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.
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.
Abstract Astronomy is a discipline primarily reliant on visual data. However, alternative data representation techniques are being explored, in particular “sonification,” namely, the representation ...of data into sound. While there is increasing interest in the astronomical community in using sonification in research and educational contexts, its full potential is still to be explored. This study measured the performance of astronomers and nonastronomers to detect a transit-like feature in time-series data (i.e., light curves), which were represented visually or auditorily, adopting different data-to-sound mappings. We also assessed the bias that participants exhibited in the different conditions. We simulated the data of 160 light curves with different signal-to-noise ratios. We represented them as visual plots or auditory streams with different sound parameters to represent brightness: pitch, duration, or the redundant duration and pitch. We asked the participants to identify the presence of transit-like features in these four conditions in a session that included an equal number of stimuli with and without transit-like features. With auditory stimuli, participants detected transits with performances above the chance level. However, visual stimuli led to overall better performances compared to auditory stimuli and astronomers outperformed nonastronomers. Visualisations led to a conservative response bias (reluctance to answer “yes, there is a transit”), whereas sonifications led to more liberal responses (proneness to respond “yes, there is a transit”). Overall, this study contributes to understanding how different representations (visual or auditory) and sound mappings (pitch, duration, and duration and pitch) of time-series data affect detection accuracy and biases.
We present ALMA Band 9 observations of the C II158 μm emission for a sample of 10 main-sequence galaxies at redshift z ˜ 2, with typical stellar masses (log M⋆/M⊙ ˜ 10.0-10.9) and star formation ...rates (˜35-115 M⊙ yr-1). Given the strong and well-understood evolution of the interstellar medium from the present to z = 2, we investigate the behaviour of the C II emission and empirically identify its primary driver. We detect C II from six galaxies (four secure and two tentative) and estimate ensemble averages including non-detections. The C II-to-infrared luminosity ratio (C II/LIR) of our sample is similar to that of local main-sequence galaxies (˜2 × 10-3), and ˜10 times higher than that of starbursts. The C II emission has an average spatial extent of 4-7 kpc, consistent with the optical size. Complementing our sample with literature data, we find that the C II luminosity correlates with galaxies' molecular gas mass, with a mean absolute deviation of 0.2 dex and without evident systematics: the C II-to-H2 conversion factor (α _C II ˜ 30 M⊙/L⊙) is largely independent of galaxies' depletion time, metallicity, and redshift. C II seems therefore a convenient tracer to estimate galaxies' molecular gas content regardless of their starburst or main-sequence nature, and extending to metal-poor galaxies at low and high redshifts. The dearth of C II emission reported for z > 6-7 galaxies might suggest either a high star formation efficiency or a small fraction of ultraviolet light from star formation reprocessed by dust.
ABSTRACT
We study the structure of spatially resolved, line-of-sight velocity dispersion for galaxies in the Epoch of Reionization (EoR) traced by C $\scriptstyle \rm II$ $158\, \mu \rm {m}$ line ...emission. Our laboratory is a simulated prototypical Lyman-break galaxy, ‘Freesia, part of the serra suite’. The analysis encompasses the redshift range 6 < z < 8, when Freesia is in a very active assembling phase. We build velocity dispersion maps for three dynamically distinct evolutionary stages (Spiral Disc at z = 7.4, Merger at z = 8.0, and Disturbed Disc at z = 6.5) using C $\scriptstyle \rm II$ hyperspectral data cubes. We find that, at a high spatial resolution of 0.005 arcsec (≃30 pc), the luminosity-weighted average velocity dispersion is $\sigma _{\rm {CII}}\simeq 23{\text {--}}38\, {\rm km\, s^{-1}}$ with the highest value belonging to the highly structured Disturbed Disc stage. Low-resolution observations tend to overestimate σC ii values due to beam smearing effects that depend on the specific galaxy structure. For an angular resolution of 0.02 arcsec (0.1 arcsec), the average velocity dispersion is $16{\!-\!}34{{\ \rm per\ cent}}$ ($52{\!-\!}115{{\ \rm per\ cent}}$) larger than the actual one. The C $\scriptstyle \rm II$ emitting gas in Freesia has a Toomre parameter $\mathcal {Q}\simeq 0.2$ and rotational-to-dispersion ratio of vc/σ ≃ 7 similar to that observed in z = 2−3 galaxies. The primary energy source for the velocity dispersion is due to gravitational processes, such as merging/accretion events; energy input from stellar feedback is generally sub-dominant ($\lt 10{{\ \rm per\ cent}}$). Finally, we find that the resolved σC ii−ΣSFR relation is relatively flat for $0.02\lt {\Sigma }_{\rm SFR}/{\rm M}_{\odot }\rm {yr}^{-1} {\rm kpc}^{-2} \lt 30$, with the majority of data lying on the derived analytical relation $\sigma \propto \Sigma _{\rm SFR}^{5/7}$. At high SFR, the increased contribution from stellar feedback steepens the relation, and σC ii rises slightly.
