M. Mateo

Peking University, Peping, Beijing, China

Are you M. Mateo?

Claim your profile

Publications (125)173.74 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We present deep photometry of the Carina dwarf Spheroidal galaxy in the B,V filters from CTIO/MOSAIC, out to and beyond the tidal radius. The accurately calibrated photometry is combined with spectroscopic metallicity distributions of Red Giant Branch stars to determine the detailed star formation and chemical evolution history. The star formation history confirms the episodic formation history of Carina and quantifies the duration and strength of each episode in great detail, as a function radius from the centre. Two main episodes of star formation occurred at old (>8 Gyr) and intermediate (2-8 Gyr) ages, both enriching stars starting from low metallicities ([Fe/H]<-2 dex). By dividing the SFH into two components, we determine that 60pm9 percent of the total number of stars formed within the intermediate age episode. Furthermore, within the tidal radius (0.48 degrees or 888 pc) a total mass in stars of 1.07pm0.08 x10^6 M_sun was formed, giving Carina a stellar mass-to-light ratio of 1.8pm0.8. Combining the detailed star formation history with spectroscopic observations of RGB stars, we are able to determine the detailed age-metallicity relation of each episode and the timescale of alpha-element evolution of Carina from individual stars. The oldest episode displays a tight age-metallicity relation over 6 Gyr with steadily declining alpha-element abundances and a possible alpha-element knee at [Fe/H]~ -2.5 dex. The intermediate age sequence displays a more complex age-metallicity relation starting from low metallicity and a sequence in alpha-element abundances with a slope much steeper than observed in the old episode, starting from [Fe/H]=-1.8 dex and [Mg/Fe]~0.4 dex and declining to Mg-poor values ([Mg/Fe]<-0.5 dex). This indicates clearly that both episodes of star formation formed from gas with different abundance patterns, inconsistent with simple evolution in an isolated system.
    09/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present deep color-magnitude diagrams (CMDs) for two Subaru Suprime-Cam fields in the Virgo Stellar Stream (VSS)/Virgo Overdensity (VOD) and compare them to a field centered on the highest concentration of Sagittarius (Sgr) Tidal Stream stars in the leading arm, Branch A of the bifurcation. A prominent population of main-sequence stars is detected in all three fields and can be traced as faint as g 24 mag. Using theoretical isochrone fitting, we derive an age of Gyr, a median abundance of [Fe/H] = dex, and a heliocentric distance of 30.9 ± 3.0 kpc for the main sequence of the Sgr Stream Branch A. The dominant main-sequence populations in the two VSS/VOD fields (Λ☉ 265°, B ☉ 13°) are located at a mean distance of 23.3 ± 1.6 kpc and have an age of ~8.2 Gyr, and an abundance of [Fe/H] = dex, similar to the Sgr Stream stars. These statistically robust parameters, derived from the photometry of 260 main-sequence stars, are also in good agreement with the age of the main population in the Sgr dwarf galaxy (8.0 ± 1.5 Gyr). They also agree with the peak in the metallicity distribution of 2-3 Gyr old M giants, [Fe/H] –0.6 dex, in the Sgr north leading arm. We then compare the results from the VSS/VOD fields with the Sgr Tidal Stream model by Law & Majewski based on a triaxial Galactic halo shape that is empirically calibrated with Sloan Digital Sky Survey Sgr A-branch and Two Micron All Sky Survey M-giant stars. We find that the most prominent feature in the CMDs, the main-sequence population at 23 kpc, is not explained by the model. Instead the model predicts in these directions a low-density filamentary structure of Sgr debris stars at ~9 kpc and a slightly higher concentration of Sgr stars spread over a heliocentric distance range of 42-53 kpc. At best there is only marginal evidence for the presence of these populations in our data. Our findings then suggest that while there are probably some Sgr debris stars present, the dominant stellar population in the VOD originates from a different halo structure that has an almost identical age and metallicity as some sections of the Sgr tidal stream.
