arXiv subjects

Carlos De Breuck

Publications and source records attributed to Carlos De Breuck.

At least 55 records · Page 3Linked to original sources

arXiv2021

The Atacama Large Aperture Submillimetre Telescope (AtLAST)

The coldest and densest structures of gas and dust in the Universe have unique spectral signatures across the (sub-)millimetre bands ($ν\approx 30-950$~GHz). The current generation of single dish facilities has given a glimpse of the potential for discovery, while sub-mm interferometers have presented a high resolution view into the finer details of known targets or in small-area deep fields. However, significant advances in our understanding of such cold and dense structures are now hampered by the limited sensitivity and angular resolution of our sub-mm view of the Universe at larger scales. In this context, we present the case for a new transformational astronomical facility in the 2030s, the Atacama Large Aperture Submillimetre Telescope (AtLAST). AtLAST is a concept for a 50-m-class single dish telescope, with a high throughput provided by a 2~deg - diameter Field of View, located on a high, dry site in the Atacama with good atmospheric transmission up to $ν\sim 1$~THz, and fully powered by renewable energy. We envision AtLAST as a facility operated by an international partnership with a suite of instruments to deliver the transformative science that cannot be achieved with current or in-construction observatories. As an 50m-diameter telescope with a full complement of advanced instrumentation, including highly multiplexed high-resolution spectrometers, continuum cameras and integral field units, AtLAST will have mapping speeds hundreds of times greater than current or planned large aperture ($>$ 12m) facilities. By reaching confusion limits below L$_*$ in the distant Universe, resolving low-mass protostellar cores at the distance of the Galactic Centre, and directly mapping both the cold and the hot (the Sunyaev-Zeldovich effect) circumgalactic medium of galaxies, AtLAST will enable a fundamentally new understanding of the sub-mm Universe.

astro-ph.IM↗

arXiv2020

Massive molecular gas reservoir around the central AGN in the CARLA J1103+3449 cluster at z=1.44

Passive early-type galaxies dominate cluster cores at z $\lesssim$1.5. At higher redshift, cluster core galaxies are observed to have still on-going star-formation, fuelled by cold molecular gas. We measure the molecular gas reservoir of the central region around the radio-loud AGN in the cluster CARLA J1103+3449 at z=1.44 with NOEMA. The AGN synchrotron emission dominates the continuum emission at 94.48 GHz, and we measure its flux at the AGN position and at the position of two radio jets. Combining our measurements with published results over the range 4.71 GHz-94.5 GHz, we obtain a flat spectral index $α= 0.14 \pm 0.03$ for the AGN core emission, and a steeper index $α= 1.43 \pm 0.04$ and $α= 1.15 \pm 0.04$ at positions close to the western and eastern lobe, respectively. The total spectral index is $α= 0.92 \pm 0.02$ over the range 73.8 MHz-94.5 GHz. We detect two CO(2-1) emission lines, both blue-shifted with respect to the AGN. Their emission corresponds to two regions, ~17 kpc south-east and ~14 kpc south-west of the AGN, not associated with galaxies. In these two regions, we find a total massive molecular gas reservoir of $M_{gas}$ = 3.9 $\pm$ 0.4 $10^{10} M_{\odot}$, which dominates (~ 60%) the central total molecular gas reservoir. These results can be explained by massive cool gas flows in the center of the cluster. The AGN early-type host is not yet quenched; its star formation rate is consistent with being on the main sequence of star-forming galaxies in the field (SFR~30-140 $M_{\odot}$/yr), and the cluster core molecular gas reservoir is expected to feed the AGN and the host star-formation before quiescence. The other cluster confirmed members show star formation rates at ~2 $σ$ below the field main sequence at similar redshifts and do not have molecular gas masses larger than galaxies of similar stellar mass in the field.

