arXiv subjects

R. Kneissl

Publications and source records attributed to R. Kneissl.

At least 19 recordsLinked to original sources

arXiv2024

JWST's PEARLS: resolved study of the stellar and dust components in starburst galaxies at cosmic noon

Dusty star-forming galaxies (DSFGs) contribute significantly to the stellar buildup at cosmic noon. Major mergers and gas accretion are often invoked to explain DSFGs' prodigious star-formation rates (SFRs) and large stellar masses. We conducted a spatially-resolved morphological analysis of the rest-frame UV/NIR emission in three DSFGs at z~2.5. Initially discovered as CO emitters by NOEMA observations of a bright Herschel source, we observed them with the JWST/NIRCam as part of the PEARLS program. The NIRCam data reveal the galaxies' stellar populations and dust distributions on scales of 250 pc. Spatial variations in stellar mass, SFR, and dust extinction are determined in resolved maps obtained through pixel-based SED fitting. The CO emitters are massive, dusty starburst galaxies with SFRs=340-2500 Msun/yr, positioning them among the most active SFGs at 2<z<3. They belong to the ~1.5% of the entire JWST population with extremely red colors. Their morphologies are disk like, with radii of 2.0-4.4 kpc, and exhibit substructures such as clumps and spiral arms. The galaxies have dust extinctions up to Av=5-7 mag extending over several kpc with asymmetric distributions that include off-center regions resembling bent spiral arms and clumps. Their NIR dust-attenuation curve deviates from standard laws, possibly implying different dust-star geometries or dust grain properties than commonly assumed in starburst galaxies. The proximity of galaxies with consistent redshifts, strong color gradients, an overall disturbed appearance, asymmetric dust obscuration, and widespread star formation collectively favor interactions (minor mergers and flybys) as the mechanism driving the CO galaxies' exceptional SFRs. The galaxies' large masses and rich environment hint at membership in two proto-structures, as initially inferred from their association with a Planck-selected high-z source.

astro-ph.GA↗

arXiv2023

Planck 2013 results X. Energetic particle effects: characterization, removal, and simulation

We describe the detection, interpretation, and removal of the signal resulting from interactions of high energy particles with the \Planck\ High Frequency Instrument (HFI). There are two types of interactions: heating of the 0.1\,K bolometer plate; and glitches in each detector time stream. The transient responses to detector glitch shapes are not simple single-pole exponential decays and fall into three families. The glitch shape for each family has been characterized empirically in flight data and these shapes have been used to remove glitches from the detector time streams. The spectrum of the count rate per unit energy is computed for each family and a correspondence is made to the location on the detector of the particle hit. Most of the detected glitches are from Galactic protons incident on the die frame supporting the micro-machined bolometric detectors. In the \Planck\ orbit at L2, the particle flux is around $5\,{\rm cm}^{-2}\,{\rm s}^{-1}$ and is dominated by protons incident on the spacecraft with energy $>$39\,MeV, at a rate of typically one event per second per detector. Different categories of glitches have different signatures in the time stream. Two of the glitch types have a low amplitude component that decays over nearly 1\,s. This component produces excess noise if not properly removed from the time-ordered data. We have used a glitch detection and subtraction method based on the joint fit of population templates. The application of this novel glitch subtraction method removes excess noise from the time streams. Using realistic simulations, we find that this method does not introduce signal bias into the \Planck\ data.

astro-ph.CO↗

arXiv2023

The ALMA Frontier Fields Survey. VI. Lensing-corrected 1.1mm number counts in Abell 2744, MACSJ0416.1-2403, MACSJ1149.5+2223, Abell 370 and Abell S1063

