arXiv subjects

S. C. Chapman

Publications and source records attributed to S. C. Chapman.

At least 55 records · Page 3Linked to original sources

arXiv2018

Dense-gas tracers and carbon isotopes in five 2.5<z<4 lensed dusty star forming galaxies from the SPT SMG sample

The origin of the high SFR observed in high-z dusty star-forming galaxies is still unknown. Large fractions of dense molecular gas might provide part of the explanation, but there are few observational constraints on the amount of dense gas in high-z systems dominated by star formation. We present the results of our ALMA program targeting dense-gas tracers (HCN(5-4), HCO+(5-4), and HNC(5-4)) in 5 strongly lensed galaxies from the SPT SMG sample. We detected two of these lines (SNR>5) in SPT-125-47 at z=2.51 and tentatively detected all three (SNR~3) in SPT0551-50 at z=3.16. Since a significant fraction of our target lines is not detected, we developed a statistical method to derive unbiased mean properties taking into account both detections and non-detections. On average, the HCN(5-4) and HCO+(5-4) luminosities of our sources are a factor of ~1.7 fainter than expected, based on the local L'HCN(5-4)-LIR relation, but this offset corresponds to only ~2 sigma. We find that both the HCO+/HCN and HNC/HCN flux ratios are compatible with unity. The first ratio is expected for PDRs while the second is consistent with PDRs or XDRs and/or mid-IR pumping of HNC. Our sources are at the high end of the local relation between the star formation efficiency, determined using the LIR/[CI] and LIR/CO ratios, and the dense gas fraction, estimated using the HCN/[CI] and HCN/CO ratios. In SPT0125-47, we found that the velocity profiles of the lines tracing dense (HCN, HCO+) and lower-density (CO, [CI]) gas are similar. In addition to these lines, we obtained one robust and one tentative detection of 13CO(4-3) and found an average I12CO(4-3)/I13CO(4-3) flux ratio of 26.1$_{-3.5}^{+4.5}$, indicating a young but not pristine interstellar medium. We argue that the combination of large and slightly enriched gas reservoirs and high dense-gas fractions could explain the prodigious star formation in these systems.

astro-ph.GA↗

arXiv2018

Fast Molecular Outflow from a Dusty Star-Forming Galaxy in the Early Universe

Galaxies grow inefficiently, with only a few percent of the available gas converted into stars each free-fall time. Feedback processes, such as outflowing winds driven by radiation pressure, supernovae or supermassive black hole accretion, can act to halt star formation if they heat or expel the gas supply. We report a molecular outflow launched from a dust-rich star-forming galaxy at redshift 5.3, one billion years after the Big Bang. The outflow reaches velocities up to 800 km/s relative to the galaxy, is resolved into multiple clumps, and carries mass at a rate within a factor of two of the star formation rate. Our results show that molecular outflows can remove a large fraction of the gas available for star formation from galaxies at high redshift.

astro-ph.GA↗

arXiv2018

A machine-learning method for identifying multi-wavelength counterparts of submillimeter galaxies: training and testing using AS2UDS and ALESS

We describe the application of the supervised machine-learning algorithms to identify the likely multi-wavelength counterparts to submillimeter sources detected in panoramic, single-dish submillimeter surveys. As a training set, we employ a sample of 695 ($S_{\rm 870μm}$ >1 mJy) submillimeter galaxies (SMGs) with precise identifications from the ALMA follow-up of the SCUBA-2 Cosmology Legacy Survey's UKIDSS-UDS field (AS2UDS). We show that radio emission, near-/mid-infrared colors, photometric redshift, and absolute $H$-band magnitude are effective predictors that can distinguish SMGs from submillimeter-faint field galaxies. Our combined radio+machine-learning method is able to successfully recover $\sim$85 percent of ALMA-identified SMGs which are detected in at least three bands from the ultraviolet to radio. We confirm the robustness of our method by dividing our training set into independent subsets and using these for training and testing respectively, as well as applying our method to an independent sample of $\sim$100 ALMA-identified SMGs from the ALMA/LABOCA ECDF-South Survey (ALESS). To further test our methodology, we stack the 870$μ$m ALMA maps at the positions of those $K$-band galaxies that are classified as SMG counterparts by the machine-learning but do not have a $>$4.3$ σ$ ALMA detection. The median peak flux density of these galaxies is $S_{\rm 870μm}=(0.61\pm0.03)$ mJy, demonstrating that our method can recover faint and/or diffuse SMGs even when they are below the detection threshold of our ALMA observations. In future, we will apply this method to samples drawn from panoramic single-dish submillimeter surveys which currently lack interferometric follow-up observations, to address science questions which can only be tackled with large, statistical samples of SMGs.

