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We study the properties of one of the most luminous hinge clumps, located on the compact group of galaxies NGC6845. Using IFS from GMOS/Gemini, complemented with archival MUSE data, we obtain oxygen abundances, ages, star formation rates, velocity fields and we also performed a single stellar populations modeling to understand the SFH of the hinge clump localized in NGC6845. We found that the hinge clump sits in a tail, having a SFR of 3.4$M_{\odot}yr^{-1}$, which is comparable with a few other extreme cases, e.g., the star clusters in the Antennae galaxy and other reported hinge clumps in the literature. In fact, this clump represents ~15\% of total SFR of NGC6845A. Large-scale modeling of the observed velocity field of NGC6845A rules out the scenario on which this hinge clump was a satellite galaxy. Indeed, its kinematics is compatible with the galactic disk of NGC6845A. Its abundance, mean value of 0.4Z$_{\odot}$, is also consistent with the metallicity gradient of the galaxy. Our analysis, suggest that the hinge clump is formed by multiple stellar populations instead of a single burst, thus having a large range of ages. We found that central clump is encompassed by a ring-like structure, suggesting that the ring-like structure represents a second-generation of star formation. In addition, the analysis of the diagnostic diagram indicates that this central region can also be being ionized by shock from stellar and supernovae winds. Finally, the derived SFR density $\Sigma=9.7M_{\odot}yr^{-1}kpc^{-2}$ of the central clump, place it in starburst regime, where gas inflows should provide gas to maintain the star formation. This work shows a resolved example of an extreme localized starburst in a compact group of galaxies., Comment: 13 pages, 11 figures

Light pollution is recognized as a global issue that, like other forms of anthropogenic pollution, has significant impact on ecosystems and adverse effects on living organisms. Multiple evidence suggests that it has been increasing at an unprecedented rate at all spatial scales. Chile, which thanks to its unique environmental conditions has become one of the most prominent astronomical hubs of the world, seems to be no exception. In this paper we present the results of the first observing campaign aimed at quantifying the effects of artificial lights at night (ALAN) on the brightness and colors of Chilean sky. Through the analysis of photometrically calibrated all-sky images captured at four representative sites with an increasing degree of anthropization, and the comparison with state-of-the-art numerical models, we show that significant levels of light pollution have already altered the appearance of the natural sky even in remote areas. Our observations reveal that the light pollution level recorded in a small town of the Coquimbo Region is comparable with that of Flagstaff, a ten times larger Dark Sky city, and that a mid-size urban area door to the Atacama Desert displays photometric indicators of night sky quality that are typical of the most densely populated regions of Europe. Our results suggest that there is still much to be done in Chile to keep the light pollution phenomenon under control and thus preserve the darkness of its night sky - a natural and cultural heritage that is our responsibility to protect., Comment: 26 pages, 18 figures, 5 tables, accepted for publication in AJ

This study focuses on Pristine$\_180956.78$$-$$294759.8$ (hereafter P180956, $[Fe/H] =-1.95\pm0.02$), a star selected from the Pristine Inner Galaxy Survey (PIGS), and followed-up with the recently commissioned Gemini High-resolution Optical SpecTrograph (GHOST) at the Gemini South telescope. The GHOST spectrograph's high efficiency in the blue spectral region ($3700-4800$~\AA) enables the detection of elemental tracers of early supernovae (\eg Al, Mn, Sr, Eu). The star exhibits chemical signatures resembling those found in ultra-faint dwarf systems, characterised by very low abundances of neutron-capture elements (Sr, Ba, Eu), which are uncommon among stars in the Milky Way halo. Our analysis suggests that P180956 bears the chemical imprints of a small number (2 or 4) of low-mass hypernovae ($\sim10-15 M_{\odot}$), which are needed to mostly reproduce the abundance pattern of the light-elements (\eg [Si, Ti/Mg, Ca] $\sim0.6$), and one fast-rotating intermediate-mass supernova ($\sim300\kms$, $\sim80-120 M_{\odot}$), which is the main channel contributing to the high [Sr/Ba] ($\sim +1.2$). The small pericentric ($\sim0.7$ kpc) and apocentric ($\sim13$ kpc) distances and its orbit confined to the plane ($\lesssim 2$ kpc), indicate that this star was likely accreted during the early Galactic assembly phase. Its chemo-dynamical properties suggest that P180956 formed in a system similar to an ultra-faint dwarf galaxy accreted either alone, as one of the low-mass building blocks of the proto-Galaxy, or as a satellite of Gaia-Sausage-Enceladus. The combination of Gemini's large aperture with GHOST's high efficiency and broad spectral coverage makes this new spectrograph one of the leading instruments for near-field cosmology investigations., Comment: Accepted version, minor editing. New figure showing Sr and Ba lines. Section 4.7 revised

