arXiv subjects

Claus Leitherer

Publications and source records attributed to Claus Leitherer.

At least 37 records · Page 2Linked to original sources

arXiv2023

HST FUV Spectroscopy of Super Star Cluster A in the Green Pea Analog Mrk 71: Revealing the Presence of Very Massive Stars

Mrk 71 is a low metallicity (Z = 0.16 Z_sun) starburst region in the local dwarf galaxy NGC 2366, hosting two super star clusters (SSCs A and B), and is recognized as a Green Pea (GP) analog with SSC A responsible for the GP properties. We present STIS and FOS far-ultraviolet (FUV) spectra of the embedded SSC Mrk 71-A obtained with the Hubble Space Telescope (HST). The STIS FUV spectrum shows the characteristic features of very massive stars (VMS, masses > 100 M_sun) and we derive an age of 1+/-1 Myr by comparison with the Charlot & Bruzual suite of spectral population synthesis models with upper mass limits of 300 and 600 M_sun. We compare the STIS spectrum with all known SSC spectra exhibiting VMS signatures: NGC 5253-5, R136a, NGC 3125-A1 and the z = 2.37 Sunburst cluster. We find that the cluster mass-loss rates and wind velocities, as characterized by the C IV P Cygni profiles and the He II emission line strengths, are very similar over Z = 0.16 to 0.4 Z_sun. This agrees with predictions that the optically thick winds of VMS will be enhanced near the Eddington limit and show little metallicity dependence. We find very strong damped Lyman-alpha absorption with log N(H I) = 22.2 cm-2 associated with Mrk 71-A. We discuss the natal environment of this young SSC in terms of radiatively-driven winds, catastrophic cooling and recent models where the cluster is surrounded by highly pressurized clouds with large neutral columns.

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arXiv2023

A study of extreme CIII]1908 & [OIII]88/[CII]157 emission in Pox 186: implications for JWST+ALMA (FUV+FIR) studies of distant galaxies

Carbon spectral features are ubiquitous in the ultraviolet (UV) and far-infrared (FIR) spectra of galaxies in the epoch of reionization (EoR). We probe the ionized carbon content of a blue compact dwarf galaxy Pox 186 using the UV, optical, mid-infrared and FIR data taken with telescopes in space (Hubble, Spitzer, Herschel) and on the ground (Gemini). This local (z~0.0040705) galaxy is likely an analogue of EoR galaxies, as revealed by its extreme FIR emission line ratio, [OIII] 88/[CII] 157 (>10). The UV spectra reveal extreme CIII] 1907, 1909 emission with the strongest equivalent width (EW) = 35.85 $\pm$ 0.73 Ådetected so far in the local (z~0) Universe, a relatively strong CIV 1548, 1550 emission with EW = 7.95 $\pm$0.45Å, but no He II 1640 detection. Several scenarios are explored to explain the high EW of carbon lines, including high effective temperature, high carbon-to-oxygen ratio, slope and upper mass of top-heavy initial mass function, hard ionizing radiation and in-homogeneous dust distribution. Both CIII] and CIV line profiles are broadened with respect to the OIII] 1660 emission line. Each emission line of CIV 1548, 1550 shows the most distinct double-peak structure ever detected, which we model via two scenarios, firstly a double-peaked profile that might emerge from resonant scattering and secondly, a single nebular emission line along with a weaker interstellar absorption. The study demonstrates that galaxies with extreme FIR emission line ratio may also show extreme UV properties, hence paving a promising avenue of using FIR+UV in the local (via HST+Herschel/SOFIA) and distant (via JWST+ALMA) Universe for unveiling the mysteries of the EoR.

