D. Reitzel

University of California, Los Angeles, Los Angeles, CA, United States

Are you D. Reitzel?

Claim your profile

Publications (91)317.81 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present new determinations of the iron abundance for 220 stars belonging to the stellar system Terzan 5 in the Galactic bulge. The spectra have been acquired with FLAMES at the Very Large Telescope of the European Southern Observatory and DEIMOS at the Keck II Telescope. This is by far the largest spectroscopic sample of stars ever observed in this stellar system. From this dataset, a subsample of targets with spectra unaffected by TiO bands was extracted and statistically decontaminated from field stars. Once combined with 34 additional stars previously published by our group, a total sample of 135 member stars covering the entire radial extent of the system has been used to determine the metallicity distribution function of Terzan 5. The iron distribution clearly shows three peaks: a super-solar component at [Fe/H]$\simeq0.25$ dex, accounting for 29% of the sample, a dominant sub-solar population at [Fe/H]$\simeq-0.30$ dex, corresponding to 62% of the total, and a minor (6%) metal-poor component at [Fe/H]$\simeq-0.8$ dex. Such a broad, multi-modal metallicity distribution demonstrates that Terzan 5 is not a genuine globular cluster but the remnant of a much more complex stellar system.
    The Astrophysical Journal 09/2014; 795(1). · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: As part of a study aimed at determining the kinematical and chemical properties of Terzan 5, we present the first characterization of the bulge stars surrounding this puzzling stellar system. We observed 615 targets located well beyond the tidal radius of Terzan 5 and we found that their radial velocity distribution is well described by a Gaussian function peaked at =+21.0\pm4.6 km/s and with dispersion sigma_v=113.0\pm2.7 km/s. This is the one of the few high-precision spectroscopic survey of radial velocities for a large sample of bulge stars in such a low and positive latitude environment (b=+1.7{\deg}). We found no evidence for the peak at \sim+200 km/s found in Nidever et al. 2012. The strong contamination of many observed spectra by TiO bands prevented us from deriving the iron abundance for the entire spectroscopic sample, introducing a selection bias. The metallicity distribution was finally derived for a sub-sample of 112 stars in a magnitude range where the effect of the selection bias is negligible. The distribution is quite broad and roughly peaked at solar metallicity ([Fe/H]\simeq+0.05 dex) with a similar number of stars in the super-solar and in the sub-solar ranges. The population number ratios in different metallicity ranges agree well with those observed in other low-latitude bulge fields suggesting (i) the possible presence of a plateau for |b|<4{\deg} for the ratio between stars in the super-solar (0<[Fe/H]<0.5 dex) and sub-solar (-0.5<[Fe/H]<0 dex) metallicity ranges; (ii) a severe drop of the metal-poor component ([Fe/H]<-0.5) as a function of Galactic latitude.
    The Astrophysical Journal 06/2014; 791(2). · 6.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Globular clusters trace the formation history of the spheroidal components of our Galaxy and other galaxies, which represent the bulk of star formation over the history of the Universe. The clusters exhibit a range of metallicities (abundances of elements heavier than helium), with metal-poor clusters dominating the stellar halo of the Galaxy, and higher-metallicity clusters found within the inner Galaxy, associated with the stellar bulge, or the thick disk. Age differences between these clusters can indicate the sequence in which the components of the Galaxy formed, and in particular which clusters were formed outside the Galaxy and were later engulfed along with their original host galaxies, and which were formed within it. Here we report an absolute age of 9.9 ± 0.7 billion years (at 95 per cent confidence) for the metal-rich globular cluster 47 Tucanae, determined by modelling the properties of the cluster's white-dwarf cooling sequence. This is about two billion years younger than has been inferred for the metal-poor cluster NGC 6397 from the same models, and provides quantitative evidence that metal-rich clusters like 47 Tucanae formed later than metal-poor halo clusters like NGC 6397.
