Publications by Dimitra Rigopoulou

Far-infrared metallicity diagnostics: application to local ultraluminous infrared galaxies

Monthly Notices of the Royal Astronomical Society Oxford University Press 470 (2017) 1218-1232

M Pereira-Santaella, D Rigopoulou, D Farrah, V Lebouteiller, J Li

<p>The abundance of metals in galaxies is a key parameter that permits to distinguish between different galaxy formation and evolution models. Most of the metallicity determinations are based on optical line ratios. However, the optical spectral range is subject to dust extinction and, for high-z objects (z &gt; 3), some of the lines used in optical metallicity diagnostics are shifted to wavelengths not accessible to ground-based observatories. For this reason, we explore metallicity diagnostics using far-infrared (far-IR) line ratios which can provide a suitable alternative in such situations. To investigate these far-IR line ratios, we modelled the emission of a starburst with the photoionization code CLOUDY. The most sensitive far-IR ratios to measure metallicities are the [OIII]52 μm and 88 μm to [NIII]57 μm ratios. We show that this ratio produces robust metallicities in the presence of an active galactic nucleus and is insensitive to changes in the age of the ionizing stellar. Another metallicity-sensitive ratio is the [OIII]88 μm/[N II]122 μm ratio, although it depends on the ionization parameter. We propose various mid- and far-IR line ratios to break this dependence. Finally, we apply these far-IR diagnostics to a sample of 19 local ultraluminous IR galaxies (ULIRGs) observed with Herschel and Spitzer. We find that the gas-phase metallicity in these local ULIRGs is in the range 0.7 &lt; Zgas/Z⊙ &lt; 1.5, which corresponds to 8.5 &lt; 12 + log(O/H) &lt; 8.9. The inferred metallicities agree well with previous estimates for local ULIRGs and this confirms that they lie below the local mass–metallicity relation.</p>

ALMA [N ii] 205 μm imaging spectroscopy of the interacting galaxy system BRI 1202-0725 at redshift 4.7

Astrophysical Journal Letters Institute of Physics 842 (2017) L16-

N Lu, Y Zhao, T Díaz-Santos, CK Xu, V Charmandaris, Y Gao, PP van der Werf, GC Privon, H Inami, D Rigopoulou, DB Sanders, L Zhu

We present the results from Atacama Large Millimeter/submillimeter Array imaging in the [N ii] 205μm fine-structure line (hereafter [N ii] ) and the underlying continuum of BRI 1202-0725, an interacting galaxy system at z = 4.7, consisting of a quasi-stellar object (QSO), a submillimeter galaxy (SMG), and two Ly emitters, all within ∼25 kpc of the QSO. We detect the QSO and SMG in both [N ii] and continuum. At the ∼1″ (or 6.6 kpc) resolution, both the QSO and SMG are resolved in [N ii] , with the de-convolved major axes of ∼9 and ∼14 kpc, respectively. In contrast, their continuum emissions are much more compact and unresolved even at an enhanced resolution of ∼0.″7. The ratio of the [N ii] flux to the existing CO(7-6) flux is used to constrain the dust temperature (T dust ) for a more accurate determination of the FIR luminosity LFIR . Our best estimated T dust equals 43 (±2) K for both galaxies (assuming an emissivity index β = 1.8). The resulting LCO(7-6) /L FIR ratios are statistically consistent with that of local luminous infrared galaxies, confirming that LCO(7-6) traces the star formation (SF) rate (SFR) in these galaxies. We estimate that the ongoing SF of the QSO (SMG) has an SFR of 5.1 (6.9) × 10^3 M⊙ yr^-1 (±30%) assuming Chabrier initial mass function, takes place within a diameter (at half maximum) of 1.3 (1.5) kpc, and will consume the existing 5 (5) × 10^11 M⊙ of molecular gas in 10 (7) × 10 7 years.

