968 research outputs found
Note and Comment
The Execution of the Insured for Crime as a Defense to the Insurer, the Policy Being Silent as to This Contingency; The Power of a Corporation to Hold and Vote Stock of Another Corporation; Effect of an Agreement Not to Compromise Without consent of Attorney Upon Contract for Contingent Fees; The Pennsylvania Supreme Court and The Pennsylvania Railroad Compan
High-ionization mid-infrared lines as black hole mass and bolometric luminosity indicators in active galactic nuclei
We present relations of the black hole mass and the optical luminosity with
the velocity dispersion and the luminosity of the [Ne V] and the [O IV]
high-ionization lines in the mid-infrared (MIR) for 28 reverberation-mapped
active galactic nuclei. We used high-resolution Spitzer Infrared Spectrograph
and Infrared Space Observatory Short Wavelength Spectrometer data to fit the
profiles of these MIR emission lines that originate from the narrow-line region
of the nucleus. We find that the lines are often resolved and that the velocity
dispersion of [Ne V] and [O IV] follows a relation similar to that between the
black hole mass and the bulge stellar velocity dispersion found for local
galaxies. The luminosity of the [Ne V] and the [O IV] lines in these sources is
correlated with that of the optical 5100A continuum and with the black hole
mass. Our results provide a means to derive black hole properties in various
types of active galactic nuclei, including highly obscured systems.Comment: accepted for publication in ApJ
A Spitzer Unbiased Ultradeep Spectroscopic Survey
We carried out an unbiased, spectroscopic survey using the low-resolution
module of the infrared spectrograph (IRS) on board Spitzer targeting two 2.6
square arcminute regions in the GOODS-North field. IRS was used in spectral
mapping mode with 5 hours of effective integration time per pixel. One region
was covered between 14 and 21 microns and the other between 20 and 35 microns.
We extracted spectra for 45 sources. About 84% of the sources have reported
detections by GOODS at 24 microns, with a median F_nu(24um) ~ 100 uJy. All but
one source are detected in all four IRAC bands, 3.6 to 8 microns. We use a new
cross-correlation technique to measure redshifts and estimate IRS spectral
types; this was successful for ~60% of the spectra. Fourteen sources show
significant PAH emission, four mostly SiO absorption, eight present mixed
spectral signatures (low PAH and/or SiO) and two show a single line in
emission. For the remaining 17, no spectral features were detected. Redshifts
range from z ~ 0.2 to z ~ 2.2, with a median of 1. IR Luminosities are roughly
estimated from 24 microns flux densities, and have median values of 2.2 x
10^{11} L_{\odot} and 7.5 x 10^{11} L_{\odot} at z ~ 1 and z ~ 2 respectively.
This sample has fewer AGN than previous faint samples observed with IRS, which
we attribute to the fainter luminosities reached here.Comment: Published in Ap
PAH Emission from Ultraluminous Infrared Galaxies
We explore the relationships between the Polycyclic Aromatic Hydrocarbon
(PAH) feature strengths, mid-infrared continuum luminosities, far-infrared
spectral slopes, optical spectroscopic classifications, and silicate optical
depths within a sample of 107 ULIRGs observed with the Infrared Spectrograph on
the Spitzer Space Telescope. The detected 6.2 micron PAH equivalent widths
(EQWs) in the sample span more than two orders of magnitude (0.006-0.8 micron),
and ULIRGs with HII-like optical spectra or steep far-infrared spectral slopes
(S_{25} / S_{60} < 0.2) typically have 6.2 micron PAH EQWs that are half that
of lower-luminosity starbursts. A significant fraction (~40-60%) of HII-like,
LINER-like, and cold ULIRGs have very weak PAH EQWs. Many of these ULIRGs also
have large (tau_{9.7} > 2.3) silicate optical depths. The far-infrared spectral
slope is strongly correlated with PAH EQW, but not with silicate optical depth.
In addition, the PAH EQW decreases with increasing rest-frame 24 micron
luminosity. We argue that this trend results primarily from dilution of the PAH
EQW by continuum emission from dust heated by a compact central source,
probably an AGN. High luminosity, high-redshift sources studied with Spitzer
appear to have a much larger range in PAH EQW than seen in local ULIRGs, which
is consistent with extremely luminous starburst systems being absent at low
redshift, but present at early epochs.Comment: 15 pages, 9 Figures; Accepted for publication in Ap
The Nature of the Near-IR Core Source in 3C 433
We report the analysis of near-infrared imaging, polarimetric and
spectroscopic observations of the powerful radio galaxy 3C433, obtained with
the HST and UKIRT telescopes. The high spatial resolution of HST allows us to
study the near-nuclear regions of the galaxy (<1 kpc). In line with previous
observations, we find that 3C433 has an unresolved core source that is detected
in all near-IR bands, but dominates over the host galaxy emission at 2.05 um.
