120 research outputs found
The evolution of galaxy clustering since z=1 from the Calar Alto Deep Imaging Survey
We present results from an investigation of the clustering evolution of field
galaxies between a redshift of z~1 and the present epoch. The current analysis
relies on a sample of ~3600 galaxies from the Calar Alto Deep Imaging
Survey (CADIS). The redshift distribution extends to z~1.1, with formal
errors of sigma_z~0.02. Thus the amplitude of the three-dimensional correlation
function can be estimated by means of the projected correlation function
w(r_p). We developed a new method to overcome the influence of redshift errors
on w(r_p). We parametrise the evolution of the clustering strength with
redshift by a parameter q, the values of which give directly the deviation of
the evolution from the global Hubble flow. From a subsample of bright galaxies
we find q=-2.28+-0.31 for Omega_m=0.3, Omega_Lambda=0.7, that is a significant
growth of the clustering strength between z=1 and the present epoch. From
linear theory of dark matter clustering growth one would only expect q=-2.
Moreover, we establish that the measured clustering strength depends on galaxy
type: galaxies with early type SEDs (Hubble type: E0 to Sbc) are more strongly
clustered at redshifts z>0.2 than later types. The evolution of the amplitude
of the two-point correlation function for these ``old'' galaxies is much slower
(q=-0.85+-0.82 for Omega_m=0.3, Omega_Lambda=0.7).Comment: 15 pages, 9 figures, accepted for publication by A&
CADIS has seen the Virgo overdensity and parts of the Monoceros and `Orphan' streams in retrospect
We reanalyze deep star counts in five CADIS fields. The data are presented as
vertical density distributions of stars perpendicular to the Galactic plane. In
three fields the profiles are consistent with each other, while in two fields
significant overdensities of stars are found. The overdensity in one field can
be associated with the Virgo overdensity which can be traced right into the
disk of the Milky Way. Using this detection we estimate the mass of the Virgo
overdensity and show that this is equivalent to the stellar content of a Local
Group dwarf spheroidal galaxy. The overdensity in the second field is more
difficult to associate with a previously known overdensity. We suggest that it
is related both to the Monoceros stream and the recently discovered Orphan
stream.Comment: 4 pages, 3 figures, accepted as Research Note by Astron. Astrophy
Absolute Magnitude Calibration for Giants based on the Colour-Magnitude Diagrams of Galactic Clusters. II-Calibration with SDSS
We present an absolute magnitude calibration for red giants with the colour
magnitude diagrams of six Galactic clusters with different metallicities i.e.
M92, M13, M3, M71, NGC 6791 and NGC 2158. The combination of the absolute
magnitudes of the red giant sequences with the corresponding metallicities
provides calibration for absolute magnitude estimation for red giants for a
given colour. The calibration is defined in the colour interval
0.45 1.30 mag and it covers the metallicity interval
+0.37 dex. The absolute magnitude
residuals obtained by the application of the procedure to another set of
Galactic clusters lie in the interval mag.
However, the range of 94% of the residuals is shorter,
mag. The mean and the standard deviation of (all) residuals are 0.169 and 0.140
mag, respectively. The derived relations are applicable to stars older than 2
Gyr, the age of the youngest calibrating cluster.Comment: 12 pages, including 5 figures and 10 tables, accepted for publication
in PASA. arXiv admin note: substantial text overlap with arXiv:1204.429
Absolute Magnitude Calibration for Red Giants based on the Colour-Magnitude Diagrams of Galactic Clusters. III-Calibration with 2MASS
We present two absolute magnitude calibrations, and , for
red giants with the colour magnitude diagrams of five Galactic clusters with
different metallicities i.e. M92, M13, M71, M67, and NGC 6791. The combination
of the absolute magnitudes of the red giant sequences with the corresponding
metallicities provides calibration for absolute magnitude estimation for red
giants for a given colour. The calibrations for and are
defined in the colour intervals and mag, respectively, and they cover the metallicity
interval dex. The absolute
magnitude residuals obtained by the application of the procedure to another set
of Galactic clusters lie in the intervals and
mag for and , respectively.
