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Richard J. Tuffs

Publications and source records attributed to Richard J. Tuffs.

36 records · Page 2Linked to original sources
arXiv2007

Modelling the SEDs of spiral galaxies

Modelling the UV/optical - infrared/submm SEDs of spiral galaxies observed with Herschel will be an essential tool to quantitatively interpret these observations in terms of the present and past star-formation activity of these systems. In this lecture we describe the SED modelling technique we have developed, its applications and tests of its predictions. We show that both the panchromatic SED modelling of individual galaxies and the B-band attenuation-inclination relation of large statistical samples suggest that spiral galaxies in the nearby Universe behave as optically thick systems in their global properties and large-scale distribution of light (central face-on B-band opacity of approx. 4). However disk galaxies are very inhomogeneous systems, having both optically thick components (e.g. spiral arms), and optically thin components (e.g. the interarm regions), the latter making galaxies transparent to background galaxies.

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arXiv2007

The Millennium Galaxy Catalogue: the B-band attenuation of bulge and disc light and the implied cosmic dust and stellar mass densities

Based on our sample of 10095 galaxies with bulge-disc decompositions we derive the empirical B-band internal attenuation--inclination relation for galaxy discs and their associated central bulges. Our results agree well with the independently derived dust models of Tuffs et al., leading to a direct constraint on the mean opacity of spiral discs of Tau_B^f = 3.8 +/- 0.7 (central face-on B-band opacity). Depending on inclination, the B-band attenuation correction varies from 0.2 -- 1.1 mag for discs and from 0.8 -- 2.6 mag for bulges. We find that, overall, 37 per cent of all B-band photons produced in discs in the nearby universe are absorbed by dust, a figure that rises to 71 per cent for bulge photons. The severity of internal dust extinction is such that one must incorporate internal dust corrections in all optical studies of large galaxy samples. This is particularly pertinent for optical HST comparative evolutionary studies as the dust properties will also be evolving. We use the new results to revise our recent estimates of the spheroid and disc luminosity functions. From our best fitting dust models we derive a redshift zero cosmic dust density of rho_{dust} ~ (5.3 +/- 1.7) x 10^5, h M_{odot} Mpc^-3. This implies that (0.0083 +/- 0.0027), h per cent of the baryons in the Universe are in the form of dust and (11.9 +/- 1.7), h per cent (Salpeter-`lite' IMF) are in the form of stars (~58 per cent reside in galaxy discs, ~10 per cent in red elliptical galaxies, ~29 per cent in classical galaxy bulges and the remainder in low luminosity blue spheroid systems/components). [Abridged]

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arXiv2006

Modelling the Pan-Spectral Energy Distribution of Starburst Galaxies: III. Emission Line Diagnostics of Ensembles of Evolving HII Regions

We build, as far as theory will permit, self consistent model HII regions around central clusters of aging stars. These produce strong emission line diagnostics applicable to either individual HII regions in galaxies, or to the integrated emission line spectra of disk or starburst galaxies. The models assume that the expansion and internal pressure of individual HII regions is driven by the net input of mechanical energy from the central cluster, be it through winds or supernova events. This eliminates the ionization parameter as a free variable, replacing it with a parameter which depends on the ratio of the cluster mass to the pressure in the surrounding interstellar medium. These models explain why HII regions with low abundances have high excitation, and demonstrate that at least part of the warm ionized medium is the result of overlapping faint, old, large, and low pressure HII regions. We present line ratios (at both optical and IR wavelengths) which provide reliable abundance diagnostics for both single HII regions or for integrated galaxy spectra, and we find a number that can be used to estimate the mean age of the cluster stars exciting individual HII regions.

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arXiv2006

Modelling the Pan-Spectral Energy Distribution of Starburst Galaxies: II. Control of the \HII Region Parameters

We examine, from a theoretical viewpoint, how the physical parameters of HII regions are controlled in both normal galaxies and in starburst environments. These parameters are the HII region luminosity function, the time-dependent size, the covering fraction of molecular clouds, the pressure in the ionized gas and the ionization parameter. The factors which control them are the initial mass function of the exciting stars, the cluster mass function, the metallicity and the mean pressure in the surrounding interstellar medium. We investigate the sensitivity of the H$α$ luminosity to the IMF, and find that this can translate to more than a factor two variation in derived star formation rates. The molecular cloud dissipation timescale is estimated from a case study of M17 to be $\sim1$ Myr for this object. Based upon HII luminosity function fitting for nearby galaxies, we suggest that the \HII region cluster mass function is fitted by a log-normal form peaking at $\sim 100 M_{\odot}$. The cluster mass function continues the stellar IMF to higher mass. The pressure in the HII regions is controlled by the mechanical luminosity flux from the central cluster. Since this is closely related to the ionizing photon flux, we show that the ionization parameter is not a free variable, and that the diffuse ionized medium may be composed of many large, faint and old HII regions. Finally, we derive theoretical probability distributions for the ionization parameter as a function of metallicity and compare these to those derived for SDSS galaxies.

