53 research outputs found
Towards a multi-tracer timeline of star formation in the LMC -- I.\ Deriving the lifetimes of H\,{\sc i} clouds
The time-scales associated with the various stages of the star formation process remain poorly constrained. This includes the earliest phases of star formation, during which molecular clouds condense out of the atomic interstellar medium. We present the first in a series of papers with the ultimate goal of compiling the first multi-tracer timeline of star formation, through a comprehensive set of evolutionary phases from atomic gas clouds to unembedded young stellar populations. In this paper, we present an empirical determination of the lifetime of atomic clouds using the Uncertainty Principle for Star Formation formalism, based on the de-correlation of H and H\,{\sc i} emission as a function of spatial scale. We find an atomic gas cloud lifetime of 48\,Myr. This timescale is consistent with the predicted average atomic cloud lifetime in the LMC (based on galactic dynamics) that is dominated by the gravitational collapse of the mid-plane ISM. We also determine the overlap time-scale for which both H\,{\sc i} and H emission are present to be very short (\,Myr), consistent with zero, indicating that there is a near-to-complete phase change of the gas to a molecular form in an intermediary stage between H\,{\sc i} clouds and H\,{\sc ii} regions. We utilise the time-scales derived in this work to place empirically determined limits on the time-scale of molecular cloud formation. By performing the same analysis with and without the 30 Doradus region included, we find that the most extreme star forming environment in the LMC has little effect on the measured average atomic gas cloud lifetime. By measuring the lifetime of the atomic gas clouds, we place strong constraints on the physics that drives the formation of molecular clouds and establish a solid foundation for the development of a multi-tracer timeline of star formation in the LMC
The ALMA REBELS Survey: The First Infrared Luminosity Function Measurement at $\mathbf{z \sim 7}
We present the first observational infrared luminosity function (IRLF)
measurement in the Epoch of Reionization (EoR) based on a UV-selected galaxy
sample with ALMA spectroscopic observations. Our analysis is based on the ALMA
large program Reionization Era Bright Emission Line Survey (REBELS), which
targets 42 galaxies at with [CII] 158\micron line scans.
16 sources exhibit a dust detection, 15 of which are also spectroscopically
confirmed through the [CII] line. The IR luminosities of the sample range from
to 12.2. Using the UVLF as a proxy to derive the
effective volume for each of our target sources, we derive IRLF estimates, both
for detections and for the full sample including IR luminosity upper limits.
The resulting IRLFs are well reproduced by a Schechter function with the
characteristic luminosity of . Our
observational results are in broad agreement with the average of predicted
IRLFs from simulations at . Conversely, our IRLFs lie significantly
below lower redshift estimates, suggesting a rapid evolution from to
, into the reionization epoch. The inferred obscured contribution to
the cosmic star-formation rate density at amounts to
which is at
least 10\% of UV-based estimates. We conclude that the presence of dust
is already abundant in the EoR and discuss the possibility of unveiling larger
samples of dusty galaxies with future ALMA and JWST observations.Comment: 9 pages, 5 figure
Metal and dust evolution in ALMA REBELS galaxies: insights for future JWST observations
ALMA observations revealed the presence of significant amounts of dust in the
first Gyr of Cosmic time. However, the metal and dust buildup picture remains
very uncertain due to the lack of constraints on metallicity. JWST has started
to reveal the metal content of high-redshift targets, which may lead to firmer
constraints on high-redshift dusty galaxies evolution. In this work, we use
detailed chemical and dust evolution models to explore the evolution of
galaxies within the ALMA REBELS survey, testing different metallicity scenarios
that could be inferred from JWST observations. In the models, we track the
buildup of stellar mass by using non-parametric SFHs for REBELS galaxies.
