Publications by Dimitra Rigopoulou


ASTROPHYSICAL JOURNAL 700 (2009) 183-198

J-S Huang, SM Faber, E Daddi, ES Laird, K Lai, A Omont, Y Wu, JD Younger, K Bundy, A Cattaneo, SC Chapman, CJ Conselice, M Dickinson, E Egami, GG Fazio, M Im, D Koo, E Le Floc'h, C Papovich, D Rigopoulou, I Smail, M Song, PP Van de Werf, TMA Webb, CNA Willmer, SP Willner, L Yan

Mid-infrared spectroscopy of infrared-luminous galaxies at z ∼ 0.5-3

Monthly Notices of the Royal Astronomical Society 395 (2009) 1695-1722

A Hernán-Caballero, I Pérez-Fournon, E Hatziminaoglou, A Afonso-Luis, M Rowan-Robinson, D Rigopoulou, D Farrah, CJ Lonsdale, T Babbedge, D Clements, S Serjeant, F Pozzi, M Vaccari, FM Montenegro-Montes, I Valtchanov, E González-Solares, S Oliver, D Shupe, C Gruppioni, B Vila-Vilaró, C Lari, FL Franca

We present results on low-resolution mid-infrared (MIR) spectra of 70 IR-luminous galaxies obtained with the infrared spectrograph (IRS) onboard Spitzer. We selected sources from the European Large Area Infrared Survey with S 15 > 0.8 mJy and photometric or spectroscopic z > 1. About half of the samples are quasi-stellar objects (QSOs) in the optical, while the remaining sources are galaxies, comprising both obscured active galactic nuclei (AGN) and starbursts. Redshifts were obtained from optical spectroscopy, photometric redshifts and the IRS spectra. The later turn out to be reliable for obscured and/or star-forming sources, thus becoming an ideal complement to optical spectroscopy for redshift estimation. We estimate monochromatic luminosities at several rest-frame wavelengths, equivalent widths and luminosities for the polycyclic aromatic hydrocarbon (PAH) features, and strength of the silicate feature in individual spectra. We also estimate integrated 8-1000 μm IR luminosities via spectral energy distribution fitting to MIR and far-IR (FIR) photometry from the Spitzer Wide-Area Infrared Extragalactic survey and the MIR spectrum. Based on these measurements, we classify the spectra using well-known IR diagnostics, as well as a new one that we propose, into three types of source: those dominated by an unobscured AGN, mostly corresponding to optical quasars (QSOs), those dominated by an obscured AGN and starburst-dominated sources. Starbursts concentrate at z ∼ 0.6-1.0 favoured by the shift of the 7.7-μm PAH band into the selection 15-μm band, while AGN spread over the 0.5 < z < 3.1 range. Star formation rates (SFR) are estimated for individual sources from the luminosity of the PAH features. An estimate of the average PAH luminosity in QSOs and obscured AGN is obtained from the composite spectrum of all sources with reliable redshifts. The estimated mean SFR in the QSOs is 50-100 M ⊙ yr -1, but the implied FIR luminosity is 3-10 times lower than that obtained from stacking analysis of the FIR photometry, suggesting destruction of the PAH carriers by energetic photons from the AGN. The SFR estimated in obscured AGN is two to three times higher than in QSOs of similar MIR luminosity. This discrepancy might not be due to luminosity effects or selection bias alone, but could instead indicate a connection between obscuration and star formation. However, the observed correlation between silicate absorption and the slope of the NIR to MIR spectrum is compatible with the obscuration of the AGN emission in these sources being produced in a dust torus. © 2009 RAS.

