# The Nature of 500 Micron Risers II: Sub-mm Faint Dusty Star Forming Galaxies

**Authors:** J. Cairns, D. L. Clements, J. Greenslade, G. Petitpas, T. Cheng, Y. Ding, A. Parmar, I. Pérez-Fournon, D. Riechers  
**arXiv:** [2203.01049](https://arxiv.org/abs/2203.01049)  
**Date:** 2022-03-02  
**Summary page:** https://www.summarizepaper.com/en/paper/2203.01049v1/

## Key points

- Study titled "The Nature of 500 Micron Risers II: Sub-mm Faint Dusty Star Forming Galaxies" by Cairns et al.
- Follow-up observations of four candidate high-redshift Dusty Star-Forming Galaxies using SCUBA-2 and SMA instruments
- Selection based on rising spectral energy distributions (SEDs) in the 250, 350, and 500$\mu$m Herschel SPIRE bands
- Deeper sub-mm observations revealed counterparts to all four 500$\mu$m risers, with three resolving into multiple systems
- Varying percentages of integrated 850$\mu$m flux density recovered from SCUBA-2 for the multiple systems, indicating dense protocluster core formation
- Photometric redshift estimates suggest three out of four galaxies likely at redshifts greater than or equal to 2
- Interpretation that selection criterion identifies intrinsically red individual galaxies at redshifts greater than 4 and multiple systems at more moderate redshifts artificially reddened due to blending effects
- Investigation of environments using SCUBA-2 maps showing potential protocluster presence at redshift greater than or equal to 2
- Bright 500$\mu$m risers with faint 850$\mu$m flux densities typically multiple systems at redshifts greater than or equal to 2, possibly located in overdensities of bright sub-mm galaxies

## Summary

In their study titled "The Nature of 500 Micron Risers II: Sub-mm Faint Dusty Star Forming Galaxies," Cairns et al. present follow-up observations of four candidate high-redshift Dusty Star-Forming Galaxies using SCUBA-2 and SMA instruments. These galaxies were selected based on their rising spectral energy distributions (SEDs) in the 250, 350, and 500$\mu$m Herschel SPIRE bands. Previous SMA observations did not find any counterparts to these sources, but the deeper sub-mm observations revealed counterparts to all four 500$\mu$m risers, with three of them resolving into multiple systems. The authors found that the SMA 345GHz observations recovered varying percentages of the integrated 850$\mu$m flux density from SCUBA-2 for the three multiple systems, indicating the presence of additional sources below the SMA detection limit forming a dense protocluster core. The fourth 500$\mu$m riser was observed at a lower frequency, preventing a similar comparison. By estimating photometric redshifts based on FIR/sub-mm colors, Cairns et al. determined that three out of four galaxies likely lie at redshifts greater than or equal to 2. This aligns with the interpretation that the selection criterion for 500$\mu$m risers identifies both intrinsically red individual galaxies at redshifts greater than 4 and multiple systems at more moderate redshifts that appear artificially reddened due to blending effects. Using SCUBA-2 850$\mu$m maps, the authors investigated the environments of these <kw>500$\mu$m risers</kw> by constructing cumulative number counts and estimating photometric redshifts for surrounding SCUBA-2 detections. They found evidence suggesting that one of the risers could potentially reside in a protocluster at redshift greater than or equal to 2. Overall, Cairns et al. infer that bright <kw>500$\mu$m risers</kw> with faint 850$\mu$m flux densities are typically multiple systems at redshifts greater than or equal to 2, possibly located in overdensities of bright sub-mm galaxies. Their findings provide valuable insights into the nature and characteristics of these <kw>sub-mm faint dusty star-forming galaxies</kw> in high-redshift environments.