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Search Results: 1 - 10 of 317623 matches for " R. O. Marzke "
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The Relative Ages of the Globular Cluster Subpopulations in M87
Andres Jordan,Patrick Cote,Michael J. West,R. O. Marzke
Physics , 2002, DOI: 10.1086/343759
Abstract: Relative ages for the globular cluster (GC) subpopulations in the Virgo giant elliptical galaxy M87 (NGC 4486) have been determined from Stroemgren photometry obtained with WFPC2 on board HST. Using a variety of population synthesis models, and assuming the GC mass at the turnover of the luminosity function is the same for both subpopulations, differential ages have been determined from the observed magnitudes at the turnover of the globular cluster luminosity function and from the mean color of each subpopulation. We measure an age difference between the two subpopulations of 0.2 +/- 1.5 (systematic) +/- 2 (random) Gyr, in the sense that the blue GCs are formally older. Thus, to within our measurement errors, the two subpopulations are found to be coeval. Combined with previous spectroscopic age determinations for M87 GCs, our results favor a picture in which the GCs associated with this galaxy are formed at high redshift, and within a period of a few Gyr.
Globular Cluster Systems and the Missing Satellite Problem: Implications for Cold Dark Matter Models
Patrick Cote,Michael J. West,R. O. Marzke
Physics , 2001, DOI: 10.1086/338670
Abstract: We analyze the metallicity distributions of globular clusters belonging to 28 early-type galaxies in the survey of Kundu & Whitmore (2001). A Monte Carlo algorithm which simulates the chemical evolution of galaxies that grow hierarchically via dissipationless mergers is used to determine the most probable protogalactic mass function for each galaxy. Contrary to the claims of Kundu & Whitmore, we find that the observed metallicity distributions are in close agreement with the predictions of such hierarchical formation models. The mass spectrum of protogalactic fragments for the galaxies in our sample has a power-law behavior, with an exponent of roughly -2. This spectrum is indistinguishable from the mass spectrum of dark matter halos predicted by cold dark matter models for structure formation. We argue that these protogalactic fragments, the likely sites of globular cluster formation in the early universe, are the disrupted remains of the "missing" satellite galaxies predicted by cold dark matter models. Our findings suggest that the solution to the missing satellite problem is through the suppression of gas accretion in low-mass halos after reionization, or via self-interacting dark matter, and argue against models with suppressed small-scale power or warm dark matter.
R. O. Marzke,M. J. Geller,L. N. da Costa,J. P. Huchra
Physics , 1995, DOI: 10.1086/117536
Abstract: (compressed version) We combine the CfA Redshift Survey (CfA2) and the Southern Sky Redshift Survey (SSRS2) to estimate the pairwise velocity dispersion of galaxies $\sig12$ on a scale of $\sim 1 \hmpc$. Both surveys are complete to an apparent magnitude limit $B(0)=15.5$. Our sample includes 12,812 galaxies distributed in a volume $1.8 \times 10^6 \hmpc3$. We conclude: 1) The pairwise velocity dispersion of galaxies in the combined CfA2+SSRS2 redshift survey is $\sig12=540 \kms \pm 180 \kms$. Both the estimate and the variance of $\sig12$ significantly exceed the canonical values $\sig12=340 \pm40$ measured by Davis \& Peebles (1983) using CfA1. 2) We derive the uncertainty in $\sig12$ from the variation among subsamples with volumes on the order of $7 \times 10^5$ \hmpc3. This variation is nearly an order of magnitude larger than the formal error, 36 $\kms$, derived using least-squares fits to the CfA2+SSRS2 correlation function. This variation among samples is consistent with the conclusions of Mo \etal (1993) for a number of smaller surveys and with the analysis of CfA1 by Zurek \etal (1994). 3) When we remove Abell clusters with $R\ge1$ from our sample, the pairwise velocity dispersion of the remaining galaxies drops to $295 \pm 99 \kms$. Thus the dominant source of variance in $\sig12$ is the shot noise contributed by dense virialized systems. 4) The distribution of pairwise velocities is consistent with an isotropic exponential with velocity dispersion independent of scale.
