410 research outputs found
AGB and SAGB stars: modelling dust production at solar metallicity
We present dust yields for asymptotic giant branch (AGB) and
super--asymptotic giant branch (SAGB) stars of solar metallicity. Stars with
initial mass reach the carbon
star stage during the AGB phase and produce mainly solid carbon and SiC. The
size and the amount of the carbon particles formed follows a positive trend
with themass of the star; the carbon grains with the largest size (m) are produced by AGB stars with ,
as these stars are those achieving the largest enrichment of carbon in the
surface regions. The size of SiC grains, being sensitive to the surface silicon
abundance, keeps around m. The mass of carbonaceous
dust formed is in the range , whereas the
amount of SiC produced is . Massive
AGB/SAGB stars with experience HBB, that inhibits
formation of carbon stars. The most relevant dust species formed in these stars
are silicates and alumina dust, with grain sizes in the range m and m, respectively. The
mass of silicates produced spans the interval and increases with the initial
mass of the star.Comment: Accepted for publication in MNRA
The WISSH quasars Project: II. Giant star nurseries in hyper-luminous quasars
Studying the coupling between the energy output produced by the central
quasar and the host galaxy is fundamental to fully understand galaxy evolution.
Quasar feedback is indeed supposed to dramatically affect the galaxy properties
by depositing large amounts of energy and momentum into the ISM. In order to
gain further insights on this process, we study the SEDs of sources at the
brightest end of the quasar luminosity function, for which the feedback
mechanism is supposed to be at its maximum. We model the rest-frame UV-to-FIR
SEDs of 16 WISE-SDSS Selected Hyper-luminous (WISSH) quasars at 1.8 < z < 4.6
disentangling the different emission components and deriving physical
parameters of both the nuclear component and the host galaxy. We also use a
radiative transfer code to account for the contribution of the quasar-related
emission to the FIR fluxes. Most SEDs are well described by a standard
combination of accretion disk+torus and cold dust emission. However, about 30%
of them require an additional emission component in the NIR, with temperatures
peaking at 750K, which indicates the presence of a hotter dust component in
these powerful quasars. We measure extreme values of both AGN bolometric
luminosity (LBOL > 10^47 erg/s) and SFR (up to 2000 Msun/yr). A new relation
between quasar and star-formation luminosity is derived (LSF propto
LQSO^(0.73)) by combining several Herschel-detected quasar samples from z=0 to
4. Future observations will be crucial to measure the molecular gas content in
these systems, probe the impact between quasar-driven outflows and on-going
star-formation, and reveal the presence of merger signatures in their host
galaxies.Comment: 19 pages, 12 figures; Accepted for publication in Astronomy &
Astrophysics on June 13, 201
The second HerschelâATLAS Data Release â III. Optical and near-infrared counterparts in the North Galactic Plane field
This paper forms part of the second major public data release of the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS). In this work, we describe the identification of optical and near-infrared counterparts to the submillimetre detected sources in the 177âdeg2 North Galactic Plane (NGP) field. We used the likelihood ratio method to identify counterparts in the Sloan Digital Sky Survey and in the United Kingdom InfraRed Telescope Imaging Deep Sky Survey within a search radius of 10âarcsec of the H-ATLAS sources with a 4Ď detection at 250âÎźm. We obtained reliable (R ⼠0.8) optical counterparts with r < 22.4 for 42â429 H-ATLAS sources (37.8âper cent), with an estimated completeness of 71.7âper cent and a false identification rate of 4.7âper cent. We also identified counterparts in the near-infrared using deeper K-band data which covers a smaller âź25âdeg2. We found reliable near-infrared counterparts to 61.8âper cent of the 250-Îźm-selected sources within that area. We assessed the performance of the likelihood ratio method to identify optical and near-infrared counterparts taking into account the depth and area of both input catalogues. Using catalogues with the same surface density of objects in the overlapping âź25âdeg2 area, we obtained that the reliable fraction in the near-infrared (54.8âper cent) is significantly higher than in the optical (36.4âper cent). Finally, using deep radio data which covers a small region of the NGP field, we found that 80â90âper cent of our reliable identifications are correct
Star formation in the hosts of high-z QSOs: Evidence from Spitzer PAH detections
We present Spitzer rest-frame mid-infrared spectroscopy of twelve z~2
mm-bright type 1 QSOs, selected from unlensed and lensed QSO samples and
covering a range of AGN optical luminosities L_5100=10^45 to 10^47 erg/s. On
top of the AGN continuum, we detect PAH emission from luminous star formation
in nine objects individually as well as in the composite spectrum for the full
