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

Afonso-Luis, A.

Babbedge, T.

Clements, D.

Farrah, D.

González-Solares, E.

Gruppioni, C.

Hatziminaoglou, E.

Hernán-Caballero, A.

La Franca, F.

Lari, C.

Lonsdale, C.

Montenegro-Montes, F. M.

Oliver, S.

Pozzi, F.

Pérez-Fournon, I.

Rigopoulou, D.

Rowan-Robinson, M.

Serjeant, S.

the SWIRE team,

Vaccari, M.

Valtchanov, I.

Vila-Vilaro, B.

English

the SWIRE team

Open Research Online (The Open University)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsA 15 m selected sample of hHigh-z starbursts andAGNsConference or Workshop ItemHow to cite:Herna´n-Caballero, A.; Pe´rez-Fournon, I.; Rowan-Robinson, M.; Rigopoulou, D.; Afonso-Luis, A.; Hatziminaoglou, E.;Gonza´lez-Solares, E.; Montenegro-Montes, F. M.; Vila-Vilaro, B.; Farrah, D.; Lari, C.; Vaccari, M.; Babbedge, T.;Oliver, S.; Clements, D.; Serjeant, S.; Pozzi, F.; La Franca, F.; Gruppioni, C.; Valtchanov, I.; Lonsdale, C. and theSWIRE team (2008). A 15 m selected sample of hHigh-z starbursts and AGNs. In: The 2nd Spitzer Conference:Infrared Diagnostics of Galaxy Evolution, 14-16 Nov 2005, Pasadena, CA. USA.For guidance on citations see FAQs.c© 2008 Ranga-Ram Chary, Harry I. Teplitz, Kartik Sheth, eds.Version: Version of RecordLink(s) to article on publisher’s website:http://www.aspbooks.org/a/volumes/article details/?paper id=28120Copyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukThe 2nd Spitzer Conference: Infrared Diagnostics of Galaxy EvolutionASP Conference Series, Vol. 381, c©2008Ranga-Ram Chary, Harry I. Teplitz, Kartik Sheth, eds.A 15 µm Selected Sample of High-z Starbursts and AGNsA. Herna´n-Caballero,1 I. Pe´rez-Fournon,1 M. Rowan-Robinson,2 D.Rigopoulou,3 A. Afonso-Luis,1 E. Hatziminaoglou,1 E.Gonza´lez-Solares,4 F. M. Montenegro-Montes,5 B. Vila-Vilaro,6 D.Farrah,7 C. Lari,5 M. Vaccari,2 T. Babbedge,2 S. Oliver,8 D. Clements,2S. Serjeant,9 F. Pozzi,10 F. La Franca,11 C. Gruppioni,10 I. Valtchanov,2C. Lonsdale7 and the SWIRE team1Instituto de Astrofisica de Canarias, 38200 La Laguna, Tenerife, Spain2Astrophysics Group, Blackett Laboratory, Imperial College London,Prince Consort Road, London SW7 2BZ, UK3Department of Astrophysics, Oxford University, Keble Road, OxfordOX1 3RH, UK4Institute of Astronomy, University of Cambridge, Madingley Road,Cambridge CB3 0HA5Istituto di Radioastronomia, INAF, via Gobetti 101, I-40129 Bologna,Italy6National Observatory of Japan 2-21-1 Osawa, Mitaka, Tokyo 181-8588,Japan7 Department of Astronomy, Cornell University, Ithaca, NY 148538 Astronomy Center, University of Sussex, Brighton BN1 9QH, UK9 Centre for Astrophysics & Planetary Science, School of PhysicalSciences, University of Kent, Canterbury, Kent CT2 7NR, UK10INAF, Osservatorio Astronomico di Bologna, via Ranzani 1, 40127Bologna, Italy11Dipartimento di Fisica, Universit Roma Tre, via della Vasca Navale84, 00146 Roma, ItalyAbstract. We report results from our Spitzer GO-1 program on IRS spec-troscopy of a large sample of Luminous Infrared Galaxies and quasars selectedfrom the European Large Area ISO Survey (ELAIS). The selected ELAIS sourceshave a wide multi-wavelength coverage, including ISOCAM, ISOPHOT, IRACand MIPS (from SWIRE), and optical photometry. Here we present the sampleselection and results from the IRS spectroscopy.1. Sample Selection and IRS ObservationsThe sources were selected from the European Large Area ISO Survey (ELAIS)final band-merged catalog of Rowan-Robinson et al. (2004). The sample con-sists of 70 sources with 15 µm fluxes larger than ∼ 1 mJy and spectroscopic orestimated photometric redshifts z > 1. Although no color cuts were applied,the objects are brighter than r ∼ 24, the limit of the Isaac Newton TelescopeWide Field Survey CCD photometry used in the optical identification of ELAISsources (Gonza´lez-Solares et al. 2005). The 15 µm observations and catalog are367368 Herna´n-Caballero et al.Figure 1. Ratio νfν(15 µm) / νfν(r) for the ELAIS-IRS sources versus r-band magnitude. Diamonds: star-forming galaxies and obscured AGN; stars:unobscured AGN.presented in Vaccari et al. (2005).Low-resolution IRS spectroscopy was carried out using all four IRS modules,covering thus the wavelength range between 5 and 40 µm. Typical total exposuretime per object was of about one hour. Figure 1 shows the ratio of νf ν at 15µm over r-band as a function of the r-band magnitude. ELAIS-IRS targetswith bright magnitudes have blue optical to 15 µm colors typical of type-1 AGN(Afonso-Luis et al. 2004; Gonza´lez-Solares et al. 2005; Hatziminaoglou