790 research outputs found
ISOPHOT Observations of Narrow-Line Seyfert 1 Galaxies
Broad infrared spectra (7-200 micrometer) of four NLS1 galaxies, obtained
with the imaging photo-polarimeter (ISOPHOT) on board the Infrared Space
Observatory (ISO), are presented. The infrared luminosities and temperatures,
opacities and sizes of the emitting dust components are derived. A comparison
between the observed infrared spectra and the optical emission line fluxes of a
sample of 16 NLS1 galaxies suggests that these objects suffer different degrees
of dust absorption according to the inclination of the line of sight with
respect to the dust distribution.Comment: Contributed talk presented at the Joint MPE,AIP,ESO workshop on
NLS1s, Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also
available at http://wave.xray.mpe.mpg.de/conferences/nls1-worksho
The far-infrared energy distributions of Seyfert and starburst galaxies in the Local Universe: ISO photometry of the 12 micron active galaxy sample
New far-infrared photometry with ISOPHOT, onboard the Infrared Space
Observatory, is presented for 58 galaxies with homogeneous published data for
another 32 galaxies all belonging to the 12 micron galaxy sample. In total 29
Seyfert 1's, 35 Seyfert 2's and 12 starburst galaxies, about half of the 12
micron active galaxy sample, plus 14 normal galaxies for comparison. The ISO
and the IRAS data are used to define color-color diagrams and spectral energy
distributions (SED). Thermal dust emission at two temperatures (one cold at
15-30K and one warm at 50-70K) can fit the 60-200 micron SED, with a dust
emissivity law proportional to the inverse square of the wavelength. Seyfert
1's and Seyfert 2's are indistinguishable longward of 100 micron, while, as
already seen by IRAS, the former have flatter SEDs shortward of 60 micron. A
mild anti-correlation is found between the [200 - 100] color and the "60 micron
excess". We infer that this is due to the fact that galaxies with a strong
starburst component, and thus a strong 60 micron flux, have a steeper
far-infrared turnover. In non-Seyfert galaxies, increasing the luminosity
corresponds to increasing the star formation rate, that enhances the 25 and 60
micron emission. This shifts the peak emission from around 150 micron in the
most quiescent spirals to shorter than 60 micron in the strongest starburst
galaxies.Comment: Accepted for publication in The Astrophysical Journal AASTeX preprint
with 49 pages and 20 figures Also available at
http://orion.ifsi.rm.cnr.it/publ.htm
Black hole growth and stellar assembly at high-z
Context. Observations indicate a strong link between star formation and black
hole (BH) growth, but some questions remain unanswered: whether both activities
are coeval or whether one precedes the other, what their characteristic
timescales are, and what kinds of physical processes are responsible for this
interplay.
Aims. We examine stellar and BH masses (M_star and M_BH) in z~2 active
systems at the peak of their AGN or star formation activity to investigate how
they are linked and whether AGN radiative or else radio power provides a
feedback mechanism that regulates the stellar growth in these systems.
Methods. We analyze the infrared (IR) spectral energy distributions of radio,
sub-millimeter and mid-IR selected AGNs at z~1-3 and constrain their stellar
and AGN luminosities using AGN and host-galaxy templates.
Results. We find evidence of increasing stellar light, thereby decreasing the
AGN mid-IR power going from mid-IR selected AGNs, to radio galaxies, and to
sub-millimeter AGNs. This trend can be explained by either decreasing Eddington
ratios or increasing offsets from the local M_BH-M_star relation. All systems
are characterized by high star formation rates regardless of their different
AGN powers, thus neither AGN radiative power nor AGN-driven radio activity
seems to influence the star formation rate in the selected AGNs. We discuss two
possible evolutionary scenarios that might link these three AGN classes.Comment: A&A Letters accepte
XMM-Newton discovery of very high obscuration in the candidate Supergiant Fast X-ray Transient AX J1714.1-3912
We have analysed an archival XMM-Newton EPIC observation that serendipitously
covered the sky position of a variable X-ray source AX J1714.1-3912, previously
suggested to be a Supergiant Fast X-ray Transient (SFXT). During the XMM-Newton
observation the source is variable on a timescale of hundred seconds and shows
two luminosity states, with a flaring activity followed by unflared emission,
with a variability amplitude of a factor of about 50. We have discovered an
intense iron emission line with a centroid energy of 6.4 keV in the power
law-like spectrum, modified by a large absorption (NH around 1e24 cm-2), never
observed before from this source. This X-ray spectrum is unusual for an SFXT,
but resembles the so-called "highly obscured sources", high mass X-ray binaries
(HMXBs) hosting an evolved B[e] supergiant companion (sgB[e]). This might
suggest that AX J1714.1-3912 is a new member of this rare type of HMXBs, which
includes IGR J16318-4848 and CI Camelopardalis. Increasing this small
population of sources would be remarkable, as they represent an interesting
short transition evolutionary stage in the evolution of massive binaries.