sample. PAH luminosity and rest frame far-infrared luminosity correlate and
extend the similar correlation for lower luminosity local QSOs. This provides
strong evidence for intense star formation in the hosts of these mm-bright
QSOs, sometimes exceeding 1000 Msun/yr and dominating their rest frame
far-infrared emission. The PAH-based limit on star formation rates is lower for
luminous z~2 QSOs that are not preselected for their mm emission. Partly
dependent on systematic changes of the AGN dust covering factor and the dust
spectral energy distribution of the AGN proper, the spectral energy
distributions of mm-faint high-z QSOs may be AGN dominated out to rest frame
far-infrared wavelengths. Towards the most luminous high-z QSOs, there is a
flattening of the relation between star formation and AGN luminosity that is
observed for lower redshift QSOs. No QSO in our sample has a PAH-measured star
formation rate in excess of 3000 Msun/yr.Comment: Accepted for publication in ApJ, 25 pages, 7 eps figure
Mid-infrared spectroscopy of two luminous submillimeter galaxies at z~2.8
Using the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope,
we have obtained rest frame mid-infrared spectroscopy of two bright
submillimeter galaxies. SMMJ02399-0136 at z=2.81 shows a superposition of PAH
emission features and a mid-infrared continuum, indicating significant and
roughly equal contributions to its bolometric luminosity from star formation
and from a Compton-thick AGN. We derive a new redshift of z=2.80 for
MMJ154127+6616 from the IRS spectrum and find this object is dominated by
starburst PAH emission. The rest frame mid- to far-infrared spectral energy
distributions are consistent with these submillimeter galaxies being scaled up
versions of local ultraluminous infrared galaxies. The mid-infrared spectra
support the scenario that submillimeter galaxies are sites of extreme star
formation and represent a key phase in the formation of massive galaxies.Comment: Accepted for publication in the Astrophysical Journal Letters. 12
pages, 3 eps figure
A backward evolution model for infrared surveys: the role of AGN- and Color-L_TIR distributions
Empirical "backward" galaxy evolution models for infrared bright galaxies are
constrained using multi-band infrared surveys. We developed a new Monte-Carlo
algorithm for this task, implementing luminosity dependent distribution
functions for the galaxies' infrared spectral energy distributions (SEDs) and
for the AGN contribution, allowing for evolution of these quantities. The
adopted SEDs take into account the contributions of both starbursts and AGN to
the infrared emission, for the first time in a coherent treatment rather than
invoking separate AGN and star-forming populations. In the first part of the
paper we consider the quantification of the AGN contribution for local universe
galaxies, as a function of total infrared luminosity. It is made using a large
sample of LIRGs and ULIRGs for which mid-infrared spectra are available in the
Spitzer archive. In the second part we present the model. Our best-fit model
adopts very strong luminosity evolution, , up to , and
density evolution, , up to , for the population of
infrared galaxies. At higher , the evolution rates drop as and
respectively. To reproduce mid-infrared to submillimeter number
counts and redshift distributions, it is necessary to introduce both an
evolution in the AGN contribution and an evolution in the
luminosity-temperature relation. Our models are in plausible agreement with
current photometry-based estimates of the typical AGN contribution as a
function of mid-infrared flux, and well placed to be compared to upcoming
Spitzer spectroscopic results. As an example of future applications, we use our
best-fitting model to make predictions for surveys with Herschel.Comment: Model available at: (http://www.physics.ubc.ca/~valiante/model) ApJ
accepte
Far-infrared spectroscopy of a lensed starburst: a blind redshift from Herschel
We report the redshift of HATLAS J132427.0+284452 (hereafter HATLAS J132427),
a gravitationally lensed starburst galaxy, the first determined 'blind' by the
Herschel Space Observatory. This is achieved via the detection of [C II]
consistent with z = 1.68 in a far-infrared spectrum taken with the SPIRE
Fourier Transform Spectrometer. We demonstrate that the [C II] redshift is
secure via detections of CO J = 2 - 1 and 3 - 2 using the Combined Array for
Research in Millimeter-wave Astronomy and the Institut de Radioastronomie
Millimetrique's Plateau de Bure Interferometer. The intrinsic properties appear
typical of high-redshift starbursts despite the high lensing-amplified fluxes,
proving the ability of the FTS to probe this population with the aid of
lensing. The blind detection of [C II] demonstrates the potential of the SAFARI
imaging spectrometer, proposed for the much more sensitive SPICA mission, to
determine redshifts of multiple dusty galaxies simultaneously without the
benefit of lensing.Comment: 6 pages, 5 figures, accepted for publication in MNRAS as a Lette
