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We present the Sloan Digital Sky Survey V (SDSS-V) Local Volume Mapper (LVM). The LVM is an integral-field spectroscopic survey of the Milky Way, Magellanic Clouds, and of a sample of local volume galaxies, connecting resolved pc-scale individual sources of feedback to kpc-scale ionized interstellar medium (ISM) properties. The 4-year survey covers the southern Milky Way disk at spatial resolutions of 0.05 to 1 pc, the Magellanic Clouds at 10 pc resolution, and nearby large galaxies at larger scales totaling $>4300$ square degrees of sky, and more than 55M spectra. It utilizes a new facility of alt-alt mounted siderostats feeding 16 cm refractive telescopes, lenslet-coupled fiber-optics, and spectrographs covering 3600-9800A at R ~ 4000. The ultra-wide field IFU has a diameter of 0.5 degrees with 1801 hexagonally packed fibers of 35.3 arcsec apertures. The siderostats allow for a completely stationary fiber system, avoiding instability of the line spread function seen in traditional fiber feeds. Scientifically, LVM resolves the regions where energy, momentum, and chemical elements are injected into the ISM at the scale of gas clouds, while simultaneously charting where energy is being dissipated (via cooling, shocks, turbulence, bulk flows, etc.) to global scales. This combined local and global view enables us to constrain physical processes regulating how stellar feedback operates and couples to galactic kinematics and disk-scale structures, such as the bar and spiral arms, as well as gas in- and out-flows., Comment: 29 pages, 12 figures, accepted for publication in The Astronomical Journal

Magnetic fields are of critical importance for our understanding of the origin and long-term evolution of the Milky Way. This is due to their decisive role in the dynamical evolution of the interstellar medium (ISM) and their influence on the star-formation process. Faraday rotation measures (RM) along many different sightlines across the Galaxy are a primary means to infer the magnetic field topology and strength from observations. However, the interpretation of the data has been hampered by the failure of previous attempts to explain the observations in theoretical models and to synthesize a realistic multi-scale all-sky RM map. We here utilize a cosmological magnetohydrodynamic (MHD) simulation of the formation of the Milky Way, augment it with a novel star cluster population synthesis model for a more realistic structure of the local interstellar medium, and perform detailed polarized radiative transfer calculations on the resulting model. This yields a faithful first principles prediction of the Faraday sky as observed on Earth. The results reproduce the observations of the Galaxy not only on global scales, but also on local scales of individual star-forming clouds. They also imply that the Local Bubble containing our Sun dominates the RM signal over large regions of the sky. Modern cosmological MHD simulations of the Milky Way's formation, combined with a simple and plausible model for the fraction of free electrons in the ISM, explain the RM observations remarkably well, thus indicating the emergence of a firm theoretical understanding of the genesis of magnetic fields in our Universe across cosmic time., Comment: 14 pages, 3 figures

We study the evolution of embedded star clusters as possible progenitors to reproduce 30 Doradus, specifically the compact star cluster known as R136 and its surrounding stellar family, which is believed to be part of an earlier star formation event. We employ the high-precision stellar dynamics code NBODY6++GPU to calculate the dynamics of the stars embedded in different evolving molecular clouds modelled by the 1D cloud/clusters evolution code WARPFIELD. We explore clouds with initial masses of $M_\text{cloud}=3.16 \times 10^{5}$ M$_\odot$ that (re)-collapse allowing for the birth of a second generation of stars. We explore different star formation efficiencies in order to find the best set of parameters that can reproduce the observation measurements. Our best-fit models correspond to a first stellar generation with masses between $1.26 \times 10^4$ - $2.85 \times 10^4 $M$_\odot$ and for the second generation we find a $M \approx 6.32\times 10^4$ M$_\odot$. Our models can match the observed stellar ages, cloud shell radius, and the fact that the second generation of stars is more concentrated than the first one. This is found independently of the cluster starting initially with mass segregation or not. By comparing our results with recent observational measurements of the mass segregation and density profile of the central zone we find close agreement, and thus provide supporting evidence for a centrally focused (re)-collapse origin to the multiple ages., Comment: 13 pages, 7 figures, 2 tables