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arXiv2005

Normal Nearby Galaxies

Following on from IRAS, ISO has provided a huge advancement in our knowledge of the phenomenology of the infrared (IR) emission of normal galaxies and the underlying physical processes. Highlights include: the discovery of an extended cold dust emission component, present in all types of gas-rich galaxies and carrying the bulk of the dust luminosity; the definitive characterisation of the spectral energy distribution in the IR, revealing the channels through which stars power the IR light; the derivation of realistic geometries for stars and dust from ISO imaging; the discovery of cold dust associated with HI extending beyond the optical body of galaxies; the remarkable similarity of the near-IR (NIR)/ mid-IR (MIR) SEDs for spiral galaxies, revealing the importance of the photo-dissociation regions in the energy budget for that wavelength range; the importance of the emission from the central regions in shaping up the intensity and the colour of the global MIR luminosity; the discovery of the ``hot'' NIR continuum emission component of interstellar dust; the predominance of the diffuse cold neutral medium as the origin for the main interstellar cooling line, [CII] 158 micron, in normal galaxies.

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arXiv2005

Modelling the ultraviolet/submillimeter spectral energy distributions of normal galaxies

We give an overview of the factors shaping the ultraviolet (UV)/optical - far-infrared (FIR)/submillimeter (submm) spectral energy distributions (SEDs) of normal (non-starburst) galaxies. Particular emphasis is placed on the influen ce of the geometry of dust and stars on the propagation of light through the int erstellar medium. Although strong constraints can be placed on the amount and la rge scale distribution of dust in disks from the appearance of the galaxies in t he optical/UV range, this dust does not account for the observed amplitude and c olour of the FIR/submm radiation. Additional, optically thick components of dust associated with the young stellar population on large and small scales are requ ired to account for the complete UV/optical - FIR/submm SEDs. Self-consistent mo dels for the calculation of SEDs of spiral galaxies are reviewed, and their pred ictions for the dust emission and the attenuation of starlight are compared and contrasted.

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arXiv2005

Normal Gas-Rich Galaxies in the Far-Infrared: The Legacy of ISOPHOT

Following on from IRAS, the ISOPHOT instrument on board the Infrared Space Observatory (ISO) has provided a huge advancement in our knowledge of the phenomenology of the far-infrared (FIR) emission of normal galaxies and the underlying physical processes. Highlights include: the discovery of an extended cold dust emission component, present in all types of gas-rich galaxies and carrying the bulk of the dust luminosity; the definitive characterisation of the spectral energy distribution in the FIR, revealing the channels through which stars power the FIR light; the derivation of realistic geometries for stars and dust from ISOPHOT imaging and the discovery of cold dust associated with HI extending beyond the optical body of galaxies.

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arXiv2004

Modelling the Pan-Spectral Energy Distribution of Starburst Galaxies: I. The role of ISM pressure & the Molecular Cloud Dissipation Timescale

In this paper, we combine the stellar spectral synthesis code STARBURST 99, the nebular modelling code MAPPINGS IIIq, a 1-D dynamical evolution model of \HII regions around massive clusters of young stars and a simplified model of synchrotron emissivity to produce purely theoretical self-consistent synthetic spectral energy distributions (SEDs) for (solar metallicity) starbursts lasting some $10^8$ years. These SEDs extend from the Lyman Limit to beyond 21 cm. We find that two ISM parameters control the form of the SED; the pressure in the diffuse phase of the ISM (or, equivalently, its density), and the molecular cloud dissipation timescale. We present detailed SED fits to Arp 220 and NGC 6240, and we give the predicted colors for starburst galaxies derived from our models for the IRAS and the Spitzer Space Observatory MIPS and IRAC instruments. Our models reproduce the spread in observed colors of starburst galaxies. Finally, we present absolute calibrations to convert observed fluxes into star formation rates in the UV (GALEX), at optical wavelengths (H$α$), and in the IR (IRAS or the Spitzer Space Observatory). (Abstract Truncated)

