Μm Emission Line Research Articles

The ALPINE-ALMA [CII] survey: The population of [CII]-undetected galaxies and their role in the L[CII]-SFR relation

The [CII] 158 μm emission line represents one of the most profitable tools for the investigation of the high-redshift galaxies in the early Universe so far. Being one of the brightest cooling lines in the rest-frame far-infrared regime of star-forming galaxies, it has been successfully exploited as a tracer of the star-formation rate (SFR) in local sources. The picture is more complex at higher redshifts, where its usability in this context is still under investigation. Recent results from the ALMA Large Program to INvestigate [CII] at Early times (ALPINE) survey suggest that there is no (or weak) evolution of the L[CII]-SFR relation up to z ∼ 6, but their reliability is hampered by the presence of a large population of [CII] nondetected galaxies. In this work, we characterize the population of [CII] nondetections in ALPINE. By stacking their ALMA spectra, we obtained a signal detected at ∼5.1σ, resulting in a [CII] luminosity of log(L[CII]/L⊙)∼7.8. When combining this value with those from the [CII] detections, we found a L[CII]-SFR relation with a slope b = 1.14 ± 0.11, which is in agreement within the uncertainties both with the linear relation found in the local Universe and with the previous findings from ALPINE at z ∼ 5. This suggests that the [CII] line can be considered a good tracer of star formation up to the distant Universe. Finally, we show that the galaxies of our sample that deviate from the observed L[CII]-SFR relation most could suffer from a less precise redshift estimation, perhaps artificially reducing their [CII] luminosity. In this respect, we claim that there is no evidence in favor of a deficit of [CII] content in high-z galaxies, in contrast with earlier studies.

ALMA Detections of [O iii] and [C ii] Emission Lines From A1689-zD1 at z = 7.13

A1689-zD1 is one of the most distant galaxies, discovered with the aid of gravitational lensing, providing us with an important opportunity to study galaxy formation in the very early universe. In this study, we report the detection of [C ii]158 μm and [O iii]88 μm emission lines of A1689-zD1 in the Atacama Large Millimeter/submillimeter Array (ALMA) Bands 6 and 8. We measure the redshift of this galaxy as z sys = 7.133 ± 0.005 based on the [C ii] and [O iii] emission lines, consistent with that adopted by Bakx et al. The observed L [O III]/L [C II] ratio is 2.09 ± 0.09, higher than that of most of the local galaxies, but consistent with other z ∼ 7 galaxies. The moderate spatial resolution of ALMA data provided us with a precious opportunity to investigate spatial variation of L [O III]/L [C II]. In contrast to the average value of 2.09, we find a much higher L [O III]/L [C II] of ∼7 at the center of the galaxy. This spatial variation of L [O III]/L [C II] was seldom reported for other high-z galaxies. It is also interesting that the peak of the ratio does not overlap with optical peaks. Possible physical reasons include a central active galactic nucleus, shock heating from merging, and a starburst. Our moderate spatial resolution data also reveal that in addition to the observed two clumps shown in previous Hubble Space Telescope images, there is a redshifted segment to the west of the northern optical clump. This structure is consistent with previous claims that A1689-zD1 is a merging galaxy, but with the northern redshifted part being some ejected material, or that the northern redshifted material stems from a third more highly obscured region of the galaxy.

Massive Molecular Gas Reservoir in a Luminous Submillimeter Galaxy during Cosmic Noon

Abstract We present multiband observations of an extremely dusty star-forming lensed galaxy (HERS1) at z = 2.553. High-resolution maps of HST/WFC3, SMA, and ALMA show a partial Einstein ring with a radius of ∼3″. The deeper HST observations also show the presence of a lensing arc feature associated with a second lens source, identified to be at the same redshift as the bright arc based on a detection of the [N ii] 205 μm emission line with ALMA. A detailed model of the lensing system is constructed using the high-resolution HST/WFC3 image, which allows us to study the source-plane properties and connect rest-frame optical emission with properties of the galaxy as seen in submillimeter and millimeter wavelengths. Corrected for lensing magnification, the spectral energy distribution fitting results yield an intrinsic star formation rate of about 1000 ± 260 M ⊙ yr−1, a stellar mass M * = 4.3 − 1.0 + 2.2 × 10 11 M ⊙ , and a dust temperature T d = 35 − 1 + 2 K. The intrinsic CO emission line (J up = 3, 4, 5, 6, 7, 9) flux densities and CO spectral line energy distribution are derived based on the velocity-dependent magnification factors. We apply a radiative transfer model using the large velocity gradient method with two excitation components to study the gas properties. The low-excitation component has a gas density n H 2 = 10 3.8 ± 0.6 cm−3 and kinetic temperature T k = 18 − 5 + 7 K, and the high-excitation component has n H 2 = 10 3.1 ± 0.4 cm−3 and T k = 480 − 220 + 260 K. Additionally, HERS1 has a gas fraction of about 0.19 ± 0.14 and is expected to last 100 Myr. These properties offer a detailed view of a typical submillimeter galaxy during the peak epoch of star formation activity.

