arXiv subjects

A. Omont

Publications and source records attributed to A. Omont.

At least 37 records · Page 2Linked to original sources

arXiv2020

Etching glass in the early Universe: Luminous HF and water emission in a QSO-SMG pair at z=4.7

(abridged) We present ALMA observations of hydrogen fluoride, HF J=1-0, H20 (220-211), and the 1.2 THz rest-frame continuum emission from the z=4.7 system BR1202-0725. BR1202-0725 is a galaxy group consisting of a QSO, a sub-millimeter galaxy (SMG), and two Ly-alpha emitters. We detected HF in emission in the QSO and possibly in absorption in the SMG, while water is detected in emission in both the QSO and SMG. The QSO is the most luminous HF emitter yet found and has the same ratio of HF emission line to infrared luminosity as a sample of local AGN and the Orion Bar. This consistency covers about 10 orders-of-magnitude in infrared luminosity, L_IR. Based on the conclusions of a study of HF emission in the Orion Bar and modeling, the HF emission in the QSO is either excited by collisions with electrons and H2 in molecular plasmas irradiated by the AGN and intense star formation or predominately by collisions with H2, with a modest contribution from electrons, in a relatively high temperature (~120 K), dense (~10^5 cm^-3) medium. Although HF should be an excellent tracer of molecular outflows, we do not find strong evidence for outflows in HF in either the QSO or the SMG. From a putative absorption feature in HF in the SMG, we estimate an upper limit on the outflow rate, dM/dt_outflow <~45 M_sun/yr. The ratio of the outflow rate to the star formation rate is <5% for the SMG. The broadness of the H2O line in the SMG, FWHM~1020 km/s, may suggest that either the gas on large scales (>4 kpc) is significantly more disturbed and turbulent due either to interactions and mass exchange with the other members of the group or to the dissipation of the energy of the intense star formation or both. The lack of significant molecular outflows in either source may imply that much of the energy from the intense star formation and AGN activity in this pair is being dissipated in their ISM.

astro-ph.GA↗

arXiv2020

Correlation between UV resilience and wavelength of narrow DIBs

Carriers of diffuse interstellar bands (DIBs) still need to be identified. In a recent paper, we reported a correlation between the DIB wavelength and the apparent UV resilience (or boost) of their carriers. We proposed that this might be an indication of the important role of conjugated elongated molecules among the DIB carriers. The aim of this paper is to further understand the origin of this correlation. The analysis of 509 optical DIBs on the lines of sight of HD 183143 and/or HD 204827 reported in the literature shows that this correlation mainly implies the 386 narrow DIBs with a band width < 1.1 A, which include most of the identified DIBs of the C2 and zeta families, while the majority of the 123 broader DIBs, including the identified sigma DIBs, do not display such a correlation. We present a possible origin of this correlation from very strong bands of large conjugated elongated molecules, such as carbon chains, polyacenes, or other catacondensed polycyclic aromatic hydrocarbons. The total amount of carbon contained in all the carriers of these narrow DIBs is a very small fraction of the interstellar carbon if their oscillator strengths are <~1. The amount of carbon locked in the carriers of the broader DIBs is higher, especially if their oscillator strengths are significantly weaker.

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arXiv2020

First detection of the 448 GHz ortho-H2O line at high redshift: probing the structure of a starburst nucleus at z = 3.63

Submillimeter rotational lines of H2O are a powerful probe in warm gas regions of the ISM, tracing scales and structures ranging from kpc disks to the most compact and dust-obscured regions of galactic nuclei. The ortho-H2O(423-330) line at 448 GHz, which was recently detected in a local luminous infrared galaxy (Pereira-Santaella et al. 2017), offers a unique constraint on the excitation conditions and ISM properties in deeply buried galaxy nuclei since the line requires high far-IR optical depths to be excited. In this letter, we report the first high-redshift detection of the 448 GHz H2O(423-330) line using ALMA, in a strongly lensed submillimeter galaxy (SMG) at z=3.63. After correcting for magnification, the luminosity of the 448 GHz H2O line is ~10^6 L_sun. In combination with three other previously detected H2O lines, we build a model that "resolves" the dusty ISM structure of the SMG, and find that it is composed of a ~1 kpc optically thin (optical depth at 100μm τ_{100}~0.3) disk component with dust temperature T_{dust} \approx 50 K emitting a total infrared power of 5e12 L_sun with surface density Σ_{IR}=4e11 L_sun kpc^{-2}, and a very compact (0.1 kpc) heavily dust-obscured (τ_{100} \gtrsim 1) nuclear core with very warm dust (100 K) and Σ_{IR}=8e12 L_sun kpc^{-2}. The H2O abundance in the core component, X_{H2O}~(0.3-5)e{-5}, is at least one order of magnitude higher than in the disk component. The optically thick core has the characteristic properties of an Eddington-limited starburst, providing evidence that radiation pressure on dust is capable of supporting the ISM in buried nuclei at high redshifts. The multi-component ISM structure revealed by our models illustrates that dust and molecules such as H2O are present in regions characterized by highly differing conditions and scales, extending from the nucleus to more extended regions of SMGs.

