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RISS 인기검색어
- 검색키워드
- 저자 : John P. Blakeslee (검색결과 12 건)
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Paudel, Sanjaya,Smith, Rory,Duc, Pierre-Alain,Cô,té,, Patrick,Cuillandre, Jean-Charles,Ferrarese, Laura,Blakeslee, John P.,Boselli, Alessandro,Cantiello, Michele,Gwyn, S. D. J.,Guhathakurta American Astronomical Society 2017 The Astrophysical Journal Vol.834 No.1
<P>The Next Generation Virgo Cluster Survey is a deep (with a 2 sigma detection limit mu g = 29 mag arcsec(-2) in the g-band) optical panchromatic survey targeting the Virgo cluster from its core to virial radius, for a total areal coverage of 104 square degrees. As such, the survey is well suited for the study of galaxies' outskirts, haloes, and low surface brightness features that arise from dynamical interactions within the cluster environment. We report the discovery of extremely faint (mu g > 25 mag arcsec(-2)) shells in three Virgo cluster early-type dwarf galaxies: VCC. 1361, VCC. 1447, and VCC. 1668. Among them, VCC. 1447 has an absolute magnitude Mg = -11.71 mag and is the least massive galaxy with a shell system discovered to date. We present a detailed study of these low surface brightness features. We detect between three and four shells in each of our galaxies. Within the uncertainties, we find no evidence of a color difference between the galaxy main body and shell features. The observed arcs of the shells are located up to several effective radii of the galaxies. We further explore the origin of these low surface brightness features with the help of idealized numerical simulations. We find that a near equal mass merger is best able to reproduce the main properties of the shells, including their quite symmetric appearance and their alignment along the major axis of the galaxy. The simulations provide support for a formation scenario in which a recent merger, between two near-equal mass, gas-free dwarf galaxies, forms the observed shell systems.</P>
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Yoon, Suk-Jin,Lee, Sang-Yoon,Blakeslee, John P.,Peng, Eric W.,Sohn, Sangmo T.,Cho, Jaeil,Kim, Hak-Sub,Chung, Chul,Kim, Sooyoung,Lee, Young-Wook IOP Publishing 2011 The Astrophysical journal Vol.743 No.2
<P>One of the conundrums in extragalactic astronomy is the discrepancy in observed metallicity distribution functions (MDFs) between the two prime stellar components of early-type galaxies-globular clusters (GCs) and halo field stars. This is generally taken as evidence of highly decoupled evolutionary histories between GC systems and their parent galaxies. Here we show, however, that new developments in linking the observed GC colors to their intrinsic metallicities suggest nonlinear color-to-metallicity conversions, which translate observed color distributions into strongly peaked, unimodal MDFs with broad metal-poor tails. Remarkably, the inferred GC MDFs are similar to the MDFs of resolved field stars in nearby elliptical galaxies and those produced by chemical evolution models of galaxies. The GC MDF shape, characterized by a sharp peak with a metal-poor tail, indicates a virtually continuous chemical enrichment with a relatively short timescale. The characteristic shape emerges across three orders of magnitude in the host galaxy mass, suggesting a universal process of chemical enrichment among various GC systems. Given that GCs are bluer than field stars within the same galaxy, it is plausible that the chemical enrichment processes of GCs ceased somewhat earlier than that of the field stellar population, and if so, GCs preferentially trace the major, vigorous mode of star formation events in galactic formation. We further suggest a possible systematic age difference among GC systems, in that the GC systems in more luminous galaxies are older. This is consistent with the downsizing paradigm whereby stars of brighter galaxies, on average, formed earlier than those of dimmer galaxies; this additionally supports the similar nature shared by GCs and field stars. Although the sample used in this study (the Hubble Space Telescope Advanced Camera for Surveys/Wide Field Channel, WFPC2, and WFC3 photometry for the GC systems in the Virgo galaxy cluster) confines our discussion to R less than or similar to R-e for giant ellipticals and less than or similar to 10 R-e for normal ellipticals, our findings suggest that GC systems and their parent galaxies have shared a more common origin than previously thought, and hence greatly simplify theories of galaxy formation.</P>
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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>
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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>
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Yoon, Suk-Jin,Sohn, Sangmo T.,Kim, Hak-Sub,Chung, Chul,Cho, Jaeil,Lee, Sang-Yoon,Blakeslee, John P. IOP Publishing 2013 The Astrophysical journal Vol.768 No.2
