The Detection of a Population of Submillimeter-Bright, Strongly-Lensed Galaxies (1011.1255v1)

Abstract: Gravitational lensing is a powerful astrophysical and cosmological probe and is particularly valuable at submillimeter wavelengths for the study of the statistical and individual properties of dusty starforming galaxies. However the identification of gravitational lenses is often time-intensive, involving the sifting of large volumes of imaging or spectroscopic data to find few candidates. We used early data from the Herschel Astrophysical Terahertz Large Area Survey to demonstrate that wide-area submillimeter surveys can simply and easily detect strong gravitational lensing events, with close to 100% efficiency.

• The paper presents a near-100% efficient flux-density criterion for detecting strongly-lensed, submillimeter-bright galaxies from wide-area surveys.
• Follow-up high-resolution observations with SMA and PdBI confirmed gravitational lensing through CO line redshift comparisons.
• This approach enables targeted studies of dust-obscured star-forming galaxies, enhancing understanding of their formation and evolution.

Detection of Submillimeter-Bright, Strongly-Lensed Galaxies

The paper focuses on harnessing gravitational lensing as an efficient tool for probing the properties of submillimeter galaxies (SMGs) using wide-area surveys. Gravitational lensing occurs when the light from distant galaxies is deflected by a foreground mass, such as an elliptical galaxy, which enhances the apparent brightness and can result in multiple images of the background source. This phenomenon is particularly useful in the submillimeter wavelengths due to the limited spatial resolution of submillimeter telescopes and the high source confusion that compels the need for indirect detection methods.

The article leverages early data from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) to demonstrate the potential of identifying strong gravitational lensing events. They claim a nearly 100% efficiency in detecting these events by focusing on a simple selection criterion of flux density in large-area submillimeter surveys. This approach benefits from the steep number counts of dust-obscured star-forming galaxies, which ensure that highly-magnified sources have significant contribution in the bright end of submillimeter counts even with modest lensing effects.

Beyond providing an observational strategy, the research utilizes high-resolution follow-up observations using the Submillimeter Array (SMA) and the IRAM Plateau de Bure Interferometer (PdBI) to confirm gravitationally lensed candidates. Redshift confirmation through carbon monoxide (CO) line emissions further corroborates the lensed nature of several detected SMGs. Additionally, the transition from optical and near-infrared (NIR) data aligns with the expectation of lensing when comparing redshifts, bolstering the notion of distinct foreground lensing galaxies and background SMGs.

Below are some critical implications and insights from the research:

• Numerical Results: The researchers identified five candidates with 500 $\mu$m flux density above 100 mJy as plausible strongly lensed galaxies, after filtering out low-redshift spiral galaxies and radio-bright AGNs.
• Theoretical Contributions: The paper supports the hypothesis that wide-area submillimeter surveys can offer a comprehensive sample of lensing events, given an efficient flux-density criterion. This fosters the detailed paper of both lens properties (like redshifts and masses) and those of the distant SMGs.
• Practical Applications: By efficiently identifying lens candidates, researchers can allocate telescopic resources towards targeted follow-up observations. This enhances the ability to paper otherwise obscured dust-laden galaxies, enabling insights into their star formation rates and overall contribution to submillimeter background emissions.
• Future Research Directions: The research exemplifies the ongoing shift towards combining lensing models with high-resolution observations to paper distant galaxy properties accurately. Expanding the H-ATLAS survey and similar initiatives could offer broader constraints on evolutionary models of massive galaxy formation. Moreover, as technology advances, particularly in broadband spectrometry, blind redshift determination could become faster, further optimizing the identification pipeline for lensed sources.

Ultimately, while confirming the lens candidates through multi-wavelength observations remains a nuanced process, this paper lays a robust foundation for gravitational lensing as a pivotal tool in extragalactic astrophysics at submillimeter wavelengths. As the field progresses, similar methodologies hold promise for studies beyond mere detection, exploring the evolutionary pathways of high-redshift, dust-obscured galaxies.