astro-ph.GA↗

arXiv2018

An ALMA survey of CO in submillimetre galaxies: companions, triggering, and the environment in blended sources

We present ALMA observations of the mid-J 12CO emission from six single-dish selected 870-micron sources in the Extended Chandra Deep Field-South (ECDFS) and UKIDSS Ultra-Deep Survey (UDS) fields. These six single-dish submillimetre sources were selected based on previous ALMA continuum observations, which showed that each comprised a blend of emission from two or more individual submillimetre galaxies (SMGs), separated on 5--10 arcsec scales. The six single-dish submillimetre sources targeted correspond to a total of 14 individual SMGs, of which seven have previously-measured robust optical/near-infrared spectroscopic redshifts, which were used to tune our ALMA observations. We detect CO(3-2) or CO(4-3) at z=2.3--3.7 in seven of the 14 SMGs, and in addition serendipitously detect line emission from three gas-rich companion galaxies, as well as identify four new 3.3-mm selected continuum sources in the six fields. Joint analysis of our CO spectroscopy and existing data suggests that 64 \pm 18% of the SMGs in blended submillimetre sources are unlikely to be physically associated. However, three of the SMG fields (50%) contain new, serendipitously-detected CO-emitting (but submillimetre-faint) sources at similar redshifts to the 870-micron selected SMGs we targeted. These data suggest that the SMGs inhabit overdense regions, but that these are not sufficiently overdense on ~100 kpc scales to influence the source blending given the short lifetimes of SMGs. We find that 21 \pm 12% of SMGs have spatially-distinct and kinematically-close companion galaxies (~8--150 kpc and <~300 km/s), which may have enhanced their star-formation via gravitational interactions.

astro-ph.GA↗

arXiv2018

An ALMA survey of the SCUBA-2 Cosmology Legacy Survey UKIDSS/UDS field: number counts of submillimeter galaxies

We report the first results of AS2UDS: an 870 $μ$m continuum survey with the Atacama Large Millimeter/Submillimeter Array (ALMA) of a total area of $\sim$ 50 arcmin$^2$ comprising a complete sample of 716 submillimeter sources drawn from the SCUBA-2 Cosmology Legacy Survey (S2CLS) map of the UKIDSS/UDS field. The S2CLS parent sample covers a 0.96 degree$^2$ field at $σ_{850}=0.90\pm0.05$ mJy beam$^{-1}$. Our deep, high-resolution ALMA observations with $σ_{\rm 870}\sim$ 0.25 mJy and a 0.15"--0.30" FWHM synthesized beam, provide precise locations for 695 submillimetre galaxies (SMGs) responsible for the submillimeter emission corresponding to 606 sources in the low resolution, single-dish map. We measure the number counts of SMGs brighter than $S_{\rm 870}\geq$ 4 mJy, free from the effects of blending and show that the normalisation of the counts falls by 28 $\pm$ 2% in comparison to the SCUBA-2 parent sample, but that the shape remains unchanged. We determine that 44$^{+16}_{-14}$% of the brighter single-dish sources with $S_{850}\geq$ 9 mJy consist of a blend of two or more ALMA-detectable SMGs brighter than $S_{870}\sim$ 1 mJy (corresponding to a galaxy with a total-infrared luminosity of $L_{IR}\geq$ 10$^{12}$ L$_\odot$), in comparison to 28 $\pm$ 2% for the single-dish sources at $S_{\rm 850}\geq$ 5 mJy. Using the 46 single-dish submillimeter sources that contain two or more ALMA-detected SMGs with photometric redshifts, we show that there is a significant statistical excess of pairs of SMGs with similar redshifts ($<$1% probability of occurring by chance), suggesting that at least 30% of these blends arise from physically associated pairs of SMGs.

