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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., Accepted for publication in ApJ

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-${\alpha}$ 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., Comment: Accepted for publication in ApJ

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$\alpha$ and [OIII] $\lambda$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., Comment: Accepted for publication in ApJ

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$\mu$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$\beta$ 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$4 kpc from the nuclei, tracing molecular gas even warmer than that between the nuclei, where the two galaxies' interstellar media are colliding. A ridgeline of high [O III]/H$\beta$ 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., Comment: 27 pages, 18 figures; accepted for publication in ApJ

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 (1200-2000\AA) 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]$\lambda\lambda$1483,87, CIV$\lambda\lambda$1548,51, HeII$\lambda$1640, OIII]$\lambda\lambda$1661,6, SiIII]$\lambda\lambda$1883,92, CIII]$\lambda\lambda$1907,9). Specifically, we focus our investigation on providing accurate diagnostics for reddening, electron density and temperature, gas-phase metallicity and ionization parameter, taking into account the different ionization zones of the ISM. We calibrate our UV toolkit using well-known optical diagnostics, analyzing archival optical spectra for all the CLASSY targets. We find that UV density diagnostics estimate ne values that are ~1-2 dex higher (e.g., ne(CIII]$\lambda\lambda$}1907,9)~10$^4$cm$^{-3}$) than those inferred from their optical counterparts (e.g., ne([SII]$\lambda\lambda$6717,31)~10$^2$cm$^{-3}$). Te derived from the hybrid ratio OIII]$\lambda$1666/[OIII]$\lambda$}5007 proves to be a reliable Te diagnostic, with differences in 12+log(O/H) within ~$\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., Comment: Accepted for publication on ApJ

Using integral field unit spectroscopy, we present here the spatially resolved morphologies of [S ii]λ6717,6731/Hα and [S ii]λ6717,6731/[O iii]λ5007 emission line ratios for the first time in a blueberry Lyα emitter (BBLAE) at z ∼ 0.047. Our derived morphologies show that the extreme starburst region of the BBLAE, populated by young (≤10 Myr), massive Wolf–Rayet stars, is [S ii] deficient, while the rest of the galaxy is [S ii] 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 Lyα photons is from our identified density-bounded H ii region of the BBLAE. This escape fraction is likely constrained by a porous dust distribution. We further report a moderate correlation between [S ii] 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.

Galactic outflows are believed to play an important role in regulating star formation in galaxies, but estimates of the outflowing mass and momentum have historically been based on uncertain assumptions. Here, we measure the mass, momentum, and energy outflow rates of seven nearby star-forming galaxies using ultraviolet absorption lines and observationally motivated estimates for the density, metallicity, and radius of the outflow. Low-mass galaxies generate outflows faster than their escape velocities with mass outflow rates up to twenty times larger than their star formation rates. These outflows from low-mass galaxies also have momenta larger than provided from supernovae alone, indicating that multiple momentum sources drive these outflows. Only 1-20\% of the supernovae energy is converted into kinetic energy, and this fraction decreases with increasing stellar mass such that low-mass galaxies drive more efficient outflows. We find scaling relations between the outflows and the stellar mass of their host galaxies (M$_\ast$) at the 2-3$\sigma$ significance level. The mass-loading factor, or the mass outflow rate divided by the star formation rate, scales as M$_\ast^{-0.4}$ and with the circular velocity as v$_\mathrm{circ}^{-1.6}$. The scaling of the mass-loading factor is similar to recent simulations, but the observations are a factor of five smaller, possibly indicating that there is a substantial amount of unprobed gas in a different ionization phase. The outflow momenta are consistent with a model where star formation drives the outflow while gravity counteracts this acceleration., Comment: 10 pages, 5 figures. Accepted for publication in MNRAS

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., Accepted by The Astronomical Journal

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., Accepted for publication in ApJ. 17 pages, 8 figures, 8 tables

Stars stripped of their envelopes from interaction with a binary companion emit a significant fraction of their radiation as ionizing photons. They are potentially important stellar sources of ionizing radiation, however, they are still often neglected in spectral synthesis simulations or simulations of stellar feedback. We modeled the radiative contribution from stripped stars by using detailed evolutionary and spectral models. We estimated their impact on the integrated spectra and specifically on the emission rates of HI-, HeI-, and HeII-ionizing photons from stellar populations. We find that stripped stars have the largest impact on the ionizing spectrum of a population in which star formation halted several Myr ago. In such stellar populations, stripped stars dominate the emission of ionizing photons, mimicking a younger stellar population in which massive stars are still present. Our models also suggest that stripped stars have harder ionizing spectra than massive stars. The additional ionizing radiation affects observable properties that are related to the ionizing emission from stellar populations. In co-eval stellar populations, the ionizing radiation from stripped stars increases the ionization parameter and the production efficiency of HI-ionizing photons. They also cause high values for these parameters for about ten times longer than what is predicted for massive stars. The hard ionizing radiation from stripped stars likely introduces a characteristic ionization structure of the nebula, which leads to the emission of highly ionized elements such as O$^{2+}$ and C$^{3+}$. We, therefore, expect that the presence of stripped stars affects the location in the BPT diagram and the diagnostic ratio of OIII to OII nebular emission lines. Our models are publicly available through CDS database and on the Starburst99 website., Comment: Accepted for publication in Astronomy & Astrophysics

We obtained HST COS G140L spectra of the enigmatic nearby blue compact dwarf galaxy II Zw 40. The galaxy hosts a nuclear super star cluster embedded in a radio-bright nebula, similar to those observed in the related blue compact dwarfs NGC 5253 and Henize 2-10. The ultraviolet spectrum of II Zw 40 is exceptional in terms of the strength of He II 1640, O III] 1666 and C III] 1909. We determined reddening, age, and the cluster mass from the ultraviolet data. The super nebula and the ionizing cluster exceed the ionizing luminosity and stellar mass of the local benchmark 30 Doradus by an order of magnitude. Comparison with stellar evolution models accounting for rotation reveals serious short-comings: these models do not account for the presence of Wolf-Rayet-like stars at young ages observed in II Zw 40. Photoionization modeling is used to probe the origin of the nebular lines and determine gas phase abundances. C/O is solar, in agreement with the result of the stellar-wind modeling.

