The VLA-COSMOS 3 GHz Large Project: Continuum data and source catalog release

Abstract: We present the VLA-COSMOS 3 GHz Large Project based on 384 hours of observations with the Karl G. Jansky Very Large Array (VLA) at 3 GHz (10 cm) toward the two square degree Cosmic Evolution Survey (COSMOS) field. The final mosaic reaches a median rms of 2.3 uJy/beam over the two square degrees at an angular resolution of 0.75". To fully account for the spectral shape and resolution variations across the broad (2 GHz) band, we image all data with a multiscale, multifrequency synthesis algorithm. We present a catalog of 10,830 radio sources down to 5 sigma, out of which 67 are combined from multiple components. Comparing the positions of our 3 GHz sources with those from the Very Long Baseline Array (VLBA)-COSMOS survey, we estimate that the astrometry is accurate to 0.01" at the bright end (signal-to-noise ratio, S/N_3GHz > 20). Survival analysis on our data combined with the VLA-COSMOS 1.4~GHz Joint Project catalog yields an expected median radio spectral index of alpha=-0.7. We compute completeness corrections via Monte Carlo simulations to derive the corrected 3 GHz source counts. Our counts are in agreement with previously derived 3 GHz counts based on single-pointing (0.087 square degrees) VLA data. In summary, the VLA-COSMOS 3 GHz Large Project simultaneously provides the largest and deepest radio continuum survey at high (0.75") angular resolution to date, bridging the gap between last-generation and next-generation surveys.

Overview of the VLA-COSMOS 3~GHz Large Project

The VLA-COSMOS 3~GHz Large Project represents a significant effort in radio astronomy, delivering continuum data and a source catalog for the renowned Cosmic Evolution Survey (COSMOS) field. Utilizing the Karl G. Jansky Very Large Array (VLA), this project involved an extensive 384 hours of observation across 3 GHz, covering an area of two square degrees. The study is paramount for understanding galaxy formation and evolution through comprehensive radio surveys.

Survey Design and Methodology

The VLA-COSMOS project employed the multiscale multifrequency synthesis technique to manage variations in spectral shape and resolution across a broad bandwidth, ensuring detailed, high-resolution imaging. The final mosaic achieves an angular resolution of $0.75\arcsec$, with a median $rms$ noise level of $\approx$2.3 $\mu$Jy~beam$^{-1}$, making it the most profound survey of its kind to date.

Noteworthy is the cataloging process, which identified \nsource radio sources down to 5$\sigma$. The project utilized both single-component and multicomponent analysis to refine source identification, delivering precision in astrometric accuracy to $0.01\arcsec$ for sources with a signal-to-noise ratio greater than 20.

Key Findings

The project calculated radio spectral indices using both the in-band method via the MSMF algorithm and cross-referencing with existing 1.4 GHz data. Survival analysis, integrating the VLA-COSMOS 1.4 GHz data, revealed a median radio spectral index of $\alpha=-0.7$, consistent with expectations for the star-forming and active galactic nucleus (AGN) populations observed.

Implications

The results have vital implications for understanding galaxy evolution, especially concerning star formation and AGN activity. The survey bridges a gap by providing unprecedented depth and resolution, lending insight into the radio emission properties of galaxies across cosmic time. It challenges existing models of radio source counts by offering empirical support for an evolving radio population down to faint flux levels.

Future Directions

The paper suggests further investigation into sub-mJy radio populations, which hold keys to understanding quenching phenomena in massive galaxies. By combining these radio data with COSMOS's rich multi-wavelength resources, researchers can explore diverse questions in galaxy evolution. The project sets a new standard for future radio surveys, offering a template for research methodologies in next-generation telescopes such as MeerKAT and SKA.

Conclusion

The VLA-COSMOS 3~GHz Large Project showcases the power of high-resolution radio surveys in cosmological studies, serving as a pivotal resource for researchers aiming to disentangle the complex processes governing galaxy formation and evolution. With its thorough data set, the project not only advances radio astronomy but also enriches our understanding of the interplay between star formation and AGN activity throughout cosmic history.