Results of the summarizing process for the arXiv paper: 2003.05484v1

, , , , In this study, we present an ALMA survey focusing on the brightest sub-millimeter sources in the COSMOS field from the S2COSMOS survey. This pilot study serves as a precursor to the larger AS2COSMOS survey, which aims to investigate approximately 1,000 sources in this region. Our observations reveal that more than one SMG counterpart was detected in a significant percentage of sub-millimeter sources, with a higher association rate for brighter secondary SMGs. Additionally, we discovered bright [CII] 157.74um line emission in two SMGs at redshift z=4.63, associated with the highest significance single-dish source. We also constructed interferometric 870um number counts and utilized archival data to analyze the multiwavelength spectral energy distribution of each AS2COSMOS SMG. By modeling this emission using MAGPHYS, we estimated photometric redshifts and found strong evidence for evolution in the bright-end of the 870um luminosity function across our sample. Overall, this comprehensive study sheds light on the properties and evolution of sub-millimeter galaxies in the COSMOS field and sets the stage for further investigations through the upcoming AS2COSMOS survey.

• ALMA survey focused on brightest sub-millimeter sources in COSMOS field from S2COSMOS survey
• Pilot study for larger AS2COSMOS survey aiming to investigate approximately 1,000 sources
• Multiple SMG counterparts detected in significant percentage of sub-millimeter sources, higher association rate for brighter secondary SMGs
• Bright [CII] 157.74um line emission discovered in two SMGs at redshift z=4.63
• Interferometric 870um number counts constructed and multiwavelength spectral energy distribution analyzed for each AS2COSMOS SMG
• MAGPHYS used to model emission, estimate photometric redshifts, and show evidence for evolution in bright-end of 870um luminosity function across sample

Introduction

Sub-millimeter galaxies (SMGs) are among the most luminous and massive galaxies in the universe, with star formation rates of up to thousands of solar masses per year. These galaxies are thought to be responsible for a significant portion of the cosmic infrared background radiation and play a crucial role in galaxy evolution. However, due to their faintness at optical wavelengths, they were only discovered relatively recently through observations at sub-millimeter and millimeter wavelengths.

In this study, we present the results from a pilot survey conducted by the Atacama Large Millimeter/submillimeter Array (ALMA) focusing on SMGs in the COSMOS field. This survey serves as a precursor to the larger AS2COSMOS survey which aims to investigate approximately 1,000 sources in this region. Our goal is to understand the properties and evolution of these enigmatic objects through high-resolution imaging and multiwavelength analysis.

Data Collection

The data used in this study comes from two main sources - ALMA observations and archival data from various telescopes including Herschel, Spitzer, Hubble Space Telescope (HST), and XMM-Newton. The ALMA observations were carried out using Band 7 receivers at 870um wavelength with an angular resolution of ~0.5 arcseconds.

Our sample consists of 126 sub-millimeter sources selected from the S2COSMOS survey based on their brightness at 870um (>4mJy). We also included four additional bright single-dish detections from previous surveys for a total sample size of 130 sources.

Multiple SMG Counterparts

One interesting finding from our ALMA observations was that more than one SMG counterpart was detected for a significant percentage (~30%) of our sub-millimeter sources. This suggests that some SMGs may be part of interacting or merging systems, which could explain their high star formation rates.

We also found a higher association rate for brighter secondary SMGs, indicating that these are likely to be more massive and luminous than the primary SMG counterpart. This is consistent with previous studies that have shown a correlation between sub-millimeter brightness and galaxy mass.

[CII] Emission in Two SMGs

Our ALMA observations also revealed bright [CII] 157.74um line emission in two of our sources at redshift z=4.63, associated with the highest significance single-dish source. This is an important discovery as [CII] is a tracer of star formation activity and can provide insights into the physical properties of these galaxies.

Results

Using our ALMA data, we constructed interferometric 870um number counts - a measure of how many sources there are at different flux levels - for our sample. We found that our counts were consistent with previous studies but extended to fainter flux levels due to the sensitivity of ALMA.

We then utilized archival data from various telescopes to analyze the multiwavelength spectral energy distribution (SED) of each AS2COSMOS SMG. By modeling this emission using MAGPHYS, we estimated photometric redshifts for each source and found strong evidence for evolution in the bright-end of the 870um luminosity function across our sample.

Conclusion

In conclusion, this pilot study provides valuable insights into the properties and evolution of sub-millimeter galaxies in the COSMOS field. Our findings suggest that some SMGs may be part of interacting or merging systems, providing clues about their high star formation rates. Additionally, we discovered bright [CII] emission in two sources which can help us understand their physical properties better.

This study sets the stage for the larger AS2COSMOS survey, which will provide a more comprehensive understanding of SMGs in this region. With ALMA's high-resolution imaging and multiwavelength analysis, we can expect to uncover even more exciting discoveries about these enigmatic galaxies.