    Nature 08/2013; 500(7460):51-3. · 38.60 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Globular clusters trace the formation history of the spheroidal components of both our Galaxy and others, which represent the bulk of star formation over the history of the universe. They also exhibit a range of metallicities, with metal-poor clusters dominating the stellar halo of the Galaxy, and higher metallicity clusters found within the inner Galaxy, associated with the stellar bulge, or the thick disk. Age differences between these clusters can indicate the sequence in which the components of the Galaxy formed, and in particular which clusters were formed outside the Galaxy and later swallowed along with their original host galaxies, and which were formed in situ. Here we present an age determination of the metal-rich globular cluster 47 Tucanae by fitting the properties of the cluster white dwarf population, which implies an absolute age of 9.9 (0.7) Gyr at 95% confidence. This is about 2.0 Gyr younger than inferred for the metal-poor cluster NGC 6397 from the same models, and provides quantitative evidence that metal-rich clusters like 47 Tucanae formed later than the metal-poor halo clusters like NGC 6397.
    07/2013;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Using a novel telescope designed for wide-field imaging to low surface brightness, we have detected extended stellar halos around nearby galaxies. These halos exhibit a wide range of structures, from streams and arcs to smooth, regular, structures. Our galaxies range from -18<Mv<-24, and we observe diameters in the range of 20 < R < 100 kpc. We find no correlation between the absolute luminosity of the galaxy and the size of the halo. We observe that some edge-on spiral galaxies with boxy bulges appear to lack a spheroidal component, even to the surface brightness limit of our survey. In face-on spiral galaxies, some of the most distant extensions appear to be spiral arms, while in other cases, only smooth light is seen. Additional correlations with environment, etc. will be discussed.
    01/2013;
  • [Show abstract] [Hide abstract]
    ABSTRACT: The globular cluster G1 in M31 is among the most massive in the Local Group and may host a supermassive central black hole of ~20,000 Msun. We have used WFC3 on HST to image G1 in the F275, B, and V bands. G1 has also been proposed as likely to host a complex stellar population like that of ω Cen, which has been proposed as a possible nucleus of a dwarf galaxy. We find an extended blue horizontal branch in G1, although it appears the blue HB is <20% of the red clump population. Although we detect a wide red giant branch, neither the RGB nor HB have the complexity of those observed in Omega Cen. We have a solid detection of an extended HB in G1, but we do not strong evidence for the extreme complexity exhibited by ω Cen.
    01/2013;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present HST observations of the white dwarf luminosity function of the globular cluster 47 Tuc, as well as a comparison with white dwarf cooling models to constrain the age. The resulting constraint is compared to similar measurements using the Main Sequence Turnoff and the white dwarf measurements in M4 and NGC6397.
    01/2013;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: NGC 4449 is a nearby Magellanic irregular starburst galaxy with a B-band absolute magnitude of -18 and a prominent, massive, intermediate-age nucleus at a distance from Earth of 3.8 megaparsecs (ref. 3). It is wreathed in an extraordinary neutral hydrogen (H I) complex, which includes rings, shells and a counter-rotating core, spanning ∼90 kiloparsecs (kpc; refs 1, 4). NGC 4449 is relatively isolated, although an interaction with its nearest known companion--the galaxy DDO 125, some 40 kpc to the south--has been proposed as being responsible for the complexity of its H I structure. Here we report the presence of a dwarf galaxy companion to NGC 4449, namely NGC 4449B. This companion has a V-band absolute magnitude of -13.4 and a half-light radius of 2.7 kpc, with a full extent of around 8 kpc. It is in a transient stage of tidal disruption, similar to that of the Sagittarius dwarf near the Milky Way. NGC 4449B exhibits a striking S-shaped morphology that has been predicted for disrupting galaxies but has hitherto been seen only in a dissolving globular cluster. We also detect an additional arc or disk ripple embedded in a two-component stellar halo, including a component extending twice as far as previously known, to about 20 kpc from the galaxy's centre.
    Nature 02/2012; 482(7384):192-4. · 38.60 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present new radial velocity measurements from the Bulge Radial Velocity Assay, a large-scale spectroscopic survey of M-type giants in the Galactic bulge/bar region. The sample of ~4500 new radial velocities, mostly in the region –10° < l < +10° and b –6°, more than doubles the existent published data set. Our new data extend our rotation curve and velocity dispersion profile to +20°, which is ~2.8 kpc from the Galactic center. The new data confirm the cylindrical rotation observed at –6° and –8° and are an excellent fit to the Shen et al. N-body bar model. We measure the strength of the TiOε molecular band as a first step toward a metallicity ranking of the stellar sample, from which we confirm the presence of a vertical abundance gradient. Our survey finds no strong evidence of previously unknown kinematic streams. We also publish our complete catalog of radial velocities, photometry, TiO band strengths, and spectra, which is available at the Infrared Science Archive as well as at UCLA.
