ABSTRACT
This paper reports Giant Metrewave Radio Telescope (GMRT) observations of the binary system HD 41004 that are among the deepest images ever obtained at 150 and 400 MHz in the search for ...radio emission from exoplanets. The HD 41004 binary system consists of a K1 V primary star and an M2 V secondary; both stars are host to a massive planet or brown dwarf. Analogous to planets in our Solar system that emit at radio wavelengths due to their strong magnetic fields, one or both of the planet or brown dwarf in the HD 41004 binary system are also thought to be sources of radio emission. Various models predict HD 41004Bb to have one of the largest expected flux densities at 150 MHz. The observations at 150 MHz cover almost the entire orbital period of HD 41004Bb, and about $20{{\ \rm per\ cent}}$ of the orbit is covered at 400 MHz. We do not detect radio emission, setting 3σ limits of 1.8 mJy at 150 MHz and 0.12 mJy at 400 MHz. We also discuss some of the possible reasons why no radio emission was detected from the HD 41004 binary system.
ABSTRACT
A multiwavelength analysis of star formation associated with the extended green object, G19.88-0.53 is presented in this paper. With multiple detected radio and millimetre components, ...G19.88-0.53 unveils as harbouring a protocluster rather than a single massive young stellar object. We detect an ionized thermal jet using the upgraded Giant Meterwave Radio Telescope, India, which is found to be associated with a massive, dense and hot ALMA 2.7 mm core driving a bipolar CO outflow. Near-infrared spectroscopy with UKIRT–UIST shows the presence of multiple shock-excited H2 lines concurrent with the nature of this region. Detailed investigation of the gas kinematics using ALMA data reveals G19.88-0.53 as an active protocluster with high-mass star-forming components spanning a wide evolutionary spectrum from hot cores in accretion phase to cores driving multiple outflows to possible UCH ii regions.
Abstract
We report the discovery of one of the largest and most distant giant radio galaxy (GRG) in the Lynx field, which was discovered using deep Giant Metre-wave Radio Telescope (GMRT) 150 MHz ...observations. The core is detected at 150 MHz and also in the VLA FIRST survey. Spectroscopic observations carried out using the IUCAA Girawali Observatory(IGO) provided a redshift value of 0.57. This redshift was later confirmed with data from the Sloan Digital Sky Survey (Data Release 12). The angular size of the GRG is 5.5 arcmin and at the redshift of 0.57, its linear size is 2.2 Mpc. At this high redshift, only a few radio sources are known to have such large linear size. In order to estimate the spectral index of the bridge emission as well as the spectral age of the source, we observed this source at the L band, 610 and 325-MHz bands with the GMRT. We present the spectral ageing analysis of the source that puts an upper limit of 20 Myr on the spectral age. The better resolution maps presented here as opposed to the original 150-MHz map shows evidence for a second episode of emission. We also find that the core is detected at all four frequencies with a spectral index of 0.85, which is steeper than normal, hence we speculate that the core may be a compact steep spectrum source, which makes this GRG a candidate triple–double radio galaxy.
Abstract Hub–filament systems (HFSs) being the potential sites of formation of star clusters and high-mass stars, provide a testbed for the current theories that attempt to explain star formation ...globally. It is thus important to study a large number of HFSs using both intensity and velocity information to constrain these objects better observationally. Here, we present a study of the HFS associated with G6.55-0.1 using newly obtained observations of the radio continuum and the J = 2–1 transition of CO, 13 CO, and C 18 O. The radio continuum maps show multiple peaks that coincide with far-infrared dust continuum peaks, indicating the presence of more than one young massive star in the hub of the HFS. We used the velocity information from the C 18 O(2–1) map to (a) show that the source G6.55-0.1 is not physically associated with the supernova remnant W28 and (b) disentangle and identify the velocity components genuinely associated with G6.55-0.1. Among the velocity-coherent structures identified in the region, we conclude that only the two filaments at 13.8 and 17.3 km s −1 contribute a total mass accretion rate of 3000 M ⊙ Myr −1 to the hub. Both the filaments also show a V-shaped structure, characteristic of gravitational collapse, in their velocity profile at the location of the hub. The estimated mass per unit length of the segments of the filaments is smaller than the critical line masses derived from virial equilibrium considerations. This suggests that the filaments are not gravitationally collapsing as a whole, although their inner parts clearly show evidence of collapse in the form of young star-forming cores. We further conclude that the observed velocity gradients are consistent with the gravitational collapse of the main source in the region as estimated from its mass and size.
