z-GAL: A NOEMA spectroscopic redshift survey of brightHerschelgalaxies

Abstract

We present the dust properties of 125 brightHerschelgalaxies selected from thez-GAL NOEMA spectroscopic redshift survey. All the galaxies have precise spectroscopic redshifts in the range 1.3 <z< 5.4. The large instantaneous bandwidth of NOEMA provides an exquisite sampling of the underlying dust continuum emission at 2 and 3 mm in the observed frame, with flux densities in at least four sidebands for each source. Together with the availableHerschel250, 350, and 500 μm and SCUBA-2 850 μm flux densities, the spectral energy distribution (SED) of each source can be analyzed from the far-infrared to the millimeter, with a fine sampling of the Rayleigh-Jeans tail. This wealth of data provides a solid basis to derive robust dust properties, in particular the dust emissivity index (β) and the dust temperature (Tdust). In order to demonstrate our ability to constrain the dust properties, we used a flux-generated mock catalog and analyzed the results under the assumption of an optically thin and optically thick modified black body emission. The robustness of the SED sampling for thez-GAL sources is highlighted by the mock analysis that showed high accuracy in estimating the continuum dust properties. These findings provided the basis for our detailed analysis of thez-GAL continuum data. We report a range of dust emissivities withβ ∼ 1.5 − 3 estimated up to high precision with relative uncertainties that vary in the range 7%−15%, and an average of 2.2 ± 0.3. We find dust temperatures varying from 20 to 50 K with an average ofTdust ∼ 30 K for the optically thin case andTdust ∼ 38 K in the optically thick case. For all the sources, we estimate the dust masses and apparent infrared luminosities (based on the optically thin approach). An inverse correlation is found betweenTdustandβwithβ ∝ Tdust−0.69, which is similar to what is seen in the local Universe. Finally, we report an increasing trend in the dust temperature as a function of redshift at a rate of 6.5 ± 0.5 K/zfor this 500 μm-selected sample. Based on this study, future prospects are outlined to further explore the evolution of dust temperature across cosmic time.