Poster abstract
Strong effects of cosmic rays on the characteristic mass of young stars in starbursts
Abstract
Up to half of all the stars in the Universe form in
starbursts spectacular events during which the star
formation rate of a galaxy rises from few solar masses per year,
typical of spirals such as the Milky-Way, to several hundred
and even thousands of solar masses per year, as in the local Ultra
Luminous Infrared Galaxies or their early Universe
counterparts. While stars form invariably out of
molecular hydrogen throughout the Universe, it is in the
densest and UV-shielded phase where the star formation initial
conditions, and the characteristic mass of the emergent young stars
are truly set. We show that cosmic ray energy
densities U_CR~10^3--10^4 times higher than those in the Galaxy will
be typical in the interstellar medium of extreme starbursts,
{\bf fundamentally altering the initial conditions for star formation
during their galaxy-wide star forming episodes.} Solving the coupled
chemical and thermal state equations for dense UV-shielded gas
reveals that the very elevated cosmic ray energy background in such
galaxies will raise the minimum temperature of this phase from
Tk(min)~10\,K, as in the Milky-Way, to Tk(min)~50--100\,K over
their entire starburst volume. These new initial conditions for
star formation, and the resulting large characteristic mass of young
stars of M_ch~3--10\,Msol, represent a new imperative for
high-density star formation in the Universe, with cosmic rays as the
key driving mechanism, operating efficiently in the high dust
extinction environments of extreme starbursts.
starbursts spectacular events during which the star
formation rate of a galaxy rises from few solar masses per year,
typical of spirals such as the Milky-Way, to several hundred
and even thousands of solar masses per year, as in the local Ultra
Luminous Infrared Galaxies or their early Universe
counterparts. While stars form invariably out of
molecular hydrogen throughout the Universe, it is in the
densest and UV-shielded phase where the star formation initial
conditions, and the characteristic mass of the emergent young stars
are truly set. We show that cosmic ray energy
densities U_CR~10^3--10^4 times higher than those in the Galaxy will
be typical in the interstellar medium of extreme starbursts,
{\bf fundamentally altering the initial conditions for star formation
during their galaxy-wide star forming episodes.} Solving the coupled
chemical and thermal state equations for dense UV-shielded gas
reveals that the very elevated cosmic ray energy background in such
galaxies will raise the minimum temperature of this phase from
Tk(min)~10\,K, as in the Milky-Way, to Tk(min)~50--100\,K over
their entire starburst volume. These new initial conditions for
star formation, and the resulting large characteristic mass of young
stars of M_ch~3--10\,Msol, represent a new imperative for
high-density star formation in the Universe, with cosmic rays as the
key driving mechanism, operating efficiently in the high dust
extinction environments of extreme starbursts.