• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.2
• /
• pp.74.1-74.1
• /
• 2012

We observed the radio sources found from the First Look Survey (FLS) field at the 1.4 GHz radio continuum emission with the Very Large Array (VLA) using the A configuration. We identify point sources and multi component sources at ${\geq}4{\sigma}$ level. We also present the submillimeter properties of the selected radio sources in the FLS field from the Herschel/SPIRE 250/350/500/${\mu}m$ and AzTEC 1.1mm surveys. The counterparts of the radio sources at submillimeter for these called 'submillimeter galaxies (SMGs)' are detected at infrared wavelength with the Spitzer MIPS 24 & 70 ${\mu}m$ sources. Based on the MMT/HECTOSPEC red-shift survey, IRS spectroscopy, and SDSS photometric red-shift survey, the radio sources are likely to be the extragalactic sources. Here, we use the star formation rate (SFR) derived from the MIPS 24 and 70 ${\mu}m$ luminosity to compare the measured SFR from the VLA 1.4 GHz luminosity. These results show that a tight correlation between the SFR from the radio luminosity and the MIPS $24{\mu}m$ rather than that from the MIPS $70{\mu}m$ luminosity. Radio and IR correlation is also used to indicate the radio and IR properties of star-formation in the galaxies and active galactic nuclei (AGNs). Using the counterpart sources selected at IR and radio wavelengths, we employ the IR/radio flux ratios to determine the properties and population of the selected galaxies.

• Publications of The Korean Astronomical Society
• /
• v.30 no.2
• /
• pp.637-639
• /
• 2015

The Korean very-long-baseline interferometry (VLBI) network (KVN) and VLBI Exploration of Radio Astrometry (VERA) Array (KaVA) is the first international VLBI array dedicated to high-frequency (23 GHz (K-band) and 43 GHz (Q-band)) observations in East Asia. To evaluate the imagine capability of KaVA, we performed imaging observations of three bright active galactic nuclei (AGNs) known for their complex morphologies: 4C 39.25, 3C 273, and M87 by KaVA at K-/Q-band. Our KaVA images reveal extended outflows with complex substructure such as knots and limb brightening, in agreement with previous observations by other VLBI facilities. Angular resolutions are better than 1.4 and 0.8 milliarcsecond (max) at K-/Q-band, respectively. KaVA achieves a high dynamic range of ~1000, more than three times the value achieved by VERA. We conclude that KaVA is a powerful array with a great potential for the study of AGN outflows, at least comparable to the best existing radio interferometric arrays.

• Publications of The Korean Astronomical Society
• /
• v.30 no.2
• /
• pp.453-455
• /
• 2015

In this paper we introduce the Plasma Physics of Active Galactic Nuclei project, which is an ongoing experiment with Korean VLBI Network (KVN) and KVN and VERA Array (KaVA) to study multi-frequency polarimetric properties on parsec scales of active galaxies. The goal of the project is to improve our understanding of fundamental jet physics, especially evolution of the relativistic outflow coupled with the large-scale magnetic field. We selected six radio-loud AGN as our targets. So far we (i) detected resolved emissions regions at 86 and 129 GHz on VLBI scales, (ii) constructed 2D spectral index maps of the outflows, and (iii) found polarizations at 22 and 43 GHz for a few targets. Here we present spectral index distributions of 3C 120 between 22 and 43 GHz and a linear polarization map of BL Lac at 43 GHz obtained with KVN.

• Journal of The Korean Astronomical Society
• /
• v.38 no.2
• /
• pp.183-186
• /
• 2005

We present results of the VLBA observation toward the radio continuum and water maser emissions in a nearby LINER galaxy NGC 1052. The jet structure observed in 2000 is similar to that in 1998, and the two jet structures in 1998 and 2000 support the sub-luminal motion with apparent velocity of 0.26c. Distribution of water maser spots are located ${\~}$0.05 pc shifted to southwest from the component which is supported to be the nucleus, and no rapid positional change of the water maser gas with respect to the central engine is seen from 1995 to 2000. The maser gas is positionally coincident with a plasma torus, and the position of the maser gas relative to the nucleus is stable from 1995 to 2000. The maser gas in NGC 1052 could be explained to be associated with the nuclear circumnuclear torus or disk like the situation found in the nucleus of NGC 4258.

• Publications of The Korean Astronomical Society
• /
• v.32 no.1
• /
• pp.267-269
• /
• 2017

We report the results of a multi-wavelength study in the North Ecliptic Pole (NEP) deep field and examine the far infrared-radio correlation (FIRC) for high and low redshift objects. We have found a correlation between the GMRT data at 610 MHz and the Herschel data at $250{\mu}m$ that has been used to define a spectral index. This spectral index shows no evolution against redshift. As a result of the study, we show a radio colour-infrared diagram that can be used as a redshift indicator.

• Journal of The Korean Astronomical Society
• /
• v.37 no.5
• /
• pp.493-500
• /
• 2004

The existence and extent of non-thermal phenomena in galaxy clusters is now well established. A key question in our understanding of these phenomena is the origin of the relativistic electrons which may be constrained by the modelling of the fine radio properties of radio halos and of their statistics. In this paper we argue that present data favour a scenario in which the emitting electrons in the intracluster medium (ICM) are reaccelerated in situ on their way out. An overview of turbulent-particle acceleration models is given focussing on recent time-dependent calculations which include a full coupling between particles and MHD waves.