Far-infrared emission in luminous quasars accompanied by nuclear outflows
Combining large-area optical quasar surveys with the new far-infrared (FIR) Herschel-ATLAS Data Release 1, we search for an observational signature associated with the minority of quasars possessing bright FIR luminosities. We find that FIR-bright quasars show broad C IV emission-line blueshifts in excess of that expected from the optical luminosity alone, indicating particularly powerful nuclear outflows. The quasars show no signs of having redder optical colours than the general ensemble of optically selected quasars, ruling out differences in line-of-sight dust within the host galaxies. We postulate that these objects may be caught in a special evolutionary phase, with unobscured, high black hole accretion rates and correspondingly strong nuclear outflows. The high FIR emission found in these objects is then either a result of star formation related to the outflow, or is due to dust within the host galaxy illuminated by the quasar. We are thus directly witnessing coincident small-scale nuclear processes and galaxy-wide activity, commonly invoked in galaxy simulations that rely on feedback from quasars to influence galaxy evolution
Addressing the Language Binding Problem With Dynamic Functional Connectivity During Meaningful Spoken Language Comprehension
During speech, how does the brain integrate information processed on different timescales and in separate brain areas so we can understand what is said? This is the language binding problem. Dynamic functional connectivity (brief periods of synchronization in the phase of EEG oscillations) may provide some answers. Here we investigate time and frequency characteristics of oscillatory power and phase synchrony (dynamic functional connectivity) during speech comprehension. Twenty adults listened to meaningful English sentences and non-sensical âJabberwockyâ sentences in which pseudo-words replaced all content words, while EEG was recorded. Results showed greater oscillatory power and global connectivity strength (mean phase lag index) in the gamma frequency range (30â80 Hz) for English compared to Jabberwocky. Increased power and connectivity relative to baseline was also seen in the theta frequency range (4â7 Hz), but was similar for English and Jabberwocky. High-frequency gamma oscillations may reflect a mechanism by which the brain transfers and integrates linguistic information so we can extract meaning and understand what is said. Slower frequency theta oscillations may support domain-general processing of the rhythmic features of speech. Our findings suggest that constructing a meaningful representation of speech involves dynamic interactions among distributed brain regions that communicate through frequency-specific functional networks
H-ATLAS/GAMA and HeViCS - dusty early-type galaxies in different environments
NKA acknowledges the support of the Science and Technology Facilities Council. LD, RJI and SJM acknowledge support from the European Research Council Advanced Grant COSMICISM. IDL gratefully acknowledges the support of the Flemish Fund for Scientific Research (FWO-Vlaanderen). KR acknowledges support from the European Research Council Starting Grant SEDmorph (P.I. V. Wild). Date of acceptance: 22/05/2015The Herschel Space Observatory has had a tremendous impact on the study of extragalactic dust. Specifically, early-type galaxies (ETG) have been the focus of several studies. In this paper, we combine results from two Herschel studies -a Virgo cluster study Herschel Virgo Cluster Survey (HeViCS) and a broader, low-redshift Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS)/Galaxy and Mass Assembly (GAMA) study -and contrast the dust and associated properties for similar mass galaxies. This comparison is motivated by differences in results exhibited between multiple Herschel studies of ETG. A comparison between consistent modified blackbody derived dust mass is carried out, revealing strong differences between the two samples in both dust mass and dust-to-stellar mass ratio. In particular, the HeViCS sample lacks massive ETG with as high a specific dust content as found in H-ATLAS. This is most likely connected with the difference in environment for the two samples. We calculate nearest neighbour environment densities in a consistent way, showing that H-ATLAS ETG occupy sparser regions of the local Universe, whereas HeViCS ETG occupy dense regions. This is also true for ETG that are not Herschel-detected but are in the Virgo and GAMA parent samples. Spectral energy distributions are fit to the panchromatic data. From these, we find that in H-ATLAS the specific star formation rate anticorrelates with stellar mass and reaches values as high as in our Galaxy. On the other hand HeViCS ETG appear to have little star formation. Based on the trends found here, H-ATLAS ETG are thought to have more extended star formation histories and a younger stellar population than HeViCS ETG.Publisher PDFPeer reviewe
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