    The Astrophysical Journal 04/2013; 769(1):14. · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present deep photometry in the B,V and I filters from CTIO/MOSAIC for about 270.000 stars in the Fornax dwarf Spheroidal galaxy, out to a radius of r_ell\sim0.8 degrees. By combining the accurately calibrated photometry with the spectroscopic metallicity distributions of individual Red Giant Branch stars we obtain the detailed star formation and chemical evolution history of Fornax. Fornax is dominated by intermediate age (1-10 Gyr) stellar populations, but also includes ancient (10-14 Gyr), and young (<1 Gyr) stars. We show that Fornax displays a radial age gradient, with younger, more metal-rich populations dominating the central region. This confirms results from previous works. Within an elliptical radius of 0.8 degrees, or 1.9 kpc from the centre, a total mass in stars of 4.3x10^7 Msun was formed, from the earliest times until 250 Myr ago. Using the detailed star formation history, age estimates are determined for individual stars on the upper RGB, for which spectroscopic abundances are available, giving an age-metallicity relation of the Fornax dSph from individual stars. This shows that the average metallicity of Fornax went up rapidly from [Fe/H]<-2.5 dex to [Fe/H]=-1.5 dex between 8-12 Gyr ago, after which a more gradual enrichment resulted in a narrow, well-defined sequence which reaches [Fe/H]\sim-0.8 dex, \sim3 Gyr ago. These ages also allow us to measure the build-up of chemical elements as a function of time, and thus determine detailed timescales for the evolution of individual chemical elements. A rapid decrease in [Mg/Fe] is seen for the stars with [Fe/H]>-1.5 dex, with a clear trend in age.
    Astronomy and Astrophysics 06/2012; · 5.08 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Deep optical photometry of the Fornax dSph in the B, V and I filters was obtained using the CTIO 4-m MOSAIC II camera over 9 nights in October 2008 and November 2009. Deep photometry for the outer fields was obtained as part of observing proposal 2008B-0397 (PI M. Mateo) supplemented by deep pointings covering the centre of Fornax as part of observing proposal 2009B-0157 (PI A. Saha). Our observing strategy was to obtain several non-dithered, long (600s) exposures for each pointing, which were stacked together to obtain the deepest photometry possible. Short (10s, 90s) exposures were also obtained, in order to sample the bright stars that are saturated in the deep images. In order to ensure accurate photometric calibration of the data set, several fields were observed in Fornax using the 0.9m CTIO telescope, under photometric conditions. Furthermore, observations were also made of Landolt standard fields (Landolt 1992, Cat II/183; Landolt 2007, Cat. J/AJ/133/2502) covering a range of different airmass and colour. Medium and high resolution spectroscopic observations are available for individual stars on the RGB in Fornax, giving measurements of [Fe/H] and the detailed abundance patterns of individual stars, from Battaglia et al. 2006, Cat. J/A+A/459/423; 2008, Cat. J/MNRAS/383/183); Starkenburg et al. 2010A&A...513A..34S; Letarte et al. 2010, Cat. J/A+A/523/A17 (1 data file).
    VizieR Online Data Catalog. 06/2012;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We studied the stellar populations of Fornax dwarf spheroidal galaxy using HST/WFPC2 imaging of 7 galaxy fields. Our observations reach the oldest main-sequence turn-off, revealing distinct stars formation episodes and allowing us to address the evolution of this prototype dwarf spheroidal galaxy known to have experienced an extended history of star formation. From our HST data, spatial gradients in the stellar content of Fornax emerge with greater clarity. The outermost fields show only stars with ages between 7–12Gyr, while the intermediate region hosts a stellar population between 4–10Gyr, and stars younger of 2 Gyr are found in the innermost fields. A clearly visible gap in the subgiant branch points to bimodality in the main star formation episode. Our observations also indicate that the inner clump detected by Coleman et al. (2004) is characterized by the presence of young stars with age about 1.8 Gyr.
