Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21930206a&link_type=abstract
American Astronomical Society, AAS Meeting #219, #302.06
Astronomy and Astrophysics
Astronomy
Scientific paper
The WMAP maximum entropy method foreground emission map is recently used to identify diffuse free-free emission sources in the Galaxy (Rahman & Murray 2010). It has been found that 18 most luminous WMAP sources produce more than half the total ionizing luminosity of the Galaxy. We observed radio recombination lines (RRLs) toward the luminous WMAP source G49 with the GBT near 1.4 GHz. Hydrogen and carbon RRLs are detected toward the source (G49.75-0.45) but no helium line is detected. The upper limit on He line implies that (nHe+/nHe)/(nH+/nH) < 0.24, which puts severe constraint on the spectrum of the ionizing sources. The ionization requirement of the WMAP sources is more than half of that can be accounted from all the radio HII regions within these regions. Murray & Rahman (2010) propose that the additional ionization is due to massive clusters (M > 104 Msun) embedded in the WMAP sources. For a standard IMF, the bulk of the ionizing flux from the cluster is due to stars of mass 40 Msun. Thus these clusters should produce enough photons with energy ≥ 24.6 eV to fully ionize helium in the diffuse regions. Our observations rule out a standard HII region picture with such massive clusters ionizing these sources. We discuss possibilities to produce `softer' spectrum for the sources ionizing the diffuse regions, which include (a) modification of the spectrum due to the diffusion of photons through clumpy ISM and (b) hot low-mass evolved stars as the source of ionization.
Anish Roshi D.
Plunkett Adele
Rosero Viviana
Vaddi Sravani
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