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Title: TWO EPOCHS OF VERY LARGE ARRAY OBSERVATIONS OF WATER MASER EMISSION IN THE ACTIVE GALAXY NGC 6240

Abstract

Studies of 22 GHz H{sub 2}O maser emission from the merging galaxy NGC 6240 with double nuclei are presented. Two epochs of Very Large Array (VLA) observations in the A-configuration in spectral-line mode were carried out at 0.1 arcsec resolution by covering the redshifted velocity range of {approx}300 km s{sup -1} with respect to the systemic velocity of the galaxy. The purpose of these new observations is twofold: to detect an H{sub 2}O maser that an earlier VLA observation pinpointed in the southern nucleus in the northern nucleus as well to clarify the kinematics of the double nuclei, and to understand the origin of the maser in the galaxy. In the second epoch, one velocity feature peaking at V{sub LSR} = 7491.1 km s{sup -1}, redshifted by {approx}200 km s{sup -1} relative to the systemic velocity, was detected only toward the southern nucleus. The detection of an H{sub 2}O maser feature at or near this velocity had never been reported in earlier observations. However, including the known velocity features at redshifted velocities, no other velocity features were observed toward either nuclei throughout these epochs. The maser remains unresolved at an angular resolution of {approx}0.''1, corresponding to a linear size ofmore » less than about 45 pc. The two epochs of VLA observations show that the maser intensity is variable on timescales of at least three months, while the correlation between the maser intensity and the radio continuum intensity is not certain from our data. It is plausible that the maser in NGC 6240 is associated with the activity of an active galactic nucleus in the southern nucleus. Alternatively, the maser can be explained by star-forming activity at the site of massive star formation in the galaxy.« less

Authors:
 [1]
  1. National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)
Publication Date:
OSTI Identifier:
21443162
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (New York, N.Y. Online); Journal Volume: 140; Journal Issue: 6; Other Information: DOI: 10.1088/0004-6256/140/6/1905
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; EMISSION; GALAXIES; GALAXY NUCLEI; MASERS; STARS; WATER; AMPLIFIERS; ELECTRONIC EQUIPMENT; EQUIPMENT; HYDROGEN COMPOUNDS; MICROWAVE AMPLIFIERS; MICROWAVE EQUIPMENT; OXYGEN COMPOUNDS