New Techniques for Relating Dynamically Close Galaxy Pairs to Merger and Accretion Rates : Application to the SSRS2 Redshift Survey
D. R. Patton,R. G. Carlberg,R. O. Marzke,C. J. Pritchet,L. N. da Costa,P. S. Pellegrini
Physics , 2000, DOI: 10.1086/308907
Abstract: We introduce two new pair statistics, which relate close galaxy pairs to the merger and accretion rates. We demonstrate the importance of correcting these (and other) pair statistics for selection effects related to sample depth and completeness. In particular, we highlight the severe bias that can result from the use of a flux-limited survey. The first statistic, denoted N_c, gives the number of companions per galaxy, within a specified range in absolute magnitude. N_c is directly related to the galaxy merger rate. The second statistic, called L_c, gives the total luminosity in companions, per galaxy. This quantity can be used to investigate the mass accretion rate. Both N_c and L_c are related to the galaxy correlation function and luminosity function in a straightforward manner. We outline techniques which account for various selection effects, and demonstrate the success of this approach using Monte Carlo simulations. If one assumes that clustering is independent of luminosity (which is appropriate for reasonable ranges in luminosity), then these statistics may be applied to flux-limited surveys. These techniques are applied to a sample of 5426 galaxies in the SSRS2 redshift survey. Using close dynamical pairs, we find N_c(-21
Ultra-Compact Dwarfs in the Coma Cluster
Kristin Chiboucas,R. Brent Tully,Ronald O. Marzke,Steve Phillipps,James Price,Eric Peng,Neil Trentham,David Carter,Derek Hammer
Physics , 2011, DOI: 10.1088/0004-637X/737/2/86
Abstract: We have undertaken a spectroscopic search for ultra compact dwarf galaxies (UCDs) in the dense core of the dynamically evolved, massive Coma cluster as part of the HST/ACS Coma Cluster Treasury Survey. UCD candidates were initially chosen based on color, magnitude, degree of resolution within the ACS images, and the known properties of Fornax and Virgo UCDs. Follow-up spectroscopy with Keck/LRIS confirmed 27 candidates as members of the Coma Cluster, a success rate > 60% for targeted objects brighter than M_R = -12. Another 14 candidates may also prove to be Coma members, but low signal-to-noise spectra prevent definitive conclusions. An investigation of the properties and distribution of the Coma UCDs finds these objects to be very similar to UCDs discovered in other environments. The Coma UCDs tend to be clustered around giant galaxies in the cluster core and have colors/metallicity that correlate with the host galaxy. With properties and a distribution similar to that of the Coma cluster globular cluster population, we find strong support for a star cluster origin for the majority of the Coma UCDs. However, a few UCDs appear to have stellar population or structural properties which differentiate them from the old star cluster populations found in the Coma cluster, perhaps indicating that UCDs may form through multiple formation channels.
Keck/LRIS Spectroscopic Confirmation of Coma Cluster Dwarf Galaxy Membership Assignments
Kristin Chiboucas,R. Brent Tully,Ronald O. Marzke,Neil Trentham,Henry C. Ferguson,Derek Hammer,David Carter,Habib Khosroshahi
Physics , 2010, DOI: 10.1088/0004-637X/723/1/251
Abstract: Keck/LRIS multi-object spectroscopy has been carried out on 140 of some of the lowest and highest surface brightness faint (19 < R < 22) dwarf galaxy candidates in the core region of the Coma Cluster. These spectra are used to measure redshifts and establish membership for these faint dwarf populations. The primary goal of the low surface brightness sample is to test our ability to use morphological and surface brightness criteria to distinguish between Coma Cluster members and background galaxies using high resolution HST/ACS images. Candidates were rated as expected members, uncertain, or expected background. From 93 spectra, 51 dwarf galaxy members and 20 background galaxies are identified. Our morphological membership estimation success rate is ~100% for objects expected to be members and better than ~90% for galaxies expected to be in the background. We confirm that low surface brightness is a very good indicator of cluster membership. High surface brightness galaxies are almost always background with confusion arising only from the cases of the rare compact elliptical galaxies. The more problematic cases occur at intermediate surface brightness. Many of these galaxies are given uncertain membership ratings, and these were found to be members about half of the time. Including color information will improve membership determination but will fail for some of the same objects that are already mis-identified when using only surface brightness and morphology criteria. Compact elliptical galaxies with B-V colors ~0.2 magnitudes redward of the red sequence in particular require spectroscopic follow-up. In a sample of 47 high surface brightness, UCD candidates, 19 objects have redshifts which place them in the Coma Cluster. Redshift measurements are presented and the use of indirect means for establishing cluster membership is discussed.
