168 research outputs found
Infrared images of reflection nebulae and Orion's bar: Fluorescent molecular hydrogen and the 3.3 micron feature
Images were obtained of the (fluorescent) molecular hydrogen 1-0 S(1) line, and of the 3.3 micron emission feature, in Orion's Bar and three reflection nebulae. The emission from these species appears to come from the same spatial locations in all sources observed. This suggests that the 3.3 micron feature is excited by the same energetic UV-photons which cause the molecular hydrogen to fluoresce
Quasar Candidates in the Hubble Deep Field
We focus on the search for unresolved faint quasars and AGN in the crude
combine images using a multicolor imaging analysis that has proven very
successful in recent years. Quasar selection was carried out both in multicolor
space and in "profile space," defined as the multi-parameter space formed by
the radial profiles of the objects in the different images. By combining the
dither frames available for each filter, we were able to obtain well-sampled
radial profiles of the objects and measure their deviation from that of a
stellar source. We also generated synthetic quasar spectra in the range 1.0 < z
< 5.5 and computed expected quasar colors. We determined that the data are 90%
complete for point sources at 26.2, 28.0, 27.8, 26.8 in the F300W, F450W, F606W
and F814W filters, respectively. We find 41 compact objects in the HDF: 8
pointlike objects with colors consistent with quasars or stars, 18 stars, and
15 slightly resolved objects, 12 of which have colors consistent with quasars
or stars. We estimate the upper limit of unresolved and slightly resolved
quasars/AGNs with V < 27.0 and z < 3.5 to be 20 objects (16,200 per deg^2). We
find good agreement among authors on the number of stars and the lack of quasar
candidates with z > 3.5. We find more quasar candidates than previous work
because of our more extensive modeling and use of all of the available color
information. (abridged)Comment: We have clarified our discussion and conclusions, added some
references and removed the appendix, which is now available from the first
author. 37 pages including 10 embedded postscript figures and 6 tables. To
appear in the Feb. 99 issue of A
Aromatic Features in AGN: Star-Forming Infrared Luminosity Function of AGN Host Galaxies
We describe observations of aromatic features at 7.7 and 11.3 um in AGN of
three types including PG, 2MASS and 3CR objects. The feature has been
demonstrated to originate predominantly from star formation. Based on the
aromatic-derived star forming luminosity, we find that the far-IR emission of
AGN can be dominated by either star formation or nuclear emission; the average
contribution from star formation is around 25% at 70 and 160 um. The
star-forming infrared luminosity functions of the three types of AGN are
flatter than that of field galaxies, implying nuclear activity and star
formation tend to be enhanced together. The star-forming luminosity function is
also a function of the strength of nuclear activity from normal galaxies to the
bright quasars, with luminosity functions becoming flatter for more intense
nuclear activity. Different types of AGN show different distributions in the
level of star formation activity, with 2MASS> PG> 3CR star formation rates.Comment: Accepted for publication in ApJ, 24 pages, 13 figure
A High Spatial Resolution Mid-Infrared Spectroscopic Study of the Nuclei and Star-Forming Regions in Luminous Infrared Galaxies
We present a high spatial (diffraction-limited) resolution (~0.3")
mid-infrared (MIR) spectroscopic study of the nuclei and star-forming regions
of 4 local luminous infrared galaxies (LIRGs) using T-ReCS on the Gemini South
telescope. We investigate the spatial variations of the features seen in the
N-band spectra of LIRGs on scales of ~100 pc, which allow us to separate the
AGN emission from that of the star formation (SF). We compare our Gemini T-ReCS
nuclear and integrated spectra of LIRGs with those obtained with Spitzer IRS.
The 9.7um silicate absorption feature is weaker in the nuclei of the LIRGs than
in the surrounding regions. This is probably due to the either clumpy or
compact environment of the central AGN or young, nuclear starburst. We find
that the [NeII] luminosity surface density is tightly and directly correlated
with that of Pa-alpha for the LIRG star-forming regions (slope of 1.00+-0.02).
Although the 11.3um PAH feature shows also a trend with Pa-alpha, this is not
common for all the regions. We also find that the [NeII]\Pa-alpha ratio does
not depend on the Pa-alpha equivalent width (EW), i.e., on the age of the
ionizing stellar populations, suggesting that, on the scales probed here, the
[NeII] emission line is a good tracer of the SF activity in LIRGs. On the other
hand, the 11.3um PAH\Pa-alpha ratio increases for smaller values of the
Pa-alpha EW (increasing ages), indicating that the 11.3um PAH feature can also
be excited by older stars than those responsible for the Pa-alpha emission.
