Photodissociation and X-Ray-Dominated Regions Wolfire, Mark G; Vallini, Livia; Chevance, Mélanie
Annual review of astronomy and astrophysics,
08/2022, Letnik:
60, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The radiation from stars and active galactic nuclei (AGNs) creates photodissociation regions (PDRs) and X-ray-dominated regions (XDRs), where the chemistry or heating is dominated by far-ultraviolet ...(FUV) radiation or X-ray radiation, respectively. PDRs include a wide range of environments, from the diffuse interstellar medium (ISM) to dense star-forming regions. XDRs are found in the center of galaxies hosting AGNs, in protostellar disks, and in the vicinity of X-ray binaries. In this review, we describe the dominant thermal, chemical, and radiation transfer processes in PDRs and XDRs, as well as give a brief description of models and their use for analyzing observations. We then present recent results from Milky Way, nearby extragalactic, and high-redshift observations.
Several important results include the following:
Predicting FIR lines from simulated galaxies Lupi, Alessandro; Pallottini, Andrea; Ferrara, Andrea ...
Monthly notices of the Royal Astronomical Society,
08/2020, Letnik:
496, Številka:
4
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
Far-infrared (FIR) emission lines are a powerful tool to investigate the properties of the interstellar medium, especially in high-redshift galaxies, where ALMA observations have provided ...unprecedented information. Interpreting such data with state-of-the-art cosmological simulations post-processed with cloudy, has provided insights on the internal structure and gas dynamics of these systems. However, no detailed investigation of the consistency and uncertainties of this kind of analysis has been performed to date. Here, we compare different approaches to estimate FIR line emission from state-of-the-art cosmological simulations, either with cloudy or with on-the-fly non-equilibrium chemistry. We find that C ii158μ predictions are robust to the model variations we explored. O i emission lines, that typically trace colder and denser gas relative to C ii158μ, are instead model dependent, as these lines are strongly affected by the thermodynamic state of the gas and non-equilibrium photoionization effects. For the same reasons, O i lines represent an excellent tool to constrain emission models, hence future observations targeting these lines will be crucial.
Abstract
We present our new Atacama Large Millimeter/submillimeter Array (ALMA) observations targeting CO(6–5) emission from three luminous Lyman-break galaxies (LBGs) at
z
spec
= 6.0293–6.2037 found ...in the Subaru/Hyper Suprime-Cam survey, whose O
iii
88
μ
m and C
ii
158
μ
m emissions have been detected with ALMA. We find a marginal detection of the CO(6–5) line from one of our LBGs, J0235–0532, at the ≃4
σ
significance level and obtain upper limits for the other two LBGs, J1211–0118 and J0217–0208. Our
z
= 6 luminous LBGs are consistent with the previously found correlation between the CO luminosity and the infrared luminosity. The unique ensemble of the multiple far-infrared emission lines and underlying continuum fed to a photodissociation region model reveals that J0235–0532 has a relatively high density of hydrogen nuclei
n
H
that is comparable to those of low-
z
(U)LIRGs, quasars, and Galactic star-forming regions with high
n
H
values, while the other two LBGs have lower
n
H
consistent with local star-forming galaxies. By carefully taking account of various uncertainties, we obtain constraints on total gas mass and gas surface density from their CO luminosity measurements. We find that J0235–0532 is located below the Kennicutt–Schmidt (KS) relation, comparable to the
z
= 5.7 LBG, HZ10, previously detected with CO(2–1). Combined with previous results for dusty starbursts at similar redshifts, the KS relation at
z
= 5–6 is on average consistent with the local one.
We present the first C II 158 μm luminosity function (LF) at z ∼ 5 from a sample of serendipitous lines detected in the ALMA Large Program to INvestigate C II at Early times (ALPINE). A study of the ...118 ALPINE pointings revealed several serendipitous lines. Based on their fidelity, we selected 14 lines for the final catalog. According to the redshift of their counterparts, we identified eight out of 14 detections as C II lines at z ∼ 5, along with two as CO transitions at lower redshifts. The remaining four lines have an elusive identification in the available catalogs and we considered them as C II candidates. We used the eight confirmed C II and the four C II candidates to build one of the first C II LFs at z ∼ 5. We found that 11 out of these 12 sources have a redshift very similar to that of the ALPINE target in the same pointing, suggesting the presence of overdensities around the targets. Therefore, we split the sample in two (a “clustered” and “field” subsample) according to their redshift separation and built two separate LFs. Our estimates suggest that there could be an evolution of the C II LF between z ∼ 5 and z ∼ 0. By converting the C II luminosity to the star-formation rate, we evaluated the cosmic star-formation rate density (SFRD) at z ∼ 5. The clustered sample results in a SFRD ∼10 times higher than previous measurements from UV–selected galaxies. On the other hand, from the field sample (likely representing the average galaxy population), we derived a SFRD ∼1.6 higher compared to current estimates from UV surveys but compatible within the errors. Because of the large uncertainties, observations of larger samples will be necessary to better constrain the SFRD at z ∼ 5. This study represents one of the first efforts aimed at characterizing the demography of C II emitters at z ∼ 5 using a mm selection of galaxies.
