Publications by Dimitra Rigopoulou

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.

Mid-infrared identifications of scuba galaxies in the CUDSS 14 hour field with the spitzer space telescope

Astrophysical Journal 644 (2006) 778-791

MLN Ashby, S Dye, JS Huang, S Eales, SP Willner, TMA Webb, P Barmby, D Rigopoulou, E Egami, H Mccracken, S Lilly, S Miyazaki, M Brodwin, M Blaylock, J Cadien, GG Fazio

We identify 17 possible 8.0 μm selected counterparts to the submillimeter galaxies in the CUDSS 14 hour field, derived from deep imaging carried out with the IRAC and MIPS instruments aboard the Spitzer Space Telescope. Ten of the 17 counterparts are not the same as those previously identified at shorter wavelengths. We argue that 8.0 μm selection offers a better means for identifying counterparts to submillimeter galaxies than near-infrared or optical selection. Based on the panchromatic spectral energy distributions (SEDs), most counterparts appear to be powered by ongoing star formation. Power-law fits to the SEDs suggest that five objects in the 8.0 μm selected counterpart sample harbor dominant active galactic nuclei (AGNs; a sixth object is identified as a possible AGN). The 3.6-8.0 μm colors of the infrared-selected counterparts are significantly redder than the general IRAC galaxy population in the CUDSS 14 hour field. © 2006. The American Astronomical Society. All rights reserved.

Infrared power-law galaxies in the chandra deep field-south: Active galactic nuclei and ultraluminous infrared galaxies

Astrophysical Journal 640 (2006) 167-184

A Alonso-Herrero, PG Pérez-González, DM Alexander, GH Rieke, D Rigopoulou, E Le Floc'h, P Barmby, C Papovich, JR Rigby, FE Bauer, WN Brandt, E Egami, SP Willner, H Dole, JS Huang

We investigate the nature of a sample of 92 Spitzer MIPS 24 μm-selected galaxies in the CDF-S, showing power-law-like emission in the Spitzer IRAC 3.6-8 μm bands. The main goal is to determine whether the galaxies not detected in X-rays (47% of the sample) are part of the hypothetical population of obscured AGNs not detected even in deep X-ray surveys. The majority of the IR power-law galaxies are ULIRGs at z > 1, and those with LIRG-like IR luminosities are usually detected in X-rays. The optical-to-IR SEDs of the X-ray-detected galaxies are almost equally divided between a BLAGN SED class (similar to an optically selected QSO) and an NLAGN SED (similar to the BLAGN SED but with an obscured UV/optical continuum). A small fraction of SEDs resemble warm ULIRGs (e.g., Mrk 231). Most galaxies not detected in X-rays have SEDs in the NLAGN+ULIRG class as they tend to be optically fainter and possibly more obscured. Moreover, the IR power-law galaxies have SEDs significantly different from those of high-z (zsp > 1) IR (24 μm) selected and optically bright (WDS IAB ≤ 24) star-forming galaxies whose SEDs show a very prominent stellar bump at 1.6 μm. The galaxies detected in X-rays have 2-8 keV rest-frame luminosities typical of AGNs. The galaxies not detected in X-rays have global X-ray-to-mid-IR SED properties that make them good candidates to contain IR-bright X-ray-absorbed AGNs. If all these sources are actually obscured AGNs, we would observe a ratio of obscured to unobscured 24 μm-detected AGNs of 2:1, whereas models predict a ratio of up to 3:1. Additional studies using Spitzer to detect X-ray-quiet AGNs are likely to find more such obscured sources. © 2006. The American Astronomical Society. All rights reserved.

Infrared power-law galaxies in the Chandra deep field-south: Active galactic nuclei and ultraluminous infrared galaxies

ASTROPHYSICAL JOURNAL 640 (2006) 167-184

A Alonso-Herrero, PG Perez-Gonzalez, DM Alexander, GH Rieke, D Rigopoulou, E Le Floc'h, P Barmby, C Papovich, JR Rigby, FE Bauer, WN Brandt, E Egami, SP Willner, H Dole, JS Huang

Mid-infrared identifications of scuba galaxies in the CUDSS 14 hour field with the Spitzer space telescope

ASTROPHYSICAL JOURNAL 644 (2006) 778-791

MLN Ashby, S Dye, J-S Huang, S Eales, SP Willner, TMA Webb, P Barmby, D Rigopoulou, E Egami, H McCracken, S Lilly, S Miyazaki, M Brodwin, M Blaylock, J Cadien, GG Fazio

Spitzer Observations of z ∼ 3 Lyman Break Galaxies: Stellar Masses and Mid-Infrared Properties