    EAS Publications Series 12/2010; 48:69 - 70.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report the discovery of two new Milky Way satellites in the neighboring constellations of Pisces and Pegasus identified in data from the Sloan Digital Sky Survey. Pisces II, an ultra-faint dwarf galaxy lies at the distance of ~180 kpc, some 15° away from the recently detected Pisces I. Segue 3, an ultra-faint star cluster lies at the distance of 16 kpc. We use deep follow-up imaging obtained with the 4-m Mayall Telescope at Kitt Peak National Observatory to derive their structural parameters. Pisces II has a half-light radius of ~60 pc, while Segue 3 is 20 times smaller at only 3 pc.
    The Astrophysical Journal Letters 01/2010; 712(1). · 6.35 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Follow-up imaging of Segue 2 was carried out on 2007 October 7 using the Megacam imager on the Multiple Mirror Telescope (MMT). On 2008 October 22-23 and 26, we obtained high-resolution spectra of 352 targets around Segue 2 using three independent fibre configurations with the Hectochelle spectrograph at the MMT. (1 data file).
    VizieR Online Data Catalog. 11/2009;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We announce the discovery of a new Milky Way satellite Segue 2 found in the data of the Sloan Extension for Galactic Understanding and Exploration (SEGUE). We followed this up with deeper imaging and spectroscopy on the Multiple Mirror Telescope (MMT). From this, we derive a luminosity of Mv=−2.5, a half-light radius of 34 pc and a systemic velocity of ∼−40 km s−1. Our data also provide evidence for a stream around Segue 2 at a similar heliocentric velocity, and the SEGUE data show that it is also present in neighbouring fields. We resolve the velocity dispersion of Segue 2 as 3.4 km s−1 and the possible stream as ∼7 km s−1. This object shows points of comparison with other recent discoveries, Segue 1, Boo II and Coma. We speculate that all four objects may be representatives of a population of satellites of satellites – survivors of accretion events that destroyed their larger but less dense parents. They are likely to have formed at redshifts z > 10 and are good candidates for fossils of the reionization epoch.
    Monthly Notices of the Royal Astronomical Society 08/2009; 397(4):1748 - 1755. · 5.52 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a kinematic study of the Orion Nebula Cluster based upon radial velocities measured by multi-fiber echelle spectroscopy at the 6.5 meter MMT and Magellan telescopes. Velocities are reported for 1613 stars, with multi-epoch data for 727 objects as part of our continuing effort to detect and analyze spectroscopic binaries. We confirm and extend the results of Furesz et al. showing that the ONC is not relaxed, consistent with its youth, and that the stars generally follow the position-velocity structure of the moderate density gas in the region, traced by $^{13}$CO. The additional radial velocities we have measured enable us to probe some discrepancies between stellar and gaseous structure which can be attributed to binary motion and the inclusion of non-members in our kinematic sample. Our multi-epoch data allow us to identify 89 spectroscopic binaries; more will be found as we continue monitoring. Our results reinforce the idea that the ONC is a cluster in formation, and thus provides a valuable testing ground for theory. In particular, our observations are not consistent with the quasi-equilibrium or slow contraction models of cluster formation, but are consistent with cold collapse models.
    The Astrophysical Journal 03/2009; 697(2). · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a spectroscopic study of Leo V, a recently discovered satellite of the Milky Way (MW). From stellar spectra obtained with the MMT/Hectochelle spectrograph we identify seven likely members of Leo V. Five cluster near the Leo V center (R < 3') and have a velocity dispersion of 2.4+2.4 –1.4 km s–1. The other two likely members lie near each other but far from the center (R ~ 13' ~ 700 pc) and inflate the global velocity dispersion to 3.7+2.3 –1.4 km s–1. Assuming the five central members are bound, we obtain a dynamical mass of M = 3.3+9.1 –2.5 × 105 M ☉ (M/LV = 75+230 –58[M/LV ]☉). From the stacked spectrum of the five central members we estimate a mean metallicity of [Fe/H]=–2.0 ± 0.2 dex. Thus, with respect to dwarf spheroidals of similar luminosity, Leo V is slightly less massive and slightly more metal rich. Since we resolve the central velocity dispersion only marginally, we do not rule out the possibility that Leo V is a diffuse star cluster devoid of dark matter. The wide separation of its two outer members implies Leo V is losing mass; however, its large distance (D ~ 180 kpc) is difficult to reconcile with MW tidal stripping unless the orbit is very radial.