The means and standard deviations of the residuals are
and , and and
mag. The derived relations are applicable to stars
older than 4 Gyr, the age of the youngest calibrating cluster.Comment: 20 pages, including 8 figures and 22 tables, accepted for publication
in PASA. arXiv admin note: substantial text overlap with arXiv:1206.275
The merger rate of massive galaxies
We calculate the projected two point correlation function for samples of
luminous and massive galaxies in the COMBO-17 photometric redshift survey,
focusing particularly on the amplitude of the correlation function at small
projected radii and exploring the constraints such measurements can place on
the galaxy merger rate. For nearly volume-limited samples with 0.4<z<0.8, we
find that 4+/-1% of luminous M_B<-20 galaxies are in close physical pairs (with
real space separation of <30 proper kpc). The corresponding fraction for
massive galaxies with M_*>2.5e10 M_sun is 5+/-1%. Incorporating close pair
fractions from the literature, the 2dFGRS and the SDSS, we find a fairly rapid
evolution of the merger fraction of massive galaxies between z=0.8 and the
present day. Assuming that the major merger timescale is of order the dynamical
timescale for close massive galaxy pairs, we tentatively infer that ~50% (70%)
of all galaxies with present-day masses M_*>5e10 M_sun (remnants of mergers
between galaxies with M_*>2.5e10 M_sun) have undergone a major merger since
z=0.8(1): major mergers between massive galaxies are a significant driver of
galaxy evolution over the last eight billion years.Comment: ApJ, in press. 8 pages, 3 figures. Expanded discussion section with
explicit discussion of merger fraction vs. close pair fraction. Change of
typical close pair timescale results in increased inferred merger rat
A New Procedure for the Photometric Parallax Estimation
We present a new procedure for photometric parallax estimation. The data for
1236 stars provide calibrations between the absolute magnitude offset from the
Hyades main-sequence and the UV-excess for different (B-V)o colour-index
intervals, i.e.: (0.3 0.4), (0.4 0.5), (0.5 0.6), (0.6 0.7), (0.7 0.8), (0.8
0.9), (0.9 1.0), and (1.0 1.1). The mean difference between the original and
estimated absolute magnitudes and the corresponding standard deviation are
rather small, +0.0002 and +/-0.0613 mag. The procedure has been adapted to the
Sloan photometry by means of colour equations and applied to a set of
artificial stars with different metallicity. The comparison of the absolute
magnitudes estimated by the new procedure and the canonical one indicates that
a single colour-magnitude diagram does not supply reliable absolute magnitudes
for stars with large range of metallicity.Comment: 26 pages, including 12 tables and 6 figures, accepted for publication
in PAS
A hole in the sky - The dependence of the galaxy luminosity function on the environment
We have developed a method to calculate overdensities in multicolour surveys, and compare the local density contrast measured in galaxy samples with different redshift error distributions. We calculated overdensities for three COMBO-17 fields, and identified a region in the CDFS, where the density is lower by a factor of 2 compared to the other two fields. This is mainly due to a deficiency of faint red galaxies. This result is in agreement with local observations in the 2dF
Estimation of Galactic Model Parameters and Metalicity Distribution in Intermediate Latitudes with SDSS
We estimated the galactic model parameters for a set of 20
intermediate-latitude fields with galactic longitudes 0<l<100 and 160<l<240,
included in the currently available Data Release 6 (DR6) of SDSS, to explore
their possible variation with galactic longitude. The local space densities of
the thick disc and halo are almost the same for all fields,
=6.52% and =0.35%, respectively, a result
different than the one cited for high-latitude fields. The thin disc's
scaleheight is 325 pc in the galactic centre changes to 369 pc in the third
quadrant, which confirms the existence of disc flare, whereas the thick disc
scaleheight is as large as 952 pc at galactic longitude l=20 and 10% lower at
l=160, which confirms the existence of the disc long bar in the direction l=27.
Finally, the variation of the axis ratio of the halo with galactic longitude is
almost flat, =0.56, except a slight minimum and a small maximum in the
second and third quadrants, respectively, indicating an effect of the long bar
which seems plausible for a shallow halo. We estimated the metallicities of
unevolved G-type stars and discussed the metallicity gradient for different
vertical distances. The metallicity gradient is d[M/H]/dz=-0.30 dex kpc
for short distances, confirming the formation of this region of the Galaxy by
dissipational collapse. However, its change is steeper in the transition
regions of different galactic components. The metallicity gradient is almost
zero for inner halo (5<z<10 kpc), indicating a formation of merger or accretion
of numerous fragments such as dwarf galaxies.Comment: 31 pages, 18 figures and 4 tables, accepted for publication in New
Astronom
Luminosity-Colours relations for thin disc main-sequence stars
In this study we present the absolute magnitude calibrations of thin disc
main-sequence stars in the optical (), and in the near-infrared
(). Thin disc stars are identified by means of Padova isochrones, and
absolute magnitudes for the sample are evaluated via the newly reduced
Hipparcos data. The obtained calibrations cover a large range of spectral
types: from A0 to M4 in the optical and from A0 to M0 in the near-infrared.
Also, we discuss the of effects binary stars and evolved stars on the absolute
magnitude calibrations. The usage of these calibrations can be extended to the
estimation of galactic model parameters for the thin disc individually, in
order to compare these parameters with the corresponding ones estimated by
statistics (which provides galactic model parameters for thin
and thick discs, and halo simultaneously) to test any degeneracy between them.
The calibrations can also be used in other astrophysical researches where
distance plays an important role in that study.Comment: 8 pages, including 12 figures and 4 tables, accepted for publication
in MNRA
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