To evaluate the impact of stellar feedback, it is critical to estimate the mass outflow rates of galaxies. Past estimates have been plagued by uncertain assumptions about the outflow geometry, metallicity, and ionization fraction. Here we use Hubble Space Telescope ultraviolet spectroscopic observations of the nearby starburst NGC 6090 to demonstrate that many of these quantities can be constrained by the data. We use the Si~{\sc IV} absorption lines to calculate the scaling of velocity (v), covering fraction (C$_f$), and density with distance from the starburst (r), assuming the Sobolev optical depth and a velocity law of the form: v$~\propto(1 -\mathrm{R}_\mathrm{i}/\mathrm{r} )^\beta$ (where R$_\mathrm{i}$ is the inner outflow radius). We find that the velocity ($\beta$=0.43) is consistent with an outflow driven by an r$^{-2}$ force with the outflow radially accelerated, while the scaling of the covering fraction ($C_f \propto \mathrm{r}^{-0.82}$) suggests that cool clouds in the outflow are in pressure equilibrium with an adiabatically expanding medium. We use the column densities of four weak metal lines and CLOUDY photoionization models to determine the outflow metallicity, the ionization correction, and the initial density of the outflow. Combining these values with the profile fitting, we find R$_\mathrm{i}$ = 63 pc, with most of the mass within 300~pc of the starburst. Finally, we find that the maximum mass outflow rate is 2.3~M$_\odot$ yr$^{-1}$ and the mass loading factor (outflow divided by the star formation rate) is 0.09, a factor of 10 lower than the value calculated using common assumptions for the geometry, metallicity and ionization structure of the outflow., Comment: 16 pages, 11 figures. Accepted for publication in MNRAS

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., Comment: 33 pages, 26 figures, accepted for publication in ApJ

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.

The gas-phase metallicity of low-mass galaxies increases with increasing stellar mass ($M_\ast$) and is nearly constant for high-mass galaxies. Theory suggests that this tight mass-metallicity relationship is shaped by galactic outflows removing metal-enriched gas from galaxies. Here, we observationally model the outflow metallicities of the warm outflowing phase from a sample of seven local star-forming galaxies with stellar masses between 10$^{7}$-10$^{11}$ M$_\odot$. We estimate the outflow metallicities using four weak rest-frame ultraviolet absorption lines, the observed stellar continua, and photoionization models. The outflow metallicity is flat with $M_\ast$, with a median metallicity of $1.0\pm0.6$ Z$_\odot$. The observed outflows are metal-enriched: low and high-mass galaxies have outflow metallicities 10-50 and 2.6 times larger than their ISM metallicities, respectively. The observed outflows are mainly composed of entrained ISM gas with at most 22% of the metals directly coming from recent supernovae enrichment. The metal outflow rate shallowly increases with $M_\ast$, as $M_\ast^{0.2 \pm 0.1}$, because the mass outflow rate shallow increases with $M_\ast$. Finally, we normalize the metal outflow rate by the rate at which star formation retains metals to calculate the metal-loading factor. The metal-loading factor inversely scales with $M_\ast$. The normalization and scaling of the metal-loading factor agree with analytic expressions that reproduce observed mass-metallicity relations. Galactic outflows fundamentally shape the observed mass-metallicity relationship., 15 pages, 7 figures, Accepted for publication in MNRAS

Commission 35 (C35), “Stellar Constitution”, consists of members of the International Astronomical Union whose research spans many aspects of theoretical and observational stellar physics and it is mainly focused on the comprehension of the properties of stars, stellar populations and galaxies. The number of members of C35 increased progressively over the last ten years and currently C35 comprises about 400 members. C35 was part of Division IV (Stars) until 2014 and then became part of Division G (Stars and Stellar Physics), after the main IAU reorganisation in 2015. Four Working Groups have been created over the years under Division IV, initially, and Division G later: WG on Active B Stars, WG on Massive Stars, WG on Abundances in Red Giant and WG on Chemically Peculiar and Related Stars. In the last decade the Commission had 4 presidents, Wojciech Dziembowski (2003-2006), Francesca D'Antona (2006-2009), Corinne Charbonnel (2009-2012) and Marco Limongi (2012-2015), who were assisted by an Organizing Committee (OC), usually composed of about 10 members, all of them elected by the C35 members and holding their positions for three years. The C35 webpage (http://iau-c35.stsci.edu) has been designed and continuously maintained by Claus Leitherer from the Space Telescope Institute, who deserves our special thanks. In addition to the various general information on the Commission structure and activities, it contains links to various resources, of interest for the members, such as stellar models, evolutionary tracks and isochrones, synthetic stellar populations, stellar yields and input physics (equation of state, nuclear cross sections, opacity tables), provided by various groups. The main activity of the C35 OC is that of evaluating, ranking and eventually supporting the proposals for IAU sponsored meetings. In the last decade the Commission has supported several meetings focused on topics more or less relevant to C35. Since the primary aim of this document is to present the main activity of C35 over the last ten years, in the following we present some scientific highlights that emerged from the most relevant IAU Symposia and meetings supported and organized by C35 in the last decade.