A wide-area GMRT 610-MHz survey of ELAIS N1 field Ishwara-Chandra, C H; Taylor, A R; Green, D A ...
Monthly notices of the Royal Astronomical Society,
10/2020, Letnik:
497, Številka:
4
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
In this paper, we present a wide-area 610-MHz survey of the ELAIS N1 field with the GMRT, covering an area of 12.8 deg2 at a resolution of 6 arcsec and with an rms noise of ∼40 $\mu$Jy ...beam−1. This is equivalent to ∼20 $\mu$Jy beam−1 rms noise at 1.4 GHz for a spectral index of −0.75. The primary goal of the survey was to study the polarized sky at sub-mJy flux densities at < GHz frequencies, alongwith a range of other science goals such as investigations into the nature of the low-frequency $\mu$Jy source populations and alignments of radio jets. A total of 6400 sources were found in this region, the vast majority of them compact. The sample jointly detected by GMRT at 610 MHz and by VLA FIRST at 1.4 GHz has a median spectral index of −0.85 ± 0.05 and a median 610-MHz flux density of 4.5 mJy. This region has a wealth of ancillary data, which is useful to characterize the detected sources. The multiwavelength crossmatching resulted optical/IR counterparts to ∼90 per cent of the radio sources, with a significant fraction having at least photometric redshift. Due to the improved sensitivity of this survey over preceding ones, we have discovered six giant radio sources (GRSs), with three of them at z ∼ 1 or higher. This implies that the population of GRS may be more abundant and common than known to date and if true, this has implications for the luminosity function and the evolution of radio sources. We have also identified several candidate-extended relic sources.
ABSTRACT
In this work, we present the results from a study using the Giant Meterwave Radio Telescope (GMRT) to search for radio emission from planets around three evolved stars namely α Tau, β UMi, ...and β Gem. Both α Tau and β UMi host massive ∼ 6 MJ mass planets at about ∼1.4 au from the central star, while β Gem is host to a 2.9 MJ mass planet at 1.7 au from the host star. We observe α Tau and β UMi at two upgraded GMRT bands: band 3 (250–500 MHz) and band 4 (550–900 MHz). We also analysed the archival observations from β Gem at 150 MHz from GMRT. We did not detect any radio signals from these systems. At 400 MHz, the 3σ upper limit is 87 μJy beam−1 for α Tau b and 77.4 μJy beam−1 for β UMi b. From our observations at 650 MHz, we place a 3σ upper limit of 28.2 μJy beam−1 for α Tau b and 33.6 μJy beam−1 for β UMi b. For β Gem b, at 150 MHz, we place an upper limit of 2.5 mJy. At 400 and 650 MHz, our observations are the deepest radio images for any exoplanetary system.
Abstract
The remnant phase of a radio galaxy is characterized by the cessation of active galactic nuclei activity, resulting in the jets ceasing to feed plasma to the radio lobes. In this paper, we ...present a search for and the characterization of remnant candidates in a 12.5 deg
2
area of the XMM-Newton Large-Scale Structure field, using deep radio observations at 325 MHz from the Giant Meterwave Radio Telescope, at 150 MHz from the LOw Frequency ARray, at 1.4 GHz from the Jansky Very Large Array (VLA), and at 3 GHz from the VLA Sky Survey. By using both morphological criteria, i.e., undetected radio core as well as spectral criteria, i.e., high spectral curvature and ultra-steep spectrum, we identify 21 remnant candidates that are found to reside mostly in non-cluster environments, and exhibit diverse properties in terms of morphology, spectral index (
α
150
1400
in the range of −1.71 to −0.75 with a median of −1.10), and linear radio size (ranging from 242 kpc–1.3 Mpc with a median of 469 kpc). Our study attempts to identify remnant candidates down to the flux density limit of 6.0 mJy at 325 MHz, and yields an upper limit on the remnant fraction (
f
rem
) to be around 5%. The observed
f
rem
seems consistent with the predictions of an evolutionary model assuming power-law distributions of the duration of the active phase and jet kinetic power with an index of −0.8 to −1.2.
