Typical Clumps Research Articles

VLT-SINFONI sub-kpc study of the star formation in local LIRGs and ULIRGs

We present a 2D study of star formation at kpc and sub-kpc scales of a sample of local (z<0.1) U/LIRGs, based on near-IR VLT-SINFONI observations. We obtained integrated measurements of the star formation rate (SFR) and star formation rate surface density, together with their 2D distributions, based on Br_gamma and Pa_alpha emission. We observe a tight linear correlation between the SFR derived from our extinction-corrected measurements and that derived from 24 micron data, and a reasonable agreement with SFR derived from total IR luminosity. Our near-IR measurements are on average a factor 3 larger than optical SFR, even when extinction corrections are applied. We found that LIRGs have a median-observed star formation rate surface density of 1.72 Msun/yr/kpc^2 for the extinction-corrected distribution, whilst ULIRGs have 0.23 Msun/yr/kpc^2, respectively. These median values for ULIRGs increase up to 2.90 Msun/yr/kpc^2, when only their inner regions, covering the same size as the average FoV of LIRGs, are considered. We identified a total of 95 individual SF clumps in our sample, with sizes within 60-1500pc, and extinction-corrected Pa_alpha luminosities of 10^5-10^8 Lsun. Star-forming clumps in LIRGs are about ten times larger and thousands of times more luminous than typical clumps in spiral galaxies. Clumps in ULIRGs have sizes similar (x0.5-1) to those of high-z clumps, having Pa_alpha luminosities similar to some high-z clumps, and about 10 times less luminous than the most luminous high-z clumps identified so far. We also observed a change in the slope of the L-r relation. A likely explanation is that most luminous galaxies are interacting and merging, and therefore their size represents a combination of the distribution of the star-forming clumps within each galaxy in the system plus the effect of the projected distance.

THE SINS SURVEY OFz∼ 2 GALAXY KINEMATICS: PROPERTIES OF THE GIANT STAR-FORMING CLUMPS

We have studied the properties of giant star-forming clumps in five z ∼ 2 star-forming disks with deep SINFONI AO spectroscopy at the ESO VLT. The clumps reside in disk regions where the Toomre Q-parameter is below unity, consistent with their being bound and having formed from gravitational instability. Broad Hα/[N ii] line wings demonstrate that the clumps are launching sites of powerful outflows. The inferred outflow rates are comparable to or exceed the star formation rates, in one case by a factor of eight. Typical clumps may lose a fraction of their original gas by feedback in a few hundred million years, allowing them to migrate into the center. The most active clumps may lose much of their mass and disrupt in the disk. The clumps leave a modest imprint on the gas kinematics. Velocity gradients across the clumps are 10–40 km s−1 kpc−1, similar to the galactic rotation gradients. Given beam smearing and clump sizes, these gradients may be consistent with significant rotational support in typical clumps. Extreme clumps may not be rotationally supported; either they are not virialized or they are predominantly pressure supported. The velocity dispersion is spatially rather constant and increases only weakly with star formation surface density. The large velocity dispersions may be driven by the release of gravitational energy, either at the outer disk/accreting streams interface, and/or by the clump migration within the disk. Spatial variations in the inferred gas phase oxygen abundance are broadly consistent with inside-out growing disks, and/or with inward migration of the clumps.

Observations of the Clumpy Shell of the L1551 Bipolar Outflow

We have studied two regions along the edges of the L1551 IRS 5 bipolar outflow where unusually bright "high-velocity" CS emission is seen. These regions are 4' west and 2' east of IRS 5; a line drawn through them passes directly through IRS 5, along the axis of the highly collimated ionized jets from the star. <P />We mapped the J = 2-1 CS emission from these two spots with 7" angular resolution, and obtained single- dish spectra of 12 molecular transitions toward both regions. The maps show that the high-velocity gas is an integral part of a clumpy shell of molecular gas along the periphery of the bipolar lobes. Typical clumps have CS brightness temperatures of 5-7 K, line widths of ∼0.8 km s<SUP>-1</SUP>, and diameters down to our resolution limit of ∼1000 AU. One of the CS clumps in the L1551-2E field is coincident with IRAS source L1551NE. The clumps are estimated to have kinetic temperatures of 20-30 K and densities of ∼4 × 10<SUP>5</SUP> cm<SUP>-3</SUP>. The total mass of high velocity gas toward each region is roughly 0.02 M<SUB>sun</SUB>; individual clumps have masses as small as 0.001 M<SUB>sun</SUB>. The chemical abundances of SO, CS, and NH<SUB>3</SUB> may be unusually large in these regions. <P />The data suggest that low velocity (V &lt; 15 km s<SUP>1</SUP>) shocks propagate into the swept-up molecular shell at these locations. Apparently the collimated high velocity jets from IRS 5 are degraded into a broader, lower velocity wind before impacting these regions.

A study by electron microscopy of the formation of new surface by Chaos chaos

The cell surface of the ameba Chaos chaos was “coated” with Alcian Blue by exposure of the cells to dilute dye solutions at 5 °C. At this temperature the amebae are immobilized. Formation of new surface was studied after rinsing the specimens and removing them to a fresh drop of medium at room temperature. Direct observations of amebae indicated that complete turnover of surface occurred in about 35 min but that the resultant new surface was probably not as convoluted as the original. Rate of formation of surface when amebae were recycled through the dye treatment was much slower. As previously reported, electron micrographs of fixed specimens showed that in dye-treated cells the surface filaments seen in untreated cells were replaced by dense clumps occurring at irregular intervals. New surface possessed all the layers of surface found in untreated cells. In sections including recently formed surface, the plasmalemma was smooth and few vesicles were seen in the underlying cytoplasm. In some sections clumps of old surface were found with surface filaments passing through them. More typically, a series of transitional profiles between typical filaments and typical clumps could be seen. Frequency counts of the clumps on photomicrographs before and after new surface formation provided no evidence for the hypothesis that there may be slippage between surface coat and underlying plasmalemma. In the cytoplasm of the uroid of amebae 15 min after return to room temperature, extensive areas of convoluted membranes bearing typical dense clumps were found. It is concluded that under the present conditions there is rapid and extensive formation of new surface which possesses all the morphological layers of the original surface. A mechanism involving interpolation of ground cytoplasm into the new surface appears to account better for the findings than one involving fusions of vesicles with the surface.