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تسجيل مستخدم جديدAn EVLA search for water megamaser emission in the submm galaxy SMM J16359+6612 at z=2.5
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R. Edmonds
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Using the Expanded Very Large Array, we have conducted a search for 22.2 GHz H2O megamaser emission in the strongly lensed submm galaxy, SMM J16359+6612 at z=2.517. This object is lensed into three components, and after a correction for magnification is applied to its submm-wavelength flux density, it is typical of the bulk of the high-redshift, submm galaxy population responsible for the 850 um extragalactic background (S(850um)~1 mJy). We do not detect any H2O megamaser emission, but the lensing allows us to place an interesting constraint on the luminosity of any megamasers present, L(H2O) < 5305 solar luminosities for an assumed linewidth of 80 km/s. Because the far-infrared luminosity in submm galaxies is mainly powered by star formation, and very luminous H2O megamasers are more commonly associated with quasar activity, it could be that blind searches for H2O megamasers will not be an effective means of determining redshifts for less luminous members of the submm galaxy population.
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Using the IRAM 30m telescope, we report the detection of the CO(3--2), CO(4--3), CO(5--4) and CO(6--5) lines in the gravitational lensed submm galaxy SMM J16359+6612 at z=2.5. The CO lines have a double peak profile in all transitions. From a Gaussia
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lso corresponds to the brightest CO emission, which is centered at $z$=2.5168, consistent with the pre-existing redshift derived from Ha. The observed CO flux in the A, B and C images is 1.2, 3.5 and 1.6 Jy kms respectively, with a linewidth of $500pm 100$ kms. After correcting for the lensing amplification, the CO flux corresponds to a molecular gas mass of $sim 2times 10 ^{10} h_{71}^{-2}$ Msun, while the extent of the CO emission indicates that the dynamical mass of the system $sim9times10^{10}$ Msun. Two velocity components are seen in the CO spectra; these could arise from either a rotating compact ring or disk of gas, or merging substructure. The star formation rate in this galaxy was previously derived to be $sim$100--500 Msun yr. If all the CO emission arises from the inner few kpc of the galaxy and the galactic CO-to-H$_2$ conversion factor holds, then the gas consumption timescale is a relatively short 40 Myr, and so the submm emission from SMM J16359+6612 may be produced by a powerful, but short-lived circumnuclear starburst event in an otherwise normal and representative high-redshift galaxy.
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