13 research outputs found
HST NICMOS imaging of z~2, 24 micron-selected Ultraluminous Infrared Galaxies
We present Hubble Space Telescope NICMOS H-band imaging of 33 Ultraluminous
Infrared Galaxies (ULIRGs) at z~2 that were selected from the 24 micron catalog
of the Spitzer Extragalactic First Look Survey. The images reveal that at least
17 of the 33 objects are associated with interactions. Up to one fifth of the
sources in our sample could be minor mergers whereas only 2 systems are merging
binaries with luminosity ratio <=3:1, which is characteristic of local ULIRGs.
The rest-frame optical luminosities of the sources are of the order 10^10-10^11
L_sun and their effective radii range from 1.4 to 4.9 kpc. The most compact
sources are either those with a strong active nucleus continuum or those with a
heavy obscuration in the mid-infrared regime, as determined from Spitzer
Infra-Red Spectrograph data. The luminosity of the 7.7 micron feature produced
by polycyclic aromatic hydrocarbon molecules varies significantly among compact
systems whereas it is typically large for extended systems. A bulge-to-disk
decomposition performed for the 6 brightest (m_H<20) sources in our sample
indicates that they are best fit by disk-like profiles with small or negligible
bulges, unlike the bulge-dominated remnants of local ULIRGs. Our results
provide evidence that the interactions associated with ultraluminous infrared
activity at z~2 can differ from those at z~0.Comment: ApJ, in press. Document revised to match the journal versio
HST NICMOS imaging of z ~ 2, 24 µm-selected ultraluminous infrared galaxies
We present Hubble Space Telescope NICMOSH-band imaging of 33 ultraluminous infrared galaxies (ULIRGs) at z ~ 2 that were selected from the 24 µm catalog of the Spitzer Extragalactic First Look Survey. The images reveal that at least 17 of the 33 objects are associated with interactions. Up to one-fifth of the sources in our sample could be minor mergers, whereas only two systems are merging binaries with luminosity ratio ≤ 3 : 1, which is characteristic of local ULIRGs. The rest-frame optical luminosities of the sources are of the order 10^(10)-10^(11) L⊙ and their effective radii range from 1.4 to 4.9 kpc. The most compact sources are either those with a strong active nucleus continuum or those with a heavy obscuration in the mid-infrared regime, as determined from Spitzer Infrared Spectrograph data. The luminosity of the 7.7 µm feature produced by polycyclic aromatic hydrocarbon molecules varies significantly among compact systems, whereas it is typically large for extended systems. A bulge-to-disk decomposition performed for the six brightest (m_H < 20) sources in our sample indicates that they are best fit by disklike profiles with small or negligible bulges, unlike the bulge-dominated remnants of local ULIRGs. Our results provide evidence that the interactions associated with ultraluminous infrared activity at z ~ 2 can differ from those at z ~ 0
Far-infrared line spectra of Seyfert galaxies from the Herschel-PACS Spectrometer
We present spectroscopic observations of FIR fine-structure lines of 26
Seyfert galaxies obtained with the Herschel-PACS spectrometer. These
observations are complemented by spectroscopy with Spitzer-IRS and
Herschel-SPIRE. The ratios of the OIII, NII, SIII and NeV lines have been used
to determine electron densities in the ionised gas regions. The CI lines,
observed with SPIRE, have been used to measure the densities in the neutral
gas, while the OI lines provide a measure of the gas temperature, at densities
below 10000 cm-3. Using the OI145/63um and SIII33/18um line ratios we find an
anti-correlation of the temperature with the gas density. Using various
fine-structure line ratios, we find that density stratification is common in
these active galaxies. On average, the electron densities increase with the
ionisation potential of the ions producing the NII, SIII and NeV emission. The
infrared emission lines arise partly in the Narrow Line Region (NLR)
photoionised by the AGN central engine, partly in HII regions photo ionised by
hot stars and partly in neutral gas in photo-dissociated regions (PDRs). We
attempt to separate the contributions to the line emission produced in these
different regions by comparing our emission line ratios to empirical and
theoretical values. In particular, we tried to separate the contribution of AGN
