http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Cho, Hyejeon,Blakeslee, John P.,Chies-Santos, Ana L.,Jee, M. James,Jensen, Joseph B.,Peng, Eric W.,Lee, Young-Wook American Astronomical Society 2016 The Astrophysical journal Vol.822 No.2
<P>We present new Hubble Space Telescope (HST) optical and near-infrared (NIR) photometry of the rich globular cluster (GC) system NGC 4874, the cD galaxy in the core of the Coma cluster (Abell 1656). NGC 4874 was observed with the HST Advanced Camera for Surveys in the F475W (g(475)) and F814W (I-814) passbands and with the Wide Field Camera. 3 IR Channel in F160W (H-160). The GCs in this field exhibit a bimodal optical color distribution with more than half of the GCs falling on the red side at g(475)-I-814 > 1. Bimodality is also present, though less conspicuously, in the optical-NIR I-814-H-160 color. Consistent with past work, we find evidence for nonlinearity in the g(475)-I-814 versus I-814-H-160 color-color relation. Our results thus underscore the need for understanding the detailed form of the color-metallicity relations in interpreting observational data on GC bimodality. We also find a very strong color-magnitude trend, or 'blue tilt,' for the blue component of the optical color distribution of the NGC 4874 GC system. A similarly strong trend is present for the overall mean I-814-H-160 color as a function of magnitude; for M-814 < -10 mag, these trends imply a steep mass-metallicity scaling with Z proportional to M-GC(1.4 +/- 0.4), but the scaling is not a simple power law and becomes much weaker at lower masses. As in other similar systems, the spatial distribution of the blue GCs is more extended than that of the red GCs, partly because of blue GCs associated with surrounding cluster galaxies. In addition, the center of the GC system is displaced by 4 +/- 1 kpc toward the southwest from the luminosity center of NGC 4874, in the direction of NGC 4872. Finally, we remark on a dwarf elliptical galaxy with a noticeably asymmetrical GC distribution. Interestingly, this dwarf has a velocity of nearly -3000 km s(-1) with respect to NGC 4874; we suggest it is on its first infall into the cluster core and is undergoing stripping of its GC system by the cluster potential.</P>
Cho, Hyejeon,Jensen, Joseph B.,Blakeslee, John P.,French, Brigham S.,Lee, Hyun-chul,Lee, Young-Wook Cambridge University Press 2012 Proceedings of the International Astronomical Unio Vol.8 No.suppl289
<B>Abstract</B><P>The surface brightness fluctuation (SBF) method at near-infrared (NIR) wavelengths is a powerful tool for estimating distances to unresolved stellar systems with high precision. The IR channel of the Wide Field Camera 3 (WFC3), installed on board the <I>Hubble Space Telescope (HST)</I> in 2009, has a greater sensitivity and a wider field of view than the previous generation of <I>HST</I> IR instruments, making it much more efficient for measuring distances to early-type galaxies in the Local Volume. To take full advantage of its capabilities, we need to empirically calibrate the SBF distance method for WFC3's NIR passbands. We present the SBF measurements for the WFC3/IR F160W bandpass filter using observations of 16 early-type galaxies in the Fornax and Virgo Clusters. These have been combined with existing (<I>g</I>475-<I>z</I>850) color measurements from the Advanced Camera for Surveys Virgo and Fornax Cluster Surveys to derive a space-based <I>H</I>160-band SBF relation as a function of color. We have also compared the absolute SBF magnitudes to those predicted by evolutionary population synthesis models in order to study stellar population properties in the target galaxies.</P>
Blakeslee, John P.,Cho, Hyejeon,Peng, Eric W.,Ferrarese, Laura,Jordá,n, André,s,Martel, André,R. IOP Publishing 2012 The Astrophysical journal Vol.746 No.1
<P>We combine new Wide Field Camera 3 IR Channel (WFC3/IR) F160W (H-160) imaging data for NGC 1399, the central galaxy in the Fornax cluster, with archival F475W (g(475)), F606W (V-606), F814W (I-814), and F850LP (z.(850)) optical data from the Advanced Camera for Surveys (ACS). The purely optical g(475)-I-814, V-606-I-814, and g(475)-z(850) colors of NGC 1399's rich globular cluster (GC) system exhibit clear bimodality, at least for magnitudes I-814 > 21.5. The optical-IR I-814-H-160 color distribution appears unimodal, and this impression is confirmed by mixture modeling analysis. The V-606-H-160 colors show marginal evidence for bimodality, consistent with bimodality in V-606-I-814 and unimodality in I-814-H-160. If bimodality is imposed for I-814-H-160 with a double Gaussian model, the preferred blue/red split differs from that for optical colors; these 'differing bimodalities' mean that the optical and optical-IR colors cannot both be linearly proportional to metallicity. Consistent with the differing color distributions, the dependence of I-814-H-160 on g(475)-I-814 for the matched GC sample is significantly nonlinear, with an inflection point near the trough in the g(475)-I-814 color distribution; the result is similar for the I-814-H-160 dependence on g(475)-z(850) colors taken from the ACS Fornax Cluster Survey. These g(475)-z(850) colors have been calibrated empirically against metallicity; applying this calibration yields a continuous, skewed, but single-peaked metallicity distribution. Taken together, these results indicate that nonlinear color-metallicity relations play an important role in shaping the observed bimodal distributions of optical colors in extragalactic GC systems.</P>