The AGN, star-forming, and morphological properties of luminous ir-bright/optically-faint galaxies


Autoria(s): Donley, J. L.; Rieke, G. H.; Alexander, D. M.; Egami, E.; Pérez González, Pablo Guillermo
Data(s)

20/08/2010

Resumo

We present the active galactic nucleus (AGN), star-forming, and morphological properties of a sample of 13 MIR-luminous (∫_24 700 μJy) IR-bright/optically-faint galaxies (IRBGs, ∫_24/f_R≲ 1000). While these z ∼ 2 sources were drawn from deep Chandra fields with >200 ks X-ray coverage, only seven are formally detected in the X-ray and four lack X-ray emission at even the 2σ level. Spitzer InfraRed Spectrograph (IRS) spectra, however, confirm that all of the sources are AGN-dominated in the mid-IR, although half have detectable polycyclic aromatic hydrocarbon (PAH) emission responsible for ∼25% of their mid-infrared flux density. When combined with other samples, this indicates that at least 30%–40% of luminous IRBGs have star formation rates in the ultraluminous infrared galaxy (ULIRG) range (∼100–2000 M_⨀ yr^−1). X-ray hardness ratios and MIR to X-ray luminosity ratios indicate that all members of the sample contain heavily X-ray obscured AGNs, 80% of which are candidates to be Compton thick. Furthermore, the mean X-ray luminosity of the sample, log L_2–10 keV(erg s^−1) ∼44.6, indicates that these IRBGs are Type 2 QSOs, at least from the X-ray perspective. While those sources most heavily obscured in the X-ray are also those most likely to display strong silicate absorption in the mid-IR, silicate absorption does not always accompany X-ray obscuration. Finally, ∼70% of the IRBGs are merger candidates, a rate consistent with that of sub-mm galaxies (SMGs), although SMGs appear to be physically larger than IRBGs. These characteristics are consistent with the proposal that these objects represent a later, AGN-dominated, and more relaxed evolutionary stage following soon after the star-formation-dominated one represented by the SMGs.

Formato

application/pdf

Identificador

http://eprints.ucm.es/38537/1/perezgonzalez44libre.pdf

Idioma(s)

en

Publicador

American Astronomical Society

Relação

http://eprints.ucm.es/38537/

http://dx.doi.org/10.1088/0004-637X/719/2/1393

10.1088/0004-637X/719/2/1393

AYA 2006-02358

AYA 2006-15698-C02-02

1255094

Direitos

info:eu-repo/semantics/openAccess

Palavras-Chave #Astrofísica #Astronomía
Tipo

info:eu-repo/semantics/article

PeerReviewed