168 research outputs found
Investigations of the optical fields of 3CR radio sources to faint limiting magnitudes - IV
A deep optical survey of the fields of 18 3CR radio sources has been carried out with the Hale 5-m telescope, using a prototype charged coupled device as a detector. These sources were among the few 3CR objects which were either previously unidentified or associated with very faint images
at the plate limit for which confirmation was required.
Ten new identifications are proposed (3C 65, 3C 68.2, 3C 175.1, 3C 239, 3C 241, 3C 267, 3C 272, 3C 289, 3C 469.1 and 3C 470), and candidates for the remaining eight sources are confirmed (3C 34, 3C 61.1, 3C 184, 3C 220.3, 3C 250, 3C 280, 3C 324, 3C 368). Of these identifications, those for 3C 68.2, 3C 175.1, 3C 250 and 3C 470 are considered provisional, since they are displaced from the radio source axes. In addition, the candidate for the 3C 61.1 is classed as a confirmed identification, although the optical field
is crowded and an unambiguous identification cannot be made on positional arguments alone. A subsample of 60 sources from the 3CR catalogue, considered by previous workers, is now (provisionally) completely identified. These new results
are used to construct luminosity distributions at S(l78) ≥ 20 Jy and S(178)≥ l0Jy, and the implications of the complete identification rate for models of source evolution formulated by other workers are examined
Luminous Compact Blue Galaxies in Intermediate Redshift Galaxy Clusters: A Significant But Extreme Butcher-Oemler Population
We identify a population of Luminous Compact Blue Galaxies (LCBGs) in two
galaxy clusters: MS0451.6-0305 (z=0.54) and Cl1604+4304 (z=0.9). LCBGs are
identified via photometric characteristics and photometric redshifts derived
from broad and narrow band images taken with the WIYN telescope and the Hubble
Space Telescope. We analyze their surface densities and clustering properties
to find they compose a statistically significant portion (42% and 53%) of the
Butcher-Oemler galaxies in both clusters, and their spatial distributions are
best characterized by a shell model. The enhancement of the projected
space-density of LCBGs with M_B<-18.5 in the clusters relative to the field is
3-10 times higher than the BO population as a whole, but 2 times lower than the
red population, except in the core where LCBGs are absent. Assuming some
fading, a natural descendant would be small, low-luminosity galaxies found
preferentially in today's clusters, such as dEs.Comment: 10 Pages, 3 figures, accepted for publication in ApJ Letter
Isolated and non-isolated dwarfs in terms of modified Newtonian dynamics
Within the framework of modified Newtonian dynamics (MOND) we investigate the
kinematics of two dwarf spiral galaxies belonging to very different
environments, namely KK 246 in the Local Void and Holmberg II in the M81 group.
A mass model of the rotation curve of KK 246 is presented for the first time,
and we show that its observed kinematics are consistent with MOND. We re-derive
the outer rotation curve of Holmberg II, by modelling its HI data cube, and
find that its inclination should be closer to face-on than previously derived.
This implies that Holmberg II has a higher rotation velocity in its outer
parts, which, although not very precisely constrained, is consistent with the
MOND prediction.Comment: Accepted in A&A as a Research Note. 6 pages, 3 figure
Recent Star Formation in Sextans A
We investigate the relationship between the spatial distributions of stellar
populations and of neutral and ionized gas in the Local Group dwarf irregular
galaxy Sextans A. This galaxy is currently experiencing a burst of localized
star formation, the trigger of which is unknown. We have resolved various
populations of stars via deep UBV(RI)_C imaging over an area with diameter \sim
5.'3. We have compared our photometry with theoretical isochrones appropriate
for Sextans A, in order to determine the ages of these populations. We have
mapped out the history of star formation, most accurately for times \lesssim
100 Myr. We find that star formation in Sextans A is correlated both in time
and space, especially for the most recent (\lesssim 12 Myr) times. The youngest
stars in the galaxy are forming primarily along the inner edge of the large H I
shell. Somewhat older populations, \lesssim 50 Myr, are found inward of the
youngest stars. Progressively older star formation, from \sim 50--100 Myr,
appears to have some spatially coherent structure and is more centrally
concentrated. The oldest stars we can accurately sample appear to have
approximately a uniform spatial distribution, which extends beyond a surface
brightness of \mu_B \simeq 25.9 mag arcsec^{-2} (or, a radius r \simeq 2.'3$).
