13 research outputs found
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Pegasus IV: Discovery and Spectroscopic Confirmation of an Ultra-faint Dwarf Galaxy in the Constellation Pegasus
We report the discovery of Pegasus IV, an ultra-faint dwarf galaxy found in archival data from the Dark Energy Camera processed by the DECam Local Volume Exploration Survey. Pegasus IV is a compact, ultra-faint stellar system (r1 2 = 41-+68 pc; MV = −4.25 ± 0.2 mag) located at a heliocentric distance of 90-+64 kpc. Based on spectra of seven nonvariable member stars observed with Magellan/IMACS, we confidently resolve Pegasus IV’s velocity dispersion, measuring sv = 3.3-+1.11.7 km s−1 (after excluding three velocity outliers); this implies a mass-to-light ratio of M1 2 LV,1 2 = 167-+99224M☉ L☉ for the system. From the five stars with the highest signal-to-noise spectra, we also measure a systemic metallicity of [Fe/H] =-2.63-+0.300.26 dex, making Pegasus IV one of the most metal-poor ultra-faint dwarfs. We tentatively resolve a nonzero metallicity dispersion for the system. These measurements provide strong evidence that Pegasus IV is a dark-matter-dominated dwarf galaxy, rather than a star cluster. We measure Pegasus IV’s proper motion using data from Gaia Early Data Release 3, finding (μα*, μδ) = (0.33 ± 0.07, −0.21 ± 0.08) mas yr−1. When combined with our measured systemic velocity, this proper motion suggests that Pegasus IV is on an elliptical, retrograde orbit, and is currently near its orbital apocenter. Lastly, we identify three potential RR Lyrae variable stars within Pegasus IV, including one candidate member located more than 10 half-light radii away from the system’s centroid. The discovery of yet another ultra-faint dwarf galaxy strongly suggests that the census of Milky Way satellites is still incomplete, even within 100 kpc
Bronchus associated lymphoid tissue (BALT) in human lung: its distribution in smokers and non-smokers.
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Hubble Space Telescope Observations of Two Faint Dwarf Satellites of Nearby LMC Analogs from MADCASH
We present a deep Hubble Space Telescope (HST) imaging study of two dwarf galaxies in the halos of Local Volume Large Magellanic Cloud (LMC) analogs. These dwarfs were discovered as part of our Subaru+Hyper Suprime-Cam MADCASH survey: MADCASH-1 is a satellite of NGC 2403 (D ∼ 3.2 Mpc), and MADCASH-2 is a previously unknown dwarf galaxy near NGC 4214 (D ∼ 3 Mpc). Our HST data reach >3.5 mag below the tip of the red giant branch (TRGB) of each dwarf, allowing us to derive their structural parameters and assess their stellar populations. We measure TRGB distances (Mpc, Mpc), and confirm the dwarfs' associations with their host galaxies. MADCASH-1 is a predominantly old, metal-poor stellar system (age ∼13.5 Gyr, [M/H] ∼ -2.0), similar to many Local Group dwarfs. Modelling of MADCASH-2's color-magnitude diagram suggests that it contains mostly ancient, metal-poor stars (age ∼13.5 Gyr, [M/H] ∼ -2.0), but that ∼10% of its stellar mass was formed 1.1-1.5 Gyr ago and ∼1% was formed 400-500 Myr ago. Given its recent star formation, we search MADCASH-2 for neutral hydrogen using the Green Bank Telescope, but find no emission and estimate an upper limit on the H i mass of <4.8 104 M o˙. These are the faintest dwarf satellites known around host galaxies of LMC mass outside the Local Group (M V,MADCASH-1 = -7.81 0.18, M V,MADCASH-2 = -9.15 0.12), and one of them shows signs of recent environmental quenching by its host. Once the MADCASH survey for faint dwarf satellites is complete, our census will enable us to test predictions from cold dark matter models for hierarchical structure formation and discover the physical mechanisms by which low-mass hosts influence the evolution of their satellites. © 2021. The American Astronomical Society. All rights reserved.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Reference ranges and sources of variability of CD4 counts in HIV-seronegative women and men.