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arXiv2020

BAT AGN Spectroscopic Survey-XX: Molecular Gas in Nearby Hard X-ray Selected AGN Galaxies

We present the host galaxy molecular gas properties of a sample of 213 nearby (0.01 10^44 erg/s) increases by ~10-100 between a molecular gas mass of 10^8.7 Msun and 10^10.2 Msun. Higher Eddington ratio AGN galaxies tend to have higher molecular gas masses and gas fractions. Higher column density AGN galaxies (Log NH>23.4) are associated with lower depletion timescales and may prefer hosts with more gas centrally concentrated in the bulge that may be more prone to quenching than galaxy wide molecular gas. The significant average link of host galaxy molecular gas supply to SMBH growth may naturally lead to the general correlations found between SMBHs and their host galaxies, such as the correlations between SMBH mass and bulge properties and the redshift evolution of star formation and SMBH growth.

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arXiv2020

Investigating orientation effects considering angular resolution for a sample of radio-loud quasars using VLA observations

Radio core dominance measurements, an indicator of jet orientation, sometimes rely on core flux density measurements from large-area surveys like Faint Images of the Radio Sky at Twenty cm (FIRST) that have an angular resolution of only 5''. Such low-resolution surveys often fail to resolve cores from the extended emission resulting in an erroneous measurement. We focus on investigating this resolution effect for a sample of 119 radio-loud quasars. We obtained continuum observations from NSF's Karl G. Jansky Very Large Array (VLA) at 10 GHz in A-array with a 0.2'' resolution. Our measurements show that at FIRST spatial resolution, core flux measurements are indeed systematically high even after considering the core-variability. For a handful of quasars, 10 GHz images reveal extended features, whereas the FIRST image shows a point source. We found that the resolution effect is more prominent for quasars with smaller angular sizes. We further computed two radio core dominance parameters R & R5100 for use in statistical orientation investigations with this sample. We also present the spectral energy distributions between 74 MHz and 1.4 GHz, which we used to measure the spectral index of the extended emission of these quasars. Our results empirically confirm that determination of radio core dominance requires high-spatial resolution data. We highlight the practical issues associated with the choice of frequency and resolution in the measurement of core and extended flux densities.

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arXiv2020

Overdensities of Submillimetre-Bright Sources around Candidate Protocluster Cores Selected from the South Pole Telescope Survey

We present APEX-LABOCA 870 micron observations of the fields surrounding the nine brightest, high-redshift, unlensed objects discovered in the South Pole Telescope's (SPT) 2500 square degrees survey. Initially seen as point sources by SPT's 1-arcmin beam, the 19-arcsec resolution of our new data enables us to deblend these objects and search for submillimetre (submm) sources in the surrounding fields. We find a total of 98 sources above a threshold of 3.7 sigma in the observed area of 1300 square arcminutes, where the bright central cores resolve into multiple components. After applying a radial cut to our LABOCA sources to achieve uniform sensitivity and angular size across each of the nine fields, we compute the cumulative and differential number counts and compare them to estimates of the background, finding a significant overdensity of approximately 10 at 14 mJy. The large overdensities of bright submm sources surrounding these fields suggest that they could be candidate protoclusters undergoing massive star-formation events. Photometric and spectroscopic redshifts of the unlensed central objects range from 3 to 7, implying a volume density of star-forming protoclusters of approximately 0.1 per giga-parsec cube. If the surrounding submm sources in these fields are at the same redshifts as the central objects, then the total star-formation rates of these candidate protoclusters reach 10,000 solar masses per year, making them much more active at these redshifts than what has been seen so far in both simulations and observations.

astro-ph.CO↗

arXiv2020

ALMA and MUSE observations reveal a quiescent multi-phase circumgalactic medium around the z~3.6 radio galaxy 4C 19.71