Different scenarios for metal and dust evolution are simulated by allowing
different prescriptions for gas flows and dust processes. The model outputs are
compared with measured dust scaling relations, by employing
metallicity-dependent calibrations for the gas mass based on the [CII]158micron
line. Independently of the galaxies metal content, we found no need for extreme
dust prescriptions to explain the dust masses revealed by ALMA. However,
different levels of metal enrichment will lead to different dominant dust
production mechanisms, with stardust production dominant over other ISM dust
processes only in the metal-poor case. This points out how metallicity
measurements from JWST will significantly improve our understanding of the dust
buildup in high-redshift galaxies. We also show that models struggle to
reproduce observables such as dust-to-gas and dust-to-stellar ratios
simultaneously, possibly indicating an overestimation of the gas mass through
current calibrations, especially at high metallicities.Comment: 16 pages + appendices, 9 Figures, 1 Table. Resubmitted to MNRAS after
moderate revisio
Cloud-Scale Molecular Gas Properties in 15 Nearby Galaxies
We measure the velocity dispersion, , and surface density, ,
of the molecular gas in nearby galaxies from CO spectral line cubes with
spatial resolution - pc, matched to the size of individual giant
molecular clouds. Combining galaxies from the PHANGS-ALMA survey with
targets from the literature, we characterize independent
sightlines where CO is detected at good significance. and
show a strong positive correlation, with the best-fit power law slope close to
the expected value for resolved, self-gravitating clouds. This indicates only
weak variation in the virial parameter
, which is - for
most galaxies. We do, however, observe enormous variation in the internal
turbulent pressure , which spans
across our sample. We find , , and
to be systematically larger in more massive galaxies. The
same quantities appear enhanced in the central kpc of strongly barred galaxies
relative to their disks. Based on sensitive maps of M31 and M33, the slope of
the - relation flattens at
, leading to high for a given
and high apparent . This echoes results found in
the Milky Way, and likely originates from a combination of lower beam filling
factors and a stronger influence of local environment on the dynamical state of
molecular gas in the low density regime.Comment: Accepted for publication in ApJ. 45 pages, 11 figures, 8 tables, 4
Appendices; key results summarized in Figure 10. Machine-readable table can
be downloaded at http://www.astronomy.ohio-state.edu/~sun.1608/datafile3.txt
prior to publication. For a brief video describing the main results of this
paper, please see https://www.youtube.com/watch?v=-_eL7t1PVq8&
The ALMA REBELS Survey: Discovery of a massive, highly star-forming and morphologically complex ULIRG at
We present Atacama Large Millimeter/Submillimeter Array (ALMA) [CII] and
continuum observations of REBELS-25, a massive,
morphologically complex ultra-luminous infrared galaxy (ULIRG; L) at , spectroscopically
confirmed by the Reionization Era Bright Emission Line Survey (REBELS) ALMA
Large Programme. REBELS-25 has a significant stellar mass of
M. From dust-continuum and ultraviolet
observations, we determine a total obscured + unobscured star formation rate of
SFR M yr. This is about four times the SFR
estimated from an extrapolated main-sequence. We also infer a [CII]-based
molecular gas mass of ,
implying a molecular gas depletion time of Gyr. We observe a [CII] velocity gradient consistent
with disc rotation, but given the current resolution we cannot rule out a more
complex velocity structure such as a merger. The spectrum exhibits excess [CII]
emission at large positive velocities ( km s), which we
interpret as either a merging companion or an outflow. In the outflow scenario,
we derive a lower limit of the mass outflow rate of 200 M yr,
which is consistent with expectations for a star formation-driven outflow.
Given its large stellar mass, SFR and molecular gas reservoir Myr
after the Big Bang, we explore the future evolution of REBELS-25. Considering a
simple, conservative model assuming an exponentially declining star formation
history, constant star formation efficiency, and no additional gas inflow, we
find that REBELS-25 has the potential to evolve into a galaxy consistent with
the properties of high-mass quiescent galaxies recently observed at .Comment: Accepted for publication in MNRAS. 21 pages, 8 figure
Reionization Era Bright Emission Line Survey: selection and characterization of luminous interstellar medium reservoirs in the z > 6.5 universe
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 deg2 area for bright [C ii]158 ÎŒm and [O iii]88 ÎŒm 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 âŒ4-5Ă 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 â„ 7Ï [C ii]158 ÎŒm lines have already been discovered, the bulk of which (13/18) also show â„3.3Ï 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 Lyα discoveries. An analysis of the completeness of our search results versus star formation rate (SFR) suggests an âŒ79% efficiency in scanning for [C ii]158 ÎŒm when the SFRUV+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