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Hubble Space Telescope Imaging of Isolated Local Volume Dwarfs GALFA Dw3 and Dw4
We present observations of the dwarf galaxies GALFA Dw3 and GALFA Dw4 with the Advanced Camera for Surveys on the Hubble Space Telescope. These galaxies were initially discovered as optical counterparts to compact H i clouds in the GALFA survey. Both objects resolve into stellar populations which display old red giant branch (RGB), younger helium-burning, and massive main sequence stars. We use the tip of the RGB method to determine the distance to each galaxy, finding distances of Mpc and Mpc, respectively. With these distances we show that both galaxies are extremely isolated, with no other confirmed objects within ∼1.5 Mpc of either dwarf. GALFA Dw4 is also found to be unusually compact for a galaxy of its luminosity. GALFA Dw3 and Dw4 contain H ii regions with young star clusters and an overall irregular morphology; they show evidence of ongoing star formation through both ultraviolet and Hα observations and are therefore classified as dwarf irregulars (dIrrs). The star formation histories of these two dwarfs show distinct differences: Dw3 shows signs of a recently ceased episode of active star formation across the entire dwarf, while Dw4 shows some evidence for current star formation in spatially limited H ii regions. Compact H i sources offer a promising method for identifying isolated field dwarfs in the Local Volume, including GALFA Dw3 and Dw4, with the potential to shed light on the driving mechanisms of dwarf galaxy formation and evolution. © 2022. The Author(s). Published by the American Astronomical Society.Open access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
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Discovery of an Ultra-faint Stellar System near the Magellanic Clouds with the DECam Local Volume Exploration Survey
We report the discovery of a new ultra-faint stellar system found near the Magellanic Clouds in the DECam Local Volume Exploration Survey. This new system, DELVE J0155-6815 (DELVE 2), is located at a heliocentric distance of D o˙ = 71 4 kpc, which places it at a 3D physical separation of 12 3 kpc from the center of the Small Magellanic Cloud and 28 -3 +4, kpc from the center of the Large Magellanic Cloud (LMC). DELVE 2 is identified as a resolved overdensity of old (τ > 13.3 Gyr) and metal-poor ( dex) stars with a projected half-light radius of and an absolute magnitude of M V =-{2.1} {-0.5} {+0.4}, mag. The size and luminosity of DELVE 2 are consistent with both the population of recently discovered ultra-faint globular clusters and the smallest ultra-faint dwarf galaxies. However, its photometrically derived age and metallicity would place it among the oldest and most metal-poor globular clusters in the Magellanic system. In the absence of spectroscopic measurements of the system's metallicity dispersion and internal kinematics, we are unable to conclusively classify this system at this time. DELVE 2 is detected in Gaia DR2 with a clear proper-motion signal, with multiple blue horizontal-branch stars near the centroid of the system with proper motions consistent with the systemic mean. We measure the system proper motion to be μ α δ, μ δ = 1.02 -0.25 {+0.24}, -{0.85}_{-0.19} {+0.18}) mas yr-1. We compare the spatial position and proper motion of DELVE 2 with simulations of the accreted satellite population of the LMC and find that it is very likely to be associated with the LMC. © 2021. The American Astronomical Society. All rights reserved.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Effect of low to moderate levels of smoking and alcohol consumption on serum immunoglobulin concentrations.
Lymphocyte subsets in subjects exposed to asbestos: changes in circulating natural killer cells.
Two Ultra-Faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration Survey
We report the discovery of two ultra-faint stellar systems found in early data from the DECam Local
Volume Exploration survey (DELVE). The �rst system, Centaurus I (DELVE J123
Two Ultra-Faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration Survey
We report the discovery of two ultra-faint stellar systems found in early data from the DECam Local Volume Exploration survey (DELVE). The rst system, Centaurus I (DELVE J123