A5039451774- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Galaxies: Formation, Evolution, Phenomena
- Gamma-ray bursts and supernovae
- Astrophysics and Star Formation Studies
- Astronomical Observations and Instrumentation
- Dark Matter and Cosmic Phenomena
- History and Developments in Astronomy
- Astro and Planetary Science
- Astrophysical Phenomena and Observations
- Adaptive optics and wavefront sensing
- Astrophysics and Cosmic Phenomena
- Cosmology and Gravitation Theories
- Scientific Research and Discoveries
- Radio Astronomy Observations and Technology
- Impact of Light on Environment and Health
- Geophysics and Gravity Measurements
- Inertial Sensor and Navigation
- Distributed and Parallel Computing Systems
- Mathematics and Applications
- Relativity and Gravitational Theory
- Cloud Data Security Solutions
- Advanced Electrical Measurement Techniques
- User Authentication and Security Systems
- Security and Verification in Computing
Large Synoptic Survey Telescope Corporation
2016-2023
NSF’s NOIRLab
2020-2022
University of Arizona
2016-2019
Association of Universities For Research In Astronomy
2019
Haverford College
2008-2017
Berkeley College
2012
University of California, Berkeley
2012
Center for Astrophysics Harvard & Smithsonian
2007-2009
European Southern Observatory
2009
Institut de Planétologie et d'Astrophysique de Grenoble
2009
We used fully cosmological, high resolution N-body + SPH simulations to follow the formation of disk galaxies with rotational velocities between 135 and 270 km/sec in a Lambda CDM universe. The include gas cooling, star formation, effects uniform UV background physically motivated description feedback from supernovae. host dark matter halos have spin last major merger redshift typical galaxy sized as measured recent large scale N--Body simulations. simulated form rotationally supported disks...
In this Letter, we report the discovery of a new dwarf satellite to Milky Way, located at (α2000, δ2000) = (15872, 5192) in constellation Ursa Major. This object was detected as an overdensity red, resolved stars Sloan Digital Sky Survey data. The color-magnitude diagram Major looks remarkably similar that Sextans, lowest surface brightness Way companion known, but with approximately order magnitude fewer stars. Deeper follow-up imaging confirms has old and metal-poor stellar population is...
In this Letter, we announce the discovery of a new satellite Milky Way in constellation Bootes at distance 60 kpc. It was found systematic search for stellar overdensities North Galactic Cap using Sloan Digital Sky Survey Data Release 5 (SDSS DR5). The color-magnitude diagram shows well-defined turn-off, red giant branch, and extended horizontal branch. Its absolute magnitude is -5.8, which makes it one faintest galaxies known. half-light radius 220 pc. isodensity contours are elongated have...
We correct the observed Milky Way satellite luminosity function for bias using published completeness limits Sloan Digital Sky Survey DR5. Assuming that spatial distribution of satellites tracks subhalos found in Via Lactea ΛCDM N-body simulation, we show there should be between ~300 and ~600 within 400 kpc Sun are brighter than faintest known dwarf galaxies may as many ~1000, depending on assumptions. By taking into account limits, radial dwarfs is consistent with our assumption full...
In this Letter, we announce the discovery of a new dwarf satellite Milky Way, located in constellation Canes Venatici. It was found as stellar overdensity north Galactic cap using Sloan Digital Sky Survey Data Release 5 (SDSS DR5). The satellite's color-magnitude diagram shows well-defined red giant branch well horizontal branch. As judged from tip branch, it lies at distance ~220 kpc. Based on SDSS data, estimate an absolute magnitude MV ~ -7.9, central surface brightness μ0, V 28 mag...
Using high-resolution cosmological hydrodynamical simulations of Milky Way-massed disk galaxies, we demonstrate that supernovae feedback and tidal stripping lower the central masses bright (−15 < MV −8) satellite galaxies. These resolve high-density regions, comparable to giant molecular clouds, where stars form. This resolution allows us adopt a prescription for H2 formation destruction ties star presence shielded, gas. Before infall, supernova from clumpy, bursty captured by this...
We investigate the formation of stellar halos four simulated disk galaxies using high-resolution, cosmological SPH + N-body simulations. These simulations include a self-consistent treatment all major physical processes involved in galaxy formation. The presented here each have total mass ∼1012 M☉, but span range merger histories. allow us to study competing importance situ star (stars formed primary galaxy) and accretion stars from subhalos building ΛCDM universe. All are surrounded by...
We present the results of a comprehensive Keck/DEIMOS spectroscopic survey ultra-faint Milky Way satellite galaxy Segue 1. have obtained velocity measurements for 98.2% stars within 67 pc (10 arcmin, or 2.3 half-light radii) center 1 that colors and magnitudes consistent with membership, down to magnitude limit r=21.7. Based on photometric, kinematic, metallicity information, we identify 71 as probable members, including some far out 87 pc. After correcting influence binary using repeated...
We report the discovery of SDSSJ1049+5103, an overdensity resolved blue stars at (α_{2000}, δ_{2000}) = (162.343, 51.051). This object appears to be old, metal-poor stellar system a distance 45 +/- 10 kpc, with half-light radius 23$\pm 10$ pc and absolute magnitude M_V -3.0^{+2.0}_{-0.7}. One star that is likely associated this companion has SDSS spectrum confirming it as horizontal branch 48 kpc. The color-magnitude diagram SDSSJ1049+5103 contains few, if any, or red giant stars, similar...
In this Letter, we study a localized stellar overdensity in the constellation of Ursa Major, first identified Sloan Digital Sky Survey (SDSS) data and subsequently followed up with Subaru imaging. Its color-magnitude diagram (CMD) shows well-defined subgiant branch, main sequence, turnoff, from which estimate distance ~30 kpc projected size ~250 × 125 pc2. The CMD suggests composite population some range metallicity and/or age. Based on its extent population, argue that is previously unknown...
