X-Ray Spectral Study of the Extended Emission, ‘the Cap’, Located 11.6 kpc above the Disk of M82

Abstract

The extended X-ray emission from 'the Cap' region located 11 ′ (11.6 kpc) above the disk of the starburst galaxy M82 has been observed with Suzaku and XMM-Newton. Owing to the good energy resolution and the large collecting area of the XIS on Suzaku, combined with similar properties of the EPIC instrument on XMM-Newton, we have clearly detected K-shell emission lines from O VII, O VIII, Ne X, Mg XI, Mg XII and the Fe-L complex. Two optically-thin thermal plasma components are required to fit the observed X-ray spectra. We have determined the metal abundances of O, Ne, Mg, Si and Fe in this region for the first time. Their metal abundance ratios agree well with those of metal-poor stars and the model prediction of metals synthesized by type-II supernovae, but they are not consistent with the metallicities of type-Ia supernovae. This result is support for the idea that the origin of the metals in the Cap is type-II supernovae explosions occurring in the starburst regions in the M82 galaxy. We discuss the possible contribution from sputtered dust grains to the metals in the Cap. An emission line consistent with the C VI transition of n = 4 to 1 at 0.459 keV is marginally detected, although it is not statistically significant at the 99% confidence level; the presence of this line would suggest charge-exchange processes in the Cap.

A hydrodynamical study of outflows in starburst galaxies with different driving mechanisms

“…This requires that the outflow timescale 5 (∼20 Myr for M82, when the cap of the outflow is at 11.6 kpc, e.g. Devine & Bally 1999;Tsuru et al 2007) is substantially shorter than the duration of the starburst episode driving it (∼100s of Myr, e.g. McQuinn et al 2010;Hashimoto et al 2018;McQuinn et al 2018;Owen et al 2019b), a result supported by observations.…”

“…Galactic outflows are a multi-phase, multi-component media (see Ohyama et al 2002;Strickland et al 2002;Melioli et al 2013;Martín-Fernández et al 2016), comprised of cool semi-ionised clumps of gas (of temperature T c ∼ 10 2 − 10 4 K -see Strickland et al 1997;Lehnert et al 1999) entrained within a hot (T h ∼ 10 7 K McKeith et al 1995;Shopbell & Bland-Hawthorn 1998), low-density X-ray emitting fluid which may extend to altitudes of several kpc (Strickland et al 2000;Cecil et al 2002b;Cecil et al 2002a). Above this, there is a cap (in M82, this is observed at 11.6 kpcsee Devine & Bally 1999;Tsuru et al 2007), with the full outflow structure extending to tens of kpc (see Veilleux et al 2005;Bland-Hawthorn et al 2007;Bordoloi et al 2011;Martin et al 2013;Rubin et al 2014;Bordoloi et al 2016). In the hot fluid region of an outflow, cooling processes are presumably important and would have a significant impact on the dynamics and evolution of the flow (Heckman 2003).…”

Large-scale distributions of mid- and far-infrared emission from the center to the halo of M 82 revealed with AKARI

“…From the ∼50% signal reduction of the PAH emission at the Cap, a comparable amount of dust might have already been lost there by sputtering destruction. Thus the dust sputtering provides a potential impact on the metal abundances measured for the X-ray plasma in the Cap as pointed out by Tsuru et al (2007). The masses of Si and Fe in the hot plasma phase are 1.4 × 10 3 × f 0.5 M and 1.8 × 10 3 × f 0.5 M , respectively (Tsuru et al 2007).…”

Charge Transfer Reactions

“…Tsuru et al (2007) concluded from a deep observation of M 82 with Suzaku that charge exchange may make a significant contribution to the observed O-K emission in an X-ray bright area of its extended X-ray halo, where the ionized superwind from M 82 can be assumed to collide with cool ambient gas. Evidence for charge exchange processes was also reported by Ranalli et al (2008) for the central region of M 82, where one of two emission lines seen in XMM-Newton spectra which cannot be accounted for by thermal plasma emission could be explained by CXE from excited O VIII ions.…”