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arXiv2003

Photometric Mapping with ISOPHOT using the "P32" Astronomical Observation Template

The ``P32'' Astronomical Observation Template (AOT) provided a means to map large areas of sky (up to 45 x 45 arcmin) in the far-infrared (FIR) at high redundancy and with sampling close to the Nyquist limit using the ISOPHOT C100 (3 x 3) and C200 (2 x 2) detector arrays on board the Infrared Space Observatory (ISO). However, the transient response behaviour of the Ga:Ge detectors, if uncorrected, can lead to severe systematic photometric errors and distortions of source morphology on maps. We describe the basic concepts of an algorithm which can successfully correct for transient response artifacts in P32 observations. Examples are given to demonstrate the photometric and imaging performance of ISOPHOT P32 observations of point and extended sources corrected using the algorithm. For extended sources we give the integrated flux densities of the nearby galaxies NGC6946, M51 and M101 and an image of M101 at 100 micron.

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arXiv2003

Infrared emission towards SN 1987A 11 years after outburst: Measurements with ISOCAM

We present measurements of the mid-infrared (MIR) emission from SN 1987A, made using the Infrared Space Observatory (ISO) 11 years after outburst. They are the only late epoch detections of this source in the thermal IR regime. The position of the source, determined from an offset to an IR-emitting star, suggests that the emission is associated with SN 1987A or its extended supernova remnant (SNR). A predominantly circumstellar origin is however suggested by the size and orientation of the IR-emitting region, which is comparable with the extension of the inner ring seen with the Hubble Space Telescope (HST). The emission is most probably from collisionally-heated circumstellar grains embedded in shocked gas downstream of the blast wave. The MIR extent is consistent with the hypothesis that the blast wave was propagating into material of moderate density interior to the thick inner ring at the epoch of the ISOCAM observations.

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arXiv2002

Far-infrared Emission from Dust in Normal Galaxies

We review the morphological and spectral energy distribution characteristics of the dust continuum emission (emitted in the 40-200 micron spectral range) from normal galaxies, as revealed by detailed ISOPHOT mapping observations of nearby spirals and by ISOPHOT observations of the integrated emissions from representative statistical samples in the local universe.

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arXiv2002

Modelling the spectral energy distribution of galaxies from the ultraviolet to submillimeter

We present results from a new modelling technique which can account for the observed optical/NIR - FIR/submm spectral energy distributions (SEDs) of normal star-forming galaxies in terms of a minimum number of essential parameters specifying the star-formation history and geometrical distribution of stars and dust. The model utilises resolved optical/NIR images to constrain the old stellar population and associated dust, and geometry-sensitive colour information in the FIR/submm to constrain the spatial distributions of young stars and associated dust. It is successfully applied to the edge-on spirals NGC891 and NGC5907. In both cases the young stellar population powers the bulk of the FIR/sub-mm emission. The model also accounts for the observed surface brightness distribution and large-scale radial brightness profiles in NGC891 as determined using the Infrared Space Observatory (ISO) at 170 and 200 mcrions and at 850 micron using SCUBA.

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arXiv2002

Far-Infrared photometry of a statistical sampleof late-type Virgo Cluster galaxies

We present deep diffraction-limited far-infrared (FIR) strip maps of a sample of 63 galaxies later than S0 and brighter than B_T 16.8, selected from the Virgo Cluster Catalogue of Binggeli, Sandage & Tammann. The ISOPHOT instrument on board the Infrared Space Observatory was used to achieve sensitivities typically an order of magnitude deeper than IRAS in the 60 and 100 micron bands and to reach the confusion limit at 170 microns. The averaged 3 sigma upper limits for integrated flux densities of point sources at 60, 100 and 170 microns are 43, 33 and 58 mJy, respectively. 54 galaxies (85.7 percent) are detected at least at one wavelength, and 40 galaxies (63.5 percent) are detected at all three wavelengths. The highest detection rate (85.7 percent) is in the 170 micron band. In many cases the galaxies are resolved, allowing the scale length of the infrared disks to be derived from the oversampled brightness profiles in addition to the spatially integrated emission. The data presented should provide the basis for a variety of statistical investigations of the FIR spectral energy distributions of gas rich galaxies in the local universe spanning a broad range in star-formation activity and morphological types, including dwarf systems and galaxies with rather quiescent star formation activity.