Young massive stars play an important role in the evolution of the interstellar medium (ISM) and the self-regulation of star formation in giant molecular clouds (GMCs) by injecting energy, momentum, and radiation (stellar feedback) into surrounding environments, disrupting the parental clouds, and regulating further star formation. Information of the stellar feedback inheres in the emission we observe, however inferring the physical properties from photometric and spectroscopic measurements is difficult, because stellar feedback is a highly complex and non-linear process, so that the observational data are highly degenerate. On this account, we introduce a novel method that couples a conditional invertible neural network (cINN) with the WARPFIELD-emission predictor (WARPFIELD-EMP) to estimate the physical properties of star-forming regions from spectral observations. We present a cINN that predicts the posterior distribution of seven physical parameters (cloud mass, star formation efficiency, cloud density, cloud age which means age of the first generation stars, age of the youngest cluster, the number of clusters, and the evolutionary phase of the cloud) from the luminosity of 12 optical emission lines, and test our network with synthetic models that are not used during training. Our network is a powerful and time-efficient tool that can accurately predict each parameter, although degeneracy sometimes remains in the posterior estimates of the number of clusters. We validate the posteriors estimated by the network and confirm that they are consistent with the input observations. We also evaluate the influence of observational uncertainties on the network performance., Comment: 32 pages, 23 figures, Accepted for publication by MNRAS on 21. January

We employ ionization-parameter mapping (IPM) to infer the optical depth of HII regions in the northern half of M33. We construct [OIII]$\lambda 5007$/[OII]$\lambda 3727$ and [OIII]$\lambda 5007$/[SII]$\lambda 6724$ ratio maps from narrow-band images continuum-subtracted in this way, from which we classify the HII regions by optical depth to ionizing radiation, based on their ionization structure. This method works relatively well in the low metallicity regime, $12 + \log(\rm O/H) \leq 8.4$, where [OIII]$\lambda\lambda4949,5007$ is strong. However, at higher metallicities, the method breaks down due to the strong dependence of the [OIII]$\lambda\lambda4959,5007$ emission lines on the nebular temperature. Thus, although O$^{++}$ may be present in metal-rich HII regions, these commonly used emission lines do not serve as a useful indicator of its presence, and hence, the O ionization state. In addition, IPM as a diagnostic of optical depth is limited by spatial resolution. We also report a region of highly excited [OIII] extending over an area $\sim$ 1 kpc across and [OIII]$\lambda5007$ luminosity of $4.9\pm 1.5\times10^{38}$ erg/s, which is several times higher than the ionizing budget of any potential sources in this portion of the galaxy. Finally, this work introduces a new method for continuum subtraction of narrow-band images based on the dispersion of pixels around the mode of the diffuse-light flux distribution. In addition to M33, we demonstrate the method on C III]$\lambda$1909 imaging of Haro~11, ESO 338-IG004, and Mrk~71., Comment: 21 pages, 18 figures, of which 4 are animated and 1 is interactive, 2 tables. Accepted in ApJ on 04 Sep 2021. The enhanced figures will be available in the final version of the paper on the ApJ website

We present the {\sc warpfield} emission predictor, {\sc warpfield-emp}, which couples the 1D stellar feedback code {\sc warpfield} with the {\sc cloudy} \hii region/PDR code and the {\sc polaris} radiative transfer code, in order to make detailed predictions for the time-dependent line and continuum emission arising from the H{\sc ii} region and PDR surrounding an evolving star cluster. {\sc warpfield-emp} accounts for a wide range of physical processes (stellar winds, supernovae, radiation pressure, gravity, thermal conduction, radiative cooling, dust extinction etc.) and yet runs quickly enough to allow us to explore broad ranges of different cloud parameters. We compare the results of an extensive set of models with SITELLE observations of a large sample of \hii regions in NGC~628 and find very good agreement, particularly for the highest signal-to-noise observations. We show that our approach of modeling individual clouds from first principles (instead of in terms of dimensionless quantities such as the ionization parameter) allows us to avoid long-standing degeneracies in the interpretation of \hii region diagnostics and enables us to relate these diagnostics to important physical parameters such as cloud mass or cluster age. Finally, we explore the implications of our models regarding the reliability of simple metallicity diagnostics, the properties of long-lived embedded clusters, and the role played by winds and supernovae in regulating \hii region and PDR line emission., Comment: 24 pages, 12 figures, submitted to MNRAS 18.09.2019