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arXiv2019

NOEMA redshift measurements of bright Herschel galaxies

Using the IRAM NOrthern Extended Millimeter Array (NOEMA), we conducted a program to measure redshifts for 13 bright galaxies detected in the Herschel Astrophysical Large Area Survey (H-ATLAS) with $S_{500μ\rm m}\ge$80 mJy. We report reliable spectroscopic redshifts for 12 individual sources, which are derived from scans of the 3 and 2 mm bands, covering up to 31 GHz in each band, and are based on the detection of at least two emission lines. The spectroscopic redshifts are in the range $2.08 10^{13}\,L_\odot$ galaxies. We also present a reanalysis of the spectral energy distributions including the continuum flux densities measured at 3 and 2 mm to derive the overall properties of the sources. Future prospects based on these efficient measurements of redshifts of high-z galaxies using NOEMA are outlined, including a comprehensive survey of all the brightest Herschel galaxies.

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arXiv2019

Discovery of a giant and luminous Lya+CIV+HeII nebula at z=3.326 with extreme emission line ratios

We present the discovery of HLock01-LAB, a luminous and large Lya nebula at z=3.326. Medium-band imaging and long-slit spectroscopic observations with the Gran Telescopio Canarias reveal extended emission in the Lya 1215Å, CIV1550Å, and HeII 1640Ålines over ~100kpc, and a total luminosity L(Lya)=(6.4+/-0.1)x10^44 erg s^-1. HLock01-LAB presents an elongated morphology aligned with two faint radio sources contained within the central ~8kpc of the nebula. The radio structures are consistent to be faint radio jets or lobes of a central galaxy, whose spectrum shows nebular emission characteristic of a type-II active galactic nucleus (AGN). The continuum emission of the AGN at short wavelengths is, however, likely dominated by stellar emission of the host galaxy, for which we derive a stellar mass M* = 2.3x10^11 Msun. The detection of extended emission in CIV and CIII] indicates that the gas within the nebula is not primordial. Feedback may have enriched the halo at at least 50 kpc from the nuclear region. Using rest-frame UV emission-line diagnostics, we find that the gas in the nebula is likely heated by the AGN. Nevertheless, at the center of the nebula we find extreme emission line ratios of Lya/CIV~60 and Lya/HeII~80, one of the highest values measured to date, and well above the standard values of photoionization models (Lya/HeII~30 for case B photoionization). Our data suggest that jet-induced shocks are likely responsible for the increase of the electron temperature and, thus, the observed Lya enhancement in the center of the nebula. This scenario is further supported by the presence of radio structures and perturbed kinematics in this region. The large Lya luminosity in HLock01-LAB is likely due to a combination of AGN photoionization and jet-induced shocks, highlighting the diversity of sources of energy powering Lya nebulae. [abridged]

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arXiv2019

Polyacenes and diffuse interstellar bands

The identification of the carriers of the diffuse interstellar bands (DIBs) remains to be established, with the exception of five bands attributed to C60+, although it is generally agreed that DIB carriers should be large carbon-based molecules (with ~10-100 atoms) in the gas phase, such as polycyclic aromatic hydrocarbons (PAHs), long carbon chains or fullerenes. More specific possible carriers among PAHs are investigated, namely elongated molecules, which could explain a correlation between the DIB wavelength and the apparent UV resilience of their carriers. We address the case of polyacenes, C4N+2-H2N+4, with N~10-18 fused rectilinear aligned hexagons. Polyacenes are attractive DIB carrier candidates because their high symmetry and large linear size allow them to form regular series of bands in the visible range with strengths larger than most other PAHs, as confirmed by recent laboratory results up to undecacene (C46H26). Those with very strong bands in the DIB spectral domain are just at the limit of stability against UV photodissociation. They are part of the prominent PAH family of interstellar carbon compounds, meaning that only ~10-5 of the total PAH abundance is enough to account for a medium-strength DIB. After summarizing the current knowledge about the properties of polyacenes and recent laboratory results, the likelihood that they might meet the criteria for being carriers of some DIBs is addressed by reviewing the following properties: wavelength and strength of their series of visible bands; interstellar stability and abundances, charge state and hydrogenation; and DIB rotation profiles. No definite inconsistency has been identified that precludes polyacenes from being the carriers of some DIBs with medium or weak strength, including the so-called C2 DIBs. But additional experimental data about long acenes and their visible bands are needed to make robust conclusions

