Publications


Predicting the observability of population III stars with ELT-HARMONI via the helium 1640 Å emission line

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 501 (2021) 5517-5537

K Grisdale, N Thatte, J Devriendt, M Pereira-Santaella, A Slyz, T Kimm, Y Dubois, SK Yi

<jats:title>ABSTRACT</jats:title> <jats:p>Population III (Pop. III) stars, as of yet, have not been detected, however as we move into the era of extremely large telescopes this is likely to change. One likely tracer for Pop. III stars is the He iiλ1640 emission line, which will be detectable by the HARMONI spectrograph on the European Extremely Large Telescope (ELT) over a broad range of redshifts (2 ≤ z ≤ 14). By post-processing galaxies from the cosmological, AMR-hydrodynamical simulation newhorizon with theoretical spectral energy distributions (SED) for Pop. III stars and radiative transfer (i.e. the Yggdrasil Models and cloudy look-up tables, respectively) we are able to compute the flux of He iiλ1640 for individual galaxies. From mock 10 h observations of these galaxies we show that HARMONI will be able to detect Pop. III stars in galaxies up to z ∼ 10 provided Pop. III stars have a top heavy initial mass function (IMF). Furthermore, we find that should Pop. III stars instead have an IMF similar to those of the Pop. I stars, the He iiλ1640 line would only be observable for galaxies with Pop. III stellar masses in excess of $10^{7}\, {\rm M}_\odot$, average stellar age $\lt 1\, {\rm Myr}$ at z = 4. Finally, we are able to determine the minimal intrinsic flux required for HARMONI to detect Pop. III stars in a galaxy up to z = 10.</jats:p>


Physical properties and scaling relations of molecular clouds: the impact of star formation

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 500 (2021) 3552-3568

K Grisdale


MOSAIC: the high multiplex and multi-IFU spectrograph for the ELT

Proceedings of SPIE - International Society for Optical Engineering Society of Photo-optical Instrumentation Engineers 11447 (2020)

G Dalton, R Sánchez-Janssen, F Hammer, S Morris, J-G Cuby, L Kaper, M Steinmetz, J Afonso, B Barbuy, M Rodrigues, I Lewis, E Bergin, C Evans

MOSAIC is the planned multi-object spectrograph for the 39m Extremely Large Telescope (ELT). Conceived as a multi-purpose instrument, it offers both high multiplex and multi-IFU capabilities at a range of intermediate to high spectral resolving powers in the visible and the near-infrared. MOSAIC will enable unique spectroscopic surveys of the faintest sources, from the oldest stars in the Galaxy and beyond to the first populations of galaxies that completed the reionisation of the Universe–while simultaneously opening up a wide discovery space. In this contribution we present the status of the instrument ahead of Phase B, showcasing the key science cases as well as introducing the updated set of top level requirements and the adopted architecture. The high readiness level will allow MOSAIC to soon enter the construction phase, with the goal to provide the ELT community with a world-class MOS capability as soon as possible after the telescope first light.


New prime focus rotator system for the WHT

Proceedings of SPIE Society of Photo-optical Instrumentation Engineers 11445 (2020) 114454S

G Dalton


Integration and early testing of WEAVE: the next-generation spectroscopy facility for the William Herschel Telescope

Proceedings of SPIE Society of Photo-optical Instrumentation Engineers 11447 (2020) 1144714

G Dalton, S Trager, DC Abrams, I Lewis, S Jin, A Molaeinezhad, E Schallig, S Hughes, M Brock, D Terrett

We present an update on the overall integration progress of the WEAVE next-generation spectroscopy facility for the William Herschel Telescope (WHT), now scheduled for first light in early-2021, with almost all components now arrived at the observatory. We also present a summary of the current planning behind the 5-year initial phase of survey operations, and some detailed end-to-end science simulations that have been implemented to evaluate the final on-sky performance after data processing. WEAVE will provide optical ground-based follow up of ground-based (LOFAR) and space-based (Gaia) surveys. WEAVE is a multi-object and multi-IFU facility utilizing a new 2-degree prime focus field of view at the WHT, with a buffered pick-and-place positioner system hosting 1000 multi-object (MOS) fibres, 20 mini integral field units, or a single large IFU for each observation. The fibres are fed to a single (dual-beam) spectrograph, with total of 16k spectral pixels, located within the WHT GHRIL enclosure on the telescope Nasmyth platform, supporting observations at R~5000 over the full 370-1000nm wavelength range in a single exposure, or a high resolution mode with limited coverage in each arm at R~20000.


