Effects of Dust on the Observed SEDs of Galaxies

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Effects of Dust on the Observed SEDs of Galaxies

• Andrew Schurer
• SISSA MAGPOP

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Andrew Schurer

• Studied at Nottingham University for four years -
  Msci in physics
• Attended lecture course on a large range of
  topics including many in astrophysics.
• Undertook several research projects including a 3
  month project on magnetic resonance.
• Currently one year into a PhD at SISSA, the
  majority of which has been spent attending a
  comprehensive series of lectures.
• Radiative Processes
• Galaxy Formation
• Observational and Classical Cosmology
• General Relativity
• High energy Astrophysics
• Extragalactic Astrophysics
• Numerical Methods
• Cosmological Perturbations and CMB
• After recombination
• At SISSA attend regular seminars given by
  internal and external experts as well as
  students.

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MAGPOP

• Member of an EU funded research and training
  network, MAGPOP, (Multi-wavelength Analysis of
  Galaxy Populations)
• As part of the MAGPOP network I have attended
• the first MAGPOP network meeting in Toledo where
  I heard many experts talk about diverse areas
  within the topic of galaxies and planned a
  collaboration with a fellow member of the MAGPOP
  network
• A MAGPOP workshop in Budapest, where I attended
  lectures on observations, stellar synthesis and
  SAMs and participated in a telescope time
  application project.
• I found these events useful as they have not only
  improved my knowledge within these areas but also
  offered an opportunity to meet other researchers
  within the field.
• In addition these events have given me an
  opportunity to present my ideas to fellow
  researchers, improving my communication skills.

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My Research

• Objectives of Magpop are to use SEDs of galaxies
  to extract key physical information about the
  galaxy and then to use this to constrain
  theoretical models of galaxy formation.
• In particular my role will be in studying the
  effect that dust reprocessing has on the SEDs of
  galaxies

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• Dust Reprocessing particularly important in
  objects with particularly high Star Formation
  Rates, e.g. Star bursts.
• Dust plays an important role in star formation
• Dense molecular clouds prevents stellar radiation
  from penetrating allowing molecules to cool and
  form stars.
• Importance increases with redshift.
• Detection of a FIR/sub-mm background by the COBE
  satellite.
• Detection of many highly extincted source at high
  Z
• Major effect on galaxy evolution theories.
• Initial studies of cosmic Star Formation Rates
  from optical surveys suggested that SFR peaked at
  about z 1 or 1.5
• IR surveys revealed that a large proportion of
  the cosmic SFR had been lost because of dust
  reprocessing.
• IR surveys suggest that SFR is constant after
  z1.
• Dust is important as a diagnostic
• Its Emission spectrum provides an indication of
  physical conditions including an estimate of SFR.

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Observational Data Sample

• Goldmine data set - Boselli (2003) (MAGPOP
  collaborator)
• Data available for wide range of wavelengths from
  radio to UV, including IR data from ISO CAM/PHOT
  and IRAS
• Optically selected Virgo sample (100 galaxies)
• Galaxies later than SO
• Whole range of morphologies and galaxy densities.
• Virgo serendipitous sample (18 galaxies)
• Representative of a mid-IR selected sample of
  nearby galaxies
• An additional 6 Virgo galaxies observered by
  ISOCAM as part of other projects
• A1367 and Coma clusters samples (contursi 2001)
  (18 galaxies)
• High star forming late time galaxies with
  peculiar morphologies (not a complete sample)
• Additional 3 galaxies in the Coma cluster

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GRASIL

• To try to recreate observations I have been using
  the dust reprocessing model GRASIL (Silva 1998),
  developed by my supervisor Gian Luigi Granato and
  Laura Silva.
• GRASIL is a code that computes the spectral
  evolution of stellar systems. These stellar
  sources are distributed realistically in a model
  galaxy which also contains dust.
• It performs a complete radiative transfer
  computation of the effect of the dust on the
  emission of the stellar sources.
• Calculates SED from radio to far UV
• includes PAH, molecular and nebular lines
• The overall evolution of the galaxy over time is
  controlled by a separate chemical evolution code
  which follows the star formation rate, initial
  mass function, metallically and residual gas
  function.