Astrophysical Journal 648 (2006) 81-94

D Rigopoulou, J.-S.Huang, C.Papovich, M.L.N.Ashby

Follow-up near-infrared spectroscopy of ultraluminous infrared galaxies observed by ISO

ASTRONOMY & ASTROPHYSICS 441 (2005) 999-1010

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

NIR spectroscopy of luminous infrared galaxies and the hydrogen recombination photon deficit

Astronomy and Astrophysics 434 (2005) 149-161

JR Valdés, S Berta, A Bressan, A Franceschini, D Rigopoulou, G Rodighiero

We report on near-infrared medium-resolution spectroscopy of a sample of luminous and ultraluminous infrared galaxies (LIRGs-ULIRGs), carried out with SOFI at the ESO 3.5 m New Technology Telescope. Because of wavelength dependence of the attenuation, the detection of the Paα or Brγ line in the Ks band should provide relevant constraints on SFR and the contribution of an AGN. We find, however, that the intensities of the Paα and Brγ lines, even corrected for slit losses, are on average only 10% and 40%, respectively, of that expected from a normal starburst of similar bolometric luminosity. The corresponding star formation rates, after correcting for the attenuation derived from the NIR-optical emission line ratios, are 14% and 60% of that expected if the far infrared luminosity were entirely powered by the starburst. This confirms the existence of a recombination photon deficit, particularly in the case of the Paα line, already found in the Brγ line in other infrared galaxies of similar luminosity. In discussing the possible causes of the discrepancy, we find unlikely that it is due to the presence of an AGN, though two objects show evidence of broadening of the Paα line and of the presence of coronal line emission. In fact, from our own observations and data collected from the literature we argue that the studied galaxies appear to be predominantly powered by a nuclear starburst. Two scenarios compatible with the present data are that either there exists a highly attenuated nuclear star forming region, and/or that a significant fraction (≃80%) of the ionizing photons are absorbed by dust within the HII regions. We suggest that observations in the Brα spectral region could constitute a powerful tool to disentangle these two possibilities. © ESO 2005.

Infrared luminous Lyman break galaxies: A population that bridges LBGs and scuba galaxies

Astrophysical Journal 634 (2005) 137-141

JS Huang, D Rigopoulou, SP Willner, C Papovich, C Shu, MLN Ashby, P Barmby, K Bundy, C Conselice, E Egami, PG Pérez-González, JL Rosenberg, HA Smith, G Wilson, GG Fazio

A deep mid- and far-infrared survey in the extended Groth strip (EGS) area gives 3.6 to 8 μm flux densities or upper limits for 253 Lyman break galaxies (LBGs). The LBGs are a diverse population but with properties correlated with luminosity. The LBGs show a factor of 30 range in indicated stellar mass and a factor of 10 range in apparent dust content relative to stellar mass. About 5% of LBGs are luminous at all wavelengths, with powerful emission at rest 6 μm. In the rest 0.9 to 2 μm spectral range these galaxies have stellar spectral slopes with no sign of an AGN power-law component, suggesting that their emission is mainly powered by intensive star formation. Galaxies in this luminous population share the infrared properties of cold Submillimeter Common-User Bolometric Array (SCUBA) sources: both are massive and dusty starburst galaxies at 2 < z < 3; their stellar mass is larger than 10 11 M⊙. We suggest that these galaxies are the progenitors of present-day giant elliptical galaxies, with a substantial fraction of their stars already formed at z ≈ 3. © 2005. The American Astronomical Society. All rights reserved.

Infrared Luminous Lyman Break Galaxies: A Population that Bridges LBGs and SCUBA Galaxies

Astrophysical Journal 634 (2005) 137-141

D Rigopoulou, J.-S.Huang, S.P.Willner, C.Papovich

FORS spectroscopy of galaxies in the Hubble Deep Field-South

Astronomy and Astrophysics 440 (2005) 61-66

D Rigopoulou, WD Vacca, S Berta, A Franceschini, H Aussel

We present low resolution multi-object spectroscopy of an I-band magnitude limited (IAB ≃ 23-23.5) sample of galaxies located in an area centered on the Hubble Deep Field-South (HDFS). The observations were obtained using the Focal Reducer/low dispersion Spectrograph (FORS) on the ESO Very Large Telescope. Thirty-two primary spectroscopic targets in the HST-WFPC2 HDFS were supplemented with galaxies detected in the Infrared Space Observatory's survey of the HDFS and the ESO Imaging Deep Survey to comprise a sample of 100 galaxies for spectroscopic observations. Based on detections of several emission lines, such as [OII]λ3727, Hβ and [OIII]λ5007, or of other spectroscopic features, we measured accurate redshifts for 50 objects in the central HDFS and flanking fields. The redshift range of the current sample of galaxies is 0.6-1.2, with a median redshift of 1.13 (at I ≃ 23.5 not corrected for completeness). The sample is dominated by starburst galaxies with only a small fraction of ellipticals (∼ 10%). For the emission line objects, the extinction corrected [OII]λ3727 line strengths yield estimates of star formation rates in the range 0.5-30 M⊙yr-1. We used the present data to derive the [OII]λ3727 luminosity function up to redshift of 1.2. When combined with [OII]λ3727 luminosity densities for the local and high redshift Universe, our results confirm the steep rise in the star formation rate (SFR) to z ≃ 1.3. © ESO 2005.

