34 research outputs found
A near infrared photometric plane for ellipticals and bulges of spirals
We report the existence of a single plane in the space of global photometric
parameters describing elliptical galaxies and the bulges of early type spiral
galaxies. The three parameters which define the plane are obtained by fitting
the Sersic form to the brightness distribution obtained from near-infrared K
band images. We find, from the range covered by their shape parameters, that
the elliptical galaxies form a more homogeneous population than the bulges.
Known correlations like the Kormendy relation are projections of the
photometric plane. The existence of the plane has interesting implications for
bulge formation models.Comment: 12 pages, LaTeX including 5 figures. To appear in the Astrophysical
Journal Letter
Radio Emission from AGN detected by the VLA FIRST Survey
Using the most recent (April 2003) version of the VLA FIRST survey radio
catalog, we have searched for radio emission from AGN taken from the
most recent (2001) version of the Veron-Cetty and Veron AGN catalog. These AGN
lie in the ~9033 square degrees of sky already covered by the VLA FIRST survey.
Our work has resulted in positive detection of radio emission from 775 AGN of
which 214 are new detections at radio wavelengths.Comment: 7 pages, 4 figures, 5 tables. Two tables are available only in
electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr
(130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/3
A low-frequency study of recently identified double-double radio galaxies
In order to understand the possible mechanisms of recurrent jet activity in
radio galaxies and quasars, which are still unclear, we have identified such
sources with a large range of linear sizes (220 917 kpc), and hence time
scales of episodic activity. Here we present high-sensitivity 607-MHz Giant
Metrewave Radio Telescope (GMRT) images of 21 possible double-double radio
galaxies (DDRGs) identified from the FIRST survey to confirm their episodic
nature. These GMRT observations show that none of the inner compact components
suspected to be hot-spots of the inner doubles are cores having a flat radio
spectrum, confirming the episodic nature of these radio sources. We have
indentified a new DDRG with a candidate quasar, and have estimated the upper
spectral age limits for eight sources which showed marginal evidence of
steepening at higher frequencies. The estimated age limits (11 52 Myr) are
smaller than those of the large-sized ( 1 Mpc) DDRGs.Comment: Accepted for publication in MNRAS. 14 pages, 7 figure
Two dimensional bulge disk decomposition
We propose a two dimensional galaxy fitting algorithm to extract parameters
of the bulge, disk, and a central point source from broad band images of
galaxies. We use a set of realistic galaxy parameters to construct a large
number of model galaxy images which we then use as input to our galaxy fitting
program to test it. We find that our approach recovers all structural
parameters to a fair degree of accuracy. We elucidate our procedures by
extracting parameters for 3 real galaxies -- NGC 661, NGC 1381, and NGC 1427.Comment: 23 pages, LaTeX, AASTEX macros used, 7 Postscript figures, submitted
to Ap
A difference boosting neural network for automated star-galaxy classification
In this paper we describe the use of a new artificial neural network, called
the difference boosting neural network (DBNN), for automated classification
problems in astronomical data analysis. We illustrate the capabilities of the
network by applying it to star galaxy classification using recently released,
deep imaging data. We have compared our results with classification made by the
widely used Source Extractor (SExtractor) package. We show that while the
performance of the DBNN in star-galaxy classification is comparable to that of
SExtractor, it has the advantage of significantly higher speed and flexibility
during training as well as classification.Comment: 9 pages, 1figure, 7 tables, accepted for publication in Astronomy and
Astrophysic
Correlations among global photometric properties of disk galaxies
Using a two-dimensional galaxy image decomposition technique, we extract
global bulge and disk parameters for a complete sample of early type disk
galaxies in the near infrared K band. We find significant correlation of the
bulge parameter n with the central bulge surface brightness and with
effective radius r_e. Using bivar iate analysis techniques, we find that , and are distributed in a plane with small scatter. We
do not find a strong correlation of n with bulge-to-disk luminosity ratio,
contrary to earlier reports. r_e and the disk scale length r_d are well
correlated for these early type disk galaxies, but with large scatter. We
examine the implications of our results to various bulge formation scenarios in
disk galaxies.Comment: 14 pages, LaTeX including 14 figures. To appear in the Astrophysical
Journa
Multi-frequency characterisation of remnant radio galaxies in the Lockman Hole field
Context. Remnant radio galaxies represent an important phase in the life-cycle of radio active galactic nuclei. It is suggested that in this phase, the jets have switched off and the extended emission is fading rapidly. This phase is not well-studied due to the lack of statistical samples observed at both low and high frequencies.
