Fine-structure Line Emission Research Articles

SOFIA/upGREAT far-infrared spectroscopy of bright rimmed pillars in IC 1848

Using the upGREAT instrument on SOFIA, we imaged the [C II] 158 µm fine structure line emission in bright-rimmed pillars located at the southern edge of the IC 1848 H II region, and carried out pointed observations of the [O I] 63 and 145 µm fine structure lines toward selected positions. The observations are used to characterize the morphology, velocity field, and the physical conditions in the G1–G3 filaments. The velocity-resolved [C II] spectra show evidence of a velocity shift at the head of the brightest G1 filament, possibly caused by radiation pressure from the impinging UV photons or the rocket effect of the evaporating gas. Archival Herschel PACS and SPIRE observations imply H2 column densities in the range 1021 –1022 cm−2 , corresponding to maximum visual extinction AV ≃ 10 mag, and average H2 volume density of ≃4500 cm−3 in the filaments. The [C II] emission traces ∼17% of the total H2 column density, as derived from dust SED fits. Photon-dominated region models are unable to explain the observed line intensities of the two [O I] fine structure lines in IC 1848, with the observed [O I] 145 µm line being too strong compared to the model predictions. The [O I] lines in IC 1848 are overall weak and the signal-to-noise ratio is limited. However, our observations suggest that the [O I] 63/145 µm intensity ratio is a sensitive probe of the physical conditions in photon-dominated regions such as IC 1848. These lines are thus excellent targets for future high-altitude balloon instruments, less affected by telluric absorption.

A benchmark for extreme conditions of the multiphase interstellar medium in the most luminous hot dust-obscured galaxy at z = 4.6

WISE J224607.6–052634.9 (W2246–0526) is a hot dust-obscured galaxy at z = 4.601, and the most luminous obscured quasar known to date. W2246–0526 harbors a heavily obscured supermassive black hole that is most likely accreting above the Eddington limit. We present observations with the Atacama Large Millimeter/submillimeter Array (ALMA) in seven bands, including band 10, of the brightest far-infrared (FIR) fine-structure emission lines of this galaxy: [OI]63 μm, [OIII]88 μm, [NII]122 μm, [OI]145 μm, [CII]158 μm, [NII]205 μm, [CI]370 μm, and [CI]609 μm. A comparison of the data to a large grid of CLOUDY radiative transfer models reveals that a high hydrogen density (nH ∼ 3 × 103 cm−3) and extinction (AV ∼ 300 mag), together with extreme ionization (log(U) = − 0.5) and a high X-ray to UV ratio (αox ≥ −0.8) are required to reproduce the observed nuclear line ratios. The values of αox and U are among the largest found in the literature and imply the existence of an X-ray-dominated region (XDR). In fact, this component explains the a priori very surprising non-detection of the [OIII]88 μm emission line, which is actually suppressed, instead of boosted, in XDR environments. Interestingly, the best-fitted model implies higher X-ray emission and lower CO content than what is detected observationally, suggesting the presence of a molecular gas component that should be further obscuring the X-ray emission over larger spatial scales than the central region that is being modeled. These results highlight the need for multiline infrared observations to characterize the multiphase gas in high redshift quasars and, in particular, W2246–0526 serves as an extreme benchmark for comparisons of interstellar medium conditions with other quasar populations at cosmic noon and beyond.

The ALMA Reionization Era Bright Emission Line Survey: The molecular gas content of galaxies at z ~ 7

A key to understanding the formation of the first galaxies is to quantify the content of the molecular gas as the fuel for star formation activity through the epoch of reionization. In this paper, we use the 158µm [C II] fine-structure emission line as a tracer of the molecular gas in the interstellar medium (ISM) in a sample of 𝓏 = 6.5–7.5 galaxies recently unveiled by the Reionization Era Bright Line Emission Survey, REBELS, with the Atacama Large Millimeter/submillimeter Array. We find substantial amounts of molecular gas (~1010.5 M⊙), comparable to those found in lower-redshift galaxies for similar stellar masses (~1010 M⊙). The REBELS galaxies appear to follow the standard scaling relations of the molecular gas-to-stellar mass ratio (µmol) and the gas-depletion timescale (tdep) with distance to the star-forming main sequence expected from extrapolations of 𝓏 ~ 1–4 observations. We find median values at 𝓏 ~ 7 of μmol = 2.6−1.44.1 and tdep = 0.5−0.14+0.26 Gyr, indicating that the baryonic content of these galaxies is dominated by the gas phase and evolves little from 𝓏 ~ 7 to 4. Our measurements of the cosmic density of molecular gas, log(ρmol/(M⊙ Mpc−3)) = 6.34−0.31+0.34, indicate a steady increase by an order of magnitude from 𝓏 ~ 7 to 4.