We present an updated version of POLARIS, a well established code designated for dust polarisation and line radiative transfer (RT) in arbitrary astrophysical environments. We extend the already available capabilities with a synchrotron feature for polarised emission. Here, we combine state-of-the-art solutions of the synchrotron RT coefficients with numerical methods for solving the complete system of equations of the RT problem, including Faraday rotation (FR) as well as Faraday conversion (FC). We validate the code against Galactic and extragalactic observations by performing a statistical analysis of synthetic all-sky synchrotron maps for positions within the galaxy and for extragalactic observations. For these test scenarios we apply a model of the Milky Way based on sophisticated magneto-hydrodynamic (MHD) simulations and population-synthesis post-processing techniques.We explore different parameters for modeling the distribution of free electrons and for a turbulent magnetic field component. We find that a strongly fluctuating field is necessary for simulating synthetic synchrotron observations on small scales, we argue that Faraday rotation alone can account for the depolarisation of the synchrotron signal, and we discuss the importance of the observer position within the Milky Way. Altogether, we conclude that POLARIS is a highly reliable tool for predicting synchrotron emission and polarisation, including Faraday rotation in a realistic galactic context. It can thus contribute to better understand the results from current and future observational missions., Comment: 22 pages, 14 figures

Star formation is an inefficient process and in general only a small fraction of the gas in a giant molecular cloud (GMC) is turned into stars. This is partly due to the negative effect of stellar feedback from young massive star clusters. In a recent paper, we introduced a novel 1D numerical treatment of the effects of stellar feedback from young massive clusters on their natal clouds, which we named WARPFIELD. Here, we present version 2 of the WARPFIELD code, containing improved treatments of the thermal evolution of the gas and the fragmentation of the feedback-driven shell. As part of this update, we have produced new cooling and heating tables that account for the combined effects of photoionization and collisional ionization on the cooling rate of the gas, which we now make publically available. We employ our updated version of WARPFIELD to investigate the impact of stellar feedback on GMCs with a broad range of masses and surface densities and a variety of density profiles. We show that the minimum star formation efficiency $\epsilon_{\mathrm{min}}$, i.e. the star formation efficiency above which the cloud is destroyed by feedback and further star formation is shut off, is mainly set by the average cloud surface density. A star formation efficiency of 1-6 % is generally sufficient to destroy a GMC. We also find star formation efficiencies per free-fall time $\epsilon_{\mathrm{ff}} \sim 0.3$ %, in good agreement with recent observations. Our results imply that stellar feedback alone is sufficient to explain the low observed star formation efficiencies of GMCs. Finally, we show that very massive clouds with steep density profiles - possible proxies of the giant clumps observed in galaxies at $z \approx 2$ - are more resilient to feedback than typical GMCs, with $\epsilon_{\mathrm{min}}$ between 1 and 12 %., Comment: 15 pages, 6 figures

In many tasks, in particular in natural science, the goal is to determine hidden system parameters from a set of measurements. Often, the forward process from parameter- to measurement-space is a well-defined function, whereas the inverse problem is ambiguous: one measurement may map to multiple different sets of parameters. In this setting, the posterior parameter distribution, conditioned on an input measurement, has to be determined. We argue that a particular class of neural networks is well suited for this task -- so-called Invertible Neural Networks (INNs). Although INNs are not new, they have, so far, received little attention in literature. While classical neural networks attempt to solve the ambiguous inverse problem directly, INNs are able to learn it jointly with the well-defined forward process, using additional latent output variables to capture the information otherwise lost. Given a specific measurement and sampled latent variables, the inverse pass of the INN provides a full distribution over parameter space. We verify experimentally, on artificial data and real-world problems from astrophysics and medicine, that INNs are a powerful analysis tool to find multi-modalities in parameter space, to uncover parameter correlations, and to identify unrecoverable parameters.

