PhD Thesis (PDF) - Department of Astronomy - University of Virginia

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Chapter 7 Summary and Future Directions 7.1 Summary We have used the Chandra X-ray Observatory to resolve the X-ray content of nearby early-type galaxies into low-mass X-ray binaries (LMXBs) and diffuse inter- stellar gas. In particular, we present detailed studies of the LMXBs and diffuse gas in four early-type galaxies and a study of the connection between LMXBs and globular clusters (GCs) in eleven early-type galaxies. We now summarize our results organized by scientific topic. 7.1.1 Luminosity Functions of Low-Mass X-Ray Binaries Chandra allows us to measure the luminosity functions (LFs) of LMXBs in early- type galaxies for the first time. These complement the LFs derived for LMXBs in the Milky Way and Andromeda galaxy, local galaxies that are still undergoing star- formation. Among LFs fit to early-type galaxies, Sarazin et al. (2001) first presented a broken power-law fit with a break at 3 × 10 38 ergs s −1 , near the Eddington limit of 276
a 1.4M⊙ neutron star (NS). They suggested that such a break might be universal. In our detailed studies of NGC 4365, NGC 4382, and NGC 4697 we detect 99, 58, and 158 sources respectively. From our results it is clear that these early-type galaxies are fit by power law LFs with little contribution above ∼ 10 39 ergs s −1 . The broken power-law LF does not seem to be universal. In NGC 4365 and NGC 4382, the best-fit LF is a cutoff power law whose cutoff luminosity is ≈ 0.9−3.1×10 39 ergs s −1 . Although a cutoff power law whose cutoff luminosity is about half that of the above galaxies is an acceptable fit for LMXBs in NGC 4697, a broken power law at ∼ 10 38 ergs s −1 is a better fit. There are two implications if the non-universality of a broken power-law proves to be true. First, the break luminosity cannot be used to estimate distances as suggested in Sarazin et al. (2001). Second, some galaxy-wide property must affect the shape of the LF. For example, the star formation history might affect the number and types of LMXBs formed. In these galaxies, we did not find a significant number of Ultra-Luminous X-ray sources (ULXs) with LX > 2 × 10 39 ergs s −1 . The small numbers of such sources seen in these galaxies are consistent with background AGNs. This appears to be a characteristic of LMXBs in early-type galaxies (Irwin et al. 2003); however, our observation of NGC 1600 may prove to be an exception to this rule. Of the 71 detected sources in this observation, 21 are ULX candidates. We expect that only 11±2 are unrelated foreground/background sources. NGC 1600 may have the largest number of ULX candidates in an early-type galaxy to date; however, cosmic variance in the number of background AGN cannot be ruled out at this time. We also found evidence for a large number of lower luminosity LMXBs that we were unable to resolve, which may support there being a large number of ULXs. 277
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LOW-MASS X-RAY BINARIES, DIFFUSE GA
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smaller GCs are more likely to cont
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GO2-3099X, GO3-4099X, AR3-4005X, GO
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her room (my apologies to her offic
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US Court expert from India), for al
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Table of contents Abstract ii Ackno
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5.2.1 Chandra X-ray Observatory . .
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List of Figures 1.1 Hubble Tuning F
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List of Tables 1.1 Galactic Low-Mas
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Chapter 1 General Introduction 1.1
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Fig. 1.1.— Hubble Tuning Fork, co
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2000). In most HMXBs, the accreted
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not get a complete picture of the L
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this, the result of dynamical inter
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is the Advanced CCD Imaging Spectro
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Chapter 2 Chandra Observations of L
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keV (Sarazin et al. 2000, 2001). Wi
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agreed with positions from the USNO
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24:00 22:00 7:20:00 18:00 16:00 18:
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Table 2.1. Discrete X-ray Sources i
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Table 2.1—Continued Source d Coun
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Table 2.2—Continued Source d Coun
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optical/IR positions of R.A. = 12 h
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log N(>L) 2.0 1.5 1.0 0.5 0.0 NGC 4
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luminosity function for luminositie
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H31 1.0 0.5 0.0 -0.5 -1.0 NGC 4365
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2.4.5 Variability We searched for v
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Number 10 8 6 4 2 NGC 4365 Optical
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LMXBs has an effective radius of 12
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component (“MEKAL”) was used fo
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Table 2.4. X-ray Spectral Fits of N
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Fig. 2.9.— Top panels: Cumulative
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we extended the spectrum down to 0.