The ALMA REBELS Survey: Dust Continuum Detections at z > 6.5
We report 18 dust continuum detections () at and out of 49 ultraviolet(UV)-bright galaxies (, observed by the Cycle-7 ALMA Large Program, REBELS
and its pilot programs. This has more than tripled the number of dust continuum
detections known at . Out of these 18 detections, 12 are reported for
the first time as part of REBELS. In addition, 15 of the dust continuum
detected galaxies also show a [CII] emission line,
providing us with accurate redshifts. We anticipate more line emission
detections from six targets (including three continuum detected targets) where
observations are still ongoing. The dust continuum detected sources in our
sample tend to have a redder UV spectral slope than the ones without a dust
continuum detection. We estimate that all of the sources have an infrared (IR)
luminosity () in a range of , except
for one with . Their
fraction of obscured star formation is significant at . Some of
the dust continuum detected galaxies show spatial offsets ()
between the rest-UV and far-IR emission peaks. These separations appear to have
an increasing trend against an indicator that suggests spatially decoupled
phases of obscured and unobscured star formation. REBELS offers the best
available statistical constraints on obscured star formation in UV-bright,
massive galaxies at .Comment: 17 pages, 9 figures, submitted to MNRA
The ALMA REBELS Survey : Average [CII] 158ÎŒm Sizes of Star-forming Galaxies from z~7 to z~4
We present the average [C II] 158 ÎŒm emission line sizes of UV-bright star-forming galaxies at z ~ 7. Our results are derived from a stacking analysis of [C II] 158 ÎŒm emission lines and dust continua observed by the Atacama Large Millimeter/submillimeter Array (ALMA), taking advantage of the large program Reionization Era Bright Emission Line Survey. We find that the average [C II] emission at z ~ 7 has an effective radius re of 2.2 ± 0.2 kpc. It is â„2Ă larger than the dust continuum and the rest-frame UV emission, in agreement with recently reported measurements for z †6 galaxies. Additionally, we compared the average [C II] size with 4 < z < 6 galaxies observed by the ALMA Large Program to INvestigate [C II] at Early times (ALPINE). By analyzing [C II] sizes of 4 < z < 6 galaxies in two redshift bins, we find an average [C II] size of re = 2.2 ± 0.2 kpc and re = 2.5 ± 0.2 kpc for z ~ 5.5 and z ~ 4.5 galaxies, respectively. These measurements show that star-forming galaxies, on average, show no evolution in the size of the [C II] 158 ÎŒm emitting regions at redshift between z ~ 7 and z ~ 4. This finding suggests that the star-forming galaxies could be morphologically dominated by gas over a wide redshift range
The lifecycle of molecular clouds in nearby star-forming disc galaxies
It remains a major challenge to derive a theory of cloud-scale (â âČ100âpc) star formation and feedback, describing how galaxies convert gas into stars as a function of the galactic environment. Progress has been hampered by a lack of robust empirical constraints on the giant molecular cloud (GMC) lifecycle. We address this problem by systematically applying a new statistical method for measuring the evolutionary timeline of the GMC lifecycle, star formation, and feedback to a sample of nine nearby disc galaxies, observed as part of the PHANGS-ALMA survey. We measure the spatially resolved (âŒ100âpc) CO-to-Hâα flux ratio and find a universal de-correlation between molecular gas and young stars on GMC scales, allowing us to quantify the underlying evolutionary timeline. GMC lifetimes are short, typically 10â30Myrâ , and exhibit environmental variation, between and within galaxies. At kpc-scale molecular gas surface densities ÎŁH2â„8Mâpcâ2â , the GMC lifetime correlates with time-scales for galactic dynamical processes, whereas at ÎŁH2â€8Mâpcâ2 GMCs decouple from galactic dynamics and live for an internal dynamical time-scale. After a long inert phase without massive star formation traced by Hâα (75-90 perâcent of the cloud lifetime), GMCs disperse within just 1â5Myr once massive stars emerge. The dispersal is most likely due to early stellar feedback, causing GMCs to achieve integrated star formation efficiencies of 4-10 perâcent. These results show that galactic star formation is governed by cloud-scale, environmentally dependent, dynamical processes driving rapid evolutionary cycling. GMCs and HâII regions are the fundamental units undergoing these lifecycles, with mean separations of 100â300pc in star-forming discs. Future work should characterize the multiscale physics and mass flows driving these lifecycles.MC and JMDK gratefully acknowledge funding
from the Deutsche Forschungsgemeinschaft (DFG, German
Research Foundation) through an Emmy Noether Research Group
(grant number KR4801/1-1) and the DFG Sachbeihilfe (grant
number KR4801/2-1). JMDK, APSH, SMRJ, and DTH gratefully
acknowledge funding from the European Research Council
(ERC) under the European Unionâs Horizon 2020 research and
innovation programme via the ERC Starting Grant MUSTANG
(grant agreement number 714907). MC, JMDK, SMRJ, and DTH
acknowledge support from the Australia-Germany Joint Research
Cooperation Scheme (UA-DAAD, grant number 57387355).