We present MUSE/VLT imaging spectroscopy of rest-frame ultraviolet emission lines and ALMA observations of the [CI] $^3$P$_1$-$^3$P$_0$ emission line, probing both the ionized and diffuse molecular medium around the radio galaxy 4C 19.71 at z~3.6. This radio galaxy has extended Ly$α$ emission over a region ~100 kpc in size preferentially oriented along the axis of the radio jet. Faint Ly$α$ emission extends beyond the radio hot spots. We also find extended CIV and HeII emission over a region of ~150 kpc in size, where the most distant emission lies ~40 kpc beyond the north radio lobe and has narrow FWHM line widths of ~180 km/s and a small relative velocity offset $Δ$v~130 km/s from the systemic redshift of the radio galaxy. The [CI] is detected in the same region with FWHM~100 km/s and $Δ$v~5 km/s, while [CI] is not detected in the regions south of the radio galaxy. We interpret the coincidence in the northern line emission as evidence of relatively quiescent multi-phase gas residing within the halo at a projected distance of ~75 kpc from the host galaxy. To test this hypothesis, we performed photoionization and photo-dissociated region (PDR) modeling, using the code Cloudy, of the three emission line regions: the radio galaxy proper and the northern and southern regions. We find that the [CI]/CIV$λλ$1548,1551 and CIV$λλ$1548,1551/HeII ratios of the two halo regions are consistent with a PDR or ionization front in the circumgalactic medium likely energized by photons from the active galactic nuclei. This modeling is consistent with a relatively low metallicity, 0.03<[Z/Z$_{\odot}$]<0.1, and diffuse ionization with an ionization parameter (proportional to the ratio of the photon number density and gas density) of log U~3 for the two circumgalactic line emission regions. Using rough mass estimates for the molecular [...]

astro-ph.GA↗

arXiv2019

A dense, solar metallicity ISM in the z=4.2 dusty star-forming galaxy SPT0418-47

We present a study of six far-infrared fine structure lines in the z=4.225 lensed dusty star-forming galaxy SPT0418-47 to probe the physical conditions of its InterStellar Medium (ISM). In particular, we report Atacama Pathfinder EXperiment (APEX) detections of the [OI]145um and [OIII]88um lines and Atacama Compact Array (ACA) detections of the [NII]122 and 205um lines. The [OI]145um / [CII]158um line ratio is ~5x higher compared to the average of local galaxies. We interpret this as evidence that the ISM is dominated by photo-dissociation regions with high gas densities. The line ratios, and in particular those of [OIII]88um and [NII]122um imply that the ISM in SPT0418-47 is already chemically enriched close to solar metallicity. While the strong gravitational amplification was required to detect these lines with APEX, larger samples can be observed with the Atacama Large Millimeter/submillimeter Array (ALMA), and should allow to determine if the observed dense, solar metallicity ISM is common among these highly star-forming galaxies.

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arXiv2019

First [NII]122$μ$m line detection in a QSO-SMG pair BRI 1202-0725 at $z=4.69$

We report the first detection obtained with ALMA of the [N II] 122$μ$m line emission from a galaxy group BRI 1202-0725 at $z=4.69$ consisting of a QSO and a submilimeter-bright galaxy (SMG). Combining with a detection of [N II] 205$μ$m line in both galaxies, we constrain the electron densities of the ionized gas based on the line ratio of [NII]122/205. The derived electron densities are $26^{+12}_{-11}$ and $134^{+50}_{-39}$ cm$^{-3}$ for the SMG and the QSO, respectively. The electron density of the SMG is similar to that of the Galactic Plane and to the average of the local spirals. Higher electron densities by up to a factor of three could, however, be possible for systematic uncertainties of the line flux estimates. The electron density of the QSO is comparable to high-$z$ star-forming galaxies at $z=1.5-2.3$, obtained using rest-frame optical lines and with the lower limits suggested from stacking analysis on lensed starbursts at $z=1-3.6$ using the same tracer of [NII]. Our results suggest a large scatter of electron densities in global scale at fixed star formation rates for extreme starbursts. The success of the [N II] 122$μ$m and 205$μ$m detections at $z=4.69$ demonstrates the power of future systematic surveys of extreme starbursts at $z>4$ for probing the ISM conditions and the effects on surrounding environments.

