Testing the Universality of the Stellar IMF with Chandra and HST

摘要: The stellar initial mass function (IMF), which is often assumed to be universal across unresolved populations, has recently been suggested "bottom-heavy" for massive ellipticals. In these galaxies, the prevalence of gravity-sensitive absorption lines (e.g. Na I and Ca II) in their near-IR spectra implies an excess low-mass ($m = 8$ $M_\odot$) would lead a corresponding deficit neutron stars black holes, therefore X-ray binaries (LMXBs), per unit luminosity galaxies. Peacock et al. (2014) searched evidence this trend found that observed number LMXBs $K$-band ($N/L_K$) was nearly constant. We extend work using new archival Chandra Observatory (Chandra) Hubble Space Telescope (HST) observations seven ellipticals where $N/L_K$ expected largest compare data with variety IMF models test are consistent $N/L_K$. reproduce result (2014), strengthening constraint slope at $m >= $M_\odot$ must Kroupa-like IMF. construct model linear combination Milky Way-like broken power-law IMF, steep ($\alpha_1=$ $3.84$) 0.5 $M_\odot$, discuss its wider ramifications limitations.