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20/05/2013 CSIRO 1
EVN search for 6.7 GHz methanol masers towards MYSOs
Anna Bartkiewicz (Torun), Marian Szymczak (Torun),
Huib van Langevelde (JIVE)
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Observatory 12 km away from Torun city
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Introduction
Torun blind survey (Szymczak et al. 2000, 2002) at 6668.518 MHz towards the Galactic planel from 5 to 85deg, b from 0.5 to +0.5 deg using 32m antenna: ca.6000 hours between 19982002. About 100 sources newly detected in
l from 20 to 40 deg.
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New singledish observations: 289 methanol sources over a two monthperiod (dec. above 22deg and density flux stronger than 7.5 Jy).(Szymczak et al. 2012)Spectra and some details available online viahttp://cosmos.astro.umk.pl/~msz/
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EVN observations (since 2003) followed MERLIN ones in order to map the 6.7 GHz methanol maser emission at milliarcsecond scale andto measure their absolute positions with better accuracy.A standard setup for the spectral line observations 2 MHz (ca.100 km/s coverage), 1024 channels (ca. 0.09 km/s channel separation), L&R Stokes phasereferenced data.In most epochs we used from 6 (4) to 9 antennas:Cm Jb Ef On Mc Nt Tr Wb Hh YbResults: maps with an rms of a few mJy beam 6 mas x 8 mas
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9 (29%) masers: complex
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12 (39%) masers: ringlike
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3 (9.5%) masers: arclike
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We know that VLBI resolves the emission...
Pandian et al. (2011) observed 82 methanol masers fromthe Arecibo catalogue using MERLIN or EVLA.
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Pandian et al. (2011):“In sources where there is a large discrepancy between the flux recovered in VLBI experiments and that measured with a single dish, we often find the missing flux to be distributed over complex structures. Hence, some relatively simple morphological structures seen in VLBI are likely to be part of a more complex emission structure in at least some sources. This makes interpretation of the origin of maser emission difficult, and multiepoch proper motion studies or complementary high resolution midinfrared or submillimeter observations are required to resolve this problem.”
Five sources overlapped with our sample.
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It has so happened...Search for methanol masers towards MYSO objects in cluster(proposal in 2009, observations in 2010)
Sample selection from the Torun catalogue: a large extent in the spectra, multiple features of flux density greater than 2 Jy, MIR counterparts in clusters characterised by extended emission at 4.5 µm (so called EGOs) which indicate outflows in MYSOs (Cyganowski et al. 2008, 2009) (Spitzer maps), 10 star forming sites barely resolved with 5.'5 beam of the Torun 32m dish,(two of them were resolved with the Arecibo dish and ATCA interferometer (Pandian et al. 2007, Caswell 2009)).
Finally we scheduled 14 pointing positions using EVN(Jb, Ef, Mc, On, Nt, Tr, Wb, Yb) on 14/03/2010,with data sampling of 0.25s yielding 2.'1 field of view (with 10% decrease in the response to a point source).
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14 pointing positions using EVN(two 10hr runs)
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120”
4.53.6 µm
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Searching for emission:
inspection of the vectoraveraged spectra by shiftingthe phasecentres from 2' to +2' in RA and Dec with 1” interval, finding the maximum intensity of a given maser featureand its phase being close to 0 deg, creation of a dirty map of size of 8”x 8” with 1 mas pixel width, making smaller maps centred at the found maximum, if all features were not recovered by the ISPEC task on the cubeof the images, the procedure was restarted with another (“missed”)feature.
The largest shift: 54” in RA and 56” in Dec for 1.25 Jy source,but failed for 47” and 47 shift for 0.65 Jy source (the peak).
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Results:
the weakest source(334 mJy), three groups distributedalong a line of 150 mas (1320 AU) with a velocity gradient, Pandian did not registerany emission using MERLINin 2007, but did using EVLAin 2008, the EVN spectrum is5 times lower than thatfrom the Torun antenna.