Although other processes are also possible, our data provides support for a
mechanism of supernova-driven expansion of the neutral gas, resulting in cold
gas pileup and compression along the H I shell and sequential star formation in
recent times.Comment: 64 pages, 22 figures, to appear in A
Cepheids and Long Period Variables in NGC 4395
Repeated imaging observations of NGC 4395 were made with the WIYN 3.5 m and
the KPNO 2.1 m telescopes. From the photometry of the resolved brighter stars
in this galaxy eleven Cepheids with periods ranging between 12 and 90 days have
been identified. The true distance modulus has been derived from the apparent
distance moduli in g, r and i. The distance modulus is 28.02 +/- 0.18 based on
the LMC P-L relation by Sandage et al. 2003; this corresponds to a distance of
4.0 +/- 0.3 Mpc. Using the P-L relation from Madore & Freedman 1991, the
distance modulus is 28.15 +/- 0.18; which corresponds to a distance of 4.3 +/-
0.4 Mpc. The reddening is calculated to be E(g-r) = 0.06 +/- 0.08 and E(r-i) =
0.10 +/- 0.08, again from the distance moduli mu_g, mu_r and mu_i. In addition,
37 other variables have been detected, the majority of which have definite
periods. They are probably all red long period variables.Comment: 54 pages, 8 figures, 8 tables, accepted for publication in the
Astronomical Journa
3D Spectrophotometry of Planetary Nebulae in the Bulge of M31
We introduce crowded field integral field (3D) spectrophotometry as a useful
technique for the study of resolved stellar populations in nearby galaxies. As
a methodological test, we present a pilot study with selected extragalactic
planetary nebulae (XPN) in the bulge of M31, demonstrating how 3D spectroscopy
is able to improve the limited accuracy of background subtraction which one
would normally obtain with classical slit spectroscopy. It is shown that due to
the absence of slit effects, 3D is a most suitable technique for
spectrophometry. We present spectra and line intensities for 5 XPN in M31,
obtained with the MPFS instrument at the Russian 6m BTA, INTEGRAL at the WHT,
and with PMAS at the Calar Alto 3.5m Telescope. Using 3D spectra of bright
standard stars, we demonstrate that the PSF is sampled with high accuracy,
providing a centroiding precision at the milli-arcsec level. Crowded field 3D
spectrophotometry and the use of PSF fitting techniques is suggested as the
method of choice for a number of similar observational problems, including
luminous stars in nearby galaxies, supernovae, QSO host galaxies,
gravitationally lensed QSOs, and others.Comment: (1) Astrophysikalisches Institut Potsdam, (2) University of Durham.
18 pages, 11 figures, accepted for publication in Ap
Calibration of the distance scale from galactic Cepheids: I Calibration based on the GFG sample
New estimates of the distances of 36 nearby galaxies are presented based on
accurate distances of galactic Cepheids obtained by Gieren, Fouque and Gomez
(1998) from the geometrical Barnes-Evans method.
The concept of 'sosie' is applied to extend the distance determination to
extragalactic Cepheids without assuming the linearity of the PL relation. Doing
so, the distance moduli are obtained in a straightforward way.
The correction for extinction is made using two photometric bands (V and I)
according to the principles introduced by Freedman and Madore (1990). Finally,
the statistical bias due to the incompleteness of the sample is corrected
according to the precepts introduced by Teerikorpi (1987) without introducing
any free parameters (except the distance modulus itself in an iterative
scheme).
The final distance moduli depend on the adopted extinction ratio {R_V}/{R_I}
and on the limiting apparent magnitude of the sample. A comparison with the
distance moduli recently published by the Hubble Space Telescope Key Project
(HSTKP) team reveals a fair agreement when the same ratio {R_V}/{R_I} is used
but shows a small discrepancy at large distance.
In order to bypass the uncertainty due to the metallicity effect it is
suggested to consider only galaxies having nearly the same metallicity as the
calibrating Cepheids (i.e. Solar metallicity). The internal uncertainty of the
distances is about 0.1 magnitude but the total uncertainty may reach 0.3
magnitude.Comment: 12 pages, 4 figures, access to a database of extragalactic Cepheids.
Astronomy & Astrophysics (in press) 200
Environmental Dependence of the Structure of Brightest Cluster Galaxies
We measure the Petrosian structural properties of 33 brightest cluster
galaxies (BCGs) at redshifts z<0.1 in X-ray selected clusters with a wide range
of X-ray luminosities. We find that some BCGs show distinct signatures in their
Petrosian profiles, likely to be due to cD haloes. We also find that BCGs in
high X-ray luminosity clusters have shallower surface brightness profiles than
those in low X-ray luminosity clusters. This suggests that the BCGs in high
X-ray luminosity clusters have undergone up to twice as many equal-mass mergers
in their past as those in low X-ray luminosity clusters. This is qualitatively
consistent with the predictions of hierarchical structure formation.Comment: 11 pages, accepted for publication in MNRA
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