We present spectra of six metal-poor stars in two the ultra-faint dwarf galaxies orbiting Milky Way (MW), Ursa Major II, and Coma Berenices obtained with Keck/High Resolution Echelle Spectrometer (HIRES). These observations include first high-resolution spectroscopic extremely ([Fe/H] < −3.0) not belonging to MW halo field star population. obtain abundance measurements upper limits for 26 elements between carbon europium. The entire sample spans a range −3.2 [Fe/H] −2.3, we confirm that each...
We examine the origin and evolution of mass-metallicity relationship (MZR, M*-Z) for galaxies using high-resolution cosmological smoothed particle hydrodynamics (SPH) + N-body simulations that include a physically motivated description supernova feedback subsequent metal enrichment. discriminate between two sources may contribute to MZR: (1) baryon loss due gas outflow or (2) inefficient star formation at lowest galaxy masses. Our simulated reproduce observed MZR in shape normalization both...
We simulate the formation of a realistic disk galaxy within hierarchical scenario structure and study its internal properties to present epoch. compare results from LambdaCDM simulation with LambdaWDM (2keV) that forms significantly less small scale structure. show how high mass force resolution in both gas dark matter components play an important role solving angular momentum catastrophe claimed previous simulations framework. The stellar material component has final specific equal 40% 90%...
We present a sample of 148 candidate RR Lyrae stars selected from Sloan Digital Sky Survey (SDSS) commissioning data for about 100 deg 2 sky surveyed twice with Δ t = 1.9946 days. Although the faint-magnitude limit SDSS allows us to detect large Galactocentric distances (∼100 kpc, or r * ∼ 21), we find no candidates fainter than 20, i.e., farther ∼65 kpc Galactic center. On assumption that all are indeed (contamination by other species variable star is probably less 10%), their volume...
Microsoft's next-generation secure computing base extends personal computers to offer mechanisms that let high-assurance software protect itself from the operating systems, device drivers, BIOS, and other running on same machine.
Using high resolution SPH simulations in a fully cosmological Lambda CDM context we study the formation of bright disk dominated galaxy that originates from "wet" major merger at z=0.8. The progenitors are themselves galaxies formed early mergers between with blue colors. A substantial thin stellar grows rapidly following last and present day properties final remnant typical type spiral galaxies, an i band B/D ~0.65, scale length 7.2 kpc, g-r = 0.5 mag, HI line width (W_{20}/2) 238 km/sec...
As part of preparations for a southern sky search faint Milky Way dwarf galaxy satellites, we report the discovery stellar overdensity in Sloan Digital Sky Survey Data Release 5, lying at an angular distance only 1.5 degrees from recently discovered Bo{\"o}tes dwarf. The was detected well above statistical noise by employing sophisticated data mining algorithm and does not correspond to any catalogued object. Overlaid isochrones using population synthesis models show that color-magnitude...
A growing number of low luminosity and surface brightness astronomical objects challenge traditional notions both galaxies star clusters. To address this challenge, we propose a definition galaxy that does not depend on cold dark matter model the universe: is gravitationally bound collection stars whose properties cannot be explained by combination baryons Newton's laws gravity. After exploring several possible observational diagnostics definition, critically examine classification...
We present Keck/DEIMOS spectroscopy of Segue 1, an ultra-low luminosity (M_V = -1.5) Milky Way satellite companion. While the combined size and 1 are consistent with either a globular cluster or dwarf galaxy, we spectroscopic evidence that this object is dark matter-dominated galaxy. identify 24 stars as members mean heliocentric recession velocity 206 +/- 1.3 kms. measure internal dispersion 4.3+/-1.2 Under assumption these in dynamical equilibrium, infer total mass 4.5^{+4.7}_{-2.5} x 10^5...
We use kinematic data from three new, nearby, extremely low-luminosity Milky Way dwarf galaxies (Ursa Major II, Willman 1, and Coma Berenices) to constrain the properties of their dark matter halos, these make predictions for gamma-ray flux annihilation particles in halos. show that 10^3 solar luminosity dwarfs are most dominated Universe, with total masses within 100 pc excess 10^6 masses. Coupled relative proximity, large imply they should have mean fluxes comparable or greater than any...
We investigate the kinematic properties and stellar population of Galactic satellite Willman 1 (Wil 1) by combining Keck/DEIMOS spectroscopy with Kitt Peak National Observatory mosaic camera imaging. Wil 1, also known as SDSS J1049+5103, is a nearby, ultra-low luminosity Milky Way companion. This object lies in region size–luminosity space (MV ∼ −2 mag, d 38 kpc, rhalf 20 pc) occupied satellites Boötes II Segue 2, but no other old system. use color–magnitude criteria to identify 45 stars...
We present new upper limits on the neutral hydrogen (HI) content within stellar half-light ellipses of 15 Galactic dwarf spheroidal galaxies (dSphs), derived from pointed observations with Green Bank Telescope (GBT) as well Arecibo L-band Fast ALFA (ALFALFA) survey and All-Sky Survey (GASS) data. All Mlim are more stringent than previously reported values, those GBT improve upon contraints in literature by a median factor 23. Normalizing V-band luminosity Lv dynamical mass Mdyn, we find...
The Large Synoptic Survey Telescope is designed to provide an unprecedented optical imaging dataset that will support investigations of our Solar System, Galaxy and Universe, across half the sky over ten years repeated observation. However, exactly how LSST observations be taken (the observing strategy or "cadence") not yet finalized. In this dynamically-evolving community white paper, we explore detailed performance anticipated science expected depend on small changes strategy. Using...