Citation Formats

Hagiwara, Yoshiaki. TWO EPOCHS OF VERY LARGE ARRAY OBSERVATIONS OF WATER MASER EMISSION IN THE ACTIVE GALAXY NGC 6240. United States: N. p., 2010. Web. doi:10.1088/0004-6256/140/6/1905.
Hagiwara, Yoshiaki. TWO EPOCHS OF VERY LARGE ARRAY OBSERVATIONS OF WATER MASER EMISSION IN THE ACTIVE GALAXY NGC 6240. United States. doi:10.1088/0004-6256/140/6/1905.
Hagiwara, Yoshiaki. 2010. "TWO EPOCHS OF VERY LARGE ARRAY OBSERVATIONS OF WATER MASER EMISSION IN THE ACTIVE GALAXY NGC 6240". United States. doi:10.1088/0004-6256/140/6/1905.
@article{osti_21443162,
title = {TWO EPOCHS OF VERY LARGE ARRAY OBSERVATIONS OF WATER MASER EMISSION IN THE ACTIVE GALAXY NGC 6240},
author = {Hagiwara, Yoshiaki},
abstractNote = {Studies of 22 GHz H{sub 2}O maser emission from the merging galaxy NGC 6240 with double nuclei are presented. Two epochs of Very Large Array (VLA) observations in the A-configuration in spectral-line mode were carried out at 0.1 arcsec resolution by covering the redshifted velocity range of {approx}300 km s{sup -1} with respect to the systemic velocity of the galaxy. The purpose of these new observations is twofold: to detect an H{sub 2}O maser that an earlier VLA observation pinpointed in the southern nucleus in the northern nucleus as well to clarify the kinematics of the double nuclei, and to understand the origin of the maser in the galaxy. In the second epoch, one velocity feature peaking at V{sub LSR} = 7491.1 km s{sup -1}, redshifted by {approx}200 km s{sup -1} relative to the systemic velocity, was detected only toward the southern nucleus. The detection of an H{sub 2}O maser feature at or near this velocity had never been reported in earlier observations. However, including the known velocity features at redshifted velocities, no other velocity features were observed toward either nuclei throughout these epochs. The maser remains unresolved at an angular resolution of {approx}0.''1, corresponding to a linear size of less than about 45 pc. The two epochs of VLA observations show that the maser intensity is variable on timescales of at least three months, while the correlation between the maser intensity and the radio continuum intensity is not certain from our data. It is plausible that the maser in NGC 6240 is associated with the activity of an active galactic nucleus in the southern nucleus. Alternatively, the maser can be explained by star-forming activity at the site of massive star formation in the galaxy.},
doi = {10.1088/0004-6256/140/6/1905},
journal = {Astronomical Journal (New York, N.Y. Online)},
number = 6,
volume = 140,
place = {United States},
year = 2010,
month =
}
  • We present the results of observations of 22 GHz H{sub 2}O maser emission in NGC 6240 and M51 made with the Karl G. Jansky Very Large Array. Two major H{sub 2}O maser features and several minor features are detected toward the southern nucleus of NGC 6240. These features are redshifted by about 300 km s{sup −1} from the galaxy’s systemic velocity and remain unresolved at the synthesized beam size. A combination of our two-epoch observations and published data reveals an apparent correlation between the strength of the maser and the 22 GHz radio continuum emission, implying that the maser excitationmore » relates to the activity of an active galactic nucleus in the southern nucleus rather than star-forming activity. The star-forming galaxy M51 hosts H{sub 2}O maser emission in the center of the galaxy; however, the origin of the maser has been an open question. We report the first detection of 22 GHz nuclear radio continuum emission in M51. The continuum emission is co-located with the maser position, which indicates that the maser arises from nuclear active galactic nucleus-activity and not from star-forming activity in the galaxy.« less
  • Very large Array (VLA) synthesis maps of the active regions AR 2505 and AR 2646 at wavelengths of 2 cm, 6 cm, and 20 cm are presented and compared with the magnetic structure of the underlying photosphere.
  • The Very Large Array (VLA) has been used to study the structuree and evolution of six solar bursts near 20 cm wavelength. In most ccases the burst emission has been resolved into looplike structures with total lengths, Lapprox.3 x 10/sup 9/ cm, brightness temperatures T/sub B/approx.10/sup 7/-10/sup 8/ K, and degrees of circular polarization p/sub c/< or approx. =90%. changes in the total intensity and circular polarization of the bursts occur on time scales as short as 10 s. The individual peaks of one multiple-component burst originated in different locations within a magnetically complicated region. Preburst heating occurred minutes beforemore » the onset of the impulsive phase of one burst, and circular polarization changes occurred minutes before the onset of the impulsive phase of another burst. In one case, a loop system emerged in the vicinity of the impulsive source, and two adjacent loop systems may have emerged and triggered the burst.« less
  • High-resolution images of the quiescent emission from two solar active regions at 20 cm (VLA) and soft X-ray (SMM FCS) wavelengths are compared. There are regions where the X-ray coronal loops have been completely imaged at 20 cm wavelength. In other regions, the X-ray radiation was detected without detectable 20 cm radiation, and vice versa. The X-ray data were used to infer average electron temperatures of about 3-million K and average electron densities of about 2.5 x 10 to the 9th/cu cm for the X-ray emitting plasma in the two active regions. The thermal bremsstrahlung of the X-ray emitting plasmamore » is optically thin at 20 cm wavelength. The 20 cm brightness temperatures were always less than T(e), which is consistent with optically thin bremsstrahlung. The low T(B) can be explained if a higher, cooler plasma covers the hotter X-ray emitting plasma. Thermal gyroresonance radiation must account for the intense 20 cm radiation near and above sunspots where no X-ray radiation is detected. 26 references.« less