Dust Properties of C ii Detected z ∼ 5.5 Galaxies: New HST/WFC3 Near-IR Observations

Abstract

We examine the rest-frame ultraviolet (UV) properties of 10 [C II]λ158 μm-detected galaxies at z∼5.5 in COSMOS using new Hubble Space Telescope/Wide Field Camera 3 near-infrared imaging. Together with preexisting 158 μm continuum and [C II]line measurements by the Atacama Large Millimeter/submillimeter Array, we study their dust attenuation properties on the IRX-βdiagram, which connects the total dust emissionto the line-of-sight dust column (∝ β). We find systematically bluer UV continuum spectral slopes (β) compared to previous low-resolution ground-based measurements, which relieves some of the tension between models of dust attenuation and observations at high redshifts. While most of the galaxies are consistent with local starburst or Small Magellanic Cloud-like dust properties, we find galaxies with low IRX values and a large range in β that cannot be explained by models of a uniform dust distribution well mixed with stars. A stacking analysis of Keck/DEIMOS optical spectra indicates that these galaxies are metal-poor with young stellar populations that could significantly alter their spatial dust distribution.

Are High-redshift Galaxies Hot? Temperature of z > 5 Galaxies and Implications for Their Dust Properties

“…Capak et al (2015;hereafter C15) provided the first study of the IRX−βdiagram at z>5 with a diverse sample of 5.1<z<5.7 galaxies observed in ALMA band 7 at restframe ∼150 μm. Together with deep HST near-IR imaging providing accurate UV colors for this sample (Barišić et al 2017), these studies suggest a significant evolution of the IRX −βrelation and its scatter at z>5 (see also Fudamoto et al 2017). Although some galaxies are found to be consistent with the relation of local starbursts, more than half of the galaxies show a substantial deficit in IRX at a range of UV colors compared to the samples at z<3.…”

“…From the reasoning in Sections 3.1 and 3.2, we expect that most of the high-redshift galaxies reside in the lower part of the IRX−βdiagram, close to the relation of the SMC. However, we also expect a large variation in the metallicity and star-forming properties of high-z galaxies (e.g., Steinhardt et al 2014;Faisst et al 2016b;Barišić et al 2017). We therefore also expect a significant scatter in IRX−β.…”

“…C15 presents today's largest and most representative sample of normal main-sequence z∼5-6 galaxies with detected [C II]emission and continuum detections or limits at 158 μm along with robust UV measurements (Barišić et al 2017). From the reasoning in Sections 3.1 and 3.2, we expect that most of the high-redshift galaxies reside in the lower part of the IRX−βdiagram, close to the relation of the SMC.…”

“…HZ10 has a lowluminosity companion (HZ10W) that is, however, not spectroscopically confirmed in either optical or FIR lines. All UV properties (morphology, luminosity, UV color) were accurately derived from deep near-IR imaging recently obtained by HST and are explained in detail in Barišić et al (2017). Table 5 provides a summary of the UV and IR properties of the C15 sample.…”

ALMA Reveals Metals yet No Dust within Multiple Components in CR7

“…Further detailed studies on how the Lyα and [C II] line profiles are related spatially require high resolution Lyα IFU observations with, e.g., MUSE, as our current Lyα spectral information is limited to clump A. . 17 Note that for the sample at z 5 6 » -, we used the most recent UV slopes as measured by Barisic et al (2017), which differ significantly from the groundbased estimates from Capak et al (2015).…”