Abstract
A multiwavelength investigation of the southern infrared dust bubble CS51 is presented in this paper. We probe the associated ionized, cold dust, molecular and stellar components. Radio ...continuum emission mapped at 610 and 1300 MHz, using the Giant Metrewave Radio Telescope, India, reveals the presence of three compact emission components (A, B, and C) apart from large-scale diffuse emission within the bubble interior. Radio spectral index map shows the co-existence of thermal and non-thermal emission components. Modified blackbody fits to the thermal dust emission using Herschel Photodetector Array Camera and Spectrometer and Spectral and Photometric Imaging Receiver data is performed to generate dust temperature and column density maps. We identify five dust clumps associated with CS51 with masses and radius in the range 810–4600 M⊙ and 1.0–1.9 pc, respectively. We further construct the column density probability distribution functions of the surrounding cold dust which display the impact of ionization feedback from high-mass stars. The estimated dynamical and fragmentation time-scales indicate the possibility of collect and collapse mechanism in play at the bubble border. Molecular line emission from the Millimeter Astronomy Legacy Team 90 GHz survey is used to understand the nature of two clumps which show signatures of expansion of CS51.
It has been known for nearly three decades that high-redshift radio galaxies exhibit steep radio spectra, and hence ultrasteep spectrum radio sources provide candidates for high-redshift radio ...galaxies. Nearly all radio galaxies with z > 3 have been found using this redshift–spectral index correlation. We have started a programme with the Giant Metrewave Radio Telescope (GMRT) to exploit this correlation at flux density levels about 10 to 100 times deeper than the known high-redshift radio galaxies which were identified primarily using the already available radio catalogues. In our programme, we have obtained deep, high-resolution radio observations at 150 MHz with GMRT for several ‘deep’ fields which are well studied at higher radio frequencies and in other bands of the electromagnetic spectrum, with an aim to detect candidate high-redshift radio galaxies. In this paper we present results from the deep 150-MHz observations of the LBDS-Lynx field, which has been already imaged at 327, 610 and 1412 MHz with the Westerbork Synthesis Radio Telescope and at 1400 and 4860 MHz with the Very Large Array. The 150-MHz image made with GMRT has an rms noise of ∼0.7 mJy beam−1 and a resolution of ∼19 × 15 arcsec2. It is the deepest low-frequency image of the LBDS-Lynx field. The source catalogue of this field at 150 MHz has about 765 sources down to ∼20 per cent of the primary beam response, covering an area of about 15 deg2. Spectral index was estimated by cross-correlating each source detected at 150 MHz with the available observations at 327, 610, 1400 and 4860 MHz and also using available radio surveys such as the Westerbork Northern Sky Survey at 327 MHz and the NRAO VLA Sky Survey and Faint Images of the Radio Sky at Twenty-cm at 1400 MHz. We find about 150 radio sources with spectra steeper than 1. About two-third of these are not detected in the Sloan Digital Sky Survey, hence are strong candidate high-redshift radio galaxies, which need to be further explored with deep infrared imaging and spectroscopy to estimate the redshift.
The Giant Metrewave Radio Telescope (GMRT) is today a frontline international facility for low-frequency radio astronomy, that has produced several exciting and important new results in the 15 years ...that it has been operational. To keep the GMRT competitive in the global arena in the future, a major upgrade of the observatory is nearing completion that will increase its sensitivity by up to three times and make it a more powerful and versatile facility. We describe the main goals of this upgrade, highlight the technical features and challenges, outline the science potential and update the current status of this venture.
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