Ratio of 850 and 22 μm flux density as a function of redshift. The red star represents our sample (WISE1013). Green triangles represent SMGs (Magnelli et al. 2012). Orange square, yellow asterisk, yellow diamonds, and purple circles are W1W2 dropouts obtained from Wu et al. (2012), Jones et al. (2014, 2015), and Fan et al. (2017) respectively. Cyan and blue crosses represent ultraluminous quasars at z = 4.7 (Leipski et al. 2010) and at z = 6.3 (Wu et al. 2015; Wang et al. 2016), respectively. Dashed lines represent flux ratios of Arp220, M82, Mrk231, type 1 quasars, and type 2 quasars calculated with SED templates (Polletta et al. 2007). The pink shaded region represents flux ratio estimated from torus templates with varying extinction ranging from N_H = 0 to N_H = 10²³ cm⁻² (Silva et al. 2004).