Supernova Remnants and Molecular Clouds

 

Dr. Jeonghee Rho

Infrared Processing and Analysis Center (IPAC) Morrisroe Lab. of Astroscience, California Institute of Technology, Pasadena, California

Abstract:

Supernovae are believed to be the source of local kinetic energy of the

interstellar medium, keeping the gas in motion and returning material

from dense molecular clouds into the more diffuse interstellar medium

and the galactic halo. Strong shock waves traversing the interstellar

clouds compress, heat, chemically alter the medium, and trigger star

formation.

I review recent Infrared Space Observatory (ISO), near-infrared and

millimeter observations of a number of supernova remnants which are

interacting with clouds.  Atomic fine-structure lines of  [C II], [N

II], [N III, [O I], [O II], [O III], [Si II], [P II], [Fe II], and two

lines of  shocked molecular hydrogen  S(3) and S(9), were detected for

three remnants using ISO. Virtually all existing atomic lines are

detected. No single shock model can account for all of the observed

lines. To explain the detected lines requires both moderate ($10^{2}$

cm$^{-3}$) and high ($\sim 10^{4}$ cm$^{-3}$) pre-shock densities, with

the moderate density shocks producing the ionic lines and the high

density shocks producing the molecular lines. The inferred high density

and warm temperatures are from heated dense clumps due to supernova

shocks, and the principal coolants of radiative shocks are [O I] 63um

and [Si II] 34.8um lines. Shock-excited far-infrared emission of

molecular hydrogen, OH, and CO are also detected, which is consistent

with collisional excitation  in warm, very dense (2x$10^{5}$ cm$^{-3}$)

gas.

We also took high resolution images of the significance coolants

molecular hydrogen and [Fe II]  using ground-based observations, which

reveal how shocks develop around clouds. We found strong correlation

between broad CO  and shocked molecular hydrogen lines. Displacements

between  molecular hydrogen  and [Fe II] structures are often observed,

showing that a single primary shock is present on large scales. We also

discover broad millimeter lines from a couple of SNRs, which are direct

evidence of the interaction between the SN shocks and molecular clouds.

The possibility of star formation induced by supernova

shocks when SN shocks interact with clouds will be discussed.