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$0.3, with morphologies ranging from extended and disturbed to compact and smooth. To complement the HST observations we also analyze observations taken with the VIMOS spectrograph on the Very Large Telescope (VLT). In our galaxy sample we identify three objects with double peak Lyman-$\alpha$ 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-$\alpha$ 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$^{-1}$)., Comment: 15 pages, 10 figures, MNRAS accepted

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 \AA\ 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., Comment: Accepted for publication in ApJ

A 3-day Focus Meeting entitled “Stellar Physics in Galaxies throughout the Universe” was held during the IAU XXIX General Assembly. The meeting brought together astrophysicists from the stellar physics, extragalactic astrophysics and cosmology communities to discuss how current and future results can foster progress in these disjoint science areas. Areas covered include stellar evolution of single and binary stars from the zero-age main-sequence to the terminal stage, the feedback of stars to the interstellar medium via radiation, dust production and chemical enrichment, and the properties of the most massive stars and of cosmologically significant stellar phases such as AGB and Wolf-Rayet stars. The limitations of our understanding of the physics of local stars and their effects on, e.g., ages, chemical composition and the initial mass function of galaxies at low to high redshift were evaluated.

© 2017. The American Astronomical Society. All rights reserved.

We report on the detection of Lyman continuum radiation in two nearby starburst galaxies. Tol 0440-381, Tol 1247-232 and Mrk 54 were observed with the Cosmic Origins Spectrograph onboard the Hubble Space Telescopes. The three galaxies have radial velocities of ~13,000 km/s, permitting a ~35 A window on the restframe Lyman continuum shortward of the Milky Way Lyman edge at 912 A. The chosen instrument configuration using the G140L grating covers the spectral range from 912 to 2,000 {\AA}. We developed a dedicated background subtraction method to account for temporal and spatial background variations of the detector, which is crucial at the low flux levels around 912 A. This modified pipeline allowed us to significantly improve the statistical and systematic detector noise and will be made available to the community. We detect Lyman continuum in all three galaxies. However, we conservatively interpret the emission in Tol 0440-381 as an upper limit due to possible contamination by geocoronal Lyman series lines. We determined the current star-formation properties from the far-ultraviolet continuum and spectral lines and used synthesis models to predict the Lyman continuum radiation emitted by the current population of hot stars. We discuss the various model uncertainties such as, among others, atmospheres and evolution models. Lyman continuum escape fractions were derived from a comparison between the observed and predicted Lyman continuum fluxes. Tol 1247-232, Mrk 54 and Tol 0440-381 have absolute escape fractions of (4.5 +/- 1.2)%, (2.5 +/- 0.72)% and, Comment: Accepted by The Astrophysical Journal

We have obtained ultraviolet spectra between 1150 and 1450 Å of four ultraviolet-bright, infrared-luminous starburst galaxies. Our selected sight-lines towards the starburst nuclei probe the conditions in the starburst-driven outflows. We detect outflowing gas with velocities of up to ∼900 km s−1. It is likely that the outflows are a major source of metal enrichment of the galaxies' halos. The mass outflow rates of several tens of M⊙ yr−1 are similar to the star-formation rates. The outflows may quench star formation and ultimately regulate the starburst.

Our Working Group (WG) studies massive, luminous stars, both individually and in resolved and unresolved populations, with historical focus on early-type (OB) stars, A-supergiants, and Wolf-Rayet stars. Our group also studies lower mass stars (e.g., central stars of planetary nebulae and their winds) which display features similar or related to those present in massive stars, and thus may improve our understanding of the physical processes occurring in massive stars. In recent years, massive red supergiants that evolve from hot stars have been included into our activities as well. We emphasize the role of massive stars in other branches of astrophysics, particularly regarding the First Stars, long duration Gamma-Ray bursts, formation of massive stars and their feedback on star formation in general, pulsations of massive stars, and starburst galaxies.

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., The Astrophysical Journal, accepted

The Advanced Camera for Surveys and the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) have been used to obtain new Hubble Space Telescope images of NGC 4038/4039 ('The Antennae'). These new observations allow us to better differentiate compact star clusters from individual stars, based on both size and color. We use this ability to extend the cluster luminosity function (LF) by approximately 2 mag over our previous WFPC2 results, and find that it continues as a single power law, dN/dL {proportional_to} L {sup {alpha}} with {alpha} = -2.13 {+-} 0.07, down to the observational limit of M{sub V} {approx} -7. Similarly, the mass function (MF) is a single power law dN/dM {proportional_to} M {sup {beta}} with {beta} = -2.10 {+-} 0.20 for clusters with ages 3 mag.« less

We have analyzed FUSE (905-1187 A) spectra of a sample of 16 local starburst galaxies. These galaxies cover almost three orders of magnitude in star-formation rates and over two orders of magnitude in stellar mass. Absorption features from the stars and interstellar medium are observed in all the spectra. The strongest interstellar absorption features are generally blue-shifted by ~ 50-300 km s–1, implying the almost ubiquitous presence of starburst-driven galactic winds in this sample. The outflow velocites increase with both the star-formation rate and the star-formation rate per unit stellar mass, consistent with a galactic wind, driven by the population of massive stars. We find outflowing coronal-phase gas (T ~105.5 K) detected via the O VI absorption line in nearly every galaxy. The O VI absorption-line profile is optically thin, is generally weak near the galaxy-systemic velocity, and has a higher mean outflow velocity than seen in the lower ionization lines. The relationship between the line width and column density for the O VI absorbing gas is in good agreement with expectations for radiatively cooling and outflowing gas. Such gas will be created in the interaction of the hot out-rushing wind seen in X-ray emission and cool dense ambient material. O VI emission is not generally detected in our sample, suggesting that radiative cooling by the coronal gas is not dynamically significant in draining energy from galactic winds. We find that the measured outflow velocities in the H I and H II phases of the interstellar gas in a given galaxy increase with the strength (equivalent width) of the absorption feature and not with the ionization potential of the species. The strong lines often have profiles consisting of a broad and optically-thick component centered near the galaxy-systemic velocity and weaker but highly blue-shifted absorption. This suggests that the outflowing gas with high velocity has a lower column density than the more quiescent gas, and can only be readily detected in the strongest absorption lines. From direct observations below the Lyman edge in the galaxy rest frame, we find no evidence of Lyman continuum radiation escaping from any of the galaxies in the sample. Moreover, the small escape fraction of light in the center of the strong C II absorption feature confirms the high opacity below the Lyman limit in the neutral ISM. The absolute fraction of escaping Lyman continuum photons is typically