First detection of the 448 GHz H2O transition in space

Astronomy & Astrophysics EDP Sciences 601 (2017) L3-

M Pereira-Santaella, E González-Alfonso, A Usero, S García-Burillo, J Martín-Pintado, L Colina, A Alonso-Herrero, S Arribas, S Cazzoli, F Rico, D Rigopoulou, TS Storchi Bergmann

We present the first detection of the ortho-H2O 4₂₃ - 3₃₀ transition at 448 GHz in space. We observed this transition in the local (z = 0.010) luminous infrared (IR) galaxy ESO 320-G030 (IRAS F11506-3851) using the Atacama Large Millimeter/submillimeter Array (ALMA). The water 4₂₃ - 3₃₀ emission, which originates in the highly obscured nucleus of this galaxy, is spatially resolved over a region of ~65 pc in diameter and shows a regular rotation pattern compatible with the global molecular and ionized gas kinematics. The line profile is symmetric and well fitted by a Gaussian with an integrated flux of 37.0 ± 0.7 Jy km s^-1 . Models predict this water transition as a potential collisionally excited maser transition. On the contrary, in this galaxy, we find that the 4₂₃ - 3₃₀ emission is primarily excited by the intense far-IR radiation field present in its nucleus. According to our modeling, this transition is a probe of deeply buried galaxy nuclei thanks to the high dust optical depths (τ 100μm &gt; 1, NH &gt; 10^24 cm^-2 ) required to efficiently excite it.

The SCUBA-2 Cosmology Legacy Survey: 850um maps, catalogues and number counts

Monthly Notices of the Royal Astronomical Society Oxford University Press 465 (2016) 1789-1806

JE Geach, JS Dunlop, M Halpern, I Smail, PVD Werf, DM Alexander, EL Chapin, SC Chapman, DL Clements, C Conselice, KEK Coppin, WI Cowley, ALR Danielson, S Eales, AC Edge, D Farrah, A Gibb, CM Harrison, NK Hine, DJB Smith, M Spaans, F Stanley, JA Stevens, AM Swinbank, T Targett

We present a catalogue of ∼3,000 submillimetre sources detected (≥3.5σ) at 850μm over ∼5 deg2 surveyed as part of the James Clerk Maxwell Telescope (JCMT) SCUBA-2 Cosmology Legacy Survey (S2CLS). This is the largest survey of its kind at 850μm, increasing the sample size of 850-μm-selected submillimetre galaxies by an order of magnitude. The wide 850μm survey component of S2CLS covers the extragalactic fields: UKIDSS-UDS, COSMOS, Akari-NEP, Extended Groth Strip, Lockman Hole North, SSA22 and GOODS-North. The average 1σ depth of S2CLS is 1.2 mJy beam−1, approaching the SCUBA-2 850μm confusion limit, which we determine to be σc ≈ 0.8 mJy beam−1. We measure the 850μm number counts, reducing the Poisson errors on the differential counts to approximately 4% at S850 ≈ 3 mJy. With several independent fields, we investigate field-to-field variance, finding that the number counts on 0.5–1° scales are generally within 50% of the S2CLS mean for S850 &gt; 3 mJy, with scatter consistent with the Poisson and estimated cosmic variance uncertainties, although there is a marginal (2σ) density enhancement in GOODS-North. The observed counts are in reasonable agreement with recent phenomenological and semi-analytic models, although determining the shape of the faint end slope (S850 &lt; 3 mJy) remains a key test. The large solid angle of S2CLS allows us to measure the bright-end counts: at S850 &gt; 10 mJy there are approximately ten sources per square degree, and we detect the distinctive up-turn in the number counts indicative of the detection of local sources of 850μm emission, and strongly lensed high-redshift galaxies. All calibrated maps and the catalogue are made publicly available.

The interstellar medium in high-redshift submillimeter galaxies as probed by infrared spectroscopy

Astrophysical Journal IOP Publishing 837 (2017)

JL Wardlow, A Cooray, W Osage, N Bourne, D Clements, H Dannerbauer, L Dunne, S Dye, S Eales, D Farrah, C Furlanetto, E Ibar, R Ivison, S Maddox, MM Michałowski, D Riechers, D Rigopoulou, D Scott, MWL Smith, L Wang, PVD Werf, E Valiante, I Valtchanov, A Verma

