Detection of a Supervoid Aligned with the Cold Spot of the Cosmic Microwave Background (1405.1566v2)

Abstract: We use the WISE-2MASS infrared galaxy catalog matched with Pan-STARRS1 (PS1) galaxies to search for a supervoid in the direction of the Cosmic Microwave Background Cold Spot. Our imaging catalog has median redshift $z\simeq 0.14$, and we obtain photometric redshifts from PS1 optical colours to create a tomographic map of the galaxy distribution. The radial profile centred on the Cold Spot shows a large low density region, extending over 10's of degrees. Motivated by previous Cosmic Microwave Background results, we test for underdensities within two angular radii, $5^\circ$, and $15^\circ$. The counts in photometric redshift bins show significantly low densities at high detection significance, $\gtrsim 5 \sigma$ and $\gtrsim 6 \sigma$, respectively, for the two fiducial radii. The line-of-sight position of the deepest region of the void is $z\simeq 0.15-0.25$. Our data, combined with an earlier measurement by Granett et al. 2010, are consistent with a large $R_{\rm void}=(220 \pm 50) h^{-1}Mpc $ supervoid with $\delta_{m} \simeq -0.14 \pm 0.04$ centered at $z=0.22\pm0.03$. Such a supervoid, constituting at least a $\simeq 3.3\sigma$ fluctuation in a Gaussian distribution of the $\Lambda CDM$ model, is a plausible cause for the Cold Spot.

• The paper identifies a significant 220 ± 50 h⁻¹ Mpc supervoid aligned with the CMB Cold Spot using combined infrared and optical data.
• It utilizes tomographic mapping and photometric redshift techniques to analyze galaxy distributions within 5° and 15° apertures, achieving up to 6σ detection significance.
• The findings imply that large-scale cosmic structures may impact CMB temperature anomalies, challenging aspects of the standard ΛCDM cosmological model.

Detection of a Supervoid Aligned with the Cold Spot of the Cosmic Microwave Background

The paper investigates a notable anomaly within the Cosmic Microwave Background (CMB), termed the Cold Spot (CS), by exploring its potential correlation with large-scale cosmic structures, specifically a supervoid. The authors employ the Wide-field Infrared Survey Explorer (WISE)-2MASS-PS1 dataset, leveraging infrared galaxy catalogs matched with Pan-STARRS1 (PS1) optical data, to assess the existence and characteristics of a supervoid that might provide a natural explanation for the low-temperature anomaly observed in CMB maps.

Methodology and Data

To probe the large-scale structure in the direction of the Cold Spot, the paper utilizes an infrared galaxy catalog primarily derived from WISE-2MASS, cross-referenced with PS1 optical colors, to construct a tomographic map of galaxy distributions. The galaxy sample used has a median redshift of approximately 0.14, facilitating the examination of cosmic voids in this redshift range. The research employs photometric redshift techniques to achieve a depth dimension for the wide-field imaging data. The authors use radial density profiles to analyze the presence and scale of cosmic voids centered on the Cold Spot, specifically examining angular radii of 5° and 15°.

Results

The research identifies a significant underdensity, interpreted as an extensive supervoid, aligning with the Cold Spot. The identified supervoid has an approximate radius of $R_{\rm void} = 220 \pm 50 h^{-1}$ Mpc with a mean underdensity $\delta_{m} \simeq -0.14$. Significantly, this void extends over tens of degrees in the sky and peaks in its density deficit at redshifts between $z \simeq 0.15$ and $z \simeq 0.25$. The detection is statistically robust, with significant underdensity signals obtained for counts within the explored angular apertures, translating to a detection significance of up to $6\sigma$.

Implications and Theoretical Considerations

The identification of a supervoid directly aligned with the Cold Spot presents evidence supporting the hypothesis that large-scale structural inhomogeneities in the universe may influence the observed anisotropies in the CMB via the integrated Sachs-Wolfe effect. This interaction supports the conclusion that fluctuations in the matter distribution in the early universe could have significant imprints on the CMB temperature maps.

In a ΛCDM cosmology framework, the inferred characteristics of this supervoid indicate a rare $3.3\sigma$ anomaly, suggesting that the large-scale cosmic structures identified may challenge standard cosmological models. Such extremes in large-scale matter distributions could necessitate refinements in our understanding of cosmic evolution and structure growth.

Future Directions

The paper concludes with a discussion on the significance of revealing connections between CMB anomalies and cosmic structures for advancing cosmological theories. Expanding the photometric redshift datasets and improving the precision of redshift distributions will be critical for exploring similar anomalies. These efforts would offer deeper insights into the full implications of voids in the context of cosmic history and potential interactions with other CMB anomalies. Moreover, it suggests pursuing larger-scale optical surveys, such as the extended Pan-STARRS data or the Dark Energy Survey, to enhance the search for matching structures in the universe.

Acknowledgments

The authors acknowledge the contributions from various collaborations and institutes, leveraging astronomical data from projects such as Pan-STARRS and WISE, supported through international partnerships and funding from multiple academic and research institutions.