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T-Ramisu: the Two-Meter Radio Mini Survey I. the Bootes Field

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T-Ramisu: the Two-Meter Radio Mini Survey I. the Bootes Field Astronomy & Astrophysics manuscript no. bootes˙wide˙field˙notable c ESO 2018 October 31, 2018 T-RaMiSu: The Two-meter Radio Mini Survey I. The Bootes¨ Field W. L. Williams1;2, H. T. Intema3;?, and H. J. A. Rottgering¨ 1 1 Leiden Observatory, Leiden University, P.O.Box 9513, NL-2300 RA, Leiden, The Netherlands e-mail: [email protected] 2 Netherlands Institute for Radio AStronomy (ASTRON), PO Box 2, 7990AA Dwingeloo, The Netherlands 3 National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475, USA Received / Accepted ABSTRACT We present wide area, deep, high-resolution 153 MHz GMRT observations of the NOAO Bootes¨ field, adding to the extensive, multi- wavelength data of this region. The observations, data reduction, and catalogue construction and description are described here. The seven pointings produced a final mosaic covering 30 square degrees with a resolution of 2500. The rms noise is 2 mJy beam−1 in the centre of the image, rising to 4−5 mJy beam−1 on the edges, with an average of 3 mJy beam−1. Seventy-five per cent of the area has an rms < 4 mJy beam−1. The extracted source catalogue contains 1289 sources detected at 5σ, of which 453 are resolved. We estimate the catalogue to be 92 per cent reliable and 95 per cent complete at an integrated flux density limit of 14 mJy. The flux densities and astrometry have been corrected for systematic errors. We calculate the differential source counts which are in good agreement with those in the literature and provide an important step forward in quantifying the source counts at these low frequencies and low flux densities. The GMRT 153 MHz sources have been matched to the 1:4 GHz NVSS and 327 MHz WENSS catalogues and spectral indices were derived. Key words. Techniques:interferometric – Surveys – Galaxies:active – Radio continuum:galaxies 1. Introduction tion of supernovae, and the acceleration, diffusion and decay of the relativistic electrons can reproduce the correlation. The low- Deep low-frequency radio surveys provide unique data which frequency spectral shape of galaxies reveals information about will help resolve many questions related to the formation the amount of free-free absorption and relating this to the dust and evolution of massive galaxies, quasars and galaxy clus- content, size, mass, total amount of star formation and environ- ters. Until now, such surveys have largely been limited by the ment of the galaxies will further constrain the radio-IR models. corrupting influence of the ionosphere on the visibility data, To date, however, few galaxies have been well studied at low but new techniques allow for the correction for these effects frequencies and those that have, show a diverse range of spectral (e.g. Cotton et al. 2004; Intema et al. 2009). Recently deep shapes (e.g. Clemens et al. 2010). (0:7 − 2 mJy beam−1) images have been made, in particu- lar with the Giant Metrewave Radio Telescope (GMRT, e.g. Faint peaked spectrum sources – Young radio-loud AGN Ananthakrishnan 2005) at 153 MHz (e.g. Ishwara-Chandra & are ideal objects to study the onset and early evolution of Marathe 2007; Sirothia et al. 2009; Ishwara-Chandra et al. classical double radio sources. They usually have synchrotron 2010). These observations can be used to study: self-absorbed spectra and compact radio morphologies. Relative Luminous radio sources at z > 4 – High redshift radio galax- number statistics have indicated that these radio sources must ies (HzRGs, e.g. Miley & De Breuck 2008) provide a unique be significantly more powerful at young ages, which may be way to study the evolution of the most massive galaxies in the preceded by a period of luminosity increase (e.g. Snellen et al. Universe. One of the most efficient ways of identifying these 2003). Multi-epoch VLBI observations of individual Gigahertz sources is to search for ultra-steep spectrum (USS) radio sources Peaked Spectrum and Compact Symmetric Objects indicate dy- α namical ages in the range of a few hundred to a few thousand arXiv:1211.1189v1 [astro-ph.CO] 6 Nov 2012 with α . −1, S ν / ν (Rottgering¨ et al. 1997; De Breuck et al. 2002). Low frequency observations provide an easy way of iden- years (e.g Polatidis & Conway 2003). Since the peak of these tifying USS sources and extending these observations to lower sources shifts to lower observed frequencies at higher redshift, flux density limits increases the distance to which these HzRGs low frequency observations, combined with multi-wavelength can be identified. Surveying larger areas increases the probabil- data, can identify