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.
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.
Abstract
The Reionization Era Bright Emission Line Survey (REBELS) is a cycle-7 ALMA Large Program (LP) that is identifying and performing a first characterization of many of the most luminous ...star-forming galaxies known in the
z
> 6.5 universe. REBELS is providing this probe by systematically scanning 40 of the brightest UV-selected galaxies identified over a 7 deg
2
area for bright C
ii
158
μ
m
and O
iii
88
μ
m
lines and dust-continuum emission. Selection of the 40 REBELS targets was done by combining our own and other photometric selections, each of which is subject to extensive vetting using three completely independent sets of photometry and template-fitting codes. Building on the observational strategy deployed in two pilot programs, we are increasing the number of massive interstellar medium (ISM) reservoirs known at
z
> 6.5 by ∼4–5× to >30. In this manuscript, we motivate the observational strategy deployed in the REBELS program and present initial results. Based on the first-year observations, 18 highly significant ≥ 7
σ
C
ii
158
μ
m
lines have already been discovered, the bulk of which (13/18) also show ≥3.3
σ
dust-continuum emission. These newly discovered lines more than triple the number of bright ISM-cooling lines known in the
z
> 6.5 universe, such that the number of ALMA-derived redshifts at
z
> 6.5 rival Ly
α
discoveries. An analysis of the completeness of our search results versus star formation rate (SFR) suggests an ∼79% efficiency in scanning for C
ii
158
μ
m
when the SFR
UV+IR
is >28
M
⊙
yr
−1
. These new LP results further demonstrate ALMA’s efficiency as a “redshift machine,” particularly in the Epoch of Reionization.
ABSTRACT
ALMA observations have revealed the presence of dust in the first generations of galaxies in the Universe. However, the dust temperature Td remains mostly unconstrained due to the few ...available FIR continuum data at redshift $z$ > 5. This introduces large uncertainties in several properties of high-$z$ galaxies, namely their dust masses, infrared luminosities, and obscured fraction of star formation. Using a new method based on simultaneous C $\scriptstyle \rm II$ 158-μm line and underlying dust continuum measurements, we derive Td in the continuum and C $\scriptstyle \rm II$ detected $z$ ≈ 7 galaxies in the ALMA Large Project REBELS sample. We find 39 < Td < 58 K, and dust masses in the narrow range Md = (0.9−3.6) × 107 M⊙. These results allow us to extend for the first time the reported Td($z$) relation into the Epoch of Reionization. We produce a new physical model that explains the increasing Td($z$) trend with the decrease of gas depletion time, tdep = Mg/SFR, induced by the higher cosmological accretion rate at early times; this hypothesis yields Td ∝ (1 + $z$)0.4. The model also explains the observed Td scatter at a fixed redshift. We find that dust is warmer in obscured sources, as a larger obscuration results in more efficient dust heating. For UV-transparent (obscured) galaxies, Td only depends on the gas column density (metallicity), $T_{\rm d} \propto N_{\rm H}^{1/6}$ (Td ∝ Z−1/6). REBELS galaxies are on average relatively transparent, with effective gas column densities around NH ≃ (0.03−1) × 1021 cm−2. We predict that other high-$z$ galaxies (e.g. MACS0416-Y1, A2744-YD4), with estimated Td ≫ 60 K, are significantly obscured, low-metallicity systems. In fact, Td is higher in metal-poor systems due to their smaller dust content, which for fixed LIR results in warmer temperatures.