Diagnosing the interstellar medium of galaxies with far-infrared emission lines

Context.Gas cooling processes in the interstellar medium (ISM) are key to understanding how star formation occurs in galaxies. Far-infrared (FIR) fine-structure emission lines can be used to infer gas conditions and trace different phases of the ISM.Aims.We model eight of the most important FIR emission lines and explore their variation with star formation rate (SFR) out toz = 6 using cosmological hydrodynamical simulations. In addition, we study how different physical parameters, such as the interstellar radiation field (ISRF) and metallicity, impact the FIR lines and line ratios.Methods.We implemented a physically motivated multi-phase model of the ISM by post-processing the EAGLEcosmological simulation and using CLOUDYlook-up tables for line emissivities. In this model we included four phases of the ISM: dense molecular gas, neutral atomic gas, diffuse ionised gas (DIG), and H IIregions.Results.Our model shows reasonable agreement (to ∼0.5 dex) with the observed line luminosity–SFR relations up toz = 6 in the FIR lines analysed. For ease of comparison, we also provide linear fits to our model results. Our predictions also agree reasonably well with observations in diagnostic diagrams involving various FIR line ratios.Conclusions.We find that [C II] is the best SFR tracer of the FIR lines even though it arises from multiple ISM phases, while [O III] and [N II] can be used to understand the DIG–H IIbalance in the ionised gas. In addition, line ratios such as [C II]/[O III] and [N II]/[O I] are useful for deriving parameters such as ISRF, metallicity, and specific SFR. These results can help interpret the observations of the FIR lines from the local Universe to high redshifts.

Tellurium emission line in kilonova AT 2017gfo

ABSTRACT The late-time spectra of the kilonova AT 2017gfo associated with GW170817 exhibit a strong emission line feature at $2.1\, {\rm \mu m}$. The line structure develops with time and there is no blueshifted absorption feature in the spectra, suggesting that this emission line feature is produced by electron collision excitation. We attribute the emission line to a fine structure line of Tellurium (Te) III, which is one of the most abundant elements in the second r-process peak. By using a synthetic spectral modelling including fine structure emission lines with the solar r-process abundance pattern beyond the first r-process peak, i.e. atomic mass numbers A ≳ 88, we demonstrate that [Te iii] $2.10\, \rm \mu m$ is indeed expected to be the strongest emission line in the near infrared region. We estimate that the required mass of Te iii is ∼10−3 M⊙, corresponding to the merger ejecta of 0.05 M⊙, which is in agreement with the mass estimated from the kilonova light curve.

Structure of the W3A Low-density Foreground Region

We present analysis of [O i] 63 μm and CO J = 5 − 4 and 8 − 7 multiposition data in the W3A region and use it to develop a model for the extended low-density foreground gas that produces absorption features in the [O i] and J = 5 − 4 CO lines. We employ the extinction to the exciting stars of the background H ii region to constrain the total column density of the foreground gas. We have used the Meudon photodissociation region code to model the physical conditions and chemistry in the region employing a two-component model with a high-density layer near the H ii region responsible for the fine-structure line emission and an extended low-density foreground layer. The best-fitting total proton density, constrained largely by the CO lines, is n(H) = 250 cm−3 in the foreground gas and 5 × 105 cm−3 in the material near the H ii region. The absorption is distributed over the region mapped in W3A and is not restricted to the foreground of either the embedded exciting stars of the H ii region or the protostar W3 IRS5. The low-density material associated with regions of massive-star formation, based on an earlier study by Goldsmith et al., is quite common, and we now see that it is extended over a significant portion of W3A. It thus should be included in modeling of fine-structure line emission, including interpreting low-velocity-resolution observations made with incoherent spectrometer systems, in order to use these lines as accurate tracers of massive-star formation.