[abridged] Probing the faint end of the number counts at mm wavelengths is important to identify the origin of the extragalactic background light in this regime. Aided by strong gravitational lensing, ALMA observations towards massive galaxy clusters have opened a window to disentangle this origin, allowing to resolve sub-mJy dusty star-forming galaxies. We aim to derive number counts at 1.1 mm down to flux densities fainter than 0.1 mJy, based on ALMA observations towards five Hubble Frontier Fields (FF) galaxy clusters, following a statistical approach to correct for lensing effects. We created a source catalog that includes 29 ALMA 1.1 mm continuum detections down to a 4.5sigma significance. We derived source intrinsic flux densities using public lensing models. We folded the uncertainties in both magnifications and source redshifts into the number counts through Monte Carlo simulations. We derive cumulative number counts over two orders of magnitude down to 0.01 mJy after correction for lensing effects. Cosmic variance estimates are all exceeded by uncertainties in our median combined cumulative counts that come from both our Monte Carlo simulations and Poisson statistics. Our number counts are consistent to 1sigma with most of recent ALMA estimates and galaxy evolution models. However, below 0.1 mJy, they are lower by 0.4 dex compared to two deep ALMA studies but consistent with ASPECS-LP to 1sigma. Importantly, the flattening found for our cumulative counts extends further to 0.01 mJy. Our results bring further support in line of the flattening of the number counts reported previously by us and ASPECS-LP, which has been interpreted by a recent galaxy evolution model as a measurement of the "knee" of the infrared luminosity function at high redshift. Our estimates of the contribution to the EBL in the FFs suggest that we may be resolving most of the EBL at 1.1mm down to 0.01 mJy.

astro-ph.GA↗

arXiv2022

Molecular gas properties of Planck-selected protocluster candidates at z~1.3-3

We report on IRAM-30m/EMIR observations of 38 red Herschel sources in 18 Planck-selected protocluster candidates (PHz). We detect 40 CO lines on a total of 24 bright Herschel sources in 14 of the 18 PHz fields. The measured average redshift is =2.25. We measure redshifts for multiple Herschel sources in eight PHz fields. In half of those fields we detect from two to three objects at similar redshifts, supporting the idea that they contain high-z protoclusters. The detection of sources at different redshifts demonstrates that foreground and background sources also contribute to the total sub-mm emission. We compare the properties of the molecular gas, and of the star formation activity of our sources with samples of normal star-forming galaxies (SFGs), sub-mm galaxies, and CO-detected cluster and protocluster galaxies at similar redshifts. We find that the PHz-IRAM sources are mainly normal SFGs, with only ~20% undergoing a starburst phase. The PHz-IRAM sources are characterized by star formation rates and gas masses that are, on average, eight and five times higher than those typical of normal SFGs at similar redshifts. Their dust temperatures, and depletion timescales are instead consistent with those of normal SFGs. The analysis of the CO spectral line energy distribution, available for ten sources, peaks at Jup=3 in most of the cases, implying low gas excitation. These properties imply that a significant fraction of the PHz-IRAM sources contains extended, and cold molecular gas reservoirs at low excitation, and that their star-formation is driven by secular processes. Multiplicity and moderate gravitational lensing might also play a role in producing the observed properties. We find that the highest star-forming protoclusters drawn from the large volume simulations, have similar SFRs as the PHz protoclusters, but separate out into a larger number of SFGs. (Abridged)

astro-ph.GA↗

arXiv2020

Planck's Dusty GEMS. VIII. Dense-gas reservoirs in the most active dusty starbursts at z~3

We present ALMA, NOEMA, and IRAM-30m/EMIR observations of the high-density tracer molecules HCN, HCO+, and HNC in three of the brightest lensed dusty star-forming galaxies at z~3-3.5, part of the Planck's Dusty GEMS sample, to probe the gas reservoirs closely associated with their exceptional levels of star formation. We obtain robust detections of ten emission lines between J_up=4 and 6, as well as several additional flux upper limits. In PLCK_G244.8+54.9, the brightest source at z=3.0, the HNC(5-4) line emission at 0.1" resolution, together with other spatially-integrated line profiles, suggests comparable distributions of dense and more diffuse gas reservoirs, at least over the most strongly magnified regions. This rules out any major effect from differential lensing. The HCO+/HCN > 1 and HNC/HCN ~ 1 line ratios in our sample are similar to those of nearby ULIRGs and consistent with photon-dominated regions without any indication of important mechanical heating or AGN feedback. We characterize the dense-gas excitation in PLCK_G244.8+54.9 using radiative transfer models assuming pure collisional excitation and find that mid-J HCN, HCO+, and HNC lines arise from a high-density phase with H2 density n~10^5-6 cm^-3, although important degeneracies prevent determining the exact conditions. The three GEMS are consistent with extrapolations of dense-gas star-formation laws derived in the nearby Universe, adding further evidence that the extreme star-formation rates observed in the most active galaxies at z~3 are a consequence of their important dense-gas contents. The dense-gas-mass fractions traced by HCN/[CI] and HCO+/[CI] line ratios are elevated, but not exceptional compared to other lensed dusty star-forming galaxies at z>2 and fall near the upper envelope of local ULIRGs. Our results also favor constant dense-gas depletion times in these populations.