Abstract
The recent discovery of dusty galaxies well into the Epoch of Reionization (redshift z > 6) poses challenging questions about the properties of the interstellar medium in these pristine ...systems. By combining state-of-the-art hydrodynamic and dust radiative transfer simulations, we address these questions focusing on the recently discovered dusty galaxy A2744_YD4 (z = 8.38, Laporte et al.). We show that we can reproduce the observed spectral energy distribution (SED) only using different physical values with respect to the inferred ones by Laporte et al., i.e. a star formation rate of SFR = 78 $\mathrm{M}_{\odot } \rm yr^{-1}$, a factor ≈4 higher than deduced from simple SED fitting. In this case, we find: (i) dust attenuation (corresponding to τV = 1.4) is consistent with a Milky Way (MW) extinction curve; (ii) the dust-to-metal ratio is low, fd ∼ 0.08, implying that early dust formation is rather inefficient; (iii) the luminosity-weighted dust temperature is high, $T_{\rm d}=91\pm 23\, \rm K$, as a result of the intense (≈100 × MW) interstellar radiation field; and (iv) due to the high Td, the Atacama Large Millimeter/submillimeter Array Band 7 detection can be explained by a limited dust mass, Md = 1.6 × 106 M⊙. Finally, the high dust temperatures might solve the puzzling low infrared excess (IRX) recently deduced for high-z galaxies from the IRX–β relation.
We study the formation and evolution of a sample of Lyman break galaxies in the epoch of reionization by using high-resolution (similar to 10 pc), cosmological zoom-in simulations part of the SERRA ...suite. In SERRA, we follow the interstellar medium thermochemical non-equilibrium evolution and perform on-the-fly radiative transfer of the interstellar radiation field (ISRF). The simulation outputs are post-processed to compute the emission of far infrared lines (C II, N II, and O III). At z = 8, the most massive galaxy, 'Freesia', has an age t(star) similar or equal to 409 Myr, stellar mass M-star similar or equal to 4.2 x 10(9)M(circle dot), and a star formation rate (SFR), SFR similar or equal to 11.5M(circle dot) yr(-1), due to a recent burst. Freesia has two stellar components (A and B) separated by similar or equal to 2.5 kpc; other 11 galaxies are found within 56.9 +/- 21.6 kpc. The mean ISRF in the Habing band is G = 7.9G(0) and is spatially uniform; in contrast, the ionization parameter is U = 2(-2)(+20) x 10(-3), and has a patchy distribution peaked at the location of star-forming sites. The resulting ionizing escape fraction from Freesia is f(esc) similar or equal to 2 per cent. While C II emission is extended (radius 1.54 kpc), O III is concentrated in Freesia-Lambda (0.85 kpc), where the ratio Sigma(O III)/Sigma(C II) similar or equal to 10. As many high-z galaxies, Freesia lies below the local C II-SFR relation. We show that this is the general consequence of a starburst phase (pushing the galaxy above the Kennicutt-Schmidt relation) that disrupts/photodissociates the emitting molecular clouds around star-forming sites. Metallicity has a sub-dominant impact on the amplitude of C II-SFR deviations.
Abstract
With the aim of improving predictions on far-infrared (FIR) line emission from Giant Molecular Clouds (GMCs), we study the effects of photoevaporation (PE) produced by external ...far-ultraviolet (FUV) and ionizing (extreme-ultraviolet) radiation on GMC structure. We consider three different GMCs with mass in the range MGMC = 103-106 M⊙. Our model includes (i) an observationally based inhomogeneous GMC density field, and (ii) its time evolution during the PE process. In the fiducial case (MGMC ≈ 105 M⊙), the PE time (tpe) increases from 1 to 30 Myr for gas metallicity Z = 0.05–1 Z⊙, respectively. Next, we compute the time-dependent luminosity of key FIR lines tracing the neutral and ionized gas layers of the GMCs, (C ii at 158 μm, O iii at 88 μm) as a function of G0, and Z until complete PE at tpe. We find that the specific C ii luminosity is almost independent of the GMC model within the survival time of the cloud. Stronger FUV fluxes produce higher C ii and O iii luminosities, however, lasting for progressively shorter times. At Z = Z⊙, the C ii emission is maximized ($L_{\rm C\,\small {II}} \approx 10^4\,\rm {L_{{\odot }}}$ for the fiducial model) for t < 1 Myr and log G0 ≥ 3. Noticeably, and consistently with the recent detection by Inoue et al. of a galaxy at redshift z ≈ 7.2, for Z ≤ 0.2 Z⊙, the O iii line might outshine C ii emission by up to ≈1000 times. We conclude that the O iii line is a key diagnostic of low-metallicity interstellar medium, especially in galaxies with very young stellar populations.
