A&A 574, A19 (2015) Astronomy DOI: 10.1051/0004-6361/201424649 & c ESO 2015 Astrophysics New constraints on dust emission and UV attenuation of z = 6.5–7.5 galaxies from millimeter observations D. Schaerer1,2, F. Boone2, M. Zamojski1, J. Staguhn3,4, M. Dessauges-Zavadsky1 , S. Finkelstein5,andF.Combes6 1 Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Versoix, Switzerland e-mail: [email protected] 2 CNRS, IRAP, 14 avenue É. Belin, 31400 Toulouse, France 3 The Henry A. Rowland Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street, MD 21218, Baltimore, USA 4 Observational Cosmology Lab., Code 665, NASA at Goddard Space Flight Center, MD 20771, Greenbelt, USA 5 The University of Texas at Austin, Austin, TX 78712, USA 6 Observatoire de Paris, LERMA, 61 Av. de l’Observatoire, 75014 Paris, France Received 21 July 2014 / Accepted 3 November 2014 ABSTRACT Context. Determining the dust properties and UV attenuation of distant star-forming galaxies is of great interest for our understanding of galaxy formation and cosmic star formation in the early Universe. However, few direct measurements exist so far. Aims. To shed new light on these questions, we have targeted two recently discovered Lyman-break galaxies (LBGs) at z ≈ 6.8and z = 7.508 to search for dust continuum and [C ii] λ158 μm line emission. Methods. The strongly lensed z ≈ 6.8 LBG A1703-zD1 behind the galaxy cluster Abell 1703 and the spectroscopically confirmed z = 7.508 LBG z8-GND-5296 in the GOODS-N field were observed with the Plateau de Bure Interferometer (PdBI) at 1.2 mm. These observations were combined with those of three z > 6.5Lyα emitters (HCM6A, Himiko, and IOK-1), for which deep measurements were recently obtained with the PdBI and ALMA. 7 Results. [C ii] is undetected in both galaxies, providing a deep upper limit of L[C II] < 2.8 × 10 L for A1703-zD1, comparable to the nondetections of Himiko and IOK-1 with ALMA. Dust continuum emission from A1703-zD1 and z8-GND-5296 is not detected with an rms of 0.12 and 0.16 mJy/beam. From these nondetections and earlier multiwavelength observations we derive upper limits on their IR luminosity and star formation rate, dust mass, and UV attenuation. Thanks to strong gravitational lensing, the achieved limit for 10 A1703-zD1 is similar to those achieved with ALMA, probing below the luminous infrared galaxy (LIRG) regime (LIR < 8.1×10 L) 7 and very low dust masses (Md < 1.6 × 10 M). We find that all five galaxies are compatible with the Calzetti IRX-β relation, their UV attenuation is compatible with several indirect estimates from other methods (the UV slope, extrapolation of the attenuation measured from the IR/UV ratio at lower redshift, and spectral energy distribution fits), and the dust-to-stellar mass ratio is compatible with that of galaxies from z = 0 to 3. From their stellar mass, the high-z galaxies studied here have an attenuation below the one expected from the mean relation of low-redshift (z ∼< 1.5) galaxies. Conclusions. More and deeper (sub-)mm data are clearly needed to directly determine the UV attenuation and dust content of the dominant population of high-z star-forming galaxies and to establish their dependence on stellar mass, redshift, and other properties more firmly. Key words. galaxies: high-redshift – galaxies: starburst – dust, extinction – galaxies: ISM – submillimeter: galaxies 1. Introduction The Lyman-break selection has been successful in tracing a large number of galaxies out to very high redshift, which has al- The strong interest for galaxy formation and evolution in the lowed constructing their luminosity function and thus determin- early Universe and the high sensitivity of millimeter interfer- ing the cosmic UV luminosity density and the associated star ometers meet ideally at high redshifts. As a result of the well- formation rate (SFR) density (Madau & Dickinson 2014,and known so-called negative k-correction, the observed flux from references therein). Despite this, little is known about the UV at- dust emission in galaxies increases with increasing distance at tenuation of these galaxies and about the associated dust proper- (sub)millimeter wavelengths, which in principle allows observa- > ties (mass, temperature, composition, etc.). Generally, the UV at- tions out to very high redshifts, z 6(cf.Blain et al. 2002). tenuation of Lyman-break galaxies (LBGs) at z > 3 is estimated Since galaxy evolution in the early Universe remains poorly un- β ff from their UV slope (e.g., Bouwens et al. 