<P>Color distributions of globular clusters (GCs) in most massive galaxies are bimodal. Assuming linear color-to-metallicity conversions, bimodality is viewed as the presence of merely two GC subsystems with distinct metallicities, which serves as a critical backbone of various galaxy formation theories. Recent studies, however, revealed that the color-metallicity relations (CMRs) often used to derive GC metallicities (e. g., CMRs of g-z, V-I, and C-T-1) are in fact inflected. Such inflection can create bimodal color distributions if the underlying GC metallicity spread is simply broad as expected from the hierarchical merging paradigm of galaxy formation. In order to test the nonlinear-CMR scenario for GC color bimodality, the u-band photometry is proposed because the u-related CMRs (e. g., CMRs of u-g and u-z) are theoretically predicted to be least inflected and most distinctive among commonly used optical CMRs. Here, we present Hubble Space Telescope (HST)/WFC3 F336W (u-band) photometry of the GC system in M84, a giant elliptical in the Virgo galaxy cluster. Combining the u data with the existing HST ACS/WFC g and z data, we find that the u-z and u-g color distributions are different from the g-z distribution in a very systematic manner and remarkably consistent with our model predictions based on the nonlinear-CMR hypothesis. The results lend further confidence to the validity of the nonlinear-CMR scenario as an explanation for GC color bimodality. There are some GC systems showing bimodal spectroscopic metallicity, and in such systems the inflected CMRs often create stronger bimodality in the color domain.</P>
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Yoon, Suk-Jin,Sohn, Sangmo T.,Lee, Sang-Yoon,Kim, Hak-Sub,Cho, Jaeil,Chung, Chul,Blakeslee, John P. IOP Publishing 2011 The Astrophysical journal Vol.743 No.2
<P>The optical color distributions of globular clusters (GCs) in most large elliptical galaxies are bimodal. Based on the assumed linear relationship between GC colors and their metallicities, the bimodality has been taken as evidence of two GC subsystems with different metallicities in each galaxy and has led to a number of theories in the context of galaxy formation. More recent observations and modeling of GCs, however, suggests that the color-metallicity relations (CMRs) are inflected, and thus colors likely trace metallicities in a nonlinear manner. The nonlinearity could produce bimodal color distributions from a broad underlying metallicity spread, even if it is unimodal. Despite the far-reaching implications, whether CMRs are nonlinear and whether the nonlinearity indeed causes the color bimodality are still open questions. Given that the spectroscopic refinement of CMRs is still very challenging, we here propose a new photometric technique to probe the possible nonlinear nature of CMRs. In essence, a color distribution of GCs is a 'projected' distribution of their metallicities. Since the form of CMRs hinges on which color is used, the shape of color distributions varies depending significantly on the colors. Among other optical colors, the u-band related colors (e. g., u-g and u-z) are theoretically predicted to exhibit significantly less inflected CMRs than other preferred CMRs (e. g., for g-z). As a case study, we performed the Hubble Space Telescope (HST)/WFPC2 archival u-band photometry for the M87 (NGC 4486) GC system with confirmed color bimodality. We show that the u-band color distributions are significantly different from that of g-z and consistent with our model predictions. With more u-band measurements, this method will support or rule out the nonlinear CMR scenario for the origin of GC color bimodality with high confidence. The HST/WFC3 observations in F336W for nearby large elliptical galaxies are highly anticipated in this regard.</P>
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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>
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Jensen, Joseph B.,Blakeslee, John P.,Gibson, Zachary,Lee, Hyun-chul,Cantiello, Michele,Raimondo, Gabriella,Boyer, Nathan,Cho, Hyejeon IOP Publishing 2015 The Astrophysical journal Vol.808 No.1
<P>We present new calibrations of the near-infrared (near-IR) surface brightness fluctuation (SBF) distance method for the F110W (J(110)) and F160W (H-160) bandpasses of the Wide Field Camera 3 Infrared Channel (WFC3/IR) on the Hubble Space Telescope. The calibrations are based on data for 16 early-type galaxies in the Virgo and Fornax clusters observed with WFC3/IR and are provided as functions of both the optical (g(475)-z(850)) and near-infrared (J(110)-H-160) colors. The scatter about the linear calibration relations for the luminous red galaxies in the sample is approximately 0.10 mag, corresponding to a statistical error of 5% in distance. Our results imply that the distance to any suitably bright elliptical galaxy can be measured with this precision out to about 80 Mpc in a single-orbit observation with WFC3/IR, making this a remarkably powerful instrument for extragalactic distances. The calibration sample also includes much bluer and lower-luminosity galaxies than previously used for IR SBF studies, revealing interesting population differences that cause the calibration scatter to increase for dwarf galaxies. Comparisons with single-burst population models show that as expected, the redder early-type galaxies contain old, metal-rich populations, while the bluer dwarf ellipticals contain a wider range of ages and lower metallicities than their more massive counterparts. Radial SBF gradients reveal that IR color gradients are largely an age effect; the bluer dwarfs typically have their youngest populations near their centers, while the redder giant ellipticals show only weak trends and in the opposite sense. Because of the population variations among bluer galaxies, distance measurements in the near-IR are best limited to red early-type galaxies. We conclude with some practical guidelines for using WFC3/IR to measure reliable SBF distances.</P>
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