astro-ph.GA↗

arXiv2019

The ALMA Frontier Fields survey V: ALMA Stacking of Lyman-Break Galaxies in Abell 2744, Abell 370, Abell S1063, MACSJ0416.1-2403 and MACSJ1149.5+2223

The Hubble Frontier Fields offer an exceptionally deep window into the high-redshift universe, covering a substantially larger area than the Hubble Ultra-Deep field at low magnification and probing 1--2 mags deeper in exceptional high-magnification regions. We aim to leverage Atacama Large Millimetre Array (ALMA) band 6 ($\approx$263\,GHz) mosaics in the central portions of five Frontier Fields to characterize the infrared (IR) properties of $1582$ ultraviolet (UV)-selected Lyman-Break Galaxies (LBGs) at redshifts of $z {\sim}$2--8. We investigated individual and stacked fluxes and IR excess (IRX) values of the LBG sample as functions of stellar mass ($\mathrm{M}_{\bigstar}$), redshift, UV luminosity and slope $β$, and lensing magnification. Two (2) LBG candidates were individually detected above a significance of $4.1{-}σ$, while stacked samples of the remaining LBG candidates yielded no significant detections. We investigated our detections and upper limits in the context of the IRX-$\mathrm{M}_{\bigstar}$ and IRX-$β$ relations, probing at least one dex lower in stellar mass than past studies have done. Our upper limits exclude substantial portions of parameter space and they are sufficiently deep in a handful of cases to create mild tension with the typically assumed attenuation and consensus relations. We observe a clear and smooth trend between $\mathrm{M}_{\bigstar}$ and $β$, which extends to low masses and blue (low) $β$ values, consistent with expectations from previous works.

astro-ph.GA↗

arXiv2019

Stochastic modeling of the time variability of ALMA calibrators

Characterizing the variability of the extragalactic sources used for calibration in the Atacama Large Millimeter/Sub-millimeter Array (ALMA) is key to assess the flux scale uncertainty of science observations. To this end, we model the variability of 39 quasars which have been used by ALMA as secondary flux calibrators using continuous time stochastic processes. This formalism is specially adapted to the multi-frequency, quasi-periodic sampling which characterizes the calibration monitoring of ALMA. We find that simple mixtures of Ornstein-Uhlenbeck processes can describe well the flux and spectral index variability of these sources for Bands 3 and 7 (91.5 and 103.5, and 343.5 GHz, respectively). The spectral shape of the calibrators are characterized by negative spectral indices, mostly between $-0.35$ and $-0.80$, and with additional concavity. The model provides forecasts, interpolations, and uncertainty estimations for the observed fluxes that depend on the intrinsic variability of the source. These can be of practical use for the ALMA data calibrator survey and data quality assurance.

astro-ph.IM↗

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.

astro-ph.GA↗

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.

astro-ph.GA↗

arXiv2018

Planck's dusty GEMS. V. Molecular wind and clump stability in a strongly lensed star-forming galaxy at z=2.2

We report the discovery of a molecular wind signature from a massive intensely star-forming clump of a few $10^9$ Msun, in the strongly gravitationally lensed submillimeter galaxy "the Emerald" (PLCK_G165.7+49.0) at z=2.236. The Emerald is amongst the brightest high-redshift galaxies on the submillimeter sky, and was initially discovered with the Planck satellite. The system contains two magnificient structures with projected lengths of 28.5" and 21" formed by multiple, near-infrared arcs, falling behind a massive galaxy cluster at z=0.35, as well as an adjacent filament that has so far escaped discovery in other wavebands. We used HST/WFC3 and CFHT optical and near-infrared imaging together with IRAM and SMA interferometry of the CO(4-3) line and 850 $μ$m dust emission to characterize the foreground lensing mass distribution, construct a lens model with Lenstool, and calculate gravitational magnification factors between 20 and 50 in most of the source. The majority of the star formation takes place within two massive star-forming clumps which are marginally gravitationally bound and embedded in a $9 \times 10^{10}$ Msun, fragmented disk with 20% gas fraction. One of the clumps shows a pronounced blue wing in the CO(4-3) line profile, which we interpret as a wind signature. The mass outflow rates are high enough for us to suspect that the clump might become unbound within a few tens of Myr, unless the outflowing gas can be replenished by gas accretion from the surrounding disk. The velocity offset of -200 km s$^{-1}$ is above the escape velocity of the clump, but not that of the galaxy overall, suggesting that much of this material might ultimately rain back onto the galaxy and contribute to fueling subsequent star formation.