Fibre links for the WEAVE instrument: the making of

Society of Photo-optical Instrumentation Engineers (2020) 114502F
Part of a series from Proceedings of SPIE

S Mignot, P Bonifacio, G Fasola, G Dalton, I Lewis

The WEAVE instrument nearing completion for the William Herschel Telescope is a fiber-fed spectrograph operating in three different modes. Two comprise deployable fibers at the prime focus for point-like objects and small integral field units (IFU), the third is a large IFU placed at the center of the field. Three distinct fiber systems support these modes and route the photons to the spectrograph located on the Nasmyth platform 33m away: the first features 960+940 fibers and is duplicated to allow configuring the fibers on one plate while observation is carried out on the other, the second has 20 hexagonal IFUs featuring 37 fibers each, the third is a large array of 609 fibers with twice the former’s diameter. The large number of fibers and the diversity of their instantiation have made procurement of the parts and assembly of the custom cables a challenge. They involve project partners in France, the UK and the Netherlands and industrial partners in France, Canada, the USA and China to combine know-how and compress the schedule by parallelizing assembly of the cables. Besides the complex management that this induces, it has called for revising the fibers’ handling to relax tolerances and for a rigorous assessment of the conformity of the products. This paper tells the story of the making of the fiber links, presents the overall organization of the procurement and assembly chains together with the inspection and testing allowing for assessing the conformance of the hardware delivered.


Final assembly, metrology, and testing of the WEAVE fibre positioner

Proceedings of SPIE Society of Photo-optical Instrumentation Engineers 11447 (2020)

S Hughes, E Schallig, I Lewis, G Dalton, D Terrett, DC Abrams, S Trager, M Brock, G Bishop, K Middleton, P Bonifacio, A Vallenari, E Carrasco, A Aguerri

WEAVE is the new wide-field spectroscopy facility for the prime focus of the William Herschel Telescope at La Palma, Spain. Its fibre positioner is essential for the accurate placement of the spectrograph’s 960 fibre multiplex. We provide an overview of the final assembly and metrology of the fibre positioner, and results of lab commissioning of its robot gantries. A completely new z-gantry for each positioner robot was acquired, with measurements showing a marked improvement in positioning repeatability. We also present the first results of the configuration soft ng, and discuss the metrology procedures that must be repeated after the positioner’s arrival at the observatory.


HARMONI: First light spectroscopy for the ELT: final design and assembly plan of the spectrographs

Ground-based and Airborne Instrumentation for Astronomy VIII SPIE (2020)

Z Ozer, H Schnetler, FT Bagci, M Booth, M Brock, N Cann, JI Capone, J Chao Ortiz, G Dalton, N Dobson, T Foster, A Hidalgo Valadez, J Kariuki, I Lewis, A Lowe, J Lynn, M Rodrigues, I Tosh, F Clarke, M Tecza, N Thatte


Simulating gas kinematic studies of high-redshift galaxies with the HARMONI integral field spectrograph

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 498 (2020) 1891-1904

MLA Richardson, L Routledge, N Thatte, M Tecza, RCW Houghton, M Pereira-Santaella, D Rigopoulou


Cold molecular gas and PAH emission in the nuclear and circumnuclear regions of Seyfert galaxies

ASTRONOMY & ASTROPHYSICS 639 (2020)