A photodissociation region (PDR) model grid in planetary nebula paradigm: dependency of C and O fine structure line emission and PDR thermal structure on central star radiation and nebular dust composition

ABSTRACT We compute a grid of photodissociation region (PDR) models. The varying parameters of the grid include effective temperature (Teff) and luminosity (L) of the radiation source, density (nH) of the nebula, PDR depth from the nebular ionization front (ΔrPDR), and densities of polycyclic aromatic hydrocarbon (PAH) molecules and amorphous carbon (AC) dust. The paradigm, including the range of the parameters used to calculate the models, corresponds to planetary nebulae (PNe). We study the heating and cooling rates, and the variation of gas kinetic temperature (TK) along the PDR depth. We evaluate fluxes of fine structure lines: [O i] 63 $\mu$m, [C ii] 158 $\mu$m, and [C i] 609 $\mu$m and flux ratios: [O i] 146/63 $\mu$m, [O i] 63/[C ii] 158 $\mu$m, and [C i] 609/370 $\mu$m, and study their variation in the parameter space: Teff, L, and nH, for different composition of PAH and AC. We further study the distribution of [O i] 146/63 $\mu$m and [O i] 63/[C ii] 158 $\mu$m ratios in the parameter spaces of nH, ΔrPDR, Teff, and L. We take the observed [O i] 146/63 $\mu$m and [O i] 63/[C ii] 158 $\mu$m ratios for a number of PNe, and compare with these ratios obtained from our models. We verify that the correlation found between the [O i] 146/63 $\mu$m and [O i] 63/[C ii] 158 $\mu$m ratios observed in real PNe is similar to that found from our PN model grid.

Searching for Converging Flows of Atomic Gas onto a Molecular Cloud

We present new observations of [C ii] 2 P 3/2 → 2 P 1/2 fine structure line emission from an isolated molecular cloud using the upGREAT instrument on board SOFIA. These data are analyzed together with archival CO J=1–0 and H i 21 cm emission spectra to investigate the role of converging atomic gas flows in the formation of molecular clouds. Bright [C ii] emission is detected throughout the mapped area that likely originates from photodissociation regions excited by UV radiation fields produced by newborn stars within the cloud. Upon spatial averaging of the [C ii] spectra, we identify weak [C ii] emission within velocity intervals where the H i 21 cm line is brightest; these are blueshifted relative to velocities of the CO and bright [C ii] emission by 4 km s−1. The brightness temperatures, velocity dispersions, and alignment with H i 21 cm velocities connect this [C ii] emission component to the cold, neutral atomic gas of the interstellar medium, known as the cold, neutral medium (CNM). We propose that this CNM feature is an accretion flow onto the farside of the existing molecular cloud. The mass infall rate is 3.2 × 10−4 M ⊙ yr−1. There is no direct evidence of a comparable redshifted component in the [C ii] or H i 21 cm spectral lines that would indicate the presence of a converging flow.

GOALS-JWST: Tracing AGN Feedback on the Star-forming Interstellar Medium in NGC 7469

We present James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) integral-field spectroscopy of the nearby merging, luminous infrared galaxy, NGC 7469. This galaxy hosts a Seyfert type-1.5 nucleus, a highly ionized outflow, and a bright, circumnuclear star-forming ring, making it an ideal target to study active galactic nucleus (AGN) feedback in the local universe. We take advantage of the high spatial/spectral resolution of JWST/MIRI to isolate the star-forming regions surrounding the central active nucleus and study the properties of the dust and warm molecular gas on ∼100 pc scales. The starburst ring exhibits prominent polycyclic aromatic hydrocarbon (PAH) emission, with grain sizes and ionization states varying by only ∼30%, and a total star formation rate of 10–30 M ⊙ yr−1 derived from fine structure and recombination emission lines. Using pure rotational lines of H2 we detect 1.2 × 107 M ⊙ of warm molecular gas at a temperature higher than 200 K in the ring. All PAH bands get significantly weaker toward the central source, where larger and possibly more ionized grains dominate the emission, likely the result of the ionizing radiation and/or the fast wind emerging from the AGN. The small grains and warm molecular gas in the bright regions of the ring however display properties consistent with normal star-forming regions. These observations highlight the power of JWST to probe the inner regions of dusty, rapidly evolving galaxies for signatures of feedback and inform models that seek to explain the coevolution of supermassive black holes and their hosts.