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arXiv2019

Large Molecular Gas Reservoirs in Star Forming Cluster Galaxies

We present CO(2-1) observations of 72 galaxies in the nearby, disturbed Antlia galaxy cluster with the Atacama Pathfinder Experiment (APEX) telescope. The galaxies in our sample are selected to span a wide range of stellar masses ($10^{8}M_{\odot}\lesssim M_{\star} \lesssim 10^{10}M_{\odot}$) and star formation rates ($0.0005M_{\odot}\text{yr}^{-1}<\text{SFR}<0.3M_{\odot}\text{yr}^{-1}$). Reaching a depth of $23\text{mJy}$ in $50\text{km}\text{s}^{-1}$ channels, we report a total CO detection rate of $37.5\%$ and a CO detection rate of $86\%$ for sources within 1 dex of the main sequence. We compare our sample with a similar sample of galaxies in the field, finding that, for a fixed stellar mass and SFR, galaxies in the Antlia cluster have comparable molecular gas reservoirs to field galaxies. We find that $\sim41\%$ (11/27) of our CO detections display non-Gaussian CO(2-1) emission line profiles, and a number of these sources display evidence of quenching in their optical images. We also find that the majority of our sample lie either just below, or far below the main sequence of field galaxies, further hinting at potential ongoing quenching. We conclude that the Antlia cluster represents an intermediate environment between fields and dense clusters, where the gentler intracluster medium (ICM) allows the cluster members to retain their reservoirs of molecular gas, but in which the disturbed ICM is just beginning to influence the member galaxies, resulting in high SFRs and possible ongoing quenching.

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arXiv2019

The Atacama Large Aperture Submillimeter Telescope (AtLAST)

The sub-mm sky is a unique window for probing the architecture of the Universe and structures within it. From the discovery of dusty sub-mm galaxies, to the ringed nature of protostellar disks, our understanding of the formation, destruction, and evolution of objects in the Universe requires a comprehensive view of the sub-mm sky. The current generation single-dish sub-mm facilities have shown of the potential for discovery, while interferometers have presented a high resolution view into the finer details. However, our understanding of large-scale structure and our full use of these interferometers is now hampered by the limited sensitivity of our sub-mm view of the universe at larger scales. Thus, now is the time to start planning the next generation of sub-mm single dish facilities, to build on these revolutions in our understanding of the sub-mm sky. Here we present the case for the Atacama Large Aperture Submillimeter Telescope (AtLAST), a concept for a 50m class single dish telescope. We envision AtLAST as a facility operating as an international partnership with a suite of instruments to deliver the transformative science described in many Astro2020 science white papers. A 50m telescope with a high throughput and 1$^\circ$ FoV with a full complement of advanced instrumentation, including highly multiplexed high-resolution spectrometers, continuum cameras and Integral Field Units, AtLAST will have mapping speeds thousands of times greater than any current or planned facility. It will reach confusion limits below $L_*$ in the distant universe and resolve low-mass protostellar cores at the distance of the Galactic Center, providing synergies with upcoming facilities across the spectrum. Located on the Atacama plateau, to observe frequencies un-obtainable by other observatories, AtLAST will enable a fundamentally new understanding of the sub-mm universe at unprecedented depths.

astro-ph.IM↗

arXiv2019

Imaging the Molecular Interstellar Medium in a Gravitationally Lensed Star-forming Galaxy at z=5.7

