1998ApJ...499..650I

Query : 1998ApJ...499..650I

1998ApJ...499..650I - Astrophys. J., 499, 650-669 (1998/June-1)

ROSAT X-ray colors and emission mechanisms in early-type galaxies.

IRWIN J.A. and SARAZIN C.L.

Abstract (from CDS):

The X-ray colors and X-ray-to-optical luminosity ratios (LX/LB) of 61 early-type galaxies observed with the ROSAT PSPC are determined. The colors indicate that the X-ray spectral properties of galaxies vary as a function of LX/LB. The brightest X-ray galaxies have colors that are consistent with thermal emission from hot gas with roughly the same metallicity of 50% solar. The spatial variation of the colors indicates that the gas temperature in these galaxies increases radially. Galaxies with medium LX/LB also have spectral properties consistent with emission from hot gas. If a simple one-component thermal model is assumed to describe the 0.1-2.0 keV X-ray emission in these galaxies, then one possible explanation for the progressive decrease in LX/LB among galaxies of this class could be the progressive decrease in metal abundance of the X-ray-emitting gas contained by the galaxies. However, stellar X-ray emission may become a complicating factor for the fainter galaxies in this medium-LX/LB class.

Galaxies with the lowest LX/LB values appear to be lacking a hot interstellar component. Their X-ray colors are consistent with those derived from the bulges of the spiral galaxies M31 and NGC 1291. In M31, the X-ray emission is resolved into discrete sources and is apparently due primarily to low-mass X-ray binaries (LMXBs). We therefore suggest that the bulk of the X-ray emission in the faintest elliptical galaxies is also due to LMXBs. Previously, the X-ray spectra of X-ray-faint galaxies had been found to be described by a hard component, which was attributed to LMXB emission, and a very soft component of unknown origin. We show that the very soft component also likely results from LMXBs, as a very soft component is seen in the X-ray spectra of the nearby LMXB Her X-1 and LMXBs in the bulge of M31. If the X-ray emission in X-ray-faint galaxies is primarily from stellar sources, then a range in LX/LB among these galaxies suggests that the stellar X-ray luminosity does not scale with optical luminosity, at least for galaxies of low optical luminosities. This could be the result of a decrease in the proportion of LMXBs with decreasing optical luminosity and/or the effects of fluctuations in the small number of LMXBs expected.


Abstract Copyright: ∼

Journal keyword(s): Galaxies: Abundances - Galaxies: Elliptical and Lenticular, cD - Galaxies: Halos - Galaxies: ISM - X-Rays: Galaxies - X-Rays: ISM