A millimetre survey of starburst dominated ultraluminous infrared galaxies at z ∼ 2

Monthly Notices of the Royal Astronomical Society 394 (2009) 1685-1694

JD Younger, A Omont, N Fiolet, JS Huang, GG Fazio, K Lai, M Polletta, D Rigopoulou, R Zylka

We present millimetre observations of a sample of 12 high-redshift ultraluminous infrared galaxies (ULIRGs) in the extended growth strip (EGS). These objects were initially selected on the basis of their observed mid-IR colours (0.0 < [3.6] - [4.5] < 0.4 and -0.7 < [3.6] - [8.0] < 0.5) to lie at high redshift 1.5 ≲ z ≲ 3, and subsequent 20-38 μm mid-IR spectroscopy confirms that they lie in a narrow redshift window centred on z ≈ 2. We detect 9/12 of the objects in our sample at high significance (>3σ) with a mean 1200 μm flux of 〈F 1200 μm〉 = 1.6 ± 0.1 mJy. Our millimetre photometry, combined with existing far-IR photometry from the Far-IR Deep Extragalactic Legacy Survey (FIDELS) and accurate spectroscopic redshifts, places constraints both sides of the thermal dust peak. This allows us to estimate the dust properties, including the far-IR luminosity, dust temperature and dust mass. We find that our sample is similar to other high-z and intermediate-z ULIRGs, and local systems, but has a different dust selection function than submillimeter-selected galaxies. Finally, we use existing 20-cm radio continuum imaging to test the far-IR/radio correlation at high redshift. We find that our sample is consistent with the local relation, implying little evolution. Furthermore, this suggests that our sample selection method is efficient at identifying ultraluminous, starburst-dominated systems within a very narrow redshift range centred at z ∼ 2. © 2009 RAS.

The space infrared telescope for cosmology and astrophysics: SPICA A joint mission between JAXA and ESA


B Swinyard, T Nakagawa, P Merken, P Royer, T Souverijns, B Vandenbussche, C Waelkens, P Davis, J Di Francesco, M Halpern, M Houde, D Johnstone, G Joncas, D Naylor, R Plume, D Scott, A Abergel, S Bensammar, J Braine, V Buat, D Burgarella, P Cais, H Dole, L Duband, D Elbaz, M Gerin, M Giard, J Goicoechea, C Joblin, A Jones, JP Kneib, G Lagache, S Madden, R Pons, F Pajot, D Rambaud, L Ravera, I Ristorcelli, L Rodriguez, S Vives, A Zavagno, N Geis, O Krause, D Lutz, A Poglitsch, W Raab, J Stegmaier, E Sturm, R Tuffs, HM Lee, B-C Koo, M Im, S Pak, W Han, J-H Park, U-W Nam, H Jin, D-H Lee, I-S Yuk, S Lee, Y Aikawa, N Arimoto, Y Doi, K Enya, M Fukagawa, R Furusho, S Hasegawa, M Hayashi, M Honda, S Ida, M Imanishi, S-I Inutsuka, H Izumiura, H Kamaya, H Kaneda, T Kasuga, H Kataza, K Kawabata, M Kawada, H Kawakita, T Kii, J Koda, T Kodama, E Kokubo, K Komatsu, H Matsuhara, T Matsumoto, S Matsuura, T Miyata, H Murakam, H Nagata, T Nagata, T Nakajima, K Naoto, R Nishi, A Noda, A Okamoto, YK Okamoto, K Omukai, T Onaka, T Ootsubo, M Ouchi, H Saito, Y Sato, S Sako, T Sekiguchi, H Shibai, H Sugita, K Sugitani, H Susa, P Tae-soo, M Tamura, Y Ueda, M Ueno, T Wada, J Watanabe, T Yamada, I Yamamura, N Yoshida, K Yoshimi, Y Yui, M Benedettini, R Cerulli, A Di Giorgio, S Molinari, R Orfei, S Pezzuto, L Piazzo, P Saraceno, L Spinoglio, T de Graauw, P de Korte, F Helmich, H Hoevers, R Huisman, R Shipman, F van der Tak, P van der Werf, W Wild, J Acosta-Pulido, J Cernicharo, J Herreros, J Martin-Pintado, F Najarro, I Perez-Fourmon, J Ramon Pardo, F Gomez, N Castro Rodriguez, P Ade, M Barlow, D Clements, M Ferlet, H Fraser, D Griffin, M Griffin, P Hargrave, K Isaak, R Ivison, M Mansour, J Laniesse, P Mauskopf, D Morozov, S Oliver, A Orlando, M Page, C Popescu, S Serjeant, R Sudiwala, D Rigopoulou, I Walker, G White, S Viti, B Winter, J Bock, M Bradford, M Harwit, W Holmes, SPICA Consortium