NIR spectroscopy of luminous infrared galaxies and the hydrogen recombination photon deficit

ASTRONOMY & ASTROPHYSICS 434 (2005) 149-161

JR Valdes, S Berta, A Bressan, A Franceschini, D Rigopoulou, G Rodighiero

Submillimetre detection of a high-redshift type 2 QSO


V Mainieri, D Rigopoulou, I Lehmann, S Scott, I Matute, O Almaini, P Tozzi, G Hasinger, JS Dunlop

Submillimeter detections of Spitzer Space Telescope galaxy populations


S Serjeant, AMJ Mortier, RJ Ivison, E Egami, GH Rieke, SP Willner, D Rigopoulou, A Alonso-Herrero, P Barmby, L Bei, H Dole, CW Engelbracht, GG Fazio, E Le Floc'h, KD Gordon, TR Greve, DC Hines, JS Huang, KA Misselt, S Miyazaki, JE Morrison, C Papovich, PG Perez-Gonzalez, MJ Rieke, J Rigby, G Wilson

Extremely red objects in the Lockman hole

Astrophysical Journal, Supplement Series 154 (2004) 107-111

G Wilson, JS Huang, PG Pérez-González, E Egami, RJ Ivison, JR Rigby, A Alonso-Herrero, P Barmby, H Dole, GG Fazio, E Le Floc'h, C Papovich, D Rigopoulou, L Bai, CW Engelbracht, D Frayer, KD Gordon, DC Hines, KA Misselt, S Miyazaki, JE Morrison, GH Rieke, MJ Rieke, J Surace

We investigate extremely red objects (EROs) using near- and mid-infrared observations in five passbands (3.6 to 24 μm) obtained from the Spitzer Space Telescope, and deep ground-based R and K imaging. The great sensitivity of the Infrared Array Camera (IRAC) camera allows us to detect 64 EROs (a surface density of 2.90 ± 0.36 arcmin-2; [3.6]AB < 23.7) in only 12 minutes of IRAC exposure time, by means of an R - [3.6] color cut (analogous to the traditional red R - K cut). A pure infrared K - [3.6] red cut detects a somewhat different population and may be more effective at selecting z > 1.3 EROs. We find ∼17% of all galaxies detected by IRAC at 3.6 or 4.5 μm to be EROs. These percentages rise to about 40% at 5.8 μm, and about 60% at 8.0 μm. We utilize the spectral bump at 1.6 μm to divide the EROs into broad redshift slices using only near-infrared colors (2.2/3.6/4.5 μm). We conclude that two-thirds of all EROs lie at redshift z > 1.3. Detections at 24 μm imply that at least 11% of 0.6 < z < 1.3 EROs and at least 22% of z > 1.3 EROs are dusty star-forming galaxies.

Identification of luminous infrared galaxies at 1 less than or similar to z less than or similar to 2.5


E Le Floc'h, PG Perez-Gonzalez, GH Rieke, C Papovich, JS Huang, P Barmby, H Dole, E Egami, A Alonso-Herrero, G Wilson, S Miyazaki, JR Rigby, L Bei, M Blaylock, CW Engelbracht, GG Fazio, DT Frayer, KD Gordon, DC Hines, KA Misselt, JE Morrison, J Muzerolle, MJ Rieke, D Rigopoulou, KYL Su, SP Willner, ET Young

The nature of luminous X-ray sources with mid-infrared counterparts

Astrophysical Journal, Supplement Series 154 (2004) 155-159

A Alonso-Herrero, PG Pérez-González, J Rigby, GH Rieke, E Le Floc'h, P Barmby, MJ Page, C Papovich, H Dole, E Egami, JS Huang, D Rigopoulou, D Cristóbal-Hornillos, C Eliche-Moral, M Balcells, M Prieto, P Erwin, CW Engelbracht, KD Gordon, M Werner, SP Willner, GG Fazio, D Frayer, D Hines, D Kelly, W Latter, K Misselt, S Miyazaki, J Morrison, MJ Rieke, G Wilson

