We report the discovery of a double-double radio galaxy (DDRG), J0041+3224, with the Giant Metrewave Radio Telescope (GMRT) and subsequent high-frequency observations with the Very Large Array (VLA). The inner and outer doubles are aligned within about 4 deg and are reasonably collinear with the parent optical galaxy. The outer double has a steeper radio spectrum compared with the inner one. Using an estimated redshift of 0.45, the projected linear sizes of the outer and inner doubles are 969 and 171 kpc respectively. The time scale of interruption of jet activity has been estimated to be about 20 Myr, similar to other known DDRGs. We have compiled a sample of known DDRGs, and have re-examined the inverse correlation between the ratio of the luminosities of the outer to the inner double and the size of the inner double, l_{in}. Unlike the other DDRGs with l_{in} larger than about 50 kpc, the inner double of J0041+3224 is marginally more luminous than the outer one. The two DDRGs with l_{in} less than about a few kpc have a more luminous inner double than the outer one, possibly due to a higher efficiency of conversion of beam energy as the jets propagate through the dense interstellar medium. We have examined the symmetry parameters and find that the inner doubles appear to be more asymmetric in both its armlength and flux density ratios compared with the outer doubles, although they appear marginally more collinear with the core than the outer double. We discuss briefly possible implications of these trends.Comment: Accepted for publication in MNRAS, 9 pages, 10 figure

We present multifrequency observations with the Giant Metrewave Radio Telescope (GMRT) and the Very Large Array (VLA) of a sample of seventeen largely giant radio sources (GRSs). These observations have either helped clarify the radio structures or provided new information at a different frequency. The broad line radio galaxy, J0313+413, has an asymmetric, curved radio jet and a variable radio core, consistent with a moderate angle of inclination to the line of sight. We attempt to identify steep spectrum radio cores (SSCs), which may be a sign of recurrent activity, and find four candidates. If confirmed, this would indicate a trend for SSCs to occur preferentially in GRSs. From the structure and integrated spectra of the sources we suggest that the lobes of emission in J0139+399 and J0200+408 may be due to an earlier cycle of nuclear activity. We find that inverse-Compton losses with the cosmic microwave background radiation dominate over synchrotron radiative losses in the lobes of all the sources, consistent with earlier studies. We also show that prominence of the bridge emission decreases with increasing redshift, possibly due to inverse-Compton losses. This could affect the appearance and identification of GRSs at large redshifts.Comment: 11 pages, 2 figures (Figure 1 shows the images of 17 sources), 4 tables. accepted for publication in Monthly Notice

We present multiwavelength investigation of morphology, physical-environment, stellar contents and star formation activity in the vicinity of star-forming region Sh 2-100. It is found that the Sh 2-100 region contains seven H ii regions of ultracompact and compact nature. The present estimation of distance for three H ii regions, along with the kinematic distance for others, suggests that all of them belong to the same molecular cloud complex. Using near-infrared photometry, we identified the most probable ionizing sources of six H ii regions. Their approximate photometric spectral type estimates suggest that they are massive early-B to mid-O zero-age-main-sequence stars and agree well with radio continuum observations at 1280 MHz, for sources whose emissions are optically thin at this frequency. The morphology of the complex shows a non-uniform distribution of warm and hot dust, well mixed with the ionized gas, which correlates well with the variation of average visual extinction (∼ 4.2 -97 mag) across the region. We estimated the physical parameters of ionized gas with the help of radio continuum observations. We detected an optically visible compact nebula located to the south of the 850 µm emission associated with one of the H ii regions and the diagnostic of the optical emission line ratios gives electron density and electron temperature of ∼ 0.67 × 10 3 cm −3 and ∼ 10 4 K, respectively. The physical parameters suggest that all the H ii regions are in different stages of evolution, which correlate well

