Wide angle and deep surveys, regardless of their primary purpose, always sample a large number of stars in the Galaxy and in its satellite system. Here we make a forecast of the expected stellar ...sample resulting from the Dark Energy Survey (DES) and the perspectives that it will open for studies of Galactic structure and resolved stellar populations in general. An estimated 1.2 X 108 stars will be sampled in DES grizY filters in the southern equatorial hemisphere. This roughly corresponds to 20% of all DES sources. Most of these stars belong to the stellar thick disk and halo of the Galaxy. DES will probe low-mass stellar and sub-stellar objects at depths from three to eight times larger than those in the Sloan Digital Sky Survey (SDSS). The faint end of the main sequence (MS) will be densely sampled beyond 10 kpc. The slope of the low mass end of the stellar initial mass function (IMF) will be constrained to within a few hundredths of dex, even in the thick disk and halo. In the sub-stellar mass regime, the IMF slope will be potentially constrained to within dlog (m)/dlog m 0.1. About 3 X 104 brown dwarf candidates and at least 7.6 X 105 white dwarf candidates will be selected, the latter embedded into the thick disk and halo, for future follow-up. The stellar halo flattening will also be constrained to within a few percent. DES will probe the MS of new Milky Way satellites and halo clusters for distances out to 120 kpc, therefore yielding stellar surface density contrasts 1.6-1.7 times larger than those attainable with SDSS. It will also allow detection of these objects in the far reaches of the stellar halo, substantially increasing the number and quality of probes to the Galactic potential. Combined with northern samples, such as the SDSS, the DES stellar sample will yield constraints on the structure and stellar populations of Galactic components in unprecedented detail. In particular, the combined sample from both hemispheres will allow detailed studies of halo and thick disk asymmetries and triaxiality.
We use the two-point correlation function to calculate the clustering properties of the SSRS2 survey, which probes two well-separated regions of the sky, allowing one to evaluate the sensitivity of ...sample-to-sample variations. Taking advantage of the large number of galaxies in the combined sample, we also investigate the dependence of clustering on the internal properties of galaxies. By comparing the correlation function calculated in redshift and real space, we find that the redshift distortion on intermediate scales is small. This result implies that the observed redshift-space distribution of galaxies is close to that in real space and that beta = Omega exp 0.6/b less than 1, where Omega is the cosmological density parameter and b is the linear biasing factor for optical galaxies. We have used the SSRS2 sample to study the dependence of xi on the internal properties of galaxies, such as luminosity, morphology, and color. We confirm earlier results that luminous galaxies (L greater than L*) are more clustered than sub-L* galaxies and that the luminosity segregation is scale-independent. We also find that early types are more clustered than late types. We also find that red galaxies are significantly more clustered than blue ones. (Author)
We measure radial gradients of the Mg sub(2) index in 15 E-E/S0 and 14 SO galaxies. Our homogeneous data set covers a large range of internal stellar velocity dispersions (2.0 < log sigma < 2.5) and ...Mg sub(2) gradients Delta Mg sub(2)/ Delta log (r/r* sub(e)) up to -0.14 mag dex super(-1). We find for the first time a noticeable lower boundary in the relation between Mg sub(2) gradient and sigma along the full range of sigma , which may be populated by galaxies predominantly formed by monolithic collapse. At high sigma , galaxies showing flatter gradients could represent objects that suffered either important merging episodes or later gas accretion. These processes contribute to the flattening of the metallicity gradients, and their increasing importance could define the distribution of the objects above the boundary expected by the "classical" monolithic process. This result is in marked contrast to previous works, which found a correlation between Delta Mg sub(2)/ Delta log (r/r* sub(e)) and sigma confined to the low-mass galaxies, suggesting that only galaxies below some limiting sigma were formed by collapse, whereas the massive ones were formed by mergers. We show observational evidence that a hybrid scenario could also arise among massive galaxies. Finally, we estimate Delta Z/H from Mg sub(2) and H beta measurements and single stellar population models. The conclusions remain the same, indicating that the results cannot be ascribed to age effects on Mg sub(2).
Wide angle and deep surveys, regardless of their primary purpose, always sample a large number of stars in the Galaxy and in its satellite system. Here we make a forecast of the expected stellar ...sample resulting from the Dark Energy Survey (DES) and the perspectives that it will open for studies of Galactic structure and resolved stellar populations in general. An estimated 1.2 x 10{sup 8} stars will be sampled in DES grizY filters in the southern equatorial hemisphere. This roughly corresponds to 20% of all DES sources. Most of these stars belong to the stellar thick disk and halo of the Galaxy. DES will probe low-mass stellar and sub-stellar objects at depths from three to eight times larger than those in the Sloan Digital Sky Survey (SDSS). The faint end of the main sequence (MS) will be densely sampled beyond 10 kpc. The slope of the low mass end of the stellar initial mass function (IMF) will be constrained to within a few hundredths of dex, even in the thick disk and halo. In the sub-stellar mass regime, the IMF slope will be potentially constrained to within dlog {phi}(m)/dlog m {approx_equal} 0.1. About 3 x 10{sup 4} brown dwarf candidates and at least 7.6 x 10{sup 5} white dwarf candidates will be selected, the latter embedded into the thick disk and halo, for future follow-up. The stellar halo flattening will also be constrained to within a few percent. DES will probe the MS of new Milky Way satellites and halo clusters for distances out to {approx_equal} 120 kpc, therefore yielding stellar surface density contrasts 1.6-1.7 times larger than those attainable with SDSS. It will also allow detection of these objects in the far reaches of the stellar halo, substantially increasing the number and quality of probes to the Galactic potential. Combined with northern samples, such as the SDSS, the DES stellar sample will yield constraints on the structure and stellar populations of Galactic components in unprecedented detail. In particular, the combined sample from both hemispheres will allow detailed studies of halo and thick disk asymmetries and triaxiality.