The Galaxy Luminosity Function at z < 0.05: Dependence on Morphology
R. O. Marzke,L. N. da Costa,P. S. Pellegrini,C. N. A. Willmer,M. J. Geller
Physics , 1998, DOI: 10.1086/306011
Abstract: We investigate the dependence of the local galaxy luminosity function on morphology using 5,404 galaxies from the recently enlarged Second Southern Sky Redshift Survey (SSRS2). Over the range -22 \le M_B \le -14 ($H_0 = 100 km/s/Mpc), the luminosity function of early-type galaxies is well fitted by a Schechter function with parameters M_*=-19.37^{+0.10}_{-0.11}, alpha=-1.00^{+0.09}_{-0.09} and phi_*=0.0044 +/- 0.0008 Mpc^{-3}. The spiral luminosity function is very similar and is well fitted by the parameters M_*=-19.43^{+0.08}_{-0.08}, alpha=-1.11^{+0.07}_{-0.06} and phi_*=0.0080 +/- 0.0014 Mpc^{-3} over the same range in absolute magnitude. The flat faint end of the early-type luminosity function is consistent with earlier measurements from the CfA Redshift Survey (Marzke et al. 1994) but is significantly steeper than the slope measured in the Stromlo-APM survey (Loveday et al. 1992). Combined with the increased normalization of the overall LF measured from intermediate redshift surveys, the flat faint-end slope of the E/S0 LF produces no-evolution models which reproduce the deep HST counts of early-type galaxies remarkably well. However, the observed normalization of the SSRS2 LF is consistent with the low value measured in other local redshift surveys. The cause of this low-redshift anomaly remains unknown. The luminosity function of irregular and peculiar galaxies in the SSRS2 is very steep: M_*=-19.78^{+0.40}_{-0.50}, alpha=-1.81^{+0.24}_{-0.24} and phi_*=0.0002 +/- 0.00008 Mpc^{-3}. The steep slope is consistent with the LFs measured for Sm-Im galaxies in the CfA survey, UV-selected galaxies (Treyer et al. 1997), star-forming field galaxies (Bromley et al. 1997) and the bluest galaxies in the SSRS2 (Marzke & da Costa 1997).
The Las Campanas Infrared Survey. IV. The Photometric Redshift Survey and the Rest-frame R-band Galaxy Luminosity Function at 0.5 <= z <= 1.5
Hsiao-Wen Chen,Ronald. O. Marzke,Patrick. J. McCarthy,P. Martini,R. G. Carlberg,S. E. Persson,A. Bunker,C. R. Bridge,R. G. Abraham
Physics , 2002, DOI: 10.1086/367787
Abstract: (Abridged) We present rest-frame R-band galaxy luminosity function measurements for three different redshift ranges: 0.5<=z<=0.75, 0.75<=z<=1.0, and 1.0<=z<=1.5. Our measurements are based on photometric redshifts for ~3000 H-band selected galaxies with apparent magnitudes 17<=H<=20 from the Las Campanas Infrared Survey. We show that our photometric redshifts are accurate with an RMS dispersion between the photometric and spectroscopic redshifts of \sigma_z/(1+z)~0.08. Using galaxies identified in the Hubble Deep Field South and Chandra Deep Field South regions, we find, respectively, that (7.3\pm 0.2) % and (16.7\pm 0.4)% of the H<=20 galaxies are at z>=1. We first demonstrate that the systematic uncertainty inherent in the luminosity function measurements due to uncertainties in photometric redshifts is non-negligible and therefore must be accounted for. We then develop a technique to correct for this systematic error by incorporating the redshift error functions of individual galaxies in the luminosity function analysis. The redshift error functions account for the non-gaussian characteristics of photometric redshift uncertainties. They are the products of a convolution between the corresponding redshift likelihood functions of individual galaxies and a Gaussian distribution function that characterizes template-mismatch variance. We demonstrate, based on a Monte Carlo simulation, that we are able to completely recover the bright end of the intrinsic galaxy luminosity function using this technique. Finally, we calculate the luminosity function separately for the total H-band selected sample and for a sub-sample of early-type galaxies that have a best-fit spectral type of E/S0 or Sab from the photometric redshift analysis.