Context. Photoelectric heating is a dominant heating mechanism for many phases of the interstellar medium. We study this mechanism throughout the Large Magellanic Cloud (LMC).Aims. We aim to quantify the importance of the [C II] cooling line and the photoelectric heating process of various environments in the LMC and to investigate which parameters control the extent of photoelectric heating.Methods. We use the BICE [C II] map and the Spitzer/SAGE infrared maps. We examine the spatial variations in the efficiency of photoelectric heating: photoelectric heating rate over power absorbed by grains, i.e. the observed [C II] line strength over the integrated infrared emission. We correlate the photoelectric heating efficiency and the emission from various dust constituents and study the variations as a function of Ha emission, dust temperatures, and the total infrared luminosity. The observed variations are interpreted in a theoretical framework. From this we estimate radiation field, gas temperature, and electron density.Results. We find systematic variations in photoelectric efficiency. The highest efficiencies are found in the diffuse medium, while the lowest coincide with bright star-forming regions (similar to 1.4 times lower). The [C II] line emission constitutes 1.32% of the far infrared luminosity across the whole of the LMC. We find correlations between the [C II] emission and ratios of the mid infrared and far infrared bands, which comprise various dust constituents. The correlations are interpreted in light of the spatial variations of the dust abundance and by the local environmental conditions that affect the dust emission properties. As a function of the total infrared surface brightness, S-TIR, the [C II] surface brightness can be described as: S [C II] = 1.25 S-TIR(0.69) [10(-3) erg s(-1) cm(-2) sr(-1)], for S-TIR greater than or similar to 3.2 x 10(-4) erg s(-1) cm(-2) sr(-1). We provide a simple model of the photoelectric efficiency as a function of the total infrared luminosity. We find a power-law relation between radiation field and electron density, consistent with other studies. The [ C II] emission is well-correlated with the 8 mu m emission, suggesting that the polycyclic aromatic hydrocarbons play a dominant role in the photoelectric heating process.

We present initial results and source lists of variable sources in the Large Magellanic Cloud (LMC) for which we detect thermal infrared variability from the SAGE (Surveying the Agents of a Galaxy's Evolution) survey, which had 2 epochs of photometry separated by three months. The SAGE survey mapped a 7 degree by 7 degree region of the LMC using the IRAC and the MIPS instruments on board Spitzer. Variable sources are identified using a combination of the IRAC 3.6, 4.5, 5.8, 8.0 \micron bands and the MIPS 24 \micron bands. An error-weighted flux difference between the two epochs is used to assess the variability. Of the ~ 3 million sources detected at both epochs we find ~ 2,000 variable sources for which we provide electronic catalogs. Most of the variable sources can be classified as asymptotic giant branch (AGB) stars. A large fraction (> 66%) of the extreme AGB stars are variable and only smaller fractions of carbon-rich (6.1%) and oxygen-rich (2.0%) stars are detected as variable. We also detect a population of variable young stellar object candidates.

Our Working Group studies massive, luminous stars, with historical focus on early-type (OB) stars, but extending in recent years to include massive red supergiants that evolve from hot stars. There is also emphasis on the role of massive stars in other branches of astrophysics, particularly regarding starburst galaxies, the first stars, core-collapse gamma-ray bursts, and formation of massive stars.

Rotation plays a major role in the evolution of massive stars. A revised grid of stellar evolutionary tracks accounting for rotation has recently been released by the Geneva group and implemented into the Starburst99 evolutionary synthesis code. Massive stars are predicted to be hotter and more luminous than previously thought, and the spectral energy distributions of young populations mirror this trend. The hydrogen ionizing continuum in particular increases by a factor of up to 3 in the presence of rotating massive stars. The effects of rotation generally increase towards shorter wavelengths and with decreasing metallicity. Revised relations between star-formation rates and monochromatic luminosities for the new stellar models are presented., 5 pages, 3 figures, to appear in IAU Symp. 255, Low-Metallicity Star Formation, ed. L. Hunt, S. Madden, & R. Schneider (Cambridge: CUP)

We present ~1000 new candidate Young Stellar Objects (YSOs) in the Large Magellanic Cloud selected from Spitzer Space Telescope data, as part of the Surveying the Agents of a Galaxy's Evolution (SAGE) Legacy program. The YSOs, detected by their excess infrared (IR) emission, represent early stages of evolution, still surrounded by disks and/or infalling envelopes. Previously, fewer than 20 such YSOs were known. The candidate YSOs were selected from the SAGE Point Source Catalog from regions of color-magnitude space least confused with other IR-bright populations. The YSOs are biased toward intermediate- to high-mass and young evolutionary stages, because these overlap less with galaxies and evolved stars in color-magnitude space. The YSOs are highly correlated spatially with atomic and molecular gas, and are preferentially located in the shells and bubbles created by massive stars inside. They are more clustered than generic point sources, as expected if star formation occurs in filamentary clouds or shells. We applied a more stringent color-magnitude selection to produce a subset of "high-probability" YSO candidates. We fitted the spectral-energy distributions (SEDs) of this subset and derived physical properties for those that were well fitted. The total mass of these well-fitted YSOs is ~2900 M_☉ and the total luminosity is ~2.1 × 10^6 L_☉ . By extrapolating the mass function with a standard initial mass function and integrating, we calculate a current star-formation rate of ~0.06 M_☉ yr^(–1), which is at the low end of estimates based on total ultraviolet and IR flux from the galaxy (~0.05 – 0.25 M_☉ yr^(–1)), consistent with the expectation that our current YSO list is incomplete. Follow-up spectroscopy and further data mining will better separate the different IR-bright populations and likely increase the estimated number of YSOs. The full YSO list is available as electronic tables, and the SEDs are available as an electronic figure for further use by the scientific community.

