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Register a new userHigh-Resolution Imaging of Water Maser Emission in the active galaxies NGC 6240 and M51
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We present the results of observations of 22GHz H2O maser emission in NGC 6240 and M51 made with the Karl G. Jansky Very Large Array. Two major H2O maser features and several minor features are detected toward the southern nucleus of NGC 6240. These features are redshifted by about 300 km/s from the galaxys 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 22GHz radio continuum emission, implying that the maser excitation relates to the activity of an active galactic nucleus in the southern nucleus rather than star-forming activity. The star-forming galaxy M51 hosts H2O 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 22GHz nuclear radio continuum emission in M51. The continuum emission is co-located with the maser position, which indicates that the maser arises from active galactic nucleus-activity and not from star-forming activity in the galaxy.
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We present the results of unbiased 22 GHz H2O water and 44 GHz class I CH3OH methanol maser surveys in the central 7x10 arcmin area of NGC 1333 and two additional mapping observations of a 22 GHz water maser in a ~3x3arcmin area of the IRAS4A region. In the 22 GHz water maser survey of NGC 1333 with sensitivity of sigma~0.3Jy, we confirmed masers toward H2O(B) in the region of HH 7-11 and IRAS4B. We also detected new water masers at ~20arcsec away in the western direction of IRAS4B or ~25arcsec away in the southern direction of IRAS4A. We could not however find young stellar objects or molecular outflows associated with them. They showed two different velocity components of ~0 and ~16 km/s, which are blue- and red-shifted relative to the adopted systemic velocity of ~7 km/s for NGC 1333. They also showed time variabilities in both intensity and velocity from multi-epoch observations and an anti-correlation between the intensities of the blue- and the red-shifted velocity components. We suggest that the unidentified powering source of these masers might be in the earliest evolutionary stage of star formation before the onset of molecular outflows. Finding this kind of water masers is only possible by an unbiased blind survey. In the 44 GHz methanol maser survey with sensitivity of sigma~0.5 Jy, we confirmed masers toward the IRAS4A2 and the eastern shock region of the IRAS2A. Both sources are also detected in 95 and 132 GHz methanol maser lines. In addition, we had new detections of methanol masers at 95 and 132 GHz toward IRAS4B. In terms of the isotropic luminosity, we detected the methanol maser sources brighter than ~5x1025 erg/s from our unbiased survey.
We report the detection of a 22GHz water maser line in the nearest (D~3.8Mpc) radio galaxy Centaurus A using the Australia Telescope Compact Array (ATCA). The line is centered at a velocity of ~960kms-1, which is redshifted by about 400kms-1 from the systemic velocity. Such an offset, as well as the width of ~120kms-1, could be consistent with either a nuclear maser arising from an accretion disk of the central supermassive black hole, or for a jet maser that is emitted from the material that is shocked near the base of the jet in Centaurus,A. The best spatial resolution of our ATCA data constrains the origin of the maser feature within <3pc from the supermassive black hole. The maser exhibits a luminosity of ~1Lo, which classifies it as a kilomaser, and appears to be variable on timescales of months. A kilomaser can also be emitted by shocked gas in star forming regions. Given the small projected distance from the core, the large offset from systemic velocity, as well as the smoothness of the line feature, we conclude that a jet maser line emitted by shocked gas around the base of the AGN is the most likely explanation. For this scenario we can infer a minimum density of the radio jet of ~>10cm-3, which indicates substantial mass entrainment of surrounding gas into the propagating jet material.
We have conducted VLBI observations of water maser and radio continuum emission in the nucleus of NGC 3079. The 22 GHz maser emission arises in compact clumps, distributed along an axis that is aligned with the major axis of the galactic disk. The velocities of the masers are consistent with their lying in the inner parsec of a molecular disk rotating in the same sense as the rest of the galaxy. However, the velocity field has a significant non-rotational component, which may indicate supersonic turbulence. The bright maser emission is not coincident with any detected compact 22 GHz continuum source, suggesting the high apparent luminosity of the maser may not due to beamed amplification of continuum emission. We observed two compact continuum sources that have inverted spectra between 5 and 8 GHz, and steep spectra between 8 and 22 GHz. NGC 3079 may be a nearby, low-luminosity example of the class of compact symmetric gigahertz-peaked spectrum (GPS) radio sources. We detected a third continuum component that lies along the same axis as the other two, strongly suggesting that this galaxy possesses a nuclear jet. Faint maser emission was detected near this axis, which may indicate a second population of masers associated with the jet.
We report ALMA Band 7 (350 GHz) imaging at 0.4 - 0.6arcsec resolution and Band 9 (696 GHz) at ~0.25arcsec resolution of the luminous IR galaxies Arp 220 and NGC 6240. The long wavelength dust continuum is used to estimate ISM masses for Arp 220 East, West and NGC 6240 of 1.9, 4.2 and 1.6x10^9 msun within radii of 69, 65 and 190 pc. The HCN emission was modeled to derive the emissivity distribution as a function of radius and the kinematics of each nuclear disk, yielding dynamical masses consistent with the masses and sizes derived from the dust emission. In Arp 220, the major dust and gas concentrations are at radii less than 50 pc in both counter-rotating nuclear disks. The thickness of the disks in Arp 220estimated from the velocity dispersion and rotation velocities are 10-20 pc and the mean gas densities are n_H2 ~10^5 cm^-3 at R < 50 pc. We develop an analytic treatment for the molecular excitation (including photon trapping), yielding volume densities for both the HCN and CS emission with n_H2 ~2x10^5 cm^-3. The agreement of the mean density from the total mass and size with that required for excitation suggests that the volume is essentially filled with dense gas, i.e. it is not cloudy or like swiss cheese.
We present 0.97 $times$ 0.53 (470 pc $times$ 250 pc) resolution CO ($J$ = 2-1) observations toward the nearby luminous merging galaxy NGC 6240 with the Atacama Large Millimeter/submillimeter Array. We confirmed a strong CO concentration within the central 700 pc, which peaks between the double nuclei, surrounded by extended CO features along the optical dust lanes ($sim$11 kpc). We found that the CO emission around the central a few kpc has extremely broad velocity wings with full width at zero intensity $sim$ 2000 km s$^{-1}$, suggesting a possible signature of molecular outflow(s). In order to extract and visualize the high-velocity components in NGC 6240, we performed a multiple Gaussian fit to the CO datacube. The distribution of the broad CO components show four extremely large linewidth regions ($sim$1000 km s$^{-1}$) located 1-2 kpc away from both nuclei. Spatial coincidence of the large linewidth regions with H$alpha$, near-IR H$_2$, and X-ray suggests that the broad CO (2-1) components are associated with nuclear outflows launched from the double nuclei.
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