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Results:
complex source with 123 maser spots, morphology agrees wellwith that derived by EVLA(Pandian et al. 2011) the shape of the EVN spectrum agrees with the single dish spectrum, but is 3 times lower, a distance of 4.9 kpc(500mas=2450 AU).
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Results:
complex source with 123 maser spots, morphology agrees wellwith that derived by EVLA(Pandian et al. 2011) the shape of the EVN spectrum agrees with the single dish spectrum, but is 3 times lower, a distance of 4.9 kpc(500mas=2450 AU).
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Results:
arched or ringlikemorphology with the extend of400 mas (4500 AU), the VLBA data are consistentin morphology (A.Brunthaler BeSSeL)
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Results:
a complex structure consistent with the MERLIN image (Pandian et al. 2011)(the redshifted part morecompact) 0.050 mas= 435 AU
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Results:
a complex structure seenusing the EVN, while onlyone linear structure was registeredwith MERLIN (Pandian et al. 2011), some resolved emission comparing with Torun spectrum, 0.050 mas= 435 AU
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Results:
two groups separated by860mas (2000AU) EVN and Torun spectraare similar in a shape,but differs in intensity (10%)
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Comparison of density fluxes obtained with single dish and the EVN:
57 per cent of the maser flux density is resolved out, missed flux ranges from 24 per cent to 86 per cent, missing flux does not depend on the distance to the source(a content of weak and diffuse maser emission is specificto an individual source), 12 out of 14 targets were observed using MERLIN or EVLA(Pandian et al. 2011) and the overall morphology agrees well with the VLBI images (almost all maser clouds have compact cores).
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All detected masers coincide within 0.5” with the EGOs.Infrared counterparts found in the literature: UKIDSSDR6 (Lukas et al. 2008) Spitzer IRAC (Fazio et al. 2004) MIPS (Rieke et al. 2004) MSX (Egan et al. 2003) SCUBA (Di Francesco et al. 2008) LABOCA, IRAM (Pandian et al. 2010) BOLOCAM (Rosolowsky et al. 2010) Herschel (Veneziani et al. 2013) SIMBA (Hill et al. 2005)
Near and far kinematic distances calculated using the code by Reid et al. (2009).The distance ambiguity resolved by 21 cm HI or 6 cm formaldehyde absorption lines (Watson et al. 2003, Pandian et al. 2009).
The online SED Fitting Tool (Robitaille et al. 2007) were used for fitting.
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The stellar mass, temperature, radius, total luminosity are typical asfor massive YSOs (Pandian et al. 2010, De Buizer et al. 2012).
Total luminosity:
Median Minimummaximum Maser luminosity L
Sun L
Sun 106L
Sun
G37.753 1178 812 2250 0.13e6 G40.282 94800 49400 216000 2.47e6 G40.425 10055 7310 21400 16.64e6 G41.123 7190 2520 15300 0.55e6 G41.16 225.2 126 342 0.14e6G41.226 1800 710 31500 0.42e6G41.348 411000 101000 486000 0.62e6G45.467 143000 143000 332000 1.41e6G45.473 28300 13300 57600 1.05e6G45.493 18700 13500 135000 0.78e6G59.782 8310 6200 9060 1.78e6
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f(x)=axb b=0.609 (150%)
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We calculated the IRAC colours [3.6][4.5] and [4.5][5.8] and MIR luminositiesof EGO objects with and without methanol maser emission (lying within a radius of 60” from the tracking centres). There is nostatistically significant differences between maser and nonmasers sources (with a limit of 80 mJy 1 rms). That is consistent with Cyganowski et al. (2009) (a sample of 20 sources). We note that the EGOs with methanol masersare brighter than the EGOs without such emission.
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Summary:
VLBI still useful determination of the maser morphologyalthough we need remember it resolves the emission, we note a slight dependence between the maser luminosity and the total luminosity of the central MYSO, in the cluster of MYSO the 6.7 GHz methanol maserswere associated with the brightest component.
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