We present photometry with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST) of stars in the Magellanic starburst galaxy NGC 4449. The galaxy has been imaged in the F435W (B), F555W (V) and F814W (I) broad-band filters, and in the F658N (Halpha) narrow-band filter. Our photometry includes ~300,000 objects in the (B, V) color-magnitude diagram (CMD) down to V < 28, and ~400,000 objects in the (V, I) CMD, down to I < 27 . A subsample of ~200,000 stars has been photometrized in all the three bands simultaneously. The features observed in the CMDs imply a variety of stellar ages up to at least 1 Gyr, and possibly as old as a Hubble time. The spatial variation of the CMD morphology and of the red giant branch colors point toward the presence of an age gradient: young and intermediate-age stars tend to be concentrated toward the galactic center, while old stars are present everywhere. The spatial variation in the average luminosity of carbon stars suggests that there is not a strong metallicity gradient (< 0.2 dex). Also, we detect an interesting resolved star cluster on the West side of the galaxy, surrounded by a symmetric tidal or spiral feature consisting of young stars. The positions of the stars in NGC 4449 younger than 10 Myr are strongly correlated with the Halpha emission. We derive the distance of NGC 4449 from the tip of the red giant branch to be D=3.82 \pm 0.27 Mpc. This result is in agreement with the distance that we derive from the luminosity of the carbon stars.

A database containing 618 active and star-forming (A/SF) galaxies and 564 normal galaxies in a 120° × 6° wide strip crossing the north Galactic pole was constructed in order to compare the global properties of "active" galaxies against a control sample of "normal" galaxies. This database combines a literature and catalog search with new optical measurements from the Fpg (red) and Jpg (blue) band images of the STScI Digitized Sky Survey (DSS). We provide alternative names, accurate coordinates, morphological type, activity classes, red and blue apparent magnitudes, 2MASS near-infrared J–H and H–K colors, apparent diameters, axial ratios, position angles, and number counts of neighboring objects in a circle of radius 50 kpc. We also present an atlas of 103 interacting and merging systems among these galaxies. The integrated properties of A/SF and normal galaxies in this sample are compared using a multivariate factor analysis, which reveals that A/SF galaxies are objects with relatively late morphological types, and are more inclined and have bluer optical colors than normal galaxies. In this sample, all merging and interacting galaxies are A/SF objects. Star-forming galaxies are objects with relatively late morphological types, lower absolute luminosities and linear sizes, bluer colors, and higher inclination than sample X-ray or radio sources, as well as Seyfert galaxies. The near-infrared colors of the sample galaxies are independent parameters and do not correlate with activity level or any other parameter of the galaxies.

We study the ionization structure of galactic outflows in 37 nearby, star forming galaxies with the Cosmic Origins Spectrograph on the Hubble Space Telescope. We use the O I, Si II, Si III, and Si IV ultraviolet absorption lines to characterize the different ionization states of outflowing gas. We measure the equivalent widths, line widths, and outflow velocities of the four transitions, and find shallow scaling relations between them and galactic stellar mass and star formation rate. Regardless of the ionization potential, lines of similar strength have similar velocities and line widths, indicating that the four transitions can be modeled as a co-moving phase. The Si equivalent width ratios (e.g. Si IV/Si II) have low dispersion, and little variation with stellar mass; while ratios with O I and Si vary by a factor of 2 for a given stellar mass. Photo-ionization models reproduce these equivalent width ratios, while shock models under predict the relative amount of high ionization gas. The photo-ionization models constrain the ionization parameter (U) between -2.25 < log(U) < -1.5, and require that the outflow metallicities are greater than 0.5 Z$_\odot$. We derive ionization fractions for the transitions, and show that the range of ionization parameters and stellar metallicities leads to a factor of 1.15-10 variation in the ionization fractions. Historically, mass outflow rates are calculated by converting a column density measurement from a single metal ion into a total Hydrogen column density using an ionization fraction, thus mass outflow rates are sensitive to the assumed ionization structure of the outflow., 30 pages, 17 tables, 14 figures. Accepted for publication in MNRAS

We present an atlas of the central regions of 75 Seyfert galaxies imaged in the near-UV with the Advanced Camera for Surveys of the Hubble Space Telescope at an average resolution of ~10pc. These data complement archival high resolution data from the Space Telescope at optical and near-IR wavelengths, creating an extremely valuable dataset for astronomers with a broad range of scientific interests. Our goal is to investigate the nature of the near-UV light in these objects, its relation to the circumnuclear starburst phenomenon, and the connection of this to the evolution and growth of the galaxy bulge and central black hole. In this paper, we describe the near-UV morphology of the objects and characterize the near-UV emission. We estimate the size and the luminosity of the emitting regions and extract the luminosity profile. We also determine the presence of unresolved compact nuclei. In addition, the circumnuclear stellar cluster population is identified, and the contribution of the stellar clusters to the total light, at this wavelength, is estimated. The size of the sample allows us to draw robust statistical conclusions. We find that {Seyfert 1} galaxies are completely dominated by its bright and compact nucleus, that remains point-like at this resolution, while we find almost no unresolved nucleus in Seyfert 2. The Seyfert types 1 and 2 are quite segregated in an asymmetry vs compactness plot. Stellar clusters are found somewhat more frequently in Sy2 (in ~70% of the galaxies) than in Sy1 (~57%), and contribute more to the total light in Sy2, but this two differences seem to be mostly due to the large contribution of the compact nucleus in Sy1, as the luminosity distribution of the clusters is similar in both Sy types.

