DESI Survey: A New Look at Quasars

Quasars are bright objects in the universe that help scientists learn more about how galaxies form and evolve. They act as guides, allowing researchers to trace the mass distribution in the cosmos over time. Since the first quasars were discovered, there has been a significant increase in their observations. The Sloan Digital Sky Survey (SDSS) has recorded over 750,000 quasars, contributing to the growing catalog of these fascinating objects.

Recently, a new survey called the Dark Energy Spectroscopic Instrument (DESI) began its work in May 2021. This survey is expected to surpass the SDSS by observing around 3 million quasars, greatly increasing the amount of data available for study. The DESI survey not only collects more data but also does it with better quality. This improvement is due to the larger telescope it uses, which is more efficient in collecting light compared to the previous surveys.

DESI selects quasars based on their brightness in three optical bands (g, r, z) and two infrared bands from other instruments. With this method, it aims to ensure high-quality data for its observations. Many quasars are known to have metal absorption systems, which occur when gas clouds absorb light from the quasars themselves. Researchers believe these systems provide valuable insight into the surrounding environment of galaxies.

#Absorption Systems

Absorption systems are important for understanding how galaxies interact with their environments. When light from a quasar passes through these gas clouds, some wavelengths are absorbed, revealing information about the composition and behavior of the gas. This process can inform scientists about the Circumgalactic Medium (CGM) around galaxies and the distribution of other galaxies in the universe.

Studies have shown that certain absorption systems, such as Magnesium II (Mg II), can reveal details about the physical states of these gas clouds, including their chemical makeup and flow dynamics. The presence of these systems aids in tracing the evolution of galaxies and their environments over time.

#The DESI Survey and Its Data

The DESI survey is set to gather data on a vast number of quasars, aiming to catalog around eight hundred thousand Mg II absorption systems. This large sample size is unprecedented and will enable researchers to delve deeper into the properties and kinematics of these systems. Moreover, the survey is expected to yield crucial data about the distribution of metals in the universe and their implications for galaxy formation and evolution.

By measuring how often absorbers are detected in quasar spectra, researchers can build a clearer picture of how galaxies interact with their surroundings and how they evolve over time. Previous smaller surveys have laid the groundwork, but the scale and quality of DESI's data are set to advance the field significantly.

#Techniques for Detection

To identify these absorption systems, scientists have developed an automated process that first fits lines to quasar spectra and then verifies these results using advanced statistical techniques. The initial stage involves searching for specific features in the spectra that indicate the presence of absorption lines.

Once a potential absorption system is detected, a more detailed analysis is performed to confirm its properties. This confirmation analyzes the data further to ensure that only high-quality results are included in the catalog.

The completeness and purity of the detection process are critical; researchers aim for a high standard to ensure their findings are reliable. Through careful analysis of the results, the researchers estimate that their detection method achieves an impressive purity of over 99% and completeness of about 82.6%.

#Findings and Statistics

As researchers sift through the data, they record findings related to the redshifts of the detected absorption systems. In their observations, they note a peak occurrence of absorbers between specific redshift ranges, indicating the distribution of these systems across the universe. This data helps draw connections between the quasars and their surrounding environments.

From their analysis, the researchers have compiled a catalog of over 16,000 absorption systems in unique quasar spectra. This suggests that roughly 20% of quasars contain identifiable Mg II absorbers, leading to an estimated 28.8% occurrence rate of absorbers in the overall quasar population.

This initial catalog reveals not just quantities but variations in properties such as equivalent widths, which provide further insight into the nature of the absorbers. The researchers anticipate that the full DESI survey will provide an even larger sample, enabling new avenues for exploration and inquiry.

#Importance of the Research

The study of Mg II absorbers opens doors to multiple areas of research in astronomy. Understanding their properties can help scientists learn about the chemical environments within galaxies and the complex interactions between galaxies and their surroundings.

Moreover, since many of the galaxies hosting these absorbers are faint and challenging to observe directly, studying the absorption systems provides a unique opportunity to gather valuable information without needing to detect the galaxies directly. This method of indirect observation is vital in astrophysics, where many celestial objects are obscured or too distant to be seen clearly.

#Visual Inspection and Quality Control

To ensure the reliability of their findings, researchers also conduct visual inspections of detected absorption systems. By randomly selecting a subset of these systems, they verify whether the absorption features truly correspond to the identified lines.

This process not only helps confirm the presence of absorption but also assesses the quality of the data. The researchers find that a significant majority of the visually inspected systems are indeed valid absorbers, bolstering their confidence in the catalog's reliability.

Following this visual inspection, the researchers make adjustments to improve the purity of the detected sample. They remove systems with positive amplitudes, which do not indicate valid absorption features. By applying strict quality cuts, they can ensure that the final catalog is as accurate as possible.

#Future Directions

The researchers plan to continue refining their detection methods to further enhance the accuracy of their findings in future catalog releases. This may involve adjusting signal-to-noise thresholds or improving detection algorithms to capture absorption systems that may currently be missed due to noise or other observational challenges.

Moreover, they are keen on studying additional metal lines associated with Mg II absorbers. By employing the knowledge gained from detecting Mg II absorption systems, they hope to identify other metal lines more effectively, enriching the catalog of data available for analysis.

#Catalog Release and Accessibility

The findings and results are organized into catalogs that researchers can access to further their studies. These catalogs include information about each absorption system, such as its unique identifier, position in the sky, and measured properties like the equivalent widths and redshift values.

The primary catalog contains all identified absorbers that appear physically plausible, while a secondary catalog includes systems that demonstrate physically impossible characteristics. This separation aids in diagnosing the accuracy of quasar redshifts and improves the understanding of the surrounding environments.

#Conclusion

The ongoing work with the DESI survey and the detection of Mg II absorption systems mark a significant milestone in astronomy. As researchers continue to analyze the data and refine their methods, the insights gained will contribute to advancing the understanding of galaxies, the distribution of matter in the universe, and the complex interactions that shape cosmic evolution.

By unveiling these absorption systems, scientists hope to address longstanding questions about how galaxies develop and the role of their environments in these processes. The data from the DESI survey is expected to provide an unprecedented view into the universe, offering a wealth of information for current and future research in astrophysics and cosmology.

The commitment to quality and accuracy in this research underscores its importance in understanding the cosmos. The extensive catalogs generated through this work not only represent a triumph in data collection but also pave the way for groundbreaking discoveries in the field of astronomy.