The KOSMA-τ PDR model

Numerical models of photodissociation regions (PDRs) are an essential tool to quantitatively understand observations of massive star forming regions through simulations. Few mature PDR models are available and the Cologne KOSMA-τ PDR model is the only sophisticated model that uses a spherical cloud geometry, thereby allowing us to simulate clumpy PDRs. We present the current status of the code as a reference for modelers and for observers that plan to apply KOSMA-τ to interpret their data. For the numerical solution of the chemical problem, we present a superior Newton-Raphson stepping algorithm and discuss strategies to numerically stabilize the problem and speed up the iterations. The chemistry in KOSMA-τ is upgraded to include the full surface chemistry in an up-to-date formulation and we discuss a novel computation of branching ratios in chemical desorption reactions. The high dust temperature in PDRs leads to a selective freeze-out of oxygen-bearing ice species due to their higher condensation temperatures and we study changes in the ice mantle structures depending on the PDR parameters, in particular the impinging ultraviolet field. Selective freeze-out can produce enhanced C abundances and higher gas temperatures, resulting in a fine-structure line emission of atomic carbon [C i] enhanced by up to 50% if surface reactions are considered. We show how recent Atacama Large Millimeter Array (ALMA) observations of HCO+ emission in the Orion Bar with high spatial resolution on the scale of individual clumps can be interpreted in the context of nonstationary, clumpy PDR ensembles. Additionally, we introduce WL-PDR, a simple plane-parallel PDR model written in Mathematica to act as a numerical testing environment of PDR modeling aspects.

Big Three Dragons: A [N ii] 122 μm Constraint and New Dust-continuum Detection of a z = 7.15 Bright Lyman-break Galaxy with ALMA

Abstract We present new Atacama Large Millimeter/submillimeter Array Band 7 observational results of a Lyman-break galaxy at z = 7.15, B14-65666 (“Big Three Dragons”), which is an object detected in [O iii] 88 μm, [C ii] 158 μm, and dust continuum emission during the epoch of reionization. Our targets are the [N ii] 122 μm fine-structure emission line and the underlying 120 μm dust continuum. The dust continuum is detected with a ∼19σ significance. From far-infrared spectral energy distribution sampled at 90, 120, and 160 μm, we obtain a best-fit dust temperature of 40 K (79 K) and an infrared luminosity of log 10 ( L IR / L ⊙ ) = 11.6 (12.1) at the emissivity index β = 2.0 (1.0). The [N ii] 122 μm line is not detected. The 3σ upper limit of the [N ii] luminosity is 8.1 × 107 L ⊙. From the [N ii], [O iii], and [C ii] line luminosities, we use the Cloudy photoionization code to estimate nebular parameters as functions of metallicity. If the metallicity of the galaxy is high (Z > 0.4 Z ⊙), the ionization parameter and hydrogen density are log 10 U ≃ − 2.7 ± 0.1 and n H ≃ 50–250 cm−3, respectively, which are comparable to those measured in low-redshift galaxies. The nitrogen-to-oxygen abundance ratio, N/O, is constrained to be subsolar. At Z < 0.4 Z ⊙, the allowed U drastically increases as the assumed metallicity decreases. For high ionization parameters, the N/O constraint becomes weak. Finally, our Cloudy models predict the location of B14-65666 on the BPT diagram, thereby allowing a comparison with low-redshift galaxies.

The prospects for observing [O iii] 52 micron emission from galaxies during the Epoch of Reionization

ABSTRACT The [O iii] 88 $\mu$m fine-structure emission line has been detected into the Epoch of Reionization (EoR) from star-forming galaxies at redshifts 6 < z ≲ 9 with ALMA. These measurements provide valuable information regarding the properties of the interstellar medium (ISM) in the highest redshift galaxies discovered thus far. The [O iii] 88 $\mu$m line observations leave, however, a degeneracy between the gas density and metallicity in these systems. Here, we quantify the prospects for breaking this degeneracy using future ALMA observations of the [O iii] 52 $\mu$m line. Among the current set of 10 [O iii] 88 $\mu$m emitters at 6 < z ≲ 9, we forecast 52 $\mu$m detections (at 6σ) in SXDF-NB1006-2, B14-6566, J0217-0208, and J1211-0118 within on-source observing times of 2–10 h, provided their gas densities are larger than about nH ≳ 102–103 cm−3. Other targets generally require much longer integration times for a 6σ detection. Either successful detections of the 52 $\mu$m line or reliable upper limits will lead to significantly tighter constraints on ISM parameters. The forecasted improvements are as large as ∼3 dex in gas density and ∼1 dex in metallicity for some regions of parameter space. We suggest SXDF-NB1006-2 as a promising first target for 52 $\mu$m line measurements. We discuss how such measurements will help in understanding the mass–metallicity relationship during the EoR.