Submillimeter galaxies (SMGs) at $z\gtrsim1$ are luminous in the far-infrared and have star-formation rates, SFR, of hundreds to thousands of solar masses per year. However, it is unclear whether they are true analogs of local ULIRGs or whether the mode of their star formation is more similar to that in local disk galaxies. We target these questions by using Herschel-PACS to examine the conditions in the interstellar medium (ISM) in far-infrared luminous SMGs at z~1-4. We present 70-160 micron photometry and spectroscopy of the [OIV]26 micron, [FeII]26 micron, [SIII]33 micron, [SiII]34 micron, [OIII]52 micron, [NIII]57 micron, and [OI]63 micron fine-structure lines and the S(0) and S(1) hydrogen rotational lines in 13 lensed SMGs identified by their brightness in early Herschel data. Most of the 13 targets are not individually spectroscopically detected and we instead focus on stacking these spectra with observations of an additional 32 SMGs from the \herschel\ archive -- representing a complete compilation of PACS spectroscopy of SMGs. We detect [OI]63 micron, [SiII]34 micron, and [NIII]57 micron at &gt;3sigma in the stacked spectra, determining that the average strengths of these lines relative to the far-IR continuum are $(0.36\pm0.12)\times10^{-3}$, $(0.84\pm0.17)\times10^{-3}$, and $(0.27\pm0.10)\times10^{-3}$, respectively. Using the [OIII]52/[NIII]57 emission line ratio we show that SMGs have average gas-phase metallicities $\gtrsim Z_{\rm sun}$. By using PDR modelling and combining the new spectral measurements with integrated far-infrared fluxes and existing [CII]158 micron data we show that SMGs have average gas densities, n, of $\sim10^{1-3}{\rm cm^{-3}}$ and FUV field strengths, $G_0\sim10^{2.2-4.5}$ (in Habing units: $1.6\times10^{-3}{\rm erg~cm^{-2}~s^{-1}}$), consistent with both local ULIRGs and lower luminosity star-forming galaxies.

The Far InfraRed Spectroscopic EXplorer (FIRSPEX)

27th International Symposium on Space Terahertz Technology, ISSTT 2016 Society of Photo-Optical Instrumentation Engineers (2016)

D Rigopoulou, BK Tan, G Yassin

The Far InfraRed Spectroscopic EXplorer (FIRSPEX) is a novel concept for an astronomy satellite mission that will revolutionise our understanding of the properties of the Interstellar Medium (ISM) and star formation through velocity resolved spectroscopic observations at multi-terahertz frequencies. FIRSPEX comprises a fully cryogenic (~4K) heterodyne payload and a ~1.2 m primary antenna to scan the sky in a number of discreet spectroscopic channels delivering 3- dimensional spectral information. The spectral range selected contains important molecular, atomic and ionic species; the majority of which cannot be observed from the ground. FIRSPEX is UK led with additional contributions from partners throughout Europe. FIRSPEX opens up a relatively unexplored parameter space that will produce an enormously significant scientific legacy by focusing on the properties of the multi-phase ISM, the assembly of molecular clouds in our Galaxy and the onset of star formation topics which are fundamental to our understanding of galaxy evolution.

The star-formation rate density from z = 0-6

Monthly Notices of the Royal Astronomical Society Oxford University Press 461 (2016) Pp. 1100-1111

M Rowan-Robinson, S Oliver, L Wang, D Farrah, D Clements, C Gruppioni, L Marchetti, D Rigopoulou, M Vaccari

We use 3035 Herschel-SPIRE 500$\mu$m sources from 20.3 sq deg of sky in the HerMES Lockman, ES1 and XMM-LSS areas to estimate the star-formation rate density at z = 1-6. 500 mu sources are associated first with 350 and 250 mu sources, and then with Spitzer 24 mu sources from the SWIRE photometric redshift catalogue. The infrared and submillimetre data are fitted with a set of radiative-transfer templates corresponding to cirrus (quiescent) and starburst galaxies. Lensing candidates are removed via a set of colour-colour and colour-redshift constraints. Star-formation rates are found to extend from &lt; 1 to 20,000 Mo/yr. Such high values were also seen in the all-sky IRAS Faint Source Survey. Star-formation rate functions are derived in a series of redshift bins from 0-6, combined with earlier far-infrared estimates, where available, and fitted with a Saunders et al (1990) functional form. The star-formation-rate density as a function of redshift is derived and compared with other estimates. There is reasonable agreement with both infrared and ultraviolet estimates for z &lt; 3, but we find higher star-formation-rate densities than ultraviolet estimates at z = 3-6. Given the considerable uncertainties in the submillimetre estimates, we can not rule out the possibility that the ultraviolet estimates are correct. But the possibility that the ultraviolet estimates have seriously underestimated the contribution of dust-shrouded star-formation can also not be excluded.