ABSTRACT
We include a fully coupled treatment of metal and dust enrichment into the Delphi semi-analytic model of galaxy formation to explain the dust content of 13 Lyman break galaxies (LBGs) ...detected by the Atacama Large millimetre Array (ALMA) REBELS Large Program at z ≃ 7. We find that the galaxy dust mass, Md, is regulated by the combination of Type II supernova dust production, astration, shock destruction, and ejection in outflows; grain growth (with a standard time-scale τ0 = 30 Myr) plays a negligible role. The model predicts a dust-to-stellar mass ratio of $\sim 0.07\!-\!0.1{{\ \rm per\ cent}}$ and a UV-to-total star formation rate relation such that log(ψUV) = −0.05 log(ψ)2 + 0.86 log(ψ) − 0.05 (implying that 55–80 per cent of the star formation is obscured) for REBELS galaxies with stellar mass $M_* = 10^{9}\!-\!10^{10} \rm M_\odot$. This relation reconciles the intrinsic UV luminosity of LBGs with their observed luminosity function at z = 7. However, 2 out of the 13 systems show dust-to-stellar mass ratios ($\sim 0.94\!-\!1.1{{\ \rm per\ cent}}$) that are up to 18 times larger than expected from the fiducial relation. Due to the physical coupling between dust and metal enrichment, even decreasing τ0 to very low values (0.3 Myr) only increases the dust-to-stellar mass ratio by a factor of ∼2. Given that grain growth is not a viable explanation for such high observed ratios of the dust-to-stellar mass, we propose alternative solutions.
ABSTRACT
We analyse FIR dust continuum measurements for 14 galaxies (redshift z ≈ 7) in the ALMA Reionization Era Bright Emission Line Survey (REBELS) Large Program to derive their physical ...properties. Our model uses three input data, i.e. (a) the UV spectral slope, β, (b) the observed UV continuum flux at 1500 Å, F1500, (c) the observed continuum flux at $\approx 158\, \mu$m, F158, and considers Milky Way (MW) and SMC extinction curves, along with different dust geometries. We find that REBELS galaxies have 28−90.5 per cent of their star formation obscured; the total (UV+IR) star formation rates are in the range $31.5 \lt {\rm SFR}/({\rm M}_\odot \, {\rm yr}^{-1}) \lt 129.5$. The sample-averaged dust mass and temperature are $(1.3\pm 1.1)\times 10^7 \, \mathrm{M}_\odot$ and 52 ± 11 K, respectively. However, in some galaxies dust is particularly abundant (REBELS-14, $M^{\prime }_{\rm d} \approx 3.4 \times 10^7 \, \mathrm{M}_\odot$), or hot (REBELS-18, $T^{\prime }_{\rm d} \approx 67$ K). The dust distribution is compact (<0.3 kpc for 70 per cent of the galaxies). The inferred dust yield per supernova is $0.1 \le y_{\rm d}/\, \mathrm{M}_\odot \le 3.3$, with 70 per cent of the galaxies requiring $y_{\rm d} \lt 0.25 \, \mathrm{M}_\odot$. Three galaxies (REBELS-12, 14, 39) require $y_{\rm d} \gt 1 \, \mathrm{M}_\odot$, which is likely inconsistent with pure SN production, and might require dust growth via accretion of heavy elements from the interstellar medium. With the SFR predicted by the model and a MW extinction curve, REBELS galaxies detected in C ii nicely follow the local LCII−SFR relation, and are approximately located on the Kennicutt–Schmidt relation. The sample-averaged gas depletion time is $0.11\, y_{\rm P}^{-2}$ Gyr, where yP is the ratio of the gas-to-stellar distribution radius. For some systems, a solution simultaneously matching the observed (β, F1500, F158) values cannot be found. This occurs when the index Im = (F158/F1500)/(β − βint), where βint is the intrinsic UV slope, exceeds $I_m^{*}\approx 1120$ for an MW curve. For these objects, we argue that the FIR and UV emitting regions are not co-spatial, questioning the use of the IRX–β relation.