Southern sky redshift survey : the catalog NICOLACI DA COSTA, L; PELLEGRINI, P. S; DAVIS, M ...
The Astrophysical journal. Supplement series,
04/1991, Letnik:
75, Številka:
4
Journal Article
Recenzirano
The catalog of radial velocities for galaxies which comprise the diameter-limited sample of the Southern Sky Redshift Survey is presented. It consolidates the data of observations carried out at the ...Las Campanas Observatory, Observatorio Nacional, and South African Astronomical Observatory. The criteria used for the sample selection are described, as well as the observational procedures and the technique utilized to obtain the final radial velocities. The intercomparison between radial velocity measurements from different telescopes indicates that the final data base is fairly homogeneous with a typical error of about 40 km/s. The sample is at present 90 percent complete, and the missing galaxies are predominantly objects with very low surface brightness for which it is very difficult to obtain optical redshifts. 20 refs.
Trichoderma filamentous fungi have been investigated due to their ability to secrete cellulases which find various biotechnological applications such as biomass hydrolysis and cellulosic ethanol ...production. Previous studies demonstrated that Trichoderma harzianum IOC-3844 has a high degree of cellulolytic activity and potential for biomass hydrolysis. However, enzymatic, biochemical, and structural studies of cellulases from T. harzianum are scarce. This work reports biochemical characterization of the recombinant endoglucanase I from T. harzianum, ThCel7B, and its catalytic core domain. The constructs display optimum activity at 55 °C and a surprisingly acidic pH optimum of 3.0. The full-length enzyme is able to hydrolyze a variety of substrates, with high specific activity: 75 U/mg for β-glucan, 46 U/mg toward xyloglucan, 39 U/mg for lichenan, 26 U/mg for carboxymethyl cellulose, 18 U/mg for 4-nitrophenyl β-D-cellobioside, 16 U/mg for rye arabinoxylan, and 12 U/mg toward xylan. The enzyme also hydrolyzed filter paper, phosphoric acid swollen cellulose, Sigmacell 20, Avicel PH-101, and cellulose, albeit with lower efficiency. The ThCel7B catalytic domain displays similar substrate diversity. Fluorescence-based thermal shift assays showed that thermal stability is highest at pH 5.0. We determined kinetic parameters and analyzed a pattern of oligosaccharide substrates hydrolysis, revealing cellobiose as a final product of C6 degradation. Finally, we visualized effects of ThCel7B on oat spelt using scanning electron microscopy, demonstrating the morphological changes of the substrate during the hydrolysis. The acidic behavior of ThCel7B and its considerable thermostability hold a promise of its industrial applications and other biotechnological uses under extremely acidic conditions.
The reconstruction of the peculiar velocity field from the 1.936-Jy IRAS-selected sample of galaxies is compared with a similar reconstruction from an optically selected sample. A general method for ...combining different samples to reconstruct a self-consistent density and peculiar velocity field is presented. The method is applied to determine how sensitive the derived peculiar velocity field is to the characteristics of the sample used. The possibility that the IRAS galaxies do not trace the general galaxy population is explored, adopting a simple model of linear biasing between the IRAS and optical samples. We find that the velocity fields derived from the two samples are consistent, within the estimated shot-noise error, for the case of no relative bias. This result suggests that the predicted peculiar velocity field based on IRAS samples is not sensitive to the sampling properties of IRAS galaxies. Combined with a previous suggestion of a relative biasing of IRAS galaxies on small scales (about 5 h-1 Mpc), this result suggests scale-dependent biasing.
New CCD observations are used to examine the accuracy of the magnitude system adopted to define the galaxy sample being employed to conduct the Southern Sky Redshift Survey Extension (SSRS2). The ...magnitude scale of the SSRS2 is based on the instrumental magnitudes of the nonstellar objects listed in the ST ScI Guide Star Catalog, converted to the B(0) system. The magnitudes derived in the photometric catalog of Lauberts and Valentijn (1989) are found to be in excellent agreement with the CCD measurements, with isophotal magnitudes showing a dispersion of about 0.13 mag, although an offset 0.15 mag in zero point may be present. The magnitudes m(SSRS2) derived from the ST ScI instrumental magnitudes correspond well to a blue magnitude measured within the B = 26 mag/sq arcsec isophote. It is argued that the ST ScI objects may provide an invaluable source for the construction of a uniform magnitude-limited sample of galaxies in the Southern Hemisphere. (AIAA)
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