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Published October 2013 | Published + Submitted
Journal Article Open

Herschel reveals the obscured star formation in HiZELS Hα emitters at z = 1.47


We describe the far-infrared (far-IR; rest-frame 8–1000-μm) properties of a sample of 443 Hα-selected star-forming galaxies in the Cosmic Evolution Survey (COSMOS) and Ultra Deep Survey (UDS) fields detected by the High-redshift Emission Line Survey (HiZELS) imaging survey. Sources are identified using narrow-band filters in combination with broad-band photometry to uniformly select Hα (and [O ii] if available) emitters in a narrow redshift slice at z = 1.47 ± 0.02. We use a stacking approach in Spitzer-MIPS mid-IR, Herschel-PACS/SPIRE far-IR [from the PACS Evolutionary Prove (PEP) and Herschel Multi-tiered Extragalactic Survey (HerMES)] and AzTEC mm-wave images to describe their typical far-IR properties. We find that HiZELS galaxies with observed Hα luminosities of L(Hα)_(obs) ≈ 10^(8.1-9.1) L_⊙ ( ≈ 10^(41.7-42.7) erg s^(−1)) have bolometric far-IR luminosities of typical luminous IR galaxies, L(8−1000μm)≈10^(11.41)^(+0.04)_(−0.06) L_⊙. Combining the Hα and far-IR luminosities, we derive median star formation rates (SFRs) of SFR_(Hα), FIR = 32 ± 5 M_⊙ yr^(−1) and Hα extinctions of A_(Hα) = 1.0 ± 0.2 mag. Perhaps surprisingly, little difference is seen in typical HiZELS extinction levels compared to local star-forming galaxies. We confirm previous empirical stellar mass (M_*) to A_(Hα) relations and the little or no evolution up to z = 1.47. For HiZELS galaxies (or similar samples) we provide an empirical parametrization of the SFR as a function of rest-frame (u − z) colours and 3.6-μm photometry – a useful proxy to aid in the absence of far-IR detections in high-z galaxies. We find that the observed Hα luminosity is a dominant SFR tracer when rest-frame (u − z) colours are ≲0.9 mag or when Spitzer-3.6-μm photometry is fainter than 22 mag (Vega) or when stellar masses are lower than 10^(9.7) M_⊙. We do not find any correlation between the [O ii]/Hα and far-IR luminosity, suggesting that this emission line ratio does not trace the extinction of the most obscured star-forming regions, especially in massive galaxies where these dominate. The luminosity-limited HiZELS sample tends to lie above of the so-called main sequence for star-forming galaxies, especially at low stellar masses, indicating high star formation efficiencies in these galaxies. This work has implications for SFR indicators and suggests that obscured star formation is linked to the assembly of stellar mass, with deeper potential wells in massive galaxies providing dense, heavily obscured environments in which stars can form rapidly.

Additional Information

© 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2013 July 4. Received 2013 July 3; in original form 2012 November 30. First published online: August 8, 2013. We thank the anonymous referee for the useful comments that helped improve this paper. EI agradece el financiamento de CONICYT/FONDECYT por el proyecto de postdoctorado N◦:3130504. DS acknowledges financial support from the Netherland Organization for Scientific research (NWO) through a Veni fellowship. IS acknowledges support from STFC, a Leverhulme Fellowship, the ERC Advanced Investigator programme DUSTYGAL and a Royal Society/Wolfson Merit Award. RJI acknowledges support in the form of ERC Advanced Investigator programme, COSMI-CISM. The HiZELS data are based on observations obtained using both the Wide Field Camera on the 3.8-m United Kingdom Infrared Telescope (operated by the Joint Astronomy Centre on behalf of the Science and Technology Facilities Council of the UK) and Suprime-Cam on the 8.2-m Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. This research has made use of data from the HerMES project (http://hermes.sussex. ac.uk/). HerMES is a Herschel Key Programme utilizing Guaranteed Time from the SPIRE instrument team, ESAC scientists and a mission scientist. The data presented in this paper will be released through the HerMES database in Marseille, HeDaM (http://hedam.oamp.fr/HerMES). SPIRE has been developed by a consortium of institutes led by Cardiff Univ. (UK) and including: Univ. Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, Univ. Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, Univ. Sussex (UK); and Caltech, JPL, NHSC, Univ. Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC, UKSA (UK); and NASA (USA). PACS has been developed by a consortium of institutes led by MPE (Germany) and including UVIE (Austria); KUL, CSL, IMEC (Belgium); CEA, OAMP (France); MPIA (Germany); IFSI, OAP/AOT, OAA/CAISMI, LENS, SISSA (Italy); IAC (Spain). This development has been supported by the funding agencies BMVIT (Austria), ESA-PRODEX (Belgium), CEA/CNES (France), DLR (Germany), ASI (Italy) and CICYT/MCYT (Spain). This research has made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.

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Published - MNRAS-2013-Ibar-3218-35.pdf

Submitted - 1307.3556v1.pdf


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