astro-ph.GA↗

arXiv2018

An ALMA survey of the SCUBA-2 Cosmology Legacy Survey UKIDSS/UDS field: Identifying candidate z~4.5 [CII] emitters

We report the results of a search for serendipitous [CII] 157.74$μ$m emitters at $z\sim4.4$-$4.7$ using the Atacama Large Millimeter/submillimeter Array (ALMA). The search exploits the AS2UDS continuum survey, which covers ~50 arcmin$^2$ of the sky towards 695 luminous ($S_{870}\gtrsim1$mJy) submillimeter galaxies (SMGs), selected from the SCUBA-2 Cosmology Legacy Survey (S2CLS) 0.96deg$^2$ Ultra Deep Survey (UDS) field. We detect ten candidate line emitters, with an expected false detection rate of ten percent. All of these line emitters correspond to 870$μ$m continuum-detected sources in AS2UDS. The emission lines in two emitters appear to be high-J CO, but the remainder have multi-wavelength properties consistent with [CII] from $z\simeq4.5$ galaxies. Using our sample, we place a lower limit of $>5\times10^{-6}$Mpc$^{-3}$ on the space density of luminous ($L_{\rm IR} \simeq 10^{13}$Lsun) SMGs at $z=4.40$-$4.66$, suggesting $\ge7$percent of SMGs with $S_{870μ{\rm m}}\gtrsim1$mJy lie at $4<z<5$. From stacking the high-resolution ($\sim0.15"$ full-width half maximum) ALMA $870μ$m imaging, we show that the [CII] line emission is more extended than the continuum dust emission, with an average effective radius for the [CII] of $r_{\rm e} = 1.7^{+0.1}_{-0.2}$kpc compared to $r_{\rm e} = 1.0\pm0.1$kpc for the continuum (rest-frame $160μ$m). By fitting the far-infrared photometry for these galaxies from $100$-$870μ$m, we show that SMGs at $z\sim4.5$ have a median dust temperature of $T_{\rm d}=55\pm4$K. This is systematically warmer than $870μ$m-selected SMGs at $z\simeq2$, which typically have temperatures around $35$K. These $z\simeq4.5$ SMGs display a steeper trend in the luminosity-temperature plane than $z\le2$ SMGs. We discuss the implications of this result in terms of the selection biases of high redshift starbursts in far-infrared/submillimeter surveys.

astro-ph.GA↗

arXiv2018

A massive core for a cluster of galaxies at a redshift of 4.3

Massive galaxy clusters are now found as early as 3 billion years after the Big Bang, containing stars that formed at even earlier epochs. The high-redshift progenitors of these galaxy clusters, termed 'protoclusters', are identified in cosmological simulations with the highest dark matter overdensities. While their observational signatures are less well defined compared to virialized clusters with a substantial hot intra-cluster medium (ICM), protoclusters are expected to contain extremely massive galaxies that can be observed as luminous starbursts. Recent claimed detections of protoclusters hosting such starbursts do not support the kind of rapid cluster core formation expected in simulations because these structures contain only a handful of starbursting galaxies spread throughout a broad structure, with poor evidence for eventual collapse into a protocluster. Here we report that the source SPT2349-56 consists of at least 14 gas-rich galaxies all lying at z = 4.31 based on sensitive observations of carbon monoxide and ionized carbon. We demonstrate that each of these galaxies is forming stars between 50 and 1000 times faster than our own Milky Way, and all are located within a projected region only $\sim$ 130 kiloparsecs in diameter. This galaxy surface density is more than 10 times the average blank field value (integrated over all redshifts) and $>$1000 times the average field volume density. The velocity dispersion ($\sim$ 410 km s$^{-1}$) of these galaxies and enormous gas and star formation densities suggest that this system represents a galaxy cluster core at an advanced stage of formation when the Universe was only 1.4 billion years old. A comparison with other known protoclusters at high redshifts shows that SPT2349-56 is a uniquely massive and dense system that could be building one of the most massive structures in the Universe today.

