Herschel-PACS far-infrared detections of Lyman-α emitters at 2.0  ≲  z  ≲  3.5^⋆,⋆⋆

I. Oteo^1,2, A. Bongiovanni^1,2, A. M. Pérez García^1,2, J. Cepa^2,1, A. Ederoclite^1,2, M. Sánchez-Portal³, I. Pintos-Castro^1,2, R. Pérez-Martínez⁴, S. Berta⁵, B. Magnelli⁵, P. Popesso⁵, F. Pozzi⁶, A. Poglitsch⁵, D. Lutz⁵, R. Genzel⁵, L. Tacconi⁵, N. Förster Schreiber⁵, E. Sturm⁵, D. Elbaz⁷, H. Aussel⁷, E. Daddi⁷, P. Andreani⁸, A. Cimatti⁹, R. Maiolino¹⁰, B. Altieri³ and I. Valtchanov³

¹ Instituto de Astrofísica de Canarias (IAC), 38200 La Laguna, Tenerife, Spain
e-mail: ioteo@iac.es
² Departamento de Astrofísica, Universidad de La Laguna (ULL), 38205 La Laguna, Tenerife, Spain
³ Herschel Science Centre (ESAC), Villafranca del Castillo, Spain
⁴ XMM/Newton Science Operations Centre (ESAC), Villafranca del Castillo, Spain
⁵ Max-Planck-Institut für Extraterrestrische Physik (MPE), Postfach 1312, 85741 Garching, Germany
⁶ INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁷ Commissariat à l’Énergie Atomique (CEA-SAp), Saclay, France
⁸ ESO, Karl-Schwarzchild-Str. 2, 85748 Garching, Germany
⁹ Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy
¹⁰ INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy

Received: 4 December 2010
Accepted: 24 January 2012

Abstract

In this work we analyse the physical properties of a sample of 56 spectroscopically selected star-forming (SF) Lyα emitting galaxies at 2.0 ≲ z ≲ 3.5 using both a spectral energy distribution (SED) fitting procedure from rest-frame UV to mid-IR and direct 160 μm FIR observations taken with the Photodetector Array Camera and Spectrometer (PACS) instrument onboard the Herschel Space Observatory. We define LAEs as those Lyα-emitting galaxies whose rest-frame Lyα equivalent widths (Lyα   EW_{rest − frame}) are above 20 Å, the typical threshold in narrow-band searches. Lyα-emitting galaxies with Lyα   EW_{rest − frame} < 20   Å are called non-LAEs. As a result of an individual SED fit for each object, we find that the studied sample of LAEs contains galaxies with ages mostly below 100 Myr and a wide variety of dust attenuations, SFRs, and stellar masses. The heterogeneity of the physical properties is also seen in the morphology, ranging from bulge-like galaxies to highly clumpy systems. In this way, we find that LAEs at 2.0 ≲ z ≲ 3.5 are very diverse, and do not have a bimodal nature, as suggested in previous studies. Furthermore, the main difference between LAEs and non-LAEs is their dust attenuation, because LAEs are not as dusty as non-LAEs. On the FIR side, four galaxies of the sample (two LAEs and two non-LAEs) have PACS detections. Their total IR luminosities place all of them in the ULIRG regime, and all are dusty objects, with A₁₂₀₀ ≳ 4 mag. This is an indication from direct FIR measurements that dust and Lyα emission are not mutually exclusive. This population of red and dusty LAEs is not seen at z ~ 0.3, which suggests an evolution with redshift of the IR nature of galaxies selected via their Lyα emission.