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 present zoom-in, adaptive mesh refinement, high-resolution (...30 pc) simulations of high-redshift (z ... 6) galaxies with the aim of characterizing their internal properties and interstellar ...medium. Among other features, we adopt a star formation model based on a physically sound molecular hydrogen prescription, and introduce a novel scheme for supernova feedback, stellar winds and dust-mediated radiation pressure. In the zoom-in simulation, the target halo hosts 'Dahlia', a galaxy with a stellar mass M... = 1.6 x 10 super( 10) M..., representative of a typical z ~ 6 Lyman-break galaxy. Dahlia has a total H2 mass of 108.5 M... that is mainly concentrated in a disc-like structure of effective radius ...0.6 kpc and scale height ...200 pc. Frequent mergers drive fresh gas towards the centre of the disc, sustaining a star formation rate per unit area of ...15 M...yr super( -1) kpc super( -2). The disc is composed of dense (n ... 25 cm super( -3)), metal-rich (Z ... 0.5 Z...) gas that is pressure supported by radiation. We compute the 158 ...m Cii emission arising from Dahlia, and find that ...95 per cent of the total Cii luminosity ($$L_...\rm C\,\small ...II......\simeq 10 greater than or equal to ..7.5...\,...\rm L..._...\odot ...$$) arises from the H2 disc. Although 30 per cent of the Cii mass is transported out of the disc by outflows, such gas negligibly contributes to Cii emission, due to its low density (n ... 10 cm super( -3)) and metallicity (Z ... 10 super( -1) Z...). Dahlia is underluminous with respect to the local Cii-SFR relation; however, its luminosity is consistent with upper limits derived for most z ~ 6 galaxies. (ProQuest: ... denotes formulae/symbols omitted.)
ABSTRACT
ALMA observations have revealed the presence of dust in galaxies in the Epoch of Reionization (EoR; redshift z > 6). However, the dust temperature, Td, remains unconstrained, and this ...introduces large uncertainties, particularly in the dust mass determinations. Using an analytical and physically motivated model, we show that dust in high-z, star-forming giant molecular clouds (GMCs), largely dominating the observed far-infrared luminosity, is warmer ($T_\mathrm{ d} \lower.5ex\hbox{$\,\, \buildrel\,\gt\, \over \sim \,\,$}60\ \mathrm{K}$) than locally. This is due to the more compact GMC structure induced by the higher gas pressure and turbulence characterizing early galaxies. The compactness also delays GMC dispersal by stellar feedback, thus $\sim 40$ per cent of the total UV radiation emitted by newly born stars remains obscured. A higher Td has additional implications: it (a) reduces the tension between local and high-z IRX–β relation, and (b) alleviates the problem of the uncomfortably large dust masses deduced from observations of some EoR galaxies.
ABSTRACT
We study the impact of deviations from the Kennicutt–Schmidt relation (quantified by the ‘burstiness’ parameter κs), gas metallicity (Z), and density (n) on the observed O iii88 μm/C ii158 ...μm surface brightness ratios (ΣO iii/ΣC ii) in nine galaxies at z ≈ 6−9. We first discuss possible biases in the measured ΣO iii/ΣC ii ratios by comparing the data with zoom-in cosmological simulations and then use a Markov Chain Monte Carlo algorithm to derive the best-fitting values of (κs, Z, n). We find that (i) the strongest dependence of ΣO iii/ΣC ii is on κs; (ii) high ratios identify starburst galaxies with short gas depletion times ($t_{\rm dep}=6-49\, \rm Myr$); (iii) a secondary dependence on density is found, with ΣO iii/ΣC ii anticorrelating with n as a result of the lower O iii critical density; and (iv) the ratio weakly depends only on Z. The nine galaxies are significantly enriched (Z = 0.2−0.5 Z⊙) and dense n ≈ 101−3 cm−3. This lends further support to the starburst scenario in which a rapid enrichment of the interstellar medium is expected.