Additional high spatial resolution observations are essential to investigate,
in a statistical way, the star formation in local LIRGs at the smallest scales
and to probe ultimately whether they share the same physical properties as
high-z LIRGs, ULIRGs and submillimiter galaxies.Comment: 23 pages (apjstyle), 19 figures, accepted for publicacion in Ap
The role of grain size in AGN torus dust models
Fits the infrared spectra from the nuclear regions of AGN can place
constraints on the dust properties, distribution, and geometry by comparison
with models. However, none of the currently available models fully describe the
observations of AGN currently available. Among the aspects least explored, here
we focus on the role of dust grain size. We offer the community a new spectral
energy distribution (SED) library, hereinafter [GoMar23] model, which is based
on the two-phase torus model developed before with the inclusion of the grain
size as a model parameter, parameterized by the maximum grain size Psize or
equivalently the mass-weighted average grain size . We created 691,200
SEDs using the SKIRT code, where the maximum grain size can vary within the
range Psize = 0.01 - 10.0um ( = 0.007 - 3.41um). We fit this new and
several existing libraries to a sample of 68 nearby and luminous AGNs with
Spitzer/IRS spectra dominated by AGN-heated dust. We find that the [GoMar23]
model can adequately reproduce up to 85-88% of the spectra. The dust grain size
parameter significantly improves the final fit in up to 90% of these spectra.
Statistical tests indicate that the grain size is the third most important
parameter in the fitting procedure (after the size and half opening angle of
the torus). The requirement of a foreground extinction by our model is lower
compared to purely clumpy models. We find that 41% of our sample requires that
the maximum dust grain size is as large as Psize =10um (= 3.41um).
Nonetheless, we also remark that disk+wind and clumpy torus models are still
required to reproduce the spectra of a non-negligible fraction of objects,
suggesting the need for several dust geometries to explain the infrared
continuum of AGN. This work provides tentative evidence for dust grain growth
in the proximity of the AGN.Comment: 26 pages, 14 figures, 4 tables, accepted for publication in A&
Torus and Active Galactic Nucleus Properties of Nearby Seyfert Galaxies: Results from Fitting Infrared Spectral Energy Distributions and Spectroscopy
We used the CLUMPY torus models and a Bayesian approach to fit the infrared spectral energy distributions and ground-based high angular resolution mid-infrared spectroscopy of 13 nearby Seyfert galaxies. This allowed us to put tight constraints on torus model parameters such as the viewing angle i, the radial thickness of the torus Y, the angular size of the cloud distribution σtorus, and the average number of clouds along radial equatorial rays N0. We found that the viewing angle i is not the only parameter controlling the classification of a galaxy into type 1 or type 2. In principle, type 2s could be viewed at any viewing angle i as long as there is one cloud along the line of sight. A more relevant quantity for clumpy media is the probability for an active galactic nucleus (AGN) photon to escape unabsorbed. In our sample, type 1s have relatively high escape probabilities, Pesc ~ 12%-44%, while type 2s, as expected, tend to have very low escape probabilities. Our fits also confirmed that the tori of Seyfert galaxies are compact with torus model radii in the range 1-6 pc. The scaling of the models to the data also provided the AGN bolometric luminosities Lbol(AGN), which were found to be in good agreement with estimates from the literature. When we combined our sample of Seyfert galaxies with a sample of PG quasars from the literature to span a range of Lbol(AGN) ~ 1043-1047 erg s-1, we found plausible evidence of the receding torus. That is, there is a tendency for the torus geometrical covering factor to be lower (f2 ~ 0.1-0.3) at high AGN luminosities than at low AGN luminosities (f2 ~ 0.9-1 at ~{}1043-1044 erg s-1). This is because at low AGN luminosities the tori appear to have wider angular sizes (larger σtorus) and more clouds along radial equatorial rays. We cannot, however, rule out the possibility that this is due to contamination by extended dust structures not associated with the dusty torus at low AGN luminosities, since most of these in our sample are hosted in highly inclined galaxies
Torus and AGN properties of nearby Seyfert galaxies: Results from fitting IR spectral energy distributions and spectroscopy
We used the CLUMPY torus models and a Bayesian approach to fit the infrared
spectral energy distributions (SEDs) and ground-based high-angular resolution
mid-infrared spectroscopy of 13 nearby Seyfert galaxies. This allowed us to put
tight constraints on torus model parameters such as the viewing angle, the
radial thickness of the torus Y, the angular size of the cloud distribution
sigma_torus, and the average number of clouds along radial equatorial rays N_0.