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arXiv2019

CO, H2O, H2O+ line and dust emission in a z = 3.63 strongly lensed starburst merger at sub-kiloparsec scales

Using ALMA, we report high angular-resolution observations of the redshift z=3.63 galaxy, G09v1.97, one of the most luminous strongly lensed galaxies discovered by the H-ATLAS survey. We present 0"2-0"4 resolution images of the rest-frame 188 and 419$μ$m dust continuum and the CO(6-5), H2O(211-202) and J=2 H2O+ line emission. We also report the detection of H$_2^{18}$O in this source. The dust continuum and molecular gas emission are resolved into a nearly complete ~1"5 diameter Einstein ring plus a weaker image in the center, which is caused by a special dual deflector lensing configuration. The observed line profiles of the CO, H2O and H2O+ lines are strikingly similar. In the source plane, we reconstruct the dust continuum images and the spectral cubes of the line emission at sub-kpc scales. The reconstructed dust emission in the source plane is dominated by a compact disk with an effective radius of 0.7kpc plus an overlapping extended disk with a radius twice as large. While the average magnification for the dust continuum is $μ$~10-11, the magnification of the line emission varies 5 to 22 across different velocity components. The emission lines have similar spatial and kinematic distributions. The molecular gas and dust content reveal that G09v1.97 is a gas-rich major merger in its pre-coalescence phase. Both of the merging companions are intrinsically ULIRGs with LIR reaching $\gtrsim 4\times10^{12}L_\odot$, and the total LIR of G09v1.97 is $1.4\times10^{13}L_\odot$. The approaching southern galaxy shows no obvious kinematic structure with a semi-major half-light radius a_s=0.4kpc, while the receding galaxy resembles an a_s=1.2kpc rotating disk. The two galaxies are separated by a projected distance of 1.3kpc, bridged by weak line emission that is co-spatially located with the cold-dust-emission peak, suggesting a large amount of cold ISM in the interacting region. (abridged)

astro-ph.GA↗

arXiv2018

Planck's Dusty GEMS. VII. Atomic carbon and molecular gas in dusty starburst galaxies at z=2 to 4

The bright [CI] 1-0 and [CI] 2-1 lines of atomic carbon are becoming more and more widely employed tracers of the cold neutral gas in high-redshift galaxies. Here we present observations of these lines in the 11 galaxies of the set of Planck's Dusty GEMS, the brightest gravitationally lensed galaxies on the extragalactic submillimeter sky probed by the Planck satellite. We have [CI] 1-0 measurements for seven, and [CI] 2-1 measurements for eight galaxies, including four galaxies where both lines are measured. We use our observations to constrain the gas excitation mechanism, excitation temperatures, optical depths, atomic carbon and molecular gas masses, and carbon abundances. Ratios of L_CI/L_ FIR are similar to those found in the local Universe, and suggest that the total cooling budget through atomic carbon has not strongly changed in the last 12 Gyr. Both lines are optically thin and trace 1 - 6 x 10^7 M_sun of atomic carbon. Carbon abundance ratios with H_2, X_CI, are between 2.5 and 4 x 10^-5, for a "ULIRG" CO-to-H_2 conversion factor of alpha_CO=0.8 M_sun/ [K km s^-1 pc^2]. Ratios of molecular gas masses derived from [CI] 1-0 and CO agree within the measurement uncertainties for five galaxies, and to better than a factor of 2 for another two with [CI] 1-0 measurements, after taking CO excitation carefully into account. This does not support the idea that intense, high-redshift starburst galaxies host large quantities of "CO-dark" gas. These results also support the common assumptions underlying most molecular gas mass estimates made for massive, dusty, high-redshift starburst galaxies, although the good agreement between the masses obtained with both tracers cannot be taken as an independent confirmation of either alpha_CO or X_CI.