The Archival Discovery of a Strong Lyα and [C ii] Emitter at z = 7.677

Abstract We report the archival discovery of Lyα emission from the bright ultraviolet galaxy Y002 at z = 7.677, spectroscopically confirmed by its ionized carbon [C ii] 158 μm emission line. The Lyα line is spatially associated with the rest-frame UV stellar emission (M UV ∼ −22, 2× brighter than M UV ⋆ ), and it appears offset from the peak of the extended [C ii] emission at the current ∼1″ spatial resolution. We derive an estimate of the unobscured SFRUV = (22 ± 1) M ⊙ yr−1 and set an upper limit of SFRIR < 15 M ⊙ yr−1 from the far-infrared (FIR) wavelength range, which globally places Y002 on the SFR(UV+IR)–L [C II] correlation observed at lower redshifts. In terms of velocity, the peak of the Lyα emission is redshifted by Δv Lyα ∼ 500 km s−1 from the systemic redshift set by [C ii] and a high-velocity tail extends up to ∼1000 km s−1. The velocity offset is up to ∼3.5× higher than the average estimate for similarly UV-bright emitters at z ∼ 6–7, which might suggest that we are witnessing the merging of two clumps. A combination of strong outflows and the possible presence of an extended ionized bubble surrounding Y002 would likely facilitate the escape of copious Lyα light, as indicated by the large equivalent width EW0(Lyα) = 24 − 6 + 5 Å. Assuming that [C ii] traces the neutral hydrogen, we estimate a H i gas fraction of M H I/M ⋆ ≳ 8 for Y002 as a system and speculate that patches of high H i column densities could contribute to explaining the observed spatial offsets between Lyα- and [C ii]-emitting regions. The low dust content, implied by the nondetection of the FIR continuum emission at rest frame ∼160 μm, would be sufficient to absorb any potential Lyα photons produced within the [C ii] clump as a result of large H i column densities.

Physical Constraints on the Extended Interstellar Medium of the z = 6.42 Quasar J1148+5251: [C ii]158 μm, [N ii]205 μm, and [O i]146 μm Observations

Abstract We report new Northern Extended Millimeter Array observations of the [C ii]158 μm, [N ii]205 μm, and [O i]146 μm atomic fine structure lines (FSLs) and dust continuum emission of J1148+5251, a z = 6.42 quasar, which probe the physical properties of its interstellar medium (ISM). The radially averaged [C ii]158 μm and dust continuum emission have similar extensions (up to θ = 2.51 − 0.25 + 0.46 arcsec , corresponding to r = 9.8 − 2.1 + 3.3 kpc , accounting for beam convolution), confirming that J1148+5251 is the quasar with the largest [C ii]158 μm-emitting reservoir known at these epochs. Moreover, if the [C ii]158 μm emission is examined only along its NE–SW axis, a significant excess (>5.8σ) of [C ii]158 μm emission (with respect to the dust) is detected. The new wide-bandwidth observations enable us to accurately constrain the continuum emission, and do not statistically require the presence of broad [C ii]158 μm line wings that were reported in previous studies. We also report the first detection of the [O i]146 μm and (tentatively) [N ii]205 μm emission lines in J1148+5251. Using FSL ratios of the [C ii]158 μm, [N ii]205 μm, [O i]146 μm, and previously measured [C i]369 μm emission lines, we show that J1148+5251 has similar ISM conditions compared to lower-redshift (ultra)luminous infrared galaxies. CLOUDY modeling of the FSL ratios excludes X-ray-dominated regions and favors photodissociation regions as the origin of the FSL emission. We find that a high radiation field (103.5–4.5 G 0), a high gas density (n ≃ 103.5–4.5 cm−3), and an H i column density of 1023 cm−2 reproduce the observed FSL ratios well.