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arXiv2022

CLASSY IV: Exploring UV diagnostics of the interstellar medium in local high-$z$ analogs at the dawn of the JWST era

The COS Legacy Archive Spectroscopic SurveY (CLASSY) HST/COS treasury program provides the first high-resolution spectral catalogue of 45 local high-z analogues in the UV (1200-2000Å) to investigate their stellar and gas properties. We present a toolkit of UV interstellar medium (ISM) diagnostics, analyzing the main emission lines of CLASSY spectra (i.e., NIV]$λλ$1483,87, CIV$λλ$1548,51, HeII$λ$1640, OIII]$λλ$1661,6, SiIII]$λλ$1883,92, CIII]$λλ$1907,9). Specifically, we focus our investigation on providing accurate diagnostics for reddening, electron density and temperature, gas-phase metallicity and ionization parameter, taking into account the different ionization zones of the ISM. We calibrate our UV toolkit using well-known optical diagnostics, analyzing archival optical spectra for all the CLASSY targets. We find that UV density diagnostics estimate ne values that are ~1-2 dex higher (e.g., ne(CIII]$λλ$}1907,9)~10$^4$cm$^{-3}$) than those inferred from their optical counterparts (e.g., ne([SII]$λλ$6717,31)~10$^2$cm$^{-3}$). Te derived from the hybrid ratio OIII]$λ$1666/[OIII]$λ$}5007 proves to be a reliable Te diagnostic, with differences in 12+log(O/H) within ~$\pm$0.3dex. We also investigate the relation between the stellar and gas E(B-V), finding consistent values at high specific star formation rates, while at low sSFR we confirm an excess of dust attenuation in the gas. Finally, we investigate UV line ratios and equivalent widths to provide correlations with 12+log(O/H) and log(U), but note there are degeneracies between the two. With this suite of UV-based diagnostics, we illustrate the pivotal role CLASSY plays in understanding the chemical and physical properties of high-z systems that JWST can observe in the rest-frame UV.

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arXiv2022

CLASSY V: The impact of aperture effects on the inferred nebular properties of local star-forming galaxies

Strong nebular emission lines are an important diagnostic tool for tracing the evolution of star-forming galaxies across cosmic time. However, different observational setups can affect these lines, and the derivation of the physical nebular properties. We analyze 12 local star-forming galaxies from the COS Legacy Spectroscopy SurveY (CLASSY) to assess the impact of using different aperture combinations on the determination of the physical conditions and gas-phase metallicity. We compare optical spectra observed with the SDSS aperture, which has a 3" of diameter similar to COS, to IFU and longslit spectra, including new LBT/MODS observations of five CLASSY galaxies. We calculate the reddening, electron densities and temperatures, metallicities, star formation rates, and equivalent widths (EWs). We find that measurements of the electron densities and temperatures, and metallicity remained roughly constant with aperture size, indicating that the gas conditions are relatively uniform for this sample. However, using the IFU observations of 3 galaxies, we find that the E(B-V) values derived from the Balmer ratios decrease ( by up to 53%) with increasing aperture size. The values change most significantly in the center of the galaxies, and level out near the COS aperture diameter of 2.5". We examine the relative contributions from the gas and stars using the H$α$ and [OIII] $λ$5007 EWs as a function of aperture light fraction, but find little to no variations within a given galaxy. These results imply that the optical spectra provide nebular properties appropriate for the FUV CLASSY spectra, even when narrow 1.0" long-slit observations are used.

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arXiv2022

CLASSY II: A technical Overview of the COS Legacy Archive Spectroscopic SurveY

The COS Legacy Archive Spectroscopic SurveY (CLASSY) is designed to provide the community with a spectral atlas of 45 nearby star-forming galaxies which were chosen to cover similar properties as those seen at high-z (z>6). The prime high level science product of CLASSY is accurately coadded UV spectra, ranging from ~1000-2000A, derived from a combination of archival and new data obtained with HST's Cosmic Origins Spectrograph (COS). This paper details the multi-stage technical processes of creating this prime data product, and the methodologies involved in extracting, reducing, aligning, and coadding far-ultraviolet (FUV) and near-ultraviolet (NUV) spectra. We provide guidelines on how to successfully utilize COS observations of extended sources, despite COS being optimized for point sources, and best-practice recommendations for the coaddition of UV spectra in general. Moreover, we discuss the effects of our reduction and coaddition techniques in the scientific application of the CLASSY data. In particular, we find that accurately accounting for flux calibration offsets can affect the derived properties of the stellar populations, while customized extractions of NUV spectra for extended sources are essential for correctly diagnosing the metallicity of galaxies via CIII] nebular emission. Despite changes in spectral resolution of up to ~25% between individual datasets (due to changes in the COS line spread function), no adverse affects were observed on the difference in velocity width and outflow velocities of isolated absorption lines when measured in the final combined data products, owing in-part to our signal-to-noise regime of S/N<20.

