196 research outputs found
Supermassive black holes with higher Eddington ratios preferentially form in gas-rich galaxies
The Eddington ratio () of supermassive black holes (SMBHs)
is a fundamental parameter that governs the cosmic growth of SMBHs. Although
gas mass accretion onto SMBHs is sustained when they are surrounded by large
amounts of gas, little is known about the molecular content of galaxies,
particularly those hosting super-Eddington SMBHs (: the
key phase of SMBH growth). Here, we compiled reported optical and
CO(1--0) data of local quasars to characterize their hosts. We found
that higher SMBHs tend to reside in gas rich (i.e., high
gas mass to stellar mass fraction = ) galaxies. We used two
methods to make this conclusion: one uses black hole mass as a surrogate for
stellar mass by assuming a local co-evolutionary relationship, and the other
directly uses stellar masses estimated from near-infrared observations. The
-- correlation we found concurs with the cosmic
decreasing trend in , as cold molecular gas is primarily
consumed by star formation. This correlation qualitatively matches predictions
of recent semi-analytic models about the cosmic downsizing of SMBHs as well. As
the gas mass surface density would eventually be a key parameter controlling
mass accretion, we need high-resolution observations to identify further
differences in the molecular properties around super-Eddington and
sub-Eddington SMBHs.Comment: 6 pages, 4 figures, accepted for publication in the Publications of
the Astronomical Society of Japan (PASJ) Lette
Do Circumnuclear Dense Gas Disks Drive Mass Accretion onto Supermassive Black Holes?
We present a positive correlation between the mass of dense molecular gas
() of pc scale circumnuclear disks (CNDs) and the
black hole mass accretion rate () in total 10 Seyfert
galaxies, based on data compiled from the literature and an archive (median
aperture = 220 pc). A typical of CNDs is
10 , estimated from the luminosity of the dense gas tracer,
the HCN() emission line. Because dense molecular gas is the site of star
formation, this correlation is virtually equivalent to the one between nuclear
star formation rate and revealed previously. Moreover, the
correlation was tighter for CND-scale gas than
for the gas on kpc or larger scales. This indicates that CNDs likely play an
important role in fueling black holes, whereas kpc scale gas does not. To
demonstrate a possible approach for studying the CND-scale accretion process
with the Atacama Large Millimeter/submillimeter Array (ALMA), we used a mass
accretion model where angular momentum loss due to supernova explosions is
vital. Based on the model prediction, we suggest that only the partial fraction
of the mass accreted from the CND () is consumed as
. However, agrees well with the total
nuclear mass flow rate (i.e., + outflow rate). Although
these results are still tentative with large uncertainties, they support the
view that star formation in CNDs can drive mass accretion onto supermassive
black holes in Seyfert galaxies.Comment: Accepted for publication in ApJ; 17 pages (including 1 page
appendix), 8 figures, 4 tables; Comments welcome
ALMA Multiple-Transition Observations of High Density Molecular Tracers in Ultraluminous Infrared Galaxies
We present the results of our ALMA observations of eleven (ultra)luminous
infrared galaxies ((U)LIRGs) at J=4-3 of HCN, HCO+, HNC and J=3-2 of HNC. This
is an extension of our previously published HCN and HCO+ J=3-2 observations to
multiple rotational J-transitions of multiple molecules, to investigate how
molecular emission line flux ratios vary at different J-transitions. We confirm
that ULIRGs that contain or may contain luminous obscured AGNs tend to show
higher HCN-to-HCO+ flux ratios than starburst galaxies, both at J=4-3 and
J=3-2. For selected HCN-flux-enhanced AGN-important ULIRGs, our isotopologue
H13CN, H13CO+, and HN13C J=3-2 line observations suggest a higher abundance of
HCN than HCO+ and HNC, which is interpreted to be primarily responsible for the
elevated HCN flux in AGN-important galaxies. For such sources, the intrinsic
HCN-to-HCO+ flux ratios after line opacity correction will be higher than the
observed ratios, making the separation between AGNs and starbursts even larger.