We use the POLARIS radiative transport code to generate predictions of the two main observables directly sensitive to the magnetic field morphology and strength in filaments: dust polarization and gas Zeeman line splitting. We simulate generic gas filaments with power-law density profiles assuming two density-field strength dependencies, six different filament inclinations, and nine distinct magnetic field morphologies, including helical, toroidal, and warped magnetic field geometries. We present idealized spatially resolved dust polarization and Zeeman-derived field strengths and directions maps. Under the assumption that dust grains are aligned by radiative torques (RATs), dust polarization traces the projected plane-of-the-sky magnetic field morphology. Zeeman line splitting delivers simultaneously the intensity-weighted line-of-sight field strength and direction. We show that linear dust polarization alone is unable to uniquely constrain the 3D field morphology. We demonstrate that these ambiguities are ameliorated or resolved with the addition of the Zeeman directional information. Thus, observations of both the dust polarization and Zeeman splitting together provide the most promising means for obtaining constraints of the 3D magnetic field configuration. We find that the Zeeman-derived field strengths are at least a factor of a few below the input field strengths due to line-of-sight averaging through the filament density gradient. Future observations of both dust polarization and Zeeman splitting are essential for gaining insights into the role of magnetic fields in star and cluster forming filaments., Comment: 16 pages, 11 figures, 1 table

SDSS-V will be an all-sky, multi-epoch spectroscopic survey of over six million objects. It is designed to decode the history of the Milky Way, trace the emergence of the chemical elements, reveal the inner workings of stars, and investigate the origin of planets. It will also create an integral-field spectroscopic map of the gas in the Galaxy and the Local Group that is 1,000x larger than the current state of the art and at high enough spatial resolution to reveal the self-regulation mechanisms of galactic ecosystems. SDSS-V will pioneer systematic, spectroscopic monitoring across the whole sky, revealing changes on timescales from 20 minutes to 20 years. The survey will thus track the flickers, flares, and radical transformations of the most luminous persistent objects in the universe: massive black holes growing at the centers of galaxies. The scope and flexibility of SDSS-V will be unique among extant and future spectroscopic surveys: it is all-sky, with matched survey infrastructures in both hemispheres; it provides near-IR and optical multi-object fiber spectroscopy that is rapidly reconfigurable to serve high target densities, targets of opportunity, and time-domain monitoring; and it provides optical, ultra-wide-field integral field spectroscopy. SDSS-V, with its programs anticipated to start in 2020, will be well-timed to multiply the scientific output from major space missions (e.g., TESS, Gaia, eROSITA) and ground-based projects. SDSS-V builds on the 25-year heritage of SDSS's advances in data analysis, collaboration infrastructure, and product deliverables. The project is now refining its science scope, optimizing the survey strategies, and developing new hardware that builds on the SDSS-IV infrastructure. We present here an overview of the current state of these developments as we seek to build our worldwide consortium of institutional and individual members., Comment: 23-page summary of the current status of SDSS-V. See also http://www.sdss.org/future/. SDSS-V is currently seeking institutional and individual members -- join us!

${\bf Aim:}$ To test the hypothesis that radiation pressure from star clusters acting on dust is the dominant feedback agent disrupting the largest star-forming molecular clouds and thus regulating the star-formation process. ${\bf Methods:}$ We perform multi-frequency, 3D, RT calculations including scattering, absorption, and re-emission to longer wavelengths for clouds with masses of $10^4$-$10^7\,$M$_{\odot}$, with embedded clusters and a star formation efficiencies of 0.009%-91%, and varying maximum grain sizes up to 200$\,\mu$m. We calculate the ratio between radiative force and gravity to determine whether radiation pressure can disrupt clouds. ${\bf Results:}$ We find that radiation acting on dust almost never disrupts star-forming clouds. UV and optical photons to which the cloud is optically thick do not scatter much. Instead, they quickly get absorbed and re-emitted by at thermal wavelengths. As the cloud is typically optically thin to far-IR radiation, it promptly escapes, depositing little momentum. The resulting spectrum is more narrowly peaked than the corresponding Planck function with an extended tail at longer wavelengths. As the opacity drops significantly across the sub-mm and mm, the resulting radiative force is even smaller than for the corresponding single-temperature black body. The force from radiation pressure falls below the strength of gravitational attraction by an order of magnitude or more for either Milky Way or starbust conditions. For unrealistically large maximum grain sizes, and star formation efficiencies far exceeding 50% do we find that the strength of radiation pressure can exceed gravity. ${\bf Conclusions:}$ We conclude that radiation pressure acting on dust does not disrupt star-forming molecular clouds in any Local Group galaxies. Radiation pressure thus appears unlikely to regulate the star-formation process on either local or global scales., Comment: 20 pages, 17 figures