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arXiv2022

The COS Legacy Archive Spectroscopy SurveY (CLASSY) Treasury Atlas

Far-ultraviolet (FUV; ~1200-2000 angstroms) spectra are fundamental to our understanding of star-forming galaxies, providing a unique window on massive stellar populations, chemical evolution, feedback processes, and reionization. The launch of JWST will soon usher in a new era, pushing the UV spectroscopic frontier to higher redshifts than ever before, however, its success hinges on a comprehensive understanding of the massive star populations and gas conditions that power the observed UV spectral features. This requires a level of detail that is only possible with a combination of ample wavelength coverage, signal-to-noise, spectral-resolution, and sample diversity that has not yet been achieved by any FUV spectral database. We present the COS Legacy Spectroscopic SurveY (CLASSY) treasury and its first high level science product, the CLASSY atlas. CLASSY builds on the HST archive to construct the first high-quality (S/N_1500 >~ 5/resel), high-resolution (R~15,000) FUV spectral database of 45 nearby (0.002 < z < 0.182) star-forming galaxies. The CLASSY atlas, available to the public via the CLASSY website, is the result of optimally extracting and coadding 170 archival+new spectra from 312 orbits of HST observations. The CLASSY sample covers a broad range of properties including stellar mass (6.2 < logM_star(M_sol) < 10.1), star formation rate (-2.0 < log SFR (M_sol/yr) < +1.6), direct gas-phase metallicity (7.0 < 12+log(O/H) < 8.8), ionization (0.5 < O_32 < 38.0), reddening (0.02 < E(B-V < 0.67), and nebular density (10 < n_e (cm^-3) < 1120). CLASSY is biased to UV-bright star-forming galaxies, resulting in a sample that is consistent with z~0 mass-metallicity relationship, but is offset to higher SFRs by roughly 2 dex, similar to z >~2 galaxies. This unique set of properties makes the CLASSY atlas the benchmark training set for star-forming galaxies across cosmic time.

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arXiv2022

Unveiling an old disk around a massive young leaking blueberry in SDSS-IV MaNGA

Extreme emission-line galaxies, such as blue compact dwarfs (BCDs), Green Peas (GPs) and blueberries in the local Universe are the potential candidates to understand the nature of galaxies that re-ionized the early Universe. Being low-mass, metal-poor starburst systems they are understood as local analogs of the high redshift Lyman Continuum (LyC) and Lyman-$α$ emitters (LAEs). Even with their proximity to us, we know little about their spatially resolved properties, most of the blueberries and GPs are indeed compact, remain unresolved. Here, we report the detection of a disk-like lower-surface brightness (LSB) stellar host with very old population around a blueberry LAE system using broad i-band imaging and integral field spectroscopic data from SDSS and SDSS-IV MaNGA surveys, respectively. The LSB stellar host is structurally similar to that observed around15 local starburst BCDs. Furthermore, the kinematics of the studied blueberry source bear sign of misalignment between the gas and stellar components. Our findings establish an intriguing thread connecting the blueberry and an LSB disk with old stellar population, and suggest that blueberries and their high redshift counterparts such as GPs do not represent peculiar cases of dwarf galaxy evolution. In fact, with respect to the structural properties of their host galaxies, they are compatible with a common evolutionary track of the main population of local BCDs.