Constraining Galaxy Overdensities around Three z ∼ 6.5 Quasars with ALMA and MUSE

Abstract We quantify galaxy overdensities around three high-redshift quasars with known [C ii]158 μm companions: PJ231–20 (z = 6.59), PJ308–21 (z = 6.24), and J0305–3150 (z = 6.61). Recent SCUBA2 imaging revealed the presence of 17 submillimeter galaxies (SMGs) with sky separations 0.′7 < θ < 2.′4 from these three quasars. We present ALMA Band 6 follow-up observations of these SCUBA2-selected SMGs to confirm their nature and redshift. We also search for continuum-undetected [C ii]158 μm emitters in the ALMA pointings and make use of archival MUSE observations to search for Lyα emitters (LAEs) associated with the quasars. While most of the SCUBA2-selected sources are detected with ALMA in the continuum, no [C ii]158 μm line emission could be detected, indicating that they are not at the quasar redshifts. Based on the serendipitous detection of CO 7–6 and [C i]809 μm emission lines, we find that four SMGs in the field of PJ231–20 are at z ∼ 2.4, which is coincident with the redshift of an Mg ii absorber in the quasar rest-frame UV spectrum. We report the discovery of two LAEs within <0.6 cMpc of PJ231–20 at the same redshift, indicating an LAE overdensity around this quasar. Taken together, these observations provide new constraints on the large-scale excess of Lyα- and [C ii]158 μm-emitting galaxies around z > 6 quasars and suggest that only wide-field observations, such as MUSE, ALMA, or JWST mosaics, can reveal a comprehensive picture of large-scale structure around quasars in the first billion years of the universe.

C II] 158 μm line emission from Orion A

Context. The [C II] 158 μm fine-structure line is the dominant cooling line of moderate-density photodissociation regions (PDRs) illuminated by moderately bright far-ultraviolet (FUV) radiation fields. This makes this line a prime diagnostic for extended regions illuminated by massive stars. Aims. We aim to understand the origin of [C II] emission and its relation to other tracers of gas and dust in PDRs. One focus is a study of the heating efficiency of interstellar gas as traced by the [C II] line to test models of the photoelectric heating of neutral gas by polycyclic aromatic hydrocarbon (PAH) molecules and very small grains. Methods. We make use of a one-square-degree map of velocity-resolved [C II] line emission toward the Orion Nebula complex, and split this out into the individual spatial components, the expanding Veil Shell, the surface of OMC4, and the PDRs associated with the compact H II region of M43 and the reflection nebula NGC 1977. We employed Herschel far-infrared photometric images to determine dust properties. Moreover, we compared with Spitzer mid-infrared photometry to trace hot dust and large molecules, and velocity-resolved IRAM 30m CO(2–1) observations of the molecular gas. Results. The [C II] intensity is tightly correlated with PAH emission in the IRAC 8 μm band and far-infrared emission from warm dust, with small variations between the four studied subregions (Veil Shell, OMC4, M43, and NGC 1977). The correlation between [C II] and CO(2-1) is very different in the four subregions and is very sensitive to the detailed geometry of the respective regions. Constant-density PDR models are able to reproduce the observed [C II], CO(2–1), and integrated far-infrared (FIR) intensities. The physical conditions in the Veil Shell of the Orion Nebula, M43, and NGC 1977 reveal a constant ratio of thermal pressure pth over incident FUV radiation field measured by G0. We observe strong variations in the photoelectric heating efficiency in the Veil Shell behind the Orion Bar and these variations are seemingly not related to the spectral properties of the PAHs. Conclusions. The [C II] emission from the Orion Nebula complex stems mainly from moderately illuminated PDR surfaces. The correlations of the different tracers ([C II], FIR, CO, 70 μm, and 8 μm emission) show small variations that are not yet understood. Future observations with the James Webb Space Telescope can shine light on the PAH properties that may be linked to these variations.

Measuring the H i Content of Individual Galaxies Out to the Epoch of Reionization with [C ii