N ii] Fine-structure Emission at 122 and 205 μm in a Galaxy at z = 2.6: A Globally Dense Star-forming Interstellar Medium

Abstract We present new observations with the Atacama Large Millimeter/submillimeter Array of the 122 and 205 μm fine-structure line emission of singly ionized nitrogen in a strongly lensed starburst galaxy at z = 2.6. The 122/205 μm [N ii] line ratio is sensitive to electron density, , in the ionized interstellar medium, and we use this to measure n e ≈ 300 cm−3, averaged across the galaxy. This is over an order of magnitude higher than the Milky Way average, comparable to localized Galactic star-forming regions. Combined with observations of the atomic carbon (C i) and carbon monoxide (CO J = 4–3) in the same system, we reveal the conditions in this intensely star-forming system. The majority of the molecular interstellar medium has been driven to high density, and the resultant conflagration of star formation produces a correspondingly dense ionized phase, presumably colocated with myriad H ii regions that litter the gas-rich disk.

Self-generated ultraviolet radiation in molecular shock waves

Context. Shocks are ubiquitous in the interstellar and intergalactic media, where their chemical and radiative signatures reveal the physical conditions in which they arise. Detailed astrochemical models of shocks at all velocities are necessary to understand the physics of many environments including protostellar outflows, supernova remnants, and galactic outflows. Aims. We present an accurate treatment of the self-generated ultraviolet (UV) radiation in models of intermediate velocity (VS = 25–60 km s−1), stationary, weakly magnetised, J-type, molecular shocks. We show how these UV photons modify the structure and chemical properties of shocks and quantify how the initial mechanical energy is reprocessed into line emission. Methods. We develop an iterative scheme to calculate the self-consistent UV radiation field produced by molecular shocks. The shock solutions computed with the Paris–Durham shock code are post-processed using a multi-level accelerated Λ-iteration radiative transfer algorithm to compute Lyman α, Lyman β, and two-photon continuum emission. The subsequent impacts of these photons on the ionisation and dissociation of key atomic and molecular species as well as on the heating by the photoelectric effect are calculated by taking the wavelength dependent interaction cross-sections and the fluid velocity profile into account. This leads to an accurate description of the propagation of photons and the thermochemical properties of the gas in both the postshock region and in the material ahead of the shock called the radiative precursor. With this new treatment, we analyse a grid of shock models with velocities in the range VS = 25–60 km s−1, propagating in dense (nH ≥ 104 cm−3) and shielded gas. Results. Self-absorption traps Lyα photons in a small region in the shock, though a large fraction of this emission escapes by scattering into the line wings. We find a critical velocity VS ~ 30 km s−1 above which shocks generate Lyα emission with a photon flux exceeding the flux of the standard interstellar radiation field. The escaping photons generate a warm slab of gas (T ~ 100 K) ahead of the shock front as well as pre-ionising C and S. Intermediate velocity molecular shocks are traced by bright emission of many atomic fine structure (e.g. O and S) and metastable (e.g. O and C) lines, substantive molecular emission (e.g. H2, OH, and CO), enhanced column densities of several species including CH+ and HCO+, as well as a severe destruction of H2O. As much as 13–21% of the initial kinetic energy of the shock escapes in Lyα and Lyβ photons if the dust opacity in the radiative precursor allows it. Conclusions. A rich molecular emission is produced by interstellar shocks regardless of the input mechanical energy. Atomic and molecular lines reprocess the quasi totality of the kinetic energy, allowing for the connection of observable emission to the driving source for that emission.

