16 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
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
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
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
GMRT mini-survey to search for 21-cm absorption in Quasar-Galaxy Pairs at z~0.1
We present the results from our 21-cm absorption survey of a sample of 5
quasar-galaxy pairs (QGPs), with the redshift of the galaxies in the range
0.03<zg<0.18, selected from the SDSS. The HI 21-cm absorption was searched
towards the 9 sight lines with impact parameters ranging from 10 to 55 kpc
using GMRT. 21-cm absorption was detected only in one case i.e. towards the
Quasar (zq=2.625 SDSS J124157.54+633241.6)-galaxy (zg=0.143 SDSS
J124157.26+633237.6) pair with the impact parameter 11 kpc. The quasar sight
line in this case pierces through the stellar disk of a galaxy having near
solar metallicity (i.e (O/H)+12=8.7) and star formation rate uncorrected for
dust attenuation of 0.1 M_odot/yr. The quasar spectrum reddened by the
foreground galaxy is well fitted with the Milky Way extinction curve (with an
Av of 0.44) and the estimated HI column density is similar to the value
obtained from 21-cm absorption assuming spin temperature of 100K. Combining our
sample with the z<0.1 data available in the literature, we find the
detectability of 21-cm absorption with integrated optical depth greater than
0.1 km\s to be 50% for the impact parameter less than 20 kpc. Using the surface
brightness profiles and relationship between the optical size and extent of the
HI disk known for nearby galaxies, we conclude that in most of the cases of
21-cm absorption non-detection, the sight lines may not be passing through the
HI gas. We also find that in comparison to the absorption systems associated
with these QGPs, z<1 DLAs with 21-cm absorption detections have lower CaII
equivalent widths despite having higher 21-cm optical depths and smaller impact
parameters. This suggests that the current sample of DLAs may be a biased
population that avoids sight lines through dusty star-forming galaxies. A
systematic survey of QGPs is needed to confirm these findings and understand
the nature of 21-cm absorbers.Comment: 17 pages, 5 tables, 19 figures, accepted for publication in MNRAS
(abstract abridged
High-Performance Computing for SKA Transient Search: Use of FPGA based Accelerators -- a brief review
This paper presents the High-Performance computing efforts with FPGA for the
accelerated pulsar/transient search for the SKA. Case studies are presented
from within SKA and pathfinder telescopes highlighting future opportunities. It
reviews the scenario that has shifted from offline processing of the radio
telescope data to digitizing several hundreds/thousands of antenna outputs over
huge bandwidths, forming several 100s of beams, and processing the data in the
SKA real-time pulsar search pipelines. A brief account of the different
architectures of the accelerators, primarily the new generation Field
Programmable Gate Array-based accelerators, showing their critical roles to
achieve high-performance computing and in handling the enormous data volume
problems of the SKA is presented here. It also presents the power-performance
efficiency of this emerging technology and presents potential future scenarios.Comment: Accepted for JoAA, SKA Special issue on SKA (2022
A review of elliptical and disc galaxy structure, and modern scaling laws
A century ago, in 1911 and 1913, Plummer and then Reynolds introduced their
models to describe the radial distribution of stars in `nebulae'. This article
reviews the progress since then, providing both an historical perspective and a
contemporary review of the stellar structure of bulges, discs and elliptical
galaxies. The quantification of galaxy nuclei, such as central mass deficits
and excess nuclear light, plus the structure of dark matter halos and cD galaxy
envelopes, are discussed. Issues pertaining to spiral galaxies including dust,
bulge-to-disc ratios, bulgeless galaxies, bars and the identification of
pseudobulges are also reviewed. An array of modern scaling relations involving
sizes, luminosities, surface brightnesses and stellar concentrations are
presented, many of which are shown to be curved. These 'redshift zero'
relations not only quantify the behavior and nature of galaxies in the Universe
today, but are the modern benchmark for evolutionary studies of galaxies,
whether based on observations, N-body-simulations or semi-analytical modelling.
For example, it is shown that some of the recently discovered compact
elliptical galaxies at 1.5 < z < 2.5 may be the bulges of modern disc galaxies.Comment: Condensed version (due to Contract) of an invited review article to
appear in "Planets, Stars and Stellar
Systems"(www.springer.com/astronomy/book/978-90-481-8818-5). 500+ references
incl. many somewhat forgotten, pioneer papers. Original submission to
Springer: 07-June-201
An evolutionary approach to modeling radial brightness distributions in elliptical galaxies
Abstract. A reasonably good description of the luminosity profiles of galaxies is needed as it serves as a guide towards understanding the process of galaxy formation and evolution. To obtain a radial brightness profile model of a galaxy, the way varies both in terms of the exact mathematical form of the function used and in terms of the algorithm used for parameters fitting for the function given. Traditionally, one builds such a model by means of fitting parameters for a functional form assumed beforehand. As a result, such a model depends crucially on the assumed functional form. In this paper we propose an approach that enables one to build profile models from data directly without assuming a functional form in advance by using evolutionary computation. This evolutionary approach consists of two major steps that serve two goals. The first step applies the technique of genetic programming with the aim of finding a promising functional form, whereas the second step takes advantage of the power of evolutionary programming with the aim of fitting parameters for functional forms found at the first step. The proposed evolutionary approach has been applied to modeling 18 elliptical galaxies profiles and its preliminary results are reported in this paper.