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arXiv2021

Tracing the Ionization Structure of the Shocked Filaments of NGC 6240

We study the ionization and excitation structure of the interstellar medium in the late-stage gas-rich galaxy merger NGC 6240 using a suite of emission line maps at $\sim$25 pc resolution from the Hubble Space Telescope, Keck NIRC2 with Adaptive Optics, and ALMA. NGC 6240 hosts a superwind driven by intense star formation and/or one or both of two active nuclei; the outflows produce bubbles and filaments seen in shock tracers from warm molecular gas (H$_2$ 2.12$μ$m) to optical ionized gas ([O III], [N II], [S II], [O I]) and hot plasma (Fe XXV). In the most distinct bubble, we see a clear shock front traced by high [O III]/H$β$ and [O III]/[O I]. Cool molecular gas (CO(2-1)) is only present near the base of the bubble, towards the nuclei launching the outflow. We interpret the lack of molecular gas outside the bubble to mean that the shock front is not responsible for dissociating molecular gas, and conclude that the molecular clouds are partly shielded and either entrained briefly in the outflow, or left undisturbed while the hot wind flows around them. Elsewhere in the galaxy, shock-excited H$_2$ extends at least $\sim$4 kpc from the nuclei, tracing molecular gas even warmer than that between the nuclei, where the two galaxies' interstellar media are colliding. A ridgeline of high [O III]/H$β$ emission along the eastern arm aligns with the south nucleus' stellar disk minor axis; optical integral field spectroscopy from WiFeS suggests this highly ionized gas is centered at systemic velocity and likely photoionized by direct line-of-sight to the south AGN.

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arXiv2021

SDSS-IV MaNGA: an observational evidence of density bounded region in a Lyman-$α$ emitter

Using Integral Field Unit (IFU) spectroscopy, we present here the spatially resolved morphologies of [SII]$λ$6717,6731/H$α$ and [SII]$λ$6717,6731/[OIII]$λ$5007 emission line ratios for the first time in a Blueberry Lyman-$α$ emitter (BBLAE) at z $\sim$ 0.047. Our derived morphologies show that the extreme starburst region of the BBLAE, populated by young ($\leqslant$ 10 Myr), massive Wolf-Rayet stars, is [SII]-deficient, while the rest of the galaxy is [SII]-enhanced. We infer that the extreme starburst region is density-bounded (i.e., optically thin to ionizing photons), and the rest of the galaxy is ionization-bounded $-$ indicating a Blister-type morphology. We find that the previously reported small escape fraction (10%) of Ly$α$ photons is from our identified density-bounded HII region of the BBLAE. This escape fraction is likely constrained by a porous dust distribution. We further report a moderate correlation between [SII]-deficiency and inferred Lyman Continuum (LyC) escape fraction using a sample of confirmed LyC leakers studied in the literature, including the BBLAE studied here. The observed correlation also reveals its dependency on the stellar mass and gas-phase metallicity of the leaky galaxies. Finally, the future scope and implications of our work are discussed in detail.

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arXiv2020

Massive Star Formation in the Ultraviolet Observed with the Hubble Space Telescope

Spectroscopic observations of a massive star formation in the ultraviolet and their interpretation are reviewed. After a brief historical retrospective, two well-studied resolved star clusters and the surrounding H II regions are introduced: NGC 2070 in the Large Magellanic Cloud and NGC 604 in M33. These regions serve as a training set for studies of more distant clusters, which can no longer be resolved into individual stars. Observations of recently formed star clusters and extended regions in star-forming galaxies in the nearby universe beyond the Local Group are presented. Their interpretation relies on spectral synthesis models. The successes and failures of such models are discussed, and future directions are highlighted. I present a case study of the extraordinary star cluster and giant H II region in the blue compact galaxy II Zw 40. The review concludes with a preview of two upcoming Hubble Space Telescope programs: ULLYSES, a survey of massive stars in nearby galaxies, and CLASSY, a study of massive star clusters in star-forming galaxies.