A Alonso-Herrero, M Pereira-Santaella, D Rigopoulou, I Garcia-Bernete, S Garcia-Burillo, AJ Dominguez-Fernandez, F Combes, RI Davies, T Diaz-Santos, D Esparza-Arredondo, O Gonzalez-Martin, A Hernan-Caballero, EKS Hicks, SF Honig, NA Levenson, C Ramos Almeida, PF Roche, D Rosario


Black Hole-Galaxy Scaling Relation Evolution From z~2.5: Simulated Observations With HARMONI on the ELT

Frontiers in Astronomy and Space Sciences 6 (2019)

B García-Lorenzo, A Monreal-Ibero, E Mediavilla, M Pereira-Santaella, N Thatte

© Copyright © 2019 García-Lorenzo, Monreal-Ibero, Mediavilla, Pereira-Santaella and Thatte. We present preliminary results on the potential of HARMONI, the first light integral field spectrograph for the ELT, to explore the evolution of central super massive black holes (SMBH)—host galaxy relation in the range from z~0.7 to z~2.5. We simulated HARMONI observations of QSO+host galaxy at different redshifts, assuming different morphologies for the host galaxy. As input, we combined MUSE observations of nearby galaxies and a theoretical QSO spectrum. These were dimmed and redshifted to the desired cosmic epoch. We scaled the total host galaxy luminosity to three different values, sampling three orders of magnitude. Likewise, we assumed two different luminosities for the central QSO. Simulations were performed for the 30×60 mas2 HARMONI spatial scale and LTAO working at 0.67 arcsec seeing. The selected wavelength range (i.e., 4,700–5,300 Å at rest-frame) was sampled at the lowest HARMONI spectral resolving power (i.e., R~3,200). This configuration included all the ingredients to estimate the host galaxy parameters and the SMBH mass, as well as for assessing the morphological type of the host galaxy.


A few StePS forward in unveiling the complexity of galaxy evolution: light-weighted stellar ages of intermediate-redshift galaxies with WEAVE

Astronomy and Astrophysics EDP Sciences 632 (2019) A9

L Costantin, A Iovino, S Zibetti, M Longhetti, A Gallazzi, A Mercurio, I Lonoce, M Balcells, M Bolzonella, G Busarello, G Dalton, A Ferre-Mateu, R Garcia-Benito, S Jin, F La Barbera, P Merluzzi, DNA Murphy, PDAL de Arriba, P Sanchez-Blazquez, M Talia, C Tortora, SC Trager, A Vazdekis, D Vergani, B Vulcani

<br><strong><i>Context. </strong></i>The upcoming new generation of optical spectrographs on four-meter-class telescopes, with their huge multiplexing capabilities, excellent spectral resolution, and unprecedented wavelength coverage, will provide invaluable information for reconstructing the history of star formation in individual galaxies up to redshifts of about 0.7.</br> <br><strong><i>Aims. </strong></i>We aim at defining simple but robust and meaningful physical parameters that can be used to trace the coexistence of widely diverse stellar components: younger stellar populations superimposed on the bulk of older ones.</br> <br><strong><i>Methods. </strong></i>We produced spectra of galaxies closely mimicking data from the forthcoming Stellar Populations at intermediate redshifts Survey (StePS), a survey that uses the WEAVE spectrograph on the William Herschel Telescope. First, we assessed our ability to reliably measure both ultraviolet and optical spectral indices in galaxies of different spectral types for typically expected signal-to-noise ratios. We then analyzed such mock spectra with a Bayesian approach, deriving the probability density function of r- and u-band light-weighted ages as well as of their difference.</br> <br><strong><i>Results. </strong></i>We find that the ultraviolet indices significantly narrow the uncertainties in estimating the r- and u-band light-weighted ages and their difference in individual galaxies. These diagnostics, robustly retrievable for large galaxy samples even when observed at moderate signal-to-noise ratios, allow us to identify secondary episodes of star formation up to an age of ∼0.1 Gyr for stellar populations older than ∼1.5 Gyr, pushing up to an age of ∼1 Gyr for stellar populations older than ∼5 Gyr.</br> <br><strong><i>Conclusions. </strong></i>The difference between r-band and u-band light-weighted ages is shown to be a powerful diagnostic to characterize and constrain extended star-formation histories and the presence of young stellar populations on top of older ones. This parameter can be used to explore the interplay between different galaxy star-formation histories and physical parameters such as galaxy mass, size, morphology, and environment.</br>


