We present the Chandra Multiwavelength Project (ChaMP) X-ray point source catalog with 66800 X-ray sources detected in 149 Chandra observations covering 610 deg super(2). The full ChaMP catalog ...sample is 7 times larger than the initial published ChaMP catalog. The exposure time of the fields in our sample ranges from 0.9 to 124 ks, corresponding to a deepest X-ray flux limit of f sub(0.5-8.0) = 9 x 10 super(-16) ergs cm super(-2) s super(-1). The ChaMP X-ray data have been uniformly reduced and analyzed with ChaMP-specific pipelines and then carefully validated by visual inspection. The ChaMP catalog includes X-ray photometric data in eight different energy bands as well as X-ray spectral hardness ratios and colors. To best utilize the ChaMP catalog, we also present the source reliability, detection probability, and positional uncertainty. To quantitatively assess those parameters, we performed extensive simulations. In particular, we present a set of empirical equations: the flux limit as a function of effective exposure time and the positional uncertainty as a function of source counts and off-axis angle. The false source detection rate is 61% of all detected ChaMP sources, while the detection probability is better than 695% for sources with counts 30 and off-axis angle < 5'. The typical positional offset between ChaMP X-ray source and their SDSS optical counterparts is 0.7" c 0.4", derived from 6900 matched sources.
We estimate the reddening and distance of the nearest starburst galaxy IC 10 using deep near-infrared JHK S photometry obtained with the Multi-Object InfraRed Camera and Spectrograph (MOIRCS) on the ...Subaru telescope. We estimate the foreground reddening toward IC 10 using the UBV photometry of IC 10 from the Local Group Survey, obtaining E(B - V) = 0.52 +/- 0.04 mag. We derive the total reddening including the internal reddening, E(B - V) = 0.98 +/- 0.06 mag, using the UBV photometry of early-type stars in IC 10 and comparing the JHK S photometry of red giant branch stars in IC 10 and the Small Magellanic Cloud. Using the Two Micron All Sky Survey point-source catalog of 20 Galactic globular clusters, we derive a relation between the metallicity Fe/HCG97 and the slope of the red giant branch in the K S - (J - K S) color-magnitude diagram. The mean metallicity of the red giant branch stars in IC 10 is estimated to be Fe/HCG97 = -1.08 +/- 0.28. The magnitude of the tip of the red giant branch (TRGB) of IC 10 in the K S band is measured to be K S,TRGB = 18.28 +/- 0.01. Based on the TRGB method, we estimate the distance modulus of IC 10 to be (m - M)0 = 24.27 +/- 0.03(random) +/- 0.18(systematic), corresponding to the distance of d = 715 +/- 10 +/- 60 kpc. This confirms that IC 10 is a member of the Local Group.
X-Ray Tail in NGC 7619 Kim, Dong-Woo; Kim, Eunhyeuk; Fabbiano, Giuseppina ...
The Astrophysical journal,
12/2008, Letnik:
688, Številka:
2
Journal Article
Recenzirano
We present new observational results of NGC 7619, an elliptical galaxy with a prominent X-ray tail and a dominant member of the Pegasus group. With Chandra and XMM-Newton observations, we confirm the ...presence of a long X-ray tail in the southwest direction; moreover, we identify for the first time a sharp discontinuity of the X-ray surface brightness in the opposite (northeast) side of the galaxy. The density, temperature, and pressure jump at the northeast discontinuity suggest a Mach number image1, corresponding to a galaxy velocity of image500 km s super(-1), relative to the surrounding hot gas. Spectral analysis of these data shows that the iron abundance of the hot gaseous medium is much higher (1-2 solar) near the center of NGC 7619 and in the tail extending from the core than in the surrounding regions (<=1/2 solar), indicating that the gas in the tail is originated from the galaxy. The possible origin of the head-tail structure is either ongoing ram pressure stripping or sloshing. The morphology of the structure is more in line with a ram pressure stripping phenomenon, while the position of NGC 7619 at the center of the Pegasus I group, and its dominance, would prefer sloshing.
We have carried out comparative study between direct
N-body technique and Fokker–Planck approach for the dynamical evolution of rotating stellar systems. Because of limitations of computing ...resources, we have restricted to relatively small
N (
∼
10
,
000
) systems compared to realistic star clusters. We found that these two different approaches generally give very similar results. Some minor differences are found to exist, but they can be understood because Fokker–Planck approach has to make some simplifying assumptions.
ABSTRACT
We have studied the dynamical evolution of rotating star clusters with mass spectrum using a Fokker–Planck code. As the simplest multimass model, we first investigated two‐component ...clusters. Rotation is found to accelerate the dynamical evolution through the transfer of angular momentum outward, as well as from high masses to low masses. However, the degree of acceleration depends sensitively on the assumed initial mass function since dynamical friction, which generates mass segregation, also tends to accelerate the evolution, and the combined effect of both is not linear or multiplicative. As long as dynamical friction dominates in the competition with angular momentum exchange, the heavy masses lose random energy and angular momentum and sink towards the centre, but their remaining angular momentum is sufficient to speed them up rotationally. This is gravo‐gyro instability. As a consequence, we find that the high‐mass stars in the central parts rotate faster than low‐mass stars. This leads to the suppression of mass segregation compared with the non‐rotating clusters. From the study of multicomponent models, we observe similar trends to the two‐component models in almost all aspects. The mass function changes less drastically for clusters with rotation. Unlike non‐rotating clusters, the mass function depends on R and z. Our models are the only ones that can predict mass function and other quantities to be compared with new observations.
We present a comprehensive study of the luminosity function and spatial structure of the globular cluster system of NGC 4472, the brightest galaxy in Virgo, based on deep wide-field Washington CT CCD ...images. With our large sample (about 2000) of bright globular clusters over a wide field, we make a definitive investigation of the spatial structures of the metal-poor and metal-rich cluster populations and find that they are systematically different: (1) the metal-rich clusters are more centrally concentrated than the metal-poor clusters and (2) the metal-rich clusters are elongated roughly along the major axis of the parent galaxy, while the metal-poor clusters are essentially spherically distributed. In general, the metal-rich clusters closely follow the underlying halo starlight of NGC 4472 in terms of spatial structure and metallicity, while the metal-poor clusters do not. Implications of the results obtained for the origin of the globular clusters in NGC 4472 are discussed. These results are consistent with many of the predictions of both the model of episodic in situ formation plus tidal stripping of globular clusters given by Forbes et al. and the Ashman and Zepf merger formation model, but each of the models also has some problems. (Author)
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