The 30 Doradus Nebula in the Large Magellanic Cloud (LMC) contains the massive starburst cluster NGC 2070 with a massive and probably younger stellar sub clump at its center: R136. It is not clear how such a massive inner cluster could form several million years after the older stars in NGC 2070, given that stellar feedback is usually thought to expel gas and inhibit further star formation. Using the recently developed 1D feedback scheme WARPFIELD to scan a large range of cloud and cluster properties, we show that an age offset of several million years between the stellar populations is in fact to be expected given the interplay between feedback and gravity in a giant molecular cloud (GMC) with a density $\gtrsim 500$ cm$^{-3}$ due to re-accretion of gas onto the older stellar population. Neither capture of field stars nor gas retention inside the cluster have to be invoked in order to explain the observed age offset in NGC 2070 as well as the structure of the interstellar medium (ISM) around it., Comment: 5 pages, 3 figures, accepted to MNRAS

Star clusters interact with the interstellar medium (ISM) in various ways, most importantly in the destruction of molecular star-forming clouds, resulting in inefficient star formation on galactic scales. On cloud scales, ionizing radiation creates \hii regions, while stellar winds and supernovae drive the ISM into thin shells. These shells are accelerated by the combined effect of winds, radiation pressure and supernova explosions, and slowed down by gravity. Since radiative and mechanical feedback is highly interconnected, they must be taken into account in a self-consistent and combined manner, including the coupling of radiation and matter. We present a new semi-analytic one-dimensional feedback model for isolated massive clouds ($\geq 10^5\,M_{\odot}$) to calculate shell dynamics and shell structure simultaneously. It allows us to scan a large range of physical parameters (gas density, star formation efficiency, metallicity) and to estimate escape fractions of ionizing radiation $f_{\rm{esc,i}}$, the minimum star formation efficiency $\epsilon_{\rm{min}}$ required to drive an outflow, and recollapse time scales for clouds that are not destroyed by feedback. Our results show that there is no simple answer to the question of what dominates cloud dynamics, and that each feedback process significantly influences the efficiency of the others. We find that variations in natal cloud density can very easily explain differences between dense-bound and diffuse-open star clusters. We also predict, as a consequence of feedback, a $4-6$ Myr age difference for massive clusters with multiple generations., Comment: 17 pages, 11 figures (additional 4 pages and 33 figures in appendix), Accepted MNRAS June 15, 2017

CR7 is the brightest Lyman-$\alpha$ emitter observed at $z>6$, which shows very strong Lyman-$\alpha$ and HeII 1640\AA\ line luminosities, but no metal line emission. Previous studies suggest that CR7 hosts either young primordial stars with a total stellar mass of $\sim 10^7\,\mathrm{M}_\odot$ or a black hole of $\gtrsim 10^6\,\mathrm{M}_\odot$. Here, we explore different formation scenarios for CR7 with a semianalytical model, based on the random sampling of dark matter merger trees. We are unable to reproduce the observational constraints with a primordial stellar source, given our model assumptions, due to the short stellar lifetimes and the early metal enrichment. Black holes that are the remnants of the first stars are either not massive enough, or reside in metal-polluted haloes, ruling out this possible explanation of CR7. Our models instead suggest that direct collapse black holes, which form in metal-free haloes exposed to large Lyman-Werner fluxes, are more likely the origin of CR7. However, this result is derived under optimistic assumptions and future observations are necessary to further constrain the nature of CR7., Comment: 21 pages, 17 figures, 2 tables, MNRAS in press