Abstract The H i gas content is a key ingredient in galaxy evolution, the study of which has been limited to moderate cosmological distances for individual galaxies due to the weakness of the hyperfine H i 21 cm transition. Here we present a new approach that allows us to infer the H i gas mass M HI of individual galaxies up to z ≈ 6, based on a direct measurement of the [C ii]-to-H i conversion factor in star-forming galaxies at z ≳ 2 using γ-ray burst afterglows. By compiling recent [C ii]-158 μm emission line measurements we quantify the evolution of the H i content in galaxies through cosmic time. We find that M HI starts to exceed the stellar mass M ⋆ at z ≳ 1, and increases as a function of redshift. The H i fraction of the total baryonic mass increases from around 20% at z = 0 to about 60% at z ∼ 6. We further uncover a universal relation between the H i gas fraction M HI/M ⋆ and the gas-phase metallicity, which seems to hold from z ≈ 6 to z = 0. The majority of galaxies at z > 2 are observed to have H i depletion times, t dep,HI = M HI/SFR, less than ≈2 Gyr, substantially shorter than for z ∼ 0 galaxies. Finally, we use the [C ii]-to-H i conversion factor to determine the cosmic mass density of H i in galaxies, ρ HI, at three distinct epochs: z ≈ 0, z ≈ 2, and z ∼ 4–6. These measurements are consistent with previous estimates based on 21 cm H i observations in the local universe and with damped Lyα absorbers (DLAs) at z ≳ 2, suggesting an overall decrease by a factor of ≈5 in ρ HI(z) from the end of the reionization epoch to the present.

Exploring the dust content of galactic haloes with Herschel – IV. NGC 3079

ABSTRACT We present the results from an analysis of deep Herschel far-infrared (far-IR) observations of the edge-on disc galaxy NGC 3079. The point spread function-cleaned Photodetector Array Camera and Spectrometer (PACS) images at 100 and 160 µm display a 25 × 25 kpc2 X-shape structure centred on the nucleus that is similar in extent and orientation to that seen in H α, X-rays, and the far-ultraviolet. One of the dusty filaments making up this structure is detected in the Spectral and Photometric Imaging Receiver 250 µm map out to ∼25 kpc from the nucleus. The match between the far-IR filaments and those detected at other wavelengths suggests that the dusty material has been lifted out of the disc by the same large-scale galactic wind that has produced the other structures in this object. A closer look at the central 10 × 10 kpc2 region provides additional support for this scenario. The dust temperatures traced by the 100–160 µm flux ratios in this region are enhanced within a biconical region centred on the active galactic nucleus, aligned along the minor axis of the galaxy, and coincident with the well-known double-lobed cm-wave radio structure and H α–X-ray nuclear superbubbles. PACS imaging spectroscopy of the inner 6 kpc region reveals broad [C ii] 158 µm emission line profiles and OH 79 µm absorption features along the minor axis of the galaxy with widths well in excess of those expected from beam smearing of the disc rotational motion. This provides compelling evidence that the cool material traced by the [C ii] and OH features directly interacts with the nuclear ionized and relativistic outflows traced by the H α, X-ray, and radio emission.

ALMA Observations of Lyα Blob 1: Multiple Major Mergers and Widely Distributed Interstellar Media

Abstract We present observations of a giant Lyα blob (LAB) in the SSA22 protocluster at z = 3.1, SSA22-LAB1, taken with the Atacama Large Millimeter/submillimeter Array. Dust continuum, along with [C ii] 158 μm and CO(4–3) line emission have been detected in LAB1, showing complex morphology and kinematics across a ∼100 kpc central region. Seven galaxies at z = 3.0987–3.1016 in the surroundings are identified in [C ii] and dust continuum emission, with two of them potential companions or tidal structures associated with the most massive galaxies. Spatially resolved [C ii] and infrared luminosity ratios for the widely distributed media (L [Cɪɪ]/L IR ≈ 10−2−10−3) suggest that the observed extended interstellar media are likely to have originated from star formation activity and the contribution from shocked gas is probably not dominant. LAB1 is found to harbor a total molecular gas mass M mol = (8.7 ± 2.0) × 1010 M ⊙, concentrated in the core region of the Lyα-emitting area. While (primarily obscured) star formation activity in the LAB1 core is one of the most plausible power sources for the Lyα emission, multiple major mergers found in the core may also play a role in making LAB1 exceptionally bright and extended in Lyα as a result of cooling radiation induced by gravitational interactions.