2014; Castellano derstood and since dust can strongly a ect our view of star for- et al. 2012) using empirical relations established at low redshift mation, it is essential to directly observe dust emission from the (e.g., the so-called Meurer relation, cf. Meurer et al. 1999), or most distant galaxies. from spectral energy distribution (SED) fits to the (rest frame) Based on observations carried out with the IRAM Plateau de Bure UV-optical part of the spectrum. Although the most direct mea- Interferometer and the IRAM 30 m telescope. IRAM is supported by sure of UV attenuation is determined by the ratio of IR/UV lu- CNRS/INSU (France), the MPG (Germany) and the IGN (Spain). minosity (Buat et al. 2005; Iglesias-Páramo et al. 2007), current Article published by EDP Sciences A19, page 1 of 10 A&A 574, A19 (2015) measurements are limited by sensitivity to z ∼< 3−4(Lee et al. mass as a function of stellar mass and how these quantities may 2012; Burgarella et al. 2013). evolve with redshift. Thanks to strong gravitational lensing, the normal sensitiv- Our paper is structured as follows: the observational data ity limit has been overcome in a few cases in the past. Livermore are described in Sect. 2. In Sect. 3 we derive the IR luminos- et al. (2012), for example, have achieved a tentative detection ity and dust masses from the observations. Simple inferences of CO in a strongly lensed z = 4.9 star-forming galaxy with on the UV attenuation and the stellar populations of the small −1 8 an SFR ≈ 40 M yr and stellar mass M ≈ 7. × 10 M, sample are derived in Sect. 4. We then discuss our results for the IRX-β relation, UV attenuation as a function of redshift and that is, properties similar to those of LBGs. The IR continuum ii of this galaxy has, however, remained undetected, with a limit stellar mass, dust mass, the [C ] luminosity, and constraints on 11 corresponding to L < 3.5 × 10 L, as reported by Livermore the SED fits of these objects in Sect. 5. Section 6 summarizes our IR Λ et al. (2012). The z = 6.56 Lyα emitting galaxy (LAE) HCM6A, main conclusions. We adopt a -CDM cosmological model with = −1 −1 Ω = . Ω = . lensed by the galaxy cluster Abell 370, has been targeted by var- H0 70 km s Mpc , m 0 3and Λ 0 7, use AB mag- ious studies aiming at detecting the dust continuum, CO, and nitudes, and assume a Salpeter IMF from 0.1 to 100 M. [C ii] emission (Boone et al. 2007; Wagg et al. 2009; Kanekar et al. 2013). From the nondetection at 1.2 mm obtained with 2. Observations MAMBO-2 at the IRAM 30 m antenna, Boone et al. (2007)de- 2.1. IRAM observations of the lensed galaxy A1703-zD1 rived an upper limit of L /L ∼< 2 and an UV attenuation of < IR UV and the GOODS-N source z8-GND-5296 AUV ∼ 0.9, which we here update using a more recent measure- ment from Kanekar et al. (2013). Until recently, this measure- We have obtained 1.2 mm observations of two sources, ment has represented the best (lowest) constraint on UV attenu- A1703-zD1 and z8-GND-5296, with the IRAM PdBI in the ation in LBGs or LAE at high redshift (z > 5). compact configuration and with the WIDEX backend cover- Two bright nonlensed LAEs, Himiko at z = 6.595 and IOK-1 ing a bandwidth of 3.6 GHz. A1703-zD1 was observed in May at z = 6.96 (Ouchi et al. 2009; Iye et al. 2006), and the gamma- and August 2013 with five antennas, z8-GND-5296 was ob- served in December 2013 with six antennas. The central fre- ray burst 090423 at z ∼ 8.2 were also targeted by Walter et al. ii (2012) with the Plateau de Bure Interferometer (PdBI) in the quency of receiver 3 was tuned to the redshifted [C ] line, 1.2 mm window, from which they concluded a low dust obscu- whose rest frequency is 1900.54 GHz, that is, 241.5 GHz for ∼ . A1703-zD1 and 223.88 GHz for z8-GND-5296. The quais- ration in these objects. Two other LAEs at z 6 5, recently ob- + + + served by González-López et al. (2014) with the PdBI in the stellar objects (QSO) 1150 497, J1259 516 and 1347 539 1.2 mm window, were also not detected (both in [C ii]andin were used as phase and amplitude calibrators for the obser- vations of A1703-zD1 and 1150+497, and 1044+719 for the the continuum). However, since their continuum sensitivity is a + factor 2−5 lower than the one achieved for the lensed galaxy observations of z8-GND-5296. The bright sources 2200 420, HCM6A and this galaxy is magnified by a factor μ ≈ 4.5, the MWC349, 3C84 and LKHA101 were also observed to calibrate effective limit on the L /L ratio, and hence the UV attenua- the absolute flux and passband.