Simbad objects: 71

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Number of rows : 71
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2026 		#notes
1 M 110 GiG 00 40 22.0572349992 +41 41 07.507220136   8.92 8.07     ~ 1370 1
2 M 32 GiG 00 42 41.82480 +40 51 54.6120 9.51 9.03 8.08     ~ 2236 2
3 M 31 AGN 00 42 44.330 +41 16 07.50 4.86 4.36 3.44     ~ 13622 1
4 NGC 507 rG 01 23 39.950 +33 15 22.22   13.0       ~ 459 1
5 NGC 524 GiP 01 24 47.7429545736 +09 32 20.089023900   11.5       ~ 494 1
6 NGC 533 rG 01 25 31.4074984248 +01 45 33.236656812   13.1 14.11     ~ 237 1
7 NGC 596 GiG 01 32 51.9046959816 -07 01 53.646821220   11.5       ~ 247 0
8 BAX 028.2522-13.7387 ClG 01 53 00.40 -13 44 18.0           ~ 389 0
9 NGC 720 Sy1 01 53 00.523 -13 44 19.25   12.4   10.36   ~ 536 0
10 NAME Magellanic Clouds GrG 03 00 -71.0           ~ 7988 0
11 NGC 1199 GiP 03 03 38.4220343160 -15 36 48.461862600   13.99 12.97 12.31 11.59 ~ 189 1
12 NGC 1269 EmG 03 17 18.5785534752 -41 06 28.628735184 9.85 9.83 8.81 8.72   ~ 445 1
13 NGC 1316 rG 03 22 41.789 -37 12 29.52 9.81 9.15 8.53 7.66   ~ 1491 1
14 NGC 1332 GiP 03 26 17.321 -21 20 07.33   11.45   9.84   ~ 378 0
15 NGC 1340 GiG 03 28 19.6251763296 -31 04 05.435465520   11.20 10.32 9.70   ~ 222 1
16 NGC 1380 Sy2 03 36 27.590 -34 58 34.68 11.32 10.94 9.93 9.37   ~ 460 1
17 NGC 1381 GiP 03 36 31.6592184144 -35 17 42.739221912 12.90 12.47 11.50 11.02   ~ 269 1
18 NGC 1387 Sy2 03 36 57.0337458600 -35 30 23.675934060 12.18 11.75 10.69 10.16   ~ 290 1
19 NGC 1399 rG 03 38 29.083 -35 27 02.67 11.05 9.74 9.59 8.12   ~ 1636 1
20 NGC 1395 SyG 03 38 29.789 -23 01 39.69   10.71   8.99   ~ 289 0
21 NGC 1404 rG 03 38 51.917 -35 35 39.81 11.53 10.69 10.00 9.03   ~ 787 1
22 NGC 1400 EmG 03 39 30.851 -18 41 17.25 12.48 12.01 10.96 10.45   ~ 309 1
23 NGC 1407 rG 03 40 11.904 -18 34 49.36   10.64 9.67 9.13   ~ 613 2
24 NGC 1427 GiG 03 42 19.4455150392 -35 23 33.169251120   11.89   10.44   ~ 298 0
25 NGC 1549 GiP 04 15 45.223 -55 35 32.50 11.22 10.48 9.79 9.08   ~ 255 1
26 NGC 1553 GiP 04 16 10.4697802536 -55 46 48.072797400 10.76 10.10 9.40 8.74   ~ 395 2
27 NGC 2300 AG? 07 32 20.486 +85 42 31.90   12.2       ~ 346 0
28 NGC 3091 BiC 10 00 14.125 -19 38 11.32   12.04 10.61 10.56 9.25 ~ 192 0
29 NGC 3115 GiG 10 05 13.9270507008 -07 43 06.982712292   11   9.37   ~ 1067 2
30 NGC 3193 GiP 10 18 24.884 +21 53 38.32 12.29 11.83 10.88 12.19   ~ 301 1
31 NGC 3585 GiG 11 13 17.109 -26 45 17.96   10.64   9.22   ~ 304 0
32 NGC 3607 Sy2 11 16 54.65687 +18 03 06.5120   13.84 12.76     ~ 490 1
33 NGC 3608 LIN 11 16 58.967 +18 08 54.71   11.7       ~ 527 0
34 NGC 3610 GiG 11 18 25.2827189856 +58 47 10.433735988   11.4       ~ 327 0
35 NGC 3640 GiG 11 21 06.852 +03 14 05.15 11.89 11.36 10.44     ~ 291 3
36 NGC 3665 GiG 11 24 43.630 +38 45 46.05 13.71 13.26 11.62     ~ 364 1
37 NGC 4125 GiP 12 08 06.017 +65 10 26.88 11.14 10.65 9.72     ~ 448 2
38 NGC 4261 LIN 12 19 23.2160630 +05 49 29.700024   13.92 12.87     ~ 1290 0
39 NGC 4291 GiG 12 20 17.699 +75 22 15.47   17.0       ~ 321 1
40 NGC 4365 GiG 12 24 28.228 +07 19 03.07   11.5       ~ 871 0
41 NGC 4371 GiG 12 24 55.4333579760 +11 42 15.144247584 12.35 11.79 10.81     ~ 345 1
42 M 84 Sy2 12 25 03.74333 +12 53 13.1393 12.67 12.09 10.49     ~ 1841 2
43 M 85 GiP 12 25 24.053 +18 11 27.89   10.2       ~ 678 0
44 M 86 GiG 12 26 11.814 +12 56 45.49 10.32 9.83 8.90   7.50 ~ 1126 1
45 M 49 Sy2 12 29 46.8 +08 00 01   13.21 12.17     ~ 2174 2
46 NGC 4474 GiG 12 29 53.5396737408 +14 04 06.881708604   12.6       ~ 278 0
47 NGC 4477 Sy2 12 30 02.1955766304 +13 38 11.543715888 11.98 11.38 10.42     ~ 419 2
48 M 87 AGN 12 30 49.42338414 +12 23 28.0436859 10.16 9.59 8.63   7.49 ~ 7815 3
49 NGC 4526 GiC 12 34 03.02853 +07 41 56.9040   10.6       ~ 707 0
50 NGC 4550 GiP 12 35 30.5913588048 +12 13 14.921166792 12.97 12.56 11.68     ~ 558 1
51 M 89 Sy2 12 35 39.80733343 +12 33 22.8308657 11.29 10.73 9.75     ~ 1037 2
52 NGC 4638 GiP 12 42 47.4239240016 +11 26 32.970950556   12.2 11.23     ~ 295 1
53 NAME NGC 4636 Group GrG 12 42 49.5 +02 41 08           ~ 570 0
54 NGC 4636 LIN 12 42 49.8333280080 +02 41 15.951929028   12.62 11.84     ~ 1156 1
55 M 60 GiC 12 43 39.9708251934 +11 33 09.688174067   10.3       ~ 1395 1
56 NGC 4697 GiG 12 48 35.8981498824 -05 48 02.482374564   10.97   9.83   ~ 895 0
57 NGC 4696 rG 12 48 49.2724775784 -41 18 39.304053252   11.21   10.7   ~ 510 3
58 NGC 4880 GiG 13 00 10.5729961968 +12 28 59.886650244   13.3       ~ 91 0
59 NGC 5044 BiC 13 15 23.9607836592 -16 23 07.547751744   11.9   10.74   ~ 531 0
60 NGC 5102 EmG 13 21 57.6100832352 -36 37 48.395156160   9.74 9.65 8.47 10.2 ~ 389 1
61 IC 4296 rG 13 36 39.03253319 -33 57 57.0730368   11.52 12.99 10.00 10.79 ~ 520 2
62 IC 4329 BiC 13 49 05.314 -30 17 45.20   11.96 11.54 10.31   ~ 192 2
63 NGC 5322 SyG 13 49 15.24 +60 11 25.8   11.3       ~ 432 2
64 NGC 5353 rG 13 53 26.7104646981 +40 16 59.200050598   11.8   10.57   ~ 309 1
65 NGC 5846 rG 15 06 29.253 +01 36 20.29   11.9   9.74   ~ 891 2
66 M 102 SyG 15 06 29.561 +55 45 47.91 11.12 10.74 9.89     ~ 578 2
67 V* HZ Her LXB 16 57 49.8110126616 +35 20 32.486555472 11.90 14.89 13.63 13.88   B3/6ep 2172 0
68 ESO 185-54 BiC 20 03 27.0429278400 -55 56 49.742007324   12.11   10.57   ~ 62 0
69 NGC 7144 GiG 21 52 42.4890937656 -48 15 13.729791132   11.87 10.71 10.39   ~ 156 1
70 NGC 7619 GiG 23 20 14.524 +08 12 22.63   12.7       ~ 472 0
71 NGC 7626 rG 23 20 42.524 +08 13 01.43   12.8       ~ 438 1

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