1,491 research outputs found
Optical photometry of the UCM Lists I and II. II-B band surface photometry and morphological discussion
We present Johnson B surface photometry for the UCM Survey galaxies.
One-dimensional bulge-disk decomposition is attempted, discussing on fitting
functions and computational procedures. The results from this decomposition,
jointly with concentration indices and an asymmetry coefficient, are employed
to study the morphological properties of these galaxies. We also compare our
results with the previous morphological classification established using Gunn r
imaging data and with other samples of galaxies. No major statistical
differences in morphology are found between red and blue data, although some
characteristics such as size and luminosity concentration vary. We find a
correlation between luminosity and size. Several parameters are used to
segregate the objects according to their morphological type.Comment: 19 pages, 20 PostScript figures, accepted for publication in A&A,
also available via anonymous ftp at
ftp://cutrex.fis.ucm.es/pub/OUT/pag/PAPERS/AA0
Outer-Disk Populations in NGC 7793: Evidence for Stellar Radial Migration
We analyzed the radial surface brightness profile of the spiral galaxy NGC
7793 using HST/ACS images from the GHOSTS survey and a new HST/WFC3 image
across the disk break. We used the photometry of resolved stars to select
distinct populations covering a wide range of stellar ages. We found breaks in
the radial profiles of all stellar populations at 280" (~5.1 kpc). Beyond this
disk break, the profiles become steeper for younger populations. This same
trend is seen in numerical simulations where the outer disk is formed almost
entirely by radial migration. We also found that the older stars of NGC 7793
extend significantly farther than the underlying HI disk. They are thus
unlikely to have formed entirely at their current radii, unless the gas disk
was substantially larger in the past. These observations thus provide evidence
for substantial stellar radial migration in late-type disks.Comment: 8 pages, 6 figure. Accepted for publication in Ap
Evidence for partial melt in the crust beneath Mt. Paektu (Changbaishan), Democratic People's Republic of Korea and China
Mt. Paektu (also known as Changbaishan) is an enigmatic volcano on the border between the Democratic People's Republic of Korea (DPRK) and China. Despite being responsible for one of the largest eruptions in history, comparatively little is known about its magmatic evolution, geochronology, or underlying structure. We present receiver function results from an unprecedented seismic deployment in the DPRK. These are the first estimates of the crustal structure on the DPRK side of the volcano and, indeed, for anywhere beneath the DPRK. The crust 60 km from the volcano has a thickness of 35 km and a bulk / of 1.76, similar to that of the Sino-Korean craton. The / ratio increases ~20 km from the volcano, rising to >1.87 directly beneath the volcano. This shows that a large region of the crust has been modified by magmatism associated with the volcanism. Such high values of / suggest that partial melt is present in the crust beneath Mt. Paektu. This region of melt represents a potential source for magmas erupted in the last few thousand years and may be associated with an episode of volcanic unrest observed between 2002 and 2005.This work was supported by the Richard Lounsbery Foundation. The UK seismic instruments and data management facilities were provided under loan number 976 by SEIS-UK at the University of Leicester. The facilities of SEIS-UK are supported by the NERC under Agreement R8/H10/64. J.O.S.H. was supported by an NERC Fellowship NE/I020342/1
Radial distribution of stars, gas and dust in SINGS galaxies. I. Surface photometry and morphology
We present ultraviolet through far-infrared surface brightness profiles for
the 75 galaxies in the Spitzer Infrared Nearby Galaxies Survey (SINGS). The
imagery used to measure the profiles includes GALEX UV data, optical images
from KPNO, CTIO and SDSS, near-IR data from 2MASS, and mid- and far-infrared
images from Spitzer. Along with the radial profiles, we also provide
multi-wavelength asymptotic magnitudes and several non-parametric indicators of
galaxy morphology: the concentration index (C_42), the asymmetry (A), the Gini
coefficient (G) and the normalized second-order moment of the brightest 20% of
the galaxy's flux (M_20). Our radial profiles show a wide range of morphologies
and multiple components (bulges, exponential disks, inner and outer disk
truncations, etc.) that vary not only from galaxy to galaxy but also with
wavelength for a given object. In the optical and near-IR, the SINGS galaxies
occupy the same regions in the C_42-A-G-M_20 parameter space as other normal
galaxies in previous studies. However, they appear much less centrally
concentrated, more asymmetric and with larger values of G when viewed in the UV
(due to star-forming clumps scattered across the disk) and in the mid-IR (due
to the emission of Polycyclic Aromatic Hydrocarbons at 8.0 microns and very hot
dust at 24 microns).Comment: 66 pages in preprint format, 14 figures, published in ApJ. The
definitive publisher authenticated version is available online at
http://dx.doi.org/10.1088/0004-637X/703/2/156
Dynamical masses of a nova-like variable on the edge of the period gap
We present the first dynamical determination of the binary parameters of an eclipsing SW Sextantis star in the 3â4âh orbital period range during a low state. We obtained time-resolved optical spectroscopy and photometry of HS 0220+0603 during its 2004â2005 low-brightness state, as revealed in the combined Small & Moderate Aperture Research Telescope System, IAC80 and M1 Group long-term optical light curve. The optical spectra taken during primary eclipse reveal a secondary star spectral type of M5.5 ± 0.5 as derived from molecular band-head indices. The spectra also provide the first detection of a DAB white dwarf in a cataclysmic variable. By modelling its optical spectrum we estimate a white dwarf temperature of 30â000 ± 5000âK. By combining the results of modelling the white dwarf eclipse from ULTRACAM light curves with those obtained by simultaneously fitting the emission- and absorption-line radial velocity curves and I-band ellipsoidal light curves, we measure the stellar masses to be M1 = 0.87 ± 0.09 Mâ and M2 = 0.47 ± 0.05 Mâ for the white dwarf and the M dwarf, respectively, and an inclination of the orbital plane of i â 79°. A radius of 0.0103 ± 0.0007 Râ is obtained for the white dwarf. The secondary star in HS 0220+0603 is likely too cool and undersized for its mass