astro-ph.GA↗

arXiv2018

The dust and [CII] morphologies of redshift ~4.5 sub-millimeter galaxies at ~200pc resolution: The absence of large clumps in the interstellar medium of high-redshift galaxies

We present deep high resolution (0.03", 200pc) ALMA Band 7 observations covering the dust continuum and [CII] $\lambda157.7μ$m emission in four $z\sim4.4-4.8$ sub-millimeter galaxies (SMGs) selected from the ALESS and AS2UDS surveys. The data show that the rest-frame 160$μ$m (observed 345 GHz) dust emission is consistent with smooth morphologies on kpc scales for three of the sources. One source, UDS47.0, displays apparent substructure but this is also consistent with a smooth morphology, as indicated by simulations showing that smooth exponential disks can appear clumpy when observed at high angular resolution (0.03") and depth of these observations ($σ_{345\text{GHz}} \sim27-47μ$Jy beam$^{-1}$). The four SMGs are bright [CII] emitters, and we extract [CII] spectra from the high resolution data, and recover $\sim20-100$% of the [CII] flux and $\sim40-80$% of the dust continuum emission, compared to the previous lower resolution observations. When tapered to 0.2" resolution our maps recover $\sim80-100$% of the continuum emission, indicating that $\sim60$% of the emission is resolved out on $\sim200$pc scales. We find that the [CII] emission in high-redshift galaxies is more spatially extended than the rest-frame 160$μ$m dust continuum by a factor of $1.6\pm0.4$. By considering the $L_{\text{[CII]}}$/$L_{\text{FIR}}$ ratio as a function of the star-formation rate surface density ($Σ_{\text{SFR}}$) we revisit the [CII] deficit, and suggest that the decline in the $L_{\text{[CII]}}$/$L_{\text{FIR}}$ ratio as a function of $Σ_{\text{SFR}}$ is consistent with local processes. We also explore the physical drivers that may be responsible for these trends and can give rise to the properties found in the densest regions of SMGs.

astro-ph.GA↗

arXiv2018

Red, redder, reddest: SCUBA-2 imaging of colour-selected \textit{Herschel} sources

High-redshift, luminous, dusty star forming galaxies (DSFGs) constrain the extremity of galaxy formation theories. The most extreme are discovered through follow-up on candidates in large area surveys. Here we present 850 $μ$m SCUBA-2 follow-up observations of 188 red DSFG candidates from the \textit{Herschel} Multi-tiered Extragalactic Survey (HerMES) Large Mode Survey, covering 274 deg$^2$. We detected 87 per cent with a signal-to-noise ratio $>$ 3 at 850~$μ$m. We introduce a new method for incorporating the confusion noise in our spectral energy distribution fitting by sampling correlated flux density fluctuations from a confusion limited map. The new 850~$μ$m data provide a better constraint on the photometric redshifts of the candidates, with photometric redshift errors decreasing from $σ_z/(1+z)\approx0.21$ to $0.15$. Comparison spectroscopic redshifts also found little bias ($\langle (z-z_{\rm spec})/(1+z_{\rm spec})\rangle = 0.08 $). The mean photometric redshift is found to be 3.6 with a dispersion of $0.4$ and we identify 21 DSFGs with a high probability of lying at $z > 4$. After simulating our selection effects we find number counts are consistent with phenomenological galaxy evolution models. There is a statistically significant excess of WISE-1 and SDSS sources near our red galaxies, giving a strong indication that lensing may explain some of the apparently extreme objects. Nevertheless, our sample should include examples of galaxies with the highest star formation rates in the Universe ($\gg10^3$ M$_\odot$yr$^{-1}$).

astro-ph.GA↗

arXiv2018

A parallel workload has extreme variability in a production environment

Writing data in parallel is a common operation in some computing environments and a good proxy for a number of other parallel processing patterns. The duration of time taken to write data in large-scale compute environments can vary considerably. This variation comes from a number of sources, both systematic and transient. The result is a highly complex behavior that is difficult to characterize. This paper further develops the model for parallel task variability proposed in the paper "A parallel workload has extreme variability" (Henwood et. al 2016). This model is the Generalized Extreme Value (GEV) distribution. This paper further develops the systematic analysis that leads to the GEV model with the addition of a traffic congestion term. Observations of a parallel workload are presented from a High Performance Computing environment under typical production conditions, which include traffic congestion. An analysis of the workload is performed and shows the variability tends towards GEV as the order of parallelism is increased. The results are presented in the context of Amdahl's law and the predictive properties of a GEV models are discussed. A optimization for certain machine designs is also suggested.

