240 research outputs found
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
Cold galaxies
We use 350 mu angular diameter estimates from Planck to test the idea that
some galaxies contain exceptionally cold (10-13 K) dust, since colder dust
implies a lower surface brightness radiation field illuminating the dust, and
hence a greater physical extent for a given luminosity. The galaxies identified
from their spectral energy distributions as containing cold dust do indeed show
the expected larger 350 mu diameters. For a few cold dust galaxies where
Herschel data are available we are able to use submillimetre maps or surface
brightness profiles to locate the cold dust, which as expected generally lies
outside the optical galaxy.Comment: 9 pages, 15 figures. Accepted for publication MNRA
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
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
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 star-formation history of the universe - an infrared perspective
A simple and versatile parameterized approach to the star formation history
allows a quantitative investigation of the constraints from far infrared and
submillimetre counts and background intensity measurements.
The models include four spectral components: infrared cirrus (emission from
interstellar dust), an M82-like starburst, an Arp220-like starburst and an AGN
dust torus. The 60 m luminosity function is determined for each chosen
rate of evolution using the PSCz redshift data for 15000 galaxies. The
proportions of each spectral type as a function of 60 m luminosity are
chosen for consistency with IRAS and SCUBA colour-luminosity relations, and
with the fraction of AGN as a function of luminosity found in 12 m
samples. The luminosity function for each component at any wavelength can then
be calculated from the assumed spectral energy distributions. With assumptions
about the optical seds corresponding to each component and, for the AGN
component, the optical and near infrared counts can be accurately modelled.
A good fit to the observed counts at 0.44, 2.2, 15, 60, 90, 175 and 850
m can be found with pure luminosity evolution in all 3 cosmological models
investigated: = 1, = 0.3 ( = 0), and
= 0.3, = 0.7.
All 3 models also give an acceptable fit to the integrated background
spectrum. Selected predictions of the models, for example redshift
distributions for each component at selected wavelengths and fluxes, are shown.
The total mass-density of stars generated is consistent with that observed,
in all 3 cosmological models.Comment: 20 pages, 25 figures. Accepted for publication in ApJ. Full details
of models can be found at http://astro.ic.ac.uk/~mrr/countmodel
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