The signature of the vibrationally excited (v2=1f) HCN J=4-3 emission line is
seen in one ULIRG, IRAS 12112-0305 NE. P Cygni profiles are detected in the
HCO+ J=4-3 and J=3-2 lines toward IRAS 15250+3609, with an estimated molecular
outflow rate of ~250-750 Mo/year. The SiO J=6-5 line also exhibits a P Cygni
profile in IRAS 12112+0305 NE, suggesting the presence of shocked outflow
activity. Shock tracers are detected in many sources, suggesting ubiquitous
shock activity in the nearby ULIRG population.Comment: 59 pages, 32 Figures (emulateapj.cls). Accepted for publication in
ApJS. Resolutions of some figures are degrade
ALMA Spatially-resolved Dense Molecular Gas Survey of Nearby Ultraluminous Infrared Galaxies
We present the results of our ALMA HCN J=3-2 and HCO+ J=3-2 line observations
of a uniformly selected sample (>25) of nearby ultraluminous infrared galaxies
(ULIRGs) at z < 0.15. The emission of these dense molecular gas tracers and
continuum are spatially resolved in the majority of observed ULIRGs for the
first time with achieved synthesized beam sizes of ~0.2 arcsec or ~500 pc. In
most ULIRGs, the HCN-to-HCO+ J=3-2 flux ratios in the nuclear regions within
the beam size are systematically higher than those in the spatially extended
regions. The elevated nuclear HCN J=3-2 emission could be related to (a)
luminous buried active galactic nuclei, (b) the high molecular gas density and
temperature in ULIRG's nuclei, and/or (c) mechanical heating by spatially
compact nuclear outflows. A small fraction of the observed ULIRGs display
higher HCN-to-HCO+ J=3-2 flux ratios in localized off-nuclear regions than
those of the nuclei, which may be due to mechanical heating by spatially
extended outflows. The observed nearby ULIRGs are generally rich in dense
(>10^5 cm^-3) molecular gas, with an estimated mass of >10^9 Msun within the
nuclear (a few kpc) regions, and dense gas can dominate the total molecular
mass there. We find a low detection rate (<20%) regarding the possible
signature of a vibrationally excited (v2=1f) HCN J=3-2 emission line in the
vicinity of the bright HCO+ J=3-2 line that may be due, in part, to the large
molecular line widths of ULIRGs.Comment: 60 pages, 14 Figures (preprint style). Accepted for publication in
ApJS. Resolutions of some figures are degrade
ALMA 0.1-0.2 arcsec resolution imaging of the NGC 1068 nucleus - compact dense molecular gas emission at the putative AGN location
We present the results of our ALMA Cycle 2 high angular resolution (0.1-0.2
arcsec) observations of the nuclear region of the nearby well-studied type-2
active galactic nucleus (AGN), NGC 1068, at HCN J=3-2 and HCO+ J=3-2 emission
lines. For the first time, due to a higher angular resolution than previous
studies, we clearly detected dense molecular gas emission at the putative AGN
location, identified as a ~1.1 mm (~266 GHz) continuum emission peak, by
separating this emission from brighter emission located at 0.5-2.0 arcsec on
the eastern and western sides of the AGN. The estimated intrinsic molecular
emission size and dense molecular mass, which are thought to be associated with
the putative dusty molecular torus around an AGN, were ~10 pc and ~several x
10^5 Msun, respectively. HCN-to-HCO+ J=3-2 flux ratios substantially higher
than unity were found throughout the nuclear region of NGC 1068. The continuum
emission displayed an elongated morphology along the direction of the radio jet
located at the northern side of the AGN, as well as a weak spatially resolved
