Tracing Dust in Spiral Galaxies: a Summary Jonathan Davies

What have I learnt? In Ghent you eat elephant sausages, dog and drink urine. If the two swans are not facing each other it means something completely different! Best comments of the workshop are due to Suzanne; about Anthony “ We should not invite these kind of people ” (too much detail that we do not need to know about). about me “ You are good to have at a workshop because you are a real pain in the But. ” Most insight is by Nick “Error bars make a good fit look bad”

 How much dust is present? 1.Face-on optical depth measured to be about 1 in the V-band (various people), but required to be 5 to account for FIR emission - energy balance problem. Is the solution warm clumpy dust? 2.Surface brightness inclination gives B-band central optical depth of 3.8! 3.Evidence for cold dust in many galaxies how does this alter gas to dust ratios? 4.What are the sources and sinks of dust - how much dust should a galaxy have? Inflows and outflows? Dust extraction time scale is an order of magnitude shorter than the dust injection timescale. 5.Are the various models, optical extinction and FIR observations consistent with the GALEX UV observations? 6.The SF history as measured by both the UV and FIR increase as you go back in time (to z=1), but the fraction of obscured SF also increases.  How much dust is present? 1.Face-on optical depth measured to be about 1 in the V-band (various people), but required to be 5 to account for FIR emission - energy balance problem. Is the solution warm clumpy dust? 2.Surface brightness inclination gives B-band central optical depth of 3.8! 3.Evidence for cold dust in many galaxies how does this alter gas to dust ratios? 4.What are the sources and sinks of dust - how much dust should a galaxy have? Inflows and outflows? Dust extraction time scale is an order of magnitude shorter than the dust injection timescale. 5.Are the various models, optical extinction and FIR observations consistent with the GALEX UV observations? 6.The SF history as measured by both the UV and FIR increase as you go back in time (to z=1), but the fraction of obscured SF also increases. Main Objectives of the workshop

 How is dust distributed with respect to the stars and the gas? 1.Radial scale length of dust longer than that of the stars - cold dust in the outskirts of galaxies? 2.Does dust follow the HI - evidence from 24u obs? 3.Is there evidence for dust above the stellar disc and in the halos of galaxies? There is evidence for dust in the IGM - it is being expelled.  How is dust distributed with respect to the stars and the gas? 1.Radial scale length of dust longer than that of the stars - cold dust in the outskirts of galaxies? 2.Does dust follow the HI - evidence from 24u obs? 3.Is there evidence for dust above the stellar disc and in the halos of galaxies? There is evidence for dust in the IGM - it is being expelled.

 What environments are responsible for dust extinction/emission in different wavelength regimes? 1.What are the relative quantities of hot dust close to SF regions, warm dust in the ISM and cold dust in dense clouds or in the very outskirts of galaxies? 2.How can this all be modeled and do we learn much more by making such complicated models. 3.How does dust temperature and density change with radius and scale height? 4.PAHs go down as the sub-mm excess goes up?  What environments are responsible for dust extinction/emission in different wavelength regimes? 1.What are the relative quantities of hot dust close to SF regions, warm dust in the ISM and cold dust in dense clouds or in the very outskirts of galaxies? 2.How can this all be modeled and do we learn much more by making such complicated models. 3.How does dust temperature and density change with radius and scale height? 4.PAHs go down as the sub-mm excess goes up?

 What are the properties of dust responsible for the bulk of emission? 1.What do we mean by cold, warm and hot dust - definitions? 2.I need to know more about how to interpret IR spectra - what does it all mean? 3.Should we be making proposals that are directed more towards measuring fundamental properties? How do they change with environment? 4.What is the origin of the FIR/radio relation ? 5.Tracing dust is the best way of tracing molecular gas. 6.What about grey dust?  What are the properties of dust responsible for the bulk of emission? 1.What do we mean by cold, warm and hot dust - definitions? 2.I need to know more about how to interpret IR spectra - what does it all mean? 3.Should we be making proposals that are directed more towards measuring fundamental properties? How do they change with environment? 4.What is the origin of the FIR/radio relation ? 5.Tracing dust is the best way of tracing molecular gas. 6.What about grey dust?

 Are there differences in the dust contents of galaxies of different morphological type? 1.Not sure what the simple answer to this is - dust morphology very different to optical morphology. 2.Optically selected samples have much more cold dust. What about those selected by their gas mass? 3.Later types have more extended dust. 4.Lower luminosity galaxies have higher specific SF rates - lower dust masses? Higher mass galaxies formed the bulk of their stars at early epochs. What does down sizing mean with regard to dust production/mass. 5.Large variations in relative atomic gas content even amongst morphologically similar early type galaxies  Are there differences in the dust contents of galaxies of different morphological type? 1.Not sure what the simple answer to this is - dust morphology very different to optical morphology. 2.Optically selected samples have much more cold dust. What about those selected by their gas mass? 3.Later types have more extended dust. 4.Lower luminosity galaxies have higher specific SF rates - lower dust masses? Higher mass galaxies formed the bulk of their stars at early epochs. What does down sizing mean with regard to dust production/mass. 5.Large variations in relative atomic gas content even amongst morphologically similar early type galaxies

The Energy Budget

 Opportunities 1.Mid-infrared - modeling the spectrum. 2.The amount of cold dust and its spatial distribution. 3.Fundamental properties of dust and how this changes in different environments. 4.The dust budget - sources and sinks of dust. 5.The energy balance.  Opportunities 1.Mid-infrared - modeling the spectrum. 2.The amount of cold dust and its spatial distribution. 3.Fundamental properties of dust and how this changes in different environments. 4.The dust budget - sources and sinks of dust. 5.The energy balance.

 The Dawn of a New Generation of Observing Facilities. 1. Herschel - early competition with GT - Open time proposals Oct 2007 and April SPIRE  photometer,  FTS. PACS  photometer, spectrograph . Beam 3-35” 2. SCUBA2 + HARP - July Legacy survey physical processes in the local Universe. 450 and 850 . Beam 5-10”, 10,000 pixel array. 3. APEX  4. SOPHIA ? 5. ALMA JWST ? 7. SPICA , but realistically way past my sunset!  The Dawn of a New Generation of Observing Facilities. 1. Herschel - early competition with GT - Open time proposals Oct 2007 and April SPIRE  photometer,  FTS. PACS  photometer, spectrograph . Beam 3-35” 2. SCUBA2 + HARP - July Legacy survey physical processes in the local Universe. 450 and 850 . Beam 5-10”, 10,000 pixel array. 3. APEX  4. SOPHIA ? 5. ALMA JWST ? 7. SPICA , but realistically way past my sunset!

All Modeling Infrared Galaxy ObservationS Thank You