    The Astrophysical Journal 03/2009; 694(2):L144. · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The color-magnitude diagrams of ~7 × 105 stars obtained for 12 fields across the Galactic bulge with the Optical Gravitational Lensing Experiment project reveal a well-defined population of bulge red clump giants. We find that the distributions of the apparent magnitudes of the red clump stars are systematically fainter when observing toward lower Galactic l fields. The most plausible explanation for this distinct trend is that the Galactic bulge is a bar whose nearest end lies at positive Galactic longitude. We model this Galactic bar by fitting the observed luminosity functions in the red clump region of the color-magnitude diagram for all fields. We find that, almost regardless of the analytical function used to describe the three-dimensional distribution of stars in the Galactic bar, the resulting models have the major axis inclined to the line of sight from 20° to 30°, with axis ratios corresponding to x0:y0:z0 = 3.5:1.5:1. This puts a strong constraint on the possible range of the Galactic bar models.
    The Astrophysical Journal 01/2009; 477(1):163. · 6.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We photometrically monitored the globular cluster M12 during a number of observing runs between 1995 and 1999 with the aim of detecting variable stars and, in particular, cluster-member eclipsing binary stars below the main-sequence turnoff. The NASA/IPAC/NExScI Star and Exoplanet Database (NStED) provides access to high precision time-series photometry from stars observed by various planet transit and photometric variability survey programs. The data presented here are the product of the observing campaign of the open cluster M12 described above.
    01/2009; -1.
  • K. von Braun, M. Mateo
    [Show abstract] [Hide abstract]
    ABSTRACT: We photometrically monitored the globular cluster NGC 3201 during a number of observing runs from 1996 through 1998 with the aim of detecting variable stars and, in particular, cluster-member eclipsing binary stars below the main-sequence turnoff. The NASA/IPAC/NExScI Star and Exoplanet Database (NStED) provides access to high precision time-series photometry from stars observed by various exoplanet transit and photometric variability survey programs. The data presented here are the product of the observing campaign of the open cluster NGC 3201 described above. }
    01/2009; -1:4.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report the discovery of a new Milky Way satellite in the constellation Leo, identified in data from the Sloan Digital Sky Survey. It lies at a distance of ~180 kpc, and is separated by 3° from another recent discovery, Leo IV. We present follow-up imaging from the Isaac Newton Telescope and spectroscopy from the Hectochelle fiber spectrograph at the Multiple Mirror Telescope. Leo V's heliocentric velocity is ~173.3 ± 3.1 km s−1, offset by ~40 km s−1 from that of Leo IV. A simple interpretation of the kinematic data is that both objects may lie on the same stream, although the implied orbit is only modestly eccentric (e ~ 0.2)
    The Astrophysical Journal 12/2008; 686(2):L83. · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: SN 1999aw was discovered during the first campaign of the Nearby Galaxies Supernova Search project. This luminous, slow-declining [Δm15(B) = 0.81 ± 0.03] Type Ia supernova was noteworthy in at least two respects. First, it occurred in an extremely low luminosity host galaxy that was not visible in the template images nor in initial subsequent deep imaging. Second, the photometric and spectral properties of this supernova indicate that it very likely was similar to the subclass of Type Ia supernovae whose prototype is SN 1999aa. This paper presents the BVRI and JsHKs light curves of SN 1999aw (through ~100 days past maximum light), as well as several epochs of optical spectra. From these data, we calculate the bolometric light curve and give estimates of the luminosity at maximum light and the initial 56Ni mass. In addition, we present deep BVI images obtained recently with the Baade 6.5 m telescope at Las Campanas Observatory that reveal the remarkably low-luminosity host galaxy.
