Global VLBI Observations of the Compact OH Megamaser Emission from III Zw 35 and IRAS 17208−0014

Diamond, P. J.; Lonsdale, Colin J.; Lonsdale, C. J.; Smith, H. E.

doi:10.1086/306681

Cited by 61 publications

(64 citation statements)

References 21 publications

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“…Similar observations of halos for other maser species have been reported in the last years. This phenomenon has been seen in OH megamasers (Diamond et al 1999), in OH masers in supernova remnants (Claussen et al 1999), in SiO masers in circumstellar envelopes (Greenhill et al 1995), in galactic H 2 O masers (Gwinn 1994) and in 25 GHz methanol masers (Sobolev et al 1998). In addition to these results, Moscadelli et al (1999) observed in W 3(OH) that a large amount of flux density was missing in the crosspower spectrum of the 12.2 GHz methanol masers.…”

Section: Summary Of the Resultsmentioning

confidence: 62%

VLBI observations of 6.7 and 12.2 GHz methanol masers toward high mass star-forming regions

Minier

Booth

Conway

2002

A&A

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Abstract. We consider the milliarsecond scale structures of three representative methanol maser sites observed at high resolution with the EVN at 6.7 GHz and with the VLBA at 12.2 GHz. These observations suggest that the majority of the individual masing regions within a maser site consist of a compact core surrounded by extended emission, i.e. a core/halo structure. In many cases, the extended emission is resolved by the shortest baselines of the VLBA. We conclude that these regions of extended emission are responsible for the missing flux density when comparing cross-power spectra on the shortest VLBI baselines to single dish spectra. The halos of diffuse emission have diameters ranging between 12 and 290 AU and their brightness temperatures depend on their diameters as T b ∝d −2.2 . The core diameters vary from 2 to 20 AU. Three possible phenomena could explain the presence of large halos around bright cores. The core/halo pattern could be the result of saturation effects in a uniform spherical maser cloud. The compact and diffuse masers could also originate in physically distinct regions: the maser core could form within highly dense gas while the maser halo could be the result of weak masers in diffuse gas. Finally, turbulence could cause the appearance of core/halo structures in a disrupted homogeneous medium. Scattering effects do not seem to play a role in the broadening of maser images since masers have similar sizes at 6.7 and 12.2 GHz.

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Section: Summary Of the Resultsmentioning

confidence: 62%

VLBI observations of 6.7 and 12.2 GHz methanol masers toward high mass star-forming regions

Minier

Booth

Conway

2002

A&A

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“…VLBI observations have mapped the OHM emission for a handful of nearby galaxies (Yates et al 2000;Pihlström et al 2001Pihlström et al , 2005Klöckner et al 2003;Lonsdale et al 2003;Rovilos et al 2003;Klöckner & Baan 2004;Richards et al 2005;Momjian et al 2006), showing that the difference in apparent optical depth between the entire galaxy and the brightest individual maser spots varies by as much as Δτ 1-4. Furthermore, the gain for individual maser spots with cloud-cloud overlap can be as high as several hundred (e.g., III Zw 35; Diamond et al 1999;Parra et al 2005), compared to the diffuse background. Since high-resolution OH maps do not exist for the vast majority of the IRS galaxies, however, we use τ app 1667 while remaining mindful of the above caveats.…”

Section: Comparing Observations and Theorymentioning

confidence: 99%

Mid-Infrared Properties of Oh Megamaser Host Galaxies. Ii. Analysis and Modeling of the Maser Environment

Willett

Darling

Spoon

et al. 2011

ApJ

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We present a comparison of Spitzer Infrared Spectrograph (IRS) data for 51 OH megamaser (OHM) hosts and 15 non-masing ultraluminous infrared galaxies (ULIRGs). 10%-25% of the OHMs show evidence for the presence of an active galactic nucleus (AGN), significantly lower than the estimated AGN fraction from previous optical and radio studies. Non-masing ULIRGs have a higher AGN fraction (50%-95%) than OHMs, although some galaxies in both samples show evidence of co-existing starbursts and AGNs. Radiative transfer models of the dust environment reveal that non-masing galaxies tend to have clumpy dust geometries commonly associated with AGN, while OHMs have deeper absorption consistent with a smooth, thick dust shell. Statistical analyses show that the major differences between masing and non-masing ULIRGs in the mid-IR relate to the optical depth and dust temperature, which we measure using the 9.7 μm silicate depth and 30-20 μm spectral slope from the IRS data. Dust temperatures of 40-80 K derived from the IRS data are consistent with predictions of OH pumping models and with a minimum T dust required for maser production. The best-fit dust opacities (τ V ∼ 100-400), however, are nearly an order of magnitude larger than those predicted for OH inversion, and suggest that modifications to the model may be required. These diagnostics offer the first detailed test of an OHM pumping model based only on the properties of its host galaxy and provide important restrictions on the physical conditions relevant to OHM production.

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“…Powerful OH maser emission has been previously detected in the circumnuclear disk of Arp220, IIIZw35, Mrk273, and IRAS17208-0014 by Lonsdale et al (1998), Diamond et al (1999), Yates et al(2000), and Diamond et al(1999), respectively. Previous VLBI observation and time series analysis of the spectra (Haschick, Bann & Peng 1994) suggests that the masers originate in a rotating torus surrounding a massive object (with a mass M of 1.5 x 10 r M 0 ) at the center of the galaxy (Watson & Wallin 1994).…”

Section: Introductionmentioning

confidence: 87%

Probing Physics and Chemistry in Circumnuclear Torus with OH

Zhang

2005

Highlights astron.

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Abstract.We observed OH maser emission at 18cm in a circumnuclear torus surrounding the center of IRAS10173+0828 using the 7 telescopes of MERLIN, together with the Lovell antenna. IRAS10173+0828 is a distant super-luminous far-infrared galaxy. The OH maser emission is remarkably narrow (FWHP = 39km s _1 ) for its strength, and the 1667 and 1665 MHz lines are well separated. The 1667 transition shows two distinct peaks displaced from one another by 100 km s~x. Using our MERLIN observational results we probe the physics in the circumnuclear torus surrounding the center of IRAS10173+0828, obtain the kinematic properties of the torus, and study the central source.

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Global VLBI Observations of the Compact OH Megamaser Emission from III Zw 35 and IRAS 17208−0014

Cited by 61 publications

References 21 publications

VLBI observations of 6.7 and 12.2 GHz methanol masers toward high mass star-forming regions

VLBI observations of 6.7 and 12.2 GHz methanol masers toward high mass star-forming regions

Mid-Infrared Properties of Oh Megamaser Host Galaxies. Ii. Analysis and Modeling of the Maser Environment

Probing Physics and Chemistry in Circumnuclear Torus with OH

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