We present the stacking analysis of a sample of 48 quasi-stellar objects (QSOs) at 4.5 < z < 7.1 detected by the Atacama Large Millimetre Array (ALMA) in the CII λ158 μm emission line to ...investigate the presence and the properties of massive, cold outflows associated with broad wings in the CII profile. The high sensitivity reached through this analysis allows us to reveal very broad CII wings tracing the presence of outflows with velocities in excess of 1000 km s−1. We find that the luminosity of the broad CII emission increases with LAGN, while it does not significantly depend on the star formation rate of the host galaxy, indicating that the central active galactic nucleus (AGN) is the main driving mechanism of the CII outflows in these powerful, distant QSOs. From the stack of the ALMA cubes, we derive an average outflow spatial extent of ∼3.5 kpc. The average atomic neutral mass outflow rate inferred from the stack of the whole sample is Ṁout ∼ 100 M⊙ yr−1, while for the most luminous systems it increases to ∼200 M⊙ yr−1. The associated outflow kinetic power is about 0.1% of LAGN, while the outflow momentum rate is ∼LAGN/c or lower, suggesting that these outflows are either driven by radiation pressure onto dusty clouds or, alternatively, are driven by the nuclear wind and energy conserving but with low coupling with the interstellar medium. We discuss the implications of the resulting feedback effect on galaxy evolution in the early Universe.
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.
Context. Feedback from accreting supermassive black holes (SMBHs) is often identified as the main mechanism responsible for regulating star formation in active galactic nucleus (AGN) host galaxies. ...However, the relationships between AGN activity, radiation, winds, and star formation are complex and still far from being understood. Aims. We study scaling relations between AGN properties, host galaxy properties, and AGN winds. We then evaluate the wind mean impact on the global star formation history, taking into account the short AGN duty cycle with respect to that of star formation. Methods. We first collect AGN wind observations for 94 AGN with detected massive winds at sub-pc to kpc spatial scales. We then fold AGN wind scaling relations with AGN luminosity functions, to evaluate the average AGN wind mass-loading factor as a function of cosmic time. Results. We find strong correlations between the AGN molecular and ionised wind mass outflow rates and the AGN bolometric luminosity. The power law scaling is steeper for ionised winds (slope 1.29 ± 0.38) than for molecular winds (0.76 ± 0.06), meaning that the two rates converge at high bolometric luminosities. The molecular gas depletion timescale and the molecular gas fraction of galaxies hosting powerful AGN driven winds are 3–10 times shorter and smaller than those of main sequence galaxies with similar star formation rate (SFR), stellar mass, and redshift. These findings suggest that, at high AGN bolometric luminosity, the reduced molecular gas fraction may be due to the destruction of molecules by the wind, leading to a larger fraction of gas in the atomic ionised phase. The AGN wind mass-loading factor η = ṀOF/SFR is systematically higher than that of starburst driven winds. Conclusions. Our analysis shows that AGN winds are, on average, powerful enough to clean galaxies from their molecular gas only in massive systems at z ≲ 2, i.e. a strong form of co-evolution between SMBHs and galaxies appears to break down for the least massive galaxies.
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.
Mrk 231 is a nearby ultra-luminous IR galaxy exhibiting a kpc-scale, multi-phase AGN-driven outflow. This galaxy represents the best target to investigate in detail the morphology and energetics of ...powerful outflows, as well as their still poorly-understood expansion mechanism and impact on the host galaxy. In this work, we present the best sensitivity and angular resolution maps of the molecular disk and outflow of Mrk 231, as traced by CO(2−1) and (3−2) observations obtained with the IRAM/PdBI. In addition, we analyze archival deep Chandra and NuSTAR X-ray observations. We use this unprecedented combination of multi-wavelength data sets to constrain the physical properties of both the molecular disk and outflow, the presence of a highly-ionized ultra-fast nuclear wind, and their connection. The molecular CO(2−1) outflow has a size of ~1 kpc, and extends in all directions around the nucleus, being more prominent along the south-west to north-east direction, suggesting a wide-angle biconical geometry. The maximum projected velocity of the outflow is nearly constant out to ~1 kpc, thus implying that the density of the outflowing material must decrease from the nucleus outwards as ~r-2. This suggests that either a large part of the gas leaves the flow during its expansion or that the bulk of the outflow has not yet reached out to ~1 kpc, thus implying a limit on its age of ~1 Myr. Mapping the mass and energy rates of the molecular outflow yields \hbox{$\rm \dot {\it M}$}M˙ OF = 500−1000 M⊙ yr-1 and Ėkin,OF = 7−10 × 1043 erg s-1. The total kinetic energy of the outflow is Ekin,OF is of the same order of the total energy of the molecular disk, Edisk. Remarkably, our analysis of the X-ray data reveals a nuclear ultra-fast outflow (UFO) with velocity −20 000 km s-1, \hbox{$\rm \dot {\it M}$} M ˙ UFO = 0.3−2.1 M⊙ yr-1, and momentum load \hbox{$\rm \dot {\it P}$} P ˙ UFO/ \hbox{$\dot {\it P}$} P ˙ rad = 0.2−1.6. We find Ėkin,UFO ~ Ėkin,OF as predicted for outflows undergoing an energy conserving expansion. This suggests that most of the UFO kinetic energy is transferred to mechanical energy of the kpc-scale outflow, strongly supporting that the energy released during accretion of matter onto super-massive black holes is the ultimate driver of giant massive outflows. The momentum flux \hbox{$\rm \dot {\it P}$} P ˙ OF derived for the large scale outflows in Mrk 231 enables us to estimate a momentum boost \hbox{$\rm \dot {\it P}$} P ˙ OF/ \hbox{$\dot {\it P}$} P ˙ UFO ≈ 30−60. The ratios Ėkin,UFO/Lbol,AGN = 1−5 % and Ėkin,OF/Lbol,AGN = 1−3 % agree with the requirements of the most popular models of AGN feedback.
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
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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.
Missing [C ii] emission from early galaxies Carniani, S; Ferrara, A; Maiolino, R ...
Monthly notices of the Royal Astronomical Society,
12/2020, Letnik:
499, Številka:
4
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
ALMA observations have revealed that C ii 158 μm line emission in high-z galaxies is ≈2–3 × more extended than the UV continuum emission. Here we explore whether surface brightness dimming ...(SBD) of the C ii line is responsible for the reported C ii deficit, and the large $L_{\rm O\, \small {III}}/L_{\rm C\, \small {II}}$ luminosity ratio measured in early galaxies. We first analyse archival ALMA images of nine z > 6 galaxies observed in both C ii and O iii. After performing several uv-tapering experiments to optimize the identification of extended line emission, we detect C ii emission in the whole sample, with an extent systematically larger than the O iii emission. Next, we use interferometric simulations to study the effect of SBD on the line luminosity estimate. About 40 per cent of the extended C ii component might be missed at an angular resolution of 0.8 arcsec, implying that $L_{\rm C\, \small {II}}$ is underestimated by a factor ≈2 in data at low (<7) signal-to-noise ratio. By combining these results, we conclude that $L_{\rm C\, \small {II}}$ of z > 6 galaxies lies, on average, slightly below the local $L_{\rm C\, \small {II}}-\mathrm{ SFR}$ relation (Δz = 6–9 = −0.07 ± 0.3), but within the intrinsic dispersion of the relation. SBD correction also yields $L_{\rm O\, \small {III}}/L_{\rm C\, \small {II}}\lt 10$, i.e. more in line with current hydrodynamical simulations.
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![A physical model for [C ii]...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0035-8711_1365-2966/small "A physical model for [C ii] line emission from galaxies")