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arXiv2018

Planck's dusty GEMS. VI. Multi-J CO excitation and interstellar medium conditions in dusty starburst galaxies at z=2-4

We present an extensive CO emission-line survey of the Planck's dusty GEMS, a small set of 11 strongly lensed dusty star-forming galaxies at z = 2-4 discovered with Planck and Herschel satellites, using EMIR on the IRAM 30-m telescope. We detected a total of 45 CO rotational lines from Jup=3 to Jup=11, and up to eight transitions per source, allowing a detailed analysis of the gas excitation and interstellar medium conditions within these extremely bright, vigorous starbursts. We applied radiative transfer models using the large velocity gradient approach to infer the spatially-averaged molecular gas densities, $n_{H_2}$~10$^{2.6-4.1}$ cm$^{-3}$, and kinetic temperatures, $T_k$~30-1000 K. In five sources, we find evidence of two distinct gas phases with different properties and model their CO ladder with two excitation components. The warm (70-320 K) and dense gas reservoirs in these galaxies are highly excited, while the cooler (15-60 K) and more extended low-excitation components cover a range of gas densities. In two sources, the latter is associated with diffuse Milky Way-like gas phases, which provides evidence that a significant fraction of the total gas masses of dusty starburst galaxies can be embedded in cool, low-density reservoirs. Finally, we show that the CO line luminosity ratios are consistent with those predicted by models of photon-dominated regions and disfavor scenarios of gas clouds irradiated by intense X-ray fields from active galactic nuclei. By combining CO, [CI] and [CII] line diagnostics, we obtain average PDR gas densities significantly higher than in normal star-forming galaxies at low-redshift, and far-ultraviolet radiation fields at least 100 times more intense than in the Milky Way. These spatially-averaged conditions are consistent with those in high-redshift SMGs and in a range of low-redshift environments.

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arXiv2018

Spitzer Planck Herschel Infrared Cluster (SPHerIC) survey: Candidate galaxy clusters at 1.3 < z < 3 selected by high star-formation rate

There is a lack of large samples of spectroscopically confirmed clusters and protoclusters at high redshifts, $z>$1.5. Discovering and characterizing distant (proto-)clusters is important for yielding insights into the formation of large-scale structure and on the physical processes responsible for regulating star-formation in galaxies in dense environments. The Spitzer Planck Herschel Infrared Cluster (SPHerIC) survey was initiated to identify these characteristically faint and dust-reddened sources during the epoch of their early assembly. We present Spitzer IRAC observations of 82 galaxy (proto-)cluster candidates at 1.3<$z_p$<3.0 that were vetted in a two step process: (1) using Planck to select by color those sources with the highest star-formation rates, and (2) using Herschel at higher resolution to separate out the individual red sources. The addition of the Spitzer data enables efficient detection of the central and massive brightest red cluster galaxies (BRCGs). We find that BRCGs are associated with highly significant, extended and crowded regions of IRAC sources which are more overdense than the field. This result corroborates our hypothesis that BRCGs within the Planck - Herschel sources trace some of the densest and actively star-forming proto-clusters in the early Universe. On the basis of a richness-mass proxy relation, we obtain an estimate of their mean masses which suggests our sample consists of some of the most massive clusters at z$\approx$2 and are the likely progenitors of the most massive clusters observed today.

astro-ph.CO↗

arXiv2018

86 GHz SiO maser survey of late-type stars in the Inner Galaxy. IV. SiO emission and infrared data for sources in the Scutum and Sagittarius-Carina arms, 20 deg < l < 50 deg

We present an 86 GHz SiO (v = 1, J = 2 ---> 1) maser search toward late-type stars located within |b|<0.5 deg and 20 deg < l < 50 deg. This search is an extension at longer longitudes of a previously published work. We selected 135 stars from the MSX catalog using color and flux criteria and detected 92 (86 new detections). The detection rate is 68%, the same as in our previous study. The last few decades have seen the publication of several catalogs of point sources detected in infrared surveys (MSX, 2MASS, DENIS, ISOGAL, WISE, GLIMPSE, AKARI, and MIPSGAL). We searched each catalog for data on the 444 targets of our earlier survey and for the 135 in the survey reported here. We confirm that, as anticipated, most of our targets have colors typical of oxygen-rich asymptotic giant branch (AGB) stars. Only one target star may have already left the AGB. Ten stars have colors typical of carbon-rich stars, meaning a contamination of our sample with carbon stars <=1.7%.

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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.