D Rigopoulou, S Rawlings, D Obreschkow

IRAC photometric analysis and the mid-IR photometric properties of Lyman-break galaxies


GE Magdis, D Rigopoulou, J-S Huang, GG Fazio, SP Willner, MLN Ashby

The properties of 70 μm-selected high-redshift galaxies in the Extended Groth Strip

Monthly Notices of the Royal Astronomical Society 385 (2008) 1015-1028

M Symeonidis, SP Willner, D Rigopoulou, JS Huang, GG Fazio, MJ Jarvis

We examine the infrared properties of 43 high-redshift (0.1 < z < 1.2), infrared-luminous galaxies in the Extended Groth Strip (EGS), selected by a deep 70 μm survey with the Multiband Imaging Photometer on Spitzer (MIPS). In addition and with reference to starburst-type spectral energy distributions (SEDs), we derive a set of equations for estimating the total infrared luminosity (LIR) in the range 8-1000 μm using photometry from at least one MIPS band. 42 out of 43 of our sources' optical/infrared SEDs (λobserved < 160 μm) are starburst type, with only one object displaying a prominent power-law near-infrared continuum. For a quantitative analysis, models of radiation transfer in dusty media are fit on to the infrared photometry, revealing that the majority of galaxies are represented by high extinction, Av > 35, and for a large fraction (∼50 per cent) the SED turns over into the Rayleigh-Jeans regime at wavelengths longward of 90 μm. For comparison, we also fit semi-empirical templates based on local galaxy data; however, these underestimate the far-infrared SED shape by a factor of at least 2 and in extreme cases up to 10 for the majority (∼70 per cent) of the sources. Further investigation of SED characteristics reveals that the mid-infrared (70/24 μm) continuum slope is decoupled from various galaxy properties such as the total infrared luminosity and far-infrared peak, quantified by the L160/L70 ratio. In view of these results, we propose that these high-redshift galaxies have different properties to their local counterparts, in the sense that large amounts of dust cause heavy obscuration and are responsible for an additional cold emissive component, appearing as a far-infrared excess in their SEDs. © 2008 RAS.

The host galaxies and black holes of typical z similar to 0.5-1.4 AGNs

ASTROPHYSICAL JOURNAL 677 (2008) 127-136

A Alonso-Herrero, PG Perez-Gonzalez, GH Rieke, DM Alexander, JR Rigby, C Papovich, JL Donley, D Rigopoulou

A 15 mu m selected sample of high-z starbursts and AGNs

ASTR SOC P 381 (2008) 367-371

A Hernan-Caballero, I Perez-Fournon, M Rowan-Robinson, D Rigopoulou, A Afonso-Luis, E Hatziminaoglou, E Gonzalez-Solares, FM Montenegro-Montes, B Vila-Vilaro, D Farrah, C Lari, M Vaccari, T Babbedge, S Oliver, D ClementS, S Serjeant, F Pozzi, F La Franca, C Gruppioni, I Valtchanov, C Lonsdale, SWIRE Team

We report results from our Spitzer GO-1 program on IRS spectroscopy of a large sample of Luminous Infrared Galaxies and quasars selected from the European Large Area ISO Survey (ELAIS). The selected ELAIS sources have a wide multi-wavelength coverage, including ISOCAM, ISOPHOT, IRAC and MIPS (from SWIRE), and optical photometry. Here we present the sample selection and results from the IRS spectroscopy.