astro-ph.GA↗

arXiv2018

The ALMA Frontier Fields Survey - IV. Lensing-corrected 1.1 mm number counts in Abell 2744, MACSJ0416.1-2403 and MACSJ1149.5+2223

[abridged] Characterizing the number counts of faint, dusty star-forming galaxies is currently a challenge even for deep, high-resolution observations in the FIR-to-mm regime. They are predicted to account for approximately half of the total extragalactic background light at those wavelengths. Searching for dusty star-forming galaxies behind massive galaxy clusters benefits from strong lensing, enhancing their measured emission while increasing spatial resolution. Derived number counts depend, however, on mass reconstruction models that properly constrain these clusters. We estimate the 1.1 mm number counts along the line of sight of three galaxy clusters, i.e. Abell 2744, MACSJ0416.1-2403 and MACSJ1149.5+2223, which are part of the ALMA Frontier Fields Survey. We perform detailed simulations to correct these counts for lensing effects. We use several publicly available lensing models for the galaxy clusters to derive the intrinsic flux densities of our sources. We perform Monte Carlo simulations of the number counts for a detailed treatment of the uncertainties in the magnifications and adopted source redshifts. We find an overall agreement among the number counts derived for the different lens models, despite their systematic variations regarding source magnifications and effective areas. Our number counts span ~2.5 dex in demagnified flux density, from several mJy down to tens of uJy. Our number counts are consistent with recent estimates from deep ALMA observations at a 3$σ$ level. Below $\approx$ 0.1 mJy, however, our cumulative counts are lower by $\approx$ 1 dex, suggesting a flattening in the number counts. In our deepest ALMA mosaic, we estimate number counts for intrinsic flux densities $\approx$ 4 times fainter than the rms level. This highlights the potential of probing the sub-10 uJy population in larger samples of galaxy cluster fields with deeper ALMA observations.

astro-ph.GA↗

arXiv2018

Weak-lensing mass calibration of the Sunyaev-Zel'dovich effect using APEX-SZ galaxy clusters

The use of galaxy clusters as precision cosmological probes relies on an accurate determination of their masses. However, inferring the relationship between cluster mass and observables from direct observations is difficult and prone to sample selection biases. In this work, we use weak lensing as the best possible proxy for cluster mass to calibrate the Sunyaev-Zel'dovich (SZ) effect measurements from the APEX-SZ experiment. For a well-defined (ROSAT) X-ray complete cluster sample, we calibrate the integrated Comptonization parameter, $Y_{\rm SZ}$, to the weak-lensing derived total cluster mass, $M_{500}$. We employ a novel Bayesian approach to account for the selection effects by jointly fitting both the SZ Comptonization, $Y_{\rm SZ}\text{--}M_{500}$, and the X-ray luminosity, $L_{\rm x}\text{--}M_{500}$, scaling relations. We also account for a possible correlation between the intrinsic (log-normal) scatter of $L_{\rm x}$ and $Y_{\rm SZ}$ at fixed mass. We find the corresponding correlation coefficient to be $r= 0.47_{-0.35}^{+0.24}$, and at the current precision level our constraints on the scaling relations are consistent with previous works. For our APEX-SZ sample, we find that ignoring the covariance between the SZ and X-ray observables biases the normalization of the $Y_{\rm SZ}\text{--}M_{500}$ scaling high by $1\text{--}2σ$ and the slope low by $\sim 1σ$, even when the SZ effect plays no role in the sample selection. We conclude that for higher-precision data and larger cluster samples, as anticipated from on-going and near-future cluster cosmology experiments, similar biases (due to intrinsic covariances of cluster observables) in the scaling relations will dominate the cosmological error budget if not accounted for correctly.

astro-ph.CO↗

arXiv2017

Upgrade for Phase II of the GERDA Experiment

The GERDA collaboration is performing a sensitive search for neutrinoless double beta decay of $^{76}$Ge at the INFN Laboratori Nazionali del Gran Sasso, Italy. The upgrade of the GERDA experiment from Phase I to Phase II has been concluded in December 2015. The first Phase II data release shows that the goal to suppress the background by one order of magnitude compared to Phase I has been achieved. GERDA is thus the first experiment that will remain background-free up to its design exposure (100 kg yr). It will reach thereby a half-life sensitivity of more than 10$^{26}$ yr within 3 years of data collection. This paper describes in detail the modifications and improvements of the experimental setup for Phase II and discusses the performance of individual detector components.