ABSTRACT
We investigate the contribution of clumps and satellites to the galaxy mass assembly. We analysed spatially resolved HubbleSpace Telescope observations (imaging and slitless spectroscopy) of ...53 star-forming galaxies at z ∼ 1–3. We created continuum and emission line maps and pinpointed residual ‘blobs’ detected after subtracting the galaxy disc. Those were separated into compact (unresolved) and extended (resolved) components. Extended components have sizes ∼2 kpc and comparable stellar mass and age as the galaxy discs, whereas the compact components are 1.5 dex less massive and 0.4 dex younger than the discs. Furthermore, the extended blobs are typically found at larger distances from the galaxy barycentre than the compact ones. Prompted by these observations and by the comparison with simulations, we suggest that compact blobs are in situ formed clumps, whereas the extended ones are accreting satellites. Clumps and satellites enclose, respectively, ∼20 per cent and ≲80 per cent of the galaxy stellar mass, ∼30 per cent and ∼20 per cent of its star formation rate. Considering the compact blobs, we statistically estimated that massive clumps (M⋆ ≳ 109 M⊙) have lifetimes of ∼650 Myr, and the less massive ones (108 < M⋆ < 109 M⊙) of ∼145 Myr. This supports simulations predicting long-lived clumps (lifetime ≳ 100 Myr). Finally, ≲30 per cent (13 per cent) of our sample galaxies are undergoing single (multiple) merger(s), they have a projected separation ≲10 kpc, and the typical mass ratio of our satellites is 1:5 (but ranges between 1:10 and 1:1), in agreement with literature results for close pair galaxies.
We investigate the strongly lensed (
μ
≃ ×10 − 100) Lyman continuum (LyC) galaxy, dubbed Sunburst, at
z
= 2.37, taking advantage of a new accurate model of the lens. A characterization of the ...intrinsic (delensed) properties of the system yields a size of ≃3 sq. kpc, a luminosity of
M
UV
= −20.3, and a stellar mass of
M
≃ 10
9
M
⊙
; 16% of the ultraviolet light is located in a 3 Myr old gravitationally bound young massive star cluster (YMC), with an effective radius of ∼8 pc (corresponding to 1 milliarcsec without lensing) and a dynamical mass of ∼10
7
M
⊙
(similar to the stellar mass) – from which LyC radiation is detected (
λ
< 912 Å). The star formation rate and stellar mass surface densities for the YMC are Log
10
(Σ
SFR
M
⊙
yr
−1
kpc
−2
) ≃ 3.7 and Log
10
(Σ
M
M
⊙
pc
−2
) ≃ 4.1, with sSFR > 330 Gyr
−1
, consistent with the values observed in local young massive star clusters. The inferred outflowing gas velocity (> 300 km s
−1
) exceeds the escape velocity of the cluster. The resulting relative escape fraction of the ionizing radiation emerging from the entire galaxy is higher than 6−12%, whilst it is ≳46 − 93% if inferred from the YMC multiple line of sights. At least 12 additional unresolved star-forming knots with radii spanning the interval 3 − 20 pc (the majority of them likely gravitationally bound star clusters) are identified in the galaxy. A significant fraction (40−60%) of the ultraviolet light of the entire galaxy is located in such bound star clusters. In adopting a formation timescale of the star clusters of 20 Myr, a cluster formation efficiency Γ ≳ 30%. The star formation rate surface density of the Sunburst galaxy (Log
10
(Σ
SFR
) = 0.5
−0.2
+0.3
) is consistent with the high inferred Γ, as observed in local galaxies experiencing extreme gas physical conditions. Overall, the presence of a bursty event (i.e., the 3 Myr old YMC with large sSFR) significantly influences the morphology (nucleation), photometry (photometric jumps), and spectroscopic output (nebular emission) of the entire galaxy. Without lensing magnification, the YMC would be associated to an unresolved 0.5 kpc–size star-forming clump. The delensed LyC and UV magnitude
m
1600
(at 1600 Å) of the YMC are ≃30.6 and ≃26.9, whilst the entire galaxy has
m
1600
≃ 24.8. The Sunburst galaxy shows a relatively large rest-frame equivalent width of EW
rest
(H
β
+ O
III
λλ
4959, 5007) ≃ 450 Å, with the YMC contributing to ∼30% (having a local EW
rest
≃ 1100 Å) and ∼1% of the total stellar mass. If O-type (ionizing) stars are mainly forged in star clusters, then such engines were the key ionizing agents during reionization and the increasing occurrence of high equivalent width lines (H
β
+ O
III
) observed at
z
> 6.5 might be an indirect signature of a high frequency of forming massive star clusters (or high Γ) at reionization. Future facilities, which will perform at few tens milliarcsec resolution (e.g., VLT/MAVIS or ELT), will probe bound clusters on moderately magnified (
μ
< 5 − 10) galaxies across cosmic epochs up to reionization.
