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
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.
Himiko is one of the most luminous Ly emitters at z = 6.595. It has three star-forming clumps detected in the rest-frame UV, with a total SFR = 20 M yr−1. We report the Atacama Large ...Millimeter/submillimeter Array (ALMA) detection of the C ii158 m line emission in this Galaxy with a significance of 8 . The total C ii luminosity (LC ii = 1.2 × 108 L ) is fully consistent with the local LC ii-SFR relation. The ALMA high-angular resolution reveals that the C ii emission is made of two distinct components. The brightest C ii clump is extended over 4 kpc and is located on the peak of the Ly nebula, which is spatially offset by 1 kpc relative to the brightest UV clump. The second C ii component is spatially unresolved (size <2 kpc) and coincident with one of the three UV clumps. While the latter component is consistent with the local LC ii-SFR relation, the other components are scattered above and below the local relation. We shortly discuss the possible origin of the C ii components and their relation with the star-forming clumps traced by the UV emission.
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 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
Galaxies represent one of the preferred candidate sources to drive the reionization of the universe. Even as gains are made in mapping the galaxy UV luminosity density to
, significant ...uncertainties remain regarding the conversion to the implied ionizing emissivity. The relevant unknowns are the Lyman-continuum (LyC) photon production efficiency
and the escape fraction
f
esc
. As we show here, the first of these unknowns is directly measurable in
z
= 4–5 galaxies based on the impact the H
α
line has on the observed IRAC fluxes. By computing a LyC photon production rate from the implied H
α
luminosities for a broad selection of
z
= 4–5 galaxies and comparing this against the dust-corrected UV-continuum luminosities, we provide the first-ever direct estimates of the LyC photon production efficiency
for the
galaxy population. We find
to have a mean value of
and
for sub-
L
*
z
= 4–5 galaxies adopting Calzetti and SMC dust laws, respectively. Reassuringly, both derived values are consistent with the standard assumed
's in reionization models, with a slight preference for higher
's (by ∼0.1 dex) adopting the SMC dust law. High values of
(∼25.5–25.8 dex) are derived for the bluest galaxies (
) in our samples, independent of dust law and consistent with results for a
z
= 7.045 galaxy. Such elevated values of
would have important consequences, indicating that
f
esc
cannot be in excess of 13% for standard assumptions about the faint-end cut-off to the LF and the clumping factor.
Tuberculosis (TB), smoking, HIV and chronic obstructive pulmonary disease (COPD) are burgeoning epidemics in developing countries. The link between TB and HIV is well established. Less well ...recognised is the strong relationship between tobacco smoking and the development and natural history of TB. These associations are of considerable relevance to public health and disease outcomes in individuals with TB. Moreover, tobacco smoking, a modifiable risk factor, is associated with poorer outcomes in HIV-associated opportunistic infections, of which TB is the commonest in developing countries. It is now also becoming clear that TB, like tobacco smoke, besides its known consequences of bronchiectasis and other pulmonary morbidity, is also a significant risk factor for the development of COPD. Thus, there is a deleterious and synergistic interaction between TB, HIV, tobacco smoking and COPD in a large proportion of the world's population. Further work, specifically mechanistic and epidemiological studies, is required to clarify the role of tobacco smoke on the progression of TB and HIV infection, and to assess the impact of smoking cessation interventions. These interactions deserve urgent attention and have major implications for coordinated public health planning and policy recommendations in the developing world.
The remarkable Hubble Space Telescope (HST) data sets from the CANDELS, HUDF09, HUDF12, ERS, and BoRG/HIPPIES programs have allowed us to map the evolution of the rest-frame UV luminosity function ...(LF) from z ~ 10 to z ~ 4. We develop new color criteria that more optimally utilize the full wavelength coverage from the optical, near-IR, and mid-IR observations over our search fields, while simultaneously minimizing the incompleteness and eliminating redshift gaps. We have identified 5859, 3001, 857, 481, 217, and 6 galaxy candidates at z ~ 4, z ~ 5, z ~ 6, z ~ 7, z ~ 7, and z ~ 10, respectively, from the ~1000 arcmin super(2) area covered by these data sets. This sample of >10,000 galaxy candidates at z > or =, slanted 4 is by far the largest assembled to date with HST. The selection of z ~ 4-8 candidates over the five CANDELS fields allows us to assess the cosmic variance; the largest variations are at z > or =, slanted 7. Our new LF determinations at z ~ 4 and z ~ 5 span a 6 mag baseline and reach to -16 AB mag. These determinations agree well with previous estimates, but the larger samples and volumes probed here result in a more reliable sampling of >L* galaxies and allow us to reassess the form of the UV LFs. Our new LF results strengthen our earlier findings to 3.4sigma significance for a steeper faint-end slope of the UV LF at z > 4, with alpha evolving from alpha = -1.64 + or - 0.04 at z ~ 4 to alpha = -2.06 + or - 0.13 at z ~ 7 (and alpha = -2.02 + or - 0.23 at z ~ 8), consistent with that expected from the evolution of the halo mass function. We find less evolution in the characteristic magnitude M* from z ~ 7 to z ~ 4; the observed evolution in the LF is now largely represented by changes in phi*. No evidence for a non-Schechter-like form to the z ~ 4-8 LFs is found. A simple conditional LF model based on halo growth and evolution in the M/L ratio (is proportional to(1 + z) super(-1.5)) of halos provides a good representation of the observed evolution.
