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Systematic Studies on Dwarf Irregular Galaxies via their SEDs

Systematic Studies on Dwarf Irregular Galaxies via their SEDs. Thanks to Dr. A. Tomita, Dr. K. Yoshikawa, and Dr. H. Hirashita. WHY study DIGs (Part I). 1930s to 1940s DIGs have been regarded as a minor group . 1970s ～ DIGs are a dominant group!. WHY study DIGs (Part II).

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Systematic Studies on Dwarf Irregular Galaxies via their SEDs

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  1. Systematic Studies on Dwarf Irregular Galaxies via their SEDs Thanks to Dr. A. Tomita, Dr. K. Yoshikawa, and Dr. H. Hirashita

  2. WHY study DIGs (Part I) 1930s to 1940s DIGs have been regarded as a minor group. 1970s ～ DIGs are a dominant group!

  3. WHY study DIGs (Part II) DIGs have nearly the same magnitude of star formation as Spirals. (Ellipticals have NO present star formation.)

  4. WHY study DIGs (Part III) Distant galaxies (= galaxies in the early Universe) Small size Irregular shape Resemble to Local DIGs. Study Local DIGs.

  5. Present Star Formation Rates from Hα Line SFR is various!

  6. Stellar continuum Past star formation Intensity Color Changes in time. Observed continuum Decomposition A mixture of various stellar populations.

  7. Past averageSFR Assumption: Age of the galaxy is the age of the universe. Past average SFR: (Total stars)/age of the galaxy.

  8. Present-to-past SFR ratios

  9. Is it a common feature? What causes such a change? Summary from present observations Star formation rate in irregulars: Changing violently in time. Can be very high compared with that in the past.

  10. Dust formation efficiency in non-evolved galaxies. (Todini & Ferrara 2001) Theoretical model of the cosmic SFR history from IR observations. Theoretical scope for galaxy formation I Importance of the study of low metallicity galaxies in the infrared: Dust amount of low-metallicity galaxies

  11. Theoretical scope for galaxy formation II H2 formation in extremely low-metallicity environment Molecular hydrogen is formed on dust grains. The H2 formation can be ineffective in primordial galaxies because of the lack of dust. In such case H2 can only be formed through reaction in gas phase. Since only H2 molecule is the coolant of gas in primeval galaxies, star formation in such galaxies is controlled by the formation rate of H2.

  12. Dependence of H2 formation on dust H2 is formed on dust grains. Xe : electron fraction H2 is formed in gas phase. Gas temperature

  13. Theoretical scope for galaxy formation III H2 formation efficiency is strongly dependent on dust temperature(e.g. Katz et al. 1999) Flux of atoms 15 K

  14. H2 formation on dust grain might be suppressed in dIrrs/BCDs because of the high dust temperature. Dust temperature has crucial importance. Furthermore…. Supernova rate and destruction rate of dust grains are related. ASTRO-F all-sky survey is a unique opportunity for these studies.

  15. How about SIRTF SINGS ? SINGS (SIRTF Nearby Galaxies Survey) Kennicutt et al. Scientific scope is similar to ours. 75 galaxies with all morphological types. 17 Irregular galaxies (only 5 is fainter than -14 mag). Is the sample enough? It seems too small, because generally irregulars are divergent in their properties, especially SFR and Z.

  16. I Zw18 (an extreme case) The lowest metallicity irregular among known galaxies (～1/50 Zsolar). The maximum detectable distance is about 10 Mpc (Kamaya & Hirashita 2001). Expectednumber of star-forming irregulars From the Local LF, about 103 irregulars/BCDs will be detected in the all sky. For secure statistical studies, all-sky survey is crucial. Homogeneous measurement including upper limits has vital importance in this study.

  17. An example of observed BCD SBS 0335-052 Size : 1”×1” Distance : 53.3 Mpc mB : 16.76 mag LB : 5.3×108 Lsolar fν(12.5μm) : 35 mJy fν(67.3μm) : 112 mJy Very hot dust! Dale et al. 2001 (astro-ph/0107108)

  18. MIR and other observations BCDs have strong UV radiation field and therefore generally hot. MIR observation is expected to be feasible. The IRC survey mode is too shallow, so IRC pointing observation of known galaxies is suitable for this purpose. But it is still not efficient, so the sky area should be limited. Then, spectroscopy…?

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