60 research outputs found
Imaging Carbon Monoxide Emission in the Starburst Galaxy NGC 6000
We present measurements of carbon monoxide emission in the central region of
the nearby starburst NGC 6000 taken with the Submillimeter Array. The J=2-1
transition of 12CO, 13CO, and C18O were imaged at a resolution of ~3''x2''
(450x300 pc). We accurately determine the dynamical center of NGC 6000 at
R.A(J2000.0)=15h49m49.5s and dec(J2000.0)=-29d23'13'' which agrees with the
peak of molecular emission position. The observed CO dynamics could be
explained in the context of the presence of a bar potential affecting the
molecular material, likely responsible for the strong nuclear concentration
where more than 85% of the gas is located. We detect a kinematically detached
component of dense molecular gas at relatively high velocity which might be
fueling the star formation. A total nuclear dynamical mass of 7x10^9 Msun is
derived and a total mass of gas of 4.6x10^8 Msun, yielding a Mgas/Mdyn~6%,
similar to other previously studied barred galaxies with central starbursts. We
determined the mass of molecular gas with the optically thin isotopologue C18O
and we estimate a CO-to-H2 conversion factor X(CO)=0.4x10^20 cm-2/(K km s-1) in
agreement with that determined in other starburst galaxies.Comment: 31 pages, 7 figures. Accepted for publication in Astronomical
Journal
Iron and alpha-element Production in the First One Billion Years after the Big Bang
We present measurements of carbon, oxygen, silicon, and iron in quasar
absorption systems existing when the universe was roughly one billion years
old. We measure column densities in nine low-ionization systems at 4.7 < z <
6.3 using Keck, Magellan, and VLT optical and near-infrared spectra with
moderate to high resolution. The column density ratios among C II, O I, Si II,
and Fe II are nearly identical to sub-DLAs and metal-poor ([M/H] < -1) DLAs at
lower redshifts, with no significant evolution over 2 < z < 6. The estimated
intrinsic scatter in the ratio of any two elements is also small, with a
typical r.m.s. deviation of <0.1 dex. These facts suggest that dust depletion
and ionization effects are minimal in our z > 4.7 systems, as in the
lower-redshift DLAs, and that the column density ratios are close to the
intrinsic relative element abundances. The abundances in our z > 4.7 systems
are therefore likely to represent the typical integrated yields from stellar
populations within the first gigayear of cosmic history. Due to the time limit
imposed by the age of the universe at these redshifts, our measurements thus
place direct constraints on the metal production of massive stars, including
iron yields of prompt supernovae. The lack of redshift evolution further
suggests that the metal inventories of most metal-poor absorption systems at z
> 2 are also dominated by massive stars, with minimal contributions from
delayed Type Ia supernovae or AGB winds. The relative abundances in our systems
broadly agree with those in very metal-poor, non-carbon-enhanced Galactic halo
stars. This is consistent with the picture in which present-day metal-poor
stars were potentially formed as early as one billion years after the Big Bang.Comment: Accepted for publication in Ap
The Dark Energy Survey : more than dark energy – an overview
This overview paper describes the legacy prospect and discovery potential of the Dark Energy Survey (DES) beyond cosmological studies, illustrating it with examples from the DES early data. DES is using a wide-field camera (DECam) on the 4 m Blanco Telescope in Chile to image 5000 sq deg of the sky in five filters (grizY). By its completion, the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. In addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of Type Ia supernovae and other transients. The main goals of DES are to characterize dark energy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large-scale structure, cluster counts, weak gravitational lensing and Type Ia supernovae. However, DES also provides a rich data set which allows us to study many other aspects of astrophysics. In this paper, we focus on additional science with DES, emphasizing areas where the survey makes a difference with respect to other current surveys. The paper illustrates, using early data (from ‘Science Verification’, and from the first, second and third seasons of observations), what DES can tell us about the Solar system, the Milky Way, galaxy evolution, quasars and other topics. In addition, we show that if the cosmological model is assumed to be +cold dark matter, then important astrophysics can be deduced from the primary DES probes. Highlights from DES early data include the discovery of 34 trans-Neptunian objects, 17 dwarf satellites of the Milky Way, one published z > 6 quasar (and more confirmed) and two published superluminous supernovae (and more confirmed)
Synthesis and fungicidal activity of 1,3-thiazoline derivatives bearing nitrophenyl group on the 2-position
ZENS. IV. Similar Morphological Changes Associated with Mass Quenching and Environment Quenching and the Relative Importance of Bulge Growth versus the Fading of Disks*
We use the low-redshift Zurich Environmental Study (ZENS) catalog to study the dependence of the quenched satellite fraction at , and of the morphological mix of these quenched satellites, on three different environmental parameters: group halo mass, halo-centric distance, and large-scale structure (LSS) overdensity. Within the two mass bins into which we divide our galaxy sample, the fraction of quenched satellites is more or less independent of halo mass and the surrounding LSS overdensity, but it increases toward the centers of the halos, as found in previous studies. The morphological mix of these quenched satellites is, however, constant with radial position in the halo, indicating that the well-known morphology–density relation results from the increasing fraction of quenched galaxies toward the centers of halos. If the radial variation in the quenched fraction reflects the action of two quenching processes, one related to mass and the other to environment, then the constancy with radius of the morphological outcome suggests that both have the same effect on the morphologies of the galaxies. Alternatively, mass and environment quenching may be two reflections of a single physical mechanism. The quenched satellites have larger bulge-to-total ratios (B/T) and smaller half-light radii than the star-forming satellites. The bulges in quenched satellites have very similar luminosities and surface brightness profiles, and any mass growth of the bulges associated with quenching cannot greatly change these quantities. The differences in the light-defined B/T and in the galaxy half-light radii are mostly due to differences in the disks, which have lower luminosities in the quenched galaxies. The difference in galaxy half-light radii between quenched and star-forming satellites is however larger than can be explained by uniformly fading the disks following quenching, and the quenched disks have smaller scale lengths than in star-forming satellites. This can be explained either by a differential fading of the disks with galaxy radius or the disks being generally smaller in the past, both of which would be expected in an inside-out disk growth scenario. The overall conclusion is that, at least at low redshifts, the structure of massive quenched satellites at these masses is produced by processes that operate before the quenching takes place. A comparison of our results with semianalytic models argues for a reduction in the efficiency of group halos in quenching their disk satellites and for mechanisms to increase the B/T of low-mass quenched satellites
ZENS. IV. SIMILAR MORPHOLOGICAL CHANGES ASSOCIATED WITH MASS QUENCHING AND ENVIRONMENT QUENCHING AND THE RELATIVE IMPORTANCE OF BULGE GROWTH VERSUS THE FADING OF DISKS
QUENCHING OF STAR FORMATION IN SLOAN DIGITAL SKY SURVEY GROUPS: CENTRALS, SATELLITES, AND GALACTIC CONFORMITY
The Role of the Peripheral Chemokine, CCL3, in Hyperalgesia following Peripheral Nerve Injury in the Rat
Outer region scaling using the freestream velocity for nonuniform open channel flow over gravel
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