The viewing angle is not the only parameter controlling the classification of a
galaxy into a type 1 or a type 2. In principle type 2s could be viewed at any
viewing angle as long as there is one cloud along the line of sight. A more
relevant quantity for clumpy media is the probability for an AGN photon to
escape unabsorbed. In our sample, type 1s have relatively high escape
probabilities, while in type 2s, as expected, tend to be low. Our fits also
confirmed that the tori of Seyfert galaxies are compact with torus model radii
in the range 1-6pc. The scaling of the models to the data also provided the AGN
bolometric luminosities, which were found to be in good agreement with
estimates from the literature. When we combined our sample of Seyfert galaxies
with a sample of PG quasars from the literature to span a range of
L_bol(AGN)~10^{43}-10^{47}erg/s, we found plausible evidence of the receding
torus. That is, there is a tendency for the torus geometrical covering factor
to be lower at high AGN luminosities than at low AGN luminosities. This is
because at low AGN luminosities the tori appear to have wider angular sizes and
more clouds along radial equatorial rays. We cannot, however rule out the
possibility that this is due to contamination by extended dust structures not
associated with the dusty torus at low AGN luminosities, since most of these in
our sample are hosted in highly inclined galaxies. (Abridged)Comment: Accepted for publication in Ap
A Nearby Old Halo White Dwarf Candidate from the Sloan Digital Sky Survey
We report the discovery of a nearby, old, halo white dwarf candidate from the
Sloan Digital Sky Survey. SDSS J110217.48+411315.4 has a proper motion of 1.75
arcsec/year and redder optical colors than all other known featureless (type
DC) white dwarfs. We present SDSS imaging and spectroscopy of this object,
along with near-infrared photometry obtained at the United Kingdom Infra-Red
Telescope. Fitting its photometry with up-to-date model atmospheres, we find
that its overall spectral energy distribution is fit reasonably well with a
pure hydrogen composition and T_eff~3800 K (assuming log g=8). That temperature
and gravity would place this white dwarf at 35 pc from the Sun with a
tangential velocity of 290 km/s and space velocities consistent with halo
membership; furthermore, its combined main sequence and white dwarf cooling age
would be ~11 Gyr. However, if this object is a massive white dwarf, it could be
a younger object with a thick disk origin. Whatever its origin, the optical
colors of this object are redder than predicted by any current pure hydrogen,
pure helium or mixed hydrogen-helium atmospheric model, indicating that there
remain problems in our understanding of the complicated physics of the dense
atmospheres of cool white dwarfs.Comment: AJ in press. 10 pages emulateapj format; 5 figure
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PMIP4-CMIP6: the contribution of the Paleoclimate Modelling Intercomparison Project to CMIP6
The goal of the Palaeoclimate Modelling Intercomparison Project (PMIP) is to understand the response of the climate system to changes in different climate forcings and to feedbacks. Through comparison with observations of the environmental impacts of these climate changes, or with climate reconstructions based on physical,
chemical or biological records, PMIP also addresses the issue of how well state-of-the-art models simulate climate changes. Palaeoclimate states are radically different from those of the recent past documented by the instrumental record and thus provide an out-of-sample test of the models used for future climate projections and
a way to assess whether they have the correct sensitivity to forcings and feedbacks. Five distinctly different periods have been selected as focus for the core palaeoclimate experiments that are designed to contribute to the objectives of the sixth phase of the Coupled Model Intercomparison Project (CMIP6). This manuscript describes
the motivation for the choice of these periods and the design of the numerical experiments, with a focus upon their novel features compared to the experiments performed in previous phases of PMIP and CMIP as well as the benefits of common analyses of the models across multiple climate states. It also describes the information
needed to document each experiment and the model outputs required for analysis and benchmarking
Dissociable Components of Cognitive Control: An Event-Related Potential (ERP) Study of Response Inhibition and Interference Suppression
Background: Cognitive control refers to the ability to selectively attend and respond to task-relevant events while resisting interference from distracting stimuli or prepotent automatic responses. The current study aimed to determine whether interference suppression and response inhibition are separable component processes of cognitive control. Methodology/Principal Findings: Fourteen young adults completed a hybrid Go/Nogo flanker task and continuous EEG data were recorded concurrently. The incongruous flanker condition (that required interference suppression) elicited a more centrally distributed topography with a later N2 peak than the Nogo condition (that required response inhibition). Conclusions/Significance: These results provide evidence for the dissociability of interference suppression and response inhibition, indicating that taxonomy of inhibition is warranted with the integration of research evidence from neuroscience
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