The ALPINE-ALMA [CII] survey

Context. Galaxy mergers are thought to be one of the main mechanisms of the mass assembly of galaxies in the Universe, but there is still little direct observational evidence of how frequent they are at z ≳ 4. Recently, many works have suggested a possible increase in the fraction of major mergers in the early Universe, reviving the debate on which processes (e.g., cold accretion, star formation, mergers) most contribute to the mass build-up of galaxies through cosmic time. Aims. To estimate the importance of major mergers in this context, we make use of the new data collected by the ALMA Large Program to INvestigate [CII] at Early times (ALPINE) survey, which attempted to observe the [CII] 158 μm emission line from a sample of 75 main-sequence star-forming galaxies at 4.4 < z < 5.9. Methods. We used, for the first time, the morpho-kinematic information provided by the [CII] emission, along with archival multiwavelength data to obtain the fraction of major mergers (fMM) at z ∼ 5. By combining the results from ALPINE with those at lower redshifts from the literature, we also studied the evolution of the merger fraction through cosmic time. We then used different redshift-evolving merger timescales (TMM) to convert this fraction into the merger rate per galaxy (RMM) and in the volume-averaged merger rate (ΓMM). Results. We find a merger fraction of fMM ∼ 0.44 (0.34) at z ∼ 4.5 (5.5) from ALPINE. By combining our results with those at lower redshifts, we computed the cosmic evolution of the merger fraction which is described by a rapid increase from the local Universe to higher redshifts, a peak at z ∼ 3, and a slow decrease toward earlier epochs. Depending on the timescale prescription used, this fraction translates into a merger rate ranging between ∼0.1 and ∼4.0 Gyr−1 at z ∼ 5, which in turn corresponds to an average number of major mergers per galaxy between 1 and 8 in ∼12.5 yr (from z = 6 to the local Universe). When convolved with the galaxy number density at different epochs, the merger rate density becomes approximately constant over time at 1 < z < 4, including values from 10−4 to 10−3 Gyr−1 Mpc−3, depending on the assumed TMM. We finally compare the specific star formation and star-formation rate density with the analogous quantities from major mergers, finding a good agreement at z > 4 if we assume a merger timescale that quickly decreases with increasing redshift. Conclusions. Our new constraints on the merger fraction from the ALPINE survey at z ∼ 5 reveal the presence of a significant merging activity in the early Universe. Whether this population of mergers can provide a relevant contribution to the galaxy mass assembly at these redshifts and through the cosmic epochs is strongly dependent on the assumption of the merger timescale. However, our results show that an evolving TMM ∝ (1 + z)−2 agrees well with state-of-the-art cosmological simulations, suggesting a considerable role of mergers in the build-up of galaxies at early times.

Interstellar Cloud Conditions Based on 63 μm [O i] Emission and Absorption in W3

Abstract We investigate the origin of self-absorption in [O i] 63 μm line emission, which is very clearly seen in approximately half of the 12 Galactic giant molecular cloud (GMC)/H ii regions observed. For this study, we observed velocity-resolved spectra of photon-dominated region (PDR) and H ii region tracers, the [O i] 63 μm, [N ii] 205 μm, and CO J = 5–4 and 8–7 lines, with the upGREAT instrument in the 4GREAT configuration on the NASA/DLR Stratospheric Observatory For Infrared Astronomy (SOFIA). To probe the origin of the [O i] absorption and line shape and what they tell us about the physical conditions, we focus on the W3 region, for which we obtained data for eight positions along a line near the H ii region W3 A. We derive the foreground column density of low-excitation atomic oxygen to be in the range 2–7 × 1018 cm − 2 . At the position of strongest [O i] emission and greatest absorbing column density, 24% of the oxygen in the PDR is in the form of low-excitation atomic oxygen. We employ the Meudon PDR code to study the chemical and thermal structure of the PDR and to understand the large column density of neutral oxygen throughout the PDR. The reduction in the integrated intensity of the [O i] 63 μm emission is a factor of ≃2–4 in directions with strong [O i] emission. The results from our sample, if general, would significantly impact the use of the [O i] 63 μm line as a tracer of massive star formation and could play a significant role in explaining the “63 μm [O i] deficit” seen in very luminous extragalactic sources.

