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Register a new userDetection of CO from SMM J16359+6612, The Multiply Imaged Submillimeter Galaxy Behind A2218
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We report the detection of CO ($J$=3$to$2) line emission from all three multiple images (A,B and C) of the intrinsically faint ($simeq$ 0.8 mJy) submillimeter-selected galaxy SMM J16359+6612. The brightest source of the submm continuum emission (B) also 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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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 Gaussian decomposition of the spectra we show that the CO line ratios, and therefore the underlying physical conditions of the gas, are similar for the blue and the redshifted component. The CO line Spectral Energy Distribution (SED; i.e. flux density vs. rotational quantum number) turns over already at the CO(5--4) transition which shows that the molecular gas is less excited than in nearby starburst galaxies and high--z QSOs. This difference mainly arises from a lower average H2 density, which indicates that the gas is less centrally concentrated than in nuclear starburst regions in local galaxies. We suggest that the bulk of the molecular gas in SMM J16359+6612 may arise from an overlap region of two merging galaxies. The low gas density and clear velocity separation may reflect an evolutionary stage of the merger event that is in between those seen in the Antennae and in the more evolved ultraluminous infrared galaxies (ULIRGs) like e.g. Mrk231.
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.
We present evidence for a Spitzer-selected luminous infrared galaxy (LIRG) behind the Bullet Cluster. The galaxy, originally identified in IRAC photometry as a multiply imaged source, has a spectral energy distribution consistent with a highly extincted (A_V~3.3), strongly star-forming galaxy at z=2.7. Using our strong gravitational lensing model presented in Bradac et al. (2006), we find that the magnifications are 10 to 50 for the three images of the galaxy. The implied infrared luminosity is consistent with the galaxy being a LIRG, with a stellar mass of M_*~2e11 M_Sun and a star formation rate of ~90 M_Sun/yr. With lensed fluxes at 24 microns of 0.58 mJy and 0.39 mJy in the two brightest images, this galaxy presents a unique opportunity for detailed study of an obscured starburst with star fomation rate comparable to that of L* galaxies at z>2.
We report spectroscopic confirmation and high-resolution infrared imaging of a z=2.79 triply-imaged galaxy behind the Bullet Cluster. This source, a Spitzer-selected luminous infrared galaxy (LIRG), is confirmed via polycyclic aromatic hydrocarbon (PAH) features using the Spitzer Infrared Spectrograph (IRS) and resolved with HST WFC3 imaging. In this galaxy, which with a stellar mass of M*=4e9 Msun is one of the two least massive ones studied with IRS at z>2, we also detect H_2 S(4) and H_2 S(5) pure rotational lines (at 3.1 sigma and 2.1 sigma) - the first detection of these molecular hydrogen lines in a high-redshift galaxy. From the molecular hydrogen lines we infer an excitation temperature T=377+68-84 K. The detection of these lines indicates that the warm molecular gas mass is 6(+36-4)% of the stellar mass and implies the likely existence of a substantial reservoir of cold molecular gas in the galaxy. Future spectral observations at longer wavelengths with facilities like the Herschel Space Observatory, the Large Millimeter Telescope, and the Atacama Pathfinder EXperiment (APEX) thus hold the promise of precisely determining the total molecular gas mass. Given the redshift, and using refined astrometric positions from the high resolution imaging, we also update the magnification estimate and derived fundamental physical properties of this system. The previously published values for total infrared luminosity, star formation rate, and dust temperature are confirmed modulo the revised magnification; however we find that PAH emission is roughly a factor of five stronger than would be predicted by the relations between the total infrared and PAH luminosity reported for SMGs and starbursts in Pope et al. (2008).
We report the detection of 1.3mm continuum and near-infrared K-band (2.2-micron) emission from the submillimeter galaxy SMM J00266+1708. Although this galaxy is among the brightest sub-mm sources detected in the blank-sky surveys (L~10^{13} L[sun]), SMM J00266+1708 had no reliable optical/near-infrared counter-part. We used sensitive interferometric 1.3mm observations with the Owens Valley Millimeter Array to accurately determine the position of the sub-mm galaxy. Follow-up near-infrared imaging with the Keck I telescope uncovered a new faint red galaxy at K=22.5 mag which is spatially coincident with the 1.3mm emission. This is currently the faintest confirmed counter-part of a sub-mm galaxy. Although the redshift of SMM J00266+1708 is still unknown, its high sub-mm/radio spectral index suggests that the system is at high redshift (z>2). Approximately 50% or more of the sub-mm galaxies are faint/red galaxies similar to that of SMM J00266+1708. These ultraluminous obscured galaxies account for a significant fraction of the total amount of star-formation at high redshift despite being missed by optical/ultraviolet surveys.
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