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arXiv2017

Molecular gas in the Herschel-selected strongly lensed submillimeter galaxies at z~2-4 as probed by multi-J CO lines

(abridged) We present the IRAM-30m observations of multiple-J CO and CI line emission in a sample of redshift ~2-4 Herschel-ATLAS SMGs. A non-negligible effect of differential lensing is found for the CO emission lines, which could have caused significant underestimations of the linewidths, hence of the dynamical masses. The CO SLEDs are found to be similar to those of the local starburst-dominated ULIRGs and of the previously studied SMGs. After correcting for lensing amplification, we derived the global properties of the bulk of molecular gas in the SMGs using non-LTE radiative transfer modelling. The gas thermal pressure is found to be correlated with star formation efficiency. Further decomposing the CO SLEDs into two excitation components, we find a low-excitation component, which is less correlated with star formation, and a high-excitation one which is tightly related to the on-going star-forming activity. Additionally, tight linear correlations between the FIR and CO line luminosities have been confirmed for the $J \ge 5$ CO lines, implying that these CO lines are good tracers of star formation. The [CI](2-1) lines follow the tight linear correlation between the luminosities of the [CI](2-1) and the CO(1-0) line found in local starbursts, indicating that CI lines could serve as good total molecular gas mass tracers for high-redshift SMGs. The total mass of the molecular gas reservoir, $(1-30) \times 10^{10} M_\odot$, suggests a typical molecular gas depletion time ~20-100 Myr and a gas to dust mass ratio $δ_{\rm GDR}$~30-100. The ratio between CO line luminosity and the dust mass appears to be slowly increasing with redshift for the SMGs, which need to be further confirmed. Finally, through comparing the linewidth of CO and H2O lines, we find that they agree well in almost all our SMGs, confirming that the emitting regions are co-spatially located.

astro-ph.GA↗

arXiv2017

An extreme proto-cluster of luminous dusty starbursts in the early Universe

We report the identification of an extreme proto-cluster of galaxies in the early Universe whose core (nicknamed Distant Red Core, DRC) is formed by at least ten dusty star-forming galaxies (DSFGs), confirmed to lie at $z_{\rm spec} = 4.002$ via detection of [CI](1-0), $^{12}$CO(6-5), $^{12}$CO(4-3), $^{12}$CO(2-1) and ${\rm H_2O} (2_{11} - 2_{02})$ emission lines, detected using ALMA and ATCA. The spectroscopically-confirmed components of the proto-cluster are distributed over a ${\rm 260\, kpc \times 310\, kpc}$ region and have a collective obscured star-formation rate (SFR) of $\sim 6500 \, M_\odot \, {\rm yr}^{-1}$, considerably higher than has been seen before in any proto-cluster of galaxies or over-densities of DSFGs at $z \gtrsim 4$. Most of the star formation is taking place in luminous DSFGs since no Ly$α$ emitters are detected in the proto-cluster core, apart from a Ly$α$ blob located next to one of the DRC dusty components and extending over $60\,{\rm kpc}$. The total obscured SFR of the proto-cluster could rise to ${\rm SFR} \sim 14,400 \, M_\odot \, {\rm yr}^{-1}$ if all the members of an over-density of bright DSFGs discovered around DRC in a wide-field LABOCA 870-$μ$m image are part of the same structure. The total halo mass of DRC could be as high as $\sim 4.4 \times 10^{13}\,M_\odot$ and could be the progenitor of a Coma-like cluster at $z = 0$. The relatively short gas-depletion times of the DRC components suggest either the presence of a mechanism able to trigger extreme star formation simultaneously in galaxies spread over a few hundred kpc or the presence of gas flows from the cosmic web able to sustain star formation over several hundred million years.

astro-ph.GA↗

arXiv2017

Witnessing the birth of the red sequence: the physical scale and morphology of dust emission in hyper-luminous starbursts in the early Universe

