187 research outputs found
Fundamental Plane Distances to Early-type Field Galaxies in the South Equatorial Strip. I. The Spectroscopic Data
Radial velocities and central velocity dispersions are derived for 238 E/S0
galaxies from medium-resolution spectroscopy. New spectroscopic data have been
obtained as part of a study of the Fundamental Plane distances and peculiar
motions of early-type galaxies in three selected directions of the South
Equatorial Strip, undertaken in order to investigate the reality of large-scale
streaming motion; results of this study have been reported in M\"uller
(1998). The new APM South Equatorial Strip Catalog () was used to select the sample of field galaxies in
three directions: (1) 15h10 - 16h10; (2) 20h30 - 21h50; (3) 00h10 - 01h30. The
spectra obtained have a median S/N per of 23, an instrumental
resolution (FWHM) of 4 , and the spectrograph resolution
(dispersion) is 100 km~s. The Fourier cross-correlation method
was used to derive the radial velocities and velocity dispersions. The velocity
dispersions have been corrected for the size of the aperture and for the galaxy
effective radius. Comparisons of the derived radial velocities with data from
the literature show that our values are accurate to 40 km~s. A
comparison with results from J\orgensen et al. (1995) shows that the derived
central velocity dispersion have an rms scatter of 0.036 in .
There is no offset relative to the velocity dispersions of Davies et al.
(1987).Comment: accepted for publication in Astronomy & Astrophysics Supplement
Serie
The extinction by dust in the outer parts of spiral galaxies
To investigate the distribution of dust in Sb and Sc galaxies we have
analyzed near-infrared and optical surface photometry for an unbiased sample of
37 galaxies. Since light in the -band is very little affected by extinction
by dust, the colour is a good indicator of the amount of extinction, and
using the colour-inclination relation we can statistically determine the
extinction for an average Sb/Sc galaxy. We find in general a considerable
amount of extinction in spiral galaxies in the central regions, all the way out
to their effective radii. In the outer parts, at D, or at 3 times the
typical exponential scale lengths of the stellar distribution , we find a
maximum optical depth of 0.5 in for a face-on galaxy. If we impose the
condition that the dust is distributed in the same way as the stars, this upper
limit would go down to 0.1.Comment: 4 pages, postscript, gzip-compressed, uuencoded, includes 2 figures.
Accepted for publication in Astronomy & Astrophysics, Letter
Flux calibration of medium-resolution spectra from 300 nm to 2500 nm: Model reference spectra and telluric correction
While the near-infrared wavelength regime is becoming more and more important
for astrophysics there is a marked lack of spectrophotometric standard star
data that would allow the flux calibration of such data. Furthermore, flux
calibrating medium- to high-resolution \'echelle spectroscopy data is
challenging even in the optical wavelength range, because the available flux
standard data are often too coarsely sampled. We will provide standard star
reference data that allow users to derive response curves from 300nm to 2500nm
for spectroscopic data of medium to high resolution, including those taken with
\'echelle spectrographs. In addition we describe a method to correct for
moderate telluric absorption without the need of observing telluric standard
stars. As reference data for the flux standard stars we use theoretical spectra
derived from stellar model atmospheres. We verify that they provide an
appropriate description of the observed standard star spectra by checking for
residuals in line cores and line overlap regions in the ratios of observed
(X-shooter) spectra to model spectra. The finally selected model spectra are
then corrected for remaining mismatches and photometrically calibrated using
independent observations. The correction of telluric absorption is performed
with the help of telluric model spectra.We provide new, finely sampled
reference spectra without telluric absorption for six southern flux standard
stars that allow the users to flux calibrate their data from 300 nm to 2500 nm,
and a method to correct for telluric absorption using atmospheric models.Comment: Reference spectra available at CDS. Published in A&A 568, A9, 201
Fundamental Plane Distances to Early-type Field Galaxies in the South Equatorial Strip. I. The Spectroscopic Data
Radial velocities and central velocity dispersions are derived for 238 E/S0 galaxies from medium-resolution spectroscopy. New spectroscopic data have been obtained as part of a study of the Fundamental Plane distances and peculiar motions of early-type galaxies in three selected directions of the South Equatorial Strip, undertaken in order to investigate the reality of large-scale streaming motion; results of this study have been reported in M\ uller (1998). The new APM South Equatorial Strip Catalog (−17.5 \u3c δ \u3c +2.5) was used to select the sample of field galaxies in three directions: (1) 15h10 – 16h10; (2) 20h30 – 21h50; (3) 00h10 – 01h30. The spectra obtained have a median S/N per ̊A of 23, an in- strumental resolution (FWHM) of ∼ 4 ̊A, and the spectro- graph resolution (dispersion) is ∼ 100 km s−1. The Fourier cross-correlation method was used to derive the radial ve- locities and velocity dispersions. The velocity dispersions have been corrected for the size of the aperture and for the galaxy effective radius. Comparisons of the derived radial velocities with data from the literature show that our values are accurate to 40 km s−1. A comparison with results from Jørgensen et al. (1995) shows that the derived central velocity dispersion have an rms scatter of 0.036 in log σ. There is no offset relative to the velocity dispersions of Davies et al. (1987)
Flows on scales of 150 Mpc?
We investigate the reality of large-scale streaming on scales of up to 150
Mpc using the peculiar motions of galaxies in three directions. New R-band CCD
photometry and spectroscopy for elliptical galaxies is used. The Fundamental
Plane distance indicator is calibrated using the Coma cluster and an
inhomogeneous Malmquist bias correction is applied. A linear bulk-flow model is
fitted to the peculiar velocities in the sample regions and the results do not
reflect the bulk flow observed by Lauer and Postman (LP). Accounting for the
difference in geometry between the galaxy distribution in the three regions and
the LP clustersconfirms the disagreement; assuming a low-density CDM power
spectrum, we find that the observed bulk flow of the galaxies in our sample
excludes the LP bulk flow at the 99.8% confidence level.Comment: 16 pages, 1 figur
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