Browsing by Author "Miller, ED"
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Item OVI in elliptical galaxies: Indicators of cooling flows(IOP Publishing, 2005-12-20) Bregman, JN; Miller, ED; Athey, AE; Irwin, JA; University of Michigan System; University of Michigan; Massachusetts Institute of Technology (MIT); Carnegie Institution for Science; University of Alabama TuscaloosaEarly-type galaxies often contain a hot X-ray-emitting interstellar medium [(3-8) x 10(6) K] with an apparent radiative cooling time much less than a Hubble time. If unopposed by a heating mechanism, the gas will radiatively cool to temperatures less than or similar to 10(4) K at a rate proportional to L-X/T-X, typically 0.03-1 M-circle dot yr(-1). We can test whether gas is cooling through the 3 x 10(5) K range by observing the O VI doublet, whose luminosity is proportional to the cooling rate. Here we report on a study of an unbiased sample of 24 galaxies, obtaining Far Ultraviolet Spectroscopic Explorer spectra to complement the X-ray data of ROSAT and Chandra. The O VI line emission was detected in about 40% of the galaxies and at a luminosity level similar to the prediction from the cooling flow model. There is a correlation between. M-O (VI) and M-X, although there is significant dispersion about the relationship, where the O VI is brighter or dimmer than expected by a factor of 3 or more. If the cooling flow picture is to be retained, then this dispersion requires that cooling flows be time-dependent, as might occur by the activity of an AGN. However, of detected objects, those with the highest or lowest values of. M-O (VI)/M-X are not systematically hot or cool, as one might predict from AGN heating.Item OVI observations of galaxy clusters: Evidence for modest cooling flows(University of Chicago Press, 2006-05-10) Bregman, JN; Fabian, AC; Miller, ED; Irwin, JA; University of Michigan System; University of Michigan; University of Cambridge; Massachusetts Institute of Technology (MIT); University of Alabama TuscaloosaA prediction of the galaxy-cluster cooling flow model is that as gas cools from the ambient cluster temperature, emission lines are produced in gas at subsequently decreasing temperatures. Gas passing through 10(5.5) K emits in the lines of O (VI) lambda lambda 1032, 1035, and here we report a FUSE study of these lines in three cooling flow clusters, Abell 426, Abell 1795, and AWM 7. No emission was detected from AWM 7, but O vi is detected from the centers of Abell 426 and Abell 1795, and possibly to the south of the center in Abell 1795, where X-ray and optical emission line filaments lie. In Abell 426 these line luminosities imply a cooling rate of 32 +/- 6M(circle dot) yr(-1) within the central r = 6.2 kpc region, while for Abell 1795 the central cooling rate is 26 +/- 7 M-circle dot yr(-1) (within r = 22 kpc), and about 42 +/- 9 M-circle dot yr(-1) including the southern pointing. Including other studies, three of six clusters have O vi emission, and they also have star formation as well as emission lines from 104 K gas. These observations are generally consistent with the cooling flow model, but at a rate closer to 30 M-circle dot yr(-1) than to the originally suggested values of 10(2)-10(3) M-circle dot yr(1).Item OVI observations of galaxy clusters: Evidence for modest cooling flows(University of Chicago Press, 2006-01-01) Bregman, JN; Fabian, AC; Miller, ED; Irwin, JA; University of Michigan System; University of Michigan; University of Cambridge; Massachusetts Institute of Technology (MIT); University of Alabama TuscaloosaA prediction of the galaxy-cluster cooling flow model is that as gas cools from the ambient cluster temperature, emission lines are produced in gas at subsequently decreasing temperatures. Gas passing through 10(5.5) K emits in the lines of O (VI) lambda lambda 1032, 1035, and here we report a FUSE study of these lines in three cooling flow clusters, Abell 426, Abell 1795, and AWM 7. No emission was detected from AWM 7, but O vi is detected from the centers of Abell 426 and Abell 1795, and possibly to the south of the center in Abell 1795, where X-ray and optical emission line filaments lie. In Abell 426 these line luminosities imply a cooling rate of 32 +/- 6M(circle dot) yr(-1) within the central r = 6.2 kpc region, while for Abell 1795 the central cooling rate is 26 +/- 7 M-circle dot yr(-1) (within r = 22 kpc), and about 42 +/- 9 M-circle dot yr(-1) including the southern pointing. Including other studies, three of six clusters have O vi emission, and they also have star formation as well as emission lines from 104 K gas. These observations are generally consistent with the cooling flow model, but at a rate closer to 30 M-circle dot yr(-1) than to the originally suggested values of 10(2)-10(3) M-circle dot yr(1).Item The size of the cooling region of hot gas in two elliptical galaxies(University of Chicago Press, 2006-05-10) Bregman, JN; Otte, B; Miller, ED; Irwin, JA; University of Michigan System; University of Michigan; University of Alabama TuscaloosaSome early-type galaxies show O VI emission, a tracer of gas at 105: 5 K, and a predicted product of gas cooling from the X-ray-emitting temperatures. We studied the spatial extent and velocity structure of this cooling gas by obtaining spectra of the O VI doublet in NGC 4636 and NGC 5846 with the Far Ultraviolet Spectroscopic Explorer. For NGC 4636, the central LWRS pointing shows that the O VI lines are double-peaked and symmetrical about the systemic velocity of the galaxy, with a separation of 210 km s(-1). An LWRS observation 3000 from the center failed to show additional O vi emission. For NGC 5846, three spectra were obtained with 400; 2000 apertures (MDRS) at the center and 400 to the east and west of the center. The O VI line flux seen in the previous LWRS is contained in the sum of the smaller apertures, with most of the flux in a single noncentral MDRS aperture, suggesting a size for the emission <= 0.5 kpc; the emission consists of a blue and red peak. For both galaxies, the O vi velocity structure is similar to that of the optical [N II] emission and is consistent with rotation. The compactness and velocity structure of the O VI emission rules out cooling flow models with broadly distributed mass dropout but is consistent with cooling flow models in which the cooling occurs primarily in the central region. The 104 K gas may be the end state of the O vi emitting gas.