The ionized gas in nearby galaxies as traced by the [NII] 122 and 205 μm transitions

Astrophysical Journal American Astronomical Society 826 (2016) 1-17

R Herrera-Camus, A Bolatto, JD Smith, B Draine, E Pellegrini, M Wolfire, K Croxall, ID Looze, D Calzetti, R Kennicutt, A Crocker, L Armus, P van der Werf, K Sandstrom, M Galametz, B Brandl, B Groves, D Rigopoulou, F Walter, A Leroy, M Boquien, FS Tabatabaei, P Beirao

The [N ii] 122 and 205 μm transitions are powerful tracers of the ionized gas in the interstellar medium. By combining data from 21 galaxies selected from the Herschel KINGFISH and Beyond the Peak surveys, we have compiled 141 spatially resolved regions with a typical size of ∼1 kpc, with observations of both [N ii] far-infrared lines. We measure [N ii] 122/205 line ratios in the ∼0.6-6 range, which corresponds to electron gas densities of n e ∼ 1-300 cm-3, with a median value of n e = 30 cm-3. Variations in the electron density within individual galaxies can be as high as a factor of ∼50, frequently with strong radial gradients. We find that n e increases as a function of infrared color, dust-weighted mean starlight intensity, and star-formation rate (SFR) surface density (ΣSFR). As the intensity of the [N ii] transitions is related to the ionizing photon flux, we investigate their reliability as tracers of the SFR. We derive relations between the [N ii] emission and SFR in the low-density limit and in the case of a log-normal distribution of densities. The scatter in the correlation between [N ii] surface brightness and ΣSFR can be understood as a property of the n e distribution. For regions with n e close to or higher than the [N ii] line critical densities, the low-density limit [N ii]-based SFR calibration systematically underestimates the SFR because the [N ii] emission is collisionally quenched. Finally, we investigate the relation between [N ii] emission, SFR, and n e by comparing our observations to predictions from the MAPPINGS-III code.

The E-ELT first light spectrograph HARMONI: capabilities and modes


NAA Thatte, F Clarke, I Bryson, H Schnetler, M Tecza, T Fusco, RM Bacon, J Richard, E Mediavilla, B Neichel, S Arribas, B Garcia-Lorenzo, CJ Evans, A Remillieux, K El Madi, J Miguel Herreros, D Melotte, K O'Brien, IA Tosh, J Vernet, P Hammersley, DJ Ives, G Finger, R Houghton, D Rigopoulou, JD Lynn, JR Allen, SD Zieleniewski, S Kendrew, V Ferraro-Wood, A Pecontal-Rousset, J Kosmalski, F Laurent, M Loupias, L Piqueras, E Renault, J Blaizot, E Daguise, J-E Migniau, A Jarno, A Bornh, AM Gallie, DM Montgomery, D Henry, N Schwartz, W Taylor, G Zins, L Fernando Rodriguez-Ramos, M Cagigas, G Battaglia, R Rebolo Lopez, J Sanchez-Capuchino Revuelta, J Luis Rasilla, E Hernandez-Suarez, J Vicente Gigante-Ripoll, J Piqueras Lopez, M Villa Martin, C Correia, S Pascal, L Blanco, P Vola, B Epinat, C Peroux, A Vigan, K Dohlen, J-F Sauvage, M Lee, A Carlotti, C Verinaud, T Morris, R Myers, A Reeves, M Swinbank, A Calcines, M Larrieu

HERUS: A CO Atlas from SPIRE Spectroscopy of local ULIRGs

Astrophysical Journal Supplement American Astronomical Society 227 (2016) 9

C Pearson, D Rigopoulou, P Hurley, D Farrah, J Afonso, J Bernard-Salas, C Borys, DL Clements, D Cormier, A Efstathiou, E Gonzalez-Alfonso, V Lebouteiller, H Spoon

