ABSTRACT
The recent discovery of high-redshift dusty galaxies implies a rapid dust enrichment of their interstellar medium (ISM). To interpret these observations, we run a cosmological simulation in ...a 30 h−1 cMpc/size volume down to z ≈ 4. We use the hydrodynamical code dustygadget, which accounts for the production of dust by stellar populations and its evolution in the ISM. We find that the cosmic dust density parameter (Ωd) is mainly driven by stellar dust at z ≳ 10, so that mass- and metallicity-dependent yields are required to assess the dust content in the first galaxies. At z ≲ 9, the growth of grains in the ISM of evolved systems log(M⋆/M⊙) > 8.5 significantly increases their dust mass, in agreement with observations in the redshift range 4 ≲ z < 8. Our simulation shows that the variety of high-redshift galaxies observed with the Atacama Large Millimeter Array can naturally be accounted for by modelling the grain growth time-scale as a function of the physical conditions in the gas cold phase. In addition, the trends of dust-to-metal and dust-to-gas (${\cal D}$) ratios are compatible with the available data. A qualitative investigation of the inhomogeneous dust distribution in a representative massive halo at z ≈ 4 shows that dust is found from the central galaxy up to the closest satellites along polluted filaments with $\rm log({\cal D}) \le -2.4$, but sharply declines at distances d ≳ 30 kpc along many lines of sight, where $\rm log({\cal D}) \lesssim -4.0$.
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
Here we investigate the evolution of a Milky Way (MW)-like galaxy with the aim of predicting the properties of its progenitors all the way from z ∼ 20 to z = 0. We apply gamesh to a ...high-resolution N-body simulation following the formation of a MW-type halo and we investigate its properties at z ∼ 0 and its progenitors in 0 < z < 4. Our model predicts the observed galaxy main sequence, the mass–metallicity and the Fundamental Plane of metallicity relations in 0 < z < 4. It also reproduces the stellar mass evolution of candidate MW progenitors in 0 ≲ z ≲ 2.5, although the star formation rate and gas fraction of the simulated galaxies follow a shallower redshift dependence. We find that while the MW star formation and chemical enrichment are dominated by the contribution of galaxies hosted in Lyman α cooling haloes, at z > 6 the contribution of star-forming minihaloes is comparable to the star formation rate along the MW merger tree. These systems might then provide an important contribution in the early phases of reionization. A large number of minihaloes with old stellar populations, possibly Population III stars, are dragged into the MW or survive in the Local Group. At low redshift dynamical effects, such as halo mergers, tidal stripping and halo disruption redistribute the baryonic properties among halo families. These results are critically discussed in light of future improvements including a more sophisticated treatment of radiative feedback and inhomogeneous metal enrichment.
ABSTRACT
We present a sub-kpc resolved study of the interstellar medium properties in SDP.81, a $z$ = 3.042 strongly gravitationally lensed, dusty star-forming galaxy, based on high-resolution, ...multiband ALMA observations of the far-infrared (FIR) continuum, CO ladder, and the C ii line. Using a visibility-plane lens modelling code, we achieve a median source-plane resolution of ∼200 pc. We use photon-dominated region (PDR) models to infer the physical conditions – far-ultraviolet (FUV) field strength, density, and PDR surface temperature – of the star-forming gas on 200-pc scales, finding a FUV field strength of ∼103−104G0, gas density of ∼105 cm−3, and cloud surface temperatures up to 1500 K, similar to those in the Orion Trapezium region. The C ii emission is significantly more extended than that FIR continuum: ∼50 per cent of C ii emission arises outside the FIR-bright region. The resolved C ii/FIR ratio varies by almost 2 dex across the source, down to ∼2 × 10−4 in the star-forming clumps. The observed C ii/FIR deficit trend is consistent with thermal saturation of the C+ fine-structure-level occupancy at high gas temperatures. We make the source-plane reconstructions of all emission lines and continuum data publicly available.
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
The increasing number of distant galaxies observed with ALMA by the ALPINE and REBELS surveys and the early release observations of the JWST promise to revolutionize our understanding of ...cosmic star formation and the assembly of normal, dusty galaxies. Here, we introduce a new suite of cosmological simulations performed with dustyGadget to interpret high-redshift data. We investigate the comoving star formation history, the stellar mass density, and a number of galaxy scaling relations such as the galaxy main sequence, the stellar-to-halo mass, and dust-to-stellar mass relations at z > 4. The predicted star formation rate and total stellar mass density rapidly increase in time with a remarkable agreement with available observations, including recent JWST ERO and DD-ERS data at z ≥ 8. A well-defined galaxy main sequence is found already at z < 10, following a non-evolving power-law, which – if extrapolated at high-mass end – is in agreement with JWST, REBELS, and ALPINE data. This is consistent with a star formation efficiently sustained by gas accretion and a specific star formation rate increasing with redshift, as established by recent observations. A population of low-mass galaxies (8 < Log(M⋆/M⊙) < 9) at z ≤ 6 − 7 that exceeds some of the current estimates of the stellar mass function is also at the origin of the scatter in the stellar-to-halo mass relation. Future JWST observations will provide invaluable constraints on these low-mass galaxies, helping to shed light on their role in cosmic evolution.
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