Browsing by Subject "midinfrared spectroscopy"

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Ionized Gas Kinematics At High Resolution. II. Discovery Of A Double Infrared Cluster In II Zw 40
(2013-04) Beck, Sara; Turner, Jean; Lacy, John; Greathouse, Thomas K.; Lahad, Ohr; Lacy, John
The nearby dwarf galaxy II Zw 40 hosts an intense starburst. At the center of the starburst is a bright compact radio and infrared source, thought to be a giant dense H II region containing approximate to 14,000 O stars. Radio continuum images suggest that the compact source is actually a collection of several smaller emission regions. We accordingly use the kinematics of the ionized gas to probe the structure of the radio-infrared emission region. With TEXES on the NASA-IRTF we measured the 10.5 mu m [S IV] emission line with effective spectral resolutions, including thermal broadening, of similar to 25 and similar to 3 km s(-1) and spatial resolution similar to 1 ''. The line profile shows two distinct, spatially coextensive, emission features. The stronger feature is at galactic velocity and has FWHM 47 km s(-1). The second feature is similar to 44 km s(-1) redward of the first and has FWHM 32 km s(-1). We argue that these are two giant embedded clusters, and estimate their masses to be approximate to 3 x 10(5) M-circle dot and approximate to 1.5 x 10(5) M-circle dot. The velocity shift is unexpectedly large for such a small spatial offset. We suggest that it may arise in a previously undetected kinematic feature remaining from the violent merger that formed the galaxy.
Millimeter Observations Of A Sample Of High-Redshift Obscured Quasars
(2009-11) Martinez-Sansigre, Alejo; Karim, Alexander; Schinnerer, Eva; Omont, Alain; Smith, Daniel J. B.; Wu, Jingwen; Hill, Gary J.; Klockner, Hans-rainer; Lacy, Mark; Rawlings, Steve; Willott, Chris J.; Hill, Gary J.
We present observations at 1.2 mm with Max-Planck Millimetre Bolometer Array (MAMBO-II) of a sample of z greater than or similar to 2 radio-intermediate obscured quasars, as well as CO observations of two sources with the Plateau de Bure Interferometer. The typical rms noise achieved by the MAMBO observations is 0.55 mJy beam(-1) and five out of 21 sources (24%) are detected at a significance of >= 3 sigma. Stacking all sources leads to a statistical detection of < S(1.2 mm)> = 0.96 +/- 0.11 mJy and stacking only the non-detections also yields a statistical detection, with < S(1.2 mm)> = 0.51 +/- 0.13 mJy. At the typical redshift of the sample, z = 2, 1 mJy corresponds to a far-infrared luminosity L(FIR) similar to 4 x 10(12) L(circle dot). If the far-infrared luminosity is powered entirely by star formation, and not by active galactic nucleus heated dust, then the characteristic inferred star formation rate is similar to 700 M(circle dot) yr(-1). This far-infrared luminosity implies a dust mass of M(d) similar to 3 x 10(8) M(circle dot), which is expected to be distributed on similar to kpc scales. We estimate that such large dust masses on kpc scales can plausibly cause the obscuration of the quasars. Combining our observations at 1.2 mm with mid-and far-infrared data, and additional observations for two objects at 350 mu m using SHARC-II, we present dust spectral energy distributions (SEDs) for our sample and derive a mean SED for our sample. This mean SED is not well fitted by clumpy torus models, unless additional extinction and far-infrared re-emission due to cool dust are included. This additional extinction can be consistently achieved by the mass of cool dust responsible for the far-infrared emission, provided the bulk of the dust is within a radius similar to 2-3 kpc. Comparison of our sample to other samples of z similar to 2 quasars suggests that obscured quasars have, on average, higher far-infrared luminosities than unobscured quasars. There is a hint that the host galaxies of obscured quasars must have higher cool-dustmasses and are therefore often found at an earlier evolutionary phase than those of unobscured quasars. For one source at z = 2.767, we detect the CO(3-2) transition, with S(CO)Delta nu = 630 +/- 50 mJy km s(-1), corresponding to L(CO(3-2)) = 3.2 x 10(7) L(circle dot), or a brightness-temperature luminosity of L'(CO(3-2)) = 2.4 x 10(10) K km s(-1) pc(2). For another source at z = 4.17, the lack of detection of the CO(4-3) line suggests the line to have a brightness-temperature luminosity L'(CO(4-3)) < 1 x 10(10) K km s(-1) pc(2). Under the assumption that in these objects the high-J transitions are thermalized, we can estimate the molecular gas contents to be M(II2) = 1.9 x 10(10) M(circle dot) and < 8 x 10(9) M(circle dot), respectively. The estimated gas depletion timescales are tau(g) = 4 Myr and <16 Myr, and low gas-to-dust mass ratios of M(g)/M(d) = 19 and <20 are inferred. These values are at the low end but consistent with those of other high-redshift galaxies.