We present high-spatial-resolution ($\sim 0.12''$ or $\approx 800 \, {\rm pc}$ at $z = 4.5$) ALMA $870\,μ$m dust continuum observations of a sample of 44 ultrared dusty star-forming galaxies (DSFGs) selected from the H-ATLAS and HerMES far-infrared surveys because of their red colors from 250 to 500 $μ$m: $S_{500} / S_{250} > 1.5$ and $S_{500} / S_{350} > 1.0$. With photometric redshifts in the range $z \sim 4$-6, our sample includes the most luminous starbursting systems in the early Universe known so far, with total obscured star-formation rates (SFRs) of up to $\sim 4,500 \, M_\odot \, {\rm yr}^{-1}$, as well as a population of lensed, less intrinsically luminous sources. The lower limit on the number of ultrared DSFGs at 870 $μ$m (with flux densities measured from the ALMA maps and thus not affected by source confusion) derived in this work is in reasonable agreement with models of galaxy evolution, whereas there have been reports of conflicts at 500 $μ$m (where flux densities are derived from SPIRE). Ultrared DSFGs have a variety of morphologies (from relatively extended disks with smooth radial profiles, to compact sources, both isolated and interacting) and an average size, $θ_{\rm FWHM}$, of $1.46 \pm 0.41\, {\rm kpc}$, considerably smaller than the values reported in previous work for less-luminous DSFGs at lower redshifts. The size and the estimated gas-depletion times of our sources are compatible with their being the progenitors of the most massive, compact, red-and-dead galaxies at $z \sim 2$-3, and ultimately of local ultra-massive elliptical galaxies or massive galaxy clusters. We are witnessing the birth of the high-mass tail of the red sequence of galaxies.

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arXiv2017

The Herschel Bright Sources (HerBS): Sample definition and SCUBA-2 observations

We present the Herschel Bright Sources (HerBS) sample, a sample of bright, high-redshift Herschel sources detected in the 616.4 square degree H-ATLAS survey. The HerBS sample contains 209 galaxies, selected with a 500 μm flux density greater than 80 mJy and an estimated redshift greater than 2. The sample consists of a combination of HyLIRGs and lensed ULIRGs during the epoch of peak cosmic star formation. In this paper, we present SCUBA-2 observations at 850 $μ$m of 189 galaxies of the HerBS sample, 152 of these sources were detected. We fit a spectral template to the Herschel-SPIRE and 850 $μ$m SCUBA-2 flux densities of 22 sources with spectroscopically determined redshifts, using a two-component modified blackbody spectrum as a template. We find a cold- and hot-dust temperature of 21.29 K and 45.80 K, a cold-to-hot dust mass ratio of 26.62 and a $β$ of 1.83. The poor quality of the fit suggests that the sample of galaxies is too diverse to be explained by our simple model. Comparison of our sample to a galaxy evolution model indicates that the fraction of lenses is high. Out of the 152 SCUBA-2 detected galaxies, the model predicts 128.4 $\pm$ 2.1 of those galaxies to be lensed (84.5%). The SPIRE 500 $μ$m flux suggests that out of all 209 HerBS sources, we expect 158.1 $\pm$ 1.7 lensed sources, giving a total lensing fraction of 76 per cent.

astro-ph.GA↗

arXiv2017

Large turbulent reservoirs of cold molecular gas around high-redshift starburst galaxies

Starburst galaxies at the peak of cosmic star formation are among the most extreme starforming engines in the universe, producing stars over ~100 Myr. The star formation rates of these galaxies, which exceed 100 $M_\odot$ per year, require large reservoirs of cold molecular gas to be delivered to their cores, despite strong feedback from stars or active galactic nuclei. Starburst galaxies are therefore ideal targets to unravel the critical interplay between this feedback and the growth of a galaxy. The methylidyne cation, CH$^+$, is a most useful molecule for such studies because it cannot form in cold gas without supra-thermal energy input, so its presence highlights dissipation of mechanical energy or strong UV irradiation. Here, we report the detection of CH$^+$(J=1-0) emission and absorption lines in the spectra of six lensed starburst galaxies at redshifts z~2.5. This line has such a high critical density for excitation that it is emitted only in very dense ($>10^5$ cm$^{-3}$) gas, and is absorbed in low-density gas. We find that the CH$^+$ emission lines, which are broader than 1000 km s$^{-1}$, originate in dense shock waves powered by hot galactic winds. The CH$^+$ absorption lines reveal highly turbulent reservoirs of cool ($T\sim 100$K), low-density gas, extending far outside (>10 kpc) the starburst cores (radii <1 kpc). We show that the galactic winds sustain turbulence in the 10 kpc-scale environments of the starburst cores, processing these environments into multi-phase, gravitationally bound reservoirs. However, the mass outflow rates are found to be insufficient to balance the star formation rates. Another mass input is therefore required for these reservoirs, which could be provided by on-going mergers or cold stream accretion. Our results suggest that galactic feedback, coupled jointly to turbulence and gravity, extends the starburst phase instead of quenching it.

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 $z \approx 3$.

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