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We also examined whether the unreso
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esolved sources in the galaxy. This
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temperature ∼0.3 keV. Matsumoto e
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log I X (counts/sec/arcmin 2 ) -1.0
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∼45% of the counts are resolved i
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Chapter 3 Chandra Observations of D
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noninteracting members (de Vaucoule
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used for spectroscopic analysis. We
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02:00.0 03:00.0 04:00.0 05:00.0 06:
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Table 3.1—Continued d a Count Rat
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We also attempted detections in mul
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sociated with extended X-ray or opt
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Fig. 3.3.— Histogram of the obser
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chip. The number of ULX candidates
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these luminosities among previously
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to 2-6 keV. Since the 6-10 keV rang
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absorption and varying power-law in
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counts occur within ∼ 4 ks. Sourc
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log I X (counts/sec/arcmin 2 ) 0.5
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tion), and βouter = 0.36 +0.01 −
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the east and northeast of NGC 1600.
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group, we assumed that they were at
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the group gas than we calculate fro
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04:55 -5:05:00 05 -5:05:10 15 -5:05
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for the spectrum: “Field” impli
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90% confidence level errors. Bracke
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we adopted the power-law model as o
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sources could be a non-trivial sour
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jection to include the emission fro
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Fig. 3.13.— Estimated gas and gra
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ackground source population cannot
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NGC 1600 that has a small spatial s
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(HMXBs). LMC X-4, an HMXB pulsar, h
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searched for the shortest time tn o
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with NGC 4697. Columns (1)-(4) list
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duration, ∆tflat, beginning at a
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the uncertainties quoted do not inc
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to persistent rate for short flares
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Chapter 5 Multi-Epoch Chandra X-ray
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the field, these different populati
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luminous (MB < −20) elliptical (E
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Although Chandra is known to encoun
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42:00.0 44:00.0 46:00.0 48:00.0 -5:
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Fig. 5.3.— Adaptively smoothed Ch
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1 × 10 −5 count s −1 arcsec
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Table 5.1—Continued Source R.A. D
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source list against which to regist
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ate from Observation 0784 alone (Pa
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Table 5.2. : Optical Properties of
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actually be an AGN. Sources 79, 80,
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two potential GC counterparts. We l
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Table 5.3—Continued X-ray Source
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Fig. 5.6.— Color (G475−Z850) -
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mass segregation of GCs with the sa
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Table 5.4. Fits to the Expected Num
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dependence are allowed to vary. Var
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NGC 4697 to convert the observed so
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Table 5.6—Continued Source LA LB
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Table 5.6—Continued Source LA LB
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Table 5.7. Combined Luminosities &
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Table 5.7—Continued Source Not De
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Fig. 5.8.— Cumulative luminosity
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LF, there are enough datapoints tha
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Fig. 5.10.— Cumulative luminosity
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Fig. 5.11.— Merged luminosities (
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Fig. 5.12.— X-ray color-color dia
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5.9 Spectral Analysis We performed
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some data loss, it allows for direc
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for 2 dof and the f-test indicates
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ple to LMXBs interior to that semi-
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est-fit (χ 2 = 56.4 for 65 dof) by
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5.10.1 Intraobservation Variability
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Fig. 5.14.— Binned lightcurve usi
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Table 5.10. Possible Flaring Source
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Fig. 5.16.— Cumulative lightcurve
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pairs of observations. In Figure 5.
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Table 5.11—Continued Source PL,AB
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Fig. 5.17.— Percentage of Analysi
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dofs and the number of combinations
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Table 5.12—Continued Source Obs.S
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of states as transient candidates.
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Long-Term Hardness Ratio Variabilit
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In the final observation, there wer
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limits). The 0.3-10 keV X-ray lumin
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Page 253 and 254: Table 6.2. Properties of Chandra Ob
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Page 271 and 272: 6.3.1 Luminosity and Mass Prior obs
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Page 281 and 282: Fig. 6.9.— Identical to Figure 6.
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Table B.2—Continued RA Dec. d GC
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investigations into improving the h
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C.4 Sivakoff Signature Soy Sauce Sk
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Blanton, E. L., Sarazin, C. L., & I
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Frogel, J. A., Persson, S. E., Matt
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Johnston, H. M. & Verbunt, F. 1996,
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Makishima, K. et al. 2000, ApJ, 535
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Porter, A. C. 1993, PASP, 105, 1250
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Verner, D. A., Ferland, G. J., Kori
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