• The Bulletin of The Korean Astronomical Society
• /
• v.39 no.2
• /
• pp.49-49
• /
• 2014

Blue Compact Dwarf galaxies (BCDs) are low-mass galaxies with recently enhanced star formation activity. Since the discovery of old stellar population in the BCDs, a number of hypotheses have been suggested as the origin of the current active star formation. One theory is tidal interactions such as fly-by and merger. In this study we test this hypothesis using a pair of BCDs, ESO 435-IG20 and ESO 435-IG16 that are separate by only ~80 kpc in projection at a similar redshift (at a ~9 Mpc distance). In the HIPASS survey, intergalactic atomic hydrogen envelope has been found to be covering both galaxies, making the pair a good candidate for the case where the star formation has been triggered by tidal interaction. We probe the gas morphology and kinematics of the BCD pair using ATCA HI data in order to find the evidence of tidal interaction. We also estimate star formation rates in the pair based on Ha emission and UV continuum, and compare with other dwarf galaxies to investigate how responsible the tidal interaction is for the enhanced star formation in this case.

• Journal of The Korean Astronomical Society
• /
• v.56 no.2
• /
• pp.159-168
• /
• 2023

The main goal of the Korean VLBI Network Calibrator Survey (KVNCS) is to expand the VLBI calibrators catalog for KVN, KaVA (KVN and VERA Array), EAVN (East-Asian VLBI Network), and other extended regions. The second KVNCS (KVNCS2) aimed to detect VLBI fringes of new candidates for calibrators in the K band. Out of the 1533 sources whose single-dish flux density in the K band was measured with KVN telescopes (Lee et al. 2017), 556 sources were observed with KVN in the K band. KVNCS2 confirmed the detection of VLBI fringes of 424 calibrator candidates over a single baseline. All detected sources had a high Signal-to-Noise Ratio (SNR) of >25. Finally, KVNCS2 confirmed 347 new candidates as VLBI calibrators in the K band, resulting in a 5% increase in the sky coverage compared to previous studies. The spatial distribution was quasi-uniform across the observable region (Dec. > -32.5°). In addition, the possibility as calibrator candidates for the detected sources was checked, using an analysis of the flux-flux relationship. Ultimately, the KVNCS catalog will not only become the VLBI calibrator list but is also useful as a database of compact radio sources for astronomical studies.

• Journal of The Korean Astronomical Society
• /
• v.37 no.5
• /
• pp.589-592
• /
• 2004

We calculate the probability to form giant radio halos (${\~}$ 1 Mpc size) as a function of the mass of the host clusters by using a Statistical Magneto-Turbulent Model (Cassano & Brunetti, these proceedings). We show that the expectations of this model are in good agreement with the observations for viable values of the parameters. In particular, the abrupt increase of the probability to find radio halos in the more massive galaxy clusters ($M {\ge} 2{\times}10^{15} M_{\bigodot}$) can be well reproduced. We calculate the evolution with redshift of such a probability and find that giant radio halos can be powered by particle acceleration due to MHD turbulence up to z${\~}$0.5 in a ACDM cosmology. Finally, we calculate the expected Luminosity Functions of radio halos (RHLFs). At variance with previous studies, the shape of our RHLFs is characterized by the presence of a cut-off at low synchrotron powers which reflects the inefficiency of particle acceleration in the case of less massive galaxy clusters.

• The Bulletin of The Korean Astronomical Society
• /
• v.36 no.2
• /
• pp.65-65
• /
• 2011

Early-type galaxies represent the end point of galaxy evolution and, despite pervasive residual star formation, are generally considered "red and dead", that is composed exclusively of old stars with no star formation. Here, their molecular gas content is constrained and discussed in relation to their evolution, supporting the continuing importance of minor mergers and/or cold gas accretion. First, as part of the Atlas3D survey, the first complete, large, volume-limited survey of CO in normal early-type galaxies is presented. At least of 23% of local early-types possess a substantial amount of molecular gas, the necessary ingredient for star formation, independent of mass and environment but dependent on the specific stellar angular momentum. Second, using CO synthesis imaging, the extent of the molecular gas is constrained and a variety of morphologies is revealed. The kinematics of the molecular gas and stars are often misaligned, implying an external gas origin in over a third of all systems, more than half in the field, while external gas accretion must be shot down in clusters. Third, many objects appear to be in the process of forming regular kpc-size decoupled disks, and a star formation sequence can be sketched by piecing together multi-wavelength information on the molecular gas, current star formation, and young stars. Fourth, early-type galaxies do not seem to systematically obey all our usual prejudices regarding star formation (e.g. Schmidt-Kennicutt law, far infrared-radio continuum correlation), suggesting a greater diversity in star formation processes than observed in disk galaxies and the possibility of "morphological quenching". Lastly, a first step toward constraining the physical properties of the molecular gas is taken, by modeling the line ratios of density- and opacity-sensitive molecules in a few objects. Taken together, these observations argue for the continuing importance of (minor) mergers and cold gas accretion in local early-types, and they provide a much greater understanding of the gas cycle in the galaxies harbouring most of the stellar mass. In the future, better dust masses and dust-to-gas mass ratios from Herschel should allow to place entirely independent constraints on the gas supply, while spatially-resolved high-density molecular gas tracers observed with ALMA will probe the interstellar medium and star formation laws locally in a regime entirely different from that normally probed in spiral galaxies.