44 research outputs found
A comparison of cosmological models with high-redshift quasars
The non-linear relationship between the monochromatic X-ray and UV
luminosities in quasars offers the possibility of using high-z quasars as
standard candles for cosmological testing. In this paper, we use a high-quality
catalog of 1598 quasars extending to redshift 6, to compare the flat and
uniformly expanding cosmological model, = ct and CDM
cosmological models which are the most debated. The quasar samples are mainly
from the XMM-Newton and the Sloan Digital Sky Survey (SDSS). The final result
is that the Akaike Information Criterion favors CDM over =ct with
a relative probability of 86.30% versus 13.70%.Comment: 10 pages, 5 figures, Accepted for publication in APS
Structure and morphology of X-ray selected AGN hosts at 1<z<3 in CANDELS-COSMOS field
We analyze morphologies of the host galaxies of 35 X-ray selected active
galactic nucleus (AGNs) at in the Cosmic Evolution Survey (COSMOS)
field using Hubble Space Telescope/WFC3 imaging taken from the Cosmic Assembly
Near-infrared Deep Extragalactic Legacy Survey (CANDELS). We build a control
sample of 350 galaxies in total, by selecting ten non-active galaxies drawn
from the same field with the similar stellar mass and redshift for each AGN
host. By performing two dimensional fitting with GALFIT on the surface
brightness profile, we find that the distribution of Srsic index (n) of
AGN hosts does not show a statistical difference from that of the control
sample. We measure the nonparametric morphological parameters (the asymmetry
index A, the Gini coefficient G, the concentration index C and the M20 index)
based on point source subtracted images. All the distributions of these
morphological parameters of AGN hosts are consistent with those of the control
sample. We finally investigate the fraction of distorted morphologies in both
samples by visual classification. Only 15% of the AGN hosts have highly
distorted morphologies, possibly due to a major merger or interaction. We find
there is no significant difference in the distortion fractions between the AGN
host sample and control sample. We conclude that the morphologies of X-ray
selected AGN hosts are similar to those of nonactive galaxies and most AGN
activity is not triggered by major merger.Comment: 5 pages, 3 figures, accepted for publication in The Astrophysical
Journal Letter
Selection and Mid-infrared Spectroscopy of Ultraluminous Star-Forming Galaxies at z~2
Starting from a sample of 24 \micron\ sources in the Extended Groth Strip, we
use 3.6 to 8 \micron\ color criteria to select ultraluminous infrared galaxies
(ULIRGs) at . Spectroscopy from 20-38 \micron\ of 14 objects verifies
their nature and gives their redshifts. Multi-wavelength data for these objects
imply stellar masses \Msun\ and star formation rates 410
\Msun yr. Four objects of this sample observed at 1.6 \micron\
(rest-frame visible) with {\it HST}/WFC3 show diverse morphologies, suggesting
that multiple formation processes create ULIRGs. Four of the 14 objects show
signs of active galactic nuclei, but the luminosity appears to be dominated by
star formation in all cases.Comment: 33 pages, 13 figures, accepted by Ap
Solution to the conflict between the resolved and unresolved galaxy stellar mass estimation from the perspective of JWST
By utilizing the spatially-resolved photometry of galaxies at in
the CEERS field, we estimate the resolved and unresolved stellar mass via
spectral energy distribution (SED) fitting to study the discrepancy between
them. We first compare derived from photometry with and without the
JWST wavelength coverage and find that can be overestimated by up to
0.2 dex when lacking rest-frame NIR data. The SED fitting process tends to
overestimate both stellar age and dust attenuation in the absence of rest-frame
NIR data, consequently leading to a larger observed mass-to-light ratio and
hence an elevated . With the inclusion of the JWST NIR photometry, we
find no significant disparity between the resolved and unresolved stellar mass
estimates, providing a plausible solution to the conflict between them out to
. Further investigation demonstrates that reliable
estimates can be obtained, regardless of whether they are derived from
spatially resolved or spatially unresolved photometry, so long as the reddest
filter included in the SED fitting has a rest-frame wavelength larger than
10000 \AA.Comment: 8 pages, 5 figures, accepted by Ap