these faint peakers and establish whether they ity of locating these rare sources. are less luminous or at very high redshift and have different host Distant starburst galaxies – The local radio-IR correlation properties (masses, starformation rates). for star forming galaxies is very tight, and seems to hold at high The accretion modes of radio sources – Radio galaxies and redshift (Kovacs´ et al. 2006). However, the physical processes radio loud quasars have been studied extensively in order to involved are poorly understood and only models that carefully reveal the details of the relationship between Active Galactic fine-tune the time scales for the heating of the dust, the forma- Nuclei (AGN) and their host galaxies, in particular how their interaction affects their evolution. The expanding jets of radio- ? Jansky Fellow of the National Radio Astronomy Observatory loud AGN provide a mechanism for the transfer of energy to 1 W. L. Williams et al.: T-RaMiSu: The Two-meter Radio Mini Survey. I. the intracluster medium and prevent the catastrophic cooling and Table 1: GMRT observation parameters for the Bootes¨ field. formation of too-massive elliptical galaxies (Fabian et al. 2006; Best et al. 2006, 2007; Croton et al. 2006; Bower et al. 2006), but Parameter Central Flanking the accretion and feedback processes and how they evolve over Observation Dates 3 June 2005 3-6 June 2006 cosmic time are not fully understood. It is known that the frac- Pointings Bootes¨ Bootes¨ A-F Primary Calibrator 3C 48 3C 48 tion of massive galaxies which are radio-loud at z ∼ 0:5 is about Total Time on Calibrator 20 min 51 min the same as observed locally (z ∼ 0:1, Best et al. 2005), while Secondary Calibrator 3C 286 3C 286 10:5 for less massive galaxies (< 10 M ), it is an order of magni- Total Time on Calibrator 9 × 10 min 10 × 4:5 min (per day) tude larger. Studies of these AGN show two different types: a Cadence 50 min 30 min “hot” mode where radiatively inefficient accretion occurs from Total Time on Target 359 min 205 min (per pointing) hot halo gas onto massive galaxies, and a “cold” mode where Integration time 16:9 s cold gas from major mergers drives high accretion rates. The Polarisations RR,LL strong evolution in the radio luminosity function is thus a re- Channels 128 sult of less massive galaxies experiencing more mergers and be- Channel Width 62:5 kHz ing more active at high z. A full understanding of the differ- Total Bandwidth 8:0 MHz Central Frequency 153 MHz ent AGN populations, their distribution in luminosity and host galaxy properties, and particularly their cosmic evolution, is im- portant for AGN and galaxy evolutionary models. Differences in their host galaxy populations will provide insight into the trig- Table 2: Pointing centres of the Bootes¨ central and flanking gering mechanisms for radio activity as well as the effect of radio fields. feedback. Field RA DEC (J2000) (J2000) In this paper we present wide, deep, high-resolution observa- Bootes¨ 14:32:05.75 +34:16:47.5 tions of the NOAO Bootes¨ extra-galactic field at 153 MHz taken Bootes¨ A 14:32:05.75 +36:06:47.5 with the GMRT. An initial, very deep, ∼ 1 mJy beam−1 rms, Bootes¨ B 14:24:19.53 +35:10:52.5 153 MHz GMRT map of this field was presented by Intema et al. Bootes¨ C 14:24:29.58 +33:20:54.5 (2011). Here we present additional pointings around this map ef- Bootes¨ D 14:32:05.75 +32:26:47.5 fectively tripling the size of the surveyed area at a slightly higher Bootes¨ E 14:39:41.92 +33:20:54.5 noise level. The Bootes¨ field is part of the NOAO Deep Wide Bootes¨ F 14:39:51.97 +35:10:52.5 Field Survey (NDWFS; Jannuzi et al. 1999) and covers ∼9 deg2 in the optical and near infra-red BW , R, I and K bands. There is a wealth of additional complementary data available for this field, including X-ray (Murray et al. 2005; Kenter et al. 2005), UV (GALEX; Martin et al. 2003), and mid infrared (Eisenhardt et al. 2004; Martin et al. 2003). The region has also been surveyed at 2. Observations and Data Reduction radio wavelengths with the WSRT at 1.4 GHz (de Vries et al. 2002), the VLA at 1.4 GHz (Higdon et al. 2005) and 325 MHz 2.1. Observations (Croft et al. 2008). Recently, the AGN and Galaxy Evolution The central Bootes¨ field was previously observed with the Survey (AGES) has provided redshifts for 23 745 galaxies and GMRT from 3 − 4 June 2005 (Intema et al. 2011). We use the : 2 ¨ AGN across 7 7 deg of the Bootes field (Kochanek et al. 2012). data from a single day of this observing run, combined with new This unique rich multiwavelength dataset, combined with the observations of six flanking fields taken during 3 − 6 June 2006 new low frequency radio data presented here, will be valuable in with the GMRT at 153 MHz.
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