We present the Herschel SPIRE Fourier Transform Spectroscopy (FTS) atlas for a complete flux limited sample of local Ultra-Luminous Infra-Red Galaxies as part of the HERschel ULIRG Survey (HERUS). The data reduction is described in detail and was optimized for faint FTS sources with particular care being taken with the subtraction of the background which dominates the continuum shape of the spectra. Special treatment in the data reduction has been given to any observation suffering from artefacts in the data caused by anomalous instrumental effects to improve the final spectra. Complete spectra are shown covering 200−671µm with photometry in the SPIRE bands at 250µm, 350µm and 500µm. The spectra include near complete CO ladders for over half of our sample, as well as fine structure lines from [CI] 370 µm, [CI] 609 µm, and [NII] 205 µm. We also detect H2O lines in several objects. We construct CO Spectral Line Energy Distributions (SLEDs) for the sample, and compare their slopes with the farinfrared colours and luminosities. We show that the CO SLEDs of ULIRGs can be broadly grouped into three classes based on their excitation. We find that the mid-J (5&lt;J&lt;8) lines are better correlated with the total far-infrared luminosity, suggesting that the warm gas component is closely linked to recent star-formation. The higher J transitions do not linearly correlate with the far-infrared luminosity, consistent with them originating in hotter, denser gas unconnected to the current star-formation. We conclude that in most cases more than one temperature components are required to model the CO SLEDs.

Star formation rates in luminous quasars at 2 < z < 3


K Harris, D Farrah, B Schulz, E Hatziminaoglou, M Viero, N Anderson, M Bethermin, S Chapman, DL Clements, A Cooray, A Efstathiou, A Feltre, P Hurley, E Ibar, M Lacy, S Oliver, MJ Page, I Perez-Fournon, SM Petty, LK Pitchford, D Rigopoulou, D Scott, M Symeonidis, J Vieira, L Wang

The HerMES submillimetre local and low-redshift luminosity functions


L Marchetti, M Vaccari, A Franceschini, V Arumugam, H Aussel, M Bethermin, J Bock, A Boselli, V Buat, D Burgarella, DL Clements, A Conley, L Conversi, A Cooray, CD Dowell, D Farrah, A Feltre, J Glenn, M Griffin, E Hatziminaoglou, S Heinis, E Ibar, RJ Ivison, HT Nguyen, B O'Halloran, SJ Oliver, MJ Page, A Papageorgiou, CP Pearson, I Perez-Fournon, M Pohlen, D Rigopoulou, IG Roseboom, M Rowan-Robinson, B Schulz, D Scott, N Seymour, DL Shupe, AJ Smith, M Symeonidis, I Valtchanov, M Viero, L Wang, J Wardlow, CK Xu, M Zemcov

The Far Infrared Spectroscopic Explorer (FIRSPEX): Probing the lifecycle of the ISM in the Universe


D Rigopoulou, M Caldwell, B Ellison, C Pearson, E Caux, A Cooray, JD Gallego, M Gerin, JR Goicoechea, P Goldsmith, C Kramer, DC Lis, S Molinari, V Ossenkopf-Okada, G Savini, BK Tan, A Tielens, S Viti, M Wiedner, G Yassin

The far-infrared/radio correlation and radio spectral index of galaxies in the SFR-M-* plane up to z similar to 2


B Magnelli, RJ Ivison, D Lutz, I Valtchanov, D Farrah, S Berta, F Bertoldi, J Bock, A Cooray, E Ibar, A Karim, E Le Floc'h, R Nordon, SJ Oliver, M Page, P Popesso, F Pozzi, D Rigopoulou, L Riguccini, G Rodighiero, D Rosario, I Roseboom, L Wang, S Wuyts



N Laporte, I Perez-Fournon, JA Calanog, A Cooray, JL Wardlow, J Bock, C Bridge, D Burgarella, RS Bussmann, A Cabrera-Lavers, CM Casey, DL Clements, A Conley, H Dannerbauer, D Farrah, H Fu, R Gavazzi, EA Gonzalez-Solares, RJ Ivison, B Lo Faro, B Ma, G Magdis, R Marques-Chaves, P Martinez-Navajas, SJ Oliver, WA Osage, D Riechers, D Rigopoulou, D Scott, A Streblyanska, JD Vieira

The SCUBA-2 Cosmology Legacy Survey: the submillimetre properties of Lyman-break galaxies at z=3-5