We present a high spatial resolution optical and infrared study of the circumnuclear region in Arp 220, a late-stage galaxy merger. Narrowband imaging using HST/WFC3 has resolved the previously observed peak in H$\alpha$+[NII] emission into a bubble-shaped feature. This feature measures 1.6" in diameter, or 600 pc, and is only 1" northwest of the western nucleus. The bubble is aligned with the western nucleus and the large-scale outflow axis seen in X-rays. We explore several possibilities for the bubble origin, including a jet or outflow from a hidden active galactic nucleus (AGN), outflows from high levels of star formation within the few hundred pc nuclear gas disk, or an ultraluminous X-ray source. An obscured AGN or high levels of star formation within the inner $\sim$100 pc of the nuclei are favored based on the alignment of the bubble and energetics arguments., Comment: Accepted for publication in ApJ. 12 pages, 10 figures

We present images from the Solar Blind Channel on HST that resolve hundreds of far ultraviolet (FUV) emitting stars in two ~1 kpc$^2$ interarm regions of the grand-design spiral M101. The luminosity functions of these stars are compared with predicted distributions from simple star formation histories, and are best reproduced when the star formation rate has declined recently (past 10-50 Myr). This pattern is consistent with stars forming within spiral arms and then streaming into the interarm regions. We measure the diffuse FUV surface brightness after subtracting all of the detected stars, clusters and background galaxies. A residual flux is found for both regions which can be explained by a mix of stars below our detection limit and scattered FUV light. The amount of scattered light required is much larger for the region immediately adjacent to a spiral arm, a bright source of FUV photons., 11 pages, 9 figures, accepted for publication in ApJ

A population of early star-forming galaxies is the leading candidate for the re-ionization of the universe. It is still unclear what conditions and physical processes would enable a significant fraction of the ionizing photons to escape from these gas-rich galaxies. In this paper we present the results of the analysis of HST COS far-UV spectroscopy plus ancillary multi-waveband data of a sample of 22 low-redshift galaxies that are good analogs to typical star-forming galaxies at high-redshift. We measure three parameters that provide indirect evidence of the escape of ionizing radiation: (1) the residual intensity in the cores of saturated interstellar low-ionization absorption-lines. (2) The relative amount of blue-shifted Lyman alpha line emission, and (3) the relative weakness of the [SII] optical emission lines. We use these diagnostics to rank-order our sample in terms of likely leakiness, noting that a direct measure of escaping Lyman continuum has recently been made for one of the leakiest members of our sample. We then examine the correlations between our ranking and other proposed diagnostics of leakiness and find a correlation with the equivalent width of the Lyman alpha emission-line. Turning to galaxy properties, we find the strongest correlations with leakiness are with the compactness of the star-forming region and the speed of the galactic outflow. This suggests that extreme feedback- a high intensity of ionizing radiation and strong pressure from both radiation and a hot galactic wind- combines to create significant holes in the neutral gas. These results not only shed new light on the physical mechanisms that can allow ionizing radiation to escape from intensely star-forming galaxies, they also provide indirect observational indicators that can be used at high-redshift where direct measurements of escaping Lyman continuum radiation are impossible., Accepted for publication in ApJ; 21 pages, 14 figures, 2 tables

One possible way for spiral galaxies to internally evolve would be for gas to flow to the center and form stars in a central disk (pseudo-bulge). If the inflow rate is faster than the rate of star formation, a central concentration of gas will form. In this paper we present radial profiles of stellar and 8 μm emission from polycyclic aromatic hydrocarbons (PAHs) for 11 spiral galaxies to investigate whether the interstellar medium in these galaxies contains a central concentration above that expected from the exponential disk. In general, we find that the two-dimensional CO and PAH emission morphologies are similar, and that they exhibit similar radial profiles. We find that in 6 of the 11 galaxies there is a central excess in the 8 μm and CO emission above the inward extrapolation of an exponential disk. In particular, all four barred galaxies in the sample have strong central excesses in both 8 μm and CO emission. These correlations suggest that the excess seen in the CO profiles is, in general, not simply due to a radial increase in the CO emissivity. In the inner disk, the ratio of the stellar to the 8 μm radial surface brightness is similar for 9 of the 11 galaxies, suggesting a physical connection between the average stellar surface brightness and the average gas surface brightness at a given radius. We also find that the ratio of the CO to 8 μm PAH surface brightness is consistent over the sample, implying that the 8 μm PAH surface brightness can be used as an approximate tracer of the interstellar medium.

