798 research outputs found
Fast-Growing SMBHs in Fast-Growing Galaxies, at High Redshifts: The Role of Major Mergers As Revealed by ALMA
We present a long-term, multi-wavelength project to understand the epoch of
fastest growth of the most massive black holes by using a sample of 40 luminous
quasars at z~4.8. These quasars have rather uniform properties, with typical
accretion rates and black hole masses of L/L_Edd~0.7 and M_BH~10^9 M_sol. The
sample consists of "FIR-bright" sources with a previous Herschel/SPIRE
detection, suggesting SFR > 1000 M_sol/yr, as well as of "FIR-faint" sources
for which Herschel stacking analysis implies a typical SFR of ~400 M_sol/yr.
Six of the quasars have been observed by ALMA in [CII]{\lambda}157.74 micron
line emission and adjacent rest-frame 150 micron continuum, to study the dusty
cold ISM. ALMA detected companion, spectroscopically confirmed sub-mm galaxies
(SMGs) for three sources - one FIR-bright and two FIR-faint. The companions are
separated by ~14-45 kpc from the quasar hosts, and we interpret them as major
galaxy interactions. Our ALMA data therefore clearly support the idea that
major mergers may be important drivers for rapid, early SMBH growth. However,
the fact that not all high-SFR quasar hosts are accompanied by interacting
SMGs, and their ordered gas kinematics observed by ALMA, suggest that other
processes may be fueling these systems. Our analysis thus demonstrates the
diversity of host galaxy properties and gas accretion mechanisms associated
with early and rapid SMBH growth
A New H I Survey of Active Galaxies
We have conducted a new Arecibo survey for H I emission for 113 galaxies with
broad-line (type 1) active galactic nuclei (AGNs) out to recession velocities
as high as 35,000 km/s. The primary aim of the study is to obtain sensitive H I
spectra for a well-defined, uniformly selected sample of active galaxies that
have estimates of their black hole masses in order to investigate correlations
between H I properties and the characteristics of the AGNs. H I emission was
detected in 66 out of the 101 (65%) objects with spectra uncorrupted by radio
frequency interference, among which 45 (68%) have line profiles with adequate
signal-to-noise ratio and sufficiently reliable inclination corrections to
yield robust deprojected rotational velocities. This paper presents the basic
survey products, including an atlas of H I spectra, measurements of H I flux,
line width, profile asymmetry, optical images, optical spectroscopic
parameters, as well as a summary of a number of derived properties pertaining
to the host galaxies. To enlarge our primary sample, we also assemble all
previously published H I measurements of type 1 AGNs for which can can estimate
black hole masses, which total an additional 53 objects. The final
comprehensive compilation of 154 broad-line active galaxies, by far the largest
sample ever studied, forms the basis of our companion paper, which uses the H I
database to explore a number of properties of the AGN host galaxies.Comment: To appear in ApJS; 31 pages. Preprint will full-resolution figures
can be downloaded from http://www.ociw.edu/~lho/preprints/ms1.pd
Simultaneous Ultraviolet and X-ray Observations of the Seyfert Galaxy NGC 4151. I. Physical Conditions in the X-ray Absorbers
We present a detailed analysis of the intrinsic X-ray absorption in the
Seyfert 1 galaxy NGC 4151 using Chandra/HETGS data obtained 2002 May, as part
of a program which included simultaneous UV spectra using HST/STIS and FUSE.
NGC 4151 was in a relatively low flux state during the observations reported
here, although roughly 2.5 times as bright in the 2 --10 keV band as during a
Chandra observation in 2000. The soft X-ray band was dominated by emission
lines, which show no discernible variation in flux between the two
observations. The 2002 data show the presence of a very highly ionized
absorber, in the form of H-like and He-like Mg, Si, and S lines, as well as
lower ionization gas via the presence of inner-shell absorption lines from
lower-ionization species of these elements. The former is too highly ionized to
be radiatively accelerated in a sub-Eddington source such as NGC 4151. We find
that the lower ionization gas had a column density a factor of ~ 3 higher
during the 2000 observation. If due to bulk motion, we estimate that this
component must have a velocity of more than 1250 km/sec transverse to our
line-of-sight. We suggest that these results are consistent with a
magneto-hydrodynamic flow.Comment: 42 pages, 14 figures. Accepted for publication in The Astrophysical
Journa
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ALMA Observations of Quasar Host Galaxies at z â 4.8
We present ALMA band-7 data of the [C ii] 157:74 m emission line and underlying far-infrared (FIR) continuum for twelve luminous quasars at z ' 4:8 powered by fast-growing supermassive black holes (SMBHs). Our total sample consists of eighteen quasars, twelve of which are presented here for the rst time. The new sources consists of six Herschel/SPIRE detected systems, which we de ne as "FIR-bright" sources, and six Herschel/SPIRE undetected systems, which we de ne as "FIR-faint" sources. We determine dust masses for the quasars hosts of Mdust 0:225:0 108M , implying ISM gas masses comparable to the dynamical masses derived from the [C ii] kinematics. It is found that on average the Mgii line is blueshifted by 500kms1 with respect to the [C ii] emission line, which is also observed when complementing our observations with data from the literature. We nd that all of our "FIR-bright" subsample and most of the "FIR-faint" objects lie above the main sequence of star forming galaxies at z 5. We detect companion sub-millimeter galaxies (SMGs) for two sources, both FIR-faint, with a range of projected distances of 20 60 kpc and with typical velocity shifts of j vj < 200kms1 from the quasar hosts. Of our total sample of eighteen quasars, 5/18 are found to have dust obscured starforming companions.ERC; STF