Follow-up NIR spectroscopy of ULIRGs observed by ISO

ASTR SOC P 381 (2008) 275-278

H Dannerbauer, D Rigopoulou, D Lutz, R Genzel, E Sturm, AFM Moorwood

We discuss low resolution near-infrared spectroscopy of an unbiased sample of 24 ultraluminous infrared galaxies (ULIRGs), selected from samples previously observed in the mid-infrared with ISO. Qualitatively, the NIR spectra of our 24 ULIRGs resemble those of starbursts. The spectroscopic classification in the NIR is in very good agreement with the MIR. For a subset of our sample for which extinction corrections can be derived from Pace and Br gamma, we find rather high Pa alpha luminosities, in accordance with the powering source of these galaxies being star formation. Furthermore, we identified two unusual objects, the first exhibiting extreme [FeII] emission and the second strong emission in H-2 rotation-vibration emission.

IRAC photometric analysis and the mid-IR photometric properties of Lyman-break galaxies

Monthly Notices of the Royal Astronomical Society 386 (2008) 11-21

GE Magdis, D Rigopoulou, JS Huang, GG Fazio, SP Willner, MLN Ashby

We present photometric analysis of deep mid-infrared (mid-IR) observations obtained by Spitzer/IRAC covering the fields Q1422+2309, Q2233+1341, DSF2237a,b, HDFN, SSA22a,b and B20902+34, giving the number counts and the depths for each field. In a sample of 751 Lyman-break galaxies (LBGs) lying in those fields, 443, 448, 137 and 152 are identified at 3.6-, 4.5-, 5.8-, 8.0-μm IRAC bands, respectively, expanding their spectral energy distribution to rest-near-IR and revealing that LBGs display a variety of colours. Their rest-near-IR properties are rather inhomogeneous, ranging from those that are bright in IRAC bands and exhibit [R] - [3.6] > 1.5 colours to those that are faint or not detected at all in IRAC bands with [R] - [3.6] < 1.5 colours and these two groups of LBGs are investigated. We compare the mid-IR colours of the LBGs with the colours of star-forming galaxies and we find that LBGs have colours consistent with star-forming galaxies at z ∼ 3. The properties of the LBGs detected in the 8-μm IRAC band (rest-frame K band) are examined separately, showing that they exhibit redder [R] - [3.6] colours than the rest of the population and that although in general, a multiwavelength study is needed to reach more secure results, IRAC 8-μm band can be used as a diagnostic tool, to separate high z, luminous AGN-dominated objects from normal star-forming galaxies at z ∼ 3. © 2008 RAS.

AEGIS: A panchromatic study of IRAC-selected extremely red objects with confirmed spectroscopic redshifts

Astrophysical Journal 660 (2007)

G Wilson, JS Huang, GG Fazio, R Yan, AM Koekemoer, S Salim, SM Faber, J Lotz, CNA Willmer, M Davis, AL Coil, JA Newman, CJ Conselice, C Papovich, MLN Ashby, P Barmby, SP Willner, R Ivison, S Miyazaki, D Rigopoulou

We study 87 extremely red objects (EROs), selected both to have color redder than R - [3.6] = 4.0 and to have confirmed spectroscopic redshifts. Together, these two constraints result in this sample populating a fairly narrow redshift range at 0.76 < z < 1.42. The key new ingredient included here is deep Spitzer Space Telescope Infrared Array Camera (IRAC) data. Based on [3.6] - [8.0] color, we demonstrate that it is possible to classify EROs as early-type galaxies, dusty starburst galaxies, or active galactic nuclei (AGNs; power-law types). We present ultraviolet-to-mid-infrared spectral energy distributions (SEDs) and Advanced Camera for Surveys (ACS) images, both of which support our simple IRAC color classification. © 2007. The American Astronomical Society. All rights reserved.