Ionized gas in the NGC 5253 supernebula: high spatial and spectral resolution observations with the JVLA and TEXES

ABSTRACT The youngest, closest, and most compact embedded massive star cluster known excites the supernebula in the nearby dwarf galaxy NGC 5253. It is a crucial target and test case for studying the birth and evolution of the most massive star clusters. We present observations of the ionized gas in this source with high spatial and spectral resolution. The data include continuum images of free–free emission with ≈0.15 arcsec resolution made with the Karl G. Jansky Very Large Array (JVLA) at 15, 22, and 33 GHz, and a full data cube of the [S iv] 10.5 μm fine-structure emission line with ≈4.5 km s−1 velocity resolution and 0.3 arcsec beam, obtained with the Texas Echelon Cross Echelle Spectrograph (TEXES) on Gemini North. We find that (1) the ionized gas extends out from the cluster in arms or jets, and (2) the ionized gas comprises two components offset both spatially and in velocity. We discuss mechanisms that may have created the observed velocity field; possibilities include large-scale jets or a subcluster falling on to the main source.

ART2: a 3D parallel multiwavelength radiative transfer code for continuum and atomic and molecular lines

ABSTRACT ART2 is a 3D multiwavelength Monte Carlo radiative transfer (RT) code that couples continuum and emission lines to track the propagation of photons and their interactions with the interstellar medium (ISM). The original ART2 has been extensively applied to hydrodynamics simulations to study panchromatic properties of galaxies and ISM. Here, we describe new implementations of non-local thermodynamic equilibrium RT of molecular and atomic fine structure emission lines, and the parallelization of the code using a number of novel methods. The new ART2 can efficiently and self-consistently produce a full spectrum that includes both continuum and lines such as [C ii], [N ii], [O iii], Ly α, and CO. These essential features, together with the multiphase ISM model and the adaptive grid, make ART2 a multipurpose code to study multiwavelength properties of a wide range of astrophysical systems from planetary discs to large-scale structures. To demonstrate the capability of the new ART2, we applied it to two hydrodynamics simulations: the zoom-in Milky Way Simulation to obtain panchromatic properties of individual galaxies, and the large-scale IllustrisTNG100 Simulation to obtain global properties such as the line intensity mappings. These products are vital for a broad array of studies. By enabling direct comparison between numerical simulations and multiband observations, ART2 provides a crucial theoretical framework for the understanding of existing and future surveys, and the synergy between multiband galaxy surveys and line intensity mappings. Therefore, ART2 is a powerful and versatile tool to bridge the gap between theories and observations of cosmic structures.

Modeling Collisional Excitation of [O i] Fine Structure Line Emission from PDRs. I. Homogeneous Clouds

Abstract Atomic oxygen (O0) plays a critical role in determining the structure of photon-dominated regions (PDRs), but reliable modeling of its emission has been hampered by the high optical depth of the 63 μm fine structure line and complexities in the excitation of the relevant fine structure levels. We discuss here radiation produced by collisional excitation of the submillimeter fine structure lines of atomic oxygen ([O I]) using recent calculations of rates for collisions with atomic and molecular hydrogen. We employ the Molpop–CEP code to include the effects of optical thickness in slab models that are characterized by uniform oxygen abundance, hydrogen density, and kinetic temperature. The particular spontaneous decay rates and collisional excitation rates connecting the three O0 fine structure levels result in population inversion of the upper, 145 μm transition. The effects of trapping are rigorously included and are reflected in the resulting line profiles that exhibit prominent self-absorption even with uniform physical conditions. We present figures for analyzing the two fine structure lines based on the intensity of the 63 μm line and the 145 μm/63 μm line ratio. For the clouds considered, the results for line intensities and line ratios are modestly different from those obtained with a large-velocity-gradient model, but the ability to calculate line profiles is an additional powerful tool. Comparison of the model results with observed line profiles suggests that cloud models with varying physical conditions are required to optimally utilize [O I] fine structure line emission to trace the energetics of PDR regions and the feedback from massive, young stars.