cs.DC↗

arXiv2018

A direct calibration of the IRX-β relation in Lyman-break Galaxies at z=3-5

We use a sample of 4178 Lyman break galaxies (LBGs) at z = 3, 4 and 5 in the UKIRT Infrared Deep Sky Survey (UKIDSS) Ultra Deep Survey (UDS) field to investigate the relationship between the observed slope of the stellar continuum emission in the ultraviolet, β, and the thermal dust emission, as quantified via the so-called 'infrared excess' (IRX = LIR/LUV). Through a stacking analysis we directly measure the 850-μm flux density of LBGs in our deep (0.9mJy) James Clerk Maxwell Telescope (JCMT) SCUBA-2 850-μm map, as well as deep public Herschel/SPIRE 250-, 350- and 500-μm imaging. We establish functional forms for the IRX-β relation to z ~ 5, confirming that there is no significant redshift evolution of the relation and that the resulting average IRX-β curve is consistent with a Calzetti-like attenuation law. We compare our results with recent work in the literature, finding that discrepancies in the slope of the IRX-β relation are driven by biases in the methodology used to determine the ultraviolet slopes. Consistent results are found when IRX-β is evaluated by stacking in bins of stellar mass, M, and we argue that the near-linear IRX-M relationship is a better proxy for correcting observed UV luminosities to total star formation rates, provided an accurate handle on M can be had, and also gives clues as to the physical driver of the role of dust-obscured star formation in high-redshift galaxies.

astro-ph.GA↗

arXiv2017

Galaxy growth in a massive halo in the first billion years of cosmic history

According to the current understanding of cosmic structure formation, the precursors of the most massive structures in the Universe began to form shortly after the Big Bang, in regions corresponding to the largest fluctuations in the cosmic density field. Observing these structures during their period of active growth and assembly - the first few hundred million years of the Universe - is challenging because it requires surveys that are sensitive enough to detect the distant galaxies that act as signposts for these structures and wide enough to capture the rarest objects. As a result, very few such objects have been detected so far. Here we report observations of a far-infrared-luminous object at redshift 6.900 (less than 800 Myr after the Big Bang) that was discovered in a wide-field survey. High-resolution imaging reveals this source to be a pair of extremely massive star-forming galaxies. The larger of these galaxies is forming stars at a rate of 2900 solar masses per year, contains 270 billion solar masses of gas and 2.5 billion solar masses of dust, and is more massive than any other known object at a redshift of more than 6. Its rapid star formation is probably triggered by its companion galaxy at a projected separation of just 8 kiloparsecs. This merging companion hosts 35 billion solar masses of stars and has a star-formation rate of 540 solar masses per year, but has an order of magnitude less gas and dust than its neighbor and physical conditions akin to those observed in lower-metallicity galaxies in the nearby Universe. These objects suggest the presence of a dark-matter halo with a mass of more than 400 billion solar masses, making it among the rarest dark-matter haloes that should exist in the Universe at this epoch.