The dense warm ionized medium in the inner Galaxy

Context. Ionized interstellar gas is an important component of the interstellar medium and its lifecycle. The recent evidence for a widely distributed highly ionized warm interstellar gas with a density intermediate between the warm ionized medium (WIM) and compact H II regions suggests that there is a major gap in our understanding of the interstellar gas. Aims. Our goal is to investigate the properties of the dense WIM in the Milky Way using spectrally resolved SOFIA GREAT [N II] 205 μm fine-structure lines and Green Bank Telescope hydrogen radio recombination lines (RRL) data, supplemented by spectrally unresolved Herschel PACS [N II] 122μm data, and spectrally resolved 12CO. Methods. We observed eight lines of sight (LOS) in the 20° < l < 30° region in the Galactic plane. We analyzed spectrally resolved lines of [N II] at 205 μm and RRL observations, along with the spectrally unresolved Herschel PACS 122 μm emission, using excitation and radiative transfer models to determine the physical parameters of the dense WIM. We derived the kinetic temperature, as well as the thermal and turbulent velocity dispersions from the [N II] and RRL linewidths. Results. The regions with [N II] 205 μm emission are characterized by electron densities, n(e) ~ 10−35 cm−3, temperatures range from 3400 to 8500 K, and nitrogen column densities N(N+) ~ 7 × 1016 to 3 × 1017 cm−2. The ionized hydrogen column densities range from 6 × 1020 to 1.7 × 1021 cm−2 and the fractional nitrogen ion abundance x(N+) ~ 1.1 × 10−4 to 3.0 × 10−4, implying an enhanced nitrogen abundance at a distance ~4.3 kpc from the Galactic Center. The [N II] 205 μm emission lines coincide with CO emission, although often with an offset in velocity, which suggests that the dense warm ionized gas is located in, or near, star-forming regions, which themselves are associated with molecular gas. Conclusions. These dense ionized regions are found to contribute ≳50% of the observed [C II] intensity along these LOS. The kinetic temperatures we derive are too low to explain the presence of N+ resulting from electron collisional ionization and/or proton charge transfer of atomic nitrogen. Rather, these regions most likely are ionized by extreme ultraviolet (EUV) radiation from nearby star-forming regions or as a result of EUV leakage through a clumpy and porous interstellar medium.

Launching the asymmetric bipolar jet of DO Tau

Context. The role of bipolar jets in the formation of stars, and in particular how they are launched, is still not well understood. Aims. We probe the protostellar jet launching mechanism using high-resolution observations of the near-infrared (IR) [Fe II]λ1.53,1.64 μm emission lines. Methods. We consider the case of the bipolar jet from Classical T Tauri star, DO Tau, and investigate the jet morphology and kinematics close to the star (within 140 au) using AO-assisted IFU observations from GEMINI/NIFS. Results. We find that the brighter, blueshifted jet is collimated very quickly after it is launched. This early collimation requires the presence of magnetic fields. We confirm velocity asymmetries between the two lobes of the bipolar jet, and also confirm no time variability in the asymmetry over a 20-year interval. This sustained asymmetry is in accordance with recent simulations of magnetised disc winds. We examine the data for signatures of jet rotation. We report an upper limit on differences in radial velocity of 6.3 and 8.7 km s−1 for the blue- and redshifted jets, respectively. Interpreting this as an upper limit on jet rotation implies that any steady, axisymmetric magneto-centrifugal model of jet launching is constrained to a launch radius in the disc plane of r0 < 0.5 and 0.3 au for the blue- and redshifted jets, respectively. This supports an X-wind or narrow disc-wind model. However, the result pertains only to the observed high-velocity [Fe II] emission, and does not rule out a wider flow launched from a wider radius. We report the detection of small-amplitude jet axis wiggling in both lobes. We rule out orbital motion of the jet source as the cause. Precession can better account for the observations but requires double the precession angle, and a different phase for the counter-jet. Such non-solid body precession could arise from an inclined massive Jupiter companion, or a warping instability induced by launching a magnetic disc wind. Conclusions. Overall, our observations are consistent with an origin of the DO Tau jets from the inner regions of the disc.

Evolution of the atomic component in protostellar outflows

Context. We present SOFIA/FIFI-LS observations of three Class 0 and one Class I outflows (Cep E, HH 1, HH 212, and L1551 IRS5) in the far-infrared [O I]63 μm and [O I]145 μm transitions. Spectroscopic [O I]63 μm maps enabled us to infer the spatial extent of warm (T ∼ 500−1200 K), low-excitation atomic gas within these protostellar outflows. Aims. Our main goal is to determine mass-loss rates from the obtained [OI]63 μm maps and compare these with accretion rates from other studies. Methods. The far-infrared [O I]63 μm emission line is predicted to be the main coolant of dense, dissociative J-shocks caused by decelerated wind or jet shocks. If proper shock conditions prevail, the instantaneous mass-ejection rate is directly connected to the [O I]63 μm luminosity. In order to unravel evolutionary trends, we analysed a set of 14 Class 0/I outflow sources that were spatially resolved in the [O I]63 emission. We compared these data with a sample of 72 Class 0/I/II outflow sources that have been observed with Herschel (WISH, DIGIT, WILL, GASPS surveys) without spatially resolving the [O I]63 μm line. Results. All our newly observed targets feature prominent [O I]63μm emission either close to the driving source (L1551 IRS5, HH 1, HH 212) or as extended jet-like or knotty emission region away from it (Cep E). The detected [O I]63 μm emission can mostly be attributed to dissociative shocks and photodissociation regions (PDRs). Flux values at 63 μm and 145 μm of all four associated continuum sources are presented. We calculated mass-loss rates connected to the low-excitation, atomic outflow component in the range of (5−50)×10−7 M⊙ yr−1. Estimated ratios between the mass loss in the outflow and the mass accretion onto the source (jet efficiency ratios) are largely in the range of Ṁout/Ṁacc ∼ 0.05 − 0.5 for the observed outflow sources, which are consistent with theoretical predictions and quoted Herschel data. Conclusions. Our new observations and a comparison with the 72 outflow sources observed with Herschel indicate that the bulk ejected material in outflows from Class 0 sources resides in the molecular component, that is mass-loss rates derived from the [O I]63 emission line significantly underestimate the total mass-loss rate during this and possibly also later phases of the star formation process.