The Magellanic Clouds provide the only laboratory to study the effect of metallicity and galaxy mass on molecular gas and star formation at high (~20 pc) resolution. We use the dust emission from HERITAGE Herschel data to map the molecular gas in the Magellanic Clouds, avoiding the known biases of CO emission as a tracer of H$_{2}$. Using our dust-based molecular gas estimates, we find molecular gas depletion times of ~0.4 Gyr in the LMC and ~0.6 SMC at 1 kpc scales. These depletion times fall within the range found for normal disk galaxies, but are shorter than the average value, which could be due to recent bursts in star formation. We find no evidence for a strong intrinsic dependence of the molecular gas depletion time on metallicity. We study the relationship between gas and star formation rate across a range in size scales from 20 pc to ~1 kpc, including how the scatter in molecular gas depletion time changes with size scale, and discuss the physical mechanisms driving the relationships. We compare the metallicity-dependent star formation models of Ostriker, McKee, and Leroy (2010) and Krumholz (2013) to our observations and find that they both predict the trend in the data, suggesting that the inclusion of a diffuse neutral medium is important at lower metallicity., Comment: 24 pages, 14 figures, accepted for publication in ApJ. FITS files of the dust-based estimates of the H2 column densities for the LMC and SMC (shown in Figures 2 and 3) will be available online through ApJ

We present a method to simultaneously model the dust far-infrared spectral energy distribution (SED) and the total infrared $-$ carbon monoxide (CO) integrated intensity $(S_{\rm IR}-I_{\rm CO})$ relationship. The modelling employs a hierarchical Bayesian (HB) technique to estimate the dust surface density, temperature ($T_{\rm eff}$), and spectral index at each pixel from the observed far-infrared (FIR) maps. Additionally, given the corresponding CO map, the method simultaneously estimates the slope and intercept between the FIR and CO intensities, which are global properties of the observed source. The model accounts for correlated and uncorrelated uncertainties, such as those present in Herschel observations. Using synthetic datasets, we demonstrate the accuracy of the HB method, and contrast the results with common non-hierarchical fitting methods. As an initial application, we model the dust and gas on 100 pc scales in the Magellanic Clouds from Herschel FIR and NANTEN CO observations. The slopes of the $\log S_{\rm IR}-\log I_{\rm CO}$ relationship are similar in both galaxies, falling in the range 1.1$-$1.7. However, in the SMC the intercept is nearly 3 times higher, which can be explained by its lower metallicity than the LMC, resulting in a larger $S_{\rm IR}$ per unit $I_{\rm CO}$. The HB modelling evidences an increase in $T_{\rm eff}$ in regions with the highest $I_{\rm CO}$ in the LMC. This may be due to enhanced dust heating in the densest molecular regions from young stars. Such simultaneous dust and gas modelling may reveal variations in the properties of the ISM and its association with other galactic characteristics, such as star formation rates and/or metallicities., Comment: 17 pages, 14 figures, Updated to match MNRAS accepted version

We present the first fully calibrated H$_2$, 1-0 S(1) image of the entire 30 Doradus nebula. The observations were conducted using the NOAO Extremely Wide-Field Infrared Imager on the CTIO 4-meter Blanco Telescope. Together with a NEWFIRM Br$\gamma$ image of 30 Doradus, our data reveal the morphologies of the warm molecular gas and ionized gas in 30 Doradus. The brightest H$_2$-emitting area, which extends from the northeast to the southwest of R136, is a photodissociation region viewed face-on, while many clumps and pillar features located at the outer shells of 30 Doradus are photodissociation regions viewed edge-on. Based on the morphologies of H$_2$, Br$\gamma$, $^{12}$CO, and 8$\mu$m emission, the H$_2$ to Br$\gamma$ line ratio and Cloudy models, we find that the H$_2$ emission is formed inside the photodissociation regions of 30 Doradus, 2 - 3 pc to the ionization front of the HII region, in a relatively low-density environment $<$ 10$^4$ cm$^{-3}$. Comparisons with Br$\gamma$, 8$\mu$m, and CO emission indicate that H$_2$ emission is due to fluorescence, and provide no evidence for shock excited emission of this line., Comment: 10 pages, 6 figures, 2 tables; accepted for publication in ApJ

