Herschel protocluster survey: a search for dusty star-forming galaxies in protoclusters atz= 2–3

Abstract

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Two sub-millimetre bright protoclusters bounding the epoch of peak star-formation activity

“…The SMG over-density in HS1700 has a distribution that peaks near the mean optical galaxy cluster centre , but is offset ∼ 40 (320 kpc) to the north compared to the optical galaxies. Kato et al (2016) have suggested a central protocluster position ∼ 2.1 north using seven Herschel-SPIRE sources having colours consistent with z ∼ 2.3, although only one of their sources confirmed to lie within the protocluster, 1700.5, which has a spectroscopic line detections and photometric redshifts locating the source at z = 2.3 (see §3.4.3 and §3.4.5). When applying our SCUBA-2 over-density analysis at the Kato et al (2016) offset position, we find no such evidence for excess.…”

“…Kato et al (2016) have suggested a central protocluster position ∼ 2.1 north using seven Herschel-SPIRE sources having colours consistent with z ∼ 2.3, although only one of their sources confirmed to lie within the protocluster, 1700.5, which has a spectroscopic line detections and photometric redshifts locating the source at z = 2.3 (see §3.4.3 and §3.4.5). When applying our SCUBA-2 over-density analysis at the Kato et al (2016) offset position, we find no such evidence for excess. The optical centroid of the protocluster is likely the most reliable tracer of the mass distribution, as the optical sources have longer duty cycles than the more active SMGs, even though the latter are likely to be more massive on average (e.g., Chapman et al 2009).…”

“…Though we lack redshift data for many of the IRAC IDs in HS1549 and HS1700, we conclude that many of our SMG IDs have colours consistent with the relevant redshift range of ALESS SMGs and the SMM J2135-0102 SED track. Using archival Herschel-SPIRE data from Kato et al (2016) we measure SPIRE colours S 500 /S 350 and S 350 /S 250 for 21/27 SCUBA-2 IDs in the HS1700 field (see Figure 5). The photometric redshifts determined by the SPIRE colours correlate to their known redshifts, with the exception of are in agreement with the known redshifts, for the exception of the QSO 1700.12.…”

A high dust emissivity index β for a CO-faint galaxy in a filamentary Lyα nebula at z = 3.1

“…We derived an infrared (IR) luminosity L IR [8−1000¯m] , a dust temperature T d and a dust emissivity index β by fitting a single temperature, optically thin modified black body model to the SPIRE 250 µm (Kato et al 2016), ALMA Band 7 850 µm (Ao et al 2017;Matsuda et al in prep), ALMA Band 3 2.7 mm, and 3 mm dust continuum emission (Figure 2). The SPIRE 250 µm flux density is measured at the position of LAB18.b and applied a source confusion noise for photometry error (Kato et al 2016). The accuracy of the ALMA Band 7 850 µm absolute flux calibration is evaluated to be within 10%, which is applied for the SED fitting ( Figure 2).…”

Extended star-forming regions within galaxies in a dense proto-cluster core at z = 2.53

“…star-forming galaxies (e.g., Venemans et al 2007;Hayashi et al 2012;Gobat et al 2013;Koyama et al 2013;Kato et al 2016;Wang et al 2016) as opposed to local galaxy clusters, which are dominated by passive elliptical galaxies. Environmental dependence of physical quantities of star-forming galaxies at z > ∼ 2, such as star-forming activity, gas metallicity, and morphology, has being investigated in many studies (see Overzier (2016) and reference therein) with the aim of understanding the early stage of the environmental effects on galaxy formation and evolution.…”