Nevertheless, AX J1714.1-3912 appears to share X-ray properties of both kinds
of HMXBs (SFXT vs sgB[e] HMXB). Therefore, further investigations of the
companion star are needed to disentangle the two hypothesis.Comment: Accepted for publication in MNRA
Near Infrared Adaptive Optics Imaging of QSO Host Galaxies
We report near-infrared (primarily H-band) adaptive optics (AO) imaging with
the Gemini-N and Subaru Telescopes, of a representative sample of 32 nearby
(z<0.3) QSOs selected from the Palomar-Green (PG) Bright Quasar Survey (BQS),
in order to investigate the properties of the host galaxies. 2D modeling and
visual inspection of the images shows that ~36% of the hosts are ellipticals,
\~39% contain a prominent disk component, and ~25% are of undetermined type.
30% show obvious signs of disturbance. The mean M_H(host) = -24.82 (2.1L_H*),
with a range -23.5 to -26.5 (~0.63 to 10 L_H*). At <L_H*, all hosts have a
dominant disk component, while at >2 L_H* most are ellipticals. "Disturbed"
hosts are found at all M_H(host), while "strongly disturbed" hosts appear to
favor the more luminous hosts. Hosts with prominent disks have less luminous
QSOs, while the most luminous QSOs are almost exclusively in ellipticals or in
mergers (which presumably shortly will be ellipticals). At z<0.13, where our
sample is complete at B-band, we find no clear correlation between M_B(QSO) and
M_H(host). However, at z>0.15, the more luminous QSOs (M_B<-24.7), and 4/5 of
the radio-loud QSOs, have the most luminous H-band hosts (>7L_H*), most of
which are ellipticals. Finally, we find a strong correlation between the
"infrared-excess", L_IR/L_BB, of QSOs with host type and degree of disturbance.
Disturbed and strongly disturbed hosts and hosts with dominant disks have
L_IR/L_BB twice that of non-disturbed and elliptical hosts, respectively. QSOs
with "disturbed" and "strongly-disturbed" hosts are also found to have
morphologies and mid/far-infrared colors that are similar to what is found for
"warm" ultraluminous infrared galaxies, providing further evidence for a
possible evolutionary connection between both classes of objects.Comment: 80 pages, accepted for publication in ApJ Supp
Keck spectroscopy of z=1-3 ULIRGs from the Spitzer SWIRE survey
(Abridged) High-redshift ultra luminous infrared galaxies contribute the bulk
of the cosmic IR background and are the best candidates for very massive
galaxies in formation at z>1.5. We present Keck/LRIS optical spectroscopy of 35
z>1.4 luminous IR galaxies in the Spitzer Wide-area Infra-Red Extragalactic
survey (SWIRE) northern fields (Lockman Hole, ELAIS-N1, ELAIS-N2). The primary
targets belong to the ``IR-peak'' class of galaxies, having the 1.6 micron
(restframe) stellar feature detected in the IRAC Spitzer channels.The spectral
energy distributions of the main targets are thoroughly analyzed, by means of
spectro-photometric synthesis and multi-component fits (stars + starburst dust
+ AGN torus). The IR-peak selection technique is confirmed to successfully
select objects above z=1.4, though some of the observed sources lie at lower
redshift than expected. Among the 16 galaxies with spectroscopic redshift, 62%
host an AGN component, two thirds being type-1 and one third type-2 objects.
The selection, limited to r'<24.5, is likely biased to optically-bright AGNs.