Aims. We present a multiwavelength study of the massive star-forming region associated with IRAS 06055+2039. Methods. Narrow-band near-infrared (NIR) observations were carried out with UKIRT-UFTI in molecular hydrogen and Brγ lines to trace the shocked and ionized gases, respectively. We have used 2MASS JHK s data to study the nature of the embedded cluster associated with IRAS 06055+2039. The radio emission from the ionized gas was mapped at 610 and 1280 MHz using the Giant Metrewave Radio Telescope (GMRT), India. Emission from warm dust and the unidentified infrared bands (UIBs) was estimated using the mid-infrared (8-21 µm) data from the MSX survey. Submillimetre emission from the cold dust at 450 and 850 µm was studied using JCMT-SCUBA. Results. For the infrared cluster associated with IRAS 06055+2039, we obtain a power-law slope of 0.43 ± 0.09 for the K s -band luminosity function (KLF), which is in good agreement with other young embedded clusters. We estimate an age of 2-3 Myr for this cluster. Apart from the diffuse emission, the high-resolution 1280 MHz map also shows the presence of several discrete sources that possibly represent high-density clumps. The morphology of shocked molecular hydrogen forms an arc towards the N-E of the central IRAS point source and envelopes the radio emission. Submillimetre emission shows the presence of a dense cloud core that is probably at an earlier evolutionary stage compared to the ionized region with shocked molecular gas lying between the two. The total mass of the cloud is estimated to be ∼7000-9000 M from the submillimetre emission at 450 and 850 µm. Conclusions. The multiwavelength study of this star-forming complex reveals an interesting scenario where regions are at different stages in the evolution of star formation.Key words. infrared: ISM -radio continuum: ISM -ISM: H II regions -ISM: individual objects: IRAS 06055+2039 IntroductionMassive stars are preferentially formed in dense cores of molecular clouds. They remain deeply embedded in the prenatal molecular gas and obscuring dust and their pre-main-sequence (PMS) time scales are much shorter compared to the low mass stars. The luminous high-mass stars also affect the parent cloud. In addition, massive stars do not form in isolation but often in clusters and associations. All these factors contribute towards making the study of the formation mechanisms of these systems very difficult. Multiwavelength studies, therefore, hold the potential to probe these complexes at different depths and unravel the least understood aspects of massive star formation.IRAS 06055+2039 (G189.78+0.34, RAFGL 5179) is a massive star-forming region chosen from the catalog of massive young stellar objects by Chan et al. (1996). G189.78+0.34 is listed as an ultracompact (UC) HII region (Shepherd & Churchwell 1996;Bronfman et al. 1996). It belongs to the Gem OB1 molecular cloud complex and is a part of the extended HII region Sh 252. It is associated with S252 A, which is one of the six compact radio sources in Sh 252 revealed...

A multiwavelength study of the star-forming regions associated with IRAS 19111+1048 and IRAS 19110+1045 has been carried out. These have been simultaneously mapped in two far-infrared bands at k eA ¼ 130 and 200 m with $1 0 angular resolution using the TIFR 1 m balloon-borne telescope. The radio emission from the ionized gas of these regions has been imaged at 1280, 610, and 325 MHz using the Giant Metrewave Radio Telescope, India. Assuming the detected compact sources to represent exciting zero-age main sequence ( ZAMS) stars, the initial mass function [(m) / m Àa ] for the IRAS 19111+1048 region is found to be quite steep, with a ¼ 5:3 AE 0:5 for the mass range 14 < m/M < 33. The near-infrared ( NIR) source coincident with the IRAS 19111+1048 peak is likely to be an embedded pre-main-sequence star. The spectral types of the ZAMS stars inferred independently from the radio and NIR measurements match very well for a good fraction of the radio sources having NIR counterparts. The best-fit radiative transfer models of the two IRAS sources are in good agreement with the observed spectral energy distributions. A uniform density distribution of dust and gas is implied for both the sources. The extents of ionized gas, number of ZAMS stars, presence of deeply embedded sources, and lower value of L/M for the cloud support the youth of IRAS 19110+1045 vis-à-vis its neighbor, IRAS 19111+1048, consistent with earlier studies.