91 research outputs found
Environments of a sample of AzTEC submillimetre galaxies in the COSMOS field
Aims. Submillimetre galaxies (SMGs) are bright sources at submillimetre wavelengths (F-850 mu m>2-5 mJy). Made up of mostly of high-z galaxies (z>1), SMGs are amongst the most luminous dusty galaxies in the Universe. These galaxies are thought to be the progenitors of the massive elliptical galaxies in the local Universe and to reside in massive haloes at early epochs. Studying their environments and clustering strength is thus important to put these galaxies in a cosmological context.Methods. We present an environmental study of a sample of 116 SMGs in 96 ALMA observation fields, which were initially discovered with the AzTEC camera on ASTE and identified with high-resolution 1.25 mm ALMA imaging within the COSMOS survey field, having either spectroscopic or unambiguous photometric redshift. We analysed their environments making use of the latest release of the COSMOS photometric catalogue, COSMOS2015, a catalogue that contains precise photometric redshifts for more than half a million objects over the 2 deg(2) COSMOS field. We searched for dense galaxy environments computing the so-called overdensity parameter as a function of distance within a radius of 5 from the SMG. We validated this approach spectroscopically for those SMGs for which spectroscopic redshift is available. As an additional test, we searched for extended X-ray emission as a proxy for the hot intracluster medium, performing an X-ray stacking analysis in the 0.5-2 keV band with a 32 '' aperture and our SMG position using all available XMM-Newton and Chandra X-ray observations of the COSMOS field.Results. We find that 27% (31 out of 116) of the SMGs in our sample are located in a galactic dense environment; a fraction that is similar to previous studies. The spectroscopic redshift is known for 15 of these 31 sources, thus this photometric approach is tested using spectroscopy. We are able to confirm that 7 out of 15 SMGs lie in high-density peaks. However, the search for associated extended X-ray emission via an X-ray stacking analysis leads to a detection that is not statistically significant.Peer reviewe
Optimal Design of Thermal Membrane Distillation Systems for the Treatment of Shale Gas Flowback Water
Shale gas production is associated with the significant consumption of fresh water and discharge of wastewater. The flowback wastewater is tied to the hydraulic fracturing technology used for completing and stimulating the horizontal wells in the very tight formations characterizing the shale formation. Treatment and reuse of these large volumes of wastewater can lead to substantial savings in fresh water usage and reduction of the negative environmental impact thereby enhancing sustainability of the shale gas industry. Such treatment requires selective and cost-effective technology.Thermal membrane distillation (TMD) is an emerging technology that offers several advatanges such as high selectivity in separating water from inorganic solutes and modular nature that can accommodate a wide range of flows. It can also utilize low-level heats that are typically available from shale-gas production and processing.The objective of this work is to develop an optimization approach for the design of TMD systems to treat flowback water. A multi-period formulation is developed to account for the time-based variation in the flowrate and concentration of the flowback water. Modeling equations are used to relate design and operating variables to performance and cost. The optimization formulation also accounts for the period-based changes in the required design and operating variables and reconciles them over the selected periods. Other constraints include quality of the permeate and water-recovery ratio. The optimization formulation and design approach are applied to a case study for the treatment of flowback water for the Marcellus Shale Play. For 75% water recovery, the cost of the permeate is about $2.6/m3. As higher recoveries are sought, the cost per m3 of permeate increases due to capital productivity factors in dealing with the decreasing amount of flowback water over time. The results are reported using a Pareto chart that trades off recovery objectives with cost of treated water
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Development of NMRI spectroscopy for improved petroleum recovery, Annex 6. Annual report, 1991
The overall objectives are to develop and apply Nuclear Magnetic Resonance Imaging (NMRI) and CT X-Ray Scanning methods for determining rock, fluid, and petrophysical properties and for fundamental studies of multiphase flow behavior in porous media. Specific objectives are to: (1) develop NMRI procedures for measuring porosity, permeability, pore size distribution, capillary pressure, and wetting characteristics, (2) apply imaging methods for improved methods of determining two- and three-phase relative permeability functions, (3) apply NMRI for development of a better understanding of dispersed phase displacement processes, and (4) apply imaging methods to develop a better understanding of saturation distribution and fingering during miscible displacements. The objectives have been organized into four subtasks. Annual progress reports for each subtask are provided
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
Unveiling the hidden universe with JWST: The contribution of dust-obscured galaxies to the stellar mass function at
The emergence of massive, optically-faint galaxies in infrared observations
has revealed that our view of the high-redshift Universe was previously
incomplete. With the advent of JWST, we can for the first time probe the
rest-frame optical emission of galaxies at with high sensitivity and
spatial resolution, thus moving towards a more complete census of the galaxy
population at high redshifts. To this end, we present a sample of 148 massive,
dusty galaxies from the JWST/CEERS survey, colour-selected using solely JWST
bands. With deep JWST/NIRCam data from 1.15m to 4.44m and ancillary
HST/ACS and WFC3 data, we determine the physical properties of our sample using
spectral energy distribution fitting with BAGPIPES. We demonstrate that our
selection method efficiently identifies massive () and dusty () sources, with a majority at and predominantly lying on the
galaxy main-sequence. The main results of this work are the stellar mass
functions (SMF) of red, optically-faint galaxies from redshifts between
: these galaxies make up a significant fraction of the pre-JWST total
SMF at , and dominate the high-mass end of the pre-JWST SMF at
and , suggesting that our census of the galaxy population needs
amendment at these epochs. While larger areas need to be surveyed in the
future, our results suggest already that the integrated stellar mass density at
may have been underestimated by
20-25% at , and 110% at .Comment: 19 pages, 10 figures, submitted to MNRA
NOEMA observations of GN-z11: Constraining Neutral Interstellar Medium and Dust Formation in the Heart of Cosmic Reionization at
We present results of dust continuum and [CII] emission
line observations of a remarkably UV-luminous () galaxy at
: GN-z11. Using the Northern Extended Millimeter Array (NOEMA),
observations have been carried out over multiple observing cycles. We achieved
a high sensitivity resulting in a
continuum depth of and a [CII] emission
line sensitivity of using
binning with a synthesized beam. Neither dust continuum
nor [CII] line emission are detected at the expected
frequency of and the sky location of
GN-z11. The upper limits show that GN-z11 is neither luminous in
nor , with a dust mass limit of and with a [CII] based molecular gas mass
limit of .