The GALEX Arecibo SDSS survey: III. Evidence for the Inside-Out Formation of Galactic Disks
We analyze a sample of galaxies with stellar masses greater than and with redshifts in the range for which HI mass
measurements are available from the GALEX Arecibo SDSS Survey (GASS) or from
the Arecibo Legacy Fast ALFA survey (ALFALFA). At a given value of , our
sample consists primarily of galaxies that are more HI-rich than average. We
constructed a series of three control samples for comparison with these HI-rich
galaxies. As expected, HI-rich galaxies differ strongly from galaxies of same
stellar mass that are selected without regard to HI content. The majority of
these differences are attributable to the fact that galaxies with more gas are
bluer and more actively star-forming. In order to identify those galaxy
properties that are causally connected with HI content, we compare results
derived for the HI sample with those derived for galaxies matched in stellar
mass, size and NUV- colour. The only photometric property that is clearly
attributable to increasing HI content, is the colour gradient of the galaxy.
Galaxies with larger HI fractions have bluer, more actively star-forming outer
disks compared to the inner part of the galaxy. HI-rich galaxies also have
larger -band radii compared to -band radii. Our results are consistent
with the "inside-out" picture of disk galaxy formation, which has commonly
served as a basis for semi-analytic models of the formation of disks in the
context of Cold Dark Matter cosmologies. The lack of any intrinsic connection
between HI fraction and galaxy asymmetry suggests that gas is accreted smoothly
onto the outer disk.Comment: 18 pages, 20 figures. Accepted for publication in MNRAS. GASS
publications and released data can be found at
http://www.mpa-garching.mpg.de/GASS/index.ph
Delta excitation in K^+-nucleus collisions
We present calculations for \Delta excitation in the (K^+,K^+) reaction in
nuclei. The background from quasielastic K^+ scattering in the \Delta region is
also evaluated and shown to be quite small in some kinematical regions, so as
to allow for a clean identification of the \Delta excitation strength. Nuclear
effects tied to the \Delta renormalization in the nucleus are considered and
the reaction is shown to provide new elements to enrich our knowledge of the
\Delta properties in a nuclear medium.Comment: 11 pages, 6 figures, LaTe
Origin of the low-mass electron pair excess in light nucleus-nucleus collisions
We report measurements of electron pair production in elementary p+p and d+p
reactions at 1.25 GeV/u with the HADES spectrometer. For the first time, the
electron pairs were reconstructed for n+p reactions by detecting the proton
spectator from the deuteron breakup. We find that the yield of electron pairs
with invariant mass Me+e- > 0.15 GeV/c2 is about an order of magnitude larger
in n+p reactions as compared to p+p. A comparison to model calculations
demonstrates that the production mechanism is not sufficiently described yet.
The electron pair spectra measured in C+C reactions are compatible with a
superposition of elementary n+p and p+p collisions, leaving little room for
additional electron pair sources in such light collision systems.Comment: 11 pages, 2 figures, \usepackage{epsfig
The origin of the light distribution in spiral galaxies
We analyse a high-resolution, fully cosmological, hydrodynamical disc galaxy simulation, to study the source of the double-exponential light profiles seen in many stellar discs, and the effects of stellar radial migration upon the spatiotemporal evolution of both the disc age and metallicity distributions. We find a âbreakâ in the pure exponential stellar surface brightness profile, and trace its origin to a sharp decrease in the star formation per unit surface area, itself produced by a decrease in the gas volume density due to a warping of the gas disc. Star formation in the disc continues well beyond the break. We find that the break is more pronounced in bluer wavebands. By contrast, we find little or no break in the mass density profile. This is, in part, due to the net radial migration of stars towards the external parts of the disc. Beyond the break radius, we find that âŒ60 per cent of the resident stars migrated from the inner disc, while âŒ25 per cent formed in situ. Our simulated galaxy also has a minimum in the age profile at the break radius but, in disagreement with some previous studies, migration is not the main mechanism producing this shape. In our simulation, the disc metallicity gradient flattens with time, consistent with an âinside-outâ formation scenario. We do not find any difference in the intensity or the position of the break with inclination, suggesting that perhaps the differences found in empirical studies are driven by dust extinction
Study of dielectron production in C+C collisions at 1 AGeV
The emission of e+e- pairs from C+C collisions at an incident energy of 1 GeV
per nucleon has been investigated. The measured production probabilities,
spanning from the pi0-Dalitz to the rho/omega! invariant-mass region, display a
strong excess above the cocktail of standard hadronic sources. The
bombarding-energy dependence of this excess is found to scale like pion
production, rather than like eta production. The data are in good agreement
with results obtained in the former DLS experiment.Comment: submitted to Physics Letters
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