component at ~2.0 arcsec on the southwestern side of the AGN. The latter
component most likely originated from star formation, with the estimated
luminosity more than one order of magnitude lower than the luminosity of the
central AGN. No vibrationally excited (v2=1f) J=3-2 emission lines were
detected for HCN and HCO+ across the field of view.Comment: 7 pages, 4 figures, accepted for publication in ApJ Letter
ALMA Investigation of Vibrationally Excited HCN/HCO+/HNC Emission Lines in the AGN-Hosting Ultraluminous Infrared Galaxy IRAS 20551-4250
We present the results of ALMA Cycle 2 observations of the ultraluminous
infrared galaxy, IRAS 20551-4250, at HCN/HCO+/HNC J=3-2 lines at both
vibrational-ground (v=0) and vibrationally excited (v2=1) levels. This galaxy
contains a luminous buried active galactic nucleus (AGN), in addition to
starburst activity, and our ALMA Cycle 0 data revealed a tentatively detected
vibrationally excited HCN v2=1f J=4-3 emission line. In our ALMA Cycle 2 data,
the HCN/HCO+/HNC J=3-2 emission lines at v=0 are clearly detected. The HCN and
HNC v2=1f J=3-2 emission lines are also detected, but the HCO+ v2=1f J=3-2
emission line is not. Given the high-energy level of v2=1 and the resulting
difficulty of collisional excitation, we compared these results with those of
the calculation of infrared radiative pumping, using the available infrared
5-35 micron spectrum. We found that all of the observational results were
reproduced, if the HCN abundance was significantly higher than that of HCO+ and
HNC. The flux ratio and excitation temperature between v2=1f and v=0, after
correction for possible line opacity, suggests that infrared radiative pumping
affects rotational (J-level) excitation at v=0 at least for HCN and HNC. The
HCN-to-HCO+ v=0 flux ratio is higher than those of starburst-dominated regions,
and will increase even more when thederived high HCN opacity is corrected. The
enhanced HCN-to-HCO+ flux ratio in this AGN-hosting galaxy can be explained by
the high HCN-to-HCO+ abundance ratio and sufficient HCN excitation at up to
J=4, rather than the significantly higher efficiency of infrared radiative
pumping for HCN than HCO+.Comment: 28 pages, 10 figures, accepted for publication in Ap
ALMA Multiple-Transition Molecular Line Observations of the Ultraluminous Infrared Galaxy IRAS 20551-4250: Different HCN, HCO+, HNC Excitation and Implications for Infrared Radiative Pumping
We present our ALMA multi-transition molecular line observational results for
the ultraluminous infrared galaxy, IRAS 20551-4250, which is known to contain a
luminous buried AGN and shows detectable vibrationally excited (v2=1f) HCN and
HNC emission lines. The rotational J=1-0, 4-3, and 8-7 of HCN, HCO+, and HNC
emission lines were clearly detected at a vibrational ground level (v=0).
Vibrationally excited (v2=1f) J=4-3 emission lines were detected for HCN and
HNC, but not for HCO+. Their observed flux ratios further support our
previously obtained suggestion, based on J=3-2 data, that (1) infrared
radiative pumping plays a role in rotational excitation at v=0, at least for
HCN and HNC, and (2) HCN abundance is higher than HCO+ and HNC. The flux
measurements of the isotopologue H13CN, H13CO+, and HN13C J=3-2 emission lines
support the higher HCN abundance scenario. Based on modeling with collisional
excitation, we constrain the physical properties of these line-emitting
molecular gas, but find that higher HNC rotational excitation than HCN and HCO+
is difficult to explain, due to the higher effective critical density of HNC.
