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Svitlana Zhukovska_ Hans-Peter Gail

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					                                                          Constraints on planet system formation
                                                        from the chemical evolution of the Galaxy
                                                                                                                     Svitlana Zhukovska, Hans-Peter Gail
                                                                                      u
                                                                            Institut f¨r Theoretische Astrophysik, ZAH, University Heidelberg, Germany



Abstract                                                                                                                                                             Multiphase ISM
The evolution of gas and dust content of the interstellar medium (ISM) is studied                                                                                    The standard three phase ISM model of McKee & Ostriker (1977) is considered,
by modelling of chemical evolution of the Galaxy. We consider injection of carbon,                                                                                                                         6                                  4
iron, silicate and SiC dust species in the ISM by asymptotic giant branch stars                                                                                      consisting of hot rarefied gas (T ∝ 10 K, n ∝ 10 cm ), warm gas (T ∝ 10 K,
                                                                                                                                                                                                                        −3   −3

and supernovae. Further processing of dust in the ISM, grain growth through                                                                                          n ∝ 10−1cm−3), and cold cloud (T ∝ 102 K, n ∝ 10cm−3). We accept the model
accretion in cold molecular clouds and destruction by SN shocks, is modelled.                                                                                        of mass exchange between ISM phases of Ikeuchi & Tomita (1983), in order to
We predict the amount and composition of dust in cold molecular clouds and in
accretion disks as a function of galactocentric radius and time.                                                                                                     reproduce oscillatory star formation history from recent observations (Rocha-
                                                                                                                                                                     Pinto 2000). The abundances of each component are determined by supernovae
                                                                                                                                                                     expanding remnants through following processes:
Chemical Evolution Model                                                                                                                                             • sweeping of a warm gas into a cold component
                                                                                                                                                                     • evaporation of cold clouds embedded in a hot gas
• We present multizone model of chemical evolution (CE) of gas and dust content                                                                                      • radiative cooling of a hot gas by collisions with a warm gas
  of the Milky Way. Star formation, infall of primordial gas and stellar feedback
  play a dominant role in evolution of element abundances of the Galaxy (Dweek                                                                                                                      30
                                                                                                                                                                                                                                                               hot
  1998). We extend the model of Dwek to include multiphase ISM, in order to                                                                                                                         25
                                                                                                                                                                                                                                                            warm
                                                                                                                                                                                                                                                             cold
                                                                                                                                                                                                                                                                          Limit-cycle evolution of gas surface densi-
                                                                                                                                                                                                                                                         total gas
  follow the evolution of element abundances of gas and dust in cold, warm and                                                                                                                                                                                            ties of multiphase ISM in the solar neigh-

                                                                                                                                                                     Surface density σ, (Mo /pc )
                                                                                                                                                                     2
                                                                                                                                                                                                                                                     Olling 2001
                                                                                                                                                                                                    20



                                                                                                                                                                                          ·
  hot components of the ISM.                                                                                                                                                                                                                                              bourhood, resulting from an open non-linear
                                                                                                                                                                                                    15
• Chemical enrichment of the ISM is determined by stellar ejecta from SN II, SN                                                                                                                                                                                           model of the ISM. black square mark in-
  Ia and asymptotic giant branch (AGB) stars. We assume that SNe II return
                                                                                                                                                                                                    10
                                                                                                                                                                                                                                                                          dicates observations of Olling & Merrifield
  enriched gas and dust to the hot component, while for AGB stars and SNIa                                                                                                                          5                                                                     (2001).
  probabilities to return gas to some phase is determined by its volume fraction.                                                                                                                   0
                                                                                                                                                                                                         0            2           4          6       8          10   12
                                                                                                                                                                                                                                          T (Gyr)
  Due to mass exchange between ISM phases heavy elements and dust can cycle
  between cold, warm and hot phases.
• Dust condensation in stellar winds of evolved stars and supernova ejecta, and
                                                                                                                                                                     Evolution of metallicities and elemental abundances
  accretion of refractory elements on pre-existing dust grains in cold clouds are
  the main processes contributing to dust content of the Galaxy. We take into                                                                                                                            0.06
                                                                                                                                                                                                                      Zh
                                                                                                                                                                                                                                                                                                 10
                                                                                                                                                                                                                      Zw
  account the main dust destructive mechanisms: sputtering, evaporative grain-                                                                                                                           0.05         Zc

  grain collisions in supernova remnants in the warm phase.
                                                                                                                                                                                                         0.04                                                                                                                               Ar



                                                                                                                                                                                                                                                                          (Nel/NH)/(Nel/NH)sun
                                                                                                                                                                              Metallicity Z