The local galaxy 8 μm luminosity function

Astrophysical Journal 664 (2007) 840-849

JS Huang, MLN Ashby, P Barmby, M Brodwin, MJI Brown, N Caldwell, RJ Cool, P Eisenhardt, D Eisenstein, GG Fazio, E Le Floc'h, P Green, CS Kochanek, N Lu, MA Pahre, D Rigopoulou, JL Rosenberg, HA Smith, Z Wang, CNA Willmer, SP Willner

A Spitzer Space Telescope survey in the NOAO Deep Wide Field in Bootes provides a complete, 8 μm-selected sample of galaxies to a limiting (Vega) magnitude of 13.5. In the 6.88 deg2 field sampled, 79% of the 4867 galaxies have spectroscopic redshifts, allowing an accurate determination of the local (z < 0.3) galaxy luminosity function. Stellar and dust emission can be separated on the basis of observed galaxy colors. Dust emission (mostly PAH) accounts for 80% of the 8 μm luminosity, stellar photospheres account for 19%, and AGN emission accounts for roughly 1%. A subsample of the 8 μm-selected galaxies have blue, early-type colors, but even most of these have significant PAH emission. The luminosity functions for the total 8 μm luminosity and for the dust emission alone are both well fit by Schechter functions. For the 8 μm luminosity function, the characteristic luminosity is νLν*;(8.0 μm) = 1.8 × 1010 L ⊙, while for the dust emission alone it is 1.6 × 10 10 L⊙. The average 8 μm luminosity density at z < 0.3 is 3.1 × 107 L⊙ Mpc-3, and the average luminosity density from dust alone is 2.5 × 107 L⊙ Mpc-3. This luminosity arises predominantly from galaxies with 8 μm luminosities (νLν) between 2 × 109 and 2 × 1010 L⊙, i.e., normal galaxies, not luminous or ultraluminous infrared galaxies (LIRGs/ULIRGs). © 2007. The American Astronomical Society. All rights reserved.

The local galaxy 8 mu m luminosity function

ASTROPHYSICAL JOURNAL 664 (2007) 840-849

J-S Huang, MLN Ashby, P Barmby, M Brodwin, MJI Brown, N Caldwell, RJ Cool, P Eisenhardt, D Eisenstein, GG Fazio, E Le Floc'h, P Green, CS Kochanek, N Lu, MA Pahre, D Rigopoulou, JL Rosenberg, HA Smith, Z Wang, CNA Willmer, SP Willner

AEGIS: A panchromatic study of IRAC-selected extremely red objects with confirmed spectroscopic redshifts


G Wilson, J-S Huang, GG Fazio, R Yan, AM Koekemoer, S Salim, SM Faber, J Lotz, CNA Willmer, M Davis, AL Coil, JA Newman, CJ Conselice, C Papovich, MLN Ashby, P Barmby, SP Willner, R Ivison, S Miyazaki, D Rigopoulou

Spitzer view of Lyman break galaxies

Proceedings of the International Astronomical Union 3 (2007) 451-454

GE Magdis, D Rigopoulou

Using a combination of deep MID-IR observations obtained by IRAC, MIPS and IRS on board Spitzer we investigate the MID-IR properties of Lyman Break Galaxies (LBGs) at z∼3, establish a better understanding of their nature and attempt a complete characterisation of the population. With deep mid-infrared and optical observations of ∼1000 LBGs covered by IRAC/MIPS and from the ground respectively, we extend the spectral energy distributions (SEDs) of the LBGs to mid-infrared. Spitzer data reveal for the first time that the mid-infrared properties of the population are inhomogeneous ranging from those with marginal IRAC detections to those with bright rest-frame near-infrared colors and those detected at 24m MIPS band revealing the newly discovered population of the Infrared Luminous Lyman Break Galaxies (ILLBGs). To investigate this diversity, we examine the photometric properties of the population and we use stellar population synthesis models to probe the stellar content of these galaxies. We find that a fraction of LBGs have very red colors and large estimated stellar masses M>51010M. We discuss the link between these LBGs and submm-luminous galaxies and we report the detection of rest frame 6.2 and 7.7 m emission features arising from Polycyclic Aromatic Hydrocarbons (PAH) in the Spitzer/IRS spectrum of an infrared-luminous Lyman break galaxy at z=3.01. © 2008 International Astronomical Union.

