UvA-DARE (Digital Academic Repository) LOFAR Low-band Antenna Observations of the 3C 295 and Boötes Fields: Source Counts and Ultra-steep Spectrum Sources-猫眼课题宝

DOI：

发表时间：

2014

期刊：

The Astrophysical Journal Letters

影响因子：

通讯作者：

中科院分区：

其他

文献类型：

作者：

R. V. van Weeren;W. Williams;C. Tasse;H. Röttgering;D. Rafferty;S. van der Tol;G. Heald;G. White;A. Shulevski;P. Best;H. Intema;S. Bhatnagar;W. Reich;M. Steinmetz;Sanne G M van Velzen;T. Ensslin;I. Prandoni;F. de Gasperin;M. Jamrozy;G. Brunetti;M. Jarvis;J. McKean;M. Wise;C. Ferrari;J. Harwood;J. Oonk;M. Hoeft;M. Kunert‐Bajraszewska;C. Horellou;O. Wucknitz;A. Bonafede;N. Mohan;A. Scaife;H. Klöckner;I. van Bemmel;A. Merloni;K. Chyży;D. Engels;H. Falcke;M. Pandey-Pommier;A. Alexov;J. Anderson;I. Avruch;R. Beck;M. Bell;M. Bentum;G. Bernardi;F. Breitling;J. Broderick;W. Brouw;M. Brüggen;H. Butcher;B. Ciardi;E. de Geus;M. DE VOS;A. Deller;S. Duscha;J. Eislöffel;R. Fallows;W. Frieswijk;M. Garrett;J. Grießmeier;A. Gunst;J. Hamaker;T. Hassall;J. Hörandel;A. J. van der Horst;M. Iacobelli;N. Jackson;E. Juette;V. Kondratiev;M. Kuniyoshi;P. Maat;G. Mann;D. McKay-Bukowski;M. Mevius;R. Morganti;H. Munk;A. Offringa;E. Orrú;H. Paas;V. Pandey;G. Pietka;R. Pizzo;A. Polatidis;A. Renting;A. Rowlinson;D. Schwarz;M. Serylak;J. Sluman;O. Smirnov;B. Stappers;A. Stewart;J. Swinbank;M. Tagger;Y. Tang;S. Thoudam;C. Toribio;R. Vermeulen;C. Vocks;P. Zarka

我们提出了低频阵列（LOFAR）低波段观测的牧夫座和3C 295领域。我们在34、46和62 MHz下拍摄的图像达到了12、8和5 mJy beam−1的噪声水平，使其成为该频率范围内获得的最深图像。总的来说，我们在这些图像中的每一个中检测到300到400个源，覆盖17-52 deg 2的区域。从观测结果中，我们得到了欧几里得归一化差分源计数。62 MHz源计数与之前的GMRT 153 MHz和超大阵列74 MHz差分源计数一致，频谱指数为−0.7。我们发现，需要-0.5的频谱指数缩放来匹配LOFAR 34 MHz源计数。这一结果也与来自38 MHz 8 C调查的源计数一致，表明射电源的平均谱指数向较低频率方向移动。我们还发现证据光谱平坦化使用的个人流量测量的源之间的34和1400兆赫，并通过计算平均超过源人口的光谱指数。为了选择可能与大质量高红移射电星系相关的超陡频谱（α <-1.1）射电源，我们计算了牧夫座场中62 MHz、153 MHz和1.4 GHz之间的频谱指数。我们将这些射电源与光学和红外目录进行交叉相关，并拟合光谱能量分布以获得光度红移。我们发现，这些超陡谱源大多位于0.7 z 2.5范围内。

We present Low Frequency Array (LOFAR) Low Band observations of the Boötes and 3C 295 fields. Our images made at 34, 46, and 62 MHz reach noise levels of 12, 8, and 5 mJy beam−1, making them the deepest images ever obtained in this frequency range. In total, we detect between 300 and 400 sources in each of these images, covering an area of 17–52 deg2. From the observations, we derive Euclidean-normalized differential source counts. The 62 MHz source counts agree with previous GMRT 153 MHz and Very Large Array 74 MHz differential source counts, scaling with a spectral index of −0.7. We find that a spectral index scaling of −0.5 is required to match up the LOFAR 34 MHz source counts. This result is also in agreement with source counts from the 38 MHz 8C survey, indicating that the average spectral index of radio sources flattens toward lower frequencies. We also find evidence for spectral flattening using the individual flux measurements of sources between 34 and 1400 MHz and by calculating the spectral index averaged over the source population. To select ultra-steep spectrum (α < −1.1) radio sources that could be associated with massive high-redshift radio galaxies, we compute spectral indices between 62 MHz, 153 MHz, and 1.4 GHz for sources in the Boötes field. We cross-correlate these radio sources with optical and infrared catalogs and fit the spectral energy distribution to obtain photometric redshifts. We find that most of these ultra-steep spectrum sources are located in the 0.7 z 2.5 range.

UvA-DARE (Digital Academic Repository) LOFAR Low-band Antenna Observations of the 3C 295 and Boötes Fields: Source Counts and Ultra-steep Spectrum Sources

文献摘要

被引文献

相似文献