Our analysis reveals: (1) the presence of a dust lane aligned close to
perpendicular (PA=70\pm5\degr) to the inner radio jet axis
(PA=-12\pm2\degr); (2) a steep slope to the near-IR SED (;
F); (3) an apparent lack of broad permitted
emission lines at near-IR wavelengths, in particular the absence of a broad
Pa emission line; and (4) high intrinsic polarization for the
unresolved core nuclear source ( per cent), with an E-vector
perpendicular (PA=83.0\pm 2.3\degr) to the inner radio jet. Using five
independent techniques we determine an extinction to the compact core source in
the range 3<A_V<67 mag. An analysis of the long wavelength SED rules out a
synchrotron origin for the high near-IR polarization of the compact core
source. Therefore, scattering and dichroic extinction are plausible polarizing
mechanisms, although in both of these cases the broad permitted lines from the
AGN are required to have a width >10^4 km/s (FWHM) to escape detection in our
near-IR spectrum. Dichroic extinction is the most likely polarization mechanism
because it is consistent with the various available extinction estimates. In
this case, a highly ordered, coherent toroidal magnetic field must be present
in the obscuring structure close to the nucleus.Comment: 12 pages, 5 figures, accepted for publication in MNRA
Strong molecular hydrogen emission and kinematics of the multiphase gas in radio galaxies with fast jet-driven outflows
Observations of ionized and neutral gas outflows in radio-galaxies (RGs)
suggest that AGN radio jet feedback has a galaxy-scale impact on the host ISM,
but it is still unclear how the molecular gas is affected. We present deep
Spitzer IRS spectroscopy of 8 RGs that show fast HI outflows. All of these
HI-outflow RGs have bright H2 mid-IR lines that cannot be accounted for by UV
or X-ray heating. This suggests that the radio jet, which drives the HI
outflow, is also responsible for the shock-excitation of the warm H2 gas. In
addition, the warm H2 gas does not share the kinematics of the ionized/neutral
gas. The mid-IR ionized gas lines are systematically broader than the H2 lines,
which are resolved by the IRS (with FWHM up to 900km/s) in 60% of the detected
H2 lines. In 5 sources, the NeII line, and to a lesser extent the NeIII and NeV
lines, exhibit blue-shifted wings (up to -900km/s with respect to the systemic
velocity) that match the kinematics of the outflowing HI or ionized gas. The H2
lines do not show broad wings, except tentative detections in 3 sources. This
shows that, contrary to the HI gas, the H2 gas is inefficiently coupled to the
AGN jet-driven outflow of ionized gas. While the dissipation of a small
fraction (<10%) of the jet kinetic power can explain the dynamical heating of
the molecular gas, our data show that the bulk of the warm molecular gas is not
expelled from these galaxies.Comment: 26 pages, 15 figures, Accepted for ublication in Ap
Structure of the X-ray Emission from the Jet of 3C 273
We present images from five observations of the quasar 3C 273 with the
Chandra X-ray Observatory. The jet has at least four distinct features which
are not resolved in previous observations. The first knot in the jet (A1) is
very bright in X-rays. Its X-ray spectrum is well fitted with a power law with
alpha = 0.60 +/- 0.05. Combining this measurement with lower frequency data
shows that a pure synchrotron model can fit the spectrum of this knot from
1.647 GHz to 5 keV (over nine decades in energy) with alpha = 0.76 +/- 0.02,
similar to the X-ray spectral slope. Thus, we place a lower limit on the total
power radiated by this knot of 1.5e43 erg/s; substantially more power may be
emitted in the hard X-ray and gamma-ray bands.
Knot A2 is also detected and is somewhat blended with knot B1. Synchrotron
emission may also explain the X-ray emission but a spectral bend is required
near the optical band. For knots A1 and B1, the X-ray flux dominates the
emitted energy. For the remaining optical knots (C through H), localized X-ray
enhancements that might correspond to the optical features are not clearly
resolved. The position angle of the jet ridge line follows the optical shape
with distinct, aperiodic excursions of +/-1 deg from a median value of
-138.0deg. Finally, we find X-ray emission from the ``inner jet'' between 5 and
10" from the core.Comment: 10 pages, 5 figures; accepted for publication in the Astrophysical
Journal Letters. For the color image, see fig1.ps or
http://space.mit.edu/~hermanm/papers/3c273/fig1.jp
- …