We consider the effects of infrared radiative pumping using the available 5-30
micron infrared spectrum and find that our observational results are well
explained if the radiation source is located at 30-100 pc from the molecular
gas. The simultaneously covered very bright CO J=3-2 emission line displays a
broad emission wing, which we interpret as being due to molecular outflow
activity with the estimated rate of ~150 Msun/yr.Comment: 37 pages, 19 figures, accepted for publication in Ap
ALMA Reveals an Inhomogeneous Compact Rotating Dense Molecular Torus at the NGC 1068 Nucleus
We present the results of our ALMA Cycle 4 high-spatial-resolution
(0.04-0.07") observations, at HCN J=3-2 and HCO+ J=3-2 lines, of the nucleus of
NGC 1068, the nearby prototypical type 2 active galactic nucleus (AGN). Our
previous ALMA observations identified the compact emission of these lines at
the putative location of the torus around a mass-accreting supermassive black
hole. We now report that we have detected the rotation of this compact
emission, with the eastern and western sides being redshifted and blueshifted,
respectively. Unlike the previously reported CO J=6-5 emission, both the
morphological and dynamical alignments of the HCN J=3-2 and HCO+ J=3-2 emission
are roughly aligned along the east-west direction (i.e., the expected torus
direction), suggesting that these molecular lines are better probes of a
rotating dense molecular gas component in the torus. The western part of the
torus exhibits larger velocity dispersion and stronger emission in the HCN
J=3-2 and HCO+ J=3-2 lines than the eastern part, revealing a highly
inhomogeneous molecular torus. The dense molecular gas in the torus and that of
the host galaxy at 0.5-2.0" from the AGN along the torus direction are found to
be counter-rotating, suggesting an external process happened in the past at the
NGC 1068 nucleus.Comment: 7 pages, 3 figures, accepted for publication in ApJL. Figures 1 and 2
are degraded. High resolution version is available at
http://www2.nao.ac.jp/~masaimanishi/N1068/N1068bMemuH.pd
ALMA observations of the submillimetre hydrogen recombination line from the type 2 active nucleus of NGC 1068
Hydrogen recombination lines at the submillimetre band (submm-RLs) can serve
as probes of ionized gas without dust extinction. One therefore expects to
probe the broad line region (BLR) of an obscured (type 2) active galactic
nucleus (AGN) with those lines. However, admitting the large uncertainty in the
continuum level, here we report on the non-detection of both broad and narrow
H26 emission line (rest frequency = 353.62 GHz) towards the
prototypical type 2 AGN of NGC 1068 with the Atacama Large
Millimeter/submillimeter Array (ALMA). We also investigate the nature of BLR
clouds that can emit submm-RLs with model calculations. As a result, we suggest
that clouds with an electron density () of 10 cm can
mainly contribute to broad submm-RLs in terms of the line flux. On the other
hand, line flux from other density clouds would be insignificant considering
their too large or too small line optical depths. However, even for the case of
cm clouds, we also suggest that the expected line flux
is extremely low, which is impractical to detect even with ALMA.Comment: 7 pages, 4 figures, and 1 table; To be published in MNRAS; This is
the version 2 of the manuscript. One significant computational error that
influences one of our previous conclusions (1602.07316) was modified
accordingly. Our sincere apology for this issu
Black versus Dark: Rapid Growth of Supermassive Black Holes in Dark Matter Halos at z ~ 6
We report on the relation between the mass of supermassive black holes
(SMBHs; M_BH) and that of hosting dark matter halos (M_h) for 49 z ~ 6
quasi-stellar objects (QSOs) with [CII]158um velocity-width measurements. Here,
we estimate M_h assuming that the rotation velocity from FWHM_CII is equal to
the circular velocity of the halo; we have tested this procedure using z ~ 3
QSOs that also have clustering-based M_h estimates. We find that a vast
majority of the z ~ 6 SMBHs are more massive than expected from the local M_BH
- M_h relation, with one-third of the sample by factors >~ 10^2. The median
mass ratio of the sample, M_BH/M_h = 6 x 10^{-4}, means that 0.4% of the
baryons in halos are locked up in SMBHs. The mass growth rates of our SMBHs
amount to ~ 10% of the SFRs, or ~ 1% of the mean baryon accretion rates, of the
hosting galaxies. A large fraction of the hosting galaxies are consistent with
average galaxies in terms of SFR and perhaps of stellar mass and size. Our
study indicates that the growth of SMBHs (M_BH ~ 10^{8-10} Msun) in luminous z
~ 6 QSOs greatly precedes that of hosting halos owing to efficient gas
accretion even under normal star formation activities, although we cannot rule
out the possibility that undetected SMBHs have local M_BH/M_h ratios. This
preceding growth is in contrast to much milder evolution of the stellar-to-halo
mass ratio.Comment: 9 pages, 6 figures, 1 table. Published in ApJ Letter
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