physics.ins-det↗

arXiv2017

The ALMA Frontier Fields Survey III: 1.1 mm Emission Line Identifications in Abell 2744, MACSJ0416.1-2403, MACSJ1149.5+2223, Abell 370, and Abell S1063

Most sub-mm emission line studies of galaxies to date have targeted sources with known redshifts where the frequencies of the lines are well constrained. Recent blind line scans circumvent the spectroscopic redshift requirement, which could represent a selection bias. Our aim is to detect emission lines present in continuum oriented observations. The detection of such lines provides spectroscopic redshift and yields properties of the galaxies. We perform a search for emission lines in the ALMA observations of five Frontier Fields clusters and assess the reliability of our detection by associating line candidates with detected galaxies in deep near-infrared imaging. We find 26 significant emission lines candidates, with observed line fluxes between 0.2-4.6 Jy km s$^{-1}$ and velocity dispersions (FWHM) of 25-600 km s$^{-1}$. Nine of these candidates lie nearby to near-infrared sources, boosting their reliability; in six cases the observed line frequency and strength are consistent with expectations given the photometric redshift and properties of the galaxy counterparts. We present redshift identifications, magnifications and molecular gas estimates for the galaxies with identified lines. We show that two of these candidates likely originate from starburst galaxies, one of which is a jellyfish galaxy, while another two are consistent with being main sequence galaxies based in their depletion times. This work highlights the degree to which serendipitous emission lines can be discovered in large mosaic continuum observations when deep ancillary data are available. The low number of high-significance line detections, however, confirms that such surveys are not as optimal as blind line scans. We stress that Monte Carlo simulations should be used to assess the line detections significances, since using the negative noise suffers from stochasticity and incurs larger uncertainties.

astro-ph.GA↗

arXiv2017

Planck's dusty GEMS. IV. Star formation and feedback in a maximum starburst at z=3 seen at 60-pc resolution

We present an analysis of high-resolution ALMA interferometry of CO(4-3) line emission and dust continuum in the "Ruby" (PLCK_G244.8+54.9), a bright, gravitationally lensed galaxy at z = 3.0 discovered with the Planck all-sky survey. The Ruby is the brightest of Planck's Dusty GEMS, a sample of 11 of the brightest gravitationally lensed high-redshift galaxies on the extragalactic sub-mm sky. We resolve the high-surface-brightness continuum and CO line emission of the Ruby in several extended clumps along a partial, nearly circular Einstein ring with 1.4" diameter around a massive galaxy at z = 1.5. Local star-formation intensities are up to 2000 M$_{\odot}$ yr$^{-1}$ kpc$^{-2}$, amongst the highest observed at high redshift, and clearly in the range of maximal starbursts. Gas-mass surface densities are a few $\times$ 10$^4$ M$_{\odot}$ pc$^{-2}$. The Ruby lies at, and in part even above, the starburst sequence in the Schmidt-Kennicutt diagram, and at the limit expected for star formation that is self-regulated through the kinetic energy injection from radiation pressure, stellar winds, and supernovae. We show that these processes can also inject sufficient kinetic energy and momentum into the gas to explain the turbulent line widths, which are consistent with marginally gravitationally bound molecular clouds embedded in a critically Toomre-stable disk. The star-formation efficiency is in the range 1-10% per free-fall time, consistent with the notion that the pressure balance that sets the local star-formation law in the Milky Way may well be universal out to the highest star-formation intensities. AGN feedback is not necessary to regulate the star formation in the Ruby, in agreement with the absence of a bright AGN component in the infrared and radio regimes.

astro-ph.GA↗

arXiv2017

The ALMA Frontier Fields Survey - II. Multiwavelength Photometric analysis of 1.1mm continuum sources in Abell 2744, MACSJ0416.1-2403 and MACSJ1149.5+2223

