RESEARCH ON ASTROPHYSICS DISCUSSED BY A.A. HAKOBYAN AND CO-RESEARCHERS

Science Letter
February 2, 2010

According to recent research from Armenia, "With the goal of providing
constraints on the nature of the progenitors of core-collapse (CC)
supernovae (SNe), we compare their radial distribution within their
spiral host galaxies with the distributions of stars and ionized gas
in spiral disks. SNe positions are taken from the Asiago catalog for
a well-defined sample of 224 SNe within 204 host galaxies."

"The SN radial distances are estimated from the deprojected separations
from the host galaxy nuclei, and normalized both to the 25th mag
arcsec(-2) blue-band isophotal radius and (for the first time)
to the statistically-estimated disk scale length. The normalized
radial distribution of all CCSNe is consistent with an exponential
law, as previously found, with a possible depletion of CCSNe within
one-fifth of the isophotal radius (less significant with scale-length
normalization). There are no signs of truncation of the exponential
distribution of CCSNe out to 7 disk scale lengths. The scale length
of the distribution of type II SNe appears to be significantly larger
than that of the stellar disks of their host galaxies, but consistent
with the scale lengths of Freeman disks. SNe Ib/c have a significantly
smaller scale length than SNe II, with little difference between types
Ib and Ic. The radial distribution of type Ib/c SNe is more centrally
concentrated than that of the stars in a Freeman disk, but is similar
to the stellar disk distribution that we infer for the host galaxies.

All CCSN subsamples are consistent with the still uncertain
distribution of H II regions. The scale length of the CCSN radial
distribution shows no significant correlation with the host galaxy
morphological type, or the presence of bars. However, low luminosity as
well as inclined hosts have a less concentrated distribution (with the
scale-length normalized radial distances) of CCSNe, which are probably
a consequence of metallicity and selection effects, respectively. The
exponential distribution of CCSNe shows a scale length consistent with
that of the ionized gas confirming the generally accepted hypothesis
that the progenitors of these SNe are young massive stars," wrote
A.A. Hakobyan and colleagues (see also Astrophysics).

The researchers concluded: "Given the lack of correlation of the
normalized radial distances of CCSNe with the morphological type of
the host galaxy, we conclude that the more concentrated distribution
of SNe Ib/c relative to SNe II must arise from the higher metallicity
of their progenitors or possibly from a shallower initial mass function
in the inner regions of spirals."

Hakobyan and colleagues published their study in Astronomy &
Astrophysics (The radial distribution of core-collapse supernovae
in spiral host galaxies. Astronomy & Astrophysics, UNKNOWN
DATE;508(3):1259-1268).

For additional information, contact A.A. Hakobyan, Byurakan
Astrophysics Observ, Armenian Branch, Byurakan 0213, Aragatzotn Prov,
Armenia.

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