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

Abstract

We present results from a 25 ksec CHANDRA ACIS-S observation of galaxies NGC4438 and NGC4435 in the Virgo Cluster. X-ray emission in NGC4438 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 W and SW of the galaxy. The X-ray emission in 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 MEKAL model 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-ray gas mass <~ 3.7x10^8 Msolar. In the nuclear region of NGC4438 X-ray emission is seen from the nucleus and from two outflow bubbles extending 360(730) pc to the NW(SE) of the nucleus. The spectrum of the NW outflow bubble plus nucleus is well fitted by an absorbed (n_H=1.9x10^{21} cm^{-2}) 0.58 keV MEKAL plasma model plus a heavily absorbed (n_H = 2.9 x10^{22} cm^{-2}) Gamma = 2, power law component. The electron density, cooling time, and X-ray gas mass in the NW outflow are ~0.5 cm^{-3}, 30 Myr and 3.5x10^6 Msolar. Weak X-ray emission is observed in the central region of NGC4435 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 NE. The spectrum of NGC 4435 is well fitted by a non-thermal power law plus a thermal component from 0.2-0.3 keV diffuse ISM gas. We argue that the X-ray properties of gas outside the nuclear region in NGC4438 and in NGC4435 favor a high velocity, off-center collision between these galaxies ~ 100 Myr ago; while the nuclear X-ray emitting outflow gas in NGC4438 has been heated only recently (within ~ 1-2 Myr) by shocks (v_s ~ 600 kms^{-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,