KEK Coppin, JE Geach, O Almaini, V Arumugam, JS Dunlop, WG Hartley, RJ Ivison, CJ Simpson, DJB Smith, AM Swinbank, AW Blain, N Bourne, M Bremer, C Conselice, CM Harrison, A Mortlock, SC Chapman, LJM Davies, D Farrah, A Gibb, T Jenness, A Karim, KK Knudsen, E Ibar, MJ Michalowski, JA Peacock, D Rigopoulou, I Robson, D Scott, J Stevens, PP van der Werf



RS Bussmann, D Riechers, A Fialkov, J Scudder, CC Hayward, WI Cowley, J Bock, J Calanog, SC Chapman, A Cooray, F De Bernardis, D Farrah, H Fu, R Gavazzi, R Hopwood, RJ Ivison, M Jarvis, C Lacey, A Loeb, SJ Oliver, I Perez-Fournon, D Rigopoulou, IG Roseboom, D Scott, AJ Smith, JD Vieira, L Wang, J Wardlow



RS Bussmann, D Riechers, A Fialkov, J Scudder, CC Hayward, WI Cowley, J Bock, J Calanog, SC Chapman, A Cooray, F De Bernardis, D Farrah, H Fu, R Gavazzi, R Hopwood, RJ Ivison, M Jarvis, C Lacey, A Loeb, SJ Oliver, I Perez-Fournon, D Rigopoulou, IG Roseboom, D Scott, AJ Smith, JD Vieira, L Wang, J Wardlow

A far-infrared spectroscopic survey of intermediate redshift (ultra) luminous infrared galaxies

Astrophysical Journal IOP Publishing 796 (2014) 63-63

GE Magdis, D Rigopoulou, R Hopwood, J-S Huang, D Farrah, C Pearson, A Alonso-Herrero, JJ Bock, D Clements, A Cooray, MJ Griffin, S Oliver, I Perez Fournon, D Riechers, BM Swinyard, D Scott, N Thatte, I Valtchanov, M Vaccari

<p style="text-align:justify;"> We present Herschel far-IR photometry and spectroscopy as well as ground-based CO observations of an intermediate redshift (0.21 ≤ z ≤ 0.88) sample of Herschel-selected (ultra)-luminous infrared galaxies (L IR &gt; 10<sup>11.5</sup> L ☉). With these measurements, we trace the dust continuum, far-IR atomic line emission, in particular [C II] 157.7 μm, as well as the molecular gas of z ~ 0.3 luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) and perform a detailed investigation of the interstellar medium of the population. We find that the majority of Herschel-selected intermediate redshift (U)LIRGs have L C II /L FIR ratios that are a factor of about 10 higher than that of local ULIRGs and comparable to that of local normal and high-z star-forming galaxies. Using our sample to bridge local and high-z [C II] observations, we find that the majority of galaxies at all redshifts and all luminosities follow an L C II –L FIR relation with a slope of unity, from which local ULIRGs and high- z active-galactic-nucleus-dominated sources are clear outliers. We also confirm that the strong anti-correlation between the L C II /L FIR ratio and the far-IR color L 60/L 100 observed in the local universe holds over a broad range of redshifts and luminosities, in the sense that warmer sources exhibit lower L C II /L FIR at any epoch. Intermediate redshift ULIRGs are also characterized by large molecular gas reservoirs and by lower star formation efficiencies compared to that of local ULIRGs. The high L C II /L FIR ratios, the moderate star formation efficiencies (L IR/$L^{\prime }_{\rm CO}$ or L IR/$M_{\rm H_{\rm 2}}$), and the relatively low dust temperatures of our sample (which are also common characteristics of high-z star-forming galaxies with ULIRG-like luminosities) indicate that the evolution of the physical properties of (U)LIRGs between the present day and z &gt; 1 is already significant by z ~ 0.3. </p>



A Cooray, J Calanog, JL Wardlow, J Bock, C Bridge, D Burgarella, RS Bussmann, CM Casey, D Clements, A Conley, D Farrah, H Fu, R Gavazzi, RJ Ivison, N La Porte, B Lo Faro, B Ma, G Magdis, SJ Oliver, WA Osage, I Perez-Fournon, D Riechers, D Rigopoulou, D Scott, M Viero, D Watson