著者人数：50名, Accepted: 2006-08-02, 資料番号: SA1000636000

We present Spitzer observations of the nearby dwarf starburst galaxy NGC 1705 obtained as part of the Spitzer Infrared Nearby Galaxies Survey. The galaxy morphology is very different shortward and longward of ~5 μm: optical and short-wavelength IRAC imaging shows an underlying red stellar population, with the central super star cluster (SSC) dominating the luminosity; longer wavelength IRAC and MIPS imaging reveals warm dust emission arising from two off-nuclear regions that are offset by ~250 pc from the SSC and that dominate the far-IR flux of the system. These regions show little extinction at optical wavelengths. The galaxy has a relatively low global dust mass (~2 × 10^5 M_☉, implying a global dust-to-gas mass ratio ~2-4 times lower than the Milky Way average, roughly consistent with the metallicity decrease). The off-nuclear dust emission appears to be powered by photons from the same stellar population responsible for the excitation of the observed Hα emission; these photons are unassociated with the SSC (although a contribution from embedded sources to the IR luminosity of the off-nuclear regions cannot be ruled out). Low-resolution IRS spectroscopy shows moderate-strength PAH emission in the 11.3 μm band in the more luminous eastern peak; no PAH emission is detected in the SSC or the western dust emission complex. There is significant diffuse emission in the IRAC 8 μm band after starlight has been removed by scaling shorter wavelength data; the fact that IRS spectroscopy shows spatially variable PAH emission strengths compared to the local continuum within this diffuse gas suggests caution in the interpretation of IRAC diffuse 8 μm emission as arising from PAH carriers alone. The nebular metallicity of NGC 1705 falls at the transition level of ~0.35 Z_☉ found by Engelbracht and collaborators, below which PAH emission is difficult to detect; the fact that a system at this metallicity shows spatially variable PAH emission demonstrates the complexity of interpreting diffuse 8 μm emission in galaxies. NGC 1705 deviates significantly from the canonical far-infrared versus radio correlation, having significant far-infrared emission but no detected radio continuum.

著者人数：49名, Accepted: 2006-06-09, 資料番号: SA1000635000

The Spitzer Infrared Nearby Galaxies Survey (SINGS) is carrying out a comprehensive multi-wavelength survey on a sample of 75 nearby galaxies. The 1-850um spectral energy distributions are presented using broadband imaging data from Spitzer, 2MASS, ISO, IRAS, and SCUBA. The infrared colors derived from the globally-integrated Spitzer data are generally consistent with the previous generation of models that were developed based on global data for normal star-forming galaxies, though significant deviations are observed. Spitzer's excellent sensitivity and resolution also allow a detailed investigation of the infrared spectral energy distributions for various locations within the three large, nearby galaxies NGC3031 (M81), NGC5194 (M51), and NGC7331. Strong correlations exist between the local star formation rate and the infrared colors f_nu(70um)/f_nu(160um) and f_nu(24um)/f_nu(160um), suggesting that the 24 and 70um emission are useful tracers of the local star formation activity level. Preliminary evidence indicates that variations in the 24um emission, and not variations in the emission from polycyclic aromatic hydrocarbons at 8um, drive the variations in the f_nu(8.0um)/f_nu(24um) colors within NGC3031, NGC5194, and NGC7331. If the galaxy-to-galaxy variations in spectral energy distributions seen in our sample are representative of the range present at high redshift then extrapolations of total infrared luminosities and star formation rates from the observed 24um flux will be uncertain at the factor-of-five level (total range). The corresponding uncertainties using the redshifted 8.0um flux (e.g. observed 24um flux for a z=2 source) are factors of 10-20. Considerable caution should be used when interpreting such extrapolated infrared luminosities., Comment: 32 pages including 16 figures; accepted for publication in the Astrophysical Journal

(Abridged) Far ultraviolet to far infrared images of the nearby galaxy NGC5194, from Spitzer, GALEX, Hubble Space Telescope and ground--based data, are used to investigate local and global star formation, and the impact of dust extinction in HII-emitting knots. In the IR/UV-UV color plane, the NGC5194 HII knots show the same trend observed for normal star-forming galaxies, having a much larger dispersion than starburst galaxies. We identify the dispersion as due to the UV emission predominantly tracing the evolved, non-ionizing stellar population, up to ages 50-100 Myr. While in starbursts the UV light traces the current SFR, in NGC5194 it traces a combination of current and recent-past SFR. Unlike the UV emission, the monochromatic 24 micron luminosity is an accurate local SFR tracer for the HII knots in NGC5194; this suggests that the 24 micron emission carriers are mainly heated by the young, ionizing stars. However, preliminary results show that the ratio of the 24 micron emission to the SFR varies by a factor of a few from galaxy to galaxy. While also correlated with star formation, the 8 micron emission is not directly proportional to the number of ionizing photons. This confirms earlier suggestions that the carriers of the 8 micron emission are heated by more than one mechanism., 66 pages, 20 figures (Figures 1-4 are in JPEG format, figures 5-20 are embedded postscript files). Accepted for publication on the Astrophysical Journal

Long-slit spectra of several dozen young star clusters have been obtained at three positions in the Antennae galaxies with the Space Telescope Imaging Spectrograph (STIS) and its 52"x0.2" slit. Based on H-alpha emission-line measurements, the average cluster-to-cluster velocity dispersion in 7 different cluster aggregates ("knots") is

We present spatially resolved Spitzer imaging of the supergiant shell region of the M81 group dwarf galaxy IC 2574 obtained as part of the Spitzer Infrared Nearby Galaxies Survey. This region harbors one of the best nearby examples of a kinematically distinct HI shell, with an associated remnant stellar cluster; the shell is initiating sequential star formation as it interacts with the surrounding interstellar medium. This region dominates the infrared luminosity of IC 2574 and is spatially resolved in all Spitzer imaging bands. We study the differences in dust temperature as a function of local environment and compare local star formation rates as inferred from H Alpha and total infrared luminosities. We find that the strong H Alpha sources are associated with regions of warm dust; however, the most luminous infrared and H Alpha sources are not necessarilyco-spatial. The coolest dust is found in the regions farthest from the rim of the shell; these regions show the best agreement between star formation rates derived from H Alpha and from total infrared luminosities (although discrepancies at the factor of 3-4 level still exist). There is considerable variation in the radio-far infrared correlation in different regions surrounding the shell. The low dust content of the region may influence the scatter seen in these relations; these data demonstrate that the expanding shell is dramatically affecting its surroundings by triggering star formation and altering the dust temperature., Comment: ApJ Letters, in press; please retrieve full-resolution version from http://www.mpia.de/homes/cannon/pubs.html

