909 research outputs found
MDia and POTS - The Munich Difference Imaging Analysis for the pre-OmegaTranS Project
We describe the Munich Difference Imaging Analysis pipeline that we developed
and implemented in the framework of the Astro-WISE package to automatically
measure high precision light curves of a large number of stellar objects using
the difference imaging approach. Combined with programs to detect time
variability, this software can be used to search for planetary systems or
binary stars with the transit method and for variable stars of different kinds.
As a first scientific application, we discuss the data reduction and analysis
performed with Astro-WISE on the pre-OmegaTranS data set, that we collected
during a monitoring campaign of a dense stellar field with the Wide Field
Imager at the ESO 2.2m telescope.Comment: 10 pages, 5 figures, accepted for publication in topical issue of
Experimental Astronomy on Astro-WISE information syste
The evolution of the color gradients of early-type cluster galaxies
We investigate the origin of color gradients in cluster early-type galaxies
to probe whether pure age or pure metallicity gradients can explain the
observed data in local and distant (z approx 0.4) samples. We measure the
surface brightness profiles of the 20 brightest early-type galaxies of
CL0949+44 (hereafter CL0949) at redshift z=0.35-0.38 from HST WF2 frames taken
in the filters F555W, F675W, F814W. We determine the color profiles (V-R)(r),
(V-I)(r), and (R-I)(r) as a function of the radial distance r in arcsec, and
fit logarithmic gradients in the range -0.2 to 0.1 mag per decade. These values
are similar to what is found locally for the colors (U-B), (U-V), (B-V) which
approximately match the (V-R), (V-I), (R-I) at redshift approx 0.4. We analyse
the results with up to date stellar population models. We find that passive
evolution of metallicity gradients (approx 0.2 dex per radial decade) provides
a consistent explanation of the local and distant galaxies' data. Invoking pure
age gradients (with fixed metallicity) to explain local color gradients
produces too steep gradients at redshifts z approx 0.4. Pure age gradients are
consistent with the data only if large present day ages (>=15 Gyr) are assumed
for the galaxy centers.Comment: 23 pages, 19 figures, Accepted for publication in A&
The Tolman Surface Brightness Test for the Reality of the Expansion. II. The Effect of the Point-Spread Function and Galaxy Ellipticity on the Derived Photometric Parameters
To complete the Tolman surface brightness test on the reality of the
expansion of the Universe, we need to measure accurately the surface brightness
profiles of the high-redshift galaxy sample. We, therefore, investigate the
effects of various sizes of point-spread-functions composed of telescope
diffraction, CCD pixel resolutions, and ground-based seeing on the measurements
of mean surface brightness. We have done the calculations using two synthetic
galaxies of effective radii of 0.70" and 0.25" with point-spread functions of
0.1, 0.3, and 0.9 arcseconds. We have also compared actual observations of
three high-redshift galaxies in the cluster Cl 1324 + 3011 (z = 0.76) made both
with the Keck telescopes in seeing of about 0.9" and with HST which has a PSF
that is approximately ten times smaller. The conclusion is that HST data can be
used as far into the galaxy image as a Petrosian metric radius of eta = 1.3
magnitudes, whereas the ground-based data will have systematic errors of up to
2.9 magnitudes in the mean surface brightness at eta values of less than 2.2
magnitudes. In the final section, we compare the differences in derived average
surface brightness for nearly circular galaxy images compared with highly
flattened images. The comparison is made by using the two reduction procedures
of (1) integrating the profile curves using circular apertures, and (2)
approximating an ``equivalent circular'' galaxy that is highly elongated by
using an ``effective'' radius of sqrt{ab}, where a and b are the semi-major and
semi-minor axis, respectively, of the best-fitting ellipse. The conclusion is
that the two methods of reduction give nearly identical results and that either
method can be used to analyze the low and high-redshift galaxy samples used in
the Tolman test.Comment: 15 pages, 9 figures; accepted for publication in Astronomical Journa
Breaking the degeneracy between anisotropy and mass: The dark halo of the E0 galaxy NGC 6703
(abridged) We have measured line-of-sight velocity profiles (VPs) in the E0
galaxy NGC 6703 out to 2.6 R_e. From these data we constrain the mass
distribution and the anisotropy of the stellar orbits in this galaxy.
We have developed a non-parametric technique to determine the DF f(E,L^2)
directly from the kinematic data. From Monte Carlo tests using the spatial
extent, sampling, and error bars of the NGC 6703 data we find that smooth
underlying DFs can be recovered to an rms accuracy of 12%, and the anisotropy
parameter beta(r) to an accuracy of 0.1, in a given potential. An
asymptotically constant halo circular velocity v_0 can be determined with an
accuracy of +- \lta 50km/s.
For NGC 6703 we determine the true circular velocity at 2.6 R_e to be 250 +-
40km/s at 95% c.l., corresponding to a total mass in NGC 6703 inside 78'' (13.5
h_50^-1 kpc), of 1.6-2.6 x 10^11 h_50^-1 Msun. No model without dark matter
will fit the data; however, a maximum stellar mass model in which the luminous
component provides nearly all the mass in the centre does. In such a model, the
total luminous mass inside 78'' is 9 x 10^10 Msun and the integrated
M/L_B=5.3-10, corresponding to a rise from the center by at least a factor of
1.6.
The anisotropy of the stellar distribution function in NGC 6703 changes from
near-isotropic at the centre to slightly radially anisotropic (beta=0.3-0.4 at
30'', beta=0.2-0.4 at 60'') and is not well-constrained at the outer edge of
the data.
Our results suggest that also elliptical galaxies begin to be dominated by
dark matter at radii of \sim 10kpc.Comment: 19 pages LaTex, 18 figures. MNRAS, in press. Also available at
http://www.astro.unibas.ch/~gerhard/papers/dm6703.ps.g
The Dynamical Fingerprint of Core Scouring in Massive Elliptical Galaxies
The most massive elliptical galaxies have low-density centers or cores that
differ dramatically from the high-density centers of less massive ellipticals
and bulges of disk galaxies. These cores have been interpreted as the result of
mergers of supermassive black hole binaries, which depopulate galaxy centers by
gravitationally slingshotting central stars toward large radii. Such binaries
naturally form in mergers of luminous galaxies. Here, we analyze the population
of central stellar orbits in 11 massive elliptical galaxies that we observed
with the integral field spectrograph SINFONI at the European Southern
Observatory Very Large Telescope. Our dynamical analysis is orbit-based and
includes the effects of a central black hole, the mass distribution of the
stars, and a dark matter halo. We show that the use of integral field
kinematics and the inclusion of dark matter is important to conclude upon the
distribution of stellar orbits in galaxy centers. Six of our galaxies are core
galaxies. In these six galaxies, but not in the galaxies without cores, we
detect a coherent lack of stars on radial orbits in the core region and a
uniform excess of radial orbits outside of it: when scaled by the core radius,
the radial profiles of the classical anisotropy parameter beta are nearly
identical in core galaxies. Moreover, they match quantitatively the predictions
of black hole binary simulations, providing the first convincing dynamical
evidence for core scouring in the most massive elliptical galaxies.Comment: 8 pages, 3 figures, accepted by Ap
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