astro-ph.GA↗

arXiv2017

Ultra-Red Galaxies Signpost Candidate Proto-Clusters at High Redshift

We present images obtained with LABOCA on the APEX telescope of a sample of 22 galaxies selected via their red Herschel SPIRE 250-, 350- and $500\textrm{-}μ\textrm{m}$ colors. We aim to see if these luminous, rare and distant galaxies are signposting dense regions in the early Universe. Our $870\textrm{-}μ\textrm{m}$ survey covers an area of $\approx0.8\,\textrm{deg}^2$ down to an average r.m.s. of $3.9\,\textrm{mJy beam}^{-1}$, with our five deepest maps going $\approx2\times$ deeper still. We catalog 86 DSFGs around our 'signposts', detected above a significance of $3.5σ$. This implies a $100\pm30\%$ over-density of $S_{870}>8.5\,\textrm{mJy}$ DSFGs, excluding our signposts, when comparing our number counts to those in 'blank fields'. Thus, we are $99.93\%$ confident that our signposts are pinpointing over-dense regions in the Universe, and $\approx95\%$ confident that these regions are over-dense by a factor of at least $\ge1.5\times$. Using template SEDs and SPIRE/LABOCA photometry we derive a median photometric redshift of $z=3.2\pm0.2$ for our signposts, with an interquartile range of $z=2.8\textrm{-}3.6$. We constrain the DSFGs likely responsible for this over-density to within $|Δz|\le0.65$ of their respective signposts. These 'associated' DSFGs are radially distributed within $1.6\pm0.5\,\textrm{Mpc}$ of their signposts, have median SFRs of $\approx(1.0\pm0.2)\times10^3\,M_{\odot}\,\textrm{yr}^{-1}$ (for a Salpeter stellar IMF) and median gas reservoirs of $\sim1.7\times10^{11}\,M_{\odot}$. These candidate proto-clusters have average total SFRs of at least $\approx (2.3\pm0.5)\times10^3\,M_{\odot}\,\textrm{yr}^{-1}$ and space densities of $\sim9\times10^{-7}\,\textrm{Mpc}^{-3}$, consistent with the idea that their constituents may evolve to become massive ETGs in the centers of the rich galaxy clusters we see today.

astro-ph.GA↗

arXiv2017

Deep submillimeter and radio observations in the SSA22 field. I. Powering sources and Lyα escape fraction of Lyα blobs

We study the heating mechanisms and Lyα escape fractions of 35 Lyα blobs (LABs) at z = 3.1 in the SSA22 field. Dust continuum sources have been identified in 11 of the 35 LABs, all with star formation rates (SFRs) above 100 Msun/yr. Likely radio counterparts are detected in 9 out of 29 investigated LABs. The detection of submm dust emission is more linked to the physical size of the Lyα emission than to the Lyα luminosities of the LABs. A radio excess in the submm/radio detected LABs is common, hinting at the presence of active galactic nuclei. Most radio sources without X-ray counterparts are located at the centers of the LABs. However, all X-ray counterparts avoid the central regions. This may be explained by absorption due to exceptionally large column densities along the line-of-sight or by LAB morphologies, which are highly orientation dependent. The median Lyα escape fraction is about 3\% among the submm-detected LABs, which is lower than a lower limit of 11\% for the submm-undetected LABs. We suspect that the large difference is due to the high dust attenuation supported by the large SFRs, the dense large-scale environment as well as large uncertainties in the extinction corrections required to apply when interpreting optical data.

astro-ph.GA↗

arXiv2017

A spatially resolved study of cold dust, molecular gas, HII regions, and stars in the $z=2.12$ submillimeter galaxy ALESS67.1

We present detailed studies of a $z=2.12$ submillimeter galaxy, ALESS67.1, using sub-arcsecond resolution ALMA, AO-aided VLT/SINFONI, and HST/CANDELS data to investigate the kinematics and spatial distributions of dust emission (870 $μ$m continuum), $^{12}$CO($J$=3-2), strong optical emission lines, and visible stars. Dynamical modelling of the optical emission lines suggests that ALESS67.1 is not a pure rotating disk but a merger, consistent with the apparent tidal features revealed in the HST imaging. Our sub-arcsecond resolution dataset allow us to measure half-light radii for all the tracers, and we find a factor of 4-6 smaller sizes in dust continuum compared to all the other tracers, including $^{12}$CO, and UV and H$α$ emission is significantly offset from the dust continuum. The spatial mismatch between UV continuum and the cold dust and gas reservoir supports the explanation that geometrical effects are responsible for the offset of dusty galaxy on the IRX-$β$ diagram. Using a dynamical method we derive an $α_{\rm CO}=1.8\pm1.0$, consistent with other SMGs that also have resolved CO and dust measurements. Assuming a single $α_{\rm CO}$ value we also derive resolved gas and star-formation rate surface densities, and find that the core region of the galaxy ($\lesssim5$ kpc) follows the trend of mergers on the Schmidt-Kennicutt relationship, whereas the outskirts ($\gtrsim5$ kpc) lie on the locus of normal star-forming galaxies, suggesting different star-formation efficiencies within one galaxy. Our results caution against using single size or morphology for different tracers of the star-formation activity and gas content of galaxies, and therefore argue the need to use spatially-resolved, multi-wavelength observations to interpret the properties of SMGs, and perhaps even for $z>1$ galaxies in general.