Simultaneous Ultraviolet and X-ray Observations of the Seyfert Galaxy NGC 4151. II. Physical Conditions in the UV Absorbers
We present a detailed analysis of the intrinsic absorption in the Seyfert 1
galaxy NGC 4151 using UV spectra from the HST/STIS and FUSE, obtained 2002 May
as part of a set of contemporaneous observations that included Chandra/HETGS
spectra. In our analysis of the Chandra spectra, we determined that the soft
X-ray absorber was the source of the saturated UV lines of O VI, C IV, and N V
associated with the absorption feature at a radial velocity of ~ -500 km/sec,
which we referred to as component D+E. In the present work, we have derived
tighter constrains on the the line-of-sight covering factors, densities, and
radial distances of the absorbers. We find that the Equivalent Widths (EWs) of
the low-ionization lines associated with D+E varied over the period from 1999
July to 2002 May. The drop in the EWs of these lines between 2001 April and
2002 May are suggestive of bulk motion of gas out of our line-of-sight. If
these lines from these two epochs arose in the same sub-component, the
transverse velocity of the gas is ~ 2100 km/sec. Transverse velocities of this
order are consistent with an origin in a rotating disk, at the roughly radial
distance we derived for D+E.Comment: 51 pages, including 12 figures. Accepted for publication in ApJ
Supplement
The Primordial Helium Abundance: Towards Understanding and Removing the Cosmic Scatter in the dY/dZ Relation
We present results from photoionization models of low-metallicity HII
regions. These nebulae form the basis for measuring the primordial helium
abundance. Our models show that the helium ionization correction factor (ICF)
can be non-negligible for nebulae excited by stars with effective temperatures
larger than 40,000 K. Furthermore, we find that when the effective temperature
rises to above 45,000 K, the ICF can be significantly negative. This result is
independent of the choice of stellar atmosphere. However, if an HII region has
an [O III] 5007/[O I] 6300 ratio greater than 300, then our models show that,
regardless of its metallicity, it will have a negligibly small ICF. A similar,
but metallicity dependent, result was found using the [O III] 5007/H
ratio. These two results can be used as selection criteria to remove nebulae
with potentially non-negligible ICFs. Using our metallicity independent
criterion on the data of Izotov & Thuan (1998) results in a 20% reduction of
the rms scatter about the best fit line. A fit to the selected data
results in a slight increase of the value of the primordial helium abundance.Comment: 10 pages, 5 figures, accepted by the Ap
Quasars as Cosmological Probes: The Ionizing Continuum, Gas Metallicity and the EW-L Relation
Using a realistic model for line emission from the broad emission line
regions of quasars, we are able to reproduce the previously observed
correlations of emission-line ratios with the shape of the spectral energy
distribution (SED). In agreement with previous studies, we find that the
primary driving force behind the Baldwin Effect (EW ~ L^beta, beta < 0) is a
global change in the SED with quasar luminosity, in that more luminous quasars
must have characteristically softer ionizing continua. This is completely
consistent with observations that show correlations between L_uv, alpha_ox,
alpha_uvx, line ratios and EWs. However, to explain the complete lack of a
correlation in the EW(NV)--L_uv diagram we propose that the more luminous
quasars have characteristically larger gas metallicities (Z). As a secondary
element, nitrogen's rapidly increasing abundance with increasing Z compensates
for the losses in EW(NV) emitted by gas illuminated by softer continua in
higher luminosity quasars. A characteristic relationship between Z and L has an
impact on the EW--L_uv relations for other lines as well. For a fixed SED, an
increasing gas metallicity reduces the EW of the stronger metal lines (the gas
cools) and that of Ly_alpha and especially HeII (because of the increasing
metal opacity), while the weaker lines (e.g., CIII] 1909) generally respond
positively. The interplay between the effects of a changing SED and Z with L
results in the observed luminosity dependent spectral variations. All of the
resulting dependences on L_uv are within the range of the observed slopes.Comment: 11 pages, 3 figures, AASTeX aas2pp4.sty, accepted for publication in
Ap
Narrow Components within the Fe Kalpha Profile of NGC 3516: Evidence for the Importance of General Relativistic Effects?
We present results from a simultaneous Chandra HETG and XMM-Newton
observation of NGC 3516. We find evidence for several narrow components of Fe
Kalpha along with a broad line. We consider the possibility that the lines
arise in an blob of material ejected from the nucleus with velocity ~0.25c. We
also consider an origin in a neutral accretion disk, suffering enhanced
illumination at 35 and 175 gravitational radii, perhaps due to magnetic
reconnection. The presence of these narrow features indicates there is no
Comptonizing region along the line-of-sight to the nucleus. This in turn is
compelling support for the hypothesis that broad Fe Kalpha components are, in
general, produced by strong gravity.Comment: 12 pages, 3 color figures. LaTeX with postscript figures. Resubmitted
June 7 2002, to Astrophysical Journal Letter
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