ABSTRACT
A tight relation between the C ii 158 $\mu$m line luminosity and star formation rate is measured in local galaxies. At high redshift (z > 5), though, a much larger scatter is observed, with ...a considerable (15–20 per cent) fraction of the outliers being C ii-deficient. Moreover, the C ii surface brightness ($\Sigma_{\rm C\, \small {II}}$) of these sources is systematically lower than expected from the local relation. To clarify the origin of such C ii-deficiency, we have developed an analytical model that fits local C ii data and has been validated against radiative transfer simulations performed with cloudy. The model predicts an overall increase of $\Sigma_{\rm C\, \small {II}}$ with ΣSFR. However, for ΣSFR ${\gtrsim} 1 \, \mathrm{M}_\odot \,{\rm yr}^{-1}\,{\rm kpc}^{-2}$, $\Sigma_{\rm C\, \small {II}}$ saturates. We conclude that underluminous C ii systems can result from a combination of three factors: (a) large upward deviations from the Kennicutt–Schmidt relation (κs ≫ 1), parametrized by the ‘burstiness’ parameter κs; (b) low metallicity; (c) low gas density, at least for the most extreme sources (e.g. CR7). Observations of C ii emission alone cannot break the degeneracy among the above three parameters; this requires additional information coming from other emission lines (e.g. O iii88 $\mu$m, C iii1909 Å, CO lines). Simple formulae are given to interpret available data for low- and high-z galaxies.
Abstract
We study the CO line luminosity (LCO), the shape of the CO spectral line energy distribution (SLED), and the value of the CO-to-H2 conversion factor in galaxies in the Epoch of Reionization ...(EoR). For this aim, we construct a model that simultaneously takes into account the radiative transfer and the clumpy structure of giant molecular clouds (GMCs) where the CO lines are excited. We then use it to post-process state-of-the-art zoomed, high resolution (30 pc), cosmological simulation of a main-sequence (M* ≈ 1010 M⊙, SFR ≈ 100 M⊙ yr− 1) galaxy, ‘Althæa’, at z ≈ 6. We find that the CO emission traces the inner molecular disc (r ≈ 0.5 kpc) of Althæa with the peak of the CO surface brightness co-located with that of the C$\, \scriptstyle \rm II$ 158 μm emission. Its LCO(1-0) = 104.85 L⊙ is comparable to that observed in local galaxies with similar stellar mass. The high (Σgas ≈ 220 M⊙ pc− 2) gas surface density in Althæa, its large Mach number ($\mathcal {M}$ ≈ 30) and the warm kinetic temperature (Tk ≈ 45 K) of GMCs yield a CO SLED peaked at the CO(7–6) transition, i.e. at relatively high-J and a CO-to-H2 conversion factor $\alpha _{\rm CO}\approx 1.5 \, \rm M_{{\odot }} \rm (K\, km\, s^{-1}\, pc^2)^{-1}$ lower than that of the Milky Way. The Atacama Large Millimeter/submillimeter Array observing time required to detect (resolve) at 5σ the CO(7–6) line from galaxies similar to Althæa is ≈13 h (≈38 h).
ABSTRACT
We study the kinematical properties of galaxies in the Epoch of Reionization via the C ii158 μm line emission. The line profile provides information on the kinematics as well as structural ...properties such as the presence of a disc and satellites. To understand how these properties are encoded in the line profile, first we develop analytical models from which we identify disc inclination and gas turbulent motions as the key parameters affecting the line profile. To gain further insights, we use ‘Althæa’, a highly resolved ($30\, \rm pc$) simulated prototypical Lyman-break galaxy, in the redshift range z = 6–7, when the galaxy is in a very active assembling phase. Based on morphology, we select three main dynamical stages: (I) merger, (II) spiral disc, and (III) disturbed disc. We identify spectral signatures of merger events, spiral arms, and extra-planar flows in (I), (II), and (III), respectively. We derive a generalized dynamical mass versus C ii-line FWHM relation. If precise information on the galaxy inclination is (not) available, the returned mass estimate is accurate within a factor 2 (4). A Tully–Fisher relation is found for the observed high-z galaxies, i.e. LC ii ∝ (FWHM)1.80 ± 0.35 for which we provide a simple, physically based interpretation. Finally, we perform mock ALMA simulations to check the detectability of C ii. When seen face-on, Althæa is always detected at >5σ; in the edge-on case it remains undetected because the larger intrinsic FWHM pushes the line peak flux below detection limit. This suggests that some of the reported non-detections might be due to inclination effects.
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![The ALPINE–ALMA [C II] survey](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-6361/small "The ALPINE–ALMA [C II] survey")