High angular resolution ALMA images of dust and molecules in the SN 1987A ejecta

Astrophysical Journal American Astronomical Society 886 (2019) 51

P Cigan, M Matsuura, HL Gomez, R Indebetouw, P Roche

We present high angular resolution (~80 mas) ALMA continuum images of the SN 1987A system, together with CO J = 2 $\to $ 1, J = 6 $\to $ 5, and SiO J = 5 $\to $ 4 to J = 7 $\to $ 6 images, which clearly resolve the ejecta (dust continuum and molecules) and ring (synchrotron continuum) components. Dust in the ejecta is asymmetric and clumpy, and overall the dust fills the spatial void seen in Hα images, filling that region with material from heavier elements. The dust clumps generally fill the space where CO J = 6 $\to $ 5 is fainter, tentatively indicating that these dust clumps and CO are locationally and chemically linked. In these regions, carbonaceous dust grains might have formed after dissociation of CO. The dust grains would have cooled by radiation, and subsequent collisions of grains with gas would also cool the gas, suppressing the CO J = 6 $\to $ 5 intensity. The data show a dust peak spatially coincident with the molecular hole seen in previous ALMA CO J = 2 $\to $ 1 and SiO J = 5 $\to $ 4 images. That dust peak, combined with CO and SiO line spectra, suggests that the dust and gas could be at higher temperatures than the surrounding material, though higher density cannot be totally excluded. One of the possibilities is that a compact source provides additional heat at that location. Fits to the far-infrared–millimeter spectral energy distribution give ejecta dust temperatures of 18–23 K. We revise the ejecta dust mass to M dust = 0.2–0.4 ${M}_{\odot }$ for carbon or silicate grains, or a maximum of <0.7 ${M}_{\odot }$ for a mixture of grain species, using the predicted nucleosynthesis yields as an upper limit.


Emission from the circumgalactic medium: from cosmological zoom-in simulations to multiwavelength observables

Monthly Notices of the Royal Astronomical Society Oxford University Press 489 (2019) 2417-2438

R Augustin, S Quiret, B Milliard, C Peroux, D Vibert, J Blaizot, Y Rasera, R Teyssier, S Frank, J-M Deharveng, V Picouet, DC Martin, ET Hamden, N Thatte, MP Santaella, L Routledge, S Zieleniewski

<p>We simulate the flux emitted from galaxy haloes in order to quantify the brightness of the circumgalactic medium (CGM). We use dedicated zoom-in cosmological simulations with the hydrodynamical adaptive mesh refinement code RAMSES, which are evolved down to <em>z</em> = 0 and reach a maximum spatial resolution of 380 <em>h</em><sup>−1</sup> pc and a gas mass resolution up to 1.8×10<sup>5</sup> h<sup>−</sup><sup>1</sup> M⊙ in the densest regions. We compute the expected emission from the gas in the CGM using CLOUDY emissivity models for different lines (e.g. Lyα, C IV, O VI, C VI, O VIII) considering UV background fluorescence, gravitational cooling and continuum emission. In the case of Lyα, we additionally consider the scattering of continuum photons. We compare our predictions to current observations and find them to be in good agreement at any redshift after adjusting the Lyα escape fraction. We combine our mock observations with instrument models for Faint Intergalactic Redshifted Emission Balloon-2 (FIREBall-2; UV balloon spectrograph) and HARMONI (visible and NIR IFU on the ELT) to predict CGM observations with either instrument and optimize target selections and observing strategies. Our results show that Lyα emission from the CGM at a redshift of 0.7 will be observable with FIREBall-2 for bright galaxies (NUV∼18 mag), while metal lines like O VI and C IV will remain challenging to detect. HARMONI is found to be well suited to study the CGM at different redshifts with various tracers.</p>