AEGIS: Infrared Spectral Energy Distributions of MIPS 70 μm–selected Sources

Astrophysical Journal Letters 660 (2007) L73-L76

D Rigopoulou, M.Symeonidis, J.-S.Huang, M.Davies

The all-wavelength extended groth strip international survey (AEGIS) data sets

Astrophysical Journal 660 (2007)

M Davis, P Guhathakurta, NP Konidaris, JA Newman, MLN Ashby, AD Biggs, P Barmby, K Bundy, SC Chapman, AL Coil, CJ Conselice, MC Cooper, DJ Croton, PRM Eisenhardt, RS Ellis, SM Faber, T Fang, GG Fazio, A Georgakakis, BF Gerke, WM Goss, S Gwyn, J Harker, AM Hopkins, JS Huang, RJ Ivison, SA Kassin, EN Kirby, AM Koekemoer, DC Koo, ES Laird, E Le Floc'h, L Lin, JM Lotz, PJ Marshall, DC Martin, AJ Metevier, LA Moustakas, K Nandra, KG Noeske, C Papovich, AC Phillips, RM Rich, GH Rieke, D Rigopoulou, S Salim, D Schiminovich, L Simard, I Smail, TA Small, BJ Weiner, CNA Willmer, SP Willner, G Wilson, EL Wright, R Yan

In this the first of a series of Letters, we present a panchromatic data set in the Extended Groth Strip region of the sky. Our survey, the All-Wavelength Extended Groth Strip International Survey (AEGIS), aims to study the physical properties and evolutionary processes of galaxies at z ∼ 1. It includes the following deep, wide-field imaging data sets: Chandra/ACIS X-ray, GALEX ultraviolet, CFHT/MegaCam Legacy Survey optical, CFHT/CFH12K optical, Hubble Space Telescope/ACS optical and NICMOS near-infrared, Palomar/WIRC near-infrared, Spitzer/IRAC mid-infrared, Spitzer/MIPS far-infrared, and VLA radio continuum. In addition, this region of the sky has been targeted for extensive spectroscopy using the Deep Imaging Multi-Object Spectrograph (DEIMOS) on the Keck II 10 m telescope. Our survey is compared to other large multiwavelength surveys in terms of depth and sky coverage. © 2007. The American Astronomical Sociey, All rights reserved.

AEGIS: Infrared spectroscopy of an infrared-luminous Lyman break galaxy at z=3.01


J-S Huang, D Rigopoulou, C Papovich, MLN Ashby, SP Willner, R Ivison, ES Laird, T Webb, G Wilson, P Barmby, S Chapman, C Conselice, B McLeod, CG Shu, HA Smith, E Le Floc'h, E Egami, CAN Willmer, GG Fazio

AEGIS: Infrared spectroscopy of an infrared-luminous lyman break galaxy at z = 3.01

Astrophysical Journal 660 (2007)

JS Huang, D Rigopoulou, C Papovich, MLN Ashby, SP Willner, R Ivison, ES Laird, T Webb, G Wilson, P Barmby, S Chapman, C Conselice, B McLeod, CG Shu, HA Smith, E Le Floc'h, E Egami, CAN Willmer, GG Fazio

We report the detection of rest-frame 6.2 and 7.7 μm emission features arising from polycyclic aromatic hydrocarbons (PAHs) in the Spitzer IRS spectrum of an infrared-luminous Lyman break galaxy at z = 3.01. This is currently the highest redshift galaxy where these PAH emission features have been detected. The total IR luminosity inferred from the MIPS 24 μm and radio flux density is 2 × 1013 L⊙, which qualifies this object as a so-called hyperluminous infrared galaxy (HyLIRG). However, unlike local HyLIRGs, which are generally associated with QSO/AGNs and have weak or absent PAH emission features, this HyLIRG has very strong 6.2 and 7.7 μm PAH emission. We argue that intense star formation dominates the IR emission of this source, although we cannot rule out the presence of a deeply obscured AGN. This LBG appears to be a distorted system in the HST ACS F606W and F814W images, possibly indicating that a significant merger or interaction is driving the large IR luminosity. © 2007. The American Astronomical Society. All rights reserved.