    The Astronomical Journal 02/2012; 143(3):57. · 4.97 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present new radial velocity measurements from the Bulge Radial Velocity Assay (BRAVA), a large scale spectroscopic survey of M-type giants in the Galactic bulge/bar region. The sample of ? new radial velocities, mostly in the region -10 < l < +10 deg and b ≈ -6 deg, more than doubles the existent published data set. The new data confirm the cylindrical rotation observed at -8 deg, and are an excellent fit to the Shen et al. (2010) N-body bar model. We also measure the strength of the TiO epsilon molecular band as a first step towards a metallicity ranking of the stellar sample, from which we confirm the presence of a vertical abundance gradient. We also publish our complete catalog of radial velocities, photometry, TiO-strengths, and spectra, which is available at the IRSA archive. We also report a possible new high velocity star, the first found in this direction, with radial velocity 447 km/sec, and space velocity 550 km/sec if its distance is 8kpc. The star is a moderately metal poor M giant in the Galactic bulge, and has apogalacticon at least 20 kpc from the nucleus.
    01/2012;
  • [Show abstract] [Hide abstract]
    ABSTRACT: NGC4449 is a Magellanic irregular galaxy with MB -18, roughly twice the luminosity of the LMC and located 3.82 Mpc from the Milky Way. We report the discovery of a new very low surface brightness dwarf companion at a projected distance if 9 kpc from the galaxy. It has a full extent of 3.5 X 7.5 kpc, with the morphology of a compact core and extended tidal tails that are roughly aligned in the direction of NGC 4449. Preliminary estimates find Mr = -13, making this a relatively luminous, yet very large, dwarf galaxy. The structure of NGC4449B is consistent with a dwarf galaxy on its first encounter, undergoing tidal disruption. Despite large amounts of HI in the vicinity, we see no signs of star formation in the dwarf and speculate that its stellar population is old. The extreme tidal structure and low surface brightness, as well as close projected distance, secure the association with NGC 4449.
    01/2012;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In Hubble Space Telescope (HST) Cycle 17, we imaged the well-known globular star cluster 47 Tucanae for 121 orbits using the Wide Field Channel of the Advanced Camera for Surveys (ACS) and both the UV/visible (UVIS) and IR channels of the newly installed Wide Field Camera 3 (WFC3) instrument (GO-11677, PI: H. Richer). This unique data set was obtained to address many scientific questions that demand a very deep, panchromatic, and panoramic view of the cluster's stellar populations. In total, the program obtained over 0.75 Ms of imaging exposure time with the three HST cameras, over a time span of 9 months in 2010. The primary ACS field was imaged in the two broadband filters F606W and F814W, at 13 orientations, for all 121 orbits. The parallel WFC3 imaging provides a panchromatic (0.4-1.7 μm) and contiguous imaging swath over a 250° azimuthal range at impact radii of 6.5-17.9 pc in 47 Tuc. This imaging totals over 60 arcmin2 in area and utilizes the F390W and F606W broadband filters on WFC3/UVIS and the F110W and F160W broadband filters on WFC3/IR. In this paper, we describe the observational design of the new survey and one of the methods used to analyze all of the imaging data. This analysis combines over 700 full-frame images taken with the three HST cameras into a handful of ultra-deep, well-sampled combined images in each of the six filters. We discuss in detail the methods used to calculate accurate transformations that provide optimal alignment of the input images, the methods used to perform sky background offsets in the input stack and the flagging of deviant pixels, and the balance reached between the input-pixel drop size onto an output supersampled pixel grid. Careful photometric, morphological, and astrometric measurements are performed on the stacks using iterative PSF-fitting techniques, and reveal unprecedented color-magnitude diagrams of the cluster extending to >30th magnitude in the optical, 29th magnitude in the UV, and 27th magnitude in the IR. The data set provides a characterization of the complete stellar populations of 47 Tuc, extending from the faintest hydrogen-burning dwarfs through the main-sequence and giant branches down to very cool white dwarf remnants in the cluster. The imaging also provides the deepest probe of the stellar populations of the background Small Magellanic Cloud galaxy, resolving low-mass main-sequence dwarfs with M 0.2 M ☉.
