182 research outputs found
CO luminosity - line width correlation of sub-millimeter galaxies and a possible cosmological application
Context. A possible correlation between CO luminosity (L_CO ) and its line
width (FWHM) has been suggested and denied in the literature. Such claims were
often based on a small, or heterogeneous sample of galaxies, and thus
inconclusive. Aims. We aim to prove or dis-prove the L_CO -FWHM correlation.
Methods. We compile a large sample of submm galaxies at z>2 from the
literature, and investigate the L_CO-FWHM relation. Results. After carefully
evaluating the selection effects and uncertainties such as inclination and
magnification via gravitational lensing, we show that there exist a weak but
significant correlation between L_CO and FWHM. We also discuss a feasibility to
measure the cosmological distance using the correlation.Comment: 4 pages, 3 figures. Accepted for publication in A&A. A related video
is at https://youtu.be/scWMFurOJi
The extinction curve of the lensing galaxy of B1152+199 at z=0.44
We present UBVRIz' photometry of the gravitational lens candidate CLASS
B1152+119 obtained with the Nordic Optical Telescope. The two QSO components
are resolved in the B, V, R, I and z' bands confirming the lensing nature of
the system. The z=0.44 lens galaxy is clearly detected in B, R, I and z' and
its position is found to be almost coincident with the faint QSO image which is
heavily extincted (relative to the brighter QSO image) by dust in the lens
galaxy. The extinction curve of the lens galaxy derived from the relative
photometry is well fitted by a Galactic extinction law with 1.3 < R_V < 2.0 and
E(B-V) ~ 1. From a simple model of the system we predict a time delay of ~ 60
days.Comment: 6 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
Galaxy pairs as a probe for mergers at z ~ 2
In this work I investigate the redshift evolution of pair fraction of a
sample of 196 massive galaxies from z = 0 to 3, selected from the COSMOS field.
We find that on average a massive galaxy undergoes ~ 1.1 \pm 0.5 major merger
since z = 3. I will review the current limitations of using the pair fraction
as a probe for quantifying the impact of mergers on galaxy evolution. This work
is based on the paper Man et al. (2011).Comment: 4 pages; to appear on the Conference Proceedings for "Galaxy Mergers
in an Evolving Universe", held in Hualien, Taiwan (October 2011
Evidence for Widespread AGN Activity among Massive Quiescent Galaxies at z ~ 2
We quantify the presence of Active Galactic nuclei (AGN) in a mass-complete
(M_* >5e10 M_sun) sample of 123 star-forming and quiescent galaxies at 1.5 < z
< 2.5, using X-ray data from the 4 Ms Chandra Deep Field-South (CDF-S) survey.
41+/-7% of the galaxies are detected directly in X-rays, 22+/-5% with
rest-frame 0.5-8 keV luminosities consistent with hosting luminous AGN
(L_0.5-8keV > 3e42 ergs/s). The latter fraction is similar for star-forming and
quiescent galaxies, and does not depend on galaxy stellar mass, suggesting that
perhaps luminous AGN are triggered by external effects such as mergers. We
detect significant mean X-ray signals in stacked images for both the
individually non-detected star-forming and quiescent galaxies, with spectra
consistent with star formation only and/or a low luminosity AGN in both cases.