We investigate the luminous X-ray sources in the Lockman Hole (LH) and the extended Groth strip (EGS) detected at 24 μm using the Multiband Imaging Photometer (MIPS) and also with the Infrared Array Camera (IRAC) on board the Spitzer Space Telescope. We assemble optical/infrared spectral energy distributions (SEDs) for 45 X-ray/24 μm sources in the EGS and LH. Only about one-quarter of the hard X-ray/24 μm sources show pure type 1 active galactic nucleus (AGN) SEDs. More than half of the X-ray/24 μm sources have stellar emission-dominated or obscured SEDs, similar to those of local type 2 AGN and spiral/starburst galaxies. One-third of the sources detected in hard X-rays do not have a 24 μm counterpart. Two such sources in the LH have SEDs resembling those of S0/elliptical galaxies. The broad variety of SEDs in the optical-to-Spitzer bands of X-ray-selected AGNs means that AGNs selected according to the behavior in the optical/infrared will have to be supplemented by other kinds of data (e.g., X-ray) to produce unbiased samples of AGNs.

Spitzer observations of the SCUBA/VLA sources in the Lockman Hole: Star formation history of infrared-luminous galaxies


E Egami, H Dole, JS Huang, P Perez-Gonzalez, E Le Floc'h, C Papovich, P Barmby, RJ Ivison, S Serjeant, A Mortier, DT Frayer, D Rigopoulou, G Lagache, GH Rieke, SP Willner, A Alonso-Herrero, L Bai, CW Engelbracht, GG Fazio, KD Gordon, DC Hines, KA Misselt, S Miyazaki, JE Morrison, MJ Rieke, JR Rigby, G Wilson

The European Large Area ISO Survey - VIII. 90-μm final analysis and source counts

Monthly Notices of the Royal Astronomical Society 354 (2004) 924-934

P Héraudeau, S Oliver, C Del Burgo, C Kiss, M Stickel, T Mueller, M Rowan-Robinson, A Efstathiou, C Surace, LV Tóth, S Serjeant, DM Alexander, A Franceschini, D Lemke, T Morel, I Pérez-Fournon, JL Puget, D Rigopoulou, B Rocca-Volmerange, A Verma

We present a re-analysis of the European Large Area Infrared Space Observatory (ISO) Survey (ELAIS) 90-μm observations carried out with ISOPHOT, an instrument on board the ISO of the European Space Agency. With more than 12 deg2, the ELAIS survey is the largest area covered by ISO in a single programme and is about one order of magnitude deeper than the IRAS 100-μm survey. The data analysis is presented and was mainly performed with the PHOT interactive analysis software but using the pairwise method of Stickel et al. for signal processing from edited raw data to signal per chopper plateau. The ELAIS 90-μm catalogue contains 237 reliable sources with fluxes larger than 70 mJy and is available in the electronic version of this article. Number counts are presented and show an excess above the no-evolution model prediction. This confirms the strong evolution detected at shorter (15 μm) and longer (170 μm) wavelengths in other ISO surveys. The ELAIS counts are in agreement with previous works at 90 μm and in particular with the deeper counts extracted from the Lockman hole observations. Comparison with recent evolutionary models show that the models of Franceschini et al. and Guiderdoni et al. (which includes a heavily extinguished population of galaxies) give the best fit to the data. Deeper observations are nevertheless required to discriminate better between the model predictions in the far-infrared, and are scheduled with the Spitzer Space Telescope, which has already started operating, and will also be performed by ASTRO-F.

Infrared array camera (IRAC) imaging of the Lockman Hole

Astrophysical Journal, Supplement Series 154 (2004) 44-47

JS Huang, P Barmby, GG Fazio, SP Willner, G Wilson, D Rigopoulou, A Alonso-Herrero, H Dole, E Egami, E Le Floc'h, C Papovich, PG Pérez-González, J Rigby, CW Engelbracht, K Gordon, D Hines, M Rieke, GH Rieke, K Meisenheimer, S Miyazaki

IRAC imaging of a 4′.7 x 4′.7 area in the Lockman Hole detected over 400 galaxies in the IRAC 3.6 and 4.5 μm bands, 120 in the 5.8 μm band, and 80 in the 8.0 μm band in 30 minutes of observing time. Color-color diagrams suggest that about half of these galaxies are at redshifts 0.6 < z < 1.3 with about a quarter at higher redshifts (z > 1.3). We also detect IRAC counterparts for six of the seven SCUBA sources and all nine XMM-Newton sources in this area. The detection of the counterparts of the SCUBA sources and galaxies at z > 1.3 demonstrates the ability of IRAC to probe the universe at very high redshifts.