ratio spectrophotometric observations acquired simultaneously with TWIN, a double-arm spectrograph, from 3400 to 10 400 Å of three star-forming regions in the H II galaxy SDSS J165712.75+321141.4. We have measured four line temperatures – T e ([O III]), T e ([S III]), T e ([O II]) and T e ([S II]) – with high-precision, rms errors of the order of 2, 5, 6 and 6 per cent, respectively, for the brightest region, and slightly worse for the other two. The temperature measurements allowed the direct derivation of ionic abundances of oxygen, sulphur, nitrogen, neon and argon. We have computed CLOUDY tailor-made models which reproduce the O 2+-measured thermal and ionic structures within the errors in the three knots, with deviations of only 0.1 dex in the case of O + and S 2+ ionic abundances. In the case of the electron temperature and the ionic abundances of S + /H + , we find major discrepancies which could be the consequence of the presence of colder diffuse gas. The star formation history derived using STARLIGHT shows a similar age distribution of the ionizing population among the three star-forming regions. This fact suggests a similar evolutionary history which is probably related to the process of interaction with a companion galaxy that triggered the star formation in the different regions almost at the same time. The hardness of the radiation field mapped through the use of the softness parameter η is the same within the observational errors for all three regions, implying that the equivalent effective temperatures of the radiation fields are very similar for all the studied regions of the galaxy, in spite of some small differences in the ionization state of different elements. Regarding the kinematics of the galaxy, the gas rotation curve shows a deviation from the circular motion probably due either to an interaction process or to an expanding bubble or shell of the ionized gas approaching us. A dynamical mass of 2.5 × 10 10 M is derived from the rotation curve.

Context. VISTA variables in the Vía Láctea is an ESO Public survey dedicated to scanning the bulge and an adjacent portion of the Galactic disk in the fourth quadrant using the VISTA telescope and its near-infrared camera VIRCAM. One of the leading goals of the VVV survey is to contribute to knowledge of the star cluster population of the Milky Way. Aims. To improve the census of Galactic star clusters, we performed a systematic and careful scan of the JHK s images of the Galactic plane section of the VVV survey. Methods. Our detection procedure is based on a combination of stellar density maps and visual inspection of promising features in the J-, Hand nd K S-band images. The material examined are VVV JHK S color-composite images corresponding to Data Release 1 of VVV. Results. We report the discovery of 493 new infrared star cluster candidates. The analysis of the spatial distribution show that the clusters are very concentrated in the Galactic plane, presenting some local maxima around the position of large star-forming complexes, such as G305, RCW 95, and RCW 106. The vast majority of the new star cluster candidates are quite compact and generally surrounded by bright and/or dark nebulosities. IRAS point sources are associated with 59% of the sample, while 88% are associated with MSX point sources. GLIMPSE 8 μm images of the cluster candidates show a variety of morphologies, with 292 clusters dominated by knotty sources, while 361 clusters show some kind of nebulosity in this wavelength regime. Spatial cross-correlation with young stellar objects, masers, and extended green-object catalogs suggest that a large sample of the new cluster candidates are extremely young. In particular, 104 star clusters associated with methanol masers are excellent candidates for ongoing massive star formation. Also, there is a special set of sixteen cluster candidates that present clear signposts of star-forming activity having associated simultaneosly dark nebulae, young stellar objects, extended green objects, and masers.