Aims: We present and study spatially resolved imaging obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) of multiple $^{12}$CO($J=$6$-$5, 8$-$7 and 9$-$8) and two H$_2$O(2$_{02}-$1$_{11}$ and 2$_{11}-$2$_{02}$) emission lines and cold dust continuum toward the gravitationally lensed dusty star forming galaxy SPT0346-52 at z=$5.656$. Methods: Using a visibility-domain source-plane reconstruction we probe the structure and dynamics of the different components of the interstellar medium (ISM) in this galaxy down to scales of 1 kpc in the source plane. Results: Measurements of the intrinsic sizes of the different CO emission lines indicate that the higher J transitions trace more compact regions in the galaxy. Similarly, we find smaller dust continuum intrinsic sizes with decreasing wavelength, based on observations at rest-frame 130, 300 and 450$μ$m. The source shows significant velocity structure, and clear asymmetry where an elongated structure is observed in the source plane with significant variations in their reconstructed sizes. This could be attributed to a compact merger or turbulent disk rotation. The differences in velocity structure through the different line tracers, however, hint at the former scenario in agreement with previous [CII] line imaging results. Measurements of the CO line ratios and magnifications yield significant variations as a function of velocity, suggesting that modeling of the ISM using integrated values could be misinterpreted. Modeling of the ISM in SPT0346-52 based on delensed fluxes indicate a highly dense and warm medium, qualitatively similar to that observed in high redshift quasar hosts.

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arXiv2019

Wide Bandwidth Considerations for ALMA Band 2

One of the main considerations in the ALMA Development Roadmap for the future of operations beyond 2030 is to at least double its on-sky instantaneous bandwidth capabilities. Thanks to the technological innovations of the past two decades, we can now produce wider bandwidth receivers than were foreseen at the time of the original ALMA specifications. In several cases, the band edges set by technology at that time are also no longer relevant. In this memo, we look into the scientific advantages of beginning with Band 2 when implementing such wideband technologies. The Band 2 receiver system will be the last of the original ALMA bands, completing ALMA's coverage of the atmospheric windows from 35-950 GHz, and is not yet covered by any other ALMA receiver. New receiver designs covering and significantly extending the original ALMA Band 2 frequency range (67-90 GHz) can now implement these technologies. We explore the scientific and operational advantages of a receiver covering the full 67-116 GHz atmospheric window. In addition to technological goals, the ALMA Development Roadmap provides 3 new key science drivers for ALMA, to probe: 1) the Origins of Galaxies, 2) the Origins of Chemical Complexity, and 3) the Origins of Planets. In this memo, we describe how the wide RF Band 2 system can help achieve these goals, enabling several high-profile science programmes to be executed uniquely or more effectively than with separate systems, requiring an overall much lower array time and achieving more consistent calibration accuracy: contiguous broad-band spectral surveys, measurements of deuterated line ratios, and more generally fractionation studies, improved continuum measurements (also necessary for reliable line flux measurements), simultaneous broad-band observations of transient phenomena, and improved bandwidth for 3 mm very long baseline interferometry (VLBI).

astro-ph.IM↗

arXiv2019

The hidden circumgalactic medium

The cycling of baryons in and out of galaxies is what ultimately drives galaxy formation and evolution. The circumgalactic medium (CGM) represents the interface between the interstellar medium and the cosmic web, hence its properties are directly shaped by the baryon cycle. Although traditionally the CGM is thought to consist of warm and hot gas, recent breakthroughs are presenting a new scenario according to which an important fraction of its mass may reside in the cold atomic and molecular phase. This would represent fuel that is readily available for star formation, with crucial implications for feeding and feedback processes in galaxies. However, such cold CGM, especially in local galaxies where its projected size on sky is expected to be of several arcminutes, cannot be imaged by ALMA due to interferometric spatial scale filtering of large-scale structures. We show that the only way to probe the multiphase CGM including its coldest component is through a large (e.g. 50-m) single dish (sub-)mm telescope.

astro-ph.GA↗

arXiv2019

Quenching by gas compression and consumption: A case study of a massive radio galaxy at z = 2.57