The Gemini High-resolution Optical SpecTrograph (GHOST) is the newest high resolution spectrograph to be developed for a large aperture telescope, recently deployed and commissioned at the Gemini-South telescope. In this paper, we present the first science results from the GHOST spectrograph taking during its commissioning runs. We have observed the bright metal-poor benchmark star HD 122563, along with two stars in the ultra faint dwarf galaxy, Ret II, one of which was previously identified as a candidate member, but did not have a previous detailed chemical abundance analysis. This star (GDR3 0928) is found to be a bona fide member of Ret II, and from a spectral synthesis analysis, it is also revealed to be a CEMP-r star, with significant enhancements in the several light elements (C, N, O, Na, Mg, and Si), in addition to featuring an r-process enhancement like many other Ret II stars. The light-element enhancements in this star resemble the abundance patterns seen in the CEMP-no stars of other ultra faint dwarf galaxies, and are thought to have been produced by an independent source from the r-process. These unusual abundance patterns are thought to be produced by faint supernovae, which may be produced by some of the earliest generations of stars., Comment: 23 pages, 9 figures, 7 tables, submitted to the AAS Journals

We present, for the first time, spatially resolved spectroscopy for the entire Hickson Compact Group 31 obtained with the MUSE instrument at the VLT,and an in-depth analysis of this compact group. To obtain a complete understanding of the system, we derived radial velocity and dispersion velocity maps, maps of the ionization mechanism of the system, chemical abundances and their distribution over the whole system, star formation rates and ages of the different star-forming regions, and the spatial distribution of the Wolf-Rayet stellar population. We also reconstructed the star formation history of the galaxies HCG 31 A, C, B and F, measured the emission-line fluxes, and performed a stellar population synthesis. Our main findings are: (i) that there is clearly disturbed kinematics due to the merger event that the system is experiencing; (ii) that the ionization is produced exclusively via star formation except for the nucleus of the galaxy HCG 31 A, where there is a small contribution of shocks; (iii) that there is low oxygen abundance distributed homogeneously through the system; (iv) that there is a prominent population of carbon Wolf-Rayet stars in the central zone of the group; and (v) that there are clear evidences of the tidal origin of the galaxies HCG 31 E, HCG 31 H, and HCG 31 F because they show quite high oxygen abundances for their stellar mass. All these findings are clear evidence that HCG 31 is currently in an early merging phase and manifesting a starburst in its central region., Comment: 20 pages, 14 figures, accepted for publication in MNRAS

Nearby merging pairs are unique laboratories in which one can study the gravitational effects on the individual interacting components. In this manuscript, we report the characterization of selected HII regions along the peculiar galaxy NGC 2936, member of the galaxy pair Arp 142, an E+S interaction, known as "The Penguin". Using Gemini South spectroscopy we have derived a high enhancement of the global star formation rate SFR=35.9 Msun/yr probably stimulated by the interaction. Star-forming regions on this galaxy display oxygen abundances that are consistent with solar metallicities. The current data set does not allow us to conclude any clear scenario for NGC 2936. Diagnostic diagrams suggest that the central region of NGC 2936 is ionized by AGN activity and the eastern tidal plume in NGC 2936 is experiencing a burst of star formation, which may be triggered by the gas compression due to the interaction event with its elliptical companion galaxy: NGC 2937. The ionization mechanism of these sources is consistent with shock models of low-velocities of 200-300 km/s The isophotal analysis shows tidal features on NGC 2937: at inner radii non-concentric (or off-centering) isophotes, and at large radii, a faint excess of the surface brightness profile with respect to de Vaucouleurs law. By comparing the radial velocity profiles and morphological characteristics of Arp 142 with a library of numerical simulations, we conclude that the current stage of the system would be about 50 +-25 Myr after the first pericenter passage., Comment: 16 Pages, 12 Figures, MNRAS accepted

