Xinyu Dai

X-RAY MICROLENSING IN RXJ1131-1231 AND HE1104-1805

We present results from a monitoring campaign performed with the Chandra X-ray Observatory of the gravitationally lensed quasars RX J1131–1231 and HE 1104–1805. We detect significant X-ray variability in all images of both quasars. The flux variability detected in image A of RX J1131–1231 is of particular interest because of its high amplitude (a factor of ~ 20). We interpret it as arising from microlensing since the variability is uncorrelated with that of the other images and the X-ray flux ratios show larger changes than the optical as we would expect for microlensing of the more compact X-ray emission regions. The differences between the X-ray and optical flux ratios of HE 1104–1805 are less dramatic, but there is no significant soft X-ray or dust absorption, implying the presence of X-ray microlensing in this system as well. Combining the X-ray data with the optical light curves we find that the X-ray emitting region of HE 1104–1805 is compact with a half-light radius 6rg , where the gravitational radius is r g = 3.6 × 1014 cm, thus placing significant constraints on AGN corona models. We also find that the microlensing in HE 1104–1805 favors mass models for the lens galaxy that are dominated by dark matter. Finally, we better characterize the massive foreground cluster near RX J1131–1231, set limits on other sources of extended X-ray emission, and limit the fluxes of any central odd images to be 30-50 (3σ) times fainter than the observed images.

ON THE BARYON FRACTIONS IN CLUSTERS AND GROUPS OF GALAXIES

We present the baryon fractions of 2MASS groups and clusters as a function of cluster richness using total and gas masses measured from stacked ROSAT X-ray data and stellar masses estimated from the infrared galaxy catalogs. We detect X-ray emission even in the outskirts of clusters, beyond r 200 for richness classes with X-ray temperatures above 1?keV. This enables us to more accurately determine the total gas mass in these groups and clusters. We find that the optically selected groups and clusters have flatter temperature profiles and higher stellar-to-gas mass ratios than the individually studied, X-ray bright clusters. We also find that the stellar mass in poor groups with temperatures below 1?keV is comparable to the gas mass in these systems. Combining these results with individual measurements for clusters, groups, and galaxies from the literature, we find a break in the baryon fraction at ~1?keV. Above this temperature, the baryon fraction scales with temperature as fb T 0.20?0.03. We see significantly smaller baryon fractions below this temperature and the baryon fraction of poor groups joins smoothly onto that of systems with still shallower potential wells such as normal and dwarf galaxies where the baryon fraction scales with the inferred velocity dispersion as fb ?1.6. The small scatter in the baryon fraction at any given potential well depth favors a universal baryon loss mechanism and a preheating model for the baryon loss. The scatter is, however, larger for less massive systems. Finally, we note that although the broken power-law relation can be inferred from data points in the literature alone, the consistency between the baryon fractions for poor groups and massive galaxies inspires us to fit the two categories of objects (galaxies and clusters) with one relation.

2MASS Reveals a Large Intrinsic Fraction of BALQSOs

The intrinsic fraction of broad absorption line quasars (BALQSOs) is important in constraining geometric and evolutionary models of quasars. We present the fraction of BALQSOs in 2MASS-detected quasars within the SDSS DR3 sample in the redshift range of 1.7 ≤ z ≤ 4.38. The fraction of BALQSOs is 40.4+ 3.4−3.3% in the 2MASS 99% database Ks-band completeness sample, and 38.5+ 1.7−1.7% in the larger 2MASS sample extending below the completeness limit. These fractions are significantly higher than the 26% reported in the optical bands for the same parent sample. We also present the fraction of BALQSOs as functions of apparent magnitudes, absolute magnitudes, and redshift in the 2MASS and SDSS bands. The 2MASS fractions are consistently higher than the SDSS fractions in every comparison, and the BALQSO fractions steadily increase with wavelength from the SDSS u to the 2MASS Ks bands. Furthermore, the i − Ks color distributions of BALQSOs and non-BALQSOs indicate that BALQSOs are redder than non-BALQSOs, with a K-S test probability of 2 × 10−12. These results are consistent with the spectral difference between BALQSOs and non-BALQSOs including both the absorption troughs and dust extinction in BALQSOs, which leads to significant selection biases against BALQSOs in the optical bands. Using a simple simulation incorporating the luminosity function of quasars and the amount of obscuration for BALQSOs, we simultaneously fit the BALQSO fractions in the SDSS and 2MASS bands. We obtain a true BALQSO fraction of (43 ± 2)% for luminous quasars (MKs −30.1 mag).

X-Ray and Optical Microlensing in the Lensed Quasar PG 1115+080

We analyzed the microlensing of the X-ray and optical emission of the lensed quasar PG 1115+080. We find that the effective radius of the X-ray emission is -->1.3+ 1.1−0.5 dex smaller than that of the optical emission. Viewed as a thin disk observed at inclination angle i, the optical accretion disk has a scale length, defined by the point where the disk temperature matches the rest-frame energy of the monitoring band ( -->kT = hc/λrest with -->λrest = 0.3 μm), of log{(rs, opt/cm)[cos(i)/0.5]½} = 16.6 ± 0.4

The Structure of the X-Ray and Optical Emitting Regions of the Lensed Quasar Q 2237+0305

log b\{ (rs,opt/cm) [cos (i)/0.5]1/2b\} = 16.6 ± 0.4

XMM-Newton Detects a Hot Gaseous Halo in the Fastest Rotating Spiral Galaxy UGC?12591

-->. The X-ray emission region (1.4-21.8 keV in the rest frame) has an effective half-light radius of -->log (r1/2,X/cm) = 15.6+ 0.6−0.9. Given an estimated black hole mass of -->1.2 × 109 M☉, corresponding to a gravitational radius of -->log (rg/cm) = 14.3, the X-ray emission is generated near the inner edge of the disk, while the optical emission comes from scales slightly larger than those expected for an Eddington-limited thin disk. We find a weak trend supporting models with low stellar mass fractions near the lensed images, in mild contradiction to inferences from the stellar velocity dispersion and the time delays.

