2004ApJ...610..183M

We present results from a 25 ks Chandra ACIS-S observation of galaxies NGC 4438 and NGC 4435 in the Virgo Cluster. X-ray emission in NGC 4438 is observed in a ∼700 pc nuclear region, a ∼2.3 kpc spherical bulge, and a network of filaments extending 4-10 kpc to the west and southwest of the galaxy. The X-ray emission in all three regions is highly correlated to similar features observed in Hα. Spectra of the filaments and bulge are well represented by a 0.4 keV MEKAL model with combined 0.3-2 keV intrinsic luminosity L_X=1.24x10⁴⁰ ergs/s, electron densities ∼0.02-0.04/cm3, cooling times of 400-700 Myr, and X-ray gas mass ≲3.7x10⁸ M_☉. In the nuclear region of NGC 4438 X-ray emission is seen from the nucleus and from two outflow bubbles extending 360 pc (730 pc) to the northwest (southeast) of the nucleus. The spectrum of the northwest outflow bubble plus nucleus is well fitted by an absorbed (n_H=1.9^+1.0_–0.4x10²¹/cm2) 0.58^+0.04_–0.10 keV MEKAL plasma model plus a heavily absorbed (n_H=2.9^+3.1_–2.0x10²²/cm2) Γ=2, power-law component. The electron density, cooling time, and X-ray gas mass in the northwest outflow are ∼0.5/cm3, 30 Myr, and 3.5x10⁶ M_☉, respectively. Weak X-ray emission is observed in the central region of NGC 4435 with the peak of the hard emission coincident with the galaxy's optical center, while the peak of the soft X-ray emission is displaced 316 pc to the northeast. The spectrum of NGC 4435 is well fitted by a nonthermal power law plus a thermal component from 0.2-0.3 keV diffuse interstellar medium gas. We argue that the X-ray properties of gas outside the nuclear region in NGC 4438 and NGC 4435 favor a high-velocity, off-center collision between these galaxies ∼100 Myr ago, while the nuclear X-ray-emitting outflow gas in NGC 4438 has been heated only recently (within ∼1-2 Myr) by shocks (v_s∼600 km/s) possibly powered by a central active galactic nucleus.