Comparing star formation rates inferred from the 2-10 keV luminosities to those
from rest-frame IR+UV emission, we find evidence for an X-ray excess indicative
of low-luminosity AGN. Among the quiescent galaxies, the excess suggests that
as many as 70-100% of these contain low- or high-luminosity AGN, while the
corresponding fraction is lower among star-forming galaxies (43-65%). The
ubiquitous presence of AGN in massive, quiescent z ~ 2 galaxies that we find
provides observational support for the importance of AGN in impeding star
formation during galaxy evolution.Comment: 9 pages, 3 figures, 3 tables; Accepted for publication in ApJ. Minor
editing changes and a few references added. Matches published versio
A spectroscopic sample of massive, evolved z~2 galaxies: Implications for the evolution of the mass-size relation
We present deep, near-infrared HST/WFC3 grism spectroscopy and imaging for a
sample of 14 galaxies at z~2 selected from a mass-complete photometric catalog
in the COSMOS field. By combining the grism observations with photometry in 30
bands, we derive accurate constraints on their redshifts, stellar masses, ages,
dust extinction and formation redshifts. We show that the slope and scatter of
the z~2 mass-size relation of quiescent galaxies is consistent with the local
relation, and confirm previous findings that the sizes for a given mass are
smaller by a factor of two to three. Finally, we show that the observed
evolution of the mass-size relation of quiescent galaxies between z=2 and 0 can
be explained by quenching of increasingly larger star-forming galaxies, at a
rate dictated by the increase in the number density of quiescent galaxies with
decreasing redshift. However, we find that the scatter in the mass-size
relation should increase in the quenching-driven scenario in contrast to what
is seen in the data. This suggests that merging is not needed to explain the
evolution of the median mass-size relation of massive galaxies, but may still
be required to tighten its scatter, and explain the size growth of individual
z=2 galaxies quiescent galaxies.Comment: 16 pages, 8 figures, accepted for publication in the Astrophysical
Journa
The rest-frame optical sizes of massive galaxies with suppressed star formation at
We present the rest-frame optical sizes of massive quiescent galaxies (QGs)
at measured at -band with the Infrared Camera and Spectrograph
(IRCS) and AO188 on the Subaru telescope. Based on a deep multi-wavelength
catalog in the Subaru XMM-Newton Deep Survey Field (SXDS), covering a wide
wavelength range from the -band to the IRAC over 0.7 deg, we
evaluate photometric redshift to identify massive ($M_{\star}\sim10^{11}\
M_\odot\rm \AAz\sim4K'K_{AB,total}=22.5\sim23.4z\sim4r_{eff}=0.21.8r_{eff}=0.7\rm\ kpcz\sim4\sim0.2z\sim4\log(r_e/{\rm kpc})= -0.44+1.77
\log(t/\rm Gyr)$. Their size growth is proportional to the square of stellar
mass, indicating the size-stellar mass growth driven by minor dry mergers.Comment: 15 pages, 11 figures, ApJ accepte
VLT/X-Shooter Near-Infrared Spectroscopy and HST Imaging of Gravitationally-Lensed z~2 Compact Quiescent Galaxies
Quiescent massive galaxies at z~2 are thought to be the progenitors of
present-day massive ellipticals. Observations revealed them to be
extraordinarily compact. The determination of stellar ages, star formation
rates and dust properties via spectroscopic measurements has up to now only
been feasible for the most luminous and massive specimens (~3x M*). Here we
present a spectroscopic study of two near-infrared selected galaxies which are
close to the characteristic stellar mass M* (~0.9x M* and ~1.3x M*) and whose
observed brightness has been boosted by the gravitational lensing effect. We
measure the redshifts of the two galaxies to be z=1.71\pm0.02 and
z=2.15\pm0.01. By fitting stellar population synthesis models to their
spectro-photometric SEDs we determine their ages to be 2.4^{+0.8}_{-0.6} Gyr
and 1.7\pm0.3 Gyr, respectively, which implies that the two galaxies have
higher mass-to-light ratios than most quiescent z~2 galaxies in other studies.
We find no direct evidence for active star-formation or AGN activity in either
of the two galaxies, based on the non-detection of emission lines. Based on the
derived redshifts and stellar ages we estimate the formation redshifts to be
z=4.3^{+3.4}_{-1.2} and z=4.3^{+1.0}_{-0.6}, respectively. We use the increased
spatial resolution due to the gravitational lensing to derive constraints on
the morphology. Fitting Sersic profiles to the de-lensed images of the two
galaxies confirms their compactness, with one of them being spheroid-like, and
the other providing the first confirmation of a passive lenticular galaxy at a
spectroscopically derived redshift z~2.Comment: accepted for publication in Ap
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