ALMA Imaging and Gravitational Lens Models of South Pole Telescope-Selected Dusty, Star-Forming Galaxies at High Redshifts (1604.05723v1)

Abstract: The South Pole Telescope has discovered one hundred gravitationally lensed, high-redshift, dusty, star-forming galaxies (DSFGs). We present 0.5" resolution 870um Atacama Large Millimeter/submillimeter Array imaging of a sample of 47 DSFGs spanning z=1.9-5.7, and construct gravitational lens models of these sources. Our visibility-based lens modeling incorporates several sources of residual interferometric calibration uncertainty, allowing us to properly account for noise in the observations. At least 70% of the sources are strongly lensed by foreground galaxies (mu_870um > 2), with a median magnification mu_870um = 6.3, extending to mu_870um > 30. We compare the intrinsic size distribution of the strongly lensed sources to a similar number of unlensed DSFGs and find no significant differences in spite of a bias between the magnification and intrinsic source size. This may indicate that the true size distribution of DSFGs is relatively narrow. We use the source sizes to constrain the wavelength at which the dust optical depth is unity and find this wavelength to be correlated with the dust temperature. This correlation leads to discrepancies in dust mass estimates of a factor of 2 compared to estimates using a single value for this wavelength. We investigate the relationship between the [CII] line and the far-infrared luminosity and find that the same correlation between the [CII]L_FIR ratio and Sigma_FIR found for low-redshift star-forming galaxies applies to high-redshift galaxies and extends at least two orders of magnitude higher in Sigma_FIR. This lends further credence to the claim that the compactness of the IR-emitting region is the controlling parameter in establishing the "[CII] deficit."

ALMA Imaging and Gravitational Lens Models of High-Redshift DSFGs

The paper provides an extensive analysis of 47 dusty, star-forming galaxies (DSFGs) selected by the South Pole Telescope, with redshifts ranging from 1.9 to 5.7. Utilizing high-resolution imaging data from the Atacama Large Millimeter/submillimeter Array (ALMA), the authors present gravitational lens models to better understand the intrinsic properties of these distant galaxies.

Key Findings

1. Gravitational Lensing of DSFGs:
   • Over 70% of the studied DSFGs show strong evidence of gravitational lensing by foreground galaxies, with a median magnification of 6.3. Some objects exhibit magnifications exceeding 30, highlighting the significant role of gravitational lensing in studying these datasets.
   • The analysis confirms that strong lensing is widespread within high-redshift DSFGs, providing valuable insight into their intrinsic properties that would otherwise remain inaccessible with direct observations.
2. Size Distribution and Magnification Bias:
   • A comparison between lensed and unlensed DSFGs reveals a consistent intrinsic size distribution. This suggests that high-magnification sources are not necessarily smaller, contradicting common assumptions about magnification bias in lensing scenarios. This finding could imply that the true size distribution of DSFGs is relatively narrow.
3. Dust Temperature and Optical Depth Correlation:
   • Using the lens models to infer the physical size of the DSFGs allowed the authors to explore the relationship between dust temperature and the wavelength where the optical depth equals unity. They found a correlation indicating that assuming a static value for this wavelength could lead to dust mass overestimations by as much as a factor of 2 for the hottest sources.
4. Infrared Compactness and the [CII] Deficit:
   • Investigating the [CII] line to far-infrared (FIR) luminosity ratio as a function of FIR luminosity surface density () extends findings from local samples to high-redshift. This research supports the notion that the compactness of the IR-emitting region is a crucial factor in determining the [CII] deficit.

Implications

These findings have significant implications for our understanding of DSFGs and their evolution. The detailed lens models highlight the importance of gravitational lensing in observing the early universe, providing a clearer view of galactic formation during cosmic history. The work emphasizes the need to carefully approach assumptions regarding dust optical depths and sizes to improve the accuracy of inferred galaxy properties, such as dust masses and star formation rates.

Future Directions

The paper suggests potential avenues for further exploration. Achieving more comprehensive datasets with high-resolution imaging could refine gravitational lens models, offering deeper insights into the morphology and star formation processes in DSFGs. Additionally, expanded analyses of FIR emission and associated cooling lines like [CII] could enhance our understanding of the interplay between galactic structure and interstellar medium conditions across cosmic epochs.

This paper contributes valuable methodologies and data, setting a foundation for subsequent investigation into the properties and processes governing high-redshift, star-forming galaxies. Through the combination of lensing analysis and submillimeter observations, researchers can continue to unravel the complexities of these celestial entities, shedding light on the broader mechanisms of galaxy evolution.