    The Astronomical Journal 12/2011; 143(1):11. · 4.97 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The ages of Galactic globular clusters provide insight into the formation history of the Milky Way. Utilizing HST photometry of unprecendented depth and wavelength coverage, we determine the main sequence turnoff ages of the nearby globular clusters NGC 6397 and 47 Tuc. The ages are determined by comparing stellar evolution models to the main sequences with a chi-squared minimization technique. Our analysis of 47 Tuc leverages the pronounced 'kink' or 'knee' feature that appears in the lower main sequence in the near-IR. We present our age estimates as probability distributions and construct confidence intervals over input parameters such as metallicity, distance, and reddening.
    01/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: In Cycle 17 we were awarded 121 orbits with HST to search for the faintest stellar populations (the coolest white dwarfs, the lowest mass main sequence stars and possibly the brown dwarfs) in 47 Tucanae. It took 10 months to secure all the data with exquisite care taken to minimize the effects of charge transfer and saturation spikes. The ACS stared at a single field for all 121 orbits but the roll angle of the telescope was varied through 180 degrees for the associated parallel fields observed with WFC3. Archival data were employed to proper motion clean the images allowing virtually complete separation of field stars and those in the background Small Magellanic Cloud from those in the cluster. In this poster, we present the resultant color-magnitude diagram for this important cluster which is a proxy for the Galactic bulge. A rich white dwarf cooling sequence is revealed which will be used to determine a cooling age for the cluster for comparison with the turnoff age (see associated poster by A. Dotter et al.). Multicolor data in other ACS filters as well as four filters with WFC3 are used to examine the spectral energy distributions of the cluster white dwarfs.
    01/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: In Cycle 17 our team was allocated 121 HST orbits to dissect the best studied globular cluster in the sky, 47 Tucanae. The HST ACS and WFC3 observations in this study represent one of the deepest images ever obtained for a nearby stellar population. In this poster, we present high-resolution UV and near-infrared imaging of the complete stellar populations of 47 Tuc over a wide field of view spanning a 180 degree azimuthal range and >10 pc radial range in the star cluster. The combined WFC3/UVIS and IR observations in each of these fields extends from well below the hydrogen burning limit in the red, up through the main sequence to the brightest giants in post main-sequence evolution in the visible, and down to the white dwarf cooling sequence in the blue. This complete stellar picture of a globular cluster has revealed several new features of the color-magnitude diagram and represents a comprehensive data base to test stellar evolution models in exquisite detail. In addition to the primary focus of studying 47 Tuc, our imaging penetrates through the star cluster to reveal a rich population of background giants and low mass dwarfs belonging to the distant Small Magellanic Cloud.
    01/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report analysis of second epoch imaging of the very deep 126 orbit ACS integration in NGC 6397, yielding the deepest proper-motion selected color-magnitude diagram of a globular cluster. We reach past the faint end of the white dwarf cooling sequence and confirm the "blue hook" caused by H2 collision-induced absorption opacity. We also confirm a suspected population of faint red proper-motion members of NGC6397, many of which lie both fainter and redder than the theoretical limit for the hydrogen burning. Other proper motion members of NGC 6397 (with unusual colors) may be white dwarf/red dwarf binaries. Our reduced proper motion plot for the field reveals (for the first time) an extended white dwarf cooling sequence in the thick disk population, along with a well populated sequence of extremely faint red stars, many of which are also fainter and redder than the theoretical hydrogen burning limit. Supported by AURA STScI GO-11633 (R. M. Rich, PI)
    01/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present chemical abundances for 100 red giant branch (RGB) and red clump stars in Plaut's low-extinction window (l,b)=(0°,-8°). The abundances were determined from equivalent width and spectrum synthesis analyses of high resolution (R=22,000), high signal-to-noise (S/N 50-100) spectra obtained with the Blanco 4m telescope and Hydra multifiber spectrograph. We confirm the existence of a vertical metallicity gradient along the Galactic bulge minor axis and that the median metallicity at b=-8° is [Fe/H] -0.3. However, the red clump stars in this field appear to be both selectively enhanced in metallicity, with a median [Fe/H] 0, and have at least a factor of two smaller radial velocity dispersion than the RGB stars. Interestingly, both the giants and clump stars exhibit similar enhanced [alpha/Fe] ratios compared to the thin and possibly thick disk trends, and the b=-8° [alpha/Fe] ratios are indistinguishable from those at b=-4°. Lastly, we compare the abundances of several additional light and heavy elements in Plaut's Window to those in other bulge fields and stellar populations.