and star formation by using a combination of Spitzer and Herschel lines, and we
found that, besides the well known mid-IR line ratios, the mixed mid-IR/far-IR
line ratio of OIII88um/OIV26um can reliably discriminate the two emission
regimes, while the far-IR line ratio of CII157um/OI63um is only able to mildly
separate the two regimes. By comparing the observed CII157um/NII205um ratio
with photoionisation models, we also found that most of the CII emission in the
galaxies we examined is due to PDRs.Comment: Accepted for publication in ApJ Main Journal on the 5th November
2014, 25 pages, 16 figure
First Stellar Velocity Dispersion Measurement of a Luminous Quasar Host with Gemini North Laser Guide Star Adaptive Optics
We present the first use of the Gemini North laser guide star adaptive optics
(LGS AO) system and an integral field unit (IFU) to measure the stellar
velocity dispersion of the host of a luminous quasar. The quasar PG1426+015
(z=0.086) was observed with the Near-Infrared Integral Field Spectrometer
(NIFS) on the 8m Gemini North telescope in the H-band as part of the Science
Verification phase of the new ALTAIR LGS AO system. The NIFS IFU and LGS AO are
well suited for host studies of luminous quasars because one can achieve a
large ratio of host to quasar light. We have measured the stellar velocity
dispersion of PG1426+015 from 0.1'' to 1'' (0.16 kpc to 1.6 kpc) to be 217+/-15
km/s based on high signal-to-noise ratio measurements of Si I, Mg I, and
several CO bandheads. This new measurement is a factor of four more precise
than a previous measurement obtained with long-slit spectroscopy and good,
natural seeing, yet was obtained with a shorter net integration time. We find
that PG1426+015 has a velocity dispersion that places it significantly above
the M-sigma relation of quiescent galaxies and lower-luminosity active galactic
nuclei with black hole masses estimated from reverberation mapping. We discuss
several possible explanations for this discrepancy that could be addressed with
similar observations of a larger sample of luminous quasars.Comment: 5 pages, 2 figures; accepted by ApJ Letter
On the Relation Between Black Hole Mass and Velocity Dispersion in Type 1 and Type 2 AGN
We present results from infrared spectroscopic projects that aim to test the relation
between the mass of a black hole M_(BH) and the velocity dispersion of the stars in its host-galaxy
bulge. We demonstrate that near-infrared, high-resolution spectroscopy assisted by adaptive
optics is key in populating the high-luminosity end of the relation. We show that the velocity
dispersions of mid-infrared, high-ionization lines originating from gas in the narrow-line region
of the active galactic nucleus follow the same relation. This result provides a way of inferring
MBH estimates for the cosmologically significant population of obscured, type 2 AGN that can
be applicable to data from spectrographs on next-generation infrared telescopes
Far-IR/Submillimeter Spectroscopic Cosmological Surveys: Predictions of Infrared Line Luminosity Functions for z<4 Galaxies
Star formation and accretion onto supermassive black holes in the nuclei of
galaxies are the two most energetic processes in the Universe, producing the
bulk of the observed emission throughout its history. We simulated the
luminosity functions of star-forming and active galaxies for spectral lines
that are thought to be good spectroscopic tracers of either phenomenon, as a
function of redshift. We focused on the infrared (IR) and sub-millimeter
domains, where the effects of dust obscuration are minimal. Using three
different and independent theoretical models for galaxy formation and
evolution, constrained by multi-wavelength luminosity functions, we computed
the number of star-forming and active galaxies per IR luminosity and redshift
bin. We converted the continuum luminosity counts into spectral line counts
using relationships that we calibrated on mid- and far-IR spectroscopic surveys
of galaxies in the local universe. Our results demonstrate that future
facilities optimized for survey-mode observations, i.e., the Space Infrared
Telescope for Cosmology and Astrophysics (SPICA) and the Cerro Chajnantor
Atacama Telescope (CCAT), will be able to observe thousands of z>1 galaxies in
key fine-structure lines, e.g., [SiII], [OI], [OIII], [CII], in a
half-square-degree survey, with one hour integration time per field of view.