Resolving the Interstellar Medium in the Nuclear Region of Two z = 5.78 Quasar Host Galaxies with ALMA

Abstract We present ALMA observations of the [C ii] 158 μm fine structure line and dust continuum emission from two quasars, SDSS J104433.04−012502.2 and SDSS J012958.51−003539.7, at z = 5.78. The ALMA observations at 0.″2 resolution map the dust and gas on kiloparsec scales. The spatially resolved emission shows a similar trend of decreasing [C ii]–far-infrared (FIR) ratios with increasing FIR surface brightnesses as was found in the infrared luminous galaxies with intense star formation. We confirm the velocity gradients of [C ii] emission found previously in SDSS J0129−0035. No clear evidence of order motion is detected in SDSS J1044−0125. The velocity maps and position–velocity diagrams also suggest turbulent gas clumps in both objects. We tentatively detect a [C ii] peak offset 4.9 kpc to the east of SDSS J1044−0125. This may be associated with an infalling companion, or node of gas outflow. All these results suggest significant dynamical evolution of the interstellar medium in the nuclear region of these young quasar-starburst systems. We fit the velocity map of the [C ii] emission from SDSS J0129−0035 with a rotating disk model. The result suggests a face-on system with an inclination angle of 16° ± 20° and constrains the lower limit of the host galaxy dynamical mass to be 2.6 × 1010 M ⊙ within the [C ii] emitting region. It is likely that SDSS J0129−0035, as well as other young quasars with supermassive black hole masses on the order of 107 M ⊙ to 108 M ⊙, falls close to the black hole and host galaxy mass relation defined by local galaxies.

Unveiling the nature of candidate high-mass young stellar objects in the Magellanic Clouds with near-IR spectroscopy

As nearby neighbors to the Milky Way, the Large and Small Magellanic Clouds (LMC and SMC) provide a unique opportunity to study star formation in the context of their galactic ecosystems. Thousands of young stellar objects (YSOs) have been characterized with large-scale Spitzer and Herschel surveys. In this paper, we present new near-IR spectroscopy of five high-mass YSOs in the LMC and one in the SMC. We detect multiple hydrogen recombination lines, as well as He I 2.058 $\mu$m, H$_2$, [Fe II], and [S III] in these highly excited sources. We estimate the internal extinction of each source and find that it is highest for sources with the youngest evolutionary classifications. Using line ratios, we assess the dominant excitation mechanism in the three sources where we detect both H$_2$ 2.12 $\mu$m and [Fe II] 1.64 $\mu$m. In each case, photoexcitation dominates over shock excitation. Finally, we detect CO bandhead absorption in one of our LMC sources. While this feature is often associated with evolved stars, this object is likely young with strong PAH and fine-structure emission lines tracing an H II region detected at longer wavelengths. Compared to high-mass YSOs in the Galaxy, our sources have higher bolometric and line luminosities, consistent with their selection as some of the brightest sources in the LMC and SMC.

SHINING, A Survey of Far-infrared Lines in Nearby Galaxies. I. Survey Description, Observational Trends, and Line Diagnostics

Abstract We use the Herschel/PACS spectrometer to study the global and spatially resolved far-infrared (FIR) fine-structure line emission in a sample of 52 galaxies that constitute the SHINING survey. These galaxies include star-forming, active-galactic nuclei (AGNs), and luminous infrared galaxies (LIRGs). We find an increasing number of galaxies (and kiloparsec-size regions within galaxies) with low line-to-FIR continuum ratios as a function of increasing FIR luminosity (L FIR), dust infrared color, L FIR to molecular gas mass ratio (L FIR/M mol), and FIR surface brightness (ΣFIR). The correlations between the [C ii]/FIR or [O i]/FIR ratios with ΣFIR are remarkably tight (∼0.3 dex scatter over almost four orders of magnitude in ΣFIR). We observe that galaxies with and ΣFIR ≳ 1011 L ⊙ kpc−2 tend to have weak fine-structure line-to-FIR continuum ratios, and that LIRGs with infrared sizes ≳1 kpc have line-to-FIR ratios comparable to those observed in typical star-forming galaxies. We analyze the physical mechanisms driving these trends in Paper II. The combined analysis of the [C ii], [N ii] 122 μm, and [O iii] 88 μm lines reveals that the fraction of the [C ii] line emission that arises from neutral gas increases from 60% to 90% in the most active star-forming regions and that the emission originating in the ionized gas is associated with low-ionization, diffuse gas rather than with dense gas in H ii regions. Finally, we report the global and spatially resolved line fluxes of the SHINING galaxies to enable the comparison and planning of future local and high-z studies.