    01/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: The Bulge Radial Velocity Assay has surveyed radial velocities for Galactic bulge M giants at b=-4 deg, b=-8 deg, and a range of fields on the minor axis. We report a striking agreement between a model N-body bar and our radial velocity data, obtained using Hydra at the CTIO 4m telescope. This is the closest agreement ever reported between radial velocity data in the bulge, and a largescale dynamical model. The N-body bar secularly evolves from a massive disk, after experiencing a buckling instability. We use the results to place upper limits on the fraction of the population that might belong to a "classical" bulge population that is not part of the bar. We also report the first analysis of metallicities from the Ca infrared triplet method, for our dataset, and how kinematics and metallicities are correlated. This research was supported by grant AST-0709479 from the National Science Foundation.
    01/2010;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present new results from BRAVA, a large-scale radial velocity survey of the Galactic bulge, using M giant stars selected from the Two Micron All Sky Survey catalog as targets for the Cerro Tololo Inter-American Observatory 4 m Hydra multi-object spectrograph. The purpose of this survey is to construct a new generation of self-consistent bar models that conform to these observations. We report the dynamics for fields at the edge of the Galactic bulge at latitudes b = –8° and compare to the dynamics at b = –4°. We find that the rotation curve V(r) is the same at b = –8° as at b = –4°. That is, the Galactic boxy bulge rotates cylindrically, as do boxy bulges of other galaxies. The summed line-of-sight velocity distribution at b = –8° is Gaussian, and the binned longitude-velocity plot shows no evidence for either a (disk) population with cold dynamics or for a (classical bulge) population with hot dynamics. The observed kinematics are well modeled by an edge-on N-body bar, in agreement with published structural evidence. Our kinematic observations indicate that the Galactic bulge is a prototypical product of secular evolution in galaxy disks, in contrast with stellar population results that are most easily understood if major mergers were the dominant formation process.
    The Astrophysical Journal 08/2009; 702(2):L153. · 6.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We propose to continue our radial velocity survey of M giant stars in the Galactic bulge, inner disk, and inner halo. The overall aim of the project is describe the kinematics of the bulge, and its abundance dependence, and to compare with dynamical models, elucidating the formation history and dynamical state of the bulge. Our aim in 2009B is to push our survey toward the plane and to complete the strip at b=- 2°, and to extend our probe of the bulge/disk/halo boundaries, with fields at b=-10° and fields extending at l>12°. The b=- 2° strip is intended to probe the mass distribution and orbit structure of the inner bulge. The band at b=-10 ° is aimed to find the point where cylindrical rotation breaks down, and to probe the region where the bulge metallicity and velocity dispersion is dropping, suggesting that we are reaching the bulge/halo boundary. The full dataset is in active use by 2 theoretical groups, being compared with N- body and self-consistent bar models.
    NOAO Proposal. 08/2009;

Publication Stats

1k Citations
317.81 Total Impact Points

Institutions

  • 2006–2013
    • University of California, Los Angeles
      • • Division of Astronomy & Astrophysics
      • • Department of Physics and Astronomy
      Los Angeles, CA, United States
    • University of British Columbia - Vancouver
      • Department of Physics and Astronomy
      Vancouver, British Columbia, Canada
  • 2007
    • Carnegie Institution for Science
      Washington, West Virginia, United States
  • 2005–2006
    • University of Virginia
      • Department of Astronomy
      Charlottesville, Virginia, United States
  • 1998–2005
    • University of California, Santa Cruz
      • Department of Astronomy and Astrophysics
      Santa Cruz, California, United States
  • 1996
    • The Ohio State University
      Columbus, Ohio, United States