Nuclear molecular outflow in the Seyfert galaxy NGC 3227

Astronomy and Astrophysics EDP Sciences 628 (2019) A65

A Alonso Herrero, S García-Burillo, M Pereira-Santaella, RI Davies, F Combes, M Vestergaard, SI Raimundo, A Bunker, T Díaz-Santos, P Gandhi, I García-Bernete, EKS Hicks, SF Hönig, LK Hunt, M Imanishi, T Izumi, NA Levenson, W Maciejewski1, C Packham, C Ramos Almeida, C Ricci, D Rigopoulou, P Roche, D Rosario, M Schartmann

ALMA observations have revealed nuclear dusty molecular disks or tori with characteristic sizes 15−40 pc in the few Seyferts and low -luminosity AGN that have been studied so far. These structures are generally decoupled both morphologically and kinematically from the host galaxy disk. We present ALMA observations of the CO(2–1) and CO(3–2) molecular gas transitions and associated (sub-) millimeter continua of the nearby Seyfert 1.5 galaxy NGC 3227 with angular resolutions 0.085 − 0.21″ (7–15 pc). On large scales, the cold molecular gas shows circular motions as well as streaming motions on scales of a few hundred parsecs that are associated with a large-scale bar. We fit the nuclear ALMA 1.3 mm emission with an unresolved component and an extended component. The 850 μm emission shows at least two extended components, one along the major axis of the nuclear disk, and the other along the axis of the ionization cone. The molecular gas in the central region (1″ ∼ 73 pc) shows several CO clumps with complex kinematics that appears to be dominated by noncircular motions. While we cannot conclusively demonstrate the presence of a warped nuclear disk, we also detected noncircular motions along the kinematic minor axis. They reach line-of-sight velocities of v − vsys = 150 − 200 km s−1. Assuming that the radial motions are in the plane of the galaxy, we interpret them as a nuclear molecular outflow due to molecular gas in the host galaxy that is entrained by the AGN wind. We derive molecular outflow rates of 5 M⊙ yr−1 and 0.6 M⊙ yr−1 at projected distances of up to 30 pc to the northeast and southwest of the AGN, respectively. At the AGN location we estimate a mass in molecular gas of 5 × 105 M⊙ and an equivalent average column density N(H2) = 2 − 3 × 1023 cm−2 in the inner 15 pc. The nuclear CO(2–1) and CO(3–2) molecular gas and submillimeter continuum emission of NGC 3227 do not resemble the classical compact torus. Rather, these emissions extend for several tens of parsecs and appear connected with the circumnuclear ring in the host galaxy disk, as found in other local AGN.


Optical integral field spectroscopy of intermediate redshift infrared bright galaxies

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (0)

M Pereira-Santaella, D Rigopoulou, GE Magdis, N Thatte, A Alonso-Herrero, F Clarke, D Farrah, S García-Burillo, L Hogan, S Morris, M Rodrigues, J-S Huang, M Tecza

The extreme infrared (IR) luminosity of local luminous and ultra-luminous IR galaxies (U/LIRGs; 11 < log LIR /Lsun < 12 and log LIR /Lsun > 12, respectively) is mainly powered by star-formation processes triggered by mergers or interactions. While U/LIRGs are rare locally, at z > 1, they become more common, they dominate the star-formation rate (SFR) density, and a fraction of them are found to be normal disk galaxies. Therefore, there must be an evolution of the mechanism triggering these intense starbursts with redshift. To investigate this evolution, we present new optical SWIFT integral field spectroscopic H{\alpha}+[NII] observations of a sample of 9 intermediate-z (0.2 < z < 0.4) U/LIRG systems selected from Herschel 250{\mu}m observations. The main results are the following: (a) the ratios between the velocity dispersion and the rotation curve amplitude indicate that 10-25% (1-2 out of 8) might be compatible with being isolated disks while the remaining objects are interacting/merging systems; (b) the ratio between un-obscured and obscured SFR traced by H{\alpha} and LIR, respectively, is similar in both local and these intermediate-z U/LIRGs; and (c) the ratio between 250{\mu}m and the total IR luminosities of these intermediate-z U/LIRGs is higher than that of local U/LIRGs with the same LIR . This indicates a reduced dust temperature in these intermediate-z U/LIRGs. This, together with their already measured enhanced molecular gas content, suggests that the interstellar medium conditions are different in our sample of intermediate-z galaxies when compared to local U/LIRGs.