Together with radiative transfer calculations, we also investigated the
possible cause of the dust poor nature of the GN-z11 showed by the blue color
in the UV continuum of GN-z11 (), and found that
deeper observations are crucial to study dust production at
very high-redshift. Nevertheless, our observations show the crucial role of
deep mm/submm observations of very high redshift galaxies to constrain multiple
phases in the interstellar medium.Comment: submitted to MNRAS, 7 pages, 4 figures, 1 tabl
The ALMA REBELS Survey : Average [CII] 158μm Sizes of Star-forming Galaxies from z~7 to z~4
We present the average [C II] 158 μm emission line sizes of UV-bright star-forming galaxies at z ~ 7. Our results are derived from a stacking analysis of [C II] 158 μm 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 ≥2× 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 μm 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 ALMA REBELS survey: obscured star formation in massive Lyman-break galaxies at z = 4-8 revealed by the IRX- and relations
We investigate the degree of dust obscured star formation in 49 massive
() Lyman-break galaxies (LBGs) at
- observed as part of the ALMA Reionization Era Bright Emission
Line Survey (REBELS) large program. By creating deep stacks of the photometric
data and the REBELS ALMA measurements we determine the average rest-frame UV,
optical and far-infrared (FIR) properties which reveal a significant fraction
(-) of obscured star formation, consistent with
previous studies. From measurements of the rest-frame UV slope, we find that
the brightest LBGs at these redshifts show bluer () colours
than expected from an extrapolation of the colour-magnitude relation found at
fainter magnitudes. Assuming a modified blackbody spectral-energy distribution
(SED) in the FIR (with dust temperature of and
), we find that the REBELS sources are in agreement with
the local ''Calzetti-like'' starburst Infrared-excess (IRX)- relation.
By reanalysing the data available for 108 galaxies at - from the
ALPINE ALMA large program using a consistent methodology and assumed FIR SED,
we show that from -, massive galaxies selected in the rest-frame
UV have no appreciable evolution in their derived IRX- relation. When
comparing the IRX- relation derived from the combined ALPINE and
REBELS sample to relations established at , we find a deficit in the
IRX, indicating that at the proportion of obscured star formation is
lower by a factor of at a given a . Our IRX-
results are in good agreement with the high-redshift predictions of simulations
and semi-analytic models for galaxies with similar stellar masses
and SFRs.Comment: 18 pages, 10 figures, 2 tables (plus 1 figure and 2 tables in the
appendix). Updated to match MNRAS accepted version after minor correction
Normal, dust-obscured galaxies in the epoch of reionization
Two serendipitously detected dust-obscured galaxies are reported at z = 6.7 and 7.4, with estimates that such galaxies provide an additional 10-25% contribution to the total star formation rate density at z > 6.Over the past decades, rest-frame ultraviolet (UV) observations have provided large samples of UV luminous galaxies at redshift (z) greater than 6 (refs. (1-3)), during the so-called epoch of reionization. While a few of these UV-identified galaxies revealed substantial dust reservoirs(4-7), very heavily dust-obscured sources at these early times have remained elusive. They are limited to a rare population of extreme starburst galaxies(8-12) and companions of rare quasars(13,14). These studies conclude that the contribution of dust-obscured galaxies to the cosmic star formation rate density at z > 6 is sub-dominant. Recent ALMA and Spitzer observations have identified a more abundant, less extreme population of obscured galaxies at z = 3-6 (refs. (15,16)). However, this population has not been confirmed in the reionization epoch so far. Here, we report the discovery of two dust-obscured star-forming galaxies at z = 6.6813 +/- 0.0005 and z = 7.3521 +/- 0.0005. These objects are not detected in existing rest-frame UV data and were discovered only through their far-infrared [C ii] lines and dust continuum emission as companions to typical UV-luminous galaxies at the same redshift. The two galaxies exhibit lower infrared luminosities and star-formation rates than extreme starbursts, in line with typical star-forming galaxies at z approximate to 7. This population of heavily dust-obscured galaxies appears to contribute 10-25% to the z > 6 cosmic star formation rate density
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
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