2,160 research outputs found
Modelling the Spoon IRS diagnostic diagram
We explore whether our models for starbursts, quiescent star-forming galaxies
and for AGN dust tori are able to model the full range of IRS spectra measured
with Spitzer. The diagnostic plot of 9.7 mu silicate optical depth versus 6.2
mu PAH equivalent width, introduced by Spoon and coworkers in 2007, gives a
good indication of the age and optical depth of a starburst, and of the
contribution of an AGN dust torus. However there is aliasing between age and
optical depth at later times in the evolution of a starburst, and between age
and the presence of an AGN dust torus.
Modeling the full IRS spectra and using broad-band 25-850 mu fluxes can help
to resolve these aliases. The observed spectral energy distributions require
starbursts of a range of ages with initial dust optical depth ranging from
50-200, optically thin dust emission ('cirrus') illuminated by a range of
surface brightnesses of the interstellar radiation field, and AGN dust tori
with a range of viewing angles.Comment: Accepted for publication by MNRAS. 8 pages, 10 figure
Panchromatic radiation from galaxies as a probe of galaxy formation and evolution
I review work on modelling the infrared and submillimetre SEDs of galaxies.
The underlying physical assumptions are discussed and spherically symmetric,
axisymmetric, and 3-dimensional radiative transfer codes are reviewed. Models
for galaxies with Spitzer IRS data and for galaxies in the Herschel-Hermes
survey are discussed. Searches for high redshift infrared and submillimetre
galaxies, the star formation history, the evolution of dust extinction, and
constraints from source-counts, are briefly discussed.Comment: to be published in IAU Symposium 284 'The Spectral Energy
Distribution of Galaxies', Preston 2012, eds. R.J.Tiffs and C.C.Popesc
Cosmological Parameters: do we already know the final answer ?
Some of the arguments which support the strong concensus for an =
0.3, = 0.7 model are reexamined. Corrections for Malmquist bias,
local flow and metallicity suggest a revised value for of 63 6
km/s/Mpc, improving the age problems for an = 1 universe. The latest
CMB results may require a high baryon density and hence new physics, for
example a strong lepton asymmetry. Difficulties for the = 1 model
with cluster evolution, the baryon content of clusters, and the evidence from
Type Ia supernovae favouring low , models, are
discussed critically.Comment: 10 pages, 3 figures. To appear in 'IDM2000: 3rd International
Workshop on Identification of Dark Matter', ed N.Spooner (World Scientific
Detailed modelling of a large sample of Herschel sources in the Lockman Hole: identification of cold dust and of lensing candidates through their anomalous SEDs
We have studied in detail a sample of 967 SPIRE sources with 5σ detections at 350 and 500 μm and associations with Spitzer-SWIRE 24 μm galaxies in the HerMES-Lockman survey area, fitting theirmid- and far-infrared, and submillimetre, spectral energy distributions (SEDs) in an automatic search with a set of six infrared templates. For almost 300 galaxies,we havemodelled their SEDs individually to ensure the physicality of the fits. We confirm the need for the new cool and cold cirrus templates, and also of the young starburst template, introduced in earlier work. We also identify 109 lensing candidates via their anomalous SEDs and provide a set of colour–redshift constraints which allow lensing candidates to be identified from combined Herschel and Spitzer data. The picture that emerges of the submillimetre galaxy population is complex, comprising ultraluminous and hyperluminous starbursts, lower luminosity galaxies dominated by interstellar dust emission, lensed galaxies and galaxies with surprisingly cold (10–13 K) dust. 11 per cent of 500 μm selected sources are lensing candidates. 70 per cent of the unlensed sources are ultraluminous infrared galaxies and 26 per cent are hyperluminous. 34 per cent are dominated by optically thin interstellar dust (‘cirrus’) emission, but most of these are due to cooler dust than is characteristic of our Galaxy. At the highest infrared luminosities we see SEDs dominated by M82, Arp 220 and young starburst types, in roughly equal proportions
The Imperial IRAS-FSC Redshift Catalogue (IIFSCz)
We present a new catalogue, the Imperial IRAS-FSC Redshift Catalogue
(IIFSCz), of 60,303 galaxies selected at 60 micron from the IRAS Faint Source
Catalogue (FSC). The IIFSCz consists of accurate position, optical,
near-infrared and/or radio identifications, spectroscopic redshift (if
available) or photometric redshift (if possible), predicted far-infrared (FIR)
and submillimetre (submm) fluxes ranging from 12 to 1380 micron based upon the
best-fit infrared template. About 55% of the galaxies in the IIFSCz have
spectroscopic redshifts and a further 20% have photometric redshifts obtained
through either the training set or the template-fitting method. For S(60)>0.36
Jy, the 90% completeness limit of the FSC, 90% of the sources have either
spectroscopic or photometric redshifts. Scientific applications of the IIFSCz
include validation of current and forthcoming infrared and submm/mm surveys
such as AKARI, Planck and Herschel, follow-up studies of rare source
populations, large-scale structure and galaxy bias, local multiwavelength
luminosity functions and source counts. The catalogue is publicly available
from http://astro.imperial.ac.uk/~mrr/fss/Comment: 12 pages, 12 figures, 1 table. Revised on 23/04/09. The catalogue has
been revised to correct the fluxes of extended sources. Accepted for
publication in MNRA
Models for infrared emission from IRAS galaxies
Models for the infrared emission from Infrared Astronomy Satellite (IRAS) galaxies by Rowan-Robinson and Crawford, by deJong and Brink, and by Helou, are reviewed. Rowan-Robinson and Crawford model the 12 to 100 micron radiation from IRAS galaxies in terms of 3 components: a normal disk component, due to interstellar cirrus; a starburst component, modeled as hot stars in an optically thick dust cloud; and a Seyfert component, modeled as a power-law continuum immersed in an n(r) variation r sup -1 dust cloud associated with the narrow-line region of the Seyfert nucleus. The correlations between the luminosities in the different components, the blue luminosity, and the X-ray luminosity of the galaxies are consistent with the model. Spectra from 0.1 to 1000 microns are predicted and compared with available observations. The de Jong and Brink, and Helou, model IRAS non-Seyfert galaxies in terms of a cool (cirrus) component and a warm (starburst) component. The de Jong and Brink estimate the face-on internal extinction in the galaxies and find that it is higher in galaxies with more luminous starbursts. In Helou's model the spectrum of the warm component varies strongly with the luminosity in that component. The three models are briefly compared
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