We present two-dimensional stellar and gaseous kinematics of the inner 0.7 $\times$ 1.2 kpc$^{2}$ of the Seyfert galaxy ESO 362-G18, derived from optical spectra obtained with the GMOS/IFU on the Gemini South telescope at a spatial resolution of $\approx$170 pc and spectral resolution of 36 km s$^{-1}$. ESO 362-G18 is a strongly perturbed galaxy of morphological type Sa or S0/a, with a minor merger approaching along the NE direction. Previous studies have shown that the [OIII] emission shows a fan-shaped extension of $\approx$ 10\arcsec\ to the SE. We detect the [OIII] doublet, [NII] and H${\alpha}$ emission lines throughout our field of view. The stellar kinematics is dominated by circular motions in the galaxy plane, with a kinematic position angle of $\approx$137$^{\circ}$. The gas kinematics is also dominated by rotation, with kinematic position angles ranging from 122$^{\circ}$ to 139$^{\circ}$. A double-Gaussian fit to the [OIII]$\lambda$5007 and H${\alpha}$ lines, which have the highest signal to noise ratios of the emission lines, reveal two kinematic components: (1) a component at lower radial velocities which we interpret as gas rotating in the galactic disk; and (2) a component with line of sight velocities 100-250 km s$^{-1}$ higher than the systemic velocity, interpreted as originating in the outflowing gas within the AGN ionization cone. We estimate a mass outflow rate of 7.4 $\times$ 10$^{-2}$ M$_{\odot}$ yr$^{-1}$ in the SE ionization cone (this rate doubles if we assume a biconical configuration), and a mass accretion rate on the supermassive black hole (SMBH) of 2.2 $\times$ 10$^{-2}$ M$_{\odot}$ yr$^{-1}$. The total ionized gas mass within $\sim$84 pc of the nucleus is 3.3 $\times$ 10$^{5}$ M$_{\odot}$; infall velocities of $\sim$34 km s$^{-1}$ in this gas would be required to feed both the outflow and SMBH accretion., Comment: 18 pages, 14 figures

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 H\alpha, [NII]$\lambda\lambda 6548, 6584$ and [SII]$\lambda\lambda 6717, 6731$, consisting of the superposition of different kinematical components on a spatial extent of few kpc: 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 2D-spectra, whereas for another one a faint detached H\alpha\ blob lacking stellar continuum is detected at the same recessional velocity ~7 kpc away from the galaxy. The individual narrower H\alpha\ components show high intrinsic velocity dispersion (\sigma ~30-80 km s$^{-1}$), suggesting together with unsharped masking HST 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 H\alpha\ components indicate in all cases large expansion velocities (full width zero intensity FWZI $\ge$ 1000 km s$^{-1}$) and very high luminosities (up to ~10$^{42}$ erg s$^{-1}$), probably showing the imprint of energetic outflows from SNe. These intriguing results underline the importance of Green Peas for studying the assembly of low-mass galaxies near and far., Comment: 11 pages, 3 figures, and 1 Table. Accepted for publication in ApJ Letters

In this thesis we presented a detailed spectroscopic study in a sample of Giant HII Regions in galaxies visible from Southern Hemisphere., Comment: This thesis is mainly composed of three chapters already published in the Monthly Notices of the Royal Astronomical Society: Chapter 2: Vol. 406, Page 1094 (2010); Chapter 3: Vol. 414, Page 3288 (2011); Chapter 4: accepted for publication (2012) (arXiv:1203.0531). PhD Thesis at Universidad Nacional de La Plata, March 2011

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 spectroscopy 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 $\eta$ and $\eta$' 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 implies 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., Comment: 21 pages, 6 figures, 8 tables, accepted by MNRAS

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 show 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 virialised 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., Comment: 12 pages, 21 figures

We analyze high signal-to-noise spectrophotometric observations acquired simultaneously with TWIN, a double-arm spectrograph, from 3400 to 10400 \AA of three star-forming regions in the HII galaxy SDSS J165712.75+321141.4. We have measured four line temperatures: Te([OIII]), Te([SIII]), Te([OII]), and Te([SII]), with high precision, rms errors of order 2%, 5%, 6% and 6%, 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 O2+ 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 S2+ ionic abundances. In the case of the electron temperature and the ionic abundances of S+/H+, we find major discrepancies which could be 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 a 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 $\eta$ is the same within the observational errors for all three regions, implying that the equivalent effective temperature 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., Comment: 18 pages, 10 figures, accepted by MNRAS