1,455 research outputs found
The Statistical Properties of Galaxies Containing ULXs
We present a statistical analysis of the properties of galaxies containing
ultraluminous X-ray objects (ULXs). Our primary goal is to establish the
fraction of galaxies containing a ULX as a function of ULX luminosity. Our
sample is based on ROSAT HRI observations of galaxies. We find that ~ 12% of
galaxies contain at least one ULX with L_X > 10^39 erg/s and ~ 1% of galaxies
contain at least one ULX with L_X > 10^40 erg/s. These ULX frequencies are
lower limits since ROSAT HRI observation would miss absorbed ULXs (i.e., with
N_H >~ 10^21 cm^-2) and those within ~ 10" of the nucleus (due to the
positional error circle of the ROSAT HRI). The Hubble type distribution of
galaxies with a ULX differs significantly from the distribution of types for
nearby RC3 galaxies, but does not differ significantly from the galaxy type
distribution of galaxies observed by the HRI in general. We find no increase in
the mean FIR luminosity or FIR / K band luminosity ratio for galaxies with a
ULX relative to galaxies observed by the HRI in general, however this result is
also most likely biased by the soft bandpass of the HRI and the relatively low
number of high SFR galaxies observed by the HRI with enough sensitivity to
detect a ULX.Comment: Accepted by Apj. 5 pages with 4 figures formatted using emulateapj.
Version with just b/w figures available at
http://www.pha.jhu.edu/~ptak/paper
FLOX/methane pump-fed engine study
FLOX and methane rocket propellant for use with modified RL-10-A-1 engin
Hydrogen adsorption and cohesive energy of single-walled carbon nanotubes
Hydrogen adsorption on crystalline ropes of carbon single-walled nanotubes (SWNT) was found to exceed 8 wt.%, which is the highest capacity of any carbon material. Hydrogen is first adsorbed on the outer surfaces of the crystalline ropes. At pressures higher than about 40 bar at 80 K, however, a phase transition occurs where there is a separation of the individual SWNTs, and hydrogen is physisorbed on their exposed surfaces. The pressure of this phase transition provides a tube-tube cohesive energy for much of the material of 5 meV/C atom. This small cohesive energy is affected strongly by the quality of crystalline order in the ropes
The role of quenching time in the evolution of the mass-size relation of passive galaxies from the WISP survey
We analyze how passive galaxies at z 1.5 populate the mass-size plane
as a function of their stellar age, to understand if the observed size growth
with time can be explained with the appearance of larger quenched galaxies at
lower redshift. We use a sample of 32 passive galaxies extracted from the Wide
Field Camera 3 Infrared Spectroscopic Parallel (WISP) survey with spectroscopic
redshift 1.3 z 2.05, specific star-formation rates lower
than 0.01 Gyr, and stellar masses above 4.5 10
M. All galaxies have spectrally determined stellar ages from fitting of
their rest-frame optical spectra and photometry with stellar population models.
When dividing our sample into young (age 2.1 Gyr) and old (age 2.1
Gyr) galaxies we do not find a significant trend in the distributions of the
difference between the observed radius and the one predicted by the mass-size
relation. This result indicates that the relation between the galaxy age and
its distance from the mass-size relation, if it exists, is rather shallow, with
a slope alpha -0.6. At face value, this finding suggests that
multiple dry and/or wet minor mergers, rather than the appearance of newly
quenched galaxies, are mainly responsible for the observed time evolution of
the mass-size relation in passive galaxies.Comment: Accepted for publication in ApJ Letters; 6 pages, 3 figures, 1 tabl
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