    The Astronomical Journal 12/2007; 124(5):2905. · 4.97 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The kinematics of stars within nearby dwarf spheroidal (dSph) galaxies imply that these systems are embedded within dominant dark matter halos having mass-to-light ratios as large as several hundred solar units. As the smallest observed dark matter structures in a Lambda-CDM Universe, dSphs offer a valuable window on early epochs of structure formation, and the mass distribution in these systems must contain fundamental information regarding the nature of dark matter. We present large samples of dSph velocities obtained using multi-object fiber systems at the Magellan and MMT telescopes. We have measured precise (+/- 2 km/s) line-of-sight velocities for nearly 5000 member stars in seven dSph satellites of the Milky Way. We discuss various mass models and their limiting assumptions. Regardless of the adopted model we find strikingly similar masses enclosed within the region common to each sample.
    12/2007;
  • [Show abstract] [Hide abstract]
    ABSTRACT: There have been recent advances in the nonparametric estimation of the distribution of dark matter in nearby dwarf spheroidal galaxies. This work uses Jeans' Equations to relate the distribution of (total) matter to velocity dispersions. The estimation of velocity dispersions is facilitated by observing certain shape restrictions, stronger that convexity in the isotropic case, that follow from Jeans' Equations. This work is reviewed, modified slightly, and extended to include some anisotropy.
    11/2007;
  • K. Chiboucas, M. Mateo
    [Show abstract] [Hide abstract]
    ABSTRACT: Observations of A3526 (Centaurus, 12:48:51.8, -41:18:21, J2000.0) were acquired with the LCO 1m and a TEK 2K Camera having a field of view of 20.48' and scale size 0.6"/pix on 1993 13-20 May and 1997 1-8 May. (1 data file).
    VizieR Online Data Catalog. 09/2007;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present preliminary results concerning the search for short-period variable stars in Tucana and LGS3 based on very deep HST/ACS imaging. In the fraction of the observed field we studied in each galaxy, a total of 133 and 30 variables were found, respectively. For Tucana, we identified 76 of them as RR Lyrae (RRL) stars pulsating in the fundamental mode (RRab) and 32 in the first-overtone mode (RRc), as well as 2 anomalous Cepheids (AC). The mean period of the RRab and RRc is 0.59 and 0.35 days, respectively. In the case of LGS3, we found 24 RRab and 4 RRc, with mean periods 0.61and 0.39 days, respectively, plus two candidate ACs. These values place both galaxies in the Oosterhoff gap.
    02/2007;
  • Source
    K. Chiboucas, M. Mateo
    [Show abstract] [Hide abstract]
    ABSTRACT: We acquired spectra for a random sample of galaxies within a 0.83 square degree region centered on the core of the Centaurus cluster. Radial velocities were obtained for 225 galaxies to limiting magnitudes of V < 19.5. Of the galaxies for which velocities were obtained, we find 35% to be member galaxies. Of the 78 member galaxies, magnitudes range from 11.8 < V < 18.5 (-21.6 < M_{V} < -14.9 for H_o = 70 km s^-1 Mpc^-1) with a limiting central surface brightness of \mu_o < 22.5 mag arcsec^-2. We constructed the cluster galaxy luminosity function by using these spectroscopic results to calculate the expected fraction of cluster members in each magnitude bin. The faint-end slope of the luminosity function using this method is shallower than the one obtained using a statistical method to correct for background galaxy contamination. We also use the spectroscopy results to define surface brightness criteria to establish membership for the full sample. Using these criteria, we find a luminosity function very similar to the one constructed with the statistical background correction. For both, we find a faint-end slope alpha ~ -1.4. Adjusting the surface brightness membership criteria we find that the data are consistent with a faint-end slope as shallow as -1.22 or as steep as -1.50. We describe in this paper some of the limitations of using these methods for constructing the galaxy luminosity function.
    The Astronomical Journal 04/2006; · 4.97 Impact Factor

Publication Stats

2k Citations
173.74 Total Impact Points

Institutions

  • 2013
    • Peking University
      • Kavli Institute for Astronomy and Astrophysics
      Peping, Beijing, China
  • 1994–2010
    • University of Michigan
      • Department of Astronomy
      Ann Arbor, MI, United States
  • 1997–1999
    • Honolulu University
      Honolulu, Hawaii, United States
  • 1995
    • Princeton University
      • Department of Astrophysical Sciences
      Princeton, New Jersey, United States