et al.2005). Objects with fainter optical IDs are identified as obscured AGN andstar-forming galaxies.2. Results from the IRS SpectroscopyThe IRS spectra were extracted from the SSC pipeline processed data usingSPICE, and individual spectra of each object were coadded. A selection ofthe IRS spectra is shown in figure 2. The IRS spectra show a wide variety ofspectral shapes and clear features (PAHs in emission and silicate absorption at9.7 µm) can be seen in a number of objects. The IRS spectra can be classifiedinto three main categories: (a) smooth featureless continuum, usually associatedwith type-1 AGN, (b) PAH features in emission and silicate absorption, and (c)silicate absorption.A 15 µm Selected Sample of High-z Starbursts and AGNs 369Figure 2. A selection of ELAIS-IRS spectra showing different types of mid-IR SEDs, including strong PAH, star-forming dominated SEDs (left), power-law continua with or without PAH features (center) and silicate absorption(right).Redshifts can be measured for a number of objects from the IRS spec-troscopy, and they agree with the optical spectroscopic redshifts, wheneveravailable. They are also consistent in most cases with the photometric red-shifts obtained from template fitting to the optical and IRAC photometry fromSWIRE (Lonsdale et al. 2003, 2004). Objects in our sample with PAH featuresand starlight-dominated optical SEDs are interpreted as star-forming galaxies.Their redshifts are in the range 0.6 < z < 1.2 and the far-IR (8-1000 µm) lumi-nosities are in the range ∼ 1011 − 1012L⊙.Some galaxies are found at higher redshifts, up to z ∼ 2. They only showsilicate in absorption and no bright PAH features. Their luminosities are in theULIRG range. Their SEDs and IRS spectra suggest they are obscured AGN.3. Comparison with Other IRS Samples of High-z GalaxiesOur sample, selected at 15 µm from the ELAIS survey, differs in redshift rangeand luminosity from those in other major IRS surveys (fig. 3). The sampleselection of Yan et al. (2005) was based in color cuts using the Spitzer 24 and 8µm bands and one optical band (R), while Houck et al. (2005) selected objectswith very red 24 µm to R band colors. Our ELAIS-IRS sample selection aimsto cover all possible types of z∼> 1 sources selected at 15 µm, regardless of their370 Herna´n-Caballero et al.Figure 3. Restframe 7 µm luminosity (νLν) versus redshift for the ELAIS-IRS sample. Objects with optical spectroscopic redshifts (mostly AGN) areshown as stars, whereas those with z estimated from their IRS spectra areplotted as plus signs. For comparison, samples from Yan et al. (2005) andHouck et al. (2005) are represented as squares and diamonds, respectively.mid-IR colors. The results show that a large fraction of the star-forming galaxiesin the sample is at z ∼ 1, as expected from the photometric redshifts estimates,and is consistent with bright PAH features (7.7 and 8.5 µm) redshifted intothe ISOCAM LW3 band (15 µm). At low redshift (z < 1) our sample includesluminous infrared star-forming galaxies and two AGN at intermediate redshifts(1.0 < z < 1.8) we find AGN, both obscured and unobscured, and star-forminggalaxies, all with restframe 7 µm luminosities comparable to those in the Yan etal. (2005) and Houck et al. (2005) samples. At z∼> 1.8 we find AGNs, typicallymore luminous than the comparison IRS samples.The ELAIS-IRS sample constitutes one of the best samples of luminousand ultraluminous IR sources with IRS spectroscopy in the redshift range (0.5< z < 1.8). A number of spectroscopic follow-up programs are underway. TheELAIS-IRS sample and detailed results are presented in Herna´n-Caballero et al.(2006).Acknowledgments. This work is based on observations made with theSpitzer Space Telescope, which is operated by the Jet Propulsion Laboratory,Caltech under NASA contract 1407.A 15 µm Selected Sample of High-z Starbursts and AGNs 371ReferencesAfonso-Luis, A. et al. 2004, MNRAS, 354, 961Gonza´lez-Solares, E. et al. 2005, MNRAS, 358, 333Hatziminaoglou, E. et al. 2005, AJ, 129, 1198Herna´n-Caballero, A. et al. 2006, in preparationHouck, J. R. et al. 2005, ApJ, 622, 105Lonsdale, C. J. et al. 2003, PASP, 115, 897Lonsdale, C. J. et al. 2004, ApJS, 154, 54Rowan-Robinson, M. et al. 2004, MNRAS, 351, 1290Vaccari, M. et al. 2005, MNRAS, 358, 397Yan, L. et al. 2005, ApJ, 628, 604

A 15 µm selected sample of hHigh-z starbursts and AGNs

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A 15 µm selected sample of hHigh-z starbursts and AGNs

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