Dust temperature in ALMA [C ii]-detected high-z galaxies

ABSTRACT At redshift z > 5, the far-infrared (FIR) continuum spectra of main-sequence galaxies are sparsely sampled, often with a single data point. The dust temperature Td,SED, thus has to be assumed in the FIR continuum fitting. This introduces large uncertainties regarding the derived dust mass (Md), FIR luminosity, and obscured fraction of the star formation rate. These are crucial quantities to quantify the effect of dust obscuration in high-z galaxies. To overcome observation limitations, we introduce a new method that combines dust continuum information with the overlying [C $\scriptstyle \rm II$] 158 µm line emission. By breaking the Md–Td,SED degeneracy, with our method, we can reliably constrain the dust temperature with a single observation at 158 µm. This method can be applied to all Atacama Large Millimeter Array (ALMA) and NOEMA [C $\scriptstyle \rm II$] observations, and exploited in ALMA Large Programs such as ALPINE and REBELS targeting [C $\scriptstyle \rm II$] emitters at high-z. We also provide a physical interpretation of the empirical relation recently found between molecular gas mass and [C $\scriptstyle \rm II$] luminosity. We derive an analogous relation linking the total gas surface density and [C $\scriptstyle \rm II$] surface brightness. By combining the two, we predict the cosmic evolution of the surface density ratio $\Sigma _{\rm H_2} / \Sigma _{\rm gas}$. We find that $\Sigma _{\rm H_2} / \Sigma _{\rm gas}$ slowly increases with redshift, which is compatible with current observations at 0 < z < 4.

Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). XII. Extended [C ii] Structure (Merger or Outflow) in a z = 6.72 Red Quasar

Abstract We present Atacama Large Millimeter/submillimeter Array [C ii] 158 μm line and far-infrared (FIR) continuum emission observations toward HSC J120505.09−000027.9 (J1205−0000) at z = 6.72 with a beam size of ∼0.″8 × 0.″5 (or 4.1 kpc × 2.6 kpc), the most distant red quasar known to date. Red quasars are modestly reddened by dust and are thought to be in rapid transition from an obscured starburst to an unobscured normal quasar, driven by powerful active galactic nucleus (AGN) feedback that blows out a cocoon of interstellar medium. The FIR continuum of J1205−0000 is bright, with an estimated luminosity of L FIR ∼ 3 × 1012 L ⊙. The [C ii] line emission is extended on scales of r ∼ 5 kpc, greater than that of the FIR continuum. The line profiles at the extended regions are complex and broad (FWHM ∼ 630–780 km s−1). Although it is not practical to identify the nature of this extended structure, possible explanations include (i) companion/merging galaxies and (ii) massive AGN-driven outflows. For the case of (i), the companions are modestly star-forming (∼10 M ⊙ yr−1) but are not detected by our Subaru optical observations (y AB,5σ = 24.4 mag). For the case of (ii), our lower limit to the cold neutral outflow rate is ∼100 M ⊙ yr−1. The outflow kinetic energy and momentum are both much lower than predicted in energy-conserving wind models, suggesting that the AGN feedback in this quasar is not capable of completely suppressing its star formation.