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arXiv2019

He II Emission from Wolf-Rayet Stars as a Tool for Measuring Dust Reddening

We calibrated a technique to measure dust attenuation in star-forming galaxies. The technique utilizes the stellar-wind lines in Wolf-Rayet stars, which are widely observed in galaxy spectra. The He II 1640 and 4686 features are recombination lines whose ratio is largely determined by atomic physics. Therefore they can serve as a stellar dust probe in the same way as the Balmer lines are used as a nebular probe. We measured the strength of the He II 1640 line in 97 Wolf-Rayet stars in the Galaxy and the Large Magellanic Cloud. The reddening corrected fluxes follow a tight correlation with a fixed ratio of 7.76 for the He II 1640 to 4686 line ratio. Dust attenuation decreases this ratio. We provide a relation between the stellar E(B-V) and the observed line ratio for several attenuation laws. Combining this technique with the use of the nebular Balmer decrement allows the determination of the stellar and nebular dust attenuation in galaxies and can probe its effects at different stellar age and mass regimes, independently of the initial mass function and the star-formation history. We derived the dust reddening from the He II line fluxes and compared it to the reddening from the Balmer decrement and from the slope of the ultraviolet continuum in two star-forming galaxies. The three methods result in dust attenuations which agree to within the errors. Future application of this technique permits studies of the stellar dust attenuation compared to the nebular attenuation in a representative galaxy sample.

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arXiv2019

A new technique for finding galaxies leaking Lyman-continuum radiation: [SII]-deficiency

The source responsible for the reionization of the Universe is believed to be the population of star-forming galaxies at $z\sim6$ to 12. The biggest uncertainty concerns the fraction of Lyman-continuum photons that actually escape from the galaxies. In recent years, several relatively small samples of "leaky" galaxies have been uncovered, and clues have begun to emerge as to both the indirect signposts of leakiness and of the conditions/processes that enable the escape of ionizing radiation. In this paper we present the results of a pilot program aimed to test a new technique for finding leaky galaxies---using the weakness of the [SII] nebular emission-lines relative to typical star-forming galaxies as evidence that the interstellar medium is optically-thin to the Lyman continuum. We use the Cosmic Origins Spectrograph on the Hubble Space Telescope to detect significant emerging flux below the Lyman edge in two out of three [SII]-weak star-forming galaxies at $z\sim0.3$. We show that these galaxies differ markedly in their properties from the class of leaky "Green-Pea" galaxies at similar redshifts: our sample galaxies are more massive, more metal-rich, and less extreme in terms of their stellar population and the ionization state of the interstellar medium. Like the Green Peas, they have exceptionally high star-formation rates per unit area. They also share some properties with the known leaky galaxies at $z\sim3$, but are significantly dustier. Our results validate a new way to identify local laboratories for exploring the processes that made it possible for galaxies to reionize the Universe.

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arXiv2019

Comparison of Theoretical Starburst Photoionisation Models for Optical Diagnostics

We study and compare different examples of stellar evolutionary synthesis input parameters used to produce photoionisation model grids using the MAPPINGS V modelling code. The aim of this study is to (a) explore the systematic effects of various stellar evolutionary synthesis model parameters on the interpretation of emission lines in optical strong-line diagnostic diagrams, (b) characterise the combination of parameters able to reproduce the spread of local galaxies located in the star-forming region in the Sloan Digital Sky Survey, and (c) investigate the emission from extremely metal-poor galaxies using photoionisation models. We explore and compare the stellar input ionising spectrum (stellar population synthesis code [Starburst99, SLUG, BPASS], stellar evolutionary tracks, stellar atmospheres, star-formation history, sampling of the initial mass function) as well as parameters intrinsic to the H II region (metallicity, ionisation parameter, pressure, H II region boundedness). We also perform a comparison of the photoionisation codes MAPPINGS and CLOUDY. On the variations in the ionising spectrum model parameters, we find that the differences in strong emission-line ratios between varying models for a given input model parameter are small, on average ~0.1 dex. An average difference of ~0.1 dex in emission-line ratio is also found between models produced with MAPPINGS and CLOUDY. Large differences between the emission-line ratios are found when comparing intrinsic H II region parameters. We find that low-metallicity galaxies are better explained by a density-bounded H II region and higher pressures better encompass the spread of galaxies at high redshift.

