Measurement of the Mass and Stellar Population Distribution in M82 With the LBT

Abstract

We present a K−band spectroscopic study of the stellar and gas kinematics, mass distribution, and stellar populations of the archetypical starburst galaxy M82. Our results are based on a single spectrum at a position angle of 67.5 • through the K−band nucleus. We used the 12 CO stellar absorption band head at 2.29 µm (CO 2.29 ) to measure the rotation curve out to nearly 4 kpc radius on both the eastern and western sides of the galaxy. Our data show that the rotation curve is flat from 1 − 4 kpc. This stands in sharp contrast to some previous studies, which have interpreted HI and CO emission-line position-velocity diagrams as evidence for a declining rotation curve. The kinematics of the Brγ, H 2 , and He I emission lines are consistent with, although characterized by slightly higher velocities than, the stellar kinematics. We derived M82's mass distribution from our stellar kinematic measurements and estimate its total dynamical mass is ∼10 10 M ⊙ . We measured the equivalent width of CO 2.29 (W 2.29 ) as a function of distance from the center of the galaxy to investigate the spatial extent of the red supergiant (RSG) population. The variation in W 2.29 with radius clearly shows that RSGs dominate the light inside 500 pc radius. M82's superwind is likely launched from this region, where we estimate the enclosed mass is 2×10 9 M ⊙ .

Cosmic rays and magnetic fields in the core and halo of the starburst M82: implications for galactic wind physics

“…In the case of CRe, our models are primarily constrained by the resolved radio observations of the starburst core and radio halo. Thus, it is useful to report the electron cooling time as a function of the critical synchrotron emission frequency for a given magnetic field strength rather than as a direct function of the CRe energy (Rybicki & Lightman 1979;Ginzburg 1989). The characteristic emission frequency is related to CRe energy and B by: The width of the band indicates the effect of increasing/decreasing the free-free clumping parameter by a factor of √ 2 compared to the default value given in Table 2.…”

“…The left panel of Figure 10 shows the energy density in each component, for each model. In the right panel of Figure 10, we use the steady-state CR distribution and spectra to constrain the acceleration the CRs might impart to the gas of M82 by calculating ∇P/ρ and comparing it to the acceleration due to gravity (denoted as the black solid line) calculated by Greco et al (2012). The density profiles used are those constrained from our models.…”

“…The dashed lines denote the ISRF. The solid black line is the acceleration due gravity based on data fromGreco et al (2012).…”

Charge-exchange emission and cold clumps in multiphase galactic outflows

“…where R is the lengthscale of the CGM and M gal is the dynamical mass of the system, which is scaled here to that of M82 (see e.g. Strickland & Heckman 2009;Greco et al 2012). The kinetic energy loss of a clump due to ram pressure drag will lead to a decay of its orbit.…”

Planckview of the M 82 galaxy

“…Both analyses find a steeply rising curve, peaking at about 25 from the galaxy center and rapidly declining in a Keplerian fashion beyond 25 , likely indicating that M 82's extended disk mass is missing, which is very peculiar and exceptional for a disk galaxy. More recently, Greco et al (2012) have presented a K-band spectroscopic study and measured the M 82 rotation curve out to about 4 ( 4 kpc) on both the eastern and western sides of the galaxy. At variance with the previous studies, it has been found that the stellar rotation velocity is flat on scales of 1−4 kpc (with only a slight decline on the eastern side) with a value of 110−120 km s −1 out to 4 kpc, thus implying an M 82 total dynamical mass of ∼10 10 M .…”