Summary
The first person‐to‐person transmission of the 2019 novel coronavirus in Italy on 21 February 2020 led to an infection chain that represents one of the largest known COVID‐19 outbreaks ...outside Asia. In northern Italy in particular, we rapidly experienced a critical care crisis due to a shortage of intensive care beds, as we expected according to data reported in China. Based on our experience of managing this surge, we produced this review to support other healthcare services in preparedness and training of hospitals during the current coronavirus outbreak. We had a dedicated task force that identified a response plan, which included: (1) establishment of dedicated, cohorted intensive care units for COVID‐19–positive patients; (2) design of appropriate procedures for pre‐triage, diagnosis and isolation of suspected and confirmed cases; and (3) training of all staff to work in the dedicated intensive care unit, in personal protective equipment usage and patient management. Hospital multidisciplinary and departmental collaboration was needed to work on all principles of surge capacity, including: space definition; supplies provision; staff recruitment; and ad hoc training. Dedicated protocols were applied where full isolation of spaces, staff and patients was implemented. Opening the unit and the whole hospital emergency process required the multidisciplinary, multi‐level involvement of healthcare providers and hospital managers all working towards a common goal: patient care and hospital safety. Hospitals should be prepared to face severe disruptions to their routine and it is very likely that protocols and procedures might require re‐discussion and updating on a daily basis.
‘Granny Smith’ apple (
Malus domestica Borkh.) fruit were treated with 1 μl l
−1 1-methylcyclopropene (1-MCP) at room temperature for 12 h. Quality of fruit stored 4 and 6 months in air, under ...different controlled atmospheres (CA) at low oxygen concentration (1.5, 1.0 and 0.7 kPa O
2), with initial low oxygen stress (ILOS) at 0.4 kPa O
2 for 2 weeks, and with or without postharvest application of the antioxidant diphenylamine (DPA) were compared. Superficial scald was controlled after long-term storage under 0.7 kPa O
2 or with ILOS followed by 1.0 kPa O
2, but not solely under 1.0 kPa O
2. 1-MCP eliminated the incidence of superficial scald under all long-term air and CA storage conditions. Core flush incidence was not affected by ILOS, but decreased at lower O
2 concentrations, and was reduced by 1-MCP or DPA. A disorder, resembling external CO
2 injuries, was observed on about 2.5% of fruits of all maturity stages treated with 1-MCP and subsequently stored in CA. Fruit treated with 1-MCP maintained greater firmness and acidity, even after 14 days at 20
°C, than untreated fruit stored under low oxygen. Total soluble solids concentrations were not influenced by 1-MCP. Degreening was effectively inhibited by 0.7 kPa O
2 or ILOS immediately after storage, but only by 1-MCP during the subsequent ripening period.
Context.
The characterization of the dynamical state of galaxies up to
z
∼ 7 is crucial for constraining the mechanisms that drive the mass assembly in the early Universe. However, it is unclear ...whether the data quality of typical observations obtained with current and future facilities is sufficient to perform a solid dynamical analysis at these redshifts.
Aims.
This paper defines the angular resolution and signal-to-noise ratio (S/N) required for a robust characterization of the dynamical state of galaxies up to the Epoch of Reionization. The final aim is to help design future spatially resolved surveys targeting emission lines of primeval galaxies.
Methods.
We investigate the C
II
-158 μm emission from six
z
∼ 6 − 7 Lyman break galaxies at three different inclinations from the S
ERRA
zoom-in cosmological simulation suite. The S
ERRA
galaxies cover a range of dynamical states: from isolated disks to major mergers. We create 102 mock observations with various data quality and apply the kinematic classification methods commonly used in the literature. These tests allow us to quantify the performances of the classification methods as a function of angular resolution and S/N.
Results.
We find that barely resolved observations, typical of line detection surveys, do not allow the correct characterization of the dynamical stage of a galaxy, resulting in the misclassification of disks and mergers in our sample by 100 and 50%, respectively. However, even when using spatially resolved observations with data quality typical of high-
z
galaxies (
S
/
N
∼ 10, and ∼3 independent resolution elements along the major axis), the success rates in the merger identification of the standard kinematic classification methods, based on the analysis of the moment maps, range between 50 and 70%. The high angular resolution and S/N needed to correctly classify disks with these standard methods can only be achieved with current instrumentation for a select number of bright galaxies. We propose a new classification method, called PVsplit, that quantifies the asymmetries and morphological features in position-velocity diagrams using three empirical parameters. We test PVsplit on mock data created from S
ERRA
galaxies, and show that PVsplit can predict whether a galaxy is a disk or a merger provided that
S
/
N
≳ 10, and the major axis is covered by ≳3 independent resolution elements.
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