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arXiv2019

Lyman continuum observations across cosmic time: recent developments, future requirements

Quantifying the physical conditions that allow radiation emitted shortward of the hydrogen ionization edge at 911.7 Å to escape the first collapsed objects and ultimately reionize the universe is a compelling problem for astrophysics. The escape of LyC emission from star-forming galaxies and AGN is intimately tied to the emergence and sustenance of the metagalactic ionizing background that pervades the universe to the present day and in turn is tied to the emergence of structure at all epochs. JWST was built in part to search for the source(s) responsible for reionization, but it cannot observe LyC escape directly, because of the progressive increase in the mean transmission of the intergalactic medium towards the epoch of reionization. Remarkable progress has been made to date in directly detecting LyC leaking from star-forming galaxies using space-based and the ground-based observatories, but there remain significant gaps in our redshift coverage of the phenomenon. Ongoing projects to measure LyC escape at low- and intermediate-z will provide guidance to JWST investigations by analyzing the robustness of a set of proposed LyC escape proxies, and also provide a closeup examination of the physical conditions that favor LyC escape. However, currently available facilities are inadequate for deeply probing LyC escape at the faint end of the galaxy luminosity function. Doing so will require facilities that can detect LyC emission in the restframe to limiting magnitudes approaching 28 $< m^*_{(1+z)900} <$ 32 for $M^*_{(1+z)1500}$ galaxies. The goal of acquiring statistically robust samples for determining LyC luminosity functions across cosmic time will require multi-object spectroscopy from spacebased flagship class and groundbased ELT class telescopes along with ancillary panchromatic imaging and spectroscopy spanning the far-UV to the mid-IR.

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arXiv2018

Physical Properties of II Zw 40's Super Star Cluster and Nebula: New Insights and Puzzles from UV Spectroscopy

We analyze far-ultraviolet spectra and ancillary data of the super star cluster SSC-N and its surrounding H II region in the nearby dwarf galaxy II Zw 40. From the ultraviolet spectrum, we derive a low internal reddening of E(B-V) = 0.07 +/- 0.03, a mass of (9.1 +/- 1.0) x 10^5 Lsol, a bolometric luminosity of (1.1 +/- 0.1) x 10^9 Lsol, a number of ionizing photons of (6 +/- 2) x 10^52 s^-1, and an age of (2.8 +/- 0.1) Myr. These parameters agree with the values derived from optical and radio data, indicating no significant obscured star formation, absorption of photons by dust, or photon leakage. SSC-N and its nebulosity are an order of magnitude more massive and luminous than 30 Doradus and its ionizing cluster. Photoionization modeling suggests a high ionization parameter and a C/O ratio where C is between primary and secondary. We calculate diagnostic emission-line ratios and compare SSC-N to local star-forming galaxies. The SSC-N nebula does not coincide with the locus defined by local galaxies. Rather, it coincides with the location of "Green Pea" galaxies, objects which are often considered nearby analogs of the galaxies reionizing the universe. Most stellar features are well-reproduced by synthetic spectra. However, the SSC-N cluster has strong, broad, stellar He II 1640 emission that cannot be reproduced, suggesting a deficit of He-enhanced stars with massive winds in the models. We discuss possible sources for the broad He II emission, including very massive stars and/or enhanced mixing processes.

