[Paper Review] Radio spectra of the WMAP catalog sources

С. А. Трушкин|arXiv (Cornell University)|Jul 10, 2003

Radio Astronomy Observations and Technology1 references3 citations

TL;DR

This study presents the most comprehensive radio spectral energy distributions for 208 extragalactic sources from the WMAP all-sky survey at 23–94 GHz, using multi-frequency flux density measurements from RATAN-600 and cross-identification with over 200,000 historical data points from 10 MHz to 245 GHz. The key finding is that 97.5% of WMAP sources are identified as known AGNs, quasars, or galaxies, with stable spectral shapes over decades and no significant systematic flux offset between WMAP and prior measurements for low-variability sources.

ABSTRACT

Compiled radio spectra are presented for 208 extragalactic sources from the catalog created from the WMAP satellite all-sky survey data in a range of 23-94 GHz taken during the first year of its operation in orbit. 205 out of 208 WMAP sources are reliably identified with radio sources from other catalogs, including also four out of five sources unidentified by the WMAP survey authors. We have found 203 WMAP sources to have optical identification: 141 quasars, 29 galaxies, 19 active galactic nuclei, 19 BL Lac-type objects and one planetary nebula, IC418. Simultaneous measurements of flux densities for 26 sources at five frequencies, 2.3, 3.9, 7.7, 11.2 and 21.7 GHz, were made with the radio telescope RATAN-600 in 2003 March. 25 sources were detected at all the frequencies, and only one, WMAP0517-0546, unidentified in other catalogs was not detected in our observations and is likely to be spurious. Using the database CATS we found a large number of identifications in different radio catalogs and in several long-term monitoring programs (GBI, UMRAO, SEST, IRAM, and others). The total number of flux density measurements that we collected in the frequency range from 10 MHz to 245 GHz for the identified WMAP sources is over 206,000, varying from 10-20 points for some southern sources to a few thousand points for sources from long-term monitorings. A considerable number of WMAP sources are variable on time scales from hours to dozens of years, nevertheless, the obtained integral spectra, including measurements in different years, may be of particular interest because these bright sources have been studied for more than forty years. The general character of the spectrum (power, flat, with a turnovers at low or high frequencies) of the WMAP sources remains unchanged.

Motivation & Objective

• . The paper aims to identify the nature of extragalactic radio sources detected in the WMAP all-sky survey at high frequencies (23–94 GHz).
• It seeks to determine whether these sources are part of known populations or represent a new class of radio emitters.
• The study investigates the long-term radio spectral behavior of these sources using multi-epoch flux measurements.
• It aims to validate the reliability of WMAP flux measurements by comparing them with historical data from long-term monitoring programs.
• The research further explores the morphological and structural properties of extended WMAP sources using NVSS, SUMSS, and FIRST radio maps.

Proposed method

• . Cross-identification of WMAP sources with radio catalogs (GB6, PMN, NVSS, FIRST, 3C/3CR, etc.) using coordinate cross-matching within 11′ windows.
• Simultaneous flux density measurements at 2.3, 3.9, 7.7, 11.2, and 21.7 GHz were conducted with the RATAN-600 radio telescope for 26 sources in March 2003.
• The CATS database was used to compile a total of 206,000 flux density measurements across frequencies from 10 MHz to 245 GHz for identified sources.
• Radio spectral energy distributions were constructed by combining WMAP data with historical data from long-term monitoring programs (GBI, UMRAO, SEST, IRAM, etc.).
• Radio maps at 1.4 GHz (NVSS) and 843 MHz (SUMSS/FIRST) were used to analyze source structure and extended emission.
• Statistical analysis of spectral indices and variability was performed over time baselines of up to 40 years, with a focus on sources showing intra-day variability (IDV).

Experimental results

Research questions

• RQ1 . Are the WMAP catalog sources consistent with known populations of extragalactic radio sources, or do they represent a new class of objects?
• RQ2 . What is the long-term spectral behavior of WMAP sources across a 40-year baseline, and how stable are their spectral indices?
• RQ3 . Is there a systematic offset between WMAP flux measurements and earlier measurements at similar frequencies for low-variability sources?
• RQ4 . How many of the WMAP sources are variable on timescales from hours to decades, and what fraction are compact IDV sources?
• RQ5 . What is the morphological structure of extended WMAP sources, and how do they compare to known extended radio galaxies?

Key findings

• . 205 out of 208 WMAP sources were reliably identified with known radio sources from other catalogs, including four of five previously unidentified sources.
• . 203 WMAP sources (97.5%) have optical identifications: 141 quasars, 29 galaxies, 19 active galactic nuclei, 19 BL Lac objects, and one planetary nebula (IC 418).
• . The source WMAP 0517–0546 was not detected at any frequency in the RATAN-600 observations and is likely spurious.
• . A total of 206,000 flux density measurements were compiled across 10 MHz to 245 GHz, enabling the most complete spectral energy distributions for these sources.
• . The spectral shape (power-law, flat, or turnover) remained stable over decades for most sources, with no significant spectral evolution observed.
• . No significant systematic differences in flux density were found between WMAP measurements and earlier observations at similar frequencies for sources with low variability indices.