[abridged] The Hubble and Spitzer Space Telescope surveys of the Frontier Fields (FF) provide extremely deep images around six massive, strong-lensing clusters of galaxies. The ALMA FF survey aims to cover the same fields at 1.1mm, with maps reaching (unlensed) sensitivities of $<$70$μ$Jy, in order to explore the properties of background dusty star-forming galaxies. We report on the multi-wavelength photometric analysis of all 12 significantly detected ($>$5$σ$) sources in the first three FF clusters observed by ALMA, based on data from Hubble and Spitzer, the VLT and Herschel. We measure the total photometry in all available bands and determine the photometric redshifts and the physical properties of the counterparts via SED-fitting. In particular, we carefully estimate the FIR photometry using 1.1mm priors to limit the misidentification of blended FIR counterparts, which strongly affect some flux estimates in previous FIR catalogs. We identify robust near-infrared (NIR) counterparts for all 11 sources with K$_s$ detection, the majority of which are quite red, with eight having $F814W-K_s\gtrsim 4$ and five having $F160W-[4.5]\gtrsim3$. From the FIR point of view, all our objects have $z_{phot}$$\sim$1--3, whereas based on the optical SED one object prefers a high-$z$ solution ($z\geq\ $7). Five objects among our sample have spectroscopic redshifts from the GLASS survey for which we can reproduce their SEDs with existing templates. This verification confirms the validity of our photometric redshift methodology. The mean redshift of our sample is $z_{phot}$=1.99$\pm$0.27. All 1.1mm selected objects are massive (10.0$<\log[M_{\star}(M_{\odot})]<$ 11.5), with high star formation rates ($<\log[SFR(M_{\odot}/yr)]> \approx$1.6) and high dust contents (8.1 $<\log[M_{dust} (M_{\odot})]<$8.8), consistent with previous ALMA surveys.

astro-ph.GA↗

arXiv2017

Planck's Dusty GEMS. III. A massive lensing galaxy with a bottom-heavy stellar initial mass function at z=1.5

We study the properties of the foreground galaxy of the Ruby, the brightest gravitationally lensed high-redshift galaxy on the sub-millimeter sky as probed by the Planck satellite, and part of our sample of Planck's Dusty GEMS. The Ruby consists of an Einstein ring of 1.4" diameter at z = 3.005 observed with ALMA at 0.1" resolution, centered on a faint, red, massive lensing galaxy seen with HST/WFC3, which itself has an exceptionally high redshift, z = 1.525 $\pm$ 0.001, as confirmed with VLT/X-Shooter spectroscopy. Here we focus on the properties of the lens and the lensing model obtained with LENSTOOL. The rest-frame optical morphology of this system is strongly dominated by the lens, while the Ruby itself is highly obscured, and contributes less than 10% to the photometry out to the K band. The foreground galaxy has a lensing mass of (3.70 $\pm$ 0.35) $\times$ 10$^{11}$ M$_{\odot}$. Magnification factors are between 7 and 38 for individual clumps forming two image families along the Einstein ring. We present a decomposition of the foreground and background sources in the WFC3 images, and stellar population synthesis modeling with a range of star-formation histories for Chabrier and Salpeter initial mass functions (IMFs). Only the stellar mass range obtained with the latter agrees well with the lensing mass. This is consistent with the bottom-heavy IMFs of massive high-redshift galaxies expected from detailed studies of the stellar masses and mass profiles of their low-redshift descendants, and from models of turbulent gas fragmentation. This may be the first direct constraint on the IMF in a lens at z = 1.5, which is not a cluster central galaxy.

astro-ph.GA↗

arXiv2017

SCUBA-2 follow-up of Herschel-SPIRE observed Planck overdensities

We present SCUBA-2 follow-up of 61 candidate high-redshift Planck sources. Of these, 10 are confirmed strong gravitational lenses and comprise some of the brightest such submm sources on the observed sky, while 51 are candidate proto-cluster fields undergoing massive starburst events. With the accompanying Herschel-SPIRE observations and assuming an empirical dust temperature prior of $34^{+13}_{-9}$ K, we provide photometric redshift and far-IR luminosity estimates for 172 SCUBA-2-selected sources within these Planck overdensity fields. The redshift distribution of the sources peak between a redshift of 2 and 4, with one third of the sources having $S_{500}$/$S_{350} > 1$. For the majority of the sources, we find far-IR luminosities of approximately $10^{13}\,\mathrm{L}_\odot$, corresponding to star-formation rates of around $1000$ M$_\odot \mathrm{yr}^{-1}$. For $S_{850}>8$ mJy sources, we show that there is up to an order of magnitude increase in star-formation rate density and an increase in uncorrected number counts of $6$ for $S_{850}>8$ mJy when compared to typical cosmological survey fields. The sources detected with SCUBA-2 account for only approximately $5$ per cent of the Planck flux at 353 GHz, and thus many more fainter sources are expected in these fields.

astro-ph.GA↗