On the Observed Diversity of Star Formation Efficiencies in Giant Molecular Clouds

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 468 (2019) 5482-5491

K Grisdale, O Agertz, F Renaud, AB Romeo, J Devriendt, A Slyz

Observations find a median star formation efficiency per free-fall time in Milky Way Giant Molecular Clouds (GMCs) on the order of $\epsilon_{\rm ff}\sim 1\%$ with dispersions of $\sim0.5\,{\rm dex}$. The origin of this scatter in $\epsilon_{\rm ff}$ is still debated and difficult to reproduce with analytical models. We track the formation, evolution and destruction of GMCs in a hydrodynamical simulation of a Milky Way-like galaxy and by deriving cloud properties in an observationally motivated way, measure the distribution of star formation efficiencies which are in excellent agreement with observations. We find no significant link between $\epsilon_{\rm ff}$ and any measured global property of GMCs (e.g. gas mass, velocity dispersion). Instead, a wide range of efficiencies exist in the entire parameter space. From the cloud evolutionary tracks, we find that each cloud follow a \emph{unique} evolutionary path which gives rise to wide diversity in all properties. We argue that it is this diversity in cloud properties, above all else, that results in the dispersion of $\epsilon_{\rm ff}$.


Torus model properties of an ultra-hard X-ray selected sample of Seyfert galaxies

Monthly Notices of the Royal Astronomical Society Oxford University Press 486 (2019) 4917-4935

I Garcia-Benete, C Ramos Almeida, A Alonso-Herrero, M Ward, JA Acosta-Pulido, M Pereira-Santaella, A Hernan-Caballero, A Asensio Ramos, O Gonzalez-Martin, NA Levenson, S Mateos, FJ Carrera, C Ricci, P Roche, I Marquez, C Packham, J Masegosa, L Fuller

We characterize for the first time the torus properties of an ultra-hard X-ray (14–195 keV) volume-limited (DL &lt; 40 Mpc) sample of 24 Seyfert (Sy) galaxies (BCS40 sample). The sample was selected from the Swift/BAT nine-month catalogue. We use high angular resolution nuclear infrared (IR) photometry and N-band spectroscopy, the CLUMPY torus models and a Bayesian tool to characterize the properties of the nuclear dust. In the case of the Sy1s, we estimate the accretion disc contribution to the subarcsecond resolution nuclear IR SEDs (∼0.4 arcsec) which is, on average, 46 ± 28, 23 ± 13, and 11 ± 5 per cent in the J, H, and K bands, respectively. This indicates that the accretion disc templates that assume a steep fall for longer wavelengths than 1 μm might underestimate its contribution to the near-IR emission. Using both optical (broad versus narrow lines) and X-ray (unabsorbed versus absorbed) classifications, we compare the global posterior distribution of the torus model parameters. We confirm that Sy2s have larger values of the torus covering factor (CT ∼ 0.95) than Sy1s (CT ∼ 0.65) in our volume-limited Seyfert sample. These findings are independent of whether we use an optical or X-ray classification. We find that the torus covering factor remains essentially constant within the errors in our luminosity range and there is no clear dependence with the Eddington ratio. Finally, we find tentative evidence that even an ultra-hard X-ray selection is missing a significant fraction of highly absorbed type 2 sources with very high covering factor tori.


