ChandraObservations of NGC 4438: An Environmentally Damaged Galaxy in the Virgo Cluster

We present results from a 25 ksec CHANDRA ACIS-S observation of galaxiesNGC4438 and NGC4435 in the Virgo Cluster. X-ray emission in NGC4438 is observedin a ~700 pc nuclear region, a 2.3 kpc spherical bulge, and a network offilaments extending 4-10 kpc to the W and SW of the galaxy. The X-ray emissionin all 3 regions is highly correlated to similar features observed in Halpha.Spectra of the filaments and bulge are well represented by a 0.4 keV MEKALmodel with combined 0.3-2 keV intrinsic luminosity of 1.24x10^{40}erg/s,electron densities ~ 0.02-0.04 cm^{-3}, cooling times of 400-700 Myr and X-raygas mass <~ 3.7x10^8 Msolar. In the nuclear region of NGC4438 X-ray emission isseen from the nucleus and from two outflow bubbles extending 360(730) pc to theNW(SE) of the nucleus. The spectrum of the NW outflow bubble plus nucleus iswell fitted by an absorbed (n_H=1.9x10^{21} cm^{-2}) 0.58 keV MEKAL plasmamodel plus a heavily absorbed (n_H = 2.9 x10^{22} cm^{-2}) Gamma = 2, power lawcomponent. The electron density, cooling time, and X-ray gas mass in the NWoutflow are ~0.5 cm^{-3}, 30 Myr and 3.5x10^6 Msolar. Weak X-ray emission isobserved in the central region of NGC4435 with the peak of the hard emissioncoincident with the galaxy's optical center; while the peak of the soft X-rayemission is displaced 316 pc to the NE. The spectrum of NGC 4435 is well fittedby a non-thermal power law plus a thermal component from 0.2-0.3 keV diffuseISM gas. We argue that the X-ray properties of gas outside the nuclear regionin NGC4438 and in NGC4435 favor a high velocity, off-center collision betweenthese galaxies ~ 100 Myr ago; while the nuclear X-ray emitting outflow gas inNGC4438 has been heated only recently (within ~ 1-2 Myr) by shocks (v_s ~ 600kms^{-1}) possibly powered by a central AGN.Comment: 40 pages, 7 figures; minor changes to conform to published version, improved spectral fits to NGC 4435, improved figures 3,5; new figures 6b,