ABSTRACT
The deep, wide-area (∼800–900 arcmin
2
) near-infrared/WFC3/IR +
Spitzer
/IRAC observations over the CANDELS fields have been a remarkable resource for constraining the bright end of ...high-redshift UV luminosity functions. However, the lack of
Hubble Space Telescope
(
HST
) 1.05
μ
m observations over the CANDELS fields has made it difficult to identify
z
∼ 9–10 sources robustly, since such data are needed to confirm the presence of an abrupt Lyman break at 1.2
μ
m. Here, we report on the successful identification of many such
z
∼ 9–10 sources from a new
HST
program (z9-CANDELS) that targets the highest-probability
z
∼ 9–10 galaxy candidates with observations at 1.05
μ
m, to search for a robust Lyman-break at 1.2
μ
m. The potential
z
∼ 9–10 candidates were preselected from the full
HST
,
Spitzer
/IRAC S-CANDELS observations, and the deepest-available ground-based optical+near-infrared observations (CFHTLS-DEEP+HUGS+UltraVISTA+ZFOURGE). We identified 15 credible
z
∼ 9–10 galaxies over the CANDELS fields. Nine of these galaxies lie at
z
∼ 9 and five are new identifications. Our targeted follow-up strategy has proven to be very efficient in making use of scarce
HST
time to secure a reliable sample of
z
∼ 9–10 galaxies. Through extensive simulations, we replicate the selection process for our sample (both the preselection and follow-up) and use it to improve current estimates for the volume density of bright
z
∼ 9 and
z
∼ 10 galaxies. The volume densities we find are 5
and
lower, respectively, than those found at
z
∼ 8. When compared with the best-fit evolution (i.e.,
) in the UV luminosity densities from
z
∼ 8 to
z
∼ 4 integrated to
(−20 mag), these luminosity densities are
and
lower, respectively, than the extrapolated trends. Our new results are broadly consistent with the “accelerated evolution” scenario at
z
> 8, consistent with that seen in many models.
We report the results of an expanded search for z ∼ 9-10 candidates over the ∼883 arcmin2 CANDELS+ERS fields. This study adds 147 arcmin2 to the search area we consider over the Cosmic Assembly ...Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) COSMOS, UDS, and EGS fields, while expanding our selection to include sources with bluer J125 − H160 colors than our previous J125 − H160 > 0.5 mag selection. In searching for new z ∼ 9-10 candidates, we make full use of all available Hubble Space Telescope (HST), Spitzer/IRAC, and ground-based imaging data. As a result of our expanded search and use of broader color criteria, three new candidate z ∼ 9-10 galaxies are identified. We also find again the z = 8.683 source previously confirmed by Zitrin et al. This brings our sample of probable z ∼ 9-11 galaxy candidates over the CANDELS+ERS fields to 19 sources in total, equivalent to one candidate per 47 arcmin2 (one per 10 WFC3/IR fields). To be comprehensive, we also discuss 28 mostly lower likelihood z ∼ 9-10 candidates, including some sources that seem to be reliably at z > 8 using the HST+IRAC data alone, but which the ground-based data show are much more likely at z < 4. One case example is a bright z ∼ 9.4 candidate, COS910-8, which seems instead to be at z ∼ 2. Based on this expanded sample, we obtain a more robust luminosity function (LF) at z ∼ 9 and improved constraints on the volume density of bright z ∼ 9 and z ∼ 10 galaxies. Our improved z ∼ 9-10 results again reinforce previous findings for strong evolution in the UV LF at z > 8, with a factor of ∼10 evolution seen in the luminosity density from z ∼ 10 to z ∼ 8.
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