APSH, SMRJ, and DTH are fellows of the International Max
Planck Research School for Astronomy and Cosmic Physics
at the University of Heidelberg (IMPRS-HD). BG gratefully
acknowledges the support of the Australian Research Council
as the recipient of a Future Fellowship (FT140101202). CNC,
AH, and JP acknowledge funding from the Programme National
âPhysique et Chimie du Milieu Interstellaireâ (PCMI) of the Centre
national de la recherche scientifique/Institut national des sciences
de lâUnivers (CNRS/INSU) with the Institut de Chimie/Institut de
Physique (INC/INP), co-funded by the Commissariat a lâ ` energie ÂŽ
atomique et aux energies alternatives (CEA) and the Centre ÂŽ
national dâetudes spatiales (CNES). AH acknowledges support ÂŽ
by the Programme National Cosmology et Galaxies (PNCG) of
CNRS/INSU with the INP and the Institut national de physique
nucleaire et de physique des particules (IN2P3), co-funded by ÂŽ
CEA and CNES. PL, ES, CF, DL, and TS acknowledge funding
from the ERC under the European Unionâs Horizon 2020 research
and innovation programme (grant agreement No. 694343).
The work of AKL, JS, and DU is partially supported by the
National Science Foundation (NSF) under Grants No. 1615105,
1615109, and 1653300. AKL also acknowledges partial support
from the National Aeronautics and Space Administration
(NASA) Astrophysics Data Analysis Program (ADAP) grants
NNX16AF48G and NNX17AF39G. ER acknowledges the support
of the Natural Sciences and Engineering Research Council of
Canada (NSERC), funding reference number RGPIN-2017-03987.
FB acknowledges funding from the ERC under the European
Unionâs Horizon 2020 research and innovation programme (grant
agreement No. 726384). GB is supported by the Fondo de Fomento
al Desarrollo CientŽıfico y Tecnologico of the Comisi Ž on Nacional de Ž
Investigacion Cient Ž Žıfica y Tecnologica (CONICYT/FONDECYT), Ž
Programa de Iniciacion, Folio 11150220. SCOG acknowledges ÂŽ
support from the DFG via SFB 881 âThe Milky Way Systemâ
(subprojects B1, B2, and B8) and also via Germanyâs
Excellence Strategy EXC-2181/1â390900948 (the Heidelberg
STRUCTURES Excellence Cluster). KK gratefully acknowledges
funding from the DFG in the form of an Emmy Noether
Research Group (grant number KR4598/2-1, PI Kreckel). AU
acknowledges support from the Spanish funding grants AYA2016-79006-P (MINECO/FEDER) and PGC2018-094671-B-I00
(MCIU/AEI/FEDER)
The lifecycle of molecular clouds in nearby star-forming disc galaxies
It remains a major challenge to derive a theory of cloud-scale (â âČ100âpc) star formation and feedback, describing how galaxies convert gas into stars as a function of the galactic environment. Progress has been hampered by a lack of robust empirical constraints on the giant molecular cloud (GMC) lifecycle. We address this problem by systematically applying a new statistical method for measuring the evolutionary timeline of the GMC lifecycle, star formation, and feedback to a sample of nine nearby disc galaxies, observed as part of the PHANGS-ALMA survey. We measure the spatially resolved (âŒ100âpc) CO-to-Hâα flux ratio and find a universal de-correlation between molecular gas and young stars on GMC scales, allowing us to quantify the underlying evolutionary timeline. GMC lifetimes are short, typically 10â30 Myrâ , and exhibit environmental variation, between and within galaxies. At kpc-scale molecular gas surface densities ÎŁ_(Hâ) â„ 8 M_â pcâ»ÂČâ , the GMC lifetime correlates with time-scales for galactic dynamical processes, whereas at ÎŁ_(Hâ) †8 M_â pcâ»ÂČ GMCs decouple from galactic dynamics and live for an internal dynamical time-scale. After a long inert phase without massive star formation traced by Hâα (75â90 perâcent of the cloud lifetime), GMCs disperse within just 1â5 Myr once massive stars emerge. The dispersal is most likely due to early stellar feedback, causing GMCs to achieve integrated star formation efficiencies of 4â10 perâcent. These results show that galactic star formation is governed by cloud-scale, environmentally dependent, dynamical processes driving rapid evolutionary cycling. GMCs and HâII regions are the fundamental units undergoing these lifecycles, with mean separations of 100â300 pc in star-forming discs. Future work should characterize the multiscale physics and mass flows driving these lifecycles
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