136 research outputs found
Molecular Gas during the Post-Starburst Phase: Low Gas Fractions in Green Valley Seyfert Post-Starburst Galaxies
Post-starbursts (PSBs) are candidate for rapidly transitioning from
star-bursting to quiescent galaxies. We study the molecular gas evolution of
PSBs at z ~ 0.03 - 0.2. We undertook new CO (2-1) observations of 22 Seyfert
PSBs candidates using the ARO Submillimeter Telescope. This sample complements
previous samples of PSBs by including green valley PSBs with Seyfert-like
emission, allowing us to analyze for the first time the molecular gas
properties of 116 PSBs with a variety of AGN properties. The distribution of
molecular gas to stellar mass fractions in PSBs is significantly different than
normal star-forming galaxies in the COLD GASS survey. The combined samples of
PSBs with Seyfert-like emission line ratios have a gas fraction distribution
which is even more significantly different and is broader (~ 0.03-0.3). Most of
them have lower gas fractions than normal star-forming galaxies. We find a
highly significant correlation between the WISE 12 micron to 4.6 micron flux
ratios and molecular gas fractions in both PSBs and normal galaxies. We detect
molecular gas in 27% of our Seyfert PSBs. Taking into account the upper limits,
the mean and the dispersion of the distribution of the gas fraction in our
Seyfert PSB sample are much smaller (mean = 0.025, std dev. = 0.018) than
previous samples of Seyfert PSBs or PSBs in general (mean ~ 0.1 - 0.2, std dev.
~ 0.1 - 0.2).Comment: 17 pages, 12 figures accepted in MNRA
Structure and Color Gradients of Ultra-diffuse Galaxies in Distant Massive Galaxy Clusters
We have measured structural parameters and radial color profiles of 108
ultra-diffuse galaxies (UDGs), carefully selected from six distant massive
galaxy clusters in the Hubble Frontier Fields (HFF) in redshift range from
0.308 to 0.545. Our best-fitting GALFIT models show that the HFF UDGs have a
median S\'ersic index of 1.09, which is close to 0.86 for local UDGs in the
Coma cluster. The median axis-ratio value is 0.68 for HFF UDGs and 0.74 for
Coma UDGs, respectively. The structural similarity between HFF and Coma UDGs
suggests that they are the same kind of galaxies seen at different times and
the structures of UDGs do not change at least for several billion years. By
checking the distribution of HFF UDGs in the rest-frame and
diagrams, we find a large fraction of them are star-forming. Furthermore, a
majority of HFF UDGs show small color gradients within
\,1\,*\, region, the fluctuation of the median radial color profile
of HFF UDGs is smaller than 0.1\,mag, which is compatible to Coma UDGs. Our
results indicate that cluster UDGs may fade or quench in a self-similar way,
irrespective of the radial distance, in less than 4 Gyrs.Comment: 17 pages, 8 figures, accepted for publication in Ap
From Starburst to Quiescence: Testing AGN feedback in Rapidly Quenching Post-Starburst Galaxies
Post-starbursts are galaxies in transition from the blue cloud to the red
sequence. Although they are rare today, integrated over time they may be an
important pathway to the red sequence. This work uses SDSS, GALEX, and WISE
observations to identify the evolutionary sequence from starbursts to fully
quenched post-starbursts in the narrow mass range , and identifies "transiting" post-starbursts which are intermediate
between these two populations. In this mass range, of galaxies are
starbursts, are quenched post-starbursts, and are the
transiting types in between. The transiting post-starbursts have stellar
properties that are predicted for fast-quenching starbursts and morphological
characteristics that are already typical of early-type galaxies. The AGN
fraction, as estimated from optical line ratios, of these post-starbursts is
about 3 times higher () than that of normal star-forming
galaxies of the same mass, but there is a significant delay between the
starburst phase and the peak of nuclear optical AGN activity (median age
difference of Myr), in agreement with previous studies.