Redshifts for 2410 Galaxies in the Century Survey Region
G. Wegner,J. R. Thorstensen,M. J. Kurtz,W. R. Brown,D. G. Fabricant,M. J. Geller,J. P. Huchra,R. O. Marzke,Shoko Sakai
Physics , 2001, DOI: 10.1086/323915
Abstract: The `Century Survey' strip covers 102 square degrees within the limits 8.5h \leq \alpha_{1950} \leq 16.5h, 29.0 degrees \leq \delta_{1950} \leq 30.0 degrees. The strip passes through the Corona Borealis supercluster and the outer region of the Coma cluster. Within the Century Survey region, we have measured 2410 redshifts which constitute four overlapping complete redshift surveys: (1) 1728 galaxies with Kron-Cousins R_{phot} \leq 16.13 covering the entire strip, (2) 507 galaxies with R_{phot} \leq 16.4 in the right ascension range 8h 32m \leq \alpha_{1950} \leq 10h 45m, (3) 1251 galaxies with absorption- and K-corrected R_{CCD, corr} \leq 16.2 covering the right ascension range 8.5h \leq \alpha_{1950} \leq 13.5h and (4) 1255 galaxies with absorption- and K-corrected V_{CCD, corr} \leq 16.7 also covering the right ascension range 8.5h \leq \alpha_{1950} \leq 13.5h. All of these redshift samples are more than 98 % complete to the specified magnitude limit.
The Century Survey: A Deeper Slice of the Universe
Margaret J. Geller,Michael J. Kurtz,; Gary Wegner,John R. Thorstensen,; Daniel G. Fabricant,; Ronald O. Marzke,; John P. Huchra,Rudolph E.,Schild,Emilio E. Falco
Physics , 1997, DOI: 10.1086/118640
Abstract: The ``Century Survey'' (CS hereafter) is a complete redshift survey of a 1$^\circ$-wide strip. It covers 0.03 steradians to a limiting m$_R$ = 16.13. The survey is 98.4% complete and contains 1762 galaxies. Large-scale features in the survey are qualitatively similar to those in other surveys: there are large voids surrounded or nearly surrounded by thin dense regions which are sections of structures like (and including) the Great Wall. The survey crosses the classical Corona Borealis supercluster. The galaxy density enhancement associated with this system extends for $\simgreat 100 h^{-1}$ Mpc (the Hubble constant is H$_0 = 100h$ km s$^{-1}$Mpc$^{-1}$). The Schechter (1976) luminosity function parameters for the CS are: $M^*_{CS} = -20.73 ^{+0.17}_{-0.18}$, $\alpha_{CS} = -1.17 ^{+0.19}_{-0.19}$, and $\phi^*_{CS} = 0.0250\pm0.0061$ Mpc$^{-3}$mag$^{-1}$. In concert with the ESO Key Program (\cite{vet97}; \cite{zuc97}) and the AUTOFIB (\cite{ell96}) surveys, the CS indicates that the absolute normalization of the luminosity function exceeds estimates based on shallower and/or sparser surveys.
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