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arXiv2018

Investigating the Lyman photon escape in local starburst galaxies with the Cosmic Origins Spectrograph

We present a study of 7 star-forming galaxies from the Cosmic Evolution Survey (COSMOS) observed with the Cosmic Origins Spectrograph (COS) on board the Hubble Space Telescope (HST). The galaxies are located at relatively low redshifts, $z\sim$0.3, with morphologies ranging from extended and disturbed to compact and smooth. To complement the HST observations we also analyze observations taken with the VIMOS spectrograph on the Very Large Telescope (VLT). In our galaxy sample we identify three objects with double peak Lyman-$α$ profiles similar to those seen in Green Pea compact galaxies and measure peak separations of 655, 374, and 275 km s$^{-1}$. We measure Lyman-$α$ escape fractions with values ranging between 5-13\%. Given the low flux levels in the individual COS exposures we apply a weighted stacking approach to obtain a single spectrum. From this COS combined spectrum we infer upper limits for the absolute and relative Lyman continuum escape fractions of $f_{\rm abs}(\rm LyC)$ = 0.4$^{+10.1}_{-0.4}$\% and $f_{\rm res}(\rm LyC)$ = 1.7$^{+15.2}_{-1.7}$\%, respectively. Finally, we find that most of these galaxies have moderate UV and optical SFRs (SFRs $\lesssim$ 10 M$_{\odot}$ yr$^{-1}$).

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arXiv2017

Carbon Abundances in Starburst Galaxies of the Local Universe

The cosmological origin of carbon, the fourth most abundant element in the Universe, is not well known and matter of heavy debate. We investigate the behavior of C/O to O/H in order to constrain the production mechanism of carbon. We measured emission-line intensities in a spectral range from 1600 to 10000 Å on Space Telescope Imaging Spectrograph (STIS) long-slit spectra of 18 starburst galaxies in the local Universe. We determined chemical abundances through traditional nebular analysis and we used a Markov Chain Monte Carlo (MCMC) method to determine where our carbon and oxygen abundances lie in the parameter space. We conclude that our C and O abundance measurements are sensible. We analyzed the behavior of our sample in the [C/O] vs. [O/H] diagram with respect to other objects such as DLAs, neutral ISM measurements, and disk and halo stars, finding that each type of object seems to be located in a specific region of the diagram. Our sample shows a steeper C/O vs. O/H slope with respect to other samples, suggesting that massive stars contribute more to the production of C than N at higher metallicities, only for objects where massive stars are numerous; otherwise intermediate-mass stars dominate the C and N production.

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arXiv2017

Ly$α$ and UV Sizes of Green Pea Galaxies

Green Peas are nearby analogs of high-redshift Ly$α$-emitting galaxies. To probe their Ly$α$ escape, we study the spatial profiles of Ly$α$ and UV continuum emission of 24 Green Pea galaxies using the Cosmic Origins Spectrograph (COS) on Hubble Space Telescope (HST). We extract the spatial profiles of Ly$α$ emission from their 2D COS spectra, and of UV continuum from both the 2D spectra and NUV images. The Ly$α$ emission shows more extended spatial profiles than the UV continuum in most Green Peas. The deconvolved Full Width Half Maximum (FWHM) of the Ly$α$ spatial profile is about 2 to 4 times that of the UV continuum in most cases. Since Green Peas are analogs of high-z LAEs, it suggests that most high-z LAEs likely have larger Ly$α$ sizes than UV sizes. We also compare the spatial profiles of Ly$α$ photons at blueshifted and redshifted velocities in eight Green Peas with sufficient data quality, and find the blue wing of the Ly$α$ line has a larger spatial extent than the red wing in four Green Peas with comparatively weak blue Ly$α$ line wings. We show that Green Peas and MUSE $z=3-6$ LAEs have similar Ly$α$ and UV continuum sizes, which probably suggests starbursts in both low-z and high-z LAEs drive similar gas outflows illuminated by Ly$α$ light. Five Lyman continuum (LyC) leakers in this sample have similar Ly$α$ to UV continuum size ratios (~1.4-4.3) to the other Green Peas, indicating their LyC emission escape through ionized holes in the interstellar medium.

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