Fainter lines such as [OIV], [NeV] and H_2 (0-0)S1 will be observed in several
tens of bright galaxies at 1<z<2, while diagnostic diagrams of active-nucleus
vs star-formation activity will be feasible even for normal z~1 galaxies. We
discuss the new parameter space that these future telescopes will cover and
that strongly motivate their construction.Comment: Accepted for publication in The Astrophysical Journal on 20/10/2011,
17 pages, 13 figure
The ~0.9 mJy sample: A mid-infrared spectroscopic catalog of 150 infrared-luminous, 24 micron selected galaxies at 0.3<z<3.5
We present a catalog of mid-infrared (MIR) spectra of 150 infrared (IR)
luminous galaxies in the Spitzer extragalactic first look survey obtained with
IRS on board Spitzer. The sample is selected to be brighter than ~0.9 mJy at 24
micron and it has a z distribution in the range [0.3,3.5] with a peak at z=1.
It primarily comprises ultraluminous IR galaxies at z>1 and luminous IR
galaxies at z<1, as estimated from their monochromatic 14 micron luminosities.
The number of sources with spectra that are dominated by an active galactic
nucleus (AGN) continuum is 49, while 39 sources have strong, star-formation
related features. For this classification, we used the equivalent width (EW) of
the 11.3 micron polycyclic aromatic hydrocarbon (PAH) feature. Several
intermediate/high z starbursts have higher PAH EW than local ULIRGs. An
increase in the AGN activity is observed with increasing z and luminosity,
based on the decreasing EW of PAHs and the increasing [NeIII]/[NeII] ratio.
Spectral stacking leads to the detection of the 3.3 micron PAH, the H2 0-0 S(1)
and S(3) lines, and the [NeV] line. We observe differences in the flux ratios
of PAHs in the stacked spectra of IR-luminous galaxies with z or luminosity,
which are not due to extinction effects. When placing the observed galaxies on
IR color-color diagrams, we find that the wedge defining AGN comprises most
sources with continuum-dominated spectra, but also contains many starbursts.
The comparison of the 11.3 micron PAH EW and the H-band effective radius,
measured from HST data, indicates that sources with EW>2 micron, are typically
more extended than ~3 kpc. However, there is no strong correlation between the
MIR spectral type and the near-IR extent of the sources. [Abridged].Comment: accepted for publication in the Astrophysical Journa
"Far-IR/Submillimeter Spectroscopic Cosmological Surveys: Predictions of Infrared Line Luminosity Functions for z < 4 Galaxies"
Not Available <P /
Insights into the collapse and expansion of molecular clouds in outflows from observable pressure gradients
International audienceThe jets launched by actively accreting black holes can generate massive outflows in galaxies, which could suppress or enhance star formation by rarefying or compressing clouds of molecular gas. To study the stability of such jet-impacted clouds, we performed astrochemical, thermally balanced, radiative transfer modelling of the CO and HCO+ emission of the galaxy IC 5063. We found that jet-related mechanical heating and cosmic rays contribute to the molecular gas heating rate and could even individually sustain it. Clouds excited by these mechanisms have temperatures and densities reflecting an order-of-magnitude increase in their internal pressure. Variations of their external pressure, deduced from [S II] and [N II] ionized gas emission, further reveal that some clouds are undergoing rarefaction and others compression. Our work shows a new viewpoint on plausible links between galactic outflows and star formation conditions: that of observable pressure gradients. It also emphasizes the role of cosmic rays in contributing to these gradients
CO kinematics unveil outflows plausibly driven by a young jet in the gigahertz peaked radio core of NGC 6328
We report the detection of outflowing molecular gas in the center of the
nearby (z = 0.014) massive radio galaxy NGC 6328. The radio core of the
galaxy, PKS B1718-649, is identified as a gigahertz peaked spectrum
source with a compact (2 pc) double radio lobe morphology. We used ALMA
CO(2-1) and CO(3-2) observations at 100 pc resolution to study the gas
kinematics up to similar to 5kpc from the galaxy center. While the bulk
of the molecular gas is settled in a highly warped disk, in the inner
300 pc of the disk and along with the orientation of the radio jet, we
identified high-excitation and high-velocity gas that cannot be
attributed to any regular kinematic component based on our detailed 3D
modeling of the ALMA data. The high-velocity dispersion in the gas also
suggests that it is not part of an inflowing, shredding structure. These
results suggest the presence of a molecular outflow of 3-8 solar masses
per year. The outflow possibly originated from the interaction of the
jet with the dense interstellar medium, even though the radio emission
is detected closer to the center than the outflow. In this sense, this
source resembles NGC 1377, 4C31.04, and ESO 420-G13, in which the
outflows are linked to faint or past jet activity