astro-ph.GA↗

arXiv2017

The most distant, luminous, dusty star-forming galaxies: redshifts from NOEMA and ALMA spectral scans

We present 1.3- and/or 3-mm continuum images and 3-mm spectral scans, obtained using NOEMA and ALMA, of 21 distant, dusty, star-forming galaxies (DSFGs). Our sample is a subset of the galaxies selected by Ivison et al. (2016) on the basis of their extremely red far-infrared (far-IR) colours and low {\it Herschel} flux densities; most are thus expected to be unlensed, extraordinarily luminous starbursts at $z \gtrsim 4$, modulo the considerable cross-section to gravitational lensing implied by their redshift. We observed 17 of these galaxies with NOEMA and four with ALMA, scanning through the 3-mm atmospheric window. We have obtained secure redshifts for seven galaxies via detection of multiple CO lines, one of them a lensed system at $z=6.027$ (two others are also found to be lensed); a single emission line was detected in another four galaxies, one of which has been shown elsewhere to lie at $z=4.002$. Where we find no spectroscopic redshifts, the galaxies are generally less luminous by 0.3-0.4 dex, which goes some way to explaining our failure to detect line emission. We show that this sample contains amongst the most luminous known star-forming galaxies. Due to their extreme star-formation activity, these galaxies will consume their molecular gas in $\lesssim 100$ Myr, despite their high molecular gas masses, and are therefore plausible progenitors of the massive, `red-and-dead' elliptical galaxies at $z \approx 3$.

astro-ph.GA↗

arXiv2017

ISM properties of a Massive Dusty Star-Forming Galaxy discovered at z ~ 7

We report the discovery and constrain the physical conditions of the interstellar medium of the highest-redshift millimeter-selected dusty star-forming galaxy (DSFG) to date, SPT-S J031132-5823.4 (hereafter SPT0311-58), at $z=6.900 +/- 0.002$. SPT0311-58 was discovered via its 1.4mm thermal dust continuum emission in the South Pole Telescope (SPT)-SZ survey. The spectroscopic redshift was determined through an ALMA 3mm frequency scan that detected CO(6-5), CO(7-6) and [CI](2-1), and subsequently confirmed by detections of CO(3-2) with ATCA and [CII] with APEX. We constrain the properties of the ISM in SPT0311-58 with a radiative transfer analysis of the dust continuum photometry and the CO and [CI] line emission. This allows us to determine the gas content without ad hoc assumptions about gas mass scaling factors. SPT0311-58 is extremely massive, with an intrinsic gas mass of $M_{\rm gas} = 3.3 \pm 1.9 \times10^{11}\,M_{\odot}$. Its large mass and intense star formation is very rare for a source well into the Epoch of Reionization.

astro-ph.GA↗

arXiv2017

Characterizing the ionospheric current pattern response to southward and northward IMF turnings with dynamical SuperMAG correlation networks

We characterize the response of the quiet time (no substorms or storms) large-scale ionospheric transient equivalent currents to north-south and south-north IMF turnings by using a dynamical network of ground-based magnetometers. Canonical correlation between all pairs of SuperMAG magnetometer stations in the Northern Hemisphere (magnetic latitude (MLAT) 50-82$^{\circ}$) is used to establish the extent of near-simultaneous magnetic response between regions of magnetic local time-MLAT. Parameters and maps that describe spatial-temporal correlation are used to characterize the system and its response to the turnings aggregated over several hundred events. We find that regions that experience large increases in correlation post turning coincide with typical locations of a two-cell convection system and are influenced by the interplanetary magnetic field $\mathit{B}_{y}$. The time between the turnings reaching the magnetopause and a network response is found to be $\sim$8-10 min and correlation in the dayside occurs 2-8 min before that in the nightside.

physics.space-ph↗