The objective of this work is to study how active galactic nuclei (AGN) influence star formation in host galaxies. We present a detailed investigation of the star-formation history and conditions of a $z=2.57$ massive radio galaxy based on VLT/X-SHOOTER and ALMA observations. The deep rest-frame ultraviolet spectrum contains photospheric absorption lines and wind features indicating the presence of OB-type stars. The most significantly detected photospheric features are used to characterize the recent star formation: neither instantaneous nor continuous star-formation history is consistent with the relative strength of the Si II $λ$1485 and S V $λ$1502 absorption. Rather, at least two bursts of star formation took place in the recent past, at $6^{+1}_{-2}$ Myr and $\gtrsim20$ Myr ago, respectively. We deduce a molecular H$_{2}$ gas mass of $(3.9\pm1.0)\times10^{10}$ M$_{\odot}$ based on ALMA observations of the [C I] $^3$P$_{2}$-$^3$P$_{1}$ emission. The molecular gas mass is only 13 % of its stellar mass. Combined with its high star-formation rate of ($1020^{+190}_{-170}$) Myr, this implies a high star-formation efficiency of $(26\pm8$) Gyr$^{-1}$ and a short depletion time of $(38\pm12)$ Myr. We attribute the efficient star formation to compressive gas motions in order to explain the modest velocity dispersions ($\leqslant$ 55 km s$^{-1}$) of the photospheric lines and of the star-forming gas traced by [C I]. Because of the likely very young age of the radio source, our findings suggest that vigorous star formation consumes much of the gas and works in concert with the AGN to remove any residual molecular gas, and eventually quenching star formation in massive galaxies.

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arXiv2019

Precipitable Water Vapor, Temperature, and Wind Statistics At Sites Suitable for mm and Submm Wavelength Astronomy in Northern Chile

Atmospheric water vapor is the main limiting factor of atmospheric transparency in the mm and submm wavelength spectral windows. Thus, dry sites are needed for the installation and successful operation of radio astronomy observatories exploiting those spectral windows. Temperature and wind are variables of special consideration when planning the installation and operation of large-aperture radio telescopes, as these parameters affect the mechanical response of radio telescopes exposed to the environmental conditions. Temperature, and in particular temperature gradients, induce thermal deformation of mechanical structures, while high wind speeds and gusts induce pointing jitter affecting the tracking accuracy of astronomical sources during the observations. This work summarizes the statistics of precipitable water vapor (PWV), temperature, and wind monitored at sites by the coastal mountain range, as well as on the west slope of the Andes mountain range in the region of Antofagasta, Chile. This information could prove useful for the planning of extended baselines for the Atacama Large Millimeter and Submillimeter Array (ALMA), and/or new radio telescope projects, such as the Atacama Large Aperture Submm/ mm Telescope (AtLAST) initiative.

astro-ph.IM↗

arXiv2018

Massive galaxies on the road to quenching: ALMA observations of powerful high redshift radio galaxies

We present 0.3" (band 6) and 1.5" (band 3) ALMA observations of the (sub)millimeter dust continuum emission for 25 radio galaxies at 1<z<5.2. Our survey reaches a rms flux density of ~50$μ$Jy in band 6 and ~20$μ$Jy in band 3. This is an order of magnitude deeper than single-dish 850 $μ$m observations, and reaches fluxes where synchrotron and thermal dust emission are expected to be of the same order of magnitude. Combining our sensitive ALMA observations with radio data from ATCA, VLA, and IR photometry from Herschel and Spitzer, we have disentangled the synchrotron and thermal dust emission. We determine the star-formation rates (SFR) and AGN IR luminosities using our newly developed spectral energy distribution fitting code MrMoose. We find that synchrotron emission contributes substantially at ~1 mm. Through our sensitive flux limits and accounting for a contribution from synchrotron emission in the mm, we revise downward the median SFR by a factor of 7 compared to previous estimates based solely on Herschel and Spitzer data. The hosts of these radio-loud AGN appear predominantly below the main sequence of star-forming galaxies, indicating that the star formation in many of the host galaxies has been quenched. Future growth of the host galaxies without substantial black hole mass growth will be needed to bring these objects on the local relation between the supermassive black holes and their host galaxies. Given the mismatch in the timescales of any star formation that took place in the host galaxies and lifetime of the AGN, we hypothesize that a key role is played by star formation in depleting the gas before the action of the powerful radio jets quickly drives out the remaining gas. This positive feedback loop of efficient star formation rapidly consuming the gas coupled to the action of the radio jets in removing the residual gas is how massive galaxies are rapidly quenched.