The time delay is inferred by comparing the broad-band near NUV-to-optical
photometry with stellar population synthesis models. We also find that
starbursts and post-starbursts are significantly more dust-obscured than normal
star-forming galaxies in the same mass range. About of the starbursts
and of the transiting post-starbursts can be classified as the
"Dust-Obscured Galaxies" (DOGs), while only of normal galaxies are
DOGs.The time delay between the starburst phase and AGN activity suggests that
AGN do not play a primary role in the original quenching of starbursts but may
be responsible for quenching later low-level star formation during the
post-starburst phase.Comment: 30 pages, 18 figures,accepted to Ap
Nobeyama 45-m CO J=1-0 Observations of Luminous Type 1 AGNs at
We have performed CO J =1-0 observations of ten galaxies hosting luminous
() type 1 active galactic nuclei
(AGNs) with the Nobeyama 45-m radio telescope. The targets are selected because
they are expected to be rich in molecular gas based on their high nebular dust
extinction (). However, no significant CO emission lines were
detected in any of the targets. The upper limits of the CO J=1-0 luminosities
are lower than expected given the molecular gas mass inferred from the nebular
. This inconsistency may be due to overestimated values
due to the lack of stellar absorption correction. Considering more reliable
values, the CO J=1-0 non-detections by Nobeyama 45-m are natural.
This suggests that our results do not contradict the conversion methods from
to molecular gas mass proposed in the literature. This survey
suggests that careful measurements as well as CO observations are
still needed to improve the measurements or estimates of the molecular gas
content of galaxies hosting luminous AGNs.Comment: 8 pages, 6 figures, Accepted for publication in PAS
No evidence for feedback: Unexceptional Low-ionization winds in Host galaxies of Low Luminosity Active Galactic Nuclei at Redshift z ~1
We study winds in 12 X-ray AGN host galaxies at z ~ 1. We find, using the
low-ionization Fe II 2586 absorption in the stacked spectra, that the
probability distribution function (PDF) of the centroid velocity shift in AGN
has a median, 16th and 84th percentiles of (-87, -251, +86) km/s respectively.
The PDF of the velocity dispersion in AGN has a median, 84th and 16th
percentile of (139, 253, 52) km/s respectively. The centroid velocity and the
velocity dispersions are obtained from a two component (ISM+wind) absorption
line model. The equivalent width PDF of the outflow in AGN has median, 84th and
16th percentiles of (0.4, 0.8, 0.1) Angstrom. There is a strong ISM component
in Fe II 2586 absorption with (1.2, 1.5, 0.8) Angstrom, implying presence of
substantial amount cold gas in the host galaxies. For comparison, star-forming
and X-ray undetected galaxies at a similar redshift, matched roughly in stellar
mass and galaxy inclination, have a centroid velocity PDF with percentiles of
(-74, -258, +90) km/s, and a velocity dispersion PDF percentiles of (150, 259,
57) km/s. Thus, winds in the AGN are similar to star-formation-driven winds,
and are too weak to escape and expel substantial cool gas from galaxies. Our
sample doubles the previous sample of AGN studied at z ~ 0.5 and extends the
analysis to z ~ 1. A joint reanalysis of the z ~ 0.5 AGN sample and our sample
yields consistent results to the measurements above.Comment: 24 pages, 11 figures, accepted in Ap
Morphological asymmetries of quasar host galaxies with Subaru Hyper Suprime-Cam
How does the host galaxy morphology influence a central quasar or vice versa?
We address this question by measuring the asymmetries of 2424 SDSS quasar hosts
at using broad-band () images from the Hyper Suprime-Cam
Subaru Strategic Program. Control galaxies (without quasars) are selected by
matching the redshifts and stellar masses of the quasar hosts. A two-step
pipeline is run to decompose the PSF and \sersic\ components, and then measure
asymmetry indices (, , and ) of each
quasar host and control galaxy. We find a mild correlation between host
asymmetry and AGN bolometric luminosity () for the full sample
(spearman correlation of 0.37) while a stronger trend is evident at the highest
luminosities (). This then manifests itself into quasar hosts
being more asymmetric, on average, when they harbor a more massive and highly
accreting black hole. The merger fraction also positively correlates with
and reaches up to 35\% for the most luminous. Compared to control
galaxies, quasar hosts are marginally more asymmetric (excess of 0.017 in
median at 9.4 level) and the merger fractions are similar (). We quantify the dependence of asymmetry on optical band which
demonstrates that mergers are more likely to be identified with the bluer bands
and the correlation between and asymmetry is also stronger in
such bands. We stress that the band dependence, indicative of a changing
stellar population, is an important factor in considering the influence of
mergers on AGN activity.Comment: 27 pages, 28 figure
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