Abstract
The neutral atomic gas content of individual galaxies at large cosmological distances has until recently been difficult to measure due to the weakness of the hyperfine H
i
21 cm transition. ...Here we estimate the H
i
gas mass of a sample of main-sequence star-forming galaxies at
z
∼ 6.5–7.8 surveyed for C
ii
158
μ
m emission as part of the Reionization Era Bright Emission Line Survey (REBELS), using a recent calibration of the C
ii
-to-H
i
conversion factor. We find that the H
i
gas mass excess in galaxies increases as a function of redshift, with an average of
M
H
i
/
M
⋆
≈ 10, corresponding to H
i
gas mass fractions of
f
H
i
=
M
H
i
/(
M
⋆
+
M
H
i
) = 90%, at
z
≈ 7. Based on the C
ii
158
μ
m luminosity function (LF) derived from the same sample of galaxies, we further place constraints on the cosmic H
i
gas mass density in galaxies (
ρ
H
i
) at this redshift, which we measure to be
ρ
H
I
=
7.1
−
3.0
+
6.4
×
10
6
M
⊙
Mpc
−
3
. This estimate is substantially lower by a factor of ≈10 than that inferred from an extrapolation of damped Ly
α
absorber (DLA) measurements and largely depends on the exact C
ii
LF adopted. However, we find this decrease in
ρ
H
i
to be consistent with recent simulations and argue that this apparent discrepancy is likely a consequence of the DLA sight lines predominantly probing the substantial fraction of H
i
gas in high-
z
galactic halos, whereas C
ii
traces the H
i
in the ISM associated with star formation. We make predictions for this buildup of neutral gas in galaxies as a function of redshift, showing that at
z
≳ 5, only ≈10% of the cosmic H
i
gas content is confined in galaxies and associated with the star-forming ISM.
ABSTRACT
Recent attempts to detect O iii 88$\, \mu$m emission from super-early (z > 10) galaxy candidates observed by JWST have been unsuccessful. Non-detections can be either due to wrong ...photometric redshifts or to the faintness of the line in such early systems. By using zoom-in simulations, we show that if redshifts of these galaxies are confirmed, they are faint and mostly fall below the local metal-poor $\rm O\, {\small III}-SFR$ relation as a result of their low ionization parameter, Uion ≲ 10−3. Such low Uion values are found in galaxies that are in an early assembly stage, and whose stars are still embedded in high-density natal clouds. However, the most luminous galaxy in our sample ($\rm {log}L_{\rm {O\, {\small III}}}/\mathrm{L}_\odot = 8.4$, Uion ≈ 0.1) could be detected by ALMA in only 2.8 h.
ABSTRACT
Recent Atacama Large Millimeter Array large surveys unveiled the presence of significant dust continuum emission in star-forming galaxies at z > 4. Unfortunately, such large programs – i.e. ...ALPINE (z ∼ 5) and REBELS (z ∼ 7) – only provide us with a single far-infrared (FIR) continuum data point for their individual targets. Therefore, high-z galaxies FIR spectral energy densities (SEDs) remain mostly unconstrained, hinging on an assumption for their dust temperature (Td) in the SED fitting procedure. This introduces uncertainties in the inferred dust masses (Md), infrared luminosities (LIR), and obscured star formation rate (SFR) fraction at z > 4. In this work, we use a method that allows us to constrain Td with a single-band measurement by combining the 158 $\mu$m continuum information with the overlying C ii emission line. We analyse the 21 C ii and FIR continuum-detected z ∼ 5 galaxies in ALPINE, finding a range of Td = 25–60 K and Md = 0.6–25.1 × 107 M⊙. Given the measured stellar masses of ALPINE galaxies, the inferred dust yields are around Md/M⋆ = (0.2–8) × 10−3, consistent with theoretical dust-production constraints. We find that eight out of the 21 ALPINE galaxies have LIR ≥ 1012 L⊙, comparable to ultraluminous IR galaxies (ULIRGs). Relying on ultraviolet-to-optical SED fitting, the SFR was underestimated by up to two orders of magnitude in four of these eight ULIRGs-like galaxies. We conclude that these four peculiar sources should be characterized by a two-phase interstellar medium structure with ‘spatially segregated’ FIR and ultraviolet emitting regions.
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