Aims. In this work, we study a sample of 23 candidate remnant radio galaxies previously selected using the Low Frequency Array at 150 MHz in the Lockman Hole field. We examine their morphologies and study their spectral properties to confirm their remnant nature and revise the morphological and spectral criteria used to define the initial sample.
Methods. We present new observations with the Karl G. Jansky Very Large Array at 6000 MHz at both high and low resolution. These observations allowed us to observe the presence or absence of cores and study the spectral curvature and steepness of the spectra of the total emission expected at these high frequencies for the remnant candidates.
Results. We confirm 13 out of 23 candidates as remnant radio sources. This corresponds to 7% of the full sample of active, restarted, and remnant candidates from the Lockman Hole field. Surprisingly, only a minority of remnants reside in a cluster (23%). The remnant radio galaxies show a range of properties and morphologies. The majority do not show detection of the core at 6000 MHz and their extended emission often shows ultra-steep spectra (USS). However, there are also remnants with USS total emission and a detection of the core at 6000 MHz, possibly indicating a variety of evolutionary stages in the remnant phase. We confirm the importance of the combination of morphological and spectral criteria and this needs to be taken into consideration when selecting a sample of remnant radio sources
Star--forming galaxies at intermediate redshifts: morphology, ages and sizes
We present the analysis of the deepest near-UV image obtained with HST using
the WFPC2(F300W) as part of the parallel observations of the Ultra Deep Field
campaign. The U-band 10sigma limiting magnitude measured over 0.2 arcsec square
is m(AB)=27.5 which is 0.5 magnitudes deeper than that in the HDF-North. We
matched the U-band catalog with those in the ACS images taken during the GOODS
observations of the CDF-South and obtained photometric-z for 306 matched
objects. We find that the UV-selected galaxies span all the major morphological
types at 0.2<z_phot<1.2. However, disks are more common at lower redshifts,
0.2<z_phot<0.8. Higher-z objects (0.7<z_phot<1.2) are on average bluer than
lower-z and have spectral type typical of starbursts. Their morphologies are
compact, peculiar or low surface brightness galaxies. The average half-light
radius (rest-frame 1200--1800 A) of the UV-selected galaxies at 0.66<z_
phot<1.5 is 0.26 +- 0.01 arcsec (2.07 +- 0.08 kpc). The UV-selected galaxies
are on average fainter (M_B=-18.43+-0.13) than Lyman Break Galaxies
(M_B=-23+-1). Our sample includes early-type galaxies that are presumably
massive and forming stars only in their cores, as well as starburst-type
systems that are more similar to the LBGs, although much less luminous. This
implies that even the starbursts in our sample are either much less massive
than LBGs or are forming stars at a much lower rate or both. The low surface
brightness galaxies have no overlap with the LBGs and form an interesting new
class of their own.Comment: 22 pages, 15 figures. Astronomical Journal Accepte
Morphologies of AGN host galaxies using HST/ACS in the CDFS-GOODS field
Using HST/ACS images in four bands F435W, F606W, F775W and F850LP, we
identify optical counterparts to the X-ray sources in the Chandra Deep Field
South in the GOODS South field. A detailed study has been made of these sources
to study their morphological types. We use methods like decomposition of galaxy
luminosity profiles, color maps and visual inspection of 192 galaxies which are
identified as possible optical counterparts of Chandra X-ray sources in the
CDFS-GOODS field. We find that most moderate luminosity AGN hosts are bulge
dominated in the redshift range (z \approx 0.4-1.3), but not
merging/interacting galaxies. This implies probable fueling of the moderate
luminosity AGN by mechanisms other than those merger driven.Comment: pdflatex, accepted in ApSS. revisions in tex