816 research outputs found
The Motions of Clusters of Galaxies and the Dipoles of the Peculiar Velocity Field
In preceding papers of this series, TF relations for galaxies in 24 clusters
with radial velocities between 1000 and 9200 km/s (SCI sample) were obtained, a
Tully-Fisher (TF) template relation was constructed and mean offsets of each
cluster with respect to the template obtained. Here, an estimate of the
line-of-sight peculiar velocities of the clusters and their associated errors
are given. It is found that cluster peculiar velocities in the Cosmic Microwave
Background reference frame do not exceed 600 k/ms and that their distribution
has a line-of-sight dispersion of 300 k/ms, suggesting a more quiescent cluster
peculiar velocity field than previously reported. When measured in a reference
frame in which the Local Group is at rest, the set of clusters at cz > 3000
km/s exhibits a dipole moment in agreement with that of the CMB, both in
amplitude and apex direction. It is estimated that the bulk flow of a sphere of
6000 km/s radius in the CMB reference frame is between 140 and 320 km/s. These
results are in agreement with those obtained from an independent sample of
field galaxies (Giovanelli et al. 1998; see astro-ph/9807274)Comment: 9 pages, 2 tables, 7 figures, uses AAS LaTex; to appear in A
The Tully-Fisher Relation and H_not
The use of the Tully-Fisher (TF) relation for the determination of the Hubble
Constant relies on the availability of an adequate template TF relation and of
reliable primary distances. Here we use a TF template relation with the best
available kinematical zero-point, obtained from a sample of 24 clusters of
galaxies extending to cz ~ 9,000 km/s, and the most recent set of Cepheid
distances for galaxies fit for TF use. The combination of these two ingredients
yields H_not = 69+/-5 km/(s Mpc). The approach is significantly more accurate
than the more common application with single cluster (e.g. Virgo, Coma)
samples.Comment: 10 pages, including 2 figures and 1 table; uses AAS LaTex. Submitted
to ApJ Letter
Программа расчёта математической модели теплового контура электролизного узла производства фтора
Объектом исследования является модель теплового контура электролизного узла производства фтора. Цель работы – разработка принципов организации и создания программы для ЭВМ расчета модели электролизного узла на примере создания программы расчета модели теплового контура узла. В процессе работы проводился анализ структуры и математического описания МЭУ с целью выбора технологии программирования и определения принципов структурной организации программы. Руководствуясь определенными принципами структурной организации и используя выбранную технологию программирования разработана программа расчета модели теплового контура электролизного узла.The object of research is a model of the thermal circuit of the electrolysis unit of fluorine production. The aim of work is development of principles of the organization and the creation of a computer program for calculating the model of the electrolysis unit by creating a program of calculation models thermal unit circuit. During the process of research analyzed the structure and the mathematical description of the EUM to select programming technology and the definition of the principles of structural organization of the program. Guided by certain principles of structural organization and using the selected programming technology developed program for calculating thermal circuit model electrolysis unit
The starburst phenomenon from the optical/near-IR perspective
The optical/near-IR stellar continuum carries unique information about the
stellar population in a galaxy, its mass function and star-formation history.
Star-forming regions display rich emission-line spectra from which we can
derive the dust and gas distribution, map velocity fields, metallicities and
young massive stars and locate shocks and stellar winds. All this information
is very useful in the dissection of the starburst phenomenon. We discuss a few
of the advantages and limitations of observations in the optical/near-IR region
and focus on some results. Special attention is given to the role of
interactions and mergers and observations of the relatively dust-free starburst
dwarfs. In the future we expect new and refined diagnostic tools to provide us
with more detailed information about the IMF, strength and duration of the
burst and its triggering mechanisms.Comment: 6 pages, 3 figures, to appear in "Starbursts: from 30 Doradus to
Lyman Break Galaxies" 2005, eds. R. de Grijs and R. M. Gonzalez Delgado
(Kluwer
Discovery of a Gas-Rich Companion to the Extremely Metal-Poor Galaxy DDO 68
We present HI spectral-line imaging of the extremely metal-poor galaxy DDO
68. This system has a nebular oxygen abundance of only 3% Z, making
it one of the most metal-deficient galaxies known in the local volume.