A puzzling non-detection of [O III] and [C II] from a z ≈ 7.7 galaxy observed with ALMA

Context. Characterizing the galaxy population in the early Universe holds the key to understanding the evolution of these objects and the role they played in cosmic reionization. However, there have been very few observations at the very highest redshifts to date. Aims. In order to shed light on the properties of galaxies in the high-redshift Universe and their interstellar media, we observe the Lyman-α emitting galaxy z7_GSD_3811 at z = 7.664 with bands 6 and 8 at the Atacama Large Millimeter/submillimeter Array (ALMA). Methods. We target the far-infrared [O III] 88 μm and [C II] 158 μm emission lines and dust continuum in the star-forming galaxy z7_GSD_3811 with ALMA. We combine these measurements with earlier observations in the rest-frame ultraviolet (UV) in order to characterize the object and compare the results to those of earlier studies that observed [O III] and [C II] emission in high-redshift galaxies. Results. The [O III] 88 μm and [C II] 158 μm emission lines are undetected at the position of z7_GSD_3811, with 3σ upper limits of 1.6 × 108 L⊙ and 4.0 × 107 L⊙, respectively. We do not detect any dust continuum in band 6 nor band 8. The measured rms in the band 8 and band 6 continua are 26 and 9.9 μJy beam−1, respectively. Similar to several other high-redshift galaxies, z7_GSD_3811 exhibits low [C II] emission for its star formation rate compared to local galaxies. Furthermore, our upper limit on the [O III] line luminosity is lower than the previously observed [O III] lines in high-redshift galaxies with similar UV luminosities. Our ALMA band 6 and 8 dust continuum observations imply that z7_GSD_3811 likely has a low dust content, and our non-detections of the [O III] and [C II] lines could indicate that z7_GSD_3811 has a low metallicity (Z ≲ 0.1 Z⊙).

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

Context. Atomic fine structure lines have been detected in the local Universe and at high redshifts over the past decades. The [C II] emission line at 158 μm is an important observable as it provides constraints on the interstellar medium (ISM) cooling processes. Aims. We develop a physically motivated framework to simulate the production of far-infrared line emission from galaxies in a cosmological context. This first paper sets out our methodology and describes its first application: simulating the [C II] 158 μm line emission in the local Universe. Methods. We combine the output from EAGLE cosmological hydrodynamical simulations with a multi-phase model of the ISM. Gas particles are divided into three phases: dense molecular gas, neutral atomic gas, and diffuse ionised gas (DIG). We estimate the [C II] line emission from the three phases using a set of CLOUDY cooling tables. Results. Our results agree with previous findings regarding the contribution of these three ISM phases to the [C II] emission. Our model shows good agreement with the observed L[C II–star formation rate (SFR) relation in the local Universe within 0.4 dex scatter. Conclusions. The fractional contribution to the [C II] line from different ISM phases depends on the total SFR and metallicity. The neutral gas phase dominates the [C II] emission in galaxies with SFR ∼ 0.01–1 M⊙ yr−1, but the ionised phase dominates at lower SFRs. Galaxies above solar metallicity exhibit lower L[C II/SFR ratios for the neutral phase. In comparison, the L[C II/SFR ratio in the DIG is stable when metallicity varies. We suggest that the reduced size of the neutral clouds, caused by increased SFRs, is the likely cause for the L[C II deficit at high infrared luminosities, although EAGLE simulations do not reach these luminosities at z = 0.

No Evidence for [C ii] Halos or High-velocity Outflows in z ≳ 6 Quasar Host Galaxies

Abstract We study the interstellar medium in a sample of 27 high-redshift quasar host galaxies at z ≳ 6, using the [C ii] 158 μm emission line and the underlying dust continuum observed at ∼1 kpc resolution with Atacama Large Millimeter Array. By performing uv-plane spectral stacking of both the high and low spatial resolution data, we investigate the spatial and velocity extent of gas and the size of the dust-emitting regions. We find that the average surface brightness profile of both the [C ii] and the dust continuum emission can be described by a steep component within a radius of 2 kpc and a shallower component with a scale length of 2 kpc, detected up to ∼10 kpc. The surface brightness of the extended emission drops below ∼1% of the peak at radius of ∼5 kpc, beyond which it constitutes 10%–20% of the total measured flux density. Although the central component of the dust continuum emission is more compact than that of the [C ii] emission, the extended components have equivalent profiles. The observed extended components are consistent with those predicted by hydrodynamical simulations of galaxies with similar infrared luminosities, where the dust emission is powered by star formation. The [C ii] spectrum measured in the mean uv-plane stacked data can be described by a single Gaussian, with no observable [C ii] broad-line emission (velocities in excess of ≳500 km s−1), which would be indicative of outflows. Our findings suggest that we are probing the interstellar medium and associated star formation in the quasar host galaxies up to radii of 10 kpc, whereas we find no evidence for halos or outflows.