Probing the interstellar medium along the lines of sight to supernovae SN 1994D and SN1994I

Details Probing the interstellar medium along the lines of sight to supernovae SN 1994D and SN1994I Probing the interstellar medium along the lines of sight to supernovae SN 1994D and SN1994I

May 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...444..165h&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 444, no. 1, p. 165-174

Astronomy and Astrophysics

Astrophysics

32

Absorption Spectra, Astronomical Spectroscopy, Interstellar Matter, Light (Visible Radiation), Line Of Sight, Supernovae, Cosmic Gases, Galactic Halos, H Alpha Line, Intergalactic Media, Interstellar Extinction, Quasars, Spectrum Analysis, Virgo Galactic Cluster

Scientific paper

We present high-resolution (approximately 8 km/s) echelle observations of SN 1994D and 1994I covering the optical Na D interstellar absorption lines and the region around H alpha. The high-quality spectra reveal a complex pattern of Na D absorption systems along the path to both supernovae. The velocity systems can be identified with contributions from the Galactic disk, the host galaxy of each supernova, and absorbing material having anomalous velocities inconsistent with simple rotation within our Galaxy or the respective host galaxies. The anomalous velocity gas along the line of sight to SN 1994D may be intergalactic in origin and is infalling toward NGC 4526, the Virgo cluster host galaxy of SN 1994D. We consider several hypotheses for the anomalous velocity systems seen toward SN 1994I. The most likely explanation is that they are optical counterparts of high-velocity clouds, normally studied in 21 cm emission, associated with either Galactic halo or the halo of the host galaxy NGC 5194(M51). These metal-bearing, low-column density clouds may be much more common than previously thought. At least some metal-line QSO absorption systems may be associated with high-velocity clouds in the halos of intervening galaxies. We use the derived Na column densities to estimate the extinction of the two supernovae. For SN 1994D, we obtain Av=0.08+ 0.08-0.04 mag, consistent with independent estimates based on considerations of the supernova colors near maximum brightness. Several complications conspire to make the extinction estimate for SN 1994I very uncertain. Our best estimate yields Av=3.1+3.1-1.5 mag, although there are reasons to believe that the true extinction is approximately less than 1.4 mag. Finally, we note that no narrow H alpha emission or absorption is detected to 2 sigma equivalent width limits of 3 mA in the spectrum of SN 1994D, a Type Ia supernova. Unfortunately, this observation does not provide very significant constraints on models of the progenitor; Sn 1994D was observed approximately 3 weeks after maximum brightness, by which time little if any H alpha would be expected even if circumstellar hydrogen were present.

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