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GRASIL - geometry

• Galaxies are composed of either a spheroid a disk
  or a combination of both.
• Two main Dust Components - Molecular clouds
  (where stars are born)
  - Interstellar medium
• Also Dust envelope around AGB stars, represents
  shell of expelled material.

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Conclusions

• This work has increase my own knowledge about
  dust reprocessing and more specifically about the
  model GRASIL.
• What it does
• How to use it
• What free parameters the models has.
• It has also improved my programming skills,
  particularly in Fortran and IDL
• Shown GRASIL is capable of recreating any late
  type galaxy.
• Through an investigation into the parameters,
  typical values have been found.
• Highlighted problems in the radio.
• Future Work
• Improve fits, increase knowledge of parameters.
• Analyse nebula emission lines and check if best
  fit models agree with other observational
  evidence.
• Detect and correct any further problems found.

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Future Work

• Improved model of PAH bands
• First version of GRASIL based on pre-ISO data,
  (following Xu De Zotti 1989)
• Following release of ISO data PAH treatment
  updated (following Li Draine 2001). ISO able to
  measure short wavelengths only in bright objects
  e.g. visual reflection nebula.
• IRAC aboard the Spitzer space telescope has
  increased sensitivity and resolution, allowing
  for better treatment of the PAH lines (Draine
  2006).
• More bands and slight changes in existing bands,
  better treatment of NIR continuum.
• GRASIL should be updated to incorporate this.

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• Evolution of Dust Grain Population
• Complex problem, need to explain how dust grains
  are produces and destroyed (Dwek 98, Morgan
  Edmunds 2003).
• The main ways in which dust grains can be
  produced are in the stellar outflow of stars such
  as AGBs and supernova and also by being built up
  in the ISM.
• Processes which lead to their destruction include
  shock waves due to supernova and collisions with
  other grains.
• GRASIL does not include any details of the
  evolution of the grain population. E.g. Birth
  and destruction of grains.
• By attempting to include these processes within
  the GRASIL model it should be possible to make it
  more physically consistent and possibly more
  accurate at high redshift.

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• Modelling embedded clusters.
• Young Massive Clusters - possibly evolutionary
  fore-runners of Globular Clusters (Tagle 2003).
• Two types blue YMCs, for whom the blue
  photosphere of the young stars is directly
  visible and embedded YMCs.
• Observations of embedded YMCs in a starburst
  environment require an angular resolution in the
  MIR which has only become available recently.
• Using new data it is possible to try to model
  embedded YMCs in starburst environments, using a
  dust model such as GRASIL.
• Can improve our understanding of starburst
  phenomena, the formation of globular clusters as
  well as about star formation itself.
• Coupling to SAMs in Munich (MAGPOP node)
• It is essential that any galaxy evolution model
  contains a correct treatment of dust in order to
  compare models to observations.
• Work with Munich to develop a GRASIL black box
  which can be attached to their SAMs.

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Summary

• Have now spent one year as part of the MAGPOP
  scheme living and working in Trieste.
• From the first year at SISSA have received a
  thorough training in a broad variety of different
  topics through lectures and seminars.
• Have attended a MAGPOP conference in Toledo and a
  workshop in Budapest, where I attended lectures
  more specific to my particular area of research
  and met potential collaborators.
• Have now begun my own research into the effect of
  dust on the SED of galaxies, which is an
  important objective of MAGPOP.
• I have used GRASIL to recreate the SEDs of
  galaxies.
• Have shown GRASIL can recreate late type galaxies
  of different type.
• Have learned about dust reprocessing and in
  particular the GRASIL model
• Have improved my programming skills.
• By giving presentations I have improved my
  communication skills.
• Plenty of opportunity for future work and future
  collaborations.