Further Evidence That Quasar X-Ray Emitting Regions Are Compact: X-Ray And Optical Microlensing In The Lensed Quasar Q J0158-4325

We use gravitational microlensing to determine the size of the X-ray and optical emission regions of the quadruple lens system Q 2237+0305. The optical half-light radius, log(R 1/2, V /cm) = 16.41 ? 0.18 (at ?rest = 2018??), is significantly larger than the observed soft, (1.1-3.5 keV in the rest frame), and hard, (3.5-21.5 keV in the rest frame), band X-ray emission. There is weak evidence that the hard component is more compact than the soft, with . This wavelength-dependent structure agrees with recent results found in other lens systems using microlensing techniques, and favors geometries in which the corona is concentrated near the inner edge of the accretion disk. While the available measurements are limited, the size of the X-ray emission region appears to be roughly proportional to the mass of the central black hole.

Chandra Observations of QSO 2237+0305

We present our XMM-Newton observation of the fastest rotating spiral galaxy UGC?12591. We detect hot gas halo emission out to 80?kpc from the galaxy center, and constrain the halo gas mass to be smaller than 4.5 ? 1011 M ?. We also measure the temperature of the hot gas as T = 0.64 ? 0.03?keV. Combining our x-ray constraints and the near-infrared and radio measurements in the literature, we find a baryon mass fraction of 0.03-0.05 in UGC?12591, suggesting a missing baryon mass of 70% compared with the cosmological mean value. Combined with another recent measurement in NGC?1961, the result strongly argues that the majority of missing baryons in spiral galaxies do not reside in their hot halos. We also find that UGC?12591 lies significantly below the baryonic Tully-Fisher relationship. Finally, we find that the baryon fractions of massive spiral galaxies are similar to those of galaxy groups with similar masses, indicating that the baryon loss is ultimately controlled by the gravitational potential well. The cooling radius of this gas halo is small, similar to NGC?1961, which argues that the majority of the stellar mass of this galaxy is not assembled as a result of cooling of this gas halo.

ON ABSORPTION BY CIRCUMSTELLAR DUST, WITH THE PROGENITOR OF SN 2012aw AS A CASE STUDY

We present four new seasons of optical monitoring data and six epochs of X-ray photometry for the doubly imaged lensed quasar Q J0158-4325. The high-amplitude, short-period microlensing variability for which this system is known has historically precluded a time delay measurement by conventional methods. We attempt to circumvent this limitation by the application of a Monte Carlo microlensing analysis technique, but we are only able to prove that the delay must have the expected sign (image A leads image B). Despite our failure to robustly measure the time delay, we successfully model the microlensing at optical and X-ray wavelengths to find a half-light radius for soft X-ray emission log(r(1/2), (X), (soft)/cm) = 14.3(-0.5)(+0.4), an upper limit on the half-light radius for hard X-ray emission log(r(1/2), (X), (hard)/cm) <= 14.6, and a refined estimate of the inclination-corrected scale radius of the optical R-band (rest frame 3100 angstrom) continuum emission region of log(r(s)/cm) = 15.6 +/- 0.3.

A STUDY OF QUASAR EVOLUTION IN THE X-RAY BAND WITH THE AID OF GRAVITATIONAL LENSING

We present the observations of the gravitationally lensed system QSO 2237+0305 (Einstein Cross) performed with the Advanced CCD Imaging Spectrometer on board the Chandra X-Ray Observatory on 2000 September 6 and on 2001 December 8 for 30.3 and 9.5 ks, respectively. Imaging analysis resolves the four X-ray images of the Einstein Cross. A possible fifth image is detected; however, the poor signal-to-noise ratio of this image combined with contamination produced by a nearby brighter image make this detection less certain. We investigate possible origins of the additional image. Fits to the combined spectrum of all images of the Einstein Cross assuming a simple power law with Galactic and intervening absorption at the lensing galaxy yields a photon index of 1.90 consistent with the range of Γ measured for large samples of radio-quiet quasars. For the first Chandra observation of the Einstein Cross this spectral model yields a 0.4-8.0 keV X-ray flux of 4.6 × 10-13 ergs cm-2 s-1 and a 0.4-8.0 keV lensed luminosity of 1.0 × 1046 ergs s-1. The source exhibits variability over both long and short timescales. The X-ray flux has dropped by 20% between the two observations, and the Kolmogorov-Smirnov test showed that image A is variable at the 97% confidence level within the first observation. Furthermore, a possible time delay of 2.7 hr between images A and B with image A leading is detected in the first Chandra observation. The X-ray flux ratios of the images are consistent with the optical flux ratios that are affected by microlensing, suggesting that the X-ray emission is also microlensed. A comparison between our measured column densities and those inferred from extinction measurements suggests a higher dust-to-gas ratio in the lensing galaxy than the average value of our Galaxy. Finally, we report the detection at the 99.99% confidence level of a broad emission feature near the redshifted energy of the Fe Kα line in only the spectrum of image A. The rest frame energy, width, and equivalent width of this feature are Eline = 5.7 keV, σline = 0.87 keV, and EW = 1200 eV, respectively.