PAHs as tracers of the molecular gas in star-forming galaxies

Monthly Notices of the Royal Astronomical Society Oxford University Press 482 (2018) 1618-1633

I Cortzen, J Garrett, G Magdis, D Rigopoulou, F Valentino, M Pereira-Santaella, F Combes, A Alonso-Herrero, S Toft, E Daddi, D Elbaz, C Gómez-Guijarro, M Stockmann, J Huang, C Kramer

We combine new CO(1–0) line observations of 24 intermediate redshift galaxies (0.03 &lt; z &lt; 0.28) along with literature data of galaxies at 0 &lt; z &lt; 4 to explore scaling relations between the dust and gas content using polycyclic aromatic hydrocarbon (PAH) 6.2 μm (L6.2), CO (⁠L′CO⁠), and infrared (LIR) luminosities for a wide range of redshifts and physical environments. Our analysis confirms the existence of a universal L6.2–L′CO correlation followed by normal star-forming galaxies (SFGs) and starbursts (SBs) at all redshifts. This relation is also followed by local ultraluminous infrared galaxies that appear as outliers in the L6.2–LIR and LIR–L′CO relations defined by normal SFGs. The emerging tight (σ ≈ 0.26 dex) and linear (α = 1.03) relation between L6.2 and L′CO indicates a L6.2 to molecular gas (⁠MH2⁠) conversion factor of α6.2 = MH2/L6.2 = (2.7 ± 1.3) × αCO, where αCO is the L′CO to MH2 conversion factor. We also find that on galaxy integrated scales, PAH emission is better correlated with cold rather than with warm dust emission, suggesting that PAHs are associated with the diffuse cold dust, which is another proxy for MH2⁠. Focusing on normal SFGs among our sample, we employ the dust continuum emission to derive MH2 estimates and find a constant MH2/L6.2 ratio of α6.2 = 12.3 M⊙/L⊙(σ ≈ 0.3 dex). This ratio is in excellent agreement with the L′CO-based MH2/L6.2 values for αCO = 4.5 M⊙/(K km s−1 pc2) which is typical of normal SFGs. We propose that the presented L6.2–L′CO and L6.2–MH2 relations will serve as useful tools for the determination of the physical properties of high-z SFGs, for which PAH emission will be routinely detected by the James Webb Space Telescope.


Resolving star formation on subkiloparsec scales in the high-redshift galaxy SDP.11 using gravitational lensing

Astrophysical Journal American Astronomical Society 867 (2018) 140

C Lamarche, A Verma, A Vishwas, GJ Stacey, D Brisbin, C Ferkinhoff, T Nikola, SJU Higdon, J Higdon, M Tecza

We investigate the properties of the interstellar medium, star formation, and the current-day stellar population in the strongly lensed star-forming galaxy H-ATLAS J091043.1-000321 (SDP.11), at z = 1.7830, using new Herschel and Atacama Large Millimeter/submillimeter Array (ALMA) observations of far-infrared fine-structure lines of carbon, oxygen, and nitrogen. We report detections of the [O iii] 52 μm, [N iii] 57 μm, and [O i] 63 μm lines from Herschel/PACS, and present high-resolution imaging of the [C ii] 158 μm line, and underlying continuum, using ALMA. We resolve the [C ii] line emission into two spatially offset Einstein rings, tracing the red and blue velocity components of the line, in the ALMA/Band 9 observations at 0farcs2 resolution. The values seen in the [C ii]/far-infrared (FIR) ratio map, as low as ~0.02% at the peak of the dust continuum, are similar to those of local ULIRGs, suggesting an intense starburst in this source. This is consistent with the high intrinsic FIR luminosity (~3 × 1012 L ⊙), ~16 Myr gas depletion timescale, and lesssim8 Myr timescale since the last starburst episode, estimated from the hardness of the UV radiation field. By applying gravitational lensing models to the visibilities in the uv-plane, we find that the lensing magnification factor varies by a factor of two across SDP.11, affecting the observed line profiles. After correcting for the effects of differential lensing, a symmetric line profile is recovered, suggesting that the starburst present here may not be the result of a major merger, as is the case for local ULIRGs, but instead could be powered by star formation activity spread across a 3–5 kpc rotating disk.

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