Surprisingly, DDO 68 is a relatively massive and luminous galaxy for its metal
content, making it a significant outlier in the mass-metallicity and
luminosity-metallicity relationships. The origin of such a low oxygen abundance
in DDO 68 presents a challenge for models of the chemical evolution of
galaxies. One possible solution to this problem is the infall of pristine
neutral gas, potentially initiated during a gravitational interaction. Using
archival HI spectral-line imaging obtained with the Karl G. Jansky Very Large
Array, we have discovered a previously unknown companion of DDO 68. This
low-mass (M 2.810 M), recently
star-forming (SFR 1.410 M yr,
SFR 710 M yr) companion has
the same systemic velocity as DDO 68 (V 506 km s; D
12.740.27 Mpc) and is located at a projected distance of 42 kpc. New HI
maps obtained with the 100m Robert C. Byrd Green Bank Telescope provide
evidence that DDO 68 and this companion are gravitationally interacting at the
present time. Low surface brightness HI gas forms a bridge between these
objects.Comment: Accepted for publication in the Astrophysical Journal Letter
Very Strong Emission-Line Galaxies in the WISP Survey and Implications for High-Redshift Galaxies
The WFC3 Infrared Spectroscopic Parallel Survey (WISP) uses the Hubble Space
Telescope (HST) infrared grism capabilities to obtain slitless spectra of
thousands of galaxies over a wide redshift range including the peak of star
formation history of the Universe. We select a population of very strong
emission-line galaxies with rest-frame equivalent widths higher than 200 A. A
total of 176 objects are found over the redshift range 0.35 < z < 2.3 in the
180 arcmin^2 area we analyzed so far. After estimating the AGN fraction in the
sample, we show that this population consists of young and low-mass starbursts
with higher specific star formation rates than normal star-forming galaxies at
any redshift. After spectroscopic follow-up of one of these galaxies with
Keck/LRIS, we report the detection at z = 0.7 of an extremely metal-poor galaxy
with 12+Log(O/H)= 7.47 +- 0.11. The nebular emission-lines can substantially
affect the broadband flux density with a median brightening of 0.3 mag, with
examples producing brightening of up to 1 mag. The presence of strong emission
lines in low-z galaxies can mimic the color-selection criteria used in the z ~
8 dropout surveys. In order to effectively remove low redshift interlopers,
deep optical imaging is needed, at least 1 mag deeper than the bands in which
the objects are detected. Finally, we empirically demonstrate that strong
nebular lines can lead to an overestimation of the mass and the age of galaxies
derived from fitting of their SED. Without removing emission lines, the age and
the stellar mass estimates are overestimated by a factor of 2 on average and up
to a factor of 10 for the high-EW galaxies. Therefore the contribution of
emission lines should be systematically taken into account in SED fitting of
star-forming galaxies at all redshifts.Comment: Accepted for publication in the Astrophysical Journal. 15 pages, 13
figure
HS 2134+0400 - new very metal-poor galaxy, a representative of void population?
We present the SAO 6m telescope spectroscopy of a blue compact galaxy (BCG)
HS 2134+0400 discovered in frame of the dedicated Hamburg/SAO survey for Low
Metallicity BCGs (HSS-LM). Its very low abundance of oxygen (12+log(O/H) =
7.44), as well as other heavy elements (S, N, Ne, Ar), assigns this dwarf
galaxy to the group of BCGs with the lowest metal content. There are only eight
that low metallicity among several thousand known BCGs in the nearby Universe.
The abundance ratios for the heavy elements (S/O, Ne/O, N/O, and Ar/O) are well
consistent with the typical values of other very metal-poor BCGs. The global
environment of HS 2134+0400 is atypical of the majority of BCGs. The object
falls within the Pegasus void, the large volume with the very low density of
galaxies with the normal (M_B* = -19.6) or high luminosity. Since we found in
voids a dozen more the very metal-poor galaxies, we discuss the hypothesis that
such objects can be representative of a substantial fraction of the void dwarf
galaxy population.Comment: 6 pages, including 2 tables and 2 postscript figures. Submitted to
Astronomy Letter
A Spectroscopic Study of a Large Sample of Wolf-Rayet Galaxies
We analyze long-slit spectral observations of 39 Wolf-Rayet (WR) galaxies
with heavy element mass fraction ranging over 2 orders of magnitude, from
Zsun/50 to 2Zsun. Nearly all galaxies in our sample show broad WR emission in
the blue region of the spectrum (the blue bump) consisting of an unresolved
blend of N III 4640, C III 4650, C IV 4658 and He II 4686 emission lines. Broad
C IV 5808 emission (the red bump) is detected in 30 galaxies. Additionally,
weaker WR emission lines are identified, most often the N III 4512 and Si III
4565 lines, which have very rarely or never been seen and discussed before in
WR galaxies. These emission features are characteristic of WN7-WN8 and WN9-WN11
stars respectively.
We derive the numbers of early WC (WCE) and late WN (WNL) stars from the
luminosities of the red and blue bumps, and the number of O stars from the
luminosity of the Hbeta emission line. Additionally, we propose a new technique
for deriving the numbers of WNL stars from the N III 4512 and Si III 4565
emission lines. This technique is potentially more precise than the blue bump
method because it does not suffer from contamination of WCE and early WN (WNE)
stars and nebular gaseous emission.
The N(WR)/N(O+WR) ratio decreases with decreasing metallicity, in agreement
with predictions of evolutionary synthesis models. The N(WC)/N(WN) ratios and
the equivalent widths of the blue bump EW(4650) and of the red bump EW(5808)
derived from observations are also in satisfactory agreement with theoretical
predictions.Comment: 49 pages, 9 figures, to appear in Astrophys.
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