We analyze the applicability of far-infrared fine-structure lines [CII] 158 micron, [OI] 63 micron and [OIII] 88 micron to reliably trace the star formation rate (SFR) in a sample of low-metallicity dwarf galaxies from the Herschel Dwarf Galaxy Survey and compare with a broad sample of galaxies of various types and metallicities in the literature. We study the trends and scatter in the relation between the SFR (as traced by GALEX FUV and MIPS 24 micron) and far-infrared line emission, on spatially resolved and global galaxy scales, in dwarf galaxies. We assemble far-infrared line measurements from the literature and infer whether the far-infrared lines can probe the SFR (as traced by the total-infrared luminosity) in a variety of galaxy populations. In metal-poor dwarfs, the [OI] and [OIII] lines show the strongest correlation with the SFR with an uncertainty on the SFR estimates better than a factor of 2, while the link between [CII] emission and the SFR is more dispersed (uncertainty factor of 2.6). The increased scatter in the SFR-L([CII]) relation towards low metal abundances, warm dust temperatures, large filling factors of diffuse, highly ionized gas suggests that other cooling lines start to dominate depending on the density and ionization state of the gas. For the literature sample, we evaluate the correlations for a number of different galaxy populations. The [CII] and [OI] lines are considered to be reliable SFR tracers in starburst galaxies, recovering the star formation activity within an uncertainty of factor 2. [Abridged], Comment: 35 pages, 13 figures, accepted for publication in A&A on May 7th 2014

We report the discovery of a new candidate ultraluminous X-ray source (ULX) in the nearby edge-on spiral galaxy NGC 891. The source, which has an absorbed flux of F_X ~ 10^-12 erg/s/cm^2 (corresponding to L_X > 10^40 erg/s at 9 Mpc), must have begun its outburst in the past 5 years as it is not detected in prior X-ray observations between 1986 and 2006. We try empirical fits to the XMM-Newton spectrum, finding that the spectrum is fit very well as emission from a hot disk, a cool irradiated disk, or blurred reflection from the innermost region of the disk. The simplest physically motivated model with an excellent fit is a hot disk around a stellar-mass black hole (a super-Eddington outburst), but equally good fits are found for each model. We suggest several follow-up experiments that could falsify these models., Comment: 6 pages, 4 figures, 1 table. Accepted to ApJ Letters

We use our new optical-imaging and spectrophotometric survey of key diagnostic emission lines in 30 Doradus, together with CLOUDY photoionization models, to study the physical conditions and ionization mechanisms along over 4000 individual lines of sight at points spread across the face of the extended nebula, out to a projected radius 75 pc from R136 at the center of the ionizing cluster NGC 2070. We focus on the physical conditions, geometry and importance of radiation pressure on a point-by-point basis, with the aim of setting observational constraints on important feedback processes. We find that the dynamics and large scale structure of 30 Dor are set by a confined system of X-ray bubbles in rough pressure equilibrium with each other and with the confining molecular gas. Although the warm (10,000K) gas is photoionized by the massive young stars in NGC 2070, the radiation pressure does not currently play a major role in shaping the overall structure. The completeness of our survey also allows us to create a composite spectrum of 30 Doradus, simulating the observable spectrum of a spatially-unresolved, distant giant extragalactic H II region. We find that the highly simplified models used in the "strong line" abundance technique do in fact reproduce our observed lines strengths and deduced chemical abundances, in spite of the more than one order of magnitude range in the ionization parameter and density of the actual gas in 30 Dor., Comment: 54 pages, 21 figures, Accepted for publication in the Astrophysical Journal

We have completed a a new optical imaging and spectrophotometric survey of a 140 x 80 pc$^2$ region of 30 Doradus centered on R136, covering key optical diagnostic emission lines including \Ha, \Hb, \Hg, [O III] $\lambda\lambda$4363, 4959, 5007, [N II] $\lambda\lambda$6548, 6584, [S II] $\lambda\lambda$6717, 6731 [S III] $\lambda $6312 and in some locations [S III] $\lambda$9069. We present maps of fluxes and intensity ratios for these lines, and catalogs of isolated ionizing stars, elephant-trunk pillars, and edge-on ionization fronts. The final science-quality spectroscopic data products are available to the public. Our analysis of the new data finds that, while stellar winds and supernovae undoubtedly produce shocks and are responsible for shaping the nebula, there are no global spectral signatures to indicate that shocks are currently an important source of ionization. We conclude that the considerable region covered by our survey is well described by photoionization from the central cluster where the ionizing continuum is dominated by the most massive O stars. We show that if 30 Dor were viewed at a cosmological distance, its integrated light would be dominated by its extensive regions of lower surface-brightness rather than by the bright, eye-catching arcs., Comment: 42 pages, 16 figures, Accepted for publication in ApJS