We present new results on the star formation history of the dwarf irregular galaxy NGC 1569. The data were obtained with Hubble Space Telescope's NICMOS/NIC2 in the F110W (J) and F160W (H) near-infrared (NIR) filters and interpreted with the synthetic color-magnitude diagram method. The galaxy experienced a complex star formation (SF) activity. The best fit to the data is found by assuming three episodes of activity in the last 1-2 Gyr. The most recent and strong episode constrained by these NIR data started ~37 Myr ago and ended ~13 Myr ago, although we cannot exclude the possibility that up to three SF episodes occurred in this time interval. The average star-formation rate (SFR) of the episode is 3.2 Msun yr-1 kpc-2, in agreement with literature data. A previous episode produced stars between 150 Myr and 40 Myr ago, with a mean SFR about 2/3 lower than the mean SFR of the youngest episode. An older SF episode occurred about 1 Gyr ago. All these SFRs are 2-3 orders of magnitude higher than those derived for late-type dwarfs of the Local Group. In all cases an initial mass function similar to Salpeter's allows for a good reproduction of the data, but we cannot exclude flatter mass functions. These results have been obtained adopting a distance of 2.2 Mpc and a reddening E(B-V)=0.56. A larger distance would require younger episodes and higher SFRs. We have explored some possible scenarios using the astrated mass in the best fit model, in order to constrain the past star formation history. We cannot rule out a low rate in the past SF but we can safely conclude that the last 1-2 Gyr have been peculiar., Accepted by AJ, 2005, vol 129, 14 pages, 9 figures

The chemical composition of high-redshift galaxies is an important property that gives clues to their past history and future evolution. Measuring abundances in distant galaxies with current techniques is often a challenge, and the canonical metallicity indicators can often not be applied. I discuss currently available metallicity indicators based on stellar and interstellar absorption and emission lines, and assess their limitations and systematic uncertainties. Recent studies suggest that star-forming galaxies at redshift around 3 have heavy-element abundances already close to solar, in agreement with predictions from cosmological models., Comment: 6 pages, 3 figures. Invited talk given at IAU Symp. 228, From Lithium to Uranium, Paris (France), 23 - 27 May, 2005. To be published in: IAU Symp. 228, From Lithium to Uranium, ed. V. Hill, P. Francois, & F. Primas (Cambridge: CUP), in press

We have incorporated the latest release of the Padova models into the evolutionary synthesis code Starburst99. The Padova tracks were extended to include the full asymptotic giant branch (AGB) evolution until the final thermal pulse over the mass range 0.9 to 5 solar mass. With this addition, Starburst99 accounts for all stellar phases that contribute to the integrated light of a stellar population with arbitrary age from the extreme ultraviolet to the near-infrared. AGB stars are important for ages between 0.1 and 2 Gyr, with their contribution increasing at longer wavelengths. We investigate similarities and differences between the model predictions by the Geneva and the Padova tracks. The differences are particularly pronounced at ages > 1 Gyr, when incompleteness sets in for the Geneva models. We also perform detailed comparisons with the predictions of other major synthesis codes and found excellent agreement. Our synthesized optical colors are compared to observations of old, intermediate-age, and young populations. Excellent agreement is found for the old globular cluster system of NGC 5128 and for old and intermediate-age clusters in NGC 4038/39. In contrast, the models fail for red supergiant dominated populations with sub-solar abundances. This failure can be traced back to incorrect red supergiant parameters in the stellar evolutionary tracks. Our models and the synthesis code are publicly available as version 5.0 of Starburst99 at http://www.stsci.edu/science/starburst99/., The revised Starburst99 code discussed in this paper will replace the current version 4.0 on our Starburst99 website by December 31, 2004. Accepted for publication in ApJ; 39 pages, 23 figures, 5 tables

To investigate the extent to which nuclear starbursts or other nuclear activity may be connected with enhanced star formation activity in the host galaxy, we perform a statistical investigation of supernovae (SNe) discovered in host galaxies from four samples: the Markarian galaxies sample, the Second Byurakan Survey (SBS) sample, the north Galactic pole (NGP) sample of active or star-forming galaxies, and the NGP sample of normal galaxies. Forty-seven SNe in 41 Mrk galaxies, 10 SNe in six SBS galaxies, 29 SNe in 26 NGP active or star-forming galaxies, and 29 SNe in 26 NGP normal galaxies have been studied. We find that the rate of SNe, particularly core-collapse (Types Ib/c and II) SNe, is higher in active or star-forming galaxies in comparison with normal galaxies. Active or star-forming host galaxies of SNe are generally of later morphological type and have lower luminosity and smaller linear size than normal host galaxies of SNe. The radial distribution of SNe in active and star-forming galaxies shows a higher concentration toward the center of the active host galaxy than is the case for normal host galaxies, and this effect is more pronounced for core-collapse SNe. Ib/c-type SNe have been discovered only in active and star-forming galaxies of our samples. About 78% of these SNe are associated with H II regions or are located very close to the nuclear regions of these active galaxies, which are in turn hosting AGNs or starburst nuclei. Besides these new results, our study also supports the conclusions of several other earlier papers. We find that Type Ia SNe occur in all galaxy types, whereas core-collapse SNe of Types Ib/c and II are found only in spiral and irregular galaxies. The radial distribution of Type Ib SNe in their host galaxies is more centrally concentrated than that of Type II and Ia SNe. The radial distances of Types Ib/c and II SNe, from the nuclei of their host galaxies, is larger for barred spiral hosts. Core-collapse SNe are concentrated in spiral arms and are often close to or in the H II regions, whereas Type Ia SNe show only a loose association with spiral arms and no clear association with H II regions.