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arXiv2001

Cold dust in late-type Virgo Cluster galaxies

We have statistically analyzed the spatially integrated far-infrared (FIR) emissions of the complete volume- and luminosity-limited sample of late-type (later than S0) Virgo cluster galaxies measured using the Infrared Space Observatory (ISO) by Tuffs et al. (2002) in bands centered on 60, 100 and 170 microns. 30 out of 38 galaxies detected at all three wavelengths contain a cold dust emission component, present within all morphological types of late-type systems ranging from early giant spirals to Blue Compact Dwarfs (BCDs), and which could not have been recognized by IRAS. The temperatures of the cold dust were found to be broadly distributed, with a median of 18 K, some 8-10 K lower than would have been predicted from IRAS. The derived total dust masses are correspondingly increased by factors of typically 6 - 13. A particularly significant result concerns the low dust temperatures (ranging down to less than 10 K) and large dust masses associated with the Im and BCD galaxies in our sample. We propose two scenarios to account for the FIR characteristics of these systems.

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arXiv2000

Modelling the spectral energy distribution of galaxies. I. Radiation fields and grain heating in the edge-on spiral NGC891

We describe a new tool for the analysis of the UV to the sub-millimeter (sub-mm) spectral energy distribution (SED) of spiral galaxies. We use a consistent treatment of grain heating and emission, solve the radiation transfer problem for a finite disk and bulge, and self-consistently calculate the stochastic heating of grains placed in the resulting radiation field. We use this tool to analyse the well-studied nearby edge-on spiral galaxy NGC891. First we investigate whether the old stellar population in NGC891, along with a reasonable assumption about the young stellar population, can account for the heating of the dust and the observed far-infrared (FIR) and sub-mm emission. The dust distribution is taken from the model of Xilouris et al. (1999), who used only optical and near-IR observations to determine it. We have found that such a simple model cannot reproduce the SED of NGC891, especially in the sub-mm range. It underestimates by a factor of 2-4 the observed sub-mm flux. A number of possible explanations exist for the missing sub-mm flux. We investigate a few of them and demonstrate that one can reproduce the observed SED in the FIR and the sub-mm quite well, as well as the observed radial profile at 850 microns. For the models calculated we give the relative proportion of the dust radiation powered by the old and young stellar populations as a function of FIR/sub-mm wavelength. In all models we find that the dust is predominantly heated by the young stellar population.

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arXiv2000

On the FIR emission from intracluster dust

We make predictions for the diffuse far-infrared (FIR) emission from dust in the intracluster medium (ICM) of the Virgo cluster using detailed information on potential dust sources, grain heating and sputtering rates available for this cluster from recent optical and X-ray studies. We show that the infrared emission from dust injected by sources inside the core region of the Virgo cluster is a factor of 10 below the detection limit of currently available telescopes. The outer regions of dynamically young clusters like the Virgo cluster have a further potential source of intracluster grains since they are still accreting freshly infalling spiral galaxies which are presumably contained in an accreting intergalactic medium (IGM). We show that cosmic ray driven winds from the infalling spirals can inject grains into a subvirial IGM that is external to the observed X-ray-emitting ICM. Sputtering during the injection process and in the IGM is weak, so that the injected grains should accumulate in the IGM until the infall brings them into contact with the hot ICM. This effect dominates the dust injection rate from known sources embedded in the hot Virgo ICM. Thus, any detection of diffuse IR emission would probe the current dust accretion rate for the cluster, acting as an indicator of the youth and the dynamical state of the cluster. The predictions for the Virgo cluster are generalised to other clusters and the possibility of detection of dynamically young clusters at cosmological distances is discussed.

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arXiv1999

IRAS 17393-3004, a late-type supergiant surrounded by a dust shell

Infrared observations of IRAS 17393-3004, including a full scan ISOSWS are presented. The ISOSWS spectrum shows two prominent dust emission peaks at lambda 10.4mu and 17.5mu confirming that the source is a luminous star surrounded by a dust shell. The spectrum of the star, deduced from modeling of the radiative transfer through a spherical shell using the DUSTY code (Ivezic et al. 1997), can be explained along with other known properties in terms of an M4 supergiant with OH, SiO and H_2O maser emission and a large mass loss of ~ 10^{-4}M(sun)yr^{-1}.

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