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 After two Atacama Large Millimeter/submillimeter Array (ALMA) observing cycles, only a handful of C ii 158 m emission line searches in z > 6 galaxies have reported a positive detection, ...questioning the applicability of the local C ii-star formation rate (SFR) relation to high-z systems. To investigate this issue we use the Vallini et al. (V13) model,based on high-resolution, radiative transfer cosmological simulations to predict the C ii emission from the interstellar medium of a z 7 (halo mass Mh = 1.17 × 1011 M ) galaxy. We improve the V13 model by including (a) a physically motivated metallicity (Z) distribution of the gas, (b) the contribution of photodissociation regions (PDRs), and (c) the effects of cosmic microwave background (CMB) on the C ii line luminosity. We study the relative contribution of diffuse neutral gas to the total C ii emission (Fdiff/Ftot) for different SFR and Z values. We find that the C ii emission arises predominantly from PDRs: regardless of the galaxy properties, Fdiff/Ftot ≤ 10%, since at these early epochs the CMB temperature approaches the spin temperature of the C ii transition in the cold neutral medium (TCMB ∼ ∼ 20 K). Our model predicts a high-z C ii-SFR relation, consistent with observations of local dwarf galaxies (0.02 < Z/Z < 0.5). The C ii deficit suggested by actual data (LCii < 2.0 × 107 L in BDF3299 at z 7.1) if confirmed by deeper ALMA observations, can be ascribed to negative stellar feedback disrupting molecular clouds around star formation sites. The deviation from the local C ii-SFR would then imply a modified Kennicutt-Schmidt relation in z > 6 galaxies. Alternatively/in addition, the deficit might be explained by low gas metallicities (Z < 0.1 Z ).
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.
A survey of high-z galaxies: serra simulations Pallottini, A; Ferrara, A; Gallerani, S ...
Monthly notices of the Royal Astronomical Society,
05/2022, Letnik:
513, Številka:
4
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
We introduce serra, a suite of zoom-in high-resolution ($1.2\times 10^4 \, {\rm M}_{\odot }$, $\simeq 25\, {\rm {pc}}$ at z = 7.7) cosmological simulations including non-equilibrium ...chemistry and on-the-fly radiative transfer. The outputs are post-processed to derive galaxy ultraviolet (UV) + far-infrared (FIR) continuum and emission line properties. Results are compared with available multiwavelength data to constrain the physical properties e.g. star formation rates (SFRs), stellar/gas/dust mass, metallicity of high-redshift 6 ≲ z ≲ 15 galaxies. This flagship paper focuses on the z = 7.7 sub-sample, including 202 galaxies with stellar mass $10^7 \, {\rm M}_{\odot }\lesssim M_\star \lesssim 5\times 10^{10}\, {\rm M}_{\odot }$, and specific star formation rate ranging from ${\rm sSFR} \sim 100\, {\rm Gyr}^{-1}$ in young, low-mass galaxies to $\sim 10\, {\rm Gyr}^{-1}$ for older, massive ones. At this redshift, serra galaxies are typically bursty, i.e. they are located above the Schmidt–Kennicutt relation by a factor $\kappa _s = 3.03^{+4.9}_{-1.8}$, consistent with recent findings for O iii and C ii emitters at high z. They also show relatively large InfraRed eXcess (IRX = LFIR/LUV) values as a result of their compact/clumpy morphology effectively blocking the stellar UV luminosity. Note that this conclusion might be affected by insufficient spatial resolution at the molecular cloud level. We confirm that early galaxies lie on the standard C ii$\!-\!\rm SFR$ relation; their observed LOIII/LCII ≃ 1–10 ratios can be reproduced by a part of the serra galaxies without the need of a top-heavy initial mass function and/or anomalous C/O abundances. O i line intensities are similar to local ones, making ALMA high-z detections challenging but feasible ($\sim 6\, \rm h$ for an SFR of $50\, \, {\rm M}_{\odot }\, {\rm yr}^{-1}$).
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.
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