astro-ph.GA↗

arXiv2018

Neutral versus ionized gas kinematics at z~2.6: The AGN-host starburst galaxy PKS 0529-549

We present a multiwavelength study of the AGN-host starburst galaxy PKS 0529-549 at z~2.6. We use (1) new ALMA observations of the dust continuum and of the [CI] 370 um line, tracing molecular gas, (2) SINFONI spectroscopy of the [OIII] 5007 Ang line, tracing ionized gas, and (3) ATCA radio continuum images, tracing synchrotron emission. Both [CI] and [OIII] show regular velocity gradients, but their systemic velocities and position angles differ by ~300 km/s and ~30 degrees, respectively. The [CI] is consistent with a rotating disc, aligned with the dust and stellar continuum, while the [OIII] likely traces an outflow, aligned with two AGN-driven radio lobes. We model the [CI] cube using 3D disc models, which give best-fit rotation velocities V~310 km/s and velocity dispersions sigma<30 km/s. Hence, the [CI] disc has V/sigma>10 and is not particularly turbulent, similar to local galaxy discs. The dynamical mass (~10^11 Msun) is comparable to the baryonic mass within the errors. This suggests that baryons dominate the inner galaxy dynamics, similar to massive galaxies at z=0. Remarkably, PKS 0529-549 lies on the local baryonic Tully-Fisher relation, indicating that at least some massive galaxies are already in place and kinematically relaxed at z~2.6. This work highlights the potential of the [CI] line to trace galaxy dynamics at high z, as well as the importance of multiwavelength data to interpret gas kinematics.

astro-ph.GA↗

arXiv2018

$HST$ Grism Confirmation of $16$ Structures at $1.4 < z < 2.8$ from the Clusters Around Radio-Loud AGN (CARLA) Survey

We report spectroscopic results from our 40-orbit $Hubble~Space~Telescope$ slitless grism spectroscopy program observing the 20 densest CARLA candidate galaxy clusters at $1.4 < z < 2.8$. These candidate rich structures, among the richest and most distant known, were identified on the basis of $[3.6]-[4.5]$ color from a $408~$hr multi-cycle $Spitzer$ program targeting $420$ distant radio-loud AGN. We report the spectroscopic confirmation of $16$ distant structures at $1.4 < z < 2.8$ associated with the targeted powerful high-redshift radio-loud AGN. We also report the serendipitous discovery and spectroscopic confirmation of seven additional structures at $0.87 < z < 2.12$ not associated with the targeted radio-loud AGN. We find that $10^{10} - 10^{11}\,M_{\odot}$ member galaxies of our confirmed CARLA structures form significantly fewer stars than their field counterparts at all redshifts within $1.4\leq z\leq 2$. We also observe higher star-forming activity in the structure cores up to $z = 2$, finding similar trends as cluster surveys at slightly lower redshifts ($1.0 < z < 1.5$). By design, our efficient strategy of obtaining just two grism orbits per field only obtains spectroscopic confirmation of emission-line galaxies. Deeper spectroscopy will be required to study the population of evolved, massive galaxies in these (forming) clusters. Lacking multi-band coverage of the fields, we adopt a very conservative approach of calling all confirmations "structures", although we note that a number of features are consistent with some of them being bona fide galaxy clusters. Together, this survey represents a unique and large homogenous sample of spectroscopically confirmed structures at high redshifts, potentially more than doubling the census of confirmed, massive clusters at $z > 1.4$.

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