                                                                                                                                                                                                                                                                                                                                Na             K
                                                                                                                                                                                                         0.03                                                                                              He           O            Si S
                                                                                                                                                                                                                                                                                                                                      P
                                                                                                                                                                                                                                                                                                                                               Ca
                                                                                                                                                                                                                                                                                                                                                               Ni
                                                                                                                                                                                                                                                                                                  1                 C                                   Fe
                                                                                                                                                                                                                                                                                                                     N Ne Al
                                                                                                                                                                                                                                                                                                                                                   Sc Cr Co
Presolar dust grains                                                                                                                                                                                     0.02
                                                                                                                                                                                                                                                                                                            Li
                                                                                                                                                                                                                                                                                                                       F Mg               Cl           Mn Cu


                                                                                                                                                                                                         0.01
                                                                                                                                                                                                                                                                                                                                                      V
                           1                                                                                 1                                                                                                                                                                                                                                                      Zn
                                                                                                                                            from AGB
                                                                                                                                             from SNII                                                        0
                                   CARBON                                                                                SILICATES           from ISM                                                             0          2        4          6    8         10   12                          0.1
                         0.1                                                                            0.1                                                                                                                                T (Gyr)                                                     0            5       10        15         20       25        30    35
                                                                                                                                                                                                                                                                                                                                 Atomic number
                                                                                                                                                                     Time evolution of metallicities in multi-
      Mass fraction




                                                                                    Mass fraction




                                                                                                                                                                     phase ISM. In current calculations we                                                                Ratio of calculated elemental abundances
                        0.01                                                                           0.01
                                                                                                                                                                     don’t include radial mixing processes in                                                             relatively to hydrogen to solar abundances
                                                                                                                                                                     the Galaxy, which would have smoothed                                                                at instant of Solar System formation at the
                       0.001                                                                          0.001                                                          strong oscillations of metallicities in hot and                                                      solar cycle. Thin black lines indicate as
                                                     from AGB                                                                                                        warm phase. Thin back lines show solar                                                               much as twice deviation from unity.
                                                      from SNII
                                                      from ISM
                                                                                                                                                                     metallicity and instant of Solar System
                      0.0001                                                                         0.0001                                                          formation.
                               0   2      4      6        8       10   12                                        0       2       4       6          8     10    12
                                              T (Gyr)                                                                                 T (Gyr)

                          1                                                                             1



                         0.1
                                   IRON
                                                                                                       0.1
                                                                                                                     SiC
                                                                                                                                                                     Dust-to-gas ratio in cold clouds
  Mass fraction




                                                                             Mass fraction




                                                                                                                                                                                                              0.01                                                                                     0.01
                        0.01                                                                          0.01



                       0.001                                                                         0.001
                                                  from AGB
                                                                                                                                                                              Dust-to-gas ratio




                                                                                                                                                                                                                                                                           Dust-to-gas ratio




                                                                                                                                                                                                             0.001                                                                                0.001
                                                   from SNII
                                                  from SNIa                                                                              from AGB
                                                   from ISM                                                                               from SNII
                      0.0001                                                                        0.0001
                               0   2      4      6        8       10   12                                    0       2       4          6       8        10    12
                                              T (Gyr)                                                                                T (Gyr)                                                             0.0001                                                                                  0.0001
Mass fractions of unprocessed C, Si, Fe and SiC grains from AGB stars and SN relatively to the                                                                                                                                 SiC
                                                                                                                                                                                                                               Iron
                                                                                                                                                                                                                                                                                                                                                           SiC
                                                                                                                                                                                                                                                                                                                                                           Iron
total mass of dust of each specices. Their values for the instant of Solar System formation (vertical                                                                                                                     Silicates                                                                                                                   Silicates
thin black lines) correspond to abundances of presolar grains.                                                                                                                                                             Carbon
                                                                                                                                                                                                                              Total
                                                                                                                                                                                                                                                                                                                                                       Carbon
                                                                                                                                                                                                                                                                                                                                                          Total
                                                                                                                                                                                                         1e-005                                                                                  1e-005
                                                                                                                                                                                                                      0      2   4    6     8 10 12 14 16 18 20                                                 0           2         4        6          8          10    12
                                                                                                                                                                                                                                             R (kpc)                                                                                        T (Gyr)
                                                                                                                                                                     Variations of dust-to-gas ratio in cold phase as a function of galactocentric radius at present
References                                                                                                                                                           time (left panel). The right panel shows the time evolution of dust-to-gas ratios in the solar
                                                                                                                                                                     neighbourhood. Thin black lines show solar galactocentric radius and instant of Solar system
Dwek, E. 1998, AphJ, 501, 64                                                                                                                                         formation, respectively.
Ikeuchi, S., & Tomita, H. 1983, PASJ, 35, 77
McKee, C. F., & Ostriker, J. P. 1977, ApJ, 218, 148
Rocha-Pinto, H. J., Scalo, J., Maciel, W., & Flynn, C. 2000, ApJ, 531, L115

				
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posted:10/5/2011
language:English
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