The SEDs of non-AGN IR-peakers resemble those of starbursts (SFR=20-500
Msun/yr) hosted in massive (M>1e11 Msun) galaxies. The presence of an AGN
component provides a plausible explanation for the spectroscopic/photometric
redshift discrepancies, as the torus produces an apparent shift of the peak to
longer wavelengths. These sources are analyzed in IRAC and optical-IR color
spaces. In addition to the IR-peak galaxies, we present redshifts and spectral
properties for 150 objects, out of a total of 301 sources on slits.Comment: Accepted for publications on Astronomy and Astrophysics (acceprance
date March 8th, 2007). 33 pages. The quality of some figures have been
degrade
Obscuration in extremely luminous quasars
The spectral energy distributions and infrared (IR) spectra of a sample of
obscured AGNs selected in the mid-IR are modeled with recent clumpy torus
models to investigate the nature of the sources, the properties of the
obscuring matter, and dependencies on luminosity. The sample contains 21
obscured AGNs at z=1.3-3 discovered in the largest Spitzer surveys (SWIRE,
NDWFS, & FLS) by means of their extremely red IR to optical colors. All sources
show the 9.7micron silicate feature in absorption and have extreme mid-IR
luminosities (L(6micron)~10^46 erg/s). The IR SEDs and spectra of 12 sources
are well reproduced with a simple torus model, while the remaining 9 sources
require foreground extinction from a cold dust component to reproduce both the
depth of the silicate feature and the near-IR emission from hot dust. The
best-fit torus models show a broad range of inclinations, with no preference
for the edge-on torus expected in obscured AGNs. Based on the unobscured QSO
mid-IR luminosity function, and on a color-selected sample of obscured and
unobscured IR sources, we estimate the surface densities of obscured and
unobscured QSOs at L(6micron)>10^12 Lsun, and z=1.3-3.0 to be about 17-22
deg^-2, and 11.7 deg^-2, respectively. Overall we find that ~35-41% of luminous
QSOs are unobscured, 37-40% are obscured by the torus, and 23-25% are obscured
by a cold absorber detached from the torus. These fractions constrain the torus
half opening angle to be ~67 deg. This value is significantly larger than found
for FIR selected samples of AGN at lower luminosity (~46 deg), supporting the
receding torus scenario. A far-IR component is observed in 8 objects. The
estimated far-IR luminosities associated with this component all exceed
3.3x10^12 Lsun, implying SFRs of 600-3000 Msun/yr. (Abridged)Comment: ApJ accepte
Obscured and powerful AGN and starburst activities at z~3.5
We report the discovery of two sources at z=3.867 and z=3.427 that exhibit
powerful starburst and AGN activities. They benefit from data from radio to X
rays from the CFHTLS-D1/SWIRE/XMDS surveys. Follow-up optical and near-infrared
spectroscopy, and millimeter IRAM/MAMBO observations are also available. We
performed an analysis of their spectral energy distributions to understand the
origin of their emission and constrain their luminosities. A comparison with
other composite systems at similar redshifts from the literature is also
presented. The AGN and starburst bolometric luminosities are ~10^13 Lsun. The
AGN emission dominates at X ray, optical, mid-infrared wavelengths, and
probably in the radio. The starburst emission dominates in the far-infrared.
The estimated star formation rates range from 500 to 3000Msun/yr. The AGN
near-infrared and X ray emissions are heavily obscured in both sources with an
estimated dust extinction Av>4, and Compton-thick gas column densities. The two
sources are the most obscured and most luminous AGNs detected at millimeter
wavelengths currently known. The sources presented in this work are heavily
obscured QSOs, but their properties are not fully explained by the standard AGN
unification model. In one source, the ultraviolet and optical spectra suggest
the presence of outflowing gas and shocks, and both sources show emission from
hot dust, most likely in the vicinity of the nucleus. Evidence of moderate
AGN-driven radio activity is found in both sources. The two sources lie on the
local M_BH-M_bulge relation. To remain on this relation, their star formation
rate has to decrease. Our results support evolutionary models that invoke radio
feedback as star formation quenching mechanism, and suggest that such a
mechanism might play a major role also in powerful AGNs.Comment: Accepted for publication in Astronomy & Astrophysics (12 pages; 6
figures); replaced version includes minor language editing and revised
reference
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